A global hybrid VS30 map with a topographic slope–based default and regional map insets
Time-averaged shear wave velocity over the upper 30 m of the earth’s surface ( V S 30 ) is a key parameter for estimating ground motion amplification as both a predictive and a diagnostic tool for earthquake hazards. The first-order approximation of V S 30 is commonly obtained through a topographic slope–based or terrain proxy due to the widely available nature of digital elevation models. However, better-constrained V S 30 maps have been developed in many regions. Such maps preferentially employ various combinations of V S 30 measurements, higher-resolution elevation models, lithologic, geologic, geomorphic, and other proxies and often utilize refined interpolation schemes. We develop a new hybrid global V S 30 map database that defaults to the global slope-based V S 30 map, but smoothly inserts regional V S 30 maps where available. In addition, we present comparisons of the default slope-based proxy maps against the new hybrid version in terms of V S 30 and amplification ratio maps, and uncertainties in assigned V S 30 values.