There is provided a method of direct waveform inversion of turning waves (311, 312, 313) to determine parameters characterizing properties of the earth or sub-sections of the earth, particularly of parts of the earth which are capable of trapping hydrocarbons with the inversion yielding from the wavefield of turning waves information representing or being equivalent to velocities or slownesses and/or the gradient of velocities or slownesses, particularly by evaluating wavefield data in the vicinity of turning points (33). The method can be applied sequentially as a survey sinking method.