EXPLOITATION OF THE IMS AND OTHER DATA FOR A COMPREHENSIVE, ADVANCED ANALYSIS OF THE NORTH KOREAN NUCLEAR TESTS

On May 25, 2009, the North Koreans conducted a second underground nuclear test in the same area as their initial 2006 test. Preliminary analysis indicated that the explosive yield of the second test was roughly 5 times that of the first, and it was found to have been well-recorded by a variety of globally distributed seismic networks. We carefully analyzed the available short-period seismic data in an attempt to define accurate locations, depths and yields for these two North Korean nuclear tests. In order to determine accurate relative locations for the two events, we made very precise arrival time measurements at 35 stations that recorded both explosions with good signal to noise ratios. The location of the 2006 explosion was then held fixed at the previously determined preferred location and the relative location of the 2009 explosion was estimated using the Joint Hypocenter Determination (JHD), Double Difference (DD) and Differential Waveform Interferometry (DWIF) location algorithms. All of these relative location techniques yielded very similar results, indicating that the 2009 test was conducted about 2.5 km west-northwest of the 2006 test. These relative seismic locations were subsequently integrated with the local topographic data and satellite imagery to define what we believe to be very reasonable and accurate locations for these two explosions. The corresponding source depths can not be reliably determined using the currently available arrival time data or th