P, S-velocity anomalies and the Vp/Vs ratio in horizontal sections at 1, 4 and 7 km depth with the corresponding values of absolute reference velocities. Dots represent the locations of events. Black lines represent the major faults mentioned in the Figure 1b. Black triangles show seismic stations. Red stars are epicenters of the three main shocks. A and B are the two faults proposed according the aftershocks distribution.