Seismic Swarm S20140330.1 in the Yellowstone Region: Geological Context and Event Analysis

The seismic swarm designated S20140330.1 occurred approximately 23 km south of Mammoth, Wyoming, within the Yellowstone volcanic system. This region lies atop the Yellowstone Caldera, a large volcanic depression formed by massive eruptions over the past 2.1 million years. The area's geology is dominated by rhyolitic lava flows, extensive hydrothermal features, and ongoing crustal deformation driven by a shallow magma reservoir and associated fluid movement.

Yellowstone experiences persistent low-level seismicity due to its active volcanic and hydrothermal setting. Earthquake swarms here typically result from the migration of magmatic or hydrothermal fluids rather than tectonic fault slip alone. Historical records indicate elevated swarm activity since 2000, with 49 documented swarms through 2014. Annual counts include 9 in 2000, 5 in 2001, 6 in 2002, 1 in 2003, 1 in 2004, 5 in 2006, 2 in 2007, 6 in 2008, 3 in 2009, 1 in 2010, 1 in 2011, 6 in 2013, and 3 in 2014. These episodes underscore the dynamic nature of the subsurface environment.

Swarm S20140330.1 began at 13:14 on 29 March 2014 and concluded at 08:54 on 2 April 2014, spanning 91 hours and 39 minutes. A total of 194 earthquakes were recorded. Analysis of the first 100 events reveals a concentration of activity on 30 March, with magnitudes ranging from small events near 0.0 to a peak of 4.8. Depths primarily clustered between 1 km and 6 km, consistent with shallow crustal processes in the caldera. Several events exhibited magnitudes of 3.0 or greater, including 3.3, 3.5, 3.6, and 4.8, while numerous readings registered as -9.9, reflecting internal classification thresholds for signal quality.

The temporal pattern shows an initial sequence of low-magnitude events followed by clusters of higher-energy releases around midday on 30 March. Depths remained shallow throughout, supporting interpretations of fluid-driven seismicity rather than deeper magmatic intrusion. Such swarms contribute to monitoring efforts aimed at detecting changes in volcanic unrest.

This event aligns with the broader pattern of episodic seismicity that characterizes the Yellowstone region. Ongoing surveillance by geophysical networks continues to track these phenomena to assess any implications for long-term volcanic hazards.

References

• SeismoSight internal swarm classification database
• USGS Yellowstone Volcano Observatory geological summaries (general caldera history)