The quake was the world's fourth largest since 1900.

Scientists from the University of California, Berkeley, the Wadia Institute of Himalayan Geology in India and the United States Geological Survey also found that the earthquake was slower than first thought.

"The earthquake lasted at least an hour and perhaps up to three hours, with much of the deformation happening more than one hour after the main shock," said Roland Buergmann, professor of earth and planetary science at UC Berkeley.

"Normally, we see deformation of the surface a few hundred kilometers away, but here we see deformation 4,500 kilometers (2,800 miles) away, and five or six times the deformation we've seen in previous quakes," he said.

More than six months later, said Buergmann, "the Earth is still ringing like a bell."

In another article in Science, Roger Bilham, a University of Colorado seismologist, said that investigating the December quake will allow scientists to "learn numerous new things about our planet, and in particular about the Pacific Northwest, where a similar earthquake could occur at any time."

All rights reserved. © 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.