Geological structures controlled the rupture process of the 2011 M9.0 Tohoku-Oki earthquake in the Northeast Japan Arc

Abstract By interpreting the 2D/3D seismic survey data acquired in the surrounding ocean areas of the Northeast (NE) Japan Arc, we clarified the detailed geological structure and demonstrated that the basic structure in the hanging-wall plate of the subduction system consists of many structural blocks (segments) separated by NW–SE trending large transcurrent faults (strike-slip faults). This structural configuration showed a close relationship with the distribution of foreshocks, mainshock, and aftershocks, coseismic slip models of the 2011 M9.0 Tohoku-Oki megathrust earthquake, coseismic slip area of M-7 class earthquakes, quasi-static slip rates, back slip rate, and seismic tomography images. In addition, the coseismic slip models revealed that the trenchward forearc of the structural blocks between the Offshore Hidaka tectonic line and the Honjo-Sendai tectonic line fitted well with the coseismic slip area of the 2011 Tohoku-Oki earthquake. These findings suggest that the structural blocks bounded by these two tectonic lines slipped rapidly trenchward when the mainshock occurred. The M7 earthquakes were also concentrated along these two tectonic lines, thereby suggesting a close relationship between seismic activity and the inherited geological structure of the overriding plate in the NE Japan forearc.