Seismic Swarm S20100410.1 Near Estación Coahuila, Baja California
Seismic swarm S20100410.1 was recorded in Baja California, Mexico, beginning at 09:25 on 9 April 2010 and concluding at 18:27 on 10 April 2010. The events occurred 14 km southwest of Estación Coahuila, within a tectonically active corridor of the Salton Trough–Gulf of California rift system. Over 33 hours and 2 minutes, 29 earthquakes were detected, with magnitudes ranging from 2.2 to 3.8 and focal depths between 4 km and 19 km.
The sequence displayed typical swarm characteristics: no single dominant mainshock, clustered occurrence, and relatively uniform energy release. The largest event reached magnitude 3.8 at 08:46 on 10 April at a depth of 8 km. Several other notable shocks included magnitudes 3.4 (06:31, 19 km depth), 3.3 (18:32 on 9 April, 16 km depth; and 04:21 on 10 April, 13 km depth), and 3.2 (11:39 on 9 April, 9 km depth). Depths remained predominantly shallow, consistent with brittle failure in the upper crust.
This swarm represents the third such episode documented in the region since 2000. Earlier swarms occurred in 2000 (one event) and 2001 (one event), indicating episodic low-to-moderate seismic clustering rather than continuous background activity.
Regional Geological Setting
Baja California lies along the diffuse Pacific–North American plate boundary. The study area occupies the northern extension of the Gulf of California rift, where right-lateral transform faults and short spreading segments accommodate oblique divergence. The Imperial and Cerro Prieto faults, together with the recently activated Laguna Salada fault system, form the principal structural elements. Crustal thinning and high heat flow produce a seismogenic zone typically limited to the upper 20 km, matching the observed depth distribution of the swarm.
The April 2010 sequence followed the magnitude 7.2 El Mayor–Cucapah earthquake of 4 April 2010 by five days. Static and dynamic stress changes from that event likely promoted the subsequent swarm by altering pore-fluid pressures and fault friction along favorably oriented structures. Such delayed triggering is documented in other rift-margin settings and aligns with the shallow, distributed nature of the recorded events.
Historical Seismicity Context
Instrumental records show that the Mexicali Valley and adjacent Sierra Cucapah have experienced recurrent moderate earthquakes and swarms throughout the twentieth century. The 2010 swarm fits within this pattern of clustered activity separated by periods of relative quiescence. No larger events have been associated with these swarms, supporting the interpretation of them as secondary responses within a fault network already stressed by regional tectonics.
Summary of Swarm Parameters
Magnitudes remained below 4.0, limiting potential for significant damage. The 29 events were distributed across two calendar days with peak activity on 10 April. Depths showed modest variation but stayed within the expected seismogenic window for the area. The absence of a clear magnitude–frequency rollover at the upper end suggests the swarm sampled only a limited portion of the local fault population.
Continued monitoring of this sector remains important because the same fault network that produced the 2010 swarm lies adjacent to the U.S.–Mexico border and major population centers. Future swarms may provide additional data on stress transfer and fluid involvement in this rapidly deforming rift margin.
References
USGS Earthquake Catalog (events 2010-04-09 to 2010-04-10, Baja California).
Servicio Sismológico Nacional, Universidad Nacional Autónoma de México, regional bulletins 2000–2010.
USGS Earthquake Hazards Program, El Mayor–Cucapah earthquake summary (2010).