USGS explains how scientists determine Yellowstone earthquake origins

The US Geological Survey published an article explaining how scientists determine whether Yellowstone earthquakes are volcanic or tectonic in origin. The article was written by David Shelly, a seismologist with the agency. It appeared in the Yellowstone Caldera Chronicles column and was published on Monday 19 October 2026.

The article stated that Yellowstone lies within the Intermountain Seismic Belt, a broad seismic zone that extends more than 800 miles from Arizona to Montana and is up to 120 miles wide. The belt separates the Colorado Plateau from a more active tectonic province to the west. Notable historical earthquakes in the greater Yellowstone area include the 1959 magnitude 7.3 Hebgen Lake earthquake and the 1975 magnitude 6.0 Norris earthquake.

Scientists said the source of stress driving an earthquake could be volcanic, caused by large-scale deformation from fluids or magma movement in the subsurface, or tectonic, caused by the slow accumulation of forces. The trigger could involve small changes in stress or fault strength induced by volcanic processes, or the accumulation of tectonic stress simply reaching the breaking point of a fault.

The article noted that earthquakes at Yellowstone are often generated by combinations of tectonic and volcanic processes. Many earthquake swarms occur when slowly accumulated tectonic stress is suddenly released due to water-rich fluids infiltrating faults and weakening them. These fluids are often derived from the deeper volcanic system.

The article explained that these water-rich fluids may be counterintuitively released as part of the ongoing cooling of magma deep beneath Yellowstone, rather than when the magma is heating up. As magma cools, water-rich fluids that were incorporated in the chemical structure of the magma may be released. These fluids episodically make their way toward the surface and may trigger earthquakes and earthquake swarms as they interact with existing tectonic faults.

Scientists said Yellowstone gets rattled by between 1,500 and 2,500 located earthquake events in a typical year. The article stated that scientists would continue to examine earthquakes using data from Yellowstone's seismic network to understand the active processes occurring beneath the surface.