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This document has been archived.

NSF Press Release


Embargoed until 2 P.M., EDT
NSF PR 00-55 - August 17, 2000

Media contact:

 Cheryl Dybas

 (703) 292-8070

Program contact:

 Robin Reichlin

 (703) 292-8556

This material is available primarily for archival purposes. Telephone numbers or other contact information may be out of date; please see current contact information at media contacts.

State-of-the-Art Measuring Techniques Show California Fault Slips Freely
Less Chance of Major Quake

Pushing the frontiers of today's techniques for monitoring earthquake fault activity, a geophysicist funded by the National Science Foundation (NSF) and affiliated with the University of California at Berkeley, assessed movement along California's northern Hayward fault and found less chance of a major quake originating on that segment than previously thought.

With the help of radar interferometry and data from global positioning satellites (GPS), and analysis of repeating microquakes six miles below the surface, Roland Bürgmann and his colleagues concluded that the deep portions of the fault steadily slip at about the same rate as does the surface. This means the rocks deep below the surface aren't locked and building up strain that could be released in a catastrophic quake.

"Our research shows no evidence of locking at any depth, which means the threat from one of our worst hazards, right in our backyard, is much reduced," said Bürgmann. "However, other hazards - from the southern Hayward fault, the San Andreas fault and other nearby faults - leave the need to build reinforced homes and the need to be prepared just as high as before." Bürgmann and his colleagues at UC Berkeley, the Lawrence Berkeley National Laboratory, the Jet Propulsion Laboratory in Pasadena, Calif., and UC Davis report their findings in the Aug. 18 issue of Science magazine.

"We're very excited about the applications of this research, "says Robin Reichlin, program director in NSF's division of earth sciences, which funded the research. "Space-based techniques are poised to revolutionize our view of Earth's crust, and the dynamic processes that lead to volcanic eruptions and earthquakes."

The Hayward fault, considered one of the most dangerous faults in California, stretches more than 60 miles from San Pablo Bay in the north to below Fremont in the south, and is a branch of the more famous San Andreas fault that extends much of the length of California.

Putting information together from several sources, the scientists estimated that the northern Hayward fault slips underground at a rate of about 5 to 7 millimeters per year, essentially the same rate as at the surface. The similar rates indicate that the fault is slipping freely without locking. Over long periods, and counting the slippage that occurs during and after earthquakes, the entire Hayward fault moves on average about 10 millimeters per year.

Most faults outside California do not slip freely, but lock at depth. Bürgmann said what may allow the northern Hayward fault - and some other state faults - to move freely is a greenish rock that underlies much of central and northern California and could serve as a lubricant: serpentinite, often called serpentine. Serpentinite, the official state rock, is soft and fractures easily.

The work was supported by the National Science Foundation, the Solid Earth and Natural Hazards program of the National Aeronautics and Space Administration, and the U.S. Geological Survey's NEHRP program.


For illustration of the radar image around the Hayward Fault see:



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