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Interpretation of vertical electrical sounding (VES) data is inherently difficult due to its ambiguity and non-linear characteristics. Conventional least square-based methods rely on a well-defined apriori model, constrained by ground information (available borehole logs and field observations of exposed lithological sections) for meaningful interpretations. In this work, a back-propagation neural network-based model was developed to estimate layer resistivities and thickness from given apparent resistivities. The model was trained and validated on noise-infused synthetic datasets. Since the effectiveness and generalisation of any model depend on its hyperparameter settings, we investigated effective methods for estimating hyperparameters such as learning rate, momentum, model architecture and learning rate scheduling parameters. It is well known that the optimal values of hyperparameters are not entirely independent of each other. Thus, any change in one hyperparameter changes the optimal range of all other hyperparameters, and thus, tuning any hyperparameter individually is futile. This warrants a joint hyperparameter tuning along with network architecture, which was carried out using a modified version of meta-heuristic black hole algorithm. The modifications include randomly flipping one or more coordinates of the population stars (solutions) whose cost function was above a threshold value decided by a mutation rate parameter. This helped in boosting the exploration capability of the algorithm and prune trajectories with higher cost functions. It is demonstrated that with a finely tuned neural network model, reasonable resistivity model parameters which interpret the ground conditions fairly well could be obtained. The model was tested on resistivity-sounding data with associated borehole lithologs and was found to be giving reasonable results. The same model was used to estimate the overburden thickness consisting of topsoil and deposited silts in Bhadradri–Kothagudem district, India. The layer thickness was consistent with those seen in cutbanks in the area. The methods of optimal hyperparameter set estimation are not exclusive to this model and can be used to train models accomplishing other geophysical tasks. [ABSTRACT FROM AUTHOR]

Electrodes are used to measure a potential difference between two points. In geophysical and geotechnical applications they are often in the form of non‐polarizable porous‐pot electrodes. Here we describe the design, construction, and testing of modular and refillable electrodes, which facilitates repair as the electrodes degrade over time. We use a chemical composition based on a metal in contact with an over‐saturated electrolyte that consists of a salt of that metal and an auxiliary salt. We compare characteristics when the electrolyte is stabilized in a clay or not, and with various states of ceramic porous plugs and two types of wood plugs. Next, we assess the long‐term stability (more than 1 month), noise (periods of 1 s to 1 hr), and temperature sensitivity of different types of electrodes. Electrodes with an electrolyte and clay formula showed lower noise (0.2–0.4 μV at periods of 1–120 s), greater long‐term stability (0.05–0.5 mV/month of smooth drift), and greater consistency between samples measured than those with no clay (noise and drift values up to four times larger). The effects from different porous plugs were negligible, with similar results for ceramic and wood types. The temperature sensitivity of the electric potential was assessed, from −3 to 35°C. All electrodes showed a temperature sensitivity of about −30 μV/°C. This is considered very low compared to some commercially available electrodes. Finally, continuous long‐term laboratory and field measurements of the potential highlight the application of the new electrodes. Key Points: Development of a modular, repairable, refillable porous‐pot electrode with an over‐saturated electrolyte, preferably stabilized in clayLong‐term measurements reveal (a) high stability, (b) smooth drift, <0.5 mV/month, and (c) low noise, 0.2–0.4 μV at a period of 1–120 sExperiments from −3 to 35°C determine a temperature sensitivity of the electric potential of about −30 μV/°C, which is considered low [ABSTRACT FROM AUTHOR]

Abstract Electrodes are used to measure a potential difference between two points. In geophysical and geotechnical applications they are often in the form of non‐polarizable porous‐pot electrodes. Here we describe the design, construction, and testing of modular and refillable electrodes, which facilitates repair as the electrodes degrade over time. We use a chemical composition based on a metal in contact with an over‐saturated electrolyte that consists of a salt of that metal and an auxiliary salt. We compare characteristics when the electrolyte is stabilized in a clay or not, and with various states of ceramic porous plugs and two types of wood plugs. Next, we assess the long‐term stability (more than 1 month), noise (periods of 1 s to 1 hr), and temperature sensitivity of different types of electrodes. Electrodes with an electrolyte and clay formula showed lower noise (0.2–0.4 μV at periods of 1–120 s), greater long‐term stability (0.05–0.5 mV/month of smooth drift), and greater consistency between samples measured than those with no clay (noise and drift values up to four times larger). The effects from different porous plugs were negligible, with similar results for ceramic and wood types. The temperature sensitivity of the electric potential was assessed, from −3 to 35°C. All electrodes showed a temperature sensitivity of about −30 μV/°C. This is considered very low compared to some commercially available electrodes. Finally, continuous long‐term laboratory and field measurements of the potential highlight the application of the new electrodes.

Exploration geophysics requires solving specific inverse problems — reconstructing the spatial distribution of the medium properties in the thickness of the earth from the geophysical fields measured on its surface. We consider inverse problems of gravimetry, magnetometry, magnetotelluric sounding, and their integration, which means simultaneous use of various geophysical fields to reconstruct the desired distribution. Integration requires the determined parameters for all the methods to be the same. This may be achieved by the spatial statement of the problem, in which the task is to determine the boundaries of geophysical objects. In our previous studies, we considered the parameterization scheme where the inverse problem was to determine the lower boundary of several geological layers. Each layer was characterized by variable values of the depth of the lower boundary along the section, and by fixed values of density, magnetization, and resistivity, both for the layer and over the entire dataset. It was demonstrated that the integration of geophysical methods provides significantly better results than the use of each of the methods separately. The present study considers an extended and more realistic model of data—a parameterization scheme with variable properties of the medium, both along each layer and over the dataset. [ABSTRACT FROM AUTHOR]

There is quite a long history in Nigeria of Geothermal energy exploration. Geothermal energy resources are available in every part of Nigeria beneath the subsurface. The resources, however, vary in concentration in all the geological parts of the country. This paper reviewed the prospects of geothermal energy exploration by using the potential field (magnetic and gravity) technique for the exploration activities. The potential field data is capable to provide information on the subsurface structures after some filtering techniques (in case of magnetic) or data corrections (in case of gravity) have been applied to the raw field data. The processed data is capable to scan the lateral and vertical extent of anomalous zones beneath the surface. Geothermal energy, if properly exploited would contribute to the generation of clean energy in Nigeria for domestic and industrial purpose. [ABSTRACT FROM AUTHOR]

A major challenge for the oil and gas industry is expediting the exploration geophysics activity. It is necessary to produce fast and accurate image of the targeted hydrocarbon reservoir, yet it involves extensive dataset due to the target location lies in deeper subsurface. Therefore, target-oriented oil and gas-reservoir imaging is currently seen as more attractive than conventional full-volume migration, in terms of computation efficiency. Through the integration of seismic redatuming with Kirchhoff migration, we presented a target-oriented imaging workflow that can effectively reduce computational cost while simultaneously enhancing the accuracy of the migrated image. Kirchhoff migration is renowned for being one of the simplest and flexible migration techniques, making it straightforward to implement. However, this migration approach is typically avoided in the presence of complex geology, as it tends to introduce artifacts in the images, thereby disrupting the interpretation beneath the complex overburden. Therefore, this paper highlighted the advantages of utilizing seismic redatuming to retrieve data beneath the overburden, followed by the utilization of the redatumed data as input for Kirchhoff migration. With an improved signal to noise ratio, the primary reflection events were amplified, providing clearer representation of the subsurface structure within the hydrocarbon reservoir or targeted area. Additionally, we utilized the benefits of Kirchhoff migration and explored the feasibility of performing patch-based migration in several areas of interest beneath the salt layer. This approach aimed to reduce both the turnaround time and the associated seismic migration costs. The developed workflow then was subsequently put to the test and applied to both a sub-salt SEG Advanced Modeling (SEAM) model and field data situated in East Malaysia. Based on the outcomes of the target-oriented migration, the proposed methodology demonstrated its capability to generate better quality and instant migrated images within the designated region. Furthermore, the feasibility of target-oriented imaging with Kirchhoff migration was substantiated through the integration of seismic redatuming, resulting in significant benefits towards seismic processing, imaging, and interpretation. [ABSTRACT FROM AUTHOR]

The Mt. Melbourne Volcanic Field is a quiescent volcanic complex located in Northern Victoria Land, Antarctica, mostly covered by ice. Its inner structure has remained largely unknown, due to the paucity of outcrops and the lack of detailed multi‐disciplinary investigations. Here we present a novel high‐resolution aeromagnetic dataset, revealing strong long‐wavelength negative anomalies superimposed by short‐wavelength positive ones forming characteristic radial patterns. Automatic lineament detection, through the Hough transform technique applied to the tilt derivative of our magnetic dataset, shows prevailing NW‐SE‐to NNE‐SSW‐trending structural features, which combined with the few structural field observations contribute to define the deformation pattern. Pre‐existing and novel magnetic property measurements, coupled with available geochronological data, are used to constrain a two‐step 3D magnetic inversion. A layer‐structured Oldenburg‐Parker's inversion was utilized to model the deep and long‐wavelength components of the magnetic field, whereas a linear inversion based on a set of shallower prisms was used to model the short‐wavelength components. The final 3D model shows widespread reversely‐polarized volcanics, which are locally intruded and superimposed, respectively by swarms of normally‐polarized dikes and radial lava flows along paleo‐valleys. These results support the onset of volcanic activity in the entire field at least in the Matuyama magnetic epoch, that is, between 2.58 and 0.78 Ma. Plain Language Summary: Airborne high‐resolution magnetic data play a crucial role in the understanding of the geological structure of ice‐buried volcanoes. In fact, an interesting property of magnetic minerals contained in volcanic rocks is that of retaining, after cooling below a certain characteristic temperature (i.e., Curie temperature), a permanent magnetization called remanent. Its direction (polarization) at the South Pole can be normal if rocks are cooled when the Earth's magnetic field presents negative inclination (as the current Brunhes epoch), whereas reverse in the case the Earth's magnetic field shows positive inclination (i.e., the Earth's magnetic field poles swap places). As a consequence, at polar latitudes, positive magnetic anomalies are associated with normally‐polarized rocks and, conversely, negative anomalies with reversely‐polarized rocks. Thanks to this property, in this study we have carried out the first reconstruction of the internal architecture of the Mt. Melbourne Volcanic Field. Our results, constrained by independent geological and geophysical information, suggest the volcanic complex is composed mainly by an older reversely‐polarized unit superimposed and intruded locally by younger normally‐polarized lava flows. Being the periods of magnetic polarity reversal well known, we have been able to estimate the beginning of a widespread volcanic activity before the last Brunhes‐Matuyama polarity reversal. Key Points: First detailed geophysical model of the internal structure of the Mt. Melbourne Volcanic FieldMagnetic anomalies and rock magnetism data suggest the field is predominantly built‐up by reversely‐polarized volcanicsOur results support an establishment of the Mt. Melbourne edifice at least at the reverse polarity Matuyama magnetic epoch [ABSTRACT FROM AUTHOR]

In their previous studies, the authors have shown that the integration of geophysical methods allows improving the quality of the solution of an inverse problem of exploration geophysics in comparison with the individual use of each of them. However, in practice, it is possible that for some measurement points, data from one of the geophysical methods used is missing. In this study, we investigate an approach associated with neural network recovery of the missing data of one geophysical method from the known data of another, and their further joint application to solve the inverse problem. In addition, we explore the effectiveness of applying multitask learning approach at the data recovery stage for the subsequent solution of the inverse problem. [ABSTRACT FROM AUTHOR]

A major challenge for the oil and gas industry is expediting the exploration geophysics activity. It is necessary to produce fast and accurate image of the targeted hydrocarbon reservoir, yet it involves extensive dataset due to the target location lies in deeper subsurface. Therefore, target-oriented oil and gas-reservoir imaging is currently seen as more attractive than conventional full-volume migration, in terms of computation efficiency. Through the integration of seismic redatuming with Kirchhoff migration, we presented a target-oriented imaging workflow that can effectively reduce computational cost while simultaneously enhancing the accuracy of the migrated image. Kirchhoff migration is renowned for being one of the simplest and flexible migration techniques, making it straightforward to implement. However, this migration approach is typically avoided in the presence of complex geology, as it tends to introduce artifacts in the images, thereby disrupting the interpretation beneath the complex overburden. Therefore, this paper highlighted the advantages of utilizing seismic redatuming to retrieve data beneath the overburden, followed by the utilization of the redatumed data as input for Kirchhoff migration. With an improved signal to noise ratio, the primary reflection events were amplified, providing clearer representation of the subsurface structure within the hydrocarbon reservoir or targeted area. Additionally, we utilized the benefits of Kirchhoff migration and explored the feasibility of performing patch-based migration in several areas of interest beneath the salt layer. This approach aimed to reduce both the turnaround time and the associated seismic migration costs. The developed workflow then was subsequently put to the test and applied to both a sub-salt SEG Advanced Modeling (SEAM) model and field data situated in East Malaysia. Based on the outcomes of the target-oriented migration, the proposed methodology demonstrated its capability to generate better quality and instant migrated images within the designated region. Furthermore, the feasibility of target-oriented imaging with Kirchhoff migration was substantiated through the integration of seismic redatuming, resulting in significant benefits towards seismic processing, imaging, and interpretation.

Artificial intelligence (AI) technology has developed through several booms and winters, and has now become a familiar part of our lives. It is a reliable tool that can save labor and improve efficiency in very tedious tasks. On the other hand, AI technology is also attracting attention and being used in our oil and gas related industries to expand production and minimize the cost of crude oil and natural gas. In this research, I would like to introduce several examples of AI applications in the field of geophysical exploration, including seismic exploration. One is in the area of data processing and the other is in the area of geological evaluation. I would also like to explain the pre-processing of input data that supports these applications. [ABSTRACT FROM AUTHOR]

Geology studies is a multi-stage activity that is began in a small scale and is became to large scale. With combining the results of each phase, study area gets smaller and eventually sites is selected as target for drilling, in order to achieve mineral deposits. Data resulting from studies of topography, geology, geochemistry, geophysics and drilling will achieve a tremendous amount of information that when they to be organized properly, reliable and useful results will presented. With regard to achieved progresses in the field of Geographic Information System(GIS), significant development occurred in the earth sciences, including obtaining, saving, retrieving, processing, displaying, using and sharing information of reference location. This paper investigates and analyzes appropriate sites of area exploration in Asaluyeh with using geophysical and satellite imagery as well as combining data. [ABSTRACT FROM AUTHOR]

Since the '60s of the last century, the calculation of the magnetic anomalies caused by 2D uniformly polarized bodies with polygonal cross‐section has been mainly performed using the popular algorithm of Talwani and Heirtzler (1962, 1964). Recently, Kravchinsky et al. (2019, https://doi.org/10.1029/2019GL082767) claimed errors in the above algorithm formulation, proposing new corrective formulas and questioning the effectiveness of almost 60 years of magnetic calculations. Here we show that the two approaches are equivalent and Kravchinsky et al.'s formulas simply represent an algebraic variant of those of Talwani and Heirtzler. Moreover, we analyze a large amount of random magnetic scenarios, involving both changing‐shape polygons and a realistic geological model, showing a complete agreement among the magnetic responses of the two discussed algorithms and the one proposed by Won and Bevis (1987, https://doi.org/10.1190/1.1442298). We release the source code of the algorithms in Julia and Python languages. Plain Language Summary: Forward magnetic calculation plays a major role in geophysics to model magnetization, location, and shape of magnetic sources. One of the most popular approaches to calculate magnetic anomalies due to two‐dimensional bodies is based on the formulas of Talwani and Heirtzler (1962, 1964), that have been widely used both for scientific and industrial applications from the sixties. Recently, these formulas have been questioned by Kravchinsky et al. (2019, https://doi.org/10.1029/2019GL082767) casting doubts on the truthfulness of all the magnetic models and interpretations obtained to date. We examined and compared the two calculation approaches, both from an analytical and numerical point of view. In detail, we corrected some inaccuracies in Kravchinsky et al.'s formulas and we found complete equivalence between the two discussed formulations, showing that they simply represent two algebraic variants of the same mathematical approach. We also performed intensive numerical tests comparing the results of the two algorithms with a third one proposed by Won and Bevis (1987, https://doi.org/10.1190/1.1442298). The three mathematical approaches gave the same magnetic responses for all the tested models, demonstrating total agreement between the three formulations. Key Points: Kravchinsky et al. (2019) claimed errors and omissions in the formulas of Talwani and Heirtzler (1962) for 2D forward magnetic calculationOur analysis reveals that Kravchinsky et al.'s formulas are algebraically equivalent to those of Talwani and HeirtzlerNumerical tests show a complete agreement among the two above formulations and the one by Won and Bevis (1987) [ABSTRACT FROM AUTHOR]

A number of empirical correlations have been achieved between the hydraulic properties measured through geoelectrical methods and water well data of Arak Aquifer located in Markazi province, Iran. The geoelectrical method of Vertical Electrical Sounding (VES) technique was used to calculate the hydraulic properties of the aquifer. Through the VES technique, the pivotal hydraulic properties such as porosity, hydraulic conductivity, and specific yield of the layers were calculated. The results of VES technique were compared with the data obtained from seven observation water wells that were already drilled as exploratory coring boreholes in the region. The results demonstrate that as the porosity and hydraulic conductivity of the water-bearing layer increase, the results of VES technique appear much identical to the water well records. Furthermore, the specific yield was calculated as 4.6% that was very close to the value of 3.5% measured through the previous pumping tests. Moreover, VES technique predicted the water table of the aquifer very close to the water level monitored in the observation water wells. The obtained correlations can be used as an alternative for drilling of new observation wells that are inefficient in time and expense, and may encounter environmental limitations of drilling and site construction.

The very first computational and most referred in the literature algorithm of Talwani and Heirtzler (1964) for calculating of the magnetic anomaly caused by two‐dimensional irregular shape subsurface structure has particular fundamental and educational significance in geophysics theory. We re‐derive this algorithm from first principles and discuss previous derivation omissions. Our resulting solution differs from the original publication. Based on our new solution we present the two‐dimensional forward magnetic modeling software and associated tutorials which are available for download from the website www.ualberta.ca/~vadim/software.htm. Additionally, we include the computation of the remnant magnetization which can be found using already published apparent polar wonder paths. Key Points: New formulas to calculate the magnetic anomaly caused by two‐dimensional irregular shape subsurface structure are derivedThe very first and most cited Talwani and Heirtzler (1964) algorithm is re‐derived and compared to the new derivationSoftware for two‐dimensional magnetic forward modeling is developed for educational and industry use [ABSTRACT FROM AUTHOR]

Oil and gas companies rely on high performance computing to process seismic imaging algorithms such as reverse time migration. Graphics processing units are used to accelerate reverse time migration, but these deployments suffer from limitations such as the lack of high graphics processing unit memory capacity, frequent CPU-GPU communications that may be bottlenecked by the PCI bus transfer rate, and high power consumptions. Recently, AMD has launched the Accelerated Processing Unit (APU): a processor that merges a CPU and a graphics processing unit on the same die featuring a unified CPU-GPU memory. In this paper, we explore how efficiently may the APU be applicable to reverse time migration. Using OpenCL (along with MPI and OpenMP), a CPU/APU/GPU comparative study is conducted on a single node for the 3D acoustic reverse time migration, and then extended on up to 16 nodes. We show the relevance of overlapping the I/O and MPI communications with the computations for the APU and graphics processing unit clusters, that performance results of APUs range between those of CPUs and those of graphics processing units, and that the APU power efficiency is greater than or equal to the graphics processing unit one. [ABSTRACT FROM AUTHOR]

In the Sudan Savanna of West Africa, Plinthosols with a petroplinthic or pisoplinthic horizon at ≤ 50 cm from the surface comprise the major soils. Because these horizons limit the rooting volume and water and nutrient storage capacities of the soils, they should be a major cause of decreased crop yield in the Sudan Savanna. However, the local distribution of Plinthosols is not precisely known, and the relationships between soil classes, effective soil depth, and crop yield, which are considered to be closely related to each other on the Plinthosol soils, are not fully understood. To clarify these relationships, we first reassessed the soil toposequence on a slope at the Institute of Environment and Agricultural Research Saria station in Burkina Faso using the current World Reference Base soil classification system. We then determined the relationships between soil classes and sorghum yield and between the effective soil depth and yield. We also assessed whether ground penetrating radar could predict the position of a petroplinthic horizon. We found (1) that Pisoplinthic Petric Plinthosols were found at the upper slope, Petric Plinthosols were found at the middle slope, and Ferric Lixisols were found at the lower to toe slope; (2) that sorghum yield was significantly larger at the Ferric Lixisols, then at the Petric Plinthosols, and lower at the Pisoplinthic Petric Plinthosols; (3) that sorghum yield was proportional to the effective soil depth at which upper boundary of petroplinthic horizon was found (n = 26, R2 = 0.78*** exclusion of waterlogged soil); and (4) that ground penetrating radar could predict the effective soil depth and the position of petroplinthic horizons (n = 4, R2 = 0.99**), suggesting that we could roughly but easily predict sorghum yield and local distribution of Plinthosols having a petroplinthic horizon using GPR. These results may enable us to take more account of the inherent soil conditions when studying soil and water conservation, fertilization methods, and crop breeding, all of which are crucial if sustainable agricultural methods are to be achieved in the Sudan Savanna. [ABSTRACT FROM AUTHOR]

Abstract: Ground roll is a significant source of noise in land seismic data, with crossline scattered ground roll particularly difficult to suppress. This noise arises from surface heterogeneities lateral to the receiver spread, and in desert regions sand dunes are a major contributor. However, the nature of this noise is poorly understood, preventing the design of more effective data acquisition or processing techniques. Here we present numerical simulations demonstrating that a barchan sand dune acts as a resonator, absorbing energy from ground roll and reemitting it over an extensive period of time. We derive and validate a mathematical framework that quantitatively describes the properties of the emitted waves and demonstrate that wave amplitude is estimable from easily measurable bulk properties of the dune. Having identified regions in time, space, and frequency space at which noise will be more significant, we propose reducing dune‐scattered noise through careful survey design and data processing. In particular, we predict that seismic noise will be lower upwind of barchan dunes, and at frequencies far from a resonant frequency 2cS/H, for dune height H and typical seismic velocity within the dune cS. This work is especially relevant to seismic acquisition in the vicinity of a dune field, where scattered noise appears incoherent and difficulties arise with alternative approaches to noise suppression. [ABSTRACT FROM AUTHOR]

SeisFlows is an open source Python package that provides a customizable waveform inversion workflow and framework for research in oil and gas exploration, earthquake tomography, medical imaging, and other areas. New methods can be rapidly prototyped in SeisFlows by inheriting from default inversion or migration classes, and code can be tested on 2D examples before application to more expensive 3D problems. Wave simulations must be performed using an external software package such as SPECFEM3D. The ability to interface with external solvers lends flexibility, and the choice of SPECFEM3D as a default option provides optional GPU acceleration and other useful capabilities. Through support for massively parallel solvers and interfaces for high-performance computing (HPC) systems, inversions with thousands of seismic traces and billions of model parameters can be performed. So far, SeisFlows has run on clusters managed by the Department of Defense, Chevron Corp., Total S.A., Princeton University, and the University of Alaska, Fairbanks. [ABSTRACT FROM AUTHOR]

Exploration geophysics is concerned with the development of methods and techniques for remote search for mineral deposits, solution of various engineering and geological problems, mining monitoring, and diagnostics of zones of rock bursts and natural and technogenic tectonic earthquakes. In this paper, we consider the diagnostic problem of exploration geophysics related to the determination of the shape and inclination angle of a plane source of natural geoelectric field, which, under certain conditions, simulates a rock failure zone, e.g., during the preparation of rock bursts at the sites of developed mineral deposits. This approach may also be useful in determining the shape and size of ore shoots by electrical measurements on the ground surface. Evaluation of the parameters of a rock failure zone is required in the case of accumulation of multiple fractures having charges of the same sign before a catastrophic failure. This problem is formulated as a Fredholm-Urysohn integral equation of the first kind. The solution of the integral equation is sought using the Tikhonov regularization method of the second order. [ABSTRACT FROM AUTHOR]

• An extensive magnetotelluric study of a high-enthalpy geothermal system has been performed for the first time in southwest Bolivia. • A 3-D inversion reveals a widespread electrical conductor at a few hundred meters depth which is interpreted as the cap rock of the geothermal system. • An extensive high-temperature hydrothermal reservoir was detected beneath the clay cap. • A conceptual model integrating geophysical, geological, and borehole data was constructed. We describe the three-dimensional magnetotelluric modeling results of Laguna Colorada - Sol de Mañana geothermal field in SW Bolivia. It is located near Laguna Colorada in the foothills of the Western Cordillera of the Andes and at the margin of the Altiplano-Puna Magma Body (APMB), which is characterized by a vast electrical conductivity anomaly and corresponding seismic anomalies in the mid and deep crust. The magnetotelluric (MT) data comprising 70 stations were modeled by a 3-D inversion. The final model shows a broad conductor at a few hundred meters in depth, which we interpret as the confining cap layer. Beneath, equally widespread, a layer of intermediate resistivity marks the high-temperature hydrothermal reservoir. Detailed interpretation of MT data with information from existing wells suggests a potential for a high-enthalpy geothermal field. [ABSTRACT FROM AUTHOR]