KINEMATIC ANALYSIS OF FAULTS IN A PHYSICAL MODEL OF GROWTH FAULTING ABOVE A VISCOUS SALT ANALOG

Syn-sedimentary faults overlying an extended ductile layer within a sandbox model provide an analogue for studying some aspects of the geometry and kinematics of basin scale extensional listric faults associated with salt rollers. The displacement analysis techniques used to examine displacement variations over fault surfaces within the sandbox model, show that displacement varies in a regular and predictable manner. Deviations from simple fault displacement patterns are due to transfers of displacement onto adjacent synthetic faults. Aggregation of the displacements on adjacent synthetic faults produces more regular patterns of displacement distribution and demonstrates the geometric coherence of the aggregated faults. Rapid upward decreases in displacement on the model faults are due to fault growth during sedimentation. Elsewhere in the model, post-sedimentary faulting is associated with very low upward displacement gradients and pre- and syn-faulting sedimentation are readily distinguished on cross-sectional fault traces. In three dimensions a non-horizontal line separating the pre-faulting and syn-faulting sequences tracks the lateral extent of a fault through time. Backstripping of fault displacements, by subtracting the fault displacement of a sedimentary horizon from the displacements of underlying horizons, gives the displacement distribution on a fault surface at the time of deposition of the backstripped horizon. Backstripped fault displacement distributions also allow examination of the general fault structure through time. Backstripping of fault displacements on one of the larger faults within the model and on an associated hanging wall synthetic splay, shows that the two structures originated as a relay zone which was breached by lateral propagation of one of the overlapping faults which form the relay zone. The backstripping technique allows determination of the geometrical changes during growth of a fault system.