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Tsunamis


Tsunamis are waves generated by the sudden displacement of a huge water mass and that can reach several metres in height when approaching the coast, causing severe damage. The word tsunami comes from the Japanese “tsu” (harbour) and “nami” (wave), meaning “harbour wave” because they are capable of causing destruction in harbours and along the coast. Tsunamis are mainly triggered by submarine or nearshore earthquakes with high magnitude. Less frequently submarine landslides, terrestrial landslides near the coast and volcanic eruptions can also generate tsunamis. Meteorite impact in the sea can also cause tsunamis, but these are very rare events.

Tsunami waves differ from usual sea waves: when the waves are wind-generated, only the most superficial layer of the water column move and the deepest part of the water column remains undisturbed, while tsunami waves are characterized by the displacement of the whole water column, from the bottom to the top. This explains the fact that tsunami waves have a high amount of energy and they are able, in some cases, to penetrate in land for even hundreds of metres and cause severe damage.

Wind-generated waves
Tsunami waves

Tsunami waves are characterized by very high wavelength (distance between two crests), reaching tens to hundreds of kilometres and in the open sea their velocity, depending on the water depth, can reach values as high as 700-800 km/hour. They can propagate for thousands of kilometres without dissipating much of their energy and, therefore, they can travel long distances and violently struck coasts very far form the source.
In the open sea tsunami waves are usually unnoticed due to the fact that their height commonly doesn’t exceed 1 meter; on the contrary when they approach the coast their velocity decreases directly proportionally to the water depth and, consequently, their height increases and can reach tens of meters.
Tsunami waves can approach the shore with different behaviours. Sometimes the trough of the wave arrives before the crest and in this case a sea withdrawal would be observed leaving dried shorelines also for several meters. This withdrawal could be a warning because the wave crest will arrive in a short time and could flood the coast. In some cases the tsunami can approach the coast looking like a wall of water, in other cases like a strong tide that rises very fast, and the sea level rises many metres.

 

Since 1988 the Istituto Nazionale di Geofisica e Vulcanologia (INGV) of Rome has carried on tsunami studies, particularly within the Euro-Mediterranean area. In this frame some researchers of the U.F. RIDGE were involved in the EU GITEC and GITEC-TWO projects and they realized the first database of the Italian tsunamis.

At present they are involved in the EU TRANSFER project as responsible for the realization of the tsunami database of the Euro-Mediterranean region and they also take part in the activities of the intergovernmental group NEAMTWS (North East Atlantic, Mediterranean and connected sea Tsunami Warning System) for the realization of a tsunami warning system in the Mediterranean sea and eastern Atlantic.
In addition, research on tsunamis in Central America is at present going on.

Post-event field surveys have been carried out after some tsunami of particular relevance, both within the national territory (Stromboli 2002) and abroad.

Researchers of the U.F. RIDGE working on tsunamis also cooperate with the INGV "Laboratorio di Divulgazione e Didattica" for the realization of a number of educational products, like exhibitions, books and audiovisual material.


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