C153629 Feasibility Study - Laserfiche WebLink

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I '. I I I I I I I I I I I I I I I I I o Develop appropriate design earthquakes. o Define hypocentral/epicentral locations, site attenuation characteristics and average peak bedrock horizontal accelera- tions. o Assess the potential for other seismically-induced hazards at the site. Michael West and Associates collected historic seismicity data (magni- tude/intensity geographic coordinates, focal depth, date, etc.) for recorded earthquakes within a 200-mile radius of the sites as compiled from computer records of the National Geophysical Data Center. Maximum Credible Earthquakes (MCE) were assigned to each seismogenic source zone likely to affect the sites. Peak horizontal bedrock accelerations attenuated to the sites were estimated using magnitude/distance rela- tionships. Based on the field work, geologic evaluation, and seismological studies, it was concluded that the Antelope Pass fault is non-seismogenic and need not be considered as a likely earthquake source affecting project design. Segments of the Gore Fault, Gore Pass Fault and Monument Creek Fault and other faults nearer to the Rock Creek area also show no con- clusive evidence of seismogenic movement. However, lineaments and geo- morphic features apparently associated with the Gore Fault, located one mile west of the Rock Creek Dam sites, are suggestive of seismogenic movement. These features, however, may also be explained by non- tectonic mechanisms and data collected in this study are insufficient to characterize these surface features as seismogenic. A conservative assessment of the potential earthquake magnitude possi- ble at the two damsites was made by selecting a hypothetical "floating" earthquake of Richter magnitude 5.5 occurring within 10 km from each site. This would result in peak horizontal bedrock accelerations rang- ing from 0.20 g to 0.34 g. Hypothetical Maximum Credible Earthquakes 2 - 2 7042W/5020W