Faults and duplexes are two major structures which contribute to the internal structure of thin-skinned fold-and-thrust wedges and the deformation of masses of layered sedimentary rock. Detailed observations of these structures from well-exposed outcrops in the central Appalachians provide the basis for a theoretical study. Emphasis is placed on mechanical analysis based on the theory for the deformation of an anisotropic cohesive Coulomb material. Theoretical results will be developed for the following three topics. (1) The interaction between intersecting wedge faults and bed-parallel faults, which controls the initiation and propagation of thrust faults in layered rock. This requires solutions for converget flow in wedge-shaped regions. (2) The initiation of duplex structures by analysis of flow instability in a confined layer. (3) The nature and orientation of velocity characteristics in an anisotropic plastic solid is determined and used to interpret the mechanical natures of thrust faults, kink bands, and the hinges of fault- bend folds. The analogs of these structutes in layer-parallel extension will also be studied, and the results applied to the interpretation of available field observations.
