The 869 J gan tsunami deposit and recurrence interval of large-scale tsunami on the Pacific coast of northeast Japan

The fore-arc region of northeast Japan is an area of extensive seismic activity and tsunami generation. On July 13, 869 a tsunami triggered by a large-scale earthquake invaded its coastal zones, causing extensive deposition of well-sorted fine sand over the coastal plains of Sendai and S ma. Sediment analysis and hydrodynamic simulation indicate that the tsunami inferred to be triggered by a magnitude 8.3 earthquake spread more than 4 km inland then coast. We postulate that the sand layer was developed by the tsunami’s first wave. Traces of largescale invasion by old tsunami as recorded in the coastal sequences of the Sendai plain show about a 1000-year reoccurrence interval. We suggest that the J gan tsunami was much larger than tsunami generated by normal earthquakes in the subduction interface. o o o o