Idaho’s Most Powerful Earthquake Really Tipped the Ritcher Scale

On March 31, 2020, Idaho experienced its most powerful earthquake in nearly 40 years. The magnitude 6.5 quake shook the central and southern parts of the state, causing minor damage and widespread reports of shaking. The earthquake was felt as far away as Montana, Utah, Nevada, and Canada. It was the second strongest earthquake ever recorded in Idaho, after the 1983 Borah Peak earthquake that measured 6.9 and killed two people.

What Caused the Earthquake?

The earthquake occurred along the Sawtooth Fault, a 40-mile-long fault that runs beneath the Sawtooth Mountains in central Idaho. The fault is part of a larger system of faults that accommodate the extension of the North American Plate as it moves westward over the Pacific Plate. The Sawtooth Fault is considered a normal fault, meaning that the crust on one side of the fault slides downward relative to the other side. This creates a steep angle between the fault plane and the surface.

The Sawtooth Fault is not well-studied, and its seismic potential is not well-known. However, geologists have found evidence of past large earthquakes along the fault, such as offset streams, scarps, and sag ponds. The last major earthquake on the fault occurred about 4,000 years ago, and the recurrence interval is estimated to be between 3,000 and 7,000 years. Therefore, the 2020 earthquake was not unexpected, but rather overdue.

How Did the Earthquake Affect Idaho?

The earthquake caused moderate to strong shaking in the epicentral area, which was about 45 miles west of Challis, Idaho. The shaking lasted for about 20 to 30 seconds, and was felt by more than 16,000 people who reported it to the U.S. Geological Survey (USGS). The earthquake triggered several aftershocks, some of which were felt by residents. The largest aftershock was a magnitude 4.8 that occurred on April 1, 2020.

The earthquake caused minor damage to buildings, roads, and infrastructure in the affected area. Some homes and businesses reported cracked walls, broken windows, fallen chimneys, and shifted foundations. Some rockslides and landslides were also reported, blocking some roads and trails. No injuries or fatalities were reported as a result of the earthquake.

The earthquake also had some unusual effects on the natural environment. Some hot springs and geysers in the region changed their behavior, either increasing or decreasing their flow and temperature. Some wells and groundwater levels also fluctuated, either rising or falling. Some wildlife, such as fish and birds, were also observed to act strangely, either fleeing or flocking to certain areas.


The 2020 Idaho earthquake was a rare and powerful event that reminded the residents of the state of the seismic hazards they face. The earthquake was the result of the tectonic forces that shape the landscape of the western U.S., and was likely overdue. The earthquake caused minor damage and widespread shaking, but no serious injuries or deaths. The earthquake also had some interesting effects on the natural features and wildlife of the region. The earthquake provided valuable data and insights for scientists and engineers who study and monitor the seismic activity and risk in Idaho and beyond.

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