Stability and failure mechanism for landslides at the Upper Continental Slope off Vesterålen, Norway
Presented by Dr. Jean-Sebastien L'HEUREUX on 23 Sep 2013 from 17:15 to 19:15
Type: Poster presentation
Session: Poster session
Track: Poster presentations
Several relatively small and spatially-isolated landslides with low mobility characterise the geomorphology of the upper continental slope off the Vesterålen islands. Here, we present results from a multidisciplinary study that integrates swath bathymetry data, high-resolution seismic reflection profiles and a multitude of geological and geotechnical laboratory tests from a 12 m long piston core in order to investigate the origin and hazard potential of these shallow landslides. Four of the landslides have their upper headwall around the 500 m isobath, whereas the main escarpments of another four landslides lie around 700 to 800 m. The slip planes of the translational landslides lie within laminated glacial marine clays, overlying a well-defined seismic horizon. These clays have a higher plasticity and water content compared to the surrounding soils (sandy clays), and they exhibit a modest strain-softening behaviour in triaxial tests. The interdisciplinary data set is used as input to various numerical analyses in order to assess the failure and triggering mechanisms for these landslides, as well as their hazard potential. Stability analyses, dynamic analyses and post-earthquake pore pressure dissipation modelling suggest that the margin is essentially stable and that it would require a large magnitude earthquake to trigger landslides. The resulting deformation and excess pore pressure generation occur primarily within the top 10 m of the soil, and they become more pronounced towards the surface. The simulations depend strongly on the input parameters, which are determined from a limited number of samples, geotechnical tests and geophysical data. Therefore, the results must be seen as preliminary. Additional sediment cores and in situ geotechnical tests data are planned to gain further insights into the variety of slope processes in this pristine region of the Norwegian margin.