Earth is still ringing from quake (Forwarded)

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Saturday, 8 January 2005

Earth is still ringing from quake

Almost two weeks after the earthquake and ensuing tsunami that devastated huge
areas of Asia, the Earth is still ringing like a bell, according to ANU scientists.

Dr Herb McQueen, from the Research School of Earth Sciences, operates a gravity
meter at Mt Stromlo Observatory and is still recording vibrations generated by
the Boxing Day earthquake.

"The main signal we now see is a steady oscillation of a few parts in 10 billion
of normal gravity, which corresponds to about a millimetre of vertical motion of
the Earth," Dr McQueen said.

"The early signals were much stronger. The Earth is regularly deformed by the
daily passage of the Sun and Moon, raising a tide in the Earth of about 20
centimetres, and the vibrations we saw on Boxing Day shortly after the
earthquake off the Indonesian coast were of a similar magnitude on our instruments.

"This is a relatively rare seismic event, which could still be making the Earth
reverberate for another couple of weeks."

The Superconducting Gravimeter is Australia's most sensitive gravity measuring
instrument and is located at Mt Stromlo Observatory. It relies on the exotic
superconducting properties of metals at extremely low temperatures to detect
faint changes in gravity caused by tides and major earthquakes. These signals
are used to map the structure of the interior of the Earth.

Charts produced by the gravimeter tracking the motion of the Earth can be viewed
online at:
http://www.rses.anu.edu.au/geodynamics/SG

Chart 2 shows the day of the quake, while chart 4 was photographed on the night
of Thursday 6 January 2005.