2019年四川长宁MS6.0地震孕震机理分析

基于四川省、贵州省、重庆市数字地震台网的三分量宽频带波形资料和震相报告数据，使用Geiger定位法和ISOLA反演方法，对长宁M_S6.0地震序列进行重定位，并反演序列中5次M_S≥5.0地震震源机制解。重定位结果显示，地震序列主要分布在白象岩-狮子滩背斜轴部，总体沿NW65°方向展布，沿该方向震源深度特征为北西深、南东浅。震源机制解反演结果显示，主震破裂表现为高倾角左旋走滑特征，节面Ⅰ走向/倾角/滑动角为20°/72°/151°，节面Ⅱ走向/倾角/滑动角为120°/62°/21°，与白象岩-狮子滩背斜轴部走向基本一致。5次地震纯双力偶（double-couple，DC）成分含量均小于70%，矩心深度均小于10 km。综合分析认为，此次长宁M_S6.0地震发震断层为发育在白象岩-狮子滩背斜的左旋走滑断层，震因为流体注入和复杂的地质构造活动。

Analysis of Seismogenic Mechanism of the 2019 Changning,Sichuan MS6.0 Earthquake

Based on the three-component broadband waveform data and seismic phase reports from the digital seismic networks in Sichuan, Guizhou and Chongqing, we use Geiger positioning method and ISOLA method to relocate the Changning M_S6.0 earthquake sequence and invert the focal mechanism of five M_S≥5.0 earthquakes in the sequence. The relocation results show that the earthquake sequence is mainly distributed in the axis of Baixiangyan-Shizitan anticline, along the direction of 65°NW. Along this direction, the focal depth features are deep in the northwest and shallow in the southeast. Inversion results of focal mechanism show that the rupture of main shock is characterized by high dip angle and sinistral strike-slip. The strike/dip/rake of nodal plane Ⅰ is 20°/72°/151°, the strike/dip/rake of nodal plane Ⅱ is 120°/62°/21°, which is basically consistent with the axial strike of Baixiangyan-Shizitan anticline. The content of pure double-couple(DC) of the five earthquakes is less than 70%, and the centroid depth is less than 10 km. Comprehensive analysis shows that the seismogenic fault of Changning M_S6.0 earthquake is a sinistral strike-slip fault developed in Baixiangyan-Shizitan anticline. We speculate that the Changning earthquake was caused by fluid injection and complex geological structure activities.