Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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Optimization of Classification of Local, Regional, and Teleseismic Earthquakes in Korean Peninsula Using Filter Bank

주파수 필터대역기술을 활용한 한반도의 근거리 및 원거리 지진 분류 최적화

  • Lim, DoYoon (Earthquake and Volcano Research Division, KMA) ;
  • Ahn, Jae-Kwang (Earthquake and Volcano Research Division, KMA) ;
  • Lee, Jimin (Earthquake and Volcano Research Division, KMA) ;
  • Lee, Duk Kee (Earthquake and Volcano Research Division, KMA)
  • 임도윤 (기상청 지진화산연구과) ;
  • 안재광 (기상청 지진화산연구과) ;
  • 이지민 (기상청 지진화산연구과) ;
  • 이덕기 (기상청 지진화산연구과)
  • Received : 2019.11.06
  • Accepted : 2019.11.18
  • Published : 2019.11.30
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Abstract

An Earthquake Early Warning (EEW) system is a technology that alerts people to an incoming earthquake by using P waves that are detected before the arrival of more severe seismic waves. P-wave analysis is therefore an important factor in the production of rapid seismic information as it can be used to quickly estimate the earthquake magnitude and epicenter through the amplitude and predominant period of the observed P-wave. However, when a large-magnitude teleseismic earthquake is observed in a local seismic network, the significantly attenuated P wave phases may be mischaracterized as belonging to a small-magnitude local earthquake in the initial analysis stage. Such a misanalysis may be sent to the public as a false alert, reducing the credibility of the EEW system and potentially causing economic losses for infrastructure and industrial facilities. Therefore, it is necessary to develop methods that reduce misanalysis. In this study, the possibility of seismic misclassifying teleseimic earthquakes as local events was reviewed using the Filter Bank method, which uses the attenuation characteristics of P waves to classify local and outside Korean peninsula (regional and teleseismic) events with filtered waveform depending on frequency and epicenter distance. The data used in our analysis were analyzed for maximum Pv values using 463 events with local magnitudes (2 < ML ≦ 3), 44 (3 < ML ≦ 4), 4 (4 < ML ≦ 5), 3 (ML > 5), and 89 outside Korean peninsula earthquakes recorded by the KMA seismic network. The results show that local and telesesimic earthquakes can be classified more accurately when combination of filtering bands of No. 3 (6-12 Hz) and No. 6 (0.75-1.5 Hz) is applied.

지진조기경보는 빠르게 도달하는 P파를 감지하고 이보다 느리게 전파되는 S파가 도달하기 전 알림을 주는 기술이다. 초기에 도달한 P파의 진폭과 우세주기를 통해 신속하게 규모와 진원을 추정하고 이를 기준으로 경보 혹은 속보를 전송하기에 P파의 분석은 신속한 지진정보에 생산에 중요한 요소이다. 하지만, 국외에서 발생한 큰 규모의 지진이 국내 관측망에서는 P파의 진폭이 크게 감쇠되어 관측되며, 이는 초기 분석단계에서 실제 규모보다 작은 국내 발생 지진으로 오분석 될 수 있다. 오분석의 결과가 그대로 수요자(국민)에게 오경보(false alarm)로 발송될 경우 지진조기경보서비스의 신뢰도를 저하 시킬 수 있으며, 신속대응이 필요한 사회 인프라시설 및 산업시설에는 경제적 손실을 야기할 수 있다. 따라서 이러한 오분석을 최대한 줄이기 위한 기술개발이 필요한 실정이다. 본 연구에서는 주파수-이격거리에 따른 감쇠특성을 이용한 필터뱅크(Filter Bank)를 사용하여 국내외 지진에 대한 분류 가능성을 검토하였다. 이를 위해 기상청 지진관측소에 기록된 2 < ML ≦ 3의 국내지진 463개, 44개(3 < ML ≦ 4), 4개(4 < ML ≦ 5), 3개(ML > 5)와 국외지진 89개를 사용하여 각 주파수영역에 따른 최대 Pv값을 산정하고 이를 분석하였다. 분석결과, 기본 설정 값보다 3번(6-12Hz)과 6번(0.75-1.5Hz) 밴드를 사용할 때 국내외 지진을 정확하게 분류할 수 있는 것으로 나타났다.

Keywords

References

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