ABSTRACT

Structural cross sections in extensional terranes can be improved significantly by restoration and balancing principles originally developed for fold-and-thrust belts. In rift basins and passive continental margins, use of restoration techniques in analysis of growth faults, elongate salt swells, and other extensional structures results in geologically valid seismic interpretations. Sections must be in depth (as opposed to two-way time) and oriented in the direction of material transport, and decompaction must accompany restoration.

Hanging-wall deformation is characterized by different processes depending on the mechanical properties of the rocks being extended, and can be approximated by various geometric and kinematic models: antithetic faulting is analogous to antithetic shear, combined antithetic and synthetic faulting is approximated by vertical shear, domino-style extension corresponds to rigid body rotation, and flexural slip/flow is modeled by bed-length balance methods. Selection of the appropriate algorithm is crucial for proper restoration and balancing.

Applications of these techniques, illustrated here using seismic data from the Gulf Coast and North Sea, include (1) evaluating and adjusting seismic interpretations, (2) projecting listric fault trajectories to depth, (3) delineating more accurately the geometry and extent of hydrocarbon reservoirs, (4) identifying new exploration leads, (5) determining the deformation history of an area, and (6) constraining the timing and direction of hydrocarbon migration and entrapment.

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