Revision of the tsunami catalogue affecting Turkish coasts and surrounding regions

The coasts of Turkey have been hit by tsunamis in the past. The first national earthquake-tsunami catalogues were compiled in the early 1980s while the most up-to-date tsunami catalogues are mainly the products of recent European projects. The EU projects GITEC and GITEC-TWO (Genesis and Impact of Tsunamis on the European Coasts) and TRANSFER (Tsunami Risk ANd Strategies For the European Region) have added important contributions in establishing and developing unified criteria for tsunami parameterisation, standards for the quality of the data, the data format and the database general architecture. On the basis of these new aspects and based on recent marine geophysical data, tsunamigenic earthquakes, tsunami intensities and their reliability have been revised. The current version of the database contains 134 events, most of which have affected the Turkish coasts seriously during the last 3500 years. The reliability index of 76 events was “probable” and “definite”, so that they could be used for assessment of the risk along the Turkish coastal region and for implementation of prevention policies.


Introduction
Destructive tsunamis have impacted many coastal communities in all of the world's oceans and seas throughout human history.The Eastern Mediterranean, including the Aegean and Black Seas, is one of these regions where many ancient descriptions of sudden and catastrophic waves have been recorded.The active tectonics of this region are the result of interactions between the northward moving African and Arabian plates and the relatively stable Eurasian Plate since the Early Pliocene (Bozkurt, 2001).The long history of devastating earthquakes is characterized by three main unique Correspondence to: Y. Altinok (yaltinok@istanbul.edu.tr)structural elements: the North Anatolian Fault Zone (NAFZ) in the North, the East Anatolian Fault Zone (EAFZ) in the East, and the Aegean-Cyprean Arc in the southern Aegean Sea (Fig. 1).The Dead Sea Fault Zone (DSFZ) interacts with the tectonics of the Cyprean Arc and has also produced big earthquakes.
Reliable tsunami databases are of great importance for a wide range of tsunami-related studies including risk evaluation, hazard assessment, wave numerical modeling and public awareness.Some of the events affecting the Turkish coasts have been mentioned previously in the tsunami catalogues and databases compiled by earlier researches: e.g.Galanopoulos (1960), Ambraseys (1962), Antonopoulos (1979), Papadopoulos and Chalkis (1984) and Papazachos et al. (1986).The first Turkish catalogue of tsunamis, on the other hand, was compiled by Soysal et al. (1981).The consequences of such events, in view of increasing coastal urbanization, can be extremely serious.The Turkish coasts are about 8300-km-long with many territorial divisions found along the low-lying coasts where about one third of the population lives (Alpar, 2009).
In the present study all available catalogues, source documents and quantitative data obtained from recent marine geophysical data have been re-examined based on the guidelines defined in GITEC (Genesis and Impact of Tsunamis on the European Coasts) and TRANSFER (Tsunami Risk ANd Strategies For the European Region) projects.The sedimentary, chemical and age data obtained from recent core samples, which may represent candidate tsunami deposits, also provided a confirmation for the catalogue data.
Published by Copernicus Publications on behalf of the European Geosciences Union.
The earthquake was accompanied by tsunami waves seen mostly in Kition, Paphos, Salamis (54).
The harbour of Paphos slid down into sea (54); the tsunami waves were observed on the SW, S and SE shores of Cyprus and in the Bay of Famagusta (54).
In the year 544/545, the sea advanced in the territories of Odessa and Thrace, with a maximum inundation of 6 km on Thrace.Many were drowned in Odessa and Balchik (24).Many people were drowned by the waves along the Bosphorus shores ( 19).The accompanying earthquake may have been related to the one in Balcik-Bulgaria in 544/545 (8,9).
Massive waves were created by the earthquake and a huge fish (porphyrion) was thrown on shore (9,19).
The earthquake set up waves in the sea between the provinces of Thrace from Bythinia that reached into Istanbul (9,15,18).
A big piece of mountain breaks off and tumbles into the sea at C ¸ınarlı, Marmara Island, creating huge waves that hit the shore and swallow up the area (6,25,45).
The waves beat the city walls of Istanbul, seriously damaging many of the dwellings therein (9); huge waves not necessarily of a tsunami but a by product of the storm in Istanbul (54); a large sea wave covered and destroyed the coastal walls of Byzantium up to their foundation (45).
Huge waves flooded the shore of Thrace at a great distance, for a mile in some place (54).The sea rushed on land and plains, reaching up to 2000 m.In some places it took off some ships at harbour and crushed them (9,11,36,41,45); the large sea wave caused great destructions in Istanbul and in several other cities of Thrace in the Marmara (45); the sea receded, leaving mud and dead fish on land behind (9,25,36,67); tsunami waves reached the Strait of Istanbul and affected Beylerbeyi (9,36).
The shipyard in Izmit collapsed and waves flooded the dockyard (9,14,38); In Istanbul tsunami waves overtopped the walls in Galata and flooded the districts of Yenikapı and Aksaray (2,9,38); depending on recent arkeological findings in Yenikapı the inundation distance in this region can be estimated as 500-600 m along the paleo-Lycus (Bayrampas ¸a) stream valley.Tremors in the sea, causing the sea to swell and engulf the galleys harboured therein (14).Tsunami waves at the coastal area between Sinop and Samsun due to the Amasya and C ¸orum earthquake (2,8,34).The waves inundated about 1.6 km landward drowning a few thousand people living in the towns and villages (14).
Tsunami waves were recognized in the coastal village Bes ¸iktas ¸-Istanbul and the inner parts of the Straits of Istanbul; uninhabited islets in the Sea of Marmara were said to have half-sunk into the sea.Izmit coasts were badly damaged by sea waves (9,14,15); strong waves were particularly effective along the Bosphorus and in the Gulf of Mudanya (14).
Rather strong tsunami at Izmir (28); the sea rose, though no slightest breath of wind was to be felt before (54).
A large tsunami wave was observed (54); the sea rushed on the land and some people were lost in Chios (5,45).
Houses on the seashore and the cellar of a brewery at Kuruc ¸es ¸me, Bosphorus, were flooded by seawater, a consequence of local land subsidence (54).
In the Gulf of Izmit the shock set up a small tsunami which propagated into the west of the Gulf where the earthquake was also felt on board of ships, causing some concern (15).A rather strong tsunami was supposedly observed in Izmit (54).
On 5 April at 03:10 a.m. a strong vertical shock demolished some city walls.The sea became wavy right away and a mass of smoke was seen rising from sea surface.
The aftershocks created waves on the sea surface (5).
113.  (2,11,17,22,28,29,38,39,41,44,55) A high water occurred within the Bosphorus, demolishing a yacht named "Mahrussa" anchored at Pas ¸abahc ¸e (4); the sea receded along the Tekirdag shores (12).The ships anchored offshore Yes ¸ilköy were aground with the recede of the sea after the earthquake and then the sea lifted the fishery boats up to a height of 2.7 m (4).Fatsa; extraordinary sea disturbances were seen at the time of the Ms = 8.0 Erzincan earthquake (2,8,33,46,65).The sea receded in Fatsa about 50 m and then advanced 20 m.In Ünye the sea receded about 100 m causing some sunken rocks to appear for the first time.The sea also receded in Ordu by about 15 m and then returned back.The initial rise of the sea level was recorded at 6 tidal stations (Tuapse, Novorossiyk, Kerch, Feodosia, Yalta, and Sevastopol) on the northern coast of the Black Sea (32).

Results and discussion
Throughout the course of time, Turkish coasts have been affected by catastrophic tsunamis (Soysal et al., 1981;Soysal, 1985;Kuran and Yalc ¸ıner, 1993;Altinok and Ersoy, 2000).In this paper, all of the known tsunami events were critically examined and re-evaluated in terms of their causes and source codes.The codes include tsunami intensities (Sieberg-Ambraseys and Papadopoulos-Imamura scales), water level rise, run-up and reliability.The obtained current version of the database contains the data on 134 tsunamigenic events over a span of 3500 years.At least 76 of the events listed in the revised database above were found to be reliable ones, with a reliability of 3 and 4. Most of the events took place in the Aegean Sea (51), Eastern Mediterranean (41) and in the Sea of Marmara (35).The majority were caused by strong earthquakes mainly occurring in the sea and in most of the cases, the affected coastal areas were less than 200 km far from the tsunami source.et al., 2001) and Turkish Navy Department SHOD.The bathymetric data in the shelf is from navigation charts, so data grid is relatively scarce.Gridding and mapping of the data were obtained by means of Generic Mapping Tools (Wessel and Smith, 1998).Active fault traces are based on previous studies by Le Pichon et al. (2001) andYaltırak (2002).Slides: GC (Ganos complex), MI (Marmara Island) and TC (Tuzla complex).
The recurrence interval of the Black Sea tsunamis is on the order of 10 to 120 years and their run-ups measured by tide gauges are not very high (Ranguelov, 1996b;<1 m;Yalc ¸ıner et al., 2004;Dotsenko and Eremeev, 2008).Although the Black Sea tsunamis are mostly regional and affect the nearest coast, our database shows that the Black Sea may be subject to some destructive tsunamis with large run-ups and inundation distances (e.g.1598 event).The quiescense period may be followed by bigger effects and the fact that there are no reported big tsunamis in the near past does not show that this phonemenon is not dangerous for the coastal communities (Ranguelov and Gospodinov, 1995).The mean repeatability of the tsunamis exceeding 5 m is more than 1000 years for Black Sea (Ranguelov, 1997(Ranguelov, , 2003)).The main tsunami sources in the Black Sea are the faults in the sea or other secondary mechanisms on the coast which can be triggered by a far-offset main shock with an epicenter on land, as in the case of the 1939 event.Although there is still some debate the possibility of submarine landslides should be considered in the Black Sea (Ranguelov et al., 2008;Vilibić et al., 2010).
Most of the large and destructive tsunamis were generated by submarine earthquakes in the Mediterranean region (SA and EM).The Aegean Arc introduces the highest tsunami potential as some infrequent but large events have been recognized in the South Aegean region where shallow and intermediate depth earthquakes possess magnitudes that exceed 7. Landslides have also locally generated some powerful tsunamis and volcanic eruptions are also important in the Southern Aegean region.The first event in the tsunami catalogues was generated by the eruption of the Santorini volcano and accompanying earthquakes.Significant stratified  9 Fokaefs and Papadopoulos (2007); 10 Gündogdu, et al. (2002); 11 Kalafat et al. (2007); 12 Kreemer and Chamot-Rooke (2004); 13 Papadimitriou and Karakostas (2006); 14 Papadopoulos et al. (2007); 15 Papazachos and Anastasia (1996); 16 Perissoratis and Papadopoulos (1999) deposits and foraminiferal assemblage may represent these Late Bronze Age tsunami deposits in Didim, SW Turkey (Minoura et al., 2000).Other sources of tsunamis which have affected the southern coasts of Turkey are mostly regional such as the Rhodes earthquakes (e.g.1303,1481,1609,1741,1863). The most distant sources, on the other hand, are the eastern Levantine coast earthquakes (e.g.140 BC, 859, 1759, 1822, 1872) and Crete earthquakes (e.g.365).Most of the historical documents provide sufficient information about the effects of tsunami waves at some locations near the coasts, but these observations are not sufficient to determine the locations and estimate the mechanisms of the sources of these tsunamis.Precise definition of quantitative source parameters is important for representing the generation mechanism of a tsunami and numerical modellings are required to examine their implications.Within the current version of the database, only 14 tsunamigenic event sources could be defined (Table 1).The recurrence interval for tsunami intensities ≥3 is on the order of 30-35 years.Submarine landslides, slumps and subsidence events are also responsible for the generation of tsunamis (Yalc ¸ıner et al., 2002).As the submarine mass movements on the continental slopes are nearshore, the generated waves arrive at the target shoreline in a short time with low dispersion and they cause extreme run-up (Synolakis et al., 2002).On the basis of recent multi-channel bathymetric data supported by seismic reflection data, numerous paleo-landslides, as well as potential ones, can be observed on the steep continental slopes of the Sea of Marmara, surrounding three deep basins (Fig. 2).The slopes, ranging in depth from −100 m to −1250 m, become steeper offshore Prince Islands and in front of the Tekirdag shelf (40-50 • ).At the skirts of the slopes, debris and material masses can be observed, as they have been transported by mass failures.Homogenite deposits in low-lying areas of the Sea of Marmara, which are usually reworked from the basin margins, are related mostly to large earthquakes and probably other seafloor deformations such as tilting, fluid or gas escapes (McHugh et al., 2006).
The earthquakes on the northern strand of the North Anatolian fault in the Sea of Marmara, which also controls its steep slopes (Yaltırak, 2002), may cause the unstable sediments deposited along the shelf to break and upper slope areas to slide down to the abysal plain during some of the strong earthquakes.Smaller scale underwater sliding structures have also been observed inside the canyon valleys and at their walls.Locations and some characteristics of the most detailed submarine failures were given in Table 2.The Ganos and Tuzla slides seem to be multislumps that have occurred in the same location or as extensions of a previous slide.All of the failure types are debris and generally occur in the proximity of related ruptures.The recurrence interval can be estimated as being more than 1000 years for all cases.
East of the Sea of Marmara, a large (7 km wide) and triangular shaped landslide lies south of Tuzla at depths between −200 and −1200 m.It has 50 m thick sediments cutting the slope of the C ¸ınarcık Basin (Görür and C ¸agatay, 2010).On the basis of 14 C analysis, it should have been activated 17 000 years ago when the Sea of Marmara was a lake with a water level of −85 to −95 m below the present mean sea level ( Özeren et al., 2010).In fact, slope failure processes were more common during the last lowstand lacustrine period prior to 12 ka BP than during the Holocene highstand marine period (Beck et al., 2007).The Tuzla landslide has been defined as a relatively recent and deep-seated rotational landslide (Gökc ¸eoglu et al., 2009).Considering they have similar depositional characteristics and slope morphology, and also their being prone to a similar tectonic regime, Gökc ¸eoglu et al. (2009) proposed that the adjoining areas on the eastern and western sides of the Tuzla complex are potential areas for future sliding.Among the landslide scenarios, the most critical and possible ones have surface areas of 20-43 km 2 and 14-33 km 2 for the western and eastern ones, respectively.The volumes were calculated as 2-4 km 3 and 0.5-1.5 km 3 .
Sarı and C ¸agatay (2006) defined 3 turbidite levels, which have sharp basal boundaries and contain transported shallow benthic foraminifer species in the cores taken from the northern slopes of the C ¸ınarcık Basin.In such a tectonically active region, historical earthquakes and associated underwater mass flows are the only plausible generation mechanisms for these turbidite levels, since other mechanisms (e.g.river floods, storms, volcanic activities, tides and gas escape) are almost out of the question in this part of the Sea of Marmara region at least since the opening of Bosphorus (7.2 ka BP).On the basis of their sedimentological characteristics, average linear sedimentation rates and available radiocarbon ages, the turbidite levels were correlated with the following earthquakes; (a) Istanbul-Thrace (intensity = X) on 26 October 986; (b) Istanbul-Kocaeli (intensity = IX) on 15 August 553 and (c) some older historical earthquakes during prehistorical times with calculated ages of ca.3600 and 3800 years BP.The date of the first event may have been written incorrectly by the researchers and it should be identical with the event that occurred on 25 October 989 (Ambraseys, 2002a, b) or 26 October 989 (Guidoboni et al., 1994).Depending on the AMS radiocarbon dating of an enigmatic layer, we recovered 253-311 cm below from the lake bottom of Küc ¸ükc ¸ekmece lagoon, which is a coastal wetland protected from the sea by a narrow strip of sandbar (300-350 m), we also agree that the 25 October 989 earthquake was tsunamigenic.
In conclusion, the earthquakes in the Sea of Marmara and co-seismic slope failures usually cause damaging tsunamis in certain coastal areas, depending on their source characteristics, distance to the source and bathymetry.Such tsunamis may pose an important threat to the coastal settlements and installations especially located in the gulfs of Izmit and Gemlik, the Kapıdag Peninsula and on the shores of Istanbul and Gelibolu.Tides are not important in the Sea of Marmara but higher sea-levels due to storm surges may cause tsunamis to become more damaging (Alpar, 2009).Therefore, tsunamis are of practical interest in risk assessment, disaster management and mitigation.Research on the characteristics of near-field tsunamis using tsunami-modeling scenarios will be definitely beneficial.The estimation of source parameters needed in modeling the tsunami waves in the Sea of Marmara and tsunami effects on the coastal areas could be made more reliable with the development of historical information, the determination of potential source areas under the sea and the availability of the underwater topography in a detailed way and using comprehensive modeling.

Conclusion
Offshore infrastructures, coastal settlements and installations, which are characterised by flat and large beaches, are prone to higher tsunami risk.The tsunami impacts on the coastal waters of Turkey since 1400 BC were re-examined following the catalogue guidelines defined in EU projects of GITEC and TRANSFER.
Most of the tsunami events in the database are associated with different fault segments.The East Aegean Arc and trench system in the Southern Aegean Sea and the North Anatolian fault system in the Sea of Marmara constitute the highest tsunamigenic potentials in the region, both for the number of occurrences and their intensity.Although the repeatability of Black Sea tsunamis is low, some destructive tsunamis with large run-ups and inundation distances have been reported.Most of the strong earthquakes (M > 6.5) offshore the Black Sea can be assumed as being potential tsunamigenic sources.Many coastal settlements in the Eastern Mediterranean have been struck in the past by large and destructive tsunamis generated by submarine earthquakes and volcanic eruptions.Considering the high seismicity of the Aegean-Cyprean Arc, earthquake-related slope failures are also a plausible triggering mechanism for powerful tsunamis.The recurrence interval is 35-65 years www.nat-hazards-earth-syst-sci.net/11/273/2011/Nat.Hazards Earth Syst.Sci., 11, 273-291, 2011 for moderate events (TI < 4), while for strong tsunami events (TI ≥ 4) it is on the order of 90-110 years.Some of the tsunamis in the Sea of Marmara might have been triggered by underwater sedimentary disturbances occurring during major earthquakes.Most of the largest slope failures and sediments flows, however, occurred at the end of the last glacial period (12-17 ka BP) when this inland sea was lacustrine (−85 to −95 m) before the transition to marine conditions.Therefore, the database of tsunamis prepared in the present study with their geological traces, provides reference material for validating digital simulations of historical events and represents a valuable basis for hazard/risk assessment.

Fig. 2 .
Fig. 2. Distribution of submarine canyons and scars of landslides superimposed on the shaded bathymetry of the Sea of Marmara which is drawn from the multibeam data seta of French institute IFREMER (Rangin et al., 2001) and Turkish Navy Department SHOD.The bathymetric data in the shelf is from navigation charts, so data grid is relatively scarce.Gridding and mapping of the data were obtained by means of Generic Mapping Tools(Wessel and Smith, 1998).Active fault traces are based on previous studies by LePichon et al. (2001) and Yaltırak (2002).Slides: GC (Ganos complex), MI (Marmara Island) and TC (Tuzla complex).

5 April 991: in
Tsunami in Holon,Ashdod and Yavne (23, 54); the sea retreated from the coast of Palestine, and then flowed back, engulfing many people, the banks of the river Euphrates overflowed (25, 54).

Table 1 .
Some of the most detailed tsunamigenic event sources.
SA: total area of disturbed sediment (scar and lobe) in km2; CV: calculated volume in km3; EV: estimated volume in km3; HH: height of headwall in m (height from failure surface to crown of scar); WDH: waterdepth at top of headwall in m; WDB: waterdepth at base in m (depth of deepest slide deposit).Ages are stratigraphical extrapolation for Ganos and Marmara Island slides (which are Holocene) and14C analysis of slide deposits for Tuzla case (Pleistocene).Geotechnical data is available for Tuzla while other cases were estimated from the multibeam bathymetry and reflection data.Reference codes: 1: Altinok et al. (2003); 2: Bas ¸and Alpar (2003); 3: Görür and C ¸agatay (2010); 4: Özeren et al. (2010).