| Title | The northern terminus of Cascadia subduction |
| |
| Author | Savard, G; Bostock, M G; Hutchinson, J; Kao, H ; Christensen, N I; Peacock, S M |
| Source | Journal of Geophysical Research, Solid Earth 2020 p. 1-17, https://doi.org/10.1029/2020JB018453 |
| Image |  |
| Year | 2020 |
| Alt Series | Natural Resources Canada, Contribution Series 20200037 |
| Publisher | American Geophysical Union |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | British Columbia; Western offshore region |
| NTS | 92B/03; 92B/04; 92B/05; 92B/06; 92B/11; 92B/12; 92B/13; 92B/14; 92C; 92E; 92F; 92G/03; 92G/04; 92G/05; 92G/06; 92G/11; 92G/12; 92G/13; 92G/14; 92J/03; 92J/04; 92J/05; 92J/06; 92J/11; 92J/12; 92J/13; 92J/14;
92K; 92L; 92M; 92N; 92O/03; 92O/04; 92O/05; 92O/06; 92O/11; 92O/12; 92O/13; 92O/14; 102I; 102J; 102O; 102P |
| Lat/Long WENS | -132.0000 -123.0000 52.0000 48.0000 |
| Subjects | geophysics; marine geology; Science and Technology; tectonics; geophysical interpretations; plate tectonics; plate boundaries; plate motions; tectonic zones; tectonic environments; subduction; Juan de
Fuca Plate; Nootka Fault Zone |
| Illustrations | location maps; seismic profiles; gravity profiles |
| Program | Public Safety Geoscience Assessing Earthquake Geohazards |
| Released | 2020 05 12 |
| 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 sub-surface 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. |
| Summary | (Plain Language Summary, not published)
The northern end of the Cascadia margin is characterized by the relative motion between the Juan de Fuca plate and the Explorer plate with respect to the
North American plate. Based on the distribution of local seismicity and velocity anomalies, we depict the tectonic evolution of the northern end of the Cascadia margin. Our model indicates that the boundary fault between the Juan de Fuca and Explorer
plates (i.e., the Nootka Fault zone) extends across northern Vancouver Island. Subduction of the Explorer plate is confined to shallow depths no farther landward than Brooks Peninsula. Also, the northern edge of the Cascadia subduction is located
between Brooks Peninsula and Nootka Island. Significant plate deformation and local seismicity are manifestations of tectonic stress concentrations in the region. |
| GEOSCAN ID | 326048 |
|
|