Unformatted text preview: how strong the ground is going to shake where you are • Weak sediments amplify the seismic shaking • 1989 Loma Prieta M W 6.9 o Probably occurred on the Sargent fault, a subsidiary strand of the SAF o Nucleated ~ 15 km NE of Santa Cruz • S.F. Bay o Avg. depth of the Bay is 4 ft, basically a big mudflat o The bay is a drowned, old river channel o Redwood poles in thick mud are the basis of the Bay Bridge because they couldn’t piledrive down to the bedrock • The Cypress Structure o A double-deck freeway in Emeryville (next to Oakland) o The slower the shear wave velocity, the weaker the sediment • 1868 “Great San Francisco Eq” M W 7.0—now called the Hayward Eq o Buildings on bayfill could not withstand earthquakes Relearned same lesson in 1906 Eq...
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- Fall '07