Scientists at Idaho State University have mapped a previously unknown and active seismic fault in the northern Rockies capable of unleashing an earthquake with a magnitude as high as 7.5....
....Glenn Thackray, chairman of the university's geosciences department, said 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 some 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.
Scientists located the fault with a remote sensing technique that relies on laser-equipped airplanes. They were able to gather 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.
Thackray said researchers believe the fault triggered two earthquakes over the past 10,000 years, one some 7,000 years ago and another 4,000 years ago, suggesting significant seismic activity occurs at the site every several thousand years.
I visited the fault scarp from the 1983 Mount Borah earthquake this summer (another illustration here). With nearly ten feet of vertical displacement in places, it's quite impressive. The mountains rose six inches while the valley floor dropped nine feet. We run a rapid on the Middle Fork of the Salmon whose main obstacle is a boulder dislodged from the cliffs by the quake 70 miles away. East-central Idaho is shaky country. Quakes here would be a big deal if the area weren't so sparsely populated.