한국지구과학회지 (Journal of the Korean earth science society)

  • 제28권2호
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  • Pages.187-201
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  • 2007
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  • 1225-6692(pISSN)
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  • 2287-4518(eISSN)
한국지구과학회 (The Korean Earth Science Society)
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한반도 횡단 자기지전류 탐사에 의한 상부 지각의 지전기적 구조 연구

Study on the Geoelectrical Structure of the Upper Crust Using the Magnetotelluric Data Along a Transect Across the Korean Peninsula

  • 이춘기 (서울대학교 지구과학교육과) ;
  • 권병두 (서울대학교 지구과학교육과) ;
  • 이희순 (경인교육대학교 과학교육과) ;
  • 조인기 (강원대학교 지구물리학과) ;
  • 오석훈 (강원대학교 지구시스템공학과) ;
  • 송윤호 (한국지질자윈연구원 지열자원연구실) ;
  • 이태종 (한국지질자윈연구원 지열자원연구실)
  • Lee, Choon-Ki (Department Earth Science Education, Seoul National University) ;
  • Kwon, Byung-Doo (Department Earth Science Education, Seoul National University) ;
  • Lee, Heui-Soon (Department Science Education, Gyeongin National University of Education) ;
  • Cho, In-Ky (Department Geophysics, Kangwon National University) ;
  • Oh, Seok-Hoon (Department Geosystem Engineering, Kangwon National University) ;
  • Song, Yoon-Ho (Geothermal Resources Group, Korea Institute of Geoscience and Mineral Resources) ;
  • Lee, Tae-Jong (Geothermal Resources Group, Korea Institute of Geoscience and Mineral Resources)
  • 발행 : 2007.04.30
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초록

한반도에서는 처음으로 동해안으로부터 서해안까지 한반도를 횡단하는 측선을 따라 자기지전류 탐사를 수행하였다. 한반도의 주된 지구조 방향인 지나방향$(N30^{\circ}E)$에 수직하게 설정된 240 km 측선을 따라 $3{\sim}8km$의 측점 간격으로 50 측점에서 자료를 획득하였다. MT 임피던스는 지역에 따라 뚜렷이 구분되는 반응이 나타나며 경기육괴, 옥천대, 경상분지 서쪽 지역, 경상분지 동쪽지역에서 각기 다른 경향의 반응을 보인다. 경상분지 서쪽 지역에서는 수백 ohm-m의 전기비저항과 $3{\sim}8km$의 두께를 가지는 퇴적층이 존재하며, 퇴적층 하부에서 $1{\sim}30$ ohm-m의 매우 낮은 전기비저항을 가지는 고전도층이 발견되었다. 옥천대에서의 자료는 위상이 $90^{\circ}$를 초과하는 매우 특이한 반응을 보이고 있으며 이러한 특이성은 매우 강한 이방성 매질의 영향에 기인하는 것으로 추정된다. 경기 육괴와 경상분지 동쪽 지역은 상부지각을 구성하는 매질이 비교적 높은 전기비저항을 가지는 매질로 이루어져있기 때문에 심부 지전기 구조를 들여다 볼 수 있는 창의 역할을 한다. 1차원 모델을 적용하였을 때 경기육괴의 경우 13 km, 경상분지 동쪽지역의 경우 18 km 두께를 가지는 층이 존재하는데 이 층이 상부지각에 해당하는 것으로 생각된다.

The first magnetotelluric (MT) transect across the Korean Peninsula was obtained traversing from the East Sea shoreline to the Yellow Sea shoreline. The MT survey profile was designed perpendicular to the strike of the principal geologic structure of the Korean Peninsula $(N30^{\circ}E)$, so-called 'China direction'. MT data were achieved at 50 sites with spacings of $3{\sim}8km$ along the 240 km survey line. The impedance responses are divided into four subsets reflecting typical geological units: the Kyonggi Massif, the Okchon Belt, the western part of the Kyongsang Basin, and the eastern part of the Kyongsang Basin. In the western part of the Kyongsang Basin, the thickness of the sedimentary layer is estimated to be about 3 km to 8 km and its resistivity is a few hundred ohm-m. A highly conductive layer with a resistivity of 1 to 30 ohm-m was detected beneath the sedimentary layer. The MT data at the Okchon Belt show peculiar responses with phase exceeding $90^{\circ}$. This feature may be explained by an electrically anisotropic structure which is composed of a narrow anisotropic block and an anisotropic layer. The Kyonggi Massif and the eastern part of Kyongsang Basin play a role of window to the deep geoelectrical structure because of the very high resistivity of upper crust. The second layers with highest resistivities in 1-D conductivity models occupy the upper crust with thicknesses of 13 km in the Kyonggi Massif and 18 km in the eastern Kyongsang Basin, respectively.

키워드

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