Development of the Site Characterization Database for the 2022 New Zealand National Seismic Hazard Model

This article presents the development of the site characterization database for the 2022 New Zealand National Seismic Hazard Model update. This database summarizes the site characterization parameters at past and present GeoNet seismic monitoring network instrument locations, including strong-motion, short-period, and broadband seismometer stations. Site characterization parameters required to assess and improve empirical ground-motion models and those used in codified seismic design frameworks internationally have been included in the database. Measurement uncertainty was assigned, and the quality of the data used to assign each parameter was classified. The site period (T0) was the most well constrained of all the site parameters, with almost half of the database classified based on high-quality measurements, with these dominated by microtremor-based horizontal-to-vertical spectral ratio. Although there was an improvement in the quality of the parameters representing the time-averaged shear-wave velocity in the uppermost 30 m of the profile (VS30), little site-specific data were available, with almost no information for rock sites. Most of these classifications were based on national maps or geologic interpretation. Depth-based parameters (Z1.0 and Z2.5) had the lowest quality overall, with very few direct measurements available to constrain these values. Despite these limitations, the quality of parameters assigned to instrument locations has improved and greatly expanded previous databases through the assignment of parameter values to the entire GeoNet seismic network.