Japan’s Whole-Country Shift Revealed: Core-Bouncing Wave After the 2011 Tohoku Quake

The magnitude-9.0 Tohoku-Oki quake struck 231 mi (372 km) northeast of Tokyo on 11 March 2011. Fifteen minutes later, GPS stations from Hokkaido to Kyushu recorded an eastward shift of about 5–6 mm, moving the Pacific-Okhotsk, Philippine Sea-Eurasian and other plate boundaries together.

CNN

The shift is linked to an ScS shear wave that traveled through mantle, bounced off liquid outer core, and returned. ~5,800 km path matches the 15-minute delay, reactivating faults at Pacific-Okhotsk and Philippine Sea-Eurasian intersections.

In 2011, when Japan was rocked by 9.0 Tohoku earthquake, something strange happened 15 minutes later; scientists missed this deep-Earth process for more than a decade

• Mainshock magnitude 9.0.

In 2011, when Japan was rocked by 9.0 Tohoku earthquake, something strange happened 15 minutes later; scientists missed this deep-Earth process for more than a decade

• GPS shift 5–6 mm (0.20–0.24 in); some reports note 20 cm Honshu displacement.

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• Affected length ? 1,800 mi (3,000 km).

New Scientist

• Energy comparable to magnitude 7.5 quake.

In 2011, when Japan was rocked by 9.0 Tohoku earthquake, something strange happened 15 minutes later; scientists missed this deep-Earth process for more than a decade

• ScS round-trip ? 15 min.

In 2011, when Japan was rocked by 9.0 Tohoku earthquake, something strange happened 15 minutes later; scientists missed this deep-Earth process for more than a decade

• Death toll >15,000–>18,000.

CNN

The finding shows that core-reflected waves can trigger large slip minutes after a megathrust quake—a hazard absent from aftershock forecasts. Detecting such events needs dense GPS and satellite coverage; poorly instrumented regions may miss similar processes, affecting subduction zones in Indonesia, Chile and the western United States.

In 2011, when Japan was rocked by 9.0 Tohoku earthquake, something strange happened 15 minutes later; scientists missed this deep-Earth process for more than a decade

Lead author Sunyoung Park warned the shift “was basically the whole of Japan moving nearly uniformly at the same time,” calling it an unknown seismic hazard. Geophysicist Amanda Thomas called it “very significant,” noting earthquakes may influence faults “for many minutes after the main rupture.” Seismologist Ekstrom said it also aided the tsunami, and Vedran Lekic said similar core-reflected events could occur elsewhere but remain undocumented without dense sensors.

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Researchers examined landslides and data errors but rejected them because they would cause localized, not nationwide, deformation. USGS expert Wendy Bohon called the observations “extraordinary” and confirmed that ScS-triggered slip across plate boundaries is unprecedented.

In 2011, when Japan was rocked by 9.0 Tohoku earthquake, something strange happened 15 minutes later; scientists missed this deep-Earth process for more than a decade

GPS shows a 5–6 mm shift, yet Ekstrom reported a 20 cm Honshu displacement. Death toll ranges from >15,000 (Economic Times) to >18,000 (NOAA). Offshore slip extent is unknown because seafloor sensors are sparse.

CNN

• “What was unusual about this movement is basically the whole of Japan was moving nearly uniformly at the same time,” — Sunyoung Park, University of Chicago

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• “The study’s broader implication is that large earthquakes may continue influencing fault systems in unexpected ways for many minutes after the main rupture, not just through aftershocks but through the passage of later-arriving seismic waves,” — Amanda Thomas, University of California, Davis

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• “We think the vigorous shaking from the original Tohoku earthquake might have already weakened the plate boundaries, making them more susceptible to be moved when the core-reflected wave came by,” — Sunyoung Park

New Scientist

• “The authors’ observations of triggered slip from this source across an area six to seven times greater than the area that broke during the main shock is extraordinary.” — Wendy Bohon, USGS

Scientific American

Planned work will map offshore deformation, test the phenomenon in other subduction zones, and embed core-reflected wave effects into seismic hazard models. Collaborations aim to densify GPS and seafloor sensors for real-time capture of similar events.

CNN