High-frequency regional records from small earthquakes (1.3 < magnitude < 4), and comparable magnitude explosions, are analyzed to find a reliable seismic discriminant in the eastern U. S. Over 500 digital, vertical-component seismograms recorded by the New York State Seismic Network in the distance ranges 10 to 610 km are used. Mean P/Lg spectral ratios in the band 1 - 25 Hz are about 0.5 and 1.25 for earthquakes and explosions, respectively, in the eastern United States. We find that the high-frequency P/Lg spectral amplitude ratio in the frequency band 5 - 25 Hz is a reliable and robust discriminant for classifying these events. A linear discriminant function analysis indicates that the P/Lg spectral amplitude ratio method provides discrimination power with a total misclassification probability of about 1%. Single-hole instantaneous explosions and ripple-fired quarry blasts have somewhat different P/Lg spectral ratios, but as a group are distinctly different from earthquakes.
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