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

The Traenadjupet Slide, located on the continental slope off Norway, was st udied using TOBI (Towed Ocean Bottom Instrument) high-resolution side-scan sonar data together with 7.5 kHz seismic records. The slide extends from th e shelf break to more than 3000 m water depth in the Lofoten Basin, implyin g 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 includ es escarpments, detached ridges of sediment, sediment streams, grooves, elo ngated highs, tabular sediment blocks, pressure ridges, and tension fractur es. The initial sediment disintegration produced detached sediment ridges t hat moved by back-tilting or through basal deformation. Transition to sedim ent streams comprising more-or-less disintegrated sediments occurred over s ome kilometres. Movement of consolidated sediments formed the tabular sedim ent blocks. The initial failure was either located near the present headwal l of the Traenadjupet Slide, or downslope from a large escarpment located a t 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 wa s characterised by high sedimentation rates during the glacial maxima. Peri ods of high sedimentation rates have promoted instability of the glacigenic sediments themselves, or more important, prevented water and/or gas to esc ape from the relatively thin layers of interglacial/interstadial sediments (<10 m), due to the low permeability of the glacigenic sediments. This coul d have led to build-up of excess pore pressure and the interglacial/interst adial sediments then have acted as planes of weakness. Triggering most like ly 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.