Two-Dimensional Compact Inversion of Magnetic Data in the Presence of Remanent Magnetization | ||
| روش های تحلیلی و عددی در مهندسی معدن | ||
| مقاله 4، دوره 8، شماره 17، اسفند 1397، صفحه 39-51 اصل مقاله (2.05 M) | ||
| نوع مقاله: مقاله پژوهشی | ||
| شناسه دیجیتال (DOI): 10.29252/anm.8.17.39 | ||
| نویسندگان | ||
| عبدالحمید انصاری* ؛ احمد قربانی؛ محمدحسین قلعه نویی | ||
| دانشکده مهندسی معدن و متالورژی، دانشگاه یزد | ||
| چکیده | ||
| Remnant magnetization causes a change in the direction and intensity of the magnetization vector. If inversion is performed regardless of remnance, in some cases it may have unreliable and misleading results. For inversion with respect to remnant magnetization, several solutions have been proposed so far, one of which is to convert the data of total magnetic field into data that is independent of the direction of magnetization. In this study, the transformation of Total Field Anomaly (TFA) into Total Magnitude Anomaly (TMA) is used. The inversion algorithm is based on improving compact inversion method and is just two-dimensional. In compact inversion, anomalies may concentrate on the surface of the earth, and thus the response is unreliable. To solve this problem, a combination of matrices and weighting functions have been used, including elements such as magnetic susceptibility and depth function. The resulting model can be smooth or compact (with sharp edges) based on changing compactness factor. The method has been tested using several synthetic and real data. The synthetic data are a 2D tabular prism, of which the top buried-depth is 20 m and the length and width are 40 to 20 m, a dipping prism with a vertical tabular nearby. The real example is magnetic data over Galinge iron-ore deposit in Qinghai province of China, and the data of four profiles have been considered for 2D inversion. Inversion even smooth or sharp, have been conducted with all models, and especially sharper models are consistent with the known geologic attributes of the magnetic sources. | ||
| کلیدواژه‌ها | ||
| Remnant Magnetization؛ Susceptibility؛ Magnetic Intensity؛ Total Magnitude Anomaly | ||
| عنوان مقاله [English] | ||
| Two-Dimensional Compact Inversion of Magnetic Data in the Presence of Remanent Magnetization | ||
| نویسندگان [English] | ||
| Abdolhamid Ansari؛ Ahmad Ghorbani؛ Mohammad Hossein Ghalehnoee | ||
| Dept. of Mining and Metallurgy, Yazd University, Iran | ||
| چکیده [English] | ||
| Remnant magnetization causes a change in the direction and intensity of the magnetization vector. If inversion is performed regardless of remnance, in some cases it may have unreliable and misleading results. For inversion with respect to remnant magnetization, several solutions have been proposed so far, one of which is to convert the data of total magnetic field into data that is independent of the direction of magnetization. In this study, the transformation of Total Field Anomaly (TFA) into Total Magnitude Anomaly (TMA) is used. The inversion algorithm is based on improving compact inversion method and is just two-dimensional. In compact inversion, anomalies may concentrate on the surface of the earth, and thus the response is unreliable. To solve this problem, a combination of matrices and weighting functions have been used, including elements such as magnetic susceptibility and depth function. The resulting model can be smooth or compact (with sharp edges) based on changing compactness factor. The method has been tested using several synthetic and real data. The synthetic data are a 2D tabular prism, of which the top buried-depth is 20 m and the length and width are 40 to 20 m, a dipping prism with a vertical tabular nearby. The real example is magnetic data over Galinge iron-ore deposit in Qinghai province of China, and the data of four profiles have been considered for 2D inversion. Inversion even smooth or sharp, have been conducted with all models, and especially sharper models are consistent with the known geologic attributes of the magnetic sources. | ||
| کلیدواژه‌ها [English] | ||
| Remnant Magnetization, Susceptibility, Magnetic Intensity, Total Magnitude Anomaly | ||
| اصل مقاله | ||
|
In some magnetic observations, it can be assumed that there is no remnant magnetization or can be neglected. In these cases, the direction of remnant magnetization is assumed to be parallel with the direction of the Earth's magnetization, and some modeling can be done with this hypothesis. But there is remnant magnetization in most cases, which, if severe, causes uncertainty in inversion of magnetic data. Although this problem was present from the beginning of the magnetic measurement, it was not important for two reasons: first, in many magnetic studies, the amount of remnant magnetization was considered to be negligible; secondly, many magnetic data were interpreted qualitatively; It was performed only for the purpose of estimating depth, in which there was no need to know the direction of magnetization [1]. However, remnant magnetization is severe and inevitable in many applications of magnetic method, including mineral exploration, regional explorations of the earth's crust and archeology. Given the above mentioned reasons, inversion result is unreliable without attention to the remnant magnetization; so many researchers have offered numerous ways to solve this problem. In general, there are three methods for inversion of magnetic data with respect to remnant magnetization: 1) inversion method with estimation for the direction of remnant magnetization, 2) inversion by converting magnetic data into the data that is independent of magnetization and 3) Magnetic Vector Inversion (MVI). | ||
| مراجع | ||
|
[1] Shearer, S., 2005, Three-dimensional Inversion of magnetic data in the presence of remanent magnetization. MSc thesis, CGEM, Colorado School of Mine.
[2] Pilkington, M., 1997, 3D magnetic imaging using conjugate gradients, Geophysics, 62, 1132-1142.
[3] Li, Y., and Oldenburg, D.W., 1996, 3-D inversion of magnetic data: Geophysics, 61, 394–408
[4] Li, Y., Oldenburg, D. W., 2003. Fast inversion of large-scale magnetic data using wavelet transforms and logarithmic barrier method, Geophys. J. Int., 152, 251 –265.
[5] Portniaguine, O., and Zhdanov, M. S., 1999, Focusing geophysical inversion images: Geophysics, 64, 874-887, doi:10.1190/1.1444596.
[6] Li, Y., Shearer, S., Haney, M., and Dannemiller, N. (2010), Comprehensive approaches to 3D inversion of magnetic data affected by remanent magnetization, GEOPHYSICS, 75(1), L1 –L11.
[7] Lourenco, J. S., and Morrison, H. F., 1973, Vector magnetic anomalies derived from measurements of a single component of the field: Geophysics, 38, 359–368.
[8] Bilim, F., and Ates, A., 2004, An enhanced method for estimation of body magnetization direction from pseudogravity and gravity data: Computers & Geosciences, 30, 161– 171.
[9] Phillips, J. D., 2005, Can we estimate total magnetization directions from aeromagnetic data using Helbig’s formulas: Earth, Planets, and Space, 57, 681–689.
[10] Dannemiller, N., and Y. Li, 2006, A new method for determination of magnetization direction: Geophysics, 71, no. 6, L69–L73.
[11] Haney, M., and Li, Y., 2002, Total magnetization direction and dip from multiscale edges: 72nd Annual International Meeting, SEG, Expanded Abstracts, 735–738.
[12] Haney, M., C. Johnston, Y. Li, and Nabighian, M., 2003, Envelopes of 2D and 3D magnetic data and their relationship to the analytic signal: Preliminary results: 73rd Annual International Meeting, SEG, Expanded Abstracts, 596–599.
[13] Shi, L., Guo, L., Chen, S., Xu, W., 2013, Dipole Correlation Method for Determination of Magnetization Direction under the Influence of Remanent Magnetization. J Geophys Remote Sensing S4: 001. doi:10.4172/2169-0049.S4-001.
[14] Nabighian, M., 1972, The analytic signal of two-dimensional magnetic bodies with polygonal cross-section: Its properties and use for automated anomaly interpretation: Geophysics, 37, 507–517.
[15] Shearer, S., and Li, Y, 2004, 3D Inversion of magnetic total gradient data in the presence of remanent magnetization: 74th Annual International Meeting, SEG, Expanded, 23, 774–777.
[16] Pedersen, L. B., 1987, Wavenumber domain expressions for potential fields from arbitrary 2, , and 3-dimensional bodies: Geophysics, 43, 626–630.
[17] Liu, S., Hu, X., Liu, T., Feng, J., Gao, W., and Qiu, L., 2013, Magnetization vector imaging for borehole magnetic data based on magnitude magnetic anomaly: Geophysics, 78, no. 3, K1–K12.
[18] Liu. S., Hu. X., Xi. Y., Liu. T., and Xu. S., 2015, 2D sequential inversion of total magnitude and total magnetic anomaly data affected by remanent magnetization: Geophysics, 80, no. 6, D429–D444.
[19] Ellis, R. G., de Wet, B., MacLeod, I. N. (2012), Inversion of magnetic data for remanent and induced sources. ASEG Extended Abstracts 2012, 1 –4.
[20] Macload. I. N., and Ellis. R. G., 2013, Magnetic Vector Inversion, a simple approach to challenge of varying direction of rock magnetization, ASEG-PESA 2013 , 1 –4.
[21] Kubota, R., and Uchiyama A., 2005, Three-dimensional magnetization vector inversion of a seamount, Earth Planets Space, 57, 691–699.
[22] Lelièvre, P. G., and Oldenburg, D.W., 2009, A 3D total magnetization inversion applicable when significant, complicated remanence is present: Geophysics, 74, no. 3, L21–L30.
[23] Pratt, D. A., McKenzie, K. B., White, A. S., 2012, the remote determination of magnetic remanence, ASEG Extended Abstracts 2012, 1-5.
[24] Last, B. J., and Kubik, K., 1983, Compact gravity inversion: Geophysics, 48, 713–721.
[25] Guillen, A., and V. Menichetti, 1984, Gravity and magnetic inversion with minimization of a specific functional: Geophysics, 49, 1354–1360.
[26] Barbosa, V. C. F., and Silva, J. B. C., 1994, Generalized compact gravity inversion: Geophysics, 59 (1), 57–68.
[27] Barbosa, V. C. F., and Silva, J. B. C., 2006, Interactive 2D magnetic inversion: A tool for aiding forward modeling and testing geologic hypotheses: Geophysics, 71 (5), P. L43–L50.
[28] Silva, F. J. S., Valéria C. F. Barbosa, and J. B. C. Silva, 2009, 3D gravity inversion through an adaptive-learning procedure, GEOPHYSICS,VOL. 74, NO. 3 MAY-JUNE 2009; P. I9–I21.
[29] Silva, F. J. S., Valéria C. F. Barbosa, and J. B. C. Silva, 2011, Adaptive learning 3D gravity inversion for salt-body imaging, GEOPHYSICS, VOL. 76, NO. 3 (MAY-JUNE 2011); P. I49–I57.
[30] Ghalehnoee. M. H., Ansari. A., & Ghorbani. A., 2017, Improving compact gravity inversion using new weighting functions. Geophys J Int; 208 (1): 546-560.
[31] Dampney, C., 1969, the equivalent source technique: Geophysics, 34, 39–53.
[32] Menke, W., Geophysical Data Analysis: Discrete Inverse Theory, 1989, Revised Edition, Academic Press, New York.
[33] Hansen, P. C., 1998, Rank-Deficient and Discrete Ill-posed Problems, SIAM publications, Philadelphia, USA. | ||
|
آمار تعداد مشاهده مقاله: 803 تعداد دریافت فایل اصل مقاله: 1,052 |
||