How earthquakes impact Wyoming

RIVERTON —  On Dec. 12, many across Fremont County may have felt the shock of a 3.8-magnitude earthquake that originated in Atlantic City around 5:30 p.m. Residents in Lander and Jeffery City experienced light shocks immediately following the earthquake, according to reports to the U.S. Geological Survey.

Several factors can influence how people experience earthquakes, including the magnitude, size of the fault, how deep in a fault an earthquake originates and what type of a fault is influenced, according to USGS Geophysicist Paul Caruso.

"It does differ depending on how the fault moves and what side of the fault you're on," he explained.

Atlantic City is near the Continental Fault System, which may have caused the recent earthquake that occurred earlier this month. No injuries or damage were reported as a result of the activity.

"Earthquakes of this size don't usually cause damage," Jana Pursley, a geophysicist for the USGS, said about  the recent activity.

Pursley said that similar magnitude earthquakes can cause items to fall off of shelves or knock over but rarely cause any significant structural damage to buildings or significant injuries.

The USGS has tracked earthquake data through sensitive seismograph machines since the 1990s. Pursley said that in Wyoming, areas near fault lines and mining and drilling industry locations are the most common factors that influence earthquakes.

The Dec. 12 earthquake was the second notable earthquake in southwest Wyoming in the past month. A 3.7-magnitude earthquake had been reported near Little America on November 17, 2025.

"We frequently see swarms of earthquakes," Caruso said about earthquakes occurring in close succession to each other. "In Wyoming, a lot of the quakes are associated with Yellowstone."

He said earthquakes near Yellowstone and the Teton range are often influenced by moving magma that can contribute to shifts in geological faults.

The strongest earthquake ever recorded in Wyoming was a result of a magnitude 7.5 earthquake that occurred just outside Yellowstone in Hebgen Lake in Montana on August 17, 1959. The earthquake, followed by several aftershocks that reached up to a 6.5 magnitude, triggered a landslide along the Madison River. As a result of the earthquake and landslide, 28 people lost their lives.

Known, active faults can be found across the state and the historical record shows that large earthquakes can occur at these locations, according to the Wyoming State Geological Survey.

"Most of Wyoming … can have a magnitude 6.5 earthquake, which can cause significant damage," according to the WSGS. "Even though such events occur infrequently, residents should prepare for such an event."

If residents are outdoors when experiencing an earthquake, WSGS recommends they remain outside and away from buildings, trees, fences and power lines. If in a vehicle, drivers should pull over to the side of the road and remain in their vehicles.

WSGS generally recommends that people who are indoors when an earthquake occurs stay inside and brace under a table, against a clear wall or in a doorway. It is also recommended to be aware of objects that can fall, including furniture or items that can easily break like windows or glass doors.

This story was published on Dec. 20, 2025.