Abstract: No moderate and strong earthquake occurred for many years in Wenxian since the M8.0 great earthquake occurring in 1879 A.D. The June 21,2006 Wenxian earthquake with M5.0 occurred in an area where the tectonic setting is complex. Seismic activity level in Wenxian would enhance after the occurrence of this earthquake(M5.0). Since the earthquake did not produce surface rupture zone,it is very difficulty to study the seismogenic fault. However,we can still study the seismogenic fault based on geological map(1∶200 000),remote sensing interpretation,inversion of focal mechanism and seismic sequence precise location method. In order to determine the future seismic risk of the region,the paper intends to analyze the earthquake causative structure by jointly using the remote sensing interpretation,various methods of inversion of focal mechanism,and double-difference earthquake location algorithm. The geological map(1:200 000)shows there are many faults in this area,and the interpretation of remote sensing reveals that only one fault named Shifang-Linjing Fault is active. Focal mechanisms derived from the two methods show that the earthquake is of left-lateral strike-slip and thrust,and the principal compressive stress is in the direction of N60°E. The results of double-difference earthquake locations also support this result. The distribution of aftershocks is related to the thrust faulting. Results of combined analyses show that the Shifang-Linjiang Fault is the seismogenic fault of this earthquake,and the direction of the principal compressive stress is N60°E.

Key words: remote sensing interpretation, amplitude-ratio method, focal mechanism, double-difference earthquake location, seismogenic tectonic

摘要： 2006年6月21日文县5.0级地震发生在构造环境复杂的地区,该地区之前已有100多年没有发生过中强地震。该地震的发生说明该地区的地震活动开始增强。文县5.0级地震没有形成地表破裂带,给研究发震构造带来了一定的困难,通过1/20万地质图、遥感资料解译、震源机制反演以及地震序列精确定位的方法依然能够研究该地震的发震构造。为判定该地区未来的地震危险性,文中采用遥感资料解译、多种方法反演震源机制、双差法地震精定位的方法联合分析该地震的发震构造。1/20万地质图显示该区域存在多条断裂,遥感资料的解译结果表明石坊-临江断裂为较活动的断裂。2种方法所得震源机制结果表明该地震为左旋走滑兼有逆冲,主压应力方向为N60°E。双差法定位结果也支持该地震为走滑兼有逆冲,余震的分布与断裂的逆冲有关。结合多种结果联合分析认为该地震的发震构造为石坊-临江断裂,主压构造应力方向为N60°E。

关键词: 遥感资料解译, 振幅比方法, 震源机制, 双差定位, 发震构造