The velocities of the seismic waves propagating in the fluid-mud layer are governed by the rheological properties and density of the fluid mud. Performing seismic transmission measurements inside the fluid mud can give good estimates of the seismic velocities and, thus, of the rheological properties and density. Laboratory ultrasonic transmission measurements of the wave velocities in the fluid-mud layer and their temporal evolution are shown. It is found that the shear-wave velocity and yield stress are positively correlated. Performing a seismic reflection survey for characterization of the fluid-mud layers could be more practical because it allows towing the sources and receivers above the top of fluid-mud layer. Interpretation of the results from a reflection survey, though, is influenced by the water layer above the fluid mud. Applying seismic interferometry to reflection measurements can eliminate the influence of the water layer and retrieve a reflection response from inside the fluid-mud layer. This eliminates the influence of the temperature and salinity of the water layer to obtain information about the seismic properties of the fluid-mud layer. To introduce the approach of retrieving and extracting the reflection response from inside the fluid-mud layer, data from laboratory measurements are used. The obtained compressional- and shear-wave velocities are validated by comparing them with values from current transmission measurements.