共查询到20条相似文献,搜索用时 498 毫秒
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Sensitivity analysis of electromagnetic (EM) measurements is important to quantify the effect of the subsurface conductivity on the measured response. Knowledge of the sensitivity functions helps in solving inverse problems related to field data. In the present paper, we have derived the sensitivity functions for exponentially varying conductivity earth models. The effect of the exponential variation of conductivity has been illustrated graphically on the sensitivity functions. The effect of varying the periods of the electromagnetic waves on the sensitivity functions has also been studied, which gives the characteristic behaviour of the sensitivity functions. This characteristic behaviour provides information about the exponentially decreasing or increasing conductivity earth models. 相似文献
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The conductivity structure of the Earth's mantle was estimated using the induction method down to 2100 km depth for the Europe–Asia region. For this purpose, the responses obtained at seven geomagnetic observatories (IRT, KIV, MOS, NVS, HLP, WIT and NGK) were analysed, together with reliable published results for 11 yr variations. 1-D spherical modelling has shown that, beneath the mid-mantle conductive layer (600–800 km), the conductivity increases slowly from about 1 S m−1 at 1000 km depth to 10 S m−1 at 1900 km, while further down (1900–2100 km) this increase is faster. Published models of the lower mantle conductivity obtained using the secular, 30–60 yr variations were also considered, in order to estimate the conductivity at depths down to the core. The new regional model of the lower mantle conductivity does not contradict most modern geoelectrical sounding results. This model supports the idea that the mantle base, situated below 2100 km depth, has a very high conductivity. 相似文献
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Finite-difference modelling of magnetotelluric fields in two-dimensional anisotropic media 总被引:4,自引:0,他引:4
An algorithm for the numerical modelling of magnetotelluric fields in 2-D generally anisotropic block structures is presented. Electrical properties of the individual homogeneous blocks are described by an arbitrary symmetric and positive-definite conductivity tensor. The problem leads to a coupled system of partial differential equations for the strike-parallel components of the electromagnetic field. E x , and H x These equations are numerically approximated by the finite-difference (FD) method, making use of the integro-interpolation approach. As the magnetic component H x , is constant in the non-conductive air, only equations for the electric mode are approximated within the air layer. The system of linear difference equations, resulting from the FD approximation, can be arranged in such a way that its matrix is symmetric and band-limited, and can be solved, for not too large models, by Gaussian elimination. The algorithm is applied to model situations which demonstrate some non-trivial phenomena caused by electrical anisotropy. In particular, the effect of 2-D anisotropy on the relation between magnetotelluric impedances and induction arrows is studied in detail. 相似文献
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Anisotropic resistivity tomography 总被引:1,自引:0,他引:1
J. V. Herwanger C. C. Pain A. Binley C. R. E. de Oliveira † M. H. Worthington ‡ 《Geophysical Journal International》2004,158(2):409-425