Depth computation and source characteristics of DPRK'S 2016-01-06, 2016-09-09 and 2017-09-03 nuclear tests using body and rayleigh waves from regional and teleseismic data

The Democratic People's Republic of Korea (DPRK aka North Korea) conducted underground nuclear explosions on January 6, 2016 (2016J), September 9, 2016 (2016S) and September 3, 2017 (2017S) since the 2006, 2009 and 2013 nuclear tests. The principal objective of this paper is to present depth determination and source characteristics for the North Korean nuclear tests using body wave and surface wave spectra. The source depths for the 2016J, 2016S and 2017S nuclear tests were estimated at 2.11 km, 1.99 km and 1.96 km, respectively using spectral nulls of Pand S- wave and Rg-wave spectra. It should be noted that our over-burial determination is significantly greater than expected from the standard experiment practice of nuclear nations. In particular we found the Rg-wave spectral nulls in North Korean nuclear tests to appear due to a most general source type of pure dip-slip motion with about 45°dip. We assume that the North Korean nuclear test source may be an inverted conical volume dipdip slip motion which could be a vertically distributed source in vertically contained shafts through mutually connected-deep tunnels. The over-burial determination would affect the interpretation of MS-mb discriminants and the estimation of the seismic yield as well.