Abstract
A phenomenon similar to a tsunami was observed by anglers and inhabitants at Saiko Lake, which is one of the five lakes located on the foot of Mt. Fuji, during the 2011 off the Pacific coast of Tohoku earthquake. In order to clarify the mechanism of this phenomenon, the author interviewed with the witnesses. The author also examined earthquake ground motions observed near the lake. As a result, surface wave exhibiting the nature of Rayleigh wave with the predominant period around 60 seconds in the observed motion which is coincident with a resonant period of the closed water body of Saiko Lake. A shaking experiment was conducted using a Saiko Lake model. It clearly explained the mechanism of a seismic seiche of Saiko Lake, which means that a resonant oscillation in the short side of the rectangular shape of the lake makes the shift to that in the long side. Then, the author concluded that the phenomenon was caused by a seismic seiche.
