Seismic Instruments最新文献

As part of studies on the search for earthquake precursors, the authors have conducted an experiment on long-term precision monitoring of variations in the resistivity of the Earth’s crust in a highly seismic region of Tajikistan. The primary data of this experiment can be considered a special type of VES profile, in which, instead of a linear coordinate, the sounding date changes from picket to picket. When processing precision monitoring data, it is necessary to solve the inverse VES problem with the highest possible accuracy. VES curve inversion programs commonly used in electric exploration do not allow this. The authors have previously developed a special method for regularizing the residual functional, which suppresses the effect of resistivity buildup, due to which the error in reconstructing the resistivity of rocks for profiles with a strong seasonal variation in resistivity is reduced by an order of magnitude. However, in some cases, the regularized algorithm strongly biases estimation of the amplitude of the seasonal resistivity variation in the lower layers of the section. In this paper, the operation of the proposed algorithm is tested in detail for nine model profiles simulating a real geoelectric section. The considered profiles differed in the characteristics of the seasonal variability of resistivity in the lower layers of the section (the phase and amplitude of seasonal effects varied). It is shown that resistivity buildup is effectively suppressed in all cases. For each model profile, the error in solving the inverse problem is estimated. The effect of a biased estimate of the amplitude of seasonal variation is studied. It is shown that in most cases, analysis of the solution makes it possible to reveal the presence of such distortions and qualitatively assess their character. It is also shown that for profile options supposedly closest to the experimental profile, the estimates have minimal bias. For all profiles, the ratio of the average and maximum errors in calculating the resistivity in different layers to the residual in the solution to the inverse problem was evaluated. This makes it possible to evaluate the actual error of the reconstructed resistivity values knowing only the fitting residual. The paper also studied the possible effect of increasing the accuracy in solving the inverse problem in the case of preliminary decomposition of the apparent resistivity curves into seasonal and flicker noise components. It is shown that for small fitting residuals, the results change insignificantly. According to the results obtained, the error in reconstructing the aperiodic (flicker noise) component of resistivity variations in the lower layers of the considered section can be decreased to 0.4%. The accuracy in reconstructing the seasonal component of resistivity variations depends on the amplitude and phase of seasonal effects in the model profile. For the considered profiles, the error varies from 1 to 2%.

A set of tectonophysical methods has been applied to reconstruct the neotectonic stresses of the southeastern Altai Mountains within the Chuya–Kurai depression and its framing structures. It is suggested that at the neotectonic stage, the tectonic structures of the Altai Mountains underwent a transformation of geodynamic conditions—a situation of sublatitudinal horizontal compression with predominant reverse-fault and transpressional movements along faults that existed up to the Neogene was replaced by horizontal shear conditions with a NNE and NE subhorizontal compression axis and WNW and NW extension axis. With such a stress field, the dominant NW-trending faults in this territory are mainly characterized by dextral strike-slip displacements, and NE-trending faults, by sinistral. Submeridionally trending faults that formed at the neotectonic stage show clear signs of extensional structures. A feature of the faults of the Chuya–Kurai depression according to these studies is a fairly small number of megafractures (indicators of shear displacements) in shear zones. This indicates dominant reverse-fault and transpressional movements over large disjunctive structures in the region in the Paleozoic and Mesozoic versus neotectonic shear movements. The results of the research are of practical importance in studying the regional seismicity.

The article presents a new method of classifying acoustic and microseismic emission (KLASI-k), which analyzes waveform parameters (the rise time amplitude RA, average frequency AF, and the waveform index WI). The method is based on k-means clustering, which makes it possible to separate subsets of events differing in scaled seismic energy (the ratio of emitted seismic energy to released seismic moment) and source duration. In classifying seismic events, there is the fundamental possibility of using the source parameters (seismic energy E_s, seismic moment M₀, and corner frequency f₀) as the features of the KLASI-k algorithm. Good correspondence is observed between the classified subsets of events in the transition from waveform parameters {RA, AF, WI} to source parameters {E_s, M₀, f₀}. The KLASI-k method was applied to the data on mining seismicity induced by two ripple-fired blasts in the Gubkin Mine of the KMAruda Mining Enterprise at the Korobkovskoe iron ore deposit. The analyzed catalogs include 77 microevents recorded after the blast on July 6, 2019 and 259 microevents after the blast on October 24, 2020. Applying the KLASI-k method has made it possible to separate two subsets in the seismic catalogs. The events in the first subset show a scaled seismic energy (E_s/M₀) higher than 10^–7 J/(N m), while those in the second subset, lower than 10^–7 J/(N m). The first type of events have a smaller source duration than those of the second type; the released seismic moment is the same.

The article provides an overview of software products developed at the Kola Branch of the Geophysical Survey of the Russian Academy of Sciences. These software products are aimed at automating the detection, location, and analysis of seismic and infrasonic events both locally (monitoring mines) and regionally (monitoring seismic and infrasonic activity in regions). A software package is also considered for searching for fragments of spent launch vehicles using signals from shock waves generated during their return to the dense layers of the atmosphere. The created software products are implemented in organizations both in the Russian Federation and abroad. Some of the programs are certified.

In the FENICS experiments, performed in 2007, 2009, 2014, and 2019 under the guidance of A.A. Zhamaletdinov, unique deep electromagnetic sounding data were obtained using grounded sections of industrial overhead power lines (OHPL) at distances from 180 to 840 km from the center of the supply line to the measuring installation. At the 2014 and 2019 stages, the components of the electromagnetic field and current strength in the source were recorded with VMTU-10 (VEGA LLC, St. Petersburg) measuring equipment, which allowed synchronous processing of measurement data with GPS referencing. Unlike the previous stages, in 2019, L-403 (Murmansk–Nikel) was used as a source with a sublatitudinal direction, which differs in a number of parameters from L-401, previously used for these purposes. The paper describes the main features of the generation of ELF–ULF radiation for geophysical research using industrial power lines.

An algorithm is described, proposed by the author for predicting the coordinates of sources, energy classes, and time of realization of expected strong earthquakes within given energy and spatiotemporal limits. It is based on the self-similarity of a seismic process in a wide energy range and includes the formation of a sampling of relatively strong earthquakes from a seismic catalog for a monitored area. In earthquake preparation zones, the nature of the epicentral distribution of weak earthquakes of representative classes that occurred during the last tenth of the seismic cycle is determined: feature vectors. They are reduced to a scale-invariant form and serve as “samples” for comparison with feature vectors of predicted (virtual) earthquakes determined from the catalog. If sufficient information is available, the parameters of the tensors of the average focal mechanisms for each preparation zone are added to the feature vectors, taking into account their weight coefficients. The prediction is assumed to be done by the least squares method (LSM), based on the criterion of best fit of all parameters for virtual earthquakes and the samples. The algorithm envisages testing by retroprediction and the creation of a computer program with machine learning for its implementation. During testing, the expected errors in the estimates of the predicted parameters are determined.

The paper considers the results of experimental studies in the wave zone of the field excited by a linear grounded antenna in the 0.4–95 Hz frequency range. As a result, the influence of the outer ionosphere on the magnetic field in the region of frequencies lower than 10 Hz is established statistically reliably. Measurements in the ultralow-frequency and lower-frequency range made it possible to estimate the state of the lower ionosphere and thus show that variations of the measured field in the frequency range less than 10 Hz are due to the influence of the outer ionosphere. Comparison of measurement results with natural electromagnetic noise, including its structured part, permitted an assumption about the relationship between an ionospheric resonator and the appearance of Alfvén resonances with the processes in the Earth’s magnetosphere. It is shown that the lithosphere, in particular, its heterogeneous structure in the field excitation region, plays a significant role in the measured frequency dependence of the field amplitude.

The study analyzed the spectra of acoustic signals obtained during uniaxial compression of artificial sandstone samples under continuous loading through the postultimate state up to failure. The authors attempt to reveal a shift towards lower values in the characteristic acoustic signal frequency as the load approaches the critical load state. The experiments were performed on a lever press in two modes: simple continuous loading and continuous loading with periodic impact on the sample by direct current. This was done in order to indicate the effect of electric current on the acoustic emission parameters. In both cases, when a load reached close-to-ultimate and postultimate states, the amplitude of the signals in the 10–20 kHz frequency range begins to significantly exceed the amplitude of the signals in frequency ranges above 20 kHz. At the final stage, immediately before the onset of an avalanche-like rise in acoustic emission activity, an increase in signals with frequencies in the 5–10 kHz range is also noted. Based on the identical behavior of the samples, the authors have concluded that the electric impact did not significantly affect the spectral acoustic signal characteristics. The shift of the frequency interval, which is accounted for the maximum RMS amplitudes of the acoustic signal, towards low frequencies may indicate either the formation of larger cracks or the appearance of additional cracks of a different mode than at lower loads (e.g., shear cracks). By itself, this phenomenon may indicate impending macrofailure.

The results of experimental studies of the effect of alternating changes in reservoir pressure on the volumetric compressibility of gas storage reservoirs have been reviewed. Several approaches to estimating volumetric compressibility are considered: integral, differential–additive and differential–discrete, which differ in their choice of the interval of effective pressure changes. It is shown that different approaches give different estimates of the volumetric compressibility of the pore space. It is established that the application of the differential–discrete approach allows the most adequate estimation of the pore compressibility during gas injection and circulation. Specific petrophysical parameters of the gas storage reservoir have been considered and, on their basis, estimates of the coefficient of volumetric compressibility of the pore space have been obtained. A methodology has been developed and tested in practice to estimate changes in vertical surface displacements of an underground gas storage facility, which takes into account actual changes in the porosity and compressibility of gas reservoirs depending on the selected operating mode. Using the developed mathematical models, we have estimated the maximum amplitude of surface subsidence of the Uvyazovskoe underground gas storage facility during simulation of gas injection and withdrawal, which reaches 61 mm when the reservoir pressure changes by ±5.0 MPa.

The Kolba permanent seismic station was installed in 2020 at the Kolba geophysical station (affiliated with the Northern Territorial Administration for Hydrometeorology and Environmental Monitoring), near the settlement of Dikson, Krasnoyarsk krai, in order to increase the sensitivity of the Arkhangelsk Seismic Network (affiliated with the N. Laverov Federal Center for Integrated Arctic Research, Ural Branch, Russian Academy of Sciences), which carries out seismic monitoring in the Barents–Kara region and adjacent areas. For regional earthquakes in the European sector of the Arctic, the representative magnitude was determined at M_Lrep = 3.4. The Kolba seismic station records local events of different nature with magnitudes from 0.8 to 1.7. The dependence of the number of revealed earthquakes on the level of microseismic noise is revealed.