A three-dimensional crustal geoelectric model of the Ukrainian Shield

A 3-D crustal geoelectric model of the Ukrainian Shield (USh) is constructed from magnetic variation data. High electrical conductivity anomalies with resistivities of 1–100 Ω m are located at depths of up to 30 km from the basement surface. A high conductivity layer with ρ = 25 Ω m and with its upper boundary at a depth of 70 km is supposed to exist in the upper mantle of the southwestern USh.     

Geoelectromagnetic and geothermic investigations in the Ihlara Valley geothermal field

The Ihlara Valley is situated within a volcanic arc that is formed by the collision of the eastern Mediterranean plate system with the Anatolian plate. In this study we will present data from a reservoir monitoring project over the Ihlara-Ziga geothermal field, located 22 km east of Aksaray, in central Anatolia.Although identified geothermal resources in the Ihlara Valley are modest, substantial undiscovered fields have been inferred primarily from the volcanic and tectonic setting but also from the high regional heat flow (150–200 mWm⁻²) on the Kir ehir Massif.In 1988 and 1990, geoelectromagnetic surveys were undertaken by MTA-Ankara to confirm the presence of a relatively shallow (≈ 0.5–1 km), hydrothermally caused conductive layer or zone. CSAMT and Schlumberger resistivity data show good correspondence with each other, and 2-D geoelectric models are also in harmony with geologic data and gravity anomalies.The depth of the resistive basement, which is interpreted as Paleozoic limestone, is 200–250 m in the western part and increases eastward (≈ 600–750 m). This may imply N-S-oriented normal faulting within the survey area. The parameters of the top layer are a resistivity of 25 to 95 ohm m and a thickness of between 100 and 250 m. The thickness of the conductive tuffs between the top layer and the basement, whose resistivity is about 4–5 o hmm, also increases eastward (from 100 to 450 m). The apparent resistivity maps for the frequencies between 32 and 2 Hz reveal a localized low resistivity anomaly to the east of Belisirma.     

3D upper crustal density structure of the Deccan Syneclise,Central India

A constrained 3D density model of the upper crust along a part of the Deccan Syneclise is carried out based on the complete Bouguer anomaly data. Spectral analysis of the complete Bouguer gravity anomaly map of the study region suggests two major sources: short wavelength anomalies (<100 km) caused primarily due to the density inhomogeneities at shallow crustal level and long wavelength anomalies (>100 km) produced due to the sources deeper than the upper crust. A residual map of the short wavelength anomalies is prepared from the complete Bouguer anomaly using Butterworth high‐pass filter (100 km cut‐off wavelength). Utilizing the constraints from deep resistivity sounding, magnetotellurics and deep seismic sounding studies, 2.5D density models have been generated along 39 profiles of this region. The mismatch between the calculated response of the a priori 2.5D model with the residual (short wavelength) gravity anomalies is minimized by introducing high‐density intrusive bodies (≥2.81 g/cm³) in the basement. With these 2.5D density models, the initial geometry of our 3D density model, which includes alluvium, Deccan trap, Mesozoic sediment and high‐density intrusive bodies in the basement up to a depth of 7 km (upper crust), is generated. In the final 3D model, Deccan trap extends from 200 m to nearly 1700 m below the 90–150 m thick Quaternary sediment. Further down, the sub‐trappean Mesozoic sediment is present at a depth range of 600–3000 m followed by the basement. The derived 3D density model also indicates six intrusive bodies of density 2.83 g/cm³ in the basement at an average depth of about 4–7 km that best fits the residual gravity anomaly of the study area.     

Three-dimensional geoelectrical model of metallogenic zones in the Kuznetsk-Alatau folded area

The three-dimensional (3D) geoelectric model of the Kuznetsk-Alatau folded area is reconstructed by magnetotelluric inversion using 3D fitting. It is established that the zones of ore mineralization within the Batenevsky massif are confined to the subvertical faults characterized by the electric resistivity of 100–300 Ω m. Blocks with ρ ≈ 10−100 Ω m are identified at a depth below 10 km in the western part of the model. The blocks are located close to the areas marked by the increased thermal flux, reduced seismic velocities, and elevated Moho boundary. This is probably associated with the presence of the rift zone in this area.

     

Electromagnetic 3D tomography of the Elbrus volcanic center according to magnetotelluric and satellite data

A geoelectric 3D model of the potentially active Elbrus volcano and its vicinities has been constructed using magnetotelluric data, which takes the volume model of the tectonic fragmentation field developed based on deciphering satellite photographs into account. An original method of searching for the correlation and determination of the character of the interrelation between the ground-based and satellite data has been used in this construction. The geoelectric 3D model constructed includes two conducting objects located at different depths. One of the objects, with a resistivity of 25–40 Ω m, located at depths of 0–10 km, is most intense at a depth of 5 km, where the object is quasi-isometric in shape and has a radius of 10 km along the 40–60 Ω m contour lines. Another object with a resistivity of 10–40 Ω m is located at a depth of ～45 km, where its dimensions along the contour line for 40 Ω m are 35 and 15 km in latitude and longitude, respectively. The thickness of the conducting core is approximately 20 km. The upper and lower objects can be interpreted as a volcano magma chamber and a volcano parent chamber, respectively.     

Hydrogeologic Controls on Induced Seismicity in Crystalline Basement Rocks Due to Fluid Injection into Basal Reservoirs

A series of M_b 3.8–5.5 induced seismic events in the midcontinent region, United States, resulted from injection of fluid either into a basal sedimentary reservoir with no underlying confining unit or directly into the underlying crystalline basement complex. The earthquakes probably occurred along faults that were likely critically stressed within the crystalline basement. These faults were located at a considerable distance (up to 10 km) from the injection wells and head increases at the hypocenters were likely relatively small (～70–150 m). We present a suite of simulations that use a simple hydrogeologic‐geomechanical model to assess what hydrogeologic conditions promote or deter induced seismic events within the crystalline basement across the midcontinent. The presence of a confining unit beneath the injection reservoir horizon had the single largest effect in preventing induced seismicity within the underlying crystalline basement. For a crystalline basement having a permeability of 2 × 10^?17 m² and specific storage coefficient of 10^?7/m, injection at a rate of 5455 m³/d into the basal aquifer with no underlying basal seal over 10 years resulted in probable brittle failure to depths of about 0.6 km below the injection reservoir. Including a permeable (k_z = 10^?13 m²) Precambrian normal fault, located 20 m from the injection well, increased the depth of the failure region below the reservoir to 3 km. For a large permeability contrast between a Precambrian thrust fault (10^?12 m²) and the surrounding crystalline basement (10^?18 m²), the failure region can extend laterally 10 km away from the injection well.     

A field test of imaging properties of rotational invariants of the magnetotelluric impedance tensor

A part of the Békés Basin (an extensional sub‐basin of the Pannonian Basin, where the basement under thick Pannonian sediments is well known from deep boreholes and from seismic measurements, and where many magnetotelluric (MT) soundings have been carried out for frequencies ranging from 1 to 10^?3 Hz) was selected as a test area to assess the imaging performances of various apparent‐resistivity definitions computed with rotational invariants of either the real part of the complex impedance tensor, or its imaginary part, or both. A comparison (based on earlier 3D numerical studies) has been made between the magnetotelluric images obtained in this way and the depths to the high‐resistivity basement, as known from boreholes and seismic investigations. The correlation coefficient between the series of basement depth values at 39 MT sites and the apparent‐resistivity values was found to be stronger and high correlation appeared at a shorter period when it was computed with apparent resistivities based on the real tensor rather than with apparent resistivities based on the imaginary tensor. In the light of our studies, ρ_{Re Z} and the impedance phase seem to be more informative than any other combination of magnetotelluric interpretation parameters.     

3-D inversion of MT data from the Sabalan geothermal field,Ardabil, Iran

Since the true Earth is 3-D in nature, a three-dimensional (3-D) inversion has clear advantages over lower dimensional inversions. We utilized a 3-D magnetotelluric (MT) inversion code, WSINV3DMT, to obtain a realistic resistivity model using a long period MT data set collected in the Northwest Sabalan geothermal field in Ardabil, Iran. The apparent resistivity and phase curves, the magnetic induction vectors, the impedance polar diagrams and the rotational invariant of impedance tensor, indicate a complex 3-D conductivity structure. After setting up the model parameters and designing the appropriate block discretization, we performed the 3-D inversions for two sets of observed data; one set includes the full MT impedance tensor and another set contains only off-diagonal elements of the MT impedance. The final model was selected according to the relative magnitude of the data misfit and the model norm with respect to various Lagrangian multipliers. The results of this study illustrate the 3-D inversion of the off-diagonal elements of MT impedance tensor is precisely enough to explain the structures related to the geothermal source. The obtained results were compared with the results of available 2-D models and they are then interpreted using all of the geological and drilling data of the area. The main outcome of this study is the precise delineation of the geometry of geothermal source that is located at the center of the study area with a surface coverage of about 7 km².     

Integrated interpretation of the magnetotelluric and magnetic data from Mahallat geothermal field,Iran

Magnetotelluric (MT) and ground magnetic surveys were conducted on the Mahallat geothermal field situated in Markazi province, central Iran, as a primary part of the explorations and developments of a geothermal energy investigation program in the region. Mahallat region has the greatest geothermal fields in Iran. MT survey was performed in November 2011 on an 8 km profile crossing the hot springs with a total of 17 stations. The 2D inversion of the determinant MT data was performed using a 2D inversion routine based on the Occam approach. The 2D resistivity model obtained from the determinant data shows a low resistivity zone at 800-2000 m depth and a higher resistivity zone above the low resistivity zone, interpreted as geothermal reservoir and cap rock, respectively. It also revealed two major concealed faults which are acting as preferential paths for the circulation of hydrothermal fluids. To obtain more geophysical evidence, a ground magnetic survey with 5000 stations was also performed over an area of 200 km² around the MT profile. Magnetic measurements show a main positive anomaly of about +1000 nT over the study area, which could be interpreted as an intrusive body with the high magnetic susceptibility (i.e. mafic and ultramafic rocks) into the sedimentary host rocks. We interpret the body as the heat source of the geothermal system. Structural index and depth estimation of the anomaly indicate that the intrusive body is similar to a cylinder extending from about one kilometer depth down to greater depths. The results of MT and magnetic investigations indicate a geothermal reservoir which proves the preliminary geological observations to a great extent.     

京津唐渤和周围地区地壳上地幔电性结构及其与地震活动性的关系

京津唐渤及其周围地区是我国的强烈地震活动区之一。自1976年以来,我们在该区开展大地电磁测深工作,完成了近30个测点。所得结果表明,本区壳内存在高导层,与地震方法确定的壳内低速层一致。平原内上地幔高导层埋深50-80公里,山区大于100公里,与地震方法确定的上地幔低速层基本一致,同时与大地热流测量、居里等温面计算和对新生代玄武岩地球化学研究结果基本吻合。本区绝大多数地震位于壳内高导层之上,强烈地震主要发生在上地幔高导层隆起的边缘。最后讨论了本区强震活动与壳内和上地幔高导层的关系。     

Grounded-source transientE-field modeling of a shallow resistive layer with 3-D inhomogeneity

There is growing interest in the use of transient electromagnetic (TEM) sounding for shallow geotechnical, environmental and groundwater investigations. Two commonly used transmitterreceiver configurations for TEM sounding are 1) loop-loop or its variation, in-loop configuration and 2) wire-loop configuration. The less common configuration of a horizontal electric dipole (HED) transmitter and receiver is treated in this study and called wire-wire configuration.Two important problems of shallow investigation in hard and soft rocks respectively are, defining 1) a fractured/fissured zone of medium resistivity, sandwiched between an overlying surface weathered rock of low resistivity and an underlying fresh compact rock of high resistivity and 2) a body of resistive sand buried in conductive clay. Lateral change in the middle layer resistivity is modeled by including a 3-D body of anomalous resistivity. The effect of perturbing the resistivity of the 3-D inclusion and the host middle layer for the wire-wire configuration is compared with that of the commonly used loop-loop configuration. The wire-wire configuration is found more sensitive to the model perturbations than the loop-loop configuration.1-D inversion of synthetic 1-D data sets for the wire-wire configuration finds resolution and estimation errors to be less than 10 percent for all the model parameters. For 3-D models, 1-D inversion results give a resolution error of 10 percent or less for the depth to, resistivity and thickness of, the 3-D inclusion. The estimate is within 10 percent of the true value for the first parameter but 40 percent for the other two. Resolution as well as estimation of the basement resistivity is always very poor.Using the wire-wire configuration, it is theoretically possible to define a buried resistive layer and any lateral change in its resistivity, subject to the above limitations of 1-D inversion. However, the basement resistivity cannot be estimated with reasonable accuracy in the presence of a lateral inhomogeneity in the overlying layer.     

Groundwater potential of the Egbe-Mopa basement area,central Nigeria

Abstract

An investigation on the groundwater potentials of the Egbe-Mopa area in central Nigeria, underlain by the Basement Complex, is presented. The investigation involved mapping of the subsurface by use of vertical electrical soundings; measurement of depth to groundwater; and evaluation of hydraulic conductivity, transmissivity and yield by means of pumping test interpretation. The results indicate subsurface units that range from three to five resistivity layers; depth to groundwater of 0–10 m; overburden thickness of 3–16 m; hydraulic conductivity of 6.2?×?10^?6 to 3.4?×?10^?4 m/s; transmissivity of 4.3?×?10^?7 to 2?×?10^?3 m²/s; and groundwater yield of 0.2–2.5 L/s. The hydraulic head assessments revealed a general northward groundwater flow direction. The study identified three aquifer potential types, of high, medium and low productivity, respectively. Based on the longitudinal conductance of the overburden units, four distinct Aquifer Protective Capacity zones were delineated, namely, poor, weak, moderate and good.

Citation Okogbue, C.O. and Omonona, O.V., 2013. Groundwater potential of Egbe-Mopa basement area, central Nigeria. Hydrological Sciences Journal, 58 (4), 826–840.     

Grounded-source TEM modelling of some deep-seated 3D resistivity structures

Long-offset transient electromagnetics (LOTEM) is now regarded as a suitable electrical method for deep exploration along with magnetotellurics (MT). In this method, the vertical magnetic-field impulse response and, occasionally, the horizontal electric-field step response of a grounded-wire source on the surface of the earth are measured. Here, these two responses are computed for 3D models of three deep resistivity structures of interest in hydrocarbon exploration: (i) a faulted graben in a resistive basement rock at a depth of 4 km beneath a conductive overburden; (ii) a facies change in a resistive layer buried at a depth of 2 km in the conductive overburden above a resistive basement; and (iii) an anticlinal uplift of a resistive layer at a depth of 1 km in the conductive overburden above a resistive basement. The results show that the sensitivity of the electric-field response to model perturbation is generally greater than that of the magnetic-voltage response. Further, the electric-field sensitivity is confined to early and intermediate times while that of the magnetic-voltage response is confined to intermediate and late times. Hence it is recommended that both electric and magnetic recordings are made in a LOTEM survey so that the final results can be presented as apparent-resistivity curves derived from the two responses jointly as well as separately.     

Exploration of geothermal structure in Puga geothermal field, Ladakh Himalayas, India by magnetotelluric studies

To understand the crustal electric structure of the Puga geothermal field located in the Ladakh Himalayas, wide band (1000 Hz–0.001 Hz) magnetotelluric (MT) study have been carried out in the Puga area. Thirty-five MT sites were occupied with site spacing varying from 0.4 to 1 km. The measurements were carried out along three profiles oriented in east–west direction. After the preliminary analysis, the MT data were subjected to decomposition techniques. The one-dimensional inversion of the effective impedance data and the two-dimensional inversion of the TE (transverse electric) and TM (transverse magnetic) data confirm the presence of low resistive (5–25 Ω m) near surface region of 200–300 m thick in the anomalous geothermal part of the area related to the shallow geothermal reservoir. Additionally, the present study delineated an anomalous conductive zone (resistivity less than 10 Ω m) at a depth of about 2 km which is possibly related to the geothermal source in the area. A highly resistive basement layer separates the surface low resistive region and anomalous conductive part. The estimated minimum temperature at the top of conductive part is about 250 °C. The significance of the deeper conductive zone and its relation to the geothermal anomaly in the area is discussed.     

Searching for Regional Crustal Velocity-Density Relations with the Use of 2-D Gravity Modelling – Central Europe Case

In this paper we search for a reference relation between seismic P-wave velocity V and density ρ _ref for the continental crust. Based on the results of modern seismic experiments, we compiled 2-D seismic models into a network of four, each about 1100–1400 km long, continental-scale seismic transects cutting all main tectonic units in Central Europe. The Moho depth (about 52 km beneath the TESZ in SE Poland, to about 25 km beneath the Pannonian Basin) and the crustal structure of this area are characterised by a large variation. This structural variation provides an interesting basis for gravity studies and especially for analysing the difference of the density structure between two major tectonic provinces of distinctive age difference: Precambrian and Phanerozoic. The 2-D gravity modelling applied for crustal cross-sections representing the regional structure, based on a unified gravity anomaly map of the area, allows for a stable determination of some general features of the regional reference velocity-density relation for the continental crust. In general three major seismo-petrological types of rocks can be distinguished: sediments, crystalline crust and mantle. In compacted sediments the reference velocity-density relation is well described by the Gardner or Nafe-Drake model. Calculated gravity anomalies, using unified velocity-density relation for the whole crystalline crust, well describe observed anomalies, with an average difference of 14 mGal. However, calculated gravity anomalies, using separated velocity-density relations for the crystalline crust of Precambrian and Phanerozoic Europe, describe observed anomalies better than for the entire crust, with an average difference 12 mGal. The most important feature of these relations is the large differentiation of the derivative dρ _ref /dV in the crystalline crust, being about 0.3 g s/m⁴ for Precambrian, and about 0.1 g s/m⁴ for the Phanerozoic crystalline crust. The modelling suggests a very small density value in the uppermost mantle ρ = 3.11 g/cm³ below the younger area, while for the older area it is ρ = 3.3 g/cm³.     

Magmatic plumbing systems of the Koryakskii–Avacha Volcanic Cluster as inferred from observations of local seismicity and from the regime of adjacent thermal springs

An analysis of local seismicity within the Avacha–Koryakskii Volcanic Cluster during the 2000–2016 period revealed a sequence of plane-oriented earthquake clusters that we interpret as a process of dike and sill emplacement. The highest magmatic activity occurred in timing with the 2008–2009 steam–gas eruption of Koryakskii Volcano, with magma injection moving afterwards into the cone of Avacha Volcano (2010–2016). The geometry of the magma bodies reflects the NF geomechanical conditions (tension and normal faults, \(S_V>S_{H_{\text{max}}}>S_{h_{\text{min}}}\)) at the basement of Koryakskii Volcano dominated by vertical stresses S _v , with the maximum horizontal stress \(S_{h_{\text{max}}}\) pointing north. A CFRAC simulation of magma injection into a fissure under conditions that are typical of those in the basement of Koryakskii Volcano (the angle of dip is 60°, the size is 2 × 2 km², and the depth is –4 km abs.) showed that when the magma discharge is maintained at the level of 20000 kg/s during 24 hours the fissure separation increases to reach 0.3 m and the magma injection is accompanied by shear movements that occur at a rate as high as 2 × 10^–3 m/s, thus corresponding to the conditions of local seismic events with Mw below 4.5. We are thus able to conclude that the use of planeoriented clusters of earthquakes for identification of magma emplacement events is a physically sound procedure. The August 2, 2011 seismicity increase in the area of the Izotovskii hot spring (7 km from the summit of Koryakskii Volcano), which is interpreted as the emplacement of a dike, has been confirmed by an increase in the spring temperature by 10–12°C during the period from October 2011 to July 2012.     

Assessing the Impact of a Heated Basement on Groundwater Temperatures in Bratislava,Slovakia

Groundwater temperature is a useful hydrogeological parameter that is easy to measure and can provide much insight into groundwater flow systems, but can be difficult to interpret. For measuring temperature directly in the ground, dedicated specifically designed monitoring wells are recommended since conventional groundwater wells are not optimal for temperature monitoring. Multilevel monitoring of groundwater temperature is required to identify contributions of different possible heat inputs (sources) on measured temperature signals. Interpreting temperature data as a cosine function, including period, average temperature, amplitude, and phase offset, is helpful. Amplitude dampening and increasing phase shift with distance from a boundary can be used for estimation of transport parameters. Temperature measurements at different depths can be used for evaluation of unknown parameters of analytical functions by optimization of regression fits in Python. These estimated parameters can be used to calculate temperatures at known water table depths which can be applied as a fixed transient boundary condition in MT3DMS to overcome the limitations of MT3DMS heat transport modeling in the unsaturated zone. In this study, temperature monitoring and modeling was used to evaluate the influence of a department store's heated basement foundation on groundwater temperature within a green space (city park), with the main outcome that 17 years after construction, the department store foundation has increased the mean groundwater temperature by 3.2 °C. Heat input evaluated by the MT3DMS model varied from 0.1 W/m² at a distance of 100 m up to 12 W/m² next to the building.     

2-D Crustal Velocity Structure Along Hirapur-Mandla Profile in Central India: An Update

The 2-D crustal velocity model along the Hirapur-Mandla DSS profile across the Narmada-Son lineament in central India (Murty et al., 1998) has been updated based on the analysis of some short and discontinuous seismic wide-angle reflection phases. Three layers, with seismic velocities of 6.5–6.7, 6.35–6.40 and 6.8 km s^–1, and upper boundaries located approximately at 8, 17 and 22 km depth respectively, have been identified between the basement (velocity 5.9 km s^–1) and the uppermost mantle (velocity 7.8 km s^–1). The layer with 6.5–6.7 km s^–1 velocity is thin and is less than 2-km deep between the Narmada north (at Katangi) and south (at Jabalpur) faults. The upper crust shows a horst feature between these faults, which indicates that the Narmada zone acts as a ridge between two pockets of mafic intrusion in the upper crust. The Moho boundary, at 40–44 km depth and the intra-crustal layers exhibit an upwarp suggesting that the Narmada faults have deep origins, involving deep-seated tectonics. A smaller intrusive thickness between the Narmada faults, as compared to those beyond these faults, suggests that the intrusive activities on the two sides are independent. This further suggests that the two Narmada faults may have been active at different geological times. The seismic model is constrained by 2-D gravity modeling. The gravity highs on either side of the Narmada zone are due to the effect of the high velocity/high density mafic intrusion at upper crustal level.     

Internal seiche pumping between sill-separated basins

Abstract

Despite their close proximity and similar dimensions (～ 200m deep × 10km long × 2km wide) the two eastern basins of Lake Lucerne, Gersauersee and Urnersee, exhibit considerable differences in their internal behaviour, particularly during late winter and spring. The two lakes are separated by a small intermediate basin (～ 120m deep × 4km long × 1km wide) with sills of approximately 90m depth at each end. We report results of a field program conducted over the period February—May, 1988, when observations were obtained from weekly CTD transects and from three thermistor string/current meter moorings deployed for two months, one near each sill and the third at the southern end of Urnersee near Fluelen. During the observation period the stratification, relative surface to bottom density difference, &Delta;ρ/ρ, was 12 × 10^?6 in Gersauersee and 4 × 10^?6 in Urnersee. Following wind events a large amplitude internal seiche in Gersauersee (vertical excursions of ～50m and period ～60 hours) effectively pumped the heavier Gersauersee bottom water onto the intermediate basin and eventually into the hypolimnion of Urnersee. Temperature spectra show a peak at this seiche frequency at all levels at the Gersauer sill but only near the bottom at the sill in Urnersee. Coherence estimates between the bottom temperatures at Gersauer sill and Fluelen showed a significant peak at period 60 hours suggesting transmission of energy from the Gersauersee seiching motion through the weaker stratification of Urnersee to Fluelen. The phase relationships indicate that the wave phase speed decreases as the wave propagates into the region of weaker stratification. Application of a simple two-layer Defant model which includes topographic variations confirms these observations. The estimated volume exchange due to seiche pumping is only a small fraction of the Urnersee hypolimnion. However, the dissipation of energy transferred from the Gersauersee seiche may be an important contribution to mixing in the deeper waters of Urnersee.     

Spatial distribution of resistivity in the hydrogeological systems,and identification of the catchment area in the Rharb basin,Morocco / Répartition spatiale de la résistivité dans les systèmes hydrogéologiques et détection des zones de captages dans le bassin du Rharb,Maroc

Abstract

Abstract Geophysical results obtained in the Rharb basin, Morocco are reported. Correlations between hydrogeological well logs reveal several water-bearing Plio-Quaternary units resting on a substrate of blue marls. Geo-electrical borehole analyses were interpreted using bi-logarithmic diagrams which indicate the permeable layers of the aquifer and also its basement. Resistivity data from NE–SW and NW–SE electrical sections allow definition of the permeable/impermeable levels, and identification of ?ditches? that may be favourable sectors for hydrogeological exploitation. Resistivity anomalies were investigated by analysing maps of resistivity at 400 and 1000 m AB. Anomalies identified in the Rharb basin are related to the thickening of the permeable bodies (sand, limestone, sandstone deposits). In the coastal zone (AB = 1000 m), there is a strong decrease of the resistivity gradient (35–10 Ω m), which is probably linked to marine intrusion. Electrical anomalies allow detection of the water-bearing zones notably in the western and southwestern parts of the Rharb basin.