Fully nonlinear flow-constitutive model simulations are employed to investigate constructive and destructive interference of counter-propagating shear waves and their associated stress profiles within a viscoelastic layer of "intermediate depth". Linear unidirectional shear waves in sufficiently thick viscoelastic layers, the viscoelastic analog of Stokes' second problem, were exploited as a rheological tool by Ferry et al. [1,2]. The extension to intermediate gap heights for linear and nonlinear driving amplitudes was studied by our group [3-5], and by Balmforth et al. [6] for viscoplastic fluids. Here we explore the nonlinear quasi-stationary response of the entire viscoelastic layer to an oscillating boundary, greater than the gap-loading limit of typical shear rheometers but less than the depth of effective attenuation. We illustrate how to tune the degree and partitioning of nonlinearity versus driving amplitude and frequency, gap height, and fluid viscoelasticity. (C) 2013 Elsevier B.V. All rights reserved.