|Ref: Short earthquake warning proposed in California
| 04.26.2007 | 07:51:40 | Views: 1674 |
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Short quake warning could save lives
SYSTEM IN WORKS OFFERS 20 SECONDS' NOTICE
By Julie Sevrens Lyons
San Jose Mercury News
After a devastating earthquake hit the Hayward Fault in 1868, a Bay Area physician shared what sounded like a half-baked idea at the time: Use wires and electric currents to sound alarm bells at the start of a major earthquake, giving a short warning to people living away from the epicenter.
Thing is, the idea - or a variation of it - is likely to become reality in California within the next decade, many seismologists now believe.
And even though 10 to 20 seconds' warning might not sound like much, what a difference it could make, experts say.
It could allow Caltrain and BART officials to slow down trains and reduce the risk of derailments. Fire stations could open their garage doors and get their engines ready to roll. Interstate metering lights could all be turned to red to keep vehicles at a stop. Elevators could be programmed to open at the nearest floor to prevent people from getting trapped when the quake hits. There could even be a public alert system, the modern-day equivalent of an air raid siren, but experts are debating whether that would promote safety - or panic.
"I think it's clear there's benefit to having a warning system like this," said Richard M. Allen, a professor at the University of California-Berkeley seismological laboratory who is among those spearheading the efforts to create such a system. "And we're developing one of the most accurate warning systems that exists."
Indeed, government and private university workers are now testing an early prototype for an earthquake warning system - one that works by measuring the fastest-moving waves from a quake, and sending an alert before the slower but more devastating waves hit.
They say it will take at least a few years to be able to put such a system into place in the Bay Area, but BART officials are already interested in the concept as it could allow them to keep some trains from entering the Transbay Tube - or speed up ones already in there. Scientists say PG&E officials are also interested, as scientists explore the idea of shutting off the public gas supply to minimize fire risk. And experts say that an early warning could help chemical manufacturers get their workers away from hazardous substances.
The concept isn't new - earthquake early-warning systems are already up and running to some degree in Japan, Mexico, Taiwan and Turkey.
But scientists say those systems wouldn't be as effective here because of the differences in geography and city design.
Mexico City, although prone to devastating quakes, has the good fortune to be situated about 180 miles from a quake zone, allowing for about 100 seconds of warning before dangerous quakes rumble through town. Japan's system is geared for earthquakes that originate offshore, also giving residents more warning time. But in the Bay Area, which was built directly on top of numerous faults, warning times wouldn't be greater than tens of seconds - tops. And that's only if new technology is used that essentially "pushes the envelope," scientists say, signaling an alarm before the older systems could.
How it works
The warning systems aren't crystal balls. They don't predict quakes before they actually happen, but work instead by sensing the motions of a temblor and sounding alarms miles away, before the shaking has had a chance to arrive there.
In Mexico City, old-fashioned seismographs wait for the peak ground shaking along the coast, estimate the size of the quake and then issue a warning if it is big enough. The warnings are sent via radio signals, which are detected by special boxes in government offices and some residential areas. The signals are also sent to radio and TV stations, which relay the warnings.
California researchers are working on a more advanced system that senses the earliest of two types of energy or motions from an earthquake, known as P-waves (primary waves). These waves move much faster than S-waves (secondary waves), the movements that cause the greatest damage during a quake.
California scientists are cautiously optimistic that within the first few seconds of an earthquake, high-tech observation stations could detect the P-waves, and a computer could then quickly estimate the expected magnitude of the quake. If it seems like a large quake - which usually can't be confirmed until the S-waves arrive - a warning would be issued immediately.
The warning wouldn't be of much help at the epicenter, where only about two seconds separate the arrival of the P- and S-waves. But farther out, the slower S-waves take a little time to appear.
During the 1989 Loma Prieta earthquake, which originated in the Santa Cruz Mountains, the majority of the fatalities occurred about 60 to 70 miles away in San Francisco and Oakland.
"If we were to have a repeat of that earthquake, we would have about 20 seconds' warning for Oakland or San Francisco," UC-Berkeley's Allen said.
That's huge, said BART spokesman Linton Johnson.
"The more heads up we can get, the safer we can make the system," he said. "You can't stop a train on a dime, but slowing it down may very well limit the number of injuries in a massive quake."
A few seconds
But scientists concede that even if a system works as well as hoped, just as many buildings will be destroyed, and many lives will still be lost. With a repeat of the Loma Prieta quake, San Jose would get "a few seconds - at most," Allen said.
"Earthquake early warning is not a panacea," said Dave Wald, a seismologist with the U.S. Geological Survey in Golden, Colo. "Some people won't get a warning."
Scientists are still trying to determine just how accurate and reliable the proposed system would be. By quickly estimating the size of an earthquake before accurate measurements are in and then sounding an alarm, the system could create unnecessary fear if the quake ends up being smaller than expected. But if the system waited until the true magnitude of a quake was known, there really wouldn't be much warning at all.
"It's inevitable there will be some false alarms," Allen said. "It's also inevitable there will be some missed alarms. The question is: How many will there be?"
There's also the question of expense. The state would need about 300 new monitoring stations, costing from $10 million to $30 million, Allen estimated.
But in many ways, the system makes sense - and it's "just a question of time when we actually implement it in California," said Tom Heaton, a professor of engineering seismology at the California Institute of Technology.
Of course, Dr. J.D. Cooper, who dreamed of a warning system nearly 139 years ago, may have thought the same thing when he commented in the San Francisco Daily Evening Bulletin: "It is well-known that these shocks are produced by a wave-motion of the surface of the Earth, the waves radiating from a center just as they do in water when a stone is thrown in.
"If this center happens to be far enough from this city," Cooper exclaimed, "we may be easily notified of the coming wave in time for all to escape from dangerous buildings before it reaches us."
Contact Julie Sevrens Lyons at firstname.lastname@example.org or (408) 920-5989.
Copyright 2007 San Jose Mercury News