Vertical force scaling in seismic source models of underground nuclear explosions

Abstract

We have reanalysed observations of body waves and surface waves for 71 well-recorded underground nuclear explosions (UNEs) that were conducted between 1977 and 1989 at the Balapan subregion of the Semipalatinsk Test Site in Kazakhstan. To reconcile differences between body-wave and surface-wave amplitudes, we solve for a scaling factor between vertical and horizontal forces in the explosion model.We find that the estimated scaling factor is anticorrelated with the scaled depth of burial for the subset of UNEs at Balapan that have published depths. The observed anticorrelation and the inferred variations in force scaling suggest that recorded surface-wave amplitudes are significantly influenced by UNE burial depth as well as by previously recognized tectonic release. As part of our analysis, we revisit the relationship between teleseismic mb(P) and yield for UNEs at Balapan, and discuss the physical basis for effectiveness of the mb-MS discriminant.