Shear wave energy contaminates the vertical component of ocean bottom seismic data worldwide, yet the mechanism that generates this Vz noise has not been adequately explained. By means of elastic finite-difference modeling we investigate scattering at the seabed as a possible cause of the phenomenon. Modeled as perturbations in shear speed, the scatterers are energized most strongly by converted waves and radiate Stoneley waves along the seabed. Resulting synthetics exhibit the characteristics of Vz noise observed on field data, in particular, converted wave moveout, coherence in the receiver domain, incoherence in the shot domain, and absence from the hydrophone.<br>