Magnitude 6.5 Earthquake Felt in Central Idaho

Release Date:

On March 31, 2020, a  magnitude 6.5 earthquake struck  near Boise, ID, in the Challis National Forest. Seismic instruments indicate the earthquake originated at a depth of 6.2 miles (10 kilometers).

During evening rush hour, at roughly 5:52 p.m. local time, a large earthquake struck about 72 miles northeast of Boise. 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 USGS is coordinating its response with the Idaho Geological Survey.

 

Aftershock Forecast [last updated April 1]

According to our forecast, over the next week there is a < 1% chance of one or more aftershocks larger than magnitude 6.5. It is likely there will be smaller earthquakes over the next week, as well, with 5 to 53 magnitude 3 or higher aftershocks. Magnitude 3 and above are large enough to be felt near the epicenter. The number of aftershocks will drop off over time, but a large aftershock can increase the numbers again, temporarily.

 

Seismic Setting

The earthquake occurred as the result of strike slip faulting within the shallow crust of the North America plate. 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. Historic seismicity in the immediate vicinity of the March 31 earthquake is sparse; no earthquakes of M5+ have occurred within 50 km of this event over the past 50 years, and the most notable historic seismicity in the region occurred about 100 km to the east on the Lost River fault zone. This was the site of the 1983 M6.9 Borah Peak earthquake (October 28, 1983), which killed 2 in Challis, and resulted in over $12M in damage in the Challis-Mackay area, and which was followed by five other M 5+ events over the following year, and most recently a M5.0 earthquake in January 1950, about 60 km to the east of today’s event. The March 31, 2020 event is the largest in Idaho since the 1983 Borah Peak earthquake.  

 

Earthquake Information/Resources

 

We will continue to update this story as more information becomes available.