海岸效应对大地电磁测深数据畸变影响研究

doi:10.11720/wtyht.2024.1528

Abstract
Figure/Table
References
Related Citation (15)

Download: PDF (14816 KB) HTML (1 KB)
Export: BibTeX | EndNote (RIS)

Abstract

Magnetotelluric (MT) data collected from offshore areas are generally distorted due to coastal effects, posing challenges in obtaining true subterranean electrical structures. Based on the model of half-space with seawater, 2D electrical isotropy and anisotropy models, and 3D electrical isotropy model, this study analyzed the distortion patterns of MT responses under coastal effects through forward modeling. Moreover, it conducted 2D and 3D inversions of MT data with or without seawater constraints. Key findings are as follows: (1) The initial frequency points of distortion in MT apparent resistivity curves are closely correlated to the distances from survey points to seawater; (2) Compared to MT responses free from coastal effects, the high-frequency sections exhibit increased amplitudes in real induction vectors only at survey points in offshore areas and higher phase tensor ellipticity, whereas the low-frequency sections display expanded influence areas subjected to coastal effects; (3) Excluding seawater constraints, the inversion results show false anomalies in offshore areas and poor reconstruction effects on subsurface anomalies. Considering seawater constraints, the constrained inversion can effectively suppress the distortion caused by coastal effects. Overall, this study will provide a significant reference for the collection, processing, and interpretation of MT data from offshore areas.

Key words： magnetotellurics coastal effect electrical anisotropy 2D and 3D forward and inverse modeling

Received: 08 December 2024 Published: 21 October 2024

ZTFLH:

P631

	Service

	E-mail this article
	Add to my bookshelf
	Add to citation manager
	E-mail Alert
	RSS
	Articles by authors
	Fu-Qiang YANG
	Hai-Zhi LIAO
	Zheng WANG
	Ya-Jun MO
	Ye-Fei LI
	Ying LIU

Cite this article:

Fu-Qiang YANG,Hai-Zhi LIAO,Zheng WANG, et al. Impacts of coastal effects on the distortion of magnetotelluric data[J]. Geophysical and Geochemical Exploration, 2024, 48(5): 1284-1293.

URL:

https://www.wutanyuhuatan.com/EN/10.11720/wtyht.2024.1528 OR https://www.wutanyuhuatan.com/EN/Y2024/V48/I5/1284

Electrical resistivity models with sea waterlayer

The initial distortion frequencies of apparent resistivity curves of MT sites in model A, changing with the site distance to sea water and the sea water depth

The phase tensor ellipses and real induction vectors from the models B1 and B2 with/without sea water
a、c—the responses from the models B1 and B2 without sea water; b、d—the responses from the models B1 and B2 with sea water

The phase tensor ellipses of different periods from the model C with/without sea water
a、c、e、g—the responses of different periods from the model C without sea water; b、d、f、h—the responses of different periods from the model C with sea water

The real induction vectors of different periods from the model C with/without sea water
a、c、e、g—the responses of different periods from the model C without sea water; b、d、f、h—the responses of different periods from the model C with sea water

The 2D inversion results without sea water constraint for the responses of models B1 (a) and B2 (b)

The 3D inversion results without sea water constraint for the responses of model C
a~d—Horizontal tangents at depths of 2.1 km, 5 km, 8.6 km and 12 km; e—profile result at x=0 km; f—profile result at y=0 km. The locations of two profiles are indicated in b. The black dotted line indicates the location of anomaly body. The white dots represent site locations

The 2D inversion results with sea water constraint for the responses of models B1 (a) and B2 (b)

The 3D inversion results with sea water constraint for the responses of model C
a~d—Horizontal tangents at depths of 2.1 km, 5 km, 8.6 km and 12 km; e—profile result at x=0 km; f—profile result at y=0 km. The locations of two profiles are indicated in b. The black dotted line indicates the location of anomaly body. The white dots represent site locations

[1]	Liu L, Bian A, Heinson G, et al. The relation of regional earthquakes to an intraplate volcano in the northern Hainan Island,China from magnetotelluric imaging[J]. Tectonophysics, 2023,862:229981.
[2]	康敏, 康健, 秦建增. 音频大地电磁法对隐伏构造的识别与应用——以河南省郑州市老鸦陈周边为例[J]. 物探与化探, 2018, 42(1):61-67.
[2]	Kang M, Kang J, Qin J Z. Identification and application of audio magnetotellurics to the hidden structure:A case study of Laoyachen in Zhengzhou,Henan Province[J]. Geophysical and Geochemical Exploration, 2018, 42(1):61-67.
[3]	孙浩, 刘营, 王正, 等. 音频大地电磁约束反演在地层识别中的应用:以哈密盆地为例[J]. 地球科学, 2022, 47(11):4280-4293.
[3]	Sun H, Liu Y, Wang Z, et al. Constrained inversion of audio magnetotelluric for identifying strata:A case study in Hami Basin[J]. Earth Science, 2022, 47(11):4280-4293.
[4]	吴旭亮, 李茂. 基于AMT的龙首山成矿带西岔地段马路沟断裂带深部发育特征[J]. 物探与化探, 2022, 46(5):1180-1186.
[4]	Wu X L, Li M. Deep occurrence characteristics of the Malugou fault zone in the Xicha section of the Longshoushan metallogenic belt determined based on AMT[J]. Geophysical and Geochemical Exploration, 2022, 46(5):1180-1186.
[5]	游越新, 邓居智, 陈辉, 等. 综合物探方法在云南澜沧老厂多金属矿区深部找矿中的应用[J]. 物探与化探, 2023, 47(3):638-647.
[5]	You Y X, Deng J Z, Chen H, et al. Application of integrated geophysical methods in deep ore prospecting of Laochang polymetallic mining area in Lancang,Yunnan[J]. Geophysical and Geochemical Exploration, 2023, 47(3):638-647.
[6]	赵宝峰, 汪启年, 郭信, 等. 汝城盆地深部构造及地热资源赋存潜力——基于重力与AMT探测的认识[J]. 物探与化探, 2023, 47(5):1147-1156.
[6]	Zhao B F, Wang Q N, Guo X, et al. Gravity survey and audio magnetotellurics-based insights into the deep structures and geothermal resource potential of the Rucheng Basin[J]. Geophysical and Geochemical Exploration, 2023, 47(5):1147-1156.
[7]	Evans R L, Hirth G, Baba K, et al. Geophysical evidence from the MELT area for compositional controls on oceanic plates[J]. Nature, 2005, 437(7056):249-252.
[8]	李飞, 董浩, 崔志强, 等. 滩涂区综合地球物理调查技术在栟茶河断裂空间展布中的应用[J]. 地质与勘探, 2020, 56(3):566-579.
[8]	Li F, Dong H, Cui Z Q, et al. Application of integrated geophysical survey technology in the spatial distribution of benchahe fault in Rudong mudflat area,Jiangsu Province[J]. Geology and Exploration, 2020, 56(3):566-579.
[9]	Yang J M, Lee C, Yoo H. Correction of the sea effect in the magnetotelluric (MT) data using an iterative tensor stripping during inversion[J]. Journal of Korean Geophysics and Geophysical Exploration, 2008,(11):286-301.
[10]	张帆, 魏文博, 金胜, 等. 海岸效应对近海地区大地电磁测深数据畸变作用研究[J]. 地球物理学报, 2012, 55(12):4023-4035.
[10]	Zhang F, Wei W B, Jin S, et al. Ocean coast effect on land-side magnetotelluric data in the vicinity of the coast[J]. Chinese Journal of Geophysics, 2012, 55(12):4023-4035.
[11]	Parkinson W D. Directions of rapid geomagnetic fluctuations[J]. Geophysical Journal International, 1959, 2(1):1-14.
[12]	Jones F W. Geomagnetic effects of sloping and shelving discontinuities of earth conductivity[J]. Geophysics, 1971, 36(1):58.
[13]	Lines L R, Jones F W. The perturbation of alternating geomagnetic fields by an island near a coastline:Reply[J]. Canadian Journal of Earth Sciences, 1973, 10(4):510-518.
[14]	Jones F W, Lokken J E. Irregular coastline and channeling effects in three-dimensional geomagnetic perturbation models[J]. Physics of the Earth and Planetary Interiors, 1975, 10(2):140-150.
[15]	Parkinson W D, Jones F W. The geomagnetic coast effect[J]. Reviews of Geophysics, 1979, 17(8):1999-2015.
[16]	Cox C. Electromagnetic induction in the oceans and inferences on the constitution of the earth[J]. Geophysical Surveys, 1980, 4(1):137-156.
[17]	Key K, Constable S. Coast effect distortion of marine magnetotelluric data:Insights from a pilot study offshore northeastern Japan[J]. Physics of the Earth and Planetary Interiors, 2011, 184(3/4):194-207.
[18]	Wang S G, Constable S, Reyes-Ortega V, et al. A newly distinguished marine magnetotelluric coast effect sensitive to the lithosphere-asthenosphere boundary[J]. Geophysical Journal International, 2019, 218(2):978-987.
[19]	李永博, 吴琼, 王刚, 等. 海岸效应对大地电磁响应的影响及校正方法[J]. 石油地球物理勘探, 2021, 56(3):631-644,417.
[19]	Li Y B, Wu Q, Wang G, et al. Study on the influence and correction method of coast effect on magnetotelluric responses[J]. Oil Geophysical Prospecting, 2021, 56(3):631-644,417.
[20]	杨文采, 方慧, 程振炎, 等. 苏鲁超高压变质带北部地球物理调查(Ⅱ)——非地震方法[J]. 地球物理学报, 1999, 42(4):508-519.
[20]	Yang W C, Fang H, Cheng Z Y, et al. Geophysical investigation of northern Sulu uhpm terrane in East China (ⅱ):Non-seismic methods[J]. Chinese Journal of Geophysics, 1999, 42(4):508-519.
[21]	Liu Y, Junge A, Yang B, et al. Electrically anisotropic crust from three-dimensional magnetotelluric modeling in the western Junggar,NW China[J]. Journal of Geophysical Research:Solid Earth, 2019, 124(9):9474-9494.
[22]	刘营, 胡道功, 许顺芳, 等. 琼北第四纪火山区电各向异性结构及其地质意义[J]. 地球科学, 2020, 45(1):330-340.
[22]	Liu Y, Hu D G, Xu S F, et al. Electrical anisotropic structure in the quaternary volcanic region of North Hainan Island and its geological implications[J]. Earth Science, 2020, 45(1):330-340.
[23]	Fischer G. Electromagnetic induction effects at an ocean coast[J]. Proceedings of the IEEE, 1979, 67(7):1050-1060.
[24]	Mackie R L, Bennett B R, Madden T R. Long-period magnetotelluric measurements near the central California coast:A land-locked view of the conductivity structure under the Pacific Ocean[J]. Geophysical Journal International, 1988, 95(1):181-194.
[25]	Key K. MARE2DEM:A 2-D inversion code for controlled-source electromagnetic and magnetotelluric data[J]. Geophysical Journal International, 2016, 207(1):571-588.
[26]	Egbert G D, Kelbert A. Computational recipes for electromagnetic inverse problems[J]. Geophysical Journal International, 2012, 189(1):251-267.
[27]	Kelbert A, Meqbel N, Egbert G D, et al. ModEM:A modular system for inversion of electromagnetic geophysical data[J]. Computers and Geosciences, 2014,66:40-53.
[28]	Caldwell T G, Bibby H M, Brown C. The magnetotelluric phase tensor[J]. Geophysical Journal International, 2004, 158(2):457-469.
[29]	Wiese H. Geomagnetische tiefentellurik teil II:Die streichrichtung der untergrundstrukturen des elektrischen widerstandes,erschlossen aus geomagnetischen variationen[J]. Geofisica Pura e Applicata, 1962, 52(1):83-103.