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 P lateau 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 poin ts are 100km in horizontal and 20km in vertical. The velocity value among g rid points were given by interpolation. An advanced fast 3-D ray tracing me thod was used to determine the seismic ray paths and synthetic arrival time s 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 coi ncident with the results from surface wave inversion; there is an evident l ow velocity zone in the lower crust of Qiangtang block; The vertical veloci ty profile along Qinghai-Tibet highway demonstrates the structure character istics of the compressed and deepened lithosphere.