The Tohoku quake and Earth's rotation

A preliminary calculation by NASA geophysicist Richard Gross after the March 11, 2011 Tohoku earthquake estimated that the redistribution of mass could have shortened the day by about 1.8 microseconds and shifted Earth’s figure axis by about 17 cm. This was a model estimate, not a direct isolated measurement of the change after the quake. The number describes the event’s calculated effect; natural variations in day length are much larger.