Quake shook Earth to core, say scientists

The quake that set off the devastating tsunami literally shook the Earth to its core, scientists believe, accelerating its rotation and shortening days by a fraction of a second. It may be necessary to add a "leap second" in years to come in order to correct the change.

Meanwhile, experts said the quake, which measured 9.0 on the Richter scale, may have shifted some small islands in the region by more than 30 metres.

Richard Gross, a geophysicist with Nasa's jet propulsion laboratory in California, said he believed a shift of mass towards the Earth's centre caused the planet to spin three microseconds - one millionth of a second - faster. It also caused the planet to tilt around 2.5cm on its axis.

"[The forcing of one tectonic plate beneath the edge of another] had the effect of making the Earth more compact and spinning faster," he said, saying that the changes were too slight to be detected by global positioning satellite networks.

Mr Gross said the circular path of the Earth's poles normally varied by up to 10 metres. As a result, an added wobble of a few centimetres was unlikely to have any long-term effects. "The rotation is not actually that precise. The Earth does slow down and change its rate of rotation," he said. When the tiny variations accumulate, planetary scientists must add a "leap second" to the end of a year, something that has not been done in many years.

Geologists said changes on the Earth's surface were more noticeable, shifting the island of Sumatra 36 metres to the south-west. Ken Hudnutt of the US Geological Survey said: "Some of the smaller islands off the south-west coast of Sumatra may have moved to the south-west by about 20 metres."

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