EARTHQUAKE SWARM IN SOUTHEAST IDAHO

Soda Springs

The earthquakes have been felt most strongly in the Soda Springs area.

Madeleine Coles

News Editor

Many rumors have been spreading about the recent earthquake swarm, but according to ISU geosciences assistant professor David Pearson, the earthquakes are completely normal and likely won’t lead to anything worse.

Earthquakes occur along faults, which are fractures in the earth’s crust, and most faults in the state occur in eastern and central Idaho.

“The important thing is that there’s no faults that are under Pocatello or Idaho Falls,” Pearson said. “So we don’t expect there will be large earthquakes directly underneath us.”

352 earthquakes associated with the Soda Springs area have occurred in the last week and a half. According to Pearson, it began when two earthquakes occurred on September, 2, one of a 2.8 magnitude and one of a 4.1 magnitude.

“Since [that earthquake] happened, there’s been all sorts of lower magnitude earthquakes that followed,” Pearson said. “If there’s a bunch of earthquakes that are about the same size and there’s nothing that’s clearly bigger than those we call it a swarm. If there’s one that seems to be bigger than all the other ones, the other ones are probably associated with it, and we call those aftershocks. It’s typical for these aftershocks to die down in frequency and intensity after the main event. It usually takes days to weeks, though it can take longer sometimes.”

The initial earthquake caused part of the fault to slip, which led to greater stress for the other areas of the fault, causing it to be more likely to slip.

“This doesn’t necessarily mean all the faults in Idaho are going to rupture because of these events,” Pearson said. “But there is a slightly elevated chance of a larger earthquake when there are smaller ones going on.”

However, even with the elevated chances, the probability is still fairly low.

Pearson also said the earthquake swarm is a great opportunity for teaching moments.

“I’m teaching a couple classes this semester, and this is something we talked about in depth in one of my graduate level classes, but I’ve also talked about it in my introductory class,” Pearson said. “It’s a good teaching moment.”

But even outside of college classes, the earthquake swarm has been a learning experience.

“The first question that everyone asks me is ‘is there going to be a larger earthquake?’,” Pearson said. “The next question people ask  is ‘does it mean that Yellowstone is going to erupt?’ So that’s a pretty big misconception: that any of this seismicity is related to Yellowstone at all. But the biggest takeaway that I would want people to get from this is that there is a hazard for earthquakes in southeast Idaho. That’s why it’s kind of a teachable moment.”

Pearson said he believes the initial earthquakes near Soda Springs likely occurred along the Western Bear Lake fault, and there is the possibility that a magnitude 7.2 earthquake will occur along that same fault; however, the probability is extremely low.

“I don’t want people to think that there’s going to be this magnitude 7.2 along these faults,” he said. “It’s a possibility, and we should prepare for that possibility. But it’s actually a pretty low chance that an earthquake would happen.”

Earthquake map

The vertical red line just to the left of Soda Springs on this map shows one of the fault lines that has been active recently.

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