Abstract
The role of the minimum horizontal compressional stress (σhmin) in the deformation of the Japanese Islands and the occurence of intraplate earthquakes were discussed. The first is the effect of decreasing σhmin, which enlarges the Coulomb failure stress. The second is the effect of an absolute value of σhmin. Large σhmin can promote a plastic flow in the upper crust resulting from a subcritical crack growth of microfractures when the maxmum horizontal compressional stress (σhmin) is small, because large σhmin and small shear stress (τ) makes cracks to be shutten and then more cracks are filled with pore water when there is less water in the upper crust. It is thought that the northeast Japanese Island (outer arc of the Tohoku district) is situated under such a stress condition. A larger part of the deformation there is probably shared by a plastic flow.
