Seismic Swarm SVS20130913.1: Analysis of Activity Near West Yellowstone, Montana

Seismic swarm SVS20130913.1 occurred approximately 25 km east-southeast of West Yellowstone, Montana, within the Yellowstone volcanic region. The event sequence began at 07:16 on 13 September 2013 and concluded at 11:53 on 17 September 2013, spanning 100 hours and 37 minutes. During this period, 243 earthquakes were recorded.

The Yellowstone area lies atop a large volcanic system characterized by a shallow crustal magma reservoir and extensive hydrothermal networks. This geology drives frequent earthquake swarms through fluid migration, gas release, and minor crustal adjustments rather than primary tectonic faulting. Swarms in this setting typically feature low-magnitude events at depths of 0–10 km, consistent with the shallow seismicity observed in SVS20130913.1.

Analysis of the first 100 events reveals predominantly small magnitudes, with values ranging from 0.2 to 2.5. The majority clustered between 0.5 and 2.0, indicating limited energy release. Depths remained shallow, averaging around 4–5 km, with most events between 1 km and 9 km; occasional negative or zero values appear in the dataset as classification artifacts. Temporal distribution showed peak activity in the initial hours, followed by a gradual decline, typical of swarm behavior driven by transient subsurface processes.

Historical records indicate 49 swarms in the region since 1 January 2000. Yearly counts include 9 in 2000, 4 in 2001, 8 in 2002, 3 in 2003, 1 in 2004, 6 in 2006, 2 in 2007, 7 in 2008, 3 in 2009, 1 in 2010, 1 in 2011, 1 in 2012, and 3 in 2013. These patterns underscore the recurrent nature of swarm activity linked to the volcanic system's ongoing dynamics.

Such sequences contribute to monitoring efforts by the U.S. Geological Survey and Yellowstone Volcano Observatory, providing data on crustal stress and fluid movement without indicating imminent volcanic unrest.

References

U.S. Geological Survey Earthquake Hazards Program
Yellowstone Volcano Observatory Annual Reports
SeismoSight internal swarm classification records