A megathrust earthquake cycle model for Northeast Japan: Bridging the mismatch between geological uplift and geodetic subsidence 6. Geodesy

Abstract

In Northeast Japan, it remains a puzzle to reconcile the mismatch between long-term (geological) uplift and late-interseismic and coseismic subsidence associated with the 2011 Tohoku earthquake. To explain this mismatch between different periods, we modeled the entire megathrust earthquake cycle in the Northeast Japan arc using a simple dislocation model with a two-layered lithosphere-asthenosphere structure in which we account for viscoelastic relaxation in the asthenosphere and tectonic erosion. The model behaves differently when the rupture stops within the lithosphere and when it cuts through the lithosphere to reach the asthenosphere. It is possible to explain the mismatch in the case where the rupture stops within the lithosphere. In the early interseismic stage, the viscoelastic response to the megathrust earthquake dominates and can compensate for late-interseismic and coseismic subsidence. In contrast, the late-interseismic stage is dominated by the locking effect with the steady slip below the rupture area. Tectonic erosion explains up to about half of the long-term uplift by landward movement of arc topography. The rest of the long-term uplift may be attributed to indirect effects of internal deformation in the arc.