# GEOPHYSICAL EXPLORATION OF THE SUBSOIL

GEO/11 - 6 CFU - 1° Semester

### Teaching Staff

SEBASTIANO IMPOSA

## Learning Objectives

The course has the stated goal of providing adequate knowledge of the use of the main investigation techniques in the application aimed at reconstruction of the subsurface . The skills required consist of a good mastery of mathematical and physical principles that govern the propagation of waves , aimed at knowledge of the subsurface

## Detailed Course Content

Electrical Methods

The electrical resistivity of rocks. Formula of Archie. Anisotropy, conductance longitudinal, transverse strength, principles of equivalence and suppression. Instrument Panel. Uplighter Section. Receiving section. Acquisition of the signal in the cases of low signal to noise ratio. Method of the resistivity. Current flow in a homogeneous medium: theoretical foundations. Electrode Devices. Profiles and surveys of resistivity. Data acquisition in the countryside. Data analysis and interpretation. Maps of apparent resistivity, pseudosections. Reconstruction of the conductive substrate impervious to hydrogeological research. Choice of investigations geo-electric surveys most appropriate for archaeological campaigns and for engineering purposes. Electrical measurements in the well. Coring conventional electrical. Choice of methodologies for use in campaign for the optimization of the surveys. Electrical Tomography 2D and 3D. Application cases.

Seismic Methods

Principles of the theory of elasticity. Elastic constants. Equation of the waveform. Waves of volume and surface waves. Propagation of the waves. Snell's Law. Principle of Fermat. Diffraction. Acoustic impedance. Coefficient of transmission and reflection seismic velocities. Seismic instrumentation. Seismic sources. Seismic reflection: horizontal reflector, normal moveout; reflector inclined, dip moveout. Methods of campaign in seismic reflection. Seismic refraction: single horizontal refractor; refractors multiple horizontal; refractor inclined. Case of vertical fault. Hidden layers. Refractors discontinuous. Method of the delay time. Method GRM (Generalized Reciprocal Method). Methods of campaign in seismic refraction. Seismic measurements in hole; method up-hole; method down-hole; method cross-hole. Choice of methodologies for use in campaign for the optimization of the surveys. Seismic tomography.

Electromagnetic Method

The Ground Penetrating Radar (georadar). Characteristics of the instrument and operating principles. Acquisition, processing and interpretation of data. Transmitting and receiving antennas. Choosing the frequency of the antenna. Considerations on prospecting G. P. R. and limits of exploration. Application Examples.

## Textbook Information

TELFORD W. M., GELDART L.P., SHERIFF R.E., KEYS D.A. - “Applied Geophysics” - Cambridge University Press, 1976.
Reynolds J.M. (1997): An introduction to Applied and Environmental Geophysics. J. Wiley & Sons, Chichester, 796 pp.
Coco G., Corrao M. “Geofisica applicata con particolare riferimento alle prospezioni sismiche, elettriche, elettromagnetiche e geotermiche. Flaccovio Dario editore, pp. 240, 2009

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