Idaho has a history of earthquakes, and many share epicenter with Tuesday’s 6.5 quake

Posted at 9:10 PM, Mar 31, 2020
and last updated 2020-04-01 00:29:15-04

Over 100 years ago, an earthquake shook Boise, damaging buildings and rattling residents, who ran out into the streets, according to the Idaho Geological Survey. It was one of the earliest significant earthquakes in state history, though it’s unclear how strong the quake was — the Richter scale, one of the first means used to measure the magnitude of earthquakes, wasn’t developed until 1935.

The Gem State is fairly prone to temblors like the one that shook Boise on Tuesday evening. Quakes have been shaking Idaho for centuries, and the Ada County Office of Emergency management says Idaho is the fifth-most earthquake-prone state after California, Alaska, Nevada and Utah.

Still, Tuesday’s earthquake might be one of Idaho’s most significant on record. It registered an initial 6.5 magnitude on the moment magnitude scale, the current means of measuring earthquake size. According to U.S. Geological Survey data, that would make it the second-strongest quake ever recorded within Idaho’s borders. Only the Borah Peak earthquake, which hit near Challis on Oct. 28, 1983, was stronger (6.9 magnitude).

Here’s a brief history of seismic events in Idaho.

Records from the Idaho Geological Survey show a handful of noteworthy earthquakes across the state in the 1800s and early 1900s. Most were in sparsely populated areas and did little damage.

In 1884, six years before Idaho became a state, a quake near the Idaho-Wyoming-Utah border caused “considerable” damage to homes in Franklin County. Others in south-central and north-central Idaho in the early 1900s and 1910s caused plaster to fall from buildings and broke dishes and windows.

The 1916 quake that “sent residents rushing into the street” in Boise (which experts advise against, by the way) was described as “violent” in Emmett and Weiser, and was felt in Montana and Oregon.

In the 1940s, two earthquakes struck the southwestern part of the state. The first, in 1945, “broke dishes at Idaho City and cracked plaster at Weiser,” records show. The second, in 1947, caused large cracks to form in “a well-constructed building” in Boise. Through the 1970s and ‘80s, earthquakes toppled chimneys and rocked homes in southeast Idaho.

But the bulk of Idaho’s significant seismic events have occurred in Central Idaho, where the Lost River Fault is located. Tuesday’s earthquake can be traced to that area, and the Borah Peak earthquake also had its epicenter in Central Idaho.

In 2010, researchers at Idaho State University discovered a new fault nearby in the Sawtooth Mountains.

The Borah Peak quake was Idaho’s deadliest and most damaging earthquake.

Two children in Challis died after they were crushed by a falling storefront while walking to school, according to a Statesman report from 1983. Several others were injured, and buildings sustained extensive damage, including one building in Mackay that collapsed. The temblor caused wide rifts to open up in the ground.

Then-Gov. John Evans declared a state of emergency for Custer County and estimated the damage at $4 million to $5 million.

“It appears seven or eight out of every 10 buildings will have to be replaced,” he told Statesman reporter Michael Zuzel.

In Boise, several buildings were evacuated, including some at Boise State University. A geology professor at the college told Zuzel that the department’s seismology instruments “went way off the scale.”

Leroy Kreider, of Boise, was hunting near Lowman when the Borah Peak earthquake hit. He told the Statesman that he saw deer fleeing before he realized what was happening.

“All of a sudden, the ground started rollin,’” he said. “The road was ripplin’ like a piece of ribbon, and the trees were crossin’ their tops.”

Idaho hasn’t had a significant quake since the 1983 Borah earthquake, but hundreds of smaller “swarms” have rippled across the southern part of the state in recent years.

In March of 2014, a series of low-magnitude quakes rumbled through the Salmon area for weeks, culminating in a 4.4-magnitude quake that broke dishes and frayed nerves in Challis. More quakes hit the area in May and again in December that year, and in January of 2015, yet another quake “gave us a good shake,” according to an employee at a Challis grocery store. That magnitude 3.7 quake was felt in Boise.

In September of 2017, a swarm of earthquakes rattled the eastern part of the state near Soda Springs for weeks. Hundreds of low-level quakes were recorded, and some speculated that the events could be forewarning for a volcanic eruption in Yellowstone. (Spoiler alert: They’re not.)

And as recently as this week, more than 600 earthquakes rumbled through Utah and Eastern Idaho following a 5.7-magnitude earthquake that struck near Salt Lake City on March 18.

Tuesday’s earthquake reportedly had as many as seven aftershocks, according to USGS: a magnitude-4.6 tremor at 6:27 p.m. and a 3.3 at 7:44 p.m., with several in between.