Abstract
Strike-slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip-slip, thrust and normal, fault systems. They are evident in map view rather than in vertical sections. Examples of duplexes are cited from both active and ancient systems and from theoretical and physical models. Duplexes may form at bends on strike-slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip-slip faults. However some may form, and many may initiate, as non-sequential ‘Riedel’ fractures at fault offsets or on straight fault segments. This process is more marked than in dip-slip systems where primary anisotropy such as bedding exerts more control on fault geometry. Strike-slip duplexes may be shunted along the fault system parallel to the regional slip vector. However, duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system. These factors mean that no section through a strike-slip system should be expected to area balance. The faults of strike-slip duplexes and imbricate fans may root in kinematically necessary low-dip faults or may converge downwards and appear in vertical sections as flower structures.
Highlights
The article considers general spatial and temporal regularities in faulting which are manifested in fault zones when they develop due to strike- and dip-slip movements of the blocks composing such zones
Major visually recorded trends of temporal changes of the structure (Fig. 3, a) are quantitatively confirmed, and it is established that the zone’s width and the quantity of active fractures increase at the beginning and decrease, whereas the length of the longest fracture is steadily increasing during evolution of the fault zone
The experimental research of shearing zones which occur in mode II and mode III show that their formation takes place according to the general temporal and spatial formation regularities
Summary
The article considers general spatial and temporal regularities in faulting which are manifested in fault zones when they develop due to strike- and dip-slip movements of the blocks composing such zones. The knowledge on such regularities is fundamental for adequate understanding of many processes which accompany faulting as in certain structural conditions these regularities occur in the initial form, whereas in other cases these regularities can be used to interpret complex patterns of fracture zones varying in types and scales. By comparing the Riedel experiment structure and the «force – displacement» curve, [Tchalenko, 1970] has defined three stages in formation of shearing zones. Tchalenko’s concepts are universal [Tchalenko, 1970], and to characterize the stages of faulting in a more detail
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