The choice of modeling material--dry sand or wet clay-affects the style and distribution of deformation in scaled experimental (analog) models of extension. For example, fault-zone widths are greater in sand than in clay, possibly reflecting the marked difference in maximum grain size of the modeling materials (<0.5 mm for dry sand vs. < 0.005 mm for wet clay). Most differences in the deformation patterns, however, reflect differences in the ductility of the modeling materials. Normal faults are long, planar and hard-linked (i.e., directly connected) in the dry sand with its low ductility, whereas normal faults are short, curved and soft-linked (i.e., not directly connected) in the wet clay with its higher ductility. A few large normal faults accommodate most deformation in the sand models, whereas a few large faults and numerous small faults accommodate most deformation the clay models. Little folding occurs in the sand models, but folds are common in the clay models.
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