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

Abstract

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.

References

  1. 권병두, 황희승, 1991, 부평 칼데라의 중력 연구, 한국지구과학회지, 12, 225-265
  2. 권병두, 권재현, 정호준, 1994, 진례칼데라의 중력이상과 지질구 조, 한국지구과학회지, 15, 392-397
  3. 권병두, 권재현, 정호준, 1995, 의성지역 금성산 칼데라와 그 부 근의 지질구조와 중력 특성, 지질학회지, 31, 125-137
  4. 박계순, 이희순, 오석훈, 권병두, 양준모, 류희영, 최종근, 2007, 의성소분지 화산 칼데라 지역에서의 복합지구물리탐사 해석, 2007년도 대한자원환경지질학회 춘계학술대회, 경주, 100- 102
  5. 엄주영, 2007, 중력과 MT 방법을 이용한 화산 칼데라의 지하구 조 연구, 서울대학교 석사학위논문
  6. 유상훈, 황종선, 민경덕, 우익, 2005, 중력, 자력 및 위성영상 자료를 이용한 의성소분지의 지질 및 지구조 연구, 자원환경지질, 38, 143-153
  7. 윤성효, 1988, 화산 환상화성암복합체의 발달사 및 콜드론구조, 지질학회지, 24, 267-288
  8. 유철, 1996, 경북 군위군 화산 칼데라에 대한 중력 및 자력탐사 연구, 연세대학교 석사학위논문
  9. 이정민, 1995, 화산 칼데라의 지하구조와 중력특성, 서울대학교 석사학위논문
  10. 이춘기, 2006, 자기지전류 탐사를 이용한 한반도 심부 지전기 구 조 연구, 서울대학교 박사학위논문
  11. 원종관, 윤선, 소칠섭, 1980, 한국지질도 신령도폭, 자원개발 연구소
  12. 장기홍, 1978, 경상분지의 층서, 퇴적 및 지구조(II), 지질학회지, 14, 120-135
  13. 장기홍, 이유대, 이영길, 서승조, 오규영, 이창훈, 1984, 경상속 유천층군의 부정합, 지질학회지, 20, 41-50
  14. 장기홍, 박순옥, 1997, 경상분지 중앙부의 구조발달사와 화산활 동사, 자원환경지질, 30, 143- 151
  15. Aramaki, S., 1992, Underground structures of the Japanese late Pleistocene calderas are mostly funnel-shaped, 29th IGC, Kyoto, Japan
  16. Bahr, K., 1991, Geological noise in magnetotelluric data: a classification of distortion types, Physics of the Earth and Planetary Interiors, 66, 24-38 https://doi.org/10.1016/0031-9201(91)90101-M
  17. Barberi, F., Cassano E., Torre La P., and Sbrana A., 1991, Structural evolution of Campi Flegrei caldera in light of volcanological and geophysical data, Journal of volcanology and geothermal research, 48, 33-49 https://doi.org/10.1016/0377-0273(91)90031-T
  18. Berdichevsky, M. N., Dmitrieve, V. I., and Pozdnjakova, E. E., 1998, On two-dimensional interpretation of magnetotelluric soundings, Geophysical Journal International, 133, 585-606 https://doi.org/10.1046/j.1365-246X.1998.01333.x
  19. Davy, B. W. and Caldwell, T. G., 1998, Gravity, magnetic and seismic surveys of the caldera complex, Lake Taupo, North Island, New Zealand, Journal of volcanology and geothermal research, 81, 69-89 https://doi.org/10.1016/S0377-0273(97)00074-7
  20. Groom, R. W., and Bailey, R. C., 1989, Decomposition of magnetotelluric impedance tensors in the presence of local three-dimensional galvanic distortion, Journal of Geophysical Research, 94, 1913-1925 https://doi.org/10.1029/JB094iB02p01913
  21. Groom, R. W., and Bailey, R. C., 1991, Analytic investigation of the effects of near-surface three-dimensional galvanic scatters on MT tensor decompositions, Geophysics, 56, 496- 518 https://doi.org/10.1190/1.1443066
  22. Harayama, S., 1992, Structure and collapse timing of deeply dissected calderas in the Japan Alps, central Japan, 29th IGC, Kyoto, Japan
  23. Hunt, T. M., 1992, Gravity anomalies, caldera structure, and subsurface geology in the Rotorua area, New Zealand, Geothermics, 21, 65-74 https://doi.org/10.1016/0375-6505(92)90068-K
  24. Jiracek, G. R., 1990, Near-surface and topographic distortion in electomagnetic induction, Survey in Geophysics, 11, 163-203 https://doi.org/10.1007/BF01901659
  25. Jones, A. G. 1988, Static shift of magnetotelluric data and its removal in a sedimentary basin environment, Geophysics, 53, 967-978 https://doi.org/10.1190/1.1442533
  26. McNeice, G. W., and Jones, A. G., 2001, Multisite, multifrequency tensor decomposition of magnetotelluric data, Geophysics, 66, 158-173 https://doi.org/10.1190/1.1444891
  27. Park, S., K., and Torres-Verdín, Carlos, 1988, A systematic approach to the interpretation of magnetotelluric data in volcanic environments with applications to the quest of magma in Long Valley, California, Journal of Geophysical Research, 93, 13265-13283 https://doi.org/10.1029/JB093iB11p13265
  28. Pous, J., Heise, W., Schnegg, P., Munoz, G., Marti, J., and Soriano, C., 2002, Magnetotelluric study of the Las Canadas caldera (Tenerife, Canary Island): structural and hydrogeological implications, Earth and Planetary Science Letters, 204, 249-263 https://doi.org/10.1016/S0012-821X(02)00956-1
  29. Rodi and Mackie, 2001, Nonlinear conjugate gradients algorithm for 2D magnetotelluric inversion, Geophysics, 66, 174-187 https://doi.org/10.1190/1.1444893
  30. Santos, F., Trota, A., Soares, A., Luzio, R., Lourenco, N., Matos, L., Almeida, E., Gaspar J., and Miranda, J., 2006, An audio-magnetotelluric investigation in Terceira Island (Azores), Journal of applied geophysics, 59, 314-323 https://doi.org/10.1016/j.jappgeo.2005.12.001
  31. Swift, C. M., 1967, A magnetotelluric investigation of an electrical conductivity anomaly in the southwestern United States, Ph. D thesis, MIT
  32. Tauber, S., Banks, R., Ritter, O., and Weckmann, U., 2003, A high-resolution magnetotelluric survey of the Iapetus Suture Zone in south-west Scotland, Geophysical Journal International, 153, 548-568 https://doi.org/10.1046/j.1365-246X.2003.01912.x
  33. Telford, W. M. Geldart, L. P., Sheriff, R. E., and Keys, D. A., 1976, Applied geophysics, Cambridge Univ. Press
  34. Unsworth, M. J., Egbert, G., and Booker, J., 1999, Highresolution electromagnetic imaging of the San Andreas fault in Central California, Journal of Geophysical Research, 105, 1131-1150
  35. Wannermaker, P. E., Booker, J. R., Jones, A. G., Chave, A. D., Filloux, J. H., Waff, H. S., and Law, L. K., 1989, Resistivity cross-section through the Juan de Fuca subduction system and its tectonic implication, Journal of Geophysical Research, 94, 14127-14144 https://doi.org/10.1029/JB094iB10p14127
  36. Yokoyama, I., and Ohkawa, S., 1986, The subsurface structure of the Aira caldera and its vicinity in southern Kyushu, Japan, Journal of volcanology and geothermal research, 30, 253- 282 https://doi.org/10.1016/0377-0273(86)90057-0
  37. Yokoyama, I., and Mena, M., 1991, Structure of La primavera caldera, Jalisco, Mexico, deduced from gravity anomalies and drilling results, Journal of volcanology and geothermal research, 47, 183-193 https://doi.org/10.1016/0377-0273(91)90108-C