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Location:
18km SW of Olancha, CA
Period:
2 Apr 2004 00:33:06 - 3 Apr 2004 09:40:14 (1 day 9 hours 7 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
28
43 swarms found nearby.
2000
S20000329.1(29.3km)
28 Mar
9 days 13 hours
115 earthquakes
S20000426.1(20.1km)
25 Apr
2 days 10 hours
53 earthquakes
S20000517.1(21.8km)
17 May
3 days 15 hours
92 earthquakes
S20000709.1(22.7km)
8 Jul
1 day 22 hours
44 earthquakes
S20000911.1(28.5km)
10 Sep
9 days 14 hours
140 earthquakes
S20000921.1(27.7km)
20 Sep
15 days 13 hours
274 earthquakes
2001
S20010414.1(24.7km)
13 Apr
6 days 9 hours
135 earthquakes
S20010423.1(26.9km)
23 Apr
8 days 21 hours
256 earthquakes
S20010610.1(27.7km)
9 Jun
4 days 3 hours
51 earthquakes
S20010714.1(27.3km)
14 Jul
67 days 13 hours
5060 earthquakes
2002
S20020721.1(14.4km)
20 Jul
3 days 21 hours
49 earthquakes
S20020907.1(27.4km)
6 Sep
2 days 1 hours
31 earthquakes
2004
28 Mar
4 days 0 hours
71 earthquakes
S20040925.1(29.5km)
24 Sep
4 days 9 hours
57 earthquakes
2005
6 Aug
7 days 5 hours
120 earthquakes
2006
S20060713.1(29.5km)
12 Jul
6 days 5 hours
67 earthquakes
S20060813.1(23.3km)
12 Aug
8 days 13 hours
97 earthquakes
2010
S20100302.1(26.6km)
1 Mar
5 days 11 hours
44 earthquakes
2012
S20120106.1(29.9km)
6 Jan
2 days 18 hours
48 earthquakes
S20121127.1(26.6km)
26 Nov
24 days 0 hours
802 earthquakes
2013
S20130611.1(27.3km)
10 Jun
3 days 18 hours
43 earthquakes
4 Aug
1 day 20 hours
50 earthquakes
23 Dec
5 days 10 hours
116 earthquakes
2014
S20140701.1(12.8km)
30 Jun
8 days 23 hours
167 earthquakes
2015
S20150608.1(27.2km)
8 Jun
1 day 13 hours
31 earthquakes
2019
S20190525.1(10.1km)
24 May
1 day 12 hours
43 earthquakes
28 May
2 days 3 hours
61 earthquakes
S20190721.1(26.7km)
20 Jul
9 days 5 hours
474 earthquakes
8 Aug
1 day 18 hours
60 earthquakes
5 Sep
1 day 4 hours
27 earthquakes
S20191116.2(29.9km)
16 Nov
3 days 4 hours
90 earthquakes
S20191201.1(28.1km)
30 Nov
27 days 2 hours
353 earthquakes
2020
5 Mar
1 day 5 hours
42 earthquakes
S20200307.1(26.9km)
6 Mar
10 days 22 hours
145 earthquakes
S20200324.1(28.0km)
23 Mar
6 days 13 hours
82 earthquakes
S20200509.2(29.5km)
8 May
3 days 23 hours
49 earthquakes
S20200604.2(15.7km)
3 Jun
5 days 19 hours
148 earthquakes
2021
17 Jan
9 hours
25 earthquakes
S20210213.1(23.3km)
12 Feb
1 day 17 hours
29 earthquakes
S20210412.1(24.1km)
11 Apr
2 days 3 hours
33 earthquakes
S20211018.1(24.3km)
17 Oct
1 day 7 hours
27 earthquakes
S20211219.1(27.2km)
18 Dec
13 days 0 hours
143 earthquakes
2024
S20240416.2(24.6km)
15 Apr
2 days 15 hours
51 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20040402.1: Analysis of Activity Near Olancha, California

An earthquake swarm designated S20040402.1 occurred 18 km southwest of Olancha, California, from 00:33 UTC on 2 April 2004 until 09:40 UTC on 3 April 2004. In 33 hours and 7 minutes, the sequence produced 28 events. Magnitudes ranged from 0.7 to 2.0, with the largest reaching 2.0 at 00:50 UTC on 2 April. Focal depths clustered between 0 km and 9 km, indicating shallow crustal sources typical of the region.

The sequence began with two closely spaced events at 00:33 UTC, followed by additional activity through the early morning hours. Peak frequency occurred between 00:33 and 02:33 UTC on 2 April, after which events became more sporadic until a final magnitude-1.4 shock at 09:40 UTC on 3 April. Depths showed modest variation, with many events between 5 km and 8 km, consistent with brittle failure in the upper crust.

Olancha lies within the Owens Valley, part of the Eastern California Shear Zone and the western margin of the Basin and Range province. The area experiences transtensional deformation driven by Pacific-North America plate motion and extension across the Sierra Nevada frontal fault system. Active faults include strands of the Owens Valley fault zone, which last produced a major surface-rupturing event in 1872 near Lone Pine. Ongoing tectonic extension sustains background seismicity and occasional swarms throughout the valley.

Swarm-type sequences are recurrent in this setting. Since 2000, thirteen swarms have been recorded in the immediate region, with earlier episodes in 2000 (six swarms), 2001 (four), and 2002 (two). These events typically involve low-magnitude earthquakes without a clear mainshock-aftershock pattern, often linked to fluid migration or aseismic slip along fault segments.

The 2004 swarm fits this established pattern. Its modest energy release and shallow depths align with the regional stress regime dominated by northwest-trending right-lateral shear and northeast-directed extension. No damage or felt reports beyond instrumental detection were associated with the sequence.

References

  • USGS Earthquake Catalog (earthquake.usgs.gov)
  • California Geological Survey, Fault Activity Map of California
  • USGS Professional Paper 1715, Geology of the Owens Valley Region