Current situation and issues of geomorphological and geological researches along the Sanriku coast, Japan, for clarification of the earthquake cycle

Pleistocene marine terrace show uplifting trend on a timescale of 10 5 years along the northernmost part of the Sanriku coast. However, chronology of marine terraces along other parts of the coast has not progressed until now because of lack of tephra layering. In addition, distribution of flat surfaces previously interpreted as marine terraces is fragmentary along the southern Sanriku coast. These geomorphological and geological studies suggest that the Sanriku coast should be seg-mented into multiple deformation areas when assessing crustal deformation related to a megathrust earthquake. For the segmentation of crustal deformation area, continuing analyses of incised valley fill succession and reconsideration of the origin and chronology of flat surfaces previously interpreted as marine terraces are needed. OSL dating method is expected to clarify the formation age of marine terraces distributed along the Sanriku coast.