Estimation of the Nucleation Location and Rupture Extent of the 1850 Xichang, Sichuan, China, Earthquake by Dynamic Rupture Simulations on a Multi‐Segment Stepover Structure

We simulated the rupture dynamics and ground motion of the 1850 Xichang, China, earthquake on the Zemuhe fault, which consists of the Lijinbao segment, the Dajing segment, the Chechejie segment, and the Songxin segment, with the curved grid finite‐difference method, and compared the simulation results with the field observed data and written records inferred data. We focused on the rupture extent of this earthquake and the effects of the maximum principal stress azimuth and nucleation location on the rupture process and the corresponding damage distribution. Numerical simulation results suggest that the regional maximum principal stress orientation that surrounds the Zemuhe fault was approximately N55°W, which is identical with the azimuth from the stress relief experiment in the neighboring area. Our simulations further imply that the nucleation location is under Lanbiluo. The simulation of this preferred nucleation location model suggests that the rupture propagated through the entire Dajing segment and the Chechejie segment, and the rupture gradually arrested at shallow depths after it transferred to the Lijinbao segment and the Songxin segment. Moreover, the simulation suggests that the rupture on the Chechejie segment was initiated at the surface and then mainly propagated downward due to the free surface effect. In addition, the Xichang earthquake may have exhibited a low rupture velocity on the Dajing segment. Furthermore, our simulation results emphasize the importance of the stepover width in the earthquake dynamics. Plain Language Summary The 1850 Xichang earthquake occurred on the nonplanar Zemuhe fault. We used physics‐based computer simulations of the rupture process to investigate the rupture length and source location of this earthquake. We found that the regional stress direction and magnitude are important to the simulation results. We also found that this earthquake mainly propagates through two segments of the Zemuhe fault (five segments in total) and the source location is approximately under Lanbiluo at a depth of 10 km. Moreover, our simulation implies that the earthquake rupture directivity has a strong effect on the surface damage distribution of the research area. Key Points We simulate the dynamic rupture and ground motion of the 1850 Xichang, China, earthquake The earthquake rupture area covers the entire Dajing and Chechejie segments, and part of the Lijinbao and Songxin segments Nucleation location, stepover width, and free sur