2011 Japan quake may have shifted country eastward via seismic waves, study finds

The massive 2011 Japan earthquake and tsunami, which claimed nearly 20,000 lives, may have triggered a previously unknown phenomenon that shifted the entire country eastward. A new study, analyzing satellite data from the magnitude 9 Tohoku-Oki earthquake, reveals that seismic waves traveling through the Earth's interior and bouncing off its core caused a significant shift.

“

We report an extraordinary observation of ground motion in Japan after the moment magnitude 9 2011 Tohoku-Oki earthquake attributed to a multiplate-interface slip event triggered by a shear wave that travelled to the Earth’s core and back.

Researchers found that these "shear waves" caused blocks of rock to slide past each other along fault lines. This seismic activity, spread over several minutes, resulted in a land shift of up to 5-6mm. While this amount of ground movement is common after large earthquakes, the sheer scale of the affected area surprised scientists.

“

Its overall length is similar to that of mainland Japan (~3,000 km), exceeding the mainshock rupture length by 6‒7 times and more than doubling that of the 2004 great Sumatra Earthquake.

The triggered slip "has the broadest rupture area of any single event yet documented," according to the study published in the journal Science. Its length is comparable to mainland Japan, exceeding the mainshock rupture length by six to seven times. Scientists emphasize the need for further study into this new type of seismic hazard, noting that it could potentially activate or reactivate a quake's main area minutes after the initial shaking has passed.

“

I think we should be aware of the fact that there could be this potential triggering of an event many minutes after [an earthquake’s] main shaking has passed.