engleski

Tsunamis of meteorological origin in the Mediterranean Sea

Significant seiche oscillations occasionally generated in certain bays and inlets of the world ocean frequently have an atmospheric rather than a seismic origin. An eyewitness would refer to them as ‘ big waves in a harbour’ (i.e. ‘ tsunamis’ , if we recall the actual Japanese origin of the term). These oscillations have a clear resemblance to seismic tsunamis. Due to their distinctive source mechanism and similarity with tsunami waves, these abnormal oscillations may be referred to as "meteotsunamis". The Mediterranean Sea is a region where such phenomenon are commonly recorded due, in part, to the fact that any abnormal sea level oscillation becomes more evident and may cause unexpected damage in a harbour where daily tides are small. At the same time, there are several specific sites in regions with pronounced resonant properties where significant meteotsunamis are quite common and destructive ; normally they have specific local names such as "rissaga" in the bays of the Balearic Islands (Spain), "marrubbio" on the coast of Sicily, and "milghuba" in Malta. In this presentation, we review some meteotsunami episodes observed in the Mediterranean. Available data are analyzed from a global perspective and a comparison between seismic tsunamis and meteorological tsunamis recorded at the same sites are performed whenever possible. Despite their different origin, both types are modified and amplified by topography in a similar way and produce similar catastrophic effects in coastal areas. Due to these similarities, it is often difficult to distinguish between these two phenomena without knowing the exact source characteristics. Recognition and separation of these two types of wave phenomena is important for the revision/improvement of the existing tsunami catalogues but also for better understanding of the generation mechanisms in order to mitigate their effects. Our analysis is based on the fact that both tsunamis and meteotsunamis are formed by the combined effects of external forcing and regional topography. So, for different events recorded at the same site, the similarities are related to their forcing while differences are related to the topography. In contrast, for the same event recorded at different stations, the resemblances are mainly associated with the source and the differences with the specific local topographic features. Specific examples of meteotsunamis are examined for the Balearic Islands and the mainland coast of Spain, for the Adriatic Sea, Malta and the Greek Islands.

tsunami; atmospheric waves; resonance

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