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When Disaster Strikes

Anticipating Quakes Means Keeping an Eye on the Calendar, Not the Clock

By Joel Achenbach
Washington Post Staff Writer
Monday, December 27, 2004; Page C01

Kerry Sieh, a Caltech geologist, was planning to fly next week to Sumatra to continue his study of the coral heads off the western coast of the Indonesian island. Biology, he knew, can be shaped by geology: Coral preserves an astonishing archival record of the planet's tectonic violence.

The coral head grows at sea level. Sometimes, however, giant chunks of the Earth's crust lurch up or down, leaving the coral either too deeply submerged or suddenly high and dry. The coral then adjusts to the new sea level. In the shape of the coral heads is a diary of past earthquakes.


Ocean waters swamped the Sri Lankan village of Maddampegama yesterday. (Gemunu Amarasinghe -- AP)

_____Tsunamis Hit South Asia_____
Photo Gallery: Scenes after tsunamis hit coastal towns, fishing villages and tourist resorts across the region.
_____Multimedia_____
Audio: The Post's Michael Dobbs describes the massive tsunami in Sri Lanka.
AP Report: Video of Devastation in South Asia
_____Earthquake Data_____
Map: Casualties in South Asia
Graphic: Making of a Tsunami
10 Deadliest Earthquakes
_____More From The Post_____
Sea Surges From Massive Quake Kill Over 13,000 Across South Asia (The Washington Post, Dec 27, 2004)
It Seemed Like a Scene From the Bible (The Washington Post, Dec 27, 2004)
Tsunamis Leave Indian Villages in Ruins (The Washington Post, Dec 27, 2004)
Thailand Tries to Recover After Devastation (The Washington Post, Dec 27, 2004)
In India, Death Roars In From The Ocean (The Washington Post, Dec 27, 2004)
Flooded Nations Get U.S. Help (The Washington Post, Dec 27, 2004)
Tsunamis' Toll Might Have Been Lessened (The Washington Post, Dec 27, 2004)

But to be an earthquake scientist is to deal with a subject that doesn't want to be fully understood. Humans search for patterns, but certain things in the world aren't very linear. There are scientists who break rocks in laboratories, trying to figure out what exactly pushes stone over the edge. They study earthquake fault lines with powerful microscopes, scrutinizing the fracture zone like biologists looking for a virus. They put Global Positioning System transmitters on mountaintops and island outcroppings, tracking the motion of the planetary surface by satellite.

Sieh knew for a fact that the crust would move again, catastrophically, off the coast of Sumatra. But when?

Yesterday, it turned out.

The 9.0 magnitude earthquake appears to be the fourth most powerful anywhere on the planet since 1900, and early reports indicate that more than 12,000 people have died, the victims of tsunamis that raced across a thousand miles of the Indian Ocean. Sieh spent much of yesterday scrambling to find out what happened to his friends in villages along the coast of Sumatra. And he worried about what would happen next.

"There's no doubt that yesterday's earthquake heightens the stakes," he said.

Sieh, who spoke about his Sumatra research earlier this month at a meeting of the American Geophysical Union in San Francisco, said the first thing he thought about when he heard of the quake is that these major events sometimes come in clusters.

He doesn't want to be alarmist. There's no evidence at the moment that earthquakes are suddenly going to ravage the planet the way hurricanes pounded Florida this year. But although minor earthquakes happen all over the world on a regular basis, the truly huge earthquakes occasionally come in bunches. There were a number of large quakes around the time of the 1906 earthquake that destroyed San Francisco. Of the 11 earthquakes of magnitude 8.5 or larger that have occurred since 1900, six happened between 1952 and 1965. And there hadn't been another on that scale until yesterday.

This latest earthquake apparently broke along a 600-mile section of the Sumatran "subduction zone," starting just north of where Sieh does his research. A subduction zone is a plate boundary where a slab of the Earth's crust surges downward beneath another slab.

"I worry about my segment of the subduction zone," he said. "My section of the subduction zone is still locked, as far as I know."

Along the curving western coast of the Indonesian archipelago, the piece of crust known as the India plate is sinking beneath another expanse of crust called the Burma plate. This process of subduction isn't smooth. It happens violently, joltingly, sometimes here and sometimes there, occasionally prefigured by a less powerful quake (a 7.7 magnitude event occurred in the same area near Sumatra two years ago), but usually without any obvious hint that a disaster is in the offing.

One of the original objections to the theory of continental drift was that no one could understand how something as heavy as a continent could move. Now scientists know that plates of the Earth are pulled downward into the planet's mantle by their own weight, that gravity is the force that puts everything in motion, and these plates are sinking at the leading edge. Subduction zones line the Pacific Rim, create the deepest oceanic trenches on the planet, and gradually pull entire continents for thousands of miles, rearranging the land masses over tens of millions of years. India has slammed into Asia, creating the Himalayas. The Atlantic Ocean has opened, spreading from a subterranean volcanic ridge in the middle. And the floor of the Indian Ocean is determined to duck beneath Sumatra, come hell or high water.

"We know a huge amount about the context in which earthquakes occur," Sieh said yesterday. But he added, "When it comes to the actual individual parsing out of the rupturing of these giant plate boundaries, they don't occur that regularly."

Major quakes occurred in Sumatra in 1797 and 1833. Sieh's research on the coral indicated that there have been clusters of giant earthquakes in this part of the world every 230 years or so, on average. So he knew that, generally speaking, it was getting to be about time for another big one.

But a general forecast of a major quake sometime in the coming decades is not the same thing as a prediction. It's not a prediction unless the time window is so narrow that it can incite dramatic changes in the behavior of people who are vulnerable.

"No one has a reliable prediction scheme," said Brian Tucker, president of GeoHazards International, a nonprofit group that tries to reduce the toll of natural disasters in developing countries. "Even if they did, the most reliable prediction would be in terms of probability. So you'd be saying that in the next six months, plus or minus three months, an earthquake of magnitude 6, plus or minus one unit, will occur" -- and even there there'd be uncertainty about the exact location.

"The public can't respond to that. What would a mayor do or a governor do with such a probabilistic prediction?" Tucker said.

Sieh said yesterday that he had hoped to find federal funding for more community outreach programs in Sumatra, but found out that the U.S. government didn't want to spend money on such a project outside the States. He learned, however, that he could get federal funding to produce a brochure to hand to tourists outside the Earthquake ride at Universal Studios in Florida.


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