Seismic Swarm S20141231.1: Analysis of Activity East of Fort Bidwell, California

The seismic swarm S20141231.1 began at 20:36 on 30 December 2014 and concluded at 21:11 on 6 February 2015. Centered 42 km east of Fort Bidwell, California, the sequence lasted 912 hours and 35 minutes and contained 1571 earthquakes. This event represents the initial swarm recorded in the region since 2000, with eight additional swarms occurring afterward. Analysis of the first 100 events reveals a predominance of low-magnitude activity. Magnitudes ranged from -0.5 to 3.1, with the majority falling between 0.5 and 1.8. Depths were generally shallow, spanning 0 to 12 km and clustering around 6 to 8 km. The largest event reached magnitude 3.1 at a depth of 9 km on 1 January 2015. Several magnitude 2+ events occurred within the opening hours, followed by a steady sequence of smaller shocks that maintained consistent shallow focal depths indicative of brittle failure in the upper crust. The region lies within the northern Basin and Range province, where extensional tectonics produce normal faulting along range-front structures. This setting hosts intermittent volcanic fields and geothermal systems that can influence fluid migration and trigger swarm-like seismicity. Historical records show that such sequences often reflect episodic strain release rather than mainshock-aftershock patterns. The swarm's temporal evolution, with rapid onset and prolonged duration, aligns with fluid-driven mechanisms commonly observed in similar extensional environments. Depths concentrated near 7 km suggest activity along or adjacent to mapped fault planes within the upper 10 km of crust. References
SeismoSight internal swarm classification S20141231.1
USGS Earthquake Hazards Program regional tectonic summaries