Earth Still Vibrating Weeks After Tsunami Quake

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MELBOURNE (Jan. 9) - 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 150,000 lives.

 

McQueen said the oscillation was fading and at current levels equated

to about a millimeter 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, theorized that a shift of mass towards the Earth's

center during the quake caused the planet to spin three millionths of

a second faster and tilt about 2.5 centimeters on its axis.

 

The geologic circumstances that set up one of the worst natural

disasters in a century were much longer in the making. How long?

 

Try 300 million years. Maybe twice that long.

 

Once, scientists believe, all the Earth's continents were combined in

a single gigantic land mass they call Pangea. But geological forces

caused it to break apart; and ever since then, the pieces, which

scientists call plates, have been drifting across the planet at an

average rate of a few inches a century.

 

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