Longsor Underwater

8/6/2019 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 these indicators presentSanta Barbara has almost all of these indicators present


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Projected Proposed Drill HolesProjected Proposed Drill Holes

120o654 120o357

Longitude (west)


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120 6 54 120 3 57

34o2237

34o2039

Latitude(nor

th)

Gaviota landslide (8 km west of Goleta feature). NoteGaviota landslide (8 km west of Goleta feature). Note

evidence of a fissure developing to the east of the head scarp.evidence of a fissure developing to the east of the head scarp.


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High resolution 3.5 kHz seismic reflection profile of

the Gaviota landslide (from Edwards et al. 1993)

Previous Gas SeepsPrevious Gas Seeps


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Previous Gas SeepsPrevious Gas Seeps


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Map ofMap of

GoletaGoletaLandslideLandslide


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H d b S


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Hydrocarbon StructuresHydrocarbon Structures

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