NOAA bolsters tsunami warning system

Officials repair deep-ocean buoys in Pacific, but no sensors set in Atlantic

Three of the six deep-ocean buoys deployed by the National Oceanic and Atmospheric Administration to detect tsunamis before they approach the Pacific Coast are inoperative.

NOAA officials deployed the six-buoy system in 1998, placing three near Alaska, two close to Oregon and Washington state, and one near the equator.

Two of the three buoys near Alaska are not working, and one of the two West Coast buoys is not transmitting data.

"Batteries can die, leakages can occur in the instrumentation package on the bottom, the buoy can have failure with rough seas — mechanically, things break," said David Oppenheimer, a U.S. Geological Survey seismologist involved in tsunami monitoring.

One out-of-action buoy has been repaired and is ready for to be put back in the ocean.

"Because of the sea in Alaska in the wintertime, they need to wait for weather that would allow them to do that in a safe manner," said Greg Romano, a spokesman for NOAA's National Data Buoy Center. He could not say when the other inoperative Alaska buoy might be repaired. Repairs on the broken West Coast buoy should occur in the next few weeks, he added, though he could not say when it would be fully restored.

The Aleutian Islands and the Pacific Northwest are near active underwater tsunami-generating seismic faults called subduction zones, in which one tectonic plate is sucked underneath another. The Dec. 26, 2004, tsunami that killed about 150,000 in Southeast Asia occurred after an earthquake in a subduction zone near Sumatra.

A 9.2 Richer-scale earthquake in the Aleutian subduction zone in 1964 caused a tsunami responsible for killing more than 120 people. In 1946, an earthquake originating in the same seismic area sent a tsunami to Hawaii, killing more than 150. An approaching tsunami sounds like "a freight train coming in from the coast," said Harold Mofjeld, a NOAA tsunami researcher.

A buoy system adequate to monitor the entire Pacific basin should include at least 21 working buoys, said Frank Gonzalez, a NOAA oceanographer. "It's kind of laughable to talk in terms of six gauges," he said. "There's room for a tsunami to sneak through."

Three-pronged approach

Buoys are one part of a three-pronged approach to monitoring the ocean for tsunamis. Geophysicists in Ewa Beach, Hawaii, and Palmer, Alaska, are on 24-hour call should an earthquake occur. Real-time telemetry from around the world comes through on dedicated phone lines and the Internet.

In the Indian Ocean, earthquake sensor coverage is sparse. It took four minutes for the Sumatra earthquake's waves to reach the nearest seismograph station in the Cocos Islands. But the system ringing the United States is not perfect either, said Harley Benz, chief scientist at the National Earthquake Information Center. A lack of money is slowing a series of planned upgrades, he said. Congressional appropriations are "roughly 10 percent of what we've asked for, of what we've been authorized for or what we need."

A denser network wouldn't speed up scientists' response time, but it would give tsunami watchers a clearer picture of how dangerous a threat the underwater rift is, Oppenheimer said.

In addition, false alarms are dangerous and costly. "People die of heart attacks, ambulances get stuck in traffic," and the next time a tsunami alarm sounds, people might be inclined to ignore it, Gonzalez said.

Tidal gauges along the coast are the final line of warning defense, but data from the gauges is of limited value. "They're meant to measure tides, not tsunamis," Gonzalez said. "They're inside of protected harbors." The best measurement is the buoys "out in the middle of the ocean, between that earthquake and you." The current network of six buoys provides minimal but sufficient coverage of America's Pacific coast, although "obviously, anything could be improved," he said.

No tsunami buoys float in the Atlantic Ocean, the Gulf of Mexico or the Caribbean, where an ongoing collision of the Atlantic and Caribbean plates creates another subduction zone.

The East Coast of the United States faces a far less onerous tsunami threat, although a submarine landslide off the coast of Newfoundland provoked a tsunami that killed 29 in 1929. A controversial scientific paper theorizes that tsunami waves up to 25 meters high could strike Florida should the active volcano on the Canary Islands collapse into the ocean.

Even the best warning system could be useless in the short time span in which tsumanis can occur. Local tsunamis, such as a wave generated by the subduction zone in the Pacific Northwest or in the Caribbean, crash into land within minutes, not hours.

"You have 20 to 30 minutes from the time the earthquake appears until the first wave comes in," Oppenheimer said. "Even if you had a warning confirmed by the buoys, it's so little time."

But the warning system in place is not adequate, he said. "The method of evacuating people is somehow getting the word out, police cruisers with speakers," Oppenheimer said. "That's not going to work in a local tsunami."

Improvements are slowly being made. In Washington state, emergency preparedness officials have installed four voice alarms, and four more are coming. Fifteen counties and towns in the Pacific Northwest participate in the federally supported TsunamiReady program, though liability worries and the money required may account for less-than-universal participation, said Guy Urban, a geophysicist with the tsunami warning center in Alaska.

A federally funded effort to map the flood path of tsunamis and place warning signs is under way but far from complete, Oppenheimer said. For example, emergency officials do not have updated inundation maps — or in some cases, any maps at all — for protecting an at-risk population of 1.8 million people living within 1 kilometer of the Pacific Ocean . "It's difficult, time-consuming work," he added.

The bottom line in some cases may be more public awareness of tsunamis. "If you feel an earthquake and it lasts more than 20 seconds, get to high ground," Urban said.

Tech helps detect tsunamis

As part of the process of detecting tsunamis, buoys anchored in water as deep as three miles transmit information via satellite to warning centers in Alaska and Hawaii.

The buoys consist of a water pressure sensor anchored to the seafloor that sends data to a tethered satellite transmitter floating on the surface. Most buoys transmit tide information every hour. A tsunami automatically triggers them to transmit at least once a minute for four hours.

Their deployment and recovery requires a ship large enough to house a crane capable of operating in rough weather. Each buoy costs about $260,000 to buy and deploy and about $200,000 a year to maintain. National Oceanic and Atmospheric Administration engineers are designing a second generation of deep-ocean buoys. One prototype is deployed off the coast of Hawaii, but it does not transmit data to the warning centers.

The two warning centers receive buoy data and telemetry from seismograms and information from a series of tidal gauges spread along the Pacific Coast. Officials at the Pacific Tsunami Warning Center near Honolulu monitor the Pacific Basin and have agreements with 25 countries to provide warning data. Officials at the West Coast and Alaska Tsunami Warning Center issue warnings to Pacific Coast states and Canada.

Both centers receive seismic data from about 10 sources, including the Internet and dedicated phone circuits routed through the National Earthquake Information Center in Golden, Colo. Although other sources use the Internet to collect data, system designers at the center chose not to send seismic data via the Web.

"We didn't want a router falling off a shelf in some earthquake zone," said David Oppenheimer, a U.S. Geological Survey seismologist.

"For some critical channels, we may get [the data] two or three different ways," said Steven Weinstein, a geophysicist at the Pacific warning center.

The latency for transmitting data via phone lines is not more than a few seconds, scientists say. The tidal gauges transmit data in real time.

— David Perera


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