s at depth and show subsequent MT monitoring parameters, particularly the phase tensor. From thes... more s at depth and show subsequent MT monitoring parameters, particularly the phase tensor. From these models, it seems that MT monitoring in a sedimentary environment at 20 .m could be sensitive to an increase of conductivity in a fault area at geothermal depths of 2-3 km if the size of the disturbed domain reaches about 10x0.3x2 km3.
For years, geophysicists have studied temporal and spatial variations of self-potential (SP) and ... more For years, geophysicists have studied temporal and spatial variations of self-potential (SP) and their relations with ore bodies, volcanism, subsurface fluid flow or earthquake processes (e.g. Fitterman, 1978). We will focus here on SP anomalies resulting from electrokinetics, i.e. smallscale interactions between a porous medium and the fluids that flow through it. We propose here a novel approach to the analysis of spatial variations of SP by introducing a wavelet-based technique that improves classical interpretation methods (e.g. Rao et al., 1970) to characterise the spatial geometry of sources at depth. Knowing the coupling coefficients between streaming flow potential and SP, this approach also provides a characterisation of the subsurface fluid flows. We illustrate our method by an application to SP data acquired around the Vulcarolo fissure on Mount Etna (Aubert, 1999).
The detection of water leakage along its transportation network has important societal impacts, s... more The detection of water leakage along its transportation network has important societal impacts, such as avoiding a large volume of water wasted along the waterways or preventing water-related chemical or physical surrounding media deterioration. Among the vast domain of destructive techniques, Ground-Penetrating Radar (GPR) is a common and efficient tool used for detection in many near-surface contexts, and it is particularly efficient in civil engineering cases, such as utility detection, due to its fine resolution and the ease of data acquisition. A peculiar form of signal enhancement appears in GPR profiles recorded over spheres and cylinders where velocity contrasts exist between the body’s material and the surrounding medium. We used this enhancement to detect potential water leakages in water pipes. After exhibiting the signal enhancement effect in a laboratory sandbox experiment using a spherical glass ball, we verified the results with numerical experiments with varied spher...
2017 9th International Workshop on Advanced Ground Penetrating Radar (IWAGPR), 2017
This study presents the results of a GPR investigation carried out at the archeological site of T... more This study presents the results of a GPR investigation carried out at the archeological site of Tingambato, in the state of Michoacán, Mexico. The aim of the study was to detect the presence of ancient buried structures, such as walls or graves and determine their geometry in order to help establish the timeline history of the site. It also aimed at producing amplitude maps and/or reflection profiles of the location and dimensions of burial targets. The survey was conducted in four areas using the 200 MHz antenna, and in one area the study was performed with a 900 MHz antenna.
Key points-All impactite formations of the Rochechouart impact structure have a clear electrical ... more Key points-All impactite formations of the Rochechouart impact structure have a clear electrical signature-Large-scale electrical investigations unveil a rough transition between impactites and unbrecciated basement, implying possible megablocks-Fracturing/brecciation in the Rochechouart basement locally reaches depths larger than 200 m Supporting Information may be found in the online version of this article.
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Near Surface 2005 - 11th European Meeting of Environmental and Engineering Geophysics, 2005
The Self-Potential (SP) method is one of the hydrogeophysical methods that provides information c... more The Self-Potential (SP) method is one of the hydrogeophysical methods that provides information concerning underground water flow. Indeed, hydraulic currents generate underground electrical currents (tens of mV) through electrokinetic coupling. Following SP time variations allows to monitor water fluxes during infiltration (e.g. Thony et al., 1997, Doussan et al., 2002, Darnet & Marquis, 2004), pumping (e.g. Darnet et al., 2003) or seepage (Titov et al., 2000).
Near Surface 2005 - 11th European Meeting of Environmental and Engineering Geophysics, 2005
P038 T-05 Aquifer imaging using CSAMT and ERT Introduction 1 Three-dimensional characterization o... more P038 T-05 Aquifer imaging using CSAMT and ERT Introduction 1 Three-dimensional characterization of near-surface aquifer systems is an important challenge for our community not only for their use as water resources but also for their use for waste disposal. This task requires methods with high precision and resolution at different scales (from 10 0 to 10 4 m). A new discipline known as hydrogeophysics is being developed by several research groups all over the world (Hubbard and Rubin 2002). New advances on the characterization of near-surface areas have taken advantage of the diversity of information that can be obtained using
Journal of Volcanology and Geothermal Research, 2017
The 2645 m-high La Fournaise volcano, located in the Southwest of Réunion Island (Indian Ocean), ... more The 2645 m-high La Fournaise volcano, located in the Southwest of Réunion Island (Indian Ocean), is a shield basaltic volcano where effusive eruptions generally occur along long fissures starting from the summit, alongside major fractures that characterize the eruptions" dynamism and effusivity. Between 1992 and 1998, the volcano underwent a quiet period during which few earthquakes were recorded. Minor seismic activity returned after 1997 and picked up in March 1998 during the 35 hours preceding the March 9 eruption. From 1996, two autonomous stations (CSV and BAV) were installed on the volcano. CSV was located inside the Enclos Fouqué caldera while BAV was positioned 8.2 km NW of the volcano summit. Horizontal components of the electric and magnetic fields were sampled every 20 seconds. Continuous time-series were available from 1996 to 1999 at CSV, and from 1997 to March 1998 at BAV. Data have been processed using both single-station and remote-reference processing. Both results show apparent resistivity variations synchronous to the eruption. Time-lapse impedance estimates are computed on overlapping time windows of about two days at both stations. The only major decrease of the observed impedance coincides with the March 1998 eruption. At CSV, the resistivity started to drop about five days before the eruption, reached several local minima until April, and then slowly increased as the volcanic crisis reduced in activity. After the end of the crisis in September 1998, the apparent resistivity recovered its pre-crisis value. The time-lapse results also show variability in directionality: sharp and elongated phase tensor ellipse residuals appear during the eruption with a N105° orientation, suggesting the emergence of an almost NS-striking dyke. A 1D background model built from MT soundings performed during the quiet period (1996 to February 1998) on which a 3D NS-striking dyke was added shows a good agreement with phase tensor residuals and spatial distribution of the resistivity variations observed during the eruption.
s at depth and show subsequent MT monitoring parameters, particularly the phase tensor. From thes... more s at depth and show subsequent MT monitoring parameters, particularly the phase tensor. From these models, it seems that MT monitoring in a sedimentary environment at 20 .m could be sensitive to an increase of conductivity in a fault area at geothermal depths of 2-3 km if the size of the disturbed domain reaches about 10x0.3x2 km3.
For years, geophysicists have studied temporal and spatial variations of self-potential (SP) and ... more For years, geophysicists have studied temporal and spatial variations of self-potential (SP) and their relations with ore bodies, volcanism, subsurface fluid flow or earthquake processes (e.g. Fitterman, 1978). We will focus here on SP anomalies resulting from electrokinetics, i.e. smallscale interactions between a porous medium and the fluids that flow through it. We propose here a novel approach to the analysis of spatial variations of SP by introducing a wavelet-based technique that improves classical interpretation methods (e.g. Rao et al., 1970) to characterise the spatial geometry of sources at depth. Knowing the coupling coefficients between streaming flow potential and SP, this approach also provides a characterisation of the subsurface fluid flows. We illustrate our method by an application to SP data acquired around the Vulcarolo fissure on Mount Etna (Aubert, 1999).
The detection of water leakage along its transportation network has important societal impacts, s... more The detection of water leakage along its transportation network has important societal impacts, such as avoiding a large volume of water wasted along the waterways or preventing water-related chemical or physical surrounding media deterioration. Among the vast domain of destructive techniques, Ground-Penetrating Radar (GPR) is a common and efficient tool used for detection in many near-surface contexts, and it is particularly efficient in civil engineering cases, such as utility detection, due to its fine resolution and the ease of data acquisition. A peculiar form of signal enhancement appears in GPR profiles recorded over spheres and cylinders where velocity contrasts exist between the body’s material and the surrounding medium. We used this enhancement to detect potential water leakages in water pipes. After exhibiting the signal enhancement effect in a laboratory sandbox experiment using a spherical glass ball, we verified the results with numerical experiments with varied spher...
2017 9th International Workshop on Advanced Ground Penetrating Radar (IWAGPR), 2017
This study presents the results of a GPR investigation carried out at the archeological site of T... more This study presents the results of a GPR investigation carried out at the archeological site of Tingambato, in the state of Michoacán, Mexico. The aim of the study was to detect the presence of ancient buried structures, such as walls or graves and determine their geometry in order to help establish the timeline history of the site. It also aimed at producing amplitude maps and/or reflection profiles of the location and dimensions of burial targets. The survey was conducted in four areas using the 200 MHz antenna, and in one area the study was performed with a 900 MHz antenna.
Key points-All impactite formations of the Rochechouart impact structure have a clear electrical ... more Key points-All impactite formations of the Rochechouart impact structure have a clear electrical signature-Large-scale electrical investigations unveil a rough transition between impactites and unbrecciated basement, implying possible megablocks-Fracturing/brecciation in the Rochechouart basement locally reaches depths larger than 200 m Supporting Information may be found in the online version of this article.
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Near Surface 2005 - 11th European Meeting of Environmental and Engineering Geophysics, 2005
The Self-Potential (SP) method is one of the hydrogeophysical methods that provides information c... more The Self-Potential (SP) method is one of the hydrogeophysical methods that provides information concerning underground water flow. Indeed, hydraulic currents generate underground electrical currents (tens of mV) through electrokinetic coupling. Following SP time variations allows to monitor water fluxes during infiltration (e.g. Thony et al., 1997, Doussan et al., 2002, Darnet & Marquis, 2004), pumping (e.g. Darnet et al., 2003) or seepage (Titov et al., 2000).
Near Surface 2005 - 11th European Meeting of Environmental and Engineering Geophysics, 2005
P038 T-05 Aquifer imaging using CSAMT and ERT Introduction 1 Three-dimensional characterization o... more P038 T-05 Aquifer imaging using CSAMT and ERT Introduction 1 Three-dimensional characterization of near-surface aquifer systems is an important challenge for our community not only for their use as water resources but also for their use for waste disposal. This task requires methods with high precision and resolution at different scales (from 10 0 to 10 4 m). A new discipline known as hydrogeophysics is being developed by several research groups all over the world (Hubbard and Rubin 2002). New advances on the characterization of near-surface areas have taken advantage of the diversity of information that can be obtained using
Journal of Volcanology and Geothermal Research, 2017
The 2645 m-high La Fournaise volcano, located in the Southwest of Réunion Island (Indian Ocean), ... more The 2645 m-high La Fournaise volcano, located in the Southwest of Réunion Island (Indian Ocean), is a shield basaltic volcano where effusive eruptions generally occur along long fissures starting from the summit, alongside major fractures that characterize the eruptions" dynamism and effusivity. Between 1992 and 1998, the volcano underwent a quiet period during which few earthquakes were recorded. Minor seismic activity returned after 1997 and picked up in March 1998 during the 35 hours preceding the March 9 eruption. From 1996, two autonomous stations (CSV and BAV) were installed on the volcano. CSV was located inside the Enclos Fouqué caldera while BAV was positioned 8.2 km NW of the volcano summit. Horizontal components of the electric and magnetic fields were sampled every 20 seconds. Continuous time-series were available from 1996 to 1999 at CSV, and from 1997 to March 1998 at BAV. Data have been processed using both single-station and remote-reference processing. Both results show apparent resistivity variations synchronous to the eruption. Time-lapse impedance estimates are computed on overlapping time windows of about two days at both stations. The only major decrease of the observed impedance coincides with the March 1998 eruption. At CSV, the resistivity started to drop about five days before the eruption, reached several local minima until April, and then slowly increased as the volcanic crisis reduced in activity. After the end of the crisis in September 1998, the apparent resistivity recovered its pre-crisis value. The time-lapse results also show variability in directionality: sharp and elongated phase tensor ellipse residuals appear during the eruption with a N105° orientation, suggesting the emergence of an almost NS-striking dyke. A 1D background model built from MT soundings performed during the quiet period (1996 to February 1998) on which a 3D NS-striking dyke was added shows a good agreement with phase tensor residuals and spatial distribution of the resistivity variations observed during the eruption.
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