Seismic Instruments最新文献

Prediction of the quantitative parameters of seismic ground motion, based on studies of strong ground records, is the final part of a set of works on assessing the seismic hazard of any territory. At the same time, the results of studying the processes of seismic wave generation and propagation in the near fields of earthquakes are of great importance for the physics of the earthquake source, being the basis for constructing an adequate model of the source and the processes occurring in it. The regularities of propagation of a seismic wave field are expressed in the equations of the relationship between the parameters of seismic vibrations and characteristics of the source and the medium. These equations can be obtained both from the theoretical positions available in today’s seismological science and from analysis of accumulated data of strong ground records. It does not require proof that the interpenetration of these two methods is the most useful for scientific progress. The trend of recent decades in the development of equations for predicting the parameters of strong ground motions is identification of several zones in the wave field with different dependences on the parameters of the medium and source. The predictive ratios obtained using this method is distinguished by a decrease in the scatter of estimates of the fluctuation parameters and compliance with empirical data. When processing statistical data using dimension and similarity theory, it was found that in the field of seismic waves, there are similar distances at which the values of the oscillation parameters are similar. In other words, there are laws for scaling the seismic ground motion parameters. A similar statement can be found in theoretical studies on generation of seismic waves by an earthquake source. The aim of the study is, using theoretical provisions on processes in the source area, to establish the laws of generation and propagation of the parameters of strong ground movements, taking into account empirical data; to develop a model of the source zone that does not contradict empirical data; and to determine the size of the earthquake source zone. The research methodology involves statistical analysis of empirical data on strong ground motion. The results yielded are attenuation equations for the amplitudes of peak ground accelerations in the fault, near-, and far-field zones; predictive equations for the prevailing periods and duration of fluctuations of strong ground motion; and estimates of the sizes of the earthquake source zone.

An automated algorithm for monitoring the areas of refraction event tracing along the profile based on the dynamic conversion was developed. Time sections of compressional- and shear-wave refractions recorded by the CDP shooting geometry in the Northeastern segment of the 3-DV survey base line were constructed. A high-velocity model of the upper part of the Earth’s crust was constructed to a depth of 2 km in the Sea of Okhotsk–Eurasian plate conjunction zone. Based on the increased velocity ratio of P- and S-waves, the refracting boundaries in the Ayan–Yuryakh block were rock sections with various lithological compositions in the sedimentary cover. The zone of reduced P-wave velocity and V_p/V_s ratio related to high rock fragmentation was identified in the high-velocity profile of the Chai–Yurya Fault zone, both above and below the refracting boundary. The velocity values of P- and S-waves (6.0–6.1 and 3.6–3.7 km/s, respectively,) and reduced V_p/V_s ratio (~1.65) due to felsic rock intrusions were recorded in the southern part of the Inyali–Debin block within the depth range of 1–1.5 km.

The results of interpreting radon-220 (thoron) and radon-222 monitoring observations, carried out in 2002–2004 in the Northern Tien Shan are presented. The prognostic capabilities of thoron as a short-term earthquakes precursor are shown. It is noted that thoron anomalies are more contrasting compared to radon-222 anomalies. Insufficient contrast of radon-222 anomalies is explained by methodological errors during observations by seismic radon stations. Thoron behavior during the earthquake preparation process is consistent with the previously established spatiotemporal patterns for radon-222 (Kozlova et al., 2021). When using gases that are part of the subsurface atmosphere, radon isotopes are the most suitable for earthquake preparation process monitoring observations. The prospect of using other gases is limited by the absence of sources of their constant generation, the presence of a cumulative effect, and the complexity in detecting them. The above also applies to using variations in the contents of chemical compounds dissolved in groundwater for prognostic purposes.

The article considers controlling vibratory motion dynamics using active dampers, making it possible to significantly reduce the level of mechanical vibrations of buildings and structures. A controlled reactive damper can be considered a highly efficient method of damping structural vibrations of structures under nonstationary (seismic) impacts. The reactive damper activation process is controlled by the “coordinate – damper electric drive” pair. Motion tracking is done via special sensors for determining linear and angular displacements. The operation principle of a reactive damper involves creating an alternating reactive force to prevent relative (bending) displacements (vibratory displacements) of a structure at target time instants. Several ways of creating a reactive jet (reactive forced action on a mechanical system) are shown: a reactive fluid jet ejected under high pressure; a reactive gas jet flowing under high pressure; a reactive jet from a burning fuel. The relations for calculating their influence are presented. The finite element method (FEM) motion equations for a construction node with an attached reactive damper are given for the central difference approximation of derivatives and using the Newmark method.

This paper discusses two methods for studying the monostatic scattering diagrams of fifth-generation aircraft: the Lockheed Martin F-22A Raptor and Sukhoi Su-57. The monostatic scattering characteristics are determined through the asymptotic modeling of the object to obtain a complete pattern of effective scattering area, hotspots, and reflected wave propagation direction and also through the experimental study using an ultrasonic radar. Based on the study results, the use of modern aircraft development methods can reduce the radar cross section of an object. This fact is confirmed by both full-scale models in modeling and experimental studies of scale models. Since an ultrasonic radar was used in the experimental study, in accordance with the electrodynamic similarity rule, the chosen frequencies corresponded to waves which would irradiate the full-scale model. The study results are presented in the form of monostatic scattering diagrams with a step of 1° for the modeling and 10° for the experimental study. The monostatic scattering diagrams are mostly similar in shape, and some differences are caused by a lower measurement step in the experiment. The experimental data are presented in the form of dBmV instead of square meters, since no conversion was made to the radar cross section values.

The mechanical concept of assessing the regional seismicity involves determining stress concentration zones in lithospheric structures considered as indicative of areas with possible seismic events. This study is aimed at developing mechanical and mathematical models and methods to study the stress–strain state of geophysical structures subjected to static loads, as well as low-frequency harmonic loads. The article presents a method to solve problems related to static interaction of a system of coating plates and an elastic substrate. In this model, the equations for displacements of the front surface and contact stresses are based on the solutions to the matrix-function Wiener–Hopf equations to which the initial problem is reduced. A specific feature of the equations is unknown functionals of the solution and its derivative on their right-hand sides, which are determined from a system of linear algebraic equations. This approach makes it possible to determine all basic characteristics of the stress–strain state of a block structure formed by two contacting plates on a deformable base. In addition to the static problem arising in the study of factors affecting stress–strain properties of the geological structures, the article also considers the problem of long-period steady-state oscillations of the coating–substrate system. In relation to low frequencies, we propose to proceed to sequential solution of several static problems.

The propagation and recording principles of seismic acoustic signals in the 3D space are considered with the case of cross-hole imaging near the boundary with abrupt changes in the elastic wave velocity. The 2D and 3D modeling of constructive interference has been carried out during a seismic survey to estimate the first Fresnel zone volume and the resolution of refracted and reflected waves in boreholes. The Fresnel volume of head waves is compressed along the boundary plane the greater, the further the oscillation source and receiver are from this boundary. The calculated Fresnel volume is given for various relative positions of sources and receivers. It is concluded that the projection of the Fresnel volume of head waves onto the plane of the high-velocity refractive layer can be obtained by drifting the source and receiver points along the normal to this layer. As a consequence, the boreholes are perpendicular to the refractive layer during cross-hole imaging, whereas the projection of the Fresnel volume of head waves onto this layer is almost independent of the source and receiver positions in the borehole. Quantitative estimates of the seismic resolution of the borehole seismoacoustic methods for studying the rock massif have been obtained.

The article presents a methodology for analyzing the reliability of geophysical methods that use portable instruments for forecasting dynamic phenomena. The need for developing this methodology is explained by the lack of recommendations in regulatory documents regarding the selection of the most appropriate method to forecast dynamic phenomena for specific conditions. This selection should be carried out by the relevant departments of coal-mining companies independently or with the help of scientific teams. Two portable devices for local prediction of rock bumps were chosen for the research: the Angel-M and Ripas devices, which implement the electromagnetic pulse method and a specific modification of the method based on parameters of artificial acoustic signals, respectively. The more reliable instrumental method based on the drilling fines yield was used as the reference one. It was assumed that the hazard level of the rock mass is the same when making predictions using the geophysical and instrumental methods. It can be quantitatively estimated as a ratio of the current value of the measured parameter to its threshold value. The reliability of the predictions made with portable devices was assessed by the correspondence of this ratio to the similar one calculated for the instrumental method. Testing of the proposed methodology at one of the Kuzbass coal mines showed insufficient reliability of predictions made using portable geophysical devices. This is probably explained by the following reasons: each of the devices does not control all of the key hazard factors of dynamic phenomena; there is no justification of the relationship between the hazard of the dynamic phenomena and the parameters controlled by the devices; when using the Ripas device, the geophone is pressed against the wall of the mine workings, so the fracturing within the near-wall rock mass significantly distorts the spectrum of the sounding acoustic signal.

The relevance of this study is to analyze a potential mechanism for the amplification and generation of electromagnetic radiation during the preparation, manifestation, and subsequent attenuation (aftershocks) of seismic events. Previous studies have shown that the impact of high-intensity ultrasound on ion-crystalline dielectrics can induce the generation of electromagnetic radiation at the ultrasound frequency and its first subharmonics. We studied samples of igneous rocks such as basalts, gabbro, and granites during our experiments. The purpose of the study was to study and subsequently analyze the physical mechanism responsible for the amplification and generation of electromagnetic radiation during the propagation of acoustic waves through igneous rock masses. Research methodology. During the research, a comprehensive approach, including methods of geophysics and engineering geology, mathematical modeling, string theory, and crystallography and mineralogy was applied. Research results. The conducted research has shown that the amplitude characteristics of the electromagnetic response to pulsed acoustic impact depend significantly on the electrical conductivity of the rock. Conclusions. The results we obtained allow us to draw the following conclusions. First, the stochastic combination of capacitive elements (“capacitors”), taking their oscillations in the seismic wave field into account, can lead to an increase in the overall potential (the effect of averaging the potential multiplier). Second, under shock wave impact, it is necessary to replace the temperature (T) in the models with the effective temperature. This substitution can increase the calculated values of the effective charge by several orders of magnitude and consequently, the intensity of electromagnetic radiation (EMR). Thus, processes such as crack formation and the propagation of powerful acoustic waves in rocks activate the contribution of practically all mineral components of these rocks to the generation of EMR.