2017年8月8日四川九寨沟7.0级地震InSAR同震形变场及断层滑动分布反演

摘要

We processed the Sentinel-1A/IW data with InSAR technology and generated the surface deformation fields caused by Jiuzhaigou Ms7.0 earthquake occurred on August 8 2017.The result shows that the overall deformation field caused by this event follows the NW direction.Main deformation region is about 50 km×50 km delimited by Tazang,Minjiang and Huya faults.The maximum displacement reaches about 14 cm,and the minimum value is about 22 cm in LOS.The displacement field indicates a left-lateral strike-slip movement of seismogenic fault.Based on ascending InSAR deformation field only,we carried out the slip distribution inversion by using a fault model with single fault plane and medium dip angle.The inversion results indicate an obvious slip concentrated area located in 1～15 km in depth.The maximum slip is about 0.86 m.The moment magnitude is Mw6.5,consistent with previous results from seismic data inversion provided by USGS.We can see that the rupture of this event has filled the rupture gap of four earthquakes larger than Mw6.0 occurred in 1973 and 1976.The coseismic Coulomb stress change shows that the rupture has produced two stress increasing zones in the depth of 10 km,～(3～5) × 105Pa.This will increase the possibility of aftershocks in this area.A large stress decreasing zone delimited by Minjiang and Tazang fault indicates the releasing of accumulated stress before the rupture.Thus,the possibility to trigger further strong aftershocks in this region is relatively small.%基于InSAR技术,利用欧空局升降轨Sentinel-1A/IW宽幅数据,获取了2017年8月8日四川九寨沟7.0级地震InSAR同震形变场,并以升降轨InSAR观测结果为约束,反演了断层滑动分布,基于三种不同接收断层计算了同震库仑应力变化.结果表明,同震形变场发生在塔藏断裂、岷江断裂和虎牙断裂交汇的三角地带,升降轨于涉位移均显示本次地震的形变场影响范围约为50 km×50 km,形变场长轴方向为NW向,升降轨观测的形变量相反,反映断层运动性质以走滑运动为主,升降轨数据观测得到的最大LOS(Line of Sight,视线向)形变量分别为～22 cm和～14cm.非对称形变场反映出断层两侧的运动差异.反演结果显示,最大滑动量约为1 m,平均滑动角为-9°,矩震级为MW6.5,地震破裂主要集中在地下1～15 km深度范围内,但整体而言本次地震破裂较为充分,基本将该区域1973年及1976年4次＞Mw6.0地震的破裂空区完全破裂.考虑到塔藏断裂和虎牙断裂的运动性质,可初步判定发震断层为虎牙断裂北侧延伸分支.基于三种不同接收断层模型的同震库仑应力变化计算结果反映出该区域以应力释放为主,进一步触发较大走滑型余震的可能性不大.