Experimentally generated normal faults in single-layer and multilayer limestone specimens at confining pressure

Abstract We examined the deformation of single-layer and multilayer rock veneers at confining pressure due to slip on an underlying, pre-existing, 70°-dipping normal fault. Single-layer specimens consisted of centimeter-thick Indiana Limestone veneers; centimeter-thick multilayer specimens consisted of three layers of Indiana Limestone or two layers of Indiana Limestone separated by a middle layer of weaker, Austin Chalk. The experiments investigated the evolution of induced deformation features — fractures, faults and folds — as functions of; (1) offset on the pre-existing normal fault, (2) confining pressure (100 MPa and 200 MPa), (3) `bedding' (three-layer specimens), and (4) compositional layering (three-layer specimens with a weak middle layer). Single-layer limestone specimens deformed at 200-MPa confining pressure provided the most reproducible results, forming arrays of nested arcuate normal faults; the concave sides of the faults faced in the hanging wall direction. Older faults of the array, propagating from the tip of the pre-existing fault, died out upward into the hanging wall. Younger faults formed towards the footwall side of the array and propagated to the upper surface of the specimen. These latter faults accommodated subsequent slip on the pre-existent fault, and in doing so, fragmented and offset the monoclinally folded upper surface of the specimen. Reducing the confining pressure to 100 MPa produced a more brittle behavior in the specimen, manifested as fewer faults with more irregular profiles and less monoclinal folding at the upper surface of the specimen. Introducing bedding and weak layering in the specimens at 100-MPa confining pressure increased the bulk ductile response of the specimen. Our model-generated deformation features share strong similarities with those documented in other laboratory normal-fault experiments in sand and clay, and with normal-fault features found in outcrop.

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