Coseismic and postseismic fault slip characteristics of the 2020 M_W6.3 Nima earthquake

The 2020 M_W6.3 Nima earthquake occurred in the northern Yibug Caka graben on the Qiangtang Block of the Tibetan Plateau. The epicentral area has complex geological structures, topography, and geomorphology, and there are few near-field ground observation stations and data. Interferometric Synthetic Aperture Radar (InSAR) has all-weather, wide ranging and high spatial resolution monitoring advantages, which can make up for the shortage of near-field ground deformation observations. However, previous studies have obtained different viewpoints regarding the seismogenic fault and coseismic and postseismic fault slip characteristics of this event. In addition, only the kinematic model has been used to extract the postseismic fault afterslip characteristics. In this study, we used ascending and descending Sentinel-1 Synthetic Aperture Radar (SAR) images and differential interferometry technology to extract the coseismic deformation fields at different viewing angles. The coseismic fault geometry and slip distribution were then inverted based on an elastic half-space dislocation model. The stress-driven postseismic afterslip model was used to model and analyze the postseismic fault slip. Finally, the earthquake seismogenic fault and the friction property characteristics of seismogenic fault zone were discussed. The ascending and descending InSAR coseismic deformation fields were continuous and smooth around the epicenter, trending NNE-SSW overall. The deformation on the southeastern side of the fault was relatively significant, and mainly decreased along the line-of-sight direction. The coseismic fault rupture was mainly normal, with a sinistral strike-slip component. The strike angle was 31.43°, and the dip angle was 45.79°. The coseismic fault slip was mainly located at 3.58-10.75 km underground, with a maximum slip of 1.33 m, and the moment magnitude was M_W6.33. The stress-driven postseismic afterslip model could better explain the almost six-month InSAR postseismic deformation field of this event. The postseismic afterslip mainly occurred on the upper, lower and southwestern sides of the southwestern segment of the significant slip area of coseismic fault, with a maximum afterslip of 47.2 cm. The seismogenic fault of this event might be a normal fault located in the middle of the Yibug Caka-Riganpei Co fault and dipping SEE, and the friction property of the seismogenic fault zone might be uneven.