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Location:
8km ESE of Ridgecrest, CA
Period:
21 Sep 2020 01:33:51 - 26 Sep 2020 04:16:25 (5 days 2 hours 42 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
99
38 swarms found nearby.
2013
3 May
1 day 22 hours
37 earthquakes
2015
S20150602.1(27.8km)
1 Jun
1 day 6 hours
36 earthquakes
2019
4 Jul
221 days 12 hours
22493 earthquakes
4 Jul
75 days 9 hours
8149 earthquakes
S20190706.4(29.9km)
5 Jul
12 days 17 hours
712 earthquakes
S20190708.2(20.7km)
7 Jul
4 days 17 hours
70 earthquakes
S20190712.1(20.0km)
11 Jul
16 hours
29 earthquakes
S20190812.1(15.3km)
12 Aug
3 days 6 hours
50 earthquakes
S20190825.1(23.0km)
24 Aug
3 days 7 hours
165 earthquakes
8 Sep
1 day 13 hours
47 earthquakes
S20190910.1(15.7km)
10 Sep
3 days 21 hours
145 earthquakes
1 Oct
4 days 13 hours
127 earthquakes
S20191005.1(24.3km)
5 Oct
3 days 16 hours
147 earthquakes
S20191006.1(10.7km)
5 Oct
1 day 18 hours
26 earthquakes
S20191014.1(10.6km)
13 Oct
1 day 23 hours
36 earthquakes
15 Oct
2 days 23 hours
108 earthquakes
30 Nov
2 days 16 hours
49 earthquakes
1 Dec
9 days 6 hours
252 earthquakes
13 Dec
22 hours
27 earthquakes
15 Dec
6 days 12 hours
188 earthquakes
22 Dec
10 days 4 hours
196 earthquakes
2020
S20200101.1(28.2km)
1 Jan
7 days 0 hours
130 earthquakes
10 Jan
22 days 10 hours
422 earthquakes
22 Jan
17 hours
24 earthquakes
7 Feb
1 day 19 hours
44 earthquakes
12 Feb
5 days 22 hours
159 earthquakes
21 Feb
5 days 20 hours
94 earthquakes
S20200322.1(12.6km)
21 Mar
10 days 13 hours
140 earthquakes
14 Apr
7 days 19 hours
130 earthquakes
8 May
3 days 21 hours
69 earthquakes
25 May
1 day 7 hours
31 earthquakes
3 Jun
9 days 16 hours
525 earthquakes
S20200708.3(27.2km)
7 Jul
13 days 9 hours
239 earthquakes
27 Jul
13 days 20 hours
183 earthquakes
13 Aug
7 days 2 hours
81 earthquakes
2021
S20210404.1(24.1km)
3 Apr
11 days 13 hours
124 earthquakes
2022
S20220715.1(12.7km)
14 Jul
4 days 3 hours
55 earthquakes
2023
S20230503.1(27.6km)
2 May
1 day 6 hours
32 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20200921.1 Near Ridgecrest, California

A seismic swarm designated S20200921.1 was recorded 8 km east-southeast of Ridgecrest, California. The sequence began at 01:33 UTC on 21 September 2020 and concluded at 04:16 UTC on 26 September 2020, spanning 122 hours and 42 minutes. During this period, 99 earthquakes were registered, with magnitudes ranging from -0.3 to 3.2 and focal depths between 0 and 11 km.

The swarm exhibited typical characteristics of clustered microseismicity, featuring numerous events below magnitude 1.0 interspersed with occasional larger shocks. The largest event reached magnitude 3.2 on 23 September at 14:17 UTC at a depth of 7 km. Activity was most intense on the first day, with 24 events recorded, gradually declining over subsequent days until termination.

Ridgecrest lies within the Eastern California Shear Zone, a region of distributed right-lateral strike-slip faulting that accommodates a portion of the Pacific-North America plate motion. The local geology comprises Quaternary alluvium overlying Mesozoic basement rocks cut by northwest-trending faults. The 2019 Ridgecrest earthquake sequence, consisting of a magnitude 6.4 foreshock and magnitude 7.1 mainshock, occurred on previously unrecognized faults and produced extensive surface rupture, highlighting the area's elevated seismic hazard.

Since 1 January 2000, 35 swarms have been documented in the region. Annual counts include one swarm each in 2013 and 2015, 19 swarms in 2019, and 14 swarms in 2020. These sequences reflect ongoing tectonic strain release along the shear zone without producing a single dominant mainshock.

Such swarms provide insight into fault zone behavior, often occurring in volumes of fractured crust where fluid migration or aseismic slip may trigger successive failures. Depths predominantly between 2 and 10 km align with the brittle-ductile transition in this portion of the Mojave Desert. The 2020 swarm's spatial and temporal patterns are consistent with post-2019 aftershock processes, though its classification remains internal to SeismoSight records.

References

USGS Earthquake Hazards Program
California Geological Survey
Southern California Earthquake Data Center