1. In a method of seismic exploration in which the amplitude of signals output by a geophone in a response to detection of a seismic wave within the earth is sampled at intervals to obtain a series of samples, the improvement which comprises applying automatic gain control compensation to said sample amplitude values, said compensation being applied according to the following steps: selecting a plurality of respective windows of said series; determining the average absolute value of the amplitude of the samples within each of said windows; determining the logarithms of said average absolute values, least means squares fitting the logarithms of said average absolute values to a logarithmic function, according to which values for parameters defining said logarithmic function are determined; and applying a gain function to each of said sample values, said gain function corresponding to said logarithmic function.