Dynamic Rupture Simulation of the 1833 Songming, Yunnan, China, M 8.0 Earthquake: Effects From Stepover Location and Overlap Distance

Abstract

Abstract Stepover structures are widely distributed in natural fault systems. The jump distance is typically easier to identify than both the stepover location and the overlap distance because of the presence of lakes and sedimentary basins around the stepover. Using the curved grid finite‐difference method, we first conducted a 3D spontaneous dynamic rupture simulation of the 1833 Songming earthquake on a continuous model of the western Xiaojiang fault to estimate the regional stress azimuth. Then, we performed rupture process simulations with different stepover structure models on the western Xiaojiang fault to investigate the effects of the stepover location and overlap distance on the dynamic rupture process. In addition, we analyzed the fault strength ratio S and rupture velocity of the preferred fault models and discussed the occurrence of supershear rupture during the Songming event. Finally, we simulated the strong ground motion with the preferred fault models for the 1833 Songming earthquake. Our simulation results suggest that the optimal regional maximum principal stress azimuth during the Songming event was N20°W. Our simulations further reveal that the Qingshuihai stepover is located in the middle of Qingshuihai Lake, and the overlap distance is 6 km; in contrast, the location of the Yangzonghai stepover is located in the southern part of Yangzonghai Lake, and the overlap distance is not constrained. Furthermore, our numerical simulation indicates that the Songming earthquake exhibited supershear rupture; however, this supershear rupture is not sustained and is easily affected by the friction parameters and nucleation location.