Within minutes of the massive earthquake off the coast of Indonesia, U.S. scientists whose job is to scan for signs of tsunamis suspected that a deadly wave was spreading through the Indian Ocean.
Had the quake happened in the Pacific Ocean, a network of monitoring stations established after previous tsunamis would have enabled scientists to produce specific warnings for coastal areas.
Such warnings might have saved thousands of lives. Two hours elapsed between the quake and the arrival of the tsunami along the coastlines of India and Sri Lanka, sufficient time to evacuate large numbers of people.
But no such monitoring system exists in the Indian Ocean.
"Probably the basic reason is that dangerous tsunamis are extremely rare in the Indian Ocean, so it probably was not perceived as a major hazard" by governments in the region, said Harold Mofjeld, a senior scientist at the Pacific Marine Environmental Laboratory in Seattle, part of the federal government's National Oceanic and Atmospheric Administration, or NOAA.
The lack of warning has drawn bitter accusations from some survivors of the disaster.
"Why didn't the people who monitor these things warn the Indian [Ocean] countries that a tsunami was about to hit them?" asked Nirj Deva, a British member of the European Parliament who was in Sri Lanka.
"Nobody was warned. All these people died unnecessarily," he said in an interview with the BBC. "I want some answers."
Nations in Asia have seismic instruments that could have told officials that a massive earthquake, capable of generating a tsunami, had struck. But even large underwater earthquakes do not always generate deadly tsunamis. Without monitoring equipment in the water, scientists could not be certain of a tsunami, and the nations bordering the Indian Ocean lacked the sort of detailed data on waves available in the Pacific Rim.
The countries along the Indian Ocean "have simply chosen not to spend the money on such a system," said Conrad C. Lautenbacher Jr., NOAA administrator.
And that's a pity, he said, because the system "is not all that expensive."
In Ewa Beach, Hawaii, where the U.S. government's Pacific Tsunami Warning Center is located, the local time was 2:58 p.m. Christmas Day when the massive earthquake began registering on seismic instruments.
Within an hour, the NOAA issued an alert to nations that take part in the Pacific Ocean tsunami warning system that there was "the possibility of a tsunami near the epicenter" of the earthquake.
Indonesia and Australia, both part of the Pacific network, were among the countries that received the warning that a wave could strike near the epicenter.
India, Sri Lanka and the Maldives, located across the Indian Ocean from the earthquake, did not receive the warning because they were not part of the Pacific system, said Douglas L. Johnson, director of the National Weather Service, which handles tsunami warnings.
"We don't have contacts in our address book for anybody in that part of the world," said Charles McCreery, director of the Pacific Tsunami Warning Center.
Scientists at the center in Hawaii tried to alert officials in the region with what few contacts they had, said retired Canadian researcher Tad Murty, who is familiar with the scientists' efforts.
"They tried to raise the alarm every possible way," Murty said. "The problem was with the countries in the Indian Ocean: Nobody really responded, and nothing much was done about it."
Without monitoring stations, neither officials in the U.S. nor Asia had specific information about the size and speed of the tsunami and where it most likely would hit.
By contrast, the Pacific monitoring network involves hundreds of seismic stations around the world, along with coastal tidal gauges and sophisticated ocean sensors known as tsunami buoys capable of detecting a centimeter's difference in ocean height.
The devices proved their worth Nov. 17, 2002, when a magnitude 7.5 earthquake struck the Aleutian Islands in Alaska.
Using the warning system, NOAA officials confirmed that the quake had produced a tsunami, but that it would be about an inch high when it reached Hawaii, Johnson said.
Before the system was devised, officials in Hawaii would have as a matter of routine evacuated the shore and coastal areas after a large earthquake.
But with the new system, "We could tell Hawaii, 'You don't need to evacuate,' " Johnson said.
On Feb. 16, ministers from dozens of nations, including some in the Indian Ocean region, will meet to sign an agreement creating an Earth Observation System to ensure that countries are warned when disasters are on the way, Lautenbacher said.
Times staff writers Charles Piller and Esther Schrader contributed to this report.