Abstract It has long been recognized that the structures that accommodate shortening within fold-and-thrust belts exhibit a wide variety of styles that reflect the mechanical behaviour of the stratigraphic units that are being deformed. The ability to characterize these different structural styles, and to understand the factors that control their variability, is essential to many applications, including petroleum geology, earthquake hazard assessment and regional geological studies. The relative contributions of different aspects of the mechanical stratigraphy and boundary conditions to determining fault-related folding style are investigated through the use of the discrete-element modelling (DEM) method in this study. Modelling emergent contractional structures within a shortening wedge with this method demonstrates that (a) The major different styles of shortening structures can all be reproduced under different mechanical circumstances within the range of realistic mechanical conditions, and (b) Different aspects of the mechanics of the deforming rock units (for example, peak strength, strain weakening, layer strength anisotropy) exert various degrees of control on the styles of structures that emerge from the models as shortening progresses. These analyses inform our understanding of the relative importance of these different factors in determining the style of structures which accommodate shortening in different fold-and-thrust belt systems.

Abstract Tephra beds are considered to be potential failure planes for submarine landslides. Here, we report on an example of a coarse-ash/lapilli-tuff bed influencing translational slides. The studied mass-transport deposit (MTD) is intercalated in the Pleistocene forearc basin fill exposed in east-central Japan. This MTD consists of stacked siltstone blocks resulting from repeated imbricate thrusts branching from the décollement. The basal slide plane is located immediately below a pumice-rich coarse ash/lapilli-tuff bed. The material comprising the slip zone is injected into the overlying coarse-ash/lapilli-tuff bed, suggesting an upwards escape of excess porewater that resulted from elevated pore pressure. To explain this mode of occurrence, we propose that the detachment preferentially occurred at the top and base of the coarse-ash-tuff-rich interval which appears to have been stronger relative to the adjacent silt-dominated interval. The pumiceous coarse-ash and lapilli-tuff bed behaved as a rigid plate on top of the high-pore-pressure slip zone, which sustained the translational slide on the gentle continental slope. Therefore, in translational submarine landslides, the preferential formation of a slide plane is caused by differing frictional resistances in the layered sediments.

Abstract Turbidity currents occur widely in submarine environments, but field-scale numerical simulations of the flow features have not been applied extensively. Here, we present a two-dimensional layer-averaged numerical model to simulate turbidity currents over an erodible sediment bed, and taking into consideration deposition, entrainment and friction. The numerical model was developed based on the open-source code, Basilisk, ensuring well-balanced and positivity-preserving properties. An adaptive spatial discretization was used, which allows multi-level refinement. The adaptive criterion is based on the dynamic features of the flow and sediment concentrations. The numerical scheme has a relatively high computational efficiency compared with models based on the Cartesian mesh. A hypothetical case based on a true large-scale landform (the Moroccan Turbidite System, offshore NW Africa) was studied. Compared with previous models, the current model accounted for the coupling between flow, sediment transportation and bed evolution. This approach may improve simulation results and also allow the simulation of complex field-scale landforms, while preserving the flow details.