The map above is an earthquake hazard map for the United States. Two factors were considered in making this map: 1) the frequency of earthquakes in different parts of the United States, and 2) how far ground shaking extends from an earthquake source (related to earthquake strength and how well vibrations travel through the bedrock in area surrounding the earthquake).
The scale used for this map represents different levels of horizontal ground shaking that have a one-in-ten chance of being exceeded in a 50 year period (shaking is expressed as a percentage of acceleration due to gravity). High values of probable ground motion (shown in red) correspond to areas with highest hazard. Low values (shown in white) correspond to areas of lowest hazard. The areas shown in white are not free from earthquakes - instead strong earthquakes that cause signficant ground motion are very rare events in those areas.
The map was produced by the United States Geological Survey. Insurance companies use these maps to set insurance rates, building designers use the maps to determine where buildings need an extra measure of reinforcement, the US government uses these maps to allocate earthquake training and preparedness budgets, and the Environmental Protection Agency uses these maps to set standards for constructing critical facilities such as power plants or waste disposal sites. For more information visit the USGS Earthquake Hazards Program website.