Groundwater Potential Assessment Using Vertical Electrical Sounding and Magnetic Methods: A Case of Adilo Catchment, South Nations, Nationalities and Peoples Regional Government, Ethiopia

Vertical electrical sounding and magnetic methods were carried out to assess groundwater potential in Adilo catchment, Kembata Tembaro Zone, South Nations, Nationalities and Peoples Regional Government, Main Ethiopian Rift. The data were acquired from eight VES points using Schlumberger electrode arrays with maximum half current electrode spacing ( AB / 2 = 500 ) and 253 magnetic data points were analyzed. The qualitative analysis of VES data was accomplished by using curves, apparent resistivity, and pseudodepths, and the quantitative interpretations of the VES data were constructed by the VES data using IPI-Res3, IPI2Win, and surfer software and constructing geoelectric section along with profiles and lithological information from the borehole and Geosoft interpretation was used for magnetic data. The VES results of the data revealed five geoelectric layers which differ in degree of fracturing, weathering, and formation. The upward continued magnetic field map anomaly to 560 m illustrated northwestern to the southwest; areas have a low magnetic anomaly. Examining the potential aquifer of profile one’s geoelectric section, the horizons of layer four were better potential aquifers as the highly fractured and weathered ignimbrite zone of layer five of VES13 was 219 m deeper than the depths of the other VES points, and along with profile two geoelectric sections, the horizon of layer four VES23 layer five has the lowest resistivity with large thickness at a depth of 253 m. Thus, the low resistivity and the large thickness of these formations are an indication of the high yield of groundwater potential in the study area.

The deep structure of the Salair fold-cover structure according to magnetotelluric studies

The results of magnetotelluric studies (MTS) performed within the Salair cover-folded structure on two profiles are considered: the Zabrodino village – the Rodnikovy village (1) and the Smaznevo village – the Kotino village (2). The profiles are oriented crosswise along the main structures and intersect Salair and the western part of the Kuznetskiy trough. The analysis of the obtained data showed that a subhorizontal underlying conducting zone is distinguished in the Earth’s crust of the Salair fold-cover structure, such zone is typical for intracontinental orogens. The zone is considered as a deep separation failure. The nature of the electrical resistance values distribution confirms the presence of the Salair thrust on the Kuznetskiy deflection. The Alambay ophiolite zone on the geoelectric section corresponds to a highly gradient region, indicating the suture zone of this structure. High resistivity values in the northern part of the Khmelevskoy trough are associated with the widespread development of granitoid massifs that are not covered by erosion.

EXPERIENCE OF COMPLEX MICROSEISMIC AND MAGNETOTELLURIC SOUNDING ON THE NORTHERN PART OF THE CENTRAL SIKHOTE-ALIN FAULT

We present the results of a study of the crustal structure of the northern part of the Central Sikhote-Alin Fault (CSAF) by methods of microseismic sounding (MSS) and magnetotelluric sounding (MTS). A geoelectric section based on MTS data and a section of relative velocities of P-waves according to MSS data were constructed and interpreted at a depth of up to 9 km and a length of 42 km. The main blocks, their boundaries, fault zones and some anomaly zones identified by microseismic and magnetotelluric sounding practically coincide. The CSAF zone is expressed by a narrow subvertical zone between high resistivity blocks. The data obtained indicate that the fault zone in the study area is impermeable. A similar structure was identified 6 km northwest of the CSAF zone, which can be traced to twice the depth (up to 20 km). It is concluded that the combination of microseismic and magnetotelluric sounding methods is promising for studying the structure of the Earth's crust in fault zones.

CORRECT DETERMINATION OF INTEGRAL CONDUCTIVITY IN SOLVING INCORRECT INVERSE PROBLEMS OF ELECTROMAGNEIC LOGGING

The paper suggests and investigates a problem statement of well-logging inverse problem that is based on the integral conductivity parameter to describe a geoelectric section. Approach was introduced for a layered cylindrical model with radially heterogeneous continuous distribution of electric properties that parametrize the problem with a function of total longitudinal conductivity. The results of hydrodynamic modeling for oil/fresh water- and brine-based drilling muds were used to study multiple propagation resistivity tool signal equivalency for two classes of models with continuous and piece-wise constant conductivity distribution. Physically based algorithm enabling one to convert one model class to the other, preserving the signal equivalency was proposed. It was demonstrated that the radial models with different radial conductivity distribution and similar integral conductivity curves are equivalent. This fact lays a rationale of using the integral conductivity parameters along with conductivity while inversion. The integral conductivity parameter can be used to build the functionals, whose minimization improves algorithm stability and enables determining functional parameters in hydrodynamic filtration models.

GEOPHYSICAL INVESTIGATION OF GROUNDWATER POTENTIAL OF A SITE IN OBALE AREA OF AKURE, NIGERIA.

Electrical Resistivity method using Vertical Electrical Soundings (VES) were carried out at a site in Aba-Oyo area FUTA Southgate area, Akure, Nigeria, with the aim to access groundwater potential of the site. The study area is underlain by crystalline rocks of the Precambrian basement complex of the Southwestern Nigeria. Twelve (12) VES were carried out using Schlumberger electrode array configuration with AB/2from 1 to 65m. The VES data generated were processed and interpreted using partial curve matching method and computer iteration techniques. The interpreted data revealed three to four geoelectric sections with varied thicknesses and resistivity. The top soil layer ranges from 44 to 181?m, lateritic clay layer ranges from 20 to 174?m, the weathered horizon resistivity ranges from 20.0 to 424.0?m while the competent rock/fresh rock has resistivity values greater than 424.0.3?m. The top soil layer resistivity and thickness ranges from 44 to 181?m and 0.4 to 2m, the lateritic clay layer resistivity and thickness range from 20 to 174?m and 1.7 to 6.0m respectively, the weathered horizon resistivity ranges from 20.0 to 424.0?m and 1.4 to 7.4m respectively while the competent rock has resistivity values greater than 424.0?m and ?m respectively. The third geoelectric layer constitutes the aquiferous zone in the 4-layer geoelectric section while the second geoelectric layer is the aquiferous zone in all the 3- layer geoelectric sections. VES station 2, 7, 9 stations shows good groundwater potential as revealed by the thick overburden and weathered layer with low resistivity values. VES stations 1, 4, 5, 6, 8, 10 and 12 shows moderate groundwater potentials while VES stations 3 and 11 are non-aquifereous in nature.

Evaluating the Earth Subsurface for Civil Engineering Site Characterization in Agege, Southwest Nigeria Using Integrated Geoelectrical and Multichannel Analysis of Surface Wave (MASW)

A geophysical investigation involving 1D Vertical Electrical Sounding (VES), 2D Electrical Resistivity Imaging (2D ERI) and Multichannel Analysis of Surface Wave (MASW) has been carried out at Agege, Lagos, Nigeria with a view to delineating the subsurface stratigraphy and locate some competent strata/stratum for founding civil engineering structures. Six (6) 200 m long traverses were established within the study area. Along these traverses, 2D ERI were carried out adopting Wenner electrode configuration. Vertical Electrical Sounding (VES) adopting Schlumberger electrode array were carried out at selected points along profiles 1, 2 and 3 to determine the lithological sequence at depth. MASW data also were acquired along traverses 1, 2 and 3. The data were processed and the result yielded interpretable 2D resistivity structure and geoelectrical parameters (layer resistivity, thicknesses and depth) from the VES. The interpreted VES results were used to generate geoelectric section while the MASW resulted in 2D velocity sections. Three subsoils including topsoil, clay and clayey sand/sand were delineated beneath the study area. The resistivity and thickness range of the layers are; topsoil (34.0-54.6 ohm-m, 0.9 – 1.7 m), clay (10.3 – 17.7 ohm-m, 8.9 – 12.3 m) and clayey sand/sand (48.9 – 323 ohm-m) while the S-wave velocity range for the subsoil falls between 40 – 500 m/sec.

Subsurface Investigation of Basement Structures Using Electrical Resistivity Methods at Zainawa Village Kano, Nigeria

Electrical Resistivity Methods involving Schlumberger Vertical Electrical Sounding (VES) and Wenner Electrical Profiling (EP) were carried out to map the Geological features of the earth subsurface in Zainawa Area of Kano State, Nigeria. Five profiles were established; consist of six (6) VES points at each profile. GEOPULSE resistivity meter (SAS 300) was used for the data acquisition. The field data obtained have been analyzed using computer software (IPI2win) which gives an automatic interpretation of the apparent resistivity. A maximum of three geoelectric subsurface layers were delineated from the VES master curves. The geoelectric section beneath the study area was composed of top soil (clayey-sandy and sandy-lateritic), weathered layer, partly weathered (fractured basement) and fresh basement. The resistivity value for the topsoil layer varies from 20 Ωm to 600 Ωm with thickness ranging from 0.5 to 7.2 m. The weathered basement has resistivity values ranging from 15 Ωm to 593 Ωm and thickness of between 2.75 to 33.04 m. The fractured basement has resistivity values ranging from 201 Ωm to 835 Ωm and thickness of between 11 to 20.4 m. The fresh basement (bedrock) has resistivity values ranging from 1161 Ωm to 3115 Ωm with infinite depth. The depth to basement map was produced to give a good picture of the basement topography within the study area. The depth to basement ranges from 11 m around VES 01 to 85 m around VES 25 m. The map also reveals linear structures (VES 05, 21, 22 and VES 23) which trends in the NE-SW direction. These structures suggest a basement depression at these points. However, the depth from the topsoil to the bedrock surface varies between 2.5 to 37.75 m.

Investigation of groundwater potential using integrated geophysical methods in Moloko-Asipa, Ogun State, Nigeria

Water is essential for livelihood, development, and industrial growth. Its exploration in sufficient quantity is required where it does not freely occur on the surface. This research was aimed to delineate aquifer regions and provide information on the subsurface lithology of Moloko-Asipa Southwestern Nigeria. A combination of eight traverses investigated with very low frequency electromagnetic (VLF-EM) method at 5 m constant sampling interval and ten vertical electrical sounding (VES) were carried out in the survey. Measurements from the VLF-EM survey were processed with Karous and Hjelt filtering to give the resistivity contrast across the selected profiles. The VES data processing involved an automatic approximation of the initial resistivity and thickness of the geoelectric layers with IPI2Win and further filtering by WinResist iteration. Estimation of Dar-Zarrouk parameters was also employed to investigate the aquifer protective capacity of the area. The processed VLF-EM results showed the geology of the area to an average depth of 25 m. The geoelectric section of the VES data revealed minimum of 3 layers from sandy top soil to weathered layer and fresh basement with an average resistivity values of 1,816, 926 and 17,503 Ωm, respectively. The integration of VLF-EM and VES in the investigation revealed that the potential for groundwater exploration in the study area is poor due to the thin nature of the weathered layer and its shallow depth to basement. The aquifer protective capacity of the area was likewise inferred to be poor.

Deep Structure of the Junction Zones of the Chuya Tectonic Depression and Its Mountainous Frame in Gorny Altai according to Magnetotelluric Studies

––Results of magnetotelluric studies (MTS) carried out along the SW–NE and W–E profiles across the Chuya depression are used to demonstrate the deep geoelectric structure of its internal field and the zones of transition to the northern (Kurai Ridge) and southern (South Chuya Ridge) mountainous frames. The Chuya depression is an area with small-block structure, with its axial part comprised of the thinnest sedimentary deposits (450–650 m). The key sites of the zones of transition from this depression to the Kurai and the South Chuya ridges manifest a complete geoelectric section of sedimentary deposits with a total thickness of 1000–1200 m. Subvertical conductive heterogeneous beds of abnormally low (<5 Ohm∙m) specific resistivity are mapped in the section of the sedimentary cover and the Paleozoic basement. They mark neotectonic faults and nodes of their intersection with the Paleozoic and Mesozoic faults. The kinematic parameters of the faults determined from the magnetotelluric data are generally consistent with the data of morphotectonic and geological studies.