Estimating the parameters of simple models from two-component on-time airborne electromagnetic data

The horizontal and vertical components of the on-time electromagnetic (EM) response can be used to estimate the parameters of simple models like thin sheets, half-spaces, thin sheets over a lower half-space and a two-layer model. The formulae used in these methods are valid in areas where the on-time response is essentially proportional to the conductivity or conductance, the so called "resistive limit". The half-space and thin-sheet over a lower half-space models can be combined to give an estimate of the conductivity for a lower half-space below a thick sheet that might be reasonable for the whole of the survey area. With this estimation an equation solver can be used to estimate the thickness and conductivity of the overlying thick sheet over the whole survey area. This latter approach seemed most appropriate for the Russell South area in the Athabasca Basin, Canada, where GEOTEM data has been collected. The output of the algorithm was generally stable. Although it did not always reliably reproduce the overburden thicknesses as measured in a set of reference drill holes, it did give an estimate that was reasonable in the relatively conductive areas.

The Effect of Viscosity and Heterogeneity on Propagation of G–Type Waves

Earthquakes yield motions of massive rock layers accompanied by vibrations which travel in waves. This paper analyses the possibility of G-type wave propagation along the plane surface at the interface of two different media which is assumed to be heterogeneous and viscoelastic. The upper layer is considered to be viscoelastic and the lower half space is considered to be an initially stressed heterogeneous half space. The dispersion equation, as well as the phase and group velocities, is obtained in closed form. The dispersion equation agrees with the classical Love type wave. The effects of the nonhomogeneity of the parameters and the initial stress on the phase and group velocities are expressed by means of a graph.

ANALYTICAL CONTINUATION OF POTENTIAL FIELDS ON THE BASIS OF F-APPROXIMATIONS

В статье рассмотрен метод аналитического продолжения потенциальных полей на основе F-аппроксимации. Разработанный автором метод позволяет выполнять аналитическое продолжение поля в верхнее и нижнее полупространство. Компьютерные технологии позволяют выполнять трансформации для данных заданных как для регулярной, так и для нерегулярной сети. Метод апробирован на модельных и фактических гравиметрических данных The method of analytical continuation of potential fields on the basis of F-approximation is considered in the article. The method developed by the author allows carrying out analytical continuation of field to the upper and the lower half-space. Computer technologies allow making transformations for data prescribed both for regular and for irregular network. The method is tested on model and actual gravimetric dat

Reply by the author to W. K. McClary

We are pleased to see Mr. McClary shed more light on the concept of a generalized primary. To construct the generalized primary of the nth interface as a transmitted output signal in the upper half‐space for the input wavelet −X in the lower half‐space not only indicates that this can be done, but that the construction is appealing and that it clarifies the entire concept.

FIELD OF A LINE SOURCE SITUATED PARALLEL TO A SURFACE-WAVE STRUCTURE COMPRISING A PAIR OF UNIDIRECTIONALLY CONDUCTING SCREENS

The problem of radiation from an electric line source situated parallel to a surface-wave structure composed of a pair of parallel unidirectionally conducting screens is considered. The screens are conducting in directions making angles α and — α, respectively, with the x axis, while the line source is directed parallel to the γ axis and is located either above or between the two screens. The problem is resolved as the superposition of symmetrical and antisymmetrical sources, since either of the two surface-wave modes that can be supported on the structure is associated with an appropriate type of excitation. Both surface-wave modes are excited in the superposed case of a line source.The radiation field is evaluated and, under suitable conditions, is seen to exhibit sharp peaks. The correspondence of these peaks with complex poles in the integral representation of the field is demonstrated. It is further observed that, when the line source is situated above the structure, the amplitude of the field components in the lower half-space is independent of the location of the source, although the phase is affected. The surface-wave power is determined and it is shown that high values of launching efficiency are readily attainable.