Seismic Swarm SVS20170814.1: Analysis of Activity Near West Yellowstone, Montana

A notable earthquake swarm designated SVS20170814.1 was recorded 28 km east-southeast of West Yellowstone, Montana. The sequence began at 06:36 on 14 August 2017 and concluded at 05:02 on 15 August 2017, encompassing 32 events over 22 hours and 26 minutes. Magnitudes ranged from 0.1 to 2.6, with the largest shock occurring at 14:04 on 14 August. Focal depths remained shallow, predominantly between 3 km and 9 km, consistent with activity in the upper crust of the region.

This swarm exemplifies the episodic seismic behavior typical of the Yellowstone volcanic field. The area lies on the eastern margin of the Yellowstone Caldera, formed approximately 631,000 years ago during the most recent major eruption. Ongoing crustal deformation arises from the underlying hotspot, which drives magma intrusion, fluid migration, and hydrothermal circulation. These processes generate frequent earthquake swarms rather than isolated mainshock-aftershock sequences.

Since 2000, 56 swarms have been documented in the vicinity. Annual counts include eight in 2000, nine in 2002, seven in 2006, six each in 2008 and 2014, and five in 2013. Such recurrent activity reflects the dynamic interplay between magmatic and tectonic stresses beneath the caldera.

Within SVS20170814.1, events clustered tightly in time and space. Early activity on 14 August featured multiple shocks near magnitude 1.0 at depths of 5–7 km. Peak energy release occurred midday with events of 2.0 and 2.6. Later phases on 15 August included four additional small-magnitude quakes at depths of 3–7 km before the sequence tapered. The absence of larger events or significant surface deformation aligns with patterns observed in prior Yellowstone swarms driven by fluid pressure changes.

Monitoring by regional seismic networks confirms that swarms of this scale pose minimal hazard to infrastructure yet provide critical data on subsurface dynamics. Continued observation supports hazard assessment for the broader Yellowstone Plateau, where similar episodes have occurred throughout the Holocene.

References

• U.S. Geological Survey, Yellowstone Volcano Observatory reports on caldera geology and seismicity (updated through 2023).
• SeismoSight internal swarm classification database for event parameters and historical statistics.