Drake Passage Seismic Swarm PS20250502.1: Geological Context and Event Analysis

A seismic swarm designated PS20250502.1 occurred in the Drake Passage, approximately 256 km south-southeast of Ushuaia, Argentina. The sequence initiated at 12:58 on 2 May 2025 and concluded at 10:06 on 3 May 2025, spanning 21 hours and 8 minutes. During this period, 15 earthquakes were recorded, beginning with a magnitude 7.4 event at a depth of 10 km. Subsequent events ranged from magnitude 5.0 to 6.4, with depths predominantly at 10 km and one at 8 km.

The Drake Passage lies at the tectonic boundary between the South American Plate and the Scotia Plate. This transform margin features strike-slip faulting and minor subduction components that accommodate relative plate motion. The region experiences elevated seismicity due to ongoing deformation along the Shackleton Fracture Zone and associated fault systems. Historical records indicate recurrent moderate-to-large earthquakes driven by these dynamics, consistent with the plate-boundary setting south of Tierra del Fuego.

The swarm’s initial magnitude 7.4 shock, located 56 km from the swarm centroid, represents the strongest event in the sequence and aligns with documented strong earthquakes in the area since 2000. Follow-on activity included multiple magnitude 5+ events clustered within the first several hours, such as the 5.5, 5.7, and 6.4 shocks. Later events tapered in frequency and magnitude, concluding with a magnitude 5.0 event. Depths remained shallow throughout, reflecting brittle failure within the upper crust typical of this transform setting.

Such swarms often arise from stress redistribution following a mainshock or from fluid migration along faults, though the precise triggering mechanism here remains under study. The concentration of events near the plate boundary underscores the area’s persistent seismic hazard, influenced by the Scotia Plate’s eastward motion relative to South America.

Geological studies of the Drake Passage highlight its role in facilitating Antarctic Circumpolar Current flow while simultaneously hosting active tectonics. Paleoseismic evidence from adjacent onshore regions in southern Patagonia documents prehistoric ruptures along similar fault trends, reinforcing the long-term activity pattern observed in modern instrumental data.

This swarm contributes to the understanding of clustered seismicity in remote oceanic plate boundaries, where monitoring relies on regional and teleseismic networks. Continued observation will refine models of stress transfer and aftershock productivity in this sector of the Scotia Arc system.

References
United States Geological Survey Earthquake Catalog
Global Centroid Moment Tensor Project
International Seismological Centre Bulletin