June 30, 2013

from PHYS Website





 


MA monitor displays the seismological chart of the earthquake

which hit Japan on March 11, 2011 at the

Geozentrum geological science center in Hanover, central Germany.

Massive earthquakes can cause distant volcanoes to sink,

according to research in Japan and Chile published on Sunday.




Massive earthquakes can cause distant volcanoes to sink, according to research in Japan and Chile published on Sunday.

The magnitude 9.0 tsunami-generating quake that occurred off northeastern Japan in 2011 caused subsidence of up to 15 centimeters (9.3 inches) in a string of volcanoes on the island of Honshu as much as 200 kilometers (120 miles) from the epicenter, a Japanese study said.

And the 8.8 magnitude Maule quake in Chile in 2010 caused a similar degree of sinking in five volcanic regions located up to 220km (130 miles) away, according to a US-led paper.

It was not clear whether the phenomenon boosted eruption risk, the authors wrote. Both the Japan and Chile quakes were of the subduction type, caused when one part of 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 2011 quake "caused east-west tension in eastern Japan," Youichiro Takada of the Disaster Prevention Research Institute at Kyoto University told AFP 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."

The researchers for the Chilean volcanoes said subsidence occurred along a stretch spanning 400km (250 miles).

As in Japan, the ground deformation in Chile occurred in huge ellipse-shaped divots up to 15km by 30km (nine miles by 18 miles) in size, although the cause appears to be different.

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

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

However, no big eruptions in this volcanic hotspot can be associated with the 2010 temblor, says the study led by Matthew Pritchard of Cornell University in New York.

Takada said the impact of the 2011 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.

The subsidence in Japan was spotted at the volcanoes,

  • Akitakoma, which last erupted in 1971

  • Kurikoma (1950)

  • Zao (1940)

  • Azuma (1977)

  • Nasu (1963)

The studies, published in the journal Nature Geoscience, used data from satellite radar which mapped terrain before and after the quakes.

 

 

 

More Information

 

 

 

 

 

 

 

 

 

Chilean Earthquake Made Volcanoes Sink

by Anne Ju

July 2, 2013

from CornellUniversity Website

 

 

 

The Nevado Chillan volcano in Chile,

one of five volcanoes that subsided following the Maule earthquake.

 

 

 

Following a major earthquake in southern Chile in 2010, several nearby volcanoes permanently sank several inches into the ground. Cornell earth scientists think they might know why - and this knowledge could help illuminate the connection between earthquakes and volcanic activity.

 

Publishing online June 30 in the journal Nature Geoscience, a study led by Matthew Pritchard, associate professor of earth and atmospheric sciences, shows that five volcanic regions within 248 miles of the 8.8-scale earthquake in Maule, Chile, sank up to 6 inches into the ground after the earthquake, almost instantly.

 

This process, called subsidence, has never been seen on this scale in volcanic regions and could lead to insights about the “plumbing systems” underneath volcanoes, Pritchard said.

 

Earth scientists have long known that earthquakes sometimes trigger volcanic eruptions.

“But in this case, there is strong evidence that earthquakes are also promoting some other kind of activity, which doesn’t lead to eruption in the volcanic region,” Pritchard said.

The Maule earthquake shared similar subsidence patterns with a 2011 earthquake in Tohoku, Japan, which earth scientists in Japan happened to be studying at around the same time.

 

After comparing notes at a conference, the two unrelated research groups came to “eerily” similar results, Pritchard said:

Both earthquakes seemed to induce subsidence around certain volcanic regions.

 

 

Provided/Matt Pritchard

A map of southern Chile shows the locations

of fault slip from the 2010 Maule earthquake.

Images from satellite radar show ground subsidence

 at five volcanic regions.

 

 

The Cornell researchers mapped the five distinct areas of subsidence following the Maule earthquake using radar imaging technology from a Japanese satellite.

 

They think the sinking was caused by the release of extremely hot water from below the earth’s surface, or geothermal fluids, that eventually flowed out of surface streams in the area.

 

In volcanic areas, magma chambers under the crust heat up mineral-rich pockets of water - a resource that geothermal energy companies are trying to tap.

 

Pritchard and colleagues contend that during the Maule earthquake, the mineral deposits were shaken loose, unclogging some pathways - like unclogging pipes in a house - which allowed a rush of water to gurgle to the surface, leading to the sinking.

 

Using the radar imaging technique called Interferometric Synthetic Aperture Radar, the researchers documented subtle ground deformations by reading changes in electromagnetic signals as they bounced back from the earth to the satellite.

 

They also used sensors for infrared imaging of heat anomalies, helping them rule out the theory of subsidence being the result of a release of hot gas.

 

They hope their insights will inspire other scientists to continuously monitor volcanic areas in earthquake zones to further study the relationship between them - particularly, whether the subsidence is somehow either stopping or enhancing volcanic eruptions, Pritchard said.

 

Also, they want to discover the parameters for triggering the subsidence:

  • How big does an earthquake have to be?

  • How far from the earthquake zone will a volcano have to be to sink?

The paper, “Subsidence at southern Andes volcanoes induced by the 2010 Maule, Chile earthquake,” includes co-authors Jennifer Jay and Scott Henderson, both graduate students with Pritchard’s group, as well as collaborators Felipe Aron, a Cornell graduate student from Chile, and Luis Lara of the National Geology and Mining Service of Chile.

 

The work was supported by NASA.