The massive earthquake that struck northeast Japan Friday (March 11) has shortened the length Earth’s day by a fraction and shifted how the planet’s mass is distributed.A new analysis of the 8.9-magnitude earthquake in Japan has found that the intense temblor has accelerated Earth’s spin, shortening the length of the 24-hour day by 1.8 microseconds, according to geophysicist Richard Gross at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Gross refined his estimates of the Japan quake’s impact – which previously suggested a 1.6-microsecond shortening of the day – based on new data on how much the fault that triggered the earthquake slipped to redistribute the planet’s mass.
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A microsecond is a millionth of a second. “By changing the distribution of the Earth’s mass, the Japanese earthquake should have caused the Earth to rotate a bit faster, shortening the length of the day by about 1.8 microseconds,” told Gross. More refinements are possible as new information on the earthquake comes to light, he added. One Earth day is about 24 hours, or 86,400 seconds, long. Over the course of a year, its length varies by about one millisecond, or 1,000 microseconds, due to seasonal variations in the planet’s mass distribution such as the seasonal shift of the jet stream.