Location:

Period:

3 Mar 2004 01:20:44 - 11 Mar 2004 04:47:24 (8 days 3 hours 26 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

172

22 swarms found nearby.

2003

S20031222.1(4.0km)

22 Dec

37 days 3 hours

2456 earthquakes

S20031222.2(4.8km)

22 Dec

15 days 17 hours

643 earthquakes

S20031223.1(24.6km)

22 Dec

1 day 0 hours

127 earthquakes

S20031224.1(3.5km)

23 Dec

2 days 19 hours

170 earthquakes

S20040101.1(28.4km)

31 Dec

2 days 2 hours

67 earthquakes

2004

S20040108.1(6.5km)

7 Jan

11 days 2 hours

217 earthquakes

S20040201.1(2.3km)

31 Jan

9 days 8 hours

199 earthquakes

S20040202.1(27.0km)

1 Feb

1 day 12 hours

34 earthquakes

S20040205.1(2.8km)

4 Feb

2 days 23 hours

57 earthquakes

S20040301.1(24.6km)

1 Mar

24 days 6 hours

484 earthquakes

S20040317.1(28.6km)

16 Mar

7 days 18 hours

281 earthquakes

S20040405.1(27.5km)

4 Apr

18 days 8 hours

226 earthquakes

S20040425.1(2.6km)

25 Apr

19 days 16 hours

216 earthquakes

S20040528.1(2.5km)

27 May

2 days 11 hours

49 earthquakes

S20040714.1(3.9km)

13 Jul

86 days 1 hours

888 earthquakes

S20040727.1(21.2km)

26 Jul

10 days 1 hours

140 earthquakes

S20041014.1(25.0km)

13 Oct

8 days 7 hours

97 earthquakes

2005

S20050427.1(11.4km)

26 Apr

3 days 20 hours

44 earthquakes

S20051002.1(27.5km)

1 Oct

10 days 17 hours

151 earthquakes

2006

S20060407.1(27.2km)

6 Apr

11 days 10 hours

151 earthquakes

2009

S20090620.2(13.7km)

20 Jun

4 days 17 hours

84 earthquakes

2025

S20251119.2(3.6km)

18 Nov

2 days 18 hours

43 earthquakes

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Seismic Swarm S20040303.1: Analysis of Activity Near Templeton, California

Seismic swarm S20040303.1 was recorded 11 km west of Templeton in San Luis Obispo County, California. The sequence began at 01:20 on 3 March 2004 and concluded at 04:47 on 11 March 2004, spanning 195 hours and 26 minutes. During this period, 172 earthquakes were detected.

Analysis of the first 100 events reveals predominantly low-magnitude activity. Magnitudes ranged from 0.3 to 3.3, with the majority falling between 0.8 and 2.2. Depths were shallow, concentrated between 2 km and 7 km, consistent with upper-crustal faulting. Early events on 3 March included a 2.8 magnitude quake at 4 km depth and a 2.6 magnitude event at 3 km. Subsequent days showed continued clustering, with notable peaks such as a 3.2 magnitude shock at 7 km on 5 March and a 3.3 magnitude event at 3 km on 6 March. Later events through 8 March maintained similar depth ranges and magnitudes below 2.1, indicating a gradual decay in intensity without a dominant mainshock.

This swarm occurred within the Central Coast Ranges, a tectonically active region shaped by the transform boundary between the Pacific and North American plates. The area lies near the San Andreas Fault system and associated subsidiary structures, including northwest-trending strike-slip faults. Shallow seismicity here often reflects distributed deformation rather than a single major fault trace. Historical patterns show recurrent swarm activity, with ten such sequences documented since 1 January 2000. Prior episodes occurred in 2003 (five swarms) and 2004 (five swarms), underscoring the region's propensity for episodic, low-magnitude clustering.

Such swarms typically arise from localized stress perturbations or fluid migration along minor faults, producing numerous events without significant surface rupture. The 2004 sequence aligns with this behavior, featuring rapid onset followed by sustained but diminishing activity over eight days. No larger triggered events were associated with the swarm.

SeismoSight internal swarm classification records
USGS earthquake catalog for regional context
California Geological Survey fault maps