Experimental modeling of migration in Shekarab active fault system (North Birjand)

The Shekarab fault system, located in the north of the Birjand city, has fault scarps parallel to main fault. Due to the structural features, mechanism of fault trends in the region, fault-related folding and the occurrence of the migration from the north to the south at Shekarab fault, modeling is done for the geometric pattern of the fault propagation, which is in accordance with the Shekarab fault zone. In this model, new scarps are formed in the footwall of the previous scarps. According to the results of modeling, the most important factor for creating alternate scarps is the north-south compression in the Shekarab thrust. At each step, by increasing the amount of shortening, the emergence of new faults are observed so that the first thrust is created on the northern side of the Shekarab zone and subsequent faults are created by increasing the amount of shortening up to a maximum of 58%, on the southern side of the zone and on the footwall of the previous faults. In this modeling, the slope of the thrusts is created in four stages of shortening varying between 60-65 degrees, which is comparable with the actual slope of the Shekarab faults of 70 degrees. According to the experimental results, the sequence of thrust creation in each modeling stage is consistent with the sequence of thrust in the Shekarab zone and with the north-south migration of the fault. According to the geometry of thrusts and back-thrust, the model of formation of structures in this fault zone is the foreland breaking sequence model so that the branches of the thrust originate from a point.