Site response and soil liquefaction in San Francisco during the Loma Prieta earthquake

ABSTRACT

During the 1989 Loma Prieta earthquake, liquefaction in San Francisco occurred at four principal locations the Marina, foot of market, south of market, and mission creek areas. The result of soil investigations in these areas are presented, and used to characterize the subsurface conditions. Digitized strong motion records at several rock sites in the vicinity of these areas are used in conjunction with response analyses, using equivalent linear procedures, to evaluate site amplification at each location and its relationship with soil liquefaction. The role of Holocene bay mud is explored with respect to its influence on peak acceleration and predominant period of ground motion. Special attention is directed to the Mission Creek area where liquefaction in 1906 and 1989 pccurred at the same locations in the eastern portions of the old creek bed, but not in its western part. Since liquefaction in the western part during the 1906 earthquake was responsible for catastrophic water main rupture and building collapse, the absence here of liquefaction in 1989 is of considerable interest. Explanations are given for this intriguing behavior.(AU)