USGS issued an update today discussing an ongoing swarm of earthquakes that continues to rock portions of Idaho well west of Yellowstone. “Seismic activity in central Idaho has been elevated for the past 20 months. These earthquakes are aftershocks of a M6.5 earthquake that occurred on March 31, 2020 –a classic example of a mainshock-aftershock sequence,” USGS said in their update. However, they also stressed that these earthquakes are not related to the Yellowstone supervolcano site located roughly 155 miles to the west.
On the evening of March 31, 2020, astrong 6.5 earthquake rocked portions of Idaho; the epicenter was based roughly 90 miles north and east of Boise and struck at 5:52pm local time / 7:52pm ET. According to the USGS, the potent earthquake struck at a depth of 10km. The earthquake struck well west of Yellowstone National Park, home to a large supervolcano. At that time, USGS said this strong earthquake, the second largest recorded earthquake in Idaho history, was not related to any volcano, including Yellowstone. Instead, this earthquake event was simply a standard tectonic event.
Since that initial large earthquake in 2020, known as a mainshock, there have been over 4,300 aftershocks in the same area. According to the USGS, this uptick in seismic activity has alarmed some people. “A common question seen after many earthquakes in the western U.S. is “Will this earthquake trigger an eruption at Yellowstone?” Or, “is this seismicity related to Yellowstone?”, USGS wrote in today’s update. However they also provided a simple answer: “no.”
According to USGS, aftershocks are a normal and forecastable phenomenon following tectonic earthquakes caused when the Earth’s crust moves past itself along fractures called faults. “This movement usually happens very quickly as stored tectonic force is released. The energy produced by the fault movement is converted into seismic waves that radiate outward from the rupture.” The Stanley earthquake rupture was about 12 miles long; its fault system is part of the Basin and Range province of the western USA, which is extending due to tectonic activity and doesn’t have any direct relation to the magmatic system beneath Yellowstone.
However, Idaho is not free of volcanic threats. On the contrary, USGS says an eventual eruption in Idaho could happen before Yellowstone.
In replying to questions asked on USGS’s Facebook page about the Idaho earthquake swarm, USGS wrote, “We typically see eruptions in the Craters of the Moon area every few thousands of years (most recent was ~2000 years ago). The last time Yellowstone erupted (which was a lava flow) was 70,000 years ago. So, yes, the odds are extremely good that Idaho will experienced numerous eruptions before anything happens at Yellowstone.”
While a volcanic eruption isn’t imminent, more after shocks are likely in Idaho. USGS says that after an earthquake the crust surrounding the ruptured fault will undergo large changes in stress. The earthquake will reduce stress in some areas of the crust but will increase stress in other areas. As the crust adjusts to its new state of stress, it produces many smaller earthquakes—aftershocks—in the area around the mainshock.