Impact of variable fault geometries and slip rates on earthquake catalogs from physics-based simulations of a normal fault

Delogkos, E.^1,, Howell, A.^2,3,, Seebeck, H.³, Shaw, B.E.⁴, Nicol, A.², Mika Lao, Y-W.^2,3, Walsh, J.J.^1,
1- Fault Analysis Group and Irish Centre for Research in Applied Geosciences (iCRAG), UCD School of Earth Sciences, University College Dublin, Dublin, Ireland.
2 - School of Earth and Environment, University of Canterbury, Christchurch, New Zealand.
3 - Te Pū Ao – GNS Science, Lower Hutt, New Zealand.
4 - Lamont Doherty Earth Observatory, Columbia University, New York, NY, USA.

Abstract - 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.

Journal of Geophysical Research: Solid Earth, 128, e2023JB026746. doi: https://doi.org/10.1029/2023JB026746, 2023.