Japan Earthquake Shortened Days, Increased Earth's Wobble
The magnitude 9.0 earthquake that struck Japan last Friday was powerful enough to shorten Earth's day by 1.8 microseconds, scientists say.
That doesn't mean shockwaves from the event somehow knocked Earth off its north-south axis, around which the planet revolves.
Instead the quake shifted what's called Earth's figure axis, an imaginary line around which the world's mass is balanced, about 33 feet (10 meters) from the north-south axis.
Earth naturally wobbles slightly as it spins, because shifting surface mass such as melting glaciers and moving ocean currents can throw the planet off balance.
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