Constraining the Seismogenic Fault Geometry of the 1923 M 7.2 Renda Earthquake on the Nonplanar Northwestern Xianshuihe Fault with Dynamic Rupture Simulations

Abstract The determination of seismogenic fault geometry of historical earthquakes is hindered by temporal distance, degradation of seismic evidence, human activities, and natural weathering processes, and typically relies on trenching, a costly and time-intensive method. We used the dynamic rupture simulation method to investigate the seismogenic fault of the 1923 M 7.2 Renda earthquake on the northwestern Xianshuihe fault. First, we constructed two fault geometry models (models A and B), which are supposedly the candidates for the seismogenic fault of this event. Then, we constructed the regional medium model and complex stress fields model, and simulated the dynamic rupture process on these two fault models using the curved grid finite-difference method. Our rupture model was constrained by the field-observed fault surface dislocations and inferred intensity. The simulation results suggest that the seismogenic fault of the 1923 Renda earthquake corresponds to model A, in which the southeastern segment of the Daofu fault segment consists of a subsidiary fault located farther from the Qianning fault segment. Our simulation results also suggest that the 1923 Renda earthquake has a surface rupture length of approximately 71 km and a moment magnitude of 7.2, and the earthquake rupture propagates through the bending part at Goupu, where the fault strike changes dramatically. This study provides valuable insights for constraining the seismogenic fault geometry of historical earthquakes in other regions.