2020年西藏尼玛M_(W)6.3地震InSAR同震形变特征与破裂滑动分布

Coseismic deformation characteristics of the 2020 Nima,Xizang M_(W)6.3 earthquake from Sentinel-1A/B InSAR data and rupture slip distribution

2020年7月22日(UTC)西藏尼玛发生M_(W)6.3地震.为准确确定地震的发震断层、反演破裂滑动分布以及评估地震危险性,本文利用合成孔径雷达差分干涉(DInSAR)技术对Sentinel-1A/B数据进行处理,获取视线向(line of sight,LOS)同震形变场,形变场显示以沉降为主,长轴呈NE向,升、降轨最大沉降量分别为~30 cm和~26 cm.采用基于序列蒙特卡罗采样的贝叶斯方法反演发震断层的位置和几何参数,并在此基础上通过最速下降法反演同震破裂滑动分布.反演结果显示:发震断层走向~30.41°±1.25°,倾角~49.52°±1.06°,属东倾断层.震中位置为(86.89°E,33.18°N),对应深度7.23 km.同震破裂只存在一个滑动中心,主要集中在3.4~11.8 km深度,最大滑动量~0.98 m,平均滑动角-74.54°,表明本次地震是以正断为主兼具少量左旋走滑,释放地震矩约为3.86×1018 N·m,对应矩震级M_(W)6.36,略大于USGS(United States Geological Survey,美国地质调查局)提供的震级.对于深度5 km和10 km位于破裂区南北端,以及深度15 km和20 km位于破裂区东西侧,其库仑破裂应力变化≥0.01 MPa,未来危险性值得更多的关注.

An earthquake with M_(W)6.3 occurred in Nima,Xizang on 22 July 2020(Coordinated Universal Time,UTC).To accurately determine its location,invert the rupture slip distribution and evaluate the seismic hazards,in this paper,differential synthetic aperture radar interferometry(DInSAR)technology was used to process the Sentinel-1A/B SAR data and obtain line of sight coseismic deformation field.The deformation field was mainly subsidence,which is in the NE direction,and the maximum subsidence of ascending and descending track was~30 cm and~26 cm,respectively.Then,the location and geometric parameters of the seismic fault were retrieved by using Bayesian methods(BM)based on Sequential Monte Carlo(SMC)sampling.On the basis,the seismic rupture slip distribution was obtained by Steepest Descent Methods(SDM).The inversion showed that the strike of~30.41°±1.25°,the dip angle of~49.52°±1.06°and it belongs to the East-dipping fault.The epicenter location was(86.89°E,33.18°N)and located at the depth of 7.23 km.Only one slip center was concentrated at the depth of 3.4~11.8 km,and the maximum slip of~0.98 m.The average rake angle of-74.54°,indicated that this earthquake was dominated by normal fault with minor left-lateral strike-slip.The seismic moment was~3.86×1018 N·m(M_(W)6.36),which was slightly larger than the results published by the USGS(United States Geological Survey).For the region with a depth of 5 km and 10 km located in the north and south end of the rupture zone,and the region with a depth of 15 km and 20 km located in the east and west sides of the rupture zone,the Coulomb failure stress change≥0.01 MPa,so the future risk deserves more attention.