A Giant Seismic Wave Hit Earth’s Core — and May Have Shifted Japan

Fifteen years after Japan’s devastating Tōhoku earthquake, scientists have identified a second event hidden inside the seismic records. A wave from the magnitude-9.0 earthquake travelled deep into Earth, reflected from the boundary of the liquid outer core, and returned to Japan roughly 15 minutes later.

The returning wave appears to have triggered subtle movement across multiple tectonic boundaries, shifting much of Japan eastward by up to six millimetres. The movement was too small and gradual to feel, but it may represent a previously unrecognised earthquake hazard.