Discrete‐element modelling of extensional fault‐propagation folding above rigid basement fault blocks

Abstract

We employed a discrete‐element technique to investigate the effects of cover strength and fault dip on the style of fault‐propagation folding above a blind normal fault. Deformation in the cover is initially characterised by an upward‐widening monocline that is often replaced, with continued slip on the basement fault, by a single, through‐going fault. Localisation on a single fault produces hangingwall synclines and footwall anticlines as a result of breaching of the earlier monocline and which do not represent ‘drag’ against the fault. As basement fault dip decreases the width of the monocline at the surface increases. Experiments varying the strength of the overburden material illustrate the control that cover strength has on both fault propagation and folding in the cover. Reduction of the strength of the cover results in: (1) the width of the monocline above the fault tip increasing, and (2) more marked footwall thinning and hangingwall thickening of beds. In contrast, an increase in cover strength results in a narrower monocline and rapid propagation of the basement fault into the cover. In multi‐layer (variable strength) experiments simultaneous faulting of competent layers and flow of weaker layers produces complex structural relationships. Faults in the cover die out up and down section and do not link to the basement fault at depth. Similarly, complex macroscopically ductile characteristics such as footwall thinning and hangingwall thickening can be juxtaposed against simple brittle fault cut‐offs. These relationships must be borne in mind when interpreting the field and seismic expression of such structures. We discuss the modelling results in terms of their implications for structural interpretation and the surficial expression of fault‐related folding in extensional settings.

Seismic Imaging of Salt-influenced Compressional Folds

“…For these reasons, this method has been used in many geological problems, especially involving the analysis of highstrain brittle deformation in the sedimentary cover such as normal faulting in layered sequences (Schöpfer et al, 2006(Schöpfer et al, , 2007a(Schöpfer et al, , 2007bEgholm et al, 2008;, fault bend folding (Strayer et al, 2004;Benesh et al, 2007), fault-propagation folding (Finch et al, 2003(Finch et al, , 2004Cardozo et al, 2005;Hardy andFinch 2006, 2007) (Hardy and Finch, 2005), and doubly vergent thrust wedges (Hardy et al, 2009), to name some examples. In all these cases, the results have a strong correspondence to the deformation seen in the field and seismic.…”

Modelling Syntectonic Sedimentation: Combining a Discrete Element Model of Tectonic Deformation and a Process-based Sedimentary Model in 3D

“…A detailed description of the LSM is given by the cited articles. An outline of the model approach and its implementation is given here (for a full description, also see Finch et al 2004;Hardy and Finch 2005). An assemblage of spherical elements of different radii is used to model the rock mass; this allows a random position of the elements avoid any isotropy or any likelihood for preferred planes of weakness (Hardy and Finch 2006).…”

“…detachment folding (Hardy and Finch 2006), thrust/extensional fault-propagation folds (Finch et al 2003(Finch et al , 2004Hardy and Finch 2005), doubly vergent thrust wedges (Hardy et al 2009) and evolution of calderas (Hardy 2008). The model approach is a variant of the "Lattice Solid Model" Place 1993, 1994).…”

“…Combining these two approaches allows us to include the simulation of both sedimentation and deformation processes in a single and more realistic model. This new tool results from the merging of two previous published works: Simsafadim-Clastic (Bitzer and Salas 2002;Gratacós 2004;Gratacós et al 2009a) and a discrete element model or DEM (Finch et al 2003(Finch et al , 2004Hardy and Finch 2005, 2006, 2007Hardy et al 2009). The former simulates sub-aquatic clastic transport and sedimentation in three dimensions, including processes of interaction, production, and sedimentation of carbonates; moreover, it is also a powerful tool for the 3D prediction of stratigraphic structures and facies distribution modelling in sedimentary basins.…”

“…We now summarize how Simsafadim-Clastic and the discrete element model work. For more detailed information on both codes, the reader is referred to more detailed descriptions in Gratacós (2004), Gratacós et al (2009aGratacós et al ( , 2009b for the Simsafadim-Clastic program; see Finch et al (2004) and Hardy and Finch (2005) for the DEM program.…”