Seismic Swarm S20140324.1 Near Iquique, Chile: Characteristics and Tectonic Context

Seismic swarm S20140324.1 was recorded between 18:36 UTC on 23 March 2014 and 10:26 UTC on 27 March 2014, approximately 97 km northwest of Iquique, Chile. Over 87 hours and 50 minutes, the swarm comprised 80 earthquakes. Event depths ranged primarily between 10 km and 47 km, with magnitudes spanning 2.2 to 5.7. The sequence featured several events above magnitude 4.0, including a peak magnitude of 5.7 at 15:45 UTC on 24 March at 17 km depth.

The swarm exhibited typical characteristics of clustered seismic activity in a subduction environment, with the majority of events occurring at intermediate depths consistent with the descending slab. Shallower events, such as those near 10–20 km, coincided with periods of higher magnitude release, notably on 24 March. The temporal distribution showed peak activity during the first 48 hours, followed by a gradual decline until termination.

The Iquique region lies within the Peru-Chile subduction zone, where the Nazca Plate converges with the South American Plate at rates of 6–7 cm per year. This tectonic regime produces frequent seismicity, including both intraslab and interface events. Northern Chile forms part of the Andean margin, characterized by the Atacama Desert and the coastal cordillera, underlain by a well-developed Benioff zone extending to depths exceeding 100 km.

Historical records indicate that since 1 January 2000, four seismic swarms have occurred in the broader area, with S20140324.1 representing the earliest documented in this timeframe. The region experienced a major megathrust earthquake of magnitude 8.2 on 1 April 2014, centered 93 km northwest of Iquique and only 7 km from the swarm centroid. This event occurred eight days after swarm termination and released substantial strain accumulated along the plate interface.

Such swarms often reflect stress redistribution within the subducting slab or along the megathrust prior to larger ruptures. The 2014 sequence aligns with patterns observed in other subduction zones, where foreshock activity precedes mainshocks by days to weeks. Depths recorded in the swarm data correspond closely to the expected geometry of the Nazca slab beneath northern Chile.

Seismic monitoring in this area benefits from dense networks operated by Chilean institutions, enabling precise location of events even at moderate magnitudes. The swarm’s progression, from initial low-magnitude activity to inclusion of events exceeding magnitude 5, illustrates the dynamic nature of strain release in this highly active margin.

References

• SeismoSight internal swarm classification S20140324.1
• USGS Earthquake Catalog (events since 2000)
• ANSS Comprehensive Earthquake Catalog for northern Chile tectonics