Investigation of Regional Source Properties of the Underground Nuclear Explosion in North Korea

摘要

We explore the source properties of the October 9, 2006, underground nuclear explosion (UNE) in North Korea from regional phases. The dense seismic stations deployed in South Korea, Japan, and China provided us unique regional observations of the UNE. The unique data set allows us to investigate the source properties by regional phases. The isotropic moment of UNE is estimated by 2.9 X 10(14) Nm from long-period waveforms. The source spectra of regional phases from the UNE are inverted. We determine the apparent moment, corner frequency, overshoot parameter, attenuation factors, and frequency power- dependence terms from the inversion. We present the inverted source spectra with comparison of theoretical source-spectral models. The inverted source spectra agree well with theoretical curves based on UNE source-spectral models. We find that the overshoot parameters of P phases are determined as close to those from theoretical UNE source-spectral models. On the other hand, the overshoot parameters of S are determined close to zero. The low overshoot parameters for S phases suggest that their excitation sources may be different from those of P phases. We analyze the source spectra of natural earthquakes at a nearby location for comparison with those of the UNE. We test P/S spectral- amplitude ratios for discrimination between UNE and earthquakes.