Early Warning System Urged for Earthquakes

Concluding that existing technology could lessen the human and economic toll of earthquakes, a federal panel Tuesday recommended development of a prototype system in California that could give “tens of seconds” of critical warning before a quake’s destructive waves strike.

The National Research Council panel said one of California’s regional seismic networks could be upgraded into an early warning system that could automatically shut down computers, gas lines, power plants and manufacturing operations to lessen quake-related damage. Such a system also could provide precious seconds for people to “duck and cover” in areas 10 kilometers or more from an earthquake’s epicenter. The lead time would be considerably less closer to the origin of the quake.

The panel’s yearlong study followed a 1989 survey by the California Division of Mines and Geology in which respondents from 150 public and private institutions showed a strong tendency to equivocate over the value of an early warning system.

Tuesday’s report offered no estimate of the cost of a state-of-the-art warning network. But William E. Benson, the National Research Council’s senior staff officer on the panel of government, industry and academic experts, said that an effective system based on the seismic network already in place in Southern California might be had for “$500,000 a year for several years.”

To build a new system from scratch, he estimated, would cost perhaps $10 million.

Until now, earthquake warnings have been provided only by fast-moving “P waves” that spread from the epicenter ahead of the jarring “shear waves” responsible for most of the destruction. But a modern warning system, equipped with hundreds of additional sensors, high-speed computers and heavily protected radio transmitters, could spread the alert even before the arrival of the P waves, the study concluded.

The warning approach got a tryout in the aftermath of the 1989 Loma Prieta quake. The U.S. Geological Survey hurriedly installed additional sensors that measured aftershocks and automatically sent radio warnings, which were received at the site of the Nimitz Freeway collapse in San Francisco. The signals arrived as much as 27 seconds before the shear waves from the aftershocks, allowing rescue workers to retreat from dangerous areas of the freeway wreckage.

In Japan, an automatic warning system has stopped Japan Railways’ famous bullet train 100 times over its 20 years of operation.

California already has in place the most extensive seismic networks in the country--a 360-station complex across the central and northern portions of the state and a system of 240 stations, operated by Caltech and the U.S. Geological Survey, along faults in the South.

But both are based on 1960s-era technology and were designed primarily for mapping earthquake structures and locating small quakes rather than for providing early warnings.

The panel made no recommendation on the location of a California system. But it suggested as one possible configuration a string of sensors 10 kilometers apart along the southernmost area of the San Andreas fault, which runs northwest from northern Imperial County, across Riverside, the southwestern corner of San Bernardino, northeastern Los Angeles County, to San Luis Obispo.

The panel suggested that development of a prototype system be accompanied by a research and development program designed to help understand the possibility of “false positives” that might trigger an expensive shutdown of industries when there is no quake.

In the earlier survey by the Division of Mines and Geology, some business and industrial officials suggested including a human link in the warning system to clear a shutdown after seismic stations detect the first shock of a quake.

But the National Research Council panel found that suggestion impractical, considering “the short times involved and the documented poor performance of human operators in rarely occurring events.”

In Japan’s experience with the bullet train system, the panel said, there has been an average of less than one false alarm per year. Because the seismicity of California is about one-tenth that of Japan, the number of false alarms would be correspondingly less, the panel suggested.