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

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 M_S5.9 (2020-03-20), Biru M_S6.1 (2021-03-19), and Shuanghu M_S5.81 (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 normal-fault earthquakes largely depends on the gravitational potential energy in the extensional environment.