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Massive quakes can cause distant volcanoes to sink, research shows

AFP-JIJI

Massive earthquakes can cause distant volcanoes to sink, according to new research coming out of Japan and Chile.

The Great East Japan Earthquake, which had a magnitude of 9.0, caused subsidence of up to 15 cm in a string of volcanoes in Honshu as much as 200 km from its epicenter under the Pacific Ocean, according to a Japanese study published Sunday.

Meanwhile, the Maule quake in Chile in 2010, magnitude 8.8, caused a similar degree of sinking in five volcanic regions up to 220 km away, according to a U.S.-led research paper.

It is not clear whether the phenomenon boosted their chance of erupting, the authors wrote.

Both the Japan and Chile quakes were of the subduction type, caused when one part of the Earth’s crust slides beneath another.

If the movement is not smooth, tension can build up over decades or centuries before it is suddenly released, sometimes with catastrophic effect.

In both cases, the sinking occurred in mountain ranges running horizontally to the quake.

The Tohoku quake “caused east-west tension in eastern Japan,” Youichiro Takada of the Disaster Prevention Research Institute at Kyoto University said in an email.

“Hot and soft rocks beneath the volcanoes, with magma at the center, were horizontally stretched and vertically flattened. This deformation caused the volcanoes to subside,” Takada said.

The researchers for the Chilean volcanoes said subsidence occurred along a 400 km stretch.

As in Japan, the ground deformation in Chile occurred in huge ellipse-shaped divots up to 15 km by 30 km in size, although the cause appears to be different.

Pockets of hot hydrothermal fluids that underpinned the volcanic areas may have escaped via rock that had been stretched and made permeable by the quake.

Two earthquakes in the Chilean subduction zone in 1906 and 1960 were followed within a year by eruptions in the Andean southern volcanic zone.

However, no big eruptions in this volcanic hot spot have been associated with the 2010 temblor, according to the study led by Matthew Pritchard of Cornell University.

Takada said the impact of the Tohoku quake on volcano risk on Honshu was unclear.

“At this stage we do not know the relation between volcanic eruption and the subsidence we found. Further understanding of the magmatic movement would be necessary,” he said.