Electrical and Electromagnetic Methods of Geophysical Prospecting

Knowledge Deepening / Consolidation

The course is also offered to exchange programme students.

Students learn the basic principles of electrical and electromagnetic geophysical methods as techniques for investigating the subsurface. They are taught the electrical and electromagnetic properties of geological formations and the factors from which they are affected They will get acquainted with the most important electrical and electromagnetic methods of applied geophysics (electrical mapping, electrical sounding, electrical resistivity tomography, induced polarization, self potential, electromagnetic VLF, TEM, magnetotelluric, etc.) in relation to the ways in which data are measured and interpreted. They will link the geological structures and subsurface targets of economic interest with their electrical and electromagnetic detection methods. They will get familiar with the applications of the electrical and electromagnetic methods through a number of examples of application from different fields such as geology and tectonics, hydrogeology, environmental research, geotechnical research, mining exploration etc.

Scope of the course and importance of electrical and electromagnetic geophysical techniques in geophysical investigations. Short introduction, field of applications through field examples. Electrical and electromagnetic properties of rocks, definitions and their relationship with the geological, hydrogeological, mining characteristics. Electrical properties of rocks, minerals and geological formations. Basic relations between electrical and other petρophysical properties. Structure of the laboratory courses Electrical methods: calculation of the geometric factor of the electrode arrays and its effect on the quality of measurements. Signal/noise ratio in relation to contact resistance. Interpretation of electrical profiling data: data from geotechnical investigation. Interpretation of electrical sounding data. Curve construction and interpretation with 2-layer model curves. Processing with computer inversion algorithm. Field data from hydrogeological and environmental research. Interpretation of electrical tomography and induced polarization data: construction of pseudosection. Processing of data using 2D DC-IP inversion software (DC2Dpro). Field data from mining exploration. Interpretation of self-potential data. Data mapping and target location. Calculation of the depth of the target. Field data from hydrogeological investigations. Electromagnetic method: Calculation of the depth of investigation in relation to the frequency and the resistivity of the host formations VLF data interpretation. Application to filtered data, finding position and target tilt and characterization of its hydrogeological potential. Indication of best location for water drilling. Combined interpretation of VLF profiles and electrical sounding data. Integrated interpretation of the 2 types of data and construction of a combined geological/geophysical section. Indication of the best position for water drilling. Interpretation of ground penetration data (GPR) measurements. Application to filtered data, buried target location (buried pipe) and calculation of its burial depth. Data are from a survey in an urban environment. Basic geoelectrical measurement, relations between potential and resistivity, four electrode arrays, geometrical factor, apparent resistivity. Electrical mapping, basic layout and arrays used, ways of measuring, data processing and interpretation, examples of applications from geotechnical and archaeological prospection. Electrical sounding. Basic measurement configuration. Presentation of measurements and qualitative interpretation of the sounding curves. Graphical interpretation of measurements with 2 layer curves. Automated interpretation with inversion algorithms. Examples of applications from geological and hydrogeological research. Electrical Resistivity Tomography. Field of applications, basic measurement processes and instrumentation for 2D/3D measurements. Presentation of measurements and qualitative interpretation of pseudosections. Automated interpretation with inversion algorithms in 2 and 3 dimensions. Examples of applications from environmental, geotechnical and mining exploration. Induced Polarization: Application and basic principles. Chargeability and its connection to minerals and rocks. Pros cons and basic applications. Presentation of measurements and their qualitative interpretation. Automated interpretation with inversion algorithms. Examples of applications from environmental, geotechnical and mining prospection Self-Potential: Application and basic principles. Natural potential sources. Pros cons and field applications. Data presentation and qualitative interpretation. Examples of applications from hydrogeological, environmental and mining exploration. Electromagnetic methods. Basic theoretical principles, field of application, definitions of basic concepts: frequency, primary and secondary field, tilt angle, phase difference, real and imaginary part of the field. Frequency of operation and depth of investigation. Tilt angle and phase methods. Basic principles and measuring devices. Compensation method and VLF method. Processing (filtering) and interpretation of measurements. Examples of applications in hydrogeological and mining research. Transient electromagnetic method (TEM). Principles of operation and basic measurement devices and procedures, basic equipment. Presentation of measurements and qualitative interpretation of dredging. Automated interpretation with inversion algorithms. Examples of applications from mining and geothermal exploration. Magnetotelluric method: Application and basic configuration of measurement, equipment. Presentation of measurements and qualitative interpretation of magnetotellluric soundings. Automated interpretation with inversion algorithms. Examples of applications from geological and geothermal investigations. Ground Penetrating Radar (GPR): Application and basic measurement configuration, equipment. Properties of geomaterials in relation to the dielectric constant and depth of investigation in relation to antenna frequency and ground conductivity. Basic application fields, pros and cons. Presentation of measurements and processing of the radargrams. Interpretation of radargrams, location and depth of targets. Examples of applications from geotechnical research and archaeology. Field demonstration of electrical and electromagnetic methods Field demonstration at locations of the Univ. Campus of the application of electrical and electromagnetic methods. Content Field demonstration of the application of geophysical methods with the participation of students in groups that includes the collection of measurements in the field using the following geophysical techniques: electrical profiling, electrical sounding, 2D electrical and IP tomography, self-potential, VLF and GPR Evaluation method for students (if done separately from the course). The students deliver a relevant report with the basic interpretation of the collected field data.

Applied geophysics, electrical and electromagnetic methods, resistivity, electrical mapping, electrical sounding, electrical tomography, induced polarization, self-potential, electromagnetic methods, VLF, transient EM (TEM), magnetotelluric method, ground penetrating radar

10-03-2020