Location:

Period:

12 Jan 2015 06:29:07 - 16 Jan 2015 05:36:02 (3 days 23 hours 6 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

157

13 swarms found nearby.

2001

S20010810.1(7.1km)

10 Aug

1 day 19 hours

59 earthquakes

2011

S20110914.2(27.2km)

14 Sep

1 day 10 hours

42 earthquakes

S20111002.1(28.0km)

1 Oct

14 days 16 hours

382 earthquakes

S20111019.1(26.9km)

19 Oct

4 days 5 hours

106 earthquakes

S20111027.1(19.8km)

27 Oct

5 days 18 hours

177 earthquakes

S20111108.1(25.1km)

7 Nov

2 days 7 hours

43 earthquakes

S20111111.1(28.9km)

10 Nov

5 days 3 hours

128 earthquakes

S20111229.1(24.7km)

29 Dec

3 days 3 hours

89 earthquakes

2012

S20120103.1(28.3km)

3 Jan

3 days 3 hours

69 earthquakes

S20120110.1(29.9km)

9 Jan

6 days 16 hours

139 earthquakes

S20120201.1(28.7km)

31 Jan

3 days 5 hours

62 earthquakes

2013

S20131109.1(5.4km)

9 Nov

21 hours

28 earthquakes

2014

S20140728.1(3.6km)

28 Jul

8 days 21 hours

346 earthquakes

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Earthquake Swarm S20150112.1 Near Graeagle, California

An earthquake swarm designated S20150112.1 occurred 1 km south-southeast of Graeagle in Plumas County, California, from 06:29 on 12 January 2015 to 05:36 on 16 January 2015. The sequence lasted 95 hours and 6 minutes and produced 157 events. Graeagle lies within the northern Sierra Nevada, where regional tectonics are shaped by the interaction between the Sierra Nevada block and the extending Basin and Range province. The area is transected by the Mohawk Valley Fault Zone and related structures that accommodate dextral shear and normal faulting, resulting in recurrent low-magnitude seismicity. Analysis of the first 100 recorded events shows magnitudes ranging from –0.2 to 2.6, with the majority below 1.0. Depths were predominantly shallow, concentrated between 0 km and 11 km, consistent with brittle failure in the upper crust. The largest events included a magnitude 2.3 at 00:54 on 13 January at 2 km depth and a magnitude 2.6 at 11:51 the same day at 5 km depth. Activity initiated with a magnitude 0.2 event, followed within 14 hours by a magnitude 2.2 shock at 4 km depth. Subsequent events clustered in time and space, displaying typical swarm characteristics of overlapping waveforms and no single dominant mainshock. Swarm activity in this sector of the Sierra Nevada is not uncommon. Since 1 January 2000, thirteen swarms have been documented near Graeagle. Earlier episodes occurred in 2001 (one swarm), 2011 (seven swarms), 2012 (three swarms), 2013 (one swarm), and 2014 (one swarm). These sequences generally exhibit similar magnitude ranges and shallow focal depths, reflecting ongoing strain release along local fault networks without producing surface rupture. The 2015 swarm remained entirely within the instrumental detection threshold and caused no reported damage. Its timing and location align with background seismicity patterns driven by tectonic loading and possible contributions from hydrothermal fluid migration in the region. Continued monitoring by regional networks provides the primary basis for characterizing such sequences and assessing their relation to longer-term fault behavior.

References

SeismoSight internal swarm classification database
USGS Earthquake Catalog (ANSS Comprehensive Catalog)
California Geological Survey, Quaternary Fault and Fold Database