PRIMARY STUDY OF CRUSTAL AND UPPER MANTLE VELOCITY STRUCTURE OF SICHUAN PROVINCE

Arrival-time data from 10 industrical explosions and 154 earthquakes recorded by 50 stations of the Sichuan Seismic Network are analyezd to formulate the different average curstal and mantle velocity models for the east basin and west tableland of Sichuan divided by the Longmenshan fault and secondary boundaries of land structure blocks. If a simple two-layer crust is assumed, we have obtained: (1) the velocity model in the eastern part has a crustal thickness of 40-41km, an upper mantle velocity (P wave) of 8.15-8.2 km/s, an 18 km thick upper crust with an average velocity of 5.82-5.9 km/s, and a 22-23 km thick lower crust with an average velocity of 6.47-6.54 km/s; (2) the velocity model in the western part has a crustal thickness of 61-64km, an upper mantle velocity (P wave) of 7.8-7.84 km/s, a 27-28.5 km thick upper crust with an average velocity of 5.82-5.96 km/s and a 34-35.5 km thick lower crust with an average velocity of 6.94-7.0 km/s. This model provides the hasis for the regional travel-time tables of Sichuan and useful constraints for researches the relationship of the crustal and mantle structure with earthquakes, the structural evolution and formation of the China land blocks and so on.