Comparative analysis of hypotheses of the geoelectric structure of the Transcaucasian region from magnetotelluric data

Various hypotheses of the geoelectric structure of the Transcaucasian region reflecting a priori geological and geophysical information and data from profile magnetotelluric (MT) soundings are analyzed. These hypotheses are used to construct simplified 3-D models of electrical conductivity differing in the patterns of the shallow and deep structure of the region. Numerical modeling of MT fields is performed. Comparative analysis of its results indicates that the most probable conductivity model consistent with the available data is a model involving a high-conductivity channel connecting the Black and Caspian seas.     

Neural network estimate of seismic velocities and resistivity of rocks from electromagnetic and seismic sounding data

The neural network estimates of seismic P- and S-wave velocities from electrical resistivity of the rocks and, vice versa, resistivity estimates from seismic velocities are presented. It is shown that, depending on the ratio between the volumes of the known data and the data to be reconstructed, the accuracy of the estimates of the P- and S-wave velocities ranges within 1–4 and 4–6%, respectively. The logarithmic resistivity is estimated from seismic P- and S-velocities as accurately as up to 15–17%. In all cases, the biggest errors are obtained when the estimates are based on correlated data.     

The construction of effective methods for electromagnetic modelling

Summary. This paper deals with the further development of finite-difference methods for electromagnetic field modelling in two-and three-dimensional cases. The main feature of the approach suggested here is the application of generalized asymptotic boundary conditions valid with the accuracy (1/ρ^N), where ρ is the distance from the heterogeneities. The finite-difference approximation of problems under solution is made using the balance method, which results in 5-point difference schemes in the 2-D case and 7-point difference schemes in the 3-D case. To solve the linear system of difference equations the successive over-relaxation (SOR) method is used, the relaxation factor being chosen during the iteration procedure. In view of the vectorial character of the problem for the 3-D case, a successive blocked over-relaxation method (SBOR) is applied.
The model's validity is based on the comparison of the fields accounted at the ground surface with those computed by the integral transformation of excessive currents, determined in the heterogeneity region using the finite-difference scheme.