| nisee |
National Information Service for Earthquake Engineering
University of California, Berkeley |
Marina Geology and Earthquake Effects.
M. G. Bonilla, USGS, Menlo Park, California.
USGS Professional Paper 1551-F
Damage in the Marina District of San Francisco was more severe than in surrounding areas in the 1906 and 1989 earthquakes. The greater earthquake damage in the Marina results from both natural and human causes. Beneath the Marina is a nortwest-trending valley cut in the bedrock. This valley is filled with clay and sand whose strength ranges from moderately strong to very weak. The bedrock valley and its filling amplify earthquake vibrations, and therefore the Marina get shaken more severely than its surroundings when an earthquake occurs. Much of the Marina is also subject to differential settlement and cracking of the ground, because artificial fill there consists almost entirely of loose sand that is saturated with water a few feet below the ground surface, and can liquefy during earthquakes. Thus, the natural setting amplifies earthquake shaking and the artificial fill adds to the shaking damage. The maps and other information resulting from this study can lead to design of safer and more economical structures in the Marina.
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