Here is the raster soil layer for the soils based on shear wave velocity of 30 meters.
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. The soil layers that are generated were based on Active Tectonic values.
Read a detailed research paper on the subject:
For more information check out the USGS Global Vs30 Map Server: http://earthquake.usgs.gov/hazards/apps/vs30/