Seismic Swarm VS20050510.1 Near Puebla, Baja California

Seismic swarm VS20050510.1 occurred 14 km south-southeast of Puebla, Baja California, Mexico. The sequence began at 16:53 on 9 May 2005 and concluded at 01:44 on 19 May 2005, spanning 224 hours and 50 minutes. During this interval, 196 earthquakes were recorded.

Analysis of the first 100 events reveals a tight temporal clustering, with the majority occurring between 9 May and 13 May 2005. Magnitudes ranged from 1.4 to 3.1, and focal depths remained consistently shallow at 5–6 km. The largest events reached magnitude 3.1 at 05:18 on 10 May and magnitude 3.0 on multiple occasions, including 21:48 on 9 May, 04:01 and 04:19 on 10 May, and 12:31 on 11 May. Lower-magnitude events (1.4–2.5) dominated the sequence, indicating a typical swarm pattern without a single dominant mainshock.

The swarm unfolded in distinct phases. Initial activity on 9 May featured events up to magnitude 3.0 within the first six hours. Activity intensified overnight into 10 May, producing several magnitude-3.0 events at depths of 6 km. By 11–13 May, the rate remained elevated but gradually declined, with events shifting slightly toward greater depths of 6 km during peak periods. Depths stabilized near 5 km for most smaller events, consistent with shallow crustal faulting.

This swarm represents the fourth documented sequence in the area since 1 January 2000. Earlier swarms occurred in 2000 (one event cluster) and 2002 (three event clusters). The recurrence suggests episodic strain release along local fault structures.

The Puebla region lies within the southern Baja California Peninsula, where the Pacific Plate interacts with the North American Plate along the San Andreas–Gulf of California transform system. This tectonic setting produces frequent shallow strike-slip and normal-faulting earthquakes. The 5–6 km depths align with known seismogenic zones in the upper crust of this transform margin. Updated regional monitoring confirms ongoing microseismicity in the area, though no larger events have been linked directly to the 2005 swarm.

SeismoSight internal classification identifies VS20050510.1 as a classic swarm driven by fluid migration or aseismic slip rather than a foreshock–mainshock–aftershock cascade. The absence of events exceeding magnitude 3.1 and the rapid decay after 13 May support this interpretation.

References
SeismoSight web site internal records for swarm VS20050510.1.
Regional tectonic summaries from the U.S. Geological Survey and Servicio Sismológico Nacional (updated through 2023).