Slope failure and mass transport processes along the Queen Charlotte Fault Zone, western British Columbia

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.

Potential Instability of Gas Hydrates along the Chilean Margin Due to Ocean Warming

“…So, better understanding of the link between gas hydrate, slope stability and earthquakes is required. Recent studies show that slope stability in active margins is higher due to seismic strengthening, hence suggesting an inverse relationship between seismicity and submarine landslides [60][61][62]. Despite that, different authors [61,63] show that high sedimentation rates in continental slopes seem to be able to counteract seismic strengthening, which is thought to be particularly high in this sector, as mentioned before.…”

Late Quaternary sea level, isostatic response, and sediment dispersal along the Queen Charlotte fault

“…Multibeam bathymetry from the central coast of Haida Gwaii and off Dixon Entrance was presented in Greene et al (2019), along with interpretation of cores collected within these blocks. All other data collected during these surveys are presented here.…”

“…3). Cores collected near the fault are dominated by dense sand and mud units that may have been compacted by seismic shaking throughout the late Pleistocene and early Holocene (Greene et al, 2019). One core just beyond the slide (core 201504-21; Fig.…”

“…The length of the Queen Charlotte-Fairweather fault system is 1330 km, slightly longer than the San Andreas fault, with a reported width of 1-5 km, and ~75% of the length is located offshore (Carlson et al, 1985). Recently, most of the offshore fault zone from south of Haida Gwaii through southeastern Alaska has been imaged in detail using multibeam echosounder (MBES) data and other geophysical techniques that have documented the fault morphology and identified features associated with localized deformation along the fault (step-overs), submarine canyons, gullies, and submarine slides adjacent to the fault (Barrie et al, 2013;Brothers et al, 2019;Greene et al, 2019).…”

Advancing from subaqueous mass movement case studies to providing advice and mitigation

“…Yet further south, near the Queen Charlotte Fault zone where earthquakes are frequent, shaking did not cause slope failure, but instead has had the opposite effect. Here, there is a relative lack of submarine landslides, which Greene et al (2018) surmise is the result of seismic strengthening (compaction) of an already sediment-starved shelf. Interestingly though, there are two medium-sized slides on the flanks of a newly discovered actively venting mud volcano, and the researchers believe that the slope is locally unstable because of the presence of gas and other fluids in the sediment.…”