Ground Motion Simulation and Bridges Collapse Fragility Analysis Across Reverse Strike-Slip Faults

This study addresses the seismic risk assessment of bridges located across reverse-oblique fault zones, focusing on the complex effects of buried reverse strike-slip faults with shallow burial depfths. The surface rupture patterns of reverse strike-slip faults may differ from the locations of surface rupture typically identified in conventional cross-fault engineering studies, presenting unique challenges for seismic assessment. First, a novel approach combining a broadband hybrid method with site-specific risk assessment results to simulate ground motions in regions adjacent to a reverse strike-slip fault. The simulation results are validated by comparing the mean log residuals with recorded data from the Luding earthquake in China. Second, taking into account the effects of fault depth, the study divides the affected area into four distinct regions based on varying ground motion characteristics, and performs time-range analyses to examine differences in permanent displacements and variability among these regions. Lastly, a relative displacement index is introduced to quantify the fragility differences across fault regions (with or without surface dislocation reversal). Three boundary effects are evaluated to assess the impact of this new index on traditional metrics used to estimate collapse probability. The results demonstrate that the broadband hybrid method, when tailored to local site conditions, effectively models ground motion variations in near-fault regions. Additionally, the study reveals that spatial variability in ground motion intensity and motion directionality significantly increase the uncertainty in collapse probability predictions. Combining peak velocity and relative dynamic displacement notably improves the overall collapse probability assessment using the ground motion intensity index, while peak velocity and relative residual displacement are more appropriate for evaluating collapse probability at specific ground motion intensities. These findings offer valuable insights into the seismic design and evaluation of bridges spanning fault zones and provide more reliable damage assessment methods for infrastructure in high-risk seismic areas.