青藏高原东部及其边缘地区的地壳上地幔三维速度结构

利用在青藏高原东部及其邻近地区记录到的１万余条近震到时资料，反演该地区的地壳上地幔三维速度结构。采用网格点模型描述三维速度结构，模型维数为２２２２６，网格点间距水平向为１００ｋｍ，垂直向为２０ｋｍ，网格点之间的速度值通过线性插值给出。采用改进了的快速三维射线追踪方法，确定三维非均匀介质中的地震射线路径和理论走时。反演结果显示，青藏高原南部的上地壳中（３０ｋｍ左右的深度）存在一低速区，这和面波反演的结果一致，羌塘块体下地壳有明显的低速异常带，青藏公路沿线的垂直速度剖面显示出岩石层受挤压增厚的构造特征。

3-D CRUST AND UPPER MANTLE VELOCITY STRUCTURE IN EASTERN TIBETAN PLATEAU AND ITS SURROUNDING AREAS

Over 10000 arrival time data of local seismic events recorded in Tibetan Plateauand its surrounding areas were used to inverse 3-D crust and upper mantle velocitystructure. The 3-D velocity structure was described by grid point model, with thedimension of 22 22 6. The intervals of grid points are 100km in horizontal and20km 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 raypaths and synthetic arrival times in 3-D inhomogeneous media. The results show thatthere is a low velocity zone in the upper crust (about 30km depth) of southem Tibet,which is coincident with the results from surface wave invereion; there is an evidentlow velocity zone in the lower crust of Qiangtang block; The vertical velocity profilealong Qinghai-Tibet highway demonstrates the structure characteristics of thecompressed and deepened lithosphere.