BERKELEY, Calif. -- Mysterious tremors deep beneath the San Andreas Fault could portend future earthquakes, according to University of California, Berkeley scientists.

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The faint tremors were detected about 15 miles southeast of Parkfield, which is known as California's earthquake capital, study leader Robert Nadeau, an assistant research seismologist at the Berkeley Seismological Laboratory, said Thursday.

Parkfield was the site of a magnitude-6.0 quake in September, nine months after the end of Nadeau's analysis period.

"This is new information from an area deep down under the fault we have not been able to look at before," Nadeau said. "If these tremors are precursory to earthquakes, there is potential here for earthquake forecasting and prediction."

Most of the tremors are five times deeper -- 20-to-40 kilometers below the surface -- than the average quake on this part of the fault.

Nadeau's team identified 110 separate tremors lasting at least four minutes from Dec. 22, 2001, to Dec. 22, 2003. The area studied was the site of the magnitude-8.0 1857 Fort Tejon earthquake.

Nadeau and graduate student David Dolenc concluded that "future increases in San Andreas Fault tremor activity may signal periods of increased probability for the next large earthquake on the Cholame segment."

David Schwartz, a geophysicist at the U.S. Geological Survey in Menlo Park, said it's uncertain what the findings mean.

"As to what they imply for the possibility of some future quake, we can't tell, and right now we can only wait and see," Schwartz told the San Francisco Chronicle.