Seismic Swarm S20100406.1 Near Progreso, Baja California
Seismic swarm S20100406.1 occurred in the region 9 km south-southwest of Progreso, Baja California, Mexico. The sequence began at 15:26 on 5 April 2010 and concluded at 23:00 on 9 April 2010, spanning 103 hours and 33 minutes. During this interval, 57 earthquakes were recorded, with magnitudes ranging from 0.5 to 3.3 and focal depths primarily between 0 and 14 km. The events clustered in time, showing peak activity on 5–6 April and a notable magnitude 3.3 shock at 07:42 on 7 April.
The swarm unfolded in a tectonically active zone where the Pacific and North American plates interact along a network of strike-slip and normal faults linked to the Gulf of California rift system. Progreso lies near the southern extension of the Imperial fault and the Laguna Salada fault, both of which accommodate dextral shear and extension. Shallow focal depths observed throughout the swarm are consistent with brittle failure in the upper crust of this transtensional regime.
Baja California has experienced recurrent earthquake swarms since at least 2000, with nine documented episodes through 2010. These include single swarms in 2000, 2005, and 2008, three in 2009, and three in 2010. Such swarms typically reflect fluid migration or aseismic slip transients rather than mainshock-aftershock sequences driven by a single large rupture.
Magnitudes remained modest, with only one event exceeding 3.0. Depths were concentrated above 10 km, indicating activity within the seismogenic layer. Temporal distribution showed an initial burst of events on 5 April, followed by sustained lower-level seismicity tapering by 9 April. No surface rupture or significant damage was associated with the swarm.
The regional geology features Quaternary alluvial deposits overlying Cretaceous granitic basement and Miocene volcanic rocks. Ongoing right-lateral motion along the plate boundary produces frequent microseismicity, with swarms serving as sensitive indicators of stress changes. Updated seismic monitoring by regional networks confirms that the 2010 activity aligns with the long-term pattern of clustered, low-magnitude events in the Progreso area.
References
USGS Earthquake Catalog (earthquake.usgs.gov)
Servicio Sismológico Nacional, Universidad Nacional Autónoma de México
Southern California Earthquake Data Center fault database