Earthquake changed rotation of the Earth

Thursday, December 30th, 2004

Roger Highfield

LONDON — The earthquake that spawned such destruction around the Indian Ocean also made the Earth wobble on its axis by an inch or so, altered regional geography by a few metres and cut the length of the day by a few millionths of a second.

It struck where one plate corresponding to the Indian Ocean floor is being pushed under another, Eurasia, along a long fault line known as a subduction zone. At the fault, which stretches from the seabed to a few miles beneath the ocean floor, the two plates slipped violently and abruptly over a 1,000-kilometre stretch.

Calculations completed at the California Institute of Techonology show the 9.0-magnitude quake may have caused movement around the fault by 20-30 metres, said Dr. Ken Hudnut of the U.S. Geological Survey. “That is a lot of slip, he added.”

In turn, this will affect the local geography, notably subsidence that led to inundation along the coastline.

“That earthquake has changed the map,” he said. “It is the permanent vertical movement along the coastline that may have had a serious human impact in this case, in that some harbours and port facilities may have been raised, lowered, or damaged such that they cannot readily be used in relief efforts.”

He added: “The small islands that lie off the coast of Sumatra itself, such as Simeulue, and even possibly the Nicobar and Andaman Islands, may have moved by several tens of centimetres up to possibly several metres.”

Dr. Ben Chao of NASA’s Goddard Space Flight Centre, said one calculation suggested the quake would cut the length of day of three millionths of a second and cause a pole shift of around an inch.

© The Vancouver Sun 2004

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