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Chilean quake shortened Earth’s day, but not by much

Posted by Lindy on March 4, 2010


http://www.latimes.com/news/local/la-me-lost-time4-2010mar04,0,6102901.story

When a magnitude 8.8 earthquake struck South America last weekend, the ground rumbled in Chile, the sea rose in the Pacific, and a day on Earth got shorter. Not by much.

Earthlings ended up losing 1.26 microseconds of a day. You can’t sense it. Nor is your dog aware of it. It will take another 2,174 years before we need reset our clocks by 1 second

The thrust-fault quake — in which plates under the Earth’s surface moved vertically — caused mass to be redistributed, said geophysicist Richard Gross, who works at the Jet Propulsion Laboratory in La Cañada Flintridge. “On average, the mass of the Earth got a bit closer to the rotation axis,” he said. As a result, Gross said, the planet rotates faster — “just like a spinning skater brings her arms in closer to her body to rotate faster.” When the planet rotates faster, the day shortens, he said.

Although the Chilean quake shortened the day by 1.26 microseconds, the 2004 Indian Ocean earthquake that triggered the catastrophic Asian tsunami shaved 7 microseconds off the day, according to Gross’ calculations.

Far from evoking that textbook illustration of a smooth round ball of continents and blue oceans, Gross describes Earth as a planet of unevenly distributed mass wobbling as it rotates, imperfectly balanced, around its axis, its physique woefully pear-shaped. “It’s a bit fatter south of the Equator,” Gross said.

“The Earth is not completely elastic. It’s kind of like putty,” he said. “If you have a sudden shock to it, it will continue to deform later in response to that shock.”

carla.hall@latimes.com

Copyright © 2010, The Los Angeles Times

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