Geophysical Study on the Geoelectrical Structure of the Hwasan Caldera in the Euisung Sub-basin Using Magnetotelluric Survey

자기지전류 탐사를 이용한 의성소분지 화산 칼데라의 지구물리학적 연구

  • Yang, Jun-Mo (Marine Resource Research Division, Korea Ocean Research and Development Institute) ;
  • Kwon, Byung-Doo (Department of Earth Science Education, Seoul National University) ;
  • Cho, In-Ky (Department of Geophysics, Kangwon National University) ;
  • Lee, Heui-Soon (Department of Science Education, Gyeongin National University of Education) ;
  • Park, Gye-Soon (Department of Earth Science Education, Seoul National University) ;
  • Um, Joo-Young (Department of Earth Science Education, Seoul National University)
  • 양준모 (한국해양연구원 해양자원연구본부) ;
  • 권병두 (서울대학교 지구과학교육과) ;
  • 조인기 (강원대학교 지구물리학과) ;
  • 이희순 (경인교육대학교 과학교육과) ;
  • 박계순 (서울대학교 지구과학교육과) ;
  • 엄주영 (서울대학교 지구과학교육과)
  • Published : 2008.05.31


To extend our detailed knowledge for the Hwasan caldera, we carried out magnetotelluric (MT) survey, which is pretty sensitive to electrical property variation in both horizontal and vertical direction of subsurface, across the Hwasan caldera with the direction of EW. The 2-D inversion results of observed MT data lead to following conclusions. Firstly, the depth of the basin basement inferred by the MT inversion results matches well with that suggested by previous potential studies, but the basement resistivity seems fairly low when compared to that of general case. This feature might be related with the large-scaled, highly conductive layer beneath the Euisung Sub-basin suggested by the previous MT study. Secondly, the high resistivity zones reaching to 4000 $\Omega{\cdot}m$ are imaged around two external ring fault boundaries. These zones are thought of as the response of the rhyolitic dykes intruding along the ring fault, and in the previous gravity data correspond to relatively high density anomalies. Thirdly, low resistivity zone reaching to 200 $\Omega{\cdot}m$ is detected around a depth of 1km beneath the central part of the caldera, which has not been yet reported in korean geophysical literatures. If we take account of the evolution model of the Hwasan caldera, this zone is regarded as the past sedimentary layer that subsided during the period of forming external ring fault system. In addition, the relatively low density anomaly observed in the central part of the caldera may be attributed to this sedimentary layer.


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