2019年四川长宁6.0级地震主震及中强余震(MS≥4.0)的震源机制及其应力场  

FOCAL MECHANISM SOLUTIONS AND STRESS FIELD OF THE 2019 CHANGNING,SICHUAN MAINSHOCK AND ITS MODERATE-STRONG AFTERSHOCKS(MS≥4.0)

作　　者：梁姗姗[1] 徐志国 盛书中[4] 张广伟 赵博 邹立晔[1] LIANG Shan-shan;XU Zhi-guo;SHENG Shu-zhong;ZHANG Guang-wei;ZHAO-Bo;ZOU Li-ye(China Earthquake Networks Center,Beijing 100045,China;Key Laboratory of Computational Geodynamics,Chinese Academy of Sciences,Beijing 100049,China;National Marine Environmental Forecasting Center,Beijing 100081,China;School of Geophysics and Measurement-control Technology,East China University of Technology,Nanchang 330013,China;National Institute of Natural Hazards of China,MEMC,Beijing 100085,China)

机构地区：[1]中国地震台网中心,北京100045 [2]中国科学院大学,计算地球动力学重点实验室,北京100049 [3]国家海洋环境预报中心,北京100081 [4]东华理工大学地球物理与测控技术学院,南昌330013 [5]应急管理部国家自然灾害防治研究院,北京100085

出　　处：《地震地质》2020年第3期547-561,共15页Seismology and Geology

基　　金：国家自然科学基金(41804053);中国地震局地壳应力研究所基本科研业务专项(ZDJ2019-16)共同资助。

摘　　要：北京时间2019年6月17日22时55分43秒,四川省宜宾市长宁县发生MS6.0地震,震源深度16km。为了更好地了解此次地震的发震构造,文中利用四川省地震局提供的震相观测报告资料,采用HYPOINVERSE 2000方法对四川长宁MS6.0主震进行重定位,并使用四川、云南、重庆和贵州区域地震台网的波形资料,采用g CAP方法反演了2019年6月17日长宁MS6.0地震序列主震的双力偶机制解、全矩张量解以及中强余震序列(MS≥4.0)事件的双力偶机制解。重定位结果显示,此次地震的主震位置为(28.35°N,104.88°E),震源深度为6.98km,为极浅源地震。震源机制结果表明,长宁MS6.0主震的发震断裂主要为逆断兼左旋走滑性质,且全矩张量解显示其含有一定比例的非双力偶成分。主震发生后,连续发生的中强余震序列表现为走滑和逆冲型断层机制,发震类型在空间上呈现分段差异分布的特征,反映了发震断层错动过程的复杂性。基于震源机制解确定的震源区域应力场方向与整体区域的构造应力场相比存在较大差异,说明整体区域构造主压应力轴方向由长宁地震前的NWW向变为震后的NEE向。综合长宁地区的区域构造地质特征和余震展布方向分析认为,此次长宁MS6.0地震是在背景应力场作用下,长宁背斜上的先存断裂破裂引起滑动而引发的,发震断层为NW走向的高倾角逆冲兼左旋走滑趋势断层。A MS6.0 earthquake with shallow focal depth of 16 km struck Changning County,Yibin City,Sichuan Province at 22:55:43(Beijing Time)on 17 June 2019.Although the magnitude of the earthquake is moderate,it caused heavy casualties and property losses to Changning County and its surrounding areas.In the following week,a series of aftershocks with MS≥4.0 occurred in the epicentral area successively.In order to better understand and analyze the seismotectonic structure and generation mechanism of these earthquakes,in this paper,absolute earthquake location by HYPOINVERSE 2000 method is conducted to relocate the main shock of MS6.0 in Changning using the seismic phase observation data provided by Sichuan Earthquake Administration,and focal mechanism solutions for Changning MS6.0 main shock and MS≥4.0 aftershocks are inferred using the g CAP method with the local and regional broadband station waveforms recorded by the regional seismic networks of Sichuan Province,Yunnan Province,Chongqing Municipality,and Guizhou Province.The absolute relocation results show that the epicenter of the main shock is located at28.35°N,104.88°E,and it occurred at an unusual shallow depth about only 6.98 km,which could be one of the most significant reasons for the heavier damage in the Changning and adjoining areas.The focal plane solution of the Changning MS6.0 earthquake indicates that the main shock occurred at a thrust fault with a left-lateral strike-slip component.The full moment tensor solution provided by gCAP shows that it contains a certain percentage of non-double couple components.After the occurrence of the main shock,a series of medium and strong aftershocks with MS≥4.0 occurred continuously along the northwestern direction,the fault plane solutions for those aftershocks show mostly strike-slip and thrust fault-type.It is found that the mode of focal mechanism has an obvious characteristic of segmentation in space,which reflects the complexity of the dislocation process of the seismogenic fault.It also shows that the Cha

关 键 词：长宁地震 地震定位 震源机制解 应力场反演 长宁背斜 先存断裂 

分 类 号：P315.2[天文地球—地震学]