Two weeks on, the Earth is still vibrating from the massive undersea earthquake off Indonesia that triggered the tsunami, Australian researchers said on Sunday.
The Australian National University (ANU) said the reverberations were similar in form to the ringing of a bell, though without the sound, and were picked up by gravity monitoring instruments.
"These are not things that are going to throw you off your chair, but they are things that the kinds of instruments that are in place around the world can now routinely measure," said ANU Earth Sciences researcher Herb McQueen.
"It is certainly above the background level of vibrations that the earth is normally accustomed to experiencing."
The magnitude 9.0 earthquake, the strongest for 40 years, struck off the coast of Indonesia's Sumatra island on Dec. 26. The tsunami it generated claimed more than 156,000 lives.
McQueen said the oscillation was fading and at current levels equated to about a millimetre of vertical motion of the earth.
Immediately after the quake the oscillation was probably in the 20 to 30 cm motion range that is typically generated in the earth by the movements of the sun and moon.
"This particular earthquake because it was 10 times larger than most of the recent large earthquakes is continuing to reverberate," McQueen said.
"We can still see a steady signal of the earth vibrating as a result of that earthquake two weeks later. From what it looks like, it appears it will probably continue to oscillate for several more weeks."
The ANU's gravity meter is housed in a fireproof basement at the Mount Stromlo Observatory near the capital Canberra and is part of a global geodynamics project established after major earthquakes in the 1960s.
U.S. scientists said just after the quake that it may have permanently accelerated the Earth's rotation -- shortening days by a fraction of a second -- and caused the planet to wobble on its axis.
Richard Gross, a geophysicist with NASA's Jet Propulsion Laboratory in California, theorised that a shift of mass towards the Earth's centre during the quake caused the planet to spin three millionths of a second faster and tilt about 2.5 cm on its axis.