Site condition evaluation using horizontal-to-vertical response spectral ratios of earthquakes in the NGA-West 2 and Japanese databases

We evaluate the usefulness of the horizontal-to-vertical (H/V) response spectral ratio as a parameter to describe site response. In particular we compare its effectiveness with that of the time-averaged shear-wave velocity to 30 m (VS30), and also look at how those two measures are correlated. The evaluation is performed considering two major compiled ground-motion databases, one being the international NGA-West 2 database, and the other being a comprehensive database from Japan. A uniform procedure is applied to pick peak frequency (fpeak) and peak amplitude (Apeak) from the averaged H/V response spectral ratio for each site in the database. The H/V peak parameters are then grouped by their behavior, and the relationship of these peak parameters to VS30 are investigated by region. We conclude that: (1) H/V offers at least as much site information as VS30; (2) H/V is of more descriptive value than VS30 for deep soil sites, having fpeak≤1 Hz; and (3) the averaged H/V response spectral ratio for a site peaks at a specific frequency which is related to the depth of deposit, and has a stable peak amplitude of ~0.45 log10 units, independent of the region. We conclude that H/V has significant advantages over VS30 as a site description variable, and note that it is in general easier (less expensive) to obtain.