Site parameters applied in NGA-Sub database

Abstract

NGA-Sub data resources are organized into a relational database. We describe the Site table within that database structure, which contains metadata for 6502 stations that have recorded earthquakes incorporated into the database. Critical site parameters for ground motion modelling are time-averaged shear-wave velocity (V-S) in the upper 30 m of the site (V-S(30)) and depths to various V-S horizons (1.0 and 2.5 km/s). We compile V-S profiles for the global study regions and use these data to compute V-S(30) where profile data is available from reliable sources. When this is not the case, which is commonly encountered in many regions, we adopt a proxy-based V-S(30)-estimation framework whereby estimates are provided, in order of preference, from locally derived models, models derived for a source region and applied to a different target region with some degree of validation, and global or source-region models applied to a target region without validation. Epistemic uncertainties in category median V-S(30) are provided when proxy-based models are required but their validation is not possible. Sediment depth terms are also evaluated using measured V-S profiles that exceed measured velocity thresholds where available or are estimated for regions having 3D seismic velocity models (e.g. Cascadia, Japan, New Zealand, and Taiwan).