Aftershocks of the announced underground nuclear tests conducted by the DPRK on 12.02.2013 and 06.01.2016 found by waveform cross correlation and confirmed by interactive analysis

There was more than a dozen of aftershocks generated by the announced nuclear test conducted by the DPRK on September 3, 2017 (DPRK6) which were found in routine interactive analysis conducted by the International Data Centre. The first DPRK aftershock was found by the method of waveform cross correlation (WCC) on September 11, 2016 after the DPRK5. Dozens of aftershocks were found by cross correlation after the DPRK6 in addition to those found in the routine processing and then confirmed by IDC analysts. The set of robust aftershocks allowed to develop, test, and apply in the routine WCC processing the multi-master method. This method was consistently applied to seismic data at IMS stations KSRS and USRK collected since 2009. Many new aftershocks were found after the third (DPRK3) and the fourth (DPRK4) announced underground nuclear tests conducted by the DPRK on 12.02.2013, and 06.01.2016, respectively. The second DPRK test (25.05.2009) had no reliable aftershock hypotheses at the level of the method sensitivity and resolution. The largest aftershocks of the DPRK3 and DPRK4 could be interpreted as related to the cavity collapse process possibly followed by a chimney collapse, not reaching the free surface. The DPRK3 and DPRK4 aftershocks were confirmed by interactive analysis.