The apparent explosion moment: Inferences of volumetric moment due to source medium damage by underground nuclear explosions

Abstract

[1] Classical explosion source theory relates isotropic seismic moment to the steady state level of the reduced displacement potential. The theoretical isotropic moment for an incompressible source region M t is proportional to cavity volume V c created by pressurization of materials around the point of energy release. Source medium damage due to nonlinear deformations caused by the explosion will also induce volume change V d and radiate seismic waves as volumetric, double-couple, and compensated linear vector dipole (CLVD) body force systems. A new source model is presented where K is a relative measure of moment M CLVD with respect to the net moment from volumetric sources V c and V d . K values from moment tensor inversions steadily decrease from ∼2.5 at lower yields to ∼1.0 for the highest-yield shots on Pahute Mesa. A value of 1.0 implies M CLVD = 0 and, by inference, small V d . We hypothesize that the extent to which damage adds (or subtracts) volumetric moment is controlled by material properties and dynamics of stress wave rebound, shock wave interactions with the free surface, gravitational unloading, and slapdown of spalled near-surface layers. This hypothesis is tested by comparing measurements of isotropic momentM I with estimates of M t based on V c scaling relationships and velocity-density models. The results support the hypothesis and the conclusion thatM I represents the "apparent explosion moment" since it has contributions from direct effects due to cavity formation and indirect effects due to material damage. Implications for yield estimation usingM I are discussed in general and for the North Korean tests.Citation: Patton, H. J., and S. R. Taylor (2011), The apparent explosion moment: Inferences of volumetric moment due to source medium damage by underground nuclear explosions,

Partitioning of Seismoacoustic Energy and Estimation of Yield and Height-of-Burst/Depth-of-Burial for Near-Surface Explosions

“…The functional form of the distance term comes from the power-law dependence discussed earlier, which becomes linear after the logarithmic transformation. The functional form of the HOB term is the hyperbolic tangent (tanh), a sigmoid function, which is similar to the one used to describe coupling as a function of DOB in Patton and Taylor (2011). The tanh function well describes the behavior for r s ≫ h s that is the case in this study.…”

Significant release of shear energy of the North Korean nuclear test on February 12, 2013

“…In this case, the generation of those wave occurs near the explosion source; probably due to oscillations of an asymmetrical shaped cavity. Patton & Taylor (2011) found that a non-isotropic radiation pattern for long-period waves might be a contribution from material damage in the source medium. Observed normal faulting mechanisms might be a consequence of slapdown of spalled layers.…”

Comment on "Advanced Seismic Analyses of the Source Characteristics of the 2006 and 2009 North Korean Nuclear Tests" by J. R. Murphy, J. L. Stevens, B. C. Kohl, and T. J. Bennett

“…The absence of "changes of large-scale morphological features or surface changes such as displaced rocks or boulders" (Schlittenhardt et al, 2010) in mountainous terrain is a robust finding from which we infer that there was minimal free-surface damage for both 2006 and 2009 tests. On the other hand, most historic nuclear tests had significant nonlinear, free-surface interactions causing permanent deformations and a dilated source medium (Patton and Taylor, 2011). This late-time rock damage (Patton, 2012) radiates long-period Rayleigh waves through a Poisson effect involving vertical extension accompanied by lateral contraction.…”

“…For this paper, we used the explosion Halfbeak (819 m, 365 kT; Springer et al, 2002). Its DOB is great enough to ensure full coupling, and the announced yield (W) is in a range in which the effects of damage on long-period Rayleigh waves are expected to be minimal due to recompaction of the source medium by spall slapdown (Patton and Taylor, 2011; see their fig. 3).…”

“…This is only approximately true between 1 and 10 kT, especially for overburied explosions and the Denny and Johnson scaling model. The TOC for m b follows from equation (20) of Patton and Taylor (2011) using the Semipalatinsk m b -logW scaling relationship of Ringdal et al (1992) and Murphy (2006), m b 0:75 logW 4:45. As such, a 1:0, b 6:09, c 0:7875, and d 1:01.…”