Raised pressures below Mount Fuji mean active volcano is in a 'critical state say scientific researchers

The magnitude-9 tremor also increased the pressure on Mount Fuji. "Our work does not say that the volcano will start erupting, but it does show that it's in a critical state," says Florent Brenguier, a researcher at the Institute of Earth Sciences (IST) in Grenoble, France, and lead author of the publication, to which the Institute of Global Physics (IPG) in Paris also contributed.

Adopting a novel approach, the scientists carried out a sort of giant echo-scan of the bowels of the Earth, based on the huge mass of data recorded after the mega-quake by Japan's Hi-net system, the densest network in the world, with 800 seismic sensors. They focused on signals commonly known as seismic noise, the result of constant interaction between ocean swell and "solid" earth. In the past such data has generally been dismissed as background interference.

By recording fluctuations in this barely perceptible subterranean noise they were able to map geological disturbances in the bedrock of Japan caused by the seismic waves following the violent quake in March 2011. "Seismic waves travel a very long way, going round the world several times," Brenguier explains. "Their movement makes the Earth's crust vibrate, and rather like a shock wave this produces breaks or cracks in the rock."


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[link to www.theguardian.com]