NEHRP Site Class Maps for the Idaho Falls-Rexburg Area, Idaho

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Keywords
Theme: NEHRP Site Class
Place: Ammon, Firth, Goshen, Lewisville, Menan Buttes, Rexburg, Rigby, Ririe, Ucon, Woodville, Idaho Falls North, Idaho Falls South, Bingham County, Bonneville County, Jefferson County, Madison County

Description
Abstract
The intensity of ground shaking during an earthquake varies according to the nature of near-surface materials. For example, shaking intensity is generally greater in areas underlain by unconsolidated materials (called “soils” by engineers) than in those underlain by firm bedrock. Engineers and architects incorporate these local site conditions into their designs to reduce damage from earthquakes. In 1997, the National Earthquake Hazards Reduction Program (NEHRP) established procedures for placing building sites into classes based upon the geotechnical properties of near-surface materials. For each NEHRP site class, coefficients adjust expected earthquake motions for local ground conditions. Earthquake ground motion parameters are generated by the U.S. Geological Survey for all parts of the United States and are available as national seismic hazard maps (http://earthquake.usgs.gov/hazards/products/). NEHRP site classes are not shown on national seismic hazard maps because local conditions are frequently too variable to accurately depict at the hazard map scale, or because the required geotechnical information is unavailable. Both NEHRP site classes and USGS national seismic hazard maps are incorporated into the International Building Code and International Residential Code.

Purpose
This map is a general guide designed to outline areas with the potential for enhanced ground shaking. Site-specific investigation is required to determine actual ground conditions for specific building sites. This is because the data used in producing the map are based on regional geologic mapping and correlation of the geotechnical properties of map units.

This map is intended to be used at a scale of 1:24,000. As with all maps, users should not apply this map, either digitally or on paper, at more detailed scales.

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