We model the inhomogeneous zone below the 8° discontinuity by random velocity fluctuations. The full waveform seismic response of a suite of stochastic velocity models is calculated using a two-dimensional finite-difference scheme. The calculated seismic sections resemble the PNE data for models where the random fluctuations have a horizontal correlation length of 5–10 km, a vertical correlation length not greater than 5 km and a standard deviation of about 2% of the average background velocity. Fluctuations with significantly larger correlation lengths give rise to coherent scattered arrivals and considerably shorter correlation lengths lead to significantly weaker scattering, none of which resemble the observed data. The preferred seismic velocity model is in agreement with an upper mantle model in which the low-velocity zone below the 8° discontinuity may contain small amounts of partially molten material. Alternatively, the combined effects of rheological weakening and small-scale anisotropy may also account for the low-velocity scattering layer.