Abstract
We report on the numerical and theoretical study of the subcritical bifurcation of parametrically
amplified waves appearing at the interface between two immiscible incompressible fluids when the
layer of the lower fluid is very shallow. As a critical control parameter is surpassed, small amplitude
surface waves bifurcate towards highly nonlinear ones, with twice their amplitude. We propose
a simple phenomenological model which can describe the observed bifurcation. We relate this
hysteresis with the change of shear stress using a simple stress balance, in agreement with numerical
results.