The urbanization zone runs mainly along the Pacific coast ( hence the name ) of Japan from Kantō region to Osaka , and the Inland Sea ( on both sides ) to Fukuoka , and is concentrated along the Tōkaidō-Sanyō rail corridor . A view of Japan at night clearly shows a rather dense and continuous strip of light ( demarcating urban zones ) that delineates the region . The high population is particularly due to the large plains – the Kantō Plain , Kinai Plain , and Nōbi Plain – which facilitate building in mountainous Japan . Coastal regions are at high risk of earthquakes and tsunamis , due to the nearby Nankai Trough ( Nankai megathrust earthquakes ) and Sagami Trough , notably the 1923 Great Kantō earthquake , and further damaging earthquakes are expected in the region ; the combination of population density and seismic activity is responsible for the high-impact earthquake and tsunami risk in Japan
1923 Great Kantō earthquake
1923 Great Kantō earthquake
Taiheiyō Belt