[ASC-media] Media Release: Earthquakes Have the Midas Touch
Guy Nolch, Australasian Science
science at control.com.au
Fri Apr 1 01:28:55 CEST 2011
For immediate release
Earthquakes Have the Midas Touch
Earthquakes are catastrophic events, but the stress changes they generate deep in the Earth mean they have not so much a silver lining, but a golden one.
Writing in the April edition of Australasian Science, published today, Dr Steven Micklethwaite of the University of Tasmania says that ancient earthquakes can be used to predict the locations of rich gold deposits – and that human-engineered earthquakes may even generate new deposits.
“Our planet is constantly under stress as its great tectonic plates grind past one another,” he writes. “It is the build up of these stresses that ultimately lead to an earthquake on a fault.”
Micklethwaite explains that earthquakes redistribute the Coulomb stress in a fault zone, and areas with greater Coulomb stress are more likely to experience aftershocks and future earthquakes.
“This idea was spectacularly verified in 1992, when a series of earthquakes hit southern California in the USA,” Micklethwaite explains. “Furthermore, each earthquake mainshock seemed to have influenced the location of the next earthquake mainshock.”
Micklethwaite decided to study the indirect influence that stress changes may have had on gold mineralisation, using fossil fault systems that are no longer active but were in the ancient past.
“The idea was a simple one. If we could calculate stress changes from earthquake events in the past, we could identify which portions of their fault damage were repeatedly activated, allowing the migration of crustal fluids.
“We found that regions of positive Coulomb stress change matched quite closely with existing gold deposits. In regions like the Mount Pleasant and St Ives goldfields in Western Australia or the Carlin goldfield in Nevada, USA, we not only matched known distributions of gold deposits but also gave predictions about where new gold deposits may be found.
“The results of our work seem to indicate that ancient slip events on faults triggered stress changes and damage, allowing fluids to migrate up through the damage networks and ultimately mineralising the Earth’s crust.
“Although this explanation seems a little convoluted, it is supported by a common feature – that many gold deposits all over the world are located on small faults next door to very large faults. This geometric relationship seems somewhat reminiscent of aftershocks and damage around a mainshock.”
Micklethwaite speculates that mini-earthquakes could be triggered to generate new gold deposits. “There are some unique places, like the geothermal springs in the Taupo Volcanic Zone in New Zealand, where we know that hot waters are precipitating fine particles of gold at the surface.
“Will we ever be able to tap such gold? Perhaps we will be able to form our own gold deposits by repeatedly triggering earthquakes in a controlled manner, and then letting nature run her course.
Dr Steven Micklethwaite on 0428 231 002
Guy Nolch (Editor) on 03 9500 0015
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