Item talk:Q114963

Studies for seismic zonation of the San Francisco Bay region

The analyses presented in the preceding six papers show that the geologic setting of the San Francisco Bay region has a dominant influence on potential earthquake hazards. The strong correlation between geologic conditions and the amount of earthquake damage in 1906 emphasizes the importance of this influence and demonstrates the need for seismic zonation. Seismic zonation can provide the logical basis for preparation of special-purpose land-use maps that, with appropriate public policy, would be a significant step toward reducing the currently expected catastrophic effects of another great earthquake (Algermissen, 1972).

Seismic zonation requires a set of integrated multidisciplinary predictions about the geologic effects of potential earthquakes. To illustrate a strategy for making such predictions, a demonstration profile has been chosen perpendicular to a segment of the San Andreas fault, along which a magnitude 6.5 earthquake has been postulated. This profile includes a wide variety of geologic conditions and provides a means for application of the analyses presented in the preceding six papers.

Earthquake hazards to life and property originate from (1) surface faulting, (2) ground shaking, (3) flooding, (4) liquefaction, and (5) landsliding. The extent to which each of these geologic effects can be predicted for an earthquake of a given magnitude and location depends on the current state of the art. To illustrate techniques and data currently available, each effect is considered for the postulated earthquake.

This paper does not provide final estimates for the total earthquake hazard along the demonstration profile. Such an objective would require analysis of individual manmade structures as well as consideration of earthquakes of other sizes and locations. Instead, this paper illustrates the extent to which the above effects can be predicted for an earthquake of this given size and location. Such an analysis demonstrates a methodology for seismic zonation based on available data.