Abstract:

The İnönü-Eskişehir fault system (İEFS) 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 Uludağ (Bursa) in the northwest to Sultanhanı in the southeast. Between İnönü and Sivrihisar, the Eskişehir fault zone of the İEFS trends WNW, but east of Sivrihisar the İEFS changes its direction to NW-SE and splays out into four fault zones, named the Ilıca, Yeniceoba, Cihanbeyli and Sultanhanı 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 İlhanyayla, Damlakuyu (Çorca) village and nearly 4 kilometres southeast of İnsuyu 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.

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