The Traenadjupet Slide, offshore Norway - morphology, evacuation and triggering mechanisms

The Traenadjupet Slide, located on the continental slope off Norway, was studied using TOBI (Towed Ocean Bottom Instrument) high-resolution side-scan sonar data together with 7.5 kHz seismic records. The slide extends from the shelf break to more than 3000 m water depth in the Lofoten Basin, implying a slide-affected area of about 14,100 km(2). The slide probably occurred during the mid-Holocene, prior to 4000 C-14 years BP. The slide scar includes escarpments, detached ridges of sediment, sediment streams, grooves, elongated highs, tabular sediment blocks, pressure ridges, and tension fractures. The initial sediment disintegration produced detached sediment ridges that moved by back-tilting or through basal deformation. Transition to sediment streams comprising more-or-less disintegrated sediments occurred over some kilometres. Movement of consolidated sediments formed the tabular sediment blocks. The initial failure was either located near the present headwall of the Traenadjupet Slide, or downslope from a large escarpment located at a present water depth of 1800 m. A combination of events led to the slope failures in this area. Sedimentation within the Traenadjupet Slide area was characterised by high sedimentation rates during the glacial maxima. Periods of high sedimentation rates have promoted instability of the glacigenic sediments themselves, or more important, prevented water and/or gas to escape from the relatively thin layers of interglacial/interstadial sediments (<10 m), due to the low permeability of the glacigenic sediments. This could have led to build-up of excess pore pressure and the interglacial/interstadial sediments then have acted as planes of weakness. Triggering most likely was caused by one large or a series of small earthquakes associated with postglacial crustal uplift of Fennoscandia. (C) 2000 Elsevier Science B.V. All rights reserved.