The Earth 'wobbled on its axis by about an inch'

The earthquake 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.

"That earthquake has changed the map," said Dr Ken Hudnut of the US Geological Survey.

According to calculations by Dr Chen Ji at Caltech, the 9.0-magnitude quake may have caused movement around the fault by 20-30 metres.

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 1,000km stretch.

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

Hudnut, of the Southern California Earthquake Hazards Assessment Project, said the energy released as the two sides of the fault slipped against each other made the Earth wobble on its axis, he said. "A piece of the Earth's crust is in a different place, though relative to the mass of the Earth it is tiny and the effects, though potentially just barely observable, will be small."

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

Another USGS research geophysicist, Dr Stuart Sipkin, agreed that the Earth would have received a "little jog", but said the islands off Sumatra would have been moved higher by the quake.

Other changes include places like Hambantota, in Sri Lanka, for instance that do not exist anymore.