Geomechanical Forward Modelling of the Genesis of Polygonal Fault Systems

Numerical modelling of the growth of polygonal fault systems

“…The underlying computational methods are discussed extensively by Períc and Crook (2004). This modelling framework has been used to solve a host of geological problems ranging from salt tectonics (Nikolinakou et al, 2014a,b) to regional fold and thrust belts (Albertz and Lingrey, 2012), as well as previous studies of polygonal fault systems (Roberts et al, 2014;Roberts, 2014). However, alternative modelling approaches such as the Discrete Element Method (DEM), which unlike the finite element continuum approach does not use a pre-defined material constitutive model but instead models the interaction of rock particle assemblages governed by Newton's laws of motion, have been used to solve similar geological problems (Finch et al, 2003;Schöpfer et al, 2009;Gray et al, 2014).…”

“…Alternative constitutive frameworks, such as the Mohr-Coulomb and Drucker-Prager models have been used in several computational geological studies (Schultz-Ela, 2003;Gradmann et al, 2009;Shin et al, 2010), however, they do not explicitly account for granular compaction and are therefore, better suited to the characterisation of lithified and crystalline rocks. Several previous studies have used an SR3 constitutive framework to model the elastoplastic deformation associated with salt diapirs rising through porous sediments (Nikolinakou et al, 2014a,b), and the investigation of polygonal faulting in unconsolidated fine-grained sediments (Roberts et al, 2014;Roberts, 2014).…”

“…However, the bulk material stiffness term used in the Shin et al (2010) Drucker-Prager models does not explicitly incorporate gravity-driven mechanical compaction of granular sediment. Roberts et al (2014) and Roberts (2014) used the ELFEN geomechanical code and a SoftRock 3 constitutive model to demonstrate that a diagenetically-triggered isotropic chemical porosity reduction, such as that caused by the transition of opal-A to opal-CT, of 5% was sufficient to localise and propagate shear fractures that resembled the geometries and network intersections of polygonal faults in two-dimensional cross-section and three-dimensional planforms. Roberts et al (2014) and Roberts (2014) also showed that a horizontal stress anisotropy of just 3% was enough to align over 80% of fault orientations to within ±10 • of the maximum horizontal stress.…”

“…Roberts et al (2014) and Roberts (2014) used the ELFEN geomechanical code and a SoftRock 3 constitutive model to demonstrate that a diagenetically-triggered isotropic chemical porosity reduction, such as that caused by the transition of opal-A to opal-CT, of 5% was sufficient to localise and propagate shear fractures that resembled the geometries and network intersections of polygonal faults in two-dimensional cross-section and three-dimensional planforms. Roberts et al (2014) and Roberts (2014) also showed that a horizontal stress anisotropy of just 3% was enough to align over 80% of fault orientations to within ±10 • of the maximum horizontal stress. Despite the advances made by these pioneering studies, our understanding of the relative magnitudes of different drivers of PFS growth is limited, and the role of gravity-driven mechanical compaction may have been overlooked as a means of accommodating polygonal fault displacement.…”

Origin and kinematics of a basin‐scale, non‐polygonal, layer‐bound normal fault system in the Levant Basin, eastern Mediterranean

“…Their unique polygonal planform suggests growth within an isotropic stress field (i.e. 𝜎 1(vertical) > 𝜎 2 = 𝜎 3 ), with this polygonal planform being highly sensitive to local changes in the prevailing stress regime (Roberts et al, 2015). For example, changes in host rock dip, and stress perturbations around salt diapirs, pockmarks and even deep-water channels all can alter the faults polygonal planform, causing them to become locally aligned or radially disposed (Carruthers et al, 2013;Goulty, 2002Goulty, , 2008Ireland et al, 2011;Morgan et al, 2015).…”