New USGS seismic hazard maps for the United States

The US Geological Survey (USGS) is preparing new seismic national maps for release in April 1996. The new maps plot probabilistic ground motions for return times of about 500, 1000, and 2500 years. Deterministic (scenario) ground-motion maps are being prepared for selected faults in the western US. Due to the diversity of tectonic settings in the US, mapping methodologies for different regions had to be modified. A four-model approach is used to eliminate the need for drawing seismic source zones to determine seismic activity levels. A logic tree approach is used to incorporate alternative models of seismic hazard and alternative relations of seismic attenuation.