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.