Strain Partitioning and the Accommodation of Oblique Convergence Along the Northern Queen Charlotte Fault

The Queen Charlotte Fault (QCF) forms a predominantly strike-slip plate boundary between the Pacific (PAC) and North American (NA) tectonic plates offshore western Canada and southeastern Alaska. With a right-lateral displacement rate of >50 mm/year, deformation along the QCF is among the fastest-slipping continental or continental-ocean transform systems globally. Along-margin changes in fault strike and degree of obliquity with respect to PAC-NA plate motion result in increasing convergence from north to south. The Transform Obliquity on the Queen Charlotte Fault and Earthquake Study (TOQUES) collected new multi-channel seismic (MCS) reflection data along a ~450 km section of the fault during the summer of 2021 aboard the R/V Marcus G. Langseth. Data were acquired using a 15-km-long streamer and a 6600 cubic inch tuned airgun array. Here, we focus on preliminary results from fault-crossing MCS profiles within the northern survey area, which is characterized by almost purely strike-slip PAC-NA plate motion and hosted the 2013 Mw 7.5 Craig, Alaska earthquake. Aftershock sequences show events clustered at depths <25 km, both to the west of the main QCF fault trace and to the east. The aftershock locations indicate the presence of seismically active faulting within the PAC plate and potentially suggest that either the main QCF dips to the east or that there are active fault strands within the NA plate. We present new MCS profiles that cross the 2013 epicentral region to investigate fault zone architecture, crustal deformation mechanisms, and structural relationships at depth. These 2D sections show a series of normal faults within the PAC crust and a slightly dipping basement eastwards. Sediments on the PAC at the base of the continental slope contain multiple vertical faults. The main QCF trace is present on the continental slope. Multiple stages of deformation are recorded by stacked sections of growth strata within mid-slope basins, which also host multiple vertical faults that cut sediments on the seafloor. These observations suggest that strike-slip deformation here may be distributed across multiple structures. On the NA plate continental shelf, we observe deformed, east-dipping strata truncated by glacial unconformities and minimal deformation of sediments at the seafloor.