The situation in the Mediterranean
The Sumatra tsunami attracted a sudden interest in a phenomenon which many of us had heard about but never really paid much attention to. However, it is wrong to think that a tsunami is a hazard only for faraway places like the Indian Ocean, the islands of the Pacific or areas particularly susceptible to earthquakes, such as Japan. There is in fact a risk of tsunami in the Mediterranean sea, as we can see from historic documents or simply by looking at the geological history of the basin. Big tsunamis have occurred here in the past, such as the one in Messina in 1908, or the one of 365 AD in Greece. The latest episode was the tsunami of Stromboli in 2002, fortunately without serious consequences as it happened in winter (30 December), when there were no crowds of tourists on the island. The waves were up to 10 metres high. As elsewhere, in the Mediterranean the cause of most tsunamis can be linked to seismic events, but we must not underestimate the effects of volcanic activity as far as Vesuvius, Etna and the Aeolian Islands are concerned, in particular Stromboli and Vulcano. The coasts most at risk are those of southern Italy, i.e. Apulia, Sicily and Calabria. Figure 1 shows a map of the tsunami sources in Italy from 79 AD to today (Italian Tsunami Catalogue, by Tinti, Maramai and Graziani, 2004).
On average, in the last four centuries Italy has seen 15 tsunamis every 100 years - a fact not to be taken lightly as far as the safety of the Italian coasts and its inhabitants is concerned.
The tsunami risk assessment can be studied by considering scenarios of future tsunamis, based obviously also on our knowledge of historical events. Figures 1 to 3 show the results of computer simulations prepared by the Tsunami Research Team at Bologna University. They refer to two distinct scenarios of tsunamis produced by violent underwater earthquakes. One scenario (Fig. 2) regards the eastern Mediterranean, with an earthquake west of Crete. Similar tsunamis occurred in 1303 and 365 AD. Fig. 3 shows the propagation of a tsunami in the central Mediterranean, caused by an earthquake off the coast of eastern Sicily, similar to the one of 1693. As we can see, the tsunamis propagate through the Mediterranean basin in a very short time. In fifteen minutes, a large area of the coast near the source of the tsunami is hit, and within an hour the tsunami has crossed the basin and arrived on the opposite coast.
The Mediterranean alert network