Syllabus
* Introduction
Subject of geoelectricity as a geophysical discipline. Classification of geoelectrical methods.
* Electrical conductivity of the earth's materials
Physical principles of the electrical conductivity. Electrical conductivity of minerals, rocks, fluids and melts. Mechanisms of the electrical conductivity in the earth, mixture laws. Electric macro-anisotropy and its possible geodynamical interpretation. Relation of the electrical conductivity to other geophysical parameters. Other electromagnetic parameters - permitivity, permeability, electrochemical parameters.
* Primary sources of the natural electromagnetic field of the Earth
Frequency range of geoelectrical induction methods, sources of the primary electromagnetic field in radio-, audio- and helio-frequency bands, their structure in time and space.
* Electromagnetic plane wave in a layered conductor - Cagniard-Tikhonov magnetotelluric model
Direct and inverse magnetotelluric problem. Plain wave impeding on the surface of a layered conductor. Cagniard-Tikhonov fundamental model of the magnetotelluric problem, impedance of a layered earth, apparent resistivity and impedance phase. Long period asymptotics of magnetotelluric curves. Analytical properties of the magnetotelluric impedance.
* Electromagnetic induction in a layered earth due to spatially non-uniform sources
Maxwell's equations in a wave number domain. Magnetotelluric and magnetic spectral impedances for a layered conductor. Magnetotelluric and geomagnetic induction soundings. Limitations of the Cagniard-Tikhonov model with a non-uniform source field. Generalization to spherical conductors - global electromagnetic soundings into the mantle depths.
* Electromagnetic field in laterally inhomogeneous structures
Classification of lateral inhomogeneities (local, regional, 2-D, 3-D). Modelling of electromagnetic fields in horizontally inhomogeneous structures (laboratory models, numerical models). Impedance tensor. Approximate models, Born approximation and its extensions, induction in a thin sheet. Distortions of the magnetotelluric curves due to lateral inhomogeneities, local/regional composite models of the magnetotelluric field. Deep geomagnetic soundings - geomagnetic transfer functions and induction arrows.
* Magnetotelluric practice, geoelectrical models
Practical aspects of magnetotelluric and geomagnetic depth soundings (instrumentation, data acquisition, data processing, interpretation). Geoelectrical projects. Electrical anomalies within the earth, their explanation in terms of thermodynamic, structural and tectonic conditions. Estimates of the electrical conductivity of the lower mantle and the earth's core.
Annotation
The course aims at explaining mechanisms that form the distribution of the electrical conductivity in the Earth's crust and mantle and their relation to thermodynamical, structural and tectonic conditions in the earth. Physical principles as well as selected practical aspects are given of electromagnetic induction methods based on the excitation by a natural geomagnetic variation field which are used for electromagnetic depth soundings of the earth.
Case studies of anomalous electrical conductivities are presented from regions corresponding to basic types of tectonic structures.