Chilean Quake May Have Shortened Earth Days
Every year the earth’s rotation slows a bit and so we have to add a second to our time keeping once in a while to keep it in sync with the old rock. Large earthquakes like the devastating tremor last week in Chile, or the Sumatran quake that triggered the massive tsunami 0f 2004 can move huge amounts of rock a bit closer to the axis of the earth. That results in an increase in speed of the earth’s rotation, NASA says:
JPL research scientist Richard Gross computed how Earth’s rotation should have changed as a result of the Feb. 27 quake. Using a complex model, he and fellow scientists came up with a preliminary calculation that the quake should have shortened the length of an Earth day by about 1.26 microseconds (a microsecond is one millionth of a second).
Perhaps more impressive is how much the quake shifted Earth’s axis. Gross calculates the quake should have moved Earth’s figure axis (the axis about which Earth’s mass is balanced) by 2.7 milliarcseconds (about 8 centimeters, or 3 inches). Earth’s figure axis is not the same as its north-south axis; they are offset by about 10 meters (about 33 feet).