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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:
43 km E of Fort Bidwell, California
Period:
26 Jul 2015 03:14:18 - 4 Aug 2015 08:52:32 (9 days 5 hours 38 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
152
20 swarms found nearby.
2007
S20070703.1(29.6km)
3 Jul
18 hours
27 earthquakes
2014
31 Jul
2 days 23 hours
51 earthquakes
4 Aug
5 days 7 hours
82 earthquakes
18 Aug
2 days 20 hours
111 earthquakes
23 Aug
1 day 19 hours
27 earthquakes
28 Aug
2 days 2 hours
36 earthquakes
14 Sep
2 days 23 hours
44 earthquakes
1 Oct
1 day 19 hours
30 earthquakes
30 Oct
2 days 7 hours
40 earthquakes
4 Nov
55 days 22 hours
1792 earthquakes
30 Dec
38 days 0 hours
1571 earthquakes
2015
11 Feb
26 days 3 hours
529 earthquakes
15 Jul
4 days 9 hours
258 earthquakes
10 Aug
10 days 1 hours
158 earthquakes
30 Aug
2 days 7 hours
43 earthquakes
13 Sep
32 days 6 hours
545 earthquakes
18 Nov
6 days 21 hours
137 earthquakes
24 Dec
18 days 2 hours
467 earthquakes
2022
S20221208.1(10.7km)
7 Dec
2 days 15 hours
44 earthquakes
2025
26 Jun
2 days 16 hours
38 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20150727.1: Analysis of Activity East of Fort Bidwell, California

Seismic swarm S20150727.1 occurred approximately 43 km east of Fort Bidwell in Modoc County, California, within the northern Basin and Range province. This region lies along the western margin of the Great Basin, where extensional tectonics drive normal faulting along structures such as the Surprise Valley Fault. The area features volcanic rocks from the Modoc Plateau and Warner Mountains, with Cenozoic basalts and andesites overlying older metamorphic basement. Seismicity here often reflects both tectonic extension and minor contributions from residual volcanic or hydrothermal processes.

The swarm initiated at 03:14 UTC on 26 July 2015 and concluded at 08:52 UTC on 4 August 2015, spanning 221 hours and 38 minutes. A total of 152 earthquakes were recorded during this interval. Analysis of the first 100 events shows magnitudes ranging from 0.8 to 4.5, with the largest shock (M4.5) occurring at 01:05 UTC on 27 July at a depth of 10 km. Depths clustered predominantly between 5 km and 10 km, consistent with shallow crustal faulting in the region. Early activity featured several events above magnitude 2.0 within the first 24 hours, including a M2.7 at 02:16 UTC and a M3.1 at 03:08 UTC on 27 July. Subsequent events maintained a steady rate with occasional clusters of M2.0–M3.0 shocks through 30 July, after which activity tapered. Depths remained stable, rarely exceeding 13 km or falling below 2 km.

Historically, the Fort Bidwell area has experienced episodic swarm activity. Since 1 January 2000, thirteen swarms have been documented, with notable clusters in 2007 (one swarm), 2014 (ten swarms), and 2015 (two swarms including the present event). Such swarms are characteristic of the Surprise Valley region, where fluid migration along faults can trigger sequences without a single dominant mainshock.

This pattern aligns with the broader tectonic framework of northeastern California, where GPS data indicate ongoing extension rates of 1–3 mm per year. No surface rupture or significant damage was associated with S20150727.1, typical for moderate-magnitude swarms in this sparsely populated terrain.

References

  • USGS Earthquake Catalog (earthquake.usgs.gov)
  • California Geological Survey, Regional Fault Maps
  • Wells et al. (2016), Surprise Valley Fault System, Geosphere
  • UNAVCO GPS Network Data, Basin and Range Extension Rates