Water helps trigger New Zealand's quakes

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Sydney, August 6 (ANI): A new research has given the clearest picture yet of the role of water in helping to trigger earthquakes in New Zealand.

According to a report by ABC News, the research was carried out by geophysicist Grant Caldwell of GNS Science in Wellington and colleagues.

The researchers used a new method for studying the processes that lead up to and cause large earthquakes.

The method, called magnetotellurics, probes earthquake zones using naturally occurring low-frequency electromagnetic waves generated by solar activity and lightning storms.

Caldwell and colleagues were able to determine how water is moving and concentrating below fault zones in the northern part of New Zealand's South Island, where the Pacific Plate slides underneath the Australian Plate.

Some geologists have long suspected that water plays a role in triggering earthquakes, but getting evidence has not always been so easy.

Caldwell and colleagues used magnetotellurics to obtain a picture of what was happening down to 100 kilometers below the earth's surface.

Electromagnetic waves penetrate the earth's surface and bounce off rocks, providing information about the electrical conductivity of rocks.

The more water rocks contain, the more conductive they are and the more they reflect the waves.

By measuring the conductivity of rocks, Caldwell and colleagues could determine where water was being concentrated.

About 70 kilometers below the surface of the subduction zone, high temperature and pressure causes water to be released from rocks of the Pacific Plate, according to Caldwell.

The water rises up and collects in cooler rocks that sit further up, on the Australian Plate, around 15 kilometers below the surface at the subduction zone.

Caldwell and colleagues found clusters of conductive (water-containing) rocks sitting just below fault lines.

"The earthquakes happen just above where the water is being concentrated," said Caldwell.

According to Caldwell, scientists believe pressure of water building up beneath the fault can get so great it can cause it to rupture, leading to an earthquake.

"The addition of water into the base of the fault makes it easier for the fault to fail," said Caldwell.

The area studied is equivalent to California's San Andreas fault system.

Geologist Professor Dave Craw, of the University of Otago describes the work as "a huge contribution to our understanding of tectonic processes at the plate boundary".

"We usually have to make guesses about fluids at depth, but this work shows where the fluid is generated, where it migrates to, and gives us an idea of how much fluid there is," said Craw. (ANI)

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