Journal of Earthquake Engineering Tsunami Catalogs for the Eastern Mediterranean, Revisited

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Tsunami Catalogs for the Eastern Mediterranean, Revisited
Nicholas Ambraseys a;Costas Synolakis bc
a Imperial College of Science and Technology, London, United Kingdom b Department of Civil and
Environmental Engineering, University of Southern California, Los Angeles, California c Department
of Environmental Engineering, Technical University of Crete, Chanea, Crete
Online publication date: 01 March 2010
To cite this Article Ambraseys, Nicholas andSynolakis, Costas(2010) 'Tsunami Catalogs for the Eastern Mediterranean,
Revisited', Journal of Earthquake Engineering, 14: 3, 309 — 330
To link to this Article: DOI: 10.1080/13632460903277593
URL: http://dx.doi.org/10.1080/13632460903277593

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JournalofEarthquakeEngineering,14:309–330,2010
Copyright(cid:2)A.S.Elnashai&N.N.Ambraseys
ISSN:1363-2469print/1559-808Xonline
DOI:10.1080/13632460903277593
Tsunami Catalogs for the Eastern Mediterranean,
Revisited
NICHOLAS AMBRASEYS1 and COSTAS SYNOLAKIS2,3
1Imperial College of Science and Technology, London, United Kingdom
2Department of Civil and Environmental Engineering, University of Southern
California, Los Angeles, California
3Department of Environmental Engineering, Technical University of Crete,
Chanea, Crete
0
1
0
2 WecriticallyexaminetsunamicatalogsfortheeasternMediterraneanpublishedinthelastdecade,by
y
Ma referencetotheoriginalsources.Suchcatalogshavebeenwidelyusedintheaftermathofthe2004

12 BoxingDaytsunamiforprobabilistichazardanalysis,evenforprojectionsinaten-yeartimeframe.

6 Wecorrectclassificationandotherspuriouserrorsandpositanewlist.Weconcludethat,forsome
2
6: events,anyassignmentofmagnitude(evenonasix-pointintensityscale)isinappropriateduetolack
0
: ofinformation.Furthermore,weassertthatanytsunamicatalog,includingours,canonlybeusedin
t
A conjunction with sedimentologic evidence to quantitatively infer return periods of large events.
]
a Statistical analyses correlating the numbers of tsunami events only from catalogs with inferred
i
n
r intensities are meaningless, at least when focusing on specific locales where only a handful of
o
if tsunamishavebeenhistoricallyreported.Quantitativehazardassessmentsbasedonscenarioevents
l
Ca ofhistorictsunamisforwhich—atbest—onlythesizeandapproximatelocationoftheparentearth-

rn quake is believed known should be undertaken with extreme caution and only with the benefit of
e
h geologicstudiestoenhancetheunderstandingofthelocaltectonics.
t
u
o
S
f Keywords Earthquakes;Tsunamis;Catalogs;Mediterranean;IntensityScale;Historical;Run-up
o

v
i
n
U
[

y: 1. Introduction
B

d
de Tsunamis are water waves generated by impulsive geological phenomena such as earth-
a
o
l quakes, landslides, and volcanic eruptions. Because of the loss of life and damage to
n
w
Do property that often transcends national boundaries, understanding the terminal effects of
tsunamis along target coastlines has been one of the quintessential problems of coastal
hydrodynamics [Liu et al., 1991]. Furthermore, studies of tsunami incidence and asso-
ciated inundation information, when available, provide indirect evidence for submarine
crustal deformations, quite often not directly measurable at sufficient resolution.
The eastern Mediterranean region is an outstanding natural laboratory as tectonic
motions are rapid and varied, reasonably understood, and have a relatively well-
documented history; moreover, a variety of source materials are at hand. For earth
scientists and earthquake engineers, the main objectives of historical research into
primary sources for paleotsunamis are to refine and extend the information contained in
secondarystudiesandcatalogs,andtoprovideanobjectivemeasureofthereliabilityand
completeness of the data retrieved. This is very important, both for hazard assessment
studies and for helping focus geological investigations.
Received13August2009;accepted21August2009.
Address correspondence to Nicholas Ambraseys, Imperial College of Science and Technology, London
SW72AZ,UK;E-mail:[email protected]
309
310 N. Ambraseys and C. Synolakis
Catalogs of historical tsunamis are written to promote knowledge of earth sciences
and evaluate their contribution to the previous state of knowledge. Obviously, the
existence of a critical catalog does not, of course, mean that no further research is left
tobeundertaken,orthatnonewsourcesremaintobediscovered.Acatalogatbestsums
up the state of knowledge at the time written, and provides a basis for new work by
identifying gaps in understanding. One example is the catalog of Heck [1947] who
thought that probabilities of recurrence can only be appraised from historic records—
we nowknow that,inmostcases,itis sediment studies andfield geologic investigations
that provide meaningful estimates of return periods.
Unfortunately, many authors sometimes do a disservice to the study of historical
seismicity and tsunamis. Their work, rather than representing a comprehensive and
critical review of the historical data, is neither critical nor comprehensive. Such works
typicallyaccepttheveracityoftheirsourceswithoutfurtherinquiry,andtheonlybasisof
comparison of their lists or inferences is with their own earlier works. They appear
unaware of scientific interpretation of historical earthquakes or of other related recent
0
01 research. Thus, certain catalogs contain a rich variety of errors which are almost impos-
2

y sible to disentangle without resorting to the original material, the latter sometimes not
a
M
2 even referred to in these newer derivative catalogs. In summary, such constructs lack
1
6 what Eco [1984] referred to as the echo of intertextuality.
2
:
6 After several experiences of the difficulties created by accepting at face value
0

t: second-handinformationfrommanytsunamicatalogsandarticles,theschemeinprepar-
A
] ing the material for a multidisciplinary study of 2,000 years of seismicity in the eastern
a
i
n Mediterranean, has been to make a fresh start, based only on original sources, in which
r
o
if both documentary and field evidence are examined in their historical and regional
l
Ca context. In this article, we constrain the analysis to tsunamis before 1928. Post 1928

rn tsunamis and earthquakes were reported in the refereed literature, intrumental measure-
e
h
t ments exist, and their describtions more easily verifiable than older and more obscure
u
o
S events.
f
o Next, we review the problems arising from the assessment of historical reports with
v
i
n the perspective gained from studies of the original material, as retrieved by Ambraseys
U
[
: [2008c], to ask the following two questions.
y
B

ed 1. How much information can we reasonably expect to extract from historical
d
oa sources?
l
n
w 2. How reliable are historical tsunami catalogs for the eastern Mediterranean?
o
D
2. Seismic Sea Waves or Tsunamis?
Theterm‘‘tsunami’’iswidelyandcasuallyused,oftentorepresentanysortofdestructive
sea wave. Ausefuldefinition, given amongothersbyLiuet al.[1991], defines tsunamis
as long gravity waves of small steepness generated by impulsive geophysical events of
theseafloor.Infact,thepropagationanddispersionofgravitywaterwaveshasbeenwell
understood for quite some time, and they depend very strongly on both water depth and
wavelength.
At wavelengths very much greater than the water depth (d), the waves do not
disperse (i.e., their propagation is almost independent of wavelength) and they travel at
p
a velocity of (gd) where g is the gravitational acceleration. Waves with this character-
istic are transoceanic, and can propagate very long distances as a discrete packet, whose
amplitudedecreasesmostlythroughgeometricalspreading.Althoughtheymayhavevery
small amplitude in the open ocean (the height of the 2004 Sumatra tsunami in the open
Tsunami Catalogs for the Eastern Mediterranean, Revisited 311
Indian Ocean was less than a meter), where their wavelength makes them unnoticeable
except to sensitive ocean-bottom pressure sensors, the slowing down of such waves in
shallowwaternearcoastlinesleadstoadramaticincreaseinamplitudeandshorteningof
their wavelength and eventual breaking. This is the process known as shoaling.
By contrast, if the wavelength is smaller than or comparable to the water depth, the
wave velocity is a strong function of wavelength. Short wavelengths travel much slower
than long ones at speeds that are frequency dependent, so the wave is dispersive, i.e., its
initial shape disintegrates into component waves rapidly: the energy does not travel as a
discrete packet and the initial wave will not cross the major ocean basins as a recogniz-
able pulse.
Both types of waves can cause destruction: the first (long waves) over very widely
separatedregions(thetsunamifromthe1960ChileearthquakedrownedpeopleinJapan),
and the second (shorter waves) locally (as in Papua New Guinea, in 1998). Long-
wavelength transoceanic tsunamis can only be generated by a source process that
producesa deformation ofthe sea surface with long horizontal scales. The most obvious
0
01 way is in a big subduction zone thrust, as in the 2004 Sumatra earthquake. In that case,
2
y the fault which moved dipped at about 2(cid:2) and slipped between the surface and about 40
a
M
2 kmdepth.Theelasticresponseattheseabedwasawarpingwithhalf-wavelength40/tan
1
6 2 = 90 km, or a total wavelength of about 380 km, much greater than the average ocean
2
:
6 waterdepthofabout4km.Moreover,theseabeddeformationwasproducedbyarupture
0

t: that travelled at about 3 km/s with a local particle velocity of about 1 m/s. Under these
A
] conditions,becausethewaterisincompressible,theseasurfaceitselfdeformstoproduce
a
i
n a wave with the same shape as the deformation of its underlying sea floor. Thus,
r
o
if modeling of these waves is relatively straightforward, in that the sense that the source
l
Ca is well understood and can be constrained by seismology: it is often taken to be a wave

rn whose initial shape is determined by the underlying elastic dislocation, produced instan-
e
h
t taneously, which is then allowed to propagate over the known bathymetry of the ocean
u
o
S floor; see Dutykh and Dias [2008] for the most recent review.
f
o Itisimportanttorealizethatnotallbigearthquakes,evennearsubductionzones,will
v
i
n producesuchtsunamis.Forexample,big(M>8)normalfaultsontheouterrisesofsubduc-
U
[
: tionzones,becausetheyaregenerallysteepdippingattypically45–60(cid:2),willlikelyproduce
y
B tsunamis with characteristic wavelengths of (cid:3)<40 km, which can be dispersive at water
d
e
d depthsgreaterthan2km.Thisisoneofthereasonswhyitissometimesdifficulttopredict
a
o
nl whetheradamagingtransoceanictsunamiwillbegenerated,andwhetherawarningshould
w
Do beissued,onlyfrominitial determination ofthe sizeandlocation ofthe earthquake;more
information is needed, and this usually takes time to acquire and digest. Much ‘‘scenario
modelling’’ofearthquake-generatedtsunamisaroundtheeasternMediterraneanisbasedon
thiskindofanalysis.Nearfield,thetsunamiimpactisverydependentonthegeometryofthe
faultthatisinputastheinitialsource,whichinthispartoftheworldisnotalwaysknown.A
further complication can arise from the rupture velocity on the fault, which can be much
slowerthanthetypicalvalueofaround3km/s,andthisalsoaffectsthetsunamigeneration
processanditsevolutionatleastnearsource.[Kervellaetal.,2007].
Much attention has been given to ‘‘tsunamis’’ generated by submarine landslides,
whether or not they are themselves caused by the shaking of earthquakes [Bardet et al.,
2003].Thedifficultyofgeneratingtransoceanictsunamisfromlandslidesisimmediately
apparent: it is not easy to generate a wavelength of a few hundred km, except by
enormous slides. Furthermore, the slide must move very fast and as a coherent block to
generatethenecessarylongwaveatthesurface.Inthesecases,takinganinstantaneously
created shape as the sea-surface source is questionable in terms of modeling nearfield
inundation.
312 N. Ambraseys and C. Synolakis
Forensic investigations of both the sedimentology and the seafloor scars left by
submarine slides show that they are usually far from coherent, single events. The slides
areoftenretrogressiveandemplacedasmultipleevents,atspeedsthatarefarbelowthose
necessarytogeneratelongwavesatthewatersurface[Massonetal.,2006].Nonetheless,
suchslidesareclearlybadnewsforanyoneinthevicinityofadjacentbeachesatthetime:
they are capable of generating very large local amplitudes and of causing great destruc-
tion, unlikely as they are to cross major ocean basins. The uncertainty involved in
modeling the evolution of such events is therefore considerable, as the source properties
are much less well determined than for simple, large, subduction zone thrusts. Okal and
Synolakis[2004]providedsomesimplesourcediscriminantsbasedonthedistributionof
run-up values to help differentiate the impact of landslide and tectonic tsunamis from
local sources.
3. Historical Information
0
01 Historical sources record large damaging sea waves, small waves not being spectacular
2

y enough to attract attention. Descriptions from which one can deduce their occurrence,
a
M
2 size, and effects are few and difficult to verify, particularly when the information is
1
6 second-handandtheeventisnotwelldescribedinthesources. Itfollows, therefore,that
2
:
6 for small waves the record is very incomplete. The record may be more complete for
0

t: large sea waves, responsible for serious loss of property or life, the kind of information
A
] that chroniclers would not have omitted to record and embellish in their writings, often
a
i
n with a tinge of exaggeration. The latter remains an issue with reports in the region—the
r
o
if governmentnewschannelofGreeceERTonthesamedayoftheApril6,2009L’Aquila,
l
Ca Italy 6.3 earthquake described it as a biblical disaster [ERT, 2009].

n
r Thisfiltering outofsmallerevents has beennotedbefore andanexcellentsummary
e
h
ut appearsinGusiakov[2008];itisclearlyreflectedintsunamiincidencearoundtheworld
o
S in the past 50 years. Before 1992, only large tsunamis were reported, and it had been
f
o
widely believed that tsunamis occur in the Pacific Ocean once every decade. Beginning
v
i
Un with the September 2, 1992 Nicaraguan tsunami [Synolakis and Okal, 2005], tsunamis
[
: startedbeingreportedandtheirdamagesurveyedatanaveragerateofoneperyearinthe
y
B Pacific. With the wide deployment of tsunamographs starting in 2005 [Bernard et al.,
d
e
d 2006],itisnowclearthat,onaverage,twotothreetsunamisoccurperyearinthePacific,
a
o
nl most of which have little or no impact reported anywhere. Since it is quite unlikely that
w
Do the seismicity has changed so rapidly within a few decades, and this reported increase
coincideswiththedeploymentofsurveyteamsandtsunamographs,onecanonlyimagine
howincompletethehistoricrecordisforsmalltsunamis.Thisisnotnecessarilythesame
as with earthquakes. Asmall earthquake may be noticed over a wide area, while a small
tsunami may not, particularly if it strikes at night. One such example is the July 1, 2009
minitsunami in southern Crete [TA NEA, 2009] which affected a small area and was
sparsely reported. Thus, any attempts to perform statistical analysis based on historic
recordsandinvokingGutenberg-andRichter-typerelationshipstoquantitativelyevaluate
future incidence of tsunamis, this should be approached with extreme caution, particu-
larly when the number of available historic reports is small.
Withtheexceptionofveryfewcasesinhistoricrecordswhichdistinguishbetweena
small and relatively large wave and provide contextual information to evaluate whether
the reference is to a ‘‘real’’ tsunami, the confirmation of the latter as ‘‘genuine’’ is very
uncertain.Thereis noguaranteethatthedistancelimitsat which atsunami wasreported
asobservedareinfactthegeographicallimitsoftheeventofitscoastal manifstationsas
itunfoldedorreflectthelimitednumberofsourcesavailableorexaminedbytheassessor.
Tsunami Catalogs for the Eastern Mediterranean, Revisited 313
For certain historicalperiods and regions of the eastern Mediterranean, a tsunamiaffect-
ing a few neighboring coastal sites may, in reality, be the signature of a relatively large
tsunamiinthefarfield.Intheearlyperiod,withtheexceptionofAlexandriaandperhaps
Cyrenaica in Libya, there were no urban centers along the whole length of north Africa
whichcouldprovideinformationabouttsunamieffects,andthesamecanbearguedabout
the south coast of Asia Minor opposite Cyprus. This restriction is less serious for the
Aegean Sea, which is clustered with islands and closely spaced population centers.
Tsunami catalogs give a conspectus of results obtained from studies of individual
eventslistedinearthquakecatalogs.Theyarenecessarilyasummary,andcannotgointo
all the details that are available for a particular event. It is essential, however, that they
provide the appropriate references to the original sources of information for the infer-
ences they publish. Parametric catalogs, which also list estimates of earthquake para-
metersandwaveheightsorrun-upareasreliableastheprimarysourcesfromwhichthey
have been extracted.
In preparing a parametric tsunami catalog, therefore, it is important, that the princi-
0
01 ples of interpretation of the phenomenon must be clearly described to allow readers to
2

y distinguish carefully between the different mechanisms that may have produced the
a
M
2 catalog entries. Waves and flooding of the coast produced by small submarine slumps,
1
6 by rockfalls and landslides, by extreme meteorological conditions, by seisches, and
2
:
6 shocks felt by vessels at sea, should not be classed as tsunamis, and they must be
0

t: identified separately. When in doubt, classification of the nature of the event should be
A
] listed as doubtful, to trigger further studies. Here we note that while the two world
a
i
n databases—which themselves are compilations of different catalogs—use a ‘‘validity’’
r
o
if index to underscore uncertainty [Gusiakov, 2008], it is unclear if the index is assigned
l
Ca consistently by the same cataloger for the entire database, as, for example, in Soloviev’s

rn catalogs, or whether estimates by different scientists for different regions are patched
e
h
t together in a single database.
u
o
S

f
o

iv 4. Mechanism
n
U
[
: It is not always possible to distinguish between the different mechanisms that triggered
y
B anyparticularwavefromitsdescriptioninhistoricalsources,whichareallvague,almost
d
e
d telegraphic. Even for several large destructive tsunamis in the past century [Messina,
a
o
nl 1908; Unimak, 1946; Amorgos, 1956; Papua New Guinea, 1998], controversy raged, or
w
Do still does, as to whether the wave responsible for most of the damage in selected locales
was triggered by a coseismic landslide or directly by the tectonic seafloor deformation
[Bardet et al., 2003; Tinti and Armigliato, 2003; Okal et al., 2003; Billi et al., 2008;
Gerardi et al., 2008].
Tsunamis generated by tectonic displacements of the sea bed are of primaryinterest
not only because of the evidence that they provide for submarine crustal deformations,
but also because their coastal effects are combined with those of the large magnitude
earthquake. There are very few cases of tsunamis of this category that can be identified
unequivocallyinthehistorical record inthe eastern Mediterranean. Here, werefertothe
region west of the Adriatic. The only case we know before 1928 confirmed beyond a
shadow of a doubt is for the earthquake of July 21, 365 AD, for which historical data,
field observations, radiocarbon data, and hydrodynamic modeling confirm that this was a
catastrophicevent.ItdidnotoccuronthesubductioninterfacebeneathCrete,butonafault
dipping30(cid:2) withintheoverridingplate,andliftedwesternCretebyupto10m(M(cid:3)8.2),
in the process generating a damaging tsunami throughout much of the eastern
Mediterranean, but likely not in the Aegean Sea [Shaw et al., 2008]. Tsunami waves
314 N. Ambraseys and C. Synolakis
of tectonic origin are probably those associated with the earthquakes of 1303, presently
under study. For other events, historical reports have not yet been correlated with field
geologic studies or modeling. Still for others, sediment studies suggest large tsunamis,
which have yet to be correlated with any historic reports; see, for example, Vo¨tt et al.
[2007] for tsunamis in the Ambracian Gulf.
TheevidencesofarfortsunamisintheMediterraneanregion,someofthemdamaging,
suggests that many are due tosubmarine sliding triggered by earthquakes or other causes.
The occurrence of such secondary earthquake effects depends on the size of shaking and
epicentral distance, butchiefly onthe inherentresistanceofthe sliding material tofailure.
This,inturn,dependsontheslopeofthedepositandthepost-failureundrainedstrengthof
the slide. Failure criteria remain anactiveareaofcutting-edge research.
Mild submarine slopes like those of the Black Sea, offshore northern Anatolia may
slump and slide and produce sea waves of noticeable heights, even when the causative
earthquake happened 50–100 km away, which is the case of the north Anatolian earth-
quake of 1939. Much of the currently available historical information about this class of
0
01 tsunamiscomesfromthelargenumberofsubmarinetelegraphcableswhichwerebroken
2
y by submarine slides in the latter part of the 19th century, triggered by earthquakes in the
a
M
2 Ionian, Aegean, and Cretan Seas, as well as in the Gulf of Corinth and elsewhere. This
1
6 information can be found in maintenance documents of the Telcon and the Anglo
2
:
6 Mediterranean Telegraph Company who had the cable repair duties since 1870, when
0

t: the cables were laid in this part of the eastern Mediterranean.
A
] Fromthesedocuments,welearnthatintheearthquakeofDecember26,1861(Ms=
a
i
n 6.4) in Egio, submarine slumping in the Gulf of Corinth played an important role in
r
o
if enhancing large-scale mass movements, originating from steep delta front and slopes. In
l
Ca this part of the Gulf, the coastline is of high relief with steep gravel and conglomerate

rn cliffsandslopegradientsrangingfrom6–45(cid:2)andthedeltafrontsextendtoadepthof150
e
h
t m, with gradients ranging from 16–25(cid:2). The Puntas front has a narrower shelf than
u
o
S Vuraikos, Keranitis, and Selinus, and a steeper delta slope. Much of this physiography
f
o is the result of gravitational mass movements in the form of slumping, retrogressive
v
i
n submarine sliding, and flows. These processes can be maintained by high sedimentation
U
[
: and triggered by instabilities induced by earthquakes, by changes of the loading condi-
y
B tionscaused byheavyrainfalls,excesspore pressures,andscouring.Soonafterthe1861
d
e
d earthquake, clear water out in the Gulf became suddenly both agitated and muddy. Both
a
o
nl the north and south coast of the central part of the Gulf of Corinth were flooded by a
w
Do smallwave.SubmarinemovementsinthispartoftheGulfareknowntohavetakenplace
even without the help from earthquakes, triggering more damaging seismic sea waves
thanin1861,affectingboththenorthandsouthcoastsoftheGulfofCorinth.Also,after
1880 cable breaks in the Gulf caused by submarine slides show that heavy rainfall,
scouring, and earthquakes can trigger and produce large mass movements along wide
fronts [Forster, 1890, p. 73–92; PEX, 1954; Ferentinos et al., 1988].
Similarly, the subcrustal earthquake of August 27, 1886 (Ms = 7.0), set up waves at
Agrilia, north of Filiatra, that flooded the coast. At the same time, the submarine
telegraph cables between Zakinthos and Iraklio, 30 miles from Filiatra, were broken at
a depth of 700 fathoms. Four knots (7.3 km) of cable were later found at a depth of 900
fathoms covered over by slide material [Forster 1890, p. 92], thus confirming that the
shock had triggered a submarine slide.
ThetsunamicausedbytheearthquakeofJuly10,1894affectedthewesternmostpart
of the coast of the Sea of Marmara. It is reported that after the earthquake the sea was
veryagitatedandinplacesretired200mleavingmanyboatsandvesselshighanddry:at
SanStefano,thewatersreturningwatersrose1.5mabovetheirnormallevel,overflowing
Tsunami Catalogs for the Eastern Mediterranean, Revisited 315
the quay and nearby shore casting small fishing boats on to the shore, where it caused
someminordamage.Depthsoundingsalongthecoasttakenaftertheearthquakeshowed
no changes. However, the submarine cable between Kartal and the Dardanelles was
ruptured 3 miles off Kartal in more than one place. The mode of rupture suggests that
the cable was sheared by the fall of slide material while local depth soundings showed
some changes in the bathymetry, suggesting a submarine slide.
AsmallwavewastriggeredbytheJune15,1995(Ms(cid:3)6.1)Egionearthquakewhich
killed 26 people through the collapse of two multi-story structures. One of us surveyed
theareathedayafterandobtainedseveralaccounts,includingthereportfromthecaptain
ofafreighter,ViaAmazonas.Theshipwasmooredat60mdepthoffshorewaitingtosail
into port the next day to unload its cargo. At night, the crew was awakened by a loud
grindingnoiseandfeltasif‘‘agiantarmwaspullingtheshipbytheanchor.’’Thecaptain
orderedtheanchorlowered.Oncethedisturbanceceased,hecheckedthesonaragainand
itshowedadepthof82m.Hewasunawareoftheearthquake,untilhewentintoportthe
next day. We interpreted this as evidence of a landslide. Later marine surveys using sub
0
01 bottomprofilersandanROVbyPapatheodorouandFerentinos[1997]confirmedseveral
2

y sediment failures in the region. While the scarps were not dated, they were inferred as
a
M
2 recent. The resulting wave caused the shoreline to advance up to 10 m inland along the
1
6 shallow beaches east of Egion and flooding a coastal road.
2
:
6 On examination, the largest number of cases of small waves in the eastern
0

t: Mediterranean reported in modern literature as tsunamis were found to be due to local
A
] flood waves caused by small submarine slumps and slides near the coast, some of them
a
i
n taking place as frequently as slopes fail on land without an earthquake trigger. It is
r
o
if reasonable to expect that this similarity exists in both sub aerial and submarine environ-
l
Ca ments and that the occurrence of sea waves of all sizes may occur with or without

rn earthquakes.Inthelastdecade,thiswasobservedwiththewavethathitFatuHivainthe
e
h
t Marquesasin1999.Itstruckthelocalschoolofmainvillageoftheislandonacalmday
u
o
S when no earthquakes had been identified as possible triggers. The field survey of Okal
f
o etal.[2002]identifiedthesourceofthetsunamiasanasesismiccollapsedweatheredcliff
v
i
n a 5 km east of the village.
U
[
: SimilarlyintheGulfofCorinth,thedamagingsea-waveofFebruary7,1963wasnot
y
B causedbyanearthquake.ItdevelopedasalongwavefrontonthesouthcoastoftheGulf,
d
e
d where in places the coast had slumped into the sea. The wave advanced and flooded the
a
o
nl opposite, north, coast of the Gulf with wave heights of up to 3 m, causing considerable
w
Do damageandthelossofonelife[Ambraseys,1963].Onexamination,itwasfoundthatthe
wave was caused by an aseismic submarine slide, a common occurrence in the Gulf,
particularly during the wet season.
Clearly, both medium and large magnitude earthquakes on land may produce sub-
marine slope failures and associated flood waves, many tens of kilometers away from the
epicentralarea.Manyofthesewavesmaynotconformstrictlytothemathematicalcriteria
to be classified as long waves, for their characteristic wavelength could be of the same
orderasthedepth.Inpastdecades,thesewaveshavebeenreferredtobymarinegeologists
as‘‘backfillwaves,’’[Plafker,1999],tounderscorethattheinitialdisturbanceisprimarilya
depressionofthewatersurface.Inthesecases,otherconditionsbeingequal,theoccurrence
ofatsunamiofthiscategoryislikelytodependmoreontheslopestabilityoftheregional
bathymetry, rather thanon the size ofa triggering earthquake.
Extensivefloodingoflow-lyingareasonthecoastsoftheAegeanandIonianSeasis
known to have occurred often due to deep barometric lows, occasionally with damaging
effects [Critikos, 1931]. Abnormal barometric conditions are known to have been strong
enough even to reverse the flow of the Strimon River for a distance of at least 4 km
316 N. Ambraseys and C. Synolakis
upstream from its delta. In one of these occasions, the river flowed upstream for about
half an hour, flooding the countryside before the current reversed itself and ran towards
the sea [Belousek, 1934].
TheearthquakeofNovember27,1914wasprecededbyfloodingofthestreetsinthe
portareaofLefkas.Thiswasduetoanexceptionallyhightideobservedinthelastweek
of November 1914, which started well before the earthquake, a typical phenomenon in
thispartoftheIonianSeaduringthewintermonths.Thetidefloodedtheharborareaand
also the landing places at Nidri, and the sea began to ebb well before the earthquake of
the 27th. This cannot be regarded as a tsunami.
Similar cases, which do not fall in the tsunami category, were reported from the
coasts of the Aegean and Marmara Seas. Most recently, Okal et al. [2008] wrote that
during a post-event field survey of the 1956 Amorgos tsunami, residents in Nisiros and
Halki reported that, on occasion, they observe large floods that cause the shoreline to
advance for tens of meters and stay for several weeks, and asked whether they could be
associated with persistent barotropic conditions they had been observing
0
01 contemporaneously.
2

y
a
M

12 5. Magnitude

6
2
:
6 In attempting to infer past tsunami inundation for the purposes of hazard mitigation or
0

t: evaluating the veracity of reports, some estimate of the magnitude of the triggering
A
] earthquakes is essential.
a
ni Surface wave magnitudes M of almost all 20th century significant earthquakes are
r S
o
lif known, while for most of the larger events of the pre-instrumental period MS can be
Ca estimatedfrommacroseismicdatawithacceptableerror;forthepurposeintended,historic

n
r events may be grouped into four sizes: V refers to events with M (cid:4) 7.8, i.e., very large;
e S
h
out L(large)toeventswith7.8>MS(cid:4)7.0,M(medium)toeventswith7.0>MS(cid:4)6.0,while
f S S (small) refers to events with 6.0 (cid:4) MS . Higher resolution is superfluous, in view of
o the fact that even for 20th century events magnitude estimates by different sources can
v
i
n differ by as much as 0.5 points. For example, the April 6, 2009 L’Aquilia earthquake
U
[
: was reported as magnitude 5.8 by INGV and 6.3 by USGS.The July 1, 2009 Southern
y
B Crete shake was reported with a 5.8 surface magnitude by the Geodynamics Instiute of
d
e
d the the National Obervatory of Athens (NOAGI), but as 6.4 by the USGS, reflecting
a
o
nl local attenuation from an event located south of the Hellenic Arc.
w
o
D
6. Focal Depth
It is of course desirable to be able to judge whether the reported tsunamis were due to a
shallow or subcrustal event. Given good macroseismic information, it is possible to
distinguish between a shallow and a lower crust/subcrustal event. The former are very
likely to be followed by many noticeable aftershocks and to demonstrate a well-defined
epicentral region. The latter are very unlikely to be followed by aftershocks, their
epicentral region cannot be defined with similar accuracy as the shallow events, while
in the far field they are likely to cause seiches, and standing waves. The location of the
earthquake and its tectonic setting may also help decide between the two alternatives.
7. Run-Up and Wave Polarity
Historical data are of little or no use for the assessment, even approximately, of the run-
up,polarity,andfirstphaseofthewaveasitadvancedonagivenlocale,unlesstheheight
Tsunami Catalogs for the Eastern Mediterranean, Revisited 317
of the wave is large, well described, and the historic description free of exaggeration.
Eveninthemodernliterature,thepolarityofthewavestartedbeingdocumentedindetail
since the 1960s. In 1995, there was an effort to differentiate between leading elevation
(LEN)andleadingdepressiondipole(LDN)orN-waves[TadepalliandSynolakis,1994].
The 2004 Boxing Day tsunami was the first time that there were detailed reports of the
polarity of the first wave arrival on both sides of the causative thrust fault; east of the
Sumatran Subduction Zone, the tsunami manifested itself as an LDN, west as an LEN
[Synolakis and Kong, 2006].
We note that there is no physical justification for any relationship between run-up
and any measure of magnitude or intensity, and such correlations might be meaningless,
particularly when the grossly subjective estimates of run-up available in historical
information are used. Even in the case of the 1998 Papua New Guinea tsunami, the
differentiationbetweenrun-upandoverlandflowdepthobservationsandtheimplications
in tsunami inundation modeling was delayed until Lynett et al. [2003]. Only with
comprehensive and detailed records spanning centuries, as sometimes available for
0
01 Japanese sites, may such relationships be meaningful and then only for the specific
2

y locales for which the records exist.
a
M

2
1

6
2 8. Tsunami Intensity
:
6
0
t: Tsunamiintensityfor20thcenturyearthquakesmaybedefinedinamannersimilartothat
A
] ofearthquakeintensity.TheEuropeanSeismologicalCommission(ESC)initsmeetingin
a
i
n Jena in 1962 established a subcommittee on tsunamis which one of us chaired for a
r
o
if number of years. In 1964, the subcommittee proposed a tsunami intensity scale, the
l
Ca ‘‘ESC-Tsunami scale’’.

n
r Therefiningofthegradingofthescalewasthendiscussedinanumberofoccasions
e
h
ut bythesubcommitteeaswellasinIUGGmeetings.Itwasagreedthenthattheformofthe
o
S scale was more suitable for grading 20th century tsunamis rather than earlier events. It
f
o
wasalsofeltthat,inasmuchaswearenotinapositiontoberigorousinourdefinitionof
v
i
Un various ratings, then the investigator should have enough leeway to use his own judge-
[
: ment without being hemmed-in by a scale that is too specific. Also, secondary effects
y
B such as coseismic slides should not be incorporated into the scale.
d
e
d By the end of the 1960s, the six-grade ‘‘ESC-Tsunami scale’’ had been tested with
a
o
nl new case histories by the subcommittee, which now included Vit Karnik and Sergei
w
Do Soloviev, to the extent that it has been used ever since for the assessment of tsunami
intensities in the Mediterranean and Atlantic coastal areas of Europe. During the same
period, discussions at International UNESCO Committee meetings for the Mitigation of
Earthquake Hazard, stressed repeatedly the need for more research and less attempt at
‘‘standardization,’’ and that this applied particularly to the improvement of the ‘‘ESC-
Tsunami scale’’ [Karnik, 1971]. When and why the ‘‘ESC-Tsunami scale’’ was renamed
the ‘‘Sieberg-Ambraseys’’ scale, we have no idea and even Professor Ambraseys never
bothered to find out.
Possiblybecausemostoftheearlytsunamifieldsurveyssince1992wereconducted
by civil and coastal engineers not familiar with classic geological field investigation
practices,mostpost1990sfieldsurveyarticlesdonotincludeanyassessmentsofseismic
or tsunami intensity [Synolakis and Okal, 2005]. However, they do include detailed
measurements of run-up and inundation, and often detailed descriptions of the damage
in specific locales. As such, they constitute historic documents. Any tsunami cataloger
interestedinparametricstudiescantheninfertsunamiintensityatthesix-pointscalewith
the same consistent bias used in the same cataloger’s inferences for earlier events. The