New Insights on Strain-Partitioning Along the Southern Queen Charlotte Fault, Offshore Haida Gwaii, Canada, from 2021 Multi-Channel Seismic Reflection Imaging

During July-Aug 2021, the Transform Obliquity along the Queen Charlotte fault and Earthquake Study (TOQUES) acquired ~4200 km of new marine multichannel seismic reflection (MCS) and wide-angle reflection/refraction data along a ~450 km section of the offshore the Canadian Cordilleran margin. The Queen Charlotte fault (QCF) is an ocean-continent transform boundary separating the North American (NA) and Pacific (PAC) plates that accommodates ~55 mm/yr of differential plate motion and has ruptured in seven M>7 earthquakes over the last century. Sustained transpressional deformation along the southern QCF has built the Queen Charlotte Terrace (QCT) offshore Haida Gwaii, British Columbia. Understanding how the southern QCF accommodates convergence has important implications for earthquake and tsunami hazards in the area, and potentially for understanding subduction initiation processes. The QCT structurally resembles an accretionary prism and is potentially the site of PAC crust underthrusting beneath NA. The 2012 M7.8 Haida Gwaii earthquake ruptured beneath the NA plate along the hypothesized underthrust interface. The aftershock sequence primarily contained normal fault earthquakes west of the main QCF trace, within the QCT and PAC plate. We show preliminary results from MCS profiles within the southern QCF segment that cross the main QCF fault trace and the QCT, acquired by the R/V Marcus G. Langseth using a 15 km streamer and a 6600 cubic inch tuned airgun array. We observe active normal faulting in the PAC plate west of the Haida Gwaii rupture area which may be associated with the observed aftershock activity. Buried normal faults on the PAC plate ~30 km to the north suggest that the PAC is not actively undergoing extensional deformation outside of the southernmost QCF. Further analysis of these data to identify fault structures within the QCT, fault architecture of the main QCF, and their structural relationships at depth will provide new insights into strain-partitioning along the southern QCF.