智利地震：地震對地軸的影響

Chile earthquake: Shock effect on Earth's axis

The earthquake that struck Chile on Saturday may have shifted the Earth's axis and created shorter days

David Adam guardian.co.uk, Tuesday 2 March 2010 23.58 GMT

The earthquake that struck Chile on Saturday may have shifted the Earth's axis and created shorter days, according to scientists at Nasa. Richard Gross, a geophysicist at Nasa's Jet Propulsion Laboratory in Pasadena, California, said the 8.8 magnitude quake could have moved the Earth's axis by 2.7 milliarcseconds (about 8cm) – enough to shorten a day by about 1.26 microseconds. A large quake can shift huge amounts of rock and alter the distribution of mass on the planet. When that distribution changes, it changes the rate at which the planet rotates, which determines the length of a day. "The length of the day should have got shorter by 1.26 microseconds," Gross told the Bloomberg news agency. "The axis about which the Earth's mass is balanced should have moved by 2.7 milliarcseconds." Gross previously used the technique to estimate the shift caused by the 2004 Sumatran quake that caused the Indian Ocean tsunami. That 9.1 magnitude quake shifted the Earth's axis by 2.3 milliarcseconds and shortened a day by 6.8 microseconds. David Kerridge, a seismologist with the British Geological Survey, said the Chile and Sumatra earthquakes were based on subduction, in which one tectonic plate slides under another, redistributing the Earth's overall mass. The effect was similar to that for an ice dancer who moved their arms in and out to accelerate and slow their spin. "As the ice skater puts 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." Earthquakes caused by plates sliding past each other, such as the recent event in Haiti, do not have the same impact on the Earth's rotation. Gross said the Chilean earthquake shifted the Earth's axis a greater distance than the larger Sumatran event because it was further from the equator. The fault that caused the Chilean quake also dips into the Earth at a steeper angle, which meant it moved more mass.

智利星期六（2010.02.27）發(fā)生的地震可能已經(jīng)使地球的軸線發(fā)生了偏移，從而使一天變短

美國宇航局的科學家說，星期六發(fā)生于智利的地震可能已經(jīng)轉移了地球的軸線，會使一天變短。加州帕薩迪納的美國宇航局噴氣推進實驗室的地球物理學家理查德格羅斯表示，8.8級地震可以將地軸推移2.7毫弧秒（約8厘米） - 足夠將一天縮短約1.26微秒。 大地震可以移動大量的巖石并改變行星上質量的分布。這種分布的變化，可以改變行星的旋轉速度，從而改變一天的長度。 “一天的長度應該縮短了1.26微秒”，格羅斯告訴彭博新聞社“地球質量的平衡軸應該移動了2.7毫弧秒。” 格羅斯以前曾用此技術估計了2004年引起印度洋海嘯的蘇門答臘地震所造成的位移。那次的9.1級地震使地軸轉移了2.3毫弧秒，將一天縮短了6.8微秒。 英國地質調(diào)查局地震學家大衛(wèi)克里奇說，智利和蘇門答臘的地震都是因為一個板塊俯沖到另一個板塊下面，使得地球的整體質量重新分配。其效果就像是一個冰上舞蹈家伸出或收回胳膊來加速或減慢旋轉的速度一樣。“滑冰者在繞滑時會伸出胳膊，當她收回胳膊時，她就會滑地越來越快。同樣道理，地球旋轉時，如果你改變了質量的分布，旋轉的速度就會變化。”由于板塊間的滑移導致的地震，例如最近發(fā)生在海地的地震，不會對地球自轉產(chǎn)生這種影響。 格羅斯說，因為智利離赤道更遠，所以智利地震對地軸造成的偏移比蘇門答臘大地震更大。引起智利地震的板塊俯沖深入地球的角度較大，這就意味著它造成的質量轉移也較大。