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Changes in Earth's rotation by quake unharmful: NASA

(Xinhua)
Updated: 2011-03-15 10:40

LOS ANGELES - The changes in Earth's rotation and figure axis caused by Japan's 9-magnitude earthquake should not have any impacts on people's daily lives, NASA's Jet Propulsion Laboratory (JPL) said on Monday.

"These changes in Earth's rotation are perfectly natural and happen all the time," JPL scientist Richard Gross said in a press release.

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Using a US Geological Survey estimate for how the fault responsible for the earthquake slipped, Gross applied a complex model to perform a preliminary theoretical calculation of how the Japan earthquake affected Earth's rotation, according to the release.

His calculations indicate that by changing the distribution of Earth's mass, the Japanese earthquake should have caused Earth to rotate a bit faster, shortening the length of the day by about 1.8 microseconds (a microsecond is one millionth of a second).

The calculations also show the Japan quake should have shifted the position of Earth's figure axis (the axis about which Earth's mass is balanced) by about 17 centimeters (6.5 inches), towards 133 degrees east longitude, said JPL in Pasadena, Los Angeles.

This shift in Earth's figure axis will cause Earth to wobble a bit differently as it rotates, but it will not cause a shift of Earth's axis in space -- only external forces such as the gravitational attraction of the sun, moon and planets can do that, according to JPL.

Both calculations will likely change as data on the quake are further refined, JPL said.

"People shouldn't worry about them (the changes)," Gross said.

"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," Gross said.

"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 1 meter (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 that while scientists can measure the effects of the atmosphere and ocean on Earth's rotation, the effects of earthquakes, at least up until now, have been too small to measure.

The computed change in the length of day caused by earthquakes is much smaller than the accuracy with which scientists can currently measure changes in the length of the day, he said.

However, since the position of the figure axis can be measured to an accuracy of about 5 centimeters (2 inches), the estimated 17-centimeter shift in the figure axis from the Japan quake may actually be large enough to observe if scientists can adequately remove the larger effects of the atmosphere and ocean from the Earth rotation measurements, Gross added.