The 20 July 2017 Bodrum-Kos Earthquake (Mw 6.6) in southwestern Anatolia, Turkey

A 6.6 (Mw) earthquake struck the western part of Gokova Gulf in the eastern Aegean Sea on July 20, 2017. The fault plane solution for the mainshock shows an E-W striking normal fault with approximately N-S (N4 degrees E) tensional axis (T-axis). Fault plane solutions for 33 aftershocks offer two groups of normal faulting with E-W and NE-SW to ENE WSW orientations. The inversion of the focal mechanisms of the aftershocks yields two different extensional stress regimes. The stress regime obtained from 12 focal mechanisms of aftershocks and the mainshock is characterized by an approximately N-S (N5 degrees E) sigma 3 axis, while the other regime calculated from 21 focal mechanisms of aftershocks exhibits sigma 3 axis in an NW-SE (N330 degrees E) direction. The latter extension significantly affects the basin's growth in the area where the earthquake occurred. Twenty-four focal mechanisms of earthquakes in and around Gokova Basin before the 2017 earthquake (1933-2017) were included in the inversion to determine the stress state effective in a larger area. The inversion yielded an extensional stress regime characterized by approximately N-S (N356 degrees E) sigma 3 axis. E-W trending faults inferred in the central part of Gokova Fault Zone, bordering Gokova Gulf in the north, also indicate N-S extension. The NW-SE extension obtained from NE-SW aftershocks appears to be locally effective in the northwest of Gokova Gulf. N-S extension, which appears to act on a regional scale, may be attributed to geodynamic effects related to the roll-back of the African subduction beneath the Aegean.