CNN.com - Scientists study clues to forecasting California quakes
By Peter Dykstra
CNN
| Studying the San Andreas fault may help forecast California earthquakes. | ||
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(CNN) -- Two researchers say they've discovered a pattern of tremors deep beneath the San Andreas Fault that someday may yield clues into unlocking the mysteries of California earthquakes.
Robert Nadeau and David Dolenc, from the University of California-Berkeley, used data collected from Parkfield, California, the self-proclaimed "Earthquake Capital of the World." The tiny central California town virtually straddles the San Andreas Fault and has become the epicenter of quake research.
The scientists recorded 110 tremors over a three-year period that preceded two significant quakes -- a 6.5-magnitude quake that killed two people and toppled structures in Paso Robles, California, last December 22, and a magnitude-6 quake centered near Parkfield earlier this year.
The series of tremors, revealed by Parkfield's High Resolution Seismic Network, were centered as deep as 20 miles below the Earth's surface. While the scientists could not say that there was a certain link between the deep tremors and the surface earthquakes, the small, deep rumbles could someday be a tool in forecasting future San Andreas quakes, the researchers say.
David Schwartz, chief of the San Francisco Bay Area Earthquake Hazards Project for the U.S. Geological Survey, said these deep tremors had never been recorded or studied on the San Andreas Fault before the Parkfield project and the Berkeley researchers' work.
Nadeau calls it "a significant advance toward understanding the processes deep in the earth which generate earthquakes."
More significant, perhaps, because a central California segment of the San Andreas may be due -- or overdue -- for a major quake. In 1995, the Working Group on California Earthquake Probabilities estimated a recurrence of a major quake in the Cholame segment of the Fault area to be about 140 years, give or take several decades. The last major quake affecting the Cholame segment was 147 years ago. Cholame is thirty miles east of Paso Robles.
In 1857, the Fort Tejon Quake ripped a 225-mile gash along the San Andreas, including the Cholame region. There were only two deaths in then-sparsely populated California, but today, a similar quake could be a major disaster, with possible impact from San Francisco to the Los Angeles Basin.
The rugged territory near Cholame is still sparsely populated, but seismologists fear that another quake in the Cholame region could trigger a larger disaster. Still, they said such a disaster -- the much-feared "Big One" -- could be decades, or even centuries, away.
At an estimated 7.9 magnitude, the Fort Tejon Quake was more than 10 times as strong as last year's San Simeon Quake. A repeat of the Fort Tejon Quake also would be substantially more severe than either of the biggest California quakes in recent memory.
The 1989 Loma Prieta Quake, which measured magnitude 7.1, killed 62 people and collapsed a section of the Bay Bridge, and the 1994 Northridge Quake, which reached 6.7 magnitude and killed 61 people in the San Fernando Valley.
The Great San Francisco Earthquake of 1906 was estimated between 7.7 and 7.9 magnitude. Some 3,000 people died as a result of the quake, most of them in fires started by ruptured gas lines.
Earlier this year, the magnitude-6 quake centered near Parkfield caused only minor damage, but it thrilled seismologists, one of whom called the temblor "the most well-recorded earthquake in history."
Nadeau emphasized scientists are still a long way from any semblance of accurate earthquake prediction, but "in the future, the hope is that we will be able to give people a notion of when they should be a little more worried, or a little less worried."
Nadeau's and Dolenc's work was published Thursday in the journal Science.
