The Salt Lake City metropolitan area is one of the most seismically hazardous urban areas in the interior of the western U.S. because of its location within the Intermountain Seismic Belt and its position adjacent to the active Wasatch fault. The elapsed time since the last large earthquake on the Salt Lake City segment of the Wasatch fault is approaching the mean recurrence interval based on the short-term paleoseismic record. In order to help raise the awareness of the general public and to help reduce earthquake risk in this area, we have developed nine microzonation maps showing surficial ground-shaking hazard. The maps are GIS-based and incorporate the site response effects of the unconsolidated sediments that underlie most of the metropolitan area within Salt Lake Valley. These nine maps, at a scale of 1:75,000, make up three sets, each consisting of three maps that display color-contoured ground motions in terms of (1) peak horizontal acceleration, (2) horizontal spectral acceleration at a period of 0.2 sec (5 Hz) and, (3) horizontal spectral acceleration at a period of 1.0 sec (1 Hz). One set of maps consists of deterministic or “scenario” maps for a moment magnitude (M) 7.0 earthquake on the Salt Lake City segment of the Wasatch fault. The two other sets are probabilistic maps for the two return periods of building code relevance, 500 and 2,500 years.

This CD contains a 41-page report and a 1:150,000-scale map defining seismic site conditions for the Wasatch Front urban corridor. This mapping, partially funded through the U.S. Geological Survey’s National Hazards Reduction Program, provides a basis for predicting how certain soils and bedrock types may respond to ground-motion amplification in a large-magnitude earthquake on the Wasatch fault. Average shear-wave velocities were used for the upper 30 meters and surficial geologic mapping to delineate and characterize earthquake-site-conditions units that relate to International Building Code site classes. Better understanding of soil properties and earthquake-site effects for the densely populated Wasatch Front allows for improved earthquake engineering and emergency planning and response. 41 pages + 1 plate