Regional seismicity in Adıyaman - Samsat (SE Turkey)

Earthquake locations in Turkey are reported by two different agencies: Disaster and Emergency Management Presidency (DEMP) and Kandilli Observatory and Earthquake Research Institute (KOERI). Both organisations use their own networks. Thus, different parameters are usually given for the same earthquake due to the differences in the number of stations and network designs. This makes it difficult to obtain a reliable regional earthquake source parameters' database catalogue. This study aims to relocate the earthquakes that occurred in Adıyaman-Samsat by using DEMP and KOERI stations records, determine the fault mechanisms and define the fault mechanism in relation to the regional tectonics, as well as provide a stable regional source parameters' database. For this purpose, 434 earthquakes (M ≥ 1.3) were relocated by combining DEMP and KOERI data, and the focal mechanisms of 32 earthquakes (M ≥ 3.5) from P-wave first motion polarities and of 25 earthquakes (M ≥ 3.6) from regional moment tensor analysis have been determined. All these events occurred in the study area during 2009-2018. The new locations of the earthquakes indicated that the earthquakes are clustered in the Samsat peninsula, at the SW part of the Bozova Fault. Additionally, some scattering epicentres were observed in the southern part of the study area. It was determined that earthquakes mainly occurred in the land areas rather than at the Atatürk Dam and at Samsat peninsula, at very shallow depths (mostly within the first 10 km of the crust). The depth distribution of the analysed earthquakes indicated that both the maximum seismicity and depth of the seismicity increased from south to north and this behaviour indicates crustal thickening due to continental-continental collision in the study area. Focal mechanisms of the analysed earthquakes showed that the dominant mechanism in the study area was NW-SE trending right lateral strike-slip faulting with both normal and reverse component. All the focal mechanisms had a NW-SE or NE-SW nodal plane compatible with the regional geological trend at the NE edge of the Samsat Peninsula, where the left lateral strike slip Lice Fault and Samsat Fault intersect. However, the identification of Samsat Fault as the main seismic source is strongly supported by the 2017 and 2018 seismic sequences in the study area.