Earthquake mechanisms in the Gulfs of Gökova, Sığacık, Kuşadası, and the Simav Region (western Turkey): Neotectonics, seismotectonics and geodynamic implications

Abstract

Abstract The mechanical behavior of continental lithosphere of Aegean region and western Turkey is one of the foremost interesting geological disputes in earth sciences. This region provides complex tectonic events which produced a strong heterogeneity in the crust as such in among most continental regions. The reasons of the ongoing lithospheric-scale extension within the Aegean region can be revealed by the correlation with the prevailing kinematic and dynamic factors such as roll-back of the subduction slab and back arc extension, westward extrusion of the Anatolian micro-plate, block rotations and transtensional transform faults. Seismological studies of earthquake source mechanisms and slip inversions play important roles on deciphering the current deformation and seismotectonic characteristics of the region. In recent years, several moderate earthquakes have occurred in the Gulfs of Gokova, Sigacik, Kusadasi, and Simav Graben. We studied source mechanisms and rupture histories of those earthquakes to retrieve the geometry of active faulting, source characteristics, kinematic and dynamic fault parameters and current deformations in western Turkey. We used teleseismic body-waveform inversions of long-period P- and SH-, and broad-band P-waveforms. We also checked first motion polarities of P-waves recorded at both regional and teleseismic stations. Inversion results revealed E–W striking normal faulting mechanisms with small amount of left-lateral strike-slip components in the Gulf of Gokova, and NE–SW oriented right-lateral strike-slip faulting mechanisms in the Gulf of Sigacik. In Simav Graben, earthquake source parameters show dominantly normal faulting mechanisms with strike-slip components. Our inversions resulted in focal depths for the earthquake ranging from 10 to 15 km and NE–SW trending T-axes directions. The finite-fault slip distribution and rupture propagation models exhibit seismic moment releases and large displacement values which essentially occurred at hypocenters of the earthquakes. The overall results exhibited uniform and circular-shaped rupture propagations along dip directions of fault planes. Although most of the focal mechanism solutions show dominantly normal faulting mechanisms associated with the E–W oriented horst–graben structures in western Turkey, there are also strike-slip faulting mechanisms related to remarkable strike-slip faults which are capable of generating damaging earthquakes, particularly in the Gulf of Sigacik and Karaburun Peninsula. Thus, we suggest that present-day deformation in the Gulfs of Gokova, Sigacik, Kusadasi, and Simav Graben (western Turkey) is still mainly driven by the N–S extensional tectonics, but we tentatively further emphasize the importance of strike-slip faults in shaping tectonic structures in the Aegean region.