Of the six buoys placed throughout the Pacific Ocean, two near Alaska have been broken for 14 months, said Greg Romano, spokesman for the National Weather Service, the branch of the National Oceanic and Atmospheric Administration that maintains the network. One off the coast of Washington broke in November and is now being repaired.
Scientists offer assurances that despite the breakdown they can rely on information gathered by earthquake sensors and tide gauges.
"We are still a fully functional warning system, even without the buoys," Paul Whitmore, chief scientist for the West Coast and Alaska Tsunami Warning Center in Palmer, Alaska, told The Seattle Times. "The impact of those buoys being out is that we have less data upon which to cancel or expand warnings."
The malfunction makes it difficult to see where a wave is headed or how big it will be when it reaches the coast, Whitmore said, which could result in false alarms.
Before the buoys were developed, the nation's 40-year-old tsunami-warning system relied on seismographs to detect and measure earthquakes.
A network of 125 tide gauges scattered from Alaska to California also helped in early detection, but they are widely spaced and aren't an accurate indicator of a wave's size.
"The old system is crude," said Eddie Bernard, director of NOAA's Pacific Marine Environmental Laboratory in Seattle. "You detect a big earthquake, and everybody evacuates."
The newer buoys were added to help reduce the number of costly false alarms, Bernard said.
They have sensors that hang near the ocean floor to detect slight ripples signaling the start of a tsunami. The buoys then transmit warnings via satellite.
In 2003, a magnitude-7.8 earthquake in Alaska triggered a localized tsunami. When the wave reached a nearby buoy, forecasters saw it was too small to be dangerous and canceled the warning.
When the network was developed, scientists said six buoys would be the minimum necessary to cover the Pacific Ocean. An ideal system throughout the Pacific would include about 21 buoys, each costing about $250,000 to build and thousands of dollars to maintain.
The current warning system is also limited in that it wouldn't help if a massive earthquake hit directly off the Pacific Coast, which could send waves crashing ashore in as little as 30 minutes.
Sen. Dianne Feinstein, D-Calif., has asked for a review to determine whether the current tsunami-warning system is adequate.
U.S. Rep. Jay Inslee, D-Wash., said he'll co-sponsor bipartisan legislation for a $30 million global-warning system with 50 new buoys and other instruments. A dozen or more of the buoys would be deployed in the Pacific.
"We need to add additional buoys, both for our own protection and to add redundancy in case these things go down," Inslee said. "The world needs a warning system, too."
Sen. Joe Lieberman, D-Conn., has proposed a similar bill. Australia, Germany and other nations also have offered to help build and maintain a warning system in the Indian Ocean.
Some experts say education is key to saving lives. Teaching people what signs to watch for and when to flee might prove more effective than new technology, said Brian Atwater, an expert on tsunamis and earthquakes who is a U.S. Geological Survey researcher at the University of Washington.
Michael Glantz, senior scientist at the National Center For Atmospheric Research, based in Colorado, said technology is worthless without systems to disseminate warnings and the money to pay for them.
"These systems are hard to keep going for events that are as rare as big tsunamis," he said.