Seismic Swarm PS20251010.2 in the Drake Passage: Geological Context and Event Analysis

The Drake Passage, situated between the southern tip of South America and the Antarctic Peninsula, represents one of the most dynamically active tectonic regions on Earth. This narrow body of water overlies complex plate boundaries involving the South American Plate, the Antarctic Plate, and the intervening Scotia Plate. Ongoing subduction, strike-slip faulting, and seafloor spreading contribute to frequent seismic activity. Historical records document multiple magnitude 7+ events in the passage, reflecting the high strain rates associated with the Shackleton Fracture Zone and related transform boundaries.

SeismoSight internal classification identifies swarm PS20251010.2 as a distinct sequence that began at 20:29 on 10 October 2025 and concluded at 18:29 on 11 October 2025. Over this 22-hour period, six earthquakes were recorded. The sequence opened with a magnitude 7.6 event at 5 km depth, followed by five aftershocks clustered near 10 km depth. Magnitudes ranged from 4.6 to 5.7, indicating a rapid energy release followed by smaller adjustments along the same fault segment.

The timing and spatial distribution suggest a mainshock-aftershock pattern rather than a classic foreshock swarm. The initial 7.6 event likely triggered the subsequent ruptures within a compact area, consistent with stress transfer along a shallow crustal fault. Depths remained shallow throughout, limiting the potential for deeper mantle involvement but increasing the likelihood of felt shaking across regional distances.

This swarm occurred in close proximity to two other significant events since 2000. A magnitude 7.6 earthquake struck on 10 October 2025 only 7 km from the swarm centroid. Earlier, the 22 August 2025 Southern Drake Passage earthquake, magnitude 7.5, was located 22 km away. These three events within months illustrate episodic clustering along the same tectonic corridor, a pattern observed in other transform margins where stored elastic strain is released in discrete pulses.

Geological monitoring in the Drake Passage benefits from both land-based stations in Tierra del Fuego and ocean-bottom seismometers deployed across the passage. Such instrumentation captures the interplay between plate motion and local fault geometry. The October 2025 sequence reinforces the need for continued surveillance, as shallow, high-magnitude events in this remote setting can still influence regional tsunami risk and maritime operations.

Further analysis of waveform data may clarify whether the swarm exploited pre-existing fractures or activated a new segment. Regardless, the concentration of energy release within 22 hours underscores the passage’s capacity for rapid seismic sequences.

References
SeismoSight internal swarm classification PS20251010.2
USGS Earthquake Catalog (regional Drake Passage entries)
Global Centroid Moment Tensor Project (plate boundary models)