A global hybrid VS30 map with a topographic slope–based default and regional map insets

Abstract

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