[SSS12-P03] Postseismic stress field in the rupture area of the 2011 Tohoku-Oki earthquake
In this study, we inverted focal mechanism solutions of earthquakes in the upper-plate of the Tohoku forearc after the Tohoku-Oki earthquake until 2017. We investigated the spatial variation of the stress field by setting a grid network of an 0.3 degree interval in the region. As a result, the direction of the axis of maximum compressive stress (σ1) and stress ratio R, (σ1-σ2)/(σ1-σ3), are found to be almost constant above the region of the large coseismic slip of the mainshock. In the area, the plunge of σ1 axis was larger than ~ 65° and the R is about 0.5 to 0.8. These results are consistent with those by Hasegawa et al. (2011) analyzing the stress state immediately after the Tohoku-Oki earthquake. Next, we investigated the post-2011 temporal changes of the stress field for the area, considered to show a common stress field. As a result, no significant rotations of the principal stress axes were identified although R value may increase in time.