Location:
Period:
17 Apr 2020 08:21:01 - 20 Apr 2020 02:49:05 (2d 18h 28m)
Volcanoes in 100km radius:
Earthquakes:
116
24 swarms found nearby.
2020
S20200117.2(19.2km)
17 Jan
3 days 13 hours
46 earthquakes
1 May
1 day 8 hours
30 earthquakes
6 Oct
1 day 4 hours
41 earthquakes
2021
30 Jul
9 hours
44 earthquakes
2022
6 Apr
4 hours
29 earthquakes
2023
26 Nov
20 hours
31 earthquakes
13 Dec
15 hours
24 earthquakes
2024
15 Feb
8 days 4 hours
308 earthquakes
24 Feb
6 days 6 hours
260 earthquakes
4 Mar
3 days 6 hours
47 earthquakes
3 Apr
4 days 22 hours
172 earthquakes
7 Jun
5 days 3 hours
152 earthquakes
30 Jul
4 days 8 hours
81 earthquakes
S20241130.1(10.1km)
29 Nov
13 days 8 hours
239 earthquakes
2025
28 Aug
9 days 6 hours
245 earthquakes
14 Nov
2 days 7 hours
36 earthquakes
2026
11 Mar
2 days 1 hours
47 earthquakes
21 Mar
12 days 0 hours
175 earthquakes
6 Aug
22 hours
24 earthquakes
13 Aug
21 hours
24 earthquakes
24 Aug
1 day 20 hours
31 earthquakes
26 Aug
2 days 5 hours
43 earthquakes
3 Sep
1 day 14 hours
29 earthquakes
S20260910.2(10.6km)
10 Sep
1 day 16 hours
48 earthquakes
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Seismic Swarm S20200418.1: Analysis of Activity Near Milford, Utah

The seismic swarm designated S20200418.1 was recorded 21 km east-northeast of Milford, Utah, beginning at 08:21 on 17 April 2020 and concluding at 02:49 on 20 April 2020. Over this 66-hour, 28-minute interval, a total of 116 earthquakes were registered. Examination of the first 100 events reveals predominantly low-magnitude activity, with the majority of events registering between -0.9 and 1.0. The largest event reached magnitude 2.4 at a depth of 6 km on 17 April at 23:32:10, followed by a magnitude 1.5 event five minutes later. Event depths remained shallow throughout the sequence, clustering between 0 and 6 km. Negative-magnitude detections, which indicate microearthquakes, comprised a substantial portion of the catalog, consistent with high-resolution monitoring of swarm-type sequences. Temporal distribution showed an initial burst of activity on 17 April, including several events near magnitude 1.0, followed by sustained low-level seismicity into 18 April. No events exceeded magnitude 2.4 during the analyzed period. The Milford region lies within the Basin and Range Province of western Utah, where active crustal extension produces normal faulting along range-bounding structures. This tectonic setting is associated with elevated heat flow and geothermal systems, notably the Roosevelt Hot Springs area located near the swarm epicenters. Such conditions can facilitate swarm activity through fluid migration along faults, promoting small-magnitude events at shallow depths without a single dominant mainshock. Historical records indicate that only one swarm has been identified in the region since 1 January 2000, with the previous occurrence also dated to 2020. This rarity underscores the episodic nature of clustered seismicity in this portion of the Great Basin.

References

  • SeismoSight internal swarm classification database
  • USGS Earthquake Catalog (regional tectonic context)
  • Utah Geological Survey publications on Basin and Range seismicity