Seismotectonics of SE Aegean inferred from precise relative locations of shallow crustal earthquakes

Abstract

We relocated the seismicity in SE Aegean that was recorded by both permanent and temporary seismic networks during 2004–2018 in order to investigate its correlation with the active faults in this area. P and S-phase travel times of best quality events were used to estimate a minimum 1D velocity model with station delays by utilizing VELEST. This velocity model and station delays were then used to obtain absolute locations of 3055 events, utilizing the probabilistic nonlinear algorithm NLLOC. The double-difference algorithm was used along with catalog and cross-correlation differential times to relocate all the events, resulting in 2200 precise relative locations with horizontal and vertical uncertainties of less than 1.0 km. The precise locations delineated faults along the Gulf of Gokova, SW of Nisyros, and Karpathos area. Based on the comparison of the resulting seismicity distribution with the regional stress field, it can be concluded that seismicity only occurred along faults with ENE-WSW strike in the area north of Tilos and N-S strike in the area south of Tilos. Seismogenic layer thickness estimated from the hypocentral depth distribution was found to vary between 12.1 and 15.4 km. Expected moment magnitudes of faults in this area were calculated by using their geometrical properties and the seismogenic layer thickness, yielding magnitudes in the range of 5.9–6.9. The fact that most of the seismically active faults in SE Aegean lie offshore increases the probability that a major earthquake will be followed by a tsunami and calls for the close monitoring of seismicity in this area.