Earthquake aftershocks felt in Boise; Custer courthouse damaged; avalanches dot Sawtooths
Two earthquake aftershocks rattled parts of the Boise area for a few seconds a little after 2 p.m. Friday. They were the latest in a series of more than 140 aftershocks since Tuesday’s magnitude-6.5 quake that was the second-largest in Idaho history.
The U.S. Geological Survey reported a magnitude-3.6 earthquake at 2:06 p.m. and a magnitude-4.3 earthquake at 2:21 p.m. Friday. Tuesday’s original quake and the aftershocks have emanated from the mountains northwest of Stanley, near Idaho 21. The 4.3 is the third-strongest aftershock, and the strongest since Tuesday.
The original quake was 19 miles northwest of Stanley.
The 6.5 quake on Tuesday has left its mark in Central Idaho. Substantial cracks have been found in the Custer County courthouse and Road & Bridge services building, both in Challis.
The cracks in the Road & Bridge building are up to 3 inches wide and there is a structural risk of collapse, Custer County Commissioner Wayne Butts said.
“Our inspection the next day, the road and bridge superintendent showed us extensive cracking in the walls and then we had the commissioner meeting and coming out of the basement we saw structural cracking in it as well,” Butts said. “We did some more looking around and we found more cracks.”
Butts explained that the county turned the damages into its insurance carrier, Idaho Counties Risk Management Program (ICRIMP).
“However, ICRIMP is so overwhelmed by claims everywhere in the state that they have hired an out-of-state contractor to come look at everybody’s damages,” Butts said.
Scott Oldham, ICRIMP claims manager, said that it’s not unusual for the company to work with contractors on these kinds of damages. He confirmed that there have been some damages, especially to older buildings in Custer County.
Water and power lines remain without damages in Custer County, Butts said.
Avalanches in the Sawtooths
Tuesday’s earthquake also occurred just after a snowstorm that brought up to 3 feet of snow in the mountains adjacent to the quake.
In addition to feeling the effects of the earthquake, many Stanley residents reported hearing the rumble of avalanches coming from the nearby Sawtooth Mountains, according to a press release from the Sawtooth National Forest. Clearing weather on Wednesday revealed “incredibly widespread avalanching” in the Sawtooths and in the mountains closer to the epicenter near Banner Summit, the release said.
“When the earthquake hit, all of the trees shook and snow was falling out of them — that image will remain in my mind forever. Almost immediately, we heard the rumbling sound of avalanches reverberating in the mountains,” Sawtooth Avalanche Center Avalanche Specialist Chris Lundy said in the release. “Even though we were in a location that was safe from avalanches, we felt very vulnerable as the mountains shook around us.”
Lundy said the next day he was able to climb higher to see the extent of the damages, and avalanches were everywhere.
While some of these avalanches may have occurred naturally prior to the earthquake, evidence suggests that the majority of them released as a direct result of the quake, the release said.
According to the Sawtooth National Forest, the slopes are not necessarily stable yet.
“While the earthquake triggered avalanches on many slopes that were teetering on the edge of sliding, steep slopes that did not release could still be waiting for a skier or snowmobiler to find the perfect spot on or near a slope to trigger an avalanche,” the release said.
The Sawtooth Avalanche Center has received reports of two human-triggered slides in the two days following the earthquake.
This story was originally published April 3, 2020 at 2:21 PM.
