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On February 17, 1996, an earthquake ( M w = 8.2) occurred northeast of Biak Island, Indonesia, and generated a tsunami. Interestingly, the tsunami runup on the southwest side of Biak Island, which did not face the epicenter, was higher than that on the side of the island facing the epicenter. It was earlier suggested that the earthquake triggered submarine landslides. However, this hypothesis remains unexplored and unconfirmed. In this study, tsunami arrival times obtained from eyewitness accounts were used to perform backward tsunami travel time modeling. Based on the backward tsunami travel time results and multibeam bathymetry, five submarine landslide candidates were identified: three located to the southwest of Biak Island and two to the south of the island. Our analysis indicates that tsunamis from a large submarine landslide off the southwest coast of Biak Island (SL 2) and a small submarine landslide off the south side of Biak Island (SL 4) contributed to the 1996 Biak tsunami event and came earlier than the main tsunami from the earthquake fault. Tsunami sources were earlier modeled only by fault parameters without considering submarine landslide sources. As a result, the models could not explain the observed runup and eyewitness tsunami arrival times for the southwest and south of Biak Island. To address this problem, we propose an approach that combines a submarine landslide model with a modified version of a previously proposed fault model. Our combined model explains the observed runup and eyewitness tsunami arrival times well (Aida's index values of the model are K = 1.00 and κ = 1.44). [ABSTRACT FROM AUTHOR]

The shelf‐slope margin is a geomorphic zone with a change in gradient between subaqueous shelves and slopes, which extends towards the submarine basin‐floor. It is important because it partitions distinct sedimentary and biogenic processes between the shallow and deep‐water realms. The initiation of a shelf‐slope profile from pre‐existing conditions, and the evolution of shelf margins in space and time has been the focus of numerous studies, particularly from seismic data sets on passive margins, although markedly less‐so from active tectonic settings. This study documents the initiation and evolution of a shelf‐slope margin in the well‐studied Eocene Aínsa Basin (Spanish Pyrenees) through the segmentation of a mixed carbonate‐siliciclastic ramp via contractional tectonics and differential subsidence. The basinward propagation of a series of thrusts through the ramp allowed the maintenance of shallow‐water, predominantly carbonate sedimentation on their uplifted hanging wall anticlines. Conversely, the deepened foot wall synclines became muddy slope environments, and their axes became the main loci of siliciclastic turbidity current bypass and deposition. The deflection of turbidity currents around uplifted areas towards the synclinal lows allowed for the continuation of carbonate production at the bathymetric highs, which kept pace with subsidence. The interface between shallow‐ and deep‐water sedimentation (i.e. the shelf‐slope margin) was an erosional and composite submarine scarp surface generated by several phases of large‐scale mass wasting of the aggrading shelf carbonates, and healing by onlap of slope turbidites against the scarp. Continued thrust propagation and basin deepening led to the progressive headward degradation of the surfaces, resulting in an apparent retrogradation of the shelf‐slope margin and onlapping slope deposits. This model for the tectonically controlled conversion of a submarine ramp into a shelf‐slope profile contrasts with conventional models that consider shelf‐slope margins to be inherently progradational after initiation. This study also challenges the notion that large‐scale degradational surfaces and thick successions of submarine landslides are inherently diagnostic of canyons and their fill. [ABSTRACT FROM AUTHOR]

Abstract In recent years, there have been worldwide reports of massive tsunamis, drawing attention to how tsunamis are intensified by submarine landslides triggered by earthquakes. However, precise data on tsunamis caused by submarine landslides are scarce, leading to insufficient information for a thorough discussion of the characteristics of such tsunamis. On the other hand, during the Noto Peninsula earthquake (Mw7.5) that occurred in Japan on January 1, 2024, a nonseismic tsunami distinct from those originating from fault ruptures were observed. To investigate its characteristics, we analyzed tide/wave gauge records, video footage, and tsunami trace heights along the coast of Toyama Bay. Furthermore, we validated scenarios capable of reproducing the observed records using an integrated landslide–tsunami model. It was found that assuming the existence of 5 submarine landslides along the underwater canyons of Toyama Bay enabled the precise explanation of multiple types of data. Additionally, our study revealed that submarine landslides occurred approximately 50 s after the earthquake, coinciding with the peak ground shaking in Toyama Bay. Compared to the seismic tsunami originating solely from the Noto Peninsula offshore fault rupture, the subsequent tsunami triggered by submarine landslides amplified the tsunami height by approximately 30% along Toyama Bay.

Abstract On February 17, 1996, an earthquake ( $${M}_{\text{w}}=$$ M w = 8.2) occurred northeast of Biak Island, Indonesia, and generated a tsunami. Interestingly, the tsunami runup on the southwest side of Biak Island, which did not face the epicenter, was higher than that on the side of the island facing the epicenter. It was earlier suggested that the earthquake triggered submarine landslides. However, this hypothesis remains unexplored and unconfirmed. In this study, tsunami arrival times obtained from eyewitness accounts were used to perform backward tsunami travel time modeling. Based on the backward tsunami travel time results and multibeam bathymetry, five submarine landslide candidates were identified: three located to the southwest of Biak Island and two to the south of the island. Our analysis indicates that tsunamis from a large submarine landslide off the southwest coast of Biak Island (SL 2) and a small submarine landslide off the south side of Biak Island (SL 4) contributed to the 1996 Biak tsunami event and came earlier than the main tsunami from the earthquake fault. Tsunami sources were earlier modeled only by fault parameters without considering submarine landslide sources. As a result, the models could not explain the observed runup and eyewitness tsunami arrival times for the southwest and south of Biak Island. To address this problem, we propose an approach that combines a submarine landslide model with a modified version of a previously proposed fault model. Our combined model explains the observed runup and eyewitness tsunami arrival times well (Aida’s index values of the model are K = 1.00 and $$\kappa$$ κ = 1.44). Graphical abstract

Abstract A moment magnitude (M w) 7.5 earthquake occurred on January 1, 2024, at the northern tip of the Noto Peninsula, Central Japan, triggering a large tsunami. Seismological and geodetic observations revealed the rupture of mapped submarine active faults. While proximal segment ruptures have been well resolved by previous research, far offshore segments have posed challenges for onshore-based inversions. This emphasizes the necessity for a comprehensive study on the fault through tsunami modeling. Here, we aimed to examine tsunami propagation and inundation using four different fault models to identify the general characteristics of the tsunami source and evaluate the complexities of earthquake- and submarine landslide-induced tsunamis. We identified the simultaneous rupture of two active fault systems as the most suitable model for explaining observed tsunami height and inundation; however, some inconsistencies with observations remained. The propagation process did not follow a concentric pattern but aligned with bathymetric heterogeneity. The findings also suggested potential amplification effects responsible for the devastation of the coast of Iida Bay and indicated a possible submarine landslide in southern Toyama Bay. The findings of the present work could benefit the exploration of a more realistic tsunami source model, considering the differences between observations and simulations. Such efforts, in collaboration with paleotsunami research, can contribute to the improved assessment of hazards from submarine active faults.

A moment magnitude (Mw) 7.5 earthquake occurred on January 1, 2024, at the northern tip of the Noto Peninsula, Central Japan, triggering a large tsunami. Seismological and geodetic observations revealed the rupture of mapped submarine active faults. While proximal segment ruptures have been well resolved by previous research, far offshore segments have posed challenges for onshore-based inversions. This emphasizes the necessity for a comprehensive study on the fault through tsunami modeling. Here, we aimed to examine tsunami propagation and inundation using four different fault models to identify the general characteristics of the tsunami source and evaluate the complexities of earthquake- and submarine landslide-induced tsunamis. We identified the simultaneous rupture of two active fault systems as the most suitable model for explaining observed tsunami height and inundation; however, some inconsistencies with observations remained. The propagation process did not follow a concentric pattern but aligned with bathymetric heterogeneity. The findings also suggested potential amplification effects responsible for the devastation of the coast of Iida Bay and indicated a possible submarine landslide in southern Toyama Bay. The findings of the present work could benefit the exploration of a more realistic tsunami source model, considering the differences between observations and simulations. Such efforts, in collaboration with paleotsunami research, can contribute to the improved assessment of hazards from submarine active faults. [ABSTRACT FROM AUTHOR]

Summary: In 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. [ABSTRACT FROM AUTHOR]

Many Mississippi River Delta studies have shown recent declines in fluvial sediment load from the river and associated land loss. In contrast, recent sedimentary processes on the subaqueous delta are less documented. To help address this knowledge gap, multicores were collected offshore from the three main river outlets at water depths of 25–280 m in June 2017 just after the peak river discharge period, with locations selected based on 2017 U.S. Geological Survey seabed mapping. The coring locations included the undisturbed upper foreset, mudflow lobes, gullies, and the undisturbed prodelta. Nine multicores were analyzed for Beryllium-7 activity, and four cores were analyzed for excess Thorium-234 activity via gamma spectrometry, granulometry and X-radiography. Our results indicate a general trend of declining 7Be and 234Th activities and inventories with increasing distance from sources and in deeper water. The core X-radiographs are graded from the predominantly physically stratified nearshore to the more bioturbated offshore, consistent with the sedimentation patterns. Sediment focusing assessed via the 7Be and 234Th sediment inventories shows preferential sedimentation in gully and lobe environments, whereas the upper foreset and prodelta focusing factors are relatively depleted. Overall, short-term sediment deposition from the main fluvial source remains active offshore from all three major river outlets, despite the overall declining river load. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Submarine landslides are a global geohazard that can displace huge volumes of loose submarine sediment, thereby triggering enormous tsunami waves and causing a serious threat to coastal cities. To investigate the generation of submarine landslide tsunamis, a three-dimensional numerical model based on the smoothed particle hydrodynamics (SPH) method is presented in this work. The model is first validated through the simulation of two underwater landslide model tests, and is then applied to simulate the movement of the Baiyun landslide in the South China Sea (SCS). The kinetics features of the submarine landslide, including the sliding velocity and runout distance, are obtained from the SPH simulation. The tsunami waves generated by the Baiyun landslide are predicted. In addition, sensitivity analyses are conducted to investigate the impact of landslide volume and water depth on the amplitude of the tsunami waves. The results indicate that the amplitude of tsunami waves triggered by submarine landslides increases with the landslide volume and decreases with the water depth of the landslide. [ABSTRACT FROM AUTHOR]

Submarine landslides shape continental margins, transfer massive amounts of sediment downslope, and can generate deadly and destructive tsunamis. Submarine landslides are common globally, yet constraining hazard potential of future events is limited by a short historical record and a wide range of possible slide dynamics. We test a novel approach to investigate slide dynamics using properties of the deformation zone induced by a large submarine landslide along the Cascadia margin, offshore Oregon. We use a simple model of a line load on a poroelastic half space to show the deformation zone size required rapid transport and deceleration. We argue that the slide moved at high speeds, aided by low dynamic frictional resistance, suggesting this event could have generated a tsunami. This method is applicable where slide‐induced impact zones are observed. Plain Language Summary: The Cascadia margin is susceptible to underwater landslides and tsunami hazards due to the active subduction zone that can produce large magnitude earthquakes. However, determining whether future submarine landslides will be tsunamigenic is challenging. While past landslide deposits can easily be identified and in many cases age‐dated, the dynamic process including the initial acceleration and velocity that created the deposit is almost never known. We present a novel approach to back‐analyze slide velocity of past landslides by using the characteristics of the deformation zone that occurred when the landslide deposit came to rest on the seafloor. Our models suggest that the slide hydroplaned while moving at high‐speeds (up to 60 m/s) with a run‐out distance of 10‐km from the source, which match the observations. While our method does not model tsunamis explicitly, the high speeds are consistent with known tsunamigenic slides. This approach provides critically important constraints on the slide velocity and therefore the hazards of submarine landslides that can occur at Cascadia. Key Points: A broad zone of impact‐induced deformation is observed immediately adjacent to the massive 44‐N Slide offshore OregonThe deformation of seafloor sediments observed at the slide terminus requires slide deceleration, implying catastrophic emplacementModeled impact forces require a slide velocity of up to 60 m/s, which may have been sufficient to generate a tsunami [ABSTRACT FROM AUTHOR]

The Makran region, which borders southern Iran and Pakistan along the Gulf of Oman, has experienced multiple tsunamis in the last century, with some being triggered by submarine landslides. However, the role played by submarine landslides has been largely neglected in tsunami hazard assessments in the western Makran. In the present study, four different submarine landslide scenarios with volumes of 10–40 km3 are simulated on 25 locations in the western Makran, resulting in 100 different hypothetical scenarios. The results indicate that Oman's coastline, a country in the western part of Makran subduction zone, is more vulnerable to the hazard of landslide-generated waves (maximum average of 3.1 m wave height) compared to Iran (maximum average 0.9 m height). Although Chabahar, Iran, and Muscat, Oman, two major cities in the region, experienced severe waves during some scenarios, it can be implied Muscat is more vulnerable to this kind of tsunami due to the significant gap between the maximum and average wave height for all scenarios. We further discuss that applying hypothetical worst-case scenarios can sometimes lead to an overestimation in tsunami hazard assessment. Therefore, more geological, sedimentological, and geotechnical considerations and studies are required for defining submarine landslide worst-case scenarios. [ABSTRACT FROM AUTHOR]

The devastating 2004 tsunamis that hit the southwestern coast of Thailand pose a serious threat to people along the coastal zone. A major aim for the tsunami hazard prediction is better prediction of the next tsunamis and their impacts. In this paper, we present the first implications of recent slope failure events of the Andaman outer shelf and upper slope based on a new detailed bathymetric data and subbottom profiler records acquired during two cruises of the MASS project in 2006 and 2007. Morphometric analysis reveals a variety of anomalous features, including: three large plateaus surrounded by moats, ruggedness and unevenness of slope morphology, and two translational submarine landslides. Two submarine landslides are studied from the detailed bathymetric data and subbottom profiler record covering the upper slope of the Andaman Sea shelf break within Thai exclusive economic zone. Maximum approximated volumes of both displaced masses are 4.8×107 m3 and 2.2×107 m3. Considering the data, there is no evidence that landslides have been the sources for tsunami hazard potential in recent geological time. These prerequisites will allow better study of slope failure events in the area. Further investigation is required to better understand obvious geotectonic phenomena. [ABSTRACT FROM AUTHOR]

The rheological behaviors of submarine landslide materials significantly affect the landslide's motion and the associated tsunami hazard. In this study, the effects of rheological behaviors on the landslide dynamics and tsunami hazard are numerically investigated. The Herschel-Bulkley rheological theory and nonlinear shallow water equation model are adopted. Taking one of the large landslides in the South China Sea (SCS), the Baiyun Slide, as an example, we investigate the impacts of remolding rates and initial/residual yield strengths on the speed and runout of landslide and the resulting tsunami wave. Further comparison of the Newtonian viscous model and the rheological model reveals the importance of the materials' properties on landslide dynamics and associated tsunami hazard. The resonance characteristics of landslide-generated tsunamis are studied through fast Fourier transform (FFT) analysis. A parameter set of (τy,0, τy,∞, Γ) = (12 kPa, 3 kPa, 0.05) is found to be optimal for the Baiyun Slide. The slide speed and runout distance are mainly affected by the residual yield strength and remolding rate. The computed arrival time is not sensitive to the rheological parameters, but a smaller residual yield strength and a larger remolding rate result in a larger tsunami amplitude. The standing wave and dominant tsunami wave periods with high energy range from 15 and 26 min. This study reveals that the rheological parameters of landslide have considerable effects on submarine landslide motion and landslide tsunami amplitude, which is helpful for the landslide-generated tsunami assessment. [ABSTRACT FROM AUTHOR]

Many Mississippi River Delta studies have shown recent declines in fluvial sediment load from the river and associated land loss. In contrast, recent sedimentary processes on the subaqueous delta are less documented. To help address this knowledge gap, multicores were collected offshore from the three main river outlets at water depths of 25–280 m in June 2017 just after the peak river discharge period, with locations selected based on 2017 U.S. Geological Survey seabed mapping. The coring locations included the undisturbed upper foreset, mudflow lobes, gullies, and the undisturbed prodelta. Nine multicores were analyzed for Beryllium-7 activity, and four cores were analyzed for excess Thorium-234 activity via gamma spectrometry, granulometry and X-radiography. Our results indicate a general trend of declining 7Be and 234Th activities and inventories with increasing distance from sources and in deeper water. The core X-radiographs are graded from the predominantly physically stratified nearshore to the more bioturbated offshore, consistent with the sedimentation patterns. Sediment focusing assessed via the 7Be and 234Th sediment inventories shows preferential sedimentation in gully and lobe environments, whereas the upper foreset and prodelta focusing factors are relatively depleted. Overall, short-term sediment deposition from the main fluvial source remains active offshore from all three major river outlets, despite the overall declining river load.

Abstract Submarine landslides shape continental margins, transfer massive amounts of sediment downslope, and can generate deadly and destructive tsunamis. Submarine landslides are common globally, yet constraining hazard potential of future events is limited by a short historical record and a wide range of possible slide dynamics. We test a novel approach to investigate slide dynamics using properties of the deformation zone induced by a large submarine landslide along the Cascadia margin, offshore Oregon. We use a simple model of a line load on a poroelastic half space to show the deformation zone size required rapid transport and deceleration. We argue that the slide moved at high speeds, aided by low dynamic frictional resistance, suggesting this event could have generated a tsunami. This method is applicable where slide‐induced impact zones are observed.

The complexity of the Kaikōura earthquake rupture and tsunami generation presented a unique opportunity to examine and learn from a modern event. This paper reviews how the five years of research following the Kaikōura tsunami have improved our understanding of the event and our knowledge of tsunami science across a range of disciplines. Teams of researchers and practitioners across disciplines of tsunami hazard modelling, palaeotsunami, risk and impact science, early warning, and emergency management learned from the event to calibrate models, enhance proxies for interpreting palaeotsunami deposits, and improve disaster risk readiness, reduction and response measures. While new scientific knowledge has been developed about the co-seismic hazard and risk facing Aotearoa-New Zealand, fundamental questions nonetheless remain about tsunami-generating sources and the likely return period for high impact events in Aotearoa-New Zealand. Further scientific endeavour is needed to investigate the onshore and offshore geological records to help improve understanding of tsunami hazard and history to underpin risk and impact assessments informing more effective disaster risk management. Lessons also emphasise a need for more effective partnership, participation, education, and engagement to increase local community capacity and capability to respond to local source tsunami events. [ABSTRACT FROM AUTHOR]

Failure at steep slopes and areas covered by a landslide can be controlled by laterally extended weak layers within the slope stratigraphy. Seismic data are essential in slope stability studies for identifying and tracking failure planes and the spatial extent of weak layers since weak layers often develop in decimeters and are buried together under 10–100 m sediment and water. Although seismic reflection profiles must be used to characterize weak layers at depths, it is challenging to visually characterize thin weak layers accurately due to the low vertical resolution. This study presents a method of merging 2D seismic data with different source resolutions on the same track to generate high-resolution broadband seismic data and perform seismic inversion to facilitate the tracing of thin weak layers. The resultant profile is a high-resolution acoustic impedance profile, which can track weak layers whose attributes are difficult to characterize using conventional methods. We also confirm the extension of the weak layer based on the porosity profile derived from the acoustic impedance of borehole 19ESDP-103 located on the seismic line used in the present study. Glide-planes, previously considered single or double layers due to their limited resolution, were further subdivided, tracked, and characterized in terms of lateral changes. [ABSTRACT FROM AUTHOR]

The basement of the Tokyo metropolitan area consists of the Miocene–Pleistocene forearc basin fills that are well exposed around Tokyo Bay, especially on the Miura and Boso peninsulas. The forearc basin fills on these two peninsulas are called the Miura and Kazusa groups, and they were deposited during the late Miocene–Pliocene and Pliocene–middle Pleistocene, respectively. Because many biostratigraphic datum planes, paleomagnetic reversal events, and other chronostratigraphic tools are available for these deposits, they provide the "type stratigraphy" of other equivalent sedimentary sequences on the Japanese islands and in the northwest Pacific. However, the use of such stratigraphic markers has not been fully applied to understand the architecture of a basin-wide unconformity between the Miura and Kazusa groups called the Kurotaki unconformity. For our study, we made correlations among the Pliocene vitric tephra beds based on their stratigraphic levels, lithologic characteristics, the chemical compositions of glass shards, and calcareous nannofossil biostratigraphy. As a result, we were able to correlate tephra beds Ng-Ky25 just above the C3n.3n normal subchronozone (4.7 Ma), IkT16-An157.5 and IkT19-An158.5 near the top of the Mammoth reverse polarity subchronozone (3.21 Ma), and Ahn-Onr (2.6–2.7 Ma) across Tokyo Bay on the Miura and Boso peninsulas. We were able to recognize erosional surfaces and coeval mass-transport deposits immediately below the top of the Mammoth reverse polarity subchronozone, which suggests that submarine landslide(s) may have produced the lack of stratigraphic horizons (4.5–3.2 Ma) in the Miura and eastern Boso regions. Basal pebbly sandstone beds pervasively cover the erosional surfaces, and they show lateral variations into the thick (up to 60 m) mass-transport deposits and overlying turbidite sandstones. The lateral variations in sediment thickness of the post-failure deposits suggest that the basin-wide erosion was associated with the initial growth of a basin-bounding structural high that separates two distinct sub-basins in the forearc basin, which resulted in the subsequent onlapping deposition in the earliest stage of the Kazusa forearc basin. The basin-wide erosion marks the initiation of tectonic reconfigurations that led to segmentation of the forearc basin around the Tokyo Bay region. [ABSTRACT FROM AUTHOR]

The evolution of a submarine landslide is a very complicated process due to slurry–water interactions. Most previous studies have focused on debris flows or turbidity currents independently. Little research has been conducted on the processes of transformation from debris flows into turbidity currents. Moreover, the underlying mechanical mechanisms of these transformation processes are not well understood. In this study, we aimed to better understand these mechanisms by simulating submarine landslide transportation processes using computational fluid dynamics. In the numerical models, the two-phase mixture module was adopted to mimic the interactions of the slurry with the ambient water, which we validated through a dam-break case. Here, the rheological behaviors of the slurries are described using the Herschel–Bulkley model. A formula for transformation rates is best fitted through a case series of debris flows. In particular, the activation stress is expressed by the dynamic pressure at the moment when the slurry starts to mobilize, which is fitted as a coefficient 6.55 × 10−5 times the shear strength. Then, two coefficients in the formula of the transformation rate are fitted as 1.61 and 0.26, respectively, based on the cases of debris flows, considering their different initial thicknesses, levels of slurry consistency and slope angles. Finally, in a real-scale debris flow case study, we demonstrate that the slurry is fully transformed before it is deposited. The expected outcome, the mechanical theory, the activation stress and the transformation rate would be applied to assess the influence area of the realistic turbidity currents and their harm to the subsea environment. [ABSTRACT FROM AUTHOR]

The instability of continental slopes damages marine engineering equipment, such as submarine pipelines, resulting in the generation of tsunamis, which endangers the safety of nearshore personnel. Therefore, research on the instability of continental slopes where submarine landslides usually occur is crucial to the risk evaluation of deepwater drilling. Previous studies were mainly based on simplified 2D and 3D models, which extend the 2D model applied on submarine slopes with complex topography. In this study, a numerical model with bathymetric data from the Qiongdongnan Basin was established. Furthermore, 3D slope stability analysis and static and dynamic analyses were conducted. The static analysis found two discussions where slopes are most likely to occur. Through the analysis of different seismic forces, the dynamic result showed that an instability area is added to the two positions where the static analysis is unstable. Topography scatters and transmits seismic waves and controls the accumulation and diffusion of seismic energy. 3D calculations and analysis revealed that the direction of slope instability is closely related to terrain inclination, slope, terrain effect, and terrain curvature. Data showed that instability situations could not be derived from a single direction or profile data. Such situations are an important factor in slope stability analysis and are critical to the prediction and evaluation of marine geological disasters. [ABSTRACT FROM AUTHOR]

Since May 2018, Mayotte Island has been experiencing seismo-volcanic activities that could trigger submarine landslides and, in turn, tsunamis. To address these hazards, we use the HySEA numerical model to simulate granular flow dynamics and the Boussinesq FUNWAVE-TVD numerical model to simulate wave propagation and subsequent inundations. We investigate 8 landslide scenarios (volumes from $11.25 \times 10^6~\text{m}^3$ to $800 \times 10^6~\text{m}^3$). The scenario posing the greatest threat involves destabilization on the eastern side of Mayotte’s lagoon at a shallow depth and can generate sea-surface deformations of up to 2 m. We show that the barrier reef surrounding Mayotte plays a prominent role in controlling water-wave propagation and in protecting the island. The tsunami travel time to the coast is very short (a few minutes) and the tsunami is not necessarily preceded by a sea withdrawal. Our simulation results provide a key to establishing hazard maps and evacuation plans and improving early-warning systems.

The September 2018 Palu (Sulawesi, Indonesia) tsunami has been a heavily debated event because multiple source models of three different types have been proposed for this tsunami: (i) The Mw 7.5 earthquake, (ii) landslides, and (iii) dual earthquake and landslide. Surprisingly, all of these three types of models were reported as being successful in the literature in terms of reproducing the existing tsunami observations. This can be partly attributed to the limited observations available for this tsunami. This study is motivated by the results of a marine bathymetric survey, which identified evidence for submarine landslides within the Palu Bay. Our modeling shows that the tsunami cannot be exclusively attributed to the Mw 7.5 earthquake. Inspired by the results of the marine survey, we propose a dual source model including a submarine landslide although most of the existing models include subaerial coastal landslides. Our dual model comprises an earthquake model, which has a length of 264 km, a width of 37 km, and a slip of 0–8.5 m, combined with a submarine landslide with a length of 1.0 km, a width of 2.0 km, and a thickness of 80.0 m located at 119.823°E and −0.792°S. [ABSTRACT FROM AUTHOR]

Ranking among the most threatening and challenging marine geological disasters, submarine landslides of different magnitudes have destroyed various pipelines, attracting widespread attention from the scientific and engineering communities. However, the relative size and spatial relation of landslides and pipelines, especially the landslide cover thickness above the pipeline, have not been explored in previous studies. As a result, the conventional analysis methods continue to change, and the practical application of these methods is difficult when a general criterion is lacking. In this study, three parameters, namely, the landslide cover thickness HC, pipeline diameter D, and span height HS, are first proposed to clarify this problem, and a unified standard analysis model is established. Second, the drag forces on pipelines with five values of HC and two values of HS under four typical Reynolds numbers are systematically analyzed using a validated computational fluid dynamic method. These analyses indicate that with increasing HC, the drag force gradually increases; however, the growth law of the drag force deviates under different HS conditions. Notably, considering the effect of HC, the maximum drag force can be increased to as much as five times the original value, and therefore, this effect cannot be ignored. Furthermore, the cause of the drag force variation is revealed by the evolution of the flow fields (e.g., streamlines, velocity vectors, and pressure). Finally, a reference value of the drag force coefficient and an adjustment factor fψC are proposed, and a standard chart methodology is established to evaluate the drag forces. [ABSTRACT FROM AUTHOR]

The aim of this study is to develop an efficient numerical scheme that is capable of simulating landslide-generated waves. The numerical scheme is based on the one-layer non-hydrostatic (NH-1L) model, a phase-solving model that can account for weakly dispersive waves. In this paper, the model is extended to include a time-varying solid bed. This NH-1L scheme is very efficient because, at each time step, only a tridiagonal Poisson pressure matrix needs to be solved. In this study, the capability of the NH-1L scheme to simulate landslide-generated waves is demonstrated by executing two types of landslide motion: constant speed and with acceleration and deceleration. Validation was performed using analytical solutions of the linear weakly dispersive (LWD) model, as well as experimental data. The NH-1L model was capable of describing the generation and propagation of water waves by a submarine landslide from relatively intermediate water to shallow water depths. [ABSTRACT FROM AUTHOR]

Analysis of high-resolution multibeam bathymetry, sub-bottom profiles, and multichannel seismic reflection data provides a novel understanding of a large-scale submarine landslide in the Cochin offshore region, southwestern continental margin of India. This massive submarine landslide is referred to name as the "Cochin slide". The Cochin slide exhibits a U-shaped slide scar with an average gradient of ~ 2°, which opens in the NNE-SSW trend in the lower slope and Laccadive Basin. The slide scar has a width of ~ 46 km and a total perimeter length of ~ 60 km, estimated with a volume of ~ 240 km3 excavated from this region. A non-sinuous channel with a length of ~ 36 km and having incisions varying from ~ 140 to 40 m from head to toe has developed within the slide scar. The submarine channel might have formed after the slide event facilitating channel incisions in the upper slope. The mass transport deposits associated with the slide have distributed over a wide area (~ 5700 sq. km.) in the lower slope and Laccadive Basin, with a maximum run-out length of ~ 138 km. The preconditioning factors or trigger mechanisms for the Cochin slide could not be precisely established yet. However, sedimentation during different geological times and the occurrence of weak layers might have contributed to the slope instability. The morphology of the Cochin slide, its correlation with the extensive faulting in the continental shelf-slope province, the presence of structural elements, and records of previous earthquakes suggest that the tectonic/geological processes strongly influence the triggering of the slide. [ABSTRACT FROM AUTHOR]

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.

Submarine landslides are a global geohazard that can displace huge volumes of loose submarine sediment, thereby triggering enormous tsunami waves and causing a serious threat to coastal cities. To investigate the generation of submarine landslide tsunamis, a three-dimensional numerical model based on the smoothed particle hydrodynamics (SPH) method is presented in this work. The model is first validated through the simulation of two underwater landslide model tests, and is then applied to simulate the movement of the Baiyun landslide in the South China Sea (SCS). The kinetics features of the submarine landslide, including the sliding velocity and runout distance, are obtained from the SPH simulation. The tsunami waves generated by the Baiyun landslide are predicted. In addition, sensitivity analyses are conducted to investigate the impact of landslide volume and water depth on the amplitude of the tsunami waves. The results indicate that the amplitude of tsunami waves triggered by submarine landslides increases with the landslide volume and decreases with the water depth of the landslide.

Landslides often occur in land slopes, estuaries, fjords, and intertidal zones in the marine environment, while landslides in tidal channels have not been systematically reported. The Zhoushan sea area is dotted with islands and crisscross tidal channels, which is a typical tidal channel development area. The data from the coastal zone and island survey, offshore engineering site selection, and environmental survey show that landslides are very common in tidal channel areas. The detailed study of this kind of landslide will enrich the research theory of submarine landslide and have important guiding significance for marine planning, development and site selection, and construction of coastal engineering in coastal areas. First, the submarine landslide in southwest of Zhujiajian Island in Zhoushan is investigated in this study. It is found that the sliding zone is parallel to the island coastline, with a length of about 250 m and an extension of 2 km, and the buried depth of the sliding surface is generally 8–10 m; then, through the self-developed seabed deformation observation system, combined with the hydrodynamic observation system, the landslide was observed in situ for 75 days. The observation results showed that the landslide slides at a constant speed along the sliding surface under the action of weight; the slides accelerate under the action of waves, and multiple sliding surfaces are generated in the landslide body at the same time. Finally, the genetic mechanism of submarine landslides in tidal channel areas is put forward.

The International Ocean Discovery Program cored Sites U1517 (Tuaheni landslide) and U1519 (Tuaheni Basin) on the Hikurangi slope, North Island, New Zealand. We employed X‐ray diffraction to document clay mineral assemblages within the muddy sediments, with the aim of testing their potential influences on slope stability. Detrital smectite dominates the clays, with average proportions of 52 wt% at Site U1517 and 53 wt% at Site U1519. Bulk sediment from Site U1517 contains up to ∼29 wt% smectite (average = 21 wt%), high enough to reduce the angle of internal friction (on average) to ∼6°. Stratigraphic sections at both sites are homogeneous; compositional excursions are not evident along inferred slip surfaces or weak layers. Smectite decreases in the "downstream" direction of the East Cape Current, and that spatial trend correlates with lower densities of slide scars. The uniformity of compositional preconditioning, however, points to other factors as determinants of slip nucleation. Plain Language Summary: Expandable clay minerals (smectite) are notorious for weakening sediments and contributing to conditions that promote landslides. The Hikurangi margin offshore North Island, New Zealand, is noted for its abundance of submarine landslides. To assess their possible causes, we analyzed clay mineral assemblages from two sites on the upper trench slope that were sampled by the International Ocean Discovery Program. Cores from Sites U1517 and U1519 display unusual degrees of compositional homogeny, with smectite as the dominant clay mineral. We did not find any compositional anomalies at inferred slip surfaces or along weak layers of the Tuaheni landslide. Instead, the entire stratigraphic succession appears to be relatively weak. With inherited preconditioning, dynamic loading during large earthquakes is probably enough to trigger landslides, especially on steeper slopes. Key Points: Hikurangi trench‐slope sediments, including muds within the Tuaheni landslide complex, contain high concentrations of detrital smectiteSmectite is abundant enough to reduce the bulk sediment's coefficient of friction, with little stratigraphic variabilityThe homogeneous mud composition results from strong currents and does not change significantly along inferred slip surfaces or weak layers [ABSTRACT FROM AUTHOR]

Submarine landslides can destroy seafloor infrastructures and generate devastating tsunamis. In spite of decades of research into the functioning of submarine landslides there are still numerous open questions, in particular how different phases of sliding influence each other. Here, we re‐analyze Ana Slide—a relatively small (<1 km3) landslide offshore the Balearic Islands, which is unique in the published literature because it is completely imaged by high‐resolution 3D reflection seismic data. Ana Slide comprises three domains: (a) a source area that is almost completely evacuated with evidence of headscarp retrogression, (b) an adjacent downslope translational domain representing a by‐pass zone for the material that was mobilized in the source area, and (c) the deposit formed by the mobilized material, which accumulated downslope in a sink area and deformed slope sediment. Isochron maps show deep chaotic seismic units underneath the thickest deposits. We infer that the rapid deposition of the landslide material deformed the underlying sediments. A thin stratified sediment unit between three lobes suggests that Ana Slide evolved in two failure stages separated by several tens of thousands of years. This illustrates the problem of over‐estimating the volume of mobilized material and under‐estimating the complexity even of relatively simple slope failures without high‐quality 3D reflection seismic data. Plain Language Summary: We investigate a submarine landslide in the Balearic Islands off Spain. The aim is to find out how such landslides work. This study is special because it can draw on a unique data set: the complete imaging of this landslide with high quality reflection seismic data. We find that previous studies have over‐estimated the volume of the mobilized material because deformed sediments below the landslide were also counted, and that the slide actually consisted of two individual slope failures that occurred at the same place but in distinct episodes separated by some tends of thousands of years. Together these results show that there is a large risk of overestimating landslide‐related tsunami hazards when this kind of reflection seismic data is not available. Key Points: Ana Slide is completely covered by 3D reflection seismic data and its kinematic development is addressedLarge parts of the volume previously interpreted as landslide material was deformed in‐situAna Slide developed during two separate phases that involved likely significantly smaller volumes of material than previously proposed [ABSTRACT FROM AUTHOR]

A submarine landslide is a well-known geohazard that can cause significant damage to offshore engineering facilities. Most standard predicting and mapping methods require expert knowledge, supervision, and fieldwork. In this research, the main objective was to analyze the potential of unsupervised machine learning methods and compare the performance of three different unsupervised machine learning models (k-means, spectral clustering, and hierarchical clustering) in modeling the susceptibility of the submarine landslide. Nine groups of geological factors were selected as the input parameters, which were obtained through field surveys. To estimate submarine landslide susceptibility, all input factors were separated into three or four groups based on data features and environmental variables. Finally, the goodness-of-fit and accuracy of models were validated with both internal metrics (Calinski–Harabasz index, silhouette index, and Davies–Bouldin index) and external metrics (existing landslide distribution, hydrodynamic distribution, and liquefication distribution). The findings of k-means, spectral clustering, and hierarchical clustering performed commendably and accurately in forecasting the submarine landslide susceptibility. Spectral clustering has the greatest congruence with environmental geology parameters. Therefore, the unsupervised machine learning model can be used in submarine-landslide-predicting studies, and the spectral clustering method performed best. Furthermore, machine learning can improve submarine landslide mapping in the future with the development of models and the extension of geological data related to submarine landslides. [ABSTRACT FROM AUTHOR]

Ischia Island is an active volcano representing the emerged sector of an E -W trending volcanic ridge largely extending undersea. Its collapsing behaviour, mainly in the form of fast-moving, terrestrial and submarine debris avalanches, has been recognized during the Holocene, but much less is known about previous gravity-driven processes. Using high-resolution multibeam bathymetric data and seismic reflection profiles, we provide evidence that the Island's southwestern flank has been involved in a slow-moving, deep-seated slope deformation that has displaced large volumes of its apron since the Late Pleistocene and until very recent or contemporary times. A long tongue of deformed seafloor, spreading up to 45 km from the Island over an area of 330 km2, between 500 and 1300 m water depths, has been detected along its southwestern slope. Different types of mass movements, genetically associated with each other, characterize this landslide: 1) a basal slump anticline, corresponding to a bulge on the bathymetry detaching at about 400 m sub-bottom depth; 2) an intermediate-mass movement chiefly consisting of debris avalanches and debris/turbiditic flows; 3) an upper mass movement consisting of hundred-metre size slumps detaching at relatively shallow depths. Conservative estimates indicate that at least 50 km3 of volcano-clastic and hemipelagic deposits have been mobilized, most of which comprise the basal slump anticline. This submarine landslide can be explained as a gravity failure of the continental slope unrelated to volcanism or rather as a process related to the dynamics of the volcanic edifice, which would imply volcano-spreading. • Oceanic and continental volcanic edifices may undergo slow collapse, named spreading • Ischia is an active volcano suspected to undergo long-term subsidence along with seismicity • Its southern, undersea section is affected by fast and long-term landslide phenomena • This long-term gravity instability can be viewed within the concept of volcano-spreading. [ABSTRACT FROM AUTHOR]

Abstract Submarine landslides can destroy seafloor infrastructures and generate devastating tsunamis. In spite of decades of research into the functioning of submarine landslides there are still numerous open questions, in particular how different phases of sliding influence each other. Here, we re‐analyze Ana Slide—a relatively small (