Insights on the Spatial Area Influencing Seismic Site Response from 2D and 1D Ground Response Analyses at Treasure Island

When modeling seismic site effects, many studies have focused on the importance of vertically characterizing the shear wave velocity (Vs) profile. However, the importance of laterally characterizing the Vs variability has generally been either overlooked or oversimplified. As such, little is known about the spatial area that influences seismic site effects, and the state-of-the-practice continues to quantify these effects by combining results from multiple onedimensional (1D) analyses, such as Vs randomization. In this study, we investigate the spatial area influencing site response at the Treasure Island Downhole Array (TIDA) by (1) performing numerical two-dimensional (2D) ground response analyses (GRAs) and (2) combining multiple 1D GRAs using all 1D Vs profiles sampled from the 2D models. We use a site-specific, largescale, Vs model that has been developed to a depth of 150 m over the entirety of Treasure Island. By comparing 2D and combined 1D GRA predictions from different lateral extents to recorded earthquake ground motions at TIDA, we systematically highlight the large spatial area that influences site response, which extends to distances as much as 1 km from the TIDA sensors.