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Thursday August 17 4:57 PM ET
Study: Earthquake Risk Not As Bad Study: Earthquake Risk Not As Bad

WASHINGTON (AP) - New measurements suggest the risk of earthquake along the northern Hayward Fault in Northern California is less than previously believed.

California researchers, using satellite measurements and other data, found that the deep portions of the fault were moving at about the same rate as the surface levels of the fault.

Since there is an even motion along all levels of the fault, the researchers said, there is no build up of strain that could be released as an earthquake.

A report on the study appears Friday in the journal Science.

Considered a dangerous fault, the Hayward extends for 60 miles from San Pablo Bay in the north to near Fremont in the south. It is a branch of the San Andreas Fault, which extends for most of the length of California.

The research suggests the northern half of the Hayward is slipping on the surface and underground at a uniform rate of less than one-quarter inch a year.

``Our research shows no evidence of locking at any depth, which means the threat from one of our worst hazards is much reduced,'' said Roland Burgmann, a University of California, Berkeley, geophysicist and first author of the Science study.

He said the earthquake risk is unchanged, however, for the southern half of the Hayward Fault and for other California faults.

Burgmann said a greenish rock called serpentine may be helping the northern Hayward to slip freely. Serpentine is a soft and crumbly rock that may act as a lubricant, allowing opposing sides of the fault to slip past each other without locking up, he said. The rock underlies much of northern and central California.

Co-authors of the paper include scientists from the Jet Propulsion Laboratory in Pasadena and the University of California, Davis.

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