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Location:
12km SSE of Anza, CA
Period:
21 Sep 2013 17:54:09 - 30 Sep 2013 04:21:07 (8 days 10 hours 26 minutes)
Volcanoes in 100km radius:
Salton Buttes(91km)
Earthquakes:
91
79 swarms found nearby.
2001
31 Oct
10 days 17 hours
471 earthquakes
2002
2 Jan
3 days 5 hours
53 earthquakes
23 Oct
2 days 17 hours
38 earthquakes
2003
S20030306.1(26.2km)
5 Mar
1 day 2 hours
35 earthquakes
S20031113.1(18.6km)
12 Nov
1 day 17 hours
31 earthquakes
2005
12 Jun
26 days 19 hours
904 earthquakes
19 Aug
3 days 23 hours
96 earthquakes
2009
S20090726.1(23.5km)
25 Jul
1 day 19 hours
29 earthquakes
S20090818.1(27.2km)
17 Aug
1 day 21 hours
39 earthquakes
2010
8 Feb
3 days 22 hours
44 earthquakes
S20100405.7(10.4km)
5 Apr
5 days 18 hours
62 earthquakes
S20100613.1(15.1km)
12 Jun
9 days 5 hours
239 earthquakes
7 Jul
35 days 19 hours
1709 earthquakes
2 Dec
10 days 0 hours
68 earthquakes
2011
S20110202.2(26.6km)
1 Feb
1 day 18 hours
43 earthquakes
18 Mar
1 day 23 hours
34 earthquakes
15 Apr
7 days 6 hours
90 earthquakes
26 Jul
4 days 1 hours
42 earthquakes
2012
20 May
4 days 2 hours
45 earthquakes
21 Jun
3 days 19 hours
39 earthquakes
29 Jun
2 days 0 hours
31 earthquakes
2013
10 Mar
72 days 2 hours
2118 earthquakes
S20130920.1(21.4km)
19 Sep
1 day 10 hours
31 earthquakes
30 Dec
8 days 18 hours
91 earthquakes
2014
S20140418.1(22.0km)
18 Apr
8 days 7 hours
191 earthquakes
7 Aug
1 day 13 hours
28 earthquakes
2015
S20150211.2(25.9km)
10 Feb
12 days 21 hours
168 earthquakes
31 Mar
38 days 7 hours
543 earthquakes
2016
9 Jun
33 days 4 hours
1773 earthquakes
19 Jul
6 days 5 hours
68 earthquakes
25 Oct
5 days 21 hours
73 earthquakes
S20161221.1(27.9km)
21 Dec
1 day 21 hours
34 earthquakes
29 Dec
4 days 7 hours
48 earthquakes
2017
S20170503.1(22.4km)
2 May
5 days 5 hours
91 earthquakes
S20170510.1(22.3km)
9 May
15 days 6 hours
129 earthquakes
S20170727.1(23.5km)
26 Jul
14 days 9 hours
192 earthquakes
S20170907.1(23.0km)
6 Sep
14 days 21 hours
245 earthquakes
S20170926.1(27.2km)
25 Sep
124 days 21 hours
2217 earthquakes
9 Nov
2 days 20 hours
44 earthquakes
2018
S20180203.1(18.8km)
2 Feb
28 days 21 hours
426 earthquakes
S20180305.1(16.6km)
4 Mar
19 days 17 hours
203 earthquakes
S20180314.1(14.5km)
13 Mar
1 day 13 hours
26 earthquakes
S20180403.1(22.2km)
2 Apr
10 days 14 hours
197 earthquakes
S20180420.1(23.9km)
19 Apr
69 days 21 hours
1109 earthquakes
S20180527.1(27.6km)
26 May
4 days 20 hours
54 earthquakes
S20180630.1(21.0km)
29 Jun
41 days 14 hours
582 earthquakes
S20180811.1(20.2km)
11 Aug
209 days 15 hours
6032 earthquakes
2019
S20190328.1(24.0km)
27 Mar
5 days 20 hours
79 earthquakes
S20190426.1(20.4km)
25 Apr
1 day 22 hours
37 earthquakes
2020
S20200109.1(24.5km)
8 Jan
11 days 9 hours
159 earthquakes
S20200122.1(23.4km)
21 Jan
3 days 12 hours
57 earthquakes
S20200202.1(23.4km)
1 Feb
8 days 17 hours
147 earthquakes
4 Apr
40 days 3 hours
2928 earthquakes
S20200526.3(23.1km)
25 May
7 days 18 hours
100 earthquakes
2 Jun
2 days 12 hours
63 earthquakes
S20200607.1(23.8km)
6 Jun
9 days 19 hours
109 earthquakes
S20200703.1(23.1km)
2 Jul
3 days 16 hours
70 earthquakes
S20200708.1(23.5km)
7 Jul
26 days 8 hours
287 earthquakes
S20200926.2(24.3km)
25 Sep
3 days 10 hours
42 earthquakes
25 Sep
2 days 2 hours
44 earthquakes
2021
S20210328.1(25.9km)
27 Mar
2 days 21 hours
33 earthquakes
S20210427.1(26.9km)
26 Apr
5 days 5 hours
80 earthquakes
S20210609.1(23.7km)
8 Jun
5 days 16 hours
126 earthquakes
S20210921.1(23.1km)
20 Sep
8 days 7 hours
216 earthquakes
2022
13 Jan
4 days 5 hours
157 earthquakes
18 May
1 day 8 hours
29 earthquakes
S20220702.1(27.1km)
1 Jul
3 days 23 hours
49 earthquakes
S20220714.1(21.7km)
13 Jul
1 day 12 hours
26 earthquakes
S20220825.1(25.4km)
25 Aug
1 day 3 hours
27 earthquakes
22 Sep
1 day 18 hours
31 earthquakes
29 Sep
4 days 5 hours
69 earthquakes
S20221026.1(24.6km)
25 Oct
1 day 10 hours
35 earthquakes
S20221231.1(18.4km)
31 Dec
2 days 20 hours
86 earthquakes
2023
S20230221.1(22.9km)
20 Feb
1 day 17 hours
25 earthquakes
S20230326.1(24.1km)
25 Mar
2 days 6 hours
38 earthquakes
2024
S20240621.1(13.3km)
20 Jun
3 days 0 hours
41 earthquakes
S20240829.1(23.4km)
28 Aug
2 days 1 hours
31 earthquakes
2025
S20250516.1(18.3km)
16 May
4 days 7 hours
45 earthquakes
S20251117.1(11.0km)
16 Nov
3 days 16 hours
56 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Analysis of Swarm S20130922.1 Near Anza, California

The earthquake swarm designated S20130922.1 occurred in the region 12 km south-southeast of Anza, California. It initiated at 17:54 UTC on 21 September 2013 and concluded at 04:21 UTC on 30 September 2013, spanning 202 hours and 26 minutes. During this interval, 91 earthquakes were recorded, with magnitudes ranging from 0.0 to 3.4 and focal depths primarily between 4 km and 14 km.

Swarm Characteristics

The sequence began with low-magnitude events clustered at depths around 8 km. Early activity included events of magnitude 1.5 and 1.3 within the first hour. A notable escalation occurred on 22 September, featuring a magnitude 3.4 earthquake at 13:10 UTC at 12 km depth, followed by numerous aftershocks between 11 km and 12 km. Subsequent days showed continued but diminishing activity, with events such as the magnitude 2.4 on 26 September at 7 km depth. The swarm exhibited typical characteristics of clustered seismicity without a dominant mainshock-aftershock pattern, instead displaying episodic bursts concentrated in the first three days.

Geological Setting

Anza lies within the central San Jacinto Fault Zone, a major right-lateral strike-slip system in southern California. This zone forms part of the broader Pacific-North American plate boundary and accommodates a significant portion of regional dextral shear. The fault zone here comprises multiple strands, including the Clark and Coyote Creek faults, with complex geometry that promotes both large earthquakes and swarm activity. Seismicity is driven by ongoing tectonic loading, with the region experiencing frequent small events due to its proximity to the San Andreas Fault system approximately 50 km to the northeast. Depths recorded in the swarm align with the seismogenic zone in this area, typically extending from 5 km to 15 km.

Historical Context

Earthquake swarms have been recurrent in the Anza region. Since 1 January 2000, 23 swarms have been documented, distributed across multiple years: one in 2001, two each in 2002, 2003, 2005, and 2009, five in 2010, four in 2011, three in 2012, and two in 2013. This pattern underscores the persistent seismic productivity of the San Jacinto Fault Zone, where swarms often occur along fault segments with heterogeneous stress distribution.

Insights from Event Data

Temporal analysis reveals peak activity on 22 September, accounting for over 25 events within hours of the largest shock. Depths remained stable around 8–12 km for most events, suggesting a consistent rupture plane. Magnitude distribution followed a typical Gutenberg-Richter relationship, with smaller events dominating after the initial cluster. The overall low energy release indicates swarm behavior driven by fluid migration or aseismic slip rather than a single large rupture.

References

  • United States Geological Survey Earthquake Catalog
  • Southern California Seismic Network reports
  • SeismoSight internal swarm classification database