Elastic modeling or migration of data recorded in a marine environment can be formulated as a coupled acoustic-elastic problem with a common boundary condition at the sea floor. A simpler alternative is to solve only the elastic wave equation, with vanishing shear moduli within the water layer. To enable the application of this approach to real problems, it is necessary to transform the recorded scalar pressure wavefield into a vector particle-displacement field. In this paper I describe a method to perform such vectorization of recorded marine data which is completely independent of the subsurface geology. Few assumptions are required for the theoretical justification of the method, the most important being that the depth of the cable is a smooth function of the receiver position. The wavefield vectorization is obtained through a simple, inexpensive, linear operation in the frequency-horizontal wavenumber domain. Except for a small reduction in the spectral resolution, good results were obtained when the method was applied to both synthetic and real data.