NASA Details Earthquake's Earth Effects

By Discovery News

The tsunami-spawning earthquake in Indonesia affected Earth's rotation and shape, shaved the length of a day and shifted the North Pole, NASA scientists said.

Richard Gross of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Benjamin Fong Chao, of NASA's Goddard Space Flight Center, Greenbelt, Md., said in a press release that all earthquakes have some effect on Earth's rotation, though their effect is usually minuscule.

"Any worldly event that involves the movement of mass effects the Earth's rotation, from seasonal weather down to driving a car," Chao said.

The recent earthquake, which struck the west coast of Indonesia on Dec. 26, registered a magnitude 9.3 the fourth-largest quake in a century, according to NASA.

The so-called mega-thrust earthquake happened when the India tectonic plate slid beneath the Burma plate beneath the Indian Ocean. The net effect of that movement was a slightly more compact Earth, the scientist said.

Because the shape of the Earth was changed slightly - it became minutely more elliptical - the earthquake also affected the way it spins on its axis, and the length of a day, the scientist said. The length of day was shortened by 2.68 microseconds.

Gross and Chao routinely calculate earthquakes' effects on polar motion. The North Pole was shifted by about 2.5 centimeters (1 inch) in the direction of 145 degrees East Longitude, they said, continuing a long-term seismic trend.

[____, "NASA" Details Earthquake's Earth Effects." Discovery News. http://dsc.discovery.com/news/briefs/20050110/tsunamieffects.html (13 January 2005)]