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May 15,1998 ~ 8 • 983-2348.135 <br />Return Period ( rs) Peak Ground Acceleration ( ) <br />100 0.02 <br />475 0.08 <br />1,000 0.13 <br />2,500 0.18 <br />The 0.08 g corresponding to the 475-yeaz return period is equivalent to the risk level for <br />non-critical structures employed u1 the 1994 UBC. This risk level, and the PGA of 0.08 g, <br />appeaz to be appropriate and reasonable for site seismic stability analyses and site <br />seismic design. The PGA of 0.08 g reflects the overall low rate of tectonic and seismic <br />activity in the region, and the consequently relatively low exposure to earthquake <br />ground motions that would be assodated with a 475-year return period. Therefore, it is <br />recommended that the 0.08 g PGA associated with the 475-year return period be used in <br />site seismic design. <br />Sincerely, <br />GOLDER ASSOCIATES INC. <br />~ o. w.~t- <br />Donald O. West <br />AssCCociate -Engineering Geologist <br />l <br />Shahnaz Vahdaru <br />Associate - Geotechnicat Engineer <br />References <br />Table 1 <br />Figures 1 and 2 <br />Attachment 1 <br />cc: T. Mandziak -Golder <br />J. Hardaway - CC&V <br />ccv~.ooc <br />Golder Associates <br />