Seismic Swarm S20141001.2 Near Fort Bidwell, California

The earthquake swarm designated S20141001.2 was recorded 43 km east of Fort Bidwell in northeastern California. It began at 12:46 on 1 October 2014 and concluded at 07:46 on 3 October 2014, encompassing 30 events over 43 hours. All activity remained at shallow depths, with the largest event reaching magnitude 3.8.

This swarm occurred within the Modoc Plateau, a region shaped by Basin and Range extension and late Cenozoic volcanism. Normal faults dominate the local structure, accommodating crustal stretching that produces frequent shallow seismicity. The Warner Mountains to the west and Surprise Valley to the east frame the tectonic setting, where Holocene fault scarps indicate ongoing deformation.

Data from the swarm show predominantly shallow foci between 0 and 4 km, with one event at 9 km. Magnitudes clustered between 1.2 and 3.8, including four events of 3.0 or greater. The sequence displayed typical swarm characteristics: rapid onset, lack of a single dominant mainshock, and gradual decay without aftershock-style Omori decay.

Since 1 January 2000, six swarms have been identified in the broader region, with S20141001.2 representing the earliest recorded. Subsequent swarms followed similar patterns of low-to-moderate magnitudes and shallow depths, underscoring episodic strain release along the same fault network.

The events highlight the importance of continuous monitoring in low-strain-rate extensional terranes. Shallow depths suggest involvement of near-surface faults or possible hydrothermal influences common in the volcanic province. No damage or felt reports beyond the immediate area were associated with the sequence.

References

SeismoSight internal swarm classification S20141001.2
USGS Quaternary Fault and Fold Database
California Geological Survey Regional Geologic Maps