Two 2025 Drake Passage earthquakes of M7.5 and M7.6 traced to an ancient fault thought dormant

Two strong earthquakes of magnitude 7.5 and 7.6 that occurred in 2025 originated within an ancient tectonic structure that scientists had previously considered fully dormant, according to tsn.ua, citing National Geographic tsn.uatsn.uatsn.uaOpen source ↗. Both events were recorded in the Drake Passage, which separates South America and Antarctica. Their epicentres lay only 15 kilometres apart, and the interval between the earthquakes was 49 days.

The results were published in late October 2026 in Communications Earth & Environment. The international team was led by Emanuele Lodolo of the Italian National Institute of Oceanography and Experimental Geophysics. The authors conclude that some geological deformation zones can remain fragile for very long periods, even after the plate itself has stopped moving independently.

An ancient transform fault under the seabed

The researchers found that the foci of both earthquakes lay along an ancient transform fault. Such faults form when neighbouring segments of oceanic crust slide parallel to each other. After the displacement stops, oceanic fracture zones remain in their place. These zones were previously regarded as completely inactive and safe.

To reconstruct the events, the team combined seismic data with detailed geophysical data on the ocean floor, including the seismic reflection method. It uses waves that pass through rock and return after reflecting from the boundaries between geological layers tsn.uatsn.uatsn.uaOpen source ↗. The data confirmed that the epicentres coincided with the ancient fault zone, where internal deformation is still concentrated.

Why the old structure became active again

The authors name two factors. First, the structure of the inherited fault lets stress gradually concentrate at specific points. Second, present-day motion and interaction between the Scotia and Antarctic plates can transmit energy over considerable distances. As a result, a fracture that appeared millions of years ago under different conditions can become active again.

The analysis also showed that volcanic melts can seep into deep rock through these weakened areas. The researchers suggest that the ancient fault now functions as a large shear zone inside a fragment of the Phoenix plate, which is gradually sinking beneath the South Shetland Islands. Fragments of this plate still lie near the Antarctic Peninsula.

The authors stress that this does not mean every old fracture is a hazard, nor that geologists can now predict the timing of future earthquakes. Whether such a zone can reactivate depends on the stresses currently acting on it, the spatial orientation of the faults and their physical properties tsn.uatsn.uatsn.uaOpen source ↗. The question of why a structure whose processes stopped long ago can become active again remains open.