A talk by Dr Simon Day of the Aon Benfield UCL Hazard Centre. The earthquake and resulting tsunami that struck the Tohoku region of Japan on March 11th, 2011, were recorded in unprecedented detail by a wide range of scientific instruments that had been installed by Japanese agencies, partly for the research purpose of understanding such events, but also with the aim of providing warning and a basis for disaster mitigation. This talk will examine the advances in earthquake and tsunami science that resulted from these records, but also consider why, despite the effort put into the research and the even greater effort put into tsunami defences and other mitigation measures, the tsunami led to so many deaths in Japan.