Seismic Swarm S20260313.2: Analysis of Activity in Atacama, Chile
A seismic swarm designated S20260313.2 occurred in the Atacama region of northern Chile between 03:48 on 13 March 2026 and 13:40 on 17 March 2026. Over 105 hours and 51 minutes, 62 earthquakes were recorded, with magnitudes ranging from 2.5 to 4.0. Depths clustered mainly between 19 and 36 km, consistent with activity along the plate interface.
The Atacama region lies within the Andean subduction zone, where the Nazca Plate descends beneath the South American Plate at rates of approximately 6–7 cm per year. This tectonic setting produces frequent seismic events, including both shallow crustal earthquakes and deeper interface ruptures. The local geology features the Atacama Desert’s arid basin-and-range topography underlain by Precambrian to Paleozoic basement rocks overlain by Mesozoic and Cenozoic volcanic and sedimentary sequences. Ongoing convergence has shaped the Andean orogen, with active fault systems accommodating strain accumulation.
Historical records indicate two prior swarms in the region since 2000: one in 2015 and another in 2020. These episodes reflect episodic stress release typical of subduction-related swarms, often without a dominant mainshock. The 2026 swarm followed a similar pattern, featuring a rapid onset of events on 13 March, including several magnitude 3.3–4.0 shocks within the first hours, followed by a gradual decline in frequency through 17 March.
Key events included multiple magnitude 4.0 earthquakes at depths of 31–33 km on 13 and 16 March, alongside numerous magnitude 3.4–3.8 events distributed throughout the sequence. Shallower events near 10–20 km occurred sporadically but remained below magnitude 4.0. The overall energy release remained moderate, suggesting distributed microfracturing rather than large-scale rupture.
Such swarms contribute to long-term monitoring of the subduction interface. Continuous seismic networks operated by Chilean institutions track these patterns to refine hazard assessments in this highly active margin. No damage or felt reports exceeding intensity IV were associated with the sequence.
References
- USGS Earthquake Catalog (earthquake.usgs.gov)
- Servicio Nacional de Geología y Minería (SERNAGEOMIN), Chile
- Global CMT Catalog for subduction zone parameters