Rosa Di Maio | Università degli Studi di Napoli "Federico II" (original) (raw)

Papers by Rosa Di Maio

Research paper thumbnail of  Predicting Electrical Resistivity in Hydrothermal and Natural Degassing Geological Systems through petrophysical and thermodynamic data: a machine learning approach

Research paper thumbnail of SOM Clustering Analysis in the Discrete Wavelet Transform Domain for Filtering Noisy Magnetotelluric Data

Proceedings, Jun 12, 2017

Research paper thumbnail of High-resolution geoelectrical characterization and monitoring of natural fluids emission systems to understand possible gas leakages from geological carbon storage reservoirs

Scientific Reports, Oct 29, 2023

Gas leakage from deep geologic storage formations to the Earth's surface is one of the main hazar... more Gas leakage from deep geologic storage formations to the Earth's surface is one of the main hazards in geological carbon sequestration and storage. Permeable sediment covers together with natural pathways, such as faults and/or fracture systems, are the main factors controlling surface leakages. Therefore, the characterization of natural systems, where large amounts of natural gases are released, can be helpful for understanding the effects of potential gas leaks from carbon dioxide storage systems. In this framework, we propose a combined use of high-resolution geoelectrical investigations (i.e. resistivity tomography and self-potential surveys) for reconstructing shallow buried fracture networks in the caprock and detecting preferential gas migration pathways before it enters the atmosphere. Such methodologies appear to be among the most suitable for the research purposes because of the strong dependence of the electrical properties of water-bearing permeable rock, or unconsolidated materials, on many factors relevant to CO 2 storage (i.e. porosity, fracturing, water saturation, etc.). The effectiveness of the suggested geoelectrical approach is tested in an area of natural gas degassing (mainly CH 4) located in the active fault zone of the Bolle della Malvizza (Southern Apennines, Italy), which could represent a natural analogue of gas storage sites due to the significant thicknesses (hundreds of meters) of impermeable rock (caprock) that is generally required to prevent carbon dioxide stored at depth from rising to the surface. The obtained 3D geophysical model, validated by the good correlation with geochemical data acquired in the study area and the available geological information, provided a structural and physical characterization of the investigated subsurface volume. Moreover, the time variations of the observed geophysical parameters allowed the identification of possible migration pathways of fluids to the surface.

Research paper thumbnail of Geological Reconstruction by 2D-ERT of the Maddaloni-Durazzano Ridge (Italy) for a Railway Line Design

Summary We present a geophysical study for the executive project of a railway tunnel across the M... more Summary We present a geophysical study for the executive project of a railway tunnel across the Maddaloni-Durazzano carbonate ridge (southern Italy). To reconstruct the geological setting of the area, a N-S oriented electrical resistivity tomography (ERT) profile, about 4 km long, was performed, which allowed an exploration depth of about 200 m from the surface level. The results of the 2D inversion model of the ERT profile clearly highlight anomalous resistive blocks that can be associated with fractured/karst sectors of the Cretaceous carbonate succession affected by significant water circulation, while there are no evident resistivity anomaly features linked to the presence of large cavities. Significantly, the geophysical model identifies at the northern end of the ERT profile, where the entrance to the tunnel was planned, the presence of the regional thrust fault bounding the northern side of the ridge, which was hypothesized by the geological cartography but not supported by field observations. The validation of the geological-structural model provided by the ERT interpretation was derived from geognostic boreholes and direct observations carried out during the excavation of a tunnel crosscutting the ERT section.

Research paper thumbnail of Le geoscienze a scuola: stato dell’arte e prospettive - Geosciences at school: state of art and perspectives

RENDICONTI ONLINE DELLA SOCIETÀ GEOLOGICA ITALIANA, Jul 1, 2018

Research paper thumbnail of Understanding the effects of leaking gas in geological carbon sequestration through geophysical characterization of natural CO2 gas emission systems

<p>Gas leakage from deep geologic storage formations to the Earth&a... more <p>Gas leakage from deep geologic storage formations to the Earth’s surface is one of the main hazards in geological carbon sequestration and storage. Permeable sediment covers or natural and artificial pathways, such as faults and well structures, are the main factors controlling surface leakages. Therefore, the characterization of natural systems, where large amounts of CO<sub>2</sub> are released, can be helpful for understanding the effects of potential gas leaks from storage carbon systems. In this framework, we propose a combined use of geoelectrical investigations (i.e., resistivity tomography and self-potential surveys) for characterizing natural CO<sub>2</sub> leakage areas, as well as gas storage sites. Such methodologies appear to be among the most suitable for revealing spatial distributions of carbon dioxide and monitoring subsurface fluid migration processes, because of the strong dependence of the electrical properties of water-bearing permeable rock, or unconsolidated materials, on many factors relevant to CO<sub>2</sub> storage (i.e., porosity, fracturing, water saturation, etc.). Indeed, the electric resistivity of porous water-bearing sediments decreases significantly when CO<sub>2</sub> dissolves in pore-water, in contrast to the effect in the gas phase and supercritical CO<sub>2</sub>, while the anomalous concentrations of natural electric charge are directly related to carbon dioxide migration along porous and fractured rock systems. The effectiveness of the suggested multi-methodological geoelectrical approach is tested in some areas of natural CO<sub>2</sub> degassing located in the Southern Apennines (Italy), which could represent natural analogues of gas storage sites. Specifically, electrical resistivity and self-potential surveys are targeted at reconstructing shallow buried fracture networks in the cap-rock and detecting preferential CO<sub>2</sub> migration pathways. Our findings are promising for imaging the CO<sub>2</sub> plume within a carbon storage reservoir and for identifying possible CO<sub>2</sub> leakages through the cap-rock formation, suggesting that the proposed approach can be very helpful also for the monitoring of carbon sequestration systems.  </p>

Research paper thumbnail of Denoising of magnetotelluric signals by polarization analysis in the discrete wavelet domain

Computers & Geosciences, Mar 1, 2017

Magnetotellurics (MT) is one of the prominent geophysical methods for underground deep exploratio... more Magnetotellurics (MT) is one of the prominent geophysical methods for underground deep exploration and, thus, appropriate for applications to petroleum and geothermal research. However, it is not completely reliable when applied in areas characterized by intense urbanization, as the presence of cultural noise may significantly affect the MT impedance tensor estimates and, consequently, the apparent resistivity values that describe the electrical behaviour of the investigated buried structures. The development of denoising techniques of MT data is thus one of the main objectives to make magnetotellurics reliably even in urban or industrialized environments. In this work we propose an algorithm for filtering of MT data affected by temporally localized noise. It exploits the discrete wavelet transform (DWT) that, thanks to the possibility to operates in both time and frequency domain, allows to detect transient components of the MT signal, likely due to disturbances of anthropic nature. The implemented filter relies on the estimate of the ellipticity of the polarized MT wave. The application of the filter to synthetic and field MT data has proven its ability in detecting and removing cultural noise, thus providing apparent resistivity curves more smoothed than those obtained by using raw signals.

Research paper thumbnail of A.C.QU.A. – Low Frequency Probe

Research paper thumbnail of Study of the groundwater regime in unsaturated slopes prone to landslides by multidisciplinary investigations: Experimental study and numerical modelling

Research paper thumbnail of Insights on the active Southern Matese Fault system through geological, geochemical, and geophysical investigations of the CO2 gas vent in the Solopaca area (southern Apennines, Italy)

Research paper thumbnail of A new frequency-domain based approach for detecting low frequency seismic events: An application to the Mt. Vesuvius seismicity

<p>The detection of low energy seismic events and tremor related to volcani... more <p>The detection of low energy seismic events and tremor related to volcanic activity in areas characterized by high background noise represents a crucial challenge for monitoring and surveillance purposes. In the last three years, the seismicity of the Mt. Vesuvius (southern Italy) has been characterized by low-magnitude volcano tectonic earthquakes, the most of which are located at depth shallower than 3 km b.s.l., while very few low-frequency earthquakes and tremor episodes are located at about 6-7 km depth. It is well known that magmatic and hydrothermal systems can play an important role in the generation of low-frequency seismic events, which could be important precursors for assessing the reawakening of a volcano. Therefore, our main objective is to develop a methodology for detecting the presence of low frequency (LF) events hidden in the background noise and not identifiable by classical detection procedures. In particular, we suggest a frequency domain approach based on a joint application of coherence analysis among signals from local network seismic stations and parameterization of the amplitude spectra according to the statistical moments. The proposed methodology has been applied to the analysis of continuous seismic signals recorded over three years at Mt. Vesuvius. Spectral parameters, such as central frequency <em>W</em><em>, </em>shape factor <em>d</em> and coherence <em>c</em>, were evaluated on 30-s windows signals in the frequency range between 2 and 40 Hz. The selection of the signal windows that could potentially contain low-frequency events or tremor signals was performed according to the following criteria: a) 0.45 < <em>δ</em><em> <</em> 0.65; b) 3 Hz < <em>W</em><em> <</em> 6 Hz and c) <em>c</em> greater than 0.5, which are based on the results of preliminary analyses of the seismicity observed at Mt. Vesuvius. The detected signal windows were visually inspected and compared with the seismic catalogues to eliminate those corresponding to earthquakes occurred outside the area of interest. For the three-years of analyzed data, more than 200 episodes of low frequency signals were identified, 120 of which are not present in the seismic catalog. Most of them appear as low-amplitude tremor episodes, with no clear evidence of P and S phases, hidden in the noisy raw signals but visible at the entire seismic network after proper signal filtering. Compared to the few LF events detected and analysed in the past, our findings suggest that the proposed methodology can be an efficient tool for detecting low-amplitude signals not easily identifiable in the background noise and could represent an improvement for the monitoring system of the Mt. Vesuvius volcanic area.</p>

Research paper thumbnail of Multi-sensor Soil Electromagnetic Sounding (MuSES) for Mars exploration

Research paper thumbnail of Study of the Simplon area geothermal anomaly in the frame of a transalpine deep railway tunnel feasibility project

Research paper thumbnail of Basic theory of electrokinetic effects associated with earthquakes

Bollettino Di Geofisica Teorica Ed Applicata, 1991

Research paper thumbnail of Modelling earth current precursors in earthquake prediction

Annals of Geophysics, Mar 18, 1997

Research paper thumbnail of Interpolation of Induced Polarization Transients by the Generalized Cole-Cole Relaxation Model

We consider a Generalized Cole-Cole (GCC) model as representative of relaxations of electric volt... more We consider a Generalized Cole-Cole (GCC) model as representative of relaxations of electric voltages in time domain Induced Polarization.

Research paper thumbnail of Two-modal cole-cole modelling of lP time domain relaxations

53rd EAEG Meeting, 1991

The dominant method for detecting and delineating native pyrite mineralization is Induced Polariz... more The dominant method for detecting and delineating native pyrite mineralization is Induced Polarization (lP). In presence of hydrocarbon reservoirs the lP anomalies are thought to he caused by epigenetic pyritization located in a plume over oil fields in a geochemically active environment. In geothermal areas the observed lP anomalies can be associated with pyrite concentrations deposited where sulfur-rich thermal waters interrnix with meteoric waters.

Research paper thumbnail of Self-potential anomalies in some Italian volcanic areas

Annals of Geophysics, Jan 18, 1996

Research paper thumbnail of Experimental evidence of resistivity frequency-dispersion in magnetotellurics in the Newberry (Oregon), Snake River Plain (Idaho) and Campi Flegrei (Italy) volcano-geothermal areas

Journal of Volcanology and Geothermal Research, Aug 1, 1991

We show that magnetotelluric measurements carried out in volcano-geothermal areas can be signific... more We show that magnetotelluric measurements carried out in volcano-geothermal areas can be significantly affected by the resistivity frequency-dispersion phenomenon. The polarization effects are recognized by comparing magnetotelluric and DC geoelectrical deep soundings performed in the same station. Indeed, the conventional separate analysis of the two data sets sometimes gives unconformable results, especially as it regards the resistivity and thickness of the conductive layers, ascribable to the geothermal fluid-filled rocks. These apparent discrepancies can be overcome by admitting the occurrence of intense induced polarization effects inside the rocks having extensive alterations due to hydrothermal paragenesis. The basic theory of the induced polarization effects over magnetotelluric measurements is at first briefly recalled. Then, three impressive field examples taken from previous experiments performed in the Newberry Volcano, Snake River Plain and Campi Flegrei geothermal areas are presented and discussed.

Research paper thumbnail of Infrastructures Souterraines De Transports - II - Les Reconnaissances Prealables en Vue Du Projet De Genie Civil (A Suivre)

(Suite de la fiche DIRR 130844). La caracterisation geomecanique des Flyschs des Apennins septent... more (Suite de la fiche DIRR 130844). La caracterisation geomecanique des Flyschs des Apennins septentrionaux en Italie (FROLDI,P) ; The NATM application in Russia (MERKIN,VE - MILLERMAN,AS) ; Utilisation du pressiometre pour la determination des caracteristiques du sol en place (MONNET,J) ; La traversee souterraine de Toulon : reconnaissances geologiques, hydrogeologiques et geotechniques (ROBERT,A - PAULY,JC - PRANEUF,JP - TOSI,M) ; Prediction of the leakage into a newly-constructed tunnel due to dam impoundment (KURITA,T - TOYOOKA,A - TANIKAWA,Y) ; Surface settlements forecast on metrotunnelling in Russia (CHEBOTAEV,VV - AUERBACH,VM - LEVCHENKO,AI) ; Optimization of stripping in a slate bank (GONZALEZ NICIEZA,C - MENENDEZ DIAZ,A - ORDIERES MERE,JB - TABOADA CASTRO,J). (Voir fiche generale DIRR 130842).

Research paper thumbnail of  Predicting Electrical Resistivity in Hydrothermal and Natural Degassing Geological Systems through petrophysical and thermodynamic data: a machine learning approach

Research paper thumbnail of SOM Clustering Analysis in the Discrete Wavelet Transform Domain for Filtering Noisy Magnetotelluric Data

Proceedings, Jun 12, 2017

Research paper thumbnail of High-resolution geoelectrical characterization and monitoring of natural fluids emission systems to understand possible gas leakages from geological carbon storage reservoirs

Scientific Reports, Oct 29, 2023

Gas leakage from deep geologic storage formations to the Earth's surface is one of the main hazar... more Gas leakage from deep geologic storage formations to the Earth's surface is one of the main hazards in geological carbon sequestration and storage. Permeable sediment covers together with natural pathways, such as faults and/or fracture systems, are the main factors controlling surface leakages. Therefore, the characterization of natural systems, where large amounts of natural gases are released, can be helpful for understanding the effects of potential gas leaks from carbon dioxide storage systems. In this framework, we propose a combined use of high-resolution geoelectrical investigations (i.e. resistivity tomography and self-potential surveys) for reconstructing shallow buried fracture networks in the caprock and detecting preferential gas migration pathways before it enters the atmosphere. Such methodologies appear to be among the most suitable for the research purposes because of the strong dependence of the electrical properties of water-bearing permeable rock, or unconsolidated materials, on many factors relevant to CO 2 storage (i.e. porosity, fracturing, water saturation, etc.). The effectiveness of the suggested geoelectrical approach is tested in an area of natural gas degassing (mainly CH 4) located in the active fault zone of the Bolle della Malvizza (Southern Apennines, Italy), which could represent a natural analogue of gas storage sites due to the significant thicknesses (hundreds of meters) of impermeable rock (caprock) that is generally required to prevent carbon dioxide stored at depth from rising to the surface. The obtained 3D geophysical model, validated by the good correlation with geochemical data acquired in the study area and the available geological information, provided a structural and physical characterization of the investigated subsurface volume. Moreover, the time variations of the observed geophysical parameters allowed the identification of possible migration pathways of fluids to the surface.

Research paper thumbnail of Geological Reconstruction by 2D-ERT of the Maddaloni-Durazzano Ridge (Italy) for a Railway Line Design

Summary We present a geophysical study for the executive project of a railway tunnel across the M... more Summary We present a geophysical study for the executive project of a railway tunnel across the Maddaloni-Durazzano carbonate ridge (southern Italy). To reconstruct the geological setting of the area, a N-S oriented electrical resistivity tomography (ERT) profile, about 4 km long, was performed, which allowed an exploration depth of about 200 m from the surface level. The results of the 2D inversion model of the ERT profile clearly highlight anomalous resistive blocks that can be associated with fractured/karst sectors of the Cretaceous carbonate succession affected by significant water circulation, while there are no evident resistivity anomaly features linked to the presence of large cavities. Significantly, the geophysical model identifies at the northern end of the ERT profile, where the entrance to the tunnel was planned, the presence of the regional thrust fault bounding the northern side of the ridge, which was hypothesized by the geological cartography but not supported by field observations. The validation of the geological-structural model provided by the ERT interpretation was derived from geognostic boreholes and direct observations carried out during the excavation of a tunnel crosscutting the ERT section.

Research paper thumbnail of Le geoscienze a scuola: stato dell’arte e prospettive - Geosciences at school: state of art and perspectives

RENDICONTI ONLINE DELLA SOCIETÀ GEOLOGICA ITALIANA, Jul 1, 2018

Research paper thumbnail of Understanding the effects of leaking gas in geological carbon sequestration through geophysical characterization of natural CO2 gas emission systems

<p>Gas leakage from deep geologic storage formations to the Earth&a... more <p>Gas leakage from deep geologic storage formations to the Earth’s surface is one of the main hazards in geological carbon sequestration and storage. Permeable sediment covers or natural and artificial pathways, such as faults and well structures, are the main factors controlling surface leakages. Therefore, the characterization of natural systems, where large amounts of CO<sub>2</sub> are released, can be helpful for understanding the effects of potential gas leaks from storage carbon systems. In this framework, we propose a combined use of geoelectrical investigations (i.e., resistivity tomography and self-potential surveys) for characterizing natural CO<sub>2</sub> leakage areas, as well as gas storage sites. Such methodologies appear to be among the most suitable for revealing spatial distributions of carbon dioxide and monitoring subsurface fluid migration processes, because of the strong dependence of the electrical properties of water-bearing permeable rock, or unconsolidated materials, on many factors relevant to CO<sub>2</sub> storage (i.e., porosity, fracturing, water saturation, etc.). Indeed, the electric resistivity of porous water-bearing sediments decreases significantly when CO<sub>2</sub> dissolves in pore-water, in contrast to the effect in the gas phase and supercritical CO<sub>2</sub>, while the anomalous concentrations of natural electric charge are directly related to carbon dioxide migration along porous and fractured rock systems. The effectiveness of the suggested multi-methodological geoelectrical approach is tested in some areas of natural CO<sub>2</sub> degassing located in the Southern Apennines (Italy), which could represent natural analogues of gas storage sites. Specifically, electrical resistivity and self-potential surveys are targeted at reconstructing shallow buried fracture networks in the cap-rock and detecting preferential CO<sub>2</sub> migration pathways. Our findings are promising for imaging the CO<sub>2</sub> plume within a carbon storage reservoir and for identifying possible CO<sub>2</sub> leakages through the cap-rock formation, suggesting that the proposed approach can be very helpful also for the monitoring of carbon sequestration systems.  </p>

Research paper thumbnail of Denoising of magnetotelluric signals by polarization analysis in the discrete wavelet domain

Computers & Geosciences, Mar 1, 2017

Magnetotellurics (MT) is one of the prominent geophysical methods for underground deep exploratio... more Magnetotellurics (MT) is one of the prominent geophysical methods for underground deep exploration and, thus, appropriate for applications to petroleum and geothermal research. However, it is not completely reliable when applied in areas characterized by intense urbanization, as the presence of cultural noise may significantly affect the MT impedance tensor estimates and, consequently, the apparent resistivity values that describe the electrical behaviour of the investigated buried structures. The development of denoising techniques of MT data is thus one of the main objectives to make magnetotellurics reliably even in urban or industrialized environments. In this work we propose an algorithm for filtering of MT data affected by temporally localized noise. It exploits the discrete wavelet transform (DWT) that, thanks to the possibility to operates in both time and frequency domain, allows to detect transient components of the MT signal, likely due to disturbances of anthropic nature. The implemented filter relies on the estimate of the ellipticity of the polarized MT wave. The application of the filter to synthetic and field MT data has proven its ability in detecting and removing cultural noise, thus providing apparent resistivity curves more smoothed than those obtained by using raw signals.

Research paper thumbnail of A.C.QU.A. – Low Frequency Probe

Research paper thumbnail of Study of the groundwater regime in unsaturated slopes prone to landslides by multidisciplinary investigations: Experimental study and numerical modelling

Research paper thumbnail of Insights on the active Southern Matese Fault system through geological, geochemical, and geophysical investigations of the CO2 gas vent in the Solopaca area (southern Apennines, Italy)

Research paper thumbnail of A new frequency-domain based approach for detecting low frequency seismic events: An application to the Mt. Vesuvius seismicity

<p>The detection of low energy seismic events and tremor related to volcani... more <p>The detection of low energy seismic events and tremor related to volcanic activity in areas characterized by high background noise represents a crucial challenge for monitoring and surveillance purposes. In the last three years, the seismicity of the Mt. Vesuvius (southern Italy) has been characterized by low-magnitude volcano tectonic earthquakes, the most of which are located at depth shallower than 3 km b.s.l., while very few low-frequency earthquakes and tremor episodes are located at about 6-7 km depth. It is well known that magmatic and hydrothermal systems can play an important role in the generation of low-frequency seismic events, which could be important precursors for assessing the reawakening of a volcano. Therefore, our main objective is to develop a methodology for detecting the presence of low frequency (LF) events hidden in the background noise and not identifiable by classical detection procedures. In particular, we suggest a frequency domain approach based on a joint application of coherence analysis among signals from local network seismic stations and parameterization of the amplitude spectra according to the statistical moments. The proposed methodology has been applied to the analysis of continuous seismic signals recorded over three years at Mt. Vesuvius. Spectral parameters, such as central frequency <em>W</em><em>, </em>shape factor <em>d</em> and coherence <em>c</em>, were evaluated on 30-s windows signals in the frequency range between 2 and 40 Hz. The selection of the signal windows that could potentially contain low-frequency events or tremor signals was performed according to the following criteria: a) 0.45 < <em>δ</em><em> <</em> 0.65; b) 3 Hz < <em>W</em><em> <</em> 6 Hz and c) <em>c</em> greater than 0.5, which are based on the results of preliminary analyses of the seismicity observed at Mt. Vesuvius. The detected signal windows were visually inspected and compared with the seismic catalogues to eliminate those corresponding to earthquakes occurred outside the area of interest. For the three-years of analyzed data, more than 200 episodes of low frequency signals were identified, 120 of which are not present in the seismic catalog. Most of them appear as low-amplitude tremor episodes, with no clear evidence of P and S phases, hidden in the noisy raw signals but visible at the entire seismic network after proper signal filtering. Compared to the few LF events detected and analysed in the past, our findings suggest that the proposed methodology can be an efficient tool for detecting low-amplitude signals not easily identifiable in the background noise and could represent an improvement for the monitoring system of the Mt. Vesuvius volcanic area.</p>

Research paper thumbnail of Multi-sensor Soil Electromagnetic Sounding (MuSES) for Mars exploration

Research paper thumbnail of Study of the Simplon area geothermal anomaly in the frame of a transalpine deep railway tunnel feasibility project

Research paper thumbnail of Basic theory of electrokinetic effects associated with earthquakes

Bollettino Di Geofisica Teorica Ed Applicata, 1991

Research paper thumbnail of Modelling earth current precursors in earthquake prediction

Annals of Geophysics, Mar 18, 1997

Research paper thumbnail of Interpolation of Induced Polarization Transients by the Generalized Cole-Cole Relaxation Model

We consider a Generalized Cole-Cole (GCC) model as representative of relaxations of electric volt... more We consider a Generalized Cole-Cole (GCC) model as representative of relaxations of electric voltages in time domain Induced Polarization.

Research paper thumbnail of Two-modal cole-cole modelling of lP time domain relaxations

53rd EAEG Meeting, 1991

The dominant method for detecting and delineating native pyrite mineralization is Induced Polariz... more The dominant method for detecting and delineating native pyrite mineralization is Induced Polarization (lP). In presence of hydrocarbon reservoirs the lP anomalies are thought to he caused by epigenetic pyritization located in a plume over oil fields in a geochemically active environment. In geothermal areas the observed lP anomalies can be associated with pyrite concentrations deposited where sulfur-rich thermal waters interrnix with meteoric waters.

Research paper thumbnail of Self-potential anomalies in some Italian volcanic areas

Annals of Geophysics, Jan 18, 1996

Research paper thumbnail of Experimental evidence of resistivity frequency-dispersion in magnetotellurics in the Newberry (Oregon), Snake River Plain (Idaho) and Campi Flegrei (Italy) volcano-geothermal areas

Journal of Volcanology and Geothermal Research, Aug 1, 1991

We show that magnetotelluric measurements carried out in volcano-geothermal areas can be signific... more We show that magnetotelluric measurements carried out in volcano-geothermal areas can be significantly affected by the resistivity frequency-dispersion phenomenon. The polarization effects are recognized by comparing magnetotelluric and DC geoelectrical deep soundings performed in the same station. Indeed, the conventional separate analysis of the two data sets sometimes gives unconformable results, especially as it regards the resistivity and thickness of the conductive layers, ascribable to the geothermal fluid-filled rocks. These apparent discrepancies can be overcome by admitting the occurrence of intense induced polarization effects inside the rocks having extensive alterations due to hydrothermal paragenesis. The basic theory of the induced polarization effects over magnetotelluric measurements is at first briefly recalled. Then, three impressive field examples taken from previous experiments performed in the Newberry Volcano, Snake River Plain and Campi Flegrei geothermal areas are presented and discussed.

Research paper thumbnail of Infrastructures Souterraines De Transports - II - Les Reconnaissances Prealables en Vue Du Projet De Genie Civil (A Suivre)

(Suite de la fiche DIRR 130844). La caracterisation geomecanique des Flyschs des Apennins septent... more (Suite de la fiche DIRR 130844). La caracterisation geomecanique des Flyschs des Apennins septentrionaux en Italie (FROLDI,P) ; The NATM application in Russia (MERKIN,VE - MILLERMAN,AS) ; Utilisation du pressiometre pour la determination des caracteristiques du sol en place (MONNET,J) ; La traversee souterraine de Toulon : reconnaissances geologiques, hydrogeologiques et geotechniques (ROBERT,A - PAULY,JC - PRANEUF,JP - TOSI,M) ; Prediction of the leakage into a newly-constructed tunnel due to dam impoundment (KURITA,T - TOYOOKA,A - TANIKAWA,Y) ; Surface settlements forecast on metrotunnelling in Russia (CHEBOTAEV,VV - AUERBACH,VM - LEVCHENKO,AI) ; Optimization of stripping in a slate bank (GONZALEZ NICIEZA,C - MENENDEZ DIAZ,A - ORDIERES MERE,JB - TABOADA CASTRO,J). (Voir fiche generale DIRR 130842).