February 2016 Earthquake Swarm Near Big Bear City, California

The February 2016 earthquake swarm, designated S20160216.1 by SeismoSight, occurred approximately 5 km NNW of Big Bear City in the San Bernardino Mountains of southern California. This seismic sequence began at 08:01 on 16 February 2016 and concluded at 20:37 on 18 February 2016, spanning 60 hours and 36 minutes. During this period, 55 earthquakes were recorded, with magnitudes ranging from 0.4 to 3.8 and focal depths predominantly between 1 km and 5 km.

The swarm's temporal distribution showed the highest activity on 16 February, including the largest event of magnitude 3.8 at 09:24:20. Subsequent days featured lower-frequency events, with the final recorded quake of magnitude 1.3 occurring at 20:37:41 on 18 February. Depths clustered around 2–5 km, consistent with shallow crustal faulting in the region. This pattern reflects typical swarm behavior, where numerous small events occur without a dominant mainshock-aftershock sequence.

The Big Bear area lies within the Transverse Ranges, a tectonically complex zone influenced by the convergence of the Pacific and North American plates. The San Andreas Fault system, located nearby, accommodates much of the lateral motion, while subsidiary faults such as the North Frontal Fault and local thrust structures contribute to regional seismicity. The San Bernardino Mountains have experienced uplift driven by compressional tectonics over millions of years, resulting in a landscape prone to both strike-slip and reverse faulting.

Historically, the region has hosted significant earthquakes, including the 1992 Landers and Big Bear events that highlighted interconnected fault networks. Since 2000, four prior swarms have been documented in the immediate vicinity: one each in 2001, 2003, 2010, and 2014. These episodes underscore the area's persistent low-to-moderate seismic activity, often linked to fluid migration or stress transfer along minor faults rather than large-scale rupture.

Such swarms provide valuable data for understanding crustal stress dynamics in southern California. Continued monitoring by networks including the Southern California Seismic Network supports improved hazard assessment for communities near Big Bear Lake and the surrounding national forest.

References

• SeismoSight internal swarm classification records
• USGS Earthquake Catalog (historical context for Big Bear region)
• Southern California Earthquake Data Center (regional fault information)