Submarine Landslides Research Articles

Investigation of offshore landslides impact on bucket foundations using a coupled SPH–FEM method

BackgroundAs the exploitation of marine resources intensifies, the impact of submarine landslides on underwater structures has become a significant issue. Existing research primarily focuses on the impact on pipelines, often neglecting the actual deformation and mechanical response of underwater structures under impact loads in numerical simulations, thus complicating the evaluation of the reliability of these engineering structures in extreme conditions. Moreover, the dynamic response of bucket foundations, a common form of underwater base, under the effect of submarine landslide impacts remains unclear.MethodsTo address this knowledge gap, we have developed a fluid-structure coupling system that employs the coupled Smoothed Particle Hydrodynamics (SPH)-Finite Element Method (FEM) to investigate a single impact process and analyze the displacement response of bucket foundations within a water-offshore landslide-bucket foundationsubgrade context. The accuracy of this developed method has been systematically verified through comparisons with previous experimental and numerical results.ResultsDuring a submarine landslide impact event, the impact force demonstrates a distinct decrease followed by stabilization, and the displacement response of the bucket foundation exhibits a rebound effect after reaching its maximum value. Furthermore, we conducted an extensive analysis of different impact angles for underwater data centers equipped with multi-bucket foundations. Our study revealed that group-bucket foundations experience a combined translation-turnover failure when subjected to submarine landslide impacts, and the most unfavorable scenario for such impact is identified. The research introduces a novel numerical simulation approach for investigating the impact of submarine landslides on complex underwater structures.

National Archive of Marine Seismic Surveys Web Portal Provides Public Access to US Exclusive Economic Zone Marine Seismic Surveys

AbstractSeismic reflection data collected within the US Exclusive Economic Zone (EEZ) represent a scientific resource with inestimable value. The US Geological Survey (USGS), in partnership with the Bureau of Ocean Energy Management (BOEM), provide unrestricted public access to seismic data acquired since 1975 through the National Archive of Marine Seismic Surveys (NAMSS) portal. This map‐searchable web portal provides access to over 1,100 two‐ and three‐dimensional (2D, 3D) marine seismic data sets collected by the USGS and by the offshore resource industry. The industry data sets are released by BOEM under The Code of Federal Regulations 30 CFR Parts 551 and 580, allowing for the release of seismic reflection data after the completed 25‐year proprietary term from the issuance of the Geological and Geophysical (G&G) permit. The web portal provides tools to filter and identify surveys within the US EEZ and navigation and shapefiles can be downloaded with each survey. Seismic data sets downloaded from NAMSS have been instrumental in numerous scientific investigations along the US EEZ. These include studies focused on offshore marine geohazards, such as fault systems and submarine landslides, as well as gas hydrates and other geologic processes. Acquisition of such data sets, especially pneumatic‐sourced surveys, is becoming progressively more difficult due to environmental concerns and associated costs, thus preservation and public access to such high‐quality data sets is critical to maintaining the ability to conduct offshore seismic reflection scientific research along the US EEZ.

Study on the geomorphological changes of deep troughs under the influence of reclamation in the Caofeidian

Reclamation projects generally change the hydrodynamics and thus affect the topography of the seabed, which is the main threat to the safety of marine engineering. The Caofeidian Reclamation Project, the largest reclamation project in China to date, involved the reclamation of coastal regions of the Hebei Province. However, the project also created several issues and flaws due to the size of the reclaimed area. Through the comparative analysis in the Caofeidian sea area of multi-phase bathymetric topography, shallow stratigraphic changes, and numerical simulation of sediment dynamics, the characteristics of surface sediments and spatial distribution of erodibility were summarized. New marine geological hazards were discovered, such as submarine landslides and erosion depressions. It was concluded that after the reclamation of the Caofeidian, the south of the deep trough was still in an erosion state, and the erosion rate increased slightly. The shear stress formed by strong tidal currents in the deep trough was greater than the critical erosion shear stress of surface sediments, which caused the erosion transport of sediments. It was the primary dynamic mechanism leading to the long-term erosion state of the deep trough.

Smoothed particle hydrodynamics approach for modelling submerged granular flows and the induced water wave generation

In this study, we develop a Smoothed Particle Hydrodynamics (SPH) 2D-model for simulating fully submerged granular flows and their arising water waves. The granular particles are characterised by a non-Newtonian flow pattern, following a Casson constitutive law, generalised by applying the infinitesimal strain theory to avoid numerical singularities inherited from the original law. The implementation of this rheological model on the weakly compressible viscous Navier-Stokes equations enables the simultaneous modelling of the motion of granular flows and their resulting water waves, establishing a monolithic representation of fluid-structure coupling. The novelty of this model lies in the numerical continuity of the generalised rheological model based mainly on the yield stress criterion, which is computed purely from the mechanical properties of granular materials, including internal friction, cohesion, and viscosity coefficients. The proposed SPH model is validated through two benchmarks available in the literature, representing a submarine landslide along an inclined plane and an immersed granular column collapse. The outcomes of our study illustrate the effectiveness of the proposed model in accurately predicting the motions of submerged granular masses and their resulting water waves, which is crucial for accurately predicting the behaviour of underwater landslides and other natural hazards.

A STUDY ON THE APPLICATION CONDITIONS OF THE INITIAL WATER LEVEL PREDICTION EQUATIONS FOR TSUNAMI ASSOCIATED WITH SUBMARINE LANDSLIDE

A STUDY ON THE APPLICATION CONDITIONS OF THE INITIAL WATER LEVEL PREDICTION EQUATIONS FOR TSUNAMI ASSOCIATED WITH SUBMARINE LANDSLIDE

Determination of ground properties and pilot experiment for submarine landslide of Ulleung Basin, East Sea

Determination of ground properties and pilot experiment for submarine landslide of Ulleung Basin, East Sea

Вероятность формирования оползней на норвежской континентальной окраине

Numerous landslides are located on the passive margin of Norway. According to the landslides number and the extent of their detachment zones, the margin can be divided into three segments (from south to north) — Scandinavian, Barents Sea and Svalbard. The fourth segment (Arctic) is the transition area located north of the Spitsbergen archipelago. In the Scandinavian segment, about forty large submarine landslide bodies have been identified on the continental slope and deeper. The Barents Sea segment is dominated by deep-sea fan deposits and relatively small landslides. No large landslides were found in the Svalbard segment. Analysis of published and original geological and geophysical data indicates that the formation of new landslides may occur in the Svalbard segment, as well as on the Vestnesa Ridge.

Convenient Method for Large-Deformation Finite-Element Simulation of Submarine Landslides Considering Shear Softening and Rate Correlation Effects

Submarine landslides pose a serious threat to the safety of underwater engineering facilities. To evaluate the safety of undersea structures, it is important to estimate and analyze the sliding processes of potential submarine landslides. In this study, a convenient model for simulating submarine landslide processes is established by using Abaqus Eulerian large deformation technology with an explicit finite element framework. The VUSDFLD Fortran subroutine is used to consider the strain-softening and rate-dependency characteristics of soil shear strength. The proposed method is validated by comparing its results with experimental data and those of mainstream numerical methods. Then, the results of a dynamic analysis of typical potential submarine landslides in the Shenhu sea area are analyzed using the proposed method. Case studies are carried out under different soil shear strength distributions, and the influence of initial stress is also analyzed. The shear strain-softening and rate-dependency effects are highly involved in the runout process. The simulated landslide’s failure mode is consistent with the geophysical interpretation of existing landslide characteristics.

Transformation of dense shelf water cascade into turbidity currents: Insights from high-resolution geophysical datasets

Dense shelf water cascade (DSWC) is a common oceanographic phenomenon on many continental shelves. Previous studies indicate that the DSWC could shape seabed physiography and carry seawater, sediment, and organic carbon a long distance from the continental shelf to the basin floor. However, it remains enigmatic how these DSWC's interact with seabed geomorphology and travel long distances from the shallow to deep marine environments. In this study, we employed high-resolution multibeam bathymetry, 2D and 3D seismic reflection, core description, and sediment grain size data from the Gippsland Basin, southeast offshore Australia. The continental shelf of the central Gippsland Basin stores sediment supplied by the along-shelf transported DSWC. By calculating the sediment motion threshold, we demonstrate that the DSWC is capable of entraining sediment from, and forming dense bottom nepheloid layers above, the seabed. Seismic reflection data reveal that cyclic steps are common on the shelf and slope, indicating a downslope-transported, supercritical current-dominated environment. Core observation and grain size analyses reveal that coarse-grained, Ta-typed turbidites are the major facies, indicating the presence of high-intensity downslope-traversing turbidity currents. Thus, supercritical turbidity currents are the dominant sedimentary process in the central Gippsland Basin. We illuminate that DSWC can interact with pre-existing seabed bathymetry created by a buried submarine landslide, resuspending sediment and igniting downslope-transported turbidity currents. The presence of numerous cyclic steps indicates that the turbidity current can evolve into a supercritical regime upon ignition, leaving complex seabed geomorphology and allowing the forming currents to travel across the shelf and extend more than 80 km down the lower slope. As revealed by our literature review, we imply that the transformation of DSWC into turbidity currents should be a common sedimentary process on outer continental shelves globally, significantly sculpting the seabed morphology and facilitating sediment and other marine particles transportation from shallow to deep sea.

Submarine landslides on the Eastern South Korea Plateau (ESKP)—Do pumice-rich tephra layers control slope stability?

Tephra layers embedded in marine sediments can be significant in controlling submarine landslide dynamics and seafloor morphology, but their preconditioning effects on slope failure remain uncertain. Here, we study the morphology and preconditioning factors of submarine landslides from a volcanically active region, the Eastern South Korea Plateau (ESKP) using a recently acquired multibeam echosounder (MBES), high-resolution sub-bottom chirp profiler, and piston core data, together with previous geophysical data. At least 50 translational landslides were identified on the southern margin of the ESKP in an area of ∼470 km2, with a relatively small volume of remobilized sediment (∼10 km3). The landslide headscarps are arcuate, up to 400 m in height, and lie at water depths of 980 to 2300 m. Landslides on the upper ESKP margin are more disintegrative (debris flow type) than those on the lower margin which consists largely of blocky type failures with small runouts. Landslide deposits identified in the cores consist of debris flows and slides/slumps while background deposits contain hemipelagic mud interbedded with ca. 10-cm-thick coarse-grained, poorly-sorted pumiceous tephra. Seismic and core integration indicate that the glide planes of the observed slides correspond to the pumice-rich tephra layers. These tephras are predominantly composed of fresh volcanic glass devoid of clay, indicating that the composition of the tephra did not control the formation of weak layers or slide planes. We infer therefore that the weakness of the glide planes resulted from high hydraulic (pore) pressure at the interface between some of the porous tephra layers and their overlying, relatively impermeable, hemipelagic mud. In addition to burial compaction and build-up of pore pressure in the tephra layers, fluid overpressure could have been facilitated by earthquakes causing granular convection within, and compaction of, the poorly sorted tephra. The landslide predominantly formed > ca. 84 ka ago, which suggests time-restricted triggering associated with a temporary increase in seismicity and/or sediments reaching their overpressure threshold during burial compaction. Our study suggests that regional occurrences of discrete layers of porous tephra deposits within finer grained hemipelagic sediments can potentially control the generation of landslides in subaqueous environments affected by explosive volcanism.

Investigation on hydrate exploitation in submarine slope: Insights from discontinuous pillar exploitation

The decomposition of natural gas hydrate (NGH) will cause a decrease in reservoir strength, which can easily induce submarine landslides when hydrate reservoirs are located on a submarine slope. Although there have been several studies on the stability of hydrate-bearing submarine slopes (HBSS), little attention has been paid to minimizing the risk of landslides due to NGH exploitation. The “multistage reduction method” based on strength reduction was described in this paper. Subsequently, “discontinuous pillar exploitation” was proposed to achieve safe extraction of NGH and avoid submarine landslides. Finally, the “discontinuous pillar exploitation” was analyzed using the “multistage reduction method”. The results show that NGH decomposition has a far-reaching impact on the HBSS; it reduces the stability of HBSS and can trigger submarine landslides. The “discontinuous pillar exploitation” can divide the continuous plastic failure zone into short discontinuous plastic zones through the setting up of pillars, which significantly improves the stability of HBSS. With the decrease in the exploitation ratio, the safety factor of the submarine slope increases continuously. When the “discontinuous pillar exploitation” is adopted for NGH production on a submarine slope, there are two positions that require special attention: the junctions between the pillars and the exploitation area (peak area of shear stress); the side of exploitation area near the top of the slope (peak area of tensile stress).

Potential triggers and development processes of submarine landslides in the Xisha Trough Basin, South China Sea

Both submarine landslides and submarine canyons can transfer large amounts of terrigenous quantities from the continental shelf to the deep sea. In some cases, they can have a close relationship to their spatial distribution, formation and evolution. Submarine landslides on the shelf–slope can provide early depressions for submarine canyons, representing the early stage of submarine canyons. The continuous downcutting process during the evolution of submarine canyons can steepen the gradient of the canyon sidewalls, which can lead to the occurrence of submarine landslides. However, the role of submarine canyons in the initiation of slope failure has been overlooked. In this study, high-resolution multibeam bathymetry data, submarine image data and 2-D seismic data were used to investigate two adjacent submarine landslides developed on the northern slope of the Xisha Trough and the spatiotemporal relationship of these landslides to the Central Canyon. We identified a steep downslope between the submarine landslides and the Central Canyon. The Central Canyon formation age was much earlier than those of the submarine landslides. The Central Canyon is filled with modern submarine landslide deposits. The characteristics of the multiple failure scarps indicate retrogressive failure of the submarine landslides. We suggest that the submarine landslides developed on the northern slope of the Xisha Trough Basin have finally been captured by the Central Canyon. We determined that the emptying of sediments at the end of the northern slope of the Xisha Trough Basin caused by the development of the Central Canyon caused the end of the northern slope of the Xisha Trough Basin to lose support, which may have affected the slope stability and could have even played a role in the initiation of submarine landslides. Consequently, the slope area along the Central Canyon may be susceptible to slope instability and slope failure processes.

Submarine landslide hazard in the Sines Contourite Drift, SW Iberia: slope instability analysis under static and transient conditions

Submarine landslide hazard in the Sines Contourite Drift, SW Iberia: slope instability analysis under static and transient conditions

A Framework for Simulating the Evolution of Underwater Landslides and Its Application to Slope Failures in Swiss Lakes

A Framework for Simulating the Evolution of Underwater Landslides and Its Application to Slope Failures in Swiss Lakes

Sedimentary porewaters record regional tectonic and climate events that perturbed a deep-sea brine pool in the Gulf of Aqaba, Red Sea

Brine pools in deep-sea environments provide unique perspectives into planetary and geological processes, extremophile microbial communities, and sedimentary records. The NEOM Brine Pool Complex was the first deep-sea brine pool system found in the Gulf of Aqaba, representing a significant extension of the geographical range and depositional setting of Red Sea brine pools. Here, we use a combination of brine pool samples collected via cast using a conductivity, temperature, depth instrument (CTD), as well as interstitial porewaters extracted from a sediment core collected in the NEOM Brine Pool to characterize the chemical composition and subsurface evolution of the brine. New results indicate that the NEOM brines and the subsurface porewaters may originate from different sources. Elemental concentrations suggest the brines in the NEOM pool are likely derived from dissolution of sub-seabed evaporites. In contrast, the sedimentary porewaters appear to have been influenced by periodic turbidite flows, generated either by earthquakes, submarine landslides, or flash floods, in which normal marine waters from the overlying Red Sea became entrained, periodically disturbing the chemistry of the brine pool. Thus, sediment porewaters beneath brine pools may record transient and dynamic changes in these deep marine depositional environments, reflecting the interplay between climate, tectonics, and sedimentation patterns along a rapidly urbanizing coastline. In concert, new results from NEOM extend the range and chemical constraints on Red Sea Brine Pools and highlight the dynamic interplay between Red Sea Deep water, dissolving evaporites, turbidites, and subsurface fluids that produce these unique depositional environments which host microbial life at the edge of habitability. In concert with sedimentological indicators, the chemistry of porewaters beneath deep-sea brine pools may present detailed records of natural hazards arising from interactions between the atmosphere, lithosphere, hydrosphere, and anthroposphere.

Discussion on different numerical treatments on the loss of hyperbolicity for the two-layer shallow water system

This paper focus on the numerical approximation of two-layer shallow water system. First, a new approximation of the eigenvalues of the system is proposed, which satisfies some interesting properties. From this approximation, we give an accurate estimation of the non-hyperbolic region, which improves significantly the one computed with the classic eigenvalues approximation. In particular, we estimate both the lower and upper boundaries of the non-hyperbolic region. We also give a simple algorithm that allows us to compute bounds for the external eigenvalues, even when complex eigenvalues arise. We design an efficient FV solver depending on the hyperbolic nature of the system, that combines the PVM-2U-FL scheme and a new solver introduced in this work, named IFCP-FL, which degenerates to the Lax–Wendroff method in smooth areas. Different strategies for the numerical treatment for the loss of hyperbolicity are considered and discussed. Two of them are based on adding a friction term, depending on the classic or the new eigenvalues approximations, and the third one considers a simplified hyperbolic model in areas with complex eigenvalues. Some numerical tests are performed, including the case of two-layer fluids with different ratio of densities. The application to a two-layer model for submarine landslides is also considered. In the latter case, we show how the treatments based on adding friction are not appropriate for this kind of applications, whereas the treatment based on changing to a hyperbolic model produces much better results.

MPMICE: A hybrid MPM‐CFD model for simulating coupled problems in porous media. Application to earthquake‐induced submarine landslides

SummaryIn this paper, we describe a soil‐fluid‐structure interaction model that combines soil mechanics (saturated sediments), fluid mechanics (seawater or air), and solid mechanics (structures). The formulation combines the Material Point Method, which models large deformation of the porous media and the structure, with the Implicit Continuous‐fluid Eulerian, which models complex fluid flows. We validate the model and simulate the whole process of earthquake‐induced submarine landslides. We show that this model captures complex interactions between saturated sediment, seawater, and structure, so we can use the model to estimate the impact of potential submarine landslides on offshore structures.

Slope instability and submarine-moat initiation: Insights from the northern South China sea margin

Submarine landslides that occur on continental margins can reshape the seafloor morphology and form steep slide scarps. Although the emplacement processes of submarine landslides have been well studied, the development of post-slide deposition has long been overlooked. Here, we use high-resolution multibeam bathymetric and three-dimensional seismic data from the northern South China Sea margin to decode how slide scarps affect bottom currents and generate associated bottom current-related features. Distinct features have been identified within the slide scars, such as sediments waves and drifts. In parallel, multiple longitudinal negative topographies are distinguished along the scarps, undercutting into underlying strata with width and depth up to 240 m and 20 m, respectively. These incisional structures are interpreted as moats, formed following the emplacement of landslides, and running along the foot of scarps that parallel to contours. The origin of these moats could thus represent an interaction between slide scars and contourite deposition. We suggested that escarpments act as morphological barriers, regionally affecting the velocity and direction of bottom currents, leading to an intensification of their velocities and their erosive ability. Furthermore, we propose a co-evolution model of submarine landslides and related moats, which elucidates and emphasizes the significance of scarps in moat initiation and evolution. Our results demonstrate that the interaction between escarpments and bottom current flow can lead to topographic remodeling and sedimentary processes on varying continental margins.

Two-phase two-layer SNS-PFEM for hydromechanical geotechnical large deformation problems

A two-phase one-layer stabilised node-based strain-smoothing Particle Finite Element Method (SNS-PFEM) was previously proposed, but it lacked the capability to simulate water-soil coupling. To address this limitation, this study presents an improved approach called the two-phase two-layer SNS-PFEM, specifically designed to handle such problems. In this method, two overlapping mesh layers are employed to independently represent the two phases. Within this framework, the water phase is characterised as an incompressible Newtonian fluid solved using the PFEM-T3 method, while the soil phase is described using an elastoplastic constitutive model, effectively addressed through a modified SNS-PFEM. To obtain the solution for the proposed two-phase two-layer approach, a fractional step algorithm is utilised, allowing efficient and accurate computations. To validate the proposed method, it is applied to various soil-water coupling problems, encompassing both quasi-static and large deformation scenarios. The first set of simulations are (1) simulation of 1D Terzaghi's consolidation test and (2) simulation of fully submerged soil subjected to gravitational load. Next, the proposed method is applied to simulate cases involving large deformation problems: (1) flow passing through a porous dam, (2) a submerged granular landslide and its induced waves and (3) a submarine progressive landslide. The results of all simulations demonstrate the robustness and versatility of the proposed method in effectively analysing large deformation multi-phase problems in the field of geotechnical engineering. This advancement is a significant step forward in accurately simulating complex interactions between water and soil, opening up new possibilities for research and analysis in geotechnical applications.

Coupling Submarine Slope Stability and Wellbore Stability Analysis with Natural Gas Hydrate Drilling and Production in Submarine Slope Strata in the South China Sea

This research explores the geomechanical challenges associated with gas hydrate extraction in submarine slope zones, a setting posing a high risk of significant geological calamities. We investigate slope and wellbore deformations driven by hydrate decomposition within a subsea environment. Utilizing Abaqus, a fluid-solid-thermal multi-field coupling model for gas hydrate reservoirs was created. Hydrate decomposition during drilling is minimal, resulting in minor formation deformation near the wellbore. However, a year of hydrate production caused a maximum displacement of up to 7 m in the wellbore and formation, highlighting the risk of submarine landslides. This indicates the need for meticulous surveillance of formation subsidence and wellhead equipment displacement. In the aftermath of a hydrate-induced submarine landslide, both the hydrate layer and the overlying strata descend together, inflicting considerable damage on the formation and wellbore. Our study presents a holistic examination of the interplay between environmental geomechanics risks and engineering structure risks for submarine slope instability and wellbore stability during hydrate development, providing crucial insights for enhancing safety measures in hydrate drilling and production, and ensuring wellbore stability.