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- Volume 14, Issue 1, 2016
Near Surface Geophysics - Volume 14, Issue 1, 2016
Volume 14, Issue 1, 2016
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Multi‐geophysical approach for the better understanding and characterization of subsurface structures
Authors De‐Bao Lu, Qi‐You Zhou, Jin‐Yi Dong and Zhong‐San ZhangABSTRACTUnderstanding and characterizing subsurface structures is challenging, especially when the objective is to investigate sites for nuclear waste disposal. This paper presents a multi‐geophysical approach for subsurface experimental investigations in which seismic data are used to improve electrical resistivity tomography quality. Different synthetic models ranging from simple to complex were created to quantitatively demonstrate the improvements enabled by the use of this strategy. Moreover, the scheme was tested at Beishan, a candidate site for the disposal of high‐level radioactive waste in northwestern China. The results show that the combination of geophysical data sources improves the interpretation of the subsurface over a single source. The root‐mean‐square level and runtime were found to rapidly decrease when using the proposed scheme.
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Application of combined time‐lapse seismic refraction and electrical resistivity tomography to the analysis of infiltration and dissolution processes in the epikarst of the Causse du Larzac (France)
Authors Rémi Valois, Pierre‐Yves Galibert, Roger Guerin and Valérie PlagnesABSTRACTIn geophysical and hydrological studies, it can be challenging to achieve a complete understanding of infiltration processes in the upper zone of a karstic aquifer since this type of medium is highly heterogeneous and may contain a perched aquifer. In an effort to further investigate such aquifers, time‐lapse electrical resistivity tomography and time‐lapse seismic refraction tomography were carried out at three different epochs and at two sites on a dolostone plateau of Southern France. The first site has a sinkhole, whereas the second covers a less efficiently drained area, which is characterized by temporary lakes during periods of heavy rain.
These studies show that shallow time‐lapse electrical resistivity tomography and time‐lapse seismic refraction tomography analyses are correlated with hydrological data because resistivities and propagation velocities decrease with increasing rainfall. Nevertheless, the Biot–Gassmann relationship does not provide an adequate explanation for the strong variations in velocity observed in the upper parts of the models. This could be explained by the dissolution process called ghost‐rock weathering, which directly attacks the dolostone rock frame of the studied area. The assessment of such processes can lead to an improved understanding of velocity variations and to the localization of dissolution processes that may affect karstic landscapes or even lead to their collapse.
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Relationships between soil hydraulic parameters and induced polarization spectra
Authors Sven Nordsiek, Efstathios Diamantopoulos, Andreas Hördt and Wolfgang DurnerABSTRACTSpectral induced polarization is a promising method to estimate soil hydraulic properties relatively quickly without interfering with the subsurface. It is essential for the interpretation of the spectral induced polarization data to understand the relationships between soil hydraulic properties and the parameters obtained from spectral induced polarization measurements. Recent studies often relate to certain types of unconsolidated sediments, e.g., artificial mixtures of sand and clay, or refer to particular pairs of soil hydraulic and complex electrical parameters. In the present study, we investigated seven samples of natural soils and a pure sand sample in the laboratory by spectral induced polarization and soil hydraulic measurements. After examining single combinations of parameters that can be expected from theoretical considerations, we calculated the correlation coefficients for all available pairs of complex electrical and soil hydraulic parameters. Based on this, two new empirical relationships are proposed and discussed in more detail. First, a linear relationship between the van Genuchten–Mualem parameter and the inverse of the normalized chargeability is described. Second, a power law was found to estimate the saturated hydraulic conductivity from the DC resistivity , the normalized chargeability , and the fluid conductivity .
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On the geoelectric structure of the Sphinx Area in Egypt
Authors Pavel O. Barsukov and Eduard B. FainbergABSTRACTA three‐dimensional model of the electrical resistivity of rocks to a depth of 150 m in the Sphinx and the Pyramid of Khephren (Giza, Egypt) area was built using the results of transient electromagnetic soundings. The technology of the soundings, the data processing, and the design of the media’s model as a result of three‐dimensional block inversion are described. The boundary of the Paleogene limestones that form the plateau of the pyramids and the underlying structure of the folded Cretaceous are defined based on geological interpretation.
The created plateau model indicated the thickness of the slightly inclined Mokattam limestones varied from 25 m to 150 m within a 1000 × 300 m2 area. Such intense changes in the limestone subface’s altitudes were controlled by the folded structure of the underlying Cretaceous carbonates. Cretaceous carbonates show low electrical resistivity, which is typical for fractured rocks saturated with saline water. Dense Mokattam limestone blocks are broken by water‐saturated zones with sub‐vertical faults in the southwest–northeast direction. The electrical resistivity in the carbonate surface layer, which lies at the base of the pyramids and Sphinx, is heterogeneous with a composition that depends on the clay content and presence of halite.
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Resistivity imaging technique to investigate the subsurface strata conditions due to blasting in underground coal mines in India
Authors K.K.K. Singh, P.K. Singh and M.P RoyABSTRACTProduction from underground coal mining in India has been decreasing since the last three decades. Blasting‐off‐the‐solid, in Indian underground mines, has been a widely practised method for winning coal while developing mine galleries in bord and pillar system. The blast holes are drilled in solid coal without free face in blasting‐off‐the‐solid method of mining and are blasted with permitted types of explosives and delay detonators. Blasting‐off‐the‐solid will play an important role in underground coal production. The mines that were planned earlier to be away from residential areas are now approaching to those areas. The coal reserves are being exploited very fast, and mine owners cannot ignore to take the coal beneath the structures/houses. In this paper, resistivity imaging technique has been used to document the change of subsurface structures/features between the surface and underground face, where blasting is carried out to extract the coal in underground coal mines. Resistivity imaging survey conducted at three mining sites revealed that there was no significant change in subsurface strata conducted during pre‐ and post‐blasting conditions. The slight change in resistivity values up to 35 Ωm up to a few metres of peripheral area of the blasting face in the mine may be either due to the effect of blast vibration and/or same void created by blasting or increase in porosity of overlying subsurface strata.
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A laboratory study to determine the effect of pore size, surface relaxivity, and saturation on NMR T2 relaxation measurements
Authors Samuel Falzone and Kristina KeatingABSTRACTIn this study, we present laboratory experiments investigating the effect of pore size and surface relaxivity on the nuclear magnetic resonance response of variably saturated sands that relax both within and outside the fast diffusion regime. We measured the NMR response of sands with a range of grain sizes (129 to 753 μm), which resulted in samples with different pore sizes, and a range of iron concentrations (0.07% to 0.38%), which resulted in sands with different values. The laboratory results showed that the relation between relaxation time and water saturation depended on the regime in which relaxation occurred. For samples relaxing in the fast diffusion regime (i.e., small pores and low surface relaxivity), the relation between relaxation time and water saturation was linear; for the remaining samples, the relation between relaxation time and saturation demonstrated a power‐law relationship with an exponent greater than one. In addition, we performed numerical simulations based on common pore‐filling mechanisms (i.e., capillary tubes or thin films). The numerical simulations did not predict the experimental results for the relative surface relaxation versus saturation trends. We conclude that, in addition to the diffusion regime in which relaxation occurs, the shape of the relaxation time versus saturation curve depends on the pore‐filling mechanism, the value of , and the pore size. The dependence of NMR relaxation on the pore‐filling mechanism of saturating porous media may complicate efforts to develop a relation between relaxation time and saturation for use in characterizing unsaturated porous media.
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Volumes & issues
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Volume 22 (2024)
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Volume 21 (2023)
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Volume 20 (2022)
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Volume 19 (2021)
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Volume 18 (2020)
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Volume 17 (2019)
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Volume 16 (2018)
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Volume 15 (2017)
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Volume 14 (2015 - 2016)
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Volume 13 (2015)
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Volume 12 (2013 - 2014)
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Volume 11 (2013)
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Volume 10 (2012)
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Volume 9 (2011)
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Volume 8 (2010)
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Volume 7 (2009)
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Volume 6 (2008)
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Volume 5 (2007)
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Volume 4 (2006)
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Volume 3 (2005)
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Volume 2 (2004)
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Volume 1 (2003)