What to know
A seaquake, tsunami in Japanese, is a series of waves produced by the rapid displacement of a large mass of water. In open water, the waves propagate very quickly over large distances, with an almost imperceptible height (at times less than one meter) but the wavelength (the distance between one wave and the next) can be tens of kilometres. As the wave approaches the coast, its speed decreases while its height increases rapidly, even by tens of meters. The first wave may not be the largest, and several minutes may pass between the arrival of one wave and the next one.
It is generally caused by strong earthquakes with epicentre at sea or near the coast. Tsunamis can also be generated by submarine or coastal landslides, by volcanic activity in the sea or near the coast and, much more rarely, from meteorites that fall into the sea.
If you live, work or travel in a coastal area, learn to recognize phenomena that could signal the arrival of a tsunami:
• A strong earthquake you have felt or heard about
• A deep and increasing noise coming from the sea, like that of a train or a low flying aircraft
• A sudden and unusual retreat of the sea, a rapid rise in sea level or a big wave extended over the whole horizon In case of tsunami waves arriving from afar, authorities may have enough time to issue an alert through TV, radio and web: trust only institutional sources and wait for them to declare the all clear. Remember that houses and buildings close to the coast aren’t always safe
• The degree of safety of a building depends on various factors, for example the typology and quality of materials used, the altitude, the distance from the shore, the number of floors, the degree to which it is exposed to the impact of the wave
• Generally, the highest floors of a concrete reinforced building, if properly built, offer adequate protection
The use of monitoring networks, the study of past events and of wave propagation models are just a few of the actions that allow to reduce the tsunami risk. Such knowledge contribute to improve territorial planning and to carry out interventions to make areas exposed to the risk safer, and also to elaborate emergency plans. Being aware and being prepared are the best ways to prevent and reduce the consequences of a tsunami.
An international alert system – Italy is one of the participating countries – is currently being tested. Such system is similar to the ones already active in the Caribbean Sea and in the Pacific and Indian Oceans, but compared to them, has some limits: in a basin such as the Mediterranean sea, arrival times are in fact very short, not allowing enough time for alerting the population. Only tsunamis caused by seismic events occurring away from the Italian coasts (e.g. in the Greek seas), the National Institute of Geophysics and Volcanology, the Institute for Environmental Protection and Research and the Civil Protection Department will have the time to alert the population through tv, radio and web. It is therefore fundamental to know well rules of behaviour, keeping in mind that the tsunami risk necessarily implies the possibility of false alarms.
Nobody knows. If can occur at any time. We know many things about tsunamis, but it is not yet possible to predict when and where they will occur.
A tsunami appears as a rapid rise in sea level or a wall of water that hits the coast, causing a flood. Sometimes we observe an initial and sudden retreat of the sea, which leaves dry ports and beaches.
Tsunami waves have much more strength than sea storms and can penetrate hundreds of meters inland (and, if the coast is very low, even kilometres), dragging everything in their path: vehicles, boats, trees, tanks and other materials, which increase their destructive potential.
All the Mediterranean coasts are exposed to tsunami risk, due to the high seismicity and to the presence of numerous active volcanoes, both emerged and submerged. Over the past thousand years, dozens of tsunamis have been documented along the Italian coasts – only some of which destructive. Eastern Sicily, Calabria, Puglia and the Aeolian archipelago are the most affected coastal areas. However, minor tsunamis have also been registered along Liguria coasts, and in the Tyrrhenian and Adriatic seas. We must also consider that the Italian coasts can be reached by tsunamis generated in areas of the Mediterranean far away from our country.