Étude régionale magnéto-tellurique des structures de la conductivité électrique sur la bordure occidentale du craton ouest africain en République du Sénégal

1982 ◽  
Vol 19 (7) ◽  
pp. 1408-1416 ◽  
Author(s):  
M. Ritz
Keyword(s):  
Reference Station ◽  
Conducting Layer ◽  
Two Dimensional ◽  
Period Range ◽  
Magnetotelluric Data ◽  
West African Craton ◽  
Magnetotelluric Soundings ◽  
Mobile Stations ◽  
Conductivité Électrique ◽  
Western Border

Magnetotelluric soundings were carried out in the Senegal Republic on the western border of the west African craton by a team of geophysicists from Mbour's Observatory, along an approximately east–west profile. This profile includes four stations about 20 km apart. The purpose of this paper is to analyse and interpret the obtained data. The magnetotelluric data were restricted to a period range of 20–300 s. The measurements were performed individually with a reference station located in the sedimentary basin at approximately 130 km from the craton border, and they allowed one to calculate the amplitude ratios of the electromagnetic field components at the mobile stations. A two-dimensional model indicates the presence of a deep conducting layer at a depth of 80 km for the four stations. For the three stations located on the craton border the introduction of a conducting layer at a depth of 30 km permits a better approximation of the data. On the other hand, the presence of a conducting layer underneath the fourth station located on the craton is not justified by the two-dimensional model.The presence of a conducting zone in the mobile zone crust seems to have resulted from a hydration process. On the craton, the crust became hydrated and the conducting level is not present. [Journal Translation]

Analysis of Anisotropic Magnetotelluric Measurements at Victoria, B.C.

1973 ◽  
Vol 10 (4) ◽  
pp. 557-570 ◽  
Author(s):  
W. Nienaber ◽  
D. R. Auld ◽  
H. W. Dosso
Keyword(s):  
Electric Field ◽  
Apparent Resistivity ◽  
Conducting Layer ◽  
Frequency Range ◽  
Entire Frequency Range ◽  
Period Range ◽  
Magnetotelluric Data ◽  
Conductivity Structure ◽  
The University ◽  
Direction Of Polarization

Magnetotelluric data were recorded at the University of Victoria for a wide period range since the summer of 1968. Data for periods between 10 s and 104 s were used for interpretation. Telluric signals were found to be strongly anisotropic for the entire frequency range. Several possible causes of this anisotropy including the land–sea interface and a geological fault at Victoria are discussed.In order to obtain a 'model' for the subsurface conductivity structure, the apparent resistivity curves for both electric field components (E parallel and E perpendicular to the direction of polarization) are combined into one interpretation. The model proposes a thin, highly conducting layer near the surface of a highly resistive earth.The validity of the rotation used in transforming anisotropic telluric data before interpretation was tested experimentally.

scholarly journals Plasmonic Refractive Index Sensors Based on One- and Two-Dimensional Gold Grating on a Gold Film

2020 ◽  
Vol 10 (4) ◽  
pp. 375-386 ◽  
Author(s):  
Jiankai Zhu ◽  
Xiangxian Wang ◽  
Yuan Wu ◽  
Yingwen Su ◽  
Tianxu Jia ◽  
...  
Keyword(s):  
Refractive Index ◽  
Composite Structure ◽  
Composite Structures ◽  
Gold Film ◽  
Grating Period ◽  
Two Dimensional ◽  
Period Range ◽  
Refractive Index Sensing ◽  
Resonance Modes ◽  
Comparison Results

Abstract In this paper, we propose two kinds of composite structures based on the one- and two-dimensional (1D&2D) gold grating on a gold film for plasmonic refractive index sensing. The resonance modes and sensing characteristics of the composite structures are numerically simulated by the finite-difference time-domain method. The composite structure of the 1D gold semi-cylinder grating and gold film is analyzed first, and the optimized parameters of the grating period are obtained. The sensitivity and figure of merit (FOM) can reach 660RIU/nm and 169RIU−1, respectively. Then, we replace the 1D grating with the 2D gold semi-sphere particles array and find that the 2D grating composite structure can excite strong surface plasmon resonance intensity in a wider period range. The sensitivity and FOM of the improved composite structure can reach 985RIU/nm and 298 RIU−1, respectively. At last, the comparison results of the sensing performance of the two structures are discussed. The proposed structures can be used for bio-chemical refractive index sensing.

scholarly journals Necessity of Terrain Correction in Magnetotelluric Data Recorded from Garhwal Himalayan Region, India

Geosciences ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 482
Author(s):  
Dharmendra Kumar ◽  
Arun Singh ◽  
Mohammad Israil
Keyword(s):  
Real Data ◽  
Terrain Correction ◽  
Himalayan Region ◽  
General Character ◽  
Period Range ◽  
Magnetotelluric Data ◽  
Heterogeneous Models ◽  
Corrected Data ◽  
Terrain Corrections ◽  
And Inversion

The magnetotelluric (MT) method is one of the useful geophysical techniques to investigate deep crustal structures. However, in hilly terrains, e.g., the Garhwal Himalayan region, due to the highly undulating topography, MT responses are distorted. Such responses, if not corrected, may lead to the incorrect interpretation of geoelectric structures. In the present paper, we implemented terrain corrections in MT data recorded from the Garhwal Himalayan Corridor (GHC). We used AP3DMT, a 3D MT data modeling and inversion code written in the MATLAB environment. Terrain corrections in the MT impedance responses for 39 sites along the Roorkee–Gangotri profile in the period range of 0.01 s to 1000 s were first estimated using a synthetic model by recording the topography and locations of MT sites. Based on this study, we established the general character of the terrain and established where terrain corrections were necessary. The distortion introduced by topography was computed for each site using homogenous and heterogeneous models with actual topographic variations. Period-dependent, galvanic and inductive distortions were observed at different sites. We further applied terrain corrections to the real data recorded from the GHC. The corrected data were inverted, and the inverted model was compared with the corresponding inverted model obtained with uncorrected data. The modification in electrical resistivity features in the model obtained from the terrain-corrected response suggests the necessity of terrain correction in MT data recorded from the Himalayan region.

DIAGRAMS FOR MAGNETOTELLURIC DATA

Geophysics ◽  
1976 ◽  
Vol 41 (4) ◽  
pp. 766-770 ◽  
Author(s):  
F. E. M. Lilley
Keyword(s):  
Impedance Tensor ◽  
Two Dimensional ◽  
Magnetotelluric Data ◽  
One Dimensional ◽  
Magnetic Components ◽  
Strike Direction ◽  
Electric And Magnetic Fields ◽  
The Relationship ◽  
Special Case ◽  
Phase Differences

Observed magnetotelluric data are often transformed to the frequency domain and expressed as the relationship [Formula: see text]where [Formula: see text] [Formula: see text] and [Formula: see text] [Formula: see text] represent electric and magnetic components measured along two orthogonal axes (in this paper, for simplicity, to be north and east, respectively). The elements [Formula: see text] comprise the magnetotelluric impedance tensor, and they are generally complex due to phase differences between the electric and magnetic fields. All quantities in equation (1) are frequency dependent. For the special case of “two‐dimensional” geology (where structure can be described as having a certain strike direction along which it does not vary), [Formula: see text] with [Formula: see text]. For the special case of “one‐dimensional” geology (where structure varies with depth only, as if horizontally layered), [Formula: see text] and [Formula: see text].

Two-Dimensional Modeling of Electron Flow Through a Poorly Conducting Layer

2015 ◽  
Vol 75 (2) ◽  
pp. 289-312
Author(s):  
J. P. Black ◽  
C. J. W. Breward ◽  
P. D. Howell
Keyword(s):  
Electron Flow ◽  
Conducting Layer ◽  
Two Dimensional ◽  
Dimensional Modeling ◽  
Flow Through

COHERENCE FUNCTIONS FOR MAGNETOTELLURIC ANALYSIS

Geophysics ◽  
1974 ◽  
Vol 39 (3) ◽  
pp. 312-320 ◽  
Author(s):  
I. K. Reddy ◽  
D. Rankin
Keyword(s):  
Data Analysis ◽  
Linear System ◽  
System Approach ◽  
Partial Coherence ◽  
Impedance Method ◽  
Two Dimensional ◽  
Magnetotelluric Data ◽  
The Earth ◽  
Principal Axes ◽  
Tensor Impedance

A multiinput linear system approach is used to study the magnetotelluric phenomena in the presence of lateral conductivity inhomogeneities in the earth. The three types of coherence functions (ordinary, multiple, and partial) are defined, and their use in magnetotelluric data analysis is illustrated with a field example. Partial coherence functions are used to determine the principal axes in the case of two‐dimensional type inhomogeneities, and as measures of three‐dimensionality in the case of non‐two‐dimensional type structures. The results obtained using coherence functions are compared with those obtained with the conventional tensor impedance method.

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