Yield estimate for the January 2016 DPRK nuclear test based on InSAR and numerical modelling with mechanical heterogeneity

Interferometric Synthetic Aperture Radar (InSAR) provides a way of measuring ground deformation caused by underground nuclear testing via a satellite remote sensing platform. We present a finite-element model (FEM) of the nuclear test site in the Democratic People's Republic of Korea (DPRK, formerly North Korea) constrained by InSAR data. The model simulates elastic deformation caused by an underground explosion and includes high-resolution topography and mechanical heterogeneity. To the best of our knowledge, we are the first to investigate the effect of mechanical heterogeneity (a layered structure in our case) on deformation modelling at the DPRK test site. Sensitivity testing shows that inclusion of topography, mechanical layering and the combined effect results in 48.2, 22.6 and 91.5 per cent increase in the maximum predicted deformation, respectively. This suggests that previous models that do not account for these complexities may overestimate the nuclear yield and/or underestimate the depth of burial (DoB). We performed a parameter search to solve for the cavity size and DoB that best reproduce ground deformation observed in ALOS-2 InSAR data covering the DPRK's 4th nuclear test (DPRK4). Using these best-fit values with a cavity-yield scaling law, we estimate the yield of DPRK4 to be 10-20 kt at a DoB of 542-826 m. Our method provides an estimate that is independent from and complementary to traditional seismic methods, which is useful for a location that is data-limited.