The role of antithetic faults in transferring displacement across contractional relay zones on normal faults

Contractional relay zones between pairs of normal faults are sometimes associated with multiple antithetic faults in a geometry similar to that found in Riedel shear zones. Detailed fault displacement profiles of outcrop examples of this geometry demonstrate that the antithetic faults accommodate the transfer of displacement between the synthetic faults that bound the relay zones. The throw on individual antithetic faults, or R ' shears, is typically constant across relay zones while the throw profile on the synthetic faults, or R shears, is stepped; the steps occurring across branchpoints with abutting R' shears. Transfer of fault displacement occurs by a combination of block rotation and irrotational block translation within the relay zone. As fault throw increases, contractional relay zones are by-passed by the linkage of the synthetic faults, in a manner analogous to the formation of P-shears by the linkage of R shears in classic Riedel shear experiments, but with the original relay zone structure still preserved within the fault zone. With yet further strain bedding may rotate into near-parallelism with the fault surface, with the original geometrical configuration of the relay zone difficult to unravel.

Automated summary

Contractional relay zones between normal faults can have multiple antithetic faults similar to Riedel shear zones. The antithetic faults transfer displacement between synthetic faults in the relay zones. The throw on antithetic faults is constant, while the throw profile on synthetic faults is stepped, occurring at branchpoints with abutting R' shears. Fault displacement transfer occurs through block rotation and translation within the relay zone. As fault throw increases, the relay zones are bypassed by the linkage of synthetic faults, preserving the original structure within the fault zone.