Assessing Basin Amplification and Rupture Directivity Effects Using Physics-Based Ground Motion Simulations in Wellington

Duo Li , Kiran Thingbaijam, Sanjay Bora, Rafael Benites, Shihao Yuan, Matt Hill, Anna Kaiser, Matt Gerstenberger

Near-surface velocity structure plays a crucial role in modulating ground motion, and, in turn, contributes to seismic risk. However, a complete understanding of the basin effect is limited, owing to the paucity of detailed shallow basin structure, geological structures and near-field seismic sources. In this study, we perform physics-based simulations of ground motions incorporating the sedimentary low-shear velocity layers in the Wellington basin to evaluate the fundamental characteristics of regional seismic responses. We simulate ground motions of frequency up to ~2 Hz for intermediate-size earthquakes around Wellington, then validate acceleration time series and spectral amplitude ratio against GeoNet strong motion records. After that, we simulate potential dynamic ruptures of Mw> 7 earthquakes on the Wellington Fault, investigating the impact of rupture directivity effects on basin amplification. Our models demonstrate distinct ground intensity patterns arising from dynamic fault ruptures, rather than from distant seismic point sources, revealing significant spatial variation in basin amplification.