Quake may have shifted Earth's axis, shortened day

The 8.8-magnitude earthquake that struck Chile on Feb. 27 was so powerful it may have tipped Earth's axis and shortened the length of a day, scientists at NASA say.

According to NASA, a complex computer model's preliminary calculation shows that Earth's days should have shortened by 1.26 microseconds (a microsecond is a one millionth of a second).

A large quake shifts enough rock to redistribute the mass of the planet, which can speed its rotation.

The change won't be noticed in day-to-day life, but is permanent.

NASA scientist Richard Gross also calculated that the quake moved Earth's figure axis (the axis about which Earth's mass is balanced) by about eight centimetres.

The figure axis is not the same as the Earth's north-south axis, of which the Earth rotates around once a day at about 1,600 kilometres. The figure axis is offset from the north-south axis by about 10 metres.

Using the same model, NASA says the devastating 9.1 magnitude quake in the Indian Ocean in 2004 shortened the day by 6.8 microseconds and shifted the axis by seven centimetres.

NASA says there are two reasons the Chile quake may have affected the figure axis more than the 2004 quake.

The Chile quake was located further away from the equator, making it more effective in affecting the figure axis.

Secondly, the fault responsible for the Chile earthquake is at a steeper angle than the fault in the 2004 earthquake. This moves Earth's mass vertically more effectively, making it more effective in shifting Earth's figure axis.

Scientists compare this to a figure skater's spin. As a figure skater goes into a spin and pulls her arms in, it speeds up her rotations.

Gross said the numbers were preliminary and may change as more information becomes available.

At least 723 people died in the Chilean quake. More than half a million houses were damaged or destroyed.

(From ctv.ca)

The NASA news article can be found here.