Postseismic deformation mechanism of the 2021 Mw7.3 Maduo earthquake, northeastern Tibetan plateau, China, revealed by Sentinel-1 SAR images

Abstract

The postseismic deformation mechanism is crucial for understanding the evolution of postseismic crustal stress, strain, and aftershocks. Here, we used ∼ 1 year Sentinel-1 data to obtain the time-dependent postseismic deformation of the 2021 Mw 7.3 Maduo earthquake and inverted afterslip distribution. We calculated the frictional parameter of the causative fault based on the time series afterslip. A wide range of viscoelastic relaxation models with varying lower crust viscosities were also tested to constrain the rheological structure. Our findings indicated that (1) Time-dependent postseismic deformation conforms to a logarithmic function. In the north of the fault, the attenuation time decreases first and then increases from east to west, while the south of the fault is the opposite. (2) The afterslip mainly occurred in the downdip direction of the coseismic slip, and there is an excellent complementary relationship between them in space. The partial shallow afterslip overlapped with the coseismic ruptures, mainly caused by the low frictional parameter (a-b = 10-3 ∼ 10-2). (3) Considering the postseismic viscoelastic relaxation, when the viscosity coefficient is small, the maximum deformation in 1 year after the earthquake is only about 6 mm, which only accounts for about 6 % of the InSAR observed deformation. It indicates that afterslip plays a significant role, and viscous relaxation plays a secondary role.