Recent Tectonic Stress Field Zoning in Tienshan Area and its Dynamic Genesis

Using 245 middle and strong earthquake focal mechanism solutions happened in the period of 1931-2004 to determine the stress districts in Tienshan area by step by step convergence method. The inverted results indicate there are 3 stress districts in Tienshan area. They are Pamirs stress district, Jiashi and its adjacent stress district and Urumchi and its adjacent district, respectively. Besides, we also get the generally characteristic of recent tectonic stress field in Tienshan area. First, its direction of the maximum compres-sional stress is about in N-S direction, but it shows a clockwise rotation from Pamirs stress district in the west to Urumchi stress district in the east from the spatial distribution. Second, each stress district has its own dif-ferent characteristic of tectonic stress field. This phenomenon indicates that the research area in the whole stress background has its local changes. And the third is that the stress regime in Tienshan area is almost Strike slip and reverse slip. On the basis of above basic research work, we try to analyse and explain the dy-namic genesis of the heterogeneity of the spatial distribution of recent tectonic stress field in Tienshan area from the force sources.