Quake may have shifted Earth's axis, shortened day
 JPL research scientists concluded the quake shortened the length of an Earth day by about 1.26 microseconds (a microsecond is one millionth of a Updated: Tue Mar. 02 2010 21:26:21 Josh Visser, CTV.ca News Staff The 8.8-magnitude earthquake that struck Chile on Feb. 27 was so powerful it may have tipped Earth's axis and shortened the length of a day, scientists at NASA say. According to NASA, a complex computer model's preliminary calculation shows that Earth's days should have shortened by 1.26 microseconds (a microsecond is one millionth of a second). A large quake shifts enough rock to redistribute the mass of the planet, which can speed its rotation. The change won't be noticed in day-to-day life, but is permanent. NASA scientist Richard Gross also calculated that the quake moved Earth's figure axis (the axis about which Earth's mass is balanced) by about eight centimetres. The figure axis is not the same as Earth's north-south axis, of which the planet rotates around once a day at about 1,600 kilometres per hour. The figure axis is offset from the north-south axis by about 10 metres. Melissa Giovanni, a geology professor with the University of Calgary, told CTV.ca that an earthquake generally has to be at least 8-magnitude to have any recordable impact on Earth's axis. "The result of this particular earthquake, because it broke some a large piece of (Earth's) crust, it's actually moved part of the mass of the Earth," she said. "An earthquake of this size, I think it broke something like 400 kilometres of crust. That amount of crust moving all at once is changing the distribution of the mass of the Earth." She added that the Richter scale that measures earthquakes is a base-10 logarithmic scale, meaning the 8.8-magnitude earthquake in Chile was about 20 times larger than the 7.1-magnitude earthquake in Haiti in January. Using the same model, NASA says the devastating 9.1 magnitude quake in the Indian Ocean in 2004 shortened the day by 6.8 microseconds and shifted the axis by seven centimetres. NASA says there are two reasons the Chile quake may have affected the figure axis more than the 2004 quake. The Chile quake was located further away from the equator, making it more effective in affecting the figure axis. Secondly, the fault responsible for the Chile earthquake is at a steeper angle than the fault in the 2004 earthquake. This moves Earth's mass vertically more effectively, making it more effective in shifting Earth's figure axis. Scientists compare this to a figure skater's spin. As a figure skater goes into a spin and pulls her arms in, it speeds up her rotations. NASA notes that the Earth's day can be increased as well. Filling China's Three-Gorge reservoir, which could hold 40 cubic kilometers of water, would increase the day by 0.06 microseconds. Gross said the numbers were preliminary and may change as more information becomes available. At least 723 people died in the Chilean quake. More than half a million houses were damaged or destroyed. http://winnipeg.ctv.ca/servlet/an/local/CTVNews/20100302/quake_nasa_100302/20100302?hub=WinnipegHome |
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