John H. Spang
Previous models for constructing, restoring and forward modeling of listric normal faults have used either vertical or inclined, antithetic simple shear. Although these models have been successfully applied in some cases, they fail to account for important attributes of major Gulf Coast listric normal faults, such as synthetic faults, fault smear, "normal" drag folding and displacement gradients from as little as zero at the top layer to a maximum at depth. The new model contains two active deformation zones or zones of shearing in the hanging wall. One active deformation zone is antithetic to the main fault and is fixed in space at bends in the fault plane. As the rocks move through the fault bend, they are sheared according to the existing model of inclined shear. The o her active deformation zone is also fixed in space at fault bends, but it is synthetic to the main fault. As the rocks pass through this zone, they are sheared both synthetically and antithetically. When the dip on the synthetic zone of shearing approaches the dip on a segment of the main fault, the method simulates the development of synthetic faults and/or fault smear. Application of this method may lead to a better prediction of fault seals and zones of porosity and fault closure.
AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas