'Seismic Signature' May Aid Early Warning
MICHELE NORRIS, host:
This year has seen its share of natural disasters. There were more earthquakes in the Indian Ocean and a big one in Pakistan. Big hurricanes blew through the Gulf Coast and Florida. Scientists have spent a lot of energy trying to predict natural disasters. They've had some success with hurricanes, but earthquakes still strike without apparent warning. As NPR's Christopher Joyce reports, there's new research that may reveal some information about a quake before the full impact can be felt.
CHRISTOPHER JOYCE reporting:
Earthquake scientists avoid the word `prediction.' That's because even though they know where earthquake faults are, and which ones are getting squeezed, they can't tell you where or when they'll rupture, and they find that very frustrating.
Mr. BILL LEITH (US Geological Survey): Oh, yes. Uh-huh. It would be great if there was a precursor to earthquakes that we could identify, I mean, even if it gave us months or a year's warning.
JOYCE: Bill Leith is a seismologist at the US Geological Survey. He says that although scientists can't predict quakes, they're getting close to knowing how big one will be the moment it hits. The secret lies in the first set of shock waves that travel out from a quake. These are called P-waves. They travel three times as fast through the earth as the more damaging S-waves that destroy buildings. Seismic instruments pick up P-waves first. If scientists work fast, says seismologist Richard Allen of the University of California at Berkeley, they can read those P-waves in a new way.
Mr. RICHARD ALLEN (University of California at Berkeley): If it's a low-frequency hum, then that's telling us that it's going to be a large-magnitude earthquake, whereas if it's a high-frequency squeal, that suggests that it's going to be a small-magnitude event.
JOYCE: Imagine the fault as a long zipper. A rupture somewhere on the fault starts to unzip it. A small quake might unzip for a few seconds; a big one, like the Sumatra quake last December, can unzip for minutes and hundreds of miles. In either case, scientists thought the initial rupture didn't tell you what was coming; you had to wait till the end to know the quake's size. Allen, writing in the journal Nature, says no. P-waves during the first four seconds of a quake can give you a rough estimate of the ultimate size. So if you live in, say, Northern California, what does this buy you?
Mr. ALLEN: In fact, what we find is that for the most damaging earthquakes, the earthquakes that would do the most severe damage to the buildings in the city of San Francisco, it's likely that they would have more than 20 seconds warning if we were to use this kind of warning system.
JOYCE: Twenty seconds isn't much; long enough for a prayer, but not enough to write your will. Nonetheless, says Allen, don't give up.
Mr. ALLEN: We're not talking about these kind of large-scale evacuations. For personal protection, we're talking about things like moving away from dangerous machinery, dangerous chemicals, getting under a desk. That's the kind of measure that you would want to take.
JOYCE: A warning system might also automatically shut down pipelines and refineries. The Geological Survey supported Allen's work and is studying how to use it. The survey's Bill Leith says the hardest part may be getting a warning out fast enough.
Mr. LEITH: If a second of data is collected and then transmitted over the Internet in a packet, then we've lost a second. So one of the results of the study might be to change the way that we transmit information in order to be able to not lose that second.
JOYCE: Japan has a warning system that automatically engages the brakes on high-speed trains when a quake hits. Taiwan, Mexico and Turkey already have similar warning networks. Leith says the survey's study envisions a system for California. As to whether or when it will work, though, he's not predicting. Christopher Joyce, NPR News.
MELISSA BLOCK (Host): You're listening to ALL THINGS CONSIDERED from NPR News.