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TitleAssessment of submarine slope failures off Vancouver Island, British Columbia
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AuthorRiedel, M; Naegeli, K; Côté, M M
SourceGeological Survey of Canada, Open File 8008, 2016, 108 pages, https://doi.org/10.4095/297904
Year2016
PublisherNatural Resources Canada
Documentopen file
Lang.English
Mediadigital; on-line
File formatpdf
ProvinceWestern offshore region
AreaVancouver Island
Lat/Long WENS-128.0000 -126.0000 49.5000 48.0000
Subjectsmarine geology; surficial geology/geomorphology; structural geology; continental slope; slope deposits; slope failures; slope stability; slope stability analyses; bathymetry; submarine features; submarine transport; landslides; landslide deposits; faults; faulting; Cascadia subduction zone
Illustrationslocation maps; tables; histograms; rose diagrams; stratigraphic columns
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Location
 
Natural Resources Canada Library - Ottawa (Earth Sciences)
 
ProgramMarine Geohazards, Public Safety Geoscience
Released2016 04 29
AbstractMultibeam bathymetric data acquired off Vancouver Island across the accretionary prism of the Cascadia subduction zone reveal a prominent segmentation of the deformation front with dominant azimuths of the ridges at ~120° and ~150° and abundant submarine landslides. Both these ridge-orientations are oblique to the direction of subduction (~45°). Ridges at a strike of ~120° show dominantly rectangular-shaped failure head-scarps and intact blocks of sediments within the failed sediment mass, whereas ridges with an azimuth of ~150° show curved head-scarps and incoherent debris in the failure mass. We propose that this systematic change in failure-style is related to the underlying thrust fault system producing steeper and taller ridges for azimuths around 150°, but less steep and tall ridges at 120°. Thus, debris-flow style failure is simply a result of higher kinetic forcing of the down-sliding sediment mass: more mixing and destruction of the coherent blocks for taller and steeper ridges, and blocks of intact sediment for gentle slopes and less elevated ridges. A segmentation of the deformation front and ridge alignment into two dominant azimuths could be a result of: a) complex interaction and competing forces from overall slab-pull (45°), b) re-activated faults orientated almost N-S (~175°) on the oceanic plate and overlying sediment cover (reflected in the magnetic stripes and abyssal plain strike-slip faulting), and c) relative orientation of the back-stop off Vancouver Island and accreted terranes (at ~127° following the coastline between Nootka Island and Port Renfrew). Extensional faulting is observed only at ridges with debris-flow style failure, which also are the ridges with larger height and steeper slopes. These extensional faults may be the result of over-steepening of the ridges and collapse of the sediment pile that can no longer withstand its own weight due to limited internal shear strength.
Summary(Plain Language Summary, not published)
Multibeam bathymetric data acquired off Vancouver Island across the accretionary prism of the Cascadia subduction zone reveal a prominent segmentation of the deformation front with dominant azimuths of the ridges at ~120° and ~150° and abundant submarine landslides. Both these ridge-orientations are oblique to the direction of subduction (~45°). Ridges at a strike of ~120° show dominantly rectangular-shaped failure head-scars and intact blocks of sediments within the failed sediment mass, whereas ridges with an azimuth of ~150° show curved head-scars and incoherent debris in the failure mass. We propose that this systematic change in failure-style is related to the underlying thrust fault system producing steeper and taller ridges for azimuths around 150°, but less steep and tall ridges at 120°. Thus, debris-flow style failure is simply a result of higher kinetic forcing of the down-sliding sediment mass.
GEOSCAN ID297904