Chile quake shifted Earth axis to shorten length of a day, says NASA

Washington, March 3 (ANI): NASA has announced that the February 27 Chile earthquake was so powerful that it likely shifted an Earth axis and shortened the length of a day.

According to a report in National Geographic News, the estimate is based on new computer-model calculations by geophysicist Richard Gross of NASA's Jet Propulsion Laboratory in California.

By speeding up Earth's rotation, the magnitude 8.8 earthquake-the fifth strongest ever recorded, according to the USGS-should have shortened an Earth day by 1.26 millionths of a second.

For comparison, the same model estimated that the magnitude 9 Sumatra earthquake in December 2004 shortened the length of a day by 6.8 millionths of a second.

Gross also estimates that the Chile earthquake shifted Earth's figure axis by about three inches (eight centimeters).

Deviating roughly 33 feet (10 meters) from the north-south axis around which Earth revolves, the figure axis is the imaginary line around which the world's unevenly distributed mass is balanced.

To explain how the Chile earthquake gave Earth a bit of a turbo boost, Keith Sverdrup, a seismologist at the University of Wisconsin-Milwaukee, who wasn't involved in the NASA calculation, turned to the image of a spinning figure skater.

"As she pulls her arms in, she starts rotating faster, he said.

Likewise, as a portion of Earth's mass drew in ever so slightly and quickly during the Chile earthquake, the planet began spinning a bit quicker.

The Chilean quake was a so-called thrust earthquake, which occurs when a large section of the Earth's surface-in this case, the Nasca tectonic plate-dives beneath an adjacent plate.

This process, called subduction, can cause earthquakes and volcanic eruptions.

"The layer of rock on the (Nasca plate) dove down into the Earth's interior, and that's like the skater pulling her arms in toward her body," Sverdrup said.

Only thrust earthquakes, with their inward motion, can shorten Earth days.

Other types of earthquakes, such as horizontal strike-slip quakes, in which two plates slide horizontally past one another, don't affect Earth's rotation.

Currently, scientists can measure the length of an Earth day with an accuracy of only about 20 millionths of a second, so the shortened day caused by the Chile earthquake can be estimated but not measured.

But "that doesn't mean that the effect isn't real," Sverdrup said.

The shortening of Earth's day caused by the Chilean earthquake won't be permanent, although exact duration of the effect can't be measured. (ANI)