Seismic Swarm S20241009.2 Near Puebla, Baja California

A seismic swarm designated S20241009.2 was recorded 7 km east-southeast of Puebla, Baja California, Mexico. The sequence began at 18:54 on 8 October 2024 and concluded at 17:05 on 9 October 2024, spanning 22 hours and 10 minutes. During this period, 25 earthquakes were registered, with magnitudes ranging from 1.2 to 3.2 and focal depths between 16 km and 25 km.

The events clustered tightly in both time and space, characteristic of swarm behavior rather than a mainshock-aftershock sequence. The largest event reached magnitude 3.2 at 06:05 on 9 October, followed closely by a magnitude 3.0 shock later that morning. Most events occurred at mid-crustal depths around 18–24 km, consistent with regional faulting patterns.

This swarm represents the third documented swarm in the area during 2024. Historical records since 2000 show 21 swarms in total, with notable activity in 2008 (four swarms) and 2010 (five swarms). Earlier episodes occurred in 2000, 2002, 2005, 2006, 2009, and 2016. Such recurrent swarms indicate persistent tectonic strain release along local structures.

The Puebla region lies within the Mexicali Valley, part of the Salton Trough tectonic province. This area forms the southern extension of the San Andreas fault system at the boundary between the Pacific and North American plates. Right-lateral strike-slip motion along northwest-trending faults, combined with minor extension, produces frequent small-magnitude seismicity. Geothermal activity and fluid migration in the subsurface further facilitate swarm-type sequences by reducing fault friction.

Seismic monitoring in northern Baja California has improved significantly since the early 2000s, allowing better documentation of low-magnitude events. The current swarm aligns with long-term patterns of distributed microseismicity observed across the Imperial and Cerro Prieto fault zones.

References
SeismoSight internal classification for swarm parameters and historical statistics.
USGS Earthquake Hazards Program for regional tectonic framework of the Salton Trough.
Servicio Sismológico Nacional (Mexico) for historical seismicity context in Baja California.