Determining the main strand of the Eskisehir strike-slip fault zone using subsidiary structures and seismicity: a hypothesis tested by seismic reflection studies

The Eskisehir Fault Zone is one of the major neotectonic structures of Turkey, extending from Inegol (Bursa) to Cihanbeyli (Konya). The fault zone presents a considerable seismic risk for the city of Eskisehir but the exact locations of active segments and the source of the major seismic event, the 1956 earthquake (M = 6.5) that occurred in the instrumental period (from 1900 to 2013), have been debated in recent literature. The structural data obtained from field studies indicate an approximately N60W-trending main strand of the right lateral strike-slip Eskisehir Fault Zone. This trend corresponds to the en echelon bends on the course of the Sarisu River. Using this concurrence, the positions of Bahcehisar and the Cukurhisar-Sultandere segments are proposed and checked by seismic reflection studies. The seismic sections disclosing positive flower structures confirm the hypothesized position of the Cukurhisar-Sultandere segment. The relocation of epicenters and focal mechanism solutions of seismic events in 1956, 1990, 2010, and 2013 indicate that the Cukurhisar-Sultandere segment might be the rupture source of the 1956 event and is a possible potential seismic source for an earthquake that could seriously affect the Eskisehir settlement.