Analysis of the 2010 Earthquake Swarm Near Progreso, Baja California

The earthquake swarm designated S20100405.1 occurred approximately 20 km west-northwest of Progreso in Baja California, Mexico. It began at 14:02 on 4 April 2010 and concluded at 11:30 on 23 May 2010. During this period of 1173 hours and 27 minutes, a total of 7938 earthquakes were recorded.

This region lies within the Mexicali Valley, part of the active transform boundary between the Pacific and North American plates. The area is influenced by the Imperial and Cerro Prieto fault systems, which accommodate right-lateral strike-slip motion. Shallow crustal seismicity is common here, often manifesting as swarms driven by tectonic loading and fluid migration along fault zones. Depths typically remain under 15 km, consistent with the brittle upper crust in this extensional-transform setting.

The initial 100 events of the swarm exhibited magnitudes between 0.5 and 4.6, with the majority falling in the 2.5–3.9 range. Depths varied from 0 to 14 km, predominantly clustered between 1 and 6 km. Activity commenced with a magnitude 1.9 event at 5 km depth, followed rapidly by several events exceeding magnitude 3.5 within the first hours. The strongest event in this subset reached magnitude 4.6 at 4 km depth on 5 April at 01:52. Temporal clustering was pronounced, with multiple events occurring within minutes during peak phases on 4 and 5 April.

Historical records indicate that ten swarms have occurred in the region since 1 January 2000. These include one swarm each in 2000, 2005, and 2006; two in 2002 and 2009; and three in 2008. Such recurrent swarms underscore the area's propensity for episodic seismic sequences rather than isolated mainshock-aftershock patterns.

The 2010 swarm aligns with the established tectonic framework of the Salton Trough–Gulf of California system, where distributed deformation produces frequent low-to-moderate magnitude events. No single large mainshock dominated the sequence, reinforcing its classification as a classic swarm.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Servicio Sismológico Nacional, Mexico (www.ssn.unam.mx)
Southern California Earthquake Data Center (scedc.caltech.edu)