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Location:
15km WNW of Johannesburg, CA
Period:
31 Jan 2009 21:09:22 - 2 Feb 2009 11:43:07 (1 day 14 hours 33 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
48
8 swarms found nearby.
2016
13 Jan
3 days 3 hours
42 earthquakes
2019
S20190710.1(13.3km)
9 Jul
6 days 20 hours
98 earthquakes
S20190720.2(14.5km)
20 Jul
9 days 7 hours
129 earthquakes
2025
10 Apr
2 days 16 hours
43 earthquakes
25 Nov
1 day 8 hours
30 earthquakes
2026
22 Jan
1 day 19 hours
28 earthquakes
S20260601.2(11.3km)
1 Jun
11 days 3 hours
117 earthquakes
S20260713.1(10.6km)
13 Jul
1 day 6 hours
46 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20090201.1 Near Johannesburg, California

Seismic swarm S20090201.1 occurred 15 km west-northwest of Johannesburg in Kern County, California. The sequence began at 21:09 on 31 January 2009 and concluded at 11:43 on 2 February 2009, lasting 38 hours and 33 minutes. During this period, 48 earthquakes were recorded.

The swarm featured a mainshock of magnitude 4.3 at a depth of 7 km, followed by numerous smaller events. Depths ranged primarily between 4 km and 9 km, with magnitudes from 0.4 to 4.3. Notable events included a magnitude 2.9 quake at 6 km depth on 1 February at 06:02 and several magnitude 1.5 events clustered around 6–7 km depth. Activity showed an initial burst of events within the first hours, followed by a gradual decline, consistent with swarm behavior rather than a classic foreshock-mainshock-aftershock pattern.

Johannesburg lies within the Mojave Desert block of southern California, a region shaped by right-lateral strike-slip faulting associated with the broader Pacific–North American plate boundary. The local geology features Precambrian to Mesozoic crystalline basement rocks overlain by Tertiary volcanic and sedimentary units. Prominent nearby structures include the Garlock Fault to the north and segments of the San Andreas system farther west, both contributing to regional strain accumulation.

The area has a documented history of seismic activity, with small to moderate earthquakes occurring regularly due to distributed faulting in the eastern California shear zone. Historical gold mining at the Rand District, active from the 1890s through the mid-20th century, exploited quartz veins within these faulted terrains but did not alter underlying tectonic processes.

This 2009 swarm aligns with the typical background seismicity of the Mojave block, where clusters of events often occur without producing surface rupture. Depths concentrated in the upper crust reflect brittle failure along pre-existing fractures. No damage or felt reports of significance were associated with the sequence.

References

  • United States Geological Survey Earthquake Catalog
  • California Geological Survey, Regional Geologic Map Series
  • Southern California Earthquake Data Center, Event Archives