Strong Magnitude 6.5 Earthquake Hits Idaho for First Time in 50 Years, as Quakes Recorded in Yellowstone and Salt Lake City

A strong earthquake has hit Idaho, with a magnitude 6.5 quake striking near the city of Boise in the Salmon-Challis National Forest. This is the first earthquake above magnitude 5 to hit anywhere in the region for over 50 years, the U.S. Geological Survey (USGS) said.

The earthquake was centered just over 70 miles from Boise, and around 200 miles from Yellowstone National Park, where several small earthquakes were also recorded.

"During evening rush hour, at roughly 5:52 p.m. local time, a large earthquake struck about 72 miles northeast of Boise," a statement from the USGS said.

"Perceived shaking for the quake was very strong. The event was widely felt, with close to 16,000 'Did You Feel It?' reports thus far submitted, but likely to have low impact."

The agency said there is a small chance of one or more aftershocks over the next week, and it is likely more smaller earthquakes will also hit.

"The number of aftershocks will drop off over time, but a large aftershock can increase the numbers again, temporarily," USGS explained.

USGS said the earthquake was the result of "strike slip faulting" in the shallow crust of the North American Plate. A strike slip fault is where vertical fractures take place. Blocks move horizontally, or parallel, to one another, with the movement either being right-lateral or left-lateral.

"The earthquake occurred in the western part of the Centennial Tectonic Belt, an area north of the Snake River Plain that is undergoing southwest-northeast extension," the USGS statement said.

earthquake map idao
Map showing the earthquake that hit Idaho on Wednesday. USGS

There has not been an earthquake of magnitude 5 or greater within a 31 mile radius of Wednesday's earthquake in the last 50 years. The biggest in recent history took place 62 miles to the east, along the Lost River fault zone. A magnitude 6.9 earthquake hit Borah Peak in 1983. This was the largest to hit Idaho and two children were killed from falling masonry. This earthquake was followed by five other events of magnitude 5 or higher.

As well as the Boise earthquake, many small earthquakes were recorded in the region on Wednesday. In Yellowstone, the two of the largest took place in the west of the park, measuring magnitudes 3.1 and 2.6. A magnitude 2.9 event was recorded southeast of this cluster. A magnitude 2.2 earthquake also struck to the east, along Miller Creek. There was no link between the Idaho earthquake and Yellowstone, Michael Poland, the scientist-in-charge of Yellowstone Volcano Observatory, told Newsweek. "Everything is normal at Yellowstone," he said.

To the south of Boise and Yellowstone, Salt Lake City has also seen a large number of earthquakes in the last few weeks. These follow a magnitude 5.7 earthquake that hit Magna, Utah, on March 18.

"There are 26 documented M5+ earthquakes within 250 km of the March 18, 2020 event in the combined University of Utah Seismograph Stations and USGS earthquake catalog, which stretches back to the late 19th century," a statement from the USGS said.

"The largest recorded earthquake was a M6.6 earthquake in March 1934, in Hansel Valley on the north shore of the Great Salt Lake. In September 1962, a M5.0 earthquake occurred in a very similar location to today's M 5.7 event, with strong shaking observed locally. Geologic investigations of the Wasatch fault indicate that large (M ~7) earthquakes occur about every 1300 years near Salt Lake City, with the most recent large earthquake about 1400 years ago."

This article has been updated to include quotes from Michael Poland.