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Opinion, arguments & analyses from the editors of Scientific American

How the earthquake in Chile could change Earth's axis

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chile earthquake shorten days change earth axis rotationThe magnitude 8.8 earthquake that jolted Chile on Saturday was felt as far away as São Paulo. But NASA scientists are proposing that its repercussions are truly global in a geophysical sense: it likely shifted Earth's axis by about eight centimeters.


Such a shift would have the effect of shaking as much as 1.26 microseconds off of Earth's daily rotation, noted NASA Jet Propulsion Laboratory scientist Richard Gross in an agency release.


Those microseconds (each one millionth of a second) might not sound like a lot, and they probably will not change your sleep patterns or birthday, but they do accumulate. And, as such, the change will be permanent, over the decades and eons, it will eventually amount to a trickle of "lost" time. (If the scientists' early estimates are on target, this quake's impact, however, will take about 130,500 years to shear off a full minute.)


But with such a fine scale (microseconds and centimeters) working on such a big mass (Earth), how can scientists calculate these details? Gross spoke with Scientific American in January 2005 to explain the concept following the then-recent undersea earthquake that caused the Indian Ocean tsunami.


Put simply, "It's what we call the ice-skater effect," David Kerridge, head of Earth hazards and systems at the British Geological Survey in Edinburgh, told Bloomberg News. "When she's going around in a circle, and she pulls her arms in, she gets faster and faster. It's the same idea with the Earth going around if you change the distribution of mass, the rotation rate changes."


This shift is hardly a one-time occurrence, however. "Any worldly event that involves the movement of mass affects the Earth's rotation," said Benjamin Fong Chao of NASA's Goddard Space Flight Center in Greenbelt, Md., in 2005, CNN reported.


If all of this change was from a magnitude 8.8 quake, could a bigger event shift the planet's rotation even more? Yes, the NASA scientists reported. A larger event, however, doesn't automatically translate into a bigger effect. The magnitude 9.1 Sumatra earthquake in 2004 is one such example. It was closer to the equator and occurred on a fault that has a shallower angle into Earth's crust, both of which contributed to it having less of an impact on Earth's axis despite its greater immediate magnitude. That the Chile fault runs at a steep angle and is located mid-hemisphere means that movement there throws more weight around as the world turns.


But, as Gross noted in his Scientific American interview, the massive shifts of Earth's plates have far less of an influence on the axis than even the breeze. "Changes in winds have by far the greatest effect on the length of the day: their effect is actually about 300 times larger."


Image of South America from space courtesy of Wikimedia Commons/NASA/JPL

The views expressed are those of the author and are not necessarily those of Scientific American.

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