Abstract
To identify paleo-tsunami history, we studied coastal lowland on Happo town, northern part of Akita Prefecture, at the eastern margin of Japan Sea. The study area faces near source region of the 1983 Japan Sea earthquake. From boring cores in these study area, we found some coarse grained sediments in organic mud and peat that were deposited in marsh. One of these coarse grained sediments has some sedimentological characteristics, such as, erosional lower contact, rip-up crusts, parallel and cross stratifications, some upward coarsening and fining units, and plant fragment laminae. These sedimentary features indicate that the deposited layer was formed by strong currents. Therefore, we interpreted these sediments as a tsunami deposits based on their sedimentary features and geographic setting around the study area. We used radiocarbon ages from plant materials to determine the ages of deposition of these tsunami deposit. Depositional age of the tsunami deposit was interpreted 13th to 15th-century by calibrated age of the 14C dating. We estimate that the tsunami event similar to the 1983 Japan Sea earthquake occurred 500 to 700 years ago.
