Geotechnical and Lifeline Aspects of the October 17,1989 Loma Prieta Earthquake in San Francisco
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The four main areas of San Francisco affected by soil liquefaction in the 1989 Loma Prieta earthquake and 1906 San Francisco earthquake are the Marina, Foot of Market, South of Market, and Mission Creek districts. Liquefaction effects involved subsidence and loss of bearing of shallow foundations, with differential settlement, racking and tilting of two to four-story timber structures. Strong ground shaking in the Marina was the principal cause of building damage. Preliminary reconnaissance indicates that the underground infrastructure influenced the pattern of soil and street displacement and may have affected the potential for soil liquefaction in certain locations. In the Mission Creek district, the presence of the Bay Area Rapid Transit (BART) system seems to have influenced the pattern of soil liquefaction. Damage in water distribution piping was located primarily in areas of strong ground shaking, liquefaction, and permanent soil displacements. The heavy concentration of Municipal Water Supply System (MWSS) damage in the Marina underscores the importance of site response in the performance of pipeline networks. Hydrants proved to be the most vulnerable component in the Auxiliary Water Supply System (AWSS), and the damage complicated firefighters' efforts in the area. The flexibility provided by the Portable Water Supply System (PWSS) was of critical importance in controlling and suppressing the fire which erupted in the Marina. The ability to operate with portable hosing and draft from a variety of water sources, including underground cisterns and fireboats, provides a valuable extra dimension in the city's emergency response.