Regional waveform inversion for crustal and upper mantle velocity structure below Chuandian region
川滇地区速度结构的区域地震波形反演研究

The crustal and upper mantle velocity structure beneath Chuandian region has been studied by using the regional waveform data from digital seismic network of Yunnan province. The inversion result shows that the P-wave velocity in upper most mantle is relatively low, about 7.8 km/s in Chuandian region, with a small positive velocity gradient in upper mantle. The weak low S-wave velocity zone is between 100 km and 160 kin. For shorter paths, the average P and S-wave velocity structures vary obviously with paths. Different from the structures within the Chuandian rhombic block, a low velocity zone in upper crust can be observed near the boundary of the block. We inferred the low velocity zone might be related to fault zone near the boundary. The existence of low velocity zone in lower crust within Chuandian rhombic block will make the block easier to slip. Because there is no obvious low velocity zone in upper and middle crust, we consider the uncoupled depth of north toward slipping of Chuandian rhombic block might be occurred at lower crust or even deeper. Based on the inversion results of different paths, the average crustal velocity model in central area of Yunnan province is also given in this paper.