Location:

Period:

15 Jan 2021 08:37:26 - 16 Jan 2021 22:51:19 (1 day 14 hours 13 minutes)

Volcanoes in 100km radius:

Mono Lake Volcanic Field(43km), Mono-Inyo Craters(43km), Mammoth Mountain(52km)

Earthquakes:

17 swarms found nearby.

2000

S20000304.1(29.9km)

4 Mar

17 hours

71 earthquakes

S20000509.1(29.9km)

9 May

21 hours

65 earthquakes

S20000622.1(29.1km)

21 Jun

2 days 3 hours

130 earthquakes

S20000801.1(29.9km)

31 Jul

1 day 1 hours

31 earthquakes

S20000818.1(29.9km)

17 Aug

1 day 8 hours

45 earthquakes

2001

S20010320.1(20.6km)

20 Mar

6 days 14 hours

96 earthquakes

2004

S20041214.1(13.5km)

13 Dec

15 days 7 hours

237 earthquakes

2008

S20080115.1(14.9km)

15 Jan

2 days 10 hours

50 earthquakes

S20080201.1(14.3km)

1 Feb

2 days 6 hours

54 earthquakes

2009

S20090831.1(7.7km)

30 Aug

2 days 4 hours

34 earthquakes

2015

S20150505.1(28.9km)

4 May

2 days 22 hours

111 earthquakes

S20150510.1(27.5km)

9 May

2 days 3 hours

35 earthquakes

2017

S20171015.2(12.5km)

15 Oct

16 hours

26 earthquakes

S20171020.1(19.4km)

19 Oct

2 days 13 hours

33 earthquakes

2020

S20200308.1(28.1km)

8 Mar

2 days 23 hours

77 earthquakes

S20200318.1(29.7km)

17 Mar

3 days 22 hours

75 earthquakes

S20200411.1(24.6km)

11 Apr

33 days 8 hours

1019 earthquakes

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Seismic Swarm S20210115.1 Near Toms Place, California: Event Analysis and Regional Context

Seismic swarm S20210115.1 was recorded beginning at 08:37 on 15 January 2021 and concluding at 22:51 on 16 January 2021, approximately 41 km north-northeast of Toms Place in Mono County, California. Over 38 hours and 13 minutes, the sequence produced 89 earthquakes. Magnitudes ranged from 0.6 to 3.9, with the largest event occurring at 22:11 on 15 January at a depth of 7 km. Depths were predominantly shallow, clustered between 0 and 10 km, consistent with typical swarm characteristics in the area.

The swarm exhibited episodic bursts of activity, particularly between 20:00 and 23:00 on 15 January and again from 06:00 to 08:00 on 16 January. Multiple events exceeded magnitude 2.5, including a 3.3 quake at 07:16 on 16 January. Smaller events below magnitude 1.5 comprised a significant portion of the sequence, reflecting the swarm's diffuse energy release rather than a single mainshock-aftershock pattern.

This activity aligns with the broader tectonic setting of eastern California, where the Sierra Nevada frontal fault system interacts with the Basin and Range province. The region experiences ongoing extension and strike-slip faulting, contributing to recurrent earthquake swarms. Proximity to the Long Valley Caldera, a large volcanic system last active in the Pleistocene, adds a component of possible magmatic or hydrothermal influence on seismicity, though most swarms remain tectonically driven.

Historical records since 2000 document 17 prior swarms in the vicinity, occurring in 2000 (5 events), 2001 (1), 2004 (1), 2008 (2), 2009 (1), 2015 (2), 2017 (2), and 2020 (3). These episodes demonstrate the area's persistent seismic productivity, with swarms typically lasting hours to days and featuring low-to-moderate magnitudes.

Monitoring of such sequences supports improved understanding of fault interactions and volcanic-tectonic coupling in the region. Continued observation remains essential given the potential for larger events in this seismically active zone.

References:
SeismoSight internal swarm classification data for S20210115.1.
United States Geological Survey earthquake catalog and regional tectonic summaries for Mono County, California.
California Geological Survey reports on Long Valley Caldera and Sierra Nevada seismicity.