Paleoseismology of the western Sürgü–Misis fault system: East Anatolian Fault, Turkey

The East Anatolian fault bifurcates into a north strand and a south strand near the City of Celikhan, Turkey. The northern strand is referred to as the Surgu–Misis fault (SMF) system, which is divided into a number of distinct fault segments based on geological and geomorphological characteristics. However, no paleoseismological data regarding the movement history of the SMF system previously have been reported. We excavated seven trenches across four segments of the SMF system to evaluate the paleoseismological history of these fault zones. These trenches exposed structural and sedimentological evidence of paleoseismic events that had primarily strike-slip displacements with secondary normal and reverse components of motion. Geochronological dating of the trench stratigraphy and event horizons provide the time elapsed since the last event and confirmed the Holocene activity of the faults. These fault segments are individually capable of producing surface-rupturing earthquakes, but may also rupture together generating large, complex, multi–segment ruptures. However, the SMF system has not produced surface-rupturing earthquakes in the last millennia, and therefore is accumulating strain. In light of our findings, we suggest that about 1.7 m of strain has accumulated across the Karatas and Yumurtalik fault segments, which is sufficient to produce moderate to large earthquakes when released seismically. The surrounding Gulf of Iskenderun is a highly industrialized district in the Eastern Mediterranean. Therefore, the data obtained from this paleoseismological investigation will contribute to a better understanding of the earthquake hazards in the region.