Abstract
A series of large blocks from the 44-North Slide, offshore Oregon, impacted the seafloor with sufficient force to induce a broad zone of deformation. In 2017, we acquired a seismic profile from the headwall area to the outer toe of this slide. Previous work identified this slide, but it has not been imaged at high resolution before this survey. A striking surficial feature is a collection of blocks that lie downslope from an amphitheater-shaped headwall. The blocks traveled up to 20-km horizontally and about 1200-m vertically down a 13° slope and now cover an area of ~100 km2. The blocks have rough and angular edges that extend up to 400-m above the surrounding seafloor. Seaward of the blocks, a 10-km zone of sediment is deformed, horizontally shortened by 8%. We interpret the strain field to be a result of the dynamic impact forces of the slide. This suggests a high-mobility failure with tsunamigenic potential. It is unclear what preconditioned and triggered this event, however, earthquake-induced failure is one possibility. Gas hydrate dissociation may have also played a role due to the presence of a bottom-simulating reflector beneath the source area. This study underscores the need to understand the dynamic processes of submarine landslides to more accurately estimate their societal impacts.
Highlights
Submarine landslides have been known to cause tsunamis that can impact coasts around the world [1,2,3,4]
This study proposes undrained loading pore pressure as the mechanism for the vertical extent of the deformation and supports McAdoo and Watts’ (2004) analysis that the southern Cascadia margin is more likely to produce tsunamigenic landslides, contributing to the hazard potential of the margin [8]
New high resolution two-dimensional reflection seismic data revealed compressional deformation features in abyssal plain sediments adjacent to the large blocks of the 44-North submarine landslide offshore Oregon. These deformational features were interpreted to be induced by the impact forces of the blocks along a distinct slip plane created by the immediate increase in pore pressure
Summary
Submarine landslides have been known to cause tsunamis that can impact coasts around the world [1,2,3,4] An example of this occurred during the 1964 great Alaska earthquake in Resurrection. Sediments with higher strength often produce thicker cohesive landslides that generate larger tsunamis compared to sediments with lower strength [6,7,8,9]. This suggests that blocky slides may be more likely to produce a tsunami as opposed to disintegrative slides. Initial acceleration [10,11,12] and maximum velocity [13,14] may be the most important parameters that influence landslide generated tsunamis, but they are usually unknown and difficult to model
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