What Spatial Area Influences Seismic Site Response: Insights Gained from Multiazimuthal 2D Ground Response Analyses at the Treasure Island Downhole Array

AbstractSite-specific subsurface conditions are known to significantly influence the frequency content and amplitude of seismic ground shaking. When attempting to model these effects, known as seismic site effects, most studies have focused on the importance of vertically characterizing subsurface g...

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Bibliographic Details
Published in:Journal of geotechnical and geoenvironmental engineering 2023-01, Vol.149 (1)
Main Authors: Hallal, Mohamad M., Cox, Brady R.
Format: Article
Language:English
Subjects:
Arrays
Azimuth
Cross-sections
Earthquake prediction
Earthquakes
Engineering profession
Geomaterials
Ground motion
S waves
Seismic activity
Seismic response
Seismic velocities
Shaking
Shear wave velocities
Technical Papers
Three dimensional models
Two dimensional analysis
Variability
Wave velocity
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Summary:AbstractSite-specific subsurface conditions are known to significantly influence the frequency content and amplitude of seismic ground shaking. When attempting to model these effects, known as seismic site effects, most studies have focused on the importance of vertically characterizing subsurface geomaterials. However, laterally characterizing the geomaterials’ variability has generally either been overlooked or oversimplified. As such, little is actually known about the spatial area that influences seismic site response. In this article, we discuss insights that have been gained regarding the spatial area that influences site response from performing two-dimensional (2D) ground response analyses (GRAs) for the Treasure Island Downhole Array (TIDA) site. In these numerical analyses, we use a site-specific, large-scale, three-dimensional (3D) shear wave velocity (Vs) model that has been developed to a depth of 150 m over the entirety of Treasure Island (an area of approximately 1.6×1.0  km2). We investigate the lateral extent influencing site response and its azimuthal variability using: (1) four cross sections with increasing lateral extent along the same azimuth; and (2) 12 cross sections with different azimuths that uniformly sample the full 3D Vs model. By comparing 2D GRA predictions 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. Although the TIDA site is often assumed to be archetype of one-dimensional (1D) site conditions, our findings support the idea that there may not be many truly 1D sites due to the large spatial area that influences site response. While some sites can be reasonably modeled using 1D GRAs, moving the engineering profession forward requires focusing our efforts on developing site-specific subsurface models over larger areas to better understand and accurately model seismic site response.
ISSN:1090-0241
1943-5606
DOI:10.1061/JGGEFK.GTENG-11023