Publication Date:
2011-05-29
Description:
North Korea detonated its first known nuclear device, a moderate-sized event in the northeastern corner of the Korean Peninsula, on 9 October 2006. A second one, several times more powerful, was set off nearby on 25 May 2009. Both were recorded at high signal-to-noise ratio (SNR) by a modern broadband (0.03-30 Hz) network of seismographs deployed since 2004 along the Sino-Korean border, and by station MDJ due north of ground zero. Spanning a wide range of station azimuth (259 degrees -11 degrees ), the near-regional (1.3 degrees -3.3 degrees ) paths are all purely continental and away from continental margins, making the resulting data uniquely suited for assessing the capabilities of an out-country network to verify the compliance by North Korea with a future comprehensive nuclear test ban treaty. The m (sub b) (Lg) magnitudes for the 2006 and 2009 nuclear explosions were determined anew, giving 4.32+ or -0.13 and 4.86+ or -0.13, respectively. We show that the M (sub S) -m (sub b) (Lg)method correctly differentiates these nuclear explosions from natural earthquakes, although the differentiation was not achieved in studies based on published m (sub b) (Lg) values. An analysis of the Pg:Lg ratio, derived from recordings of the two nuclear tests and of four regional earthquakes selected for their comparable magnitudes (4.2〈 or =m (sub b) 〈 or =4.8), reveals that the ratios associated with the explosion and earthquake populations showed surprisingly little overlap for a broad frequency range of 3 to 11 Hz. In principle, M (sub S) -m (sub b) can also be used to correctly identify the nuclear tests as explosions, but the m (sub b) measurement for such moderate-sized events is not as robust as the m (sub b) (Lg) measurement, rendering this traditionally favored method less practical.
Print ISSN:
0037-1106
Electronic ISSN:
1943-3573
Topics:
Geosciences
,
Physics
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