Three-dimensional shear wave velocity structure and distribution image of V-P/V-S beneath the Weihe fault depression

Using the seismic data observed by the seismic networks in Shaanxi province and neighbor regions, we studied seismic tomographic imaging of the crusta l S wave velocity in the Weihe fault basin by overlapping-shear iterative r econstruction method with the two-points fast ray tracing technique. On the basis of the velocity ratio V-P/V-S in the same region is calculated. The results show that (1) there are two strong lateral no homogenous regions of S wave velocity distribution, one of which is Heyang-Yongji region on the boundary between Shaanxi and Shaanxi provinces and the other is Tongchuan-J ingyang zone. Those two areas are located in a region where different tecto nic units meet, and differential movement is significant and different rock strata are interceded; (2) the historical strong earthquakes occurred main ly in S wave high-velocity regions on their boundaries; (3) a region with h igh V-P/V-S value (highest of 2.1) is enclosed by the areas of Chunhua, Yao xian and Jingyang.