Seismic models of detachment and faulted detachment folds

Detachment folds constitute a common structural style in fold-thrust belts and typically form in stratigraphic packages defined by relatively competent cover units underlain by ductile units. PSTM images through these structures contain artifacts resulting from lateral velocity variations between the cover sediments and the core units, steep dips, and complex fold-fault relationships, making them difficult to interpret. Understanding these artifacts and pitfalls in PSTM seismic models enables improved interpretations of PSTM data in natural structures. We conducted 2D seismic modeling for detachment folds models to study the effect of these complexities on PSTM data. Seismic pull-ups and push-downs of the strata underneath the salt or shale substrate are related to the relative velocities of the cover sediments and the core units. A specific example of an Appalachian Plateau structure demonstrates how the relative velocities can influence the seismic image. Progressive evolution of the structures to disharmonic and lift off folds results in enhanced pull-ups and poorer imaging of steep limb segments. For faulted detachment folds, faulted limbs and footwall zones are poorly imaged and marked by wide low-reflectivity bands, making fault interpretation difficult.