161 EARTHQUAKES: Swarm could be coming to end but experts say temblors might continue for another week or longer

University of Utah Seismograph Stations image The colored squares show the epicenters of the 161 earthquakes that have occurred since Sept. 2 in Southeast Idaho.

University of Utah Seismograph Stations image
The colored squares show the epicenters of the 161 earthquakes that have occurred since Sept. 2 in Southeast Idaho.

By Journal Staff

After being rocked by dozens of earthquakes since Sept. 2, the earthquake swarm in Southeast Idaho could be concluding or at least slowing down.

But earthquake experts say it’s difficult to determine anything for sure because after only five quakes occurred Thursday and another five on Friday, 10 quakes struck Saturday morning through afternoon.

The temblors bring the total since the swarm began to 161 quakes as of Saturday afternoon. All of the quakes have occurred in the Caribou County area east, southeast and northeast of Soda Springs.

They have been felt throughout Southeast Idaho and as far away as Logan, Ogden and Salt Lake City in northern Utah.

Earthquake experts say the worst-case scenario is that the swarm ends with a destructive 7.0 magnitude quake that will destroy buildings and kill people, but the chances of that are slim.

Dr. David Pearson, an Idaho State University geologist who studies earthquakes, said scientists who have researched some of the faults in Southeast Idaho have concluded that the 7.0 quake is possible at some point in the region’s future, but the current earthquake swarm is not necessarily an indication that it will occur anytime soon.

Pearson said the faults in Southeast Idaho that produce earthquakes have not been extensively studied and this makes it difficult to determine when a destructive 7.0 earthquake could occur.

He said it’s possible that one byproduct of the current earthquake swarm is that earthquake experts might start paying more attention to Southeast Idaho and its temblor potential. If more research on Southeast Idaho’s seismic activity occurs, Pearson said there will be more information about what’s going on under the Earth’s surface here so that seismic activity such as earthquake swarms can be better explained.

There has been more extensive research done on northern Utah’s earthquake potential and that region can expect a major earthquake sometime in the next 50 years, the experts say.

Pearson said Southeast Idaho’s smaller population and lack of destructive earthquakes is why the region hasn’t attracted more attention from those who study quakes.

The current earthquake swarm began on the night of Sept. 2 when 34 quakes occurred. Those were followed by another 34 quakes last Sunday, 28 on Monday, 20 on Tuesday, 25 on Wednesday, five on Thursday, five on Friday and 10 as of Saturday afternoon. All 161 of the quakes were reported by University of Utah Seismograph Stations.

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. Sept. 2. 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 the 5.3 magnitude temblor that hit Southeast Idaho last weekend.

The U.S. Geological Survey said that a 7.0 magnitude quake will inflict “considerable damage” on ordinary houses and buildings and will cause such structures to partially collapse. Such temblors will also cause chimneys, factory smoke stacks and walls to collapse, according to the USGA.

Fortunately no damage to structures or injuries to people have been reported as a result of any of the 161 earthquakes that have struck Southeast Idaho since Sept. 2. There have been reports that the quakes have caused some sink holes in the backcountry of Caribou and Bear Lake counties, but these have not been confirmed.

If a destructive 7.0 magnitude earthquake did occur, it could happen in the Caribou County area near the epicenters of the 161 quakes or it could happen elsewhere in the region where faults also exist, Pearson said.

He said other locations where the 7.0 quake could happen include Fremont, Teton, Oneida, Franklin and Bear Lake counties, southeast Bannock County and eastern Bonneville County.

But Pearson said the fact that fewer earthquakes have occurred during the past few days likely means the earthquake swarm is coming to an end. Still he said the quakes might not stop for anther week and swarms have been known to continue for months in rare cases.

Pearson also said future seismic activity is possible in the Caribou County area because of the faults there.

But in regard to the current earthquake swarm, authorities say Southeast Idaho has never seen so many earthquakes in such a short time frame.

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.

The good news is that the experts don’t expect a big destructive quake to occur in Southeast Idaho during the next several days.

But more shaking as the earthquake swarm eventually peters out is a definite possibility.