Electromagnetic Sounding of the Earth

Electromagnetic Sounding of the Earth's Interior

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

Hardbound, 404 Pages

Published: November 2006

Imprint: Elsevier

ISBN: 978-0-444-52938-1

Contents

  • PrefacePart 1 EM sounding methods1. 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 model1.3. Ocean effect in Sq variations1.4. Ocean effect of geomagnetic storms1.5. Magnetic fields due to ocean tides1.6. Magnetic fields due to ocean circulation1.7. Mapping conductivity anomalies in the Earth's mantle from space1.8. Conclusions2. Magnetovariational method in deep geoelectrics (M. Berdichevsky, V. Dmitriev, N. Golubtsova, N. Mershchikova, and P. Pushkarev)2.1. Introduction2.2. On integrated interpretation of MV and MT data2.3. Model experiments2.4. 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 studies3.3. On the TEM-FAST technology3.4. Transformation of E(t) data into ¡(h)3.5. One-dimensional inversion and TEM-FAST's resolution3.6. Joint inversion of TEM and DC soundings3.7. Side effects in TEM sounding3.7.1. Superparamagnetic effect in TEM 3.7.2. Effect of induced polarization3.7.3. Antenna polarization effect (APE)4. Seismoelectric methods of Earth study (B. Svetov)4.1. Seismoelectric effect (SE) of the first kind4.2. Seismoelectric effect of the second kind: historical outline and elements of theory4.3. Physical interpretation of seismoelectric phenomena4.4. Modeling of seismoelectric fields4.5. Laboratory studies of seismoelectric effects on rock samples4.6. Experimental field and borehole seismoelectric studiesPart 2 Forward modeling and inversion techniques5. 3-D EM forward modeling using balance technique (V. Spichak)5.1. Modern approaches to the forward problem solution5.1.1. Methods of integral equations5.1.2. Methods of differential equations5.1.3. Mixed approaches5.1.4. Analog (physical) modeling approaches5.2. Balance method of EM fields computation in models with arbitrary conductivity distribution5.2.1. Statement of the problem5.2.2. Calculation of the electric field5.2.3. Calculation of the magnetic field5.2.4. Controlling the accuracy of the results5.3. Method of the EM field computation in axially symmetric media5.3.1. Problem statement5.3.2. Basic equations5.3.3. Boundary conditions5.3.4. Discrete equations and their numerical solution5.3.5. Code testing6. 3-D EM forward modeling using integral equations (D. Avdeev)6.1. Introduction6.2. Volume integral equation method6.2.1. Traditional IE method6.2.2. Modified iterative dissipative method6.3. Model examples6.3.1. Induction logging problem 6.3.2. Airborne EM example 6.4. Conclusion7. Inverse problems in modern magnetotellurics (V. Dmitriev, M. Berdichevsky)7.1. Three features of multi-dimensional inverse problem7.1.1. Normal background7.1.2. On detailness of multi-dimensional inversion7.1.3. On redundancy of observation data7.2. Three questions of Hadamard7.2.1. On the existence of a solution to the inverse problem7.2.2. On the uniqueness of the solution to the inverse problem7.2.3. On the instability of the inverse problem7.3. Magnetotelluric and magnetovariational inversions in the light of Tikhonov's theory of ill-posed problems7.3.1. Conditionally well-posed formulation of inverse problem7.3.2. Optimization method7.3.3. Regularization method8. Joint robust inversion of magnetotelluric and magnetovariational data (Iv.M. Varentsov)8.1. Adaptive parametrization of a geoelectric model8.1.1. A background structure and windows to scan anomalies8.1.2. A priori model structure and constrains8.1.3. Window with correlated resistivities of inversion cells8.1.4. Window with finite functions8.2. Inverted and modelling data8.3. Inversion as a minimization problem8.3.1. Minimizing functional8.3.2. Robust misfit metric8.3.3. Cycles of Tikhonov's minimization8.3.4. Newtonian minimization techniques8.3.5. Solution of linear newtonian system and choice of scalar newtonian step8.3.6. Multi-level adaptive stabilization8.3.7. Post-inversion analysis8.4. Study of inversion algorithms using synthetic data sets8.4.1. Comparison of three model parameterization schemes in 2-D inversion8.4.2. 2-D inversion with numerous finite functions8.4.3. 3-D inversion example8.4.4. Resolution of a system of local conductors using the CR-parameterization8.4.5. Reduction of strong data noise and static shift8.5. Conclusions9. Artificial neural network inversion of EM data (V. Spichak) 9.1. Backpropagation technique9.2. Creation of teaching and testing data pools9.3. Effect of the EM data transformations on the quality of the parameters' recognition9.3.1. Types of the activation function at hidden and output layers9.3.2. Number of the neurons in a hidden layer9.3.3. Effect of an extra hidden layer9.3.4. Threshold level 9.4. Effect of the input data type9.5. Effect of the volume and structure of the training data pool 9.5.1. Effect of size 9.5.2. Effect of structure9.6. Extrapolation ability of ANN9.7. Noise treatment9. 8. Case history: ANN reconstruction of the Minou fault parameters9.8.1. Geological and geophysical setting9.8.2. CSAMT data acquisition and processing9.8.3. 3-D imaging Minou fault zone using 1-D and 2-D inversion 9.8.4. ANN reconstruction of the Minou geoelectrical structure9.8.5. 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 observation10.2 Multi-site schemes for estimation of transfer operators10.3. Temporal stability of transfer operators10.4. Methods for the analysis and interpretation of simultaneous EM data10.5. Conclusions11. Magnetotelluric field transformations and their application in interpretation (V. Spichak)11.1. Linear relations between MT field components11.2. Point transforms of MT data11.2.1. Impedance transforms11.2.2 Apparent resistivity type transforms11.2.3. Induction and perturbation vectors11.3. Examples of the use of MT field point transforms for the interpretation11.3.1. Dimensionality indicators11.3.2. Local and regional anomalies11.3.3. Constructing resistivity images in the absence of prior information11.4. Integral transforms11.4.1. Division of the MT field into parts11.4.2. Transformation of the field components into each other11.4.3. 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 exploration12.1.1. Statement of the problem12.1.2. Numerical modeling12.2. Testing hypotheses of the geoelectric structure of the Transcaucasian region from magnetotelluric data12.2.1. Geological and geophysical characteristics of the region12.2.2. Alternative conductivity models12.2.3. Numerical modeling of magnetotelluric fields12.2.4. Conclusions12.3. MT imaging internal structure of volcanoes12.3.1. Simplified model of the volcano12.3.2. Synthetic MT pseudosections 12.3.3. Methodology of interpretation of the MT data measured over the relief surface12.4. Simulation of MT monitoring of the magma chamber conductivity 12.4.1. Geoelectric model of a central type volcano12.4.2. Detection of the magma chamber by MT data12.4.3. Estimation of MT data resoling power with respect to the conductivity variations in the magma chamber12.4.4. “Guidelines” for MT monitoring electric conductivity in a magma chamber12.5. Simulation of MT monitoring the ground water salinity12.5.1. Statement of the problem 12.5.2. Modeling of the salt water intrusion zone mapping by audio MT data13. Regional magnetotelluric explorations in Russia (V. Bubnov, E. Aleksanova, M. Berdichevsky, P. Pushkarev, A.Yakovlev, D.Yakovlev)13.1. Introduction13.2. Observation technology13.3. MT-data processing, analysis and interpretation13.4. Case histories: 13.4.1. East-European craton13.4.2. Caucasus, the Urals, Siberia and North East Russia14. EM studies at seas and oceans (N. Palshin)14.1. Conductivity structure of sea and ocean floor14.1.1. 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 studies14.2.1. 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 oceans14.3.1. 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

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