Influence of ramp geometry and orientation on fault propagation folding: Insights from the 3D finite element method

Abstract Structural geologists have extensively studied fault-related folds because of their diversity, economic significance, and relationship to seismicity. In this study, we present five series of 3D finite-element models (A, B, C, D, and E) to investigate the effect of ramp geometry and orientation, as well as the friction coefficient, on the evolution of the geometry of fault-propagation folds (FPFs) in a convergent system. Series A, B, C, D, and E examine the effect of ramp dip, listric ramp, concave ramp, oblique ramp, and friction coefficient on FPFs. The results of the models show that 1) although the fold amplitude depends on the slip and dip of the fault, increasing them does not always increase the amplitude, 2) The slip and amplitude gradients become larger in the case of listric faults compared to angular faults of similar dip, 3) The amplitude uplift contours for series A, B, and E are parallel to each other, hence these series produce inclined folds while for series C and D these contours are not parallel, so these series create double-plunging and plunging folds, respectively, 4) The influence of variation in along-strike (Series C and D) and parameters that affect the entire FPFs (Series E) on the structural evolution of the FPFs are greater than variation in the cross-section (Series A and B) so that the concave ramps (Series C) and variation in frictions (Series E) change the folding styles. Hence, these parameters are two key factors in the style of fault-related folding.