TurkishJournalofEarthSciences (TurkishJ.EarthSci.),Vol.10, 2001,pp.69-82. Copyright©TÜB‹TAK TheJune6,2000,Orta(Çank›r›,Turkey)Earthquake: SourcedfromaNewAntitheticSinistralStrike-slip StructureoftheNorthAnatolianFaultSystem,the DodurgaFaultZone AL‹KOÇY‹⁄‹T,BORAROJAY,MUSTAFAC‹HAN&ARDAÖZACAR MiddleEastTechnicalUniversity,FacultyofEngineering,DepartmentofGeologicalEngineering, TectonicResearchUnit,TR-06531,Ankara-TURKEY (e-mail:[email protected]) Abstract: The‹smetpafla-Karg›sectionoftheNorthAnatolianFaultSystem(NAFS)consistsofsixsubfaultzones, namelytheEskipazar,theUlusu,theTosya,theÇerkefl-Kurflunlu,theDevrezandthenewlydetectedDodurgafault zone(DFZ).Togetherthesefaultzonesformawell-developeddextralstrike-slip-faultingpattern,inwhichtheDFZ isanantitheticsecondarystrike-slipcomponent,indicatedbyfocal-mechanismsolutionsofmoderateandlarge earthquakesthathaveoccurredinthe‹smetpafla-Karg›sectionoftheNAFS. TheDFZisa∼36-km-long,∼N-S-trendingstrike-slipstructurelocatedintheareabetweenSaçakvillageinthe northandKösrelikvillageinthesouth.Pre-UpperPliocenerocksarecutandtectonicallyoffsetforadistanceof about6km.UpstreamtributariesoftheDevrezRiveraredeviatedintheshapeofan“S”andareoffsetsinistrally upto2.5km.Thesevaluesexplaina2.3mm/yrrateofslipontheDFZ.Inaddition,severalPlio-Quaternarypull- apartbasinsoccurwithintheDFZ. Anintermediate-magnitude(Mw=6.0),shallow-focusearthquake,theOrtaearthquake,struckonTuesday, June6,2000,at5:42(localtime)intheOrtaarea,andresultedintwodeathsandseveredamagetoatotalof 4842structures,almostallofrural-styleconstruction.Mostofseveredamagewasconfinedtoanarrowareaalong theDodurgafault;thatis,themasterstrandoftheDFZ.Isoseismallinesdisplayanellipsoidalpatternwithalong axisthatparallelstheDodurgafault.Bothfore-andafter-shocksoftheJune6,2000Ortaearthquakeforma highlyconcentrated,N-S-trendingdistributionpatternthatparallelstheDFZ.Focal-mechanismsolutionsofthe mainshockcarriedoutbyvariousseismographicstations,exceptforDER-DDRstation,indicatesinistralstrike-slip faultingwithanormal-slipcomponent.Consequently,takentogetherthesefieldobservationsandseismological dataindicatethattheDodurgafaultisanantitheticsinistralstrike-slipstructureincludedintheNAFS,andthatthe June6,2000Ortaearthquakeresultedfromitsactivation. KeyWords: NorthAnatolianFaultSystem,AntitheticFault,SinistralStrike-slipFault,OrtaEarthquake KuzeyAnadoluFaySistemindeTan›mlananSolYanalAt›ml›BirFayKufla¤›: DodurgaFayKufla¤›ve6Hairan2000TarihliOrta(Çankar›-Türkiye) Depremi Özet: KuzeyAnadoluFaySisteminin(KAFS)‹smetpafla-Karg›bölümüEskipazar,Ulusu,Tosya,Çerkefl-Kurflunlu, Devrezveyenitan›mlananDodurgafaykufla¤›(DKF)olmaküzerealt›adetalt-faykuflaklar›ndanoluflur.Bufay kuflaklar›n›ntamam›iyigeliflmiflsa¤yanal-at›ml›faydeseniolufltururvebusistemiçerisindeDFKyanalat›m bileflenliikincilantitetikyap›y›temsileder. Yaklafl›k36kmuzunlu¤undavekuzey-güneyuzan›ml›biryanal-at›ml›fayolanDFK,kuzeydeSaçakve güneydeKösrelikköyleriaras›ndayeral›r.ÜstPliyosenöncesikayatopluklar›n›kesenveöteleyenfaykufla¤› boyuncabelilenenhareket6kmkadard›r.Devrez›rma¤›n›nmembadereleri“S”flekillidönmüflvesolyanalolarak 2.5km’yekadarat›lm›flt›r.Bude¤erler,DFZüzerinde2.3mm/yrkaymamiktar›verir.BunlarailavetenDFZ üzerindebirçokPliyo-Kuvaternerçek-ay›rhavzalargeliflmifltir. Ortaölçekli(Mw=6.0)ves›¤odakl›,Ortadepremi,6Haziran2000sal›sabah›saat5.42(yerelzamanile) Ortabölgesinivurdu.Deprem,ikiölümeveço¤ua¤›rolmaküzerek›rsaltarzdainflaedilmifltoplam4852yap›n›n hasargörmesinenedenoldu.Ço¤unluklahasarDFZ’ninanakoluolanDodurgafay›üzerindedarbirkuflaktaolufltu. Eflde¤ersismike¤rilerininuzunekseniDodurgafay›naparalleluzananelipsoidalbirdesenoluflturur.6Haziran 2000OrtaDepreminöncülveardç›ldepremlerininda¤›l›m›kuzey-güneyyönündebiryo¤unlaflmagösterip, Dodurgafaykufla¤›naparalelliksunarlar.DER-DDRd›fl›ndaçeflitlisismografistasyonlar›ndayap›lanodak mekanizmas›çözümlemelerinormalbileflenlisolyanal-at›ml›faylanmagöstermektedir.Sonuçolarak,arazijeolojisi gözlemlerivesismikverilerbirlikteDodurgafay›n›nKAFS’iiçindeantitetiksolyanal-at›ml›fayoldu¤unuve6 Haziran2000Ortadepremininbufay›nhareketlenmesiileolufltu¤unuortayakoymaktad›r. AnahtarSözcükler: KuzeyAnadoluFaySistemi,AntitetikFay,SolYanal-at›ml›Fay,OrtaDepremi. 69 DODURGAFAULTZONEANDJUNE6,2000ORTAEARTQUAKE Introduction approximatelyN-S-trending,leftlateralstrike-slipfault ∼ Anintermediate-magnitude(Mw=6.0),shallow-focus(8- zonelocated 5kmwestoftheOrtacounty(thelargest 33km)earthquakestruckonTuesday,June6,2000,at settlementnearesttothefieldepicenteroftheseismic 5:42(localtime).Thisseismiceventwasfeltoverawide event),wenamedtheDodurgafaultzone.Accordingly, regionincludingmanycities,countiesandvillages,suchas theseismiceventishereinfirstnamedtheJune6,2000 Çank›r›,Kastamonu,Zonguldak,Karabük,Bolu,Ankara, Ortaearthquake. Kayseri,Çerkefl,Kurflunlu,Atkaracalar,Orta,Çubukand Thispaperaims:(1)tointroduceanewstructure,the fiabanözü,andcausedseveredamagetoadobestructures Dodurgafaultzone;(2)toexplainitsgeometric- inruralareas.Earlymorningonsameday,thefield kinematiccharacteristicsandrelationshipswiththeNAFS; epicenterofthisseismiceventwasannouncedasÇerkefl and(3)toexplainanddocumenttheoriginoftheJune6, countybyanationalseismographicstation,Kandilli 2000Ortaearthquakeandtheseveredamageitcaused ObservatoryandEarthquakeResearchInstitute,‹stanbul- tostructuresintheOrtaarea. Turkey.Later,severalnationalandinternational seismographicstationsthatrecordedthiseventcalculated itsvariousseismicparameters(Table1).Thus,basedon RegionalTectonicSetting instrumentaldataobtainedfromseismographicstations TurkeyislocatedintheMediterranean-Himalayaseismic (Table1),thefieldepicenterofthiseventwasfoundto zone,andapproximately90%ofthecountryisunder besomewhereinornearOrtacounty,15-25kmSEof seismichazard.Themainstructuresthatareresponsible Çerkeflcounty.However,untiltheoccurrenceofthis forhighseismicityinTurkeyandadjacentareasarethe seismicevent,therewasnoinformationaboutafault NorthAnatolian,EastAnatolianandDeadSeafault mappedorreportedfromthisarea.Therefore,the systems,andtheHellenic-westCyprusarc(Figure1).The sourceofthisearthquakeremainedanunsolved Hellenic-westCyprusarcisanactivesubductionzone geologicalproblemforashorttime.Forthisreason,we alongwhichtheAfricanplatehasbeensubductingata wenttotheOrta(Çank›r›)area,visitedalloftheseverely sliprateof35mm/yrnorthwardsbeneaththeTurkish damagedsettlements,anddetectedthestructurethat platelet(McKenzie1972;LePichon&Angelier1979; producedthisseismicevent,andmappeditindetailona Meulenkampetal. 1988;Kahle etal. 1998).TheDead 1/25,000scaletopographicmap.Thisstructure,an SeaFaultSystemisasinistraltransformfaultseparating Table1. Variousseismicparametersofthe2000June6Orta(Çank›r›)earthquake. Origin Location Focal Seismic FaultPlane Date Time Lat°.N-Long°.E depth Magnitude Moment Duration Mechanism Geographical References* (yyyy/mm/dd) (GMT) (km) (Mo) (second) Solution Region (strike/dip/rake) 18 2000/06/06 02:41:53.2 40.65–32.92 8 Mw=6.0 1.25x10 Nm ~6 1.02°/46°/-29° Orta(Çank›r›) TT 2.111°/70°/-132° 2000/06/06 02:41:53.16 40.621–32.967 33 Ms=6.1 - - 1.340°/26°/-53° Orta(Çank›r›) USGS-NEIC 2.122°/69°/-106° 2000/06/06 02:41:51.46 40.63–33.03 10.5 Md=5.9 - ~10 1.262°/88°/-139° Orta(Çank›r›) DER-DDR 2.170°/49°/-03° 2000/06/06 - 40.67–32.97 10 Md=5.9 - - - Çerkefl(Çank›r›) KOERI 18 2000/06/06 02:41:52.0 40.75–32.70 15 Mw=6.0 1.11x10 Nm ~5.4 1.356°/39°/-47° Orta(Çerkefl) HARVARD 2.126°/62°/-119° 2000/06/06 - 40.60–33.00 33 Ms=6.1 - - 1.359.6°/47.6°/-46.8° Orta(Çank›r›) ERI 2.125°/58°/-126° * TT:TuncayTaymaz-‹stanbulTechnicalUniversity,DepartmentofGeophysicalEngineering,USGS-NEIC:TheUnitedStatesofGeo logicalSurvey–NationalEarthquakeInformationCenter, DER-DDR:DepartmentofEarthquakeResearch,GeneralDirectorateofDisasterAffairs,KOERI:KandilliObservatoryandEarthquakeResearchInstitute,HARVARD:HarvardUniversitySeismology Group,ERI:TokyoUniversityEarthquakeResearchInstitute. 70 0 0 260 300 34 0 22 BLACKSEA 42 GREECE ‹stanbul Zonguldak Kastamonu 4 Tekirda¤ 7 6 •sp 1 Karg› 0 D 41 8 S H Ladik KEPHALONIA O 2 NORTHANATOLIANFAULTSYSTEM EURASIAN FAULTZONE B G PLATE ‹znik Geyve Beldibi 3 5 Çank›r› 9 Erzincan Edremit Ankara Figure2 Karl›ova 1943/11/26 390 1944/02/01 Tosya-Ladik Bolu-Çerkefl Earthquake Earthquake Kayseri M=7.6 VanLake Athens M=7.6 SaltLake L‹S SUTURE ZONE B‹T AEGEANSEA ANATOLIANPLATELET EASTANATOLIANFAULTSYSTEM KahramanMarafl 370 HELLENICARC ARABIANPLATE A.KOÇY‹⁄‹T, 350 CYPRUSARC PLINYTRENCH LEGEND •sp ‹smetpaflarailwaystation STRABOTRENCH Strike-slipfault ET AL. Activesubductionzone 330 EASTMEDITERRANEANSEA Suturezone Fault-planesolution DEADSEAFAULTSYSTEM Relativemotionsenseofplates Dead 310 Sea 1.Ulusu-Gerede-AbantSubfaultZone 2.TosyaSubfaultZone 3.Çerkefl-KurflunluSubfaultZone N AFRICANPLATE 4.Karadere-Kaynafll›SubfaultZone 0 5.DodurgaFaultZone 29 6.Hendek-Y›¤›lcaSubfaultzone 7.NorthernMarmaraFault 8.GanosFault 0200 Central REDSEA km Line 9.Yenice-GönenSubfaultZone B:Bolu,G:Gerede,D:Düzce, H:Hendek,O:Orta,S:Sakarya 71 Figure1. SimplifiedmapshowingthestudyareaandmajorneotectonicstructuresofTurkeyandadjacentareas(Focal-mechanismsolutions weretakenfromCan›tez& Büyükafl›ko¤lu1984). DODURGAFAULTZONEANDJUNE6,2000ORTAEARTQUAKE theArabianPlateintheeastfromtheAfricanPlateinthe InthesecondpatternorgeometryoftheNAFS,the west.TheAfricanPlateismovingNNWatanaverageslip masterstrand(Y-shear)firstbifurcatesintoseveral rateof18mm/yr(DeMets etal. 1994;Reilinger etal. subfaultzones,faultsetsandisolatedfaultsofvarying 1997;Kahle etal. 1998).ThedextralNorthAnatolian sizes,andthentheyrejoinandrebifurcateseveraltimes, andsinistralEastAnatolianfaultsystemsare leavingbehindaseriesoflensoidalhighlands(pressure intracontinentaltransformfaults,alongwhichthewedge-