While Japan, perhaps tbe world's most earthquake-prone country, has learned how to build structures to withstand earthquakes, it apparently has not yet been able to fully cope with tsunamis. Japan has a warning system for tsunamis, but on Monday night the waves reached Okushiri at about the same time as the warning, five minutes after the earthquake. The only way to save human lives is to evacuate immediately, even without a warning. Waves Up to 35-Feet High Professor Shuto estimated that the wave that struck Okushiri ranged from 10 to 16 feet high, but noted that he said he had not completed his calculations. A researcher for the Meterologicval Agency estimated, based on a survey of the site, that the waves were as high as 35 feet.
Tsunamis are gigantic versions of the ripples produced by a pebble tossed into a still pond.
But in tsunamis, the water is displaced not by a pebble, but by an earthquake, volcanic eruption or other violent undersea movement. A huge mass of water can be displaced. The tsunami's speed depends on the depth of the water above the displaced sea bed. In the case of the tsunami on Monday, where the water was about 6,000 feet deep, the wave travels at 300 miles per hour. As the wave approaches the land and the ocean becomes shallower, the water in the back of the wave catches up to the water in the front, and the wave height mounts.