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Note:This page contains AI-generated content for informational and entertainment purposes only. It may contain inaccuracies. Raw event data is from USGS and EMSC. All statistics, lists, and derived information are generated by this site. Full disclaimerFound an error?
Location:
9 km E of San Simeon, California
Period:
1 Oct 2005 17:52:02 - 12 Oct 2005 11:00:07 (10 days 17 hours 8 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
151
18 swarms found nearby.
2003
S20031222.1(29.1km)
22 Dec
37 days 3 hours
2456 earthquakes
S20031222.2(26.9km)
22 Dec
15 days 17 hours
643 earthquakes
22 Dec
1 day 0 hours
127 earthquakes
S20031224.1(27.2km)
23 Dec
2 days 19 hours
170 earthquakes
31 Dec
2 days 2 hours
67 earthquakes
2004
S20040201.1(25.5km)
31 Jan
9 days 8 hours
199 earthquakes
1 Feb
1 day 12 hours
34 earthquakes
S20040205.1(26.0km)
4 Feb
2 days 23 hours
57 earthquakes
1 Mar
24 days 6 hours
484 earthquakes
S20040303.1(27.5km)
3 Mar
8 days 3 hours
172 earthquakes
16 Mar
7 days 18 hours
281 earthquakes
4 Apr
18 days 8 hours
226 earthquakes
S20040425.1(28.8km)
25 Apr
19 days 16 hours
216 earthquakes
S20040528.1(29.9km)
27 May
2 days 11 hours
49 earthquakes
26 Jul
10 days 1 hours
140 earthquakes
13 Oct
8 days 7 hours
97 earthquakes
2006
6 Apr
11 days 10 hours
151 earthquakes
2009
S20090620.2(14.1km)
20 Jun
4 days 17 hours
84 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20051002.1: Analysis of Activity Near San Simeon, California

A notable earthquake swarm, designated S20051002.1, occurred 9 km east of San Simeon, California, between 17:52 on 1 October 2005 and 11:00 on 12 October 2005. Over 257 hours and 8 minutes, the sequence produced 151 events. This activity reflects the persistent seismicity along the central California coast, where the boundary between the Pacific and North American plates generates frequent small-magnitude earthquakes.

The region lies within the San Andreas Fault system and associated subsidiary structures, including the Hosgri and Oceanic faults. These strike-slip features accommodate right-lateral motion at rates of approximately 34–36 mm per year. Historical records show that the area experienced a magnitude 6.5 event in December 2003, which originated on a blind thrust fault segment near the coast. Such events underscore the potential for both swarm-type sequences and larger mainshock-aftershock patterns in this tectonically active zone.

Analysis of the first 100 recorded events reveals a predominance of microearthquakes with magnitudes between 1.0 and 2.0. Depths clustered between 2 km and 6 km, consistent with shallow crustal faulting in the Franciscan Complex basement rocks. Notable larger events included a magnitude 4.0 shock at 13:48 on 2 October, followed by a magnitude 3.4 event two minutes later. Subsequent peaks reached magnitude 3.9 on 8 October. The temporal distribution showed the highest rates during the first 48 hours, after which activity declined gradually while maintaining a steady background rate through 12 October.

Swarm behavior of this type has been documented repeatedly in the region. Since 1 January 2000, sixteen swarms have been identified, with five occurring in 2003 and eleven in 2004. These episodes typically involve hundreds of events without a clear mainshock, driven by fluid migration or aseismic slip along pre-existing fault planes.

The 2005 sequence fits established patterns of low-magnitude, shallow seismicity that rarely produces surface rupture but contributes to long-term strain release. Continued monitoring remains essential given the proximity to populated coastal communities and critical infrastructure.

  • SeismoSight internal swarm classification records
  • USGS Earthquake Catalog (historical swarm statistics)