2024 Volume 80 Issue 17 Article ID: 24-17069
Oarai in Ibaraki Prefecture is one of the towns damaged by the 2011 Tohoku-Pacific Ocean Earthquake Tsunami (3.11 Tsunami). The town developed around the port, but the construction of offshore breakwaters caused sedimentation and the shoreline moved forward about 400 m. The old sea walls remain in front of residential areas far from the current shoreline, having fulfilled their purpose. In addition, there are mainly four large RC buildings around the port. Numerical simulations were carried out to compare the tsunami attenuation effects of the old sea walls, large buildings and the breakwaters, and found that the combination of the old sea walls and breakwaters reduced the inundation area by up to 10% for the 3.11 tsunami. On the other hand, the four large buildings alone hold a tsunami attenuating effect, although the rate of decrease becomes lower. It was also found that the tsunami attenuating effect remained, although the absolute effect was smaller for all facilities in the case of the design tsunami which is quite huge using countermeasure of the nuclear power plant.
