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Local News - updated 9:39 PM ET Aug 18
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Friday August 18 03:39 PM EDT
San Francisco Fault Less Dangerous San Francisco Fault Less Dangerous

BERKELEY -- University of California scientists say the northern half of the Hayward Fault that runs beneath the east San Francisco Bay Area may not be as dangerous as previously thought.

However, they caution the findings don't reduce the risk of earthquake from that fault and others crisscrossing the region.

"The hazard is still high," said U.S. Geological Service scientist David Schwartz. "The shaking doesn't care where a line on the map is drawn."

The new findings, published Thursday in Science magazine, stem from research by UC Berkeley geophysicist Roland Burgmann. Using new measuring techniques, Burgmann and his team concluded that the northern section of the Hayward fault is moving at about the same rate at the surface and deep underground.

That means there isn't the kind of pressure buildup that can result in a catastrophic earthquake.

The Hayward fault stretches more than 60 miles and is a branch of the San Andreas Fault. The northern segment begins at the Oakland/Berkeley border and ends in San Pablo Bay.

Last year, a statewide team of seismologists estimated a 32 percent chance of a major earthquake originating somewhere on the Hayward fault in the next 30 years. A major quake is one of magnitude 6.7 or greater.

Looking at the northern half of the fault separately, the team calculated a risk of 16 percent. That figure is unchanged because it took into account the findings by Burgmann's team, which included scientists from the Jet Propulsion Lab in Pasadena, the Lawrence Berkeley National Laboratory and UC-Davis.

"In terms of the need for people to be prepared for earthquakes and retrofit their house, this study doesn't make a difference at all," Burgmann said.

The focus of the study, Burgmann said, was the high-tech methods used to study earthquake mechanics. The team used data from satellites measuring ground motion to determine movement of the fault within a few millimeters. They combined that with analysis of microquakes, tremors too small to be felt that indicate movement miles below ground.

Scientists concluded that the northern segment of the Hayward fault is slipping underground at a rate of about 5 to 7 millimeters per year, about the same as it does at the surface.

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