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Geotechnical Investigation Report Detroit Lake Water Reservoir <br />Detroit, Oregon <br />Table C-4: Input Earthquake Parameters <br />PHGAPHGA at Site Using PHGA Used (g) <br />Measured (g)Attenuation Relationships (g)(this analysis) <br />Crustal Earthquake Models <br />El Centro0.320.210.21 <br />Taft0.180.210.21 <br />Topanga/Northridge0.330.210.21 <br />Intraslab Earthquake Models <br />Puget Sound 19650.190.140.14 <br />Western Washington 490.160.140.14 <br />CSZ Interface Models <br />Michoacán0.160.110.11 <br />Petrolia/Cape Mendocino0.420.110.11 <br />C.4 SEISMIC HAZARDS <br />Based on our subsurface exploration, literature review, analysis, and experience, a summary of the <br />seismic hazards at the site are as follows: <br />Earthquake induced landslides <br />• – The slope of the proposed water reservoir site area is <br />relatively gentle with decomposed bedrock fairly close to the ground surface. Site soils are <br />not susceptible to earthquake slope instability. Due to relatively flat slopes and low <br />liquefaction potential, we do not consider earthquake-induced landslides to be a significant <br />hazard at this site. <br />Liquefaction/Settlement <br />• – Materials at the site consists colluvium and fill to a maximum <br />depth of 4 feet underlain by generally fine-grained (silt and clay) soil with variable sand and <br />gravel content that is interpreted to be decomposed volcanic tuff. The tuff is stiff to very stiff <br />below 4.5 feet bgs. We interpret bedrock to be fairly close to the ground surface. These soils <br />are not susceptible to liquefaction. <br />Fault surface rupture <br />• – The closest potentially active fault zone is the Clackamas River <br />fault zone, located approximately 22 km from the site based on the referenced published <br />geologic mapping. Thus, fault surface rupture is not a risk. <br />Tsunami inundation/seiche/subsidence <br />•– The site is inland and elevated away from <br />tsunami inundation and subsidence zones and away from large bodies of water that may <br />develop seiches. Accordingly, tsunami or seiche events do not represent a seismic hazard <br />to the site. <br />November 23, 2009 <br />Project No. 72852.000 <br />C-4 <br />