Core-reflected wave from 2011 Tohoku quake shifted Japan

A new scientific study has revealed that the catastrophic magnitude 9.0 Tohoku earthquake that struck Japan in 2011 triggered a previously unknown phenomenon: a seismic wave that traveled to Earth's core and back, causing the entire country to shift eastward minutes after the main shock. The research, led by University of Chicago seismologist Sunyoung Park and published on June 18, 2026, in the journal Science, documents the first recorded instance of a core-reflected wave triggering widespread fault movement.

Approximately 15 minutes after the main earthquake on March 11, 2011, a subtle but uniform eastward ground shift of about 5 to 6 millimeters was detected across the entire Japanese archipelago. This movement was recorded by hundreds of GPS stations from Hokkaido in the north to Kyushu in the south. Researchers were initially puzzled because the shift occurred without a corresponding earthquake at that exact moment and was simultaneous across a vast area spanning multiple tectonic plate boundaries.

After analyzing extensive GPS and seismic data, Park and her colleagues concluded the shift was caused by a specific type of seismic wave known as an ScS wave. Generated by the...