Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
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Gravity Field Interpretation for the Deep Geological Structure Analysis in Pohang-Ulsan, Southeastern Korean Peninsula

한반도 남동부 포항-울산지역 심부 지질구조 분석을 위한 중력장 해석

  • Sohn, Yujin (Department of Geology, College of Natural Sciences, Kyungpook National University) ;
  • Choi, Sungchan (Department of Geology, College of Natural Sciences, Kyungpook National University) ;
  • Ryu, In-Chang (Department of Geology, College of Natural Sciences, Kyungpook National University)
  • 손유진 (경북대학교 자연과학대학 지질학과) ;
  • 최승찬 (경북대학교 자연과학대학 지질학과) ;
  • 유인창 (경북대학교 자연과학대학 지질학과)
  • Received : 2020.07.22
  • Accepted : 2020.09.22
  • Published : 2020.10.28
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Abstract

Even after the Gyeongju earthquake and the Pohang earthquake, hundreds of aftershocks and micro-earthquakes are still occurring in the southeastern part of the Korean Peninsula. These phenomena mean that the stress is constantly working, implying that another huge earthquake may occur in the future. Therefore, the gravity field interpretation method was used to analyze the deep geological structure of the Pohang-Ulsan region in the southeastern Korean Peninsula. First, a gravity survey was performed to collect the insufficient data and to calculate the detailed Bouguer gravity anomaly in the study area. Based on the gravity anomaly data, the location, direction, and maximum depth of deep fault lines were analyzed using the inversion methods "Curvature analysis" and "Euler deconvolution method". As a result, it is interpreted that at least six fault lines(C1~C6) exist in deep depth. The deep fault line C1 is well correlated to the Yeonil Tectonic Line(YTL), suggesting that YTL is extended up to about 4000m deep. The deep fault line C2 consists of several segment faults and well correlated to the fault lines on the surface. Inferred fault lines C3, C4, and C5 have an NW-SE direction, which is parallel to the Ulsan fault. The deep fault line C6 has the direction of NE-SW, and it is interpreted that the eastern boundary fault of Eoil Basin is extended to the deep. Comparing the inferred fault lines with the distribution of micro-earthquakes, the location of the deep fault line C1 is well correlated to the hypocenter of micro-earthquakes. This implies that faults in deep depth are related to the recent earthquakes in the southeastern Korean Peninsula.

규모 5 이상의 경주지진과 포항지진이 발생한 이후에도 한반도 남동부에서는 여전히 수백 건의 여진과 미소 지진이 발생하고 있다. 이러한 현상은 응력이 계속 작용하고 있다는 것을 의미하며, 또 다른 큰 지진이 발생할 수도 있음을 암시한다. 따라서 본 연구에서는 한반도 남동부 포항-울산지역의 심부 지질구조를 분석하기 위해 중력장 해석 방법을 사용하였다. 먼저 연구지역의 부족한 중력 데이터를 수집하기 위해, 중력 탐사를 시행하여 기존 자료보다 정밀한 부게 중력이상을 계산하였다. 중력이상 데이터를 바탕으로 역산 방법인 "곡률 분석 (Curvature analysis)"과 "오일러 곱풀기 방법(Euler deconvolution method)"을 이용하여, 한반도 남동부의 심부 단층의 위치 및 방향성과 최대 깊이를 분석하였다. 그 결과, 본 연구지역에는 최소 6개의 심부 단층(C1~C6)이 존재하는 것으로 해석된다. 심부 단층선 C1은 방향성과 위치가 연일구조선과 일치하는 것으로 보아, 연일구조선이 최대 약 4000m 깊이까지 이어져 있는 것으로 해석된다. 심부 단층선 C2는 여러 개의 분절된 단층들로 이루어져 있으며, 지표의 단층들과 잘 대비된다. 심부 단층선 C3, C4와 C5는 북서-남동 방향의 울산단층과 평행한 방향성을 가지는 것으로 분석되며, 초기 백악기에 남북 방향의 응력을 받아 형성되었으나 퇴적물에 덮여 지표에 드러나지 않는 것으로 판단된다. 심부 단층선 C6는 북동-남서 방향성을 가지며, 어일분지의 동쪽 경계단층이 심부로 이어져 있는 것으로 사료된다. 분석한 심부 단층선과 미소 지진 발생 현황을 대비한 결과, 심부 단층선 C1과 2018년~2019년 동안 한반도 남동부에서 발생한 미소 지진의 분포가 대략 일치하는 것을 확인하였다. 이는 심부에 존재하는 단층과 최근 발생하는 지진이 연관이 있다는 것을 시사한다.

Keywords

References

  1. 기상청 (2017) 9.12 지진 대응보고서, 140p.
  2. 기상청 (2018) 포항지진 분석 보고서, 41p.
  3. Cheon, Y., Son, M., Song, C.W., Kim, J.-S. and Sohn, Y.K.(2012) Geometry and kinematics of the Ocheon Fault System along the boundary between the Miocene Pohang and Janggi basins, SE Korea, and its tectonic implications. Geoscience Journal, v.16, p.253-273. https://doi.org/10.1007/s12303-012-0029-0
  4. Choi, S.C., Gotze, H.J., Meyer, U. and DESIRE Group (2011) 3-D density modelling of underground structures and spatial distribution of salt diapirism in the Dead Sea Basin. Geophysical Journal International, v.184(3), p.1131-1146. https://doi.org/10.1111/j.1365-246X.2011.04939.x
  5. Choi, S.C., Oh, C.-W. and Gotze, H.J.(2013) Threedimensional density modeling of the EGM2008 gravity field over the Mount Paekdu volcanic area. Journal of Geophysical Research, v.118(7), p.3820-3836. https://doi.org/10.1002/jgrb.50266
  6. Choi, S.C., Ryu, I.C. and Gotze, H.J.(2015) Depth distribution of the sedimentary basin and Moho undulation in the Yellow Sea, NE Asia interpreted by using satellite-derived gravity field. Geophysical Journal International, v.202, p.41-53. https://doi.org/10.1093/gji/ggv108
  7. Choi, S.C., Ryu, I.C., Gotze, H.-J. and Chae, Y. (2017) Spatial distribution of hydrocarbon reservoirs in the West Korea Bay Basin in the northern part of the Yellow Sea, estimated by 3-D gravity forward modelling. Geophysical Journal International, v.208, p.75-85. https://doi.org/10.1093/gji/ggw369
  8. Choi, S.C. and Ryu, I.C. (2018) Spatial distribution of hydrocarbon reservoirs in the West Korea Bay Basin in the northern part of the Yellow Sea, estimated by 3D gravity forward modeling. Journal of the Geological Society of Korea, v.54(6), p.641-656 (in Korean with English abstract). https://doi.org/10.14770/jgsk.2018.54.6.641
  9. Choi, S.C., Ryu, I.C. and Lee, Y.C. (2019) An analysis of the intraplate Earthquake(2016M5.8 GY) that occurred in the Gyeongsang Basin in the SE of the Korean Peninsula, based on 3D modelling of the gravity and magnetic Field. Geophysical Journal International, v.217, p.90-107. https://doi.org/10.1093/gji/ggz001
  10. Choi, S.C., Ryu, I.C., Lee, Y.C, Son, Y.J. (2020) Gravity and magnetic field interpretation to detect deep buried paleobasinal fault lines contributing to intraplate earthquakes: a case study from Pohang Basin, SE Korea. Geophysical Journal International, v.220, p.490-500. https://doi.org/10.1093/gji/ggz464
  11. Gim, J.H, Jeong, J.O., Gihm, Y.S., Gu, H.C. and Sohn, Y.K. (2016) Depositional environments and processes of the subsurface dacitic volcanic clastic deposits in the Miocene Janggi Basin, SE Korea. Journal of the Geological Society of Korea, v.52(6), p.775-798 (in Korean with English abstract). https://doi.org/10.14770/jgsk.2016.52.6.775
  12. Gotze, H.J. and Schmidt, S. (2002) Geophysical 3D modeling using GIS-Functions. 8th Annual Conference of the International Association for Mathematical Geology, Terra Nostra, p.87-92.
  13. Gu, H.C. and Hwang, I.G. (2017) Depositonal history of the Janggi Conglomerate controlled by tectonic subsidence, during the early stage of Janggi Basin evolution. Journal of the Geological Society of Korea, v.53(2), p.221-240 (in Korean with English abstract). https://doi.org/10.14770/jgsk.2017.53.2.221
  14. Gu, H.C., Gim, J.H. and Hwang, I.G. (2018) Variation in depositional environments controlled by tectonics and volcanic activities in the lower part of the Seongdongri Formation, Janggi Basin. Journal of the Geological Society of Korea, v.54(1), p.21-46 (in Korean with English abstract). https://doi.org/10.14770/jgsk.2018.54.1.21
  15. Jung, S., Kim, M.S., Cho, H., Son, M. and Sohn, Y.K. (2012) Basin fills and geological structures of the Miocene Yangpo subbasin in the Janggi-myeon, Pohang, SE Korea. Journal of the Geological Society of Korea, v.48, p.49-68 (in Korean with English abstract).
  16. KIGAM (2014) Regoinal geophysical anomaly mapping, GP2013-020-2014(2) published by Korea Institute of Geology, Mining and Materials(in Korean with English abstract).
  17. Kim, M.-C., Kim, J.-S., Jung, S., Son, M. and Sohn, Y.K. (2011) Biomodal volcanism and classification of the Miocene basin fills in the northern area of the Janggimyeon, Pohang, SE Korea. Journal of the Geological Society of Korea, v.47, p.585-612 (in Korean with English abstract).
  18. Kim, M.-C., Gihm, Y.S., Son, E.-Y., Son, M., Hwang, I.G., Shinn, Y.J. and Choi, H. (2015) Assessment of the potential for geological storage of $CO^2$ based on structural and sedimentologic characteristics in the Miocene Janggi Basin, SE Korea. Journal of the Geological Society of Korea, v.51(3), p.253-271 (in Korean with English abstract). https://doi.org/10.14770/jgsk.2015.51.3.253
  19. Korean Government Commission on the Cause of the Pohang Earthquake. (2019) Final report of the Korean Government Commission on Relations between the 2017 Pohang Eathquake and EGS Project, 457p.
  20. Lee, H., Kim, J.C., Ko, K., Ghim, Y.S., Kim, J. and Lee, S.R. (2018) Characteristics of sand volcanoes caused by 2017 Pohang Earthquake-induced liquefaction and their paleoseismological approach. Journal of the Geological Society of Korea, v.54(3), p.221-235 (in Korean with English abstract). https://doi.org/10.14770/jgsk.2018.54.3.221
  21. Lee, Y.C. (2008) Precise geoid and gravity anomaly in and around Jeju island. Ph.D. thesis, Pusan National University, Pusan, 143p (in Korean).
  22. Longman, I.M. (1959) Formulas for computing the tidal accelerations due ro Moon and Sun. Journal of Geophysical Research, v.64, p.2351-2355. https://doi.org/10.1029/JZ064i012p02351
  23. Park. J.M., Kim, H.C., Lee, Y., Shim, B.O. and Song, M.Y. (2009) Thermal properties of rocks in the republic of Korea. The Korean Society of Economic and Environmental Geology, v.42(6), p.591-598 (in Korean with English abstract).
  24. Pasteka, R., Richter, F.P., Karcol, R., Brazda, K. and Hajach, M. (2009) Regularized derivatives of potential fields and their role in semi-automated interpretation methods. Geophysical Prospecting, v.57(4), p.507-516. https://doi.org/10.1111/j.1365-2478.2008.00780.x
  25. Reid, A.B., Allsop, J.M., Granser, H., Millet, A.T. and Somerton, I.W. (1990) Magnetic interpretation in three dimensions using Euler deconvolution. Geophysics, v.55(1), p.80-91. https://doi.org/10.1190/1.1442774
  26. Roberts, A. (2001) Curvature attributes and their application to 3D interpreted horizons. First Break, v.19(2), p.85-100. https://doi.org/10.1046/j.0263-5046.2001.00142.x
  27. Ryu, I.-C., Choi, S.-G. and Wee, S.-M. (2006) An Inquiry into the Formation and Deformation of the Cretaceous Gyeongsang (Kyongsang) Basin, Southeastern Korea, The Korean Society of Economic and Environmental Geology, v.39(2), p.129-149 (in Korean with English abstract).
  28. Son, M., Kim, J.-S., Chong, H.-Y., Lee, Y.-H. and Kim, I.S. (2007) Characteristics of the Cenozoic crustal deformation in SE Korea and their tectonic implications, The Korean Journal of Petroleum Geology, v.13, p.1-16 (in Korean with English abstract).
  29. Son M., Song, C.W., Kim, M.C., Cheon, Y.B., Jung, S., Cho, H., Kim, H.G., Kim, J.S. and Sohn, Y.K. (2013) Miocene Crustal Deformation, Basin Development, and Tectonic Implication in the Southeastern Korean Peninsula. Journal of the Geological Society of Korea, v.49(1), p.93-118(in Korean with English abstract).
  30. Son, M., Song, C.W., Kim, M.-C., Ceon, Y., Cho, H. and Sohn, Y.K. (2015) Miocene tectonic evolution of the basins and fault systems, SE Korea: dextral, simple shear during the East Sea (Sea of Japan) opening. Journal of the Geological Society, v.172, p.664-680. https://doi.org/10.1144/jgs2014-079
  31. Shin, Y.H. and Ko, I.S. (2019) Gravity anomaly in the Taebaeksan mineralized zone. Journal of the Geological Society of Korea, v.55(4), p.403-413. (in Korean with English abstract) https://doi.org/10.14770/jgsk.2019.55.4.403
  32. Tamura, Y. (1982) A computer program for calculating the tide generation force. The publications of the international latitude observatory of Mizusawa, v.16, p.1-19.
  33. Thomson, D.T. (1982) EULDPH: A new technique for making computer-assisted depth estimates from magnetic data. Geophysics, v.47(1), p.31-37. https://doi.org/10.1190/1.1441278
  34. Yoo H.J., Herrmann R.B., Cho K.H. and Lee K. (2007), Imaging the three dimensional crust of the Korean Peninsula by joint inversion of surface-wave dispersion and teleseismic receiver functions. Bulletin of the Seismological Soceity of America, v.97(3), p.1002-1011. https://doi.org/10.1785/0120060134
  35. Yoon, S.H. and Chough, S.K. (1995) Regional strike slip in the eastern continental margin of Korea and its tectonic implications for the evolution of Ulleung Basin East Sea (Sea of Japan). Geological Society of America bulletin, v.107, p.83-97. https://doi.org/10.1130/0016-7606(1995)107<0083:RSSITE>2.3.CO;2
  36. Zhang, C., Mushayandebvu, M.F., Reid, A.B., Fairhead, J.D. and Odegard, M.E.(2000) Euler deconvolution of gravity tensor gradient data. Geophysics, v.65(2), p.512-520. https://doi.org/10.1190/1.1444745