Seismic Instruments最新文献

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.

Earlier, the authors carried out a unique experiment on long-term continuous precision monitoring of crustal resistivity variations in a highly seismic region. The result 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. Standard programs for inversion of VES curves do not allow this, and even with very small fitting residuals, the actual error in reconstructing the resistivity can be huge due to equivalence effects. The authors have previously developed a special method for regularizing the residual functional, which multiply increases the accuracy in solving the inverse problem for the considered type of resistivity section, and a method for obtaining realistic, rather than underestimated estimates of the solution error. To do this, a package of synthetic resistivity profiles is formed that imitates a real section, the VES direct problem is solved, and time series of apparent resistivity are constructed, on which noise similar to real noise is superimposed. After that, the VES inverse problem is solved and the errors in reconstructing the model resistivity curves are analyzed. Such calculations were carried out both for the total signals and their components, obtained as a result of decomposition of the apparent resistivity series into physically determined components. The developed approach makes it possible to solve the inverse VES problem with heretofore unattainable accuracy. We emphasize that a reliable estimate of the solution errors is provided not by the convergence criteria of the inversion algorithm (they are almost always overly optimistic), but by direct calculations of the direct and inverse problems for synthetic profiles similar to real signals. In the present article, the profile of the experimental VES curves obtained in the course of this experiment is inverted. Series of resistivity variations are calculated in four layers of a geoelectric section with a duration of more than 12 years. It has been established that the upper layer of the section is characterized by trend and seasonal changes in resistivity with a large amplitude. Significant anomalous seasonal effects were found in the second layer of the section. For the third layer, the presence of small-amplitude seasonal effects was established, while there are no significant resistivity trends. Variations in the resistivity of the fourth layer are less reliably estimated; to detect the effects of external factors on electrical resistivity, it is necessary to use signal stacking methods.

The paper proposes a method for searching for the M2 tidal harmonic in seismicity, based on the construction of time series of conditional accumulated seismic energy (CASE) with a given discretization and their adaptive spectral analysis. The preliminary results of testing this method on seismic observations throughout the territory of California for the period 1983–2012 are presented. For the first time, the fundamental harmonic of the lunar tide M2 was reliably identified in weak seismicity variations at a significance level above 5σ in the range of energy classes 5–9. Confinement of areas with significant M2 amplitudes to the San Andreas Fault and its branches was established.

At the stages of the FENICS experiment conducted in 2014 and 2019, unique data on deep electromagnetic sounding with grounded sections of industrial power lines were obtained at distances from 180 to 940 km from the center of the supply line to the measuring installation. The electromagnetic field components were recorded by VMTU-10 measuring equipment (VEGA, St. Petersburg). The fluctuations of the current in the supply line were recorded as a time series with a sampling rate of 1 kHz. Based on synchronous time series of the field components at the observation points and the current strength in the supply vibrator, estimates of the power spectra of the autocorrelation and cross-correlation functions of the recorded values were calculated using fast Fourier transform (FFT). The resulting spectral characteristics were used to determine the amplitudes of the field components of the source and phase shifts between them, as well as to estimate the impedance tensor components. To do this, correction factors were calculated for the ratio of the apparent resistivity values for the horizontal magnetic field component to those for the impedance and electric field. A 2D interpretation is made and estimates of the resistivity allocation at depth are obtained for two sublongitudinal and sublatitudinal profiles of the Karelia–Kola region.

To solve many geological and geophysical problems, in particular, prediction of strong earthquakes, seismic zoning, and earthquake-resistant construction, it is necessary to have reliable data on the distribution of earthquake hypocenters in the study area. In turn, the completeness of data on the distribution of earthquake hypocenters and accuracy of their determination largely depend on the efficiency of the observation system. We evaluate the efficiency of the actual network of seismological observations in Karelia, which consists of seven seismic stations. The efficiency of the seismological observation network is estimated by the minimum magnitudes of seismic events recorded in the considered region and the minimum errors in determining the main parameters (origin time and hypocentral coordinates) of the recorded events. Calculation of the minimum earthquake magnitudes for the Karelian seismological network shows that a station amplification of 30 000, the network is able to record earthquakes with a magnitude slightly less than 2, with a tendency towards a decrease in this minimum magnitude, provided that the event is recorded by at least three stations. The errors in determining earthquake epicentral coordinates in latitude δφ (km) and longitude δλ (km) do not exceed 1–2 km in the center of the network, and 6 and 11 km on the periphery, respectively. The system’s errors in determining the depths of earthquake sources H (km) do not exceed 5 km in the vicinity of the stations and 25 km throughout the territory of Karelia.

Historical earthquakes of Minusinsk okrug of Yenisei Province are studied. Information in mass media and professional literature of the second half of the 1800s–early 1900s make it possible significantly to enrich the very limited knowledge on regional seismicity. Materials on six earthquakes missing in former basic macroseismic catalogs are presented, as well as original information from unknown sources on four earthquakes. As a result of the study, one can classify the territory as an area of moderate seismicity. The maximum observed intensity does not exceed 7 on the MSK-64 scale.

An improved statistical method for determining the resonance frequencies of soils from spectral H/V ratios is presented. The combination of developed methodological and computational techniques makes it possible to identify with high reliability the resonance frequencies of the soil sequence and fundamental frequencies of the natural vibrations of structures and their elements based on engineering seismological observations. The authors demonstrate the possibility of refining the seismic soil model of a site and compiling spatial models of the change in depths of seismic boundaries of layers of the soil sequence from the results of frequency analysis of records of microseisms and seismic events. The use of the described engineering and seismological observations and methodological techniques makes it possible to instrumentally estimate the increase in amplitudes of vibrations of structures and their individual elements at resonance frequencies and obtain a sufficiently detailed seismometric floor-by-floor description of the vibrational characteristics of buildings and structures.