Abstract
We found a sand layer correlative to the Jogan tsunami in the Kumanosaku archeological site, Miyagi Prefecture, Japan. The sand layer was interbedded with organic mud with lower sharp contact. The basal part of the sand layer was deformed like a series of elliptical balls convexing downward, which may have resulted from sediment loading. A thin mud layer above the deformed sand suggested changes in current velocities during the event. The sand is characterized by a mixture of freshwater and brackish diatom species and by lack of marine planktonic species. Radiocarbon ages suggest that the sand dates to AD 745-930 (2σ), and written records for this period describe an earthquake and tsunami in 869, which is the so-called Jogan event.
