E. Rizzo,1 B. Suski, and A. Revil
S. Straface and S. TroisiReceived 26 February 2004; revised 30 June 2004; accepted 12 July 2004; published 7 October 2004.
Abstract. The flow of groundwater during a pumping test experiment is responsible for a measurable electrical field at the ground surface owing to the electrokinetic coupling between the Darcy velocity and the electrical current density. This electrical field can be measured passively with a network of nonpolarizable electrodes connected to a digital multichannel multimeter with a high internal impedance (>10 Mohm). These so-called self-potential signals can be used to track the pattern of groundwater flow in the subsurface. A field test was performed using a set of 53 Pb/PbCl2 electrodes plus an additional electrode used as a unique reference in the field and a set of five piezometers to monitor the position of the piezometric surface. Using appropriate Green’s functions, the electrical response is analyzed in terms of piezometric head distribution. This new methodology, which we call ‘‘electrography,’’ allows visualization of preferential fluid flow pathways and the distribution of heads during pumping test experiments. Using a conditioning technique, this method could allow inversion of the hydraulic conductivity distribution around a pumping well.
INDEX TERMS: 0925 Exploration Geophysics: Magnetic and electrical methods; 1832 Hydrology: Groundwater transport; 5104 Physical Properties of Rocks: Fracture and flow; 5109 Physical Properties of Rocks: Magnetic and electrical properties; 5114 Physical Properties of Rocks: Permeability and porosity; KEYWORDS: self-potential, pumping test, transmissivity
Citation: Rizzo, E., B. Suski, A. Revil, S. Straface, and S. Troisi (2004), Self-potential signals associated with pumping tests experiments, J. Geophys. Res., 109, B10203, doi:10.1029/2004JB003049.
A. Jardani, A. Revil, and J. P. DupontReceived 19 March 2005; revised 26 April 2006; accepted 2 May 2006; published 1 July 2006.
Abstract. A 3D tomography algorithm of self-potential (SP) signals is applied for the first time to the localization of subsurface cavities. A specific application is made to a marl-pit in Normandy (North-West of France). A SP map with a total of 221 (5 m-spaced) measurements shows a negative anomaly with an amplitude of 8 mV associated with the position of the marl pit. To explain these data, we solved the boundary-value problem for the coupled hydro- electric problem associated with the presence of the cavity using a finite-element code. The numerical simulations point out the role of open conduits in electrical charge accumulation near the roof of the cavity and the resistivity contrast between the cavity and the surrounding formation. We applied successfully a SP tomography algorithm showing that the roof of the cavity was associated with a monopole charge accumulation due to the entrance of the ground water flow in a network of open cracks. Citation: Jardani, A., A. Revil, and J. P. Dupont (2006), Self-potential tomography applied to the determination of cavities, Geophys. Res. Lett., 33, L13401, doi:10.1029/
A. Crespy, A. Revil, N. Linde, S. Byrdina, A. Jardani, A. Boléve, and P. HenryReceived 12 March 2007; revised 8 September 2007; accepted 5 November 2007; published 30 January 2008.
Abstract. Four sandbox experiments were performed to understand the self-potential response to hydro-mechanical disturbances in a water-infiltrated controlled sandbox. In the first two experiments, 0.5 mL of water was abruptly injected through a small capillary at a depth of 15 cm using a syringe impacted by a hammer stroke. In the second series of experiments, 0.5 mL of pore water was quickly pumped out of the tank, at the same depth, using a syringe. In both type of experiments, the resulting self-potential signals were measured using 32 sintered Ag/AgCl medical electrodes. In two experiments, these electrodes were located 3 cm below the top surface of the tank. In two other experiments, they were placed along a vertical section crossing the position of the capillary. These electrodes were connected to a voltmeter with a sensitivity of 0.1 mV and an acquisition frequency of 1.024 kHz. The injected/pumped volumes of water produced hydro- mechanical disturbances in the sandbox. In turn, these disturbances generated dipolar electrical anomalies of electrokinetic nature with an amplitude of few microvolts. The source function is the product of the dipolar Green’s function by a source intensity function that depends solely on the product of the streaming potential coupling coefficient of the sand to the pore fluid overpressure with respect to the hydrostatic pressure. Numerical modeling using a finite element code was performed to solve the coupled hydro-mechanical problem and to determine the distribution of the resulting self-potential during the course of these experiments. We use 2D and 3D algorithms based on the cross-correlation method and wavelet analysis of potential fields to show that the source was a vertical dipole. These methods were also used to localize the position of the source of the hydromechanical disturbance from the self-potential signals recorded at the top surface of the tank. The position of the source agrees with the position of the inlet/outlet of the capillary showing the usefulness of these methods for application to active volcanoes.
Citation: Crespy, A., A. Revil, N. Linde, S. Byrdina, A. Jardani, A. Boléve, and P. Henry (2008), Detection and localization of hydromechanical disturbances in a sandbox using the self-potential method, J. Geophys. Res., 113, B01205, doi:10.1029/2007JB005042.
A. Jardani, A. Revil, A. Boléve, A. Crespy, J.-P. Dupont, W. Barrash,
and B. Malama
Abstract. An algorithm is developed to interpret self-potential (SP) data in terms of distribution of Darcy velocity of the ground water. The model is based on the proportionality existing between the streaming current density and the Darcy velocity. Because the inverse problem of current density determination from SP data is underdetermined, we use Tikhonov regularization with a smoothness constraint based on the differential Laplacian operator and a prior model. The regularization parameter is determined by the L-shape method. The distribution of the Darcy velocity depends on the localization and number of non-polarizing electrodes and information relative to the distribution of the electrical resistivity of the ground. A priori hydraulic information can be introduced in the inverse problem. This approach is tested on two synthetic cases and on real SP data resulting from infiltration of water from a ditch. Citation: Jardani, A., A. Revil, A. Bole`ve, A. Crespy, J.-P. Dupont, W. Barrash, and B. Malama (2007), Tomography of the Darcy velocity from self-potential measurements, Geophys. Res. Lett., 34, L24403, doi:10.1029/2007GL031907.
Key Words. time-lapse, deformation, ﬂuid ﬂow, biogeochemical processes
Abstract. Geophysical methods can be used to create images of the Earth’s in- terior that constitute snapshots at the moment of data acquisition, In many applications, it is important to measure the temporal change in the subsurface, because the change is associated with deformation, ﬂuid ﬂow, temperature changes, or changes in material properties, We present an overview of how noninvasive geophysical methods can be used for this purpose, We focus on monitoring mechani- cal properties, ﬂuid transport, and biogeochemical processes, and present case studies that illustrate the use of geophysical methods for detecting time-lapse changes in associated properties.First published online as a Review in Advance on February 1, 2007
J. Castermant, C.A. Mendonc¸ a, A. Revil, F. Trolard, G. Bourrié
and N. Linde
Abstract. Negative self-potential anomalies can be generated at the ground surface by ore bod- ies and ground water contaminated with organic compounds. These anomalies are connected to the distribution of the redox potential of the ground water. To study the relationship between redox and self-potential anomalies, a controlled sandbox experiment was performed. We used a metallic iron bar inserted in the left-hand side of a thin Plexiglas sandbox filled with a calibrated sand infiltrated by an electrolyte. The self-potential signals were measured at the surface of the tank (at different time lapses) using a pair of non-polarizing electrodes. The self-potential, the redox poten- tial, and the pH were also measured inside the tank on a regular grid at the end of the experiment. The self-potential distribution sampled after six weeks presents a strong negative anomaly in the vicinity of the top part of the iron bar with a peak amplitude of −82 mV. The resulting distributions of the pH, redox, and self-potentials were interpreted in terms of a geobattery model combined with a description of the elec- trochemical mechanisms and reactions occurring at the surface of the iron bar. The corrosion of iron yields the formation of a resistive crust of fougerite at the surface of the bar. The corrosion modifies both the pH and the redox potential in the vicinity of the iron bar. The distribution of the self-potential is solved with Poisson’s equation with a source term given by the divergence of a source current density at the surface of the bar. In turn, this current density is related to the distribution of the redox potential and electrical resistivity in the vicinity of the iron bar. A least-squares inver- sion method of the self-potential data, using a 2D finite difference simulation of the forward problem, was developed to retrieve the distribution of the redox potential.
A. Revil, A. Finizola, S. Piscitelli, E. Rizzo, T. Ricci, A. Crespy, B. Angeletti, M. Balasco, S. Barde Cabusson, L. Bennati, A. Bole`ve, S. Byrdina, N. Carzaniga, F. Di Gangi, J. Morin, A. Perrone, M. Rossi, E. Roulleau, and B. Suski.Received 23 September 2007; revised 8 March 2008; accepted 2 April 2008; published 24 July 2008.
Abstract. La Fossa cone is an active stratovolcano located on Vulcano Island in the Aeolian Archipelago (southern Italy). Its activity is characterized by explosive phreatic and phreatomagmatic eruptions producing wet and dry pyroclastic surges, pumice fall deposits, and highly viscous lava flows. Nine 2-D electrical resistivity tomograms (ERTs; electrode spacing 20 m, with a depth of investigation >200 m) were obtained to image the edifice. In addition, we also measured the self-potential, the CO2 flux from the soil, and the temperature along these profiles at the same locations. These data provide complementary information to interpret the ERT profiles. The ERT profiles allow us to identify the main structural boundaries (and their associated fluid circulations) defining the shallow architecture of the Fossa cone. The hydrothermal system is identified by very low values of the electrical resistivity (<20 W m). Its lateral extension is clearly limited by the crater boundaries, which are relatively resistive (>400 W m). Inside the crater it is possible to follow the plumbing system of the main fumarolic areas. On the flank of the edifice a thick layer of tuff is also marked by very low resistivity values (in the range 1 – 20 W m) because of its composition in clays and zeolites. The ashes and pyroclastic materials ejected during the nineteenth-century eruptions and partially covering the flank of the volcano correspond to relatively resistive materials (several hundreds to several thousands W m). We carried out laboratory measurements of the electrical resistivity and the streaming potential coupling coefficient of the main materials forming the volcanic edifice. A 2-D simulation of the groundwater flow is performed over the edifice using a commercial finite element code. Input parameters are the topography, the ERT cross section, and the value of the measured streaming current coupling coefficient. From this simulation we computed the self-potential field, and we found good agreement with the measured self-potential data by adjusting the boundary conditions for the flux of water. Inverse modeling shows that self-potential data can be used to determine the pattern of groundwater flow and potentially to assess water budget at the scale of the volcanic edifice.
Department of Hydrogeophysics and Porous Media, European Center for Research in Environmental Geosciences, CNRS-CEREGE, Aix-en-Provence, FranceReceived 9 July 2001; revised 8 February 2002; accepted 13 February 2002; published 7 August 2002.
INDEX TERMS: 3914 Mineral Physics: Electrical properties; 5114 Physical Properties of Rocks: Permeability and porosity; 5139 Physical Properties of Rocks: Transport properties; 5109 Physical Properties of
Rocks: Magnetic and electrical properties; 1832 Hydrology: Groundwater transport; KEYWORDS: self-potential, electrokinetic, volcano, electric properties, fluid disruption, zeta potential
A. Revil and G. Saracco, P. Labazuy
Abstract. The formation of a magmatic intrusion at depth is responsible for the formation of various thermohydromechanical (THM) disturbances including the upsurge of shock waves and diffusion of pressure fronts in the volcanic system. We couple electromagnetic theory (Maxwell equations) and thermoporoelasticity (Biot equations) to look at the ground surface electrical signature of these THM disturbances. The nature of this coupling is electrokinetic, i.e., associated with water flow relative to the mineral framework and the drag of the excess of charge located in the vicinity of the pore water/mineral interface (the groundwater flow disturbance being related here to the THM disturbances in drained conditions). A new set of laboratory data shows that the electrokinetic coupling is very substantial in fractured basaltic and volcaniclastic materials, and in scoria with several hundreds of millivolts of electrical potential gradient produced per megapascal of pore fluid pressure variations. Our theoretical analysis predicts the diffusion of electromagnetic disturbances and quasi-static electrical signals. These signals can be used as precursors of a volcanic eruption. Indeed, electromagnetic phenomena recorded at the ground surface of a volcanic system, once properly filtered to remove external contributions, provide a direct and quasi-instantaneous insight into the THM disturbances occurring in the heart of the volcanic structure prior and during a volcanic event. Tomography of the quasi-static electrical field is discussed and applied to self-potential profiles performed at the Piton de la Fournaise volcano during the preparation phase of the March 1998 eruption.
INDEX TERMS: 0925 Exploration Geophysics: Magnetic and electrical methods; 1832 Hydrology: Groundwater transport; 5109 Physical Properties of
Rocks: Magnetic and electrical properties; 5114 Physical Properties of Rocks: Permeability and porosity;
5139 Physical Properties of Rocks: Transport properties; KEYWORDS: self-potential, geoelectric, forecasting, volcanic activity, tomography, shock wave
A. Revil, A. Finizola, F. Sortino and M. RipepeAccepted 2003 October 28. Received 2003 October 28; in original form 2003 May 22
SUMMARY. Stromboli volcano (Italy) is characterized by a permanent mild explosive activity disrupted by major and paroxysmal eruptions. These strong eruptions could be triggered by phreato- magmatic processes. With the aim of obtaining a better understanding of ground water flow in the vicinity of the active vents, we carried out a set of geophysical measurements along two profiles crossing the Fossa area (through the Pizzo, the Large and the Small Fossa craters). These measurements include electrical resistivity, induced polarization, self-potential, temper- ature and CO2 ground concentration. These methods are used in order to delineate the crater boundaries, which act as preferential fluid flow pathways for the upflow of hydrothermal fluids. The absence of fumarolic activity in the Fossa area and the ground temperature close to 100 ◦C at a depth of 30 cm indicate that the hydrothermal fluids condense close to the ground surface.
Part of this condensed water forms a shallow drainage network (<20 m) in which groundwater
flows downslope toward a perched aquifer. The piezometric surface of this aquifer is located
∼20 m below the topographic low of the Small Fossa crater and is close (<100 m) to the active vents. Electrical resistivity tomography, temperature and CO2 measurements show that this
shallow aquifer separates the underlying hydrothermal body from the ground surface. Further
studies are needed to ascertain the size of this aquifer and to check its possible implications for the major and paroxysmal events observed at the Stromboli volcano.
Key words: fluid flow, CO2 soil concentration, Self-potential, Stromboli, volcanic activity.
A. Finizola,1,2 A. Revil,3 E. Rizzo,4 S. Piscitelli,4 T. Ricci,5 J. Morin,2,6 B. Angeletti,3
L. Mocochain,3 and F. Sortino1
Received 8 May 2006; revised 15 July 2006; accepted 31 July 2006; published 7 September 2006.
 Finding the geometry of aquifers in an active volcano is important for evaluating the hazards associated with phreato- magmatic phenomena and incidentally to address the problem of water supply. A combination of electrical resistivity tomography (ERT), self-potential, C02, and temperature measurements provides insights about the location and pattern of ground water flow at Stromboli volcano. The measurements were conducted along a NE-SW profile across the island from Scari to Ginostra, crossing the summit (Pizzo) area. ERT data (electrode spacing 20 m, depth of penetration of 200 m) shows the shallow architecture through the distribution of the resistivities. The hydrothermal system is characterized by low values of the resistivity (<50 S m) while the surrounding rocks are resistive (>2000 S m) except on the North-East flank of the volcano where a cold aquifer is detected at a depth of
80 m (resistivity in the range 70 – 300 S m). C02 and temperature measurements corroborate the delineation of the hydrothermal body in the summit part of the volcano while a negative self-potential anomaly underlines the position of the cold aquifer. Citation: Finizola, A., A. Revil, E. Rizzo, S. Piscitelli, T. Ricci, J. Morin, B. Angeletti, L. Mocochain, and F. Sortino (2006), Hydrogeological insights at Stromboli volcano (Italy) from geoelectrical, temperature, and CO2 soil degassing investigations, Geophys. Res. Lett., 33, L17304, doi:10.1029/
A. revil, H. Schwaeger and L. M. Cathles III, P.D. Manhardt / September 10, 1999