Depth Calculation for the January 06, 2016, the September 09, 2016 and the September 03, 2017 Nuclear Tests of North Korea from Detailed Depth Phases Using Regional and Teleseismic Arrays

North Korea has conducted six underground nuclear explosions so far. In this study, we determined source depth and characterization for the 2016J, 2016S and 2017S tests which were conducted on January 6, 2016 (2016J), September 9, 2016 (2016S) and September 3, 2017 (2017S), respectively. It has been difficult to ascertain the accurate depth of North Korean nuclear explosions due to paucity of data and information. We explore the depth calculation for the North Korean nuclear tests based on the detailed depth phases using teleseismic and regional arrays. We present the coherent spectral nulls from the average spectra of pP + P/sP + P and pPn + Pn/sPn + Pn which correlate with the depth phases showing 180° phase reversals with the P-wave arrivals. We estimated the burial depths at 2.12, 2.10, 1.98 km for the 2016J, 2016S and 2017S nuclear tests, respectively, We anticipate our absolute findings to be significant since in the past depth estimates for North Korean nuclear tests have been inconclusive and unclear owing to not only paucity of data but also trade-offs of the relative assessment based on the satellite images between the true source location and the tunnel entrance for the 2006 nuclear test used as a reference event.