Seismic Swarm S20100408.1: Analysis of Activity near Estación Coahuila, Baja California

An earthquake swarm designated S20100408.1 was recorded in northern Baja California, Mexico, beginning at 03:06 on 7 April 2010 and concluding at 04:28 on 4 May 2010. The events were centered approximately 10 km south-southwest of Estación Coahuila. Over 649 hours and 22 minutes, a total of 638 earthquakes were registered.

The first 100 events of the swarm provide a representative sample of its characteristics. These occurred primarily between 7 and 12 April 2010, with magnitudes ranging from 1.5 to 4.4 and focal depths concentrated between 3 km and 19 km. The sequence began with events at 9 km depth, including a magnitude 4.3 earthquake at 04:23 on 7 April and a magnitude 4.4 event at 06:36 the same day. Subsequent activity showed a mix of depths, with many events clustered around 9–14 km. Notable larger events included a magnitude 3.9 at 19:13 on 11 April (18 km depth) and a magnitude 3.8 at 00:46 on 11 April (17 km depth). Depths generally remained shallow, consistent with regional crustal structure.

The swarm location lies within the tectonically active boundary zone between the Pacific and North American plates. Northern Baja California experiences distributed deformation along northwest-trending strike-slip faults and pull-apart basins linked to the Gulf of California rift system. This setting produces frequent small-to-moderate earthquakes, often occurring in swarms rather than classic mainshock-aftershock sequences.

Seismic swarms have been recurrent in the broader region. Since 2000, seventeen such swarms have been documented, with yearly counts as follows: one in 2000, two in 2002, one in 2005, one in 2006, three in 2008, three in 2009, and six in 2010. These episodes reflect ongoing plate-boundary strain accumulation and release along the Imperial, Cerro Prieto, and related fault systems.

The 2010 swarm exhibited typical swarm behavior, with events distributed over weeks and no single dominant mainshock. Magnitudes remained modest, and the concentration of activity at mid-crustal depths aligns with the brittle-ductile transition zone in this part of the plate margin. Such patterns are common where fluid migration or aseismic slip may trigger clustered seismicity.

References

USGS Earthquake Catalog (events through 2023)
Servicio Sismológico Nacional (Mexico)
Global Centroid Moment Tensor catalog
Peer-reviewed literature on Gulf of California tectonics (2010–2023 updates)