Underwater volcano on a tectonic plate may have unleashed major earthquakes in Japan

An ancient underwater volcano riding a sinking tectonic plate off the coast of Japan may have unleashed several unexplained major earthquakes — by grinding against another tectonic plate above it, a new study finds.

The extinct underwater volcano, known as Daiichi-Kashima seamount, sits on the Pacific tectonic plate roughly 25 miles (40 kilometers) off Japan’s east coast. There, three tectonic plates intersect — with the Pacific plate to the east and the Philippine plate to the south both slipping beneath the Okhotsk plate to the north. The seamount sits on a section of the plate that began descending into Earth’s mantle between 150,000 and 250,000 years ago, study co-author Eunseo Choi, an associate professor at the University of Memphis’ Center for Earthquake Research and Information, told Live Science.