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http://www.nytimes.com/2004/12/27/science/27science.html

With No Alert System, Indian Ocean Nations Were Vulnerable
By ANDREW C. REVKIN

Published: December 27, 2004

The earthquake that struck northwest of Sumatra, Indonesia, at dawn yesterday was a perfect wave-making machine, and the lack of a tsunami warning system in the Indian Ocean essentially guaranteed the devastation that swept coastal communities around southern Asia, experts said.

Although waves swamped parts of the Sumatran coast and nearby islands within minutes, there would have been time to alert more distant communities if the Indian Ocean had a warning network like that in the Pacific, said Dr. Tad Murty, an expert on the region's tsunamis who is affiliated with the University of Manitoba in Winnipeg.

Within 15 minutes of the earthquake, in fact, scientists running the existing tsunami warning system for the Pacific, where such waves are far more common, sent an alert from their Honolulu hub to 26 participating countries, including Thailand and Indonesia, that destructive waves might be generated by the Sumatra tremors.

But there was no way to convey that information speedily to countries or communities an ocean away, said Dr. Laura S. L. Kong, a Commerce Department seismologist and director of the International Tsunami Information Center, an office run under the auspices of the United Nations.

Phone calls were hurriedly made to countries in the Indian Ocean danger zone, she said, but not with the speed that comes from pre-established emergency planning.

"Outside the Pacific these things don't occur very often at all so the challenge is how to make people and government officials aware," she said.

Tsunamis, sometimes referred to as tidal waves but having nothing to do with tidal forces, are generated when an earthquake, eruption or landslide abruptly moves the seabed, jolting the waters above.

Resulting waves can cross thousands of miles of deep ocean at near jetliner speeds as near-invisible disturbances before welling up in shallower coastal waters to heights of 30 feet or more.

But even at such speeds, prompt warnings can provide ample time to evacuate people, Dr. Murty and other experts said. The Pacific network of stations gauging wave and earthquake activity is able to alert potential targets within minutes.

Tsunamis have swept the Indian Ocean, as well, oceanographers said yesterday, noting one that killed several hundred people near Bombay in 1945 and another - one of the earliest tsunamis recorded in the region - that ravaged what is now Bangladesh and other parts of the Bay of Bengal in 1762.

With population densities enormously high in many parts of coastal southern Asia, the region should have started setting up such a network long ago, said Dr. Murty, who is originally from India.

Other scientists have voiced similar concerns. At a meeting in June of the Intergovernmental Oceanographic Commission, a United Nations body, experts concluded that the "Indian Ocean has a significant threat from both local and distant tsunamis" and should have a warning network.

But Dr. Murty said India, Thailand, Malaysia and other countries in the region "see this as a Pacific problem."

"I have a feeling that after this tragedy that may change," he said.

The earthquake near Sumatra was the fifth most potent in the world in the last 100 years and the worst in 40 years, registering a magnitude of 9.0. It was followed by more than a dozen aftershocks, but none of those were expected to produce dangerous waves, federal geologists said.

The quake occurred at one of the many seams in the ever-shifting crust of the earth where one plate slips beneath another in an incessant, but spasmodic process. In this case, the quake was set off by an abrupt slippage along 700 miles of the seam where the plate beneath the Indian ocean slides under the Indonesian archipelago.

This caused a vast stretch of seabed to shift about 50 feet, said geologists at the National Earthquake Information Center in Golden, Colo.

The biggest danger from earthquakes on land tends to come when the earth heaves horizontally, as is the case along the San Andreas fault in California. But faults where earthquakes tend to cause abrupt vertical motion, like the ones along western Indonesia, pose the biggest risk of generating tsunamis because they can act like a giant piston, deforming the sea. In such submarine earthquakes, gravity and the incompressibility of water force the seas above to react immediately to the change thousands of feet below.

"You're taking hundreds of miles of ocean bottom and moving it dozens of feet," said David Wald, a seismologist at the center. "That displaces a huge amount of water. The water at the surface starts to shift downhill and that makes a tsunami."

Most research on such waves and efforts to create warning systems have focused on the Pacific, where the Ring of Fire, a great arcing seam of volcanic and tectonic activity, causes a significant tsunami about once a decade.

One of the first efforts to alert communities to impending tsunamis came in Hawaii in the 1920's, said Dr. George D. Curtis, a tsunami expert affiliated with the University of Hawaii at Hilo.

A geologist at Hawaii's volcano observatory, upon detecting telltale tremors, would call local harbor officials and tell them to have boats moved to safety, Dr. Curtis said. Efforts greatly intensified in 1946, after a powerful earthquake in the Aleutian island chain of Alaska unexpectedly sent waves smashing into Hawaii, killing more than 150 people.

In 1948, the United States created its Pacific Tsunami Warning Center, which has been linked to an international data and warning network since 1965.

Any underwater earthquake with a magnitude greater than 6.5 starts the process, Dr. Murty said, and if a single wave gauge signals that the ocean is reacting, an alert is issued. But there has been little work done outside the Pacific, other than informal discussions, to expand the tsunami monitoring network.

"There's no reason for a single individual to get killed in a tsunami," Dr. Murty said. "The waves are totally predictable. We have travel-time charts covering all of the Indian Ocean. From where this earthquake happened to hit, the travel time for waves to hit the tip of India was four hours. That's enough time for a warning."