Fault propagation in pull-apart basins and its implication on depocenter migration: A discontinuum-based numerical study

Understanding of fault propagation in pull-apart basins is important due to its control on the depocenter migration, which is a common characteristic of pull-apart basins; nevertheless, the evolution law of faults in the pull-apart basin is not very clear. Most studies based on physical simulations have rarely paid attention to the relationship between fault propagation and migration of the depocenter. In this study, we simulate the fault propagation in the underlapping, neutral and overlapping releasing bend via the discrete element simulation method and discuss the corresponding migration of the depocenter. In this paper, more parameters (maximum shear force, distribution of tensile contact force, measuring stress) were used together to find out the evolution law of faults in line with natural basins. The results reveal the process of fault propagation, which has not been proposed in the previous simulating and case studies: the fault propagates from the ends of the master faults to the centre of the releasing bend and then proceeds externally. Consequently, the depocenter of the basin, which has undergone migration, experiences a transition from the dual depocenter state at the ends of the master faults to being a single depocenter at the centre of releasing bend and finally further expands in an outward direction. The characteristics of fault development and depocenter migration for the Khanguet Sidi Neji-Gafsa (KSG) Basin, the Vienna basin and the Gulf of California are in accord with the results observed in the simulation. This study provides a new understanding of the fault propagation in pull-apart basins and can assist in the interpretation of the evolutionary stages that pull-apart basins undergo. Based on the PFC2D software, the propagation of faults and depocenter migration in a pure strike-slip pull-apart basin are investigated. The modelling result produces new findings that the faults propagate from the ends of the master faults to the center of the releasing bend and then proceed externally.image