The present invention relates to an improved downhole seismic source for the simultaneous generation of elliptically polarized shear wave seismic energy and compression wave seismic energy coupled into a borehole. The source of the present invention is capable of receiving several kilowatts of energy downhole to depths of several thousand feet. An orbital vibrator, energized by a hydraulic power means is disposed within a housing. The orbital vibrator imparts an orbital motion which generates seismic wave energy in the borehole. A cable supports the hydraulic power means and the orbital vibrator at selected positions along the borehole for coupling of the seismic wave energy into the borehole.