A groundbreaking study published in Nature Geoscience suggests that a new tectonic fault may be forming beneath the Atlantic Ocean, potentially increasing the risk of powerful earthquakes and tsunamis across the region. The research, led by Prof João Duarte from the University of Lisbon, sheds light on the mysterious seismic activity near Portugal, which has historically experienced devastating earthquakes despite being far from known fault lines.
One of the most catastrophic events in the region’s history was the 1755 Lisbon earthquake, a magnitude 8.7 tremor that killed tens of thousands and generated tsunami waves reaching as far as the Caribbean. A similar, though smaller, earthquake occurred in 1969, claiming 25 lives. These events puzzled scientists because they occurred on relatively flat oceanic plains, without the typical geological features associated with major seismic activity.
Duarte’s team focused on the Horseshoe Abyssal Plain, a deep-sea area southwest of Portugal. Through seismic data and computer modelling, they discovered signs of a geological process known as delamination, where the base of the Earth’s tectonic plate is peeling away from the upper layers—similar to the sole of a shoe detaching. This phenomenon is rare in oceanic crust, which typically behaves like a “crème brûlée”, with a rigid layer atop a softer one.
The researchers believe that over millions of years, water infiltrated the crust, weakening it chemically and enabling parts of the mantle to sink into the Earth’s interior. This could mark the beginning of a new subduction zone—where one tectonic plate slides beneath another—a process responsible for the world’s most catastrophic earthquakes, such as those in the Indian Ocean in 2004 and Japan in 2011.
The emergence of such a zone in the Atlantic could have profound geological implications, potentially leading to the formation of a future supercontinent. However, the immediate concern is the increased seismic hazard for coastal communities around the Atlantic basin.
Prof Duarte emphasised the importance of preparedness, noting that while the exact timing of such quakes cannot be predicted, the risk is real and growing. “You don’t need to know exactly when it will rain to carry an umbrella,” he said. “It’s the same with earthquakes – we must be ready.”
