Analysis and application of the responses of the frequency selection method of telluric electricity field
YANG Tian-Chun1(), HU Feng-Ming1, YU Xi1, FU Guo-Hong1, LI Jun2, YANG Zhui3
1. School of Earth Sciences and Spatial Information Engineering, Hunan University of Science and Technology, Xiangtan 411201, China 2. Nuclear Geological Survey of Hunan, Changsha 410007, China 3. Hunan Puqi Geologic Exploration Equipment Institute, Changsha 410000, China
As an inevitable physical phenomenon in the application of frequency-domain electromagnetics, the static shift effect is generally suppressed or eliminated by correction. This study proposed a new approach of directly utilizing the static shift effect of natural electromagnetic methods to explore shallow electrical anomalies. The frequency selection method of telluric electricity field (FSM) is to study the variations in electrical properties of subsurface media by measuring several horizontal electric field components with different frequencies generated on the surface by the natural alternating electromagnetic field. In this study, the forward modeling of FSM data was conducted using the two-dimensional finite element method. The modeling results are shown as follows: (1) In the case of low-resistivity anomalies near the surface, the curves of horizontal electric field components along the survey line on the surface showed the same morphologies as the FSM-derived curves, with significant low-potential anomalies above the low-resistivity anomalies; (2) As the calculated frequencies increased, both the profile curves and the pseudosection map of electric field components exhibited a static shift effect, indicating that the FSM-derived anomalies were mainly caused by the static shift effect. Both the FSM application results and the drilling verification results showed that with the presence of groundwater, the FSM-derived profile curves and pseudosection map exhibited a significant static shift effect, which was consistent with the CSAMT exploration results. As indicated by theoretical and practical research, it is feasible to directly use the components of the telluric electricity field for the exploration of shallow electrical anomalies. Moreover, shallow geological exploration can be conducted by utilizing the static shift effect of the frequency domain electromagnetics.
杨天春, 胡峰铭, 于熙, 付国红, 李俊, 杨追. 天然电场选频法的响应特性分析与应用[J]. 物探与化探, 2023, 47(4): 1010-1017.
YANG Tian-Chun, HU Feng-Ming, YU Xi, FU Guo-Hong, LI Jun, YANG Zhui. Analysis and application of the responses of the frequency selection method of telluric electricity field. Geophysical and Geochemical Exploration, 2023, 47(4): 1010-1017.
Di Q Y, Zhu R X, Xue G Q, et al. New development of the electromagnetic (EM) methods for deep exploration[J]. Chinese Journal of Geophysics, 2019, 62(6):2128-2138.
[2]
Zonge K L. Comparison of time,frequency and phase measurement in IP[J]. Geophysical Prospecting, 1972, 20:626-648.
doi: 10.1111/gpr.1972.20.issue-3
[3]
Jones A G. Static shift of magnetotelluric data and its removal in a sedimentary basin environment[J]. Geophysics, 1988, 53(7):967-978.
doi: 10.1190/1.1442533
[4]
Kaufman A A. Reduction of the geological noise in magnetotelluric sounding[J]. Geoexploration, 1988, 25:145-161.
doi: 10.1016/0016-7142(88)90010-5
[5]
Zonge K L, Hughes L J. Controlled source audio-frequency magnetotellurics[M]// Nabighian M N. Electromagnetic Methods: Theory and Practice, Society of Exploration Geophysicists, 1988.
[6]
Andrieux P, Wightman W E. The so-called static corrections in magnetotelluric measurements[C]// 54th Ann. Mtg., Soc. Expl. Geophys., Expanded Abstracts, 1984:43-44.
[7]
Sternberg B K, Washburne J C, Pellerin L. Correction for the static shift in magnetotellurics using transient electromagnetic soundings[J]. Geophysics, 1988, 53:1459-1468.
doi: 10.1190/1.1442426
Chen Q L, Zhang X, Hu W B. Static migration correction of magnetotelluric sounding curve in carbonate area of South China[J]. Journal of Jianghan Petroleum Institute, 1999, 21(3):30-32.
Yang S, Bao G S, Li A Y. The static migration to MT data and the impedance tensor static correction method[J]. Journal of CentralSouth University of Technology, 2002, 33(1):8-13.
Yu S B, Zheng J B, Gao M L, et al. CSAMT static correction method based on wavelet transform modulus maxima and thresholds[J]. Chinese Journal of Geophysics, 2017, 60(1):360-368.
Yang T C, Xia D L, Wang Q R, et al. Theoretical research and application of frequency selection method for telluric electricity field[M]. Changsha: Central South University Press, 2017.
Yang J. Experimental results and theoretical study of the stray current method in karst area[J]. Geophysical and Geochemical Exploration, 1982, 6(1):41-54.
Yang T C, Chen Z C, Liang J, et al. Theoretical analysis of sounding anomaly and field application of the natural electric field frequency selection sounding method in groundwater exploration[J]. Earth Science Frontiers, 2020, 27(4):302-310.
doi: 10.13745/j.esf.sf.2020.6.34
[16]
Yang T C, Gao Q S, Li H, et al. New insights into the anomaly genesis of the frequency selection method:Supported by numerical modeling and case studies[J]. Pure and Applied Geophysics, 2023. http://doi.org/10.1007/s00024-022-03220-8
[17]
Ren Z, Kalscheuer T, Greenhalgh S, et al. A goal-oriented adaptive finite-element approach for plane wave 3-D electromagnetic modeling[J]. Geophysical Journal International, 2013, 194(2):700-718.
doi: 10.1093/gji/ggt154
Yang T C, Zhang Z F, Xu D G, et al. Fast determination of shallow groundwater wells in a granite area[J]. Hydrogeology & Engineering Geology, 2017, 44(5):20-24,32.
[19]
王汪汪. 可控源音频大地电磁法二维各向异性正演研究[D]. 北京: 中国地质大学, 2017.
[19]
Wang W W. Controlled-source audio-frequency magnetotelluric two-dimensional modeling for arbitrary anisotropy structures[D]. Beijing: China University of Geosciences (Beijing), 2017.
