Precise observations of travel time changes of P and S waves from 11 explosions at the same shot point in the Charlevoix region, Quebec, have been determined by separate cross correlations of the P and S waveforms. The changes in P and S wave travel times are equal to within ¿4 ms and lead to the relation that dα = 3dβ. From the theory of O'Connell and Budiansky (1977) the derivatives of the normalized P and S wave velocities with respect to the normalized S wave velocity define the changes in crack density parameter &egr; and the partial saturation parameter &zgr;. Increases in travel time observed in the Charlevoix region suggest that the crack density parameter &egr; increases, while the partial saturation parameter &zgr; decreases, in agreement with the dilatancy hypothesis (Nur, 1972)>