Earthquake Swarm S20140824.1: Analysis of Seismicity Near Fort Bidwell, California

The earthquake swarm designated S20140824.1 occurred approximately 42 km east of Fort Bidwell in northeastern California. This sequence began at 10:57 on 23 August 2014 and concluded at 06:08 on 25 August 2014, spanning 43 hours and 10 minutes. During this period, 27 earthquakes were recorded, with the majority exhibiting magnitudes below 2.0 and depths predominantly near the surface.

The largest event reached magnitude 3.1 at a depth of 1 km on 23 August at 14:24:37. Other notable events included a magnitude 2.6 at 16:34:55, a magnitude 2.5 at 20:16:39, and a magnitude 2.4 at 16:43:14, all at shallow depths. Several events occurred at greater depths, such as 28 km at 15:04:12 and 15 km at 23:38:16, indicating varied focal mechanisms within the sequence. The swarm displayed typical characteristics of clustered, low-magnitude activity without a dominant mainshock-aftershock pattern.

This swarm aligns with the broader tectonic setting of the Modoc Plateau and adjacent Basin and Range province. The region features extensive volcanic deposits from Miocene to Holocene epochs, including basaltic lava flows and pyroclastic materials associated with the Cascade arc influence. Active normal faulting along structures such as the Surprise Valley Fault contributes to ongoing extension, facilitating fluid migration and swarm-type seismicity. Historical volcanic activity in nearby fields underscores the potential interplay between tectonics and magmatic processes in modulating earthquake clusters.

Since 2000, four swarms have been documented in the area, with one occurring in 2007 and three in 2014, highlighting episodic seismicity patterns. Such events provide insight into crustal stress release and fluid dynamics in this volcanically influenced terrain.

• SeismoSight internal swarm classification records
• USGS Earthquake Catalog for regional context
• California Geological Survey reports on Modoc Plateau geology