Researchers analyzed the data taken from seismographs of that region collected in 2011 and 2012 with a special focus being ... a surge in activity of deep long-period earthquakes at the beginning ...

A government panel has determined that a major earthquake that rocked northeastern Japan on Feb. 13 affected wide areas because of its deep focus, which was much deeper than the 2011 Great East ...

said the Nov. 14 earthquake is classified as a “deep-focus earthquake” because its hypocenter was deep underground. It struck inside the Pacific Plate, which runs underneath near Japan.

Warren, L. M., E. C. Baluyut, T. Osburg, K. Lisac, and S. Kokkinen, Fault-plane orientations of intermediate-depth and deep-focus earthquakes in the Japan-Kuril ...