The Application Of XinJiang JiaShi Region's Middle And Small Earthquake Moment Tensors Inversion

In this paper,we use the data of JiaShi earthquake sequence which was recorded by KAS station and WUS station of the regional digital station network in XinJiang near source region. We have calculated moment tensor solutions of more than 100 Ms≥3.5 earthquakes from 2001 to 2004 by the body waveform inverse. At the same time,we compared our result with Harvard CMT result. The result shows that our result is comparatively trusty.We have analyzed the change of JiaShi local stress field before and after the Ms6.8 earthquake of Feb.24th,2003 with the moment tensor solutions which we have calculated. As a comparison,we calculate focal mechanism solutions of more than 30 Ms≥3.5 events by P and S first motion and their amplitude ratio in 1998. In addition,we analyze the stress field change before and after the two strong earthquakes in 1998. For further study,we calculate the tectonic stress field by using Mw≥6.0 events in XinJiang and its surround region since 1976. At last,we analyze the stress field and fault character in different period of time by using Mw≥5.0 events in JiaShi region from 1977.Summing up the analyse and study from above,we get following conclusions:①The character of the stress field in JiaShi region from 2001 to 2004 (Ms≥3.5) calculated by the moment tensor inverse is as following: the principal compressive stress field is approximately in the NS direction and the principal tensile stress field is approximately in the EW direction.②Our study shows that the stress field of middle and small events is disorderly before the three strong shocks of Aug.2nd ,and Aug.27th 1998 and Feb.24th 2003 .③Our research finds that the local region stress field exist turning and returning,and the fault character change in different phase from 1977 to 2003.④The western part of Tianshan mountain of Xinjiang region exists stable tectonic stress field,and the principal compressive stress field is approximately in the NS direction,and the principal tensile stress field direction is approximately in the EW direction.⑤We think that there perhaps exists a barrier in the south of JiaShi earthquake swarm which is the reason of turning and returning of the stress field direction.⑥We think that the reason of Ms 6.8 earthquake on Feb.24th 2003 results from the superposition of the remainder stress field principal compressive stress and triggering stress field principal compressive stress in the same direction.Finally,we analyze possible factors which maybe effect the conclusions which we have gotten.