In reality, as strike-slip faults become large and developed, their behavior changes and becomes more complex. Īn idealized strike-slip fault runs in a straight line with a vertical dip and has only horizontal motion, thus there is no change in topography due to motion of the fault. These occur between two or more large bounding faults which usually have large displacements. Strike-slip duplexes occur at the stepover regions of faults, forming lens-shaped near parallel arrays of horses. The identification of such structures, particularly where positive and negative flowers are developed on different segments of the same fault, are regarded as reliable indicators of strike-slip. Fault zones with dominantly reverse faulting are known as positive flowers, while those with dominantly normal offsets are known as negative flowers. As the faults tend to join downwards onto a single strand in basement, the geometry has led to these being termed flower structure. with a small component of shortening) or transtensional (with a small component of extension). In cross-section, the displacements are dominantly reverse or normal in type depending on whether the overall fault geometry is transpressional (i.e. In detail, many strike-slip faults at surface consist of en echelon and/or braided segments, which in many cases were probably inherited from previously formed Riedel shears. The somewhat oblique segments will link downwards into the fault at the base of the cover sequence with a helicoidal geometry. The linkage often occurs with the development of a further set of shears known as 'P shears', which are roughly symmetrical to the R shears relative to the overall shear direction. With further displacement, the Riedel fault segments will tend to become fully linked until a throughgoing fault is formed. These two fault orientations can be understood as conjugate fault sets at 30° to the short axis of the instantaneous strain ellipse associated with the simple shear strain field caused by the displacements applied at the base of the cover sequence. The R shears are then linked by a second set, the R' shears, that forms at about 75° to the main fault trace. The dominant set, known as R shears, forms at about 15° to the underlying fault with the same shear sense. At low levels of strain, the overall simple shear causes a set of small faults to form. This will also be the case where an active strike-slip zone lies within an area of continuing sedimentation. In the early stages of strike-slip fault formation, displacement within basement rocks produces characteristic fault structures within the overlying cover. The presence of stepovers during the rupture of strike-slip fault zones has been associated with the initiation of supershear propagation (propagation in excess of the S-wave velocity) during earthquake rupture. This is backed up by evidence that the rupture of the 2001 Kunlun earthquake jumped more than 10 km across an extensional stepover. Numerical modelling has suggested that jumps of at least 8 km, or possibly more are feasible. For active strike-slip systems, earthquake ruptures may jump from one segment to another across the intervening stepover, if the offset is not too great. In the case of a dextral fault zone, a right-stepping offset is known as an extensional stepover as movement on the two segments leads to extensional deformation in the zone of offset, while a left-stepping offset is known as a compressional stepover. The areas between the ends of adjacent segments are known as stepovers. When strike-slip fault zones develop, they typically form as several separate fault segments that are offset from each other. Deformation styles Development of Riedel shears in a zone of dextral shear Flower structures developed along minor restraining and releasing bends on a dextral (right-lateral) strike-slip fault Stepovers Strike-slip tectonics is characteristic of several geological environments, including oceanic and continental transform faults, zones of oblique collision and the deforming foreland of zones of continental collision. Where the displacement along a zone of strike-slip deviates from parallelism with the zone itself, the style becomes either transpressional or transtensional depending on the sense of deviation. Areas of strike-slip tectonics are characterised by particular deformation styles including: stepovers, Riedel shears, flower structures and strike-slip duplexes. Where a zone of strike-slip tectonics forms the boundary between two tectonic plates, this is known as a transform or conservative plate boundary. Strike-slip tectonics or wrench tectonics is a type of tectonics that is dominated by lateral (horizontal) movements within the Earth's crust (and lithosphere). Structure and processes associated with zones of lateral displacement in the Earth's crust
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