Abstract - The geometry, formation and breaching of relays on segmented thrusts have been studied for faults with maximum displacements of 0.64-8m which outcrop in well bedded sequences. Two and near-three dimensional data permit characterisation of thrust geometries and displacements at contractional, extensional and neutral relays. Thrusts at contractional relays are separated by asymmetric folds, with steep to moderate bed dips (ca 30-75º) between fault segments and shallow bed dips outside the relay. Folds verge in the direction of relative hangingwall motion, with the steeper limb defining a parallelogram-shaped zone between thrusts. Rapid decreases in fault displacements within relays are mirrored by an increase in fold amplitude. High displacement gradients (0.17 – 1.0) are mainly accommodated by bed rotations within relays and aggregate displacements are maintained across segment boundaries reflecting the transfer of fault slip to folding. Fault segments form after minimal displacement and folds grow between segments as displacement accrues on the thrusts. With increasing finite displacement thrust tips remain fixed relative to stratigraphy but move relative to each other in a slip-parallel direction. Thrust relays breach with increasing fault displacement. Contractional relays remain intact at higher displacements than extensional relays. High bedding-thrust angles and fault separation promote relay longevity.
Journal of Structural Geology, 24, 709-727, 2002.