By Sid Perkins
A 200-kilometer-long, 500-meter-thick layer of rocks now lying high in the mountains of Italy is recognized as the remains of an erosive subduction zone that was active under the sea millions of years ago, scientists say. The first-of-its-kind discovery provides new clues about ancient seismic activity along this interface between tectonic plates, and also insight into what may be happening along many quake-prone subduction zones today.
When a tectonic plate made of ocean crust and one formed of relatively light continental rocks collide, the continental plate typically overrides the oceanic plate, forcing it back down into Earth’s mantle. When friction between the moving plates locks them in place, immense stresses build up along these subduction zones—stresses that can, when released, trigger great earthquakes and devastating tsunamis (SN: 1/8/05, p. 19).