Regional Electromagnetic Induction Studies Using Long Period Geomagnetic Variations

Chandrasekhar, E.

doi:10.1007/978-94-007-0323-0_3

Cited by 8 publications

(3 citation statements)

References 46 publications

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“…These are found at about 100.0 to 400.0 km in the upper mantle and beyond 850.0 km within the lower mantle. This two layers agree with: (i) Onwumechili and Ogbuehi (1967) who showed that the depth of perfectly conducting layer in Nigeria to be exactly at 200.0 km; (ii) Chandrasekhar (2011) who calculated that the average depth of a substitute conductor beneath the India region is about 1200.0 km. Slight fluctuations in the conductivity profile are observed at about 400.0 to 1000.0 km depths and is attributed to the changes in phase of olivine atoms (which is the chief constituent of mantle rocks) at greater depths.…”

Section: Discussionsupporting

confidence: 88%

Mantle electrical conductivity determination employing the ionospheric solar quiet day (Sq) currents in the Southern African regions

Ngozi¹,

Francisca²,

Daniel³

et al. 2022

Int. J. Phys. Sci.

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Solar quiet (Sq) daily currents variation obtained in the Hermanus (34.34 o S, 19.22 o E), Tsumeb (19.24 o S, 17.72 o E), Hartebeesthoek (25.68 o S, 28.09 o E) and Maputo (25.97 o S, 32.57 o E), were employed in determining the mantle electrical conductivity depth profile of the Southern African region. The external and internal contributions in the solar quiet field were separated using the spherical harmonic analysis (SHA), after which, the transfer functions were used to compute the electrical conductivity depth profiles of the region. A downward increase was observed in electrical conductivities and deep depth of penetration within the Earth regions. In Hartebeesthoek, Hermanus, Maputo and Tsumeb, the evaluated average electrical conductivity values are 0.028 Sm -1 , 0.039 Sm -1 , 0.057 Sm -1 and 0.0.025 Sm -1 at depths of 76.4 km, 84.1 km,141.0 km and 111.5 km at the respective maximum depths of penetration of 1052.8 km, 1467.0 km, 1160.8 km and 1289.5 km in Hartebeesthoek, Hermanus, Maputo and Tsumeb, the calculated electrical conductivity reached the maximum values of 0.498 Sm -1 , 0.323 Sm -1 , 0.387 Sm -1 and 0.187 Sm -1 respectively. Discontinuities were observed in all the profiles but are more prominent in Tsumeb region near 390.0 -750.0 km, 820.0 -980.0 km and 200.0 -300.0 km. From these results, we are stating that the effects from the deeper 3-D structures (such as gold, copper etc), the hydrated transition zone and effect from the ocean contribute to the greater depth of Sq penetration.

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Section: Discussionsupporting

confidence: 88%

Mantle electrical conductivity determination employing the ionospheric solar quiet day (Sq) currents in the Southern African regions

Ngozi¹,

Francisca²,

Daniel³

et al. 2022

Int. J. Phys. Sci.

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“…It is clear that the ELF-EM method is an effective tool for probing the deep underground in a variety of geologic settings [20]. Considering that the skin depth increases as frequency decreases, ELF waves at a proper frequency can penetrate several to ten kilometers below the Earth's surface [8,25], and therefore the received response contains rich information about the deep stratigraphic structure. With a renewed interest in deep exploration, for the first time, Bannister [13] measured the effective Earth conductivity at 45 and 75 Hz beneath the antennas of the Wisconsin Test Facility, and Fraser-Smith [6] measured the man-made ELF signals from the Russian ELF transmitter near the polar region.…”

Section: Introductionmentioning

confidence: 99%

A Spherical “Earth–Ionosphere” Model for Deep Resource Exploration Using Artificial ELF-EM Field

Zheng

2022

Remote Sensing

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Fully coupled lithosphere, atmosphere, and ionosphere theory has demonstrated that extremely low-frequency electromagnetic (ELF-EM) fields present a broad application prospect in deep resource exploration, but previous studies have ignored the contribution of the Earth’s curvature. This study extends the theory of ELF-EM over a stratified Earth to the case where the Earth’s curvature must be taken into account, and presents an analytical solution of the ELF-EM field excited by a grounded horizontal antenna in a spherical Earth–ionosphere model, whose theoretical approach and solution method are notably different from the flat Earth–ionosphere model. Additionally, the Earth is treated as a concentric-layered sphere rather than an ideal homogeneous sphere. We aim to investigate the effects of the Earth’s curvature on the surface field, so as to broaden the coverage of the ELF wave in resource exploration. The solution is mathematically accurate and physically reasonable, since it reflects the sphericity and radially stratified structure of the Earth. We first verify the correctness and reliability of the proposed method by comparing the results with FDTD in a full-space spherical model. Additionally, we then compared the spherical results with the conventional controlled-source electromagnetic method and flat Earth–ionosphere results. The results show that when the distance between the transmitter and the receiver is comparable to the Earth radius, the spherical model better reflects the resonance of the wave in the cavity, suggesting that the effect of the Earth’s curvature is not negligible. Then, the numerical simulations conducted to investigate the properties of the EM fields and their sensitivities to the conductivity at depth in the Earth are discussed. Finally, the EM responses of some simple electrical conductivity structures models are modeled to illustrate their prospects in future resource exploration.

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“…Electromagnetic induction in the Earth by time-varying electromagnetic field variations at different frequencies helps to use electrical conductivity parameters to provide insight into the structure and physical states of the interior regions of the Earth [1]. With the deepening of geodynamic research and the critical and immediate need for deep resource exploration, the large-scale electromagnetic method has attracted more attention as a promising candidate technology for deep exploration technology [1][2][3][4][5]. Since the skin depth is inverse proportional to working frequency, low-frequency electromagnetic waves have the ability to achieve deeper penetration.…”

Section: Introductionmentioning

confidence: 99%

Propagation of ELF Electromagnetic Waves Over a Curved Stratified Ground and its Application in Geophysical Prospecting

Zheng¹,

2021

IEEE Access

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Electromagnetic waves radiated by a vertical electric dipole related to deep resource exploration are discussed. According to the tangential components of the field are continuous on the element interface, the spherical harmonic series expression of extremely low-frequency (ELF) electromagnetic waves in the "earth -ionosphere" model is derived, in which the earth is regarded as a curved stratified ground. The Schumann resonance serves to verify the correctness and reliability of the formula and algorithm. And our method is compared with the traditional large-scale electromagnetic method. The forward response curves of the two methods are in good agreement on the ELF band. By comparison, we can find that our method performs best when the distance between the transmitting source and receiving point is greater than 500km. To estimate the effects on the electromagnetic waves associated with resource exploration, we first discussed the ability of our method to identify formations, and then discussed the electromagnetic response characteristics of the earth as two-layer and three-layer models, which are sufficient to show the basic characteristics of the electromagnetic field in the "earth-ionosphere". The results show that, as an emerging large-scale exploration method, the wireless electromagnetic method can be well used to detect the deep underground electrical structures.

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Regional Electromagnetic Induction Studies Using Long Period Geomagnetic Variations

Cited by 8 publications

References 46 publications

Mantle electrical conductivity determination employing the ionospheric solar quiet day (Sq) currents in the Southern African regions

Mantle electrical conductivity determination employing the ionospheric solar quiet day (Sq) currents in the Southern African regions

A Spherical “Earth–Ionosphere” Model for Deep Resource Exploration Using Artificial ELF-EM Field

Propagation of ELF Electromagnetic Waves Over a Curved Stratified Ground and its Application in Geophysical Prospecting

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