Fine Structure Research of Crust and Upper Mantle in Western Sichuan Basin and its Adjacent Regions

This research make use of a large number of teleseism waveform record coming from 123 stations, for the purpose of knowing the crust and upper mantle subtle structure of Sichuan Basin and its adjacent area, furthermore getting more information about the plate movement such as its direction or the process, by means of the receiver function, linear inversion and H-kappa method, ultimately having a comprehensive analysis based on the previous results. there are the conclusions:The crust thickness of our research area vary enormously on the east-west direction, the subtraction between the maximum and minimum is 29 km.The average of the crust thickness in Sichuan Basin is 39.4 km, which exist huge deposits of sediments in the surface, and the lower wave velocity ratio, which is the ratio of the shear wave velocity and the longitudinal wave velocity, illustrating this ares is a kind of the rigid block. There are thicker crust in Longmen Shan fault. The transition region between the south-Longmen Shan fault and Sichuan Basin features higher wave velocity ratio, resulting from the mantle material up welling. Songpan-Ganzi block's crust thickness has lateral variations of 58~65 km, where there is a low velocity layer existing in the shape of trapezoid at the middle and lower crust. The area features higher average of the wave velocity ratio. It could be inferred that under the long-term pressure eastward from the Tibetan plateau, the Songpan-Ganzi block is squeezed and deforming. The crust in Western Sichuan Plateau is much thick, there may be partial melting area because of the higher wave velocity ratio. The average of crust thickness in Chuan-Dian block is 58.5 km.There is a low velocity layer at the middle crust.