TSUNAMI IN MEDITERRANEAN SEA

Transcription

1 TSUNAMI IN MEDITERRANEAN SEA Giuseppe Mastronuzzi Dipartimento di Geologia e Geofisica, Università degli Studi Aldo Moro, Bari, Italy Laboratorio Gis Geoambientale e di Telerilevamento LaGAT-TA, II Facoltà di Scienze a Taranto, Università degli Studi Aldo Moro, Bari, Italy Abstract The worldwide growth of coastal urbanization has induced even more populous concentrations of cities, industrial complexes, power stations - also nuclear -, and harbours etc..., in event-vulnerable coastal areas. Coastal areas are prone to paroxysmal events of different origins posing major threats to its natural and anthropic features. Recent meteorological- and/or geodynamic-genetic events resulted in severe economic damage and significant loss of life. In particular, tsunami can hit any coastal zone in the world with short or no-alarm period. In the Mediterranean basin, the short distance substantially annuls this possibility. In addition, the concept of ICZM underlines the necessity to consider every morpho-dynamic event in relation to human activities. The task is the implementation of scientific and cultural systems and tools capable of supporting effective coastal management, suggesting tsunami risk maps for example which would be essential for coastal planners to realize effective civil-protection measures and procedures. Key words: coastal area, tsunami, Mediterranean sea, coastal risk. Premise The increased extension of human presence in coastal areas, and the clustering of economic and industrial activities around them, has made such areas particularly prone to the consequences of the impact of low frequency - high magnitude events. They are exemplified by tsunamis and exceptional sea-storms, which add their devastating effects to those of rising sea-levels and local land subsidence. The surge induced by the increasingly more frequent sea storms, in combination with eustatic sea-level rise, locally amplified by sedimentary or tectonic subsidence, determines recurrent flooding of wide coastal areas. The features of the sea bottom, and of coastal areas, induce different degrees of coastal risk and vulnerability. Geomorphology pre-dispose some coastal areas to the flooding generated by catastrophic rains in combination with exceptional sea storms. Recent floods of Myamar (2008), Bangladesh (2007), Lousiana (U.S.A.) (2005) and Philippines (2004) were not unexpected. However, the particular type of urbanisation, its extent and the local social organisation of its presence, made every preventive intervention or management plan quite difficult. The tsunami that occurred on December 26th, 2004 was the largest between the known ones. It was, perhaps, the most horrific and deadly natural event that never hit the coastal area in human history. About people died in the poor urban areas facing the Indian Ocean. This is, of course, besides the infrastructure facilities that were extensively damaged. Natural coastal areas were flooded and radically modified (i.e.: Paris et al., 2008; Cochard et al., 2008). More recently, on September 29, 2009, a further new tsunami hit the coasts of the Samoa Islands in Melanesia. In this case, as well, the poor communities distributed along the coast registered the highest number of human losses. In both cases, the destructive impact seem to have been driven by the under-estimation of a tsunami s potential effects and of the scarce knowledge of tsunami sciences. Since it is extremely low in happening frequency, the probability of the impact of a tsunami is rarely taken into account by planners, with the exception of circumpacific areas where higher degrees of frequency and intensity of these phenomena imposed the realization of the need for a modern system of alert (early warning system) for the mitigation of a tsunami s impact. Only recently, the combined efforts of the European scientific community in collaboration with Egypt and Turkey, suggested a scientific Project TRANSFER - Tsunami Risk And strategies For the European Region, Coordinated by Prof. Stefano Tinti, which permits a real improvement of the knowledge useful to develop and implement an early warning system for the Euro-Mediterranean region ( (UNESCO, 2002). In the past, extreme events were less destructive mainly because less human value was directly exposed to their impact. Despite this fact, the legend and the chronicle of coastal populations are both a reminder of the disastrous effects of sea-waves impacting human settlements all over the world, from the Maori in New Zealand to the Japanese fishermen of Sendai region, and the clericals of the Beauport Abbaye in Bretagne. Procopio da Cesarea (VI sec) reminds us of the effects of the quirks of Porfirione; the sea monster that every 50 years generated waves capable of killing professional sailors and destroying coastal settlements in the Bosphorus area (Guerra gotica, VII, 29). Moreover, the myth of Atlantide is frequently correlated to the destruction of the Minoan civilization as consequence of the eruption of the Santorini volcano around 1620 B.C. that was combined with a strong earthquake causing a tremendous tsunami that destroyed many ancient settlements in Northern Crete but even a fast falling sea level, favoured the exodus of the Israelites from Egypt passing through the Red Sea! 1

2 The Egyptian Journal Of Environmental Change More practically, it is known that many villages and towns along the coasts of the Mediterranean were destroyed by the impact of paroxysmal events, of marine or continental genesis, like storms, tsunami or alluvial inundation (i.e.: Bruins et al., 2008). In Southern Italy, the inhabitants of the coastal areas of Apulia, Calabria and Sicily remind us of the effects of tsunamis occurred over the last five centuries, some of which they have actually described in historical chronicles, and others are too recent to be forgotten (i.e.: Gravina et al., 2005; Maramai et al., 2005; Mastronuzzi et al., 2007). The tsunami which destroyed Messina in Sicily and Reggio in Calabria on December 28, 1908, was caused by a strong earthquake whose epicentre was in the Ionian Sea, not far from the coast. Numerous coastal villages were destroyed by tsunami inundation. In Reggio, the run-up reached a height of 13 m, killing thousands of people (i.e.: Piatanesi and Tinti., 2002; Tinti and Armigliato, 2003). During the past few years, worldwide catalogues of tsunami events were elaborated for different regions of the world (i.e.: Soloviev et al., 2000; Maramai et al., 2003; Tinti et al., 2007; NGDC, 2008; ICMMG, 2008; USGS, 2008); they comprise far more than 2000 events during the past 4000 years (Sheffers and Kelletat, 2003; Scheffer and Scheffer, 2007). In spite of this high-magnitude low-frequency events are considered to have played an important role in the morphological evolution of many coastlines (i.e.: Bryant et al., 1996; Dawson, 1994; Bryant, 2001). Frequently, the scientific community underestimates the important role of sedimentological and morphological studies in the evaluation of future predictive scenarios entrusting the assessment of the tsunami impact only to geodynamic/mathematical models. They underrate the advantages deriving from the study of field evidence to: ì - individuate the areas hit by tsunami in the past; ìì - set up a chronology of past events; ììì - validate the model. A nonmultidisciplinary approach to the tsunami analysis in the Integrated Coastal Zone Management (ICZM) could make future impacts even more destructive. The Mediterranean area The Mediterranean area represents the collision zone between the European and African plates. The general features of this basin cover every process - seismic, volcanic or morphological - whose effects could be the generation of a tsunami. In fact, this basin comprises a number of geodynamic regions affected by different seismic activity extended from West to East, from the Tell Atlas in North Africa, crossing the Calabro-Peloritan Arc and the Appennine in Sicily and Italy, to the Albanides - Dinarides chains and the Hellenic arc in the Balcanic area, which continue in the North Anatolian fault to the North of the Turkey- and in Cyprus-Arc and in the Aksu thrust in its Easternmost part. Furthermore, the concentration of earthquakes epicentres that borders the Levantine Sinai micro-plate, individuate active seismic area between the African and the Arabian plates (Fig. 1). This short and schematic review should not be seen as an under-evaluation of the seismic activity concentrated in the long list of tectonic lineaments that cross the main ones. Geodynamic active structures continue in the continental shelf North and South of the Gargano Promontory (i.e.: Tremiti fault to the North and Gondola fault to the South) that is one of the most seismic areas in the Italian peninsula. Notwithstanding this, the analysis of recent seismicity points out that the Adria plate is affected by a relevant activity, even if lower than what is typical of the surrounding chains. In particular, in its Eastern side; the Balcanic thrust is cut by several like parallel faults. The right-lateral strike slip; Cefalonia fault, substantially separates the Eurasian plate from the Aegean - Asian microplate and is considered responsible for the strongest seismic activity in the area. On the other hand, in the centre of the Mediterranean basin, on the bottom of the Ionian sea the multiple plate junction of Africa, Adria and the Aegean, define different types of plate boundaries by collision, subduction, transformational faulting and spreading. In this area, the most representative active faults can be recognised in the surrounding areas of Sicily. Here, the normal fault system is mostly located off-shore in front of the coastal area from Messina to the Etna volcano, Catania and Siracusa. To the South, it joins the Iblean- Maltese scarp system and define an area characterised by a high level of crustal seismicity at high intensity (i.e.: Monaco e Tortorici, 2007). Moreover, all the Mediterranean sea is characterised by very deep bottom ranging from the 3000 m of the Western basin and of the Thyrrenian sea, up to the m that characterise the Ionian sea in its central part, which is crossed by the Mediterranean ridge. It is limited by the active Hellenic arc and by the high seismic zones of the Peloponnese and Crete in Greece up to Ciprus. Furthermore, these areas, as also the Calabrian Arc, show a shelf break very close to the steep mountains which directly dip into the sea (Fig. 2). These features make possible large landslides occur. Evidence of several marine landslides has been surveyed all along the continental scarp of the Mediterranean basin (i.e: Ridente et al., 2008). Some of them are considered as a direct consequence of strong earthquakes occurring inland like that which in 1783 induced the collapse in to the sea of a large part of the Monte Faci, near Scilla, on the Western side of Calabria causing some thousands of casualties. However, sediments ascribed to turbidite currents have been found in the Ionian and Sirte abyssal plains. They have been correlated to the landslides generated by the tsunami caused by the Santorini eruption and to its caldera collapse (Cita and Aloisi, 2000). 2

3 Directly correlated to the possibility of landslides, is the presence of active volcanoes, as is the case in the Sicily channel, the Thyrreanian and in the Aegean seas (Fig. 2). In the first case, between Euroasian and African plates an important active rifting area is marked by still active volcanoes (Civile et al., 2008). A part from the above mentioned case of the Santorini eruption, there is another case in recorded history about the effects of the Vesuvio eruption in 79 a.d., in which lavas reached the sea. Besides, the recent eruptions of Stromboli in the Aeolian islands (December 30, 2002), to the North of Sicily, have caused the collapse of a part of the flank of the volcano whose effect was the generation of a tsunami that hit the Northern coast of Sicily and of the Western ones of Calabria (Maramai et al., 2005). Recently, catastrophic scenarios have been drawn for all Mediterranean coasts as a result of the possibility of new collapses into the sea of a part of the Monte Etna caused by its eruption (Pareschi et al., 2006). Evidence of tsunami impact According to Bryant (2001), about the 10% of tsunamis in the world occurred in the Mediterranean Sea and about the 7% of earthquakes which hit this region produced a tsunami. In spite of a lot of catalogues reporting a long list of tsunamis occurring during the last 4000 years, only recently the approach to the tsunami science changed. The first catalogues were built using, when possible, seismological sources coupled with results of the hard and long study of historical sources like classic texts, documents and descriptions. Historical studies pointed out a relevant number of tsunamis along the Italian coasts, but also Dalmatian, Albanian, Greek and Turkish ones. Despite an incredible availability of indirect data that needed only to be validated by direct surveys aimed to individualize geological evidence of the impact of these extreme events, few field researches were performed up to the 1990s of the 20 th century. Moreover, they were devoted to the study of evidence ascribed to the occurrence of contemporary tsunami. For example, the generation, the propagation and the impact in the Aegean islands of the July 9, 1956 tsunami generated different studies about its physical aspects and about its sedimentological effects on the coast (Galanopoulos, 1957; Ambraseys 1960; Papazachos et al., 1985; Dominey-Howes, 1996; 2002; Perissoratis and Papadopolous; 1999). However, despite the pioneering study performed by Heck (1947) on the morphological effects of the December 28, 1908 tsunami in Messina strait, the first field researches were performed in Mediterranean sea only between the end of the 20 th century and the beginning of the 21 st century: along the coast of central Greece (Pirazzoli et al., 1999) and of Southern Italy (Mastronuzzi and Sansò, 2000; Gianfreda et al. 2001) and along the coast of Cyprus (i.e.: Kelletat and Schellmann, 2002; Whelan and Kelletat, 2002). Following these scientists, many new studies on the sedimentological and morphological evidence of the impact of tsunami were performed all around the Mediterranean basin from West in Algeria (Maouche et al., 2009) to East (Morhange et al., 2006). The growth of this kind of specific knowledge is testified by the numerous new publications produced in the last 10 years concerning all relative subjects of the field of tsunami and its sciences from the recognisation of out-of-place layers (i.e.: De Martini et al., 2003; Vött et al.2006) (Fig. 3), to the study of out-of-size deposits, like megaboulders (i.e.: Scicchitano et al., 2007; Vött et al., 2008; Scheffers et al., 2008) (Figg. 4, 5), mega-berms (i.e.: Mastronuzzi et al., 2007; Maouche et al., 2009) or mega washover fans (i.e.: Gravina et al., 2005; Vött et al., 2006) (figg. 6, 7), to the hydrodynamic modelling (i.e.: Pignatelli et al., 2009) and to the digital techniques aimed for risk assessment (Marsico et al., 2009). Scientific debates regarding the reliability of attributing out-of-place layers and out-of-size boulders and wash-overs to the tsunami s impact, rather than to an exceptional storm, is still open. Generally, along the coasts of the Mediterranean sea the scattering inland of megaboulders is attributed to tsunami. However, in some cases, there are evidences that boulders emplacement has been produced by extreme storms (i.e.: Mastronuzzi and Sansò, 2004; Mastronuzzi et al., 2006) as normally possible in the open ocean where wave climate is really different (Hansom et al., 2008 and references therein). The presence of open sea microphauna in the sediment cored far form the shoreline seems to be evidence of flooding generated by tsunami (i.e.: De Martini, 2003). Up to the present, the correlation between the absolute or relative - age of a tsunami s supposed sediment, and a strong earthquakes known by chronicles, is considered the best witness of a tsunami s impact. On the other hand, some particular features of the Mediterranean coasts facilitate this kind of researches. The wide and semi- continuous presence in the time of human settlements permits the possibility for the presence of some chronological records - like archaeological/historical findings and chronicles helping in the age determination of accumulated sediments and shaped landforms. The wave climate of the Mediterranean sea is well known and never characterised by gigantic waves like those generated by tropical or high latitude storms. Due to the limited fetch and wind speed, also in the presence of meteorological events such as tropical cyclones (i.e.: Lionello et al., 2006 and references therein), waves don t reach the periods and the height of those characteristic of the oceans. Their impact on the coast is lower in energy. As a consequence, it is easier to individualize landforms or sediments whose size and position respect the limit of inland penetration of the storm waves. At last, the micro- 3

4 The Egyptian Journal Of Environmental Change tidal features of the biggest part of the Mediterranean basin allows a good evaluation of the upper limit of flooding. If a limit exists in the study of tsunami s hydrodynamics in this basin, it is connected to the extreme indentation of its coastline. Locally, it could have had the effect of augmenting the height of a storm-generated impacting wave and the inwardness limit of its flooding, which, in the case of a very flat coast, could induce a shaping of the landscape at a distance compatible to a tsunami (i.e.: Mastronuzzi et al., 2006). Discussion: Till now about three hundred events have been recognised in the Mediterranean basin by modern research techniques within the framework of geophysic, sedimentological, morphological, biological, archaeological and historical investigations (Fig. 8). Together they allow the risk to be assessed. In fact, these researches tend to define the recurrence period although only from statistical point of view - and the intensity of tsunami as well as the structures responsible for their genesis. The collected data are extremely important even if in several cases they do not allow the tsunami run-up and direction to be defined. However, the available data-set highlight the fact that the occurrence of tsunami is not negligible. Furthermore, they represent the starting point for the assessment of risk linked to these phenomena. All the obtained information arranged in a GIS devoted to the Coastal Area Use Capability definition are of fundamental importance for the management of coastal areas according to the concept of the Integrated Coastal Zone Management and for the planners of civil protection procedures (i.e.: Papathoma et al., 2003; Dominey-Howes and Papathoma, 2007). The use of hydrodynamic equations and/or of mathematical models (i.e.: Nott, 2003; Hills & Mader, 1997; Goto et al, 2007) in relation to the coastal morphological features, allows the modelling of the maximum flooding and of the risk expected (p.e.: Mastronuzzi et al., 2006; Pignatelli et al., 2009). As shown in the previous pages, the new morphological data are related to tsunami that hit the Mediterranean coasts in the last four millennia. Unluckily, the available data are generally still incomplete. Sedimentological data derive by the study of sediment cored in wetlands and deltas, or in deep sea bottom in which the natural morphodynamic processes permit the registration of a long series of paroxysmal events, generally represented by out of places layer entrapped in normal sediments. The scientific discussions about the possibility to differentiate without doubts the sediments deposited by tsunami from those accumulated by exceptional storms is still open in spite of a lot of studies performed all along the world s coasts (i.e.: Bridge, 2008 and references therein). The study of the sediments accumulated by recent tsunami occurred in the Far-East permitted us to improve our knowledge (i.e.: Moore et al., 2006; Richmond et al., 2007). However, every coastal area has its own particular dynamics, susceptibility and sensitivity (i.e.: Paris et al., 2007; 2008; Goto et al., 2007). It is difficult or fraudulent to affirm that two waves should have absolutely the same effects. Along rocky coasts, however, the normally active coastal processes karst solution, abrasion, erosion, cliff shaping - reduce the time of morphological persistence. In this sense, the available data refers to a span of time equal to a few centuries, at a time, since recent tsunamis or storms - could have modified or erased the effects of the older ones (i.e.: Mastronuzzi e Sansò, 2004; Mastronuzzi et al., 2006). Considering that the main aim is to define the tsunami risk, researchers must concentrate their efforts on the definition of two parameters: ì the tsunami hazard; ìì the tsunami vulnerability. The first one expresses the possibility that a tsunami might occur in an area during a span of time whose definition depends on the frequency study of past events. The second indicates the damages produced by a tsumani s impact on an area. It depends on the energy stored in the impacting tsunami which can be strongly influenced by its genesis and by local morphology. The morphology of the sea bottom is a factor of primary importance in this process since it can cause the convergence or divergence of wave rays because of refraction, inducing very different effects on the coast. Vulnerability depends also on the value directly exposed to the events: demographic distribution, social and economic structure, type of settlements. Social and political organization can increase or reduce the damage, influencing the risk. Another feature that augments the tsunami risk in the Mediterranean basin is the extremely short distance between tsunami-genic areas and the exposed coast, which obviously reduces or cancels the alarm time. From the occurrence of the tsunami-genic event, to the impact of the waves on the coast, the time could be less than an hour. An early warning system, if well organised and publicised to the coastal inhabitants which needs high levels of social organisation - can reduce the loss of the human life. Nonetheless it cannot, reduce the damage on human economic structures. Starting from ICZM as a concept of prevention, coastal planning is the only instrument capable of mitigating the risk. As experienced by the recent tsunami in the far East and clearly indicated for European coastal area by Dawson et al. (2004), it has been shown that according to the particular features of the Mediterranean basin, it cannot be considered out of tsunami risk. Its coasts need to be studied to improve the knowledge of the past tsunami events. Collected data 4

5 must be integrated in a GIS devoted to assess the tsunami risk all along the European, African and Asian coasts. In particular, field researches must increase in volume and improve in targeting to meet the following objectives: 1 - Hazard assessment: 1.a - Individuation of potential generative areas; 1.b - reconstruction of historical sequence; 1.c - reconstruction of frequency; 2 - Vulnerability assessment 2.a - Determination of emerged and submerged morphological features of Mediterranean coasts; 2.b - analysis of major effects; 2.c - reconstruction of the hydrodynamic features of impacting waves; 2.d - realisation of flooding maps. The availability of another level of information concerning the value exposed to the impact, permits the final assessment of the coastal risk using GIS in which mathematic relations and algorithm between different levels have been developed and adopted Conclusion The field surveys of the coastal landscape all around the Mediterranean coasts should allow the recognition of paleo-tsunami deposits and landforms, the evaluation of tsunami frequency, intensity and propagation direction suggesting the tsunamogenic area. On the other hand, a direct survey of coastal areas and the use of hydrodynamic equations implemented by data derived by digital surveys (terrestrial laser scanner or LIDAR techniques) and by the remote sensing, altogether, should permit a mathematical and geophysical model, which, in turn, should be able to evaluate the possible future flooding of the next tsunami. This data set will allow coastal hazard, vulnerability and value to be defined and tsunami risk maps for the entire coastal area of the Mediterranean basin to be realized. The long list of recent paroxysmal events has been recently elongated by the recent tragedy of the earthquake that destroyed Haiti. It was known that this area is one of the more exposed to the probability that a strong earthquake could occur; nevertheless no action were in progress to minimize the possible effect of future events. The awareness that an increase in population density translates into an increase of risk, must be accepted by planners and governments. Tragedy can hit rich and poor regions without discrimination or regard to politics, religion or colour of skin. The task of the tsunami scientists community should be not only to improve this particular knowledge but, mainly, to promote the multidisciplinary approach to these phenomena, which despite their different genesis always exerts massive destruction and devastation whenever it occurs. It is necessary to give to governments a practical, experienced and working instruments that permit them to defend human life against the tsunami impact: This is all the more important as the scientific community, the local and national administrations and the potentially affected coastal population must not be unprepared for the next event (Mastronuzzi, Brückner, Sansò, Vött, 2010). Aknowledgements I would like to thank Prof. Dr. Magdy Torab and his fantastic team for the organisation of SIWA 2009 and for the received invitation to attend it. Moreover, I thank my team, C.Pignatelli, A. Piscitelli, M.Milella, A. Marsico and L.Pennetta for the continuous collaboration that permitted me to write the exposed considerations. This paper collects part of the results of the activity financed by the S1 2007/09 Project from INGV Istituto Nazionale di Geofisica e Vulcanologia DPC Dipartimento Protezione Civile (Project Leaders: S. Barba, C. Doglioni; Resp UOL Bari: Prof. G. Mastronuzzi) and by MIUR-UNIBA Research Project It is an Italian contribution to IGCP Project n 495 Quaternary Land- Ocean Interactions: Driving Mechanisms and Coastal Responses. (Project Leaders: Dr. A. Long, Univ. of Durham, UK, and Dr. S. Islam, Univ. of Chittangong, Bangladesh). Bibliography Ambraseys N.N. (1960). The seismic sea wave of July 9, 1956, in the Greek Archipelago. Journal of Geophysical Research, 65(4), Bartel P., Kelletat D. (2003). Erster Nachweis holozäner Tsunamis im Westlichen Mittelmeergebiet (Mallorca, Spanien) mit einem Vergleich von Tsunamiund Sturmwellenwirkung auf Festgesteinsküsten. Ber. Forsch. Technol.-Center Kiel Büsum 28, Bridge J.S. (2008). Discussion of articles in Sedimentary features of tsunami deposits Sedimentary Geology 211, 94. Bryant E.A., Young R. W., Price D. M. (1996). Tsunami as a major control on coastal evolution, SouthEastern Australia. Journal of Coastal Research, 12, Bryant E.A. (2001). Tsunami. The Underrated Hazard. Cambridge University Press, Cambridge, UK, 320 pp. Bruins H.J., MacGillivray J.A., Synolakis C.E., Benjamini C., Keller J., Kisch H.J., Klugel A., Van der Plicht J. (2008). Geoarchaeological tsunami deposits at Palaikastro (Crete) and the Late Minoan IA eruption of 5

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8 The Egyptian Journal Of Environmental Change coast of South-Eastern Sicily (Italy). Marine Geology, 238(1-4), Soloviev S.L., Solovieva O.N., Go C.N., Kim K.S., Shchetnikov N.A. (2000). Tsunamis in the Mediterranean Sea 2000 B.C A.D.. Advances in Natural and Technological Hazards Research, Kluwer Academic Publisher, 242. Tinti S., Armigliato A. (2003). The use of scenarios to evaluate tsunami impact in South Italy. Marine Geology, 199(3-4), Tinti S., Maramai A., Graziani L. (2007). The Italian Tsunami catalogue (ITC), Version 2. UNESCO (2002). Tsunami Early Warning and Mitigation System in the North Eastern Atlantic, the Mediterranean and Connected Seas. NEAMTWS, Implementation Plan. Version 3.4, Intergovernmental Oceanographic Commission, Technical Series, 73, 46 pp. USGS (2008). Vött A., Brückner H., May M., Lang F., Herd R., Brockmüller S. (2008). Strong tsunami impact on the Bay of Aghios Nikolaos and its environs (NW Greece) during Classical-Hellenistic times. Quaternary International, 181, Vött A., May M., Brückner H., Brockmüller S. (2006). Sedimentary evidence of late Holocene tsunami events near Lefkada Island (NW Greece). Zeitschrift für Geomorphologie N.F. Suppl., 146, Whelan F., Kelletat D. (2002). Geomorphic evidence and relative and absolute dating results for tsunami events on Cyprus. Science of Tsunami Hazards, 20(1),

9 Captions Fig. 1 - Map of seismicity with M 4.5 for the period ; black line is a sketch of plate boundaries (modified from Pondrelli et al., 2002) Fig. 2 Deeper areas (more than 2000m) in the Mediterranean Sea and main volcanic districts; it is evident the short extension of the continental shelf between high mountain chains and shelf break, as well as the gradient of the continental slope. 1- Sardinia sea (max c.a 3000 m); 2 Tyrrhenian sea (max c.a 3500 m); 3 Ionian sea (max c.a 5000 m); 4 Eastern basin (max c.a 4000 m); A Tyrrhenian district; B - Sicily Channel district; C Aegean district; a Mount Etna volcano; b Mount Somma Vesuvio volcano; c Campi Flegrei volcano (chart n. 360 INT 300 Istituto Idrografico della Marina, Genova, Italy) 9

10 The Egyptian Journal Of Environmental Change Fig. 3 Sandy-pebble levels sandwiched in silt sediments in corers sampled near Lefkada sound, Ionian Islands, Greece. Fig. 4 Boulders accumulated by the Lisboa tsunami in 1755 near Cabo Trafalgar, Spain (from Prof. E. Pranzini, University of Florence, Italy). 10

11 Fig. 5 Terrestrial laser scanner survey of the boulder field accumulated by the impact of tsunami(s) near Siracusa, Eastern Sicily, Italy. Fig. 6 Cauto washover fan in the Lesina Lake, Northern Apulia, Italy, produced by the 493 a.d. tsunami (from Prof. M. Caldara, university of Bari, Italy). Fig. 7 The Gyrapetra tsunami chevron (about/post a.d. tsunami) (on the left) and the town of Lefkada (on the right), Ionian Islands, Greece. 11

12 The Egyptian Journal Of Environmental Change Fig. 8 - Ubication of main sedimentological and geomorphological evidence of Holocene tsunami impact along Mediterranean coasts (modified from Scheffers et al., 2008). 12