Focal Mechanism Solutions of Lushan Mw 6.6 Earthquake Sequence and Stress Field for Aftershock Zone

Zhang Zhiwei; Zhou Longquan; Cheng Wanzheng; Ruan Xiang; Liang Mingjian

doi:10.3799/dqkx.2015.154

Abstract：In order to investigate seismogenic structure and seismic mechanism of Lushan Mw 6.6 earthquake on 20 April 2013, based on focal mechanism solutions of 114 M≥3.0 aftershocks from 20 April to 1 June 2013,we analyzed spatial and temporal distribution characteristic of focal mechanism and stress field.The results are as follows.(1 )The focal mechanism types of Lushan M≥3.0 aftershocks show that thrust type is dominant faulting behavior,strike-slip type takes second place,normal type is least,the orientation of P-axis have a good consistency,the dominant direction is near NWW-SEE,dip angle is from 0° to 30°,it shows that aftershock activities are controlled by regional stress field.(2)The orientations of compressive stress (S1) exists obvious space partition difference in Lushan aftershock zone,the epicenter of main shock as boundary,the S1 orientation presents NWW in the south of aftershock zone,and it is anticlockwise rotation from NW to NE in the north of aftershock zone. The dislocation type of causative fault in the north of aftershock zone is mainly characterized by thrust with the component of strike-slip.(3)The change of S1 orientation with time is not obvious,it presents near NWW direction,but its dip angle gradu-ally becomes level,stress tensor variance gradually becomes big,and the focal mechanism is mainly thrust behavior all the time,but it becomes relatively untidy with time,it reflects that seismic source stress field continually adjusts with time.(4) The depth profiles show that angle between S1 direction and causative fault strike is 80°-120°in most area,it is almost per-pendicular to fault strike,the trend of focal fault plane is NW,it shows that Lushan earthquake sequence is controlled by near level compressive stress which is perpendicular to causative fault,it belongs to typical thrust fault.