Abstract Multibeam echosounder (MBES) images, 3.5 kHz seismic-reflection profiles and piston cores obtained along the southern Queen Charlotte Fault Zone are used to map and date mass-wasting events at this transform margin – a seismically active boundary that separates the Pacific Plate from the North American Plate. Whereas the upper continental slope adjacent to and east (upslope) of the fault zone offshore of the Haida Gwaii is heavily gullied, few large-sized submarine landslides in this area are observed in the MBES images. However, smaller submarine seafloor slides exist locally in areas where fluid flow appears to be occurring and large seafloor slides have recently been detected at the base of the steep continental slope just above its contact with the abyssal plain on the Queen Charlotte Terrace. In addition, along the subtle slope re-entrant area offshore of the Dixon Entrance shelf bathymetric data suggest that extensive mass wasting has occurred in the vicinity of an active mud volcano venting gas. We surmise that the relative lack of submarine slides along the upper slope in close proximity to the Queen Charlotte Fault Zone may be the result of seismic strengthening (compaction and cohesion) of a sediment-starved shelf and slope through multiple seismic events.

Abstract The state of stress in the lithosphere is the product of a variety of forces that act on the plates. The interior region of a plate may be stressed by large-scale plate-driving forces, local density contrasts in'the plate, regional thermal anomalies, the residual effects of past tectonic events, or load redistribution caused by glaciation, volcanism, or erosion/sedimentation. Investigation of the tectonic in-situ stress field can enhance our understanding of mid-plate deformation and may also elucidate the relative importance of the various forces acting on the plates. To this end we have assembled deformation, seismicity, and stress data for the mid-plate region of the North American plate. Our area of study covers continental North America and the oceanic portions of the North American plate, excluding zones of deformation along the plate boundaries. Excluded are the Mid- Atlantic Ridge and the shear and subduction boundaries associated with the Caribbean plate (covered by other chapters in this volume) and the entire western Cordillera of Canada and the United States (from the eastern Rocky Mountains front to the Pacific coast). The state of stress in the broad, intensely deformed western part of the North American plate is considered to be influenced primarily by local processes related to Pacific-North American plate interaction. Numerous techniques and stress indicators provide information on the principal tectonic stresses in the crust and, for the oceans, the mantle lithosphere. Compilations of available data show that stress orientations inferred from different methods or techniques quite often agree within the accuracy