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<br /> <br />(2) to compile and analyze instrumentally-recorded seismicity and <br />historic felt reports in the project azea and surrounding region; <br />(3) to identify azeal seismic source zones and faults likely to pose a <br />significant hazazd to the site in question; <br />(4) to perform a probabilistic seismic hazard analyses for each <br />specifically identified azeal seismic source zone and fault; <br />(5) to estimate site-specific ground motions for use in engineering <br />analyses. <br />The primary products of the PSHA are site-specific ground motions <br />and response spectra for use in engineering analyses. The results of <br />the PSHA aze expressed either as a relationship between peak and <br />effective (bedrock) accelerations for probabilities ofnon-exceedance in <br />time periods of interest or as a relationship between peak and effective <br />(bedrock) accelerations for return periods ranging from 100 to 100,000 <br />yeazs (annual exceedance probabilities of 10-' to 10-'). For any speci- <br />fied level of risk, the corresponding peak and effective bedrock accel- <br />erations from all earthquake sources can be determined. Zero period <br />bedrock accelerations may then be used to generate standazd response <br />spectra or to scale response spectra from historic earthquakes compara- <br />ble to those expected to occur in central Colorado. <br />1.2 SCOPE OF STUDIES <br />Seismotectonic hazard studies for Trout Creek dam were keyed to the <br />degree of hazard risk, the availability and reliability of existing data <br />and the potential for economically generating new data which would <br />alter or impact conclusions regazding hazards and subsequent <br />engineering studies (West, 1987). A critical aspect of this approach is <br />the requirement to evaluate whether or not the proposed work will <br />provide a reasonable return of useful information versus cost. Assess- <br />ment of earthquake hazards should be based on sound engineering, <br />scientific, and economic rationales. <br />The studies performed generally follow practices and procedures <br />developed by the Colorado State Engineer, U.S. Bureau of <br />2 <br />