One of the reasons that the 2011 tsunami overran many coastal barriers in Japan is that the coastal land moved due to the earthquake which lowered the coastal barriers.
The coastal land was moved due to the active subduction of the Pacific plate present beneath the Okhotsk plate under the land of japan. The movement in the Pacific tectonic plate pushed the mainland below and the sea-bed in an upward direction. This caused the ocean water to raise, paving way for a tsunami.
Japan's position is near the four tectonic plates that are a part of Earth's crust. These plates are the Eurasian plate, Filipino plate, Pacific plate, and North American plate.
Due to continuous movements of slipping, locking, creeping, and jolting, the plates create an immense amount of pressure between them. When the pressure is released at a certain point, it creates a disturbance in land and sea-bed, leading to earthquakes and tsunamis.
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