Seismic Instruments最新文献

The results of an experimental study of seismic vibrations at the site for the construction of the Siberian Ring Photon Source (SKIF), which is a synchrotron radiation source of the fourth plus generation at 3 GeV and a perimeter of 480 m, have been considered. Seismic vibrations are a hindrance that reduces the accuracy of the experimental setup when studying materials with precision accuracy and resolution. The experiment was performed with broadband seismological equipment used at seismological stations. Seismic vibrations from different types of sources have been investigated: natural and man-made earthquakes, industrial explosions, noises of automobile and railway transport, vibrations from industrial equipment at enterprises located away from the facility under construction. Natural earthquakes create the strongest broadband impact on the site. Man-made earthquakes in the area of the Gorlovka coal basin can create short-term strong seismic impacts. Industrial explosions in terms of the seismic impact on the site are significantly inferior to the effects of earthquakes and are characterized by a more limited spectral composition of vibrations. The noises of motor transport cover frequencies from 4 to 30 Hz and quickly fade away along the site with distance from the road. Railway noises have the characteristic appearance of a set of multiple harmonics covering a wide frequency range with a duration of up to 10 min. Monochromatic signals from the operation of industrial equipment on and off the site are recorded at the site. At the same time, both continuous signals and those that occur episodically are recorded. A special class consists of monochromatic oscillations with a slowly varying frequency. The information on the level, spectrum, and duration of seismic vibrations necessary for calculating the seismic protection of the SKIF Central Research Center during its creation and development of a seismological monitoring system that compensates for the seismic effect on the accuracy of experiments was obtained.

Transient processes in gravimetric data spanning more than 12 years are considered. During this time, more than 15 trips were made from the fundamental gravimetric point Ledovo to the first class point Zapolskoe and back using two CG 5 Autograv automated relative gravimeters. The most significant parameters that affect the readings of the instruments were identified: ambient temperature, the values of the zero drift of the sensing element of the gravimeter, and the direct increment of gravity. The zero drift was taken into account using a second-order polynomial prediction, and the remaining two parameters were described by a logarithmic dependence. The natural logarithm equation allows describing the functions by measuring the coefficient before the logarithm (logarithmic) and additional (linear). The value of the logarithmic coefficients characterizing the duration of transient processes has a linear dependence on temperature, which means that it can characterize the measurement time at the point in the case of a significant temperature change. The magnitude of the linear coefficients characterizing the increase in gravity depends linearly on temperature when the instruments are moved to a colder environment. When the instruments are moved to a warmer environment (10°), the dependence becomes more complex, possibly random, which also requires an increase in the measurement time at the point. The usual duration of measurements at gravimetric stations is 10 min. The relevance of taking temperature into account at measurement points depends on the required accuracy, for example, for a temperature difference of 10°C, the RMS of gravimetric measurements was ±0.025 mGal.

Recognition of a seismic event by the type of its phenomenon (earthquake or explosion, and if an explosion, then a subsurface or open pit explosion) at a regional scale on its seismogram is a problem that many researchers worldwide attempt to solve. A detailed review of Russian and global publications on this topic has been produced. This review made it possible to formulate the most promising directions on which research is underway. Thus, this study, which offers another approach to creating a discriminatory feature, may be useful for improving the results of recognition of a seismic event. The proposed method is based on continuous wavelet analysis of the seismogram from a single receiver. Two additional transformations (constructing the frequency envelopes to waveletogram and their cross-correlation at a given time) sequentially translate this result into a compact frequency-time portrait of the event. This technique was tested on seismograms of several events, the nature of which is a priori known. Recognition is possible both visually (including machine vision methods) and automatically. For the first option, the key features of frequency-time portraits of events to which attention should be paid are formulated. For the second case, a method for determining the numerical characteristics measured by the obtained images is defined. It is shown that these characteristics are naturally divided into clusters that correspond to the nature of the events.

Distributed acoustic sensing (DAS) is a technology that uses a fiber optic cable as a linear array of virtual seismic sensors. The article allows the reader to learn a little more about DAS data, mainly from the theoretical viewpoint, and correct some existing misconceptions; it gives an overview of the development of DAS and its modifications. The objective of this work is to discuss the advantages and prospects of distributed fiber optic sensors and the possibilities of expanding the boundaries of their practical applications and to clarify the problems and limitations faced by seismologists using DAS. Ways of overcoming the existing limitations are also described. The article identifies areas which need to be developed for wider dissemination of distributed measurements; it lists some commercialized applications and applications in which experiments will soon turn into routine geophysical measurements.

A new short-period borehole seismometer TBSC6 designed and produced at the Dukhov All-Russian Scientific Research Institute on Automatics provides proportional transformation of vertical seismic velocity oscillation to electrical signal. The seismometer has been designed for installation in boreholes with an inner diamter of 145–220 mm and inclination up to 3.5°. In its technical features (frequency range 0.5–100 Hz, linearity less than 0.006%, noise level less then –10 dB of the low seismic noise model, dynamic range greater than 145 dB, temperature range –25 to 50°C), the seismometer corresponds with the best short-period borehole seismometers in the world. The features achieved make it possible to use the short-period borehole seismometer for seismological observations of both far and local seismic sources and also for seismic situation monitoring in the vicinity of hydrotechnical structures, nuclear power plants, etc.. Auxiliary equipment (locking device, installation complex set with the borehole ahead) provides seismometer installation in boreholes with an inner diameter 145–220 mm at depth down to 100 m. Borehole ahead saves borehole tube with an outer diameter of 150–250 mm.

An approach to recognizing the types of seismic event sources is proposed, based on the combination of several heterogeneous parameters of event records and information about the territory where the seismic event occurred. The following recording parameters are used: the ratio of the amplitudes of body waves, the ratio of parts of the spectra at high and low frequencies, the magnitude, and the spectral constancy parameter. Territorial information includes data on the presence of waterbodies, glaciers, mines, and simplified information on natural seismic activity. Their joint use is done with a special type of Bayesian belief network. The decisions made by the network are probabilistic in nature; the probability is understood in the Bayesian sense, i.e., as the degree of confidence in the truth of the judgment, which consists in attributing an event to one of the types (mine explosion, other explosion on land, underwater explosion, earthquake, icequake). The approach is implemented as a software system, which is included in the program for the interactive analysis of seismic event records LOS.

Aftershocks following a large earthquake are an inevitable part of the preparation and occurrence of large earthquakes. Depending on the location of the epicenter, tectonic–structural conditions of the epicentral zone, and earthquake intensity on the Earth’s surface, an aftershock cluster can cover different surface areas. Establishing the quantitative relationships between the aftershock zone and the main parameters of the earthquake (magnitude, rupture length, and slip value) can contribute to improving the model of an earthquake as a natural physical phenomenon. The extents of aftershock and deformation zones, as well as macroseismic changes on the Earth’s surface, indirectly indicate the intensity of the mainshock and the presence of portions with different degrees of weakening of rocks in the epicentral zone. This paper proposes a method to determine the area of such an aftershock zone using a deformational model of earthquake preparation and nucleation proposed earlier by the author. A new expression is obtained for determining the area of an aftershock zone depending on (i) the length of the rupture formed during the earthquake and (ii) the average slip along the rupture; expressions for the logarithmic and linear dependences of this area on the earthquake magnitude are also obtained. It is shown that the areas of the aftershock and deformation zones around an earthquake source are identical.

Earlier, it was shown that conventional algorithms for solving the inverse VES problem cannot achieve the accuracy required for precision monitoring of a geoelectric section, and regularized algorithms were proposed to improve the accuracy and stability of solving the inverse VES problem. In this paper, we test the resistivity contrast stabilization algorithm on synthetic data. For modeling, a geoelectric section is used, similar to the section of the Garm test site both in the set of layers and their resistivities, and in the characteristics of seasonal variations, as well as noise. It is shown that regularization of the inverse problem greatly reduces errors. The most significant effect is achieved by suppressing the buildup of resistivity. Estimates are obtained for the accuracy in solving the inverse problem, which can be achieved when working with experimental data.

The article presents the results of analyzing aftershock sequences initiated by underground nuclear tests conducted in North Korea in 2016 and 2017. Waveform cross-correlation and a multimaster method applied to phase association allowed us to find and analyze 91 aftershocks and group them into clusters associated with the underground explosions on September 9, 2016 (DPRK-5) and September 3, 2017 (DPRK-6). The duration, intensity, and sporadic nature of these two sequences indicate specific mechanisms of seismic energy release, which are probably related to the interaction of the destruction zones of DPRK-5 and DPRK-6 explosions and the collapse of their cavities with the gradual advance of the collapse columns to the free surface. The aftershock activity in 2021 suggested that the collapse process was not yet completed and predicted the occurrence of new aftershocks in the near future, which could end in the collapse column reaching the free surface. These assumptions were confirmed; during the preparation of this work, a strong aftershock with a magnitude of 3.85 was recorded on February 11, 2022, which, according to preliminary estimates, indicates the beginning of the final stage of the advance of the collapse column to the surface, the probability of which is discussed in this study.

The paper presents the results of the analytical and hardware development of a bipolar sensor for the concentration of small atmospheric ions, designed for long-term geophysical field observations. Theoretical estimates of the response function of the sensor are obtained. The dependence of the concentration of small atmospheric ions on the magnitude of the measured current of the aspiration capacitor and ion mobility spectrum is given. Numerical computations of the trajectories of small ions in an aspiration condenser of specified dimensions and geometry are performed. The probability of recording ions depending on their mobility is found. The circuit solutions and algorithms for the functioning of the hardware of the devices are described. Based on the development materials, prototypes of sensors are made. The technical characteristics and recommendations for the use of devices are given. Unlike analogues, the device is resistant to environmental influences. The sensors are tested in laboratory conditions and during the field observations of the electricity of the atmospheric boundary layer. In addition to being used as a part of a ground-based complex for geophysical observations, the developed sensor was used in an instrumental platform for balloon observations aloft. As a result of testing the devices, it was found that the functioning of the sensors is stable and the data are representative.