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- Title
The Northern Terminus of Cascadia Subduction.
- Authors
Savard, G.; Bostock, M. G.; Hutchinson, J.; Kao, H.; Christensen, N. I.; Peacock, S. M.
- Abstract
The Juan de Fuca (JDF) plate system is pivoting and breaking apart as a result of resistance to subduction. At the northern end, the Explorer (EXP) plate moves independently of the JDF plate along the Nootka Fault Zone (NFZ), which forms an unstable triple junction with the JDF ridge and the Sovanco Fracture Zone. We trace the subsurface extension of the NFZ using tomography by combining results from a new nearshore study with a previous ocean‐bottom study and other geophysical constraints. Cross sections from the offshore NFZ through central Vancouver Island suggest a strong fold in the subducting lithosphere (∼40°). Near the deformation front, the NFZ is defined by microseismicity that extends into oceanic mantle with low VP/VS (<1.7) values. This anomaly extends to the NE below the continental shelf with a more northerly trajectory than common NFZ depictions through the seismicity concentration off Nootka Island. Tremor locations and receiver functions indicate that this more northerly trajectory persists across Vancouver Island. We propose a revised tectonic evolution for the NFZ that leads to (i) an EXP microplate confined to shallow depths below the convergent margin and which underthrusts North America no farther landward than Brooks Peninsula and (ii) a northern edge of Cascadia subduction that cuts between Brooks Peninsula and Nootka Island. The plate fold offshore Nootka Island and abundant seismicity there and at Brooks Peninsula are ascribed to stress concentrations on either side of the NFZ associated with deformation at the edges of more competent JDF, EXP, and North American plates. Key Points: Geophysical evidence redefines Nootka Fault Zone/Juan de Fuca plate edge across Vancouver IslandPlate fold develops over ≤50 km within northern Juan de Fuca plate edge off Nootka IslandProposed tectonic configuration confines Explorer plate to shallow depths at/seaward of Vancouver Island coast
- Subjects
VANCOUVER Island (B.C.); CASCADIA subduction zone; FAULT zones; LITHOSPHERE; PLATE tectonics
- Publication
Journal of Geophysical Research. Solid Earth, 2020, Vol 125, Issue 6, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2019JB018453