The seismic swarm designated PS20071118.1 occurred approximately 89 km south-southwest of Tocopilla in northern Chile’s Antofagasta Region. It began at 17:54 UTC on 17 November 2007 and concluded at 15:24 UTC on 18 November 2007, spanning 21 hours and 30 minutes. During this interval, five earthquakes with magnitudes between 5.1 and 5.9 were recorded at depths ranging from 7 km to 33 km.
The sequence unfolded as follows: an initial event of magnitude 5.9 at 14 km depth on 17 November at 17:54 UTC, followed by a magnitude 5.2 shock at 7 km depth 19 minutes later. A third event of magnitude 5.1 occurred at 29 km depth later that evening. On 18 November, a magnitude 5.7 earthquake struck at 33 km depth around midday, and the swarm ended with a magnitude 5.2 event at 19 km depth in mid-afternoon.
Northern Chile lies above the convergent boundary where the Nazca Plate subducts beneath the South American Plate at a rate of approximately 6–7 cm per year. This tectonic setting produces frequent large-magnitude earthquakes and associated aftershock sequences. The Tocopilla area experienced a major megathrust event of magnitude 7.7 on 14 November 2007, only days before the swarm. The timing and proximity of the five events suggest they formed part of the post-seismic adjustment following that mainshock.
Since 1 January 2000, only one swarm has been identified in the immediate vicinity according to internal classification records, making PS20071118.1 the sole documented swarm in the period. The 2007 Tocopilla mainshock and its aftershocks, including this swarm, highlight the region’s persistent seismic productivity driven by ongoing plate convergence and crustal deformation along the Andean margin.
Seismic activity of this type contributes to the long-term understanding of stress transfer and fault interaction within subduction zones. Depths between 7 km and 33 km indicate rupture within both the upper crust and the interface zone, consistent with the structural architecture of the central Andean subduction system. Continued monitoring in the region supports improved hazard assessment for coastal communities situated along the seismically active margin.
USGS Earthquake Catalog (historical records 2000–2024)
Global CMT Project (moment-tensor solutions)
Chilean National Seismological Center annual reports