Now, a team of researchers has zeroed in on what could be the deepest earthquake ever detected, shaking up scientists' understanding of them. In 2015, a 7.9 magnitude earthquake struck beneath Japan's Bonin Islands. One of the aftershocks occurred deeper than the original earthquake itself, at 467 miles. It's so deep that it nears the layer of Earth known as the lower mantle, reports Andrei Ionescu for Earth.com.