"The USGS has released a new Quaternary Fault and Fold Database that summarizes geologic, geomorphic, and geographic information for about 2,000 Quaternary faults in the United States. This online database at http://Qfaults.cr.usgs.gov/ contains information on faults and associated folds that are believed to be sources of earthquakes greater than magnitude 6 (M>6). The database is limited to structures with documented activity during the Quaternary (past 1.6 m.y.) because this period of geologic time is most relevant for studies of active earthquake faults. Earthquakes occur when faults move beneath the Earthʼs surface. When the earthquake is large enough, movement will continue up to the surface and produce scarps, folds, or other geologic evidence of ground deformation. Although not all future earthquakes will occur on known faults, virtually all occur on preexisting faults. Thus, the faults included in this database have the most potential for future large earthquakes and provide a fairly accurate picture of earthquake hazards in the United States."
U.S. Geological Survey: http://www.usgs.gov/