As Africa and Eurasia slowly collide, the rumble of the Earth paints a picture of what was once part of the surface of our planet, now inverted in the depths of the Mediterranean.
Spain is unusually prone to rare deep **, and a new study suggests that this overturned tectonic plate may be involved.
Sun Daoyuan, a geologist at the University of Science and Technology of China, and Megan Miller from the Australian National University explained: "Since 1954, there have been five close deep sources of more than 600 kilometers deep under [the Spanish city] of Granada.
** at this depth is usually followed by strong aftershocks. But when Sun and Miller looked at Spain's 2010 data, they didn't see aftershocks.
When tectonic plates push against each other, they often displace, so one plate slides underneath the other, a process known as subduction. Sometimes, these collisions disrupt the sinking parts of the plates, elevate the crust to form mountains, and link the fates of the two plates together.
Other times, the wrestling crust will remain separate but stacked, with one of the plates gradually sinking further into the mantle. This is what is happening at the border between the African and Eurasian plates, where the Mediterranean seabed is gradually sinking beneath Europe.
When a plate is exposed to seawater, its uppermost layer forms aqueous magnesium silicate. As the plates sink, these silicates dehydrate and become more brittle, more likely to occur, and slow the waves in a way that scientists can detect.
The wave during Granada 2010 lasted for an unusually long period of time, with additional phases of activity in the later stages. This can be explained by the fact that the **wave moves more slowly at the bottom of the Alboran plate rather than at the top.
"A large amount of water is carried to the mantle transition zone, which indicates that the plates are relatively cold," Sun explained. ”。
Considering the relatively young age of the seafloor in the western Mediterranean, for the plates to remain cool, the subduction speed must be quite fast, such as a moderate velocity of about 70 mm per year. ”
The rapid rate at which the plates are sinking seems to have helped this part of the earth's crust flip and take away a bag of water. This plate rollback process occurs when gravity helps the plate to rotate vertically downward, just like a subduction.
The new study went a step further and concluded that it had been completely flipped with the silicate sideways falling, which could explain the strange complexity of the tectonic structure in the area, as well as the occasional occurrence of ** at depths of more than 600 km.
"[This] confirms that the plate beneath the Bertici Islands in southern Spain is a subducted oceanic lithosphere," the team wrote.
The study was published in The Record.