| Description | Spatial | Attributes |
Maps of National Earthquake Hazard Program (NEHRP) site class and liquefaction susceptibility are presented for an area adjacent to the Snake River that includes portions of Bingham, Bonneville, Jefferson, and Madison counties, and the cities of Firth, Shelley, Idaho Falls, Ammon, Ucon, Rigby, Menan, Ririe, and Rexburg. The site class maps were constructed using 1:24,000-scale geologic mapping and a regional compilation of shear wave velocity and standard penetration resistence for near-surface materials. No regional geotechnical data was found for some geologic units. In these cases, site classes were based upon published classifcation of similar units in the western United States. The liquefaction susceptibility maps were constructed with 1:24,000-scale geologic maps by relating deposit age, texture, and environment of deposition to susceptibility. Only unconsolidated deposits were assigned a liquefaction susceptibility. Areas of bedrock overlain by >10 ft of unconsolidated materials were classified on the basis of the overlying deposits. Since liquefaction susceptibility increases with a shallow water table, indicators of potentially saturated conditions are also shown. These include seasonally saturated soils and depth-to-water contours. The soil information was taken from published county soil maps. The depth-to-water contours were created using geostatistical analysis of water well logs.
Present data classes of NEHRP site class and liquefaction susceptibility