The latest earthquake swarm in central Idaho could help scientists better understand quake belts extending from Yellowstone National Park.
The most recent swarm in the Challis area started this week and so far 20 quakes have been recorded, the largest a 3.7 magnitude on Monday.
No damage has been reported.
Scientist Mike Stickney of the Montana Bureau of Mines and Geology based in Butte, Montana, says a portable seismograph left in place after a swarm last summer has helped pinpoint the earthquakes.
He says they're being produced by different triggers, indicating a complex process.
He says the fault runs under Challis and is within the Centennial Tectonic Belt extending west from Yellowstone National Park.
But he says scientists don't have a clear understanding of all the forces at work.