Wald et al. (2004) first, and Wald and Allen (BSSA, 2007, in press), more fully, describe a methodology for deriving maps of seismic site conditions using topographic slope as a proxy. Vs30 measurements (the average shear-velocity down to 30 m) are correlated against topographic slope to develop two sets of coefficients for deriving Vs30: one for active tectonic regions that possess dynamic topographic relief, and one for stable continental regions where changes in topography are more subdued. These coefficients have been applied to continental U.S. by Wald and Allen, and in other regions around the world by Allen and Wald (USGS Open File Report, 2007, in review). They also compared topographic slope-based Vs30 maps to existing site condition maps based on geology and observed Vs30 measurements, where they were available, and found favourable results.
Documentation include NEHRP building site classification in pdf
Source of Global Vs30 Map Server : U.S. Geological Survey.
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