Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
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Validation on the Bodywave Magnitude Estimation of the 2017 DPRK's Nuclear Test by Source Scaling

지진원 상대비율 측정법을 이용한 2017년 북한 핵실험의 실체파 규모 검증

  • Kim, Tae Sung (Earthquake Research Center, Korea Institute of Geoscience and Mineral Resources)
  • 김태성 (한국지질자원연구원 지진연구센터)
  • Received : 2018.11.16
  • Accepted : 2018.12.11
  • Published : 2018.12.28
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Abstract

Democratic Peoples' Republic of Korea (DPRK) conducted the $6^{th}$ underground nuclear test at the Punggye-ri underground nuclear test site on September 27, 2017 12 hours 30 minutes of Korean local time. Comprehensive Nuclear-Test Ban Treaty Organization (CTBTO) under U.N. announced the body wave magnitude of the event was mb 6.1 while U.S. Geological Survey (USGS)'s calculation was mb 6.3. In this study, the differences of the magnitude estimates were investigated and verified. For this purpose, a source scaling between the $5^{th}$ and $6^{th}$ event, which's epicenters are 200 meters apart, was performed using seismic data sets from 30 broadband stations. The relative amplitude variations of the $6^{th}$ event compared to the $5^{th}$ event in the frequency domain was analyzed through the scaling. The increased amount of the bodywave magnitude $m_b$ for the $6^{th}$ event was calculated at 1 Hz, which was compared to those from USGS and CTBTO's calculations.

북한은 대한민국 지역시간으로 2017년 9월 3일 12시 30분 함경북도 길주군 풍계리 핵실험장에서 6차 지하핵실험을 실시하였다. 북한 6차 핵실험의 실체파 규모 측정에 있어서 미국지질조사국은 $m_b$ 6.3으로 발표한 반면 UN 산하 포괄적핵실험금지조약기구는 $m_b$ 6.1로 발표하여 상이한 값을 제시하였다. 본 연구에서는 이러한 규모의 차이를 규명하고 규모계산을 검증하고자 하였다. 이를 위해 진앙이 200 m 상호 이격된 5차 핵실험과 6차 핵실험의 지진원 상대비율을 30개 광대역 지진관측소 자료를 이용하여 측정하였다. 지진원 상대비율 측정을 통해 5차 핵실험에 대비한 6차 핵실험의 진폭변화가 주파수 영역에서 어떠한 양상을 보이는지 분석하고 실체파 규모 계산의 기준이 되는 1 Hz에서의 실체파 규모 $m_b$의 증가량을 계산하였고 이를 미국지질조사국과 포괄적핵실험금지조약기구에서 발표한 북한 5차 핵실험 대비 6차 핵실험의 실체파 규모 증가량과 비교하였다.

Keywords

JOHGB2_2018_v51n6_589_f0001.png 이미지

Fig. 1. The location of the 30 Broadband stations used for source scaling is illustrated with blue triangle. The black square represents DRPK‘s Punggye-ri underground nuclear test site.

JOHGB2_2018_v51n6_589_f0002.png 이미지

Fig. 2. An example of seismic waveform pairs from DPRK’s 5th and 6th underground nuclear tests is shown, which was the recording at the station CHNB. Top trace is the waveform recorded from the 5th test while bottom trace is the one from the 6th test. First 6.4 seconds of waveform is chosen for power spectrum calculation.

JOHGB2_2018_v51n6_589_f0003.png 이미지

Fig. 3. Source scaling result is illustrated. Spectral ratios in green represent source scaling of the 30 pairs of vertical component from the 30 broadband stations while the ensemble median of these is shown with red.

Table 1. Bodywave magnitude (mb) estimates on the DPRK’s 5th an 6th nuclear tests

JOHGB2_2018_v51n6_589_t0001.png 이미지

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