V S 30 ‐based site amplification factors are commonly used to account for local site effects in hybrid broadband ground‐motion simulation when site‐specific data are limited. Validation against observations allows for testing alternative semi‐empirical V S 30 ‐based models and establishing proper protocols for their application in forward analyses. This article validates alternative implementations of V S 30 ‐based site factors using 5218 ground motions from 479 small‐magnitude events recorded at 212 sites in New Zealand, which represent a wide range of site conditions. The investigation of (Fourier) effective amplitude spectra (EAS) residuals allows for a direct assessment of the low‐frequency (LF; f 1 Hz) components of the hybrid broadband simulation approach, and the corresponding effect of the site “adjustment.” Before applying the site factor, the LF simulation exhibits systematic underprediction and the HF simulation displays systematic overprediction. The use of site factors based on semi‐empirical models for EAS, developed in the last decade, results in comparable, or slightly better, prediction performance compared with response spectra‐based models commonly used in previous validation studies. A greater LF underprediction was identified at sites located within sedimentary basins that are less constrained by site data or not properly modeled in the LF simulation due to limitations in spatial discretization. A simple protocol is proposed for the application of the LF site factor based on a basin‐type and geomorphic site categorization, which reduces the variability of EAS site‐to‐site prediction residuals by up to 0.1 natural log units. The explicit incorporation of the parameter Z 1.0 , or alternatively, the use of a host‐to‐target correction factor demonstrates that a significant portion of the HF systematic overamplification in the frequency range 1.0–3.0 Hz can be explained by V S profile features not accounted for by V S 30 alone. These findings can inform the application of site adjustments in future studies and guide advancements in the LF and HF simulation components.
Kuncar et al. (Sun,) studied this question.