This site from the USGS's Earthquake Hazards Program describes a new 3D computer model of the upper 20 miles of the Earth's crust in the greater San Francisco Bay Area. The model combines 100 years of surface geologic mapping with decades of research into the seismic properties of the rocks in the Bay Area along with information from boreholes and variations in the Earth's gravity and magnetic fields. By assigning velocities to rock types in the 3D model, geologists can gain an impression of the extent of areas of low shear velocity that are most likely to experience localized strong shaking and future earthquake damage. The new model will enable scientists to forecast strong ground motions, predict where destructive liquefaction of the ground may occur, locate earthquakes more accurately, and define the extent of groundwater aquifers and model the subsurface transport of contaminants.
