The 2011 Tohoku earthquake tsunami hit wide stretch of the Pacific coast of Japan and measured tsunami inundation heights showed significant variations within the same bay. Ryori Bay, located in Iwate prefecture, is one of such bays. The authors reported the presence of the short period wave developed complex fluid motion in the Ryori Bay. This study aims to investigate the physical mechanisms of such complex tsunami behaviors based on numerical simulation. The results showed the locally tsunami concentrating and the short period wave were derived from multiple wave reflection and wave dispersion in a specific shallow area respectively. Furthermore, the superposition of short period wave was suggested to have significant impacts on local amplification of tsunami and thus damage on coastal structures.
