Sn wave tomography in the uppermost mantle beneath the China continent and adjacent regions

The Sn velocity image in the uppermost mantle beneath the China continent is constructed by the tomography method using 43646 travel times from Annual Bulletin of Chinese Earthquakes. Main results are: (1) The average Sn velocity is 4.55km/s in whole China, and velocity perturbations vary from -0.14km/s to 0.15km/s. (2) In general, Sn velocity is low in eastern China and, high in western China. The remarkable high Sn velocity mainly exists in the Tarim, Juggar, Turpan-Hami, eastern Qaidam, Sichuan basins and the region south to the Sichuan basin. In the Ordos platform and Taiwan straits, the Sn velocity is high. The low Sn velocity mainly appears in the whole North China basin, 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, the northern Qingzang plateau and the South-North seismic zone, the Sn velocity is slightly low. (3) The Sn velocity variations are related to tectonic activity, crustal thickness and the Earth's heat flow. We obtain a linear regression relation between the Sn velocity and the crustal thickness and a linear regression relation between the Sn velocity and heat flow. (4) The Sn velocity variations are generally consistent with the pattern of Pn velocity variations.