A seismic event bounced off Earth’s core and shifted an island country

Researchers found that about 15 minutes after the March 11, 2011 magnitude‑9.0 quake, nearly all of Japan shifted eastward by about 5–6 mm — a permanent, nationwide lurch caused by seismic waves that dove to Earth’s core and bounced back.
That “core‑bounce” movement released energy comparable to a magnitude 7.5 but was spread so broadly it would be hard to separate any damage from the main quake and aftershocks.
Japan’s dense GPS/seismic network made the discovery possible, and scientists say similar core‑returned waves could occur elsewhere and might even be anticipated because the round‑trip timing is about 15 minutes.