← Back to Sessions

Crustal Architecture Across the Queen Charlotte Fault Zone North of Haida Gwaii, British Columbia From 2d Tomography

Description: 

The Queen Charlotte fault (QCF) is a 900-km-long dextral strike-slip fault system separating the Pacific Plate from the North American Plate offshore western British Columbia and southeastern Alaska, and is one of the fastest-slipping strike-slip faults in the world, accommodating ~50-57 mm/yr of slip along a highly localized fault zone. While dominantly a dextral transform system, there remains considerable debate about mechanism(s) of oblique convergent strain accommodation ranging from incipient subduction to intraplate deformation. Additionally, seismogenesis along the active fault zone may be partially controlled by material contrasts across the fault, but little is known about the velocity structure at seismogenic depths. Ocean-bottom seismometer (OBS) seismic refraction data collected as part of the 2021 Transform Obliquity on the Queen Charlotte fault and Earthquake Study (TOQUES) project were designed to 1) determine the extent of potential Pacific Plate underthrusting beneath North America and 2) provide insight into the material contrast across the fault at seismogenic depths. We modeled refracted arrivals recorded by 25 OBS located along a >200-km-long linear transect crossing the QCF just north of Haida Gwaii, British Columbia. Our resulting 2D tomographic model images the velocities across the fault zone at up to ~30 km depths, providing the first-ever constraints on the lithospheric architecture in this key tectonic region. We observe high P-wave velocities (> 6 km/s) at relatively shallow depths (<5 km), and greater velocity heterogeneity on the North American side of the plate boundary that we attribute to the seismically fast Wrangellia and Alexander accreted terranes. We also find that the QCF aligns with a relatively sharp contrast in seismic velocity, with the slower velocities on the Pacific side of the plate boundary at seismogenic depths (~5-20 km in this area). Lastly, our velocity models do not present strong evidence for underthrusting north of Haida Gwaii, but we do show seismic reflections within the North American crust at <30 km depths.

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: Maureen

Student Presenter: No

Invited Presentation: 

Authors