Review articleHistorical and pre-historical tsunamis in the Mediterranean and its connected seas: Geological signatures, generation mechanisms and coastal impacts
Introduction
A tsunami is a series of sea waves with long-period and long wave-length generated by an abrupt deformation of the seafloor or by other sudden disturbance of the water. The energy of vertical movement of such a disturbance is transferred to the water mass and causes a sea level change at the source region. Underwater and/or coastal earthquakes, volcanic eruptions, as well as landslide processes are sources that can generate a tsunami. Large meteorites that may impact the ocean should not be ruled out as possible agents of tsunami generation. Tsunami waves propagate outwards from the generating area in all directions, the main direction of energy propagation being controlled by the dimensions and orientation of the causative source. During its propagation in deep water the tsunami proceeds as a series of ordinary gravity waves with a speed depending on the water depth. In the near-shore domain, a large amount of energy is carried by both amplified water level and strong currents. Hence, tsunamis cause scouring, erosion, deposition, slope failures as well as damage or even destruction in coastal communities, marine structures and other facilities, cultivated land and natural environment.
Due to active geodynamic processes the seismicity in the Mediterranean region is high. The tsunami activity although being not so frequent threatens seriously the communities along the coastal zones of the Mediterranean basin (e.g. CIESM, 2011). Active tectonics of the Mediterranean and adjacent areas are predominantly driven by the present-day convergence between the African and Eurasian plates (e.g. Argus et al., 1989, DeMets et al., 2010). Subduction of oceanic crust and/or collision takes place along active orogenic belts, namely from west to east, the Gibraltar Arc, the Calabrian Arc, the Hellenic Arc and the Cyprus Arc. Ongoing motion along transform boundaries of adjacent plates, such as the Arabian plate and smaller crustal blocks, like the Anatolian “micro-plate”, add more complexity to the active Mediterranean geodynamics and the resulting geological processes (sea also in Mascle and Mascle, 2012) (Fig. 1).
Tsunami generation is dependent on several factors, including seismogenic faulting, volcanic activity, landslide processes and offshore sedimentation. Therefore, these elements are extensively reviewed for the Mediterranean area and connected seas with the aim to provide the geological and geodynamic framework within which the tsunami generation takes place (Fig. 1, Fig. 2).
In the Mediterranean region and connected seas, i.e., the Marmara Sea, Black Sea and SW Iberian Margin in the NE Atlantic Ocean, tsunami sources threaten all coastal zones. In fact, historical documentary sources together with geological evidence, e.g. paleotsunami sediment deposits and geomorphological features, archeological findings, as well as instrumental data and recent observations have provided a long record of tsunami events produced by submarine or coastal earthquakes, volcanic eruptions and landslides. A few of those events were basin-wide, others, however, were either regional or only local tsunamis. In this paper we do not examine the so-called meteotsunamis (e.g. Monserrat et al., 2006), that are tsunami-like sea waves attributed to atmospheric changes rather than to seismic and other geodynamic processes.
One of the cornerstones for building up an effective strategy aiming at the tsunami risk mitigation in the Mediterranean region is the knowledge of the past tsunami activity, the potential tsunami sources and generation mechanisms in the frame of the complex geodynamic setting of the region. However, for many historical events, including recent ones, the causative sources and generation mechanisms still remain unidentified. This calls for the need to better determine these sources, to improve our capabilities to discriminate between seismic and aseismic mechanisms, and to characterize tsunami sources. The relatively low number of tsunamis that are known so far creates serious difficulties in developing standard and low-uncertainty statistical and probabilistic approaches for the tsunami hazard estimation in the way it is applied in the probabilistic seismic hazard assessment. Therefore, the ongoing identification of paleotsunamis by means of onshore and offshore geological methods, e.g. sedimentary records, is of particular value to extend the historical data bases and tsunami time series.
In this review paper we focus into the geological, archeological, historical and instrumental records of tsunamis and their impact on coastal communities of the Mediterranean region. The tsunami record is interpreted in the frame of the complex geological and seismotectonic setting. We determine also the main tsunamigenic zones and their relative potential for tsunami generation, examine empirical criteria but also inputs from numerical modeling to discriminate between seismic and aseismic sources as well as between different types of generation mechanisms, identify significant gaps in our current knowledge, discuss consequences for the tsunami hazard assessment, and conclude with some important lines for future tsunami research in the region.
Section snippets
Geological and geodynamic setting of the Mediterranean region
The Mediterranean region is characterized by successive, connected Neogene fold- and thrust belts and associated foreland and backarc basins (Fig. 1). Over this area, Tethys oceanic lithosphere domains, originally present between Eurasia and African–Arabian plates, have been progressively subducted (e.g. Cavazza et al., 2004). The systems are typically characterized by arcuate, narrow compressional zones and extended basins with a distribution of relief and morphologies that roughly resemble
Historical and pre-historical records of tsunamis
A widely spread perception among the general public is that tsunamis are lacking in the Mediterranean Sea. This could be interpreted by the relatively low frequency of strong tsunami occurrence which disfavor maintenance of memory. However, examination of the instrumental, historical, archeological and geological records of tsunamis has shown that all basins of the Mediterranean and its connected seas have experienced such waves in the past (e.g. see review in Papadopoulos, 2009 and references
Geological signature of tsunamis
As in all natural events, especially if rare, a careful observation and analysis of past occurrences are the basis for understanding them and for developing models and scenarios to forecast future occurrences. Historical tsunami records are known to be a powerful tool for this scope, but in recent times it was more and more proven that geological records of past tsunamis are also a precious source of information to integrate and extend back in time historical records. Geological data can
Tsunami zonation
In the Mediterranean region a variety of tsunamigenic sources has been recognized which can be classified according to geographic distribution, tsunamigenic potential and generation mechanisms. In an earlier effort to determine the geography of historical tsunamis in Greece and surrounding regions, Papadopoulos and Chalkis (1984) were able to determine 10 coastal areas which are the most prone to experience tsunamis in the Aegean Sea, the Ionian Sea, the Marmara Sea and offshore Albania. Later
Summary and some implications
In the last century or so, strong tsunamis and their causative processes were documented in the Mediterranean Sea and its connected seas from tide-gauge and other instrumental records, eyewitness accounts and pictorial material. The investigation of tsunamis in the historical and pre-historical periods is supported by a variety of documentary sources, onshore and offshore geological signatures including geomorphological imprints, and in some instances by field observations in selected coastal
Acknowledgments
The National Observatory of Athens, the University of Bologna, the Istituto Nazionale di Geofisica e Vulcanologia (INGV), the Hellenic Center for Marine Research, the Middle East Technical University as well as the Universidad de Cantabria acknowledge co-funding from the EU-FP6 TRANSFER research project, 2006–2009, contract n. 037058. The National Observatory of Athens, the University of Bologna and the Universidad de Cantabria are co-funded by the DG ECHO of EU, project NEARTOWARN, 2012–2013,
References (333)
- et al.
Linear elastic fracture mechanics explains the past and present evolution of the Aegean
Earth and Planetary Science Letters
(2004) The 1755 Lisbon Tsunami; evaluation of the tsunami parameters
Journal of Geodynamics
(1998)Geotechnical characteristics and slope stability on the Ebro margin, Western Mediterranean
Marine Geology
(1990)- et al.
Large boulders along the south-eastern Ionian coast of Sicily: storm or tsunami deposits?
Marine Geology
(2010) - et al.
Geoarchaeological tsunami deposits at Palaikastro (Crete) and the Late Minoan IA eruption of Santorini
Journal of Archaeological Science
(2008) - et al.
Seismotectonics of the Ibero-Maghrebian region
Tectonophysics
(1995) - et al.
Adria, the African promontory, in Mesozoic Mediterranean paleogeography
Earth Science Reviews
(1979) - et al.
Morphologic resilience and depositional processes due to the rapid evolution of the submerged Sciara del Fuoco (Stromboli Island) after the December 2002 submarine slide and tsunami
Geomorphology
(2008) - et al.
New findings of Bronze Age homogenites in the Ionian Sea: geodynamic implications for the Mediterranean
Marine Geology
(1984) - et al.
Deep-sea tsunami deposits in the eastern Mediterranean: new evidence and depositional models
Sedimentary Geology
(1996)