Seismic Swarm S20140404.1: Insights from Northern Chile

Seismic swarm S20140404.1 occurred 82 km southwest of Iquique, Chile, between 10:01 on 3 April 2014 and 09:14 on 10 April 2014. Over 167 hours and 12 minutes, the sequence produced 68 earthquakes, with magnitudes ranging from 2.4 to 5.6 and focal depths between 6 km and 46 km. The events clustered tightly in both space and time, characteristic of swarm behavior in subduction settings.

The swarm began with several moderate shocks on 3 April, including events of magnitude 4.9 at 6 km depth and 4.8 at 16 km depth. Activity continued at a steady rate through 4–7 April, featuring repeated magnitude 4+ events at shallow to intermediate depths. Peak intensity occurred on 8 April with a magnitude 5.6 shock at only 6 km depth, followed by a magnitude 5.2 event on 9 April at 9 km. The sequence tapered off by 10 April, ending with smaller events near 37–42 km depth.

Northern Chile lies above the subduction interface where the Nazca Plate descends beneath the South American Plate at approximately 6–7 cm per year. This tectonic regime generates frequent seismicity, including both large megathrust earthquakes and smaller clustered sequences. The Iquique region experienced a major Mw 8.2 earthquake on 1 April 2014, only days before the swarm onset, placing the recorded activity within an aftershock-rich environment.

Depth distribution shows a predominance of events between 6 km and 25 km, consistent with the seismogenic portion of the plate interface and overlying crust. Shallower events (under 15 km) tended to carry higher magnitudes, while deeper events remained generally below magnitude 4.0. This pattern aligns with stress redistribution following the preceding mainshock.

Since 1 January 2000, three swarms have been documented in the broader region, with S20140404.1 representing the first recorded swarm of 2014. The sequence illustrates how post-mainshock stress changes can trigger prolonged, diffuse seismic release without a single dominant aftershock.

Such swarms provide valuable data for refining local seismic hazard models. Continued monitoring of similar sequences helps constrain rupture processes along the northern Chile margin, where historical great earthquakes have repeatedly demonstrated the area’s capacity for significant seismic energy release.

References

• SeismoSight internal swarm catalogue (S20140404.1 parameters)
• USGS Earthquake Catalog (regional tectonics and plate motion rates)