THE MAGAZINE

Tsunami Warning

By Robert Elliot

Spurred by the havoc wreaked by the tsunami that hit South Asia and Southeast Asia in December 2004, a system of sophisticated buoys is being stretched across the Indian Ocean to give the region’s residents advance warning the next time a gigantic wave speeds towards their shores.

The National Oceanic and Atmospheric Administration (NOAA) joined the Thai government a few months ago in launching the first Deep-ocean Assessment and Reporting of Tsunami (DART) buoy station halfway between Thailand and Sri Lanka, at 9 degrees north lattitude and 89 degrees east longitude. A second will be placed between September and November of this year off of Indonesia. A total of 22 buoys will string along the Sumatra fault line when the project is due to be wrapped up at the end of 2008.

It usually takes an earthquake measuring seven or more on the Richter scale to generate a tidal wave, says Curt Barrett, director of the Indian Ocean Tsunami Warning System for NOAA. The DARTS will ensure NOAA and governments do not raise alarms unless they are justified. “We don’t want to cry wolf. It helps the credibility and reliability of the warning service to have this equipment out there,” he says.

The earthquake that triggered the 2004 wave, also referred to as the “Asian Tsunami,” measured between 9.1 and 9.3 in magnitude. From the quake’s epicenter off the western coast of northern Sumatra, a tsunami sprang up that pounded the coastlines of Indonesia, Sri Lanka, India, Thailand, and other countries with waves up to 100 feet high that carried a total energy equal to about five megatons of TNT. Nearly 230,000 people died in that catastrophe. 

The Asian Tsunami took between 15 minutes and seven hours to hit the shores of affected states. Sumatra’s northern reaches were impacted very quickly, while Sri Lanka and India’s east coast were hit between 90 minutes and two hours later. Despite being close to the epicenter of the earthquake, Thailand was also struck about two hours later because the tsunami traversed the shallow Andaman Sea slowly.

The warning time the DART buoys, or “tsunameters,” will give to nations that are in the way of an onrushing wave varies according to locale. The system was designed to give countries like Sri Lanka, India, and Thailand an hour’s notice. Others don’t have nearly as much cushion. “If you are in Indonesia, you go to high ground, because you don’t have any time. The tsunameter gives you about 15 minutes advance warning,” says Barrett.

Developed by the NOAA Pacific Marine Environmental Laboratory in Seattle, Washington, the buoys are about 20 feet in diameter. The stations have a bottom pressure sensor that is anchored to the seafloor and connected to the moored buoy on the surface of the sea. An acoustic link transmits data from the bottom to the buoy, and a satellite relays the information to ground stations.

The buoys cost $400,000 to build and have to be serviced twice a year. They have to be totally replaced every two to three years after getting pounded by waves, worn by the salt air, or simply running out of batteries. Bankrolled by the U.S. Agency for International Development (USAID), the buoys take six days to deploy.

Barrett says despite their costliness and high maintenance, the buoys are inexpensive compared to the elaborate system used by Japan. The $10 million Japanese system is a cable that runs along the sea bed and has sensors every few kilometers to pick up dangerous waves and earthquake tremors. “That’s nothing anyone could afford or maintain in the Indian Ocean,” Barrett says.

The Thai buoy will be maintained by the Thai Meteorological Department and National Disaster Warning Center. The data it produces will be available to all nations via the World Meteorological Organization Global Telecommunications System. The eventual network of 22 buoys will be part of an end-to-end warning system that will encompass tide gauges, communications upgrades, modeling, and dissemination systems for Thailand, Indonesia, India, the Maldives, and Sri Lanka.

In the meantime, the NOAA Pacific Tsunami Warning Center in Hawaii and the Japan Meteorological Agency are providing tsunami advisories and alerts to 27 Indian Ocean countries on an interim basis. It is up to the countries to figure out how to warn their citizens.

On the other side of the globe, the United States is placing another chain of tsunameters in the Pacific and Atlantic Oceans, and in the Caribbean Sea. A total of 39 buoys are expected to be in position by the end of 2007; 26 have already been installed. Some were already afloat in December 2004 and picked up the most far-flung traces of the Asian Tsunami.


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