Five years and $15 million ago, the federal government issued its only official earthquake prediction: The central California town of Parkfield would be severely shaken by 1993.
Recent rumblings suggest the forecast soon may come true."They definitely elevate my belief that the earthquake is likely to happen in the next few months," said Evelyn Roeloffs, scientist in charge of the U.S. Geological Survey's Parkfield earthquake prediction experiment.
After a three-year lull, seismic activity increased during the summer and particularly this month near tiny Parkfield. The town is halfway between Los Angeles and San Francisco in grassy, oak-dotted ranchland of the Cholame Valley, which straddles the mighty San Andreas Fault.
It was in the valley that actor James Dean died in a 1955 car crash.
Moderate to strong quakes measuring 5.5 to 6.3 on the Richter scale have ruptured a 20-mile-long section of the fault near Parkfield roughly every 22 years since 1857. The most recent was in 1966. The quakes caused little damage in the valley, where about 200 people now live.
The temblors' regularity prompted a 1985 Geological Survey prediction that another magnitude-6 quake was 95 percent likely during a 10-year period centered around January 1988, which meant by no later than January 1993.
The Parkfield prediction is the only one ever issued by the federal government and endorsed by California and federal scientific panels.
The Geological Survey has spent $15 million installing scores of seismometers and other sensors and instruments near Parkfield, making it "the most heavily instrumented piece of fault in the world," survey spokeswoman Pat Jorgenson said.
Researchers hope the sensors will help them recognize changes in the Earth in the months, days, hours and minutes before the predicted magnitude-6 jolt, allowing them to issue a short-term public warning.