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I. Mechanics of Thrusts and Nappes |
Cities Services Company, Energy Resources Group, Exploration and Production Research Laboratory, Box 3908, Tulsa, OK 74102, U.S.A.
Elastic dislocation models are used to calculate the displacements of the ground surface produced by a thrust fault climbing section. The models show that the surface uplift is asymmetrical with the steepest slope above and ahead of the fault. The gradient of the surface uplift becomes steeper and the magnitude of the uplift increases as: (1) the fault dip increases; (2) the fault becomes shallower; and (3) the shear modulus of the material above the fault decreases relative to the shear modulus of the material containing the fault. Elastic dislocation, photoelastic, and clay models are used to predict the orientation of secondary faults which might be produced by a thrust fault climbing section. In general, the secondary faults strike parallel to the master fault, but the dislocation models show that there are regions in both the hanging and foot walls where the secondary fault strikes are not parallel to the master fault. The models suggest that a thrust fault in a homogeneous medium is likely to extend itself with about the same dip, while a thrust fault moving from a stronger material into a weaker material is likely to flatten and become layer-parallel. High-angle antithetic faults or back thrusts in the hanging wall are associated with a thrust fault propagating through a homogeneous medium, but layer-parallel antithetic faults are more likely than high-angle antithetic faults in the hanging-wall when a thrust fault is propagating from a stronger to a weaker medium.
