Location:

Period:

3 Jul 2007 06:34:42 - 4 Jul 2007 01:30:02 (18 hours 55 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

3 swarms found nearby.

2014

S20140824.1(29.9km)

23 Aug

1 day 19 hours

27 earthquakes

2015

S20150727.1(29.6km)

26 Jul

9 days 5 hours

152 earthquakes

2025

S20250627.1(27.5km)

26 Jun

2 days 16 hours

38 earthquakes

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Seismic Swarm S20070703.1: Analysis of Activity Near Fort Bidwell, California

A seismic swarm designated S20070703.1 occurred 29 km NNE of Fort Bidwell in Modoc County, California. The sequence began at 06:34 on 3 July 2007 and concluded at 01:30 on 4 July 2007, lasting 18 hours and 55 minutes. During this period, 27 earthquakes were recorded, with magnitudes ranging from 0.9 to 2.6 and focal depths predominantly between 0 and 7 km.

The events clustered in time, showing peak activity between 09:00 and 18:00 on 3 July. The largest shock reached magnitude 2.6 at 11:20, followed by several events of magnitude 2.0–2.1. Depths remained shallow throughout, consistent with activity in the upper crust. Negative depth values listed for three events likely reflect minor location uncertainties rather than subsurface anomalies.

This swarm took place within the Modoc Plateau, a volcanic province characterized by extensive basalt and andesite flows of Miocene to Quaternary age. The region lies at the western margin of the Basin and Range extensional province, where normal and strike-slip faults accommodate ongoing crustal stretching. Historical seismicity in Modoc County includes both isolated events and occasional swarms, often linked to fluid migration along pre-existing fractures in volcanic terrain.

Geological mapping indicates that the swarm epicentral area sits near the intersection of northwest-trending range-front faults and northeast-trending lineaments associated with the ancestral Cascade arc. Although no surface rupture was reported, the shallow depths suggest the activity occurred on minor faults within the volcanic pile rather than on major range-bounding structures.

Such swarms are common in the northern California–southern Oregon border region and typically do not culminate in larger mainshock–aftershock sequences. The modest magnitudes and short duration of S20070703.1 align with this pattern, indicating a localized release of tectonic strain without significant hazard implications.

References

USGS Earthquake Catalog (ANSS Comprehensive Catalog)
California Geological Survey, Geologic Map of California
USGS Professional Paper 1515, Quaternary Geology of the Modoc Plateau
SeismoSight internal swarm classification S20070703.1