2011 Tohoku Earthquake Caused Entire Country of Japan to Shift Eastward, Study Reveals

More than a decade after the catastrophic magnitude 9.0 Tohoku-Oki earthquake struck Japan in March 2011, researchers have uncovered a remarkable phenomenon: the entire country moved eastward by up to six millimeters about 15 minutes after the main shock. This subtle but widespread ground shift was triggered by seismic waves that traveled deep into the Earth, bounced off the planet's core, and returned to the surface, according to a study published in the journal Science on June 18, 2026.

Lead author Sunyoung Park, an assistant professor of geophysics at the University of Chicago, and her team analyzed Global Navigation Satellite System (GNSS) data from across Japan. They observed a uniform, step-like eastward displacement of the landmass that occurred simultaneously at multiple tectonic plate boundaries. Initially puzzled by the signal, the researchers ruled out possibilities such as a processing error or a direct aftershock, as no known earthquake corresponded to that timing.

The explanation lies in ScS waves—seismic waves that plunge through the Earth's mantle, reflect off the iron core, and rise back to the surface. Normally, these waves lose energy and dissipate before returning, but the Tohoku earthquake was so powerful that the ScS wave survived the 5,800-kilometer (3,600-mile) round trip. When it resurfaced about 13 minutes after the main shock, it still carried enough energy to reactivate the tectonic plate boundary, causing the entire country to nudge eastward toward the Japan trench over a period of 100 to 200 seconds.

This phenomenon represents a previously undocumented type of earthquake hazard. While dynamic earthquake triggering—where seismic waves from one quake set off another—has been observed before, the action of ScS waves causing widespread, uniform slip across an area six to seven times larger than the original rupture zone is extraordinary, said earthquake geologist Wendy Bohon, who was not involved in the study. The findings suggest that long after the main shaking has stopped, ScS waves could return to the surface and trigger additional ruptures or aftershocks in distant locations.

Park noted that the shift likely went unnoticed by people in Japan because it occurred gradually over minutes. Without offshore GPS data, it is possible the movement extended beyond the length of Japan. The researchers are now investigating whether similar events have occurred at other subduction zones, such as the San Andreas Fault in the western United States, though data limitations may pose challenges. The study underscores that even years after a major disaster, seismologists continue to learn from the Tohoku quake, which killed more than 18,000 people and caused an estimated $220 billion in damage.