A seismic swarm designated S20260526.1 was recorded 23 km northeast of Calama in northern Chile’s Antofagasta Region. The sequence began at 10:27 UTC on 25 May 2026 and concluded at 18:46 UTC on 30 May 2026, spanning 128 hours and 18 minutes. During this interval, 68 earthquakes were detected, with hypocentral depths consistently between 88 km and 120 km.
The largest event reached magnitude 6.9 at 21:52 UTC on 25 May, at 109 km depth. Subsequent notable shocks included a magnitude 5.1 earthquake at 05:23 UTC on 27 May (102 km depth) and a magnitude 4.2 event at 00:20 UTC on 26 May (117 km depth). The majority of events clustered between magnitudes 2.5 and 4.2, exhibiting a typical swarm pattern of rapid onset followed by gradual decay without a single dominant mainshock-aftershock sequence.
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 convergent margin produces both shallow megathrust earthquakes and intermediate-depth seismicity within the subducting slab. The Calama area sits within the Central Volcanic Zone of the Andes, where the slab dips at angles of 25–30 degrees at depths of 80–120 km, conditions that favor intraslab faulting driven by dehydration embrittlement and slab bending stresses.
Intermediate-depth earthquakes in this segment commonly occur between 80 km and 130 km, consistent with the observed swarm depths. The region experiences elevated background seismicity due to the combination of slab pull, phase transitions in the downgoing plate, and possible fluid migration along preexisting faults.
The broader Calama–Antofagasta corridor has recorded multiple destructive events linked to the same subduction dynamics. Notable historical earthquakes include the 1877 Iquique event (estimated Mw 8.5–8.8) and the 2007 Tocopilla earthquake (Mw 7.7), both of which produced significant ground shaking across the Atacama Desert. Intermediate-depth activity has also been documented, such as the 1950 and 2005 sequences near the same latitude, which displayed similar depth ranges and swarm-like characteristics.
The temporal distribution of the 68 events, with peak rates in the first 24 hours after the magnitude 6.9 shock, aligns with fluid-triggered or stress-perturbation mechanisms commonly observed in subduction zones. The narrow depth band (mostly 100–115 km) suggests activation along a discrete portion of the slab, possibly a reactivated normal fault within the oceanic lithosphere. No surface rupture or significant afterslip at shallower depths was indicated by the available data.
Such swarms contribute to the long-term seismic energy release in northern Chile and help delineate slab structure. Continued monitoring remains essential given the region’s history of both intraslab and interface events capable of producing widespread shaking.
References
SeismoSight internal classification S20260526.1
USGS Earthquake Catalog (regional subduction parameters)
Servicio Nacional de Geología y Minería (SERNAGEOMIN), Chile – Andean seismicity reports