Seafloor Geodesy Delineates Fast Relocking of the Tohoku Megathrust

Fourteen years of seafloor and onshore geodetic data show the subduction fault has returned to a locking state comparable to that before 2011.

Fourteen years of postseismic seafloor geodetic observations after the 2011 magnitude 9 Tohoku earthquake revealed that the subduction megathrust has returned to a locking state similar to its pre-earthquake condition, according to a study published in Science science.org.

Researchers combined the seafloor geodetic measurements with onshore geodetic data, analyses of repeating earthquakes, and numerical modeling. These tools delineated how afterslip interrupted the recovery of megathrust locking while stress relaxation proceeded simultaneously in the viscoelastic upper mantle.

The observations indicate that the fault reached this relocked state despite ongoing upper-mantle stress relaxation. The authors noted that these findings improve the understanding of earthquake-cycle physics and future seismic hazards across subduction zones.