TurkishJournalofEarthSciences (TurkishJ.EarthSci.),Vol.12, 2003,pp.67-90. Copyright©TÜB‹TAK ExtensionalNeotectonicRegimethroughtheNEEdgeof theOuterIspartaAngle,SWTurkey: NewFieldandSeismicData AL‹KOÇY‹⁄‹T&A.ARDAÖZACAR MiddleEastTechnicalUniversity,DepartmentofGeologicalEngineering, TectonicResearchUnit,TR-06531Ankara,Turkey (e-mail:akoc@metu.edu.tr) Abstract: TheAkflehir-AfyonGraben(AAG)isa4–20-km-wide,130-km-longNW–trendingdepressionthat separatescentralAnatoliaintheNEandtheIspartaAngle(IA)intheSW.Itssouthwesternmargin-boundingfault determinesthenortheastedgeoftheouterIAthatwaspreviouslyinterpretedasacompressionalneotectonic structure,whereasourfieldevidenceandrecentseismicdatasubstantiatedthatitisanoblique-slipnormalfault characterisinganextensionalneotectonicregime. TheAAGhasanepisodicandasymmetricalevolutionaryhistory.Thisisindicatedbytwosuperimposedgraben infillsandstructures.Theolderinfillisfolded,thrust-faultedandEarly-earlyMiddleMioceneinage.Theyounger infillisundeformed(nearlyhorizontal),Plio-Quaternaryinage,andoverliestheolderinfillwithangular unconformity.TotalthrowamountsaccumulatedonbothSWandNEmargin-boundingfaults,namelytheAkflehir MasterFault(AMF)andtheKaragöztepeMasterFault(KMF)sincetheLatePlioceneandEarlyPleistocene,are 870mand200m,respectively.Assumingauniformmotion,thesevaluesindicatemotionratesof0.3mm/yrand 0.2mm/yr,respectively,andtheasymmetricalnatureoftheAAG.Kinematicanalysisofsurfaceslipdataofboth theAMFandKMFshowedanoblique-slipmotionwithaminorright-lateralstrike-slipcomponent,andaNE–SW- directedextension.Theyalsofitwellwithresultsoffocalmechanismsolutionsoftworecentseismicevents,namely the2000December15Sultanda¤›(Mw=6.0)andthe2002February3Çay(Mw=6.5)earthquakes.Theyhave beensourcedfromthereactivationoftheAkflehir-P›narkayaandSultanda¤›-MaltepesectionsoftheAMF.TheÇay earthquakecauseddevastatingdamagetostructuresandlossoflifeintheregion.TheÇayearthquakehasalsoled tothedevelopmentofgroundrupturesandsurfacedeformation.Thegeometryofthegroundrupturesandfocal mechanismsolutionsofbothearthquakesprovedoncemorethatthesouthernmargin-boundingfaultoftheAAG orthenortheasternedgeoftheIAisanoblique-slipnormalfault. Consequently,allofthesefieldandseismicdatarevealanextensionalneotectonicregimethroughthe northeastedgeoftheouterIAdespitethepreviouslyreportedcompressionalneotectonicregime. KeyWords: Akflehir-AfyonGraben,IspartaAngle,extensionalneotectonicregime,Sultanda¤›andÇay(Afyon) earthquakes IspartaAç›s›’n›n(GBTürkiye)KDD›flKenar›ndaGenifllemeliYenitektonikRejim: YeniAraziveSismikVeriler Özet: Akflehir-AfyonGrabeni(AAG)4–20kmgenifllikte,130kmuzunluktaveKBgidiflli,aktifbirçöküntüalan› olup,KDdayeralanortaAnadoluveGBdayeralanIspartaAç›s›’n›(IA)birbirindenay›r›r.AAG’ninGBkenar›n›ve IA’n›nKDkenar›n›s›n›rlayanfay,dahaönce,s›k›flmatürübiryap›olarakyorumlanm›flt›r.Halbukibizimarazi verilerimizveyenisismikveriler,bufay›n,genifllemeliyenitektonikrejimikarakterizeedenverevat›ml›normalbir fayoldu¤unukan›tlam›flt›r. AAGaral›kl›(fas›lal›)vebak›fl›ms›zbirgeliflimtarihçesinesahiptir.Grabeninbuniteli¤i,üstüstegelmiflikiayr› grabendolgusuvegrabeninkendineözgüyap›s›ilebelirginlikkazan›r.Dahayafll›olangrabendolgusuk›vr›ml›ve bindirmefayl›oluperkenOrtaMiyosenyafll›d›r.Dahagençolangrabendolgusuisehemenhemenyataykonumlu olups›k›flmatüründehiçbirdeformasyongeçirmemifltir.Pliyo-Kuvaterneryafll›olangrabendolgusu,dahayafll› olangrabendolgusuüzerindeaç›l›uyumsuzlukileyeral›r.AAG’ninGBveKDkenarlar›n›s›n›rlayanfaylar(Akflehir veKaragöztepeAnaFaylar›,AMFveKMF)boyunca,GeçPliyosenveErkenPliyostesen’denberigerçekleflmiflolan toplamdüfleyat›mmiktarlar›s›rayla870mve200mdir.Faylarüzerindekidevinimintekdüzeoldu¤ukabul edilirse,bude¤erler,grabeninikikenar›boyuncagerçekleflendevinimh›z›n›ns›rayla0.3mm/y›lve0.2mm/y›l oldu¤unuveAAG’ninbak›fl›ms›zniteli¤iniaç›kcagösterir. Yüzeydeherikianafay(AMFveKMF)düzlemindenal›nankaymaverilerininkinematikanalizi,bufaylar üzerindekidevinimin,azmiktardasa¤yanaldo¤rultubilefleniolanverevat›ml›birdevinimoldu¤unu,ayr›ca genifllemenindeKD–GBdo¤rultusundagerçekleflmekteoldu¤unugöstermifltir.Araziverileriyleeldeedilenbu sonuç,15Aral›k2000Sultanda¤›(Mw=6.0)ve3fiubat2002Çay(Mw=6.5)depremlerininodakmekanizmas› 67 NEOTECTONICSOF OUTER ISPARTA ANGLE çözümleriyleeldeedilensonuçlariledeçokiyibirflekildeötüflmektedir.HerikidepremdeAkflehirAnaFay›’n›n (AMF)Akflehir-P›narkayaveSultanda¤›-Maltepebölümlerininetkinlikkazanmas›ndankaynaklanm›flt›r.Çay depremi,bölgedekiyap›larday›k›c›hasaravecankayb›nayolaçarken,ayn›zamandayüzeyk›r›klar›n›noluflmas›n› dasa¤lam›flt›r.Gerekyüzeyk›r›klar›n›ngeometrisi,gerekseherikidepreminodakmekanizmas›çözümleri,AAG’nin GBkenar›n›veIA’n›nKDkenar›n›s›n›rlayanfaylar›n(AkflehirFayZonu)verevat›ml›normalfaylaroldu¤unubir kezdahakan›tlam›flt›r. Sonuçolarak,tümarazivesismikveriler,IspartaAç›s›nda’s›nda,dahaönceönerilmifloldu¤ugibis›k›flmal›bir yenitektonikrejimde¤il,genifllemelibiryenitektonikrejim’invarl›¤›n›ortayakoymufltur. AnahtarSözcükler:Akflehir-AfyonGrabeni,IspartaAç›s›,genifllemelineotektonikrejim,Sultanda¤›veÇay(Afyon) depremleri Introduction thetypeofneotectonicregimecontrollingalloftheIA.In ThemajorneotectonicstructuresshapingTurkeyand general,ideassuggestedforthesolutionofthese adjacentareasaretheright-lateralNorthAnatolianFault problemscanbecategorisedintotwogroups:(1)the System(NAFS),theleft-lateralEastAnatolianandthe westernandeasternedgesoftheouterIAaredetermined DeadSeafaultsystems(EAFS,DSFS),andtheHellenic- bytheNE-trending,left-lateralandso-called“Fethiye- Cyprusactivesubductionzone(Figure1).Inadditionto Burdurfaultzone”,andtheNW–trending“Sultanda¤ thesemajorstructures,therearealsosomeothersecond- thrust”,respectively,andaccordinglytheneotectonic orderfaultzonescuttingacrossanddividingthe regimethroughouttheIAiscompressional(Boray etal. Anatolianplateintosmallerblocks.Thesearetheleft- 1985;Barka etal. 1995;Uysal1995;Altunel etal. lateralCentralAnatolianFaultZone(CAFZ),theright- 1999);(2)incontrasttotheideasofthisfirstgroupof lateralSaltLakeFaultZone(SLFZ),andthe‹nönü- authors,asecondgroupofauthors(Koçyi¤it1996; EskiflehirandAkflehiroblique-slipnormalfaultzones Glover&Robertson1998)suggestthattheIAhasnot (Figure1).TheNorthAnatolianandtheEastAnatolian experiencedacompressionaltectonicregimeafterthe faultsystemsaretheintracontinentaltransformplate earlyMessinianphaseofcompressionaldeformation,i.e., boundariesalongwhichtheAnatolianplatehasbeen theneotectonicregimeintheIAisextensional.Inthe escapinginaWSWdirectionontotheoceaniclithosphere sameway,thewesternandeasternboundaryfaultsof oftheAfricanplatealongtheHellenic-Cyprussubduction theouterIAareneitheraleft-lateralstrike-slipfaultnor zonesincetheLatePliocene(Koçyi¤it&Beyhan1998). athrustfault,becausetheyareoblique-slipnormalfaults Oneofgeologicallycomplicatedareascomprisingthe asindicatedbybothseismicandfielddata(Koçyi¤it AnatolianplateistheIspartaAngle(IA).ThisisanS–and 1983,1984,1996,2000;Koçyi¤it etal. 2000a,b; “∧”-shapedmorphotectonicstructureabout260km Kocaefe&Ataman1976;McKenzie1978;Taymaz& long,380kmwideoutliningAntalyaBayintheEastern Price1992;Price&Scott1994;Y›lmaztürk&Burton MediterraneanSea(Figure1). 1999;Cihan&Koçyi¤it2000;Özacar&Koçyi¤it2000). TheIAwasoriginallydefinedandreportedby Themainaimofthispaperis:(1)topresentnewfield Blumental(1951).Thefirstattemptexplainingitsorigin datafromawell-definedneotectonicstructure,the wasmadebyDumont(1976).However,theoriginofthe Akflehir-AfyonGrabenanditsmargin-boundingfaults, IAisstillunderdebate,butmostauthorsacceptthatitis theAkflehirFaultZone(AFZ)thatdeterminestheeastern apalaeotectonicstructureresultingfromthenorthward edgeoftheouterIA,and(2)tointerprettheminthelight curvatureoftheoriginally~E –W-trendingTauride ofseismicdataobtainedfromtwoveryrecentseismic orogenicbeltduetonappeemplacementsandrelated events,the2000December15Sultanda¤›(Afyon)and clockwiseandanticlockwiserotationsinEarly the2002February3Çayearthquakessourcedfromthe Palaeocene–earlyMessiniantimes(Poisson1977;Akay& activationoftheAkflehir-P›narkayaandSultanda¤›- Uysal1985;Glover&Robertson1998;Piper etal. MaltepesectionsoftheAkflehirMasterFault(AMF) 2002). (Figure1).Allthesedataallowustosuggestthatthe Othergeologicalproblemsdiscussedwidelyinboth masterfaultoftheAFZisanactiveoblique-slipnormal thenationalandinternationalliteraturearethekinematic faultandthattheneotectonicregimethroughtheeastern naturesofthewesternandeasternedgesoftheIA,and 68 300 Black Sea 350 Ýstanbul e EURASIAN PLATE n Sea of Marmara o N Z lt 0 100 au F System n km lia North Anatolian Fault to 0 na 40 ANATOLIAN st A Eskiþehir hea Bursa Ankara PLATE Nort Ýnönü-Eskiþehir Edremit CENTRAL ANATOLIA Taymaz & Tan Erzincan Karlýova (2001) EMSC Fault Zone Salt Lake Lake Afyon Lake Fault Zone Zone Van Salt A.KOÇY‹⁄‹T&A.A.ÖZACAR Ç Kayseri Fault 2002.02.03 2000.12.15 S Akþehir An 0 ta g Suture 38 r le Study Zone a Ilgýn Niðde Aegean Area Bitlis Sea Isparta Burdur Konya Anatolian East Anatolian Fault SystemARABIAN PLATE Outer Isp TAURIDES Karaman Angle Adana Isparta Central LEGEND Antalya area of extensional neotectonic strike-slip fault Inner regime Rhodes thrust fault with area of strike-slip neotectonic strike-slip Anamur regime with normal component component area of strike-slip neotectonic regime with thrust component subduction zone Mediterranean Sea area of compressional suture zone neotectonic regime oblique-slip Pliny Arc Cyprus Arc movement direction of plates normal fault Cyprus Strabo Arc approximate outlines of outer strike-slip fault and inner Isparta angles AFRICAN PLATE with normal Hellenic Arc Dead Sea Fault System S: Sultandað county Ç: Çay component Figure1. SimplifiedmapshowingtheneotectonicsubdivisionofTurkeyandadjacentareas,andthestudyarea(sourceoffocalmechanism