An earth impedance determination and compensation system for use with a seismic vibrator utilizes output signals from accelerometers on the baseplate and reaction mass portions of the vibrator to create a signal indicative of the near-surface weathered earth layer impedance below the baseplate. The impedance signal is utilized to generate parameter signals which are indicative of the compressional and shear wave patterns generated by the baseplate and may be used to more rapidly and accurately design seismic source arrays to optimize the wave pattern emanating therefrom. One of the parameter signals is directly indicative of the travel time thickness of the weathered surface layer and may be used to accurately determine the static correction factor attributable solely to weathered layer topography. The parameter signals are also utilized to generate a weathered layer filter signal which is combined with a ground force signal to generate a signal that is indicative of the actual wave form sent into the sub-weathered layer earth area and may be used in the cross-correlation process to significantly enhance the accuracy thereof. The weathered layer filter signal is also used in conjunction with a predetermined wave form signal to generate a corrective drive signal that is fed back to the main vibrator drive system. The use of this corrective drive signal controls the vibrator in a manner such that the seismic waves generated thereby into the sub-weathered layer region are maintained in a predetermined form regardless of changes of earth impedance below the vibrator baseplate.