P-wave spectra have been computed from several mine blast records. Amplitudes of the low frequency peaks were found to correlate with the total size of the explosion. This agrees with theoretical source spectra calculations for multiple-delayed shots. The theoretical calculations also show that at higher frequencies (excepting multiples of the delay frequency), the spectral amplitudes are determined by the maximum charge per delay and not by the total charge size. Synthetic seismograms have been computed for various source and absorption models. To obtain reasonable agreement with observed waveforms requires at least 10 shots delayed at intervals of 0.2 sec or more. These delays are much larger than those normally used between individual holes in a blast (i.e., 17 msec) but are typical of delays between rows of shots. Thus, it appears that the seismic waveforms are more sensitive to the number of rows and the row delay than they are to the total number of shots and the individual delays in a blast.

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