At noon on Saturday September 1, 1923, the earthquake hit, registering 8.3 on the Richter scale. Seismologists found the epicentre was in Sagami Bay, about 80 km south of Tokyo, where a 100- by 100-kilometer segment of the Philippine oceanic plate broke against the Eurasian continental plate, releasing a massive amount of tectonic energy. Minutes later came the dreaded huge tsunami, with a height of 12 meters. In Yokohama, a city built on landfill, practically every structure was ruined. As fires swept across Tokyo, 75% of all buildings suffered severe structural damage. The quake cut most of the water mains. Of the population of 4.5 million, 2% to 3% were killed. Two million people were homeless. Two per cent of Japan's total national wealth was destroyed. Emergency food and clothing was provided by an international relief effort.