Monitoring North Korea Nuclear Tests: Comparison of 1st and 2nd Tests

북한 핵실험 모니터링 : 1, 2차 비교

  • Received : 2010.08.02
  • Accepted : 2010.08.20
  • Published : 2010.08.31

Abstract

Two suspicious events, which were claimed as underground nuclear tests by North Korea, were detected in the northern Korean Peninsula on October 9, 2006 and May 25, 2009. The KIGAM and Korea-China Joint seismic stations are distributed uniformly along the boundaries between North Korea and adjacent countries. In this study, the data from broadband stations with the distance of 200 to 550 km from the test site are used to analyze and compare two nuclear tests of North Korea. By comparing the time differences of the Pn-wave arrival times of 1st and 2nd tests at multiple stations, the relative locations of two test sites could be calculated precisely. From the geometrical calculation with the velocity of Pn wave $V_{Pn}$ = 8 km/s, the 2nd test site is estimated to move in the WNW direction from 1st one with the distance of 2 km. Body wave magnitude, mb of the 2nd test, which was announced officially as the network average of 4.5, varies widely with the directional location of stations from 4.1 to 5.2. The magnitude obtained from Lg wave, $m_b$(Lg), shows less variation between 4.3 to 4.7 with the average of 4.6. The moving-window spectra of time traces of 1st and 2nd tests show very similar pattern with different scale level. In addition, the corner frequencies of P wave of 1st and 2nd tests at each station show no or negligible difference. This indicates the burial depths of two tests might be very similar. The relative yield amount of the 2nd test is estimated 8 times larger than that of the 1st from the weighted average of ground-velocity amplitude ratios.

References

  1. Hong, T.-K., Baag, C.-E., Choi, H., and Sheen, D.-H., 2008, Regional seismic observations of the 9 October 2006 underground nuclear explosion in North Korea and the influence of crustal structures on regional phases, J. Geophys. Res., 113, B03305, doi:10.1029/2007JB004950.
  2. Lay, T., and Wallace T., 1995, Modern Global Seismology, Academic Press.
  3. Shin, J. S., Sheen, D.-H., and Kim, G., 2010, Regional observations of the second North Korean nuclear test on 2009 May 25, Geophys. J. Int., 180, 243-250. https://doi.org/10.1111/j.1365-246X.2009.04422.x
  4. Taylor, S. R., 1991, Regional seismic observations from NTS explosions, Explosion Source Phenomenology, AGU Geophysical Monograph, 65, 185-196.
  5. Zhao, L.-F., Xie, X.-B., Wang, W.-M., and Yao, Z.-X., 2008, Regional seismic characteristics of the 9 October 2006 North Korean nuclear test, Bull. Seism. Soc. Am., 98, 2571-2589. https://doi.org/10.1785/0120080128