2020 年 8 巻 1 号 p. 13-25
Water–level fluctuations resembling long period waves, which differ from normal wind waves, were observed immediately after the Tohoku earthquake of 2011 in multiple locations, such as lakes in Yamanashi Prefecture, the fjords of Norway, and other sites located far away from the epicenter. Not many research on similar abnormal water–level fluctuations have been conducted thus far and, in many cases, these studies have treated the phenomena as seiches. However, researchers have not established concrete wave generation mechanisms and evaluation methods, and their awareness of this phenomenon and disaster prevention remains low. In this study, the authors sought to select a quantitative impact assessment method and learn more about this phenomenon. The authors used previous research and eyewitness accounts to judge that onsite slosh dynamics caused the waves to generate, and the authors attempted to recreate this phenomenon using a 3-D slosh dynamic analysis. After comparing laboratory results to verify the validity of the analysis, the authors recreated past examples of waves and also made future predictions. As a result, the authors were able to recreate abnormal water–level fluctuations based on this method. In addition, the authors identified water damage risks to in-land lakes and waterways of inner parts of bays. These are different from risks posed by tsunamis. The waves are formed immediately after the onset of an earthquake.