Source Directivity, Signal Decorrelation, Spectral Modulation and Analysis of Spatio-temporal Patterns of Multiple Explosions

—?Spectral modulation is used as a criterion for discriminating multiple mining explosions from earthquakes and single blasts. Features in the spectra of regional arrivals from quarry blasts may be explained by the spatio-temporal configuration of shot patterns and are explored via a model based on spatial waveform decorrelation and propagation delay (directivity) effects. The phenomenon of decreasing modulation with decreasing average phase velocities of the seismic wave arrivals can be attributed to a trend of decreasing similarities of waveforms with increasing distance between individual explosions making up the shot pattern for the respective arrivals. Rescaling of the modulation patterns with respect to frequency can be explained by the Doppler effect.¶The postulated relationship between shot pattern layouts and sizes, together with their firing sequences, on one hand, and the similarities and differences in modulation characteristics among the various regional arrivals, on the other hand, can be used to derive information about the mining practices in a region that is otherwise not accessible. Moreover, such analyses could be utilized for detecting unusual activities in the CTBT monitoring system.