On March 31, a 6.5 magnitude earthquake rolled through Idaho’s Sawtooth mountain range, northeast of Boise. It was the second largest earthquake to strike Idaho, according to the Idaho Statesman. (The strongest temblor in Idaho history, 1983’s Borah Peak earthquake, registered as a magnitude 6.9.)
But the region hasn’t stopped shaking since. The area has experienced a string of aftershocks in the months following the quake, some registering as high as magnitude 4.8. The shaking has been so strong, in fact, that a popular beach along Stanley Lake in the Sawtooth National Recreation Area has sunk into the water.
“The most probable cause for the ‘disappearing’ of the inlet delta is a combination of liquefaction and compaction of saturated sediments and some possible sliding and later spreading on the delta toward the deeper part of the lake,” Claudio Berti, director and state geologist of the Idaho Geological Survey, said in a statement.
The March 31 earthquake occurred 16 miles north of the Sawtooth Fault, a 40-mile stretch of fault line discovered nearly a decade ago. Geologists have largely believed the fault was inactive, but the latest round of quakes have reinvigorated interest in the region.
Geologists are puzzling over exactly what caused an earthquake in the otherwise quiet region. Some researchers suspect the Sawtooth Fault is actually longer than expected. Others believe the fault is now taking advantage of openings in Earth’s crust and is slowly pushing north. One theory suggests energy from the Sawtooth Fault could have jumped to a nearby unknown fault, spurring the recent series of earthquakes.