3-D crust and upper mantle velocity structure in eastern Tibetan Plateau and its surrounding areas

Over 10 000 arrival time data of local seismic events recorded in Tibetan Plateau and its surrounding areas were used to inverse 3-D crust sind upper mantle velocity structure. The 3-D velocity structure was described by grid point model, with the dimension of 22 x 22 x 6. The intervals of grid points are 100km in horizontal and 20km in vertical. The velocity value among grid points were given by interpolation. An advanced fast 3-D ray tracing method was used to determine the seismic ray paths and synthetic arrival times in 3-D inhomogeneous media. The results show that there is a low velocity zone in the upper crust (about 30km depth) of southern Tibet, which is coincident with the results from surface wave inversion; there is an evident low velocity zone in the lower crust of Qiangtang block; The vertical velocity profile along Qinghai-Tibet highway demonstrates the structure characteristics of the compressed and deepened lithosphere.