2022年6月1日四川芦山MS6.1地震的发震构造与力学机制探讨

2022年6月1日17时00分08秒（北京时间）四川雅安市芦山县发生M_S6.1地震，此次地震是继2008年汶川M_S8.0、2013年芦山M_S7.0地震后发生在龙门山断裂带的又一显著地震，与后者在空间上仅相距9 km.为揭示此次地震的发震构造特征及其与2013年芦山M_S7.0地震的关系，进而理解龙门山断裂带强震孕育动力学过程与地震危险性，本文采用CAP全波形反演方法计算了芦山M_S6.1地震的震源机制解，利用多阶段定位法对2013年芦山M_S7.0地震以来余震区地震进行了精确定位，并基于库仑应力讨论两次地震的应力触发关系.结果显示，芦山M_S6.1地震的震源机制解为：节面Ⅰ的走向、倾角和滑动角分别为221°、40°和105°；节面Ⅱ的参数为22°、52°和78°，矩心深度14 km，震源机制断层面解呈现一组与龙门山断裂带性质接近的节面.反演给出的P轴方位角为120°，倾角为6°，反映了此次地震主要受NWW-SEE向水平挤压应力作用，与龙门山断裂带南段背景构造应力场一致.地震精定位结果显示芦山M_S6.1地震序列发生在2013年芦山M_S7.0地震发震断层北西侧的一条倾向南东的反冲断层上，据此可判断震源机制解的节面Ⅱ为发震断层面.在此基础上，通过指定发震与接收断层，计算获得2013年芦山M_S7.0地震对此次M_S6.1地震所在断层的最大库仑应力加载值可达1.5 MPa，说明前者对后者有显著的触发作用.

Discussion on seismogenic structure and mechanical mechanism of the 1 June 2022 MS6.1 Sichuan Lushan earthquake

The 2022 MS6.1 Lushan earthquake struck Lushan country, Ya'an city in Sichuan Province, China on June 1 at 17:00:08 (Beijing time). This earthquake occurred in Longmenshan fault zone after the 2008 MS8.0 Wenchuan earthquake and the 2013 MS7.0 Lushan earthquake, and only 9 km away from the Lushan event. To reveal the seismogenic structural characteristics of this earthquake and its possible relationship with the 2013 MS7.0 Lushan earthquake, and further understanding the dynamic process and seismic risk of strong earthquake in Longmenshan fault zone, we used CAP full waveform inversion method to calculate the focal mechanism solution of the MS6.1 Lushan earthquake, and relocated the aftershock events of the 2013 Lushan MS7.0 event using a hybrid multi-stage method, and further discussed the stress trigger relationship of the two events based on Coulomb stress change. The results show that the focal mechanism solution of the MS6.1 Lushan earthquake is: the strike, dip and slip angles of nodal plane Ⅰ are 221°, 40° and 105°, and the parameters of nodal plane Ⅱ are 22°, 52° and 78° respectively, the centroid depth is 14 km, and the fault plane solution of the focal mechanism shows a similar nodal plane to that of the Longmenshan fault zone. The inversed azimuth and dip angle of P-axis are 120° and 6°, reflecting that the earthquake was mainly affected by NWW-SEE horizontal compression stress, which is consistent with the background tectonic stress field of the southern section of the Longmenshan fault zone. The seismic relocation demonstrates that the MS6.1 Lushan earthquake occurred on a SE-dipping back-thrust fault on the NW side of the seismogenic fault of the 2013 MS7.0 Lushan earthquake, suggesting that the nodal plane Ⅱ is the fault plane. Finally we calculate the Coulomb stress change caused by the 2013 MS7.0 Lushan earthquake on the fault plane of the MS6.1 earthquake, and found the maximum Coulomb stress change reaches 1.5 MPa, indicating that the significant triggering effect between them.