SOURCE DEPTH DETERMINATION OF THE DPRK’S SIX NUCLEAR TESTS (2006, 2009, 2013, 2016J, 2016S, AND 2017) USING REGIONAL AND TELESEISMIC DATA

North Korea conducted underground nuclear explosions on October 9, 2006 (m_b 4.3), May 25, 2009 (m_b 4.7), February 12, 2013 (m_b 5,1), January 6, 2016 (m_b 5,1), September 9, 2016 (m_b 5,3) and September 3, 2017 (m_b 6,3). We estimated source depths for the North Korean nuclear tests using regional and teleseismic data. We found the burial depth at around 2 km for all North Korean nuclear tests using spectral nulls using pP+P/sP+P and pPn + Pn/ sPn+Pn including spectral minima (holes) of the fundamental-mode Rayleigh wave amplitude spectra. It should be noted that utilizing azimuth averaged spectra from the observations is most appropriate to estimate depth for unknown sources in the nonlinear topographic region such as the North Korean nuclear test sites. It is also noticeable to have found spectral anomalies depending on not only source effects but also the site effects. We found higher spectral nulls at the Fennoscandian Shield stations like ARCES and FINES due to the higher crustal velocity resulting in the fast P-wave arrivals with high Q and low attenuation containing high frequencies which very fit to underground nuclear detection, whereas spectral nulls at ASAR are found to be much lower because there is the Great Artesian Basin beneath the array including the low velocity zone in the upper mantle as well. These phenomena are also observed from spectral nulls due to reflection from the bottom of the 660-km Discontinuity by a deep-focus earthquake. It is also notable that the possibility of the over-burial detonation would affect MS : mb and seismic yield for the North Korean underground nuclear tests [1].

1. Kim, S.G. Forensic Explosion Seismology: Technologies and Applications / S.G. Kim, Ye. Gitterman. – Cambridge Scholars Publishing, UK. – 2020 . – 531 pp.

2. Phillips, W.S. Accounting for lateral variations of the upper mantle gradient in Pn tomography studies / W.S. Phillips, M.L. Begnaud, C.A. Rowe, L.K. Steck, S.C. Myers, M.E. Pasyanos, S. Ballard // Geophys. Res. Lett., 2007. – 35 (14). – 10.1029/2008GL034211.

3. Rodnikov, A. G. The deep structure of active continental margins of the Far East (Russia) /A. G. Rodnikov, N. A. Sergeyeva, L. P. Zabarinskaya, N. I. Filatova, V. B. Piip, V. A. Rashidov // Russian Journal of Earth Sciences, 2008. – 10 (4). – ES4002. https://doi.org/10.2205/2007es000224.

4. T.W. Chung A quantitative study on the crustal structure of the Korean Peninsula based on The earthquakes from 1991 to 1994 / T.W. Chung // J. Kor. Earth Sci. Soc., 1995. – 16 (2). – P. 152–157.

5. Kim, S.G. Investigation of post-sites using local seismic tomography in the Korean Peninsula / S.G. Kim, H. Bae // Kr. Soc. Econ. Environ. Geol., 2006. – 39 (2). – P. 111–128.

6. Springer, D. L. Secondary sources of seismic waves from underground nuclear explosions / D.L. Springer // Bulletin of the Seismological Society of America, 974. – 64 (3). – Р 581–594.

7. King, C. Y. Teleseismic source parametersof the Longshot, Milrow, and Cannikin nuclear explosions / C. Y. King, A. M. Abo-Zena, J. N. Murdock // Journal of Geophysical Research, 1974. – 79(5). – Р. 712–718.

8. Tsai, Y B. Amplitude spectrs of surface wave from small earthquakes and undecgound nuclear explosions / Y B.Tsai, K. Aki // J. Geophys. Rex., 1971. – 76. – Р. 3940–3952.

9. Douglas, A., Corbishley, D. J., Blamey, C., & Marshall, P. D. (1972). Estimating the firing depth of underground explosions / A.Douglas, , D. J.Corbishley, C.Blamey, P. D. Marshall // Nature, 1972. – 237. – Р. 26–28.

10. Langston, C. Evidence for the subducting lithosphere under southern Vancouver Island and western Oregon from teleseismic P wave conversions / C. Langston // Journal of Geophysical Research: Solid Earth, 1980. – 86 (B5). – Р. 3857–3866.

11. Okal, E.A. A Student’s Guide to Teleseismic Body Wave Amplitudes / E.A. Okal // Seismological Research Letters, 1992. – 63 (2). – Р. 169–180. – DOI: 10.1785/gssrl.63.2.169.

12. Fox, B.D., Selby N.D., Heyburn R. , Woodhouse J.H. Shallow seismic source parameter determination using intermediate-period surface wave amplitude spectra / B.D.Fox, N.D.Selby, R. Heyburn , J.H.Woodhouse // Geophys. J. Int., 2012. – vol. 191. – Р. 601–615.

13. Heyburn, R. Estimating earthquake source depths by combining surface wave amplitude spectra and teleseismic depth phase observations / R. Heyburn, D.Neil, B. Fox // Geophysical Journal International, 2013. – 94 (2). – Р. 1000–1010.

14. Massé, R. P. Review of seismic source models for underground nuclear explosions / R. P.Massé // Bulletin of the Seismological Society of America, 1981. – 71(4). – Р. 1249–1268.

15. Patton, H. J. Effects of shock‐induced tensile failure on m b ‐M S discrimination: Contrasts between historic nuclear explosions and the North Korean test of 9 October 2006 / H. J. Patton, S. R. Taylor // Geophys. Res. Lett., 2008. – 35. – L14301

16. Rodgers, A. J. Simulation of topographic effects on seismic waves from shallow explosions near the North Korean nuclear test site with emphasis on shear wave generation / A. J. Rodgers, N. A. Petersson, B. Sjogreen // J. Geophys. Res., 2010. – Sol. Ea. 115. – B11309. – doi: 10.1029/2010JB007707

17. Bonner, J. B. Aspects of Rg and Lg generation from the Shagan depth of burial explosions / J. B. Bonner, H. J. Patton, A. C. Rosca, H. Hooper, J. Orrey, M. Leidig, and I. Gupta // Рaper presented at 25th Seismic Research Review: Nuclear Explosion Monitoring: Building the Knowledge Base, Natl. Nucl. Security Admin., Washington, D. C., 2003.

18. Vavryčuk, V. Non-isotropic radiation of the 2013 North Korean nuclear explosion // V. Vavryčuk, S. G. Kim // Geophysical Research Letters, 2014. – 41(20). 10] – Р. 7048–7056. – https://doi.org/10.1002/2014GL06126.

19. Cho, C. Comparison of results of relative location methods and moment tensor inversion for the nuclear explosions experimented in North Korea / C. Cho, J. S. Shin, G. Kim // S31A-2722, 2016AGU Fall Meeting, San Francisco, 2016. – P. 10–12.

20. Udias, A. Principle of seismology / A.Udias // United Kingdom: Cambridge University Press. – 1999. – 475 pp.

21. Israelsson, H. A note on the location of the North Kotran nuclear test on Jan 6, 2016 / H. Israelsson // Technical note 2016-01. – Washington: SeismicInfra Research. – 2016.

22. Murphy, J. R. Advanced seismic analyses of the source characteristics of the 2006 and 2009 North Korean Nuclear Tests / J. R. Murphy, Stevens, B. C. Kohl, T. J. Bennett // Bulletin of the Seismological Society of America, 2013. – 103 (3). – P. 1640–1661.

23. Pabian, F. Contemplating a third nuclear test in North Korea / F. Pabian, S. Hecker // Bull. Atomic. Scientists, opinion, 6 August, 2012. – http://www.thebulletin.org/web-edition/features/contemplating-third-nuclear-test-north-korea.

24. Zhang, M. High-precision location and yield of North Korea’s 2013 nuclear test / M. Zhang, L.Wen // Geophysical Research Letters, 2013. – 40. – 2941–2946. – doi: 10.1002/grl.50607.

25. Tian, D. Collapse and Earthquake Swarm after North Korea's 3 September 2017 Nuclear Test / D.Tian, J. Yao, L. Wen // Geophysical Research Letters. – Apr 2018. – P. 3976–3983.

26. Gitterman, Y. Spectral modulation effect in teleseismic P-waves from North Korean nuclear tests recorded in broad azimuthal range and possible source depth estimation / Y.Gitterman, S. G. Kim, R .Hofstetter // Pure and Applied Geophysics, 2015. – 173 (4). – P.1157–1174. – https://doi.org/10.1007/s00024-015-1169-8.

27. Kim, S. G. Estimating depth and source characteristics of nuclear tests by the Democratic People’s Republic of Korea in 2006, 2009 and 2013 using regional and teleseismic network / S. G. Kim, Y. Gitterman, G. Lee, S. Vavrycuk, V., Kim, M. // Science and Technology, CTBTO, SnT2015, Vienna, Austria. 2015. – P. 22–26.

28. Kim, S. G. Depth determination and source characteristics of the North Korean nuclear tests (2006, 2009, 2013 and 2016) using local and teleseismic arrays / S. G. Kim, Y. Gitterman, S. Lee, V. Vavrycu // Final Paper Number: S34A-02, AGU Fall Meeting, San Francisco, December 12–16. – 2016.

29. Closmann, P. J. On the predictionof cavity radius produced by an underground nuclear explosion/P. J. Closmann//Journal of Geophysical Research, 1969, – 74 (15). – P. 3935–3939.

30. Springer, D. L. Secondary sources of seismic waves from underground nuclear explosions /D. L. Springer//Bulletin of the Seismological Society of America, 1974. – 64 (3). – P. 581–594.