United States National Seismic Hazard Maps

T he U.S. Geological Survey's maps of earthquake shaking hazards provide information essential to creating and updating the seismic design provisions of building codes and insurance rates used in the United States. Periodic revisions of these maps incorporate the results of new research. Buildings, bridges, highways, and utilities built to meet modern seismic design provisions are better able to withstand earthquakes, not only saving lives but also enabling critical activities to continue with less disruption. These maps can also help people assess the hazard to their homes or places of work and can also inform insurance rates. The 2008 U.S. Geological Survey National Seismic Hazard Maps for the United States are based on current information about the rate at which earthquakes occur in different areas and on how far strong shaking extends from earthquake sources. Colors on this particular map show the levels of horizontal shaking that have a 2-in-100 chance of being exceeded in a 50-year period. Shaking is expressed as a percentage of g (g is the acceleration of a falling object due to gravity). The National Seismic Hazard Maps are revised periodically by the USGS to include new research results on earthquake faults, crustal deformation, and earthquake ground shaking. The timing of the updates is designed to coincide with the schedule for updates of model building codes. During the update process, USGS solicits recommendations for improvements from the earth science and engineering communities, prepares draft maps that are vetted regionally, and solicits both public and expert opinion in review of the maps before they are finalized. Producing these maps is a key responsibility of the USGS in the four-agency, congressionally established National Earthquake Hazards Reduction Program (NEHRP). The NEHRP agencies work cooperatively with appropriate national building codes and standards organizations to ensure that the most up to date and technically sound earthquake engineering design technology is available for use around the Nation. and USGS—view the implementation of building codes as a central purpose of this partnership and the best means to ensure that buildings and other structures in local communities are adequately protected against natural hazards. America's first line of defense against earthquakes is the construction of buildings that can withstand severe shaking. Cities and counties rely on the seismic design provisions in building codes to ensure that structures can resist the earthquakes that are probable in their region. The variations in the seismic threat across the …