Relative Locations of the October 2006 and May 2009 DPRK Announced Nuclear Tests Using International Monitoring System Seismometer Arrays

Waveform data recorded at seven of the International Monitoring System (IMS) seismometer arrays are used to measure the relative times of teleseismic P signals with three methods: analyst picks, and two methods that make full use of the capabilities of seismometer arrays, the cross correlation of array beams and the average of channel-by-channel cross correlations. These times are used to estimate the relative locations of the 9 October 2006 and 25 May 2009 Democratic People’s Republic of Korea announced underground nuclear tests. The 2009 test is found to have occurred about 1.8±0.8 km to the west and 0.4±0.6 km to the north of the 2006 test. The use of cross correlation reduces the standard deviation of the travel-time residuals from ∼0.05 to ∼0.01 sec, enabling the two epicenters to be statistically distinguished with high confidence. This result demonstrates the power of a small number of IMS seismometer arrays at teleseismic distances to detect and relatively locate small explosions with high precision.