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 compressional 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 different 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 dynamic genesis of the heterogeneity of the spatial distribution of recent tectonic stress field in Tienshan area from the force sources.
TheTienshan range extends 2500 kilometers from east to west across Central Asia. To the south, the Tienshan are separated from theKunlun Mountains and the Tibetan Plateau by the broad, hyper-arid Tarim Basin and Taklimakan Desert. To the north are the Kazakh Shield and the broad Junggar Basin, another large desert. According to incomplete statistic, about 400 destructive earthquakes of magnitude more than 4.7 have happened from 1600 to the end of 1986. Among them, there are 3 earthquakes of magnitude equal or larger than 8.0, 6 with the magnitude between 7.0–7.9, 39 with the magnitude between