Contemporary tectonic stress field on boundaries of active tectonic blocks in and around western China

Contemporary tectonic stress field on boundaries of active tectonic blocks in and around western China mainland is obtained from the data of Harvard CMT solution and reliable focal mechanism solutions from 1920 to 1999 selected by Xu Zhonghuai. We obtained the stress field by testing input and checking FMSI code(Gephart) many times. Most of the maximum principal stress sigma;1 axes on active tectonic boundaries are horizontal. To the west of 90deg;E in and around western China mainland, the horizontal sigma;1 axes are nearly in N-S direction. In the northeastern area of Qingzang plateau, the horizontal sigma;1 axes are nearly NE-SW. In the southeastern area of Qingzang plateau, the horizontal sigma;1 axes turn around clockwise around eastern end of Himalaya arc. The minimum principal stress sigma;3 axes show two dominant dip angles. In Xiyu active tectonic block region and on some segments of the northeastern edge of Qingzang plateau, the sigma;3 axes are steep, while in the Qingzang block region the sigma;3 axes are horizontal. So there are more thrust earthquakes in the Xiyu block region and on some segments of the northeastern edge of Qingzang plateau than in the Qingzang plateau block region. The stress field on the same active tectonic boundary is heterogeneous. On north Tianshan belt, south Tianshan belt, west Qinling-Delingha belt, Minshan-Longmenshan belt and Anninghe-Xiaojiang belt, the heterogeneity is relatively weak. On west Kunlun belt, Haiyuan-Qilian belt, east Kunlun belt, Mani-Yushu belt, Lancangjiang belt and western belt of west Yunnan block, the heterogeneity is relatively strong. The heterogeneity on Kalakunlun-Jiali belt and Himalaya belt is more notable. Due to limited focal mechanism data, this paper only gave the stress field on some segments of the active tectonic block boundaries.