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

摘要

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 V-p/V-s 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 V-p (lithological) and V-p/V-s (petrological) models of the study area. The resulting P-wave velocities describe intrusive magmatic bodies, sediment thickness and the structure of the basin. The V-p/V-s 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 40km are determined. The upper crust (0-8km) has V(p)4.6km/s, whereas in the middle crust (similar to 9-20km) a V-p perturbation between 4.6 and 5.8km/s is observed. In the lower crust (similar to 20-35km), V-p changes from 5.9 to 7.3km/s and in the upper mantle layer (below 36km), V-p exceeds 7.4km/s. In all cases, seismic velocities are well-resolved in the first 40km. 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 20km depth, while Moho depth is observed to vary between 30 and 40km in the study area.