<?xml version="1.0" encoding="US-ASCII" standalone="no"?>
<!--Generated by ThunderDome XBRL - 08:34PM UTC 2026-08-06--><link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple"/>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-document-and-entity-information" xlink:href="geos-20260630.xsd#statement-document-and-entity-information" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-document-and-entity-information" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag" xlink:label="dei_AmendmentFlag" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode" xlink:label="dei_CityAreaCode" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate" xlink:label="dei_CurrentFiscalYearEndDate" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="dei_DocumentFiscalPeriodFocus" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus" xlink:label="dei_DocumentFiscalYearFocus" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems" xlink:label="dei_DocumentInformationLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable" xlink:label="dei_DocumentInformationTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate" xlink:label="dei_DocumentPeriodEndDate" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport" xlink:label="dei_DocumentQuarterlyReport" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport" xlink:label="dei_DocumentTransitionReport" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType" xlink:label="dei_DocumentType" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1" xlink:label="dei_EntityAddressAddressLine1" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown" xlink:label="dei_EntityAddressCityOrTown" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode" xlink:label="dei_EntityAddressPostalZipCode" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince" xlink:label="dei_EntityAddressStateOrProvince" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey" xlink:label="dei_EntityCentralIndexKey" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="dei_EntityCommonStockSharesOutstanding" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus" xlink:label="dei_EntityCurrentReportingStatus" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany" xlink:label="dei_EntityEmergingGrowthCompany" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber" xlink:label="dei_EntityFileNumber" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory" xlink:label="dei_EntityFilerCategory" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode" xlink:label="dei_EntityIncorporationStateCountryCode" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent" xlink:label="dei_EntityInteractiveDataCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName" xlink:label="dei_EntityRegistrantName" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany" xlink:label="dei_EntityShellCompany" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness" xlink:label="dei_EntitySmallBusiness" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber" xlink:label="dei_EntityTaxIdentificationNumber" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber" xlink:label="dei_LocalPhoneNumber" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle" xlink:label="dei_Security12bTitle" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName" xlink:label="dei_SecurityExchangeName" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol" xlink:label="dei_TradingSymbol" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="dei_DocumentInformationTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentInformationTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityCentralIndexKey" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityRegistrantName" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_AmendmentFlag" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_CurrentFiscalYearEndDate" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentFiscalPeriodFocus" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentFiscalYearFocus" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentType" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentQuarterlyReport" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentPeriodEndDate" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentTransitionReport" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityFileNumber" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityIncorporationStateCountryCode" xlink:type="arc"/>
    <link:definitionArc order="13" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityTaxIdentificationNumber" xlink:type="arc"/>
    <link:definitionArc order="14" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityAddressAddressLine1" xlink:type="arc"/>
    <link:definitionArc order="15" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityAddressCityOrTown" xlink:type="arc"/>
    <link:definitionArc order="16" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityAddressStateOrProvince" xlink:type="arc"/>
    <link:definitionArc order="17" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityAddressPostalZipCode" xlink:type="arc"/>
    <link:definitionArc order="18" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_CityAreaCode" xlink:type="arc"/>
    <link:definitionArc order="19" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_LocalPhoneNumber" xlink:type="arc"/>
    <link:definitionArc order="20" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_Security12bTitle" xlink:type="arc"/>
    <link:definitionArc order="21" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_TradingSymbol" xlink:type="arc"/>
    <link:definitionArc order="22" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_SecurityExchangeName" xlink:type="arc"/>
    <link:definitionArc order="23" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityCurrentReportingStatus" xlink:type="arc"/>
    <link:definitionArc order="24" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityInteractiveDataCurrent" xlink:type="arc"/>
    <link:definitionArc order="25" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityFilerCategory" xlink:type="arc"/>
    <link:definitionArc order="26" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntitySmallBusiness" xlink:type="arc"/>
    <link:definitionArc order="27" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityEmergingGrowthCompany" xlink:type="arc"/>
    <link:definitionArc order="28" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityShellCompany" xlink:type="arc"/>
    <link:definitionArc order="29" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityCommonStockSharesOutstanding" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-consolidated-balance-sheets-current-period-unaudited-parentheticals" xlink:href="geos-20260630.xsd#statement-consolidated-balance-sheets-current-period-unaudited-parentheticals" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-consolidated-balance-sheets-current-period-unaudited-parentheticals" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="us-gaap_PreferredStockSharesAuthorized" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="us-gaap_PreferredStockSharesIssued" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="us-gaap_PreferredStockSharesOutstanding" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares" xlink:label="us-gaap_TreasuryStockCommonShares" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockSharesAuthorized" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockSharesIssued" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockSharesOutstanding" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesAuthorized" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesIssued" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesOutstanding" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TreasuryStockCommonShares" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-1-significant-accounting-policies" xlink:href="geos-20260630.xsd#statement-note-1-significant-accounting-policies" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-1-significant-accounting-policies" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_CustomerOneMember" xlink:label="geos_CustomerOneMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis" xlink:label="srt_MajorCustomersAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain" xlink:label="srt_NameOfMajorCustomerDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain" xlink:label="srt_NameOfMajorCustomerDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember" xlink:label="srt_SubsidiariesMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableMember" xlink:label="us-gaap_AccountsReceivableMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="us-gaap_ConcentrationRiskBenchmarkDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="us-gaap_ConcentrationRiskBenchmarkDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="us-gaap_ConcentrationRiskByTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="us-gaap_ConcentrationRiskTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="us-gaap_ConcentrationRiskTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="us-gaap_CustomerConcentrationRiskMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:label="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonUsMember" xlink:label="us-gaap_NonUsMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerMember" xlink:label="us-gaap_RevenueFromContractWithCustomerMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SignificantAccountingPoliciesTextBlock" xlink:label="us-gaap_SignificantAccountingPoliciesTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_MajorCustomersAxis" xlink:to="srt_NameOfMajorCustomerDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_ConcentrationRiskByTypeAxis" xlink:to="us-gaap_ConcentrationRiskTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:to="us-gaap_ConcentrationRiskBenchmarkDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="srt_ConsolidatedEntitiesAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="srt_SubsidiariesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="srt_StatementGeographicalAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="us-gaap_NonUsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="us-gaap_ConcentrationRiskByTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ConcentrationRiskTypeDomain" xlink:to="us-gaap_CustomerConcentrationRiskMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_ConcentrationRiskByTypeAxis" xlink:to="us-gaap_ConcentrationRiskTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ConcentrationRiskBenchmarkDomain" xlink:to="us-gaap_AccountsReceivableMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:to="us-gaap_ConcentrationRiskBenchmarkDomain-default" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="srt_MajorCustomersAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_NameOfMajorCustomerDomain" xlink:to="geos_CustomerOneMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_MajorCustomersAxis" xlink:to="srt_NameOfMajorCustomerDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ConcentrationRiskBenchmarkDomain" xlink:to="us-gaap_RevenueFromContractWithCustomerMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_SignificantAccountingPoliciesTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-2-revenue-recognition" xlink:href="geos-20260630.xsd#statement-note-2-revenue-recognition" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-2-revenue-recognition" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis" xlink:label="srt_ProductOrServiceAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="us-gaap_DisaggregationOfRevenueTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerTextBlock" xlink:label="us-gaap_RevenueFromContractWithCustomerTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubscriptionAndCirculationMember" xlink:label="us-gaap_SubscriptionAndCirculationMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:label="us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:label="us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:label="us-gaap_TimingOfTransferOfGoodOrServiceDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransferredOverTimeMember" xlink:label="us-gaap_TransferredOverTimeMember" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:to="us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_ProductOrServiceAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_SubscriptionAndCirculationMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_RangeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:to="us-gaap_TransferredOverTimeMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:to="us-gaap_TimingOfTransferOfGoodOrServiceDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisaggregationOfRevenueTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_RevenueFromContractWithCustomerTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-3-fair-value-of-financial-instruments" xlink:href="geos-20260630.xsd#statement-note-3-fair-value-of-financial-instruments" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-3-fair-value-of-financial-instruments" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_GeovoxMember" xlink:label="geos_GeovoxMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:label="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosuresTextBlock" xlink:label="us-gaap_FairValueDisclosuresTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="us-gaap_BusinessAcquisitionAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="geos_GeovoxMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_FairValueDisclosuresTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables" xlink:href="geos-20260630.xsd#statement-note-4-trade-accounts-and-financing-receivables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PromissoryNoteForSaleOfProductMember" xlink:label="geos_PromissoryNoteForSaleOfProductMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PromissoryNoteMember" xlink:label="geos_PromissoryNoteMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PromissoryNotesMaturesJanuary2027Member" xlink:label="geos_PromissoryNotesMaturesJanuary2027Member" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PromissoryNotesMaturesJanuary2029Member" xlink:label="geos_PromissoryNotesMaturesJanuary2029Member" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_SubsidiaryOilAndGasProductManufacturingOperationsInTheRussianFederationMember" xlink:label="geos_SubsidiaryOilAndGasProductManufacturingOperationsInTheRussianFederationMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_ThreePromissoryNotesMember" xlink:label="geos_ThreePromissoryNotesMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_TwoPromissoryNotesMember" xlink:label="geos_TwoPromissoryNotesMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_WirelessSeismicEquipmentCustomerMember" xlink:label="geos_WirelessSeismicEquipmentCustomerMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:label="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember" xlink:label="us-gaap_DiscontinuedOperationsDisposedOfBySaleMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis" xlink:label="us-gaap_DisposalGroupClassificationAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain" xlink:label="us-gaap_DisposalGroupClassificationDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain" xlink:label="us-gaap_DisposalGroupClassificationDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansNotesTradeAndOtherReceivablesDisclosureTextBlock" xlink:label="us-gaap_LoansNotesTradeAndOtherReceivablesDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableTypeDomain" xlink:label="us-gaap_ReceivableTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableTypeDomain" xlink:label="us-gaap_ReceivableTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:to="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="us-gaap_ReceivableTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_DisposalGroupClassificationAxis" xlink:to="us-gaap_DisposalGroupClassificationDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_PromissoryNotesMaturesJanuary2027Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="us-gaap_ReceivableTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_PromissoryNotesMaturesJanuary2029Member" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_ThreePromissoryNotesMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_TwoPromissoryNotesMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_WirelessSeismicEquipmentCustomerMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_PromissoryNoteForSaleOfProductMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_DisposalGroupClassificationAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisposalGroupClassificationDomain" xlink:to="us-gaap_DiscontinuedOperationsDisposedOfBySaleMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_DisposalGroupClassificationAxis" xlink:to="us-gaap_DisposalGroupClassificationDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:to="geos_SubsidiaryOilAndGasProductManufacturingOperationsInTheRussianFederationMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:to="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain-default" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_PromissoryNoteMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_LoansNotesTradeAndOtherReceivablesDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-5-inventories" xlink:href="geos-20260630.xsd#statement-note-5-inventories" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-5-inventories" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_SemifinishedGoodsAndComponentPartsMember" xlink:label="geos_SemifinishedGoodsAndComponentPartsMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryCurrentTable" xlink:label="us-gaap_InventoryCurrentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryDisclosureTextBlock" xlink:label="us-gaap_InventoryDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesInventoryAxis" xlink:label="us-gaap_PublicUtilitiesInventoryAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain" xlink:label="us-gaap_PublicUtilitiesInventoryTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain" xlink:label="us-gaap_PublicUtilitiesInventoryTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_PublicUtilitiesInventoryAxis" xlink:to="us-gaap_PublicUtilitiesInventoryTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InventoryCurrentTable" xlink:to="us-gaap_PublicUtilitiesInventoryAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PublicUtilitiesInventoryTypeDomain" xlink:to="geos_SemifinishedGoodsAndComponentPartsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_PublicUtilitiesInventoryAxis" xlink:to="us-gaap_PublicUtilitiesInventoryTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InventoryCurrentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryCurrentTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_InventoryDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-6-property-plant-and-equipment" xlink:href="geos-20260630.xsd#statement-note-6-property-plant-and-equipment" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-6-property-plant-and-equipment" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember" xlink:label="srt_SubsidiariesMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:label="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="us-gaap_SubsequentEventTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="srt_ConsolidatedEntitiesAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="srt_SubsidiariesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-7-rental-equipment" xlink:href="geos-20260630.xsd#statement-note-7-rental-equipment" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-7-rental-equipment" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_LeaseReceivableMember" xlink:label="geos_LeaseReceivableMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_LeasesDisclosureTextBlock" xlink:label="geos_LeasesDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:label="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquipmentMember" xlink:label="us-gaap_EquipmentMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableTypeDomain" xlink:label="us-gaap_ReceivableTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableTypeDomain" xlink:label="us-gaap_ReceivableTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleLeasebackTransactionTable" xlink:label="us-gaap_SaleLeasebackTransactionTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="us-gaap_ReceivableTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SaleLeasebackTransactionTable" xlink:to="srt_RangeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SaleLeasebackTransactionTable" xlink:to="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_EquipmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SaleLeasebackTransactionTable" xlink:to="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_LeaseReceivableMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="us-gaap_ReceivableTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SaleLeasebackTransactionTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SaleLeasebackTransactionTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="geos_LeasesDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-8-longterm-debt" xlink:href="geos-20260630.xsd#statement-note-8-longterm-debt" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-8-longterm-debt" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_WoodforestNationalBankMember" xlink:label="geos_WoodforestNationalBankMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis" xlink:label="us-gaap_CreditFacilityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain" xlink:label="us-gaap_CreditFacilityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain" xlink:label="us-gaap_CreditFacilityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtDisclosureTextBlock" xlink:label="us-gaap_DebtDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable" xlink:label="us-gaap_DebtInstrumentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LetterOfCreditMember" xlink:label="us-gaap_LetterOfCreditMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="us-gaap_LineOfCreditFacilityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember" xlink:label="us-gaap_LineOfCreditMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_LineOfCreditFacilityAxis" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_CreditFacilityAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="us-gaap_LineOfCreditMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_LineOfCreditFacilityAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="geos_WoodforestNationalBankMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_LineOfCreditFacilityAxis" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="srt_RangeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="us-gaap_LetterOfCreditMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtInstrumentTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_DebtDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-9-stockbased-compensation" xlink:href="geos-20260630.xsd#statement-note-9-stockbased-compensation" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-9-stockbased-compensation" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramTable" xlink:label="srt_ShareRepurchaseProgramTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="us-gaap_RestrictedStockUnitsRSUMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="srt_ShareRepurchaseProgramTable" xlink:to="us-gaap_AwardTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockUnitsRSUMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="srt_ShareRepurchaseProgramTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="srt_ShareRepurchaseProgramTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-10-loss-per-common-share" xlink:href="geos-20260630.xsd#statement-note-10-loss-per-common-share" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-10-loss-per-common-share" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareTextBlock" xlink:label="us-gaap_EarningsPerShareTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="us-gaap_RestrictedStockUnitsRSUMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_RestrictedStockUnitsRSUMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_EarningsPerShareTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-11-commitments-and-contingencies" xlink:href="geos-20260630.xsd#statement-note-11-commitments-and-contingencies" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-11-commitments-and-contingencies" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_AquanaLLSMember" xlink:label="geos_AquanaLLSMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_GeovoxMember" xlink:label="geos_GeovoxMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCommitmentsTable" xlink:label="us-gaap_OtherCommitmentsTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_OtherCommitmentsTable" xlink:to="us-gaap_BusinessAcquisitionAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="geos_GeovoxMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="geos_AquanaLLSMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_OtherCommitmentsTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherCommitmentsTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-12-segment-information" xlink:href="geos-20260630.xsd#statement-note-12-segment-information" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-12-segment-information" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingDisclosureTextBlock" xlink:label="us-gaap_SegmentReportingDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_SegmentReportingDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-13-income-taxes" xlink:href="geos-20260630.xsd#statement-note-13-income-taxes" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-13-income-taxes" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTable" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxDisclosureTextBlock" xlink:label="us-gaap_IncomeTaxDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_EffectiveIncomeTaxRateReconciliationTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_IncomeTaxDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-14-exit-and-disposal-costs" xlink:href="geos-20260630.xsd#statement-note-14-exit-and-disposal-costs" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-14-exit-and-disposal-costs" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_The2026OrganizationalChangePlanMember" xlink:label="geos_The2026OrganizationalChangePlanMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain" xlink:label="us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain" xlink:label="us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOnFutureEarningsAndCashFlowsResultingFromExitPlanAxis" xlink:label="us-gaap_EffectsOnFutureEarningsAndCashFlowsResultingFromExitPlanAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReducedEmployeeExpensesMember" xlink:label="us-gaap_ReducedEmployeeExpensesMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringAndRelatedActivitiesDisclosureTextBlock" xlink:label="us-gaap_RestructuringAndRelatedActivitiesDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanAxis" xlink:label="us-gaap_RestructuringPlanAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanDomain" xlink:label="us-gaap_RestructuringPlanDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanDomain" xlink:label="us-gaap_RestructuringPlanDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:label="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_EffectsOnFutureEarningsAndCashFlowsResultingFromExitPlanAxis" xlink:to="us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_RestructuringPlanAxis" xlink:to="us-gaap_RestructuringPlanDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:to="us-gaap_RestructuringPlanAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RestructuringPlanDomain" xlink:to="geos_The2026OrganizationalChangePlanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_RestructuringPlanAxis" xlink:to="us-gaap_RestructuringPlanDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:to="us-gaap_EffectsOnFutureEarningsAndCashFlowsResultingFromExitPlanAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain" xlink:to="us-gaap_ReducedEmployeeExpensesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_EffectsOnFutureEarningsAndCashFlowsResultingFromExitPlanAxis" xlink:to="us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_RestructuringAndRelatedActivitiesDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-significant-accounting-policies-policies" xlink:href="geos-20260630.xsd#statement-significant-accounting-policies-policies" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-significant-accounting-policies-policies" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PolicyTable" xlink:label="geos_PolicyTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountingPoliciesAbstract" xlink:label="us-gaap_AccountingPoliciesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationsPolicy" xlink:label="us-gaap_BusinessCombinationsPolicy" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskCreditRisk" xlink:label="us-gaap_ConcentrationRiskCreditRisk" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy" xlink:label="us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOrDisposalOfLongLivedAssetsPolicyTextBlock" xlink:label="us-gaap_ImpairmentOrDisposalOfLongLivedAssetsPolicyTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyTextBlockAbstract" xlink:label="us-gaap_PolicyTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PriorPeriodReclassificationAdjustmentDescription" xlink:label="us-gaap_PriorPeriodReclassificationAdjustmentDescription" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpensePolicy" xlink:label="us-gaap_ResearchAndDevelopmentExpensePolicy" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UseOfEstimates" xlink:label="us-gaap_UseOfEstimates" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PolicyTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="geos_PolicyTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_PolicyTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PolicyTextBlockAbstract" xlink:to="us-gaap_AccountingPoliciesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_UseOfEstimates" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_PriorPeriodReclassificationAdjustmentDescription" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_ConcentrationRiskCreditRisk" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_ImpairmentOrDisposalOfLongLivedAssetsPolicyTextBlock" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_BusinessCombinationsPolicy" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_ResearchAndDevelopmentExpensePolicy" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-2-revenue-recognition-tables" xlink:href="geos-20260630.xsd#statement-note-2-revenue-recognition-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-2-revenue-recognition-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="us-gaap_DisaggregationOfRevenueTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTableTextBlock" xlink:label="us-gaap_DisaggregationOfRevenueTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromExternalCustomersByGeographicAreasTableTextBlock" xlink:label="us-gaap_RevenueFromExternalCustomersByGeographicAreasTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisaggregationOfRevenueTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_DisaggregationOfRevenueTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_RevenueFromExternalCustomersByGeographicAreasTableTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-3-fair-value-of-financial-instruments-tables" xlink:href="geos-20260630.xsd#statement-note-3-fair-value-of-financial-instruments-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-3-fair-value-of-financial-instruments-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:label="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTextBlock" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:label="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables-tables" xlink:href="geos-20260630.xsd#statement-note-4-trade-accounts-and-financing-receivables-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_ScheduleOfAccountsReceivableTableTextBlock" xlink:label="geos_ScheduleOfAccountsReceivableTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableAllowanceForCreditLossTableTextBlock" xlink:label="us-gaap_AccountsReceivableAllowanceForCreditLossTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="geos_ScheduleOfAccountsReceivableTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_AccountsReceivableAllowanceForCreditLossTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-5-inventories-tables" xlink:href="geos-20260630.xsd#statement-note-5-inventories-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-5-inventories-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_ScheduleOfInventoryCurrentAndNoncurrentTableTextBlock" xlink:label="geos_ScheduleOfInventoryCurrentAndNoncurrentTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryCurrentTable" xlink:label="us-gaap_InventoryCurrentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InventoryCurrentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryCurrentTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="geos_ScheduleOfInventoryCurrentAndNoncurrentTableTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-6-property-plant-and-equipment-tables" xlink:href="geos-20260630.xsd#statement-note-6-property-plant-and-equipment-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-6-property-plant-and-equipment-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:label="us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-7-rental-equipment-tables" xlink:href="geos-20260630.xsd#statement-note-7-rental-equipment-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-7-rental-equipment-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseTableTextBlock" xlink:label="geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleLeasebackTransactionTable" xlink:label="us-gaap_SaleLeasebackTransactionTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SaleLeasebackTransactionTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SaleLeasebackTransactionTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseTableTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-10-loss-per-common-share-tables" xlink:href="geos-20260630.xsd#statement-note-10-loss-per-common-share-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-10-loss-per-common-share-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-12-segment-information-tables" xlink:href="geos-20260630.xsd#statement-note-12-segment-information-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-12-segment-information-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_ScheduleOfRevenueGeneratedByTheCompanysSubsidiariesTableTextBlock" xlink:label="geos_ScheduleOfRevenueGeneratedByTheCompanysSubsidiariesTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongLivedAssetsByGeographicAreasTableTextBlock" xlink:label="us-gaap_LongLivedAssetsByGeographicAreasTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReconciliationOfRevenueFromSegmentsToConsolidatedTextBlock" xlink:label="us-gaap_ReconciliationOfRevenueFromSegmentsToConsolidatedTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="geos_ScheduleOfRevenueGeneratedByTheCompanysSubsidiariesTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ReconciliationOfRevenueFromSegmentsToConsolidatedTextBlock" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_LongLivedAssetsByGeographicAreasTableTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-1-significant-accounting-policies-details-textual" xlink:href="geos-20260630.xsd#statement-note-1-significant-accounting-policies-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-1-significant-accounting-policies-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_CreditTermsForTradeReceivables" xlink:label="geos_CreditTermsForTradeReceivables" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_CustomerOneMember" xlink:label="geos_CustomerOneMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_ExtendedCreditTermsForTradeReceivables" xlink:label="geos_ExtendedCreditTermsForTradeReceivables" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_NumberOfMajorCustomers" xlink:label="geos_NumberOfMajorCustomers" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis" xlink:label="srt_MajorCustomersAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain" xlink:label="srt_NameOfMajorCustomerDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain" xlink:label="srt_NameOfMajorCustomerDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember" xlink:label="srt_SubsidiariesMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsAndNotesReceivableNet" xlink:label="us-gaap_AccountsAndNotesReceivableNet" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableMember" xlink:label="us-gaap_AccountsReceivableMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="us-gaap_ConcentrationRiskBenchmarkDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="us-gaap_ConcentrationRiskBenchmarkDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="us-gaap_ConcentrationRiskByTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="us-gaap_ConcentrationRiskTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="us-gaap_ConcentrationRiskTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="us-gaap_CustomerConcentrationRiskMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:label="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonUsMember" xlink:label="us-gaap_NonUsMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="us-gaap_ResearchAndDevelopmentExpense" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashCurrent" xlink:label="us-gaap_RestrictedCashCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax" xlink:label="us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerMember" xlink:label="us-gaap_RevenueFromContractWithCustomerMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_MajorCustomersAxis" xlink:to="srt_NameOfMajorCustomerDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_ConcentrationRiskByTypeAxis" xlink:to="us-gaap_ConcentrationRiskTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:to="us-gaap_ConcentrationRiskBenchmarkDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="srt_ConsolidatedEntitiesAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="srt_SubsidiariesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="srt_StatementGeographicalAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="us-gaap_NonUsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="us-gaap_ConcentrationRiskByTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ConcentrationRiskTypeDomain" xlink:to="us-gaap_CustomerConcentrationRiskMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_ConcentrationRiskByTypeAxis" xlink:to="us-gaap_ConcentrationRiskTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ConcentrationRiskBenchmarkDomain" xlink:to="us-gaap_AccountsReceivableMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:to="us-gaap_ConcentrationRiskBenchmarkDomain-default" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="srt_MajorCustomersAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_NameOfMajorCustomerDomain" xlink:to="geos_CustomerOneMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_MajorCustomersAxis" xlink:to="srt_NameOfMajorCustomerDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ConcentrationRiskBenchmarkDomain" xlink:to="us-gaap_RevenueFromContractWithCustomerMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RestrictedCashCurrent" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_CreditTermsForTradeReceivables" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_ExtendedCreditTermsForTradeReceivables" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_NumberOfMajorCustomers" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AccountsAndNotesReceivableNet" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ResearchAndDevelopmentExpense" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-2-revenue-recognition-details-textual" xlink:href="geos-20260630.xsd#statement-note-2-revenue-recognition-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-2-revenue-recognition-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_ContractWithCustomerLiabilityRevenueRecognizedIncludingBalance" xlink:label="geos_ContractWithCustomerLiabilityRevenueRecognizedIncludingBalance" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_ContractWithCustomerTerm" xlink:label="geos_ContractWithCustomerTerm" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_WriteoffOfRentReceivable" xlink:label="geos_WriteoffOfRentReceivable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis" xlink:label="srt_ProductOrServiceAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalizedContractCostNetCurrent" xlink:label="us-gaap_CapitalizedContractCostNetCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent" xlink:label="us-gaap_ContractWithCustomerLiabilityCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:label="us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLoss" xlink:label="us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLoss" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="us-gaap_DisaggregationOfRevenueTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligation" xlink:label="us-gaap_RevenueRemainingPerformanceObligation" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubscriptionAndCirculationMember" xlink:label="us-gaap_SubscriptionAndCirculationMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:label="us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:label="us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:label="us-gaap_TimingOfTransferOfGoodOrServiceDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransferredOverTimeMember" xlink:label="us-gaap_TransferredOverTimeMember" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:to="us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_ProductOrServiceAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_SubscriptionAndCirculationMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_RangeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:to="us-gaap_TransferredOverTimeMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:to="us-gaap_TimingOfTransferOfGoodOrServiceDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisaggregationOfRevenueTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_ContractWithCustomerTerm" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_WriteoffOfRentReceivable" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ContractWithCustomerLiabilityCurrent" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CapitalizedContractCostNetCurrent" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLoss" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RevenueRemainingPerformanceObligation" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_ContractWithCustomerLiabilityRevenueRecognizedIncludingBalance" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-3-fair-value-of-financial-instruments-details-textual" xlink:href="geos-20260630.xsd#statement-note-3-fair-value-of-financial-instruments-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-3-fair-value-of-financial-instruments-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_GeovoxMember" xlink:label="geos_GeovoxMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:label="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="us-gaap_BusinessAcquisitionAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="geos_GeovoxMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables-details-textual" xlink:href="geos-20260630.xsd#statement-note-4-trade-accounts-and-financing-receivables-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_NotesReceivableInterestRateStatedPercentage" xlink:label="geos_NotesReceivableInterestRateStatedPercentage" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_NotesReceivablePeriodicPayment" xlink:label="geos_NotesReceivablePeriodicPayment" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_NotesReceivableTerm" xlink:label="geos_NotesReceivableTerm" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PromissoryNoteForSaleOfProductMember" xlink:label="geos_PromissoryNoteForSaleOfProductMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PromissoryNoteMember" xlink:label="geos_PromissoryNoteMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PromissoryNotesMaturesJanuary2027Member" xlink:label="geos_PromissoryNotesMaturesJanuary2027Member" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PromissoryNotesMaturesJanuary2029Member" xlink:label="geos_PromissoryNotesMaturesJanuary2029Member" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_SubsidiaryOilAndGasProductManufacturingOperationsInTheRussianFederationMember" xlink:label="geos_SubsidiaryOilAndGasProductManufacturingOperationsInTheRussianFederationMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_ThreePromissoryNotesMember" xlink:label="geos_ThreePromissoryNotesMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_TwoPromissoryNotesMember" xlink:label="geos_TwoPromissoryNotesMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_WirelessSeismicEquipmentCustomerMember" xlink:label="geos_WirelessSeismicEquipmentCustomerMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:label="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember" xlink:label="us-gaap_DiscontinuedOperationsDisposedOfBySaleMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis" xlink:label="us-gaap_DisposalGroupClassificationAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain" xlink:label="us-gaap_DisposalGroupClassificationDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain" xlink:label="us-gaap_DisposalGroupClassificationDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesReceivableGross" xlink:label="us-gaap_NotesReceivableGross" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableTypeDomain" xlink:label="us-gaap_ReceivableTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableTypeDomain" xlink:label="us-gaap_ReceivableTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesTypeLeaseInterestIncome" xlink:label="us-gaap_SalesTypeLeaseInterestIncome" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesTypeLeaseLeaseReceivable" xlink:label="us-gaap_SalesTypeLeaseLeaseReceivable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:to="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="us-gaap_ReceivableTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_DisposalGroupClassificationAxis" xlink:to="us-gaap_DisposalGroupClassificationDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_PromissoryNotesMaturesJanuary2027Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="us-gaap_ReceivableTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_PromissoryNotesMaturesJanuary2029Member" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_ThreePromissoryNotesMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_TwoPromissoryNotesMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_WirelessSeismicEquipmentCustomerMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_PromissoryNoteForSaleOfProductMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_DisposalGroupClassificationAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisposalGroupClassificationDomain" xlink:to="us-gaap_DiscontinuedOperationsDisposedOfBySaleMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_DisposalGroupClassificationAxis" xlink:to="us-gaap_DisposalGroupClassificationDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:to="geos_SubsidiaryOilAndGasProductManufacturingOperationsInTheRussianFederationMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:to="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain-default" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_PromissoryNoteMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NotesReceivableGross" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_NotesReceivableInterestRateStatedPercentage" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_NotesReceivablePeriodicPayment" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SalesTypeLeaseLeaseReceivable" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SalesTypeLeaseInterestIncome" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_NotesReceivableTerm" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLosses" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-5-inventories-details-textual" xlink:href="geos-20260630.xsd#statement-note-5-inventories-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-5-inventories-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_SemifinishedGoodsAndComponentPartsMember" xlink:label="geos_SemifinishedGoodsAndComponentPartsMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryCurrentTable" xlink:label="us-gaap_InventoryCurrentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryRawMaterials" xlink:label="us-gaap_InventoryRawMaterials" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryWriteDown" xlink:label="us-gaap_InventoryWriteDown" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesInventoryAxis" xlink:label="us-gaap_PublicUtilitiesInventoryAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain" xlink:label="us-gaap_PublicUtilitiesInventoryTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain" xlink:label="us-gaap_PublicUtilitiesInventoryTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_PublicUtilitiesInventoryAxis" xlink:to="us-gaap_PublicUtilitiesInventoryTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InventoryCurrentTable" xlink:to="us-gaap_PublicUtilitiesInventoryAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PublicUtilitiesInventoryTypeDomain" xlink:to="geos_SemifinishedGoodsAndComponentPartsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_PublicUtilitiesInventoryAxis" xlink:to="us-gaap_PublicUtilitiesInventoryTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InventoryCurrentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryCurrentTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryWriteDown" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryRawMaterials" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-6-property-plant-and-equipment-details-textual" xlink:href="geos-20260630.xsd#statement-note-6-property-plant-and-equipment-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-6-property-plant-and-equipment-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_GainLossOnDerecognitionOfAssets" xlink:label="geos_GainLossOnDerecognitionOfAssets" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember" xlink:label="srt_SubsidiariesMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation" xlink:label="us-gaap_Depreciation" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="us-gaap_SubsequentEventTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="srt_ConsolidatedEntitiesAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="srt_SubsidiariesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_GainLossOnDerecognitionOfAssets" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_Depreciation" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-7-rental-equipment-details-textual" xlink:href="geos-20260630.xsd#statement-note-7-rental-equipment-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-7-rental-equipment-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_LeaseReceivableMember" xlink:label="geos_LeaseReceivableMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:label="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="us-gaap_AccountsReceivableNetCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquipmentExpense" xlink:label="us-gaap_EquipmentExpense" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquipmentMember" xlink:label="us-gaap_EquipmentMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextRollingTwelveMonths" xlink:label="us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextRollingTwelveMonths" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeaseTermOfContract" xlink:label="us-gaap_LessorOperatingLeaseTermOfContract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableTypeDomain" xlink:label="us-gaap_ReceivableTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableTypeDomain" xlink:label="us-gaap_ReceivableTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleLeasebackTransactionTable" xlink:label="us-gaap_SaleLeasebackTransactionTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="us-gaap_ReceivableTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SaleLeasebackTransactionTable" xlink:to="srt_RangeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SaleLeasebackTransactionTable" xlink:to="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_EquipmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SaleLeasebackTransactionTable" xlink:to="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_LeaseReceivableMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="us-gaap_ReceivableTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SaleLeasebackTransactionTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SaleLeasebackTransactionTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LessorOperatingLeaseTermOfContract" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AccountsReceivableNetCurrent" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextRollingTwelveMonths" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EquipmentExpense" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-8-longterm-debt-details-textual" xlink:href="geos-20260630.xsd#statement-note-8-longterm-debt-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-8-longterm-debt-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_CashReservePledged" xlink:label="geos_CashReservePledged" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_DebtInstrumentCovenantCurrentRatio" xlink:label="geos_DebtInstrumentCovenantCurrentRatio" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_DebtInstrumentCovenantInterestCoverageRatio" xlink:label="geos_DebtInstrumentCovenantInterestCoverageRatio" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_DebtInstrumentCovenantMinimumConsolidatedTangibleNetWorth" xlink:label="geos_DebtInstrumentCovenantMinimumConsolidatedTangibleNetWorth" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_DebtInstrumentCovenantMinimumLiquidity" xlink:label="geos_DebtInstrumentCovenantMinimumLiquidity" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_WoodforestNationalBankMember" xlink:label="geos_WoodforestNationalBankMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis" xlink:label="us-gaap_CreditFacilityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain" xlink:label="us-gaap_CreditFacilityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain" xlink:label="us-gaap_CreditFacilityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable" xlink:label="us-gaap_DebtInstrumentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentVariableInterestRateTypeExtensibleEnumeration" xlink:label="us-gaap_DebtInstrumentVariableInterestRateTypeExtensibleEnumeration" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LetterOfCreditMember" xlink:label="us-gaap_LetterOfCreditMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit" xlink:label="us-gaap_LineOfCredit" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="us-gaap_LineOfCreditFacilityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember" xlink:label="us-gaap_LineOfCreditMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt" xlink:label="us-gaap_LongTermDebt" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDebtIssuanceCosts" xlink:label="us-gaap_PaymentsOfDebtIssuanceCosts" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_LineOfCreditFacilityAxis" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_CreditFacilityAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="us-gaap_LineOfCreditMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_LineOfCreditFacilityAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="geos_WoodforestNationalBankMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_LineOfCreditFacilityAxis" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="srt_RangeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="us-gaap_LetterOfCreditMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtInstrumentTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LongTermDebt" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_DebtInstrumentCovenantMinimumConsolidatedTangibleNetWorth" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_DebtInstrumentCovenantMinimumLiquidity" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_DebtInstrumentCovenantCurrentRatio" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_DebtInstrumentCovenantInterestCoverageRatio" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LineOfCredit" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_CashReservePledged" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PaymentsOfDebtIssuanceCosts" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtInstrumentVariableInterestRateTypeExtensibleEnumeration" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-9-stockbased-compensation-details-textual" xlink:href="geos-20260630.xsd#statement-note-9-stockbased-compensation-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-9-stockbased-compensation-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramTable" xlink:label="srt_ShareRepurchaseProgramTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="us-gaap_RestrictedStockUnitsRSUMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="srt_ShareRepurchaseProgramTable" xlink:to="us-gaap_AwardTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockUnitsRSUMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="srt_ShareRepurchaseProgramTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="srt_ShareRepurchaseProgramTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AllocatedShareBasedCompensationExpense" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-10-loss-per-common-share-details-textual" xlink:href="geos-20260630.xsd#statement-note-10-loss-per-common-share-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-10-loss-per-common-share-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="us-gaap_RestrictedStockUnitsRSUMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_RestrictedStockUnitsRSUMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-11-commitments-and-contingencies-details-textual" xlink:href="geos-20260630.xsd#statement-note-11-commitments-and-contingencies-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-11-commitments-and-contingencies-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_AquanaLLSMember" xlink:label="geos_AquanaLLSMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_BusinessCombinationContingentConsiderationEarnOutPeriod" xlink:label="geos_BusinessCombinationContingentConsiderationEarnOutPeriod" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_BusinessCombinationRequiredContinuedEmploymentOfKeyEmployeesPeriod" xlink:label="geos_BusinessCombinationRequiredContinuedEmploymentOfKeyEmployeesPeriod" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_GeovoxMember" xlink:label="geos_GeovoxMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCommitmentsTable" xlink:label="us-gaap_OtherCommitmentsTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_OtherCommitmentsTable" xlink:to="us-gaap_BusinessAcquisitionAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="geos_GeovoxMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="geos_AquanaLLSMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_OtherCommitmentsTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherCommitmentsTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_BusinessCombinationContingentConsiderationEarnOutPeriod" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_BusinessCombinationRequiredContinuedEmploymentOfKeyEmployeesPeriod" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-12-segment-information-details-textual" xlink:href="geos-20260630.xsd#statement-note-12-segment-information-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-12-segment-information-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments" xlink:label="us-gaap_NumberOfOperatingSegments" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments" xlink:label="us-gaap_NumberOfReportableSegments" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NumberOfOperatingSegments" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NumberOfReportableSegments" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-13-income-taxes-details-textual" xlink:href="geos-20260630.xsd#statement-note-13-income-taxes-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-13-income-taxes-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTable" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_EffectiveIncomeTaxRateReconciliationTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncomeTaxExpenseBenefit" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-14-exit-and-disposal-costs-details-textual" xlink:href="geos-20260630.xsd#statement-note-14-exit-and-disposal-costs-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-14-exit-and-disposal-costs-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_The2026OrganizationalChangePlanMember" xlink:label="geos_The2026OrganizationalChangePlanMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectOnFutureCashFlowsAmount" xlink:label="us-gaap_EffectOnFutureCashFlowsAmount" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain" xlink:label="us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain" xlink:label="us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOnFutureEarningsAndCashFlowsResultingFromExitPlanAxis" xlink:label="us-gaap_EffectsOnFutureEarningsAndCashFlowsResultingFromExitPlanAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReducedEmployeeExpensesMember" xlink:label="us-gaap_ReducedEmployeeExpensesMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" xlink:label="us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCharges" xlink:label="us-gaap_RestructuringCharges" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanAxis" xlink:label="us-gaap_RestructuringPlanAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanDomain" xlink:label="us-gaap_RestructuringPlanDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanDomain" xlink:label="us-gaap_RestructuringPlanDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringReserve" xlink:label="us-gaap_RestructuringReserve" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:label="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_EffectsOnFutureEarningsAndCashFlowsResultingFromExitPlanAxis" xlink:to="us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_RestructuringPlanAxis" xlink:to="us-gaap_RestructuringPlanDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:to="us-gaap_RestructuringPlanAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RestructuringPlanDomain" xlink:to="geos_The2026OrganizationalChangePlanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_RestructuringPlanAxis" xlink:to="us-gaap_RestructuringPlanDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:to="us-gaap_EffectsOnFutureEarningsAndCashFlowsResultingFromExitPlanAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain" xlink:to="us-gaap_ReducedEmployeeExpensesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_EffectsOnFutureEarningsAndCashFlowsResultingFromExitPlanAxis" xlink:to="us-gaap_EffectsOnFutureEarningsAndCashFlowsByTypeOfEffectDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EffectOnFutureCashFlowsAmount" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RestructuringCharges" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RestructuringReserve" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-3-fair-value-of-financial-instruments-contingent-consideration-details" xlink:href="geos-20260630.xsd#statement-note-3-fair-value-of-financial-instruments-contingent-consideration-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-3-fair-value-of-financial-instruments-contingent-consideration-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_BusinessCombinationContingentConsiderationLiabilityAcquiredDuringPeriod" xlink:label="geos_BusinessCombinationContingentConsiderationLiabilityAcquiredDuringPeriod" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_BusinessCombinationContingentConsiderationLiabilityFairValueAdjustments" xlink:label="geos_BusinessCombinationContingentConsiderationLiabilityFairValueAdjustments" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_GeovoxMember" xlink:label="geos_GeovoxMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:label="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="us-gaap_BusinessAcquisitionAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="geos_GeovoxMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_BusinessCombinationContingentConsiderationLiabilityAcquiredDuringPeriod" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_BusinessCombinationContingentConsiderationLiabilityFairValueAdjustments" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables-schedule-of-trade-accounts-and-notes-receivable-details" xlink:href="geos-20260630.xsd#statement-note-4-trade-accounts-and-financing-receivables-schedule-of-trade-accounts-and-notes-receivable-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables-schedule-of-trade-accounts-and-notes-receivable-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableGross" xlink:label="us-gaap_AccountsReceivableGross" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNet" xlink:label="us-gaap_AccountsReceivableNet" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivable" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AccountsReceivableGross" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AllowanceForDoubtfulAccountsReceivable" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AccountsReceivableNet" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables-schedule-of-notes-receivable-details" xlink:href="geos-20260630.xsd#statement-note-4-trade-accounts-and-financing-receivables-schedule-of-notes-receivable-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables-schedule-of-notes-receivable-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PromissoryNotesMaturesJanuary2027Member" xlink:label="geos_PromissoryNotesMaturesJanuary2027Member" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_SalesTypeLeaseMember" xlink:label="geos_SalesTypeLeaseMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:label="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesAndLoansReceivableNetCurrent" xlink:label="us-gaap_NotesAndLoansReceivableNetCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesAndLoansReceivableNetNoncurrent" xlink:label="us-gaap_NotesAndLoansReceivableNetNoncurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesReceivableGross" xlink:label="us-gaap_NotesReceivableGross" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesReceivableNet" xlink:label="us-gaap_NotesReceivableNet" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableTypeDomain" xlink:label="us-gaap_ReceivableTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableTypeDomain" xlink:label="us-gaap_ReceivableTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="us-gaap_ReceivableTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_PromissoryNotesMaturesJanuary2027Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="us-gaap_ReceivableTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ReceivableTypeDomain" xlink:to="geos_SalesTypeLeaseMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NotesReceivableGross" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLosses" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NotesReceivableNet" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NotesAndLoansReceivableNetCurrent" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NotesAndLoansReceivableNetNoncurrent" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-5-inventories-schedule-of-inventories-details" xlink:href="geos-20260630.xsd#statement-note-5-inventories-schedule-of-inventories-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-5-inventories-schedule-of-inventories-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_InventoryCurrentAndNoncurrent" xlink:label="geos_InventoryCurrentAndNoncurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryCurrentTable" xlink:label="us-gaap_InventoryCurrentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryFinishedGoods" xlink:label="us-gaap_InventoryFinishedGoods" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNet" xlink:label="us-gaap_InventoryNet" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNoncurrent" xlink:label="us-gaap_InventoryNoncurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryRawMaterials" xlink:label="us-gaap_InventoryRawMaterials" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryValuationReserves" xlink:label="us-gaap_InventoryValuationReserves" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryWorkInProcess" xlink:label="us-gaap_InventoryWorkInProcess" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InventoryCurrentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryCurrentTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryFinishedGoods" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryWorkInProcess" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryRawMaterials" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryValuationReserves" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_InventoryCurrentAndNoncurrent" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryNet" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InventoryNoncurrent" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-6-property-plant-and-equipment-summary-of-property-plant-and-equipment-details" xlink:href="geos-20260630.xsd#statement-note-6-property-plant-and-equipment-summary-of-property-plant-and-equipment-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-6-property-plant-and-equipment-summary-of-property-plant-and-equipment-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BuildingAndBuildingImprovementsMember" xlink:label="us-gaap_BuildingAndBuildingImprovementsMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember" xlink:label="us-gaap_ConstructionInProgressMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="us-gaap_FurnitureAndFixturesMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandAndLandImprovementsMember" xlink:label="us-gaap_LandAndLandImprovementsMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MachineryAndEquipmentMember" xlink:label="us-gaap_MachineryAndEquipmentMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="us-gaap_PropertyPlantAndEquipmentGross" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ToolsDiesAndMoldsMember" xlink:label="us-gaap_ToolsDiesAndMoldsMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransportationEquipmentMember" xlink:label="us-gaap_TransportationEquipmentMember" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_LandAndLandImprovementsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_BuildingAndBuildingImprovementsMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_MachineryAndEquipmentMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_FurnitureAndFixturesMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_ToolsDiesAndMoldsMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_ConstructionInProgressMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_TransportationEquipmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentGross" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentNet" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-7-rental-equipment-rental-equipment-details" xlink:href="geos-20260630.xsd#statement-note-7-rental-equipment-rental-equipment-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-7-rental-equipment-rental-equipment-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseAccumulatedDepreciation" xlink:label="geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseAccumulatedDepreciation" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseAfterAccumulatedDepreciation" xlink:label="geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseAfterAccumulatedDepreciation" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseBeforeAccumulatedDepreciation" xlink:label="geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseBeforeAccumulatedDepreciation" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquipmentMember" xlink:label="us-gaap_EquipmentMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleLeasebackTransactionTable" xlink:label="us-gaap_SaleLeasebackTransactionTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SaleLeasebackTransactionTable" xlink:to="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_EquipmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SaleLeasebackTransactionTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SaleLeasebackTransactionTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseBeforeAccumulatedDepreciation" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseAccumulatedDepreciation" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_PropertyPlantAndEquipmentLessorAssetUnderLeaseAfterAccumulatedDepreciation" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-12-segment-information-long-lived-assets-by-location-details" xlink:href="geos-20260630.xsd#statement-note-12-segment-information-long-lived-assets-by-location-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-12-segment-information-long-lived-assets-by-location-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_CA" xlink:label="country_CA" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_CO" xlink:label="country_CO" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_GB" xlink:label="country_GB" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US" xlink:label="country_US" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoncurrentAssets" xlink:label="us-gaap_NoncurrentAssets" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:label="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:to="srt_StatementGeographicalAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_US" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_CA" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_CO" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_GB" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NoncurrentAssets" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-consolidated-balance-sheets-current-period-unaudited" xlink:href="geos-20260630.xsd#statement-consolidated-balance-sheets-current-period-unaudited" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-consolidated-balance-sheets-current-period-unaudited" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_RentalEquipmentNet" xlink:label="geos_RentalEquipmentNet" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsNotesAndLoansReceivableNetCurrent" xlink:label="us-gaap_AccountsNotesAndLoansReceivableNetCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent" xlink:label="us-gaap_AccountsPayableCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalCommonStock" xlink:label="us-gaap_AdditionalPaidInCapitalCommonStock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent" xlink:label="us-gaap_AssetsCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="us-gaap_AssetsCurrentAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="us-gaap_CommitmentsAndContingencies" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent" xlink:label="us-gaap_ContractWithCustomerLiabilityCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet" xlink:label="us-gaap_DeferredIncomeTaxLiabilitiesNet" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill" xlink:label="us-gaap_Goodwill" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNet" xlink:label="us-gaap_InventoryNet" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNoncurrent" xlink:label="us-gaap_InventoryNoncurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent" xlink:label="us-gaap_LiabilitiesCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="us-gaap_LiabilitiesCurrentAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermAccountsNotesAndLoansReceivableNetNoncurrent" xlink:label="us-gaap_LongTermAccountsNotesAndLoansReceivableNetNoncurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityCurrent" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:label="us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="us-gaap_OtherAssetsNoncurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesCurrent" xlink:label="us-gaap_OtherLiabilitiesCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockValue" xlink:label="us-gaap_PreferredStockValue" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashCurrent" xlink:label="us-gaap_RestrictedCashCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="us-gaap_StockholdersEquityAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockValue" xlink:label="us-gaap_TreasuryStockValue" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AssetsCurrentAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_RestrictedCashCurrent" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AccountsNotesAndLoansReceivableNetCurrent" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_InventoryNet" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AssetsCurrent" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_InventoryNoncurrent" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="geos_RentalEquipmentNet" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_PropertyPlantAndEquipmentNet" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_LongTermAccountsNotesAndLoansReceivableNetNoncurrent" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_OperatingLeaseRightOfUseAsset" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_Goodwill" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNet" xlink:type="arc"/>
    <link:definitionArc order="13" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_OtherAssetsNoncurrent" xlink:type="arc"/>
    <link:definitionArc order="14" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_Assets" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LiabilitiesCurrentAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_AccountsPayableCurrent" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_OperatingLeaseLiabilityCurrent" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_ContractWithCustomerLiabilityCurrent" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_OtherLiabilitiesCurrent" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LiabilitiesCurrent" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_DeferredIncomeTaxLiabilitiesNet" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_Liabilities" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_CommitmentsAndContingencies" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquityAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_PreferredStockValue" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_CommonStockValue" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_AdditionalPaidInCapitalCommonStock" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_TreasuryStockValue" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquity" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-consolidated-statements-of-operations-unaudited" xlink:href="geos-20260630.xsd#statement-consolidated-statements-of-operations-unaudited" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-consolidated-statements-of-operations-unaudited" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_RentalMember" xlink:label="geos_RentalMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis" xlink:label="srt_ProductOrServiceAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenue" xlink:label="us-gaap_CostOfRevenue" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenueAbstract" xlink:label="us-gaap_CostOfRevenueAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareAbstract" xlink:label="us-gaap_EarningsPerShareAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic" xlink:label="us-gaap_EarningsPerShareBasic" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="us-gaap_EarningsPerShareDiluted" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyTransactionGainLossBeforeTax" xlink:label="us-gaap_ForeignCurrencyTransactionGainLossBeforeTax" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDispositionOfAssets" xlink:label="us-gaap_GainLossOnDispositionOfAssets" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossProfit" xlink:label="us-gaap_GrossProfit" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating" xlink:label="us-gaap_InterestExpenseNonoperating" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest" xlink:label="us-gaap_InvestmentIncomeInterest" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense" xlink:label="us-gaap_NonoperatingIncomeExpense" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpenseAbstract" xlink:label="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpenses" xlink:label="us-gaap_OperatingExpenses" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpensesAbstract" xlink:label="us-gaap_OperatingExpensesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss" xlink:label="us-gaap_OperatingIncomeLoss" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="us-gaap_OtherNonoperatingIncomeExpense" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember" xlink:label="us-gaap_ProductMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProvisionForDoubtfulAccounts" xlink:label="us-gaap_ProvisionForDoubtfulAccounts" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="us-gaap_ResearchAndDevelopmentExpense" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesAbstract" xlink:label="us-gaap_RevenuesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpense" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_ProductOrServiceAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_ProductMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="geos_RentalMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RevenuesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RevenuesAbstract" xlink:to="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CostOfRevenueAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CostOfRevenueAbstract" xlink:to="us-gaap_CostOfRevenue" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CostOfRevenueAbstract" xlink:to="us-gaap_GrossProfit" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OperatingExpensesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_SellingGeneralAndAdministrativeExpense" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_ResearchAndDevelopmentExpense" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_ProvisionForDoubtfulAccounts" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_OperatingExpenses" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_GainLossOnDispositionOfAssets" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_OperatingIncomeLoss" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_InterestExpenseNonoperating" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_InvestmentIncomeInterest" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_ForeignCurrencyTransactionGainLossBeforeTax" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_OtherNonoperatingIncomeExpense" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_NonoperatingIncomeExpense" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_IncomeTaxExpenseBenefit" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_NetIncomeLoss" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EarningsPerShareAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareBasic" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareDiluted" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-consolidated-statements-of-cash-flows-unaudited" xlink:href="geos-20260630.xsd#statement-consolidated-statements-of-cash-flows-unaudited" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-consolidated-statements-of-cash-flows-unaudited" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_AmortizationOfDiscountOnNoteReceivable" xlink:label="geos_AmortizationOfDiscountOnNoteReceivable" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_GainLossFromSaleOfUsedRentalEquipment" xlink:label="geos_GainLossFromSaleOfUsedRentalEquipment" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_InventoriesTransferredToRentalEquipment" xlink:label="geos_InventoriesTransferredToRentalEquipment" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_IssuanceOfNotesReceivableInConnectionWithSaleOfUsedRentalEquipment" xlink:label="geos_IssuanceOfNotesReceivableInConnectionWithSaleOfUsedRentalEquipment" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_ProceedsFromSaleOfUsedRentalEquipment" xlink:label="geos_ProceedsFromSaleOfUsedRentalEquipment" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="us-gaap_AmortizationOfIntangibleAssets" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSoldDepreciation" xlink:label="us-gaap_CostOfGoodsAndServicesSoldDepreciation" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxesAndTaxCredits" xlink:label="us-gaap_DeferredIncomeTaxesAndTaxCredits" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationNonproduction" xlink:label="us-gaap_DepreciationNonproduction" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:label="us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDispositionOfAssets1" xlink:label="us-gaap_GainLossOnDispositionOfAssets1" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxesPaidNet" xlink:label="us-gaap_IncomeTaxesPaidNet" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsAndNotesReceivable" xlink:label="us-gaap_IncreaseDecreaseInAccountsAndNotesReceivable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsPayableTrade" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableTrade" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInInventories" xlink:label="us-gaap_IncreaseDecreaseInInventories" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherOperatingLiabilities" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryWriteDown" xlink:label="us-gaap_InventoryWriteDown" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:label="us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDebtIssuanceCosts" xlink:label="us-gaap_PaymentsOfDebtIssuanceCosts" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:label="us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireEquipmentOnLease" xlink:label="us-gaap_PaymentsToAcquireEquipmentOnLease" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromDivestitureOfInterestInSubsidiariesAndAffiliates" xlink:label="us-gaap_ProceedsFromDivestitureOfInterestInSubsidiariesAndAffiliates" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" xlink:label="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleOfShortTermInvestments" xlink:label="us-gaap_ProceedsFromSaleOfShortTermInvestments" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProvisionForDoubtfulAccounts" xlink:label="us-gaap_ProvisionForDoubtfulAccounts" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealizedInvestmentGainsLosses" xlink:label="us-gaap_RealizedInvestmentGainsLosses" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashCurrent" xlink:label="us-gaap_RestrictedCashCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetIncomeLoss" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_DeferredIncomeTaxesAndTaxCredits" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_DepreciationNonproduction" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_CostOfGoodsAndServicesSoldDepreciation" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AmortizationOfIntangibleAssets" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="geos_AmortizationOfDiscountOnNoteReceivable" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ShareBasedCompensation" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ProvisionForDoubtfulAccounts" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_InventoryWriteDown" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="geos_GainLossFromSaleOfUsedRentalEquipment" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_GainLossOnDispositionOfAssets1" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_RealizedInvestmentGainsLosses" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInAccountsAndNotesReceivable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInInventories" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInAccountsPayableTrade" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireEquipmentOnLease" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="geos_ProceedsFromSaleOfUsedRentalEquipment" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfShortTermInvestments" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromDivestitureOfInterestInSubsidiariesAndAffiliates" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsOfDebtIssuanceCosts" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RestrictedCashCurrent" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SupplementalCashFlowInformationAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_IncomeTaxesPaidNet" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:to="geos_IssuanceOfNotesReceivableInConnectionWithSaleOfUsedRentalEquipment" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:to="geos_InventoriesTransferredToRentalEquipment" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-consolidated-statements-of-comprehensive-income-loss-unaudited" xlink:href="geos-20260630.xsd#statement-consolidated-statements-of-comprehensive-income-loss-unaudited" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-consolidated-statements-of-comprehensive-income-loss-unaudited" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:to="us-gaap_ComprehensiveIncomeNetOfTax" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-2-revenue-recognition-disaggregation-of-revenue-details" xlink:href="geos-20260630.xsd#statement-note-2-revenue-recognition-disaggregation-of-revenue-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-2-revenue-recognition-disaggregation-of-revenue-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_EnergySolutionsMember" xlink:label="geos_EnergySolutionsMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_IntelligentIndustrialMember" xlink:label="geos_IntelligentIndustrialMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_SmartWaterMember" xlink:label="geos_SmartWaterMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis" xlink:label="srt_ConsolidationItemsAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain" xlink:label="srt_ConsolidationItemsDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain" xlink:label="srt_ConsolidationItemsDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis" xlink:label="srt_ProductOrServiceAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="us-gaap_DisaggregationOfRevenueTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember" xlink:label="us-gaap_OperatingSegmentsMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember" xlink:label="us-gaap_ProductMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain" xlink:label="us-gaap_SegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain" xlink:label="us-gaap_SegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="us-gaap_StatementBusinessSegmentsAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ConsolidationItemsAxis" xlink:to="srt_ConsolidationItemsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementBusinessSegmentsAxis" xlink:to="us-gaap_SegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_ConsolidationItemsAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidationItemsDomain" xlink:to="us-gaap_OperatingSegmentsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ConsolidationItemsAxis" xlink:to="srt_ConsolidationItemsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="us-gaap_StatementBusinessSegmentsAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SegmentDomain" xlink:to="geos_SmartWaterMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_StatementBusinessSegmentsAxis" xlink:to="us-gaap_SegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_ProductOrServiceAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_ProductMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SegmentDomain" xlink:to="geos_EnergySolutionsMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SegmentDomain" xlink:to="geos_IntelligentIndustrialMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisaggregationOfRevenueTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-2-revenue-recognition-revenue-by-geographic-area-details" xlink:href="geos-20260630.xsd#statement-note-2-revenue-recognition-revenue-by-geographic-area-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-2-revenue-recognition-revenue-by-geographic-area-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_CA" xlink:label="country_CA" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_MX" xlink:label="country_MX" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US" xlink:label="country_US" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_OtherMember" xlink:label="geos_OtherMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AsiaMember" xlink:label="srt_AsiaMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EuropeMember" xlink:label="srt_EuropeMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis" xlink:label="srt_ProductOrServiceAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SouthAmericaMember" xlink:label="srt_SouthAmericaMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="us-gaap_DisaggregationOfRevenueTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember" xlink:label="us-gaap_ProductMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_StatementGeographicalAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="srt_AsiaMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_ProductOrServiceAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_ProductMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_CA" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="srt_EuropeMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_MX" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_US" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="srt_SouthAmericaMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="geos_OtherMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisaggregationOfRevenueTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-10-loss-per-common-share-computation-of-loss-per-share-details" xlink:href="geos-20260630.xsd#statement-note-10-loss-per-common-share-computation-of-loss-per-share-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-10-loss-per-common-share-computation-of-loss-per-share-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareAbstract" xlink:label="us-gaap_EarningsPerShareAbstract" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic" xlink:label="us-gaap_EarningsPerShareBasic" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="us-gaap_EarningsPerShareDiluted" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:label="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EarningsPerShareAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareBasic" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareDiluted" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-12-segment-information-schedule-of-revenue-generated-by-the-companys-subsidiaries-details" xlink:href="geos-20260630.xsd#statement-note-12-segment-information-schedule-of-revenue-generated-by-the-companys-subsidiaries-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-12-segment-information-schedule-of-revenue-generated-by-the-companys-subsidiaries-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_CanadaSubsidiaryMember" xlink:label="geos_CanadaSubsidiaryMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_UnitedKingdomSubsidiaryMember" xlink:label="geos_UnitedKingdomSubsidiaryMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_UnitedStatesSubsidiaryMember" xlink:label="geos_UnitedStatesSubsidiaryMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues" xlink:label="us-gaap_Revenues" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_EntityDomain" xlink:to="geos_UnitedStatesSubsidiaryMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_EntityDomain" xlink:to="geos_CanadaSubsidiaryMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_EntityDomain" xlink:to="geos_UnitedKingdomSubsidiaryMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_Revenues" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-12-segment-information-summary-of-revenue-by-geographic-area-details" xlink:href="geos-20260630.xsd#statement-note-12-segment-information-summary-of-revenue-by-geographic-area-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-12-segment-information-summary-of-revenue-by-geographic-area-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_CA" xlink:label="country_CA" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_MX" xlink:label="country_MX" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US" xlink:label="country_US" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_OtherMember" xlink:label="geos_OtherMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AsiaMember" xlink:label="srt_AsiaMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EuropeMember" xlink:label="srt_EuropeMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SouthAmericaMember" xlink:label="srt_SouthAmericaMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues" xlink:label="us-gaap_Revenues" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="srt_StatementGeographicalAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="srt_AsiaMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_CA" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="srt_EuropeMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_MX" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_US" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="srt_SouthAmericaMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="geos_OtherMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_Revenues" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-3-fair-value-of-financial-instruments-fair-value-by-hierarchy-details" xlink:href="geos-20260630.xsd#statement-note-3-fair-value-of-financial-instruments-fair-value-by-hierarchy-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-3-fair-value-of-financial-instruments-fair-value-by-hierarchy-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_GeovoxMember" xlink:label="geos_GeovoxMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:label="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="us-gaap_BusinessAcquisitionAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="geos_GeovoxMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables-schedule-of-allowance-for-credit-losses-details" xlink:href="geos-20260630.xsd#statement-note-4-trade-accounts-and-financing-receivables-schedule-of-allowance-for-credit-losses-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-4-trade-accounts-and-financing-receivables-schedule-of-allowance-for-credit-losses-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_AccountsReceivableAllowanceForCreditLossWriteoff1" xlink:label="geos_AccountsReceivableAllowanceForCreditLossWriteoff1" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivable" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableRecoveries" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivableRecoveries" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProvisionForLoanLeaseAndOtherLosses" xlink:label="us-gaap_ProvisionForLoanLeaseAndOtherLosses" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AllowanceForDoubtfulAccountsReceivable" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ProvisionForLoanLeaseAndOtherLosses" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AllowanceForDoubtfulAccountsReceivableRecoveries" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_AccountsReceivableAllowanceForCreditLossWriteoff1" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-note-12-segment-information-summary-of-segment-information-details" xlink:href="geos-20260630.xsd#statement-note-12-segment-information-summary-of-segment-information-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-note-12-segment-information-summary-of-segment-information-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_EnergySolutionsMember" xlink:label="geos_EnergySolutionsMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_ImpairmentInventoryObsolescenceAndStockBasedCompensationExpenses" xlink:label="geos_ImpairmentInventoryObsolescenceAndStockBasedCompensationExpenses" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_IntelligentIndustrialMember" xlink:label="geos_IntelligentIndustrialMember" xlink:type="locator"/>
    <link:loc xlink:href="geos-20260630.xsd#geos_SmartWaterMember" xlink:label="geos_SmartWaterMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis" xlink:label="srt_ConsolidationItemsAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain" xlink:label="srt_ConsolidationItemsDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain" xlink:label="srt_ConsolidationItemsDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember" xlink:label="us-gaap_CorporateNonSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenue" xlink:label="us-gaap_CostOfRevenue" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAndAmortization" xlink:label="us-gaap_DepreciationAndAmortization" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDispositionOfAssets" xlink:label="us-gaap_GainLossOnDispositionOfAssets" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossProfit" xlink:label="us-gaap_GrossProfit" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpense" xlink:label="us-gaap_InterestExpense" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest" xlink:label="us-gaap_InvestmentIncomeInterest" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpenses" xlink:label="us-gaap_OperatingExpenses" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss" xlink:label="us-gaap_OperatingIncomeLoss" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember" xlink:label="us-gaap_OperatingSegmentsMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain" xlink:label="us-gaap_SegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain" xlink:label="us-gaap_SegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="us-gaap_StatementBusinessSegmentsAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ConsolidationItemsAxis" xlink:to="srt_ConsolidationItemsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementBusinessSegmentsAxis" xlink:to="us-gaap_SegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="srt_ConsolidationItemsAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidationItemsDomain" xlink:to="us-gaap_OperatingSegmentsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ConsolidationItemsAxis" xlink:to="srt_ConsolidationItemsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="us-gaap_StatementBusinessSegmentsAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SegmentDomain" xlink:to="geos_SmartWaterMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_StatementBusinessSegmentsAxis" xlink:to="us-gaap_SegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SegmentDomain" xlink:to="geos_EnergySolutionsMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SegmentDomain" xlink:to="geos_IntelligentIndustrialMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidationItemsDomain" xlink:to="us-gaap_CorporateNonSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CostOfRevenue" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_GrossProfit" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OperatingExpenses" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_GainLossOnDispositionOfAssets" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OperatingIncomeLoss" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentIncomeInterest" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InterestExpense" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DepreciationAndAmortization" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="geos_ImpairmentInventoryObsolescenceAndStockBasedCompensationExpenses" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.geospace.com/20260630/role/statement-consolidated-statements-of-stockholders-equity-unaudited" xlink:href="geos-20260630.xsd#statement-consolidated-statements-of-stockholders-equity-unaudited" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.geospace.com/20260630/role/statement-consolidated-statements-of-stockholders-equity-unaudited" xlink:type="extended">
    <link:loc xlink:href="geos-20260630.xsd#geos_CommonStockOutstandingMember" xlink:label="geos_CommonStockOutstandingMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="us-gaap_AdditionalPaidInCapitalMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:label="us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember" xlink:label="us-gaap_RetainedEarningsMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding" xlink:label="us-gaap_SharesOutstanding" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation" xlink:label="us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross" xlink:label="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember" xlink:label="us-gaap_TreasuryStockCommonMember" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockSharesAcquired" xlink:label="us-gaap_TreasuryStockSharesAcquired" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="geos_CommonStockOutstandingMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AdditionalPaidInCapitalMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_TreasuryStockCommonMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharesOutstanding" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquity" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TreasuryStockSharesAcquired" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-roles-2026.xsd#eedm1" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain" xlink:label="us-gaap_VariableRateDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember" xlink:label="us-gaap_SecuredOvernightFinancingRateSofrMember" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="us-gaap_SecuredOvernightFinancingRateSofrMember" xlink:type="arc"/>
  </link:definitionLink>
</link:linkbase>
