Geophysics and Geophysical Exploration (지구물리와물리탐사)

Korean Society of Earth and Exploration Geophysicists (한국지구물리·물리탐사학회)
권호 표지
DOI QR코드

DOI QR Code

Distribution of Electrically Conductive Sedimentary Layer in Jeju Island Derived from Magnetotelluric Measurements

MT 탐사자료를 이용한 제주도 지역의 전도성 퇴적층 분포 연구

  • Received : 2013.12.13
  • Accepted : 2014.02.10
  • Published : 2014.02.28
Download PDF
⟨ Previous Next ⟩

Abstract

We investigate the spatial distribution of highly conductive layer using the one-dimensional inversions of the new magnetotelluric (MT) measurements obtained at the mid-mountain (400 ~ 900 m in elevation) western area of Jeju Island and the previous MT data over Jeju Island, Korea. The conductive layer indicates the sedimentary layer comprised of Seoguipo Fomation and U Formation. There is a definite positive correlation between the top of conductive layer and the earth surface in elevation. On the contrary, the bottom of conductive layer has a negative correlation with the surface elevation. In other words, the conductive layer has a shape of convex lens, which is thickest in the central part. The basement beneath the conductive layer could be concave in the central part of Jeju Island. A kriging considering the correlation between the layer boundary and the surface elevation provides a reliable geoelectric structure model of Jeju Island. However, further studies, i.e. three-dimensional modeling and interpretation integrated with other geophysical or logging data, are required to reveal the possible presence of three-dimensional conductive body near the subsurface vent of Mt. Halla and the causes of the bias in the depths of layer estimated from MT and core log data.

최근 제주도 서부 중산간(해발고도 400 ~ 900 m) 지역에서 획득된 자기지전류(MT) 탐사자료와 제주도 중산간 전역에서 획득되었던 기존 MT 탐사 자료의 1차원 역산을 통하여 서귀포층과 U층으로 대표되는 퇴적층에 해당하는 저비 저항층의 분포형태를 살펴보았다. 저비저항층의 상부경계는 제주도 표고와 매우 높은 양의 상관관계를 가지고 있으며 하부경계는 표고와 음의 상관관계를 가진다. 즉, 저비저항층은 제주도 중앙부에서 두꺼운 렌즈 형태를 하고 있으며 그 하부의 기반암은 중앙부에서 오목한 형태일 가능성이 높다. 이러한 표고와의 상관성을 고려하는 크리깅을 수행하여 제주도의 지전기 구조 모델을 제시하였다. 하지만 한라산의 화도를 따라 3차원 형태의 저비저항 이상체가 존재할 가능성과 시추공 자료와의 차이를 발생시키는 원인을 규명하기 위하여 3차원 모델링과 다른 지구물리탐사나 물리검층 자료와의 복합해석이 요구된다.

Keywords

References

  1. Berdichevsky, M. N., Vanyan, L. L., and Dmitriev, V. I., 1989, Methods used in the U.S.S.R to reduce near-surface inhomogeneity effects on deep magnetotelluric sounding, Phys. Earth Planet. Inter., 53, 194-206. https://doi.org/10.1016/0031-9201(89)90003-4
  2. Cleveland, and William, S., 1979, Robust Locally Weighted Regression and Smoothing Scatterplots, Journal of the American Statistical Association, 74, 829-836. https://doi.org/10.1080/01621459.1979.10481038
  3. Goovaert, P. 1997, Geostatistics for Natural Resources Evaluation, Applied Geostatistics Series. xiv +, New York, Oxford.
  4. Jones, A., 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
  5. Koh, G. W., 1997, Characteristics of the groundwater and hydrogeologic implications of the Seoguipo Formation in Cheju Island, Ph. D. Thesis, Pusan National University, 325p.
  6. Koh, G. W., Park, J. B., Kang, B. R., Kim, G. P., and Moon, D. C., 2013, Volcanism in Jeju Island. Journal of the Geological Society of Korea, 49, 209-230.
  7. Kwon, B.D., Lee, H., Jung, G., and Jung, S., 1995, Investigation of subsurface structure of Cheju Island by gravity and magnetic methods, Econ. Environ. Geol., 28, 395-404.
  8. Lee, H., 1994, Geophysical study of subsurface structure of Cheju Island, Ph. D. Thesis, Seoul National University, 172p.
  9. Lee, T. J., Lee, S. K., Lee, C. K., Park, I. H., Song, Y., and Uchida, T., 2008, Two-dimensional Magnetotelluric Surveys for investigating possible deep geothermal regime in the midmoutain area of Jeju Island, The Korean Society Mineral and Energy Resources Engineers, 45, 315-325.
  10. Lee, T. J., Nam, M. J., Lee, S. K., Song, Y., and Uchida, T., 2009. The Jeju dataset: Three-dimensional interpretation of MT data from mid-mountain area of Jeju Island, Korea. J. Appl. Geophys., 68, 171-181. https://doi.org/10.1016/j.jappgeo.2008.11.006
  11. Likelybrooks, D. W., 1986. Modeling earth resistivity structure for MT data: A comparison of rotationally invariant and conventional earth response functions (abstact), EOS Trans. AGU, 67, 918.
  12. Nam, M. J., Kim, H. J., Song, Y., Lee, T. J., and Suh, J. H., 2009, Three-dimensional topographic and bathymetric effects on magnetotelluric responses in Jeju Island, Korea, Geophys. J. Int., 176, 457-466. https://doi.org/10.1111/j.1365-246X.2008.03993.x
  13. Oh, J., Yi, S., Yoon, S., Koh, G. W., Yun, H., and Lee, J. D., 2000, Subsurface stratigraphy of Jeju Island. Journal of the Geological Society of Korea, 36, 181-194.
  14. Weaver, J. T., and Agarwal, A. K., 1993, Automatic 1-D inversion of magnetotelluric data by the method of modeling, Geophys. J. Int., 112, 115-123. https://doi.org/10.1111/j.1365-246X.1993.tb01441.x
  15. Yang, J., Min, D. J., and Yoo, H. S., 2010. Sea effect correction in magnetotelluric (MT) data and its application to MT soundings carried out in Jeju Island, Korea, Geophys. J. Int., 182, 727-740. https://doi.org/10.1111/j.1365-246X.2010.04676.x
  16. Yang, J., Lee, C. K., Min, D., Lee, H., and Lee, T. J., 2012, 1-D crustal resistivity structure revealed by sea effect corrected magnetotelluric (MT) data obtained at Jeju Island, Korea, Journal of Applied Geophysics, 76, 92-101. https://doi.org/10.1016/j.jappgeo.2011.10.011