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Home > Research > Nuclear Test Monitoring > Detection Seismology > Capability Assessment > Monitoring North Korea’s nuclear test site

Monitoring North Korea’s nuclear test site

On 9 October 2006 North Korea conducted an underground nuclear explosion at a test site near Kimchaek. The explosion was detected by several seismic stations in the International Monitoring System (IMS), and was also reported by the United States Geological Survey (USGS). The event magnitude was reported as 4.1 by the International Data Center (IDC) in Vienna, Austria and 4.2 by the USGS. We analyzed the recorded waveforms at selected seismic stations in order to investigate the capability of the global seismic network to monitor the North Korean test site for possible future explosions. Our analysis is based upon the so-called Site-Specific Threshold Monitoring (SSTM) approach. Using actual seismic data recorded by a given network, SSTM calculates a continuous “threshold trace”, which provides, at any instance in time, an upper magnitude bound on any seismic event that could have occurred at the target site at that time.

Operational IMS Network, North Korean test site, 9 Oct 2006 (day 282).

The network selected for this study (above left) comprises in general those IMS stations which had the best signal-to-noise ratio (SNR) for the 9 October explosion plus the Chinese station at Mudanjiang (MDJ), about 370 km north of the test site. We also included the South Korean array (KSRS), which recorded the nuclear explosion, but was not operational in the IDC at the time.

Registrations from KSRS-array 2006-282:01:35:30.

The figure above illustrates the procedure for tuning of the KSRS array for site-specific monitoring of the North Korean test site. All of the stations were tuned in a similar way. The upper trace shows the short-term-average (STA) of the optimally filtered (3-8 Hz) P-beam steered towards the epicenter of the North Korean event. The filtered and unfiltered P-beams are shown in traces nos. 2 and 3. Trace no. 4 shows the short-term-average of the optimally filtered S- beam (1-3 Hz) for the same event. The filtered and unfiltered S-beams are shown in traces nos. 5 and 6. The vertical scale for each trace is in digital counts.