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In fault-related folds that develop purely by kink-band migration, fold limbs widen through time while maintaining a fixed dip (Suppe et al., 1992), as illustrated in the sequential model involving pre-growth strata only (above left). Material is incorporated into the fold limb by passing through an active axial surface, which at depth is generally pinned to a bend or tip of a fault (Suppe, 1983; Suppe and Medwedeff, 1990). The fold limb in growth strata is bounded by the active axial surface and the growth axial surface, an inactive axial surface that defines the locus of particles originally deposited along the active axial surface. In these sequential models, the synclinal axial surface is active, and the anticlinal axial surface is inactive. In the case where sedimentation rate exceeds uplift rate (above center), strata are folded through the synclinal axis and incorporated into the widening fold limb. The dip of folded growth strata is equal to dip of the fold limb in pre-growth strata. The width of the dip panel for each growth horizon corresponds to the amount of fold growth that occurred subsequent to the deposition of that marker. As a result, younger horizons have narrower fold limbs than do older horizons, forming narrowing upward fold limbs or kink bands in growth strata (growth triangles). In the case where uplift rate exceeds sedimentation rate (above right), each increment of folding produces a discrete fold scarp located where the active axial surface projects to the Earth’s surface (Shaw et al., 2004). Subsequent deposits onlap the fold scarp, producing stratigraphic pinchouts above the fold limb. Fold scarps and stratigraphic pinch-outs are displaced laterally and folded as they are incorporated into widening limbs. Contractional fault-related folding theories that exclusively invoke kink-band migration include fault-bend folding (Suppe, 1983), constant-thickness and fixed axis fault-propagation folding (Suppe and Medwedeff, 1983), and basement-involved (triple junction) folding (Narr and Suppe, 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.