Comparison of the Seismic Response of Offshore Slopes Using 1, 2, or 3 Ground Motion Components

Carlton, Brian; Kaynia, Amir M.

doi:10.4043/26961-ms

Cited by 5 publications

(5 citation statements)

References 7 publications

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“…The modelling attempt of this study included only one dimension of earthquake shaking, whereas seismic waves in reality affect the sedimentary sequence in three dimensions (Carlton and Kaynia, 2016). The lower earthquake frequencies are closer to the resonance frequency of sediment layers and attenuate more slowly within the sediments.…”

Section: Quantification Of Trigger Mechanisms Of the Tampen Slidementioning

confidence: 99%

NE Atlantic continental slope stability from a numerical modeling perspective

Bellwald

Urlaub

Hjelstuen

et al. 2019

Quaternary Science Reviews

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Trough mouth fans are environments characterized by high sediment supply during glacial stages and the occurrence of large-scale instabilities. The geological record indicates that several of these environments have failed repeatedly resulting in large submarine landslides. The roles of sedimentation rate, weak layers, glacial loading and unloading as well as seismic activity on triggering megaslides in trough-mouth-fan systems is still unclear. A better understanding of the preconditioning factors, triggers and consequences of these landslides is crucial due to the hazard they pose to coastal communities and offshore industries.In this paper, we focus on the North Sea Trough Mouth Fan, which is the result of massive glacial sediment input delivered to the shelf edge through the Norwegian Channel, southeast Nordic Seas margin. The Tampen Slide, one of several large paleo-landslides that have happened within the North Sea Trough Mouth Fan, took place at c. 130 ka (end of MIS 6), and removed an estimated 1800 km 3 of sediment.Here, we use boundary conditions from the Tampen Slide and 2D Finite Element Modeling (Abaqus software from Simulia) to evaluate the effects of variations in sedimentation rates as well as sediment properties on the generation of excess pore pressure, fluid flow, and slope stability along the axis of the trough-mouth-fan system. The model domain, 40 km in length and 2 km in height, is dominated by glacigenic debris flows and glacimarine sediment deposits. We use geotechnical data measured on samples of glacigenic and glacimarine sediment deposits from the nearby Ormen Lange gas field area to constrain the model. We evaluate the stability of the slope under various scenarios, including constant sediment loading, episodic changes in sedimentation rates and abrupt pulses in sediment delivery for a 61 kyr period (MIS 6). The models show that increased sedimentation rates during glacial stages do not generate sufficient excess pore pressure to set off a landslide. Furthermore, the simulated overpressures for the different sedimentation scenarios do not significantly differ at the end of the model runs. The results also highlight the importance of a basal glacimarine sediment layer underneath the rapidlydeposited sediments for the build-up of overpressure. Consequently, this glacimarine sediment layer has the inherited potential to act as a weak layer facilitating instability. However, as overpressure due to 3 sediment deposition alone does not result in slope failure, we couple the preconditioned slope with earthquake ground shaking. Based on attenuation models, an earthquake of approximately M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the landslide. Therefore, we suggest glacial sedimentation and a glacimarine sediment layer to represent preconditioning factors, and seismic shaking as the final trigger mechanism for the Tampen Slide, i.e. similar to the situation that lead to the development of the Storegga Slide in the same area.

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Section: Quantification Of Trigger Mechanisms Of the Tampen Slidementioning

confidence: 99%

NE Atlantic continental slope stability from a numerical modeling perspective

Bellwald

Urlaub

Hjelstuen

et al. 2019

Quaternary Science Reviews

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“…To avoid wave reflections along the model boundaries, tied boundary conditions (Zienkiewicz et al, 1989) were defined in both horizontal directions at each elevation of the mesh to constrain the model to deform as a shear beam and achieve a free-field condition. The approach of using of 3-D brick elements in OpenSees has been applied verified against models implemented in PLAXIS 3D and FLAC 3D (Carlton et al, 2020) and PLAXIS 2D (Løkke and Carlton, 2022) in the simulation of multidirectional shaking in offshore slopes. Soriano (2021) simulated by means of 3-D brick element columns the experimental response of instrumented gentle slopes in soft clay and tested in a geotechnical centrifuge with good agreement between the experimental and numerical results in terms of accelerations throughout the slopes and seismic displacements.…”

Section: Numerical Model Parametersmentioning

confidence: 99%

Numerical modelling of the seismic response of gentle slopes in Southeastern Brazil

Camelo

Almeida

Madabhushi

et al. 2022

Marine Georesources & Geotechnology

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The offshore Campos Basin, located in Southeastern Brazil represents an important area in the Brazilian economy as it is one of the most prolific oil-producing basins in the country. With the development of offshore infrastructures in this region, structural design and location must consider different geohazards. This paper addresses the seismic response of gentle submarine slopes subjected to small-to-moderate-sized earthquakes, representative of the Brazilian seismic conditions. The seismic analyses employed numerical modeling, with a nonlinear constitutive model.A set of bedrock ground motions representative of the offshore Campos Basin seismicity was obtained, employing a Uniform Hazard Response spectrum for the region and earthquakes from the Pacific Earthquake Engineering Research (PEER) database. Numerical modelling results showed that, even for small slope angles and moderate earthquakes, there is an accumulation of permanent displacements and shear strains in the downslope direction can affect the stability and performance of existing offshore infrastructures. The findings of this research provide a valuable reference for the prediction of seismic displacements, shear strains and seabed amplification or attenuation of earthquakes on gentle slopes in deep-water deposits similar to those found in the offshore Campos Basin.

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“…For the 100 m deep soil profile, multi-directional shaking predicted 30% increase in excess pore pressure at large depths, which reduced to 10% at the soil surface, whereas the 20 m deep soil profile predicted an increase in excess pore pressure between 20% and 40%. Carlton and Kaynia (2016) conducted a number of numerical simulations in which 3-D slopes of NC clay with simple Mohr-Coulomb failure criterion were subjected to one-component and 3-component earthquake excitations. Through a number of case studies, they observed that inclusion of the earthquake component perpendicular to the slope direction increases the permanent downslope displacements and shear strains in the slope by 25%-50% and by 10%-50%, respectively.…”

Section: Multi-directional Shakingmentioning

confidence: 99%

“…Response of slope for 3-component (above) vs one-component (below) earthquake (adapted fromCarlton & Kaynia, 2016) …”

mentioning

confidence: 99%

Earthquake Geotechnics in Offshore Engineering

Kaynia

2018

Recent Advances in Earthquake Engineering in Europe

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This paper presents a number of geotechnical issues encountered in earthquake design of offshore structures and subsea facilities. Parallel with construction of traditional structures such as jackets and gravity-based structures, a considerable effort has recently been put to field developments in deep water. This has brought about other challenges that are largely dependent on geotechnical knowledge. This paper addresses some of the more recent approaches and solutions in geotechnical earthquake design of both shallow water and deep-water structures and facilities such as platforms with large bases, pipelines traversing slopes and seabed installations. It is demonstrated how incorporation of radiation damping and nonlinear soil-structure interaction in offshore installations could optimize the design. Considering the importance of earthquake stability of slopes in deep water development, special attention is given to highlighting several key issues in the earthquake response of submarine slopes including strain softening and three-dimensional shaking.

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Comparison of the Seismic Response of Offshore Slopes Using 1, 2, or 3 Ground Motion Components

Cited by 5 publications

References 7 publications

NE Atlantic continental slope stability from a numerical modeling perspective

NE Atlantic continental slope stability from a numerical modeling perspective

Numerical modelling of the seismic response of gentle slopes in Southeastern Brazil

Earthquake Geotechnics in Offshore Engineering

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