Shrinking Daylight

Daytime is now 2.68 microseconds shorter because of last month's tsunami.

The massive force unleashed by an earthquake off the coast of Indonesia altered the shape of Earth in a number of minute yet significant ways, NASA scientists have determined.
In data released this week, NASA determined that the Dec. 26 earthquake moved the North Pole, which constantly jiggles slightly, 2.5 centimeters--about an inch--in an eastward shift that is part of a long-term seismic shift.

Earth also became slightly more round, as the planet's oblateness, the quality of being flattish on top and bulging at the equator, decreased by a small amount. Further, daytime decreased by 2.68 microseconds because Earth now spins slightly faster on its axis. The phenomenon is similar to a figure skater in a twirl pulling his or her arms in slightly closer.

All earthquakes affect the shape of the planet, but the force of the recent tsunami-inducing quake--the fourth-largest recorded in 100 years--was particularly strong. Benjamin Chao of NASA's Goddard Space Flight Center compared the impact of the quake to the potential impact of the Three Gorges Dam project in China.

If filled, the massive gorge created by the dam would hold 40 cubic kilometers (10 trillion gallons) of water. That shift of mass would increase the length of a day by only 0.06 microseconds and make the Earth only very slightly more round in the middle and flat on the top. It would shift the pole position by about two centimeters (0.8 inches).
"Any worldly event that involves the movement of mass affects the Earth's rotation, from seasonal weather down to driving a car," Chao said in a statement.