The April 2010 Earthquake Swarm South of Alberto Oviedo Mota, Baja California

The April 2010 earthquake swarm, designated S20100405.4, occurred in northern Baja California, Mexico, approximately 14 km south of Alberto Oviedo Mota. It began at 23:20 on 4 April 2010 and concluded at 05:40 on 12 April 2010, spanning 174 hours and 19 minutes during which 271 earthquakes were recorded. This swarm took place in a tectonically active zone along the Pacific–North American plate boundary, where right-lateral strike-slip faulting predominates as part of the San Andreas fault system extending southward into the Gulf of California rift. The swarm initiated shortly after the magnitude 7.2 Sierra El Mayor–Cucapah mainshock of 4 April 2010, whose epicenter lay roughly 12 km from the swarm centroid. The first 100 events exhibited magnitudes ranging from 0.5 to 4.6, with the majority clustered between 2.5 and 4.0. Depths were predominantly 9 km, though isolated events reached 5 km, 6 km, 10 km, and 11 km. Early activity featured several events above magnitude 4.0 within the first hours, including a 4.6 event at 01:25 on 5 April, followed by a gradual decline in both frequency and maximum magnitude. Later events in this initial sequence remained mostly below magnitude 4.0, with occasional spikes to 3.9 and 4.2. The broader region has experienced recurrent seismic swarms since 2000, with 12 documented episodes through 2010. These occurred in the years 2000 (1 swarm), 2002 (2), 2005 (1), 2006 (1), 2008 (3), 2009 (2), and 2010 (2). Such swarms reflect the area’s complex fault network, including segments of the Laguna Salada and related faults that accommodate transform motion between spreading centers in the Gulf of California. The 2010 mainshock and its associated swarm underscore the potential for clustered seismicity in this setting, where stress transfer along strike-slip structures can trigger prolonged sequences of moderate events without a single dominant aftershock sequence. Geological mapping and regional tectonics indicate that the swarm’s location lies within Quaternary alluvial and lacustrine deposits overlying crystalline basement rocks deformed by active faulting. Historical records show that similar moderate-magnitude activity often precedes or follows larger ruptures along the plate-boundary faults, consistent with the observed timing relative to the Sierra El Mayor–Cucapah event.

References

USGS Earthquake Hazards Program – El Mayor–Cucapah Earthquake Summary Servicio Sismológico Nacional, Universidad Nacional Autónoma de México – Regional Seismicity Reports Southern California Earthquake Data Center – Baja California Fault Database