Location:

Period:

26 Jun 2019 08:01:55 - 2 Jul 2019 23:08:59 (6 days 15 hours 7 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

11 swarms found nearby.

2003

S20030628.1(25.2km)

27 Jun

23 hours

25 earthquakes

2005

S20050107.1(8.7km)

6 Jan

2 days 11 hours

30 earthquakes

2008

S20080729.2(26.6km)

29 Jul

4 days 0 hours

128 earthquakes

2013

S20131109.2(23.5km)

8 Nov

1 day 16 hours

33 earthquakes

2015

S20151230.1(17.1km)

29 Dec

5 days 15 hours

111 earthquakes

2018

S20180829.1(26.3km)

29 Aug

2 days 20 hours

63 earthquakes

2019

S20190531.1(0.9km)

30 May

20 days 5 hours

1003 earthquakes

S20190829.1(4.8km)

28 Aug

4 days 15 hours

69 earthquakes

2024

S20240907.1(9.0km)

7 Sep

1 day 8 hours

40 earthquakes

2025

S20250801.2(12.5km)

31 Jul

1 day 5 hours

30 earthquakes

S20251017.1(26.5km)

16 Oct

2 days 2 hours

31 earthquakes

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Seismic Swarm S20190627.1: Analysis of Activity Near Glen Avon, California

A notable earthquake swarm designated S20190627.1 occurred in the region 5 km NNW of Glen Avon, California. The sequence initiated at 08:01 on 26 June 2019 and concluded at 23:08 on 2 July 2019, spanning 159 hours and 7 minutes. During this period, 93 earthquakes were recorded, with magnitudes ranging from 0.4 to 3.0 and focal depths primarily between 2 km and 13 km.

The swarm exhibited typical characteristics of clustered seismic activity, beginning with low-magnitude events and featuring intermittent peaks. The largest event reached magnitude 3.0 at a depth of 11 km on 27 June 2019. Subsequent activity included several events above magnitude 1.5, concentrated in the initial days before tapering off. Depths remained shallow throughout, consistent with crustal deformation in the area.

Glen Avon lies within the tectonically active Peninsular Ranges province of Southern California. This region experiences ongoing strain accumulation due to the interaction of the Pacific and North American plates along major fault systems, including the nearby San Jacinto and Elsinore faults. Shallow seismicity here often reflects distributed faulting and fluid migration in fractured bedrock.

Historical records indicate that swarm events are recurrent in this locale. Since 1 January 2000, seven such swarms have been documented, occurring in 2003, 2005, 2008, 2013, 2015, 2018, and 2019. These episodes underscore the persistent low-level seismic hazard in the Inland Empire, where swarms serve as indicators of regional stress release without producing a dominant mainshock.

The 2019 swarm contributed to ongoing monitoring efforts, highlighting the value of dense seismic networks in distinguishing swarm behavior from foreshock sequences. No significant surface rupture or damage was associated with the events, aligning with the modest energy release observed.

References

SeismoSight internal classification records for swarm S20190627.1.
USGS Earthquake Catalog for regional fault context.