Probing the interseismic locking state of the Xianshuihe fault based on a viscoelastic deformation model

The interseismic locking state of tectonic faults is essential for regional seismic hazard assessments. However, it is challenging to obtain this parameter reliably due to the weak deformation and complex model configurations. To better probe the fault locking state, more reliable physical models and well-covered observations are required. Here we investigate the locking state of the Xianshuihe fault based on a new-developed viscoelastic deformation model. Meanwhile, we combine GPS velocities from 13 new near-field stations and existing stations in this region to improve the spatial resolution. Similar to the theoretical predictions, our results indicate that the elastic model will clearly overestimate the fault locking depth and seismic moment accumulation rate, and the fault slip rate inferred from the elastic model is slightly lower than that from the viscoelastic model. Relying on the locking distribution inferred from the viscoelastic model, we identify four potential asperities on the Xianshuihe fault. More importantly, we find a clear spatial correlation between the fault locking distribution and the rupture extent of historical earthquakes, which indicates that the fault locking state may control the rupture extent and thus the magnitude of earthquakes. In addition, our results show that the 2022 M6.8 Luding earthquake only ruptured the south part of a potential asperity, and the accumulated energy in the northern unruptured area is equivalent to an M(w)6.9 earthquake, where the seismic hazard deserves special attention.