An Automatic Procedure to Determine the Fundamental Site Resonance: Application to the Iranian Strong Motion Network

Abstract

We present an objective technique for assessing the fundamental resonance frequency ( $${\text{f}}_{0}$$ ) of a given site through horizontal-to-vertical (H/V) spectral ratio. H/V spectral ratios have been determined from 5%-damped spectral acceleration derived from strong-motion time histories recorded at accelerograph stations. The technique has been applied to an updated comprehensive strong ground-motion database from Iran. In this study, the resultant $${\text{f}}_{0}$$ values have been also evaluated through visual inspection of average H/V response spectral ratios for each station as well as detailed inspection of vertical and horizontal spectral components of all events recorded at each station. The technique has been applied to 389 stations of the Iran Strong Motion Network (ISMN), from which $${\text{f}}_{0}$$ values have been determined for 266 stations. The determined $${\text{f}}_{0}$$ values have been used to estimate time-averaged shear-wave velocity in the upper 30 m ( $${\text{V}}_{{{\text{S}}30}}$$ ), taking into account the correlation between H/V parameters and measured $${\text{V}}_{{{\text{S}}30}}$$ values at recording stations. Results and corresponding model uncertainties have been compared with other related studies conducted for Japan, Central and Eastern North America as well as a global model. In comparison with other datasets, the Iranian $${\text{V}}_{{{\text{S}}30}}$$ model shows the highest $${\text{V}}_{{{\text{S}}30}}$$ values among all models. We use the region-specific equation developed in this study to estimate $${\text{V}}_{{{\text{S}}30}}$$ values for 63 stations of ISMN where no other site characterization was available.