Alert buoys not up to warning of tsunami

A detection system that was expanded after the Indian Ocean tsunami that killed 230,000 people has experienced significant outages and can no longer be relied on, a new report finds.

The system, known as Dart, or Deep-ocean Assessment and Reporting of Tsunamis, was expanded from six deep-ocean buoy stations to 39 in the months after the huge 2004 earthquake off Indonesia that spawned killer waves which reached as far as the east coast of Africa.

Though there are Dart buoys in the Atlantic and the Caribbean, most of them are located around the Pacific Ocean's "Ring of Fire" to give advance warning to Washington, Oregon, California and Alaska, where a tsunami landfall is thought more likely.

But at any given time, 30 per cent or more of the buoys have been inoperable, according to a report from the National Research Council.

An alarming number of buoys have broken their moorings and drifted away.

The buoy stations have also suffered failures in sensors that can detect a sea level rise of as little as 7.5mm.

Other systems on the sophisticated buoy stations have also had problems.

"As a consequence of the pervasive outages of Dart stations, the Tsunami Warning Centres cannot depend on the Dart network for tsunami forecasting," said the report, which was requested by Congress.

The Dart buoys are designed to track the giant waves as they cross the ocean at the speed of a jetliner. But the report also warned that serious gaps in preparedness persist among coastal communities, coastal states and the federal government when it comes to tsunamis that could reach the shore minutes after being triggered by an earthquake or underwater landslide.

The most serious tsunami threat in the United States involves just such a scenario. The Cascade subduction zone where tectonic plates collide off the coast of Washington, Oregon and northern California is overdue for a mega-quake that could easily reach a magnitude of 9.0 on the Richter scale.

The quake could trigger a tsunami that by some estimates could be 27m tall and arrive on the northwest coast in minutes.

"There won't be time for warnings," said John Orcutt, a professor at the Scripps Institution of Oceanography who chaired the committee that wrote the report.

- AAP