A central Idaho earthquake swarm could provide insight into plate tectonics in Yellowstone National Park.
A series of quakes shook the Challis area this past week. Every quake originated from the northern part of the Lost River Fault. The largest measured so far had a magnitude of 3.7. From The Missoulian:
“’There’s obviously a fault down there at depth to produce these, and the town of Challis happens to be built on top of it,” said scientist Mike Stickney of the Montana Bureau of Mines and Geology based in Butte, Montana. “We have no indication that it’s leading to a larger event.’”
Stickney added a few different agents are at work in this earthquake swarm, none of which are fully understood. He also stated the swarm—occurring in the Centennial Tectonic Belt, which extends west from Yellowstone—cannot be explained by Yellowstone’s geologic hotspot. From The Missoulian:
“It clearly is somehow related,” Stickney said. “I’m not blaming the belts on Yellowstone, but the fact that they extend into and out of Yellowstone is not a coincidence.”
Also perplexing, scientists say, is that the earthquakes are so far from tectonic plates on the West Coast.
“That’s the fundamental question that we don’t know,” Stickney said. “It’s related to plate tectonics, but no one knows why this is occurring so far from a plate boundary. Nobody understands why these belts are located where they are.”
This is not the first time Challis has been the focus of an earthquake swarm study. Earlier this month, Stickney, along with Kris Pankow (associate director of the University of Utah Seismograph Stations), made a presentation about an earthquake swarm that visited Challis last summer to the 2014 American Geophysical Union in San Francisco.
The main appeal the Challis quakes offer to scientists, Pankow surmised, is the insights they offer into the Intermountain Seismic Belt. This Belt, unlike the Centennial one, runs north and south from Yellowstone, under multiple state boundaries. Possible causes of the earthquake swarm include stretching crust or heated water movement.
According to Pankow, however, there is still information that needs to be analyzed, both about the current Challis swarm and last summer’s swarm.