Seismic Swarm off the Coast of Tarapaca, Chile, March 2014

A seismic swarm designated PS20140317.1 was recorded off the coast of Tarapaca, Chile, between 21:16 UTC on 16 March 2014 and 08:32 UTC on 17 March 2014. Over this 11-hour-16-minute interval, nine earthquakes were registered. The sequence began with a magnitude 6.7 event at 20 km depth, followed by a magnitude 5.0 at 19 km. Subsequent events included magnitudes 5.1 at 10 km, 2.9 at 37 km, 5.2 at 10 km, 6.4 at 21 km, and three additional shocks of magnitudes 5.0, 5.1, and 5.2 at depths between 8 km and 10 km. The swarm occurred within the Peru-Chile subduction zone, where the Nazca Plate descends beneath the South American Plate. Convergence rates in this segment average 6–7 cm per year, producing frequent moderate-to-large earthquakes and occasional seismic swarms. Depths recorded during the swarm ranged from 8 km to 37 km, consistent with activity along the plate interface and within the overriding crust. Northern Chile has a well-documented history of large megathrust events. The March 2014 swarm preceded the April 2014 Iquique sequence by roughly two weeks. That sequence included a magnitude 8.2 mainshock on 1 April located 93 km northwest of Iquique and a magnitude 7.7 aftershock on 3 April located 53 km southwest of Iquique. The swarm’s epicentral area lay approximately 40 km from the magnitude 8.2 epicenter. Such swarms can reflect localized stress redistribution along the locked portion of the subduction interface. The two largest events (magnitudes 6.7 and 6.4) occurred within hours of each other, suggesting rapid triggering or cascading failure on adjacent fault patches. Shallower events later in the sequence may indicate afterslip or fluid migration at the up-dip limit of the seismogenic zone.

References

USGS Earthquake Hazards Program, “Seismicity of the Earth 1900–2013: Nazca Plate and South America,” 2014. USGS Earthquake Catalog, events of 1–3 April 2014 near Iquique, Chile.