Determining shear wave velocity from tube wave characteristics

A method is provided for processing seismic data records, such as VSP data obtained from a borehole having an interface between a borehole fluid and a rock formation. The seismic data records comprise of tube waves, pseudo-Rayleigh waves, guided waves or surface waves measured at the formation-fluid interface. A transform (eg wavelet transform) is applied to pairs of seismic records to generate a pair of two dimensional fields (wavelet fields). The phase velocities of the tube waves are computed by applying a cross correlation to the wavelet fields and analysing the distribution of maxima and minima of phase differences in the phase field of the cross correlation. The phase velocities are then inverted to compute the shear velocities.