What would a tsunami look like in the Mediterranean?

Computer model shows the spread and consequences of tidal waves after earthquakes

The beach of Matala on the south coast of Crete could be flooded during a tsunami in the eastern Mediterranean. © Olaf Tausch (CC-by-sa 3.0)
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Land under the Mediterranean? A computer model shows the consequences of a tsunami in the earthquake regions of the Mediterranean. The coasts of Sicily and Crete are therefore threatened by flooding in the event of a seaquake. The model is to help in the future to prepare for catastrophic tsunamis after strong earthquakes, the researchers write in the journal "Ocean Science".

The Mediterranean is an earthquake region: Especially on Sicily and the Greek islands, the ground shakes more frequently. The cause is the slow collision of two large tectonic plates: The African plate is sliding steadily under the Eurasian plate. In the Mediterranean, a whole network of distortions and borders is emerging that is not yet fully understood. But it is clear that it sometimes rumbles - and sometimes it comes to pronounced strong earthquake.

Regular tsunamis in the Mediterranean

Particularly from the Pacific it is known that earthquakes can cause tsunamis when they take place at the seabed. However, even in the Mediterranean, such events are surprisingly frequent: about ten percent of all tsunamis worldwide occur there, and on average once a century, a particularly large tidal wave is created. The Mediterranean is densely populated and many large cities lie along the coasts. In addition, a tsunami only has to cover a relatively short distance to the coast. A strong tsunami could therefore lead to a catastrophe without much forewarning time.

Scientists working with Achilleas Samaras from the University of Bologna, Italy, have studied how such a tidal wave could spread after a major earthquake in the region and how much land it would flood. For this purpose, the researchers created a computer model based on data on the depth of the sea, the course of the coastlines and the topography under water.

Simulation of Tsunami tidal waves after an earthquake southwest of Crete. Ar Samaras et al., Ocean Science, 2015 (CC-by-sa 3.0)

Knowledge gaps in the tsunami model

"The biggest source of knowledge about tsunami models is what happens when tsunami waves reach the coastline and rush inland, " explains Samaras. When the waves reach the shallow water off the coast, they raise themselves higher. In addition, depending on the terrain, they can change their direction but how accurate is it for the Mediterranean. display

This knowledge gap should close the new model. "We simulate the formation of a tsunami by installing earthquake shifts either on the ocean floor or on the surface, " explains Samaras. "The model then simulates how these disturbances the tsunami waves spread, how they change in the near future, and how they flood the coast."

Flood after earthquake of magnitude 7

The researchers paid special attention to the coast of the islands of Sicily and Crete. These are among the tectonically most active regions in the Mediterranean and have been the scene of tsunamis several times in the past. In each of these locations, the scientists simulated an earthquake with a magnitude of 7.0 and tracked how the generated waves behaved in the model.

Height profile of an affected coastal section on Crete. Up to a height of five meters (yellow line), a tsunami in the simulation floods the coast. Samaras et al., Ocean Science, 2015; base images from Google Earth, 2015

In both cases, the resulting tsunamis flooded the coastal strips to a height of about five meters above sea level. In Crete, the damage was greater than in Sicily: almost three and a half square kilometers of land were there in the model under water, on the Sicilian coast, it was about 0.6 square kilometers.

With a magnitude of 7.0, the simulated earthquakes are anything but weak. A similarly strong quake hit the region around the Sicilian city of Messina in 1908. Thousands of people died in the subsequent tsunami with waves over ten meters high.

Do not repeat disasters of the past

Even further back in the past, there were already much stronger quakes: A whole earthquake swarm with protected strengths between 8.0 and 8.5 shattered the Cretan coast in the year 365 and destroyed it Virtually all ancient cities on the island. The resulting tsunami flooded cities in Italy, Greece, Egypt and Libya today. In ancient Alexandria alone, according to historical sources, 5, 000 people died.

The scientists hope that with the help of their model such disasters will be limited in the future. While they can not prevent the earthquakes and tsunamis, the simulations could help with the preparation: "Our simulations could help authorities and politicians to create a comprehensive database of tsunami scenarios in the Mediterranean, " says Samaras. "In each scenario, they could identify vulnerable coastal regions and plan their countermeasures accordingly." (Ocean Science, 2015, in press)

(European Geosciences Union (EGU), 27.08.2015 - AKR)