"A new Southern California Earthquake Center study has quantified how local geologic conditions affect the shaking experienced in an earthquake. The important geologic factors at a site are (1) softness of the rock or soil near the surface and (2) thickness of the sediments above hard bedrock. Even when these "site effects" are taken into account, however, each earthquake exhibits unique "hotspots" of anomalously strong shaking. Better predictions of strong ground shaking will therefore require additional geologic data and more comprehensive computer simulations of individual earthquakes."
U.S. Geological Survey: http://www.usgs.gov/