Earthquake shakes Silver Valley

MULLAN –– Folks settling in for the evening on Monday night got quite the shock when an earthquake briefly rattled through the area.

Rampant speculation littered social media, with many wondering if the shaking was related to an underground air blast, an explosion, or an earthquake. 

According to the United States Geological Survey (USGS), the epicenter of the 3.3-magnitude (M3.3) quake was three kilometers north of Mullan, but people from as far away as the Kingston/Cataldo area reported feeling, seeing, or even hearing something.  

Monday’s earthquake was measured at a depth of five kilometers, which classifies it as a shallow-focus earthquake. Shallow-focus earthquakes are any earthquake measured at a depth of 70 kilometers or less and occur more often than deep-focus quakes. Shallow-focus earthquakes are more destructive than their deeper counterparts because they release more energy.  

Shoshone County is no stranger to geological activity, with several significant faults coursing through the area, but it was the first quake of its size in almost three years.  

According to Steve Sobieszczyk with USGS, there have been five earthquakes with a M3 or greater in the Mullan area since 2000, including a M3 that occurred on May 22, 2022.  

Idaho in general is a geological hotbed; this is due to its proximity to an area known by geologists as the Basin and Range Province. Consequently, hundreds of geological faults are created due to the seismic activity in this region. In the Silver Valley, the Osburn Fault runs the length of the county and is prone to seismic activity.   

Predicting if Monday’s quake was an isolated incident or part of a larger seismic event may be challenging, due largely to the area being a fairly seismically active region.   

“Generally speaking, since this is an earthquake prone area, it's likely that there will be future quakes,” Sobieszczyk said. “Knowing when or how big is a harder question to answer. Earthquakes generally occur in sequences (e.g., a mainshock with aftershocks). Aftershocks are expected, but the rate of aftershocks can vary quite a bit from sequence to sequence. However, aftershocks may also be very small in magnitude, not felt by people in the area, and some may even be too small to be picked up by seismic networks.” 

The entire cause of the recent earthquake is unknown, but they are usually due to built-up stress on tectonic plates due to their shifting.  

According to USGS’s catalogued records, which date back to just 1985, the largest earthquake within 100 kilometers of the most recent one, happened on December 22, 1998, when a M4.7 shook the area along the Idaho/Montana border. 

In March 2020, North Idaho experienced a hefty aftershock from a M6.5 quake that originated outside of Challis, Idaho. People in grocery stores reported items falling from shelves from the shaking.  

The 1983 Borah Peak earthquake, Idaho’s strongest earthquake, was a magnitude 6.9, and resulted in the deaths of two people in Challis near the earthquake’s epicenter.