Effects of shock-induced tensile failure on mb-Ms discrimination:: Contrasts between historic nuclear explosions and the North Korean test of 9 October 2006

Rayleigh wave excitation is studied for an explosion source model consisting of a superposition of isotropic (monopole), tensile failure, and tectonic release point sources. The body-force representation for shock-induced, deep-seated tensile failure is a compensated linear vector dipole CLVD, where the relative strength of the CLVD is given by an index K. Rayleigh wave amplitudes are reduced owing to destructive interference between an explosive monopole and a CLVD source with vertical axis of symmetry in extension (K > 1). The effect of tensile failure on M-s is to enhance the explosion-like characteristics on a plot of m(b)-M-s. This model suggests that the success of the m(b)-M-s discriminant results from the fact that nuclear tests were conducted under containment practices for which tensile failure is ubiquitous, while the North Korean nuclear test of 9 October 2006 is a harbinger of poor m(b)-M-s performance when tensile failure is completely suppressed.