Technique for the imaging crystalline basement according to the DSS data

The method of deep seismic sounding (DSS), the observation systems in which are characterized by an irregular arrangement of both sources and receivers along the profile, a significant step between receivers, as well as maximum source-receiver distances exceeding several hundred kilometers, makes it possible to obtain an image of the crystalline basement using seismic migration fields of reflected/refracted waves. The main part of the existing migration methods, the use of which makes it possible to form an image of the deep structure of the study area in the dynamic characteristics of the recorded wave field, is focused on processing seismic data obtained by the method of reflected waves with multiple overlap observation systems (MOV—CDP). And, as a rule, these migration methods are designed for a smooth change in speed with depth. At the same time, at the boundary of the crystalline basement, the speed changes very sharply, which must be taken into account when processing data using migration. The proposed method for constructing an image of the crystalline basement is based on the use of finite-difference migration of the field of reflected/refracted waves, which was developed at the Institute of Geophysics named after S. I. Subbotin National Academy of Sciences of Ukraine. This migration method is designed to isolate supercritically reflected and refracted waves recorded from the basement in the far zone of the source and takes into account the full trajectory of waves passing through a two-layer medium, at the boundary of which there is a significant jump in velocity. Thus, the migration of the field of reflected/refracted waves makes it possible to obtain a correct image of the structure of the refractive layer of the crystalline basement. The article describes in detail the algorithm of the technique for constructing an image of the crystalline basement using finite-difference migration of the field of reflected/refracted waves and its difference from similar methods of migration. The advantages and disadvantages of the proposed method are shown when solving problems of regional seismic research. Explained and illustrated the features of constructing the image of violations on the border of the foundation. The effectiveness of the technique is demonstrated on a model example and real seismic data observed by the DSS method on the territory of Ukraine.

Radiophysical methods for modelling frozen soils dielectric permittivity in the southern Vitim plateau (Eastern Siberia, Russia)

The article presents the results of applying the radiophysical method for modelling the dielectric permittivity on the example of Haplic Chernozem Molliglossic soils in the south of the Vitim plateau, depending on VHF and UHF wavelengths, temperature, and soil moisture. Depending on the heterogeneity of moisture reserves and heat content, the soil is considered as a three-layer medium with different soil characteristics. A difference in the frequency dispersion of the complex dielectric permittivity over the entire soil profile in the VHF and UHF ranges has been established.

Evaluation of Electrophysical Properties of Soils in the Slope Zones of the Foundation During GPR Survey

The article describes a new method for conducting a ground penetrating radar survey of slope zones of soil objects of transport infrastructure. In the lithological section of these objects, there are sub-horizontal and inclined soil boundaries, as well as slope zones. Traditional survey methods (drilling, pitting), as well as the standard GPR method, make it possible to reliably survey at these objects, as a rule, only the zones under the horizontal main ground of the subgrade and sub-horizontal sections of the ground outside its boundaries. Survey under inclined surfaces is often difficult or technically impossible; geophysical methods, just like traditional ones, provide initial information that is exceedingly difficult for further decoding. The sections are filled with re-reflections and noises, and the process of decoding them is associated with great methodological problems.This paper presents a new method for determining speed of propagation of radio waves in the slope zones of the foundation. The initial information is the data obtained during the survey using the common depth point (CDP) method, using a well-known survey technique and a standard set of hardware. The novelty of the article results is determined by the algorithm for processing the measurement results developed by the authors. The software implementation made on its basis makes it possible to obtain the hodograph equation considering the slope of the layers. Defining geometric characteristics of embankments associated with the presence of slopes of variable steepness have been considered. A technique for calculating propagation speed of radio waves for a two-layer medium with a boundary inclined to the scanning surface has been proposed. The validity of the developed method was verified using finite-difference time-domain modelling.The article provides examples of practical application of the developed method in the GPR survey of real track foundation objects (transport infrastructure objects). The method proposed in the article makes it possible to increase the informative area of the surveyed diameters. At the same time, the accuracy of the GPR method is preserved, the area of its application for obtaining reliable information is increased to 60 % of the cross-sectional area of the foundation.

Magnetic Holography and Its Application to Data Storage

The principle of magnetic holograms and its application to holographic memory are reviewed. A magnetic hologram was recorded through a thermomagnetic recording as a difference in magnetization direction and reconstructed with the magneto-optical effect. To achieve a bright reconstruction image, it is important to record deep magnetic fringes on the materials with large Faraday rotation coefficients. This technique was applied to the holographic memory using transparent magnetic garnets as a recording material. The first reconstruction image was dark and noisy, but improvements in the recording conditions resulted in error-free recording and reconstruction of the magnetic hologram. To form deep magnetic fringes, insertion of heat dissipation (HD) layers into recording layer was proposed. It was found that this HD multilayer medium showed diffraction efficiency higher than that of a single layer medium, and error-free recording and reconstruction were also achieved, using magnetic assisted recording. These results suggest that HD multilayer media have potential applications in recording media of magnetic holographic data storage. In future, a high recording density technique, such as multiple recording, should be developed.

Absolute Measurement of Material Nonlinear Parameters Using Noncontact Air-Coupled Reception

Nonlinear ultrasound is often employed to assess microdamage or nonlinear elastic properties of a material, and the nonlinear parameter is commonly used to quantify damage sate and material properties. Among the various factors that influence the measurement of nonlinear parameters, maintaining a constant contact pressure between the receiver and specimen is important for repeatability of the measurement. The use of an air-coupled transducer may be considered to replace the contact receiver. In this paper, a method of measuring the relative and absolute nonlinear parameters of materials is described using an air-coupled transducer as a receiver. The diffraction and attenuation corrections are newly derived from an acoustic model for a two-layer medium and the nonlinear parameter formula with all corrections is defined. Then, we show that the ratio of the relative nonlinear parameter of the target sample to the reference sample is equal to that of the absolute nonlinear parameter, and this equivalence is confirmed by measurements on three systems of aluminum samples. The proposed method allows the absolute measurement of the nonlinear parameter ratio or the nonlinear parameter without calibration of the air-coupled receiver and removes restrictions on the selection of reference samples.

Calculation scheme of ground freezing depth in Terskol

During the construction of avalanche-retaining geotechnical structures in mountainous areas comes up the problem of fixing and stability of these structures in conditions of seasonal and/or long-term freezing of the ground. This paper evaluates the influence of snow cover and air temperature on the depth of freezing and soil stability based on the developed calculation scheme for the winter seasons 2015/16-2019/20 in the Elbrus region. The calculation scheme was based on the problem of thermal conductivity of a three-layer medium (snow, frozen, and thawed soil) with a phase transition at the boundary. The heat balance equation included the energy of the phase transition, the inflow of heat from the thawed ground and the outflow to the frozen ground, and, in the presence of snow cover, through it to the atmosphere.