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TitleFrom mid-plate to subduction zone: stratigraphy of the northeast Juan de Fuca Plate, offshore British Columbia
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorRohr, K M M; King, H; Riedel, M; Schmidt, U
SourceGeological Survey of Canada, Current Research (Online) 2019-4, 2019, 14 pages, Open Access logo Open Access
PublisherNatural Resources Canada
Mediaon-line; digital
File formatpdf (Adobe® Reader®)
ProvinceBritish Columbia; Western offshore region
NTS92D; 102A
AreaVancouver Island; Pacific Ocean
Lat/Long WENS-129.2000 -126.0000 48.9000 47.1000
Subjectsmarine geology; surficial geology/geomorphology; stratigraphy; paleontology; geophysics; Science and Technology; geophysical surveys; seismic surveys, marine; seismic reflection surveys; seismic profiles, marine; bathymetry; marine sediments; landslide deposits; debris flow deposits; submarine fans; geological history; depositional history; sedimentation rates; diagenesis; sedimentary structures; tectonic history; deformation; faulting; tectonic setting; subduction zones; submarine troughs; hydrothermal systems; bedrock geology; structural features; faults; lithology; sedimentary rocks; core analysis; sedimentary basins; biostratigraphy; lithostratigraphy; Juan de Fuca Plate; Cascadia Subduction Zone; Nitinat Fan; Cascadia Basin; Vancouver Sea Valley; Juan de Fuca Sea Valley; Ocean Drilling Program Site 1027; Ocean Drilling Program Site 1032; Ocean Drilling Program Site 888; Phanerozoic; Cenozoic; Quaternary
Illustrationslocation maps; geoscientific sketch maps; profiles; seismic profiles
ProgramOffshore Geoscience
Released2019 11 01; 2020 01 23
AbstractQuaternary sedimentary stratigraphy in Ocean Drilling Program site 1027 was tied to three regional multichannel seismic reflection profiles across the northeastern Juan de Fuca plate to the Cascadia subduction zone. A velocity gradient from a refraction study provided a good fit to convert depth of stratigraphic horizons to two-way traveltime. Topography of basement ridges prevents correlating time horizons older than 0.76 Ma on a regional scale on seismic reflection sections. By that time sediments had filled almost to the top of basement ridges and deposition of the Nitinat fan had begun. After 0.46 Ma, coarser sediments and debris flows were deposited from the fan into the seaward reaches of Cascadia Basin, and above the 0.28 Ma time horizon, the reflection character of deposits around the fan is that of poorly sorted mass-transport deposits with intermittent layering. More than half of the sediments in the trench are from the Nitinat fan; they are approximately 2 Ma younger than previously thought. Growth faults created by bending stresses from the sediment load and subduction are primarily observed in intervals that predate the Nitinat fan and accumulated at slower sedimentation rates. These faults appear to be utilizing extensional faults that are part of the original fabric of the igneous crust.
Summary(Plain Language Summary, not published)
We correlated results of drilling in middle of the Juan de Fuca plate to acoustic profiles that connect the mid-plate over 100-125 km to the trench outboard of the subduction zone. We found that sediments in the trench are younger than previously thought. This affects models of how earthquakes might occur in the uppermost parts on the megathrust fault of the subduction zone and how large a tsunami might be generated. Sediments act like an insulating blanket on the hot igneous plate resulting in a warm subducted plate. Rupture on a megathrust could then occur at shallower levels under the continental slope than previously thought.

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