NASA Mar 15, 2011 :
Japan quake shortened Earth’s day, shifted axis
The 9.0 magnitude earthquake that ravaged Japan also shortened Earth's day by just over one-millionth of a second (1.8 microseconds to be exact), according to NASA. It also shifted the Earth's axis by about 6.5 inches.
By changing the distribution of the planet's mass, the quake likely caused the Earth to spin a tiny bit faster, says research scientist Richard Gross of NASA's Jet Propulsion Laboratory in Pasadena, Calif., thus shortening the time the planet takes to rotate each day.
The quake also shifted the position of the Earth's "figure" axis (which is different from the planet's north-south axis). This shift in Earth's figure axis will cause Earth to wobble a bit differently as it rotates, but it won't cause a shift of the Earth's axis in space -- only external forces such as the gravitational attraction of the sun, moon and planets could do that.
Gross says a change in Earth's mass and rotation isn't cause for alarm, and isn't unusual:
"Earth's rotation changes all the time as a result of not only earthquakes, but also the much larger effects of changes in atmospheric winds and oceanic currents," he says. "Over the course of a year, the length of the day increases and decreases by about a millisecond, or about 550 times larger than the change caused by the Japanese earthquake.
"The position of Earth's figure axis also changes all the time, by about 3.3 feet over the course of a year, or about six times more than the change that should have been caused by the Japan quake."
Gross said the changes in Earth's rotation and figure axis caused by earthquakes should not have any impacts on our daily lives. "These changes in Earth's rotation are perfectly natural and happen all the time," he says. "People shouldn't worry about them."
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