Abstract
Despite the gently dipping slopes (ca 1°), large-scale submarine slope failures have occurred on the mid-Norwegian continental margin (Storegga, Sklinnadjupet, Traenadjupet), suggesting the presence of special conditions predisposing to failure in this formerly glaciated margin. With a volume estimated between 2,400 and 3,200 km3 and an affected area of approximately 95,000 km2, the Storegga slide represents one of the largest and best-studied submarine slides of Holocene age known worldwide. Finite element modeling of slope failure indicates that a large (6.5 < Ms < 7.0) seismic triggering mechanism would not be sufficient to cause failure at more than 110 m below the seabed as observed for the slip planes at Storegga (northern sidewall). This implies that other factors (e.g., liquefaction, strain softening, gas charging, rapid burial) are needed to explain the occurrence of the Storegga slide with a deep surface of failure. In this paper, we discuss the importance of the compaction effect of rapidly accumulated sediments in the slide area. During compaction, sediment grains reorganize themselves, thereby, expelling pore water. Consequently, depending on sedimentation rate and permeability, excess pore pressures might result beneath less permeable sediments. Our modeling and cross-checking illustrate how excess pore pressure generation due to high sedimentation rate could explain the development of layers of weakness, and thus, how such a large slide might have been initiated in deep sediments. Using the highest sedimentation rate estimated in the area (36 and 27 m/kyr between 16.2 and 15 kyr BP), 1D modeling shows excess pore pressure values of around 200 kPa at a depth of 100 m below the seafloor 15 kyr BP and 60 kPa at a depth of 100 m at the time of the slide (8 kyr BP). Excess pore pressure apparently drastically reduced the resistance of the sediment (incomplete consolidation). In addition, 2D modeling shows that permeability anisotropies can significantly affect the lateral extent of excess pore pressure dissipation, affecting, that way, normally consolidated sediments far from the excess pore pressure initiation area.
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Acknowledgments
This work is a contribution to the COSTA European project under contract EVK3-1999-00028. We would like to thank Berit O. Hjelstuen for providing a complete set of figures in the Helland Hansen area and Daniel O. Hayba from the USGS for his support in the use of BASIN2 software. Thanks to Manon Wilken for digitizing slide areas outlines off the Norwegian margin, to T. J. Kvalstad (NGI) for a preliminary review which distinctly improved an earlier version of the manuscript, and to Geoff Corner, Maarten Vanneste, and Dr. Roy Sidle for improving the manuscript at a final stage.
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Leynaud, D., Sultan, N. & Mienert, J. The role of sedimentation rate and permeability in the slope stability of the formerly glaciated Norwegian continental margin: the Storegga slide model. Landslides 4, 297–309 (2007). https://doi.org/10.1007/s10346-007-0086-z
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DOI: https://doi.org/10.1007/s10346-007-0086-z