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 (V_S) of the upper 30 meters (V_S30), the depth to the horizons of shear-wave velocity larger than 1.0 km/s (Z_1.0), 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 V_S30-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.