Abstract

Site amplification models using relatively simple site proxies (e.g., averaged shear‐wave velocity and soil depth) do not capture site‐specific resonance effects observed at soil sites having a high shear‐wave velocity impedance contrast. We present a model to supplement ergodic site amplification equations to consider these effects (i.e., our model is additive to ergodic equations in a natural log sense). The model is conditional on properties of horizontal‐to‐vertical (H/V) spectral ratios recorded at the site of interest and consists of a frequency‐domain pulse function parameterized by site period, pulse amplitude, and pulse width. H/V spectral ratio peaks are observed in 97% of sites in our data set. When no appreciable H/V spectral ratio peak is present, we provide a broadband adjustment to the ergodic model. Because H/V spectral ratios are typically measured under small‐strain (effectively viscoelastic) conditions but applied in engineering practice for stronger shaking conditions, our model modifies site period for nonlinear site‐response effects. The model adapts in an empirical manner H/V spectral ratio attributes measured from Fourier amplitude spectral ratios to horizontal response spectral amplification using a data set from Japan composed of sites having sufficient recordings to produce stable mean H/V spectral ratios. Compared to an ergodic model that does not consider H/V spectral ratios, application of the proposed model reduces natural log within‐event standard deviation by an average of 0.04.

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