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(General News)
Tsunami hazard in the western Mediterranean

Tsunami risk in western Mediterranean is determined by the exposure of Spanish, Moroccan and Algerian coasts to two different seismic areas - the Alboran sea and the Atlas belt in north-western Algeria - by the high population density – mostly in Spain and Algeria - and by the importance of coastal tourism infrastructure in Spain.

A recent article “tsunami hazard at the western Mediterranean Spanish coast from seismic sources” published on Natural Earth Science, analyses the potential tsunami sources close to the Iberian Peninsula and identifies the areas where the impact of a tsunami would be greater. The tsunami threat over the Spanish Mediterranean coast and the Balearic Islands was estimated reviewing 22 possible tsunami sources, compiling maximum wave elevation maps and calculating tsunami travel times through numerical modelling.

Regional maximum wave elevation maps for the worst tsunamigenic source of the Alboran Sea and for the northern Algerian sources for the south-eastern Iberian Peninsula. The colour shading varies with the maximum wave elevation as shown in the colour scale.

In general – the article reports - the northern Algerian sources resulted to pose a greater risk to the Spanish coast than the Alboran Sea sources. Tsunamis generated in northern Algeria, would affect the provinces of Almeria and Alicante, and especially the islands of Ibiza and Formentera with probable severe damage. The province of Almeria is at a high risk of being affected by a tsunami because it can be reached by virtually all sources of the Alboran Sea and the North West of Algeria.

With reference to a possible Mediterranean Fukushima, the first conclusion that we may draw from the reserach is that the Vandellòs Nuclear Power Plant situated very close to the sea near Tarragona lies in a quite low tsunami risk area. Although for properly evaluating the tsunami risk along the coast of Catalonia, also the scenario of the 1373 earthquake in the Central Pyrenees-Catalonia region along with its associated tsunami in Barcelona should be evaluated. 
Saturday, 12 May 2012
(General News)
Tsunami risk in France

A wait and see policy is unacceptable considering the seriousness of the tsunami threat says the study on the vulnerability of the French Mediterranean coasts to tsunamis recently presented to the French Senat in order to highlight French coasts at high tsunami risk and call for stronger commitment to action.

The report classifies the most dangerous tsunami-generating zones for French Mediterranean coasts - 59 seismic zones and 20 underwater landslide zones on the French continental shelf – simulates extreme but possible events that could generate tsunamis and identifies the most vulnerable coastal areas.

Six scenarios where chosen as having the greatest tsunami-generating potential. Three earthquake scenarios:

A 6.8 magnitude earthquake with an epicentre situated some fifty kilometres off the coast of the French Riviera in the Liguria Sea. A 6.7 magnitude earthquake centred in the Gulf of Lion, one hundred kilometres from Perpignan. A 7.8 magnitude earthquake situated 25 km North of the Algerian coast.

And three underwater landslide scenarios:

A landslide located some twenty kilometres off the north-western coast of Corsica. A landslide located some fifty kilometres off the coast of Perpignan, in the area of the Lacaze-Hérault underwater canyon. A landslide estimated at nearly twenty-five kilometres South-East of Nice.

Simulations of these 6 scenarios indicated:

The synthesis of these 6 scenarios resulted in a first map of the French Mediterranean coast displaying the estimated level of vulnerability to tsunami.

Saturday, 12 May 2012
(General News)
Tsunami hazard in the eastern Mediterranean

Nearly a third of the large historical earthquakes along the Dead Sea Transform (DST) fault system have produced submarine landslides and consequently tsunamis which devastated the eastern Mediterranean coast – highlights the research project “Tsunami Hazard evaluation of the eastern Mediterranean:Historical Analysis and Selected Modeling” carried out by the Earth and Planetary Sciences Department of the Santa Cruz University in California. Therefore it is important to assess the likelihood of a future earthquake from that source.

Examination of the seismic history of the DST and estimates of the strength accumulated in the DST indicate “3-5 m of potential slip which is most likely to be released in a large earthquake (M>7). Thus there should be great concern in Syria, Lebanon and in Israel, not only for the possible occurrence of a near-future large earthquake, but also for the significant likelihood that the earthquake will be accompanied by a tsunami produced by an offshore slump within minutes of the mainshock”.

The eastern Mediterranean – including the coasts of Egypt along the Nile Delta and Sinai, Israel, Lebanon, Syria and the Bay of Iskendrun (Alexandretta) in southern Turkey - stands out for its rather long and detailed earthquake and tsunami historiography. Researchers prepared a detailed compilation of historical reports of tsunamis and earthquakes for this area, tried to correlate tsunamis with earthquakes and to identify possible future tsunami triggering events.

Researchers concluded that, of the 20 reliably reported tsunamis that struck the Levant coast, 10 were triggered by earthquakes that originated along the Dead Sea Transform (DST) fault system - an on-shore seismic zone. Of the other ten tsunamis, eight were associated with sources in the Cypriot and the Hellenic Arcs, and Italy, and two have unknown origin.

Observations allowed researchers to recognize and model two principal mechanisms for the generation of tsunamis that will likely affect this region in the future: submarine landslides produced by on-land earthquake (DST system), and earthquakes originating beneath the sea on nearby seismic zones (Hellenic Arc, Cypriot Arc). Two earthquakes (Cypriot Arc and Beirut Thrust) and one “on land earthquake – submarine landslide’ scenarios were simulated and allowed to conclude that the landslide related tsunamis would produce average waves of 4-6 m, whereas tsunamis directly produced by earthquakes would be much smaller, 1-3 m.

Saturday, 12 May 2012
(General News)
The West Hellenic Arc and the devastating earthquake of AD 365

Many tsunamis documented in the Mediterranean region are caused by strong earthquakes occurring in the area offshore Crete Island, one of the most active seismic areas in the Euro-Mediterranean region known as the West Hellenic Arc and Trench (WHA-T) system. The largest tsunami event ever occurred in the Mediterranean Sea, which devastated Alexandria in Egypt and caused important damages also on the Sicilian and Croatian coasts, originated in AD 365 from an earthquake in West Crete. When is next strong tsunami originating from this source due to happen?

WHA-T starts from Zakynthos Island to the North and ends to the eastern part of Crete. Localities reported on the map were associated with tsunami inundations.

A research by the Institute of Geodynamics, National Observatory of Athens on ”Tsunami hazard in the eastern Mediterranean Sea: strong earthquakes and tsunamis in the West Hellenic Arc and trench system” collected data on earthquake and tsunami occurred in the WHA-T area, investigated the average recurrence of strong tsunamis and performed probabilistic tsunami hazard assessment.

Statistical analysis indicated that tsunamis of low or moderate intensity recur every few years, which means rather frequently. Strong tsunamis, however, are rare. The average recurrence of devastating tsunamis like the one of 365 AD resulted of the order of 1277 years.

In reality – researchers say - the last tsunami event of this intensity occurred in the West Hellenic Arc in 365 AD. The actual time elapsed from the last event is equal to 1643 years. Then, the frequency of occurrence of large-size tsunamis seems significantly overestimated by the intensity-frequency statistics and thus not so reliable. The research concludes that the number of tsunami events considered in the statistical analysis is very small, thus making the statistics extremely sensitive, particularly for large-size events which are of very low frequency. Therefore large tsunamis result to be more and more unpredictable.
Saturday, 12 May 2012
(General News)
Tsunami hazard assessment in the northern Aegean sea

The South Aegean Sea saw, in 1630 B.C, the most significant tsunami ever seen by mankind because of its very large size and its possible impact on Late Bronze Age (LBA) civilizations, such as the Minoan civilization on the Island of Crete. It was caused by the eruption and collapse of the Thera volcano on the island of Santorini.

Considering the historical tsunami records of the Turkish and Greek coastlines, there is a high potential for the generation of large tsunamis around the Aegean Sea – according to the research “Tsunami hazard assessment in the northern Aegean sea” by the Institute of Applied Geosciences of the Berlin University of Technology. Researchers identified and mapped the Aegean coastal areas of Turkey and Greece that may be prone to flooding if catastrophic tsunami events occur. Satellite images, Digital Elevation Model (DEM) data and a GIS spatial database were used to point out sensitive zones which require proper tsunami emergency planning.

The research also assessed  the impact and spatial destructiveness of a potential tsunami on the Turkish and Greek Aegean coasts against various parameters: a) width of the continental shelf; b) shore bathymetry; c) energy focusing effects; d) coastal topography; e) tsunami terminal velocity and run-up height; f) type of land use in the affected coast - including density of vegetation and buildings.

The most recent large tsunami in the Mediterranean occurred in the Cyclades islands in the South Aegean Sea on 9 July 1956 after a M=7.4 earthquake. The tsunami-generating source was near Santorini. A submarine landslide was probably involved in the tsunami generation mechanism. Extensive destruction was reported in port facilities in the area, small and large vessels, cultivated land and property, and at least four people drowned.

Another large tsunami was generated in the Aegean sea in September 1650 during the eruption of Columbo, a submarine volcano on the North-East of Santorini Island. The volcanic activity began on 26 September. During a pause of activity, sea swell encircled the island and the wave inundated the eastern coast and swept away churches, enclosures, boats, trees and agricultural land. On the eastern and western coast of Patmos Island and on Ios Island, tsunami runup heights of 30 m, 50 m and 16 m respectively, were reported. Ships and fishing boats moored at Heraklion, northern Crete, were violently swept offshore, while vessels were crushed when the wave struck the city walls. The volcanic and seismic calm before the tsunami struck indicates that it was generated by submarine landslides or collapse of the volcanic cone rather than by a strong earthquake or volcanic explosion.

The study by the Berlin University of Technology was also intended to constitute the basis for a future tsunami alert system and to provide local governments with recommendations on disaster risk reduction activities.

Saturday, 12 May 2012
(General News)
Tsunami hazard in the central Mediterranean

Central Mediterranean is exposed to three potential earthquake-related tsunami sources – indicates the article “Earthquake-generated tsunamis in the Mediterranean Sea: Scenarios of potential threats to southern Italy” published in 2008 on the Journal of Geophysical Research. These are: the Tell system in the Algeria-Tunisia offshore capable of generating earthquakes up to magnitude 7.0, the southern Tyrrhenian Sea thrust system capable of triggering earthquakes of magnitude 7.0 and higher, and the Hellenic Arc proven to be capable of generating frequent and occasionally very large earthquakes of magnitude greater than 8.0.

Tectonic map of the Mediterranean basin. Yellow dots indicate seismic events. Color-shaded ribbons highlight the main areas capable of generating tsunamis that pose significant hazard to Mediterranean shore-facing settlements.

For each of the investigated tsunami source zones, researchers simulated possible earthquake-related scenarios leading to tsunami and prepared maps of the maximum wave height, and of tsunami travel time.

Research results indicate that the greatest threat to central Mediterranean European and African coasts would come from earthquakes along the Hellenic Arc source zone. Waves with average maximum height of 1 m or higher are expected along most of southern and eastern Sicily (from Trapani to Messina) and the South-Eastern coasts of the southern Italy peninsula (from Reggio Calabria to Cantanzaro, Taranto, Brindisi and almost Bari). Travel time for waves reaching southern Italy and the south-eastern coasts of Sicily would be between 60-70 min.

Earthquakes along the southern Tyrrhenian source zone could produce low energy tsunamis. They estimated the average maximum wave height is around 0.2 m. Waves of 0.5 m and higher would affect only few localities around the northern coast of Sicily such as Palermo, Trapani, and Milazzo. The average wave travel times to these locations would vary between 5-10 min.

The Algeria-Tunisia offshore source zone can generate tsunamis that would have a great impact on the coasts of Sardinia. The western coast of Sicily would be affected by maximum wave heights in the order of 0.5 m. Wave travel times would be in the order of 40-50 min.

Algeria-Tunisia offshore Source Zone

Southern Tyrrhenian Source Zone

Hellenic Arc Source Zone

Saturday, 12 May 2012
(General News)
Potential consequences of tsunami on an industrial plant processing hazardous materials

Limiting industrial development along tsunami-prone coasts in the Mediterranean is very difficult to impose –highlights a European Commission Joint Research Centre report on the Potential consequences of tsunami impact on an industrial facility on the north eastern coast of Sicily - as many hazardous areas in the Mediterranean are already heavily industrialized and it may be decided to accept certain risks from infrequently occurring hazards as long as they do not outweigh the benefits derived from an industrial activity.

The publication which was produced under the EU –funded Tsunami Risk and Strategies for the European Region (TRANSFER) analyzed two credible tsunami scenarios - an earthquake along the Capo Vaticano fault in Calabria, source of an earthquake and tsunami on 8 September 1905 which devastated many towns and villages and resulted in more than 500 victims, and a land-slide at Stromboli. The study assesses the potential damage to an oil refinery and the hazardous-materials releases resulting from the tsunami impacts.

Although the conclusions indicate that in the two considered scenarios, the consequences of potential hazardous materials releases, fires or explosions triggered by the tsunamis are likely to be small, the document make recommendations for preventive and preparedness measures that can be taken to reduce the risk of tsunami-triggered chemical accidents and to mitigate their consequences if they do occur.

Land-use planning is the obvious way to avoid the impact of a tsunami, and limiting industrial development along tsunami-prone coasts minimises the hazard associated with the inundation – the research says. Land-use restrictions are, however, difficult to impose to already industrialized areas. In most cases supplementary measures are required to protect hazardous facilities. This means that static and hydrodynamic wave action on structures needs to be considered during the design and operation of an industrial plant and tsunami protection measures such as offshore breakwalls or onshore barriers are to be installed to reducing the tsunami force. These barriers could also prevent collision of debris with tanks or equipment containing hazardous materials and avoid the releases of toxic, flammable or explosive substances.

Saturday, 12 May 2012
(General News)
Should we fear a Mediterranean Fukushima?

Are devastating tsunamis possible in the Mediterranean?

Although less frequent than those in the Pacific or Indian oceans, tsunamis in the Mediterranean Sea have caused extensive damage and loss of life. This is due to the significant frequency of tsunami events – according to the European Environment Agency 200 tsunamis were recorded over the last 500 years around the Mediterranean and the University of Bologna indicated that on average, in the last four centuries Italy has seen 15 tsunamis every 100 years - to the considerable population density along the Mediterranean coasts - around 150 million people concentrated on the 46,000 kms of coastline, with 110 million of them living in cities and some 200 million tourists arriving every year - and to the limited consideration of the tsunami risk in land use planning policies.

Tsunamis can be triggered by three types of geologic events causing the displacement of significant volumes of water: earthquakes, large landslides and volcanic activities.

Submarine earthquakes can abruptly deform the sea floor displacing huge quantities of water. Earthquakes can also trigger the destabilisation of large amounts of sediments deposited on coastal or submarine slopes causing giant landslides which displace large amounts of water and generate a tsunami. These landslides may take place right after the earthquake or may be delayed for days, weeks, or months.

Tsunamis are characterized by large wavelengths and velocities of approximately 700km/h in deep waters where they generate small waves (0.3 meters) and therefore are very difficult to detect. The wavelength causes a slowing down of these waves in shallower waters to around 100km/h. When tsunamis reach the shoreline they build up wave heights up to 30m and more.

How a seaquake wave behaves. As the depth of the sea decreases, so the speed and length of the wave decrease, while the height of the wave increases. (Credit: UNESCO - International Tsunami Information Centre)

In the Mediterranean, due to short travel times and thus very short early warning possibilities tsunami waves can cause severe damages. Most of the reported Mediterranean tsunamis occurred in the most seismic and volcanically active regions like the Aegean, Ionian and Tyrrhenian Seas, the Sea of Marmara and subsequently along the Algerian margin and Cyprus arc, or off-delta areas.

It is impossible to forecast tsunamis; it is only possible to outline potential impact areas associated with geologically active - earthquake and volcano - zones. However not every earthquake, volcanic eruption or submarine landslides necessarily trigger tsunamis.

To identify which Mediterranean coastal zones are particularly exposed to tsunami hazards, PPRD South collected and reviewed the results of various researches, scientific studies, tsunami simulations and tsunami risk assessment in the Mediterranean. Then, on the basis of existing risk maps and studies, the Programme tried to estimate the risks of nuclear or chemical accidents triggered by a tsunami. Finally, PPRD South outlined the existing legal provisions and recommendations for preventing tsunami-chemical accident domino effects in the Mediterranean.

Index of the articles

Impressing video simulations show potential tsunamis propagating across the Mediterranean basin Recent Mediterranean Tsunamis Tsunami hazard in the western Mediterranean Tsunami risk in France Tsunami hazard in the eastern Mediterranean The West Hellenic Arc and the devastating earthquake of AD 365 Tsunami hazard in the northern Aegean sea Tsunami hazard in central Mediterranean Is there a risk of tsunami-nuclear accident domino effect in the Mediterranean? Is there a risk of tsunami-chemical accident domino effect in the Mediterranean? Potential consequences of tsunami on an industrial plant processing hazardous materials The provision of the Seveso II Directive for preventing tsunami-chemical accident domino effects It is rare that just one cause leads to a chemical accident, usually there is a combination of factors - UNEP document says
Thursday, 12 May 2011
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