Quaternary Activity of the Cihanbeyli and Yeniceoba Fault Zones: ‹Nönü-Eskiflehir Fault System, Central Anatolia
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Turkish Journal of Earth Sciences (Turkish J. Earth Sci.), Vol. 16, 2007, pp. 471–492. Copyright ©TÜB‹TAK Quaternary Activity of the Cihanbeyli and Yeniceoba Fault Zones: ‹nönü-Eskiflehir Fault System, Central Anatolia ERMAN ÖZSAYIN & KAD‹R D‹R‹K Hacettepe University, Department of Geological Engineering, Tectonic Research Laboratory, TR-06800 Ankara, TURKEY (e-mail: [email protected]) Abstract: The ‹nönü-Eskiflehir fault system (‹EFS) is one of the most important fault systems in Central Anatolia and consists of a series of NW–SE- to WNW–ESE-trending fault zones extending from Uluda¤ (Bursa) in the northwest to Sultanhan› in the southeast. Between ‹nönü and Sivrihisar, the Eskiflehir fault zone of the ‹EFS trends WNW, but east of Sivrihisar the ‹EFS changes its direction to NW–SE and splays out into four fault zones, named the Il›ca, Yeniceoba, Cihanbeyli and Sultanhan› fault zones and extends to south of Tuzgölü in the east. The NW–SE- trending Yeniceoba fault zone (YFZ), exposed between Günyüzü in the west and Yeniceoba in the east, controls the northern margin of the Kelhasan horst and the southern margin of the Yeniceoba basin. Along this fault zone two sets of superimposed slickenlines indicate older pure right-lateral strike-slip faulting and younger normal faulting with a right-lateral component. The NW–SE-trending Cihanbeyli fault zone (CFZ) is well exposed between north of Sülüklü in the west and Cihanbeyli in the east. It controls the southern margin of the Kelhasan horst, and is marked by fault scarps, triangular facets, alluvial fans and alignment of springs. Recent detailed field mapping and kinematic analysis along the fault planes between Pliocene lacustrine carbonates and younger fluvial clastic rocks has shown that the CFZ consists of a series of parallel normal faults. However, kinematic analysis of the fault slip-plane data indicates that the fault planes cutting the Pleistocene–Holocene clastic sediments of the Cihanbeyli Graben at the southeastern tip of the CFZ are normal faults with a minor sinistral component. The kinematic analyses of fault-slip data clearly indicate that the area experienced NNE–SSW extension. Recent horizontal terrace deposits cut by a series of steeply-dipping normal faults with minor strike-slip component in ‹lhanyayla, Damlakuyu (Çorca) village and nearly 4 kilometres southeast of ‹nsuyu village, which are located on the YFZ and CFZ, indicate that the activity of both CFZ and YFZ continues, controlled by NNE–SSE-directed extension, in the Quaternary. The distribution of earthquake epicentres supports this view and suggests recent activity along the fault zones. Key Words: Neotectonic, Quaternary activity, kinematic analysis, Tuzgölü, Central Anatolia, ‹nönü-Eskiflehir fault system, Cihanbeyli fault zone, Yeniceoba fault zone Cihanbeyli ve Yeniceoba Fay Zonlar›’n›n Kuvaterner Aktivitesi: ‹nönü-Eskiflehir Fay Sistemi, Orta Anadolu Özet: Bat›da (Uluda¤), güneybat›da Sultanhan› aras›nda yer alan, gidifli KB–GD ile BKB–DGD aras›nda de¤iflen bir dizi fay zonundan oluflan ‹nönü-Eskiflehir fay sistemi (‹EFS), Orta Anadolu’daki en önemli fay sistemlerinden birisidir. ‹EFS’nin en bat› ucundaki kolu olan Eskiflehir fay zonu ‹nönü ile Sivrihisar aras›nda BKB–DGD gidifllidir. ‹EFS, Sivrihisar civar›nda do¤rultular› KB–GD olan dört fay zonuna ayr›larak Tuzgölü’nün güneyine kadar devam eder. Bunlar Il›ca, Yeniceoba, Cihanbeyli ve Sultanhan› fay zonlar›d›r. Bat›da Günyüzü, do¤uda Yeniceoba aras›nda yüzeyleyen KB–GD gidiflli Yeniceoba fay zonu (YFZ) Kelhasan yükselimi’nin kuzey kenar›n› ve Yeniceoba Ovas›’n›n güney kenar›n› kontrol eder. Fay düzlemleri üzerinde üst üste (süperimpoze) gözlenen iki fay çizi¤i seti daha eski sa¤ yanal do¤rultu at›ml› bir faylanmay›, ve daha genç olan sa¤ yanal bileflenli normal bir faylanman›n varl›¤›na iflaret eder. KB–GD gidiflli Cihanbeyli fay zonu (CFZ) bat›da Sülüklü kuzeyi, do¤uda ise Cihanbeyli aras›nda çok belirgin olarak yüzeylenir. Kelhasan yükselimi’nin güney kenar›n› kontrol eden fay zonu, fay diklikleri, üçgen yüzeyler, alüvyon yelpazeleri ve su kayna¤› dizilimleri ile karakterize olur. Pliyosen gölsel kireçtafllar› ile daha genç akarsu klastikleri aras›ndaki fay düzlemlerinde yap›lan güncel ayr›nt›l› saha çal›flmalar› ve kinematik analizler CFZ’nun birbirine paralel ve tamamen normal fay karakterli fay serilerinden olufltu¤unu göstermektedir. Halbuki, CFZ’nun güneydo¤u ucunda yer alan Cihanbeyli Grabeni içinde yer alan Pleyistosen–Holosen yafll› klastikleri kesen faylardaki kayma düzlemi verileri bu faylar›n çok az sol yanal at›m bileflenli normal faylar oldu¤unu göstermifltir. Tüm fay düzlemlerinin kinematik analizi ise, bölgenin tansiyonel rejimin etkisi alt›nda oldu¤unu ve genifllemenin KKB–GGD do¤rultusunda geliflti¤ini göstermifltir. YFZ ve CFZ üzerinde yer alan ‹lhanyayla, Damlakuyu köyü ve ‹nsuyu köyünün yaklafl›k 4 km do¤usunda yüzeyleyen, yatay konumdaki güncel taraça çökellerini kesen oldukça dik e¤imli, az miktarda do¤rultu at›m bileflenine sahip normal faylar, Cihanbeyli ve Yeniceoba fay zonlar›n›n her ikisinin de Kuvaterner’de aktif oldu¤unu ve KKD–GGB yönlü bir aç›lman›n etkisinde olduklar›n› belirtir. Aletsel dönemde meydana gelen ve deprem d›fl merkezleri fay zonu üzerinde yer alan depremlerin varl›¤› ise, aktivitenin günümüzde de devam etti¤ini kan›tlamaktad›r. Anahtar Sözcükler: güncel tektonik, Kuvaterner aktivite, kinematik analiz, Tuzgölü, Orta Anadolu, ‹nönü-Eskiflehir fay sistemi, Cihanbeyli fay zonu, Yeniceoba fay zonu 471 ‹NÖNÜ-ESK‹fiEH‹R FAULT SYSTEM, CENTRAL ANATOLIA Introduction Konya-Eskiflehir neotectonic district west of Tuzgölü is Four major neotectonic structures shape Turkey and the eastern continuation of extension in west-southwest adjacent areas. These are the right-lateral North Anatolia. The ‹nönü-Eskiflehir fault system is the most important shear zone in this district. Numerous previous Anatolian Fault System, the left-lateral East Anatolian and studies pointed out the importance of this system (Ünalan Dead Sea fault systems, and the Aegean-Cyprus active & Yüksel 1978; fiaro¤lu et al. 1987; Koçyi¤it 1991; subduction zone. Besides these major structures, there Koçyi¤it et al. 1991; Dirik & Göncüo¤lu 1995; Koçyi¤it & are some second order structures which divide the Beyhan 1998; Altunel & Barka 1998; Bozkurt 2001; Anatolian plate into smaller blocks. These second order Koçyi¤it & Erol 2001; Dirik & Erol 2003; Koçyi¤it 2003, structures are the left-lateral Central Anatolian Fault 2005). The WNW–ESE-trending western part of the System, the right-lateral Tuzgölü Fault Zone, the ‹nönü- system is exposed between Uluda¤ and NW of Sivrihisar. Eskiflehir fault system (‹EFS) and the Akflehir oblique-slip Northwest of Sivrihisar, the system changes its trend to normal fault zones (Dirik & Göncüo¤lu 1996; Koçyi¤it & NW and splays into three branches, namely the Ilıca, Beyhan 1988; Koçyi¤it et al. 2000; Dirik 2001; Koçyi¤it Yeniceoba and Cihanbeyli fault zones (Koçyi¤it 1991; 2003, 2005; Koçyi¤it & Özacar 2003; Dirik & Erol Çemen et al. 1999; Dirik & Erol 2000, 2003; Koçyi¤it & 2003). The North Anatolian and the East Anatolian fault Özacar 2003; Koçyi¤it 2005). The shear zone merges systems are the intracontinental plate boundaries, active with the Altınekin fault zone southeast of Cihanbeyli. This since the Late Pliocene, along which the Anatolian plate is fault zone was first called the ‘Zıvarık Fault System’ by escaping to the WSW onto the oceanic lithosphere of the Erol (1969), but with the name change from Zıvarık to African plate along the Aegean-Cyprus subduction zone Altınekin, it has been renamed the ‘Altınekin fault zone’ (e.g., Koçyi¤it & Beyhan 1998; Koçyi¤it & Özacar 2003; by Dirik & Erol (2003, Figure 1). However, at the same Yaltırak et al. 2005; Kaymakcı et al. 2006; Aksoy et al. time the fault zone was also named the ‘Konya-Bulok 2007; Bektafl et al. 2007). fault zone’ by Koçyi¤it (2003). In this study, we prefer to Within these major structures four Neotectonic utilize the name ‘Altınekin fault zone’, as the type locality provinces can be defined, namely: East Anatolian of this fault zone is in ‘Altınekin County’ where it is contractional province, North Anatolian province, Central characterized by seismically active grabens, hence the Anatolian province and West Anatolian province (fiengör priority of this terminology. The southeastern extension et al. 1985; Bozkurt 2001). The East Anatolian of the ‹EFS is the Sultanhanı fault zone (Figure 1). Altunel contractional province is characterized by an N–S & Barka (1998) stated that the western part of this zone compressional tectonic regime. The North Anatolian consists of sinistral oblique faults with a normal Province, located north of the North Anatolian Fault component and separates the Aegean/Western Anatolian System (NAFS), is characterized by numerous strike-slip block from the Central Anatolian block. Koçyi¤it (2003) faults with a strong E–W thrust component (fiengör et al. named the fault zone the ‹nönü-Eskiflehir fault zone and 1985). The West Anatolian Province is characterized by based on more recent studies (Koçyi¤it 2005) concluded NNW–SSE continental extension; E–W-trending grabens that it is the north-northeast boundary of the southwest and intervening horsts are its most prominent features Turkey extensional province. Although the existence of (e.g., Bozkurt & Mittwede 2005; Erkül et al. 2005; the ‹EFS has been known for years and its western part Tokcaer et al. 2005; Yücel-Öztürk et al. 2005; Ersoy & is well defined, few kinematic studies have been made in Helvacı