Rheological profile across the northeastern Japan lithosphere toward precise modeling of the 2011 Tohoku Oki Earthquake

Abstract

A two-dimensional rheological profile crossing the northeastern Japan arc was created to evaluate and distinguish various styles of post-seismic deformation relating to the Tohoku-Oki earthquake. The calculated profile is based on recent rock-mechanics studies and geophysical observations that explain observed patterns of geodetic strain accumulation and shallow seismicity prior to the earthquake. Viscosities were then calculated assuming stress-change magnitudes commonly associated with interplate earthquakes. Recently derived flow laws for various rocks and minerals predict the presence of weak zones that developed via processes likely operating in the lithosphere (e.g., partial melting and shear zone development). Strain localization into weak zones explains low viscosity estimates (-Pa s) from post-seismic creep after inland earthquake events. Our calculations reveal significant lateral variations in strengths and viscosities across the northeastern Japan arc. These viscoelastic lithospheric structures should be taken into account in order to differentiate viscous relaxation from other post-seismic deformation processes.