Seismic Swarm S20220611.1: Earthquake Activity Near Mammoth, Wyoming

A seismic swarm designated S20220611.1 occurred 21 km south-southwest of Mammoth, Wyoming, from 13:39 on 10 June 2022 until 10:00 on 13 June 2022. Over 68 hours and 20 minutes, the sequence produced 62 earthquakes. This event aligns with the established pattern of swarm seismicity in the Yellowstone region, where clusters of small-magnitude events frequently occur without a single dominant mainshock. The earthquakes exhibited magnitudes ranging from 0.1 to 2.4, with the largest reaching 2.4 on 13 June. Depths concentrated between 2 km and 9 km, consistent with shallow crustal processes. Activity began with events near magnitude 0.9 at 6–7 km depth on 10 June and intensified on 11 June, including multiple events of magnitude 2.0–2.3. Further notable activity occurred on 12 and 13 June, featuring the peak magnitude 2.4 event at 7 km depth. Most events remained below magnitude 1.5, reflecting the swarm’s diffuse character. The location places the swarm within the Yellowstone volcanic system, a large caldera formed by massive eruptions over the past 2.1 million years. The most recent caldera-forming event occurred approximately 631,000 years ago. Ongoing magmatic and hydrothermal processes drive the region’s seismicity. Earthquake swarms here commonly result from fluid migration, crustal stress changes, or minor magmatic movement rather than tectonic fault rupture alone. Since 1 January 2000, 86 swarms have been recorded in the area. Annual counts show variability, with peaks of 10 swarms in 2000, 7 each in 2008, 2013, 2014, 2021, and lower activity in intervening years, including single swarms in several years such as 2003–2005 and 2010–2011. This distribution underscores the recurrent nature of swarm activity tied to Yellowstone’s dynamic subsurface environment. Such sequences provide valuable data on local stress regimes and fluid pathways. The modest magnitudes and shallow depths observed in S20220611.1 match typical patterns documented across prior Yellowstone swarms, supporting continued monitoring of the volcanic system.

References

SeismoSight internal swarm classification records. USGS Earthquake Hazards Program, Yellowstone seismic monitoring data.