Mountain-size chunk of rock hiding under Japan is channeling earthquakes

An underground mountain-sized chunk of rock may be affecting paths of large earthquakes in southern Japan.

The dense igneous rock, known as the Kumano pluton, is lurking about 3.1 miles (5 kilometers) below the surface beneath Japan’s Kii Peninsula. It sits in the crust of the continental Eurasian plate. Under this slab of continental crust, the oceanic Philippine plate is taking a dive toward the Earth‘s mantle, a process called subduction. New research suggests that the heavy pluton within the Eurasian plate changes the slope of that dive, forcing the Philippine plate down more steeply.