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

摘要

We present an objective technique for assessing the fundamental resonance frequency (f0) 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 f0 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 f0 values have been determined for 266 stations. The determined f0 values have been used to estimate time-averaged shear-wave velocity in the upper 30 m (VS30), taking into account the correlation between H/V parameters and measured VS30 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 VS30 model shows the highest VS30 values among all models. We use the region-specific equation developed in this study to estimate VS30 values for 63 stations of ISMN where no other site characterization was available.