Diapositive 1

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Lundi 19 Juin 2006  9h30-10h30 Xavier Le
Pichon (Collège de France) Présentation du
contexte tectonique et questions posées pour le
problème du risque de tsunamis 10h30-11h15 Aless
andra Maramai (Institut National de Géophysique
et de Volcanologie de Rome, Italie) Tsunamis in
the Mediterranean Sea and new data for a revision
of historical cases in Italy 11h15-12h00 Hélène
Hébert (CEA, DASE/LDG, Bruyères-le-Châtel) Aléa
tsunami en Méditerrannée quelques contraintes
données par la simulation numérique sur les
expositions historiques et futures 12h00-12h30
Sinan Ozeren (Université Technique d'Istanbul,
Turquie) Modélisation des tsunamis produits par
les glissements 14h00-15h00 Efim Pelinovsky
(Académie des Sciences, Russie) et Christian
Kharif (IRPHE, Marseille) Les risques de
tsunamis sur les côtes françaises de
Méditerranée 15h00-16h00 Nabil Sultan et Bruno
Savoye (Ifremer, Brest) Mécanisme d'effondrement
en 1979 du port de Nice mesures in-situ et
modélisation 16h30-17h30 Jacques Deverchère
(Université de Bretagne Occidentale, Brest)
Tectonique de la marge nord-africaine et risques
de glissement 18h Cocktail offert par
l'Europôle de l'Arbois
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Le problème du risque de tsunami en Méditerranée
Occidentale contexte tectonique et quelques
réflexions

• Xavier Le Pichon,
• Collège de France,
• Aix-en-Provence

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I use here the restrictive definition of tsunami
of Tinti et al. (2004) for their new catalogue of
Italian tsunamis Tsunami is a series of sea
waves generated by a large-scale source that can
be 1) the sudden displacement of the sea-floor
due to tectonic dislocation, or 2) the motion of
a body sliding along the sea-floor. I thus
limit myself to discussing two possible sources,
relatively large underwater earthquakes able to
produce sizeable tsunamis (average magnitude 6.8
in our area according to Soloviev et al., 2000)
and underwater giant slides (of the order of km3
or tens of km3).
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Earthquake created tsunami the giant Indian
tsunami of Dec 26 2004

• A tsunami caused by a giant magnitude Mw 9.3
  subduction earthquake

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An incredibly large human disaster
Miller, Science 12 August 2005
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An earthquake created tsunami
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Magnitude 9.3, a surface rupture equivalent to
half the surface of France! Ammon et al.,
Science, May 20 2005
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A model for the distribution of uplift and
subsidence
Ammon et al., Science, 20 mai 2005
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The 8.7 following March earthquake did not create
a destructive tsunami
William Power, 2005 http//www.gns.cri.nz/
30/03/2005
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Giant submarine slides can also cause tsunamis
Nisbet et al. 2004
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The giant 3500 km3 8150 BP Storegga tsunami
Bondevik et al. 2005
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Bondevik et al. 2005
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Bondevik et al. 2005
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Bondevik et al. 2005
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Impossibility of evaluating quantitatively the
tsunami risk on the coasts of Balearic and
Ligurian seas

• Only two relatively modest tsunamis (intensity 3
  on a 6 degrees scale) are well documented on
  these coasts that are shielded by Corsica and
  Sardinia from the Tyrrhenian. One was generated
  by a slump, the other by an earthquake.

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Ideally, one should be able to evaluate the
return period as a function of the wave amplitude
but this is impossible to do with the data
available
Dawson et al. 2004
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The 1979 submarine landslide Nice event
Assier-Rzadkiewicz et al. 2000
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Assier-Rzadkiewicz et al. 2000
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The 1887 earthquake createdLigurian tsunami

• The only relatively well observed and modeled
  natural tsunami

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A 6.3 earthquake
Ferrari 1991
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Italian Tsunami Catalogue http//www.ingv.it/tsu
nami
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Eva et al. 1997
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A second difficulty The plate tectonic
context Geodesy indicates that the 5/6 mm/yr
Africa/Europe motion is entirely absorbed south
of Sardinia. Any eventual effect of the
Africa/Europe motion on the northern Ligurian and
Balearic seas can only be indirect, through the
clockwise rotation of Apulia. And I consider this
effect as unlikely. -Thus the only possible
location for great tsunamigenic earthquakes
susceptible to affect French coasts is the plate
boundary along northernmost North Africa.
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(No Transcript)
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Nocquet Calais, 2003
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Hollenstein et al. 2003
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Nocquet Calais, 2004
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No well evidenced effect of the Apulian
rotation. The idea of a well localized
rotation pole in the Po plain is difficult to
defend.
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Calais et al, 2000
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Nocquet Calais, 2004
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Calais et al, 2000
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The stress field in southern France is highly
heterogeneous - This heterogeneity implies that
local forces dominate over boundary applied ones.
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Baroux et al. 2001
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Baroux et al. 2001
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Important lateral variations of volume forces are
present due to rapid variation in Moho depth and
topography
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Moho depth after Chamot-Rooke et al.,
1999, Stress field after Baroux et al., 2001
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Is the 1755 Lisbon tsunami a possible model for a
future North African margin earthquake? SW of
Portugal, a diffuse 100 km wide plate boundary
absorbs 4 mm/yr of convergence with rare episodic
great earthquakes
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Hayward et al. 1999
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Sartori et al. 1994
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Hayward et al. 1999
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A well recorded tsunamigenic event, the 1969 Mw
7.9 earthquake
Fukao 1973
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Fukao 1973
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An intra-oceanic diffuse plate boundary of
high elastic rigidity
Fukao 1973
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Localization of the 1969 tsunami
Gjevik et al. 1997
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The 8.75 1755 Lisbon earthquake, the largest felt
area for shallow earthquakes
Johnston 1996
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Johnston 1996
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Dispersion in proposed earthquake locations
possibly in part due to complex multiple sources
Villanova et al. 2003
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Villanova et al. 2003
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Source area of tsunami is somewhere SW of Portugal
Mendes et al. 1999
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Baptista et al. 2003
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Gracia et al. 2003
Source area most probably coincides with diffuse
plate boundary SW of Portugal
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But is this type of diffuse plate boundary
present along North Africa?
Buforn et al. 2004
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The Boumerdès 2003 margin earthquake
Ayadi et al. 2003
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Ayadi et al. 2003
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Alternatively, could we consider that a giant
landslide in the Balearic or Ligurian seas could
produce a catastrophic tsunami?
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Giant landslides have now been discovered
everywhere in the oceans
Maslin et al. 2004
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Maslin et al. 2004
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Low latitude before 13 000 BP High latitude after.
Maslin et al. 2004
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The giant 500 km3 22 000 BP Balearic turbidite
deposit
Rothwell et al. 1998
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Rothwell et al. 1998
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Rothwell et al. 1998
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• 1) In summary, in historical times, no
  catastrophic tsunamis (5 or 6 intensity) are
  known to have occurred on the northern margins of
  the Ligurian and Balearic islands and we are
  sheltered by Sardinia and Corsica from the
  dangerous Tyrrhenian sources. It thus seems to me
  impossible to make a quantitative complete
  evaluation of the risk for our Ligurian and
  Balearic margins.
• 2) However giant submarine slides have occurred
  during glacial lower sea-level periods. They are
  much less likely today but can we exclude their
  possibility?
• 3) In addition, the slow recent shortening
  deformation of the African margin has not
  produced known high intensity earthquakes (8 or
  more) and the style of deformation there does not
  suggest that they are likely. But the experience
  of the Lisbon earthquake suggests that very long
  continuous sources are not necessary to produce
  giant earthquakes within a highly stressed wide
  boundary. There several sources may be ruptured
  nearly simultaneously. I would like to be sure
  that we can exclude this possibility.

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Mardi 20 Juin 2006  9h30-10h15  Sébastien
Migeon (Géosciences Azur, Villefranche-sur-Mer)
Les glissements sous-marins de la marge nord
ligure impact des apports sédimentaires, des
séismes et de la tectonique salifère 10h45-11h00
Pierre Henry (CEREGE/Collège de France,
Aix-en-Provence) Observatoires sous-marins et
rôle pour la détection des glissements
sous-marins et des tsunamis 11h00-12h00
Stefano Tinti (Université de Bologne, Italie)
Numerical aspects of investigation on the
Mediterranean tsunamis and implication for a
Mediterranean Early Warning System 12h00-13h00
Xavier Le Pichon (Collège de France) Reprise
des questions ouvertes et discussion