Three-dimensional ground motion of coupled basin-mountain topography near a reverse fault: Insights from dynamic rupture source modeling

Understanding the seismic response of complex sites near active reverse faults is crucial for mitigating earthquake-induced risks to infrastructure in geologically dynamic regions. However, existing research predominantly focuses on isolated geomorphic units, leaving the seismic behavior of composite topographies under dynamic fault rupture largely unexplored. This study employs a dynamic rupture model and the spectral element method to simulate three-dimensional (3D) ground motion characteristics in environments with coupled basin and mountain topography. The analysis focuses on the role of topography and on inter-topographic interactions between adjacent geomorphic units to characterize their combined influence on ground motion. The results show that significant near-field effects occur in the near-fault region, including permanent displacements and velocity pulses attributed to fling-step phenomena, and that the ground motion on the hanging wall is more pronounced than on the footwall. Seismic waves, after being reflected and superimposed within mountains and basins, amplify ground motion amplitudes and increase shaking duration. These processes produce strong topographic amplification, with peak ground velocity (PGV) and peak ground acceleration (PGA) at the mountain summit increasing by 58% and 79%, respectively, while being amplified by factors of 6.2 and 2.9 within the basin. The barrier effect of the mountains reduces ground motion in the basin as their height increases, with peak ground displacement (PGD) attenuated by up to 20%. The modification of seismic waves by the basin, in turn, alters ground motion patterns in the mountains on the far side of the fault. This study elucidates the patterns of 3D ground motion heterogeneity and coupled topographic interactions, offering valuable insights for seismic risk management in near-fault complex sites.