Tsunami risk in western Mediterranean is determined by the exposure of Spanish, Moroccan and Algerian coasts to two different seismic areas - the Alboran sea and the Atlas belt in north-western Algeria - by the high population density – mostly in Spain and Algeria - and by the importance of coastal tourism infrastructure in Spain.

A recent article “tsunami hazard at the western Mediterranean Spanish coast from seismic sources” published on Natural Earth Science, analyses the potential tsunami sources close to the Iberian Peninsula and identifies the areas where the impact of a tsunami would be greater. The tsunami threat over the Spanish Mediterranean coast and the Balearic Islands was estimated reviewing 22 possible tsunami sources, compiling maximum wave elevation maps and calculating tsunami travel times through numerical modelling.

Regional maximum wave elevation maps for the worst tsunamigenic source of the Alboran Sea and for the northern Algerian sources for the south-eastern Iberian Peninsula. The colour shading varies with the maximum wave elevation as shown in the colour scale.

In general – the article reports - the northern Algerian sources resulted to pose a greater risk to the Spanish coast than the Alboran Sea sources. Tsunamis generated in northern Algeria, would affect the provinces of Almeria and Alicante, and especially the islands of Ibiza and Formentera with probable severe damage. The province of Almeria is at a high risk of being affected by a tsunami because it can be reached by virtually all sources of the Alboran Sea and the North West of Algeria.

With reference to a possible Mediterranean Fukushima, the first conclusion that we may draw from the reserach is that the Vandellòs Nuclear Power Plant situated very close to the sea near Tarragona lies in a quite low tsunami risk area. Although for properly evaluating the tsunami risk along the coast of Catalonia, also the scenario of the 1373 earthquake in the Central Pyrenees-Catalonia region along with its associated tsunami in Barcelona should be evaluated. 

Central Mediterranean is exposed to three potential earthquake-related tsunami sources – indicates the article “Earthquake-generated tsunamis in the Mediterranean Sea: Scenarios of potential threats to southern Italy” published in 2008 on the Journal of Geophysical Research. These are: the Tell system in the Algeria-Tunisia offshore capable of generating earthquakes up to magnitude 7.0, the southern Tyrrhenian Sea thrust system capable of triggering earthquakes of magnitude 7.0 and higher, and the Hellenic Arc proven to be capable of generating frequent and occasionally very large earthquakes of magnitude greater than 8.0.

Tectonic map of the Mediterranean basin. Yellow dots indicate seismic events. Color-shaded ribbons highlight the main areas capable of generating tsunamis that pose significant hazard to Mediterranean shore-facing settlements.

For each of the investigated tsunami source zones, researchers simulated possible earthquake-related scenarios leading to tsunami and prepared maps of the maximum wave height, and of tsunami travel time.

Research results indicate that the greatest threat to central Mediterranean European and African coasts would come from earthquakes along the Hellenic Arc source zone. Waves with average maximum height of 1 m or higher are expected along most of southern and eastern Sicily (from Trapani to Messina) and the South-Eastern coasts of the southern Italy peninsula (from Reggio Calabria to Cantanzaro, Taranto, Brindisi and almost Bari). Travel time for waves reaching southern Italy and the south-eastern coasts of Sicily would be between 60-70 min.

Earthquakes along the southern Tyrrhenian source zone could produce low energy tsunamis. They estimated the average maximum wave height is around 0.2 m. Waves of 0.5 m and higher would affect only few localities around the northern coast of Sicily such as Palermo, Trapani, and Milazzo. The average wave travel times to these locations would vary between 5-10 min.

The Algeria-Tunisia offshore source zone can generate tsunamis that would have a great impact on the coasts of Sardinia. The western coast of Sicily would be affected by maximum wave heights in the order of 0.5 m. Wave travel times would be in the order of 40-50 min.

Algeria-Tunisia offshore Source Zone

Southern Tyrrhenian Source Zone

Hellenic Arc Source Zone

The European-Mediterranean Seismic Hazard Map, in terms of peak ground acceleration with a 10% chance of being exceeded in 50 years for stiff soil condition, was developed within the framework of the European Seismological Commission and UNESCO. The map received the Award for Excellence in Cartography of the International Cartographic Association, at the 21st International Cartographic Conference, 2003.

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