Sensors on Fault Trigger Warning : Quake Alert Plan: Can It Make a Difference?

If a devastating earthquake were about to strike, would you want to know about it 30 to 60 seconds before it hit?

That might not be enough time to run out and buy quake insurance, but it is enough to take some precautions and possibly save a few lives, according to scientists who are looking into the possibility of setting up an earthquake warning system in California.

Southern California seems particularly well suited for such a system because the most dreaded of faults, the San Andreas, is some distance from the most densely populated areas. Sensors along the San Andreas could telegraph a warning that a catastrophic quake has struck up to a minute and a half before the deadly shock waves hit the population centers.

Time Lag

The time lag could be less--depending on which segment of the San Andreas breaks loose--but some warning could be given even if the quake hits along the part of the San Andreas that is closest to the metropolitan areas.

The San Andreas is believed capable of generating the largest earthquake credible for this region, but smaller quakes closer to developed areas could actually do more damage, and the advance warning would be much shorter for closer faults.

However, a number of scientists believe that Southern California should seriously consider developing a system that will give some warning, even if very brief, of a catastrophic quake. It would be the first earthquake warning system in the country.

“A lot of people are playing around with it,” said Thomas H. Heaton, chief scientist of the U.S. Geological Survey’s seismological laboratory in Pasadena and one of the principal backers of the idea. The Southern California system envisioned by Heaton would be similar to a system that has been in effect in Japan for 20 years, but it would be much broader in scope.

Heaton sees an automated system that would instantly shut down some key facilities to reduce losses when the earthquake hits. However, at this point no one is sure what those facilities might be, and a feasibility study authorized by the state Legislature has not been funded.

Others carry the possibilities further. Brian Tucker, geophysics officer of the California Division of Mines and Geology, believes the warning could even include flashing red lights in schools to give children enough time to get under their desks before the quake hits.

Tucker is the man who would carry out the feasibility study if it is ever funded. The cost for the study was originally estimated at $200,000, “but we could learn something for less,” he said.

“I prefer to call it a cost-benefit study,” Tucker said, “because there’s no question that it is feasible. The only question is whether the benefit would be greater than the cost.”

Detect Movement

When an earthquake strikes, low-intensity waves are sent out from the epicenter, traveling at about four miles per second. They can be detected by seismometers some distance from the fault, even though the ground motion from those first waves is so slight that “you wouldn’t even feel it,” Heaton said.

Meanwhile, “the fault is unzipping itself” as the quake ruptures down the fault zone at about half that speed, Heaton said. It is this movement down the fault that generates the powerful shock waves that can cause buildings to collapse many miles away.

Heaton said news of the first movement could be transmitted electronically from the epicenter “to areas that may be strongly shaken when seismic energy propagates to them.”

Civil Defense Warnings

That electronic impulse could trigger existing civil defense warning systems, such as sirens. Tucker believes that it also could be used to turn on audio cassettes at radio stations, thus broadcasting a warning and telling people to stay calm.

He suggested that anyone wanting to use the system could tie into it electronically and that automatic responses could be programmed according to the user’s needs.

The time between the warning and the arrival of the shock waves would depend on the distance between the fault and the system’s user.

Geologists believe that a major earthquake of magnitude 8 on the Richter scale will strike along the southern San Andreas Fault in the next 10 to 30 years.

The largest earthquake to hit Southern California in the last two centuries struck in 1857. The epicenter was below the Central California community of Parkfield, and the quake ruptured southward along the San Andreas.

90-Second Warning

If that quake were to be repeated, an early warning system could detect that it was on its way about a minute and a half before the shock waves hit Los Angeles, Heaton said.

The warning time would shrink to “probably about a minute” if the Salton Sea segment on the southern San Andreas ruptured instead of the Parkfield leg, since the southern segment is much closer to Los Angeles, he added.

If the epicenter was near Palm Springs, the warning would be reduced to “maybe 10 or 20 seconds.”

Tucker went to Japan last year to study the Japanese system, which was designed solely to stop the high-speed bullet trains whenever seismometers indicate that “a certain threshold has been reached” in ground motion from earthquake activity, he said.

He said that in 1966, one year after the bullet train line began operation, an earthquake damaged the tracks. Mindful that hundreds could have been killed if a train had been roaring across that section at that moment, Japan decided to develop an early warning system, and “within a year they had the basic system started,” Tucker said.

Halted in 70 Seconds

When seismometers detect activity that could be strong enough to damage the tracks, the train automatically screeches to a halt in 70 seconds, he said. It has done that 100 times since the system was activated two decades ago.

“Nearly all of those have been legitimate quakes, with only two or three false alarms,” Tucker said. One false alarm was caused by a mouse crawling across a sensor, he added.

However, although the trains, which carry about 2,000 riders each, have been stopped an average of five times a year, Japanese officials cannot point to a single life saved by the system. The quakes that stopped the trains simply have not been strong enough to have caused one to derail, even if the trains had not been stopped. As a result, the Japanese have “raised the threshold” so that stronger ground motion will be required to trigger the warning.

Japan plans to invest about $20 million for 100 additional sensors for the bullet trains, but officials there “haven’t succeeded so far in making the system available to other parts of society,” Tucker said.

“That’s very sobering,” he added.

Undermine Credibility

One reason for the hesitancy is that false alarms, regardless of how infrequent, would undermine the credibility of the system and cause considerable problems. And the arena is fraught with legal quagmires, including:

- Who would be liable for injuries suffered because of an early warning?

- Is a factory manager liable for people who are hurt while taking evasive actions?

- Is the manager liable if he or she has access to the warning system, but does nothing?

These are among the questions Tucker hopes to consider in his feasibility study.

One question that may determine whether the system is built is simply who would use it.

In response to a query from The Times, a spokesman for Southern California Edison said:

“There’s not much we could do in 30 to 60 seconds.”

Concern for Computers

Fil Bernal, supervisor of emergency preparedness for the Southern California Gas Co., said an advance warning could allow the company to shut down its computers before the temblor hits, thus protecting the integrity of its files. But he said it is not practical to think of shutting off the gas throughout 39,000 miles of pipelines.

Other officials also singled out their computers because if a computer system is damaged by a quake, much of its data could be jeopardized.

However, not all authorities are enthusiastic about an early warning system.

Richard Andrews, former director of the state Seismic Safety Commission and the Southern California Earthquake Preparedness Project who is now chief of the Southern California office of the state Office of Emergency Services, is lukewarm to the proposal.

“There’s no doubt the idea is very attractive,” he said, “but I question how high a priority it should be. The cost would probably be quite substantial, and you’re talking about a technical system that’s on a very fine trigger.

“This is sort of a seismological ‘Star Wars.’ ”

Concern for False Alarms

Andrews worries about false alarms, and he doubts whether the system would be worth what it would cost. He also doubts that much could be done in the brief period between the warning and the quake.

He agrees with the Geological Survey’s Heaton on the scientific value of such a system, however.

“It would be a very excellent scientific tool,” Heaton said, because it would provide instantaneous data on the strength, direction and location of major ground motions. “We would know very quickly what kind of disaster we were dealing with.”

Heaton, who said he has a deep fear of being stuck in an elevator, has one objective he hopes any such system would achieve.

“I would love it if the elevators would go to the nearest floor and open the doors.”