Abstract: A seismic exploration method is described in which a vibratory source transmits into the earth a series of discrete wave packets of different center frequencies, at least some of which are not uniformly spaced in frequency. Some of the center frequencies may, for example, be related to each other as a geometric progression. Each wave packet that is transmitted into the earth preferably has a modulation envelope according to a sinusoidal modulating wave that eliminates transient effects due to termination of the wave packet and minimizes the number of discrete wave packets required to define a given frequency band width. The received waves are recorded and later summed with a zero phase relationship relative to a common reference time. The composite record is similar to that obtained from an explosive source.