Imaging the Crustal Structure Throughout the East Anatolian Fault Zone, Turkey, by Local Earthquake Tomography

Abstract

This paper presents new models of the seismic velocity structure of Eastern Anatolia, Turkey. We applied a local earthquake tomography method to arrival time data produced by local and regional events in Eastern Anatolia to understand the three-dimensional seismic velocity and Vp/Vs models and their correlation with the geological evolution and tectonic processes in the study area. The data are obtained from 78 broadband seismic stations, owned by the Earthquake Department of the Disaster and Emergency Management Presidency, for the period between 2008 and 2017. Seven depth cross sections are taken along various segments of the East Anatolian Fault Zone. Travel times of 53,099 phase readings (29,122 P-phase and 23,977 S-phase picks) from 4249 high-quality earthquake recordings are analysed to develop 3-D Vp (lithological) and Vp/Vs (petrological) models of the study area. The resulting P-wave velocities describe intrusive magmatic bodies, sediment thickness and the structure of the basin. The Vp/Vs structures aid to limit the position of the faults, areas of weakness, and gas- or liquid-saturated units with regions of high pore pressure. Four main seismic crustal layers down to 40 km are determined. The upper crust (0–8 km) has Vp ≤ 4.6 km/s, whereas in the middle crust (~ 9–20 km) a Vp perturbation between 4.6 and 5.8 km/s is observed. In the lower crust (~ 20–35 km), Vp changes from 5.9 to 7.3 km/s and in the upper mantle layer (below 36 km), Vp exceeds 7.4 km/s. In all cases, seismic velocities are well-resolved in the first 40 km. Tomograms are compatible with the geological characteristics of the region. Dominant high P-velocity values are observed beneath the collision zone. Conrad discontinuity is detectable at 20 km depth, while Moho depth is observed to vary between 30 and 40 km in the study area.