Seafloor geodesy delineates fast megathrust relocking after the giant 2011 Tohoku earthquake.

Seafloor geodesy shows the megathrust relocking after the 2011 magnitude 9 Tohoku earthquake is already at a locking state today similar to pre-earthquake conditions.

• Why it matters: Recovering the megathrust’s locking after a great event is key for earthquake-cycle physics and for assessing future hazards.
• What they did: Using 14 years of postseismic seafloor geodetic observations, combined with onshore geodesy, repeating-earthquake analyses, and numerical modeling, the study tracks how afterslip and viscoelastic stress relaxation shape relocking.
• The result: Relocking is interrupted by afterslip and accompanied by stress relaxation in the viscoelastic upper mantle, implying the system has largely returned to its earlier locking state despite ongoing relaxation.

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