Location:

Period:

24 Oct 2019 22:07:07 - 25 Oct 2019 22:22:40 (1 day 15 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

13 swarms found nearby.

2008

S20080730.1(28.6km)

29 Jul

4 days 1 hours

76 earthquakes

2011

S20111027.1(29.3km)

27 Oct

5 days 18 hours

177 earthquakes

S20111108.1(27.1km)

7 Nov

2 days 7 hours

43 earthquakes

S20111229.1(24.8km)

29 Dec

3 days 3 hours

89 earthquakes

2012

S20120110.1(29.7km)

9 Jan

6 days 16 hours

139 earthquakes

2013

S20130314.1(19.0km)

13 Mar

1 day 19 hours

44 earthquakes

S20130317.1(17.2km)

17 Mar

1 day 18 hours

135 earthquakes

S20130321.2(17.8km)

20 Mar

5 days 20 hours

251 earthquakes

S20130728.1(22.5km)

27 Jul

1 day 0 hours

25 earthquakes

S20130731.1(24.3km)

31 Jul

2 days 18 hours

57 earthquakes

2014

S20140619.1(17.6km)

19 Jun

1 day 17 hours

115 earthquakes

2018

S20180522.1(13.7km)

22 May

15 hours

26 earthquakes

2023

S20230602.1(20.5km)

1 Jun

3 days 5 hours

45 earthquakes

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Seismic Swarm S20191025.1: Analysis of Activity Near Chilcoot-Vinton, California

The seismic swarm designated S20191025.1 occurred approximately 4 km southeast of Chilcoot-Vinton in eastern Plumas County, California. It initiated at 22:07 UTC on 24 October 2019 and concluded at 22:22 UTC on 25 October 2019, encompassing a total duration of 24 hours and 15 minutes. During this interval, 40 earthquakes were recorded, with magnitudes ranging from -0.5 to 2.3 and focal depths predominantly between 7 and 11 km.

The sequence exhibited typical swarm characteristics, featuring a rapid onset of small-magnitude events without a distinct mainshock-aftershock pattern. The largest event, magnitude 2.3, occurred at 00:29 UTC on 25 October at a shallow depth of 3 km. Subsequent activity remained diffuse, with events clustered tightly in both time and space. Depths showed minor variation, averaging around 8–9 km, consistent with brittle failure in the upper crust of this tectonically active region.

Eastern Plumas County lies within the transitional zone between the Sierra Nevada and the Basin and Range province. This area experiences distributed extensional deformation along northwest-trending faults associated with the Walker Lane belt. Historical seismicity reflects ongoing strain accumulation and release, influenced by both tectonic extension and possible volcanic influences from nearby Quaternary features. The swarm’s location aligns with known zones of elevated microseismicity in the northern Sierra Nevada.

Regional records indicate recurrent swarm activity. Since 1 January 2000, twelve swarms have been documented in the vicinity. These occurred in the following years with the indicated event counts: 2008 (1), 2011 (3), 2012 (1), 2013 (5), 2014 (1), and 2018 (1). Such episodes underscore the persistent, low-level seismic productivity of the area, where swarms often serve as indicators of fluid migration or aseismic slip processes at depth.

The 2019 swarm contributed to the established pattern of episodic, clustered seismicity without producing felt shaking or surface rupture. Continued monitoring remains essential for characterizing long-term hazard in this portion of the Walker Lane transition zone.

References

USGS Earthquake Catalog (event data and regional context)
California Geological Survey – Quaternary Fault and Fold Database
SeismoSight internal swarm classification records