KOBE, Japan (AP) — Hawaii is among the most tsunami-ready places in the world. When an alert is issued, beachside sirens go off and urgent messages are flashed on television and broadcast on radio. Evacuation maps on telephone book covers point people to higher ground. But most of the time, no damaging tsunami hits the shore.
The Pacific Ocean early warning system’s high false alarm rate – estimated at 75 percent – is getting more attention these days as experts and nations work to extend similar protection to the Indian Ocean following the tsunami disaster in southern Asia.
“It’s definitely one of our biggest challenges,” said Charles McCreery, director of the Pacific Tsunami Warning System in Honolulu, which sends seismic data and tsunami bulletins to 26 nations around the Pacific. The network was begun in 1965.
In addition to the problem of false alarms, experts say there is a dearth of information on landslides that trigger tsunamis and a wide disparity in the ability of Pacific nations to respond to alerts. Much work remains to upgrade the system with new technology.
“You have to take that model and update it,” said Eddie N. Bernard, director of the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory in Seattle.
Accuracy is an important element. Officials say a mega-tsunami in the Pacific won’t be missed by the sensors, and point out that monitors can get seismic information much more quickly than they used to. But the high false alarm rate undermines public confidence and dilutes the impact of alerts. Another issue is money: An unnecessary evacuation in Hawaii in 1994 cost an estimated $30 million in business disruptions and other costs.
Tsunami warnings are compiled using a variety of information. The most immediate data come from seismic readings: Monitors can alert nations within minutes of a large earthquake, and can then update the magnitude from subsequent readings within an hour.
But only a tiny percentage of undersea earthquakes cause dangerous tsunami, meaning subsequent readings from sea level monitors are crucial to forecasting big waves. And that data can take hours to arrive.
“It depends on the network,” said Michel Jarraud, secretary-general of the World Meteorological Organization. “In some cases, we expect it to take two hours.”
A major advance has come with Deep-ocean Assessment and Reporting of Tsunami buoys – known as DART – deployed by the United States in the Pacific in October 2002. There are now seven in operation, six operated by the United States and one by Chile.
The system consists of an ocean-floor sensor and an acoustic cable linking it to a buoy. The sensor measures any tsunami, and the buoy quickly transmits data to a monitoring station via satellite. The system was successful in November 2003, when it allowed authorities to withdraw a false tsunami bulletin within an hour of a 7.8-magnitude quake in Alaska’s Aleutian islands.
“It worked – we were actually able to cancel a warning,” said Bernard. The tsunami that later hit Hawaii was a mere one-inch high. The avoidance of an unnecessary evacuation saved the island state an estimated $68 million.
The buoy system won a major boost with Washington’s recent announcement of a dramatic expansion of its tsunami warning network to the Atlantic and Caribbean Sea. Under the $37.5 million plan, the number of the buoys under U.S. control will be increased from six to 38, Bernard said.
Quakes with magnitudes of more than 9 – such as the Dec. 26 temblor off Sumatra – virtually guarantee tsunami. But the ability to predict tsunami from smaller quake depends on part on the type of tremor, with those that vertically displace water being the most dangerous.
Attention has focused on new technologies that allow scientists to measure the deformation of the earth along dangerous faults with satellites, using Interferometric Synthetic Aperture Radar. Seismologists and others hope someday to use those measurements to monitor the pressure building between plates as a way of predicting when a devastating quake will occur.
“It allows engineers to concentrate their resources on places where hazard is the highest,” said James H. Whitcomb, deputy director of the Division of Earth Sciences at the National Science Foundation in Arlington, Va.
Any warning system, however, starts to break down when the tsunami-generating quake is so close to a coastline that there is very little time to get an alert to residents – meaning the education and preparation of local communities to recognize the warning signs and evacuate are crucial.
“Education saves lives,” Bernard said. “No system is going to get to you in five minutes.”
Comments