Rheological structure of northeastern Japan lithosphere based on geophysical observations and rock mechanics

摘要

Based on recent results on rock mechanics and geophysical observations, I constructed rheological (strength and viscosity) profiles across the northeastern Japan lithosphere. The profiles well explain patterns of present-day geodetic strain accumulation and shallow seismicity. Experimentally derived flow laws also predict the presence of weak zones by mechanisms likely operated in the lithosphere (e.g., partial melting and shear zone development). The strain localization into weak zones explains the estimates of low viscosity (10~(19)-10~(20) Pas) from post-seismic creep after a large inland earthquake. The strain localization into weak zones also efficiently accumulates elastic strains at the base of upper seismogenic faults locked during interseismic periods resulting in the reactivation of pre-existing fault systems in the northeastern Japan.