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Note:This page contains AI-generated content for informational and entertainment purposes only. It may contain inaccuracies. Raw event data is from USGS and EMSC. All statistics, lists, and derived information are generated by this site. Full disclaimerFound an error?
Location:
5km WSW of Anza, CA
Period:
25 Sep 2017 04:08:03 - 28 Jan 2018 01:15:07 (124 days 21 hours 7 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
2217
61 swarms found nearby.
2002
S20021024.3(25.3km)
23 Oct
2 days 17 hours
38 earthquakes
2003
5 Mar
1 day 2 hours
35 earthquakes
2005
S20050612.1(26.1km)
12 Jun
26 days 19 hours
904 earthquakes
S20050820.1(26.9km)
19 Aug
3 days 23 hours
96 earthquakes
2009
25 Jul
1 day 19 hours
29 earthquakes
2010
S20100708.1(27.8km)
7 Jul
35 days 19 hours
1709 earthquakes
S20101203.2(26.9km)
2 Dec
10 days 0 hours
68 earthquakes
2011
1 Feb
1 day 18 hours
43 earthquakes
S20110416.1(22.6km)
15 Apr
7 days 6 hours
90 earthquakes
S20110727.1(26.0km)
26 Jul
4 days 1 hours
42 earthquakes
2012
S20120630.1(29.2km)
29 Jun
2 days 0 hours
31 earthquakes
2013
S20130922.1(27.2km)
21 Sep
8 days 10 hours
91 earthquakes
2014
26 Jan
2 days 4 hours
38 earthquakes
S20140418.1(14.3km)
18 Apr
8 days 7 hours
191 earthquakes
9 May
2 days 9 hours
44 earthquakes
2015
10 Feb
12 days 21 hours
168 earthquakes
S20150401.1(28.7km)
31 Mar
38 days 7 hours
543 earthquakes
2016
14 Jun
7 days 5 hours
80 earthquakes
S20160720.2(28.5km)
19 Jul
6 days 5 hours
68 earthquakes
S20161221.1(10.4km)
21 Dec
1 day 21 hours
34 earthquakes
S20161230.1(25.1km)
29 Dec
4 days 7 hours
48 earthquakes
2017
S20170503.1(20.2km)
2 May
5 days 5 hours
91 earthquakes
S20170510.1(19.3km)
9 May
15 days 6 hours
129 earthquakes
8 Jun
3 days 22 hours
61 earthquakes
S20170727.1(20.6km)
26 Jul
14 days 9 hours
192 earthquakes
S20170907.1(19.3km)
6 Sep
14 days 21 hours
245 earthquakes
2018
2 Feb
28 days 21 hours
426 earthquakes
S20180305.1(17.6km)
4 Mar
19 days 17 hours
203 earthquakes
S20180403.1(19.6km)
2 Apr
10 days 14 hours
197 earthquakes
S20180420.1(19.9km)
19 Apr
69 days 21 hours
1109 earthquakes
26 May
4 days 20 hours
54 earthquakes
S20180630.1(19.9km)
29 Jun
41 days 14 hours
582 earthquakes
S20180811.1(19.1km)
11 Aug
209 days 15 hours
6032 earthquakes
2019
S20190328.1(22.0km)
27 Mar
5 days 20 hours
79 earthquakes
S20190426.1(19.4km)
25 Apr
1 day 22 hours
37 earthquakes
2020
S20200109.1(13.0km)
8 Jan
11 days 9 hours
159 earthquakes
S20200122.1(19.1km)
21 Jan
3 days 12 hours
57 earthquakes
1 Feb
8 days 17 hours
147 earthquakes
29 Feb
6 days 16 hours
67 earthquakes
S20200526.3(13.1km)
25 May
7 days 18 hours
100 earthquakes
S20200607.1(18.2km)
6 Jun
9 days 19 hours
109 earthquakes
S20200703.1(17.9km)
2 Jul
3 days 16 hours
70 earthquakes
S20200708.1(19.7km)
7 Jul
26 days 8 hours
287 earthquakes
25 Sep
3 days 10 hours
42 earthquakes
18 Dec
5 days 0 hours
66 earthquakes
2021
27 Mar
2 days 21 hours
33 earthquakes
26 Apr
5 days 5 hours
80 earthquakes
S20210609.1(20.4km)
8 Jun
5 days 16 hours
126 earthquakes
20 Sep
8 days 7 hours
216 earthquakes
2022
18 Apr
8 days 1 hours
76 earthquakes
S20220519.2(29.1km)
18 May
1 day 8 hours
29 earthquakes
1 Jul
3 days 23 hours
49 earthquakes
S20220922.1(29.5km)
22 Sep
1 day 18 hours
31 earthquakes
S20220930.2(29.5km)
29 Sep
4 days 5 hours
69 earthquakes
25 Oct
1 day 10 hours
35 earthquakes
2023
S20230221.1(13.5km)
20 Feb
1 day 17 hours
25 earthquakes
S20230305.1(21.5km)
5 Mar
1 day 2 hours
25 earthquakes
25 Mar
2 days 6 hours
38 earthquakes
2024
28 Aug
2 days 1 hours
31 earthquakes
2025
S20250516.1(13.9km)
16 May
4 days 7 hours
45 earthquakes
28 Nov
7 days 2 hours
82 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20170926.1 Near Anza, California

The seismic swarm designated S20170926.1 occurred 5 km west-southwest of Anza in Riverside County, California. It began at 04:08 UTC on 25 September 2017 and concluded at 01:15 UTC on 28 January 2018, spanning 2,997 hours and 7 minutes. During this interval, 2,217 earthquakes were recorded.

Analysis of the first 100 events reveals predominantly low-magnitude activity. Magnitudes ranged from -0.1 to 2.1, with the majority below 1.0 and only a few exceeding 1.5. Depths varied between 2 km and 17 km, clustering most frequently between 4 km and 6 km. Early events on 25 September included several at depths of 4–6 km with magnitudes of 0.4–2.1, while subsequent days showed continued shallow activity interspersed with occasional deeper occurrences up to 17 km. This pattern is consistent with fluid-driven swarm behavior rather than a single mainshock-aftershock sequence.

The Anza region lies within the Peninsular Ranges province of southern California, part of the broader San Andreas Fault system. The area is influenced by the northwest-trending San Jacinto Fault Zone, which accommodates a significant portion of the Pacific-North America plate boundary slip. Right-lateral strike-slip motion along these faults generates frequent seismicity. The local geology features crystalline basement rocks of the Peninsular Ranges Batholith overlain by sedimentary units, with faulting concentrated along narrow zones that can produce earthquake swarms through aseismic slip and fluid migration.

Historical records indicate 26 swarms in the region since 1 January 2000. These occurred in the following years with the listed event counts: 2002 (1), 2003 (1), 2005 (2), 2009 (1), 2010 (2), 2011 (3), 2012 (1), 2013 (1), 2014 (3), 2015 (2), 2016 (4), and 2017 (5). Such recurrent swarms highlight the persistent seismic hazard in this portion of the fault system.

SeismoSight internal classification.
Data source: SeismoSight swarm catalog S20170926.1.