Location:

Period:

27 Oct 2011 06:37:09 - 2 Nov 2011 01:01:54 (5 days 18 hours 24 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

177

15 swarms found nearby.

2001

S20010810.1(25.1km)

10 Aug

1 day 19 hours

59 earthquakes

2011

S20110914.2(8.2km)

14 Sep

1 day 10 hours

42 earthquakes

S20111002.1(10.2km)

1 Oct

14 days 16 hours

382 earthquakes

S20111019.1(8.2km)

19 Oct

4 days 5 hours

106 earthquakes

S20111108.1(5.3km)

7 Nov

2 days 7 hours

43 earthquakes

S20111111.1(10.5km)

10 Nov

5 days 3 hours

128 earthquakes

S20111229.1(5.3km)

29 Dec

3 days 3 hours

89 earthquakes

2012

S20120103.1(9.3km)

3 Jan

3 days 3 hours

69 earthquakes

S20120110.1(10.7km)

9 Jan

6 days 16 hours

139 earthquakes

S20120201.1(10.0km)

31 Jan

3 days 5 hours

62 earthquakes

2013

S20131109.1(25.2km)

9 Nov

21 hours

28 earthquakes

2014

S20140728.1(19.7km)

28 Jul

8 days 21 hours

346 earthquakes

2015

S20150112.1(19.8km)

12 Jan

3 days 23 hours

157 earthquakes

2017

S20170627.1(24.8km)

27 Jun

4 days 8 hours

69 earthquakes

2019

S20191025.1(29.3km)

24 Oct

1 day 0 hours

40 earthquakes

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Seismic Swarm S20111027.1 Near Sattley, California

Seismic swarm S20111027.1 was recorded 2 km west of Sattley in Sierra County, California. The sequence began at 06:37 on 27 October 2011 and concluded at 01:01 on 2 November 2011, spanning 138 hours and 24 minutes. A total of 177 earthquakes were detected during this period.

Analysis of the first 100 events reveals a characteristic swarm pattern dominated by low-magnitude activity. The sequence initiated with a magnitude 4.7 event at 11 km depth. Subsequent events were predominantly below magnitude 1.0, with occasional peaks reaching 2.4. Depths clustered between 10 km and 16 km, indicating a relatively consistent focal zone within the upper crust. Negative magnitudes, down to -0.4, reflect the high sensitivity of the monitoring network in capturing microseismicity. The temporal distribution shows dense clustering in the initial hours, gradually tapering over subsequent days.

This swarm occurred within the northern Sierra Nevada, a region shaped by Cenozoic uplift and active tectonics along the Sierra Nevada frontal fault system. The area lies near the boundary between the Sierra Nevada block and the Basin and Range province, where extensional forces contribute to seismic strain. Historical records since 2000 indicate four documented swarms in the vicinity, with one event in 2001 and three in 2011. Such episodic clusters are consistent with fluid migration or minor fault slip in this tectonically active margin.

The 2011 swarm did not produce reported damage or surface rupture, aligning with the modest energy release typical of these sequences. Depths and magnitudes suggest activation along pre-existing fractures rather than a single through-going fault. Ongoing monitoring in the Sierra Nevada continues to refine understanding of these transient seismic episodes and their relation to regional stress fields.

References

SeismoSight internal swarm classification records
USGS Earthquake Catalog (historical swarm verification)
California Geological Survey regional tectonic summaries