Electromagnetic Sounding of the Earth's Interior, Volume 40

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

10. 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 9º50'N 14.3.5. Mantle Electromagnetic and Tomography Experiment (MELT) 14.4. Deep seafloor EM studies in the Northwestern Pacific

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

• Presents theoretical and methodological findings, as well as examples of applications of recently developed algorithms and software in solving practical problems
• Describes the practical importance of electromagnetic data through enabling discussions on a construction of a closed technological cycle, processing, analysis and three-dimensional interpretation
• Updates current findings in the field, especially with MT, magnetovariational and seismo-electriccal methods and the practice of 3D interpretaions

geochemists, geophysists