Dating of active normal fault scarps in the Büyük Menderes Graben (western Anatolia) and its implications for seismic history

Fault scarps, if well-preserved, include precise evidence of past earthquakes. Using cosmogenic 36Cl dating, the timing and slip of paleoearthquakes are recoverable beyond the available earthquake archives. One of the appropriate seismically active regions to apply 36Cl dating is western Anatolia, where its deformation is influenced by an N-S extensional regime, where the horst-graben structures are characterized by normal faults. We have studied well-preserved (meta-) carbonates Kalafat and Yavansu fault scarps in the westernmost part of the Büyük Menderes Graben within western Anatolia. The distribution of cosmogenic 36Cl against height along the fault surfaces indicates that faults experienced minimum three high paleoseismically active phases. The recovered ages of seismic events are ca. 15, 8.4, and 3.6 ka, with vertical components of slip of ca. 0.7, 0.9 and 3.1 m, respectively, for the Kalafat Fault, and ca. 7.9, 3.4, and 2.0 ka with vertical components of slip of ca. 0.6, 3.5, and 2.6 m, respectively, for the Yavansu Fault. The recurrence interval of active periods is generally becoming shortened over time. The ruptures mostly occurred as clustered earthquakes close in time with magnitudes of 6.5–7.1. The vertical slip rates of >0.1, 0.1, and 1.5 mm/yr, and >0.1, 0.8, and 1.9 mm/yr were calculated for the Kalafat and Yavansu faults, respectively. Long-term slip rates were also estimated about 1.0 and 0.6 mm/yr for the Kalafat and Yavansu faults, respectively. Considering the fault lengths, they are capable of producing earthquakes with magnitudes larger than 6.5, and are seismogenic faults