A seismic prospection method in which a compression seismic wave is emitted into the subsoil and sensors are used to collect seismic data having at least a shear component, and in which the data corresponding to said shear component is processed to deduce information about the geology of the subsoil, the method being characterized in that an estimate of the ratio: ∫ Z 0 Z ⁢ v p ·   ⁢ ⅆ l / ∫ Z 0 Z ⁢ v s ·   ⁢ ⅆ l is determined where vp and vs are values for real local compression and shear speeds, where l is the depth coordinate in the subsoil, where Z is the value of this depth coordinate at the bottom surface of the last layer to be analyzed, and the seismic data is inverted in order to deduce the local values of compression and shear speed for said layer to be analyzed, by using a model in which this estimate is used for the invariant parameter &ggr;eff.