Seismic Instruments最新文献

This study considers the hardware and methodological possibilities for increasing the information content of seismological observations in the epicentral zone of a platform earthquake without obvious surface manifestations. It is shown that the microseismic background analysis conducted during the installation of several seismic stations is efficient for both identifying the source location and refining the geodynamic features of the environment in the epicentral zone. The results of the coherent-time analysis of recordings at the three-component registration made to identify endogenous microcracks hidden by microseismic noise are presented. Their power, number, and azimuths are calculated. The possibility of using an autostructural function for the time series of a stream of micropulses at long-term recording of microseisms is shown to identify the self-organization of crustal blocks by similarities in their geodynamics. The requirements for the seismic equipment necessary for the observations are discussed.

The data on seismic activations (SAs) in Italy, Greece, and Turkey for the 17th–19th centuries are analyzed to clarify the common patterns of SA occurrence in the different seismically active regions associated with similar geodynamic conditions. The time clustering of strong earthquakes (М ≥ 5.6, I ≥ IX) in Italy, Greece, and Turkey in the 17th–19th centuries has made it possible to identify a number of SAs of various durations both in each country and in the whole region. However, the revealed recurrences are extremely uneven in the time range, the number of earthquakes, and the intervals between the individual SAs. Italy is recorded to have had 12 SAs; the 17th and 18th centuries are characterized by the maximum seismic activity, declining gradually by the 19th century. Nine and eight SAs were detected in Greece and Turkey, respectively, with seismic activity increasing strongly in these countries in the 19th century. The periods of common seismic activation for the entire region are also defined: 1658–1680, 1694–1743, 1766–1791, and 1846–1867.

We present the results of very high-resolution seismic profiling (VHR) and underwater electrical resistivity tomography (ERT) measurements in the Petrozavodsk Bay of Lake Onega, which were carried out to research the structure of Quaternary sediments. According to the VHR, five seismic sequences were identified during the seismic stratigraphy analysis, and a three-layer geoelectric section was obtained using ERT. The next step was an accomplishment of 2D ERT inversion based on reflectors from the VHR data. The joint interpretation of geophysical data was completed on the basis of comparative and cluster analyses with reference to the well and known geological data. During the research new information was obtained about the physical properties of the bottom sediments. The results indicate the need to apply such an approach to the interpretation of geophysical data and the prospects for the joint application of VHR and ERT acquisitions.

A method is proposed for calculating scalar products of pairs of seismic events that are closest in time to isolate sequences of epicenters of crustal earthquakes (chains) connected in space and time. To verify the developed methodology, the model and real catalogs of earthquakes of the Garm region in Tajikistan are compared. The efficiency of the proposed algorithm is shown. Based on the totality of the results of the allocation of chains, the issues that complicate the detection of the mentioned structures in the general case are considered. In the process of applying the created program to the real catalog of earthquakes of the Garm region, the existence of four pairwise orthogonal prevailing directions in their orientation was established. There were also some changes in the time of the predominant role of the selected strike of chains of earthquake epicenters. It is possible that these changes may reflect some elements of the dynamics of the seismic process in the Garm region.

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.