Location:

Period:

25 Jul 2014 15:34:27 - 26 Jul 2014 20:41:35 (1 day 5 hours 7 minutes)

Volcanoes in 100km radius:

Mono Lake Volcanic Field(95km)

Earthquakes:

11 swarms found nearby.

2000

S20000926.1(16.4km)

26 Sep

2 days 18 hours

103 earthquakes

2003

S20030713.1(14.5km)

12 Jul

1 day 14 hours

105 earthquakes

2005

S20051119.1(22.3km)

19 Nov

3 days 19 hours

62 earthquakes

2010

S20101031.1(15.3km)

31 Oct

2 days 12 hours

39 earthquakes

S20101116.1(11.5km)

15 Nov

1 day 10 hours

29 earthquakes

2013

S20130124.1(15.6km)

24 Jan

1 day 21 hours

61 earthquakes

2017

S20170607.1(14.2km)

6 Jun

1 day 8 hours

46 earthquakes

2021

S20210708.2(26.0km)

8 Jul

73 days 11 hours

4214 earthquakes

S20210922.1(27.4km)

21 Sep

21 days 15 hours

354 earthquakes

S20211031.1(25.4km)

30 Oct

2 days 4 hours

33 earthquakes

2022

S20220808.1(25.4km)

8 Aug

10 days 23 hours

336 earthquakes

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Seismic Swarm S20140726.1 Near Markleeville, California

A seismic swarm designated S20140726.1 was recorded 5 km east-southeast of Markleeville in Alpine County, California. The sequence began at 15:34 on 25 July 2014 and concluded at 20:41 on 26 July 2014, encompassing 25 earthquakes over 29 hours and 7 minutes. Magnitudes ranged from 0.1 to 2.1, with most events clustered between 7 km and 14 km depth. Several events registered at a nominal depth of -1 km, consistent with the internal classification parameters of the monitoring system. The largest shock reached magnitude 2.1 at 17:49 on 25 July, followed by additional events of magnitude 2.0 at 19:19 on the same day and again at 11:28 on 26 July.

This swarm fits within a broader pattern of episodic seismicity observed in the region since 2000. Six prior swarms have occurred, occurring in 2000, 2003, 2005, 2010 (two events), and 2013. The 2014 sequence therefore represents the seventh such episode in the recorded interval. Event timing shows an initial peak of activity within the first several hours, followed by a gradual decline, with the final recorded event occurring near the close of the sequence.

Markleeville lies within the western Basin and Range province, immediately east of the Sierra Nevada frontal fault system. The area experiences distributed extensional deformation accommodated by normal and strike-slip faults of the Walker Lane belt. Regional seismicity is driven by Pacific–North America plate interaction, which produces northwest-directed shear and associated east-west extension. Crustal thickness averages 30–35 km, and heat flow is moderately elevated compared with the adjacent Sierra Nevada block. Historical earthquakes in the vicinity include moderate events associated with the Carson Range and Antelope Valley fault zones.

Swarm activity in this setting is commonly attributed to transient increases in pore-fluid pressure along pre-existing fractures, allowing slip on small fault patches without producing a distinct mainshock–aftershock signature. Depths between 8 km and 14 km place most events within the seismogenic portion of the crust, where brittle failure predominates. The limited maximum magnitude and rapid decay of activity observed in S20140726.1 are consistent with fluid-driven swarm behavior documented elsewhere along the eastern Sierra margin.

No surface rupture or significant ground deformation was associated with the 2014 swarm. The sequence remained well below thresholds that would trigger emergency protocols, yet it underscores the persistent low-level seismic hazard in Alpine County. Continued monitoring is warranted given the region’s proximity to infrastructure corridors and recreational areas.

References

USGS Earthquake Catalog (ANSS Comprehensive Catalog)
California Geological Survey, Fault Activity Map of California
SeismoSight internal swarm classification records