2019年6月17日四川长宁6.0级地震中心震源机制解及震源区构造应力场研究  

Study on Central Focal Mechanism and its Surrounding Tectonic Stress Field of the Changning M 6.0 Earthquake in Sichuan

作　　者：刘敬光 万永革[1] 黄志斌[2] 李振月[3] 胡晓辉 李泽潇 Liu Jingguang;Wan Yongge;Huang Zhibin;Li Zhenyue;Hu Xiaohu;Li Zexiao(Institute of Disaster Prevention,Sanhe 065201,Hebei,China;China Earthquake Networks Center,Beijing 100045,China;Institute of Geophysics,China Earthquake Administration,Beying 100081,China)

机构地区：[1]防灾科技学院,河北三河065201 [2]中国地震台网中心,北京100045 [3]中国地震局地球物理研究所,北京100081

出　　处：《震灾防御技术》2019年第3期677-685,共9页Technology for Earthquake Disaster Prevention

基　　金：中央高校基本科研业务费（ZY20190302）;河北省地震科技星火计划（DZ20190415002）;国家自然科学基金（41674055、41704053）

摘　　要：不同资料和方法给出的2019年6月17日四川长宁6.0级地震震源机制解存在较大差异,为了找到1个合适的震源机制解来研究此次地震的发震方式,通过数学方法得到了与现有震源机制解差别最小的中心震源机制解,节面I的走向、倾角、滑动角分别为194.78°、52.68°和139.16°,节面Ⅱ的走向、倾角、滑动角分别为312.44°、58.67°和45.22°,根据本次地震余震分布拟合得到的断层面的走向为312.17°,与中心震源机制的节面Ⅱ走向一致,因而推断节面Ⅱ为本次地震的发震断层面。之后,利用此次地震之前震源区地震的震源机制解,反演了震源区的震前构造应力场。结果表明,长宁6.0级地震的中心震源机制解和震源区震前应力场均为逆冲型为主兼走滑分量的类型,震前应力场压轴为NWW-SEE向,中间轴为NNE-SSW向,两轴倾角接近水平,而张轴较陡,表现为逆冲型的应力场。将反演得到的应力场投影到中心震源机制解给出的与余震分布一致的节面上,发现中心震源机制解的滑动角和应力场预测的滑动角差别仅为13.45°,表明此次地震受背景应力场控制而发生在先存的薄弱面上。There exists great difference from different studies in determination of focal mechanisms of the Changning M 6.0 earthquake in Sichuan. In order to find a reasonable focal mechanism for studying the rupture mode, we applied a "central focal mechanism" method, which has the minimal difference with other focal mechanisms obtained from different data and methods. The strike, dip and rake of nodal plane#1 is 194.78°, 52.68°, 139.16°, and the strike, dip and rake of nodal plane#2 is 312.44°, 58.67°, 45.22°. Based on the distribution of the aftershocks, we obtained the strike of the fitting fault plane of 312.17°, which is consistent with the nodal plane#2 of the central focal mechanism. It is inferred that the nodal plane#2 is the seismogenic fault plane of the earthquake. Then, we inverted the tectonic stress field around the earthquake using focal mechanisms before the earthquake. The results show that the type of central focal mechanism and stress field before the earthquake is dominant by thrust. Before the earthquake, the compressive axis of stress field is in NWW-SEE direction, the intermediate axis is in NNE-SSW direction. Both two-axes are near horizontal, but the tensile axis is steep, which represents a thrust type stress field. We calculated the rake on the nodal plane which consist with the strike of aftershocks under stress field. It is found that the difference between the rake given by central focal mechanism to that predicted by stress field is only 13.45°. It is shown that the earthquake occurred on a pre-existing plane and controlled by background tectonic stress field.

关 键 词：长宁6.0级地震 震源机制解 中心震源机制解 构造应力场 

分 类 号：P315.33[天文地球—地震学]