Regional Seismic Characteristics of the 9 October 2006 North Korean Nuclear Test

Abstract

We investigate the regional seismic signature of the 9 October 2006 North Korean nuclear test. Broadband regional data for the nuclear test and a group of earthquakes close to the test site were obtained between December 2000 and November 2006. Epicentral distances from the stations to the test site are between 371 and 1153 km. We first use these regional events to calibrate the Lg-wave magnitude in the network. Then the network is used to calculate m b Lg 3:93 for the North Korean nuclear explosion. Using a modified fully coupled magnitude-yield relation, the yield of the North Korean nuclear test is estimated to be 0.48 kt. Because of large uncertainties in the source depth, the estimate is preliminary. The P=S-type spectral ratios Pg=Lg, Pn=Lg, and Pn=Sn are calculated for the nuclear explosion and a group of earthquakes close to the test site. At frequencies above 2 Hz, the network-averaged P=S spectral ratios clearly separate the 9 October 2006 explosion from the regional earthquakes. Our result indicates that a single-blast explosion in the North Korea region shows different seismic characteristics from an earthquake. Any well-coupled single-blast explosion detonated in this region with yield similar to that for the North Korean nuclear test has a large probability of being identified by a regional seismic network such as the one adopted in this study.

Simulation of topographic effects on seismic waves from shallow explosions near the North Korean nuclear test site with emphasis on shear wave generation

“…We assumed the density and seismic wave speeds were constant throughout the medium, assigning values to 5190 m/s, 3000 m/s and 2500 kg/m 3 for the P and S wave velocity and density, respectively. We assumed relatively fast wave speeds corresponding to the presumed granitic geology [ Zhao et al , 2008; Bonner et al , 2008; Ford et al , 2009]. Furthermore, we assumed purely elastic propagation for two reasons: it is much more computationally efficient to perform the calculations assuming no attenuation; and we are interested in isolating the effects of topographic scattering.…”

“…Note that surface relief varies dramatically in the immediate vicinity of the estimated event locations, with peaks and valleys of characteristic scale lengths of 1–5 km. The DPRK test locations shown in Figure 1a are in a region of granite lithology (see for example the geologic map of Zhao et al [2008, Figure 9]); however, the valley floors are probably filled with lower‐velocity sediments. Some variations in the geology are reported to the east (basalt), south (calcite, marble) and west (basalt).…”

Significant release of shear energy of the North Korean nuclear test on February 12, 2013

“…For an explosion, the Pg/Lg ratio is expected to be significantly higher than for a tectonic event, as the compressional nature of an explosion ideally does not radiate shear energy. Recent studies analysed those kind of data for the previous two nuclear tests in North Korea (NK2006 and NK2009) and determined an explosive character (Kim & Richards 2007;Zhao et al 2008;Shin et al 2010;Hong 2013;Ford et al 2009;Ford et al 2012).…”

Satellite Earth Observations Support CTBT Monitoring: A Case Study of the Nuclear Test in North Korea of Oct. 9, 2006 and Comparison with Seismic Results

“…Test-site bias corrections have been derived for the main test sites of nuclear weapon states in Nevada (carried out by USA and UK), Semipalatinsk and Novaya Zemlya (former USSR), Lop Nor (China) and Tuamotu (France), SCHLITTENHARDT (1988), but are not known for the Korean test site. However, the geological and environmental conditions in the region with Cretaceous and Precambrian rocks (General Geological Map, 1945) suggest typical wet hard rock conditions with little or only weak absorption (high seismic quality factor Q) of seismic body waves below the test site (ZHAO et al, 2008).…”