AbstractA new model of the average shear-wave velocity in the uppermost 30 m has been generated by extrapolation of discrete velocity profiles using surface geology at several scales. Statistical methods have been applied to create a map that is no more complicated than is supported by the velocity data; several geologic units with similar responses are grouped together. The resulting map is simpler than previous ones and yet fits the observed velocity profiles better than earlier, more complicated maps. Analysis within a geographic information system will permit updates and modification of the map as new velocity data are added.