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Transpression Along the Southern Queen Charlotte Fault: Underthrusting and Strain Partitioning of the Queen Charlotte Terrace

Description: 

The Queen Charlotte Fault (QCF) is a part of the Pacific-North America plate boundary, one of Earth’s fastest slipping continent-ocean transforms, and the source of some of Canada’s most significant earthquake hazards. The 2012 M7.8 Haida Gwaii thrust earthquake reinvigorated interest in the QCF, especially in its southern section. Mechanisms to accommodate the extremely oblique convergence (from ~5-20) fall into two end members: oceanic crustal thickening or incipient subduction. Both mechanisms could produce the Queen Charlotte Terrace, an uplifted complex west of the QCF offshore Haida Gwaii. The Queen Charlotte Terrace’s crustal structure is crucial for understanding the tectonics and seismic hazards of this region, but previous imaging is limited to shallow penetrating, low-resolution studies that leave most of the deep crustal structure largely unknown. We use multichannel seismic reflection data acquired with a 15 km-long hydrophone streamer to image the crustal structure offshore Haida Gwaii, including the Pacific plate, the Queen Charlotte Terrace, the QCF, and the North American continental shelf. Our images reveal a downwarped and faulted Pacific plate, a Queen Charlotte Terrace with sub-parallel ridges underlain by landward dipping thrust faults, a localized strike-slip fault that coincides with the surface trace of the QCF, and minimally deformed shallow (<2 km) sediments along North American shelf. Beneath the Queen Charlotte Terrace, continuous underthrusting Pacific plate crust and sediments, topped by a décollement, indicates that recent convergence is accommodated by underthrusting. Thrust faults branch off the décollement and accrete oceanic sediments, building up the Queen Charlotte Terrace. Oblique slip on the frontal thrusts implies that strain is partially partitioned along Haida Gwaii, so the QCF may be slipping at less than the full plate rate. Older oblique strike-slip faults close to the western side of the QCF suggest that the system may have begun with distributed strike-slip on oceanic basement-cutting faults before evolving towards its current configuration as a crustal sliver.

Session: Structure, Seismicity and Dynamics of the Queen Charlotte-Fairweather Fault System
[Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Collin

Student Presenter: Yes

Invited Presentation: 

Authors