From Newsday [via Preposterous Universe]:
Major earthquakes can change the rate of Earth’s rotation, scientists said yesterday, but it’s not yet clear if the 9.0 quake actually did so – and, if so, by how much.
If the rotation rate was changed, it was by less than three microseconds, said gravity expert Richard Gross of the Jet Propulsion Laboratory in Pasadena, Calif. A microsecond is one millionth of a second.
“We won’t know for weeks,” said geophysicist Thomas Herring of the Massachusetts Institute of Technology. “The most accurate measurements will take about three weeks to get all of the data processed. So it’s a guess, as of now.”