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Underground water `triggers quakes`

Last Updated: Tuesday, August 11, 2009 - 13:07

Washington: Scientists have revealed
that underground water plays a key role in triggering powerful
earthquakes, an insight they claim could help seismologists to
save human lives.

An international team has examined the role of water
crushed out of the Earth`s crust deep below the surface in
triggering powerful earthquakes, changing the dynamics of the
fault and eventually causing volcanoes to form.

According to lead scientist Grant Caldwell of New
Zealand, "In actively deforming regions like New Zealand,
deformation will promote electrical inter-connection of any
fluid present in the rocks below the depth at which the rocks
are hot enough to become slightly ductile or soft.

"Thus localised ductile shear zones containing
small amounts of fluid will be conductive compared to their
surroundings. Measurements of the low frequency electro
magnetic waves produced by solar activity and worldwide
thunderstorm activity allow us to see electrically conductive
zones deep within the earth.

"A line of these measurements (known as
magnetotelluric or MT soundings) across the northern part of
the South Island show that localised zones of high electrical
conductivity occur about 15 km below some of the major faults
in Marlborough."

The results support the idea that the high
conductivity zones observed below major strike-slip faults in
New Zealand and elsewhere (eg the San Andreas Fault in
California) mark ductile shear zones.

"This provides information on the deformation
occurring beneath the part of the fault that breaks in large
earthquakes and insight into the mechanisms that ultimately
cause earthquakes," Caldwell said.

The findings are published in the `Nature` journal.

Bureau Report

First Published: Tuesday, August 11, 2009 - 13:07

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