Non-Invasive Subsurface Site Characterization for Seismic Ground Response Analyses
Featuring Dr. Brady Cox, Utah State University
The importance of accurately predicting site effects for engineering infrastructure projects in seismically active regions cannot be overstated.
Numerical earthquake wave propagation simulations, known as ground response analyses (GRAs), are commonly performed in an attempt to estimate the site-specific, frequency-dependent amplification of seismic waves (i.e., site effects) as they travel from a reference bedrock condition up through soil layers to the ground surface.
One-, two-, and three-dimensional (1D, 2D, and 3D) GRAs have been developed. However, recent studies have revealed that recorded ground motions at more than 50% of borehole array sites are modeled using 1D GRAs. While 3D GRAs are theoretically plausible, they remain largely inaccessible due to a lack of adequate and affordable site characterization methods that can be used to develop 3D subsurface shear wave velocity (Vs) models down to depths required for ground response studies.
In this presentation, Dr. Brady Cox will detail several seismic site characterization methods usable in developing subsurface models for use in 1D, 2D and 3D GRAs. Dr. Cox will discuss methods such as horizontal-to-vertical spectral ratios (HVSR or H/V) of ambient noise, multi-channel analysis of surface waves and microtremor array measurement.
Additionally, a new geostatistical approach that can be used for building large pseudo-3D Vs models as a means to rationally account for spatial variability in GRAs will be presented. Each of these methods will be discussed from the perspective of case history applications, including comparisons between recorded and GRA-predicted ground motions at several borehole array sites.
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