A seismic swarm designated S20251115.1 occurred 15 km northeast of Milford in Beaver County, Utah, between 18:46 on 14 November 2025 and 02:18 on 17 November 2025. Over 55 hours and 32 minutes, the swarm produced 36 earthquakes, all of low magnitude ranging from 0.3 to 1.6. Depths were shallow, predominantly between 1 and 2 km, with one event at 0 km.
The events clustered without a dominant mainshock, a pattern typical of swarm activity driven by fluid migration along fractures rather than sudden tectonic rupture. Magnitudes remained below levels likely to cause damage, consistent with microseismicity in the area.
Milford lies within the Basin and Range Province of western Utah, where east-west crustal extension produces north-south trending normal faults. This tectonic setting generates frequent small earthquakes across the Intermountain Seismic Belt. The specific location northeast of Milford sits near the margins of the Mineral Mountains, a range with Miocene volcanic and intrusive rocks overlying older Precambrian basement. Geothermal activity in the broader Milford area reflects ongoing heat flow and fluid circulation within fractured crystalline rock, conditions that can facilitate earthquake swarms.
Seismic swarms have occurred repeatedly in this portion of Utah since at least 2000. Records indicate 17 swarms between 2000 and 2025, with yearly counts as follows: one in 2019, four in 2020, one in 2021, one in 2022, two in 2023, seven in 2024, and one in 2025. These episodes typically involve low-magnitude events at shallow depths and are monitored for possible links to geothermal or hydrothermal processes.
The November 2025 swarm fits this regional pattern. Its brief duration and uniform depth distribution suggest a localized trigger, possibly related to transient fluid pressure changes along pre-existing faults. No larger events accompanied the sequence, and activity ceased abruptly after the final recorded shock.
Ongoing monitoring by regional seismic networks continues to track microseismicity in the Milford vicinity, providing data that improves understanding of extensional tectonics and geothermal systems in the eastern Great Basin.
USGS Earthquake Hazards Program. Earthquake Catalog for Utah.
Utah Geological Survey. Seismic Monitoring and Fault Studies.
University of Utah Seismograph Stations. Annual Earthquake Reports.