Earthquakes
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Study links geothermal energy with earthquakes - Sentinel and Enterprise

Study links geothermal energy with earthquakes - Sentinel and Enterprise | Earthquakes | Scoop.it
Study links geothermal energy with earthquakes
Sentinel and Enterprise
At CalEnergy's Imperial Valley operation, the company taps into naturally heated deep-water reservoirs located thousands of feet below the surface.
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Scientists seek foolproof signal to predict earthquakes: Could magnetic waves be the trustworthy tool?

Scientists seek foolproof signal to predict earthquakes: Could magnetic waves be the trustworthy tool? | Earthquakes | Scoop.it
For centuries people have tried to predict earthquakes-with no success. Magnetic signals from rocks deep inside the earth are the latest prospect.

 

The dream is to be able to forecast earthquakes like we now predict the weather. Even a few minutes' warning would be enough for people to move away from walls or ceilings that might collapse or for nuclear plants and other critical facilities to be shut down safely in advance of the temblor. And if accurate predictions could be made a few days in advance, any necessary evacuations could be planned, much as is done today for hurricanes.

 

Scientists first turned to seismology as a predictive tool, hoping to find patterns of foreshocks that might indicate that a fault is about to slip. But nobody has been able to reliably distinguish between the waves of energy that herald a great earthquake and harmless rumblings.

 

Seismologists just can't give a simple yes or no answer to the question of whether we're about to have a large earthquake, said Thomas Jordan, director of the University of Southern California's Southern California Earthquake Center at a meeting of the American Geophysical Union (AGU) in San Francisco in December.

 

So some scientist have turned their attention to other signals, including electricity, that might be related to activity occurring below ground as a fault prepares to slip

 

One theory is that when an earthquake looms, the rock "goes through a strange change," producing intense electrical currents, says Tom Bleier, a satellite engineer with QuakeFinder, a project funded by his parent company, Stellar Solutions, of Cambridge, Massachusetts.

 

"These currents are huge," Bleier said at the AGU meeting. "They're on the order of 100,000 amperes for a magnitude 6 earthquake and a million amperes for a magnitude 7. It's almost like lightning, underground."


Via Dr. Stefan Gruenwald
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Earthquakes make gold veins -- pressure changes in Earth crust cause precious metals to deposit

Earthquakes make gold veins -- pressure changes in Earth crust cause precious metals to deposit | Earthquakes | Scoop.it

Scientists have long known that veins of gold are formed by mineral deposition from hot fluids flowing through cracks deep in Earth’s crust. But a study published today in Nature Geoscience has found that the process can occur almost instantaneously — possibly within a few tenths of a second.

 

The process takes place along 'fault jogs' — sideways zigzag cracks that connect the main fault lines in rock, says first author Dion Weatherley, a seismologist at the University of Queensland in Brisbane, Australia.

When an earthquake hits, the sides of the main fault lines slip along the direction of the fault, rubbing against each other. But the fault jogs simply open up. Weatherley and his co-author, geochemist Richard Henley at the Australian National University in Canberra, wondered what happens to fluids circulating through these fault jogs at the time of the earthquake.

 

What their calculations revealed was stunning: a rapid depressurization that sees the normal high-pressure conditions deep within Earth drop to pressures close to those we experience at the surface. For example, a magnitude-4 earthquake at a depth of 11 kilometres would cause the pressure in a suddenly opening fault jog to drop from 290 megapascals (MPa) to 0.2 MPa. (By comparison, air pressure at sea level is 0.1 MPa.) “So you’re looking at a 1,000-fold reduction in pressure,” Weatherley says.

 

Big earthquakes will produce bigger pressure drops, but for gold-vein formation, that seems to be overkill. More interesting, Weatherley and Henley found, is that even small earthquakes produce surprisingly big pressure drops along fault jogs. “We went all the way to magnitude –2,” Weatherley says — an earthquake so small, he adds, that it involves a slip of only about 130 micrometres along a mere 90 centimetres of the fault zone. “You still get a pressure drop of 50%,” he notes.

 

That, Weatherley adds, might be one of the reasons that the rocks in gold-bearing quartz deposits are often marbled with a spider web of tiny gold veins. “You [can] have thousands to hundreds of thousands of small earthquakes per year in a single fault system,” he says. “Over the course of hundreds of thousands of years, you have the potential to precipitate very large quantities of gold. Small bits add up.”

 

Weatherley says that prospectors might be able to use remote sensing techniques to find new gold deposits in deeply buried rocks in which fault jogs are common. “Fault systems with lots of jogs can be places where gold can be distributed,” he explains.

 

But Taka’aki Taira, a seismologist at the University of California, Berkeley, thinks that the finding might have even more scientific value. That’s because, in addition to showing how quartz deposits might form in fault jogs, the study reveals how fluid pressure in the jogs rebounds to its original level — something that could affect how much the ground moves after the initial earthquake.


Via Dr. Stefan Gruenwald
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