Friday, April 12, 2013

Is there an earthquake in our future?

Geologists to conduct regional seismic study

Express Staff Writer

Could Blaine County be walloped by an earthquake? Geologists from the Idaho Geological Survey at the University of Idaho think so, and they are working this month to find the areas of the county most likely to be affected by seismic activity.

In 2010, the Idaho Geological Survey discovered the Stanley fault, which the survey says likely caused the formation of the Sawtooth Mountains. 

The fault is at least 25 miles long and could be up to 40 miles, running through the upper end of Redfish Lake and at least as far south as Pettit Lake. Idaho State University researchers said the fault has been active twice in the past 10,000 years, with major quakes 4,100 and 7,000 years ago. 

The fault is one of four major active faults in Idaho, joining those at the base of the Lost River Range, the Lemhi Range and the Beaverhead Range. The Lost River Range fault was the cause of the 1983 Borah Peak earthquake, which had a magnitude of 7.3 and caused two deaths.

William Phillips, Idaho Geological Survey research geologist, said the Stanley fault has the potential to be almost as dangerous.

“The fault could potentially produce earthquakes large enough to strongly shake the Sun Valley area,” he said. “Our work is designed to identify areas in the Wood River Valley which are susceptible to amplification of shaking or ground liquefaction during an earthquake.”

The Idaho Geological Survey states that soil liquefaction can cause structures to sink or topple.

Geologists will conduct surveys at multiple sites in Bellevue, Hailey, Ketchum and Sun Valley beginning April 15. The surveys are carried out by dropping a 150-pound weight on the ground and using geophone sensors, which convert ground movement into voltage that can measure seismic activity.

The team will use that data to determine the type and thickness of deposits below the surface and how they will react during earthquakes. Team leader Kerrie Weppner said in a press release that the survey does not damage the ground’s surface, and no explosives or large trucks are used.

The survey will be completed by April 20, and the results will be analyzed and shared with local emergency planners and county and city officials.

Results will also be available to the public on the agency’s website, The information available will include a map showing ground response to seismic shaking and susceptibility to liquefaction, which is most likely to occur in sandy deposits and loose clay.

Results are expected to be available by September. The study is being funded by the Idaho Geological Survey and the Idaho Bureau of Homeland Security.

Kate Wutz:

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