TOKYO — In the country that gave the world the word tsunami, the Japanese nuclear establishment largely disregarded the potentially destructive force of the walls of water. The word did not even appear in government guidelines until 2006, decades after plants — including the Fukushima Daiichi facility that firefighters are still struggling to get under control — began dotting the Japanese coastline.

The lack of attention may help explain how, on an island nation surrounded by clashing tectonic plates that commonly produce tsunamis, the protections were so tragically minuscule compared with the nearly 46-foot tsunami that overwhelmed the Fukushima plant on March 11. Offshore breakwaters, designed to guard against typhoons but not tsunamis, succumbed quickly as a first line of defense. The wave grew three times as tall as the bluff on which the plant had been built.

Japanese government and utility officials have repeatedly said that engineers could never have anticipated the magnitude 9.0 earthquake — by far the largest in Japanese history — that caused the sea bottom to shudder and generated the huge tsunami. Even so, seismologists and tsunami experts say that according to readily available data, an earthquake with a magnitude as low as 7.5 — almost garden variety around the Pacific Rim — could have created a tsunami large enough to top the bluff at Fukushima.

After an advisory group issued nonbinding recommendations in 2002, Tokyo Electric Power Company, the plant owner and Japan’s biggest utility, raised its maximum projected tsunami at Fukushima Daiichi to between 17.7 and 18.7 feet — considerably higher than the 13-foot-high bluff. Yet the company appeared to respond only by raising the level of an electric pump near the coast by 8 inches, presumably to protect it from high water, regulators said.