Print this pageDeformation Associated with Extensional and Inversion Structures: Differences between Sand and Clay Models
EISENSTADT, GLORIA, MARTHA OLIVER WITHJACK
Scaled physical models are often used to guide seismic interpretation of complex structures or constrain areas of poor seismic resolution. When applying modeling results, it is important to understand that some deformation patterns in models are due to the choice of modeling material. Dry sand and wet clay are the most commonly used modeling materials. To determine the sensitivity of modeling results to different materials, we compared deformation patterns in identical sand and clay models of extension and inversion models.
Deformation patterns are similar in sand and clay models of extensional structures. Faulting accommodates most deformation in sand models, whereas both faulting and folding occur in clay models. Fewer faults develop in sand than in clay models, and faults have greater displacements, wider spacing, and less curvature in sand than in clay models.
Inversion models of clay and sand differ significantly. Pre-existing normal faults in sand models show only minor reactivation during inversion with most deformation accommodated by new thrust faults. In contrast, pre-existing normal faults in clay models experience major reactivation during inversion with few new thrust faults developing.
Based on these comparisons, we conclude that sand is a poor modeling material for inversion experiments because its extremely low cohesive strength prohibits significant reactivation of pre-existing faults. Modeling results should be applied to structural interpretation only after thoroughly understanding the effects of the chosen modeling material.