A seismic swarm designated S20241130.1 was recorded 16 km northeast of Milford, Utah. The sequence began at 08:46 on 29 November 2024 and concluded at 17:11 on 12 December 2024, encompassing 239 earthquakes over 320 hours and 24 minutes. This activity aligns with the region’s established pattern of episodic earthquake clusters driven by extensional tectonics in the Basin and Range Province.
The swarm’s first 100 events displayed consistent characteristics. Magnitudes ranged from 0.0 to 1.8, with the majority falling between 0.8 and 1.4. Depths were predominantly 2 km, though several events occurred at 1 km and one at 3 km. Timing showed clustering, particularly in the initial 48 hours and around midday on 30 November and 1 December 2024. These shallow, low-magnitude events produced no reported surface damage but contributed to the cumulative seismic energy release typical of swarm sequences.
Milford lies within Beaver County in western Utah, where the crust experiences ongoing extension along north-south trending normal faults. The nearby Mineral Mountains expose Miocene volcanic and intrusive rocks linked to past magmatic activity. Geothermal gradients remain elevated due to residual heat from these intrusions, supporting hot-spring systems and potential fluid migration that can influence seismicity. Earthquake swarms in this setting often reflect fluid pressure changes or aseismic slip along fault networks rather than mainshock-aftershock sequences.
Historical records indicate 15 swarms have occurred in the area since 1 January 2000. These episodes cluster in recent years, with six recorded in 2024, two in 2023, one in 2022, one in 2021, four in 2020, and one in 2019. The recurrence suggests persistent tectonic and hydrothermal conditions that repeatedly generate swarm activity without producing larger mainshocks.
Such patterns are consistent with the broader seismotectonic framework of the Great Basin, where strain is accommodated through distributed faulting. Monitoring networks operated by the University of Utah Seismograph Stations and the U.S. Geological Survey provide continuous data that help distinguish swarm behavior from isolated tectonic events. Continued observation of parameters such as event rate decay and depth distribution will refine understanding of the driving mechanisms in this sector of the Basin and Range.
SeismoSight internal swarm classification S20241130.1
University of Utah Seismograph Stations regional catalog
U.S. Geological Survey Quaternary fault and fold database
Geological Survey of Utah Mineral Mountains volcanic field reports