--> Abstract: How Do Modes of Extension Affect Normal-Fault Geometry, Displacement Variations and Population Dynamics? by Amber B. Granger, Martha O. Withjack, and Roy W. Schlische; #90039 (2005)

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How Do Modes of Extension Affect Normal-Fault Geometry, Displacement Variations and Population Dynamics?

Amber B. Granger, Martha O. Withjack, and Roy W. Schlische
Rutgers University, Piscataway, NJ

Knowledge of normal-fault geometries, displacement variations and spatial distribution is crucial for understanding hydrocarbon trap development. We constructed three scaled experimental clay models that simulate different extensional modes: block translation with no internal deformation, block translation with internal deformation above a thin ductile layer, and block translation with internal deformation above a thick ductile layer. The normal faults in all three extensional modes strike subperpendicular to the displacement direction and are initially segmented, with maximum displacement at segment centers and minimum displacement at segment tips. The extensional mode profoundly affects fault shape, the number of faults with depth, the displacement distribution with depth, and the style of deformation. With block translation alone, all faults form at the block edge. The main fault zone is listric, movement on which creates a rollover fold cut by antithetic faults. Fault segments are soft-linked at the surface and hard-linked at depth, the greatest number of faults occurs near the base, and fault displacement increases with depth. Deformation is similar for the other two modes of extension. Domino-style faults develop. Faults are planar, the greatest number of faults occurs near the base, and fault displacement increases and then decreases with depth. Fault displacement values approach zero near the base of the block overlying a thin ductile layer, whereas fault displacement values are finite at the base of the block overlying a thick ductile layer. Thus, with only shallow data, it would be difficult to distinguish between these two extensional modes.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005