Applicability of the Site Fundamental Frequency as a VS30 Proxy for Central and Eastern North America

We introduce a new proxy measure for V-S30 (time-averaged shear-wave velocity in the upper 30 m) for central and eastern North America (CENA). The new proxy is the site fundamental frequency (f(peak)), measured from the horizontal-to-vertical (H/V) spectral ratios of recorded ground motion (or ambient noise). In this study, H/V spectral ratios are obtained from 5% damped pseudospectral acceleration (PSA) from seismograph stations in CENA using the Next Generation Attenuation-East (NGA-East) database. We correlate the measured V-S30 values at recording stations with the corresponding f(peak) values to obtain a predictive relationship for V-S30. The uncertainty of the V-S30 estimate using the f(peak)-based model is small (0: 14 log 10 units) in comparison to that for the proxy-based methods (e.g., topographic slope and surface geology proxies) used in the NGA-East database (0: 25 log 10 units). However, values of f(peak) can be obtained for only about 23% of the NGA-East recording stations due to data and site-type limitations. Reducing the error in V-S30 estimates can potentially reduce the variability of ground-motion prediction equations (GMPEs). To test this hypothesis, we use the f(peak)-based V-S30 estimates and select one of the proponent NGA-East GMPE models. For a selected database, we are able to reduce the GMPE variability (sigma) by 3% on average, for PSA at 1-10 Hz, just using the f(peak)-based proxy to estimate V-S30. Greater variability reductions could be achieved by replacing V-S30 with improved site characterization parameters, including f(peak), in the GMPEs.