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Location:
18km NE of Olancha, CA
Period:
30 Aug 2009 07:05:58 - 2 Sep 2009 02:26:30 (2 days 19 hours 20 minutes)
Volcanoes in 100km radius:
Ubehebe Craters(77km)
Earthquakes:
47
10 swarms found nearby.
2000
S20000426.1(19.5km)
25 Apr
2 days 10 hours
53 earthquakes
S20000517.1(18.6km)
17 May
3 days 15 hours
92 earthquakes
S20000709.1(17.3km)
8 Jul
1 day 22 hours
44 earthquakes
2002
S20020721.1(29.0km)
20 Jul
3 days 21 hours
49 earthquakes
2009
23 May
6 days 9 hours
88 earthquakes
30 Sep
19 days 1 hours
636 earthquakes
2011
3 May
1 day 10 hours
50 earthquakes
2020
S20200623.1(11.7km)
22 Jun
25 days 3 hours
1110 earthquakes
2021
S20210412.1(23.7km)
11 Apr
2 days 3 hours
33 earthquakes
S20211018.1(20.5km)
17 Oct
1 day 7 hours
27 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20090830.1 Near Olancha, California

The seismic swarm designated S20090830.1 occurred 18 km northeast of Olancha, California, in Inyo County. It began at 07:05 on 30 August 2009 and concluded at 02:26 on 2 September 2009, spanning 67 hours and 20 minutes. During this interval, 47 earthquakes were recorded. The events clustered in a compact area typical of swarm activity, where numerous earthquakes occur without a single dominant mainshock.

The largest event reached magnitude 3.8 at a reported depth of 0 km, occurring at 07:05:58 on 30 August. Subsequent notable events included magnitudes of 3.6 and 3.3, both at shallow depths. The majority of earthquakes registered below magnitude 2.0, with depths predominantly between 0 and 5 km. Several events showed depths of 0 km or negative values, consistent with near-surface or very shallow activity. A secondary cluster of events appeared on 1 September, including a magnitude 2.9 at 05:42:45.

This swarm aligns with the region's documented seismic patterns. Since 1 January 2000, five swarms have been identified in the area, occurring in 2000 (three swarms), 2002 (one swarm), and 2009 (this event). The 2009 swarm represents the most recent in this sequence within the recorded period.

The Olancha vicinity lies within the southern Owens Valley, part of the Eastern California Shear Zone. This zone accommodates dextral shear between the Pacific and North American plates through a network of strike-slip and normal faults. The local geology features Quaternary alluvial deposits overlying older metamorphic and granitic basement rocks of the Sierra Nevada and Inyo Mountains. Proximity to the Coso Volcanic Field to the south introduces additional influences from geothermal and volcanic processes that can contribute to shallow seismicity.

Historical context includes the great 1872 Owens Valley earthquake, which produced surface rupture along the Owens Valley Fault and reached an estimated magnitude of 7.4–7.9. Modern monitoring has revealed recurring low-magnitude swarms in the broader region, often linked to fluid migration or minor fault adjustments rather than large tectonic releases.

Analysis of the 2009 swarm indicates a rapid onset followed by gradual decay in activity. Shallow focal depths suggest involvement of near-surface structures, potentially influenced by local hydrology or geothermal gradients. No significant damage or felt reports beyond the immediate area were associated with the sequence.

References

  • SeismoSight internal swarm classification records
  • USGS earthquake catalog data for Inyo County, California
  • Geological Survey of California regional tectonic summaries