Dynamic Rupture and Near-Fault Ground-Motion Simulation of the 1973 MS7.6 Luhuo, China, Earthquake

Abstract

The 1973 MS7.6 Luhuo earthquake is the most representative strike-slip event in the Xianshuihe fault zone, yet published source models differ markedly, and the mechanism that arrested its rupture near Renda remains poorly understood. Using spectral-element dynamic rupture simulations with a nonplanar fault geometry, three-dimensional velocity model, and depth-dependent initial stress field, we test whether fault geometry or inherited stress heterogeneity controlled the termination. Our results show that N75° W is the optimal maximum principal stress orientation, yielding surface offsets, a bilateral rupture mode, and an intensity pattern consistent with observations. Fault geometry alone cannot explain the termination: continuous and dipping faults rupture completely, and a 1 km stepover at Renda blocks the rupture jump yet leaves minor slip on the secondary fault. Introducing the 1923 Daofu earthquake stress change as a low-stress barrier instead terminates rupture near Renda, and simulated magnitude, offsets, and intensity then agree with observations. A compliant damage zone raises coseismic slip and lowers the moment magnitude while contracting the meizoseismal zone, whereas topography barely alters the rupture but appreciably modulates ground motion. These findings demonstrate that inherited stress heterogeneity, rather than fault geometry, can be the primary control on rupture arrest and can inform seismic hazard assessment for the Sichuan-Yunnan fault system.