Longsor Underwater

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    Underwater Landslides as CausesUnderwater Landslides as Causes

    of Tsunamisof Tsunamis

    A multidisciplinary and integrated researchA multidisciplinary and integrated research

    approachapproach

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    Research Program MethodologyResearch Program Methodology

    General ApproachGeneral Approach

    Field ProgramField Program

    Laboratory Testing and ExperimentsLaboratory Testing and Experiments

    Geotechnical ModelingGeotechnical Modeling

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    PremisePremise

    Underwater landslides can cause tsunamisUnderwater landslides can cause tsunamis

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    Tsunami Generation by

    Rotational Slump

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    Tsunami Generated by

    Translational Slide

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    Historical EventsHistorical Events

    18121812Santa Barbara, California (25m, 5min)Santa Barbara, California (25m, 5min)

    19291929Grand Banks, Newfoundland (10m, 30min)Grand Banks, Newfoundland (10m, 30min)

    19461946UnimakUnimak, Alaska (30m, 45min), Alaska (30m, 45min)19751975KalapanaKalapana, Hawaii (8m, 5min), Hawaii (8m, 5min)

    19921992Flores Island, Indonesia (30m, 3min)Flores Island, Indonesia (30m, 3min)

    19981998Papua New Guinea (15m)Papua New Guinea (15m)

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    Slump

    Meters

    Maximum tsunamiMaximum tsunami

    amplitude aboveamplitude abovesea level as thesea level as the

    wave approacheswave approaches

    Sissano Lagoon,Sissano Lagoon,PNGPNG

    Tappin et al. (2001)Tappin et al. (2001)

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    Multidisciplinary ProgramMultidisciplinary Program

    Integrated project approachIntegrated project approach

    MultiMulti--institutionalinstitutional

    MultiMulti--disciplinesdisciplines GeologicalGeological

    GeotechnicalGeotechnical

    GeophysicalGeophysical

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    Underwater Landslide Triggering MechanismsUnderwater Landslide Triggering Mechanisms

    There are at least 15 different possible activators

    for underwater landslides, which include the

    following: Seismic ground motion

    Liquefaction of sediment Rapid Sediment accumulation or over-steepening

    Overpressures/Underconsolidation

    Other: erosion, creep, gas etc.

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    Geological/Geotechnical Needs forGeological/Geotechnical Needs for

    Hydrodynamic ModelingHydrodynamic Modeling

    Landslide shape and massLandslide shape and mass

    Dynamics of mass movementDynamics of mass movement Final deformationFinal deformation

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    Possible Proposed Study AreaPossible Proposed Study Area

    Santa Barbara CA:Santa Barbara CA:

    Seismic activity is documentedSeismic activity is documented

    Several wellSeveral well--defined underwater landslidesdefined underwater landslides

    Water depths, sizes conducive to causing tsunamisWater depths, sizes conducive to causing tsunamis

    Considerable preliminary work completedConsiderable preliminary work completed

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    RecommendedRecommended Study AreaStudy Area

    Santa Barbara

    ffshore Santa Barbara near Goleta Slide, CA (box shown in imageffshore Santa Barbara near Goleta Slide, CA (box shown in image

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    120o319 119o5721 119o5123

    34o2053

    34o1755

    Longitude (west)

    Latitude(north

    )

    Expanded view of the Goleta slide feature; 14.6 km by 10.5

    km, in water depth ranging from 90 to 580 meters.

    S bb f G lS bb tt f G l t

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    Subbottom of GoletaSubbottom of Goleta

    High Resolution boomer

    seismic reflection profile

    along eastern lobe of the

    Goleta slide.

    S bb f G l

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    Subbottom of GoletaSubbottom of Goleta

    High resolution boomer seismic reflection profile

    along eastern lobe of the Goleta slide (continued)

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    Preliminary Tsunami Modeling For Goleta SlidePreliminary Tsunami Modeling For Goleta Slide

    Goleta Santa Barbara

    M

    Maximum tsunami amplitudes propagating towards andMaximum tsunami amplitudes propagating towards and

    away from Goleta from assumed 1812 slide. Simulationaway from Goleta from assumed 1812 slide. Simulation

    predicts 22m maximum runpredicts 22m maximum run--up above sea level.up above sea level.

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    Flow Chart Relating Project ActivitiesFlow Chart Relating Project Activities

    Geological Data Geotechnical Data

    Landslide

    Models

    Tsunami

    Models

    Hazard

    Prediction

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    Field ProgramField Program

    Seismic reflection profiling

    Remotely Operated Vehicle (ROV)

    Sediment Sampling: cores and borings

    In situ testing:

    Pore pressure, vane shear and/or cone penetrometer

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    Sampling and In Situ Testing Program

    Long, Large-diameter Piston Cores:

    Large-diameter Gravity Cores:

    Multi-Cores or Box Cores:

    Pore pressure:

    Vane or Cone Penetrometer:

    Geotechnical Borings or other:

    20-30m length

    taken at same sites

    selected sites

    5-6m penetration

    Selected sites

    50-80m penetration

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    Survey tracks and field sampling and testing locations at theGoleta feature. Note sites outside slide zone (in unfailed regions)

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    Laboratory ProgramLaboratory Program

    Core analyses: multi-sensor core logging, x-ray/photo,

    vane shear, water content/density

    Geological analyses: grain size, carbonate, dating,

    mineralogy Geotechnical analyses: index properties, triaxial shear

    strength, cyclic DSS, creep, consolidation, permeability

    Geotechnical Stratigraphy

    Physical model: centrifuge testing of slope

    Example of Geotechnical Stratigraphy

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    0 5 0 1 0 0

    S t re s s ( k P a )

    'v o

    'C

    C R D w i th h i g h e r

    s t ra in ra te

    IL

    c '

    0 1 0 2 0 3 0

    S u ( k P a )

    M V u n d .

    M V r e m .

    0 1 0 0 2 0 0

    w ( % )

    w

    w p

    w L

    0

    2

    4

    6

    8

    1 0

    1 2

    1 4

    1 6

    L i t h o l o g y

    (Sed i . : S i l t y C lay)

    Depth(m)

    O l ive Gray-

    O l ive

    L ight B r . /Gr .

    Dark layer

    B rown / G ray

    O l i ve G ray

    Lt . O l . G rayA S H L A Y E R

    B o t t om o f

    C o r e

    D a r k G r a y

    Lam i na t es

    U n i t 1

    U n i t 2

    U n i t 3

    U n i t 4

    1 .2 1 .5 1 .8 b ( g /c m 3 )

    M S C L

    ca lc . (w)

    Example of Geotechnical Stratigraphy

    JPCJPC--32/LGC32/LGC--28, Gulf of Mexico, rim of Bornhauser Basin, (1915 m28, Gulf of Mexico, rim of Bornhauser Basin, (1915 m

    depth). Note the four geotechnical units. The profile on the rdepth). Note the four geotechnical units. The profile on the rightight

    includes results of 23 consolidation tests, indicating significaincludes results of 23 consolidation tests, indicating significantntunderconsolidation below 4 m (high excess pore pressures).underconsolidation below 4 m (high excess pore pressures).

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    Geotechnical Modeling of Slope StabilityGeotechnical Modeling of Slope Stability

    Limit Equilibrium

    Finite/Boundary Element Analysis

    Stochastic analysis of failure

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    Proposed MultiProposed Multi--Year Task ScheduleYear Task Schedule

    Year

    Quarter 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

    Prelim. Data Anal.

    Survey and ROV

    Field Sampl./Testing

    Field Monitoring (?)

    Manned Sub.

    Lab. Testing

    Centrifuge Exper.

    Geotech. Modeling

    Hydrodyn. Modeling

    Key: Intense Program Moderate Program Light Program

    41 2 3

    (?)

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    Why Santa Barbara?Why Santa Barbara?

    Seismic activity is documented

    Preliminary work completed

    Slope relatively uncomplicated, well-defined failures

    Water depths and landslide size are tsunamigenic

    Pre- and post-failure seabed sampling

    Convenient logistics for field work

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    Cheers, and thank youCheers, and thank you

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    Indicators of Potential TsunamigenicIndicators of Potential Tsunamigenic

    LandslidesLandslidesThick sediment accumulation Nearby seismic activity

    Active gas, water, or oil seeps Formation of mud volcanoes

    Formation of authigenic carbonates Compressional tectonics

    Control fault beneath the slope Steep continental slope

    Subsiding tectonic blocks High sedimentation rate

    Cracks exposed in surficial sediment Previous landsliding activity

    Inhomogeneous bedding layers Rapidly convergent margin

    Santa Barbara has almost all of thes