Sn Wave Tomography of the Uppermost Mantle Beneath the China Continent and Adjacent Regions

Abstract

AbstractSn velocity image of the uppermost mantle beneath the China continent is reconstructed by tomographic inversion using 43646 Sn travel times selected from Annual Bulletin of Chinese Earthquakes. The main results are: The average Sn velocity is 4.55km/s for the whole study region, and the velocity perturbations range from –0.14 km/s to 0.15 km/s. In general, Sn velocity is low in eastern China and high in western China. Remarkably high Sn velocity is found in the Tarim, Juggar, Tulufan‐Hami, eastern Qaidam, Sichuan basins and the region south to the Sichuan basin. In the region of the Ordos platform and Taiwan straits, Sn velocity is also slightly high. Low Sn velocity is seen mainly in the whole North China basin, the region east to the Bohai bay, northern Shanxi, and the Tancheng‐Lujiang fault zone. In addition, in the middle and lower reaches of the Yangzi river, northern Qingzang plateau and the South‐North seismic zone, Sn velocity is relatively low. Sn velocity variations are related with tectonic activity, crust thickness and the Earth's heat flow. We have obtained a linear regression relation between Sn velocity and crust thickness, and a linear regression relation between Sn velocity and heat flow. Sn velocity lateral variation is generally consistent with the pattern of Pn velocity variation.