Location:

Period:

20 Dec 2018 13:24:02 - 23 Dec 2018 08:39:10 (2 days 19 hours 15 minutes)

Volcanoes in 100km radius:

Soda Lakes(86km)

Earthquakes:

11 swarms found nearby.

2003

S20031009.1(29.7km)

8 Oct

2 days 19 hours

40 earthquakes

2005

S20050916.1(10.8km)

16 Sep

1 day 12 hours

81 earthquakes

2013

S20130605.1(1.4km)

5 Jun

2 days 0 hours

56 earthquakes

S20130617.1(1.9km)

16 Jun

6 days 16 hours

72 earthquakes

2017

S20171226.1(18.2km)

26 Dec

22 hours

33 earthquakes

2018

S20181205.1(4.0km)

4 Dec

1 day 21 hours

39 earthquakes

2019

S20190911.1(16.2km)

11 Sep

18 hours

26 earthquakes

2020

S20200321.1(0.2km)

21 Mar

14 days 4 hours

402 earthquakes

2021

S20210426.1(25.9km)

25 Apr

3 days 1 hours

45 earthquakes

S20210528.2(25.6km)

28 May

16 hours

33 earthquakes

2024

S20240721.2(26.0km)

20 Jul

1 day 13 hours

51 earthquakes

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Seismic Swarm S20181220.1: Analysis of Activity Near Indian Hills, Nevada

Seismic swarm S20181220.1 occurred 5 km east-northeast of Indian Hills, Nevada, from 13:24 UTC on 20 December 2018 to 08:39 UTC on 23 December 2018. Over 67 hours and 15 minutes, the sequence produced 45 earthquakes. The largest event reached magnitude 3.6 at a depth of 8 km, followed by numerous smaller events with magnitudes predominantly below 1.5 and depths ranging from 0 to 12 km.

The swarm initiated with two notable shocks of magnitudes 3.6 and 3.2 within the first six minutes, both at approximately 7–8 km depth. Subsequent activity consisted of low-magnitude events clustered between 6 and 11 km depth, with occasional shallower or deeper outliers. Activity tapered after 22 December, concluding with a cluster of small events near 10 km depth on 23 December. No events exceeded magnitude 2.0 after the initial day.

This sequence aligns with Nevada’s broader tectonic setting within the Basin and Range province and the northern Walker Lane belt. The region accommodates northwest-directed dextral shear between the Pacific and North American plates at rates of 8–10 mm per year. Active normal and strike-slip faults, including segments of the Carson Range frontal fault system, generate frequent small-to-moderate earthquakes. Historical records document recurrent earthquake swarms in the Indian Hills area, with six documented episodes since 2000: one each in 2003, 2005, and 2017, two in 2013, and the 2018 event described here.

Swarm behavior in this setting typically reflects fluid migration or aseismic slip along favorably oriented faults rather than mainshock-aftershock sequences driven by static stress transfer. Depths between 4 and 12 km correspond to the brittle-ductile transition zone where such processes commonly occur. The modest maximum magnitude and rapid decay of event sizes are consistent with previous swarms in the same locale.

Continued monitoring by regional seismic networks remains essential given the proximity of the swarm to populated areas of Carson Valley and infrastructure along U.S. Highway 395. No damage or felt reports beyond minor shaking were associated with the 2018 sequence.

References

U.S. Geological Survey Earthquake Hazards Program
Nevada Seismological Laboratory, University of Nevada, Reno
SeismoSight internal swarm classification records