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Geohazards : objectives of this seminar
Clarification of what comprises or does not comprise ageohazard
Introduction to a wide range of common and not-so-
common geohazards
Correlation of geohazards with specific geologicalenvironments
Evaluation of geohazard-related risks for subsea
installations
How to mitigate geohazard-related risk
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Geohazards : what is a geohazard?
Most geohazards are initially identified from geophysical data.
Geohazards comprise naturally occurring seabed featuresor sub-surface conditions that may pose a risk to the installationor operational life of subsea structures and pipelines.
The identification of potential geohazards should be one
of the primary goals of any site or pipeline route survey.
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When is a Hazard not a Geohazard?
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Hazards that are not Geohazards
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Hazards that are not Geohazards
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Hazards that are not Geohazards
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Hazards that are not Geohazards
http://tv-antenna.com/heavy-seas
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Hazards that are not Geohazards
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Geohazard Evaluation : Assess the quality of theavailable information and identify the environment
What type and quality of data are available?
What type of geological environment?
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Geohazard Evaluation : Assess the quality
Are the data site specific?
Are the geophysical interpretations confirmed by geotechnicaldata?
Are the different data sets consistent with each other?
Is the equipment used fit for purpose?
Have the data been processed and presented in a sensiblemanner?
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Geohazards : Identify the environment
areas of current and wave action
polar latitudes
tropical latitudes
glaciated terrains
areas affected by sea level changes
zones of gas escape ultra deep water
near shore areas
zones of structural weakness
Individual geohazardsmay be associatedwith more than onetype of environment
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Geohazards Generated by Current or Wave Action
ripples
megaripples
sand waves
flutes scour
lag deposits
slope failures
steep gradients
often connected withnearshore environments,but exceptions to therule exist
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Geohazards Generated by Current or Wave Action
Megaripples
Height between trough andcrest from 0.1 m to 1.0 m,
wavelengths greater than 1m (AGI)
These are the ones towatch...
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Geohazards Generated by Current or Wave Action
Sand Waves:> 1 m amplitudes
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Sand Waves
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Comparison of DTM imagery Bathymetry (m)
m
ITT DTM Rock dumper DTMKP 8.300KP 8.300
KP 7.650KP 7.650
Geohazards Generated by Current or Wave Action
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Comparison of DTM imagery : Slope angles (in degrees)
ITT DTM Rockdumper DTM
KP 7.650 KP 7.650
KP 8.300 KP 8.300
Geohazards Generated by Current or Wave Action
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Comparison of survey data :
X
X
X
X
Geohazards Generated by Current or Wave Action
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Geohazards Generated by Current or Wave Action
Flutes and Megaflutes
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Geohazards Generated by Current or Wave Action
Scour
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Geohazards Generated by Current or Wave Action
Lag
Deposits
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Geohazards Associated with High Latitudes
iceberg impacts
iceberg scarring
ice pits
sea ice scour
gas hydrates
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Geohazards Associated with High Latitudes
Iceberg impact
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Geohazards Associated with High Latitudes
Iceberg Scours
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Geohazards Associated with High Latitudes
Ice pits
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Geohazards Associated with High Latitudes
Sea Ice
Scour
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Gas Hydrates
Geohazards Associated with High Latitudes
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Geohazards Associated with Low Latitudes
coral reefs
carbonate sediments
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Geohazards Associated with Low Latitudes
Coral Reefs
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Geohazards Associated with Low Latitudes
Carbonate Sediments
a soil (or rock) which
requires geotechnical
testing for identification
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Geohazards Associated with Glaciated Terrains
GlacialTopography
scars
pits kettles
drumlins
eskers
end moraines
rock glaciers
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Geohazards Associated with Glaciated Terrains
Dropstones
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BuriedBoulders
Geohazards Associated with Glaciated Terrains
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Geohazards Associated with Glaciated Terrains
Steep Gradients
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Geohazards Associated with Glaciated Terrains
Bedrock Highs
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UnstableSlopes
Geohazards Associated with Glaciated Terrains
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Geohazards: Features Generated during Changesin Sea Level
hardpan
peat
gyttja
shallow gas
submerged terraces
lag deposits
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Geohazards: Features Generated during Changesin Sea Level
Hardpan
a soil, which requires geotechnical testing
for identification
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Geohazards: Features Generated during Changesin Sea Level
Peat deposits
a soil, which requires
geotechnical testing
for identification
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Geohazards: Features Generated during Changesin Sea Level
Gyttja
a soil, which requires
geotechnical testing
for identification
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Geohazards: Features Generated during Changesin Sea Level
Submerged Terraces
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Geohazards: Gas Features
pockmarks
cemented ground
cold water corals
shallow gas
mud volcanoes
gas hydrates
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Geohazards: Gas Features
Pockmarks
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Geohazards: Gas Features
CementedGround
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Geohazards: Gas Features : Cold Water Corals
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Shallow Gas
Geohazards: Gas Features
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Geohazards: Gas Features: Mud Volcanoes
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Geohazards: Gas Features: Mud Volcanoes
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Geohazards: Gas Features: Mud Volcanoes
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Geohazards: Gas Features:
Gas Hydrates
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Geohazards associalted with ultra-deep water
soft clay
gas hydrates
slope failure
gas release features shallow faulting
deep water corals
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Geohazards associalted with ultra-deep water
A soil, which requiresidentification (or
confirmation) bygeotechnical testing
Soft Clay
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Soft Clay
foundations
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Soft Clay
backfill
(not strictly a geohazard,but a soils issue)
G h d i lt d ith lt d t
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Shallow faulting
Geohazards associalted with ultra-deep water
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G h d i f j t l k
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Earthquakes
destroy stuff
Geohazards in zones of major crustal weakness
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Geohazards in zones of major crustal weakness
Liquefaction
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Geohazards in zones of major crustal weakness
Volcanism
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Geohazards in zones of major crustal weakness
Tsunamis