Benthic foraminiferal evidence on origin of possible submarine tsunami deposit formed by the 2011 off the Pacific Coast of Tohoku earthquake tsunami

Tsunami by the 2011 off the Pacific Coast of Tohoku Earthquake brought significant damage along the northeastern Japan coast. After events, we conducted marine survey to clarify the influence of earthquake/tsunami to sea bottom environments. As the results, we found the 2011 earthquake- and/or tsunami-induced turbidites at 13 sites from outer shelf (122 m in water depth) to trench slope (5522 m) off Sanriku. At two sites from slope (893 m and 1446 m), the turbidites have sharp erosional bases, and upward-fining graded structures started from v.f.s-c.silt. Basal sands include abundant benthic foraminifera. In our preliminary investigation, a meaningful occurrence of species inhabiting the outer shelf areas have recognized, suggesting transport of sediment from outer shelf by tsunami-induced turbidity currents. Increasing of friction velocity by tsunami in the shelf area is most probable mechanism on the sediment resuspension including benthic foraminiferal tests.