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Location:
8 km E of Ridgecrest, CA
Period:
30 Nov 2019 04:38:19 - 2 Dec 2019 21:01:23 (2 days 16 hours 23 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
49
30 swarms found nearby.
2013
3 May
1 day 22 hours
37 earthquakes
2019
S20190704.1(10.5km)
4 Jul
221 days 12 hours
22493 earthquakes
4 Jul
75 days 9 hours
8149 earthquakes
S20190708.2(28.2km)
7 Jul
4 days 17 hours
70 earthquakes
S20190712.1(27.0km)
11 Jul
16 hours
29 earthquakes
12 Aug
3 days 6 hours
50 earthquakes
8 Sep
1 day 13 hours
47 earthquakes
S20190910.1(22.5km)
10 Sep
3 days 21 hours
145 earthquakes
1 Oct
4 days 13 hours
127 earthquakes
5 Oct
1 day 18 hours
26 earthquakes
13 Oct
1 day 23 hours
36 earthquakes
15 Oct
2 days 23 hours
108 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
10 Jan
22 days 10 hours
422 earthquakes
22 Jan
17 hours
24 earthquakes
S20200208.1(14.1km)
7 Feb
1 day 19 hours
44 earthquakes
S20200213.1(10.9km)
12 Feb
5 days 22 hours
159 earthquakes
21 Feb
5 days 20 hours
94 earthquakes
S20200322.1(19.4km)
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
S20200727.1(16.9km)
27 Jul
13 days 20 hours
183 earthquakes
13 Aug
7 days 2 hours
81 earthquakes
21 Sep
5 days 2 hours
99 earthquakes
2022
S20220715.1(18.6km)
14 Jul
4 days 3 hours
55 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20191201.2: Analysis of Activity East of Ridgecrest, California

A seismic swarm designated S20191201.2 was recorded 8 km east of Ridgecrest, California, beginning at 04:38 UTC on 30 November 2019 and concluding at 21:01 UTC on 2 December 2019. Over 64 hours and 23 minutes, the sequence comprised 49 earthquakes. Magnitudes ranged from 0.0 to 2.7, with the largest event (magnitude 2.7) occurring on 1 December at 09:53 UTC at a depth of 8 km. Depths throughout the swarm were predominantly shallow, between 2 km and 11 km, consistent with activity in the brittle upper crust.

The swarm exhibited typical characteristics of clustered seismicity, with events distributed across multiple small faults rather than a single mainshock-aftershock sequence. Early activity on 30 November included several events of magnitude 1.0–2.1 at depths of 3–11 km. Activity intensified on 1 December, featuring the peak magnitude alongside numerous smaller shocks, many at depths of 4–6 km. The final events on 2 December were low-magnitude and shallow. No events exceeded magnitude 3.0, indicating limited energy release compared with larger regional sequences.

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 American plate boundary motion. The local geology is dominated by Quaternary alluvial deposits overlying Mesozoic basement rocks, with active faulting influenced by the nearby Garlock Fault to the south and the Little Lake Fault zone. Historical deformation in the area reflects ongoing tectonic strain accumulation and release along immature fault networks.

Since 2000, twelve swarms have been documented in the broader Ridgecrest region. Prior episodes occurred in 2013 (one swarm) and 2019 (eleven swarms). The December 2019 swarm followed the major July 2019 Ridgecrest earthquake sequence, which ruptured multiple previously unmapped faults and produced surface offsets. Post-mainshock swarms in this setting are common as afterslip and viscoelastic relaxation redistribute stress on adjacent structures.

Seismic monitoring in the region benefits from dense instrumentation deployed after the 2019 main events, enabling precise location of small-magnitude activity. Depths recorded during S20191201.2 align with the seismogenic zone thickness of approximately 10–12 km observed in the Mojave Desert. Continued low-level seismicity underscores the area’s elevated background hazard within the Walker Lane–Eastern California Shear Zone transition.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
California Geological Survey Regional Fault Maps
Southern California Earthquake Data Center (scedc.caltech.edu)