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Thursday, 6 August 2009.
Press Release: Science Media Centre.
Water deep below fault zones helps generate quakes
- Geological research from New Zealand published today in the prestigious journal Nature highlights the crucial role of underground water in triggering powerful earthquakes.
New Zealand is perched precariously on a major tectonic boundary, where the Pacific and Australian plates collide. The subduction zone beneath the South Island, formed as one plate dives beneath the other, is one of the youngest on the planet, and it is one of the few places where this process can be studied on land.
The new paper, from an international team including New Zealand researchers from GNS Science, examines 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.
Paper co-authors Grant Caldwell and Hugh Bibby of GNS Science comment:
"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 electromagnetic waves produced by solar activity and world-wide 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 localized 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 (e.g. 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."