Yellowstone has seen a spate of seismic activity since early February, with over 200 incidents recorded in the latest earthquake swarm.
According to the U.S. Geological Survey, all the quakes have occurred approximately 8 miles northeast of West Yellowstone, Montana.
It’s worth noting here: the current earthquake swarm does not portend the imminent eruption of the Yellowstone caldera.
Seismic activity around Yellowstone National Park is commonplace, especially earthquake swarms. Last summer, for instance, the USGS recorded over 1600 quakes by early August. Indeed, the current earthquake swarm is happening in the same area as last year’s. You can see a map of the current swarm contrasted with last year’s below, courtesy of the University of Utah Seismographic Stations. From the USGS:
The present swarm started on February 8, with a few events occurring per day. On February 15, seismicity rates and magnitudes increased markedly. As of the night of February 18, the largest earthquake in the swarm is M2.9, and none of the events have been felt. All are occurring about 8 km (5 mi) beneath the surface.
The University of Utah Seismograph Stations, which is responsible for seismic monitoring in the Yellowstone region, uses a standard definition of an earthquake swarm—an increase in earthquake rates within a given area over a relatively concentrated period of time without a single large “mainshock.”
Swarms reflect changes in stress along small faults beneath the surface, and generally are caused by two processes: large-scale tectonic forces, and pressure changes beneath the surface due to accumulation and/or withdrawal of fluids (magma, water, and/or gas).
As mentioned, swarms are a normal part of Yellowstone. Indeed, the USGS has termed the current level of seismic activity “relatively weak.”
Although it is not known when the earthquake swarm will wind down, both the USGS and UUSS will continue to monitor the situation and use data from both this swarm and last year’s swarm to refine their instruments and flesh out understanding of Yellowstone’s seismic dynamics.