Sumatra earthquake 'changed Earth's gravity'
Satellite data showing the gravity changes for the Sumatra-Andaman earthquake
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Friday, 04, Aug 2006 12:03
The earthquake which struck south-east Asia on Boxing Day, 2004, changed the Earth's surface and its gravity, according to a new study.
As well as the massive impact on human life in the region - nearly 230,000 people lost their lives and a further one million were displaced - new data from Nasa's two Grace (Gravity Recovery and Climate Experiment) satellites reveals that the 9.1 magnitude quake raised the seafloor in the region by several metres for thousands of square miles.
"The earthquake changed the gravity in that part of the world in two ways that we were able to detect," said Dr Shin-Chan Han, a research scientist in the school of Earth sciences at Ohio State University, in the August 3rd edition of the journal Science.
Firstly, the raising of the seafloor changed the geometry of the area and altered previous global positioning satellite (GPS) measurements from the areas.
Secondly, the density of the rock beneath the seafloor was changed, and an increase or decrease in density produces a notable gravity change, Dr Han said.
The results have been added to the latest seismic computer model, which Dr Han believes will "validate the quality of the model itself and therefore improve our knowledge about the Earth's dynamics".
Other findings from the Grace satellites, which have been orbiting the Earth since 2002, include the fact that the changing flow of the massive Mekong river affects gravity measurements for the area.
Dr Han added that the expansion of the current mission - dubbed Grace Two - might allow for the detection of major quakes (measuring between seven to 8.9 on the Richter scale), which occur frequently.