Use of P coda for determination of yield on nuclear explosions

Spectral analysis of P and P coda from NTS explosions recorded at NORSAR shows that magnitudes based on spectral integration of P coda provide a significantly more precise measure of yield than those based on the initial P. Coda amplitudes and spectra are considerably less sensitive to near-source variations than the direct P. A plot of P-coda magnitude, after correcting for the effects of attenuation in the upper mantle and the source spectrum based on knowledge of approximate yield or mb, versus log yield appears to have a slope of unity. This implies that P coda from several stations (with different but known t* values) can be combined to improve the yield determinations further. Single station P coda from Soviet explosions can also be used to determine relative yields that appear to be at least as precise as those from Lg based on a network of stations.