--> 3-D Trishear: Parameters and Possibilities

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3-D Trishear: Parameters and Possibilities

Abstract

Implementing trishear using a 3D algorithm can help predict bed geometries that have been sheared in areas around a propagating fault tip, explaining features observed in many real world structures. The method, which was initially developed in 2D as an alternative to the kink-band technique, requires the hanging wall to move at a constant velocity relative to a fixed footwall while velocity decreases towards the footwall within a triangular zone above the fault tip (or “trishear zone”). Applying trishear allows modelling of complex fault-associated fold geometries that otherwise would not be captured using traditional geometrical restoration and forward modelling methods. As in 2D space, implementation of trishear in 3D is controlled by user-defined parameters including the magnitude of displacement, the propagation/slip ratio, the angle of the trishear zone and the initial position of the zone. Each of these parameters, which can be varied laterally along fault strike in Midland Valley's Move2015 software, ultimately influence the geometry of the fold/fault relationship. Here several case studies including; the development of the East Kaibab Monocline in Southern Utah and a fault-propagation fold within the Niger Delta, demonstrate how trishear parameters can be implemented and tested in geographical space and allow the validity of the subsequent fold geometries to be considered. In both cases the results can be compared and contrasted against previously published work and other structural techniques including stress and strain analysis.