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Bollettino di Geofisica Teorica ed Applicata Vol. 55, n. 2, pp. 469-484; June 2014
DOI 10.4430/bgta0097
469
Tsunamigenic potential of local and distant tsunami sources
threatening SW Peloponnese
G.A. PAPADOPOULOS, E. DASKALAKI, A. FOKAEFS and T. NOVIKOVA
Institute of Geodynamics, National Observatory of Athens, Greece
(Received: July 5, 2012; accepted: April 8, 2013)
ABSTRACT The area of SW Peloponnese situated in the western segment of the Hellenic Arc is
characterized by high rate of seismicity. However, the tsunami hazard in the area is
poorly understood. In this paper we focus our attention in the local and distant tsunami
sources threatening coastal zones of SW Peloponnese and in the evaluation of their
tsunamigenic potential. It was found that only three historically documented tsunami
events were produced by seismic sources activated in SW Peloponnese: 1886, 1899,
1947. However, they were only local tsunamis very likely produced by submarine Earth
slumps rather than by co-seismic fault displacements. One may not rule out, however,
the possibility that local tsunami sources unknown so far would activate in the future.
In addition, for the tsunami hazard assessment in SW Peloponnese one may consider
tsunami sources bearing potential to produce distant or even basin-wide large tsunamis
such as the seismic ones of A.D. 365 and 1303 and the volcanic one of Minoan times.
Indeed, numerical simulations showed that those tsunamis may have arrived at SW
Peloponnese coastal zones with hazardous wave amplitudes. This applies particularly
to the Minoan and the 365 events.
Key words: tsunami, Peloponnese, earthquakes, SEAHELLARC.
© 2014 – OGS
1. Introduction
The area of SW Peloponnese, which is situated at the north part of the western segment of
the Hellenic Arc (Fig. 1), was hit by several earthquakes during the historical and instrumental
record of seismicity (Galanopoulos, 1941; Papazachos and Papazachou, 2003; Papadopoulos,
2011). SW Peloponnese was the test-area for the earthquake and tsunami hazard assessment
within the framework of the EU-FP6 research project Seismic and Tsunami Risk AssessmentSeismic and Tsunami Risk Assessment
and Mitigation Scenarios in the western Hellenic Arc [SEAHELLARC: see PapouliaSEAHELLARC: see Papoulia et
al. (2014)]. In view of this, a probabilistic seismic hazard approach was performed by
SEAHELLARC Working Group (2010) on the basis of a new seismotectonic zonation and of an
updated earthquake catalogue.
From historical documentation it results that SW Peloponnese is threatened mainly by
tsunamis which are tectonically associated with the segment of western Hellenic Arc and Trench
(HA-T) system. An updated tsunami catalogue for western HA-T and its value for the tsunami
hazard assessment was published and discussed by Papadopoulos et al. (2010) who compiled
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Boll. Geof. Teor. Appl., 55, 469-484 Papadopoulos et al.
new data and evaluated critically past catalogues and data compilations published by several
authors (Galanopoulos, 1960; Ambraseys, 1962, 2009; Antonopoulos, 1980; Papadopoulos
and Chalkis, 1984; Soloviev, 1990; Guidoboni et al., 1994; Papazachos and Papazachou, 1997;
Soloviev et al., 2000; Papadopoulos, 2001, 2009; Papadopoulos and Vassilopoulou, 2001;
Guidoboni and Comastri, 2005). However, the seismic tsunami source which produced the
large wave of 1303 in the eastern HA-T (e.g., Guidoboni and Comastri, 1997; Papadopoulos et
al., 2007; Papadopoulos, 2011) should be also considered as threatening SW Peloponnese. In
addition, the extreme tsunami produced by the Minoan eruption of the Thera volcano should not
be ruled out as a component of the long-term tsunami hazard assessment.
In this paper we have investigated the potential associated with local and distant tsunami
sources threatening SW Peloponnese. To this aim we reviewed the tsunami history of the
area from documentary sources as well as from coastal geological observations. In addition,
the tsunami sources were determined and their tsunami potential was qualitatively evaluated.
Then, the two extreme tsunamis of A.D. 365 and of the 17
th
century B.C. Minoan eruption were
simulated numerically and water elevation parameters were calculated for Methoni and Pylos,
that is for two coastal sites which were of particular interest to the SEAHELLARC research
project.
Fig. 1 - The high rate of seismicity along the Hellenic Arc is exemplified by the series of strong earthquakes that
occurred there during 2008 (after Papadopoulos et al., 2009). One of them was the large Methoni earthquake of 14
February 2008 which occurred offshore SW Peloponnese and is discussed in the text.
Tsunamigenic potential in SW Peloponnese Boll. Geof. Teor. Appl., 55, 469-484
471
2. Historical tsunami sources
Historically known tsunami sources which are of interest for the tsunami hazard assessment
in a relatively small target area of the Mediterranean Sea, such as SW Peloponnese, can be
classified on the basis of two different criteria. The first criterion regards the maximum distance,
d, of the epicentre of the causative earthquake from the target area. However, tsunami hazard
is meaningful only if the wave arrives in the target area with amplitude of at least 0.5 m, since
it is a minimum wave amplitude threshold capable to cause some damage. According to a
consensus reached among specialists working for the North East Atlantic and Mediterranean
Tsunami Warning System (NEAMTWS) coordinated by IOC/UNESCO, the criterion of distance
classifies a tsunami as local or regional if d < 100 km or < 400 km, respectively. A tsunami is
characterized as basin-wide one when d > 400 km. Although such a type of classification is
arbitrary and certainly subjective it is a realistic one for the physiographic peculiarities of the
Mediterranean Sea. By considering mean sea depth of h = 500 m and that the ray propagation
theory is a good approximation for the tsunami travel times, we find out that a tsunami arrives
at epicentral distance of d = 100 km or d = 400 km in less than 25 minutes or in less than 95
minutes, respectively; the tsunami velocity is calculated by the formula v = (gh)
1/2
, where g is
the gravity acceleration.
Tsunamis caused not only in local but also in regional distances are of interest for the tsunami
potential assessment in the SW Peloponnese. This point of view is justified by that distant but
sizable tsunamis propagate well away from their sources and may significantly affect remote
coastal zones. A characteristic example of this type was the large A.D. 365 tsunami which is
believed that was generated offshore western Crete by a big earthquake measuring estimated
magnitude on the order of 8.3 or even larger [e.g., see an exhaustive review in Papadopoulos
(2011)]. Contemporary historical sources indicated that the 365 event was a basin-wide
tsunami which inundated many coastal zones in the eastern Mediterranean basin, one of them
being Methoni in SW Peloponnese as described reliably by Ammianus Marcellinus and other
contemporary historians (Guidoboni et al., 1994). Another example is the large tsunami of 1303,
which was caused also by a big earthquake rupturing the eastern segment of HA-T between
Crete and Rhodes and measuring estimated magnitude on the order of 8.0. That wave affected
large part of the eastern Mediterranean basin and propagated also towards the Ionian Sea and the
SW Peloponnese (e.g., Guidoboni and Comastri, 1997).
The second criterion for tsunami classification relies on the tsunami generation mechanism
which is related not only to seismic but also to non-seismic sources, that is to volcanic eruptions
and to coastal and/or submarine slumps. The term seismic source applies when the tsunami
wave is caused directly by the co-seismic fault displacement. However, for historical tsunamis it
is hardly verifiable given that the tsunami may be caused by slumps triggered by the earthquake
process (e.g., Gerardi et al., 2008; Billi et al., 2010).
In the next section historic and pre-historic, local and distant tsunami events produced
by seismic and non-seismic mechanisms, which were reported to impact SW Peloponnese
are reviewed critically with the aim to evaluate their possible source areas and generation
mechanisms.
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Boll. Geof. Teor. Appl., 55, 469-484 Papadopoulos et al.
3. Past tsunami record
3.1. Minoan tsunami, 17
th
century B.C.
From the tsunamis listed in the existing catalogues the chronologically first, that may had
some impact in the area of SW Peloponnese, was the large wave generated by the 17
th
century
B.C., Late Bronge Age (LBA) eruption of Thera (Santorini) volcano, the so-called Minoan
tsunami. Sedimentary deposits inferred to be from LBA tsunami inundation were described by
several authors (see reviews: Papadopoulos, 2009, 2011; Novikova et al., 2011) but documented
ones were found in coastal sediments in Didim and Fethiye, SW Turkey (Minoura et al., 2000);
in north Crete in the archaeological sites of Gouves (Minoura et al., 2000) and of Palaikastro
(McCoy and Papadopoulos, 2001; Bruins et al., 2008); within the LBA volcanic succession
in Thera at two localities (McCoy and Heiken, 2000); on the continental shelf off Caesareaon the continental shelf off Caesarea shelf off Caesareashelf off Caesarea
Maritima, Israel (Goodman-Tchernov et al., 2009); and possibly in east Sicily (De Martini2009); and possibly in east Sicily (De Martini et
al., 2010). Additional evidence comes from the deep ocean with the discovery of reworked2010). Additional evidence comes from the deep ocean with the discovery of reworkedAdditional evidence comes from the deep ocean with the discovery of reworked
sea-floor sediments, known as homogenites (e.g., Kastens and Cita, 1981; Cita et al., 1984).
Based on the geological evidence one may reasonably suggest that the field of wave propagation
was exceptionally large in the eastern Mediterranean basin and that wave amplitudes, with
consequent coastal inundation and run-up, also may have been exceptional contrary to
studies that suggested otherwise (Dominey-Howes, 2004; Pareschi et al., 2006). Although
there is no evidence for LBA tsunami inundation in SW Peloponnese, in the next section we
investigated this possibility based on numerical simulation of the tsunami by assuming two main
tsunamigenic mechanisms, that is caldera collapse and massive pyroclastic flows.
3.2. July 21, 365
The earthquake and tsunami events of July 21, 365 were documented in a large number of
documentary sources as well as by archaeological and geological field observations reviewed
shortly in the next section. The historical, geological and archaeological evidence leave little
doubt that the 365 tsunami was a basin-wide wave generated by 6-9 m co-seismic uplift in the
area of western HA-T and that it may have inundated several coastal localities in the eastern
Mediterranean basin including NW Crete, north Egypt in Alexandria, Panephysis and the
Nile Delta, eastern Sicily, in unidentified areas of the Aegean Sea and possibly in Epidavros,
today modern Cavtat near Dubrovnik in Dalmatia, Adriatic Sea. Of particular interest is what
very likely happened in Methoni, SW Peloponnese. According to the contemporary historian
Ammianus Marcelinus “Some great ships were hurled by the fury of the waves on to roof tops (as
happened in Alexandria), and others were thrown up to two miles from the shore. We ourselves
on our travels saw a Spartan ship disintegrating after the long decay near the town of Mothone
(Methoni)” [translation in English by Guidoboni et al. (1994)]. However, it is not clear if ships
thrown up to two miles from the shore were observed in Methoni or in Alexandria. We have
suggested that SW Peloponnese did not escape tsunami inundation and, therefore, water elevation
parameters were calculated based on numerical simulation of the 365 tsunami (see next section).
3.3. August 8, 1303
This was a big earthquake documented in a long series of Greek, Venetian and Arabic historical
sources (Guidoboni and Comastri, 1997, 2005). The earthquake caused extensive destruction in
Tsunamigenic potential in SW Peloponnese Boll. Geof. Teor. Appl., 55, 469-484
473
a large area of the eastern Mediterranean but mainly in the eastern and central parts of Crete.
From ground failures observed as far as north Egypt, Papadopoulos (2011) was able to estimate
earthquake magnitude on the order of 8.0. The basin-wide tsunami inundated not only near-field
coastal sites, such as Heraklion in Crete, but also remote localities in Alexandria and in the Ionian
and southern Adriatic Sea. However, very little is known about the geological signature of thissouthern Adriatic Sea. However, very little is known about the geological signature of thisAdriatic Sea. However, very little is known about the geological signature of this
large tsunami. In Cape Punta, SE Peloponnese, Scheffers and Scheffers (2008) observed marine
organisms attached on many boulders proving that boulders were transported inland by extreme
wave events, likely tsunamis, at a
14
C-AMS date of around 1300 cal A.D., which may represent
geological trace of the 1303 tsunami.
3.4. March 9, 1630
This was a very strong earthquake known from several documentary sources and having its
source possibly offshore NW Crete, to the west of Kythira Island [see review in Papadopoulos
(2011)]. De Viazis (1893) published a series of documents archived in the Venetian
administration of Zakynthos Island and containing independent testimonies of three captains
sailing around Kythira Strait at the time of the earthquake occurrence. Their descriptions leave
no doubt that they ran a great danger because of strong tsunami waves traveling towards south
and SE. Remnants of wrecks and bodies of shipwrecked persons were also observed. When one
of the captains arrived into the port of Kythira at the south of the island, today Kapsali port,
he was told that at the same time an earthquake of moderate strength was felt and that a slight
inundation was observed at the pier. Such a strong tsunami very possibly was of seismic origin.
There is no documentation that the tsunami affected the target area of SW Peloponnese.
3.5. September 20, 1867
This strong earthquake struck the area of Mani in SE Peloponnese, particularly the town of
Gythion and the villages of Areopolis and Paganea where houses collapsed and several people
were killed (Schmidt, 1879; Galanopoulos, 1950). In his detailed description, Schmidt (1879)
reported that the sea flooded severely the coast of Gythion Bay and left many fish on land. The
sea disturbance was observed from early dawn till 09:00 in the morning. At Chania, Crete, as
well as in Zakynthos and in Argostoli of Cephalonia Island, the sea motion occurred slowly
from 05:30 am till 10:00 am. The sea became calm again after repeated waves and periods of
back wash. The tsunami reached as far as Serifos and Syra, in the Cyclades island complex,
south Aegean Sea. Flooding of the coast was also reported from Kalamata, SW Peloponnese,
where many fish were left onshore. Papadopoulos (2011) suggested that the tsunamigenic source
should be placed in Lakonikos Gulf offshore to the south of Gythion.
3.6. August 27, 1886
This was a large, destructive, possibly interplate earthquake that ruptured the SW
Peloponnese and causing very extensive destruction in Filiatra and in many other towns
and villages; at least 326 persons were killed and more than 796 were injured [see reviews:
Galanopoulos (1941) and Papazachos and Papazachou (2003)]. The earthquake was of long
duration in Heraklion, Crete, being felt in remote places of the Mediterranean Sea, such as
Malta, Trieste, Alexandria, Cairo, Syria and Asia Minor. Along a coastal segment stretching in
SW Peloponnese at a length of ~ 35 km, from Agrilio to the north up to the bay of Navarino
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Boll. Geof. Teor. Appl., 55, 469-484 Papadopoulos et al.
(Pylos) to the south, a coastal strip 10 to 15 m wide was inundated for a while (Galanopoulos,
1941). According to a report of Forster (1890), director of the East Telegraph Company in
Zakynthos, and a correspondence of the newspaper of Heraklion “Nea Evdomas” (1886), a
telegraph cable between Crete and Zakynthos was entirely cut at a distance of about 29 miles
offshore to the south of Zakynthos (Stavrakis, 1890), which may indicate either submarine
slumps and/or turbidite currents triggered by the earthquake. To conclude, at all evidence the
1886 earthquake caused submarine slumps offshore SW Peloponnese and a local tsunami of low
intensity.
3.7. January 22, 1899
The SW part of Peloponnese was hit again by a very strong shock which caused widespread
damage in Kyparissia, in Filiatra as well as in many villages of the area. The coastal town of
Marathoupole was inundated by a local tsunami not exceeding 1 m in height, while in Zakynthos
a ~ 40 cm wave height was reported (Mitzopoulos, 1900; Eginitis, 1901). Galanopoulos (1941)
suggested that this tsunami was possibly triggered by co-seismic submarine slump. The very local
nature of the wave makes that suggestion a likely one.
3.8. October 6, 1947
This was a large earthquake which caused widespread damage to many towns and villages
in the area of SW Peloponnese (Galanopoulos, 1949). Three persons were killed and 20 injured;
landslides were also reported. In Methoni, a local tsunami advanced 15 m inland. Galanopoulos
(1949) attributed the wave to an offshore slide which may have occurred about 6 km south-SW
off the coast since the slope of the sea flour is particularly steep there.
4. Tsunami potential
From the historical review presented in the previous section it results that the area of SW
Peloponnese is threatened by seismic sources of basin-wide tsunamis very likely produced by co-
seismic fault displacements, such the 365 and 1303 ones. On the other hand, there are also sources
which could be characterized as non-seismic in the sense that they caused only local tsunamis
very likely not directly by the seismic faulting but rather by submarine slumps as a mechanism
triggered by the earthquake. At all evidence this happened with the large earthquake of AugustAugust
27, 1886 as well as with the strong earthquakes of January 22, 1899 and October 6, 1947. The as well as with the strong earthquakes of January 22, 1899 and October 6, 1947. Theof January 22, 1899 and October 6, 1947. The. The
possible impact in SW Peloponnese of the large tsunami caused by the Minoan eruption in Thera
remains only as a hypothesis since no geological or archaeological evidence is at place.
The relatively low number of tsunamis reported in SW Peloponnese combined with the high
uncertainty as regards the mechanisms of tsunami generation and the precise positions of the
sources allow only for a qualitative evaluation of the tsunami potential in that region. In addition,
we were able to perform numerical simulations and to calculate hydrodynamic parameters as
components of the hazard associated with extreme tsunami events in the region. In this respect
three basin-wide tsunamis are of interest; the Minoan tsunami of volcanic origin as well as
the tectonic tsunamis of A.D. 365 and 1303. The simulation of the 1303 tsunami produced by
a magnitude 8.0 seismic source striking in parallel to the Hellenic trench between Crete and
Tsunamigenic potential in SW Peloponnese Boll. Geof. Teor. Appl., 55, 469-484
475
Rhodes has shown a very strong energy directivity from the source towards the Egyptian coast
and particularly to the Alexandria coastal zone (Özsoy et al., 1982; Tinti et al., 2005; Hamouda, Hamouda,
2006). However, the wave attenuates strongly towards the west and, therefore, only small wave
amplitudes are expected in SW Peloponnese coastal localities. In view of this, our interest was
focused to the extreme tsunami produced by the big earthquake of A.D. 365, which is suggested
that ruptured the western segment of the HA-T. Of interest was also the extreme Minoan tsunami
produced by the LBA eruption of the Thera volcano. For both of these events we were able to
assume alternative source mechanisms as well as to control our results in comparison with the
results obtained by other authors.
4.1. Numerical simulation of the Minoan tsunami
The tsunami generated by the LBA eruption of Thera was simulated by several authors whosunami generated by the LBA eruption of Thera was simulated by several authors whowas simulated by several authors who
assumed as source mechanisms either the caldera collapse or the massive pyroclastic flows
(e.g., Minoura et al., 2000; Pareschi et al., 2006; Bruins et al., 2008). Recently, Novikova
et al. (2011) assumed several alternatives as regards the tsunami generation mechanism and
reproduced the expected water elevation in a number of synthetic tide-gauge records forsynthetic tide-gauge records for
selected nearshore (~20 m depths) sites of northern Crete, the Cyclades Islands, SW Turkey(~ 20 m depths) sites of northern Crete, the Cyclades Islands, SW Turkeydepths) sites of northern Crete, the Cyclades Islands, SW Turkey the Cyclades Islands, SW Turkeythe Cyclades Islands, SW Turkey
and Sicily. The first mechanism involved the entry of pyroclastic flows into the sea, assuming The first mechanism involved the entry of pyroclastic flows into the sea, assumingThe first mechanism involved the entry of pyroclastic flows into the sea, assumingmechanism involved the entry of pyroclastic flows into the sea, assuminginvolved the entry of pyroclastic flows into the sea, assuming flows into the sea, assumingflows into the sea, assuming
a thick flow (55 m; 30 km
3
) entering the sea along the south coast of Thera in three alternative coast of Thera in three alternativecoast of Thera in three alternativealternative
directions but all directed towards northern Crete. Flows were modelled as a solid block that. Flows were modelled as a solid block thatFlows were modelled as a solid block that
slowly decelerates along a horizontal surface. The second mechanism assumed caldera collapse horizontal surface. The second mechanism assumed caldera collapsehorizontal surface. The second mechanism assumed caldera collapse
with two extremes as regards the volume, that is 19 km, that is 19 kmthat is 19 km19 km
3
as the minimum and 34 km34 km
3
as the
maximum. Caldera collapse was modelled as a dynamic landslide producing a series of rapidmodelled as a dynamic landslide producing a series of rapid
vertical displacements.
Modelling was performed with use of the software package GEOWAVE (Watts et al., 2003),
which is a combination of TOPICS and FUNWAVE. TOPICS uses a variety of curve fitting of curve fittingof curve fitting
techniques and was designed (Grilli and Watts, 1999) as an approximate simulation tool that as an approximate simulation tool thatas an approximate simulation tool that
provides surface elevations and water velocities as initial conditions for tsunami propagation. and water velocities as initial conditions for tsunami propagation.and water velocities as initial conditions for tsunami propagation.
The numerical model FUNWAVE (Wei and Kirby, 1995; Wei et al., 1995; Kirby 1995; Kirby1995; Kirby et al., 1998,
2003; Kennedy et al., 2000) performs wave propagation simulation, based on the fully non- propagation simulation, based on the fully non-propagation simulation, based on the fully non-
linear Boussinesq theory using a predictor-corrector scheme. The simulation duration was 4 theory using a predictor-corrector scheme. The simulation duration was 4theory using a predictor-corrector scheme. The simulation duration was 4
hours. For pyroclastic flow scenarios the maximum number, n, of time steps was 6,000 with a
time step ΔΤ = 1.7 s, while for caldera collapse scenarios we got= 1.7 s, while for caldera collapse scenarios we got n = 10,000 and ΔΤ = 3.1 s. The= 3.1 s. The
nearshore wave amplitudes from the mean sea level calculated by Novikova et al. (2011) varied
from a few metres to 28 m along northern Crete for three pyroclastic flows scenarios. However,
pyroclastic flow penetration into the sea water causes very strong tsunami wave directivity
and, therefore, the wave amplitudes obtained for those scenarios are strongly dependent on
the azimuth of the pyroclastic flow penetration. For the caldera collapse with the conservative
volume of 19 km
3
tsunami wave amplitudes ranging from 24 m in the near-field domain to 0.8
m in SW Turkey coastal localities were obtained. However, for the caldera collapse with the
upper extreme volume of 34 km
3
tsunami amplitudes were generally 2.5 - 3.0 times larger than
those generated by the smaller volume of collapse.
With the aim to check the possible impact of the Minoan tsunami in SW Peloponnese, the
numerical simulation performed by Novikova et al. (2011) was extended in two additional
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Boll. Geof. Teor. Appl., 55, 469-484 Papadopoulos et al.
synthetic tide-gauge stations located in Methoni and Pylos. The tide-gauge station in Pylos was
placed in the sea side of the small Island of Sfaktiria which occupies the opening of the Pylos
bay to the Ionian Sea. To avoid high uncertainties involved due to poor bathymetry coverage in
the shallow water domain the two synthetic stations were installed offshore Methoni and Pylos
at sites of water depth 27 and 32 m, respectively. Calculations were repeated for alternative sites
situated at water depth of 8.7 m for Methoni and 3.7 m for Pylos and showed no remarkable
change of the results. Bathymetric 1 arcmin data set obtained from the GEneral BathymetricBathymetric 1 arcmin data set obtained from the GEneral Bathymetricobtained from the GEneral Bathymetricfrom the GEneral BathymetricGEneral BathymetricBathymetric
Chart of the Oceans (GEBCO) were used for the simulation grid for eastern Mediterranean and of the Oceans (GEBCO) were used for the simulation grid for eastern Mediterranean andof the Oceans (GEBCO) were used for the simulation grid for eastern Mediterranean and Mediterranean andMediterranean and
southern Aegean Sea regions. In coastal areas of SW Peloponnese, however, supplementary areas of SW Peloponnese, however, supplementary, however, supplementary
bathymetric data from the Hydrographic Service, Greek Navy, on a grid of 0.5 arcmin, were Navy, on a grid of 0.5 arcmin, wereNavy, on a grid of 0.5 arcmin, were
utilized. For the Aegean Sea computations, based on GEBCO spatial domain a grid with computations, based on GEBCO spatial domain a grid withcomputations, based on GEBCO spatial domain a grid witha grid withgrid with
500 m uniform spacing was reconstructed with water depth measured from mean lower waterwas reconstructed with water depth measured from mean lower waterreconstructed with water depth measured from mean lower water mean lower watermean lower water
level. For the caldera collapse mechanism, additional constraints concerning bathymetric constraints concerning bathymetricconstraints concerning bathymetric
variability in and around Thera Island varies from 380 m in the source of tsunami generation to Thera Island varies from 380 m in the source of tsunami generation toThera Island varies from 380 m in the source of tsunami generation to toto
100 - 400 m in the area surrounding Thera. m in the area surrounding Thera.
Scenarios of thick (55 m; 30 kmthick (55 m; 30 km
3
) pyroclastic flows directed from south Thera towards northpyroclastic flows directed from south Thera towards north
Crete were determined by selecting three different azimuths for the flow penetration into the
sea water: 120°, 145°, 200°. These three azimuths were selected since there is volcanological
evidence indicating that the major amount of pyroclastic flow was directed from the volcanic
cone to the south (McCoy and Heiken, 2000). Constant kinematics was considered for the
three scenarios with flow velocity of 170 m · s
-1
, flow duration of 500 s and run-out distance of
40 km. The strong directivity in tsunami energy propagation is clearly illustrated in Fig. 2. In
fact, the wave amplitudes recorded synthetically in both Methoni and Pylos decrease rapidly
with the counterclockwise change of the penetration azimuth of the pyroclastic flow (Fig. 3). The
highest peak-to-peak wave amplitudes were obtained for azimuth of 120°; 2.5 m in Methoni and
4.0 m in Pylos. For azimuth of 200°
peak-to-peak wave amplitudes were only 0.25 and 0.65 m
in Methoni and in Pylos, respectively. This result is absolutely consistent with the same pattern
of systematic decrease of tsunami amplitudes from west to east along north Crete.
Remarkable water elevation disturbance was caused from the tsunami generated by the
caldera collapse mechanism. The conservative scenario of caldera collapse volume of 19 km
3
produced peak-to-peak tsunami wave amplitude of the same order of 2.5 m in both Methoni
and Pylos. However, the upper extreme of the caldera collapse volume of 34 km
3
produced
amplitudes of 3.7 m in Methoni and 4.5 m in Pylos.
Regardless the tsunami generation mechanism, the synthetic wave amplitudes obtained
certainly underestimate the real ones given that the synthetics were calculated for virtual tide-
gauges installed at sites situated at water depths of 27 m in Methoni and 32 m in Pylos.
4.2. Numerical simulation of the A.D. 365 tsunami
Most of the efforts to simulate the large tsunami of A.D. 365 (e.g., Tinti et al., 2005; Fischer
and Babeyko, 2007; Lorito et al., 2007; Shaw et al., 2008; Yolsal et al., 2008) underestimated
the wave amplitudes as compared to the ones expected from the historical and geological record
of the tsunami. This may be due to a number of reasons, such as the source characteristics
and the gross bathymetry particularly in the shallow water domain. Recently, Novikova et al.
(2012) simulated the 365 wave by shifting the purely thrust seismic source of M = 8.3 along the
Tsunamigenic potential in SW Peloponnese Boll. Geof. Teor. Appl., 55, 469-484
477
Fig. 2 - Water elevation in south Peloponnese due to tsunami produced by pyroclastic flow during the Minoan eruption
of Thera. Pyroclastic flow penetration by counter clockwise azimuth of 120° (upper panel), 145° (middle panel) and
200° (lower panel).
western HA-T segment from south of Crete to the NW of Crete and by utilizing three grids of
bathymetry, a coarse for the Mediterranean Sea, an intermediate for the Aegean Sea and a fine
for local application, e.g., in Alexandria. Uniform seismic slip of 10 m was adopted as an initial
condition by applying the elastic dislocation model derived by the Okada’s (1985) code but also
by empirical relationships for the seismic source (Well and Coppersmith, 1994; Konstantinou
Fig. 3 - Synthetic tide-gauge records in Methoni (left) and Pylos (right) due to tsunami produced by pyroclastic flow
during the Minoan eruption of Thera. Pyroclastic flow penetration by counter clockwise azimuth of 120° (upper row),
145° (upper row) and 200° (lower row).
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Boll. Geof. Teor. Appl., 55, 469-484 Papadopoulos et al.
Tsunamigenic potential in SW Peloponnese Boll. Geof. Teor. Appl., 55, 469-484
479
et al., 2005). Shear modulus of μ = 33 GPa was inserted in the calculations. A strong tsunami
energy directivity was found depending on the position of the source. For near-field coastal
sites, such as Phalasarna and Balos in NW Crete, maximum peak-to-peak wave amplitudes up
to 7 m were found for a seismic source rupturing between Peloponnesus and west Crete at a
strike of 345°. These amplitudes are absolutely consistent with the historically and geologically
documented ones.
In this paper the same modelling scheme was applied to investigate hydrodynamic tsunami
parameters in the coastal sites of Methoni and Pylos of SW Peloponnese. Table 1 lists the
seismic source characteristics while the source geometry is illustrated in Fig. 4 along with the
initial surface water elevation. The distribution of the maximum water elevation at all times after
the tsunami generation clearly shows (Fig. 5) that the maximum wave amplitudes are observed(Fig. 5) that the maximum wave amplitudes are observed
in the near-field domain, that is in the Phalasarna and Balos sites of NW Crete where the peak-
to-peak amplitudes exceed 6 m. Because of the NW-SE strike of the seismic source, strong
tsunami energy directivity is observed towards SW in the Mediterranean Sea and partly in the
Fig. 4 - Initial surface water elevation after a tsunami generation produced by uniform seismic slip of 10 m in a M
w
=8.3
source striking 345°. Other source parameters are described in Table 1.
Strike (deg.) 345
Dip (deg.) 30
Rake (deg.) 90
Centroid depth (km) 20
Fault length (km) 258
Fault width (km) 56
Seismic slip (m) 10
Magnitude (Mw) 8.3
Table 1 - Earthquake source parameters of the 365 large tsunamigenic earthquake.
480
Boll. Geof. Teor. Appl., 55, 469-484 Papadopoulos et al.
southwestern part of the Aegean Sea. However, as one may expect tsunami wave amplitudes
drastically reduce towards NW, that is in the area of SW Peloponnese. In fact, the time histories
of synthetic tide-gauge records in Methoni and in Pylos show that the peak-to-peak amplitudes
were about 1.2 m and 1.5 m, respectively (Fig. 6). Again the expected real amplitudes should
be significantly higher than the synthetic ones as explained earlier in relation to the Minoan
tsunami simulation.
Fig. 5 - Maximum surface water elevation at all times after a tsunami generation produced by a uniform seismic slip of
10 m in a M
w
=8.3 source striking 345°. Other source parameters are described in Table 1.
Fig. 6 - Synthetic tide-gauge records in Methoni (left) and Pylos (right) due to tsunami produced by a uniform seismic
slip of 10 m in a M
w
=8.3 source striking 345°.
Tsunamigenic potential in SW Peloponnese Boll. Geof. Teor. Appl., 55, 469-484
481
5. Discussion
The number of tsunami events that reportedly hit the area of SW Peloponnese is relatively
low as compared to the high seismicity rate of the western HA-T segment. The tsunamigenic
mechanism remains unclear for several historical tsunamis caused by strong earthquakes such the
1630 and 1867 ones. Still, it is not well understood why some large earthquakes were tsunamigenic
while others were not. For example, the earthquake of Mw = 6.9 that ruptured offshore Methoni that ruptured offshore Methoni
on February 14, 2008 did not cause even a small tsunami (Papadopoulos et al., 2008) which still
needs explanation. This was also the case of the large earthquake which occurred offshore to
the south of Zakynthos with magnitude Mw = 6.6 on November 18, 1997. The large historical 1997. The large historical
earthquake of August 27, 1886 only caused a local tsunami due to submarine slumps occurringAugust 27, 1886 only caused a local tsunami due to submarine slumps occurring 1886 only caused a local tsunami due to submarine slumps occurring
offshore SW Peloponnese. In view of those important uncertainties, the evaluation of the potential
of tsunami sources threatening SW Peloponnese is possible to be described by qualitative rather
than by quantitative approaches.
6. Conclusions
Historical documentary sources indicated that in SW Peloponnese local tsunamis were
produced by three very strong earthquake events: August 27, 1886; January 22, 1899 and October
6, 1947. However, the local tsunami waves were very likely triggered by submarine co-seismic
Earth slumps occurring in the Gulf of Kyparissia after the events of 1886 and 1899 and further
southwards in Methoni and Pylos after the 1947 earthquake. No local tsunami sources are known
to have activated in SW Peloponnese before 1886 but this may be due to poor documentation of
the earthquake and tsunami history of the area. One may not rule out the possibility that local
tsunami sources unknown so far would activate in the future.future.
The area of SW Peloponnese, however, is also threatened by regional or basin-wide large
tsunamis such as the A.D. 365 and 1303 ones. Our numerical simulation of the 365 large tsunami
has shown that for a magnitude 8.3 seismic source of pure thrust and striking 345°
the nearshore
peak-to-peak wave amplitudes expected in Methoni and in Pylos equal to about 1.2 and 1.5 m,
respectively, which certainly are considerable from the hazard point of view, given that even
higher wave should be expected along the shore.
The results of numerical simulations performed by other authors (Özsoy et al., 1982; Tinti
et al., 2005; Hamouda, 2006) for the 1303 magnitude 8.0 seismic source in the eastern segment
of HA-T lead to the conclusion that tsunami amplitudes in SW Peloponnese localities are not
expected to exceed 0.5 m, which implies no serious hazard component. As regards the large
tsunami produced by the big LBA eruption of the Thera volcano the numerical simulations that
we performed showed that peak-to-peak tsunami wave amplitude exceeding 3 m and 4.5 m should
have occurred in Methoni and Pylos, respectively, particularly for the caldera collapse scenario.
We concluded that in SW Peloponnese the potential for tsunami generation is relatively low
but this may be only a conservative result due to the poor historical documentation and poor
understanding of tsunami generation mechanisms in that area. However, for plans of tsunami
hazard assessment, it is important to take into account that SW Peloponnese coastal zones are
also threatened by distant and basin-wide large tsunami sources, such as the seismic ones of
A.D. 365 and 1303 and the volcanic one of Minoan times.
482
Boll. Geof. Teor. Appl., 55, 469-484 Papadopoulos et al.
Acknowledgements. This paper is a contribution to the research project SEAHELLARC, EU-FP6, contract
no. 037004. The authors are thankful to two reviewers since their critical commentaries helped in improving
the initial manuscript.
REFERENCES
Ambraseys N.N.; 1962:; 1962:1962:: Data for the investigation of the seismic sea-waves in the eastern Mediterranean.. Bull.ull.
Seismol. Soc. Am., 52, 895-913.
Ambraseys N.N.; 2009: Earthquakes in the Mediterranean and Middle East - a multidisciplinary study of seismicity
up to 1900. Cambridge, UK, 947 pp.
Antonopoulos J.; 1980: Data for investigation on seismic sea-waves events in the eastern Mediterranean from the
birth of Christ to 1980 A.D. Ann. Geof., 33, 141-248.
Billi A., Minelli L., Orecchio B. and Presti D.; 2010: Constraints to the cause of three historical tsunamis (1908, 1783
and 1693) in the Messina Straits region, Sicily, southern Italy. Seismol. Res. Lett., 81, 907-915.
Bruins H.J., MacGillivray J.A., Synolokis C.E., Benjamini C., Keller J., Kisch H.J., Klugel A. and van der Plicht J.;
2008: Geoarchaeological tsunami deposits at Palaikastro (Crete) and the Late Minoan IA eruption of Santorini.
J. Arch. Sci., 35, 191-212.
Cita M.B., Camerlenghi A., Kastens K.A. and McCoy F.W.; 1984: New findings of bronze age homogenites in the
Ionian sea: geodynamic implications for the Mediterranean. Mar. Geol., 55, 47-62.
De Martini P.M., Barbano M.S., Smedile A., Gerardi F., Pantosti D., Del Carlo P. and Pirrotta C.; 2010: A unique
4000 year long geological record of multiple tsunami inundations in the Augusta Bay (eastern Sicily, Italy). Mar.
Geol., 276, 42-57.
De Viazis S.; 1893: Megas en Kriti seismos kata to 1629 (a great earthquake in Crete during 1629). Parnassos, 16,
218-221 (in Greek). (in Greek).
Dominey-Howes D.; 2004: A re-analysis of the Late Bronge Age eruption and tsunami of Santorini, Greece, and the
implications for the volcano-tsunami hazard. J. Volcanol. Geotherm. Res., 130, 107-132.
Eginitis D.; 1901: Resultats des observations sismiques, faites en Grece pendant l’annee 1899. Ann. Obs. Nat.
Athènes, 3, 21-27.
Fischer K.D. and Babeyko A.; 2007: Modelling the 365 A.D. Crete earthquake and its tsunami. Geophys. Res. Abstr.,
9, 09458.
Forster W.A.; 1890: Earthquake origin. Trans. Seismol. Soc. Jpn., 15, 73-92.
Galanopoulos A.G.; 1941: Das riesenbeben der Messenischen kóste von 27 August 1886. Praktika tis Akadimias
Athinon, 16, 120-126.
Galanopoulos A.G.; 1949: The Koroni, Messinia, earthquake of October 6, 1947. Bull. Seismol. Soc. Am., 39, 33-39.
Galanopoulos A.G.; 1950: Die seismizität von Messenien. Gerlands Beitr. Geophyz., 61, 144-162.
Galanopoulos A.G.; 1960: Tsunamis observed on the coasts of Greece from antiquity to present time. Ann. Geofis.,
13, 369-386.
Gerardi F., Barbano M.S., De Martini P.M. and Pantosti D.; 2008: Discrimination of tsunami sources (earthquake
versus landslide) on the basis of historical data in eastern Sicily and southern Calabria. Bull. Seismol. Soc. Am.,
98, 2795-2805, doi:10.1785/0120070192.
Goodman-Tchernov B.N., Dey H.W., Reinhardt E.G., McCoy F.W. and Mart Y.; 2009: Tsunami waves generated by
the Santorini eruption reached eastern Mediterranean shores. Geol., 37, 943-946.
Grilli S.T. and Watts P.; 1999: Modelling of waves generated by a moving submerged body: applications to
underwater landslides. Eng. Anal. Boundary Elem., 23, 645-656.
Guidoboni E. and Comastri A.; 1997: The large earthquake of 8 August 1303 in Crete: seismic scenario and tsunami
in the Mediterranean area. J. Seismol., 1, 55-72.
Guidoboni E. and Comastri A.; 2005: Catalogue of earthquakes and tsunamis in the Mediterranean area, 11th - 15th
century. INGV - SGA, Bologna, Italy, 1034 pp.
Guidoboni E., Comastri A. and Traina G.; 1994: Catalogue of ancient earthquakes in the Mediterranean area up to
the 10th century. INGV - SGA, Bologna, Italy, 504 pp.
Hamouda A.Z.; 2006: Numerical computations of 1303 tsunamigenic propagation towards Alexandria, Egyptian
coast. J. Afr. Earth Sci., 44, 37-44, doi:10.1016/j.jafrearsci.2005.11.005.
Tsunamigenic potential in SW Peloponnese Boll. Geof. Teor. Appl., 55, 469-484
483
Kastens K.A. and Cita M.B.; 1981: Tsunamis-induced sediment transport in the abyssal Mediterranean Sea. Bull.
Geol. Soc. Am., 92, 845-857.
Kennedy A.B., Chen Q., Kirby J.T. and Dalrymple R.A.; 2000: Boussinesq modelling of wave transformation,
breaking, and run-up I: 1D. J. Waterw. Port Coastal Ocean Eng., 126, 39-47.
Kirby J.T., Wei G., Chen Q., Kennedy A.B. and Dalrymple R.A.; 1998; FUNWAVE 1.0. Fully nonlinear Boussinesq
wave model, documentation and user’s manual, Res. Report CACR-98-06. Cent. Appl. Coastal Res., Dep. Civil
Eng., Univ. of Delaware, Newark, DE, USA, 80 pp.
Kirby J.T., Chen Q., Noyes T.J., Elgar S. and Guza R.T.; 2003: Evaluation of low frequency prediction of a
Boussinesq wave model: field cases. In: Proc. Int. Soc. Offshore Polar Eng., ISOPE, Honolulu, HI, USA, pp. 396-
403.
Konstantinou K., Papadopoulos G.A., Fokaefs A. and Orfanogiannaki K.; 2005: Empirical relationships between
aftershock dimensions and magnitude for earthquakes in the Mediterranean Sea region. Tectonophys., 403, 95-
115.
Lorito S., Tiberti M.M., Basili R., Piatanesi A. and Valensise G.; 2007: Earthquake-generated tsunamis in the
Mediterranean Sea: scenarios of potential threats to southern Italy. J. Geophys. Res., 113, B01301, doi:10.1029/
2007JB004943.
McCoy F.W. and Heiken G.; 2000: Tsunami generated by the Late Bronze Age eruption in Thera (Santorini), Greece.
Pure Appl. Geophys., 157, 1227-1256.
McCoy F.W. and Papadopoulos G.A.; 2001: Tsunami generation during the Late Bronze Age eruption of Thera:
evidence from tsunami deposits on Thera, Crete, west Turkey and the deep sea (abstr.). Am. J. Arch., 105, 258-
259.
Minoura K., Imamura F., Kuran U., Nakamura T., Papadopoulos G.A., Takahasi T. and Yalciner A.C.; 2000:
Discovery of Minoan tsunami deposits. Geol., 28, 59-62.
Mitzopoulos C.; 1900: Die erdbeben von Tripolis und Triphylia in den jahren 1898 und 1899. Petermann’s Mittheil.,
46, 277-284.
Novikova T., Papadopoulos G.A. and McCoy F.W.; 2011: Modeling of tsunami generated by the Giant Late
Bronze Age eruption of Thera, south Aegean Sea, Greece.Sea, Greece., Greece. Geophys. J. Int., 186, 665-680, doi:10.1111/j.1365-
246X.2011.05062.x.
Novikova T., Papadopoulos G.A., Ezz M. and Kijko A.; 2012: The large 365 earthquake and tsunami in the Hellenic
arc revisited: implications for tsunami hazard assessment. Geophys. Res. Abstr., 14, 9600.
Okada Y.; 1985: Surface deformation due to shear and tensile faults in a halfspace. Bull. Seismol. Soc. Am., 75,
1135-1154.
Özsoy E., Ünluata Ü. and Aral M.; 1982: Coastal amplification of tsunami waves in the eastern Mediterranean. J.
Phys. Oceanogr., 12, 117-126.
Papadopoulos G.A.; 2001: Tsunamis in the east Mediterranean: a catalogue for the area of Greece and adjacent seas.
In: Proc. Workshop Tsunami Risk Assess. Beyond 2000: Theory, Practice, Plans, Moscow, Russia, pp. 34-42.
Papadopoulos G.A.; 2009: Tsunamis in the Mediterranean SeaSea. In: Woodward J. (ed), The physical geography of the
Mediterranean, Oxford University Press, UK, pp. 493-512.
Papadopoulos G.A.; 2011: A seismic history of Crete: earthquakes and tsunamis 2000 B.C. - 2011 A.D. Ocelotos
Publ., Athens, Greece, 415 pp.
Papadopoulos G.A. and Chalkis B.; 1984: Tsunamis observed in Greece and the surrounding area from antiquity up
to the present times. Mar. Geol., 56, 309-317.
Papadopoulos G.A. and Vassilopoulou A.; 2001: Historical and archaeological evidence of earthquakes and tsunamis
felt in the Kythira Strait, Greece. In: Hebenstreit G.T. (ed), Tsunami research at the end of a critical decade,
Kluwer, Dordrecht, The Netherlands, pp. 119-138.
Papadopoulos G.A., Daskalaki E., Fokaefs A. and Giraleas N.; 2007: Tsunami hazard in the eastern Mediterranean:
strong earthquakes and tsunamis in the east Hellenic Arc and trench system. Nat. Hazard Earth Sys. Sc., 7, 57-64.
Papadopoulos G.A., Tinti S., Armigliato A., Charalampakis M., Fokaefs A., Karastathis V., Gallazzi S., Pagnoni G.
and Tonini R.; 2008: The Mw 6.9 earthquake of February 14, 2008 offshore SW Peloponnese: understanding
its non-tsunamigenic nature and the implications from the tsunami warning point of view. In: Proc. 31st Europ.
Seismol. Comm. General Assembly, Crete, Greece, p. 310.
Papadopoulos G.A., Karastathis V., Charalambakis M. and Fokaefs A.; 2009: A storm of strong earthquakes in Greece
during 2008. EOS Trans. AGU, 90(46), doi:10.1029/2009EO460001.
484
Boll. Geof. Teor. Appl., 55, 469-484 Papadopoulos et al.
Papadopoulos G.A., Daskalaki E., Fokaefs A. and Giraleas N.; 2010: Tsunami hazard in the eastern Mediterranean
sea: strong earthquakes and tsunamis in the west Hellenic Arc and trench system. J. Earthquake Tsunamis, 4, 145-
179.
Papazachos B.C. and Papazachou C.B.; 1997: The earthquakes of Greece. Ed. Ziti, Thessaloniki, Greece, 304 pp.
Papazachos B.C. and Papazachou C.B.; 2003: The earthquakes of Greece. Ed. Ziti, Thessaloniki, Greece, 286 pp. (in
Greek).
Papoulia J., Makris J., Mascle J., Slejko D. and Yalçiner A.; 2014: The EU SEAHELLARC project: aims and main
results. Boll. Geof. Teor. Appl., 55, 241-248, doi: 10.4430/bgta 0100.
Pareschi M., Favalli M. and Boschi E.; 2006: Impact of the Minoan tsunami of Santorini: simulated scenarios in the
eastern Mediterranean. Geophys. Res. Lett., 33, 1-6.
Scheffers A. and Scheffers S.; 2008: Tsunami deposits on the coastline of west Crete (Greece). Earth Planet. Sci. Lett.,
259, 613-624.
Schmidt J.F.; 1879: Studien über erdbebenüber erdbeben erdbeben. A. Georgi, Leipzig, Germany, 360 pp
SEAHELLARC Working Group; 2010: Preliminary seismic hazard assessments for the area of Pylos and
surrounding region (SW Peloponnese). Boll. Geof. Teor. Appl., 51, 163-186.
Shaw B., Ambraseys N.N., England P.C., Floyd M.A., Gorman G.J., Higham T.F.G., Jackson J.A., Nocquet J.M., Pain
C.C. and Piggott M.D.; 2008: Eastern Mediterranean tectonics and tsunami hazard inferred from the A.D. 365
earthquake. Nat. Geosci., 1, 268-276, doi:10.1038/ngeo151.
Soloviev S.L.; 1990: Tsunamigenic zones in the Mediterranean Sea. Nat. Hazards, 3, 183-202.
Soloviev S.L., Solovieva O.N., Go C.N., Kim K. and Shchetnikov N.A.; 2000: Tsunamis in the Mediterranean Sea
2000 B.C. - 2000 A.D. Adv. Nat. Tech. Hazards Res., Kluwer Academic Publichers, Dordrecht, The Netherland,
vol. 13, 237 pp.
Stavrakis N.; 1890: Statistiki tou plithysmou tis Kritis meta diaforon geografikon, istorikon, archaeologikon,
ekklisiastikon ktl. eidiseon peri tis nisou. Anastatiki Ekdosi, D.N. Karavia, Vivliothiki Istorikon Meleton, 125,
1978, Athens, 207 pp. (in Greek).
Tinti S., Armigliato A., Pagnoni G. and Zaniboni F.; 2005: Scenarios of Giant tsunamis of tectonic origin in the
Mediterranean. ISET J. Earthquake Tech., 42, 171-188.
Watts P., Grilli S.T., Kirby J.T., Fryer G.J. and Tappin D.R.; 2003: Landslide tsunami case studies using a Boussinesq
model and a fully nonlinear tsunami generation model. Nat. Hazards and Earth Syst. Sci., 3, 391-402.
Wei G. and Kirby J.T.; 1995: Time-depended numerical code for extended Boussinesq equations. J. Waterw. Port
Coastal Ocean Eng., 121, 251-261.
Wei G., Kirby J.T., Grilli S.T. and Subramanya R.; 1995: A fully nonlinear Boussinesq model for free surface waves.
Part 1: highly nonlinear unsteady waves. J. Fluid Mech., 294, 71-92.
Wells D.L. and Coppersmith K.J.; 1994: New empirical relationships among magnitude, rupture length, rupture
width, rupture area, surface displacement. Bull. Seismol. Soc. Am., 84, 974-1002.
Yolsal S., Taymaz T. and Yalçiner A. C.; 2008: Earthquake source rupture characteristics along the Hellenic Arc and
simulation of the A.D. 365 Crete earthquake and its tsunami. Geophys. Res. Abstr.,
10, 00065.
Corresponding author: Gerassimos A. Papadopoulos
Institute of Geodynamics, National Observatory of Athens
P.O. Box 20048, 11810 Athens, Greece
Phone: +30-210-3490165; fax: +30-210-3490165; e-mail: papadop@noa.gr
