Earth's crust is 'unzipping' beneath Italy — and that could explain most of the earthquakes in the region

The crust under Italy is "unzipping" and falling away into the mantle, new research finds.

This process is the driver of much of the seismic activity in the Apennine Mountains, the long chain of peaks that runs like a spine down the Italian peninsula. This area provides a unique look into the swan song of subduction, or the movement of a slab of oceanic crust under a neighboring chunk of continental crust, said study lead author Stefano Tavani, a geoscientist at the University of Florence.

"We are experiencing the very, very late-stage to the subduction, and the tectonics is driven by a different engine, which is this unzipping," Tavani told Live Science.

The Mediterranean region, between Africa and Eurasia, is a patchwork quilt of tectonic microplates and mountain ranges, making the geology of the region extremely intricate. The big-picture geology is driven by the fact that the African plate, to the south, has been pushing northward, squeezing the crust and driving the sinking of an ancient ocean, the Tethys, into the mantle beneath the Apennine Mountains. This process has been ongoing for about 50 million years.

Along the Apennines, this process created a push-and-pull of forces. As the African plate subducted under the Eurasian plate, the boundary of the subduction zone was making its own march toward the African plate, causing the crust on the Eurasian side to stretch and thin, creating two large basins: an older one in the Mediterranean Sea west of Corsica and Sardinia, and a younger one, the Tyrrhenian Sea segment of the Mediterranean east of Corsica and Sardinia, which formed roughly 10 million years ago. Until now, the driver behind the extension creating these basins and the compressional forces building the Apennines has not been entirely clear, Tavani said.

To better understand this unusual tectonic movement, Tavani and his colleagues integrated earthquake record and ground movements from GPS and satellite measurements with the tectonic models of the plate movements and found that under the Apennines, the lower crust is peeling away and dropping into the mantle — a process called delamination. It is this delamination, and not the subduction of one plate under another, that causes most of the seismic activity in the Appennines, the researchers reported in their study published this month in the journal Communications Earth & Environment. In a few more million years, Tavani said, the lower crust will finish dropping away and the two plates will weld together.

There are other places around the world where similar processes are happening, such as in the Hellenic trench south of Greece, Tavani said. The findings "could be applied to other several systems," he said, "because in the end, it is a kind of very late-stage plate tectonics."