Are you prepared? - Tsunami risk

What is a tsunami?
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 kilometers. 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.

What causes a tsunami?
It is generally caused by strong earthquakes with epicenter 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.

Is Italy exposed to tsunami risk?
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.

What happens along the coasts?
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 kilometers), dragging everything in their path: vehicles, boats, trees, tanks and other materials, which increase their destructive potential.

When will the next tsunami occur?
It is not possible to predict: it 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.

Is there an Italian alert system?

In 2017, the SiAM - Sistema di Allertamento Nazionale per i Maremoti Generati da Sisma was instituted in Italy. Three organizations cooperate in this system: the Ingv - National Institute of Geophysics and Volcanology, which operates through the Cat - Tsunami Warning Center; Ispra - Superior Institute for Environmental Protection and Research; and the Department of Civil Protection.
The Ingv's Cat assesses the possibility that an earthquake with an epicenter at sea or near the coast could trigger a tsunami. On the basis of these assessments, the Civil Protection Department broadcasts alert messages with the aim of activating, as quickly as possible, the National Civil Protection Service and informing the population. Finally, the maritime data provided by Ispra allows for the confirmation or non-confirmation of a possible tsunami.
SiAM is part of the international warning system that was established in the Mediterranean on the model of those active in the Caribbean Sea and the Pacific and Indian oceans. Compared to these, however, it has limitations because in a shallow sea like the Mediterranean, wave arrival times are very short, which reduces the possibility of alerting the population. It is therefore important to be well aware of the rules of conduct, while remembering that tsunami risk inevitably involves false alarms.

What to do to reduce the risk?

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.

What to know

In a shallow sea as the Mediterranean, wave arrival times are very short. Authorities may not have time to issue an alert. So if you live, work or travel in a coastal area it is even more important to recognize phenomena that may indicate 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

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.