4-D tomographic change of V p and V p / V s structure before destructive earthquakes: a case study of the Sivrice-Elazığ earthquake (mw = 6.8), Eastern Turkey

A destructive earthquake (Mw 6.8) occurred at Sivrice-Elazig on the East Anatolian Fault Zone (EAFZ) on 24th January, 2020, causing loss of life and property. During the period of historical and instrumental seismology, destructive earthquakes have occurred at certain periodic intervals on the EAFZ, and micro-earthquake activity is also a frequent tectonic event. In this study, time-dependent four-dimensional tomography images of the Hazar-Sincik segment, one of the six segments of the EAFZ that produced the Sivrice earthquake, were obtained for the first time using the local earthquake tomography method. Synthetic tests show that data sets from before and after the Sivrice earthquake can produce reliable results in the Hazar-Sincik segment up to 20 km deep. Low Vp and Vp/Vs values were observed before the Sivrice earthquake, and an increase in Vp/Vs rates was detected after the Sivrice earthquake. Low Vp and Vp/Vs values along the Bitlis-Zagros Thrust Belt indicate that this area may present a high earthquake hazard. Very low Vp velocities on the Erkenek segment, which has produced destructive earthquakes in the past make us think that this region is still loaded with stress and that potential earthquakes in the future are likely. The results show that Vp and Vp/Vs characteristics change radically after a major earthquake. The reasons for these changes include the evolution of underground porosity and permeability values after major earthquakes. Detecting the area of seismological changes underground with time-dependent four-dimensional tomographic images can provide an important basis for earthquake prediction research.