Earthquake Scenario And Probabilistic Ground Shaking Maps For The Salt Lake City Utah Metropolitan Area

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.

Geologic hazards are naturally occurring processes that present a risk to life and property. This report provides information for the Monroe City area, in Utah's central Sevier Valley, to reduce losses from geologic hazards. Surficial-geologic mapping provides the basis on which individual geologic hazards are identified and mapped. Alluvial-fan and basin-fill deposits cover most of the map area. Other deposits consist of colluvium, artificial fill, spring travertine, and volcanic bedrock. The geologic hazards maps show where hazards may exist. The maps should be used to inform citizens and developers of potential risks and for local government officials to make prudent land-use planning decisions. The maps are general, and site-specific studies are needed to demonstrate site suitability prior to development. Typical risk-reduction methods for these geologic hazards generally include avoidance or engineering design to reduce the risk to an acceptable level.

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

Contains more than 200 papers in the following topic areas: new mapping technologies; new developments in hazard estimation; seismic hazard mapping for engineering and codes; seismic mapping, planning, and local government policy; financial risk management, and lifelines and utilities. Organized by topic with a comprehensive table of contents and author index.

"This volume addresses the impact of the geological sciences, from 1963-2013, in such areas as geologic hazards, mineral resources, energy resources, water resources, soil resources, geology and health, geologic education, and the informing of general public policy. The chapters focus on how earth science informs and benefits society"--Provided by publisher.

This CD contains a 33 page report, appendix, and plate. This study presents the results of fault-trench excavations near Santaquin, Utah, and includes discussion of (1) previous paleoseismic investigations on the Nephi segment, (2) the geology of the Santaquin trench site and excavations (3) paleoseismic results, including the timing of the most recent surface-faulting earthquake, fault displacement and slip rate, and surface-faulting earthquake recurrence and (4) implications for the segmentation of the southern Wasatch fault zone.