NASA: Quake Shifted Earth's Axis, Shortened Day

(March 1) -- Apart from claiming the lives of hundreds of people and wreaking enormous property damage, Chile's massive earthquake has likely altered the distribution of the Earth's overall mass, scientists from NASA say.

As a result, the length of a day is now a little shorter than it was before Saturday's magnitude 8.8 earthquake.

"The length of the day should have gotten shorter by 1.26 microseconds [millionths of a second]," Richard Gross, a geophysicist at NASA's Jet Propulsion Laboratory, told Bloomberg. "The axis about which the Earth's mass is balanced should have moved by 2.7 milliarcseconds [about 8 centimeters or 3 inches]."

The speed that the Earth rotates also increased slightly in 2004 following the earthquake that struck off the coast of Sumatra, Indonesia. That 9.1 earthquake shortened the length of an Earth day by 6.8 microseconds, scientists say.

The reason is that sudden changes in the dimensions of the Earth's tectonic plates, like those experienced in the earthquakes in Chile and Indonesia, can alter the velocity.

David Kerridge, the head of Earth hazards and systems at the British Geological Survey in Edinburgh, likened the change in rotation speed to what happens when a figure skater draws her arms in close to her body while spinning. "As she pulls her arms in," Kerridge told Bloomberg, "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."