Seismic Swarm Analysis: S20140323.1 Near Iquique, Chile

A seismic swarm designated S20140323.1 was recorded 86 km northwest of Iquique, Chile, between 13:22 on 22 March 2014 and 12:22 on 24 March 2014. Over the 46-hour 59-minute period, 41 earthquakes were detected, with magnitudes ranging from 2.3 to 4.9 and focal depths between 10 km and 46 km. The sequence began with a magnitude 4.5 event at 41 km depth and included multiple events above magnitude 4.0, such as a magnitude 4.9 at 10 km depth shortly after onset and additional magnitude 4.6 and 4.4 shocks distributed across the first two days. Later activity featured smaller events clustered around 40–45 km depth before concluding with a magnitude 4.1 event at 19 km depth.

This swarm occurred within the tectonically active forearc of northern Chile, where the Nazca Plate subducts beneath the South American Plate at a rate of approximately 6–7 cm per year. The subduction interface in this segment has produced great earthquakes historically, including the 1877 Iquique event of estimated magnitude 8.5–9.0. The 2014 swarm preceded the magnitude 8.2 Iquique mainshock of 1 April 2014 by roughly ten days, consistent with patterns of precursory seismicity observed in subduction zones worldwide. Depths recorded during the swarm align with both the plate interface and overlying crustal volumes, reflecting stress accumulation and release along the megathrust and subsidiary faults.

Since 1 January 2000, only three swarms have been identified in the broader region according to SeismoSight internal classification, with S20140323.1 representing the earliest documented episode. The events illustrate typical swarm behavior: a rapid onset, lack of a single dominant mainshock, and gradual decay in both rate and magnitude. Such sequences provide valuable data for understanding short-term seismic hazard in northern Chile’s highly coupled subduction segment.

Geological context is further defined by the Atacama Desert’s arid setting and the presence of the Coastal Cordillera, where active faulting accommodates part of the plate-boundary strain. Updated seismic monitoring networks operated by Chilean and international agencies continue to track microseismicity in this zone, confirming persistent activity linked to the ongoing subduction process.

References: USGS Earthquake Hazards Program – Regional tectonics and historical seismicity of northern Chile. Global CMT Catalog – Focal mechanisms and depth distribution along the Peru-Chile Trench. Servicio Nacional de Geología y Minería (SERNAGEOMIN) – Andean subduction zone characteristics.