Description Based on lectures given in the First Russian School-Seminar on electromagnetic soundings of the Earth held in Moscow on 15th November,
2003, this book acquaints scientists and technologists with the latest achievements in theory, techniques and practical applications
of the methods of electromagnetic sounding. This three part text covers the methods considered for Earth electromagnetic sounding on
a global, regional, and local scale; modern methods for solving forward and inverse problems of geoelectrics, particularily contemporary
approaches to the EM data modeling and interpretation in the class of three-dimensional models; and the results of regional EM on-land
and sea soundings
Audience
geochemists, geophysists
Contents Preface
Part 1 EM sounding methods
1. Global 3-D EM induction in the solid Earth and the oceans (A. Kuvshinov)
1.1. Forward problem
formulation
1.2. Basic 3-D Earth conductivity model
1.3. Ocean effect in Sq variations
1.4. Ocean effect of geomagnetic storms
1.5.
Magnetic fields due to ocean tides
1.6. Magnetic fields due to ocean circulation
1.7. Mapping conductivity anomalies in the Earth's mantle
from space
1.8. Conclusions
2. Magnetovariational method in deep geoelectrics (M. Berdichevsky, V. Dmitriev,
N. Golubtsova, N. Mershchikova,
and P. Pushkarev)
2.1. Introduction
2.2. On integrated interpretation of MV and MT data
2.3. Model experiments
2.4. MV-MT study of the
cascadian subduction zone (EMSLAB experiment)
3. Shallow investigations by TEM-FAST technique: methodology and examples
(P. Barsukov,
E. Fainberg, E. Khabensky)
3.1. Introduction
3.2. Advantages of TEM in shallow depth studies
3.3. On the TEM-FAST technology
3.4. Transformation
of E(t) data into !(h)
3.5. One-dimensional inversion and TEM-FAST's resolution
3.6. Joint inversion of TEM and DC soundings
3.7. Side
effects in TEM sounding
3.7.1. Superparamagnetic effect in TEM
3.7.2. Effect of induced polarization
3.7.3. Antenna polarization effect
(APE)
4. Seismoelectric methods of Earth study (B. Svetov)
4.1. Seismoelectric effect (SE) of the first kind
4.2. Seismoelectric effect
of the second kind: historical outline and elements of theory
4.3. Physical interpretation of seismoelectric phenomena
4.4. Modeling
of seismoelectric fields
4.5. Laboratory studies of seismoelectric effects on rock samples
4.6. Experimental field and borehole seismoelectric
studies
Part 2 Forward modeling and inversion techniques
5. 3-D EM forward modeling using balance technique (V. Spichak)
5.1. Modern
approaches to the forward problem solution
5.1.1. Methods of integral equations
5.1.2. Methods of differential equations
5.1.3. Mixed
approaches
5.1.4. Analog (physical) modeling approaches
5.2. Balance method of EM fields computation in models with arbitrary conductivity
distribution
5.2.1. Statement of the problem
5.2.2. Calculation of the electric field
5.2.3. Calculation of the magnetic field
5.2.4.
Controlling the accuracy of the results
5.3. Method of the EM field computation in axially symmetric media
5.3.1. Problem statement
5.3.2.
Basic equations
5.3.3. Boundary conditions
5.3.4. Discrete equations and their numerical solution
5.3.5. Code testing
6. 3-D EM forward
modeling using integral equations (D. Avdeev)
6.1. Introduction
6.2. Volume integral equation method
6.2.1. Traditional IE method
6.2.2.
Modified iterative dissipative method
6.3. Model examples
6.3.1. Induction logging problem
6.3.2. Airborne EM example
6.4. Conclusion
7. Inverse problems in modern magnetotellurics (V. Dmitriev, M. Berdichevsky)
7.1. Three features of multi-dimensional inverse problem
7.1.1. Normal background
7.1.2. On detailness of multi-dimensional inversion
7.1.3. On redundancy of observation data
7.2. Three questions
of Hadamard
7.2.1. On the existence of a solution to the inverse problem
7.2.2. On the uniqueness of the solution to the inverse problem
7.2.3. On the instability of the inverse problem
7.3. Magnetotelluric and magnetovariational inversions in the light of Tikhonov's theory
of ill-posed problems
7.3.1. Conditionally well-posed formulation of inverse problem
7.3.2. Optimization method
7.3.3. Regularization
method
8. Joint robust inversion of magnetotelluric and magnetovariational data (Iv.M. Varentsov)
8.1. Adaptive parametrization of
a geoelectric model
8.1.1. A background structure and windows to scan anomalies
8.1.2. A priori model structure and constrains
8.1.3.
Window with correlated resistivities of inversion cells
8.1.4. Window with finite functions
8.2. Inverted and modelling data
8.3. Inversion
as a minimization problem
8.3.1. Minimizing functional
8.3.2. Robust misfit metric
8.3.3. Cycles of Tikhonov's minimization
8.3.4. Newtonian
minimization techniques
8.3.5. Solution of linear newtonian system and choice of scalar newtonian step
8.3.6. Multi-level adaptive stabilization
8.3.7. Post-inversion analysis
8.4. Study of inversion algorithms using synthetic data sets
8.4.1. Comparison of three model parameterization
schemes in 2-D inversion
8.4.2. 2-D inversion with numerous finite functions
8.4.3. 3-D inversion example
8.4.4. Resolution of a system
of local conductors using the CR-parameterization
8.4.5. Reduction of strong data noise and static shift
8.5. Conclusions
9. Artificial
neural network inversion of EM data (V. Spichak)
9.1. Backpropagation technique
9.2. Creation of teaching and testing data pools
9.3. Effect of the EM data transformations on the quality of the parameters' recognition
9.3.1. Types of the activation function at hidden
and output layers
9.3.2. Number of the neurons in a hidden layer
9.3.3. Effect of an extra hidden layer
9.3.4. Threshold level
9.4.
Effect of the input data type
9.5. Effect of the volume and structure of the training data pool
9.5.1. Effect of size
9.5.2. Effect
of structure
9.6. Extrapolation ability of ANN
9.7. Noise treatment
9. 8. Case history: ANN reconstruction of the Minou fault parameters
9.8.1. Geological and geophysical setting
9.8.2. CSAMT data acquisition and processing
9.8.3. 3-D imaging Minou fault zone using 1-D
and 2-D inversion
9.8.4. ANN reconstruction of the Minou geoelectrical structure
9.8.5. Discussion and conclusions
Part 3 Data processing,
analysis and interpretation
10. Arrays of simultaneous electromagnetic soundings: design, data processing and analysis (Iv. M. Varentsov)
10.1. Simultaneous systems for natural EM fields observation
10.2 Multi-site schemes for estimation of transfer operators
10.3. Temporal
stability of transfer operators
10.4. Methods for the analysis and interpretation of simultaneous EM data
10.5. Conclusions
11. Magnetotelluric
field transformations and their application in interpretation (V. Spichak)
11.1. Linear relations between MT field components
11.2.
Point transforms of MT data
11.2.1. Impedance transforms
11.2.2 Apparent resistivity type transforms
11.2.3. Induction and perturbation
vectors
11.3. Examples of the use of MT field point transforms for the interpretation
11.3.1. Dimensionality indicators
11.3.2. Local
and regional anomalies
11.3.3. Constructing resistivity images in the absence of prior information
11.4. Integral transforms
11.4.1.
Division of the MT field into parts
11.4.2. Transformation of the field components into each other
11.4.3. Synthesis of synchronous MT
field from impedances and induction vectors
12. Modeling of magnetotelluric fields in 3-D media (V. Spichak)
12.1. A feasibility
study of MT method application in hydrocarbon exploration
12.1.1. Statement of the problem
12.1.2. Numerical modeling
12.2. Testing hypotheses
of the geoelectric structure of the Transcaucasian region from magnetotelluric data
12.2.1. Geological and geophysical characteristics
of the region
12.2.2. Alternative conductivity models
12.2.3. Numerical modeling of magnetotelluric fields
12.2.4. Conclusions
12.3.
MT imaging internal structure of volcanoes
12.3.1. Simplified model of the volcano
12.3.2. Synthetic MT pseudosections
12.3.3. Methodology
of interpretation of the MT data measured over the relief surface
12.4. Simulation of MT monitoring of the magma chamber conductivity
12.4.1. Geoelectric model of a central type volcano
12.4.2. Detection of the magma chamber by MT data
12.4.3. Estimation of MT data
resoling power with respect to the conductivity variations in the magma chamber
12.4.4. ?Guidelines? for MT monitoring electric conductivity
in a magma chamber
12.5. Simulation of MT monitoring the ground water salinity
12.5.1. Statement of the problem
12.5.2. Modeling of
the salt water intrusion zone mapping by audio MT data
13. Regional magnetotelluric explorations in Russia (V. Bubnov, E. Aleksanova,
M. Berdichevsky, P. Pushkarev, A.Yakovlev, D.Yakovlev)
13.1. Introduction
13.2. Observation technology
13.3. MT-data processing, analysis
and interpretation
13.4. Case histories:
13.4.1. East-European craton
13.4.2. Caucasus, the Urals, Siberia and North East Russia
14.
EM studies at seas and oceans (N. Palshin)
14.1. Conductivity structure of sea and ocean floor
14.1.1. Background conductivity structure
of the ocean crust and upper mantle
14.1.2. Principle objectives of marine EM studies
14.2. Instrumentation for marine EM studies
14.2.1.
Seafloor controlled source frequency and transient EM sounding
14.2.2. Measurements of variations of natural EM fields on the seafloor
14.3. Some results of EM sounding in seas and oceans
14.3.1. Studies of gas hydrates in seabed sediments of continental slopes
14.3.2.
Studies of buried salt dome-like structures
14.3.3. The Reykjanes Axial Melt Experiment: Structural Synthesis from Electromagnetics
and Seismics (RAMESSES project)
14.3.4. Seafloor MT soundings of the Eastern-Pacific rise at 9?50'N
14.3.5. Mantle Electromagnetic
and Tomography Experiment (MELT)
14.4. Deep seafloor EM studies in the Northwestern Pacific
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