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In fault-related folds that develop purely by limb rotation with fixed hinges (i.e., inactive axial surfaces), the dip of the fold limb increases with each increment of folding as illustrated in the sequential model involving pre-growth strata only (left). In the case where sedimentation rate exceeds uplift rate (center), strata are progressively rotated with each increment of folding. Thus, older growth horizons dip more steeply than do younger horizons, yielding a pronounced fanning of limb dips in growth strata. Fold limb width, however, remains constant. In the case where uplift rate exceeds sedimentation rate, growth strata also exhibit a fanning of limb dips. However, growth strata typically onlap the fold limb. Contractional fault-related folding theories that exclusively invoke limb rotation include certain classes of detachment folds (Dahlstrom, 1990; Hardy and Poblet, 1994). From AAPG Studies in Geology #53: Seismic Interpretation of Contractional Fault-Related Folds, An AAPG Seismic Atlas, edited by John H. Shaw, Christopher D. Connors and John Suppe, 2005. Pages 1-59.