Elucidation of sedimentological mechanism of gravity flows by tsunamis

对仙台湾沿岸陆相和近岸至近岸沉积物进行了沉积学和微古生物分析，以阐明海啸退缩引起的沉积物迁移和沉积过程。海啸发生后，沉积物颗粒和硅藻的分布格局呈现向海迁移的趋势。有人提出，由于海啸的反冲，原本分布在陆地和沿海地区的沉积物被运到了近海。生活在近海地区的浮游和底栖生物物种的分布格局表明，海啸向陆地迁移的证据很少。这表明，在研究区域的近海海底，没有发生海啸抬高引起的沉积物向陆地的重新分布。海啸的反冲刷可能会引起泥沙流，将大量沿海材料运往海洋。

Sedimentological and micropaleontological analyses of terrestrial and nearshore to offshore sediments recovered from the coast of the Sendai Bay were performed to clarify the processes of sediment transport and deposition by the tsunami retreat. The distribution pattern of sediment grains and diatom frustules showed seaward migration after the tsunami event. It has been suggested that sediments originally distributed in terrestrial and coastal zones were transported offshore due to the tsunami backwash. The distribution pattern of planktonic and benthic species living in offshore zones showed slight evidence of landward migration by the tsunami. This suggests that landward redistribution of sediments by the tsunami run-up did not occur in the offshore seafloor of the study area. It is possible that tsunami backwashes induce sediment flows that transport a large amount of coastal materials seaward.