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TitleSignificant geometric variation of the subducted plate beneath the northernmost Cascadia subduction zone and its tectonic implications as revealed by the 2014 MW 6.4 earthquake sequence
AuthorHutchinson, J; Kao, HORCID logo; Riedel, M; Obana, K; Wang, KORCID logo; Kodaira, S; Takahashi, T; Yamamoto, Y
SourceEarth and Planetary Science Letters vol. 551, 116569, 2020 p. 1-11,
Alt SeriesNatural Resources Canada, Contribution Series 20200460
PublisherElsevier B.V.
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia
NTS92E; 92L/01; 92L/02; 92L/03; 92L/04; 92L/05; 92L/06; 92L/07; 92L/08; 102A/01; 102A/02; 102A/07; 102A/08
AreaVancouver Island; Canada
Lat/Long WENS-129.0000 -126.4167 50.4167 49.2500
Subjectstectonics; Science and Technology; plate tectonics; Cascadia subduction zone; Nootka fault zone
Illustrationslocation maps; graphs; cross-plots; diagrams
Released2020 09 23
AbstractAt the northernmost extent of the Cascadia subduction zone, the Explorer plate subducts at approximately 2 cm/yr, less than half the rate of the Juan de Fuca plate to the south. The boundary between these two plates is known as the Nootka fault zone, which is one of the focuses of the Seafloor Earthquake Array Japan-Canada Cascadia Experiment (SeaJade). During this survey, an MW 6.4 earthquake occurred on 24 April 2014. This event and the subsequent aftershocks (referred to as the Nootka Sequence) reveal an approximately 40-km-long subducted fault within the Explorer Plate to the north of the Nootka fault zone. We infer that the fault is a subducted conjugate fault because of its nearly identical orientation to those seaward of the subduction front within the Nootka fault zone. The depth distribution and focal mechanisms of the aftershocks indicate significant margin-parallel deformation of the subducting plate. The subduction interface at the Nootka Sequence fault has been deflected downward to the northwest from a depth of approximately 15 – 25 km over a distance of 25 km. We propose two possible scenarios that are modified from previously suggested slab-tear model with induced margin-parallel mantle flow to explain the significant deformation of the young, warm subducting Explorer plate. To the northwest of this change in slab geometry, a lack of seismic activity above the plate interface indicates that the Explorer plate has partially decoupled from the overriding North America plate. We conclude that the geometric variation separating the southern Explorer plate from the north, along with decoupling and a possible intraslab tear, may be a significant combination to resist the propagation of a megathrust rupture across this boundary.

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