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The Earth will continue to oscillate for over three months after the earthquake and tsunami that devastated huge areas of Asia, an ANU earth scientist has predicted.
 Dr Herb McQueen, from the Research School of Earth Sciences, operates a gravity meter underground at Mt Stromlo Observatory. Known as a Superconducting Gravimeter, it’s capable of detecting minute variations in the strength of the Earth’s surface gravity.
Since the earthquake that caused the tsunami on Boxing Day 2004, the facility and others around the world have been monitoring vibrations of the whole Earth with a surface movement of up to a tenth of a millimetre.
“The main signal we now see, the so called ‘breathing mode’ in which the Earth uniformly expands and contracts very slightly, is producing a steady oscillation of a few parts in a hundred billion of normal gravity. While this sounds minute it is well within the range of our instruments.
“This mode is not strongly damped by internal friction, so it persists longer than others and our extrapolation of its present decay tells us that it will still be detectable in early April.
“The early signals were much stronger. A surface wave in the solid earth about a centimetre high circled the planet several times in the hours following the earthquake. The ground acceleration caused by this wave swamped the daily tidal signals we usually observe on the gravity record.”
The gravity meter was one of the few instruments to escape destruction in the bushfires of January 2003.
It operates 24 hours a day, seven days a week.
“We lost power during the fire which put it out of action for a few weeks, and there was a lot of smoke damage requiring a major cleanup, but we had it working again within two months.”
Operated in collaboration with the National Astronomical Observatory in Japan, the Superconducting Gravimeter is Australia’s most sensitive gravity measuring instrument.
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.
The gravity meter is extremely stable over long periods, making it ideal for tidal and longer period observations.
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