Constraints on burial depth and yield of the 25 May 2009 North Korean test from hydrodynamic simulations in a granite medium

Abstract

Yield : depth of burial (DoB) tradeoff curves (TOCs) based on seismic magnitudes of the 25 May 2009 North Korean test depend strongly on the choice of empirical cavity radius (R c) scaling model. Ambiguities over R c scaling, particularly at large scaled DoB (SDoB), translate into unacceptably large systematic errors on yield estimates for this test. Hydrodynamic calculations involving realistic material response models offer a viable alternative to characterize R c scaling for a range of SDoB where limited data from past nuclear tests exist. Results of such calculations are presented for a granite medium with a material response validated by modeling four phenomenological criteria for past nuclear tests in granite (free field velocity, energy partitioning into the seismic wavefield, velocity attenuation, and measured R c). These results unambiguously favor the R c scaling model of Denny and Johnson (DJ91) and the TOC based on that model. Lower bounds on yield and DoB of the North Korean test are constrained by predictions of an SDoB threshold for free surface damage from 2-D simulations since no such reported damage was observed for this test. Constrained by the hydrodynamic simulations, the DJ91 model indicates the minimum yield and DoB for the 25 May 2009 North Korean test is 5.7 kilotons and 375 m. Copyright 2011 by the American Geophysical Union.