Investigating the Mechanics of Fault-Bend Folding with the Discrete Element Method
After producing this mechanically layered hangingwall strata, we initiate slip on the underlying fault by driving an elastic, vertical backstop. This backstop produces shortening and contraction in the system that localizes as folding above a bend in the fault. For this study, we examine both anticlinal (ramp-to-flat) and synclinal (flat-to-ramp) fault geometries of various ramp dips. Additionally, new particles are generated and deposited as shortening of the model progresses, thereby producing sequential growth layers which record the history of folding. These resulting growth and pregrowth fold architectures are then analyzed in comparison to kinematic theories often used to relate fold characteristics to fault activity and slip.
These analyses show that the DEM models produce the first-order fold geometries predicted by the kinematic theory of fault-bend folding. We note, however, that the development of folding within the growth strata deviates from this theory as manifest by a steepening of the limb dips with depth. We believe this deviation from kinematic fault-bend folding to be a realistic feature of fold development resulting from an axial zone of finite width produced and controlled by the mechanical properties of the strata.