Site characteristics of TSMIP strong-motion stations in Taiwan using the Horizontal‐to‐Vertical Spectral Ratio method

The free-field strong earthquake stations of the Taiwan Strong Motion Instrument Program (TSMIP), distributed throughout Taiwan, have provided rich and high-quality seismic data over the years. Its data indirectly enhances Taiwan's earthquake-prevention and disaster-reduction capabilities. Due to the importance of seismic site effects in the research of strong-ground motion, the National Center for Research on Earthquake Engineering (NCREE) cooperated with the Central Weathering Administration (CWA) to carry out the Engineering Geological Database for TSMIP (EGDT) containing three site parameters, including Vs₃₀, Z_1.0, and κ₀, and site classification. However, the CWA gradually renewed TSMIP stations since 2017, leading to the establishment and elimination of some stations. The new stations lack any earthquake site characteristics or classification information, which will make future research and the application of various strong earthquakes difficult. Besides, while Taiwan has produced numerous site characteristic studies based on microtremor or earthquake HVSR analysis, a comprehensive and systematic study of HVSR site characteristics for TSMIP strong-motion stations has been lacking. This study uses continuous seismic data from the GDMS-2020 database of CWA to extract seismic ambient noise and earthquake data for assessing site characteristics and the predominant frequencies of each TSMIP station using HVSR analysis. By establishing representative HVSRs for different site classifications using stations with well-known site parameters, we evaluated the site classifications of new stations without site information. Finally, an HVSR site database of the new TSMIP network is established and comprehensively discussed.