Surprising new evidence is helping scientists track the origins of mysterious earthquakes that have been rattling Southwest Iberia in recent months.
According to new research, slabs of ocean floor off the coast of southern Europe are peeling away from the Earth’s crust, a geological process that was once believed to only occur in continents.
The discovery also shows how portions of the oceanic lithosphere, which is normally considered too rigid to fracture in this manner, appear to be detaching from the crust located above them. The research, published in Nature Geoscience, offers unique insights into the way subduction zones, which scientists characterize as veritable “engines” behind plate tectonics, first begin.
Additionally, the new findings may also shed light on the origins of some of Europe’s most destructive earthquakes, including one of the most catastrophic earthquakes in Portugual’s history, which occurred near Lisbon in 1755.
An Enigma Unfolds Off the Iberian Coast
In the past, geologists have recognized two primary ways that Earth’s outer shell is recycled. One involves the subduction of oceanic plates beneath continental plates, and the other involves the process of delamination of continental lithosphere, where heavy layers of mantle detach beneath mountains.
By contrast, oceanic lithosphere was believed to be too powerful and inflexible for delamination to occur. However, the new evidence from observations off the Iberian Coast is turning that assumption on its head.
New Evidence from Undersea
By employing seismic tomography, researchers involved in the new Nature Geosciences study were able to identify a dense, high-velocity anomaly beneath the seafloor to the southwest of the Iberian Peninsula.
Based on the available data, this seems to be a block of ancient oceanic lithosphere, which the researchers believe separated and is now sinking into the surrounding mantle.
To build their case, the team relied on numerical simulations, which helped them reproduce the underlying process believed to give rise to this phenomenon. This revealed that the convergence between tectonic plates and a weaker layer that had been converted to serpentine has separated and is sinking into the mantle.
Numerical simulations reproduced the process, showing that convergence between tectonic plates and a weaker layer that had been serpentinized (a process where certain rocks are transformed into serpentine through hydration and metamorphic processes) likely allowed the separation to occur.
Driving Europe’s Most Powerful Earthquakes?
The identification of this mechanism has revealed a potential solution for a longstanding mystery involving how new subduction zones begin. After the onset of delamination, it may be that conditions are ripe for one plate to dive beneath another, which could identify a process that both drives earthquake activity and has likely played a significant role in the reshaping of Earth’s surface over time.
The research team behind the new study also argues that oceanic delamination in this region may have been a powerful driver behind some of Europe’s largest earthquakes, including the Great Lisbon Earthquake of 1755, a magnitude 8.5–8.7 earthquake that rocked Portugual, and the magnitude 7.9 San Vincente quake of 1969.
Fundamentally, by revealing that even oceanic lithosphere can delaminate, the team’s findings present new challenges to past assumptions about the rigidity of Earth’s ocean floors, and also expands our understanding of the processes that govern tectonic activity.
Additionally, the new research both highlights the dynamic forces behind Europe’s western edge, while also suggesting that similar hidden processes may very likely be unfolding in other parts of the world that may possess geological similarities to the Southern European coastal region.
The new paper, “Seismic evidence for oceanic plate delamination offshore Southwest Iberia,” appeared in Nature Geoscience on August 27, 2025.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.