Assessment of seismic ground motion incoherency induced by subsurface topography using dynamic centrifuge tests

Seismic ground motion incoherency due to spatial variability has a significant impact on soil-foundation-structure systems, including vital infrastructures such as nuclear power plants, long-span bridges, and pipelines. For the first time, this study employs dynamic centrifuge tests to investigate ground motion coherency functions affected by subsurface topography. A fleet of earthquakes was excited to the soil models with flat and inclined layering, each, and the coherency functions at the ground surface were compared across different separation distances and frequency bands. The analysis reveals that topography significantly influences seismic coherency, with a greater incoherency observed in the inclined layering case. Additionally, a comparison of coherency at the surface and the deeper depth indicates that the greater surface-to-bedrock depth results in a more pronounced incoherency effect. This study demonstrates the feasibility of using well-controlled physical modelling to explore seismic ground motion incoherency caused by ray-path effect. The results are expected to elucidate how local conditions affect seismic coherency, thereby enhancing infrastructure stability solutions.