Folding of a single viscous layer: Exact infinitesimal-amplitude solution

The folding of a single viscous layer embedded in an uniformly shortening medium is analyzed mathematically by superposing the mean flow corresponding to uniform shortening and a perturbing flow corresponding to folding. The mean flow is coupled to the perturbing flow in the boundary conditions applying at the layer-medium interfaces. These are expanded according to the surface-wave approximation in hydrodynamics, and the solution applies when the amplitude of folding is small. Folding with interfacial adherence and interfacial slip are both treated. The dominant wavelenghts obtained do not agree with those presented in Biot (1959a) and Remberg (1963a, 1970b).