The Southern California Earthquake Center revisits the San Andreas fault.

The Earthquake Center is planning a new series of paleoseismic studies of the San Andreas fault over the next few years. (Paleoseismology is a term that denotes the investigation of individual earthquakes well after their occurrence.) The San Andreas was the focus of the first paleoseismic studies in southern California by Kerry Sieh and others in the 1970s and 1980s. But with the inception of the Earthquake Center in 1991, the emphasis shifted to the Los Angeles metropolitan area and its many faults posing a hazard to the urban environment.

While much remains to be done to characterize the earthquake history in the Los Angeles basin, important new questions regarding the San Andreas and its potential impact on the adjacent metropolitan areas have emerged:

• What are the maximum magnitudes of events on the San Andreas?
• Does the fault largely rupture segment by segment or by cascading through multiple segments?
• What is the most likely direction of rupture propagation?

How do these questions bear on the issues of the so-called "earthquake deficit" and the potential for generating very large, long-period, long-duration ground shaking in the heart of the LA basin -- shaking that may adversely affect some of our largest structures including bridges and high-rise buildings?

Contacts:

James Dolan, USC (213) 740-8599; Kerry Sieh, Caltech (626) 395-6115; Tom Heaton, Caltech (626) 395-4232; Kim Olsen, UCSB (805) 893-7394; David Jackson, UCLA (310) 825-0421.

References:

Robert S. Yeats, Kerry Sieh, Clarence R. Allen, The Geology of Earthquakes, Oxford University Press, 1997.

The Paleoseismology Web Site:

http://gldade.cr.usgs.gov/paleosei/ppmain.htm