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 įlower 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). Video showing motion in a strike-slip fault.īends along strike-slip faults create areas of compression or tension between the sliding blocks (see Chapter 2).Structure and processes associated with zones of lateral displacement in the Earth's crust If the opposing block moves right, it is dextral motion. If the block on the opposing side of the fault moves left relative to the observer’s block, this is called sinistral motion. The direction of the strike-slip movement is determined by an observer standing on a block on one side of the fault. In pure strike-slip motion, fault blocks on either side of the fault do not move up or down relative to each other, rather move laterally, side to side. Strike-slip faults are most commonly associated with transform plate boundaries and are prevalent in transform fracture zones along mid-ocean ridges. Strike-slip faults have side-to-side motion.
\): Ketobe Knob in the San Rafael Swell of Utah displays an example of a thrust fault.
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