Nuclear monitoring requires identification of small events observed at regional distances for which Lg is generally the largest seismic phase. Recent research, including ours, has provided significantly better understanding of the generation of Lg from explosions, but the new concepts have not yet been fully exploited for improving discrimination between low magnitude explosions and earthquakes in different regions of the world. Our analysis of spectrograms, which display spectral energy versus time, shows that Lg from explosions alone is generally followed by several distinct arrivals with progressively lower frequency contents, probably due to the scattering of explosion-generated Rg into S at several discrete near-source locations. This promising new discriminant may offer a distinct advantage over other seismic methods of discrimination, since it may not require the region of interest to be calibrated with the help of earlier known-type seismic events. Moreover, regional discrimination based on the Lg wavetrain can be especially useful when signal-to-noise considerations for a small event preclude the use of other seismic phases.

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