Seismic Swarm S20140601.1: Analysis of Wyoming Earthquake Activity in 2014

Seismic swarm S20140601.1 was recorded in Wyoming between 08:02 on 31 May 2014 and 13:12 on 6 June 2014. Over 149 hours and 10 minutes, a total of 232 earthquakes were registered. Analysis of the first 100 events reveals predominantly low-magnitude activity, with magnitudes ranging from 0.2 to 3.5 and focal depths concentrated between 2 km and 10 km. The largest event reached magnitude 3.5 at a depth of 4 km on 31 May at 22:25:00. Most events clustered at depths of 4–7 km, indicating shallow crustal processes typical of swarm sequences. The temporal distribution shows an initial burst of activity on 31 May, followed by sustained but fluctuating rates through early June. Early events included magnitudes of 2.6, 2.8, and 3.5, while later ones on 3 June featured several above magnitude 2.0, including a 3.4 at 10 km depth. This pattern reflects episodic energy release without a single dominant mainshock, consistent with fluid-driven or magmatic swarm dynamics observed in tectonically active continental interiors. Wyoming lies within the Intermountain Seismic Belt, a zone of distributed crustal extension and faulting that extends from Montana through Idaho and Utah. The state's geology features Precambrian basement rocks overlain by Phanerozoic sedimentary sequences deformed during the Laramide orogeny, approximately 70–40 million years ago. Ongoing seismicity is influenced by the Yellowstone hotspot, which has produced voluminous volcanism and associated hydrothermal systems over the past 2 million years. These systems can trigger earthquake swarms through pore-pressure changes in the crust. Historical data indicate 51 swarms have occurred in the region since 1 January 2000. Annual counts vary, with peaks in 2000 (10 swarms), 2002 (6), 2008 (6), and 2013 (6). The 2014 sequence represents one of four swarms that year, underscoring the recurrent nature of clustered seismicity in this setting. Depths and magnitudes in S20140601.1 align with patterns seen in prior swarms, where events rarely exceed magnitude 4.0 and remain shallow. Such swarms contribute to understanding regional hazard by highlighting zones of elevated microseismicity. Continued monitoring supports refined models of crustal stress and fluid migration beneath Wyoming's varied topography of basins, ranges, and volcanic fields.

References

SeismoSight internal classification data for swarm S20140601.1.
USGS Earthquake Hazards Program regional reports on Intermountain Seismic Belt.