Triggering mechanisms of slope instability processes and sediment failures on continental margins: a geotechnical approach

Abstract

The Costa target areas exhibit the variability of slope instabilities needed to improve our understanding of sediment physical and mechanical properties in areas prone to sliding. That is why in this project, we have analysed the different slope failures events from different parts of the Costa target areas, which reflect diverse triggering mechanisms. The aim of the first part of this study was to identify the geotechnical response of the sediment to different external mechanisms (earthquake, rapid sedimentation and gas hydrate melting). We have focused on the relation between external mechanisms and the consequence change in the in-situ stress state and the physical, mechanical, and elastic properties of the sediment.In the second part of the paper, the geotechnical properties of the sediment from different Costa areas are presented. Comparison between observed geotechnical properties and the theoretical behaviour was done in order to improve our understanding of the origin of the different observed slides. D

Frictional heating lubrication for submarine landslide

“…Now, we discuss the ranges of p s (0, t) and Qr specified in this study. To date, it has been discovered that the magnitude of p s depends on sedimentation rates, soil permeability, and over-consolidated thickness (Gordon and Flemings 1998;Flemings 2000, 2002;Sultan et al 2004a;Flemings et al 2008;Stigall and Dugan 2010). For example, as shown in the drilling measurements by Flemings et al (2008) in the deepwater Gulf of Mexico, offshore Louisiana, the value of p s (called as "overpressure" in Flemings et al 2008) increased with the vertically downward depth below the seafloor, e.g., increasing to 1 -2 MPa when the depth was increased to 200 -300 mbsf, and then the p s value changed insignificantly at depths > 300 mbsf.…”

“…Many studies have suggested possible factors that can trigger submarine landslides, e.g., earthquakes, hurricanes or cyclic loading, oversteepening of slopes, overpressure, gas hydrate dissociation, sea-level change, and volcanic activity (Prior and Coleman 1982;Weaver and Kuijpers 1983;Moore et al 1989;Assier-Rzadkiewicz et al 2000;Sultan et al 2004a, b;Fine et al 2005). However, it is still a question why submarine landslides can occur on slopes as low as 1° and travel a long distance over such mild slopes.…”

“…Even for snow avalanches, "weak layer" was also well recognized (Heierli et al 2008). As far as we know, there are several types of "weak layers" observed in field investigations, for example, (1) sandy layers where gas hydrates dissociate (Sultan et al 2004b); (2) consolidated clayey areas of high sedimentation rates (Dugan and Flemings 2000;Sultan et al 2004a); (3) sandy silt layers that can liquefy during earthquakes (Kokusho and Kojima 2002); (4) rapid accumulation events, e.g., turbidity currents or debris flows, over a clay-rich seabed (Hansen et al 2011); and (5) sensitive clay layers; i.e., clayey sediments with a "strain-softening" behaviour Dey et al 2016). The "strain-softening" implies that just a small distortion can cause a tremendous deformation of soil (like a "collapsing" or "contracting" of soil texture) leading to a significant reduction of the porosity, which for undrained conditions will induce an increase of pore pressure there and therefore decrease the soil strength (Thakur 2011).…”

The Case for Large M > 7 Earthquakes Felt in the UK in Historical Times

“…One other mechanism that has been suggested, for instance, is that slides may be triggered by escape of gas hydrates (Bugge et al, 1987;Vogt and Jung, 2002). Recent studies, though, incline towards viewing earthquakes as the most likely external triggering factor Sultan et al, 2004). Holmes et al (1998) consider that earthquakes may have triggered slide movements on the Barra Fan, and Baltzer et al (1998) conclude that at least one earthquake (probably just before or during the early Devensian, i.e.…”

“…The morphology of the slide suggests that it was due to triggering by an earthquake, possibly associated with the Victory Transfer Zone Sultan et al, 2004;Wilson et al, 2004), and an attempt has been made to model the effects of earthquake loading on slope stability in the area (Jackson et al, 2004).…”