In CSAMT exploration, the using of the artificial sources not only improves the signal-to-noise ratio of the data, but also brings a series of distortion effects, such as shadow and source overprint effects. This paper attempts to introduce a distortion effect caused by the target in the survey area. Although it is often ignored, it always plagues the data interpretation. In CSAMT method, the primary current has determined direction due to the source. When the primary current encounters electrical interfaces, the induced charge will accumulate on it and generate local current, causing local distortion. The anomaly body stretches in the direction of the vertical primary current, and a false anomaly with opposite polarity appears on both sides of the target. If the direction of the primary current is different, the accumulation position of the induced charge is also different, which will result in different shapes of the anomalies in observed data. This paper confirms the existence of the distortion by taking four simple models as examples and explains it from the physical mechanism. On this basis, the paper summarizes the relationship between inversion and distortion. If our code can simulate the distortion effect in the forward, we do not need to remove it before the inversion. Otherwise, it must be removed.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Tax calculation will be finalised during checkout.
An Z, Di Q (2016) Investigation of geological structures with a view to HLRW disposal, as revealed through 3D inversion of aeromagnetic and gravity data and the results of CSAMT exploration. J Appl Geophys 135:204–211
An Z, Di Q, Fu C (2013a) Geophysical evidence through a CSAMT survey of the deep geological structure at a potential radioactive waste site at Beishan, Gansu, China. J Environ Eng Geophys 18(1):43–54
An Z, Di Q, Wang R (2013b) Multi-geophysical investigation of geological structures in a pre-selected high-level radioactive waste disposal area in Northwestern China. J Environ Eng Geophys 18(2):137–146
Avdeeva A, Moorkamp M, Avdeev D, Jegen M, Miensopust M (2015) Three-dimensional inversion of magnetotelluric impedance tensor data and full distortion matrix. Geophys J Int 202(1):464–481
Berdichevsky M, Dmitriev V (1976) Basic principles of interpretation of magnetotelluric sounding curves. Geoelectric and geothermal studies. Akademiai Kiado, Budapest, pp 165–221
Bibby H, Caldwell T, Brown C (2005) Determinable and non-determinable parameters of galvanic distortion in magnetotellurics. Geophys J Int 163(3):915–930
Di Q, Wang M, Shi K, Zhang G (2002) An applied study on prevention of water bursting disaster in mines with the high resolution V6 system. Chin J Geophys 45:787–792 (in Chinese with English abstract)
Di Q, Unsworth M, Wang M (2004) 2.5D CSAMT modeling with the finite element method over 2D complex earth media. Chin J Geophys 47:825–829 (in Chinese with English abstract)
Di Q, An Z, Fu C, Wang Z (2018) Imaging underground electric structure over a potential HLRW disposal site. J Appl Geophys 155:102–109
Fu C, Di Q, An Z (2013) Application of the CSAMT method to groundwater exploration in a metropolitan environmentGroundwater exploration with CSAMT. Geophysics 78(5):B201–B209
Goldstein M, Strangway D (1975) Audio-frequency magnetotellurics with a grounded electric dipole source. Geophysics 40(4):669–683
Groom R, Bailey R (1989) Decomposition of magnetotelluric impedance tensors in the presence of local three-dimensional galvanic distortion. J Geophys Res Solid Earth 94(B2):1913–1925
Jiracek G (1990) Near-surface and topographic distortions in electromagnetic induction. Surv Geophys 11(2–3):163–203
Jones A (2012) Distortion of magnetotelluric data: its identification and removal. The magnetotelluric method: theory and practice. Cambridge University Press, Cambridge, pp 219–302
Kuznetzov A (1982) Distorting effects during electromagnetic sounding of horizontally non-uniform media using an artificial field source. Earth Phys 18(1):130–137
Ledo J (2005) 2-D versus 3-D magnetotelluric data interpretation. Surv Geophys 26(5):511–543
Lei D, Fayemi B, Yang L et al (2017a) The non-static effect of near-surface inhomogeneity on CSAMT data. J Appl Geophys 139:306–315
Lei D, Di Q, Wu J, Wang X, Liu Y, Fayemi O, Luan X, Zhang W (2017b) Anti-interference test for the new SEP instrument: CSAMT study at Dongguashan Copper Mine, China. J Environ Eng Geophys 22(4):339–352
Li X, Bai D, Yan Y (2016) Three-dimensional inversion of magnetotelluric resistivity model with galvanic distortion. Chin J Geophys 59(6):2302–2315 (in Chinese with English abstract)
MacLennan K, Li Y (2013) Denoising multicomponent CSEM data with equivalent source processing techniques. Geophysics 78(3):E125–E135
Nabighian M (1991) Electromagnetic methods in applied geophysics. Society of Exploration Geophysicists, Oklahoma
Neukirch M, Rudolf D, Garcia X, Galiana S (2019) Amplitude-phase decomposition of the magnetotelluric impedance tensorMT amplitude-phase decomposition. Geophysics 84(5):E301–E310
Neukirch M, Galiana S, Garcia X (2020) Appraisal of magnetotelluric galvanic electric distortion by optimizing amplitude and phase tensor relations. Geophysics 85(3):E79–E98
Sternberg B, Washburne J (1988) Correction for the static shift in magnetotellutics using transient electromagnetic soundings. Geophysics 53(11):1459–1468
Swift C (1967) A magnetotelluric investigation of an electrical conductivity anomaly in the southwestern United States. Massachusetts Institute of Technology, Princeton University. Ph.D. Dissertation
Tang W, Li Y, Oldenburg D, Liu J (2018) Removal of galvanic distortion effects in 3D magnetotelluric data by an equivalent source technique. Geophysics 83(2):E95–E110
Wang R, Wang M, Di Q et al (2009) 2D numerical study on the effect of conductor between the transmitter and survey area in CSEM exploration. Appl Geophys 6(4):311–318
Wang R, Yin C, Wang M, Di Q (2015) Laterally constrained inversion for CSAMT data interpretation. J Appl Geophys 121:63–70
Wynn J, Mosbrucker A, Pierce H, Spicer K (2016) Where is the hot rock and where is the ground water–Using CSAMT to map beneath and around Mount St. Helens. J Environ Eng Geophys 21(2):79–87
Yan S, Junmei F (2004) An analytical method to estimate shadow and source overprint effects in CSAMT sounding. Geophysics 69(1):161–163
Zhdanov M, Lee S, Yoshioka K (2006) Integral equation method for 3D modeling of electromagnetic fields in complex structures with inhomogeneous background conductivity. Geophysics 71(6):G333–G345
Zhou N, Hou D, Xue G (2018) Effects of shadow and source overprint on grounded-wire transient electromagnetic response. IEEE Geosci Remote Sens Lett 15(8):1169–1173
Zonge K, Hughes L (1991) Controlled source audio-frequency magnetotellurics. Electromagnetic methods in applied geophysics. Society of Exploration Geophysicists, Oklahoma, pp 713–810
This paper was funded by a Grant from the National Natural Science Foundation of China (Nos. 41964006, 4141964003 and 41864004), Jiangxi Provincial Natural Science Foundation (20202BABL201026 and 20202BAB201013).
Conflict of interest
The authors declare that they have no conflict of interest.
About this article
Cite this article
Wang, XX., Deng, JZ. & Ren, JL. Distortion effects caused by target abnormal bodies in CSAMT exploration. Acta Geophys. 68, 1653–1665 (2020). https://doi.org/10.1007/s11600-020-00494-1
- Controlled source audio-frequency magnetotellurics
- Distortion effects
- Galvanic effects
- Target abnormal body