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Location:
27km WSW of Westmorland, CA
Period:
18 Aug 2021 18:00:59 - 20 Aug 2021 18:37:33 (2 days 36 minutes)
Volcanoes in 100km radius:
Salton Buttes(34km), Prieto, Cerro(92km)
Earthquakes:
37
18 swarms found nearby.
2006
S20060630.1(21.8km)
29 Jun
5 days 14 hours
126 earthquakes
S20061129.1(26.0km)
29 Nov
1 day 4 hours
34 earthquakes
2008
S20080527.1(26.8km)
27 May
9 hours
47 earthquakes
30 Oct
2 days 14 hours
105 earthquakes
2009
VS20090417.1(29.3km)
17 Apr
1 day 13 hours
29 earthquakes
S20090721.1(25.2km)
20 Jul
1 day 10 hours
32 earthquakes
S20091101.1(21.5km)
1 Nov
12 hours
26 earthquakes
2010
PS20100405.1(110.6km)
4 Apr
1 hours
5 earthquakes
S20100517.2(21.9km)
16 May
3 days 18 hours
47 earthquakes
2012
VS20120323.1(25.3km)
22 Mar
2 days 22 hours
73 earthquakes
2013
VS20130404.1(28.8km)
3 Apr
2 days 12 hours
59 earthquakes
VS20130603.1(26.0km)
3 Jun
3 days 15 hours
134 earthquakes
2018
13 May
2 days 22 hours
70 earthquakes
2020
10 May
5 days 22 hours
133 earthquakes
2024
S20240803.1(21.9km)
2 Aug
2 days 23 hours
54 earthquakes
2025
S20250422.1(28.6km)
22 Apr
10 hours
28 earthquakes
2026
18 May
3 hours
43 earthquakes
S20260702.1(28.2km)
1 Jul
1 day 21 hours
31 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20210819.1: Analysis of Activity Near Westmorland, California

A seismic swarm designated S20210819.1 was recorded 27 km west-southwest of Westmorland, California, in the Imperial Valley. The sequence began at 18:00 UTC on 18 August 2021 and concluded at 18:37 UTC on 20 August 2021, spanning 48 hours and 36 minutes. During this period, 37 earthquakes were registered, with magnitudes ranging from 1.2 to 3.9 and focal depths between 1 km and 11 km.

The swarm exhibited typical characteristics of clustered seismicity in the region, featuring an initial burst of events on 18 August followed by sustained activity through 19 August and a final event on 20 August. Notable events included a magnitude 3.9 earthquake at 21:45 UTC on 18 August at 7 km depth and a magnitude 3.8 event minutes later at 3 km depth. Subsequent activity remained below magnitude 3.0, with many events clustered between 3 km and 7 km depth.

The Imperial Valley lies within the Salton Trough, a tectonically active pull-apart basin formed by the interaction of the Pacific and North American plates along the San Andreas Fault system. This setting includes the Brawley Seismic Zone and the Imperial Fault, where right-lateral strike-slip motion dominates. High heat flow from underlying magmatic intrusions and geothermal activity contributes to fluid-driven seismicity, a common mechanism for earthquake swarms in the area. Depths recorded in this swarm align with the shallow brittle crust typical of the region, generally less than 15 km.

Historical records since 2000 indicate 14 prior swarms in the vicinity, occurring in 2006 (two events), 2008 (two), 2009 (three), 2010 (two), 2012 (one), 2013 (two), 2018 (one), and 2020 (one). These sequences reflect the area's recurrent swarm behavior, often linked to aseismic slip and pore-pressure changes rather than mainshock-aftershock patterns.

Such swarms provide insight into local stress regimes and fault interactions without necessarily indicating imminent larger earthquakes. Monitoring continues through regional networks to track any evolution in activity.

References

United States Geological Survey Earthquake Catalog California Geological Survey Regional Fault Maps Southern California Seismic Network Reports