InSAR揭示的青藏高原近期正断型地震形变特征与指示意义

Characteristics of normal-fault earthquake deformation in the Qinghai-Tibet Plateau revealed by InSAR

正断层在青藏高原的隆升扩展演化中发挥了重要作用.本文使用InSAR技术处理Sentinel-1 SAR影像数据获得了2020至2021年发生在青藏高原内部3次正断型地震的同震形变场.基于Okada弹性位错模型和形变场信息反演了断层几何参数和断层面滑动分布,精确地确定了发震断层位置.研究结果显示高原内部的这些正断型地震均以正断层活动方式为主,但还兼有一定的走滑运动;发震断层主要为倾角<60°的次级隐伏断层,且均为浅源地震,滑动分布主要集中在12 km以上.结合地球物理资料,我们分析认为正断型地震广泛分布在青藏高原中部和南部弥散型地块内,不局限于半地堑构造相关地区,并且正断型地震的发生更依赖于伸展环境中的重力势能.伴随正断层活动的走滑运动也反映了青藏高原内部物质向东运移的运动学和动力学特征.

The north-south convergence and east-west extension of the Tibet Plateau are accommodated by a series of active strike-slip and normal faults,and normal-fault earthquakes are very active in the plateau.During 2020 to 2021,there were three normal-fault earthquakes,namely,the Dingri MS5.9(2020-03-20),Biru MS6.1(2021-03-19),and Shuanghu MS5.81(2021-03-30)earthquakes.These three earthquakes were evenly distributed in the middle and southern parts of the plateau,which provides a favorable case for us to study the seismic deformation characteristics using interferometric synthetic aperture radar(InSAR)technology.We used InSAR technology and Sentinel-1 SAR image data to generate the coseismic deformation field of the three normal-fault earthquakes in the Tibetan Plateau.The results showed that the normal-fault earthquakes in the plateau were not pure normal-fault types,and the coseismic deformation field showed both subsidence deformation and strike-slip deformation.Based on the Okada elastic dislocation model and the coseismic deformation fields,we constrained and inverted the geometric parameters and the slip distribution of the fault plane to accurately determine the locations of the seismogenic faults.The seismogenic faults were mainly secondary concealed faults with dip angles<60°,all of which were shallow earthquakes.The slip distribution was mainly concentrated within 12 km.Combined with geophysical recognition,we inferred that normal-fault earthquakes are widely distributed in the Qinghai-Tibet Plateau,and not limited to areas related to half-graben structure,and that the occurrence of normalfault earthquakes largely depends on the gravitational potential energy in the extensional environment.