Seismic Site Effects of Horizontal-to-Vertical Spectral Ratios for the Strong-Motion Stations in Taiwan

The resonant frequency and site amplification of Horizontal-to-Vertical Spectral Ratio (HVSR) for a site have become common and useful site parameters. The present site database for the strong-motion stations of TSMIP (Taiwan Strong Motion Instrumentation Program) in Taiwan only included conventional parameters, including the averaged shear-wave velocity (VS) of the upper 30 meters (VS30), the depth to the horizons of shear-wave velocity larger than 1.0 km/s (Z1.0), and the high-frequency decay parameter (kappa; κ0). In order to complete the HVSR-based site parameters of the database, the earthquake-based HVSR (eHVSR) and microtremor-based HVSR (mHVSR) are conducted for the TSMIP stations within the site database based on the standard procedures suggested by recent studies. The characteristics of eHVSRs and mHVSRs for different VS30-based site classifications are evaluated and discussed. The relationships between HVSR-based parameters, including resonant frequency and amplification, and conventional parameters are systematically assessed. Although the differences between eHVSR and mHVSR are non-negligible for some stations, the results still show high correlations between their derived site parameters and realistic site conditions. The HVSR-based site parameters of the TSMIP stations would be reliable for further studies of strong motion prediction and simulation, seismic hazard analysis, etc, in Taiwan.