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Multidimensional Site Effects at the Treasure Island Downhole Array Using Seismo-VLAB and a Site-specific 3D Model

Over the past decade, numerous studies have examined ground motions recorded at borehole array sites and found that, on average, more than 50% of sites are poorly modeled using one-dimensional (1D) ground response analyses (GRAs). These discrepancies have been generally attributed to limitations of conventional 1D site assumptions, which disregard complex wave propagation effects resulting from laterally variable subsurface conditions present at most sites. Many studies have thus attempted to perform two- and three-dimensional (2D and 3D, respectively) GRAs. While these studies have provided useful insights, the vast majority have modeled spatial variability using stochastic spatially correlated random fields, have been limited to idealized single-layer profiles, have performed theoretical assessments without validation against actual ground motion observations and/or have been scaled down due to the computational demands of existing 2D/3D finite element software. Indeed, the lack of realistic site-specific 2D/3D subsurface models needed for multi-dimensional GRAs and the daunting computational costs of current software are fundamental limitations that hinder improved modeling of site effects in engineering practice. In this study, we aim to address both of these challenges by utilizing a framework called the ‘H/V geostatistical approach’ to develop large-scale, site-specific, 3D shear wave velocity (Vs) models and a new, open-source, finite element software called ‘Seismo-VLAB’ to optimize large-scale 2D/3D finite element analyses. The investigations are performed at the Treasure Island Downhole Array and involve 2D GRAs using cross-sections across different azimuths and lateral extents, as well as 3D GRAs using different incorporated areas. By comparing the site response predictions relative to recorded earthquake motions in the borehole array, we investigate the lateral area influencing site response and show that the site-specific 3D Vs model is capable of replicating wave scattering and more complex wave propagation phenomena observed in the recorded ground motions at the site.

Session: Site Response Characterization in Seismic Hazard Analysis II

Type: Oral

Room: Regency E-G

Date: 4/22/2022

Presentation Time: 10:45 AM Pacific

Presenting Author: Mohamad M. Hallal

Student Presenter: Yes

Additional Authors