Factors affecting seismic response of submarine slopes

Abstract

Abstract. The response of submerged slopes on the continental shelf to seismic or storm loading has become an important element in the risk assessment for offshore structures and "local" tsunami hazards worldwide. The geological profile of these slopes typically includes normally consolidated to lightly overconsolidated soft cohesive soils with layer thickness ranging from a few meters to hundreds of meters. The factor of safety obtained from pseudo-static analyses is not always a useful measure for evaluating the slope response, since values less than one do not necessarily imply slope failure with large movements of the soil mass.This paper addresses the relative importance of different factors affecting the response of submerged slopes during seismic loading. The analyses use a dynamic finite element code which includes a constitutive law describing the anisotropic stress-strain-strength behavior of normally consolidated to lightly overconsolidated clays. The model also incorporates anisotropic hardening to describe the effect of different shear strain and stress histories as well as bounding surface principles to provide realistic descriptions of the accumulation of the plastic strains and excess pore pressure during successive loading cycles. The paper presents results from parametric site response analyses on slope geometry and layering, soil material parameters, and input ground motion characteristics. The predicted maximum shear strains, permanent deformations, displacement time histories and maximum excess pore pressure development provide insight of slope performance during a seismic event.

Quantifying the role of sandy–silty sediments in generating slope failures during earthquakes: example from the Algerian margin

“…A series of numerical simulations were conducted using the AMPLE2000 software by in order to investigate the influence of slope inclination, soil thickness and ground motion parameters. Biscontin and Pestana (2006) results show that even for slope angles lower than 5°, the slope inclination remains the key parameter in terms of accumulation of strain and amount of permanent displacement. Regarding sediment accumulations, it appears that shallow layers can accumulate larger strains and higher pore pressure ratios than deeper layers, which are able to dissipate the earthquake energy at the end of the earthquake shaking (Biscontin and Pestana 2006).…”

“…Biscontin and Pestana (2006) results show that even for slope angles lower than 5°, the slope inclination remains the key parameter in terms of accumulation of strain and amount of permanent displacement. Regarding sediment accumulations, it appears that shallow layers can accumulate larger strains and higher pore pressure ratios than deeper layers, which are able to dissipate the earthquake energy at the end of the earthquake shaking (Biscontin and Pestana 2006). The present work is based on data acquired during three successive oceanographic cruises carried out after the Boumerdès earthquake (Déverchère 2003;Sultan 2004;Savoye 2005).…”

“…Beyond the liquefaction process, the excess pore pressure generated by a seismic event may migrate during or shortly after the time of the earthquake shaking and can be trapped under layers characterized by slower dissipation of pore pressure. The result may be a decrease in effective stress and in stiffness or strength, which could cause larger deformations that otherwise may not be present (Biscontin and Pestana 2006).…”

“…Recently, the response of submarine slopes to seismic loading was studied numerically by Biscontin and Pestana (2006). A series of numerical simulations were conducted using the AMPLE2000 software by in order to investigate the influence of slope inclination, soil thickness and ground motion parameters.…”

Slope failure repetition in active margin environments: Constraints from submarine landslides in the Hellenic fore arc, eastern Mediterranean

“…Our analysis assumes that the earthquake acceleration is applied over a significantly long period of time so that the induced stress can be considered constant [e.g., Hampton et al, 1996]. This may lead to some minor uncertainties in slope stability analysis due to dynamic behavior of the sediment, e.g., accumulation of plastic strain or shear-induced excess pore water pressures with increasing number of loading cycles [e.g., Sultan et al, 2004;Biscontin and Pestana, 2006]. However, as this simplified approach was successfully applied in other studies [e.g., Urgeles et al, 2006;Strasser et al, 2007;ten Brink et al, 2009;Stigall and Dugan, 2010], we adopt it here to gain insights on trigger quantity requirements and constraints.…”