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TitleSeismic structure of the northern Cascadia accretionary prism: evidence from new multichannel seismic reflection data
AuthorSpence, G D; Hyndman, R D; Davis, E E; Yorath, C J
SourceContinental Lithosphere: Deep Seismic Reflections; by Meissner, R (ed.); Brown, L (ed.); Dürbaum, H -J (ed.); Franke, W (ed.); Fuchs, K (ed.); Seifert, F (ed.); Geodynamics Series vol. 22, 1991 p. 257-263,
Alt SeriesGeological Survey of Canada, Contribution Series 57290
PublisherAmerican Geophysical Union
Meeting4th International Symposium on Deep Reflection Profiling of the Continental Lithosphere; Bayreuth; DE; September 4-7, 1990
Mediapaper; on-line; digital
File formatpdf
ProvinceWestern offshore region
Subjectsseismic profiles, marine; seismic reflection surveys; continental margins; oceanic crust; pore pressures; subduction zones; sedimentary wedges; terranes; faults; plate tectonics; plate margins; plate boundaries; Crescent Terrane; accretionary prism
AbstractWithin the Cascadia accretionary prism west of Vancouver Island, new marine seismic reflection profiles totalling 722 km provide improved images which enable the three-dimensional variation of structures along the margin to be determined. At the deformation front, landward dipping thrusts spaced roughly 5 km apart are commonly observed which may penetrate to near the top of the subducting oceanic crust. Along lines separated by 3 km, the amount of displacement on a given fault is seen to vary significantly along the margin. Seaward dipping faults occasionally develop, propagating upward from the frontal thrust. In one region above gently-dipping oceanic crust, a shallow taper sediment wedge has formed, implying high pore fluid pressures along the detachment surface at the top of the oceanic crust. The detachment exhibits a strong reflection probably indicative of high fluid pressure. The accretionary prism is bounded by a landward dipping continental backstop, formed by the marine volcanic Crescent Terrane. The base of this terrane is imaged extending down to near the top of the subducting oceanic crust, so that little sediment is available for deeper subduction or underplating. The seaward part of the Crescent Terrane appears to have been uplifted, probably as a response to the accretion of prism sediments.