摘要：Tsunami that hit Japan in 2011 shocked the world. The earthquake at the coast of the Pacific Ocean was 9.0 on Richter scale leading to 10 meters of wave. The epicentre was reported to be off the coast of Oshika Peninsula, at the east coast of Tohoku, at a depth of 244 kilometres. The earthquake and tsunami caused more than 20,000 victims in six prefectures. In an effort to anticipate to the tsunami, Japan has long build walls around the beach directly face the Pacific Ocean—the walls are known as seawall. In this paper, facts show that the effectiveness of seawall in reducing the energy of tsunami is accompanied by tremendous destructive energy. Analysis in this research was done using a software named CADMAS Surf 2D with numerical analysis method. Observations were made using two variants of heights of seawall, two meters and three meters. Both are observed based on the heights of the wave coming from the Ocean, after passing through the seawall, and at some points of observation. The level of damage caused by the seawall was due to turbulence just behind the construction that resulted in crushing, scouring, and or destructive energy, the energy was even bigger after passing the seawall. Nevertheless, tsunami wave height and velocity decreased significantly after the seawall.
