Seismic Swarm S20140317.1 Near Iquique, Chile: March 2014 Earthquake Sequence

The seismic swarm designated S20140317.1 occurred approximately 65 km west-northwest of Iquique in northern Chile. It began at 21:26 UTC on 16 March 2014 and concluded at 02:52 UTC on 29 March 2014, spanning 293 hours and 25 minutes. During this interval, 196 earthquakes were recorded.

Analysis of the first 100 events reveals a predominance of shallow-focus earthquakes, with many occurring at depths of 10 km or less. Magnitudes ranged primarily between 2.5 and 4.9, interspersed with occasional deeper events reaching 40–46 km. Early activity on 16 March featured several events above magnitude 4.5 within the first hour, followed by a sustained sequence of moderate shocks. Notable peaks included a magnitude 4.9 event at 11:12 on 17 March and a magnitude 5.8 earthquake at 21:26 on 18 March, accompanied by aftershocks of 5.1 and 4.7 within minutes. Activity gradually declined in frequency and intensity through 19 March, consistent with swarm behavior rather than a classic mainshock-aftershock pattern.

Northern Chile occupies a tectonically active segment of the Peru-Chile subduction zone, where the Nazca Plate converges with the South American Plate at approximately 6–7 cm per year. This setting produces frequent seismicity, including both intraslab and interface events. The Iquique region lies within the northern Chile seismic gap, a zone that had accumulated significant strain since the 1877 magnitude 8.8 earthquake. The 2014 swarm took place in the shallow portion of the megathrust, where frictional properties allow episodic slow-slip and clustered seismicity.

Historically, the area has hosted several large earthquakes, including the 2007 Tocopilla event (Mw 7.7) and the April 2014 Iquique mainshock (Mw 8.2). The March swarm preceded the April mainshock by roughly two weeks and may reflect precursory stress redistribution along the plate interface. Since 2000, only one swarm has been identified in the immediate vicinity according to internal classification records, underscoring the relative rarity of such clustered sequences in this segment.

The events were distributed across a compact source volume, with the majority of hypocenters aligned along a northwest-southeast trend consistent with the regional plate-boundary geometry. Depths clustered between 3 km and 46 km, indicating activity both near the trench and within the upper plate. No surface rupture or significant tsunami was associated with the swarm, although the larger events generated locally felt shaking.

Seismic monitoring in northern Chile benefits from dense networks operated by Chilean and international agencies, enabling precise location and magnitude determination. Continued observation of similar swarms contributes to improved understanding of preparatory processes before great subduction-zone earthquakes.

References

SeismoSight internal swarm classification records.
USGS Earthquake Catalog, regional seismicity data for northern Chile.
Global CMT and ISC catalogs for historical events in the Peru-Chile Trench.