Japan Earthquake Shortened Days

Japan Earthquake Shortened Days

Day on Earth is shortened by 1.8 microseconds, by the 2011 Japan earthquake.

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The magnitude 9.0 earthquake that struck Japan was powerful enough to shorten Earth's day by 1.8 microseconds and throw an extra 6.7 inches (17 centimeters) into the planet's wobble, scientists say.

Data from high-precision GPS instruments show that parts of Japan shifted by as much as 13 feet (4 meters) as the fault plates lurched due to the earthquake. This allowed scientists to calculate how much Earth's overall mass distribution had shifted and thus how much wobble was affected.

The shifting mass also affected the planet's spin rate, according to geophysicist Richard Gross, of NASA's Jet Propulsion Laboratory in Pasadena, California. He compares what happened to a figure skater pulling her arms closer to her body, causing her to spin faster.

Because Earth is big, the effect is tiny—a microsecond is only a millionth of a second. For most of us, Gross said, "it has no real practical consequence."

Researchers are more intrigued by the change in Earth's wobble, which could inform future space missions, and the data collected on small earthquakes leading up to the main event, which may help with earthquake prediction.

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