Seismic Instruments最新文献

In order to determine how large urban agglomerations affect the biosphere, the Moscow Geophysical Monitoring Center (part of the Institute of Geosphere Dynamics, Russian Academy of Sciences) has been operating since 2014. The center organizes the continuous instrumental observations of geophysical fields and meteorological parameters in the near-surface atmosphere. The data obtained in the denter allow the specialists to assess the negative effects of the Moscow megalopolis on the environment, in particular, to reveal the sources of artificial disturbances in the geophysical fields. Taking into account that the new problems have emerged and that there is the necessity to expand the technical capabilities of the center, an upgrade was done in 2021–2022: the list of recording instruments was expanded and the observation methods and data analysis were updated.

A description of the software and main services of the digital Internet platform (DP) for complex geophysical monitoring of hazardous geological processes in the Baikal rift system is presented. The DP is a client-server application with a web interface. The practical result of the work is detection of precursors during the preparation of the Kudara earthquake (December 9, 2020). The DP makes it possible to provide information support for geophysical monitoring tasks, performing the complex task of integrating and analyzing data coming from several geophysical sites in the Baikal region in order to assess the state of the geological environment and predict the manifestations of hazardous processes.

The article briefly describes Orenburg oblastal seismic network. It includes the location of seismic stations and technical equipment, etc. The basic characteristics of the network, such as its sensitivity, the completeness of the earthquake catalog, etc., are considered. The location and properties of the main seismic boundaries in the region have been estimated using data from a single broadband station: sediment–basement, the Moho, and mantle transition zone. Records of remote earthquakes and the receiver function method were used to determine the boundaries.

Rates of modern movements are an important factor in the modern geodynamics of the Baikal Rift System. Reflection of strong earthquakes in the experimental values of displacements is discussed, as well as the question of modern vertical movements. According to absolute gravimetry and space geodesy measurements of vertical and horizontal movement rates at the Talaya seismic station (Baikal Rift) for 1992–2022, the displacement rates were determined as 1.7–1.9 mm/year SEE with respect to the point of Irkutsk (Siberian Platform). A set of methods was used to obtain the vertical movement rates for different epochs prior to, during, and after the Kultuk earthquake (2008, M = 6.3, 25 km to epicenter). Subsidence rates vary from 1.1 to 3.3 mm/yr. Possible signs of preparation of Baikal earthquakes have been identified

The article presents experimental results of parallel testing of component magnetic sensors of various types—coil, torque optical-mechanical, and magnetomodulation. Experimental estimations of the level of self-noise of tested sensors are produced and compared with early known data. It has been experimentally determined that the most reliable and stable estimation of self-noise may be obtained in the group of sensors of the same type or by deliberately using a less noisy sensor as a reference. It is shown that experimental estimation of self-noise for coil sensor may significant differently from a theoretical one in the range of low frequencies. It is shown that a coil sensor has the best noise performance, whereas a sensor based on magnetomodulation transducer is the noisiest.

The article begins with a review of publications on low-frequency noise suppression techniques. Denoising seismograms of earthquakes, explosions, and other seismic events is the goal of the study. It demonstrates that a branch in the theory and practice of seismogram processing is currently being actively developed, in which they are analyzed in a two-dimensional time–frequency plane. Additional second- and third-level add-ons appear in addition to the existing methods, which makes it difficult both to understand the essence of the methods and interpret their results. In our article, we attempted to order things in them. As an alternative to numerous add-ons to time–frequency analysis, we proposed our own approach. We believe that it will not only make the analysis clearer, but also increase its accuracy. Our method is based on the application of fingerprint technology to the results of continuous wavelet transform of a seismogram. In difficult cases, we recommend using a more advanced version of it: the redundant fingerprint method. It provides a convenient opportunity to objectively assess the frequency responses of all components of the seismogram. Based on the results of analysis, the automatic information system can select the optimal cutoff frequency for the filter in order to clear the seismogram of low-frequency noise and minimally distort the signal shape. This is especially important if the spectra of both partially overlap and if the noise intensity is high. The method may find itself in demand for automatic classification of seismic events by the nature of their source using machine learning technologies.

The paper is devoted to development of a portable vibrating unit and study of its applicability in generating seismic waves. The solution to developing a portable vibrating unit problem capable of generating a stable seismic signal in the target frequency range is very important. Existing solutions are cumbersome and cannot be widely applied in engineering seismic exploration. The paper describes in detail the design of the vibrator source, the stages of output laptop signals testing, the power amplifier, and haptic transducer control. Signals with different frequency sweeps were used during field acquisition. The recorded data were processed by multichannel analysis of surface waves. As a result of comparing the amplitude spectra and dispersion images of the surface wave, it was found that a hyperbolic (low-dwell) sweep signal generates a surface wave train in the entire frequency range (10–150 Hz), but does not produce high-frequency interference waves in cement concrete pavement as opposed to other sweep signals and sledgehammers. Based on the field data processing results, we reconstructed a one-dimensional shear-wave velocity model for soils and concluded on the success, practicability, and increased (compared to a sledgehammer) efficiency of using the developed vibrator source for acquisition and analysis of surface wave data for engineering seismology problems. The undoubted advantages of using a vibration source are controllability of the frequency content and its repeatability. The use of such vibroseis devices combined with stationary seismic recording systems is a promising direction for solving seismic monitoring problems.

The paper analyzes the results of ground-based and satellite repeat geodetic observations at a gas and oil field. The set of available geological, geophysical, and geodetic data has made it possible to conduct a comparative analysis with theoretical vertical and horizontal displacements at the field. Analytical calculations were done with the deformable reservoir model. The results of the comparative analysis and conclusions indicate both regular correspondence and inconsistent results between theory and observations.

The article presents a preparatory stage for solving the thermoelasticity problem for a halfspace with relief. The effect of the relief on diurnal and season variations of the temperature in the upper layer of the crust induced by temperature variations the in atmosphere is studied. The case of weak two-dimensional relief is discussed. In this paper, we say that relief is weak if: (1) the angle of inclination of a relief element to the horizon is small; (2) the thickness d of the heated layer is small compared to the radius of curvature of the line of the relief. For the diurnal mode, we have d ≈ 15 cm, for the seasonal mode, d ≈ 3 m. The heat equation with a boundary condition of the first kind is considered, and an approximate analytical solution is obtained. The results are compared with the numerical solution, which can be considered. The approximate formula gives a satisfactory result if: (1) the angle of inclination of a relief element to the horizon does not exceed 0.2 rad; (2) the curvature of the line of relief does not exceed 2.4 × 10^–2 m^–1 for the diurnal mode and 1.2 × 10^–3 m^–1 for the seasonal mode. In this case the relative discrepancy between the numerical and approximate analytical solutions is less then 4% if the depth ≤20d. Temperature variations at a depth of 20d are already almost completely absent: the amplitude does not exceed ~10^–9–10^–8°C. Therefore, the underlying layers do not significantly effect on displacements and tilts of relief elements located near the surface.