The seismic swarm PS20071114.1 occurred 82 km south of Tocopilla, Chile, between 15:40 UTC on 14 November 2007 and 03:07 UTC on 17 November 2007. Over 59 hours and 26 minutes, 23 earthquakes were recorded, beginning with a magnitude 7.7 event at 40 km depth. This sequence unfolded within the highly active subduction zone of northern Chile.
Tocopilla lies along the Peru-Chile Trench, where the Nazca Plate converges with and subducts beneath the South American Plate at approximately 6–7 cm per year. This tectonic setting produces frequent megathrust earthquakes and associated aftershock sequences. The region features a narrow continental margin, coastal cordillera, and the hyper-arid Atacama Desert, underlain by thickened Andean crust. Historical seismicity includes the great 1877 Iquique earthquake and multiple events exceeding magnitude 7 in the 20th century, underscoring the persistent strain accumulation along this segment of the plate boundary.
The swarm initiated with the 7.7 mainshock, followed by events of magnitudes 5.2 to 6.8 clustered over the subsequent days. Notable activity included two magnitude 5.7 earthquakes within seconds of each other on 14 November, a magnitude 6.3 and 6.8 pair on 15 November, and several magnitude 5.5 events on 16 and 17 November. Depths ranged primarily between 9 km and 48 km, consistent with both intraslab and interface seismicity in the subduction zone. The spatial distribution remained concentrated near the initial epicenter, reflecting localized stress release along a limited fault segment.
Geological interpretation of such swarms in northern Chile points to aftershock triggering mechanisms driven by static stress changes and fluid migration within the subducting slab. The 2007 sequence contributed to the broader seismic cycle that later culminated in the 2014 Iquique earthquake farther north. Updated regional monitoring by Chilean and international networks continues to refine models of plate coupling and seismic hazard in this area, where recurrence intervals for large events span decades to centuries.
This swarm exemplifies the clustered nature of seismicity in mature subduction zones. Analysis of event timing and magnitude distribution reveals a typical decay pattern following the mainshock, with no evidence of independent triggering beyond standard aftershock processes. Continued study of these sequences aids in distinguishing between background seismicity and precursory activity ahead of future large earthquakes.
References:
USGS Earthquake Catalog (2007 Tocopilla event records)
Chilean National Seismological Center historical bulletins
Plate boundary models from the National Earthquake Information Center
Subduction zone parameters from the Global CMT Project