Seismic Swarm S20221115.1: Analysis of Activity Near Mammoth, Wyoming
A seismic swarm designated S20221115.1 occurred 21 km SSW of Mammoth, Wyoming, between 15:45 on 14 November 2022 and 21:23 on 16 November 2022. Over 53 hours and 38 minutes, 48 earthquakes were recorded. This event aligns with the region's established pattern of episodic swarm activity driven by hydrothermal and magmatic processes.
The swarm initiated with a magnitude 2.5 event at 7 km depth on 14 November at 15:45:04 UTC. Subsequent events ranged from negative magnitudes to 1.6, with depths predominantly between 1 km and 10 km. Early activity featured shallow events, including several at 1–3 km, before shifting toward slightly deeper hypocenters averaging 6–8 km during the peak period on 15 November. Magnitudes remained low overall, with only five events exceeding magnitude 1.0. The sequence concluded with a magnitude 0.0 event at 8 km depth on 16 November.
The Mammoth area lies within the Yellowstone volcanic system, situated above a continental hotspot that has produced extensive rhyolitic and basaltic volcanism over the past 2 million years. The current caldera, formed approximately 631,000 years ago during the Lava Creek eruption, continues to exhibit uplift, subsidence, and fluid-driven seismicity. Mammoth Hot Springs, roughly 21 km northeast of the swarm epicenter, represents an active hydrothermal outflow zone linked to the same magmatic heat source. Regional faults, including segments of the Gallatin and Madison ranges, accommodate extensional stresses that facilitate fluid migration and earthquake swarms.
Historical records since 2000 document 92 swarms in the vicinity, with notable clusters in 2000 (10 events), 2008 (7), 2013 (7), 2014 (7), 2021 (7), and 2022 (8). These recurrent episodes reflect the dynamic interplay between magmatic recharge, hydrothermal circulation, and tectonic stress release characteristic of the Yellowstone Plateau.
Insights from S20221115.1 indicate a typical swarm signature: high event frequency over a short duration, low maximum magnitudes, and variable but generally shallow depths consistent with fluid involvement. The progression from mixed shallow-to-mid crustal depths suggests initial fracturing followed by sustained pressurization at hydrothermal levels. No escalation to higher-magnitude tectonic events was observed, consistent with the predominantly aseismic behavior of the broader volcanic field.
This swarm contributes to ongoing monitoring efforts that track deformation and seismicity as indicators of volcanic unrest. Continued observation remains essential given Yellowstone's status as an active caldera system.
References SeismoSight internal swarm classification S20221115.1 USGS Yellowstone Volcano Observatory geological summaries (standard regional framework)