The gradual collision of Africa and Eurasia has triggered seismic activity, revealing a portion of the Earth's surface overturned and submerged beneath the Mediterranean.
Spain's Mediterranean coast is subject to periodic and intense earthquakes, with a recent study suggesting a potential link to the upturned tectonic plate. The study was published in The Seismic Record.
As tectonic plates collide, it causes one plate to slip beneath the other in a process called subduction. This collision sometimes destroys the descending plate, causing the crust to form mountains, ultimately binding the two plates. On other occasions, the slabs can be separate but stacked, with one slowly dipping into the Earth's mantle.
As the sinking slab descends into ocean water, it forms hydrous magnesium silicates in its top layers, which dry out and becomes fragile, making it vulnerable to seismic activity. The prolonged seismic waves of the 2010 Granada earthquake may be due to slower movement at the bottom of the Alboran slab.
"A significant amount of water has been carried down to the mantle transition zone, indicating a relatively cold slab," said Daoyuan Sun, co-author of the study and geologist from the University of Science and Technology of China. "Considering a relatively young seafloor age in the western Mediterranean, for the slab to remain cool, the subduction speed must be quite fast, such as a moderate speed of about 70 millimeters per year.”
The slab's rapid plunge caused this section of Earth's crust to flip, pulling a pocket of water with it, as gravity made it rotate vertically downward. According to the study, the slab has fully overturned, landing with its silicate side down, explaining the peculiar complexity of the region's tectonic formations and sporadic earthquakes more than 600 kilometers deep.
The research team found that the tectonic slab beneath the Betics of southern Spain "is a subducted oceanic lithosphere," describing the formation of the Beltic-Rif or Gibraltar arc, shaping the western Mediterranean.