In this study, we investigated damaged situation of floating structures in Miyagi Pref. caused by tsunamis in the Great East Japan Earthquake and it made clear that some structures mooring with pile were flowed away. However, structures mooring with chains were never flowed away. we used a case of Izushima, Onagawa-town to examine a mechanism suffered floating structures that mooring with piles and chains. In the case of pile mooring, from the result of examination, it was estimated that piles were left out by tsunami water level rising. In the case of chain mooring, at the result of numerical calculation using by STOC and mooring simulation, it was found that dredging anchor blocks became important factor against outflow.
