Sumatra Quake Shook Entire Earth

New Technology Reveals True Strength of Tremor

(AP)  At that spot the Eurasian plate was being pulled downward by the descending Indo-Australian plate. The quake released the edge of the Eurasian plate, which sprang up, lifting the ocean floor and sending the sea water off in the giant wave that killed so many, the researchers reported.

They said the higher sea floor displaced so much water from the Bay of Bengal and the Andaman Sea that sea level worldwide was raised 0.004 inch.

"No point on Earth remained undisturbed," wrote Roger Bilham of the University of Colorado.

Indeed, ground movement of as much as 0.4 inch occurred everywhere on Earth's surface, though it was too small to be felt in most areas.

And the temblor "delivered a blow to our planet" that was felt for weeks, noted a team of researchers led by Jeffrey Park of Yale University.

His group calculated that the quake caused the planet to oscillate like a bell, at periods of about 17 minutes, which they were able to measure for weeks afterward. A similar phenomenon was first noted in the 1960 quake in Chile.

The initial Dec. 26 Sumatra quake is estimated to have had a magnitude of 9.1 to 9.3, and a second quake to the south on March 28 registered 8.6.

By comparison, the 1960 Chile earthquake was magnitude 9.5 and the 1964 Alaska earthquake was magnitude 9.2. California's 1989 Loma Prieta earthquake had a magnitude of 6.9.

Among the other findings reported in the various papers:

In Sri Lanka, more than 1,000 miles from the epicenter, the ground moved nearly 4 inches.

The rupture spread from south to north, resulting in a Doppler effect in instruments measuring it. Seismometers in Russia recorded the quake at a higher frequency because it was moving toward them, while those in Australia measured a lower frequency as it moved away.

When the surface waves from the Sumatra quake reached Alaska they triggered a swarm of 14 local earthquakes in the Mount Wrangell area.