Geologists Aim To Map Faults, Assess Earthquake Risk Around Stanley
BY Mark Dee
Summer is off to a shaky start northwest of Stanley, which has seen more than one hundred small earthquakes since the first day of June.
While the earthquakes have rattled residents and visitors, they also offer an opportunity to better understand the seismically active—and largely unknown—landscape beneath the surface of the northern Sawtooth Valley.
The first quake shook the mountains around Valley Creek about 9.5 miles northwest of Stanley on June 1. As of Friday morning, the United States Geological Survey logged 103 total earthquakes of all magnitudes centered in the region in the six days since—more than one every hour and a half. Eighteen registered above 3.0 on the Richter scale, and two reached 4.0, strong enough to rattle windows but not cause significant damage. The cluster fits what geologists call a “swarm” of earthquakes: “higher-than-normal number of small earthquakes over a short period of time in a small area,” according to the University of Idaho’s Idaho Geological Survey.
No damage has been reported, Stanley Mayor Steve Botti told the Wood River Weekly on Thursday. As of last week, seismologists haven’t told him that the situation is dangerous, and he expects summer visitation to continue at a normal clip.
“These have all been what I’d consider minor earthquakes. There’s shaking, but nothing falling off shelves, anything like there,” Botti said. “People have been concerned—not that there’s damage, but whether they’ll get stronger. And nobody knows.”
Seismic study faces headwinds
Botti knows what a stronger quake can do. He was mayor on March 31, 2020, when a 6.5-magnitude earthquake, the second largest recorded in Idaho, hit the area about 15 miles northwest of Stanley. (The current cluster is about halfway between the city and the epicenter of the larger quake.) The Richter scale is logarithmic, not linear: The 6.5 magnitude earthquake was 316.3 times bigger than the 4.0s seen this time, releasing 5,623.4 times more energy, according to USGS calculations. More than 2,000 aftershocks followed, of which Botti estimates he felt some 500.
The 2020 earthquake left a mark in the Sawtooths, toppling the popular Arrowhead and Finger of Fate rock formations and liquidating a beach at Stanley Lake. Those landmarks sat close to the Sawtooth fault, which runs along the west side of the basin near the base of the mountains. So far, the Idaho Geological Survey isn’t sure if the new event is tied to that fault, or how it relates to the 2020 earthquake.
“The cluster of new earthquakes is not directly correlated to the aftershock sequence, although a lot of early aftershock activity from the March 2020 earthquake extended…through this same region,” the Survey said in a statement. “Recording and analyzing ongoing and future earthquakes will help identify the structure that is hosting these events.”
The Valley Creek area remains a bit of a mystery to geologists, but its study is a rising priority. To date, though, implementation is difficult, according to Idaho State Geologist Claudio Berti.
Following the 2020 earthquake, the state geological survey placed one instrument in the area—enough to observe seismic activity, but not to accurately locate all the small events that can explain the current swarm. For that, scientists “theoretically” need three seismographs in close range at the minimum, Berti said, but “in reality” the survey would have six or seven seismographs nearby to chart earthquake behavior. Siting those instruments has been a challenge.
“We have had a really hard time getting access to land,” Berti said. “Sometimes, it’s hard to get the right landowner. Sometimes, if it’s public land, whether state or federal, the amount of paperwork required to gain permits is just insurmountable.”
Lately, it’s particularly tough to for state agencies to set up such studies on federal land in Idaho—and Idaho is over 60% federally managed. Special Use Permits on Federal Lands require applicants to be liable and indemnify work on federal land. Idaho Attorney General Raul Labrador, who cosigned the state into a multi-state lawsuit over control of federal lands, has directed state employees and agencies to not sign these permits. So, the Idaho Geological Survey, a state agency, can’t apply for permits to place instruments.
“For us, with the exception of a few private parcels, we can’t put a seismometer anywhere between Grandjean and Challis, which is a pretty big chunk of Idaho,” Berti said. “So, we try to get creative.”
In the past week, Berti has worked with Botti, the Stanley mayor, on finding private property owners willing to host instruments, which are about the size of a loaf of bread. When we spoke on June 6, Berti said he hoped to get them in the area in the weekend ahead.
Mapping won’t help forecast when an earthquake will hit; to date, that remains impossible, Berti said. But it is valuable for a bunch of reasons beyond the pure science of it. For one, it will help Stanley understand the geothermal potential of its surrounding areas. (The hot springs around the valley are a function of its geological structure, Berti said.) More pressing, though, is its value for hazard mitigation.
“Despite the fact that we can’t predict [when a fault will move], we can gain enough understanding to create a worst-case scenario on that fault. It’s very different to know that a fault is only going to generate a magnitude four earthquake than it is to know it can generate a magnitude eight.”
What is the Sawtooth fault capable of? Berti doesn’t know—but can confidently say it is capable of something bigger than the 6.5 earthquake of 2020. The evidence, he said, is in the rough-hewn peaks of the Sawtooths themselves. A trained eye can see uplifts and scarps in the rock itself; while the 2020 quake was the largest recorded in the valley, it didn’t do anything to raise the rocks that way. At some point, something more powerful did. To us, it happened an impossibly long time ago—USGS study at Redfish Lake found evidence of quakes 4,300 and 7,600 years ago . To the mountains, it was just the other day.
“It’s important to know whether it happened all at once, or its happened 20 times,” Berti said. “It’s one thing if an earthquake [raises the rock] 10 meters—that’s a hell of an earthquake. If earthquakes make it in many steps of a couple of feet, that’s a completely different story.”
Living in Earthquake Country
“In Idaho, there are a lot of things we have to keep in mind,” Berti said, “and earthquakes should be one of them.”
Blaine County sits south of the more active areas in Central Idaho, but still within what the USGS calls the Intermountain Seismic Belt. The county is considered at “medium” earthquake risk “at this time,” County Disaster Services Coordinator Chris Corwin told the Wood River Weekly. That’s mostly because there isn’t a known fault close to the Wood River Valley, though research could change Corwin’s outlook.
“With the activity in the Stanley area and a more recently studied fault in the Salmon River Valley, we might have to do a little more research on how big of an earthquake could come from this fault and how it might impact us,” Corwin said. The Borah Quake in 1983, to date the largest recorded in Idaho, managed to damage buildings in Blaine County, Corwin said, “but nothing catastrophic.” If geologists find closer fault or evidence of stronger potential earthquakes, the county may have to re-evaluate its risk, Corwin said.
Earthquakes are part of the county’s Hazard Mitigation Plan, and the county has an Emergency Operations Plan in case of a catastrophic earthquake. That includes ties to state and federal partners better equipped for urban search and rescue.
“Certainly, our first responders would help with initial searches but if something as big as an earthquake does affect us, they could be busy dealing with their own damaged property and loved ones,” Corwin said.
In the meantime, Corwin suggests that residents prepare for possible earthquakes like they would a wildfire.
“They can’t forecast them, but they have a pretty good understanding of when things might get worse,” he said. “Know where your valuables are, have a plan for evacuation and keep informed of what is going on and what scientists are saying. There are things you can do even before a swam hits. Look at ways to protect your home: Is your water heater strapped in? Are large bookcases secured to the wall? [What about] large piece of art or decorations?”
For Berti, Idaho’s landscape is a constant reminder of the activity underneath our feet. Without earthquakes, “the landscape would be boring—like Iowa, not Idaho.”
“We should look at the Sawtooth Mountains and say, ‘Wow, something big made that, and made it not long ago, and keeps making it., keeping it fresh. It’s the underlying forces that create a landscape. So, every time you see some big peaks, you should think there’s got to be a fault nearby.”
