Numerical Investingations into the Mechanics of Low-angle Normal Faults Using the Discrete Element Method (DEM); Effects of Fault Angle, Syn-kinematic Sedimentation and Relative Fault Strength

Low-angle detachment faults have been proposed to be key-structures in accommodating crustal extension in numerous locations globally. The low-angle geometry, however, conflicts with Anderson's classic theory of faulting, which favors normal faults that dip at approximately 60°. By conducting two-dimensional (2D) simulations using the discrete element method (DEM), we probe the effects of different initial fault angles (10°-45°), the addition of sediment in the rifting process, and the strength of the fault relative to the wall rocks, on the activity or inactivity of a prescribed low-angle normal fault. In accordance with Anderson's theory, normal faults with dip values lower than 60° require additional mechanisms to maintain active slip. Both the addition of sediment during the rifting process and anomalously weak faults have been proposed as potential mechanisms that can localize slip along a fault with low-angle geometry. Our study investigates how these proposed mechanisms alter the limits of activity along these low-angle faults, and controls the resulting hanging-wall deformation, for comparison with natural examples.