智利地震：地震对地轴的影响

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）发生的地震可能已经使地球的轴线发生了偏移，从而使一天变短

美国宇航局的科学家说，星期六发生于智利的地震可能已经转移了地球的轴线，会使一天变短。加州帕萨迪纳的美国宇航局喷气推进实验室的地球物理学家理查德格罗斯表示，8.8级地震可以将地轴推移2.7毫弧秒（约8厘米） - 足够将一天缩短约1.26微秒。 大地震可以移动大量的岩石并改变行星上质量的分布。这种分布的变化，可以改变行星的旋转速度，从而改变一天的长度。 “一天的长度应该缩短了1.26微秒”，格罗斯告诉彭博新闻社“地球质量的平衡轴应该移动了2.7毫弧秒。” 格罗斯以前曾用此技术估计了2004年引起印度洋海啸的苏门答腊地震所造成的位移。那次的9.1级地震使地轴转移了2.3毫弧秒，将一天缩短了6.8微秒。 英国地质调查局地震学家大卫克里奇说，智利和苏门答腊的地震都是因为一个板块俯冲到另一个板块下面，使得地球的整体质量重新分配。其效果就像是一个冰上舞蹈家伸出或收回胳膊来加速或减慢旋转的速度一样。“滑冰者在绕滑时会伸出胳膊，当她收回胳膊时，她就会滑地越来越快。同样道理，地球旋转时，如果你改变了质量的分布，旋转的速度就会变化。”由于板块间的滑移导致的地震，例如最近发生在海地的地震，不会对地球自转产生这种影响。 格罗斯说，因为智利离赤道更远，所以智利地震对地轴造成的偏移比苏门答腊大地震更大。引起智利地震的板块俯冲深入地球的角度较大，这就意味着它造成的质量转移也较大。