基于多元约束方法的2020年四川青白江M_(S)5.1地震构造研究  

STUDY ON THE SEISMOTECTONICS OF THE QINGBAIJIANG M_(S)5.1 EARTHQUAKE IN SICHUAN PROVINCE IN 2020 BY MULTIPLE CONSTRAINT METHOD

作　　者：徐芳 鲁人齐[1] 王帅 江国焰[3] 龙锋[4] 王晓山[5] 苏鹏[1] 刘冠伸 XU Fang;LU Ren-qi;WANG Shuai;JIANG Guo-yan;LONG Feng;WANG Xiao-shan;SU Peng;LIU Guan-shen(State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China;College of Geomatics Science and Technology,Nanjing Tech University,Nanjing 211800,China;School of Geodesy and Geomatics,Wuhan University,Wuhan 430079,China;Sichuan Earthquake Agency,Chengdu 610041,China;Hebei Earthquake Agency,Shijiazhuang 050021,China)

机构地区：[1]中国地震局地质研究所,地震动力学国家重点实验室,北京100029 [2]南京工业大学,测绘科学与技术学院,南京211800 [3]武汉大学,测绘学院,武汉430079 [4]四川省地震局,成都610041 [5]河北省地震局,石家庄050021

出　　处：《地震地质》2022年第1期220-237,共18页Seismology and Geology

基　　金：国家自然科学基金(41872206);国家重点研发计划项目(2021YFC3000604)共同资助。

摘　　要：2020年2月3日,四川省成都市青白江区发生M_(S)5.1地震,震中位于川西盆地的龙泉山断裂带北段。龙泉山断裂带北段存在东、西2支断层,2条断层与震中的距离相近。目前,此次地震的发震断层、地震成因与动力来源尚不清楚。文中尝试采用多元约束方法,将地球物理学、地震学、大地测量学理论和构造地质学与断层相关褶皱理论相结合,对青白江M_(S)5.1地震进行了综合研究。地震反射剖面揭示了龙泉山背斜北段的基本构造特征,为发育在4~6km深度的中下三叠统膏盐滑脱层之上的逆冲断层和反冲断层的组合,且具有突破式断层传播褶皱特征;研究中采用CAP波形反演法得到了此次地震的震源矩心深度和震源机制解,其中震源矩心深度为5km,表明地震与浅层断层活动有关;震源机制解的节面Ⅰ为18°/32°/100°,节面Ⅱ为186°/59°/84°;通过Hyposat定位法和双差定位法对青白江地震序列进行重定位,得到主震的震中位置为(30.73°N,104.48°E),定位的61次余震主要集中分布于龙泉山断裂带北段东支附近,且具有较好的关联性,东支断层的产状与震源机制解节面Ⅰ一致,为倾向NW的低角度逆断层。研究提取了震中附近的InSAR同震形变场,同震形变量最大可达4cm;地震造成的形变在震中西北部为隆起,东南部为凹陷,且最大凹陷部位位于震中与龙泉山东支断裂之间,符合东支断裂逆冲的活动特征。文中通过多学科交叉的多元约束,对2020年青白江M_(S)5.1地震的发震构造进行了详细分析,厘定了发震断层并探讨了可能的地震动力学背景,可为龙泉山地区的断层活动性分析和地震风险评估提供一定的科学依据。On February 3,2020,an earthquake with a magnitude M_(S)5.1 occurred in Qingbaijiang District,Chengdu City,Sichuan Province.The epicenter is located in the north segment of the Longquan Shan fault zone in the western Sichuan Basin.This fault zone locates in the forebulge of the foreland thrust belt of the Longmen Shan fault zone in the southeast margin of Tibetan plateau and is the east boundary of the western Sichuan foreland basin at the same time,so it has special tectonic significance.There are two branch faults in the north segment of Longquan Shan fault zone,which are distributed on the east and west sides,respectively,and the epicenter distance is almost similar to the two faults.At present,the seismogenic fault,earthquake genesis and dynamic source of the earthquake are not clear.As this earthquake is a moderate earthquake event,it is usually very uncertain to interpret it with structural geological or seismological data alone.Therefore,this study attempts to carry out a comprehensive study on the Qingbaijiang M_(S)5.1 earthquake by performing cross fusion of multi-disciplinary data,adopting the multi-constraint method from geophysics,seismology and geodesy,and combining with structural geology and fault related fold theory.We collected three seismic reflection profiles located in the north segment of the fault zone to reveal the basic structural characteristics underground.The detachment layer in the middle-lower Triassic Jialingjiang-Leikoupo formation is developed at the depth of 4~6km below the anticline,and two obvious opposite thrust faults are developed on the two wings of the anticline,which are breakthrough fault-propagation fold deformation.The east branch thrust fault gradually rises from the detachment layer of Leikoupo formation to the surface,and the west branch thrust fault is exposed on the surface and connected with the detachment layer downward.The waveform data recorded by 14 fixed stations within 150km from the epicenter of Sichuan seismic network are studied and collected.The focal dep

关 键 词：青白江M_(S)5.1地震 地震反射剖面 地震重定位 InSAR同震形变 龙泉山断裂带 

分 类 号：P315.2[天文地球—地震学]