A swarm of low-magnitude earthquakes has been shaking southeast Idaho since Saturday evening, leading some to wonder what is likely to happen next.
The most alarming scenario would end with a very destructive 7.0 magnitude earthquake capable of destroying buildings and killing people, though experts say that’s not likely to happen.
David Pearson, an Idaho State University geologist who studies earthquakes, said people should be prepared for it nonetheless.
“There is most likely not going to be a larger earthquake but there is the possibility of a larger one,” Pearson said. “I don’t want to say everything is fine here because there’s the possibility it won’t be.”
There have been 100 earthquakes in southeast Idaho since Saturday evening — all near Soda Springs in Caribou County, the most powerful of which was a magnitude 5.3. There were four quakes early Tuesday morning, at least 28 throughout the day on Monday, 34 throughout the day on Sunday and 34 on Saturday night. All 100 of the quakes were reported by University of Utah Seismograph Stations.
All of the quakes occurred in Caribou County — east, northeast and southeast of Soda Springs, the county’s largest city with a population of about 3,000 people. The closest earthquake to Soda Springs occurred 1 mile east of the city, while the farthest were about 20 miles to the northeast and southeast. The 5.3 magnitude quake was about 10 miles to the east of the city.
No damage to structures or injuries to people have been reported.
Earthquake country
Although a swarm of 100 quakes is very unusual for southeast Idaho, Pearson said it’s definitely not unusual to have earthquakes near Soda Springs and along the Idaho-Wyoming border because of the faults that run through that part of the region. Lee Liberty, a research professor in Boise State University’s geosciences department, said Idaho is actually part of “earthquake country,” coming somewhere in the top 10 U.S. states for seismic activity.
“Foreshocks, aftershocks and swarms are all very normal for earthquakes,” Shannon Kobs Nawotniak, an ISU geosciences assistant professor, said. “It will take a little while for the rocks to finish settling into new positions, and each wiggle as it settles into place is giving us another small earthquake.”
The big question is what’s going to happen next.
“We don’t necessarily know,” Pearson said.
Pearson said he can dispel two rumors floating around. One is that the quakes were somehow caused by the test detonation of a hydrogen bomb by North Korea this past weekend. Secondly, Pearson said the earthquake swarm near Soda Springs does not mean there’s going to be a volcanic eruption at Yellowstone National Park.
“This has nothing to do with North Korea or Yellowstone,” Pearson said.
Pearson said there are a plethora of monitoring devices around Yellowstone that would indicate a volcanic eruption was going to occur, and those monitoring devices are showing no such indications.
He also said that the chance of southeast Idaho experiencing a destructive 7.0 magnitude earthquake is many times greater than the chance of Yellowstone experiencing a volcanic eruption. Liberty said a magnitude 5.0 quake happens somewhere in Idaho about every five years on average. Our state sees a magnitude 6.0 event every 25 years or so.
Although a 7.0 magnitude earthquake probably won’t happen, Pearson is advising southeast Idahoans to make sure they secure all heavy objects in their houses to walls to keep them from falling. He also said it would be wise to remove anything heavy that’s above your bed so it can’t fall on you and cause injury.
But more likely than the earthquake swarm ending with a very destructive earthquake, Pearson said, are much less catastrophic scenarios — that the most powerful quake occurred at the beginning of the swarm and it’s being followed by smaller quakes, or that the swarm will end up being a series of similarly sized quakes.
Thus far the most powerful temblor in the swarm was the second quake to occur. It was a 5.3 magnitude earthquake and struck at 5:56 p.m. Saturday. Authorities say it’s been years since southeast Idaho experienced a quake of 5.0 magnitude or greater. Such quakes can cause damage to houses and other buildings.
By comparison, a 7.0 magnitude quake would be at least 50 times bigger than Saturday evening’s 5.3 magnitude temblor.
Although experts believe a 7.0 magnitude quake is a definite possibility at some point in southeast Idaho’s future, Idaho itself has never experienced a quake that powerful. The strongest quake in state history was a 6.9 magnitude temblor that struck in 1983 between Mackay and Challis. That quake killed two children and damaged several buildings.
Caribou County authorities said there was some panic when the quakes started on Saturday evening. Since then people have calmed down, according to emergency management officials.
The quakes have been felt as far away as Salt Lake City, Ogden and Logan in northern Utah and throughout Southeast Idaho, including Pocatello, Fort Hall and Blackfoot.
Pearson said if a 7.0 earthquake does strike, it will likely occur near Soda Springs and inflict the most damage on Caribou County. Much less damage will occur in southeast Idaho’s biggest cities, because they’re much farther away from the faults in Caribou County, Pearson said.
Pearson said a 7.0 magnitude earthquake could be very devastating to Caribou County’s economy because it could damage and/or destroy the mining facilities that are the county’s largest employers. ISU geosciences staff on Tuesday said the possibility of an earthquake of that magnitude is remote.
What would happen here?
What would a higher-magnitude earthquake mean for Boise? Not a whole lot, said BSU’s Liberty. We might feel some trembling here, but not much else.
“I wouldn’t anticipate significant damage from an earthquake in southeast Idaho. I think the biggest impact would be the influx of people,” Liberty said.
The fatal 1983 earthquake was felt in Boise, he said, but Challis is also closer to Boise than Soda Springs.
And Boise doesn’t necessarily need to brace for its own spate of quakes, either. A look at Idaho’s fault lines shows the Treasure Valley more or less in the clear, while places like Challis and Pocatello are closer to fault lines. Still, Liberty said, it’s nice to be prepared. He echoed Pearson’s advice and said a “go bag” is never a bad idea in anticipation of any kind of emergency or disaster.
As earthquakes go, Liberty added, this swarm isn’t something to write home about.
“This is tiny in terms of an earthquake event,” he said.
Preparing to respond
Caribou County emergency management officials said the county’s emergency responders have already been on a heightened state of alert because of wildfire season. The earthquake swarm is presenting yet another reason for them to be ready to respond at a moment’s notice.
Two years ago, Caribou County emergency management officials received earthquake disaster training from the Federal Emergency Management Agency. The cluster of smaller earthquakes is causing the county’s emergency responders to contemplate how they would handle a much larger earthquake — so if a 7.0 temblor occurs they’ll be better prepared, emergency management officials said.
The U.S. Geological Survey said a 7.0 magnitude quake would cause “considerable damage” to ordinary houses and buildings, including partial collapse. Such temblors could also cause chimneys, factory smoke stacks and walls to collapse, according to the USGS.
Caribou County emergency management officials have checked on one building — North Gem High School in Bancroft — to make sure it’s safe. The school is more than 100 years old and there were concerns from school officials that the earthquakes could have damaged it. But emergency management officials said the school has endured the quakes without any issues and is safe.
Earthquake swarms have been known to continue for weeks or even months. Caribou County emergency management officials said they think the current swarm could continue for another two weeks.
If a big quake does occur, there are several Caribou County schools and churches that are designated to be shelters for anyone who’s displaced. Additional emergency resources would be called in from other southeast Idaho counties, the state and possibly even the federal government to help Caribou County deal with casualties and the extensive damage that’s expected.
This story was originally published September 05, 2017 2:37 PM.