Reactivation of the Adıyaman Fault (Turkey) through the Mw 5.7 2007 Sivrice earthquake: An oblique listric normal faulting within the Arabian-Anatolian plate boundary observed by InSAR

On February 21, 2007, a moderate-sized (Mw 5.7) earthquake struck the town of Sivrice (Elazig, Turkey) located within the East Anatolian Fault (EAF) zone that forms the boundary between the Arabian and Anatolian plates. The earthquake source parameters of the mainshock reported by different agencies are significantly different. In the mean time, the relation of this earthquake to the EAF has not been fully explored. In this study, we combine remotely sensed Synthetic Aperture Radar data obtained from ENVISAT ASAR images (European Space Agency) with relocated seismicity to map the observed surface displacement field, resolve the earthquake source parameters and determine the fault plane geometry. We calculated coseismic interferograms from both ascending and descending orbits and modeled them by elastic dislocations on rectangular fault surfaces using a downhill simplex simulated annealing algorithm. InSAR analysis and seismicity distribution reveal that the earthquake took place on the Adıyaman fault (AF), a major southern splay of the EAF. The ruptured part of the AF has a listric geometry with an oblique normal slip (rake −73±21°), and a strike of N42°E. The computed coseismic slip is 64±18 cm with a moment magnitude of Mw 5.9. The resolved fault plane has a steep dip (greater than 80°) near the surface and mildly dipping at depths between 3.6 and 8.5 km (dip 63±4°). The kinematics of the faulting is supported by the observed transtensional left-lateral strike-slip regime in the region of tectonic depression of Hazar Lake.