Effects of network-average magnitude bias on yield estimates for underground nuclear explosions

Abstract

Summary. The ISC body-wave magnitude, mb ISC, of presumed underground nuclear explosions in Kazakhstan, USSR, is shown to be systematically biased, by comparison to that recorded at the array station EKA (mb EKA). Linear regression gives: This is found to be due in part to anelastic attenuation effects on mbEm, but several characteristics of the ISC data (in particular, histograms of all contributing individual station magnitudes) demonstrate that the bias is also due to network-averaging effects. For the smaller explosions, those stations with a positive mb bias dominate the data set, but the remainder of the network fails to detect the event. Conversely, for larger explosions, additional stations, with negative mb bias will detect. Accepted magnitude: yield (Y) relationships will thus be in error if applied with mb Isc. Use of published station corrections for EKA allows estimation of an mb EKA: Y relationship, and hence, from the mb 1sC: mb EKA comparison, a magnitude: yield relationship which takes account of network-average bias. This is: