We develop a two-step methodology combining multiple surface deformation measurements above a salt extraction site (Vauvert, France) in order to overcome the difference in resolution and accuracy. Using this 3-D velocity field, we develop a model to determine the kinematics of the salt layer. The model shows a collapse of the salt layer beneath the exploitation. It also identifies a salt flow from the deepest and most external part of the salt layer towards the center of the exploitation.