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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:
2km SE of Redlands, CA
Period:
9 Sep 2017 18:00:28 - 13 Sep 2017 06:53:02 (3 days 12 hours 52 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
53
11 swarms found nearby.
2003
27 Jun
23 hours
25 earthquakes
2005
S20050107.1(27.3km)
6 Jan
2 days 11 hours
30 earthquakes
S20050616.1(13.8km)
16 Jun
1 day 19 hours
67 earthquakes
2010
13 Feb
12 days 3 hours
213 earthquakes
2013
8 Nov
1 day 16 hours
33 earthquakes
2014
3 Jul
10 days 3 hours
258 earthquakes
2015
S20151230.1(28.4km)
29 Dec
5 days 15 hours
111 earthquakes
2020
S20200305.1(23.8km)
5 Mar
10 hours
27 earthquakes
22 May
2 days 15 hours
44 earthquakes
2025
S20250801.2(26.8km)
31 Jul
1 day 5 hours
30 earthquakes
16 Oct
2 days 2 hours
31 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm Near Redlands, California: September 2017 Analysis

A seismic swarm designated S20170910.1 occurred 2 km southeast of Redlands, California, beginning at 18:00 on 9 September 2017 and concluding at 06:53 on 13 September 2017. Over this 84-hour, 52-minute period, 53 earthquakes were recorded. Magnitudes ranged from 0.5 to 2.3, with the largest event registering at 2.3 on 10 September at 22:42:39 UTC and a depth of 6 km. Depths predominantly clustered between 4 and 6 km, though several events reached 12–16 km.

The sequence featured an initial event of magnitude 1.0 at 16 km depth on 9 September, followed by a cluster of small events on 10 September, including multiple magnitudes above 1.4 between 16:00 and 18:00 UTC. Activity continued at lower rates on 11 and 12 September before tapering with a final magnitude 0.7 event at 15 km depth on 13 September. This pattern reflects typical swarm behavior, where numerous small events occur without a dominant mainshock-aftershock sequence.

Redlands lies in Southern California's Inland Empire, a region shaped by the complex interaction of the Pacific and North American tectonic plates along the San Andreas Fault system. The local geology includes the San Jacinto Fault zone to the east and strands of the San Andreas Fault to the north, producing ongoing strain accumulation and release through frequent small-magnitude seismicity. Historical records indicate that the area has hosted seven documented swarms since 1 January 2000, occurring in 2003 (1 swarm), 2005 (2 swarms), 2010 (1 swarm), 2013 (1 swarm), 2014 (1 swarm), and 2015 (1 swarm). These episodes underscore the persistent low-level seismic productivity characteristic of the fault network.

Such swarms provide valuable data for monitoring crustal stress changes in a densely populated region. Depths in the 4–6 km range align with the brittle upper crust where most regional microseismicity nucleates. The 2017 swarm remained well below damaging thresholds, consistent with the area's background rate of felt but non-destructive events.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
California Geological Survey regional fault maps
SeismoSight internal swarm classification records