It may even have caused the planet to wobble on its axis, according to US scientists.
   
Richard Gross, a geophysicist with Nasa's Jet Propulsion Laboratory in California, theorised on Tuesday that a shift of mass towards the Earth's centre during the quake on Sunday has actually affected the planet.

It now spins three microseconds (millionth of a second) faster and has tilted about 2.5cm on its axis.
   
When one huge tectonic plate beneath the Indian Ocean was forced below the edge of another "it had the effect of making the Earth more compact and spinning faster", Gross said.
   
He said changes predicted by his model probably are too minuscule to be detected by a global positioning satellite network that routinely measures changes in Earth's spin, but said the data may reveal a slight wobble. 
   
Continual change

The Earth's poles travel in a circular path that normally varies by about 10m, so an added wobble of 0.025m is unlikely to cause long-term effects, the scientist said.
   
"That continual motion is just used to changing. The rotation is not actually that precise. The Earth does slow down and change its rate of rotation."
   
When those 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, Gross added.
   
Scientists have long theorised that changes on the Earth's surface such as tide and groundwater shifts and weather could affect its spin but they have not had precise measurements to prove it, Caltech seismologist Hiroo Kanamori said.
   
"Even for a very large event, the effect is very small," Kanamori said. "It's very difficult to change the rotation rate substantially."