Pn Velocity Tomography in Xinjiang, China and Adjacent Regions

Abstract

AbstractTravel times of more than 20 000 Pn rays from earthquakes in Xinjiang and adjacent regions are used in a tomographic study to map the lateral variations and anisotropy of Pn velocity of the uppermost mantle. The tomographic results indicate that the average Pn velocity in the Xinjiang region is 8.2 km/s, which is higher than the average 8.0 km/s for the whole mainland of China. The velocity varies between –0.3 km/s and 0.2 km/s. In the Junggar basin, there is an obvious high velocity area, which is well consistent with the topography and has the maximal velocity 8.4 km/s. On the whole, abnormal high Pn velocity also appears in the Tarim basin. It is possibly because both the basins are stable, and tectonic activity and deformation are weak there. The low Pn velocity mainly exists in the transition area between basins and mountains, which is possibly attributed to strong tectonic activity. A definite low Pn velocity region to the south of the Tarim basin is possibly related to strong magmatic and tectonic activity. Anisotropy of Pn velocity is generally weak within basin regions and strong on the edges of basins. Anisotropy in the south of Xinjiang is possibly produced by northward creep of the mantle material driven by collision between the Indian and Eurasian plate.