Analogue modeling of through-going process and development pattern of strike-slip fault zone

摘要

Nine sets of sand-box experiments were designed according to actual geologic data to investigate the evolution pattern and development mechanism of simple shear strike-slip fault zone using the fault CT scanning technique. The experimental results show that R (Riedel) shears were developed early and more in number, and one set of these faults intersected with the principal displacement zone (PDZ) at relatively lower angle; the P shears (being in symmetrical distribution with the R shears) and Y shears (subparallel to PDZ) were developed later than the R shears, and the fault zone was through-going only after the formation of Y shears. The through-going process of strike-slip fault zone can be divided into four stages: embryonic stage, R (Riedel) shears development stage, P shears and Y shears development stage, and through-going stage of fault zone. In the process, the faults developed progressively from the basement to the top cover, the faults spread upward in the profile at embryonic stage, and then converged toward the PDZ on the plane at R shears development stage. The modeling supports that the en echelon structure developed in “helicoidally drag” pattern, however, the length of the en echelon fault grew linearly doubling the growth rate of its depth, and the fault intersection angle with the PDZ decreased in quadratic function with the increase of its depth. The analysis reveals that cover thickness and the maximum principal stress direction are the main factors causing the difference in “helicoidally drag” structure. The modeling provides guidance for the strike-slip fault interpretation and evolution study, and layering and segmenting faults in the marine carbonates of the Tarim Basin.