Seismic Swarm PS20140401.1: Analysis of the 2014 Iquique Sequence

The seismic swarm designated PS20140401.1 occurred 93 km northwest of Iquique, Chile, between 23:46 UTC on 1 April 2014 and 09:38 UTC on 4 April 2014. Over 57 hours and 52 minutes, 43 earthquakes were recorded. The sequence initiated with a magnitude 8.2 mainshock at 25 km depth, followed by numerous aftershocks, including events of magnitude 6.9, 6.5, 7.7, and 6.4. Depths ranged primarily between 10 km and 35 km, consistent with the shallow subduction interface in this sector of the Andean margin.

Northern Chile lies within the Peru-Chile Trench subduction zone, where the Nazca Plate converges with the South American Plate at approximately 65–80 mm per year. This tectonic setting produces frequent megathrust earthquakes and associated aftershock sequences. The Iquique region occupies a portion of the northern Chile seismic gap, an area that had not experienced a major rupture since the 1877 earthquake of estimated magnitude 8.5–9.0. The 2014 sequence partially filled this gap.

Geological records indicate that the coastal Atacama region features uplifted marine terraces and active fault systems influenced by both subduction and crustal shortening. Historical seismicity since 2000 includes five identified swarms, with PS20140401.1 marking the first in the instrumental record for this classification. Strong events in the vicinity comprise the magnitude 8.2 earthquake of 1 April 2014 (80 km from the swarm center) and the magnitude 7.7 event of 3 April 2014 (44 km from the swarm center).

The temporal distribution of the swarm shows peak activity within the first 12 hours after the mainshock, with magnitudes decreasing overall but punctuated by larger aftershocks such as the magnitude 7.7 at 22 km depth on 3 April. Depths remained shallow, reflecting slip along the plate interface rather than deeper intraslab processes. Such sequences are typical in subduction environments, where stress transfer triggers secondary ruptures on adjacent segments.

The 2014 activity highlighted the persistent seismic hazard along the northern Chilean margin. Ongoing monitoring by regional networks continues to track strain accumulation, underscoring the potential for future large events in remaining unruptured portions of the gap.

References
USGS Earthquake Catalog
Global CMT Catalog
SeismoSight internal swarm classification data