| Title | Assessment of submarine slope failures off Vancouver Island, British Columbia |
| Download | Downloads |
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| Licence | Please note the adoption of the Open Government Licence - Canada
supersedes any previous licences. |
| Author | Riedel, M; Naegeli, K; Côté, M M |
| Source | Geological Survey of Canada, Open File 8008, 2016, 108 pages, https://doi.org/10.4095/297904  Open Access |
| Image |  |
| Year | 2016 |
| Publisher | Natural Resources Canada |
| Document | open file |
| Lang. | English |
| Media | digital; on-line |
| File format | pdf |
| Province | Western offshore region |
| Area | Vancouver Island |
| Lat/Long WENS | -128.0000 -126.0000 49.5000 48.0000 |
| Subjects | marine 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 |
| Illustrations | location maps; tables; histograms; rose diagrams; stratigraphic columns |
| Program | Public Safety
Geoscience Marine Geohazards |
| Released | 2016 04 29 |
| Abstract | 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-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.
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| 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 ID | 297904 |
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