Japan's 2011 megaquake sent a seismic wave nearly 2,900 km to Earth's core, which returned 13 minutes later and shifted the entire country eastward

• The movement was far too small for anyone to notice, but Japan's highly sensitive GPS network detected the nationwide shift almost simultaneously.
• Scientists were unable to explain the unusual signal for 15 years because it did not match the main earthquake, any aftershock or anothe