Infrastructure located on the seabed is vulnerable to earthquake-triggered submarine landslides, although the propagation of failure and the post-seismic movement of slides on the continental margin or in a submarine canyon have not been well interpreted. A three-dimensional depth-averaged method was used to revisit the initiation, progressive failure, and runout of two typical scenarios: a back-analysis of the deep-seated Ashton Seamount landslide and a scenario prediction in a canyon system in the South China Sea. For the former, the shear band is propagated extensively through a weak layer prior to the slab failure of thick overlying sediment. The influence of soil sensitivity on initial co-seismic softening may be insignificant, while it severely affects the subsequent shear band propagation and runout. The ratio of the affected area approaches six as soil sensitivity is increased from two to five. In the canyon system, several fully softened regions may be caused independently on steep canyon flanks. These regions are then progressively expanded and merged during the earthquake. The sliding masses move along several canyon channels before converging at the gully junctions. Sediment downslope is removed during the initial slope failure, thereby impairing the support provided to the upslope sediment and suggesting more retrogressive failures even after the earthquake. As a result, a peak velocity of 40.8 m/s and an affected area of 23.4 km² are predicted.

Submarine landslides are a major geohazard in deep water, posing a severe threat to the safety of seabed infrastructure. Progressive failure on gentle slopes is commonly governed by strain softening of soils and shear band propagation (SBP). Several criteria have been developed analytically and numerically to predict catastrophic failure initiated from a pre-existing fully softened zone. In this study, dynamic SBPs during the progressive formation of an externally softened zone are investigated. Strength degradation is caused by both externally imposed softening and cumulative shear deformation. The governing dynamic equation is solved using a finite difference method. Depending on the extent of externally imposed softening, finite SBP followed by slope re-equilibration and catastrophic SBP are identified. The critical length of the externally softened zone required for catastrophic failure is quantified for different terminal strengths and formation durations. Two limiting lengths of the externally softened zone are determined. Below the lower limit, catastrophic failure cannot be triggered even when the zone is fully softened. Above the upper limit, only a slight strength reduction below the gravitational shear stress is sufficient to initiate catastrophic failure. The effect of the duration of externally imposed softening is also explored. Simple empirical criteria are proposed to predict both limiting lengths for practical application.

With the increasing research on particles and biocolloids in terrestrial and aquatic systems, the transport and deposition of particles and biocolloids in porous media has become an important research topic. Based on the transport and deposition experiments of heavy metal pollutants and suspended-colloidal particles (SPs) in porous media, a nonlinear attachment-detachment model with adsorption hysteresis is proposed, which uses an adsorption function and scanning desorption isotherms to model the deposition effect of SPs. The reaction rate constant related to hysteretic characteristics essentially reflects the nonequilibrium hydrodynamic process during the transport of SPs. Static deposition tests and column experiments with pulse injection are used to calibrate the transport parameters. Column penetration experiments are performed under variable injection concentrations and seepage velocities. The results show that there is good agreement between simulated and experimental breakthrough curves (BTCs).This model shows that increasing or decreasing the seepage velocity results in substantial changes in the penetration concentration of SPs, which is closely related to the adsorption hysteresis and the deposition dynamics of SPs. When the injection concentration is increased, the effluent concentration clearly increases, which reflects a nonlinear deposition process. In contrast, with a decrease in the injection concentration, the release effect of the already deposited SPs prolongs the penetration process, which is also related to the hysteresis. Previously proposed linear attachment-detachment models probably result in an overestimation of the adsorption capacity of porous media.