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Electrical conductivity of the continental crust
SITE 1NVESTIGATIONS:GEOPHYSICS Based on the generalized Biot’s theory in anisotropic porous media the characteristic equations of the seismic wave propagation in transversely isotropic porous media were derived. It is shown that in the porous media there are four kinds of dispersive and attenuative waves (two quasi-longitudinal waves, one quasi-shear wave, and one pure shear wave). In this essay, the analytical velocity formulas for four kinds of waves were derived. The coupling coefficients among the kinds of seismic wave propagation are also presented. (from English summary) 955183 Migration/inversion for transversely isotropic elastic media D. W. S. Eaton & R. R. Stewart, Geophysical Journal 119(2), 1994, pp 667-683. Znternatiod, Seismic migration and inversion attempt to infer petrographical and structural parameters from seismic data, and both are driven by an underlying mathematical model for wave propagation in the earth. In this sense, migration can be regarded as the first step in a general linearized-inversion scheme; this viewpoint is adopted in formulating a joint migration/inversion method for anisotropic elastic media. The derivation is based on the distortion-wave Born approximation, where approximate Green’s functions for the background medium are determined using asymptotic ray theory. Several TI model parameterixation schemes are evaluated for a vertical-incidence narrow-aperture recording configuration. (Authors) 955184 Theoretical Rayleigb and Love waves from an explosion in prestressed source regions D. G. Harkrider, J. L. Stevens & C. B. Archambeau, Bulletin - Seismological Society of America, 84(5), 1994, pp 14101442. Expressions and synthetics for Rayleigh and Love waves generated by theoretical tectonic release models are presented. The multipole formulas are given in terms of the strengths and time functions of the source potentials. This form of the Rayleigh and Love wave expressions is convenient for separating the contribution to the Rayleigh wave due to the compressional and shear-wave source radiation and the contribution of the upgoing and downgoing source radiation for both Rayleigh and Love waves. (from Authors) 955185 The use of tomographic imaging in mineral exploration B. C. Dyer 8z A. Fawcett, Exploration t Mining Geology, 3(4), 1994, pp 383-387.
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data are used to construct electrical conductivity/depth profiles for the continental crust, which, when compared with profiles obtained from magnetotelluric observations, demonstrate that a mid to lower crust composed of amphibolite saturated with 0.5 M NaCl shows electrical conductivities sufftcient to explain conductivity/depth profiles for the continental crust inferred from geophysical measurements. (from Authors) 955187 Self-potential and IP prospecting. Implications for the assessment of mineral deposits in the Russian Far Eastern Shelf B. L. Stolov, Geology of the Pacific Ocean, 10(2), 1994, pp 271-284. The problem of expanding the area of potential ore resources by exploiting the Russian Far East shelf is considered. Possibilities offered by the self-potential and IP techniques which have been successfully used for onshore ore prospecting are discussed. Preliminary geoelectrical models for oreless shelf areas are proposed, as well as for ore-promising areas containing solid ore and placer deposits in water 20-100 m deep. The models were used in mathematical modeling to produce theoretical self-potential curves of vertical electrical sounding. It is shown that curves of apparent polarixability indicate areas with both solid ore and placer deposits. (from Author) 955188 On the calculation of 3-D apparent resistivity responses with conductive plates C. Barajas & C. Flares, Geofisica Znternacionaf, 33(3), 1994, pp 431-446. An integral equation technique is applied for modeling the three-dimensional apparent resistivity response of a set of conductive plates immersed in a homogeneous or stratified earth. In implementing the algorithm, the Fredhohn integral equation of the second kind is transformed into a matrix equation and solved for the components of distributed current dipoles lying on the planes of the plates. The apparent resistivity at the earth’s surface is obtained from the secondary potentials produced by the current dipoles. The accuracy of the computed responses is examined in five test models. (from Authors) 955189 A new method to define the fuRsone resistivity in horizontal electric dipole frequency soundings on a layered Earth (in Chinese) Tang Jing-Tian & He Ji-Shari,, Acta Geophysics Sinica, 37(4), 1994, pp 543-552.
The basis of the tomographic velocity imaging technique is briefly described and an application of the method to detect and image a cross-section through a chromite pod is presented. Using the chromite application as an example, the relative costs of tomographic data acquisition and processing are compared with those of diamond drilling to obtain similar resolution. A number of different tomographic survey configurations and the potential role of the method in surface and underground exploration are discussed. (Authon)
The definition of effective resistivity and its algorithms in horizontal electric dipole frequency electromagnetic soundings are discussed on the basis of the unity of electromagnetic field. The effective resistivity improves the curves pattern of the wave-zone apparent resistivity significantly. (from English summary)
955186 Electrical conductivity of the continental crust P. W. J. Glover & F. J. Vine, Geophysical Research Letters, 21(22), 1994, pp 2357-2360.
955190 3-D inversion in subsurface electrical surveying - I. Theory M. Dabas, A. Tabbagh & J. Tabbagh, Geophysical Journal International, 119(3), 1994, pp 975-990.
The paper reports conductivity data obtained using a cell designed to make measurements on rocks saturated with saline fluids. The results show that the conductivity of saturated samples of acidic rocks is explicable entirely in terms of conduction through the pore fluid whereas the conductivity of saturated basic rocks requires the presence of an additional conduction mechanism(s). The experimental
The problem of 3-D inverse modelling in Direct Current (DC) surveys is addressed in this paper. First, forward modelling of the response of 3D bodies in DC surveys is carried out by the moment method. Secondly, inverse modelhng is carried out by a classical least-squares (LS) scheme that includes the Levenberg-Marquardt constraints formalism. Two approximations; Born and localized non-linear, were tested. Finally,
225A
data are used to construct electrical conductivity/depth profiles for the continental crust, which, when compared with profiles obtained from magnetotelluric observations, demonstrate that a mid to lower crust composed of amphibolite saturated with 0.5 M NaCl shows electrical conductivities sufftcient to explain conductivity/depth profiles for the continental crust inferred from geophysical measurements. (from Authors) 955187 Self-potential and IP prospecting. Implications for the assessment of mineral deposits in the Russian Far Eastern Shelf B. L. Stolov, Geology of the Pacific Ocean, 10(2), 1994, pp 271-284. The problem of expanding the area of potential ore resources by exploiting the Russian Far East shelf is considered. Possibilities offered by the self-potential and IP techniques which have been successfully used for onshore ore prospecting are discussed. Preliminary geoelectrical models for oreless shelf areas are proposed, as well as for ore-promising areas containing solid ore and placer deposits in water 20-100 m deep. The models were used in mathematical modeling to produce theoretical self-potential curves of vertical electrical sounding. It is shown that curves of apparent polarixability indicate areas with both solid ore and placer deposits. (from Author) 955188 On the calculation of 3-D apparent resistivity responses with conductive plates C. Barajas & C. Flares, Geofisica Znternacionaf, 33(3), 1994, pp 431-446. An integral equation technique is applied for modeling the three-dimensional apparent resistivity response of a set of conductive plates immersed in a homogeneous or stratified earth. In implementing the algorithm, the Fredhohn integral equation of the second kind is transformed into a matrix equation and solved for the components of distributed current dipoles lying on the planes of the plates. The apparent resistivity at the earth’s surface is obtained from the secondary potentials produced by the current dipoles. The accuracy of the computed responses is examined in five test models. (from Authors) 955189 A new method to define the fuRsone resistivity in horizontal electric dipole frequency soundings on a layered Earth (in Chinese) Tang Jing-Tian & He Ji-Shari,, Acta Geophysics Sinica, 37(4), 1994, pp 543-552.
The basis of the tomographic velocity imaging technique is briefly described and an application of the method to detect and image a cross-section through a chromite pod is presented. Using the chromite application as an example, the relative costs of tomographic data acquisition and processing are compared with those of diamond drilling to obtain similar resolution. A number of different tomographic survey configurations and the potential role of the method in surface and underground exploration are discussed. (Authon)
The definition of effective resistivity and its algorithms in horizontal electric dipole frequency electromagnetic soundings are discussed on the basis of the unity of electromagnetic field. The effective resistivity improves the curves pattern of the wave-zone apparent resistivity significantly. (from English summary)
955186 Electrical conductivity of the continental crust P. W. J. Glover & F. J. Vine, Geophysical Research Letters, 21(22), 1994, pp 2357-2360.
955190 3-D inversion in subsurface electrical surveying - I. Theory M. Dabas, A. Tabbagh & J. Tabbagh, Geophysical Journal International, 119(3), 1994, pp 975-990.
The paper reports conductivity data obtained using a cell designed to make measurements on rocks saturated with saline fluids. The results show that the conductivity of saturated samples of acidic rocks is explicable entirely in terms of conduction through the pore fluid whereas the conductivity of saturated basic rocks requires the presence of an additional conduction mechanism(s). The experimental
The problem of 3-D inverse modelling in Direct Current (DC) surveys is addressed in this paper. First, forward modelling of the response of 3D bodies in DC surveys is carried out by the moment method. Secondly, inverse modelhng is carried out by a classical least-squares (LS) scheme that includes the Levenberg-Marquardt constraints formalism. Two approximations; Born and localized non-linear, were tested. Finally,