Inversion of co-seismic deformation and source parameters for the 2023 Jishishan Ms6.2 earthquake with high-frequency GNSS and InSAR constraints

Abstract

On December 18, 2023, a magnitude 6.2 earthquake occurred in the Jishishan region of Gansu Province, which not only attracted widespread attention, but also triggered academic discussions about the tendency of earthquake faults. Currently, there is no uniform academic consensus on whether the Jishishan earthquake fault is east- or west-dipping. In order to more accurately understand the source parameters and fault characteristics of this earthquake, this study obtains the accurate co-seismic deformation field based on high-frequency GNSS and InSAR observations, and uses it as a constraint for in-depth analysis. First, the Bayesian inversion method is used to determine the seismic source parameters. This method is able to estimate the seismic source characteristics more accurately by combining observational data and a priori information. Subsequently, the slip distribution of the fault plane is inverted to further understand the slip characteristics of the seismic fault, and the homogeneous elastic semi-infinite dislocation model is used to simulate and compute the seismic 3D deformation field and the distribution of stress changes on the fault plane. The results show that (1) the maximum horizontal deformation observed by GNSS is 12.93 mm, while the maximum line-of-sight deformation for InSAR uptracking and downtracking is 7.64 cm and 7.84 cm, respectively; (2) the slip distribution model and simulated three-dimensional deformation field indicate that the Jishishan earthquake is a typical retrograde-cum-slip event with some slip component, which occurs on a northeast-tilted fault with a strike of 319°, with a dip of 39° and a slip angle of 104°; meanwhile, the study suggests that the source of this earthquake may be the hidden fault at the southern margin of the Lajishan Mountains; (3) the co-seismic Coulomb stress results show that the northern margin of the Lajishan Mountains is undergoing the maximum stress loading, and a high seismic hazard may exist in this area in the future.