--> ABSTRACT: Normal Faulting Beneath a Ductile Layer: Experimental Modeling of Deformation Patterns in the Cover Sequence, by M. O. Withjack and J. S. Callaway; #91021 (2010)

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Normal Faulting Beneath a Ductile Layer: Experimental Modeling of Deformation Patterns in the Cover Sequence

WITHJACK, MARTHA OLIVER,  J. SYBIL CALLAWAY

We studied deformation patterns produced by normal faulting beneath a ductile layer (salt and shale) using scaled physical models. In the models, a 1-cm-thick layer of silicone putty represents the ductile layer, and a 3-cm- thick layer of dry sand represents the cover sequence. Movement on a precut, 45 degree-dipping surface below the silicone putty simulates normal faulting. We examined the effect of viscosity on structural development by varying displacement rates, and used surface photographs and reconstructions of model cross sections to define structural evolution.

Initially, a monocline develops in the cover sequence above the sub- ductile normal fault. Soon after, a detached graben forms near the footwall hinge of the monocline, and later a detached reverse fault forms near the hanging-wall hinge. As displacement on the sub-ductile fault increases, the detached normal fault that dips in the same direction as the sub-ductile normal fault becomes the main detached fault. The other detached faults (normal and reverse) move down and toward the hanging-wall side of the sub-ductile fault. Eventually, they become inactive, and are replaced by parallel faults closer to the main detached fault. This process repeats itself throughout the experiment producing a systematic age progression of faulting in the cover sequence. Models with the higher displacement rates (simulating a higher viscosity ductile layer) have the most complex deformation patterns, the greatest strike variations, and the greatest disruption of the fault-age progression.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.