A study of the crust-mantle velocity structure beneath the Yushu earthquake zone and its adjacent areas

In this paper the crustal velocity structure is obtained along Yushu earthquake zone, using wide angle reflection and refraction data. The results reveal strong vertical and lateral heterogeneities in the crust, as well as the basic characteristics of the crustal velocity structure and the tectonics along the seismic sounding profile. Results show that crustal velocity structure is featured with significant regional heterogeneity both in the longitudinal and lateral directions. The crust is of layered structure, and the crystalline basement interface undulates greatly beneath the study area, which is about 8km in thickness beneath Yushu and gradually thins northwards to 2.5km beneath the Stake 400.0km at Wenquan. There are good correlations of the depressions and uplifts on basement interface with different tectonic units. The crust gradually thins towards both south and north direction to a thickness of 62km from 72km beneath Nangqian and Yushu. There exist big undulations in 2D velocity contours and the interfaces in the crust between Stakes 200.0~400.0km, and there is presence of an arc-shaped depression in the Moho beneath the Yushu area.