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TitleGeometry of the subducting Juan de Fuca plate: new constraints from SHIPS98
DownloadDownload (whole publication)
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorTréhu, A M; Brocher, T M; Creager, K C; Fisher, M A; Preston, L A; Spence, G; SHIPS98 Working Group
SourceThe Cascadia subduction zone and related subduction systems - seismic structure, intraslab earthquakes and processes, and earthquake hazards; by Kirby, S (ed.); Wang, KORCID logo (ed.); Dunlop, S (ed.); Geological Survey of Canada, Open File 4350, 2002 p. 25-32, Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesUnited States Geological Survey, Open-file Report 02-328
PublisherNatural Resources Canada
MeetingIntraslab Earthquakes in the Cascadia Subduction System: Science and Hazards; Victoria; CA; September 18-21, 2000
Documentopen file
Mediaon-line; digital
RelatedThis publication is contained in The Cascadia subduction zone and related subduction systems - seismic structure, intraslab earthquakes and processes, and earthquake hazards
File formatpdf
ProvinceWestern offshore region
NTS92A; 92B
AreaGeorgia Strait; Puget Sound; Juan de Fuca Sound; Olympic Mountains; Olympic Peninsula; United States of America; Canada
Lat/Long WENS-126.0000 -122.0000 49.0000 47.0000
Subjectstectonics; structural geology; geophysics; subduction zones; plate tectonics; tectonic elements; tectonic environments; tectonic interpretations; plate motions; subduction; lithosphere; oceanic lithosphere; deformation; seismicity; seismic surveys; seismic surveys, ship; seismic reflection surveys; seismic velocities; Cascadia Subduction Zone; Cascadia Margin; Juan de Fuca Plate; Juan de Fuca Slab; Mendocino Transform; SHIPS98; Cenozoic
Illustrationssketch maps; seismic profiles; velocity models; graphs
Released2002 06 11; 2016 08 31
AbstractWe have processed seismic reflection profiles acquired in the Strait of Juan de Fuca, inverted travel times of first arrivals from onshore recordings of the offshore shots to determine the velocity of the upper crust in this region and inverted the travel times of first and secondary arrivals that undershoot the central core of the Olympic Mountains. The seismic reflection profiles show a pattern of crustal reflectivity similar to that recorded beneath Vancouver Island. Inversion of first arrivals, interpreted to be diving waves through the upper and mid-crust indicate a 5 - 7 km-deep linear, northwest-trending basin beneath the southwestern shore of the Strait and uplift of the basement Crescent terrane rocks beneath the northwestern shore. Velocities beneath the central Olympic Peninsula at 15 - 25 km depth show strong lateral variation, with higher velocities underlying the surface exposures of the Crescent terrane and lower velocities at these depths beneath the Olympic core rocks. Inversion of secondary seismic arrivals interpreted to be reflections from the base of the crust of the subducted Juan de Fuca plate indicate that the Moho is at a depth of about 34 km beneath the western Strait of Juan de Fuca and dips about 7o to the east, reaching a depth of about 46 km beneath the eastern boundary of Olympic National Park. Correlating these results with results of previous experiments on Vancouver Island and in southwestern Washington confirm earlier interpretations of an arch in the subducted slab beneath the Olympic peninsula but indicate that the arch is asymmetric and less pronounced than previously thought. We attribute both the northwest-trending folding of the Crescent terrane and the asymmetry in the shape of the subducting slab to resistance to the northward motion of the Paleocene-age Cascadia forearc terrane by the thick lithosphere of the pre-Tertiary terranes of British Columbia.

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