Physics-Based Ground-Motion Simulations of the 2023 Mw 6.0 Jishishan Earthquake: Reproducing the Observed Macroseismic Intensity Using Broadband Hybrid Source Models

The 2023 Mw 6.0 Jishishan earthquake in China caused severe damage and fatalities. Waveform analyses indicate that using a 1 Hz cutoff frequency underestimates broadband ground motions by about 70% for peak ground velocity (PGV) and up to 90% for peak ground acceleration. Physics-based simulations up to 3.5 Hz using an inverted finite-fault rupture model still underestimate PGV due to missing high-frequency components, emphasizing the need for broadband rupture models. In this study, we develop a broadband hybrid source model incorporating deterministic features of the inverted finite-fault model. Simulations with this hybrid source model produce PGV values that better match observations. Further analyses demonstrate that, for the 2023 Jishishan earthquake, ground motions simulated using the hybrid source model are jointly controlled by large-scale rupture characteristics (e.g., slip distribution and rupture velocity), which are generally well constrained by finite-fault inversion, and rise-time distributions, which are typically poorly constrained. These findings emphasize the importance of broadband hybrid source models for improving physics-based ground-motion simulations and in turn, seismic hazard assessment.