Seismic Swarm SVS20130106.1 in the Yellowstone Region

Seismic swarm SVS20130106.1 occurred 55 km east-southeast of West Yellowstone, Montana, beginning at 03:50 on 6 January 2013 and concluding at 18:00 on 7 January 2013. Over 38 hours and 10 minutes, the swarm produced 54 earthquakes. Magnitudes ranged from -0.7 to 2.1, with the majority of events registering below 1.5. Depths were predominantly shallow, concentrated between 1 and 3 km, although a cluster of events on 7 January reached depths of 10–12 km.

The sequence displayed classic swarm characteristics, featuring a rapid onset of low-magnitude events without a dominant mainshock. Early activity on 6 January included multiple events near 2 km depth, followed by intermittent bursts throughout the day. Activity continued into 7 January with slightly deeper events before tapering off by evening. Such patterns reflect clustered microseismicity rather than a typical foreshock-mainshock-aftershock sequence.

The swarm location lies within the northeastern extent of the Intermountain Seismic Belt, adjacent to the Yellowstone volcanic system. This region experiences ongoing deformation driven by the Yellowstone hotspot, which has produced one of North America’s largest calderas. Crustal stresses arise from a combination of magmatic inflation, hydrothermal fluid migration, and regional extensional tectonics. Earthquake swarms are a recurrent feature here, often linked to the movement of pressurized fluids through fractured volcanic rock rather than direct magma intrusion.

Historical records indicate persistent swarm activity in the broader area. Since 1 January 2000, 14 swarms have been documented, occurring in 2002 (5 events), 2004 (1), 2006 (1), 2008 (1), 2009 (4), 2010 (1), and 2011 (1). These episodes underscore the dynamic nature of the subsurface environment, where episodic fluid release repeatedly triggers seismic unrest without leading to volcanic eruption.

Ongoing monitoring by the U.S. Geological Survey and the Yellowstone Volcano Observatory continues to track such activity as part of routine assessment of the caldera’s behavior. The 2013 swarm remained well within normal background levels for the region and posed no elevated hazard.

References
SeismoSight internal swarm classification SVS20130106.1
U.S. Geological Survey, Yellowstone Volcano Observatory seismic catalogs and regional tectonic summaries