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Fault Could Threaten Rocky Mountain Town

November 18, 2010

Scientists at Idaho State University have mapped a previously unknown and active seismic fault in the Rocky Mountains.

The newly discovered fault is located in central Idaho and could unleash an earthquake with a magnitude as high as 7.5.

Glenn Thackray, chairman of the university’s geosciences department, told Reuters that the 40-mile-long fracture in the Earth’s crust at the base of the Sawtooth Mountains near the tiny mountain town of Stanley is cause for concern.

“There’s a chance in the next few decades there will be an earthquake on this fault, and if it does happen it will be a rather large earthquake,” he said.

A 7.5 tremor is considered a major earthquake that is capable of causing heavy damage.

Thackray said that a trembler like this would be felt at an epicenter near Stanley, home to about 100 year-round residents, with moderate shaking expected to extend from the resort community of Sun Valley to capital city of Boise.

Scientists found the fault with a remote sensing technique that relies on laser-equipped airplanes.  They gathered data about its history by analyzing sediment cores lifted from Redfish Lake, a mountain lake on the fault line famous for its historic sockeye salmon runs.

According to Thackray, researchers believe the fault triggered two earthquakes over the past 10,000 years, one about 7,000 years ago and another 4,000 years ago.  This could suggest that seismic activity occurs at the site every several thousand years.

“Predicting when a fault might rupture is a real uncertainty of science,” Thackray told Reuters. “The problems with earthquakes and faults are they don’t follow reliable patterns.”

Given the findings, it may be important for towns like Stanley to revamp building codes and emergency preparedness plans.

In 1983, a fault at Idaho’s tallest mountain caused a 6.9 magnitude earthquake.  The Borah Peak earthquake killed two children when a storefront collapsed in the central Idaho town of Challis and damaged buildings within a 50-mile radius.

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