Tsunamis aren't unique to Asia. Every day, scientists from Hawaii to California are on guard, watching for giant waves that could swamp U.S. shores.
The monitoring system is complex, drawing upon seismic stations, deep-ocean detectors, sea surface buoys, satellites and onshore sea-level gauges. But if a tsunami is detected, the advice is simple: Get to higher ground as fast as you can.
Tsunami waves are most often caused by seismic disturbances in the ocean, which abruptly push huge volumes of water out from the fault's center. Underwater landslides and even meteor impacts can set off tsunamis as well.
In the open ocean, a tsunami's effect may be hardly noticeable, amounting to less than 3 feet (1 meter) in sea-level change. But as the wave reaches shore, coastal waters can rise by tens of feet — as was the case in the Indian Ocean catastrophe.
Experts said the death toll in Asia might have been far lower if the authorities in the affected nations had a better warning system.
"Had they had tide gauges installed, many of these people who were farther away from the epicenter could have been saved, because they would have been able to track the waves and tell the people along the coast to move off the beach," Waverly Person, a geophysicist at the U.S. Geological Survey, told NBC's "Today" show.
It was an earlier catastrophe — the Alaska earthquake of 1964, which sparked a deadly tsunami — that led the United States to establish its federal tsunami-monitoring system, managed by the National Oceanic and Atmospheric Administration, or NOAA.
The heart of NOAA's system is a network of six deep-ocean monitors, or "tsunameters," stretching from Alaska's Aleutian islands to the middle of the Pacific Ocean. The focus is on the Pacific, rather than other oceans, as that's where the tsunamis with the biggest impact on the West Coast originate.
Each tsunameter has a pressure recorder anchored to the seafloor, which watches for patterns that could hint at an earthquake or underwater landslide capable of generating a tsunami. The recorder's readings are beamed up to a buoy, then relayed to NOAA's network of geostationary weather satellites (known as the Geostationary Operational Environmental Satellites, or GOES).
The real-time satellite data are analyzed at NOAA's tsunami warning centers in Hawaii and Alaska, which is in charge of issuing alerts to emergency officials and the U.S. military. But the tsunameter system is just one source of information — and not always the most important source, said Paul Whitmore, scientist in charge at the West Coast / Alaska Tsunami Warning Center in Palmer, Alaska.
"Earthquake information travels a lot faster than the tsunami wave travels," he explained. The first alert may well be issued based on seismic data even before a tsunameter registers the wave. NOAA draws upon readings from about a dozen government agencies and universities, Whitmore said.
In the first stages of a potential tsunami alert, "we have to make decisions so fast, all we look at is earthquake magnitude and location," he said.
Scenario for a tsunami alert
Tsunami alerts are generally issued less than once a year in the United States, with the most recent one sent out in November 2003, Whitmore said. Then it's up to local authorities to get the word out. "The most critical part of the whole system is that local area response," Whitmore said. "We issue the warnings — they're the ones who act."
Over the years, state and local authorities have drawn up their own tsunami emergency plans, including signs pointing to evacuation routes. Some counties have even set up high-tech tsunami warning sirens on Pacific beaches. But experts emphasize that you shouldn't wait for the sirens to go off.
"If you feel a big earthquake and live on the coast, just head 100 feet above sea level — or even if you can't get above 100 feet, get a mile inland," Whitmore said.
Another option involves what George Crawford, who deals with tsunami preparedness at Washington state's Emergency Management Division, calls "vertical evacuation." Some people survived the Indian Ocean tsunami because they took shelter in the upper floors of tall buildings.
Tsunami waves can roll in and out for up to 12 hours, so experts emphasize that coastal residents shouldn't go back home right after the initial flood.
"Once they've evacuated to higher ground, they should tune in to the media and make sure they don't go back until they hear the all-clear," said Mark Clemens, a spokesman for Washington's Emergency Management Division.
Once a tsunami strikes, NOAA draws upon a network of about 100 coastal sea-level monitoring stations to keep track of how serious the flooding gets and how long it lasts.
Waiting for the Big One?
Since the 1964 earthquake, only a handful of tsunami-related deaths have been recorded in the United States — most recently in 1994, when an underwater landslide touched off high waves in Alaska's Skagway Harbor, killing a worker who was repairing a dock.
But emergency officials note that the Cascadia Subduction Zone, an area of the Pacific floor off the coast of Washington and Oregon, is capable of generating a magnitude-9.0 seaquake like the one that sparked last weekend's tsunami. Last year, geologists reported evidence that such a Cascadia quake was behind a killer tsunami that rolled all the way to Japan in 1700.
Today, such a disturbance would trigger giant waves on the coast of Washington, Oregon and northern California. "If there was going to be a major tsunami, that's the most likely scenario," Whitmore said.
That's why Crawford is putting so much work into Washington state's warning system, as well as plans to mitigate the effects of a tsunami if it hits. He expects the Federal Emergency Management Agency to issue guidelines for tsunami preparedness in the next year or two.
Such guidelines could recommend constructing "safe havens" to survive interaction with a tsunami wave, equipping port facilities with automatic shutoff valves to minimize fuel leaks and even landscaping the coastline to counter a tsunami's force.
Crawford said some coastal residents actually add to their tsunami risk by removing sand dunes to improve their ocean view. "What you've just done is, you've taken down a perfect natural barrier against tsunami," he said.
NOAA spends about $3 million annually to operate the two tsunami warning centers and $4.5 million on the tsunami mitigation programs, said Jeff LaDouce, director of the Pacific region for NOAA's National Weather Service.
"That's the key to all of this," LaDouce said of the mitigation efforts. "The hardest part is getting the information to somebody who can do something, and having people who know what to do."
What about the Atlantic?
Because tsunamis are closely linked to volcanic activity around the Pacific "Ring of Fire," NOAA focuses on the potential threat to the West Coast rather than the East Coast. That's not to say tsunamis don't happen in the East, however: In 1929, for example, a magnitude-7.2 earthquake and submarine landslide off the coast of Newfoundland set off a giant wave that killed 29 people in Newfoundland and Nova Scotia.
Four years ago, scientists reported evidence that cracks in the continental shelf off the Carolina coast could give way, setting off a tsunami wave that could endanger the Carolinas as well as Virginia and Washington, D.C.
And just this year, geophysicist Bill McGuire of the London-based Benfield Hazard Research Center warned that the collapse of a volcano in the Canary Islands could set off a "mega-tsunami" threatening America's East Coast.
Other scientists said such an event was highly unlikely. Nevertheless, they agreed that more monitoring stations were needed — not only in the Canary Islands, but in the Indian Ocean and other potential seismic hotspots as well.