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Health, Science, Environment

Do earthquakes elsewhere predict shaking in New Madrid?

This article first appeared in the St. Louis Beacon, March 1, 2010 - An earthquake in Haiti in January. An earthquake in Japan the following month. An earthquake in Chile the day after that.

Coincidence, or a pattern that should worry people living so close to the New Madrid Fault?

The three quakes in the news recently have little to do with each other, earthquake experts in St. Louis say. And they can't do much to tell when or whether a Big One will rock southeast Missouri.

"Seismographs will pick up anything," says Bob Hermann, the Otto Nuttli professor of geophysics at Saint Louis University. "Probably once a day somewhere in the world there will be an earthquake with magnitude of 6.0 or above."

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Adds Douglas Wiens, chairman of the department of Earth and Planetary Sciences at Washington University:

"They're too far apart to really affect each other, Normally, earthquakes really only affect another earthquake within 100 miles or so."

The 8.8-magnitude quake that hit Chile over the weekend struck on the fault zone known as the Nazca plate, which is under the eastern part of the Pacific Ocean, bumping up against the west coast of South America. Initial data indicate it occurred at the northern edge of the quake along the same plate that occurred in 1960 and measured 9.5 - the largest ever measured since the invention of the seismograph in the 19th century.

The earthquake in Haiti, which was centered near the capital of Port-au-Prince Jan. 12 and killed more than 200,000, had a magnitude of 7.0. A quake measuring 6.9 hit the southern coast of Japan late Friday but little damage was reported.

The difference in the effects of such large earthquakes depends on how close they strike to populated areas and how well the buildings are constructed to withstand the movement of the earth, Wiens and Herrmann said in interviews.

"If the Haiti earthquake had happened under a city where the construction was more prepared," Wiens said, "there wouldn't have been nearly the same loss of life.

"The Haiti quake wasn't that large, in terms of how we think of earthquakes. Several earthquakes that large occur every year. The problem was it was right underneath the city, and the construction was so poor and emergency services were poor."

Herrmann said the loss of life would be much less "if everybody lived outside and there were no trees and nothing else to fall on you." But even then, he noted, the risk would not drop to zero.

"There can be landslides, or breaks in dams," he said. "There are all sorts of interesting ways to get killed."

Explaining how the quakes occur, Herrmann said that the Earth is "a big heat engine that moves. Earth had heat in it from when it was formed as a planet, and it has heat from radioactive decay. That heat can melt rock, so the rock over a long period of time will move."

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When one plate strikes another and things get stuck, the result is an earthquake. The Nazca plate, he said, is approaching South America at a rate of several inches a year.

"That may not seem like much," Herrmann said, "but if you have several hundred years between earthquakes, it has to make up that gap over that period of time, and the sudden release of energy gives you the earthquake."

The tsunami that resulted from the Chilean quake did not cause the devastation that resulted from a similar wave that was triggered by an earthquake in Sumatra in 2004. Wiens said that a better system of warning about tsunami has been put in place in recent years, and the data that will be collected from the weekend event will help move scientists' knowledge forward even more.

Wiens said that the warnings issued over the weekend for Hawaii and other places were prudent, even though the tsunami hit with less force than forecast.

"Some people think that because the beaches were evacuated and there wasn't a devastating tsunami, the action wasn't appropriate," he said. "But you want to err on the side of warning people instead of not warning people and having people die."

Herrmann notes that anyone who has flown into the airport at Hilo, Hawaii, and seen what appears to be a large park has witnessed what a tsunami can do. That park, he said, is land cleared by a tsunami set off by an earthquake in Alaska in 1946.

Now that the earthquake in Chile has struck, scientists will use the information it generated to refine the science further. But no one expects to be able to pinpoint with much precision when -- or where -- the next big quake will strike.

"Nobody had foreseen it," Wiens says of the Chilean quake, "in the sense of understanding it would happen this year or even this decade, but this was an area everyone knew was subject to large, dangerous earthquakes.

"I think we've gotten somewhat better at identifying the likelihood of an earthquake over a 10 or 20 year period, but there's no way to predict one on a year-to-year or a day-to-day basis."

"Within the first five minutes," Herrmann adds, "The U.S. Geological Survey knew they had a big earthquake down there. Within 20 minutes, they knew it was a very big earthquake. Within an hour, they had an idea of the size of the chunk of the earth that had actually moved, 250 miles north-south by perhaps 60 miles perpendicular to that. Something with that big an extent, it could affect a lot of areas.

"It could have been worse. The good thing about it, though, is that this thing has popped off now, so it may be another 100 years or so until it pops off again, so you have another generation or so of people who can prepare for it."

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