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Location:
3km E of Westmorland, CA
Period:
30 Sep 2020 10:06:45 - 9 Oct 2020 11:34:31 (9 days 1 hour 27 minutes)
Volcanoes in 100km radius:
Salton Buttes(9km), Prieto, Cerro(82km)
Earthquakes:
1724
106 swarms found nearby.
2000
11 May
2 days 10 hours
52 earthquakes
S20000614.1(28.7km)
14 Jun
2 days 16 hours
145 earthquakes
2001
S20011113.1(24.1km)
13 Nov
23 hours
99 earthquakes
2002
24 Feb
1 day 2 hours
31 earthquakes
2003
S20030301.1(22.7km)
1 Mar
23 hours
52 earthquakes
13 Apr
1 day 18 hours
32 earthquakes
S20030524.1(17.8km)
23 May
1 day 22 hours
161 earthquakes
20 Sep
1 day 8 hours
31 earthquakes
2004
15 Mar
2 days 20 hours
64 earthquakes
2005
29 Aug
10 hours
24 earthquakes
VS20050831.1(10.7km)
31 Aug
11 days 21 hours
953 earthquakes
S20050920.1(13.4km)
19 Sep
2 days 11 hours
50 earthquakes
2008
VS20080316.1(10.7km)
15 Mar
5 days 22 hours
111 earthquakes
27 May
9 hours
47 earthquakes
2 Jun
2 days 13 hours
145 earthquakes
29 Sep
1 day 4 hours
37 earthquakes
S20081030.1(25.4km)
30 Oct
2 days 14 hours
105 earthquakes
2009
S20090321.1(23.5km)
21 Mar
2 days 3 hours
50 earthquakes
S20090324.1(24.6km)
24 Mar
6 days 21 hours
410 earthquakes
17 Apr
1 day 13 hours
29 earthquakes
13 Jun
1 day 5 hours
53 earthquakes
VS20090801.1(11.9km)
1 Aug
3 days 10 hours
106 earthquakes
S20090924.1(12.6km)
24 Sep
19 hours
28 earthquakes
2 Oct
2 days 23 hours
43 earthquakes
S20091101.1(14.9km)
1 Nov
12 hours
26 earthquakes
7 Nov
5 hours
36 earthquakes
17 Nov
1 day 19 hours
142 earthquakes
23 Nov
4 days 3 hours
69 earthquakes
2010
10 Jan
10 days 2 hours
233 earthquakes
22 Jan
2 days 3 hours
46 earthquakes
21 Feb
1 day 20 hours
28 earthquakes
4 Apr
6 days 21 hours
132 earthquakes
PS20100405.1(103.8km)
4 Apr
1 hours
5 earthquakes
22 Apr
1 day 4 hours
38 earthquakes
5 Aug
1 day 0 hours
26 earthquakes
S20100828.1(18.3km)
28 Aug
1 day 2 hours
32 earthquakes
VS20101112.1(11.8km)
11 Nov
1 day 10 hours
28 earthquakes
13 Dec
12 hours
49 earthquakes
S20101215.1(12.7km)
15 Dec
1 day 4 hours
101 earthquakes
27 Dec
11 hours
66 earthquakes
31 Dec
1 day 14 hours
33 earthquakes
2011
VS20110108.1(10.3km)
7 Jan
2 days 20 hours
94 earthquakes
27 Mar
1 day 18 hours
42 earthquakes
2 Apr
1 day 12 hours
34 earthquakes
1 Jul
1 day 2 hours
36 earthquakes
2012
S20120209.1(12.4km)
8 Feb
2 days 0 hours
29 earthquakes
VS20120219.1(14.1km)
19 Feb
1 day 18 hours
86 earthquakes
26 Feb
2 days 1 hours
88 earthquakes
S20120229.1(11.0km)
29 Feb
14 hours
34 earthquakes
3 Mar
3 days 11 hours
72 earthquakes
22 Mar
2 days 22 hours
73 earthquakes
20 May
2 days 1 hours
33 earthquakes
8 Jun
19 hours
95 earthquakes
S20120826.1(14.3km)
26 Aug
11 days 23 hours
972 earthquakes
S20120910.1(21.1km)
9 Sep
1 day 1 hours
28 earthquakes
24 Sep
1 day 17 hours
51 earthquakes
2013
18 Feb
4 days 14 hours
57 earthquakes
3 Apr
2 days 12 hours
59 earthquakes
28 Apr
2 days 2 hours
41 earthquakes
VS20130516.1(10.0km)
16 May
5 days 21 hours
135 earthquakes
3 Jun
3 days 15 hours
134 earthquakes
19 Aug
3 days 21 hours
47 earthquakes
27 Aug
1 day 17 hours
37 earthquakes
8 Oct
1 day 23 hours
83 earthquakes
13 Oct
2 days 10 hours
83 earthquakes
16 Oct
1 day 21 hours
50 earthquakes
31 Oct
16 hours
31 earthquakes
27 Nov
1 day 7 hours
52 earthquakes
21 Dec
1 day 8 hours
65 earthquakes
2014
VS20140328.1(10.8km)
28 Mar
1 day 16 hours
34 earthquakes
2015
21 May
1 day 13 hours
38 earthquakes
2016
29 Jul
1 day 9 hours
30 earthquakes
S20160926.1(17.2km)
26 Sep
6 days 7 hours
322 earthquakes
31 Oct
23 hours
39 earthquakes
S20161231.1(17.0km)
31 Dec
3 days 4 hours
317 earthquakes
2018
S20180513.1(27.9km)
13 May
2 days 22 hours
70 earthquakes
17 Jun
1 day 9 hours
26 earthquakes
2019
S20190115.1(28.2km)
15 Jan
4 hours
24 earthquakes
17 Jan
4 days 13 hours
71 earthquakes
2020
5 May
1 day 14 hours
56 earthquakes
9 Aug
4 days 12 hours
319 earthquakes
22 Oct
2 days 5 hours
53 earthquakes
13 Nov
23 hours
38 earthquakes
26 Nov
1 day 10 hours
27 earthquakes
2021
4 Jan
21 hours
43 earthquakes
10 Jan
6 hours
26 earthquakes
31 Jan
23 hours
38 earthquakes
8 Feb
3 days 9 hours
117 earthquakes
18 Mar
14 hours
27 earthquakes
4 Jun
19 days 4 hours
2347 earthquakes
S20210611.1(19.6km)
11 Jun
4 hours
26 earthquakes
S20210823.1(10.4km)
23 Aug
2 days 11 hours
48 earthquakes
2022
S20220420.1(22.9km)
19 Apr
3 days 1 hours
71 earthquakes
20 Sep
23 hours
39 earthquakes
2023
30 Apr
17 hours
68 earthquakes
3 Oct
1 day 11 hours
29 earthquakes
9 Dec
18 hours
34 earthquakes
2024
10 Feb
1 day 21 hours
26 earthquakes
14 Feb
1 day 12 hours
31 earthquakes
S20240518.1(21.6km)
18 May
2 days 19 hours
306 earthquakes
20 Dec
12 hours
48 earthquakes
2025
10 Apr
1 day 9 hours
64 earthquakes
22 Apr
10 hours
28 earthquakes
11 Jul
1 day 18 hours
132 earthquakes
2026
S20260510.1(16.7km)
9 May
4 days 16 hours
477 earthquakes
S20260518.1(28.8km)
18 May
3 hours
43 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20200930.1 Near Westmorland, California

Seismic swarm S20200930.1 began at 10:06 on 30 September 2020 and concluded at 11:34 on 9 October 2020, centered 3 km east of Westmorland in Imperial County, California. Over 217 hours and 27 minutes, the sequence produced 1724 earthquakes. The events occurred within the tectonically active Salton Trough, a pull-apart basin formed by right-lateral shear along the Pacific–North American plate boundary.

The first 100 events, recorded between 30 September 2020 at 10:06:45 and 1 October 2020 at 00:03:32, exhibited magnitudes from 0.4 to 4.3 and focal depths predominantly between 1 km and 9 km. Early activity consisted of low-magnitude events (0.4–1.6) clustered at 2–4 km depth. Magnitudes increased markedly after 22:00 on 30 September, culminating in a 4.3 event at 23:31:51 on 30 September at 4 km depth. Subsequent events included multiple shocks above magnitude 3.0, with depths shifting slightly deeper (up to 9 km) during the peak phase before returning to shallower levels. This pattern reflects typical swarm behavior driven by fluid migration along pre-existing faults rather than a single mainshock–aftershock sequence.

The Imperial Valley experiences frequent earthquake swarms owing to its position at the southern terminus of the San Andreas Fault system, where the Brawley Seismic Zone and Imperial Fault accommodate oblique extension and strike-slip motion. Geothermal fluids and sediment compaction further promote swarm activity by reducing effective normal stress on faults. Historical records maintained by SeismoSight document 81 swarms in the region since 1 January 2000, distributed across multiple years with notable concentrations in 2009 (11 swarms), 2010 (13), 2012 (11), and 2013 (13). Earlier swarms occurred in 2000–2005 and 2008, while activity remained lower in 2014–2019 before resuming in 2020.

Such sequences rarely produce damaging ground shaking when magnitudes remain below 5.0, yet they provide valuable data on fault interactions and stress transfer within the broader San Andreas system. Continued monitoring supports improved forecasting of potential larger events in this high-strain-rate corridor.

References
SeismoSight internal swarm classification S20200930.1
USGS Earthquake Hazards Program regional tectonics summary
California Geological Survey Imperial Valley fault maps