The constant rise in the number of victims that has been noted over the last two decades can essentially be explained not by an increase in the number of unpredictable occurrences, but rather by the increasing vulnerability of humankind to such events. This is due to anarchic development in high-risk zones, to the concentration of population on the coast and to the shortage of information systems. Natural disasters are also amplified by the imbalances caused by man-made changes (soil cover) and by climatic variability, to the point where it is difficult to distinguish between what is natural and what is linked to human activity. Some hazards such as volcanic eruptions have been studied for a long time now and have benefited from technological developments in surveillance tools which make them relatively easy to forecast. Others still resist such predictions, such as earthquakes or tsunamis, which are triggered by underwater earthquak...