Secondary sources of seismic waves from underground nuclear explosions

Surface-reflected seismic energy from underground explosions, in the form of a pP phase and a spall-closure (slapdown) phase, P s , may contribute to the P wave and coda seen at teleseismic distances. In this report, delay times corresponding to pP − P and P s − P are estimated from surface-zero accelerograms for a number of U.S. underground nuclear explosions and are presented for use by the seismological community. When compared with published estimates, these pP − P estimates are in reasonable agreement but the P s − P estimates are at wide variance. No ready explanation is at hand for the disagreement.