Earthquakes, which are sometimes the cause of violent tsunamis when their epicentre is at sea, and many volcanic eruptions have often claimed victims and caused considerable damage, and these phenomena are still very often unpredictable. The earthquake that struck Lisbon on 1st November 1755, whose epicentre was in the Atlantic, 200 km off the coast, left its mark on Portugal’s history. Followed by a violent tsunami, it almost totally destroyed the capital, whose centre was submerged by waves 5 to 15 metres high, and claimed 60,000 victims. Voltaire echoed this event in his Poème sur le désastre de Lisbonne (1756) and in Candide (1759), and drew philosophical lessons from it.
Japan’s magnitude 9 Tohoku earthquake off the Pacific coast in March 2011 was followed by a tsunami that devastated the region and was responsible for 90% of the 16,000 victims. Despite a warning, the tsunami triggered the Fukushima nuclear disaster, with the backup and security facilities of several nuclear power plant reactors and the electricity grid having been destroyed or damaged by the waves.
Little progress has been made in developing techniques for detecting an earthquake on the ocean floor and simultaneously sending a long-distance warning. Seismometers can be placed on the ocean floor but, as well as being expensive to install and requiring maintenance, they are fragile and cannot broadcast data in real time. Buoys called MERMAID (Mobile Earthquake Recorder in Marine Areas by Independent Divers), which can be immerged and equipped with hydrophones, can detect noises in the water of various origins, such as those caused by vibrations during an earthquake. But these buoys are few and far between.
For several years now, oceanographers and seismologists have been turning their attention to undersea telecommunications cables. They are laid on the seabed in a fixed location and can transmit information and data in optical fibres, carrying energy to amplify them in repeaters installed every 70 km or so. To pick up a signal and transmit a tsunami warning remotely, all we would need to do is install sensors in the repeaters to measure the movement of the ocean floor and variations in water pressure and temperature; the fibres would transmit warning signals picked up on land over long distances.[1] These cables could also contribute to a better understanding of the increase in water temperature at depth caused by global warming.
Fearing a repeat of the 1755 disaster — the Azores region being critical ...
