A seismic swarm designated S20240731.1 was recorded 14 km northeast of Milford, Utah. The sequence began at 20:18 UTC on 30 July 2024 and concluded at 04:20 UTC on 4 August 2024, spanning 104 hours and 2 minutes. During this period, 81 earthquakes were registered.
The swarm occurred within the Basin and Range Province, an extensional tectonic regime marked by normal faulting and crustal thinning. The Milford area lies along the Intermountain Seismic Belt, where active faults accommodate regional strain. Shallow focal depths between 2 km and 4 km are typical for this setting and consistent with brittle failure in the upper crust. No surface rupture or damage was associated with the events.
Event magnitudes ranged from –0.4 to 1.4, with the two largest shocks (both M 1.4) occurring on 31 July and 2 August. Depths clustered at 2–3 km, indicating a compact source volume. The temporal distribution showed peak activity on 31 July, followed by a gradual decline through 4 August. Such patterns are characteristic of swarms, in which no single mainshock dominates and energy release remains distributed.
Historical records indicate 13 swarms have occurred in the same region since 1 January 2000. Annual counts are as follows: 2020 (4), 2021 (1), 2022 (1), 2023 (2), and 2024 (5). This frequency underscores persistent low-level tectonic or hydrothermal processes near Milford.
The 2024 swarm aligns with the area’s established seismic character. Continued monitoring by regional networks supports improved understanding of fault behavior and hazard assessment in western Utah.
USGS Earthquake Catalog
University of Utah Seismograph Stations
Utah Geological Survey – Basin and Range tectonics reports