Location:

Period:

27 Jun 2017 09:02:02 - 1 Jul 2017 17:15:22 (4 days 8 hours 13 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

20 swarms found nearby.

2004

S20040612.1(10.8km)

12 Jun

1 day 20 hours

35 earthquakes

2005

S20050521.1(28.3km)

21 May

1 day 10 hours

39 earthquakes

S20050626.1(14.8km)

26 Jun

4 days 0 hours

149 earthquakes

S20050918.1(29.8km)

17 Sep

2 days 13 hours

34 earthquakes

2007

S20070509.1(29.8km)

8 May

2 days 16 hours

36 earthquakes

2008

S20081121.2(30.0km)

21 Nov

1 day 17 hours

26 earthquakes

2011

S20110914.2(16.7km)

14 Sep

1 day 10 hours

42 earthquakes

S20111002.1(14.7km)

1 Oct

14 days 16 hours

382 earthquakes

S20111019.1(16.7km)

19 Oct

4 days 5 hours

106 earthquakes

S20111027.1(24.8km)

27 Oct

5 days 18 hours

177 earthquakes

S20111108.1(20.6km)

7 Nov

2 days 7 hours

43 earthquakes

S20111111.1(14.3km)

10 Nov

5 days 3 hours

128 earthquakes

S20111229.1(23.0km)

29 Dec

3 days 3 hours

89 earthquakes

2012

S20120103.1(15.6km)

3 Jan

3 days 3 hours

69 earthquakes

S20120110.1(14.6km)

9 Jan

6 days 16 hours

139 earthquakes

S20120201.1(14.9km)

31 Jan

3 days 5 hours

62 earthquakes

S20120408.2(28.7km)

8 Apr

2 days 17 hours

45 earthquakes

S20120627.1(27.9km)

26 Jun

3 days 22 hours

58 earthquakes

2014

S20140404.2(28.2km)

3 Apr

1 day 13 hours

40 earthquakes

2015

S20150408.1(28.1km)

8 Apr

2 days 9 hours

57 earthquakes

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Seismic Swarm S20170627.1 Near Sierraville, California: A Detailed Overview

The seismic swarm designated S20170627.1 was recorded 13 km south of Sierraville in Sierra County, California. Activity commenced at 09:02 on 27 June 2017 and concluded at 17:15 on 1 July 2017, spanning 104 hours and 13 minutes. During this interval, 69 earthquakes were registered, with magnitudes ranging from -0.9 to 3.9 and depths from -2 km to 11 km.

The sequence initiated with a magnitude 3.7 event at 09:02:02 on 27 June, followed rapidly by additional shocks including a magnitude 3.9 at 09:09:21. Subsequent notable events included magnitude 2.9 quakes at 09:04:48, 09:16:28, and 10:35:47, as well as a magnitude 3.1 at 12:14:11. Later activity featured a magnitude 2.8 on 27 June at 16:17:38 and a magnitude 2.4 on 28 June at 16:24:37. Many events clustered at shallow depths near or above sea level, with deeper occurrences up to 11 km recorded toward the swarm's end.

Swarm sequences such as this typically involve numerous small to moderate earthquakes occurring in a concentrated area over days to weeks, often without a single dominant mainshock. The 2017 event displayed this pattern, with the largest magnitudes concentrated in the first day and a gradual decline in both frequency and intensity thereafter. Depths remained predominantly shallow, consistent with activity along near-surface fault structures.

The Sierraville region lies within the northern Sierra Nevada, influenced by extensional tectonics associated with the Basin and Range province and the Walker Lane belt. This setting features active normal and strike-slip faulting that accommodates regional crustal deformation. Historical seismicity in the area reflects ongoing tectonic adjustments along faults such as those in the Sierra Nevada frontal fault system. Past swarms have been documented in similar geological environments, underscoring the area's recurrent seismic character.

Since 1 January 2000, twenty swarms have occurred in the vicinity. These include one in 2004, three in 2005, one each in 2007 and 2008, seven in 2011, five in 2012, and one each in 2014 and 2015. The 2017 swarm fits within this established pattern of episodic clustered seismicity.

References

US Geological Survey Earthquake Hazards Program California Geological Survey Regional Fault Maps SeismoSight Internal Swarm Classification Database