Seismic Swarm S20240212.1 Near El Centro, California

A seismic swarm designated S20240212.1 was recorded 2 km NNW of El Centro, California. The sequence began at 08:36 on 12 February 2024 and concluded at 11:17 on 15 February 2024, spanning 74 hours and 41 minutes. During this period, 363 earthquakes were registered. Analysis of the first 100 events reveals a rapid onset with the largest shock reaching magnitude 4.8 at 17 km depth. Subsequent events included multiple shocks above magnitude 3.0 within the initial hour, followed by a progressive decline in both frequency and magnitude. Depths for these events ranged primarily between 7 km and 22 km, with the majority clustered between 10 km and 15 km. Magnitudes spanned from 0.9 to 4.8, consistent with typical swarm behavior in the region. The Imperial Valley, where El Centro is located, forms part of the Salton Trough, a tectonically active pull-apart basin within the boundary zone between the Pacific and North American plates. Right-lateral strike-slip faulting dominates, with the Imperial Fault and Brawley Seismic Zone serving as key structures. This setting produces elevated background seismicity and recurrent earthquake swarms, often linked to fluid migration and geothermal processes associated with the nearby Salton Sea. Historical records indicate 26 swarms in the area since 1 January 2000. These occurred in the following years with the listed counts: 2000 (1), 2003 (2), 2005 (1), 2008 (1), 2009 (4), 2010 (6), 2011 (1), 2012 (1), 2016 (2), 2017 (2), 2019 (2), 2021 (1), 2022 (1), and 2023 (1). Such sequences underscore the persistent seismic character of the Imperial Valley without producing a single dominant mainshock. The February 2024 swarm aligns with established patterns of clustered, moderate-magnitude activity in this fault system. No surface rupture or significant damage was associated with the events.

References

USGS Earthquake Catalog California Geological Survey Regional Fault Maps Southern California Seismic Network Reports