In situ pore pressures: What is their significance and how can they be reliably measured?

The Storegga Slide complex: repetitive large scale sliding with similar cause and development

“…Deposition-generated overpressures are also interpreted to be important for other slides in the North Atlantic region (Laberg et al, 2003;Long et al, 2003;Piper and McCall, 2003). Excess pore pressures are detected in deposits behind the Storegga Slide headwall today (Strout and Tjelta, 2005). Overpressures related to the dissociation of gas hydrates, which also would follow climate cycles are not excluded as an additional factor causing overpressures, as suggested by Sultan et al (2003).…”

Morphology and mechanics of submarine spreading: A case study from the Storegga Slide

“…The upslope dip of the internal extension faults within the slab is interpreted as an indication that the extensional forces acting on the slab decreased upslope and the frictional drag on the base of the slab increased upslope. The latter may have been due to a decrease in excess pore pressure in the failing layer upslope (away from the source of the overall retrogressive Storegga Slide, as suggested by Strout and Tjelta [2005]). Alternatively, the physical character or thickness of the failing layer (believed to be contouritic glaciomarine sediments [ Berg et al , 2005]) may have varied with water depth, as is seen in present‐day distribution of post‐Storegga Slide sediments [ Bryn et al , 2005b].…”

“…Thus, at 1.5 km from the upslope limit we increase γ linearly from 10 kN m −2 to 10.5 kN m −2 at the headwall. Unloading of the sediment after the LGM has reduced pore pressures in sediments close to the headwall, while measured pore pressures are higher near the North Sea Fan [ Bryn et al , 2003; Strout and Tjelta , 2005]. Pore pressure ( u ) is thus decreased from 1000 kN m −2 at the downslope limit to 600 kN m −2 at the upslope limit of the slab [ Strout and Tjelta , 2005].…”

“…Unloading of the sediment after the LGM has reduced pore pressures in sediments close to the headwall, while measured pore pressures are higher near the North Sea Fan [ Bryn et al , 2003; Strout and Tjelta , 2005]. Pore pressure ( u ) is thus decreased from 1000 kN m −2 at the downslope limit to 600 kN m −2 at the upslope limit of the slab [ Strout and Tjelta , 2005]. The cohesion ( c ) in this part of the Storegga Slide is spatially constant at 7 kN m −2 [ Sultan et al , 2004b].…”

The last phase of the Storegga Slide: simulation of retrogressive slide dynamics and comparison with slide-scar morphology

“…Extensive geophysical, geological, and geotechnical investigations were carried out (Bryn et al, 1998Berg et al, 2005;Forsberg and Locat, 2005;Strout and Tjelta, 2005). The major objective was to assess the present-day stability in the vicinity of the field development area, and in addition to understand the mechanisms causing the release and the extensive spreading of the Storegga Slide.…”