关键词: 震源机制解, 地震活动, 区域应力场, P轴仰角

Abstract: The paper presents the focal mechanism solutions of 74 earthquakes with M_S≥4.5 from 2003 to 2008 in Xinjiang and analyzes the regional stress field characteristics reflected by these focal mechanism solutions in Xinjiang in this period.Then,discussion has been made combining with the seismicity image and regional stress field from 1990 to 2008.The result shows that,spatial seismic activity patterns of earthquakes with M_S≥5 in Xinjiang are quite different between 1990-2003 and 2004-2008.The seismic activity of mid-strong earthquakes or larger from 1990 to 2003 concentrated in the Aletai seismic belt,the eastern Tianshan mountains and the Arjin-Kunlun mountains tectonic belt.During this period,there occurred respectively the M_S7.3 Zaisang earthquake in June,1990,the M_S7.8 Mani earthquake in 1997,the M_S8.1 west of Kunlun mountain pass earthquake in 2001and the M_S7.9 earthquake in the border area between China,Russia and Mongolia in 2003.Since 2004,the seismic activity of mid-strong earthquakes showed a trend of decreasing towards west in Xinjiang.The azimuth of the principal compression stress P axis of focal mechanism solutions is NNW,which is slightly different from the background stress field of near SN and the earlier result of NNE obtained by the author.It reflects the changing characteristic of the large-scale regional stress field in different times in Xinjiang.The inversion result of three regional stress fields reveals some difference in space.The middle area of Tianshan mountains is obviously under the stress field of NNW direction;In the west of South Tianshan mountains-Wuqia and Hetian area and its surroundings,the principal compression stress has the characteristic of NE.The change of elevation angles of the principal compression stress P axis in the focal mechanism solutions of mid-strong earthquakes is obviously related with the strong and weak seismic activities in Xinjiang.

Key words: focal mechanism solutions, seismic activity, regional stress field, elevation angle of P axis