Surprising new evidence is helping scientists track the origins of mysterious earthquakes that have been rattling Southwest Iberia in recent months. The discovery also shows how portions of the oceanic lithosphere, which is normally considered too rigid to fracture in this manner, appear to be detaching from the crust located above them. One involves the subduction of oceanic plates beneath continental plates, and the other involves the process of delamination of continental lithosphere, where heavy layers of mantle detach beneath mountains. By contrast, oceanic lithosphere was believed to be too powerful and inflexible for delamination to occur. Based on the available data, this seems to be a block of ancient oceanic lithosphere, which the researchers believe separated and is now sinking into the surrounding mantle.