Wyniki wyszukiwania - Biblioteka Nauki

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Assessing the efects of 1D assumption violation in vertical electrical sounding (VES) data processing and interpretation

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Mashhadi S. R. , Ramazi H. , Asgarpour Shahreza M.

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tom Vol. 68, no. 1

105--122

EN

This research aimed to discover the possible efects of 1D assumption violations on VES data interpretations. In order to do so, 1D inversion results of logarithmically spaced and linearly spaced VES measurements are compared with their relevant 2D inverted models. Some real case studies are also examined by 1D and 2D inversions to test the results. It is found that linearly spaced VES measurements are not really suitable for 1D inversion in the case of 1D assumption violations and logarithmically spaced VES can better handle these problematic features. In the case of semi-infnite horizontal layers and also small surface resistivity inhomogeneities, logarithmically spaced VES datasets mostly provide a reliable 1.5D model while linearly spaced VES datasets sufer from remarkable artifacts. In the case of vertical structures, both linearly spaced and logarithmically spaced VES techniques fail. In this case (i.e., a vertical dike), artifacts in the form of “extra layer” appear in those VES stations that are adjacent to the dike. However, for VES stations on the dike structure, no extra layer appears in the 1D inversion result. It must be emphasized that 1D violating features are not improbable in many geological situations so they must be considered in mind when processing and interpreting the geophysical VES data.

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Parametric characterization, protectivity and potentiality of shallow hydrogeological units of a medium-sized housing estate, Shelter Afrique, Akwa Ibom State, Southern Nigeria

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Ekanem K. R. , George N. J. , Ekanem A. M.

Acta Geophysica

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2022

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tom Vol. 70, no 2

879--895

EN

Geoelectrical resistivity technology (GRT) constrained by geological information was used to map the hydrokinetic properties, as well as the protectivity and potentiality of groundwater system in a medium-sized and sort after housing estate in Southern Nigeria. The GRT deployed involved Schlumberger 1-D vertical electrical resistivity sounding (VES) and 2-D electrical resistivity tomography (ERT). The primary and secondary geoelectric indices were used in tandem with existing geological information to estimate the hydrodynamic parameter maps of the shallowest aquifer unit, maximally exploited in the area for optimal management of the unconfined aquifer system beneath. Total porosity (0.282–0.691), specific yield (0.040–0.107), field capacity/specific retention (0.242–0.623) and storage-dependent drainability efficiency (SDE) (7.6– 40.5%) were determined to depict the saturation dynamics in the study area. Results showed that the area has optimal release of pore water when the storage-dependent drainability efficiency is greater than 21%. The ensemble of potential index parameters such as transmissivity (57.4–4339.2 m2 /day), transverse resistance/aquifer potential scale (453.6–152,756.5 Ωm2), permeability (91.7–7269.7 mD) and hydraulic conductivity (57.4–4339.2 m/day) showed optimal potentiality but poor to moderate protectivity as evidenced by longitudinal conductance index (0.004–0.6218 Siemens). As many individuals have strong affinities to live in this fast, newly developed and competitive housing estate, it is a healthy practice that efficiently managed waste disposal arrangements/measures be put in place in order to ward of the exposure of leachates and other organic/inorganic wastes from permeating/draining into the already naturally vulnerable underlying hydrogeological units, where groundwater extracted for diverse use is stored.

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Rozpoznanie złoża piaskowców budowlanych z wykorzystaniem geofizycznych badań elektrooporowych i georadarowych

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Klityński W. , Stelmach K. , Stefaniuk M. , Karczewski J.

Przegląd Geologiczny

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2014

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tom Vol. 62, nr 10/2

621--628

EN

The paper presents the application of Vertical Electrical Sounding (VES) and Ground Penetrating Radar (GPR) into recognition of the geometry and vertical differentiation of a deposit of color sandstones that are commonly used as elevation stones in building industry. The investigations covered sandstones of Lower Cretaceous age (Albian) that occur at the foothills of the Che³mo Mt. near Kolonia Grabowie (Radomsko district, £ódŸ province). The former quarry of Grabowie is situated in the forest area of the landscape park and this blocked further exploitation from the documented deposit. On a limited scale sandstone is still quarried form the southern edge of the old quarry. However, poor recognition of the deposit hampers the effective exploitation. The objective of the geological investigations was to examine a new part of the deposit including identification of the roof and the bottom of sandstone complex, the thickness of overlying rocks, location of faults and weathered zones, as well as recognition of the lithology down to a depth of 8 m below ground surface. Resistivity distribution in the study area was assessed with the use of VES. Much higher resistivity of sandstones as compared to surrounding rocks was advantageous. Owing to high resolution GPR, the deposit boundaries could be delineated and the stratification within the sandstone complex could be represented. The investigations resulted in construction of 2D models of the deposit and surrounding rocks and gave information on the lithology.

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Analiza możliwości zastosowania metody tomografii elektrooporowej (ERT) do rozpoznania miąższości pokrywy laterytowej

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Pacanowski G. , Czarniak P. , Piechota A. , Mieszkowski R.

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2016

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tom Vol. 64, nr 4

245--253

EN

The paper discusses the problem of determining the thickness of a laterite cover using electrical resistivity tomography (ERT) in a selected area of the Seram Island in Indonesia. Seram Island lies in the tropical zone between the Seram and Banda seas. The laterite covers are rich in nickel, cobalt, iron and other metals. Concentrations of these metals in the laterites are high enough to form economic deposits. A significant part of the report concerns the measurement technique (ERT method) in difficult climatic (high humidity and temperature) and topographic conditions (equatorial jungle with significant variations in elevation) and the methods of processing and interpretation of the acquired data. The problem seems very interesting, because geophysical prospecting is currently more and more often conducted in poorly accessible regions of the world. Additionally, there are no sufficient and commonly available publications that would allow us to get acquainted with local measurement problems by potential contractors of similar geophysical investigations. The primary result of the geophysical survey was to determine the electrical resistivity of bedrock and laterite. This was the basis for the development of sections of electrical resistive distribution for the ERT profiles, which enabled to estimate the depth to the crystalline basement and the laterite thickness. It also facilitated to produce a map of laterite thickness, which may be an important material to develop the concept of searching and mining of nickel and cobalt ore.