2019年6月17日四川长宁M_S6.0地震序列震源机制解与发震构造分析  

Focal mechanism solutions and seismogenic structure of the 17 June 2019 M_S6.0 Sichuan Changning earthquake sequence

作　　者：易桂喜[1] 龙锋[1] 梁明剑[1] 赵敏[1] 王思维[1] 宫悦[1] 乔慧珍[1] 苏金蓉[1] YI GuiXi;LONG Feng;LIANG MingJian;ZHAO Min;WANG SiWei;GONG Yue;QIAO HuiZhen;SU JinRong(Sichuan Earthquake Agency, Chengdu 610041, China)

机构地区：[1]四川省地震局

出　　处：《地球物理学报》2019年第9期3432-3447,共16页Chinese Journal of Geophysics

基　　金：国家自然科学基金(41574047);国家重点研发项目(2018YFC150330501);2019年地震预测预报运维专项共同资助

摘　　要：2019年6月17日,在青藏高原东缘四川盆地南缘宜宾市长宁县发生M_S6.0地震,其后5天内相继发生了珙县M_S5.1、长宁M_S5.3和珙县M_S5.4强余震;7月4日,在珙县珙泉镇再次发生M_S5.6地震.因灾害叠加,本次地震序列导致13人死亡,200多人受伤,大量房屋受损,造成了重大的人员伤亡和财产损失.本文基于四川区域地震台网提供的地震资料,采用多阶段定位方法,对长宁M_S6.0地震序列早期(2019年6月17日至22日)余震进行了重新定位,同时,利用CAP波形反演方法,获得了序列中截止至7月4日的16次M_S≥3.6地震的震源机制解与震源矩心深度,对该序列的发震构造进行了初步分析.长宁M_S6.0地震序列重新定位后的610次M_L≥1.5地震分布显示余震区呈NW-SE向展布,长约25km,宽5km;序列震源深度在0~10km区间,深度均值约3.2km,但空间上呈西深东浅的分布特征.长宁M_S6.0地震位于余震区的东南端,具单侧破裂特征.CAP波形反演结果显示长宁M_S6.0地震序列以逆冲和逆冲兼走滑型地震为主;16次M_S≥3.6地震的震源矩心深度在1~7km范围,平均深度3.5km,与定位结果一致,揭示本次长宁地震序列发生在上地壳浅部.根据序列空间分布、震源机制解及震区构造特征,推测本次长宁M_S6.0地震序列的发生可能与长宁-双河复式大背斜中白象岩-狮子滩背斜和双河场褶皱及其伴生断层活动有关,位于余震区西北段的6月17日珙县M_S5.1、22日珙县M_S5.4及7月4日珙县M_S5.6地震应为6月17日长宁M_S6.0地震触发白象岩-狮子滩背斜伴生断层活动所致.序列发震构造整体呈NE-SW向挤压为主、兼具一定NW-SE向拉张分量的构造变形特征,与南侧2018年12月16日兴文M_S5.7和2019年1月3日珙县M_S5.3地震所呈现的NW-SE向挤压、NE-SW向拉张构造变形特征具有显著差异,揭示四川盆地南缘地带处于构造变形模式的转换区域,所处构造环境的变化导致本次长宁地震序列震源区�On June 17,2019,an MS6.0 earthquake hit the Changning County in Yibin City,the southern margin of Sichuan Basin in the eastern Tibetan Plateau.During the following five days,strong aftershocks of MS5.1,MS5.3 and MS5.4 occurred successively.On July 4,2019,anotherMS5.6 earthquake occurred at Gongquan Town in Gongxian.During these events,13 people and more than 200 people were killed and injured,respectively.A large number of houses were damaged,resulting in heavy casualties and property losses.Based on the seismic data provided by Sichuan Regional Seismic Network,we relocated the early events of the MS6.0 Changning earthquake sequence from June 17 to 22,2019 by using the multi-stage location method.Meanwhile,the focal mechanism solutions and centroid depths of 16 MS≥3.6 earthquakes before4 July 2019 were also calculated by using the CAP inversion method.Finally,the seismogenic structure of the sequence is preliminarily analyzed.The distribution of relocated 610 ML≥1.5 events shows that the aftershock area is 25 km long and 5 km wide in a NW-SE trending.The focal depths range from 0 to 10 km and the mean depth is about 3.2 km,the total sequence is deep in the west and shallow in the east.The MS6.0 Changning earthquake is located at the southeastern end of the aftershock zone,showing its unilateral rupture behavior.The focal mechanism solutions show that the seismogenic structure system of the sequence was dominated by thrust and oblique thrust faulting mode;the centroid depths of 16 MS≥3.6 earthquakes are within 1~7 km,and the average depth is about 3.5 km,which is consistent with the relocation result.This observation reveals that the Changning earthquake sequence occurred in the shallow part of the upper crust.Based on the spatial distribution of the sequence,focal mechanism solutions and structural characteristics of the seismogenic area,it is inferred that the occurrence of the MS6.0 Changning earthquake sequence may be related to the Baixiangyan-Shizitan anticline and the Shuanghechang anticline and their

关 键 词：长宁M_S6.0地震 重新定位 震源机制 发震构造 构造变形 

分 类 号：P315[天文地球—地震学]