Quake Might Have Shortened Length of Day

We won't notice, but JPL's computers might

By Jonathan Lloyd
|  Tuesday, Mar 2, 2010  |  Updated 5:18 PM PDT
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The length of a day might have been shortened by Saturday's earthquake in Chile, according to a geophysicist at Jet Propulsion Laboratory in Pasadena. But it's unlikely you'll miss that 1.26 millionth of a second.

Richard Gross and colleagues calculated that the quake shortened the length of a day -- every day, not just the day on which the quake occurred -- by 1.26 microseconds (0.00000126 seconds).
 
That's because the magnitude-8.8 quake probably shifted the Earth's axis, Gross said. An earthquake can move some of the earth's mass closer to its axis, which makes the planet rotate faster.

For example, skaters increase their angular spin speed by clutching their arms to their torsos. Move the arms out, the speed is slowed.

"The length of the day should have gotten shorter by 1.26 microseconds (millionths of a second)," Gross said Monday in an e-mailed reply to questions from Business Week. "The axis about which the Earth’s mass is balanced should have moved by 2.7 milliarcseconds (about 8 centimeters or 3 inches)."

In 2004, the magnitude-9.1 Sumatran quake that triggered an Indian Ocean tsunami shifted the axis by about 2.3 milliarcseconds, Gross said. That shortened the day by 6.8 microseconds.
 

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