Observatoires sousmarins et rle pour la dtection des glissements sousmarins et des tsunamis

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Observatoires sous-marins et rôle pour la
détection des glissements sous-marins et des
tsunamis

• Pierre Henry, CEREGE - Collège de France
• Roland Person, IFREMER, Brest
• Anne Deschamps, Nicole Bethoux, Geosciences Azur,
  Villefranche-sur-Mer et Sophia-Antipolis

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Tsunami Sources

• Earthquakes
• Tsunami source model
• Static (before/after) topography change
• A priori knowledge of fault geometry is required
• Volcanoes
• Multiple source types
• Caldeira collapse (Santorin, Krakatau)
• Landslides
• Explosions
• Slope instabilites
• Tsunami source model
• Dynamic effects must be included
• Detection
• Remote vs. in situ sensors

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New sounds from the shallow and deep ends of
subduction
Very-low frequency earthquakes
Obara and Ito (2005) Davis et al. (2006)
Tremors
Obara (2002)
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Very low frequency earthquakes -Obara and Ito
(2005)
Regular
VLF
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Related Questions - What is the difference
between an accretionary wedge and a landslide ?

• Detection
• What is the importance of slow slip (rupture
  propagation velocity ltlt Rayleigh wave velocity)
  in tsunami generation during an earthquake ?
• How do silent slip events make noise ?
• Prevision
• Is the catastrophic evolution of landslides
  controlled by the properties of the sliding
  surface ?
• What controls the seismic-aseismic transition in
  subduction zones ?
• Mechanics
• How does fluid pressure vary in a decollement and
  how does it relate with deformation ?

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Sismomètres fond de mer large bandes
Crawford et al., BSSA, accepté
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LIMO

• Installatin of (Cabled) Borehole Observatories on
  the Ligurian Margin
• Pierre Henry, Roland Person, Charles K. Paull,
  Nicole Béthoux, Anne Deschamps, Achim Kopf,
  Sébastien Migeon, Barbara Romanowicz, Etienne
  Ruellan, Françoise Sage, Bruno Savoye, Ralph
  Stephen, Nabil Sultan.

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Observatory context

• ESONET Network of Excellence
• Optical cable link to ANTARES Neutrino telescope
• IODP needs test site for borehole instrumentation
• Ifremer center in Toulon can provide logistic
  support (ROV servicing)

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LIMO - Science focus

• Approach gravity driven processes at different
  scales
• Alpine collapse, margin failure and subduction
  initiation
• Failure of sedimented slope
• Coupling between stress, pore-pressure and strain
• external forcing (sea level, fluid migration,
  sedimentation and compaction, airports) vs.
  internal processes (dilatancy, compaction)
• Influence of coastal aquifers on offshore slope
  stability

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Seismometer borehole(s)

• Cased (ROV accessible) hole
• Broadband
• Test short period strings (SEIS-Cork)
• Location
• Ideally above seismicity cluster N of Var canyon
• Alternate on Var Levee

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Hydrogeology boreholes

• Address permeability-scale dependency in clay
  rich hemipelagite/turbidite series.
• Develop alternatives to packers and CORKs.

CORK (cased hole) accessible inner casing partial
retrievability
Wireline instrument passive monitoring non
retrievable
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Submarine slope monitoring

• Strain and pore pressure
• Observatory components
• repeat AUV surveys -gt evolution of morphology (E.
  Ruellan)
• seafloor
• OBS tiltmeter (P. Charvis, Y. Guglielmi)
• Fiber optic distributes strain and temperature
  sensor network
• below seafloor
• pore pressure, temperature (N. Sultan, J.F.
  Rollin)
• electrical conductivity (coastal sites - P.
  Pezard)
• strain (tiltmeters ?)
• Implementation
• Need for a seafloor drill -gt alternate platform
• MeBo ? (Bremen University, A. Kopf)
• Telemetry

limo-3B
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What will be the main benefit for society ?

• Awareness
• Would Damocles feel better with a strain meter ?