GEOPHYSICAL METHODS OF EXPLORATION

The main objective of the course is to provide students with the necessary tools to process and use geophysical data in order to obtain information on the subsoil.

Knowledge and understanding:

- theoretical basis on seismic methods;

- theoretical basis on electrical methods;

- theoretical bases on seismic hazard and local seismic response.

Ability to apply knowledge:

- ability to acquire and analyze geophysical datasets for the subsurface exploration;

- ability to process local seismic response data.

Autonomy of judgment:

- ability to argue personal interpretations on geophysical datasets.

Communication skills

Frontal lectures, practical training.

Should teaching be carried out in mixed mode or remotely, it may be necessary to introduce changes with respect to previous statements, in line with the programme planned and outlined in the syllabus.

Learning assessment may also be carried out on line, should the conditions require it.

Knowledge of physics, mathematics and geophysics.

Introduction 1: Geophysical methods and applications, Planning of a geophysical survey; target identification¸ choice of stations interval, noise.

Introduction 2: Features of geophysical methodologies used in urban areas; Invasive and not invasive approaches; Traditional and innovative geophysical methodologies.

Seismology: seismic waves, reflection and transmission of incident rays, critical refraction, diffraction, intrinsic attenuation, spherical divergence, scattering, seismic sources, identification and registration of seismic waves.

Seismic refraction: halfspace and direct wave equation, horizontal layer and refracted wave equation, horizontal layers, inclined layer, non-planar discontinuities, survey, case histories.

Seismic reflection: horizontal layer and reflected wave equation, normal moveout, horizontal layers and rms velocity, multiple reflections, survey and horizontal-vertical resolution, data processing, applications and case histories.

Other seismic methods: Cross-hole test, Down-hole test, Cono sismico, Suspension logging test, MASW (multichannel analysis surface waves), Seismic tomography, Refraction microtremor analysis. Practical section about recording and processing MASW, Refraction Microtremor data, applications and case histories.

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. Applications and case histories.

Seismic Risk and Seismic Hazard, Building Vulnerability, Seismic Hazard Assessment: deterministic approach, probabilistic approach, Probabilistic Hazard Estimation, Design Earthquake Evaluation Criteria, Seismic Microzonation and Hazard Scenarios, Local Geology and Ground Assessment, Effects due to Heterogeneity, Presence of Geometric and Topographic Irregularities, Presence of Tectonic Structures and Cavities, Response spectrum, Calculation of local seismic response, Structuring a local seismic response study by numerical modeling, Microtremors, Nakamura Technique, Spectral ratios (HVSR, H/Href), Modeling, Examples of macro and micro seismic zoning.

Exercises on propagation of seismic waves.

Exercises of seismic refraction with REFRACT.

Exercises on the use of REXEL, STRATA, EERA, DEEPSOIL programs for local response modeling.

Tutorial on MASW and Refraction Microtremor, HVSR prospecting.

Exercises on interpretation of reflection seismic data through OPENDTECT.

1.      G. Lanzo, F. Silvestri (1999). RISPOSTA SISMICA LOCALE. Argomenti di Ingegneria Geotecnica 10, Edizioni Hevelius.

2.      C. Mancuso (1996). MISURE DINAMICHE IN SITO. Argomenti di Ingegneria Geotecnica 4, Edizioni Hevelius

3.      M. Corrao e G. Coco (2021). Geofisica applicata. Con particolare riferimento alle prospezioni sismiche, elettriche, elettromagnetiche e geotermiche. Flaccovio Dario editore.

4.      J.M. Reynolds (2011). An Introduction to Applied and Environmental Geophysics (Second Edition). Wiley-Blackwell Editore.

5.      P. Kearey et al. (2002). An Introduction to Geophysical Exploration. Blackwell Editore.

6.      L. Nori, P. Di Marcantonio (2014). Manuale pratico di risposta sismica locale. Dal sismogramma allo spettro di progetto con Rexel e Strata.

7.      Notes.

The exam consists of an oral test aimed at ascertaining the level of knowledge and understanding reached by the student on the theoretical and methodological contents indicated in the program. 

Verification of learning can also be carried out remotely, should the conditions require it.

What are the similarities and differences between the different seismic methods of exploration?

What does the maximum depth that can be investigated with a geophysical profile depend on?

Illustrate the main steps of data processing in a reflection seismic survey.

Geoelectric characterization of the subsoil by means of 2D sections.

Sections in contrasting impedance

Illustrate what the Dix equation is and what it is used for.

Talk about MASW and ReMi techniques.

Describe the different steps for assessing the local seismic response.