
New mega-earthquake hotspot could be forming beneath the Atlantic

For centuries, scientists have puzzled over why Portugal has suffered huge earthquakes despite lying far from the world’s major fault lines. Science Focus reported.
On 1 November 1755, Lisbon was devastated by a magnitude 8.7 quake that killed tens of thousands and sent tsunami waves as far as the Caribbean. More recently, a magnitude 7.8 tremor struck off Portugal’s coast in 1969, killing 25 people.
One of the problems is that these earthquakes occurred on a completely flat plain, far from the faults,” Prof João Duarte, a geologist at the University of Lisbon and lead author of the study, told BBC Science Focus.
After the 1969 earthquake, people started to realise that something strange was going on, because it had the signature of a subduction zone, yet there isn’t one there.”
Subduction zones – where one tectonic plate dives beneath another – are responsible for the planet’s most devastating 'megathrust' quakes, such as the 2004 Indian Ocean and 2011 Tōhoku disasters. But the Atlantic has long been considered relatively calm as its plates slowly drift apart along a mid-ocean ridge.
Duarte’s team pieced together seismic records and computer models of the Horseshoe Abyssal Plain, a stretch of deep seafloor southwest of Portugal. They found evidence that the mantle – the hot, dense layer beneath Earth’s crust – is peeling away in a process called delamination.
“The base of the plate is separating like the sole of a shoe peeling off,” Duarte said. “That was the first Eureka moment when I thought, ‘aha, there’s something there’. The second was when the computer models also showed delamination was happening.