Proposed Uniform Building Code Seismic Risk Zone Revision in Southeast Idaho

摘要

A number of scientific studies concerning geology and seismicity in the Southeast Idaho region have been conducted within the last ten years. The results of these studies, as well as some recent national seismic risk evaluations, indicate that the present Uniform Building Code (UBC) seismic risk zone classification for a major portion of the Southeast Idaho region is excessively high. The objective of the work presented herein is utilization of the scientific evidence to propose a revised UBC seismic risk zone map for Southeastern Idaho where a portion of the present seismic risk Zone 3 is revised to Zone 2. Regional geological information, including known and suspected faults, is presented. A comprehensive summary of magnitude and location of recorded regional earthquake epicenters and their relation to the proposed UBC seismic zone modification is presented. Correlation between the geology of the region and recorded seismic events with the proposed UBC zone revision is shown. A rationale, based on recognized seismic risk studies, is developed for location of the proposed UBC seismic risk zone lines. Correlation with existing national risk zones is shown and inherent conservatisms are discussed. Finally, the detailed location of the proposed revised zone lines is presented. It is noted that the revision affects Southeastern Idaho and small regions of Southwestern Montana and Northwestern Utah. 17 figures, 2 tables. (ERA citation 05:016933)