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NR 2004-7
April 15, 2004

Contact: Anita Gore
Ed Wilson
Mark Oldfield
Don Drysdale
(916) 323-1886

SAN ANDREAS QUAKE COMING BUT NOT NECESSARILY IMMINENT:
IT’S SMART TO BE PREPARED, BUT STAY CALM

SACRAMENTO -- While agreeing that a period of relative quiet on the San Andreas Fault may be nearing an end, acting California State Geologist Michael Reichle emphasized Thursday that a widely publicized report by a University of Oregon geologist is not a prediction of a cataclysmic earthquake in the immediate future.

“It’s fair to say that every day we’re one day closer to the so-called Big One,” said Reichle, who heads the California Geological Survey for the state’s Department of Conservation. “But people shouldn’t jump to the conclusion that this report means the Big One is imminent. It is simply another reminder that we need to be prepared for the inevitability of major earthquakes in California.”

Added Department of Conservation Director Darryl Young: “It’s not the end of the world, but it should be the beginning of your preparation.”

University of Oregon geologist Ray Weldon presented a paper about his research at the annual meeting of the Seismological Society of America on Wednesday. Dr. Weldon’s trenching work on the San Andreas Fault at Wrightwood, 60 miles northeast of downtown Los Angeles, indicated that, since 3000 B.C., historically long periods of relatively little seismic activity on that section of the fault have been followed by clusters of large earthquakes.

The last major rupture of the southern San Andreas Fault occurred on January 9, 1857. The Fort Tejon earthquake may have been the most powerful in California history, with an estimated magnitude of 7.9. While the quake left a 220-mile surface scar, it killed only two people because of its remote epicenter and the relatively small population in the area at the time. A temblor of that size in the modern-day Los Angeles area could kill hundreds and do billions of dollars in property damage.

The southernmost section of the San Andreas Fault in the Coachella Valley has not had an earthquake in approximately 300 years.

“Scientists have long considered this section of the fault to be ripe for an earthquake,” Reichle noted. “What’s new in Dr. Weldon’s report is the indication of a pattern: quiet periods, clusters of earthquakes, quiet periods, clusters. We know that on the scale of years earthquakes can cluster. Between 1812 and 1906, there were five earthquakes magnitude 7 or greater in California, two of them along the San Andreas fault near Los Angeles. Since the San Francisco earthquake, 98 years ago Sunday, the San Andreas has been fairly quiet.

“Dr. Weldon may be right that we are nearing the verge of a switch, but the timing of that switch is highly uncertain. It could be 30 years or more. We don't yet completely understand the dynamics of the earth's crust.”

In 2001, California Geological Survey seismologist Tousson Toppozada presented a paper to the Seismological Society of America stating that historical data indicated a pattern that could mean increased seismic activity in the Bay Area within 20 years of the 1989 Loma Prieta earthquake.

In addition to studying and mapping earthquakes, landslides and mineral resources, the Department of Conservation administers programs to safeguard agricultural and open-space land; regulates oil, gas and geothermal wells in the state; promotes beverage container recycling; and ensures reclamation of land used for mining.

  • Click here to read about a California Earthquake Prediction Evaluation Council analysis of prediction research being done at UCLA.

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