Self Potential Research Papers - Academia.edu (original) (raw)

Anomalies in self potential (SP) are usually explained in terms of geochemical activity. However, there are other sources of current which cause complications in the interpretation. In particular, DC telluric currents can be generated outside the survey region. Contrasts in resistivity cause current channelling and secondary voltages can be induced by leakage. The effect can be demonstrated using network theory and internal sources can be emphasized by subtraction. Joint surveys are required to demonstrate correlations with apparent resistivity.

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- Geophysics, Geophysical Survey, Geophysical Prospecting, Network Theory

Geophysical imaging methods provide solutions to a wide range of environmental and engineering problems: protection of soil and groundwater from contamination; safe disposal of chemical and nuclear waste; geotechnical site testing for... more

- by Prem Sharma
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- Geography, Geophysical Survey, Data acquisition, Nuclear Waste
- by Robert Kalin
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- Rock magnetism, Fuel Cell, Multidisciplinary, Electrical Resistance

Integrated electrical and electromagnetic surveys were carried out in hard rock areas of Purulia district (West Bengal), India, for delineation of groundwater-bearing zones that would be suitable for construction of deep tube-wells for large amounts of water. Groundwater movement that occurs through fractures in hard rocks is suitable to be delineated by very low frequency (VLF) electromagnetic surveys. A detailed survey of the area was done using a VLF-WADI instrument and appropriate locations were selected for further study using Schlumberger resistivity sounding. Hence, the entire area was surveyed in a relatively short time by the combined use of resistivity and electromagnetic surveys.

A pre-requisite in slope stability analyses is that the internal structure and the mechanical properties of the soil or rock mass of the slope, are known or can be estimated with a reasonable degree of certainty. Geophysical methods to determine the internal structure of a soil or rock mass may be used for this purpose. Various geophysical methods and their merits for slope stability analyses are discussed. Seismic methods are often the most suitable because the measurements depend on the mechanical properties that are also important in the mechanical calculation of slope stability
analyses. Other geophysical methods, such as electromagnetic, electric resistivity, self-potential, and gravity methods, may be useful to determine the internal structure, but require a correlation of found boundaries with mechanical properties.

- by Robert H R G K Hack
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- Geophysics, Rock Mechanics, Soil Mechanics, Slope Stability
- by Irfan Mustawa Hidayat
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- Self Potential

1 2 ERT and SP investigations were conducted in carbonate rocks of the Dinant Synclinorium 3 (Walloon Region of Belgium) to find suitable locations for new water wells in zones with 4 little hydrogeological data. Since measured information in the boreholes needed to be 5 representative of the area, large fractured zones were searched for the drillings. Large ERT 6 profiles (320 to 640 meters) allowed us to image the resistivity distribution of the first 60 7 meters of the subsurface and to detect and characterize (in terms of direction, width and 8 depth) fractured zones expected to be less resistive. Data errors, depth of investigation (DOI) 9

- by O. Kaufmann and +2
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- Geophysics, Applied Geophysics, Applied, Geomatic Engineering

The Causse of El Hajeb belongs to the Tabular Middle Atlas (TMA), in which thousands of karst landforms have been identified. Among them, collapse dolines and dissolution sinkholes have been highlighted as a source of environmental risks and geo-hazards. In particular, such sinkholes have been linked to the degradation of water quality in water springs located in the junction of the TMA and Saïss basin. Furthermore, the developments of collapse dolines in agricultural and inhabited areas enhance the risk of life loss, injury, and property damage. Here, the lack of research on newly formed cavities has exacerbated the situation. The limited studies using remote sensing or geophysical methods to determine the degree of karstification and vulnerability of this environment fail to provide the spatial extent and depth location of individual karst cavities. In order to contribute to the effort of sinkhole risk reduction in TMA, we employed remote sensing and geophysical surveys to integrate electrical resistivity tomography (ERT) and self-potential (SP) for subsurface characterization of four sinkholes identified in the Causse of El Hajeb. The results revealed the existence of sinkholes, both visible and non-accessible at the surface, in carbonate rocks. The sinkholes exhibited distinct morphologies, with depths reaching 35 m. Topography, geographic coordinates and land cover information extracted on remote sensing data demonstrated that these cavities were developed in depressions in which agricultural activities are regularly performed. The fusion of these methods benefits from remote sensing in geophysical surveys, particularly in acquisition, georeferencing, processing and interpretation of geophysical data. Furthermore, our proposed method allows identification of the protection perimeter required to minimize the risks posed by sinkholes.

A peat layer is normally occurred in the Nile Delta at shallow depths, ranging from 5 to 15.5 meters with a maximum thickness of 3.5 meters. In this work, the area of southern Mansoura City was covered by a shallow geoelectrical survey aiming to delineate the peat layer to assist the engineers for future planning of the infra structures in the area. The survey included self potential (SP), induced polarization (IP) and time domain electromagnetic (TDEM) techniques.

- by Mohamed Metwaly
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- High Resolution, Depth Map, Self Potential, Induced Polarization

Abstrak— Telah dilakukan percobaan yang berjudul. Analisa Struktur Lapisan Bawah Permukaan Lapangan GOR Pertamina Menggunakan Metode Self Potential. Percobaan ini bertujuan untuk menganalisis penyebab potensial alami dibawah permukaan lapangan GOR pertamina. Percobaan ini menggunakan prinsip metode Self Potential (SP). Pada percobaan ini digunakan alat dan bahan berupa 5 buah porous pot, larutan CuSO 4 , GPS, multimeter, kabel, meteran, palu, dan laptop dengan software Surfer dan Ms. Excel. Larutan CuSO 4 dilarutkan dan dimasukkan ke dalam porous pot. Selanjutnya adalah penentuan titik –titik dan line yang digunakan. Pada percobaan ini ada 6 line dan tiap 1 line ada 16 titik, dimana jarak antar titik adalah 2 meter. Kemudian masing-masing titik dilubangi menggunakan palu sebagai tempat penempatan porous pot. Lalu, porous pot ditempatkan di 2 titik yang akan dicari beda potensialnya dan diukur dengan multimeter. Pengukuran berpindah ke titik selanjutnya menggunakan metode gradient. Seluruh titik tersebut dihitung koordinatnya menggunakan GPS. Pada data 6 line 6, nilai beda potensialnya terbesar yakni 15,2 mV dan nilai anomali yang didapat juga semakin besar, yakni sebesar 30,7. Sebaliknya, pada data ke 2 line 4 nilai beda potensialnya terkecil yakni-17,3 mV, sehingga nilai anomali yang diperoleh juga semakin kecil, yakni-34,8 mV. Semakin negative (kecil) nilai anomali yang dihasilkan, maka akan semakin besifat konduktif. Begitu pula sebaliknya. Jadi dapat disimpulkan bahwa di permukaan bawah tanah GOR Pertamina ITS terdapat aliran fluida yang menjadi penyebab potensial alami.

- by Sulistiyawati Dewi Kiniasih
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- Jurnal Geofisika, Geofisika, Self Potential

The particle swarm optimization (PSO) method was applied to the inversion of single and multiple self-potential (SP) data anomalies caused by buried bodies with simple geometry like spheres, cylinders and inclined sheets. The inversion parameters are the depth of the body, the location of the anomaly, the electric current dipole moment, the polarization angle or the inclination angle and the half-width in the sheet-like body case. The algorithm was tested on synthetic data with single and multiple SP anomalies and applied to two experimental data from Surda area (India) and Vilarelho da Raia (Portugal). The inversion results showed good agreement with the previous results obtained using other techniques. The great advantage of the PSO method is that it is fast and does not require assumptions about the shape of the source of the SP anomaly.

- by Fernando Santos
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- Engineering, Earth Sciences, Geophysics, Algorithms

We explore the possible relationships between a structural heterogeneity, the hydrothermal system, and the intrusive activity at Piton de la Fournaise volcano. Geological and geophysical data show that as the result of repeated collapses (the last one in 2007), a cylinder of faulted, fractured, and crumbled rocks must exist between the surface and the top of a magma reservoir at about sea level. This structure constitutes a major geological heterogeneity. An obvious spatial correlation exists between this column of fractured and brecciated rock and the location of (1) most of the seismic activity, (2) a low-resistivity dome, (3) a huge self-potential anomaly, (4) thermal evidence of hydrothermal activity, and (5) the root of magma intrusions. The dominant factors that make this structural heterogeneity a trap for the activity are probably its higher permeability and its weaker mechanical strength. Evidence exists for the presence of an active hydrothermal system confined in this permeable zone. The long-term stability of the activated zone above sea level and the similarity of the pre-eruptive crises, in spite of the inferred large perturbation of the magmatic system in 1998, suggest a common triggering mechanism for all the eruptions since at least the first data recorded by the observatory in 1980. This mechanism can be purely magmatic, resulting from the pressurization of a reservoir, but we also propose that the hydrothermal system may play a role in the development of volcanic instabilities. A qualitative model is proposed to explain the triggering of magma intrusions by hydrothermal processes, and its speculative aspects are discussed. This work represents a first attempt to integrate the structural and dynamic information in a unified framework at Piton de la Fournaise.

- by Jean-françois Lénat
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- Geology, Sea Level, Spatial Correlation, Self Potential

The self-potential method was employed to investigate the zones of mineralization within the Abakaliki High. The survey was done at the left flank of the Enugu-Abakaliki expressway using the one fixed-one movable electrode technique on a grid measuring 2.6km by 2.0km. Seventy-five observations were made within the grid. It was discovered that more than 70% of the study area recorded high negative SP values (-500mv -800mv) indicating a zone of mineralization while some other parts showed zones of little or no mineralization due to their low SP values. The iso-potential map obtained shows a number of elongated centers with maxima between -0.5v and -0.9v.

- by Joseph Ebeniro and +2
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- Self Potential
- by Francesco Sortino and +1
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- Geology, Geochemistry, Geophysics, Magnetotelluric

This article compares the efficiency of application of induced polarization (IP) and resistivity in characterizing a contamination plume due to landfill leakage in a typical tropical environment. The resistivity survey found denser... more

- by Joe Rodriguez
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- Geology, Geophysics, Geothermal Energy, Geophysical Survey

Internal erosion and the development of sinkholes and other piping features is one of the major reasons for embankment dam failures. Geophysical methods have the potential of detecting internal erosion and anomalous seepage at an early stage before the safety and integrity of the dam is at stake. Two non-invasive and cost effective geophysical methods (electrical resistivity and self-potential) were used to investigate the internal seepage at Crystal Lake Dam, Washington County, MO. Previous engineering drilling and grouting programs had been applied to the dam to minimize and control seepage through the body of the dam. However, due to lack of information about the problematic areas (seepage flow paths) through the body of the dam, grouting procedures were not as effective as hoped. In an effort to delineate seepage pathways prior to a second phase of grouting, geophysical data were acquired.

- by Estella Atekwana
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- Electrical Resistance, Cost effectiveness, Preferential Flow, Moisture Content

In this paper we present a study of the structural setting of the volcanic island of Ischia by the analysis and interpretation of high-resolution aeromagnetic and self-potential data recently acquired over the island. The magnetic data allowed us to locate the main anomaly sources and lineaments of the island and its offshore surroundings, while the self-potential (SP) data provided information on both the structural pattern of the resurgent caldera and the high-temperature fluid circulation. An inversion of the acquired magnetic and SP data, and a joint modelling of the magnetic data and of a previous gravity data set along a SW-NE profile allowed us to build a model of the island. The model is characterized by the presence of an igneous-very likely trachytic-structure, whose top is located at 1200-1750 m b.s.l. Such a body, possibly formed by several neighbouring intrusions, has a density contrast with the pyroclastic cover of about 0.4 gr/cm 3 and its centralwestern part, below Mt. Epomeo, seems to be demagnetized. The demagnetization should be connected to the high geothermal gradient measured in this portion of the island and may be due to hydro-chemical alteration processes and/or to the possible presence of partially melted spots within the intrusion. Our outcome is consistent with the results of previous geophysical, geo-volcanological and geothermal studies.

- by Antonio Rapolla
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- Geology, Geochemistry, Geophysics, Volcanology

Plio-Quaternary volcanism played an important role in the present physical state of Eastern Anatolia. Mount Nemrut, situated to the west of Lake Van is one of the main volcanic centers in the region, with a spectacular summit caldera 8.5×7 km in diameter. The most recent eruptions of the volcano were in 1441, 1597 and 1692. Nemrut Lake covers the western half

- by Philippe Labazuy
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- Geology, Geochemistry, Geophysics, Volcanology

New geoelectrical techniques have been applied to the study of the Giarrossa landslide in the Lucano Appennines of southern Italy. Dipole-dipole electrical resistivity tomographies (ERT) and selfpotential (SP) surveys were carried out using innovative techniques for data acquisition and inversion. The ERT showed the presence of a conductive zone at a depth of about 25-35 m associated with the landslide body and some shallow high-resistivity nuclei associated with intercalations (calcilutitic, calcarenitic blocks, etc.) in the disturbed material. Two SP areal surveys, undertaken after the winter and summer seasons, highlighted equipotential contours following the landslide boundary and an electrical field predominantly negative in the source zone and positive in the accumulation zone.

- by F. Sdao
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- Civil Engineering, Geology, Seasonality, Data acquisition

The self-potential (SP) method for mineral exploration is seldom used on land, primarily because of electrode noise problems and nonunique interpretations. Marine measurements of the horizontal gradient of the SP field, on the other hand, are relatively simple to make with an array of electrodes towed behind a ship. With low ship speeds of 5 to 10 km/hour, dense spatial sampling (∼1 m) can be obtained with resolution of better than 1 µV/m. In this paper we report on gradient SP data recorded on the continental shelf of South Australia by a horizontal array of towed electrodes approximately 20 m above the seafloor. Ocean waves and swells with periods of 5 to 15 s yielded large amplitude signals ±20 µV/m, but subseafloor mineralization produced SP gradient anomalies of ±50 µV/m and widths of 2 km or more in a number of parallel traverses. Integrating the observed SP gradients along each line delineated SP anomalies of amplitude up to −100 mV. Self-potential and magnetic anomaly data show limited spatial correlation and have different wavelengths, suggesting that SP sources are probably nonferrous minerals, such as graphite, and are deeper than the magnetic sources. The source of the SP signal is probably reduction-oxidation (redox) potential (E h) variations across a conducting body below the seafloor. We approximate the source as being two dimensional and find the most probable locations of line sources by an image reconstruction method. Numerical finite-element modeling of more realistic source regions suggests shallow, easterly dipping (∼15 •) conductors of 1 .m in the uppermost 2 km.

- by Nader Fathianpour
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- Geophysics, Self Potential, Continental Margin

A particle swarm optimization scheme (PSO) has been applied to determine the various parameters of simple polarized bodies from their self-potential signals. The problem of finding the unknown parameters, the depth to the electric source (z), electric charge polarization angle (0), electric dipole moment (k) and shape factor (q) of buried body, is transferred lo a minimum of an objective function of these parameters. The minimization is performed by using a robust form of an unconstrained Particle Swarm Optimization. (PSO) scheme selected based on the advantages of the inertia weight that regulates the exploration space. The validity of the technique has been tested on synthetic data with and without noises. The obtained pararneters are in
congruence wiith the model parameters when using noise free model. The noise levels implentented in the data for error studies are 90 dB and 80 dB of the signal to noise ratio (SNR). Simple statistical analysis using rms errors shows that the method is not
sensitive to noise levels rtp to 80 dB. This confirms the stability of the used method. The error in the estimated parameters, when increasing the depth, was also studied. In all cases, the computed depth is found to be in agreement with the true one (the maximum
error was 0.25 %). In comparison with the Genetic based (GA) techniques, the present technique shows a better minimum rms error. However, both the evolutionary computations based on algorithms GA and PSO give very close results. Three of the sited
field examples from Germany and Turkey have been analyzed and interpreted by the PSO technique.

- by Maha Abdel Azeem
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- Particle Swarm Optimization, Self Potential

Abstract. A new technique is presented for automatic inversion of SP anomalies due to a polarized infinitely conductive simple geometrical source model structures, based on an artificial intelligence search strategy entitled genetic algorithm (GA) and the evolution theory. The genetic algorithm is used to find the minimum of fitness or cost function of the unknown depth, polarization angle, and shape factor. The study of synthetic examples shows fast and stable recovery of the true parameters even if the input data contain different percentages of noise. The GA leads to very realistic values for the inverted parameters in all tested examples and the root-mean squared error (rms) between the true and inverted field is accepted. The technique is further applied to real examples from Germany and Turkey.

- by Maha Abdel Azeem
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- Genetic Algorithms, Inversion, Self Potential

Following suggestions by several authors that the gravity may play a role in the collapse of the wavefunction during the measurement process, we have made a study of the Schrodinger-Newton Equation, which is a single particle equation, in which the degrees of freedom of the associated gravitational field of the particle are incorporated in an averaged self-consistent manner through the addition of a gravitational self-potential. We show that there exists a class of stationary self-bound solutions whose energy eigenvalues can be determined exactly using an asymptotic method. Since this equation has also been investigated in other contexts like plasma physics and astrophysics, our solutions are of larger interest. This analysis provides us with a length scale within which the predictions of standard quantum mechanics are valid, but beyond which the gravitational effects dominate. These effects do not permit spatial superpositions of wavefunction beyond this scale, leading toa possible quantum to classical transition dependent on the mass of the particle. We find a limiting mass, that is effectively the Planck mass, above which this equation may not be valid.

- by vikram soni
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- Plasma Physics, Quantum Mechanics, Mathematical Sciences, Physical sciences

We examined the sensitivity of azimuthal self potential (ASP) and azimuthal resistivity surveys (ARS) to hydraulic anisotropy in a laboratory fracture block model. Both ASP and ARS measurements are influenced by anisotropy (due to the strike of major fracture sets) and heterogeneity (due to variable fracture density) of the block model. The polarity of the self potential defines the flow direction and the self potential magnitude within a single fracture set is observed to increase with flow rate. Whereas the ARS anisotropy is primarily controlled by fracture density/connectivity (and hence presumably hydraulic conductivity) ASP anisotropy appears diagnostic of (1) hydraulic gradient driving flow within fracture sets, and (2) fracture density (presumably controlling the strength of the streaming potential coefficient). Preliminary field data from the New Jersey Highlands illustrate that ASP surveys can define hydraulic anisotropy in fractured rock environments. Our results suggest that combined interpretation of ASP and ARS can lead to improved geoelectrical characterization of fracture rock anisotropy.

- by DeBonne Wishart
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- Rock magnetism, Multidisciplinary, Flow Rate, Streaming Potential

A new approach is proposed in order to interpret spontaneous potential (self-potential) anomalies related to simple geometric-shaped models such as sphere, horizontal cylinder, and vertical cylinder. This approach is mainly based on using neural network inversion of SP anomalies, particularly modular algorithm, for estimating the parameters of different simple geometrical bodies. However, Hilbert transforms are involved to determine the origin location in order to reduce the parameters which minimize the ambiguity in the inverted models. The inversion has been tested first on synthetic data from different models, using only one well-trained network. The results of inversion show that the parameter values derived by the inversion are identical to the true values of parameters. Noise analysis has been also examined, where the results of the inversion produce acceptable results up to 10% of white Gaussian noise.

- by Prof. Dr. Mansour A Al-Garni
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- Geophysics, Shape Modeling, Neural Network, Hilbert transform

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.

- by Ginette Saracco and +1
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- Rock magnetism, Multidisciplinary, Transport Properties, Electromagnetic Theory

ERT and SP investigations were conducted in carbonate rocks of the Dinant Synclinorium (Walloon Region of Belgium) to find suitable locations for new water wells in zones with little hydrogeological data. Since boreholes information needed to be representative of the area, large fractured zones were searched for the drillings. Large ERT profiles (320 to 640 m) allowed us to image the resistivity distribution of the first 60 m of the subsurface and to detect and characterize (in terms of direction, width and depth) fractured zones expected to be less resistive. Data errors, depth of investigation (DOI) indexes and sensitivity models were analyzed in order to avoid a misinterpretation of the resulting images. Self-potential measurements were performed along electrical profiles to complement our electrical results. Some negative anomalies possibly related to preferential flow pathways were detected. A drilling campaign was conducted according to geophysical results. 'Ground truth' geological data as well as pumping tests information gave us a way to assess the contribution of geophysics to a drilling program. We noticed that all the wells placed in low resistivity zones associated with SP anomalies provide very high yields and inversely, wells drilled in resistive zones or outside SP anomalies are limited in terms of capacity. An apparent coupling coefficient between SP signals and differences in hydraulic heads was also estimated in order to image the water table.

- by V. Hallet
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- Geophysics, Hydrogeology, Applied Geophysics, Applied

— The long-term monitoring of the electric self-potential (SP) in geophysical systems is affected by electrode degradation and drift. This error contribution can be reduced if the electrodes of measuring dipoles are referenced to the same accessory electrode, moved in turn at each pole. The benefit of this travelling electrode referencing scheme (TER) has been evaluated in a dedicated experiment performed from March 2000 to March 2001 at Tribhuvan University, Nepal. Two prototype monitoring points separated by 55 m have been instrumented with pairs of lead-lead chloride Petiau electrodes, installed in buckets filled with salted bentonite at a depth of 1 and 2 meters. The electrical potential at 1 and 2 meters depth was also accessible from the surface by pipes filled with salted bentonite. Over one year, the measurement error, defined as the standard deviation of the difference between the measured potential and the true SP at a given time, is estimated to be 5 mV. This error value is reduced to less than 1 mV with TER. After correction, a smooth annual variation with amplitude of 10 to 15 mV is observed and is interpreted as streaming potentials associated with the monsoon and subsequent drying. These results provide significant guidelines for precision long-term SP monitoring, in particular in tropical volcanic or tectonically active regions.

- by Surendra Pant
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- Geophysics, Standard Deviation, Noise reduction, Measurement Error

The potential for the geophysical characterization of fractured rock bulk anisotropy using azimuthal self potential gradient (ASPG) method was investigated at four fractured rock field sites in the New Jersey Highlands (NJH) province. A visual (from polar plots) and empirical (from linear regression of cross plots) correlation exists between ASPG measurements and dominant fracture strike orientations mapped at three of the four study sites, with the magnitude of the SP signal positively correlated to the number of fractures (N) along the same azimuth. This result is consistent with recent electrokinetic theory that invokes a dependence of the streaming potential coupling coefficient on microgeometry in addition to hydraulic gradient. Based on local surface drainage patterns and regional fracture orientations, the direction of the positive lobe of the ASPG signal appears indicative of the likely flow direction within fracture sets. Three repeat measurements at one site over a one year period consistently reproduced the ASPG lobes along major and minor fracture sets, although the magnitude of the self potential varied along the major strike set possibly due to variable rates of groundwater flow. Whereas ASPG captured hydraulic-anisotropy at three of four sites, resistivity anisotropy only dominated azimuthal resistivity surveys (ARS) data at one site. Our results suggest that ASPG is a surprisingly simple, effective tool for characterization of fracture-dominated media. In addition to defining the fracture-induced hydraulic anisotropy, the direction of fracturecontrolled flow is evident from the polarity of the SP signal. ª

- by DeBonne Wishart
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- Hydrology, Hydraulics, Theory, Fracture

In 1996 Self-Potential (SP) and Telluric±Telluric (TT) surveys were performed in the Asal rift, in the Republic of Djibouti, in order to study water circulation through the rift, from Ghoubbet Strait to Asal lake located 11 km Northwest, and at the altitude of 155 m below sea level. SP surveys reveal two main positive anomalies, several kilometres wide, up to 150 mV in amplitude, parallel to the rift and separated by a relatively large (1 km) negative anomaly. The northern anomaly is well centred above the active rift. The central part of the anomaly is cut by a sharp and narrow negative anomaly (200 mV in amplitude, 150 m width) due to a major fault running from Ghoubbet Strait to Asal lake. The two positive anomalies are interpreted by ground seawater owing toward Asal lake and warmed up during their advance by the strong geothermal¯ux existing beneath the rift. The negative anomalies are most probably due to large and rapid¯uid transfer along faults and high permeable geologic beds bending toward Asal lake. The rapid¯ow would prevent any large heating of the ground water. The largest negative anomaly, which isolates the two positive ones, gives new valuable information on the tectonics. The extension of the northern positive anomaly to the Southwest is stopped by a fault located about 1 km to the North of a normal fault considered until now, as a major rift structure. The 16 Telluric±Telluric (TT) surveys point out three behaviours of the telluric ®eld. Near Ghoubbet Strait and inland the telluric ®eld is well polarised in a N90±1008E direction and the amplitude expresses a medium to a low resistivity beneath the recording sites. This pattern is the signature of the coast effect and the regional polarisation of the ®eld. Along normal faults bordering the rift the SE±NW polarisation seems to be controlled by the rift tectonics. Inside the rift the telluric ®eld becomes weaker, indicating a decay of the resistivity. In the central part of the rift the telluric ®eld amplitude becomes 1/3 of the generally recorded amplitude and the polarisation cannot be estimated. It is corresponding to very low resistive areas in agreement with high positive SP values. q

- by Asal Asal
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- Geology, Geochemistry, Geophysics, East Africa

Ubinas volcano, the historically most active volcano in Peru straddles a low-relief high plateau and the flank of a steep valley. A multidisciplinary geophysical study has been performed to investigate the internal structure and the fluids flow within the edifice. We conducted 10 self-potential (SP) radial (from summit to base) profiles, 15 audio magnetotelluric (AMT) soundings on the west flank and a detailed survey of SP and soil temperature measurements on the summit caldera floor. The typical "V" shape of the SP radial profiles has been interpreted as the result of a hydrothermal zone superimposed on a hydrogeological zone in the upper parts of the edifice, and depicts a sub-circular SP positive anomaly, about 6 km in diameter. The latter is centred on the summit, and is characterised by a larger extension on the western flank located on the low-relief high plateau. The AMT resistivity model shows the presence of a conductive body beneath the summit at a depth comparable to that of the bottom of the inner south crater in the present-day caldera, where intense hydrothermal manifestations occur. The lack of SP and temperature anomalies on the present caldera floor suggests a self-sealed hydrothermal system, where the inner south crater acts as a pressure release valve. Although no resistivity data exists on the eastern flank, we presume, based on the asymmetry of the basement topography, and the amplitude of SP anomalies on the east flank, which are approximately five fold that on the west flank, that gravitational flow of hydrothermal fluids may occur towards the deep valley of Ubinas. This hypothesis, supported by the presence of hot springs and faults on the eastern foot of the edifice, reinforces the idea that a large part of the southeast flank of the Ubinas volcano may be altered by hydrothermal activity and will tend to be less stable. One of the major findings that stems from this study is that the slope of the basement on which a volcano has grown plays a major role in the geometry of the hydrothermal systems. Another case of asymmetrical composite cone edifice, built on a steep topography, is observed on El Misti volcano (situated 70 km west of Ubinas), which exhibits a similar SP pattern. These types of edifices have a high potential of spreading and sliding along the slope owing to the thicker accumulation of low cohesion and hydrothermally altered volcanic products.

- by E. Delcher and +2
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- Structural Geology, Structural Control, Field Survey, Electrical Resistance

A resistivity survey using Wenner array was carried out in June 2000 in a granite region of Northern Portugal, where an active landfill is operating since 1998, to detect the possible spread of contamination. This survey was complemented with a self-potential (SP) survey, a dipole-dipole (DD) array profile and azimuthal Vertical Electrical Sounding arrays (VES). The location of these profiles was highly constrained by the available space in the landfill facility and by the available geological data, mainly fracturing. Significant groundwater circulation was detected, which is characterized by a low resistivity zone (b400 V m), with a fairly well defined configuration. Chemical analysis of water samples collected in boreholes inside the landfill facility and on springs around it confirmed the presence of water contamination. The presence of a very well delimited anomaly with low resistivity (b200 V m) just beneath the leachate collector system strongly suggests that the groundwater contamination is due to a landfill leak. Results of azimuthal VES are consistent with the structural data obtained outside the landfill, revealing that the strikes of the prevailing fracture systems inside the landfill are generally NW-SE to NNE-SSW, which seems to facilitate the downward propagation of contaminants. D

- by Mário Gonçalves
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- Geophysics, Applied Geophysics, Waste Disposal, Geomatic Engineering

The occurrences of gold and disseminated sulfides lie as a part of the shearing fault zone that extends from the north to the south of the study area for a length of about 25 km. The gold and disseminated sulfides are located on the alteration shear zone which is composed of quartz-feldspathic highly ferruginated rock (gossans) occupying the eastern and central parts of the area. Mineralogical analyses that were done on bedrock samples of the oxidized and alteration zones indicated that there are two anomalous spots of gold contents; the first one has values ranging from 5 to 49 g ton-1 and the second anomaly has values ranging from 150 to 502.5 g ton-1. Magnetic, self-potential, resistivity and induced polarization surveys were applied at Wadi El Beida area to delineate the mineral ore deposits in terms of depths and extensions through the structural shearing zone. The quantitative interpretation of magnetic data was carried out by using two techniques; the first is 3D magnetic inversion using Euler deconvolution and the second is magnetic models using the MAGMOD program. The results of the magnetic interpretation indicated that the depths of such ore deposits range from 35.9 to 52.7 m and the half width ranged from 27.2 to 87.8 m. The SP contour maps show negative anomalies with ranges from −70 to 20 mV. Most of these anomalies occupy the shear, silicified zones, alterations and rock contacts. The SP anomalies are correlated with other geophysical ones and also with the geological sources. Quantitative interpretation was done on the selected anomalies along the coded lines on the normal SP contour map. The quantitative interpretation of self-potential anomalies (SP) was carried out using two techniques; the first is a new algorithm constructed by Monteiro Santos (2009) using particle swarm optimization (PSO) and the second is the code constructed by Caglar (2000). The depths range from 20 to 60 m. The gradient resistivity survey was carried out simultaneously with IP measurements. The low-resistivity zones coincide with the altered and sheared acidic meta-volcanics. The quantitative interpretation technique determined the conductive bodies' parameters using the Schulz method (1985) where the depth to the top of the ore body ranged from 21 to 62 m while the maximum width ranged from 52 to 165 m. The induced polarization-chargeability data were measured in the time domain. The positive anomalies on the IP-chargeability map coincide with the sites of alterations, shears and contact zones. Four dipole-dipole sections were carried out along the anomalous sites selected from the constructed maps in the study area and were inverted using the RES2DINV program. The results of resistivity and IP inversions indicated that there are conductive and chargeable

- by Sultan Sultan
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- Civil Engineering, Geophysics, Case Study, Dipole

A study of the geoelectrical structure of the central part of Piton de la Fournaise volcano (Réunion, Indian Ocean) was made using direct current electrical (DC) and transient electromagnetic soundings (TEM). Piton de la Fournaise is a highly active oceanic basaltic shield and has been active for more than half a million years. Joint interpretation of the DC and TEM data allows us to obtain reliable 1D models of the resistivity distribution. The depth of investigation is of the order of 1.5 km but varies with the resistivity pattern encountered at each sounding. Two-dimensional resistivity cross sections were constructed by interpolation between the soundings of the 1D interpreted models. Conductors with resistivities less than 100 ohm-m are present at depth beneath all of the soundings and are located high in the volcanic edifice at elevations between 2000 and 1200 m. The deepest conductor has a resistivity less than 20 ohm-m for soundings located inside the Enclos and less than 60–100 ohm-m for soundings outside the Enclos. From the resistivity distributions, two zones are distinguished: (a) the central zone of the Enclos; and (b) the outer zone beyond the Enclos. Beneath the highly active summit area, the conductor rises to within a few hundred meters of the surface. This bulge coincides with a 2000-mV self-potential anomaly. Low-resistivity zones are inferred to show the presence of a hydrothermal system where alteration by steam and hot water has lowered the resistivity of the rocks. Farther from the summit, but inside the Enclos, the depth to the conductive layers increases to approximately 1 km and is inferred to be a deepening of the hydrothermally altered zone. Outside of the Enclos, the nature of the deep, conductive layers is not established. The observed resistivities suggest the presence of hydrated minerals, which could be found in landslide breccias, in hydrothermally altered zones, or in thick pyroclastic layers. Such formations often create perched water tables. The known occurrence of large eastward-moving landslides in the evolution of Piton de la Fournaise strongly suggests that large volumes of breccias should exist in the interior of the volcano; however, extensive breccia deposits are not observed at the bottom of the deep valleys that incise the volcano to elevations lower than those determined for the top of the conductors. The presence of the center of Piton de la Fournaise beneath the Plaine des Sables area during earlier volcanic stages (ca. 0.5 to 0.150 Ma) may have resulted in broad hydrothermal alteration of this zone. However, this interpretation cannot account for the low resistivities in peripheral zones. It is not presently possible to discriminate between these general interpretations. In addition, the nature of the deep conductors may be different in each zone. Whatever the geologic nature of these conductive layers, their presence indicates a major change of lithology at depth, unexpected for a shield volcano such as Piton de la Fournaise.

- by Jean-françois Lénat and +1
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- Geology, Indian Ocean, Water Table, Hydrothermal Alteration

An inversion algorithm is developed to estimate the depth and the associated model parameters of the anomalous body from the gravity or self-potential (SP) whole measured data. The problem of the depth (z) estimation from the observed data has been transformed into a nonlinear equation of the form F(z) = 0. This equation is then solved for z by minimizing an objective functional in the least-squares sense. Using the estimated depth, the polarization angle and the dipole moment or the depth and the amplitude coefficient are computed from the measured SP or gravity data, respectively. The method is based on determining the root mean square (RMS) of the depths estimated from using all s-values for each shape factor. The minimum RMS is used as a criterion for estimating the correct shape and depth of the buried structure. When the correct shape factor is used, the RMS of the depths is always less than the RMS computed using wrong shape factors. The proposed approach is applicable to a class of geometrically simple anomalous bodies, such as the semi-infinite vertical cylinder, the dike, the horizontal cylinder and the sphere, and it is tested and verified on synthetic examples with and without noise. This technique is also successfully applied to four real datasets for mineral exploration, and it is found that the estimated depths and the associated model parameters are in good agreement with the actual values.

- by Khalid Essa
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- Civil Engineering, Geophysics, Data Interpretation, Mineral exploration

Temperatures of 100 ‡C are measured at 3 km depth in a well located on the resurgent dome in the center of Long Valley Caldera, California, despite an assumed s 800 ‡C magma chamber at 6^8 km depth. Local downflow of cold meteoric water as a process for cooling the resurgent dome is ruled out by a Pecle ¤t-number analysis of temperature logs. These analyses reveal zones with fluid circulation at the upper and lower boundaries of the Bishop Tuff, and an upflow zone in the metasedimentary rocks. Vertical Darcy velocities range from 10 to 70 cm a 31 . A 21-km-long geoelectrical profile across the caldera provides resistivity values to the order of 10 0 to s 10 3 6m down to a depth of 6 km, as well as variations of self-potential. Interpretation of the electrical data with respect to hydrothermal fluid movement confirms that there is no downflow beneath the resurgent dome. To explain the unexpectedly low temperatures in the resurgent dome, we challenge the common view that the caldera as a whole is a regime of high temperatures and the resurgent dome is a local cold anomaly. Instead, we suggest that the caldera was cooled to normal thermal conditions by vigorous hydrothermal activity in the past, and that a present-day hot water flow system is responsible for local hot anomalies, such as Hot Creek and the area of the Casa Diablo geothermal power plant. The source of hot water has been associated with recent shallow intrusions into the West Moat. The focus of planning for future power plants should be to locate this present-day flow system instead of relying on heat from the old magma chamber. ß

- by Claudia Schütze
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- Geology, Geochemistry, Geophysics, Volcanology
- by André Revil
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- Geology, Geochemistry, Geophysics, Ground Water

Self potential (SP) method is needed to determine the water injection flow under the soil surface. Self potential method is appropriate to use in mapping the distribution of fluid flow anomalies. Several self potential research applications have been done in some areas. In this research, it is explained the research materials and procedure. Thefirstis measuring instrumnets which is a Potential DVM (digital Voltmeter), 4 pieces of porous pot electrode, copper sulfida solution, roll meter, cable-roll, and table form of mapping the data, and also communication tools if needed. The second step was design the large of the overlay topograpic map which will be surveyed and the geology map of the surveyed area.It also determines the measuring tracks in the surveyed extent which will be used later for the reference to divide the measuring grid. The third was calibrating each of the pair of porous pot electrode. The fourth step was to collect the data.Theresearch which has been done in the library garden of State Univerity of Malang in East Java is obtained the data of the scale tension value in the mV unit. This data, then was interpolated to be self potential map. The map describes the electical caracteristic of the research area.The collection of the data is done by space gridding 5 meters with all the 165 data. The data has the large 35 x 5 in the left side and in the right side is 30 x 5. The space between porous pot electrode is 5 meters. It is found that the leftside area of the library garden is potential toobtain the water source with the water rate can fulfill the daily needs of the surrounding people. Furthermore, it is possible to get a new water source beside the current exist water source. This new water source shows the caracteristic of the under soil surface.

- by FERUM M PRANITA
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- Geophysics, Physics, Self Potential

This paper introduces a new optimization technique termed as Recursive Ant Colony Optimization (RACO), a modified form of ant colony method (ACO), for finding best probable solution to a combinatorial problem. ACO simulates the social behavior of ants, optimizing their path from the nest to food source. The movement of an ant is random and the shortest path is found

- by Upendra K. Singh
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- Mathematics, Computer Science, Information Technology, Finite Element Methods

Jharia coal fire is the biggest insitu coal fire in India, covering over 18 sq.km, and having serious adverse effects over the environment. Monitoring the advancement of fire has became an essential requirement in that area. Earlier monitoring methods could only tell about the surface extension of the fire. Potential variations over the fire due to the relatively less understood thermoelectric effect has helped in monitoring the active fire sites. High negative anomalies of about -75mV were obtained over the heated zone. The inversion of the potential data using ELW method with FORTRAN based codes has helped in getting the surface as well as subsurface location of fire. It has also helped in calculating the structural index over the burnt zone.This helped in getting the geometry of the causative body. This study has helped in locating the shallow fire zones. Here we have obtained -75mV, -50mV and -44mV anomalies over three lines, and on inversion the depth of the fire obtained was 3.06m, 4.47m and 5.22m respectively. The temperature over the fire was about 340degC and the burning front had a spherical geometry (as obtained from the structural index).

- by Debjeet Mondal
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- Geohazards, Inversion, Self Potential, Jharia Coalfield

Geophysics has shown effectiveness in identify areas contaminated by urban solid wastes, contributing to become more effective sounding programs directed to collect of samples and installation of monitoring systems. In this context, this work had as purpose evaluating the potentialities of the integration of geophysical methods (resistivity, induced polarization and self-potential) in the environmental characterization of the area of the sanitary landfill of the city of Bauru-SP. The self-potential method allowed to detect the direction of the underground flow. The resistivity and induced polarization methods allowed to identify anomalies inside of the saturated zone, that characterize the presence of contamination generated for the migration of the percolated proceeding of the disposal of solid waste. This contamination is confirmed by direct investigation (chemical analysis of the water collected in the monitoring wells). The geophysical methods used had supplied a great number of information about the several characteristics related to interaction between waste disposal area and environment.

- by Vagner Elis
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- Waste Disposal, Solid waste, Chemical Analysis, Self Potential

1] Self-potential (SP) data are collected over an area of approximately 250 m 2 at the Department of Energy Savannah River Site where there is known subsurface dense nonaqueous phase liquid (DNAPL) contamination. Nonpolarizing electrodes are used to measure the SP signal on a two-dimensional (2-D) surface grid with 2-m spacing in both horizontal directions, and four borehole arrays with 3.7-m electrode spacing and 25.6-m total depth. The primary contaminants, tetrachloroethylene (PCE) and trichloroethylene (TCE), are known to undergo redox reactions in the environment. Variations in the subsurface redox conditions are proposed as an electrochemical source for the SP signals measured in this investigation. A 3-D self-potential inversion algorithm is used to find an electrical current source model, taking into account the resistivity structure derived from a 3-D spectral induced polarization survey at the same field location. The sources and sinks of electrical current can be related to the zones of relative high or low redox potential and are therefore interpreted in the context of contaminated areas. These results are reasonably correlated with DNAPL concentration data obtained from several ground-truth well measurements, indicating that the SP sources can be an indicator of contaminated areas where electrochemical source mechanisms are active. In several cases, however, the SP sources and contaminant concentrations are not correlated, reflecting the spatial variability of biogeochemical parameters in the Earth that control the SP response in addition to concentration. More extensive geochemical ground-truth information is therefore needed to validate the self-potential source inversion methodology and develop it as a predictive tool in the context of contaminated sites.

- by Darrell Coles
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- Environmental Engineering, Civil Engineering, Water resources, Applied Economics

Ground water flow associated with pumping and injection tests generates self-potential signals that can be measured at the ground surface and used to estimate the pattern of ground water flow at depth. We propose an inversion of the self-potential signals that accounts for the heterogeneous nature of the aquifer and a relationship between the electrical resistivity and the streaming current coupling coefficient. We recast the inversion of the self-potential data into a Bayesian framework. Synthetic tests are performed showing the advantage in using selfpotential signals in addition to in situ measurements of the potentiometric levels to reconstruct the shape of the water table. This methodology is applied to a new data set from a series of coordinated hydraulic tomography, self-potential, and electrical resistivity tomography experiments performed at the Boise Hydrogeophysical Research Site, Idaho. In particular, we examine one of the dipole hydraulic tests and its reciprocal to show the sensitivity of the self-potential signals to variations of the potentiometric levels under steady-state conditions. However, because of the high pumping rate, the response was also influenced by the Reynolds number, especially near the pumping well for a given test. Ground water flow in the inertial laminar flow regime is responsible for nonlinearity that is not yet accounted for in self-potential tomography. Numerical modeling addresses the sensitivity of the self-potential response to this problem.

- by Bwalya Malama
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- Ground Water, Electrical Resistance, Water Table, Laminar Flow

Accurate and precisely located self-potential (SP), temperature (T) and CO 2 measurements were carried out in the summit area of Stromboli along 72 straight profiles. SP data were acquired every metre and T data every 2.5 m. CO 2 concentrations were acquired with the same density as T, but only along seven profiles. The high density of data and the diversity of the measured parameters allows us to study structures and phenomena at a scale rarely investigated. The shallow summit hydrothermal activity (Pizzo-Fossa area) is indicated by large positive SP, T and CO 2 anomalies. These anomalies are focused on crater faults, suggesting that the fracture Editorial responsibility: J.

- by Mariano Valenza and +1
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- Geology, High Frequency, High Density Concrete, Sampling Technique

We present and discuss the results of an integrated electrical and electromagnetic survey in the active volcanic area of Ž . Ž . Ž . Ž . Mount Somma-Vesuvius Naples, Italy . Dipolar geoelectrics DG , self-potential SP and magnetotellurics MT were used to investigate the shallow and deep regions of the volcanic area. The DG apparent resistivity pseudosection along a N-S profile across the Vesuvius cone showed the existence of a largely extended conductive zone, closely in correspondence to the Somma caldera, including in the middle the top terminal part of the Vesuvius main plumbing system. The SP data, collected over the whole volcanic area, showed the existence of a W-E-directed wide band of weak positive anomalies, indicating again a conductive zone, not only including the whole Somma caldera but also extending towards the Tyrrhenian sea. A roughly N-S-trending narrow fracture system, cutting the lowest Mount Somma eastern slopes, was further evident from the SP data. A new SP tomographic inversion procedure allowed to detect a large positively charged nucleus in the depth range 600-2200 m b.g.l., located beneath the westernmost portion of a former caldera, related to the Avellino plinian eruption. The geophysical interpretation of this large positive anomaly was made using Onsager's theory of coupled electrokinetic and thermoelectric flows. The final interpretation was that the shallow, conductive central zone is very likely made up of an intensively altered and mineralised block of cemented volcanic breccia. Finally, the MT data, distributed along two perpendicular profiles, enabled us to obtain the first significant picture of the deep electrical structure of the volcano. The Bostick inversion revealed the existence of a conductive intracrustal layer, including a perched more conductive zone located roughly beneath the central-western sector of the Vesuvius apparatus. q 1998 Elsevier Science B.V. All rights reserved.

- by Rosa Di Maio
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- Geology, Geochemistry, Geophysics, Volcanology

A new R & D project to develop novel techniques for monitoring and modeling reservoir mass and heat flows is described. Integrated reservoir modeling and simulation technology is being developed which will improve the quality of mathematical reservoir models by taking account of geophysical data sets such as changes in micro-gravity, selfpotential, resistivity and seismic properties in addition to the conventional data sets usually employed in reservoir engineering studies. Computational feasibility studies of reservoir monitoring using geophysical survey techniques were performed based on a steady-state three-dimensional model of a hypothetical (but realistic and typical) geothermal reservoir system which was developed using a numerical reservoir simulator.

- by Marcelo Ribera
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- Microgravity, Seismic, Resistivity, Reservoir modeling