...Take a closer look...
Population Map
Japan's estimated population is 126,659,683 people with 13,185,502 people living in Tokyo and the map above shows us that the population in Japan is the most dense along the coastline and in low-lying areas. The information we get from the second map below is that the Philippine Sea Plate, the North American Plate and the Eurasian Plate meet near Tokyo and the Pacific Plate is located a bit further away from Tokyo, so especially Tokyo is exposed to devastating earthquakes. Keeping those facts in mind it is obvious, what devastating situations an earthquake would cause, as the population is very dense in those areas where the three Tectonic Plates meet. If an earthquake occurs and causes a tsunami it would even be worse, as there is very little protection - but that is exactly what happened in Fukushima...
Tectonic plates map
Seismic hazard map
Over 160,000 people died in Japan in the past because of tsunamis. Nowadays Japan has established an effective tsunami pre-warning-system, regular training programs for the population and most Japanese coastal towns are protected with dikes. But the fact that they only protected the nuclear power plants, which are located right at the coast, through dikes is irresponsible, as they know that they those places are at a high risk of experiencing a tsunami caused by an earthquake. In addition, they did not have a back up plan to prevent the reactors from exploding when all cooling systems failed. In addition, we can conclude that the buildings are not built safely, because if they were, there would not have been 127'300 buildings totally collapsing and 273'000 buildings half collapsing in the Tohoku earthquake.