Role of faulting and gas hydrate in deep-sea landslides off Vancouver Island
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Role of faulting and gas hydrate in deep-sea landslides off Vancouver Island. or. Recipe for slumping: Lift, cut, shake, but maybe freeze first. George Spence. Collaborators include: Carol Lopez Ross Haacke Tark Hamilton Michael Riedel + many others.

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Role of faulting and gas hydrate in deep-sea landslides off Vancouver Island

or

Recipe for slumping:

Lift, cut, shake, but maybe freeze first

George Spence

Collaborators include:

Carol Lopez Ross Haacke

Tark Hamilton Michael Riedel

+ many others


Storegga Slide : mother of all landslides Vancouver Island

  • mass failure area equiv to Iceland

  • headwall ~250 km long

  • runout ~800 km

  • Multiple events (3?)

  • oldest, biggest 250 ka

  • most recent 8.2 ka


1929 Grand Banks earthquake (M 7.2), slump and tsunami Vancouver Island

  • tsunami : 28 deaths; observed in Portugal

  • undersea cable breaks out to 500 km (turbidity currents)

  • failure area 20,000 km2, sed vol 100-150 km3 (thickness ~5 m)

(Fine et al. 2005)


1998 Papua New Guinea earthquake (M 7.1) and tsunami Vancouver Island

  • tsunami : 2200 deaths

  • tsunami source : motion on low-angle fault plus slump


slump amphitheatre

(Synolakis et al. 2002)

Papua New Guinea slide


Cascadia margin, Vancouver Island Vancouver Island

Swath bathymetry, U Washington 2004


U1326 Vancouver Island

U1326 : IODP drilling, 2005


U1326 Vancouver Island


U1326 Vancouver Island


Cascadia margin setting Vancouver Island

BSR (Bottom Simulating Reflector)

Base of gas hydrate

Deformation

front

Basin

Sediments

Accretionary Prism

Sediments

Oceanic Crust


Methane Hydrate Structure Vancouver Island

Carbon + hydrogen (centre) trapped in ice lattice


Multichannel seismic 10 50 hz
Multichannel seismic 10-50 Hz Vancouver Island

BSR

BSR


U1326 : Vancouver Island

array of ocean bottom seismometers


OBS high-vel (85-110 mbsf) Vancouver Island

BSR at 240-260 mbsf

U1326 downhole log high-vel: hydrate

OBS velocities


High vel: hydrate? Vancouver Island

BSR

  • BSR depth well-constrained at 250-260 mbsf

  • high-vel shallow hydrate layer extends laterally for 4-6 km

U1326 :

Final Velocity Model – Line 2

Depth (km)


slump Vancouver Island

seismic reflection lines


slump Vancouver Island

Scarps: up to 75 m high

BSR

NW

SE

NW

SE

2.4 s

3.0 s

Line 13

Line 21


Margin-perpendicular faults Vancouver Island

: extensional, with motion parallel to least-compressive stress direction


extension cracks Vancouver Island

What produced these margin-perpendicular faults?


Expansion cracks on Vancouver Islandridge are due to longitudinal flexure, i.e. tension on outside edge

tension

compression

Better analogy : bend a baguette




Volume of slumped material : 0.6 km to A2

Vertical extent of slump coincident with base of hydrate


Slump Mechanisms to A

  • Gas hydrate dissociation

  • High pore fluid pressures

  • Contrasting seds & physical properties, e.g. glacial vs. de-glacial vs. interglacial

  • Earthquakes


1. to A

  • Hydrate may increase sediment strength by cementing grains (but increase depends on how hydrate is distributed, and how much hydrate is present)

  • Is there coincidence between glide plane and base of hydrate?


2. to A High pore fluid pressures

High fluid flux (e.g. high sed rates; compaction at convergent margin) produces high pore pressures

High pore pressure reduces sed strength (i.e. reduces grain-to-grain contact)

Frontal ridge is region of greatest deformation and greatest fluid flux


Mounds and slumps, offshore Nicaragua to A

slope seds

decollement

Overpressure at decollement

(Talukder et al. 2008)


key core to A

3. Contrasting sed properties

Coring program Aug 2008 : Haacke, Riedel, Pohlmann, Hamilton, Enkin, Rose, and others


Key core at intersection of headwall and glide plane to A

Bottom of core contains older seds, much stiffer and stronger than overlying seds found found everywhere else, which are likely weakde-glacial deposits (~14 kyr)

Top of stiff sediments may provide the glide plane.


4. to A Earthquakes

  • acceleration-induced sliding

  • earthquakes may produce excess pore pressures

  • Coring cruise Aug 2008 :

  • series of 10-17 turbidites found overlying the slumped deposits, which is comparable to the number of earthquakes since last glacial period, i.e. consistent with slumps occuring at de-glacial time


Ridge on slope off Van Is to A

Original data

bubble pulse

BSR


bowtie to A

Predictive deconvolution


Migration to A


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