Quake shortened Earth's daysBy Simon Lauder
Scientists say the Chilean earthquake was strong enough shift the Earth on its axis and make each day a fraction shorter.
Early analysis by NASA shows the axis of the Earth should have moved by about eight centimetres after the Chile earthquake.
But Dr David Kerridge from the British Geological Survey says only experts will notice the change.
"It's nothing that's going to affect anybody in daily life, but it's something that just follows from the daily physics of how rotating objects behave," he said.
He says the quake was strong enough to alter the distribution of the earth's mass and therefore speed up the rotation of the planet.
"The Oceanic plates and Nazca plate was pushing and has been thrust down underneath the South American plate. So the South American plate would have been flexed downwards," he said.
"The probability is that when the flexing downwards is released and the South American plate would have moved up, so that would have moved mass further away from the rotation axis and that would be the cause of the change."
He says people can understand how the shift speeds up the earth's rotation if you imagine an ice skater spinning on an axis that runs from her head to her toes.
"When she puts her arms out, then she rotates quite slowly. When she brings her arms in, she begins to rotate much faster," he said.
"That's because she is decreasing her moment of inertia by bringing in her arms, by bringing the mass closer to the rotation axis. But angular momentum stays the same, which means rotation rate increases.
"Here it's the same kind of effect, but a very, very tiny one given the huge mass of the earth and the very small changes that have been made at the surface."
NASA geophysicist Richard Gross has told the Bloomberg newsagency the quake sped up the rotation of the earth enough to shorten the day by an estimated 1.26 millionths of a second.
The same model showed the 2004 Sumatra quake, which generated the Indian Ocean tsunami, should have shortened each day by 6.8 microseconds.
http://www.abc.net.au/news/stories/2010/03/03/2835090.htm?section=justin