Mahalanobis Distance Method for Enhancing Magnetotelluric Data Processing: A Case Study from the Rochechouart Impact Structure, France

Document Type : Research Article

Authors

1 Department of Earth Physics, Institute of Geophysics, University of Tehran, Tehran, Iran.

2 Department of Earth Sciences, Geosciences Paris-Saclay Laboratory (GEOPS), Université Paris-Saclay, Orsay, France.

3 CEREGE, Aix-Marseille Université, CNRS, IRD, INRAE, Aix-en-Provence, France.

4 CIRIR – Center for International Research and Restitution on Impacts and on Rochechouart, Rochechouart, France.

Abstract

One of the primary challenges in magnetotelluric data processing is the presence of noise and outliers (anomalous values). These disturbances often come from human-made sources such as power lines, electronic devices, and nearby infrastructure. They can significantly affect the results related to apparent resistivity and phase, leading to unreliable models of subsurface electrical resistivity.
To identify and remove these outlier and noisy components, the Mahalanobis distance method is proposed as an effective solution. This approach — applied here in a four-dimensional feature space comprising the real and imaginary parts of two components of the impedance transfer function — calculates the distance of each data point from the dataset, meanwhile accounting for variances, covariances, and correlations between variables, thereby enabling the detection of anomalous points more accurately than simpler (2D) approaches.
In this study, to identify outliers, we applied the Mahalanobis distance method to real data from a single MT station located at the Chassenon Forage site within the Rochechouart impact structure, France. The results demonstrate that this approach not only improves the accuracy of subsequent analyses and enables the extraction of more precise information from subsurface structures, but also reduces processing time by efficiently eliminating contaminated windows before final impedance estimation.

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References

Ajithabh, K. S., & Patro, P. K. (2023). SigMT: An open-source Python package for magnetotelluric data processing. Computers & Geosciences, 171, 105270. https://doi.org/10.1016/j.cageo.2022.105270
Borah, U. K., Patro, P. K., & Suresh, V. (2015). Processing of noisy magnetotelluric time series from Koyna-Warna seismic region, India: A systematic approach. Annales Geophysicae, 58(2), G0222. https://doi.org/10.4401/ag-6690
Cagniard, L. (1953). Basic theory of the magneto-telluric method of geophysical prospecting. Geophysics, 18(3), 605-635. https://doi.org/10.1190/1.1437915
Chave, A. D., Thomson, D. J., & Ander, M. E. (1987). On the robust estimation of power spectra, coherences, and transfer functions. Journal of Geophysical Research: Solid Earth, 92(B1), 633–648. https://doi.org/10.1029/JB092iB01p00633
Daud, Y. (2010). Electromagnetic method: Success story in geothermal exploration & possibility for hydrocarbon exploration. College Textbook, Depok.
Egbert, G. D. (1997). Robust multiple-station magnetotelluric data processing. Geophysical Journal International, 130(2), 475–496. https://doi.org/10.1111/j.1365-246X.1997.tb05661.x
Egbert, G. D., & Booker, J. R. (1986). Robust estimation of geomagnetic transfer functions. Geophysical Journal International, 87(1), 173–194. https://doi.org/10.1111/j.1365-246X.1986.tb04552.x
Efron, B. (1982). The jackknife, the bootstrap, and other resampling plans. Society for Industrial and Applied Mathematics, Philadelphia.
Fowler, R., Kotick, B., & Elliot, R. (1967). Polarization analysis of naturally and artificially geomagnetic micropulsations. Journal of Geophysical Research, 72, 2871–2883. https://doi.org/10.1029/JZ072i011p02871
Gamble, T. D., Goubau, W. M., & Clarke, J. (1979). Magnetotellurics with a remote magnetic reference. Geophysics, 44(1), 53–68. https://doi.org/10.1190/1.1440923
Hermance, J. F. (1973). Processing of magnetotelluric data. https://doi.org/10.1016/0031-9201(73)90060-5
Jenkins, G. M. (1968). Spectral analysis and its applications. Holden-Day, Inc., San Francisco.
Jones, A., &Jodicke, H. (1984). Magnetotelluric transfer function estimation improvement by a coherence-based rejection technique. SEG Technical Program Expanded Abstracts. https://doi.org/10.1190/1.1894081
Kato, Y., & Kikuchi, T. (1950). Scientific Reports of Tohoku University, Series 5, Geophysics, 2, 139.
Keller, G. V., & Frischknecht, F. C. (1966). Electrical methods of geophysical prospecting. Pergamon Press, New York, NY.
Mahalanobis, P. C. (1936). On the generalized distance in statistics. Proceedings of the National Institute of Sciences of India, 2(1), 49–55.
Platz, A., &Weckmann, U. (2019). An automated new pre-selection tool for noisy magnetotelluric data using the Mahalanobis distance and magnetic field constraints. Geophysical Journal International, 218(3), 1853–1872. https://doi.org/10.1093/gji/ggz197
Price, A. T. (1950). Quarterly Journal of Mechanics and Applied Mathematics, 3, 385.
Quesnel, Y., Sailhac, P., Lambert, P., Lambert, A., & Dyment, J. (2021). Multiscale geoelectrical properties of the Rochechouart impact structure, France. Geochemistry, Geophysics, Geosystems, 22(12), e2021GC010036. https://doi.org/10.1029/2021GC010036
Rikitake, T. (1946). Bulletin of the Earthquake Research Institute, Tokyo University, 24, 1.
Ritter, O., Junge, A., & Dawes, G. J. (1998). New equipment and processing for magnetotelluric remote reference observations. Geophysical Journal International, 132(3), 535–548. https://doi.org/10.1046/j.1365-246X.1998.00440.x
Simpson, F., & Bahr, K. (2005). Practical magnetotellurics. Cambridge University Press. https://doi.org/10.1017/CBO9780511614095
Smirnov, M. Yu. (2003). Magnetotelluric data processing with a robust statistical procedure having a high breakdown point. Geophysical Journal International, 152(1), 1–7. https://doi.org/10.1046/j.1365-246X.2003.01733.x
Swift, C. M. (1967). A magnetotelluric investigation of an electrical conductivity anomaly in the southwestern United States. Ph.D. Thesis, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts.
Tikhonov, A. N. (1950). DokladyAkademiiNauk S.S.S.R., 73, 295.
Vozoff, K. (1972). The magnetotelluric method in the exploration of sedimentary basins. Geophysics, 37, 98–141. https://doi.org/10.1190/1.1440228
Weckmann, U., Ritter, O., & Haak, V. (2005). Effective noise separation for magnetotelluric single site data processing using a frequency domain selection scheme. Geophysical Journal International, 161(3), 635–652. https://doi.org/10.1111/j.1365-246X.2005.02608.x
Journal of the Earth and Space Physics
Volume 51, Issue 4
online publication date: 17 March 2026
March 2026
Pages 75-88

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