Location:

Period:

20 Jul 2009 12:10:20 - 21 Jul 2009 22:47:14 (1 day 10 hours 36 minutes)

Volcanoes in 100km radius:

Salton Buttes(55km)

Earthquakes:

18 swarms found nearby.

2006

S20060630.1(21.7km)

29 Jun

5 days 14 hours

126 earthquakes

2007

S20070117.1(15.9km)

17 Jan

3 days 20 hours

64 earthquakes

2009

S20090818.1(26.4km)

17 Aug

1 day 21 hours

39 earthquakes

2010

S20100314.1(17.8km)

13 Mar

2 days 5 hours

39 earthquakes

S20100405.6(21.1km)

4 Apr

1 day 11 hours

38 earthquakes

2015

S20150531.1(25.4km)

31 May

2 days 9 hours

45 earthquakes

2017

S20171207.1(21.9km)

6 Dec

4 days 12 hours

120 earthquakes

2018

S20180513.1(28.2km)

13 May

2 days 22 hours

70 earthquakes

2020

S20200510.1(20.2km)

10 May

5 days 22 hours

133 earthquakes

2021

S20210819.1(25.2km)

18 Aug

2 days 0 hours

37 earthquakes

2022

S20220510.1(15.1km)

9 May

13 hours

26 earthquakes

S20220825.1(29.1km)

25 Aug

1 day 3 hours

27 earthquakes

S20221008.1(15.1km)

7 Oct

8 hours

28 earthquakes

2023

S20230324.1(23.9km)

23 Mar

2 days 2 hours

50 earthquakes

2024

S20240803.1(21.1km)

2 Aug

2 days 23 hours

54 earthquakes

2025

S20250320.2(20.9km)

19 Mar

6 days 15 hours

81 earthquakes

2026

S20260518.1(27.3km)

18 May

3 hours

43 earthquakes

S20260702.1(18.6km)

1 Jul

1 day 21 hours

31 earthquakes

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Seismic Swarm S20090721.1 Near Ocotillo Wells, California

The seismic swarm designated S20090721.1 occurred approximately 9 km west-southwest of Ocotillo Wells in San Diego County, California. It began at 12:10 on 20 July 2009 and concluded at 22:47 on 21 July 2009, encompassing a total duration of 34 hours and 36 minutes. During this interval, 32 earthquakes were recorded.

This swarm is characteristic of clustered seismic activity common in the Salton Trough region. The events ranged in magnitude from 0.6 to 3.6, with the largest shock occurring at 12:10 on 20 July 2009 at a depth of 11 km. Subsequent activity included multiple events between magnitudes 1.0 and 2.9, predominantly at depths of 4–8 km, though isolated deeper occurrences reached 13 km. The sequence featured two notable clusters on 21 July, with magnitudes up to 2.9 and 2.4 occurring within minutes of each other around 13:21.

Ocotillo Wells lies within the tectonically active Salton Trough, a sediment-filled extensional basin formed by the interaction of the Pacific and North American plates. The area is influenced by strands of the San Andreas Fault system, including the San Jacinto and Elsinore fault zones, which accommodate significant right-lateral strike-slip motion. Historical seismicity in the region reflects ongoing plate boundary deformation, with the trough experiencing frequent small-magnitude events due to its high strain rate and geothermal activity.

Since 1 January 2000, two prior swarms have been documented in the vicinity: one in 2006 and another in 2007. These episodes underscore the recurrent nature of swarm-type seismicity in this part of Southern California, where fluid migration or aseismic slip may trigger sequences without a single dominant mainshock.

The 2009 swarm provides insight into the temporal and spatial patterns of microseismicity along local fault structures. Most events clustered at shallow to mid-crustal depths, consistent with brittle failure in the upper seismogenic zone. No damage or felt reports of significance were associated with the sequence, aligning with its modest magnitude distribution.

References

SeismoSight internal swarm classification database
USGS Earthquake Catalog (historical regional context)