Tectonic and velocity structure of the Gulf of Gökova, southwest Anatolia, determined by double-difference seismic tomography: the 20 July 2017 Mw6.5 Bodrum Earthquake

Abstract

The 20 July 2017 Mw6.5 Bodrum main shock that occurred in the Gulf of Gökova is one of the largest earthquakes in the north-south extensional Aegean region. In this study, we generated the first three-dimensional local earthquake tomography for the Gökova region using the double-difference tomography algorithm to provide a contribution to discussions on the source fault of the main shock. The 2500 earthquake records of the magnitude ≥ 2.3 between 01 January 2017 and 31 December 2017 were chosen from the 18 strong-motion accelerometer and 12 weak-motion seismometer stations. The P- and S-wave velocity models and Vp/Vs ratio model of the study area were created, and 1442 earthquakes were relocated. With the help of seismic tomographic imaging, we concluded that the main shock occurred on the south-dipping Gökova Fault Zone, not on the so-called north-dipping fault plane suggested in some studies. We also determined that some earthquakes that occurred in 2017 were associated with a north-dipping normal fault observed up to 10 km depth immediately north of the Gökova Fault Zone. Additionally, the Datça-Kale Main Breakaway Fault, which separates the sedimentary cover and the basement rocks, was also determined in the tomographic profiles. The kinematic analysis of moment tensor solutions of the earthquakes with magnitudes greater than 4, twenty-one of which were generated in this study, is consistent with the north-south extensional tectonic regime in the Aegean region.