Development of the Taiwan Generic Rock Seismic Velocity Profile

Reference velocity profiles for ground‐motion models (GMMs) provide more information about the site condition represented by the GMM than the simple site parameters used in the GMMs, such as $VS30$ (time‐averaged S‐wave velocity of top 30 m strata from the surface). A reference velocity profile for generic soft‐rock site conditions is developed for Taiwan using multiple data sets to span the depth range from 0 to 16 km. The measured $VS$ profiles from PS‐logging at strong‐motion stations with $VS30$ between 610 and 930 m/s (i.e., 760 m/s ± 20%) were selected to define the top 30 m of the profile. The velocity profiles obtained from multiple existing geophysical studies were then used to extend the $VS$ profile to seismic bedrock (⁠$VS$ of 3.5 km/s). A corresponding generic rock P‐wave velocity (⁠$VP$⁠) profile was developed using $VP$ from PS‐logging measurements and an empirical relationship between $VP$ and $VS$ for the deeper part of the profile. The proposed Taiwan Generic Rock (TWGR) model has $VS30$ of 754 m/s, $Z1.0$ (thickness of sediments with $VS<1.0km/s$⁠) of 29 m, $Z2.5$ (thickness of sediments with $VS<2.5km/s$⁠) of 2.1 km, and $κ0$ (spectral decay slope) of 0.052 s. The $VS$ values of the TWGR profile at depths of 50 m–8 km are smaller than from the generic rock profile with $VS30=760m/s$ for California, which lead to different site amplifications between soft‐rock sites in Taiwan and California. The TWGR provides information on the applicability of the large empirical data set of strong‐motion recordings from Taiwan to other regions.