Days a bit shorter since Chile quake

Weeks after the Feb. 27 earthquake hit Chile, a blackout affected millions of residents Sunday. The country is trying to recover from the 8.8-magnitude earthquake that rocked the country last month and caused a tsunami that damaged the country's coastal region and put other countries throughout the Pacific on alert. Strong aftershocks hit the country March 5 and again March 11.
By Associated Press
Wednesday, March 3, 2010

NEW YORK -- Earth's days may have gotten a little bit shorter since the massive earthquake in Chile, but don't feel bad if you haven't noticed.

The difference is just about one-millionth of a second.

Richard Gross, a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and colleagues calculated that Saturday's quake shortened the day by 1.26 microseconds. A microsecond is one-millionth of a second.

The length of a day is the time it takes for the planet to complete one rotation -- 86,400 seconds or 24 hours.

An earthquake can make Earth rotate faster by nudging some of its mass closer to the planet's axis, just as ice skaters can speed up their spins by pulling in their arms. Conversely, a quake can slow the rotation and lengthen the day if it redistributes mass away from that axis, Gross said Tuesday.

Gross said the calculated changes in the length of the day are permanent. So a bunch of big quakes could add up to make the day shorter, "but these changes are very, very small." So small, in fact, that scientists can't record them directly. Gross said actual observations of the length of the day are accurate to five-millionths of a second. His estimate of the effect of the Chile quake is less than a quarter of that span.

"I'll certainly look at the observations when they come in," Gross said, but "I doubt I'll see anything."

© 2010 The Washington Post Company