Earthquakes Change the Earth

The March 11, magnitude 9.0 earthquake in Japan may have shortened the length of each Earth day and shifted its axis. Using a United States Geological Survey estimate for how the fault responsible for the earthquake slipped, research scientist Richard Gross of NASA's Jet Propulsion Laboratory, Pasadena, Calif., applied a complex model to perform a preliminary theoretical calculation of how the Japan earthquake-the fifth largest since 1900-affected Earth's rotation. His calculations indicate that by changing the distribution of Earth's mass, the Japanese earthquake should have caused Earth to rotate a bit faster, shortening the length of the day by about 1.8 microseconds (a microsecond is one millionth of a second). There are about 86,400 seconds (86 billion microseconds) in a day, so the impact of the earthquake is quite small. The calculations also show the Japan quake should have shifted the position of Earth's figure axis (the axis about which Earth's mass is balanced) by about 6.5 inches, towards 133 degrees east longitude. The Earth's figure axis is not the same as its north-south axis in space, which it spins around once every day at a speed of about 1,000 mph. The figure axis is the axis around which the Earth's mass is balanced.
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