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

- ability of expository synthesis and use of appropriate technical-scientific language.

Frontal lectures, pratical 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.

Introduction 1: Data analysis: analog-digital conversion, spectral analysis, convolution, deconvolution, correlation, filtering.

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 hazard and evaluation of Local Seismic Response: Hazard evaluation: deterministic and probabilistic approaches; Criteria used to select design earthquake; Seismic microzoning and hazard scenarios; Non-linear behavior of soft soils; Site effects linked to heterogeneities, geometric and topographic irregularities, faults and cavities; Local seismic response evaluation: Modeling, Analytic and Experimental approaches (Nakamura technique, Spectral ratios – HVSR, HSSR; Practical section about recording and processing seismic data.

Exercises on sampling techniques and seismic signal processing.

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 (2009). 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.