Izvestiya, Physics of the Solid Earth最新文献

In light of the ongoing global climate changes, the timely study of cryolithozone objects is crucial to prevent potential natural and man-made disasters. Geophysical methods are also widely used to investigate permafrost strata. The transformation of sounding data into apparent electrical resistivity (AER) is a common procedure for electromagnetic methods for exploring the geological environment and allowing one to quickly obtain general information about its structure. The measurement system for pulsed electromagnetic monitoring of the cryolithozone that is discussed in the article consists of a set of field sources and receivers that are mounted inside nonconductive housings and immersed in two different wells. A method has been proposed for converting the pulsed sounding data into apparent resistivity for all recording times. The transformation algorithm is based on selecting a resistivity of a homogeneous conducting half-space so that the signal for this resistivity corresponds to the measured signal. To develop the algorithm, the behavior of signals was studied and their transformations in half-spaces with an arbitrary resistivity were plotted. Examples are provided to determine apparent resistivity in models of the thawing upper layer of frozen rock at different distances between wells. It has been shown that at early times, when the signal reaches its maximum value and becomes measurable, the apparent resistivity provides a qualitative description of the geoelectric model, while the resistivity of the thawed layer can be accurately determined. The obtained values of the apparent resistivity are necessary for understanding the depth of thawing and allow the development of a reliable starting model for the subsequent inversion of pulsed sounding data with precise spatial localization of the boundary between frozen and thawed rocks.

The rheology of the Earth’s mantle is studied on the basis of data on the Love numbers for ten tidal components (M2, Mqm, Msqm, Mtm, Mstm, SN, Mf, Msf, Mm, and Msm). An adaptation of the Preliminary Reference Earth Model (PREM) is used to model the internal structure of the Earth, while the inelasticity is modeled using the Andrade rheology. The Andrade model depends on two empirical parameters (α and ζ) that are unknown for mantle minerals at high pressures and temperatures and very slow deformations. As a result, in various problems of planetary geophysics where inelasticity in the interior of planets or satellites must be taken into account, authors are often faced with the difficulty of which values of the Andrade rheology parameters to use. To address this issue, an Earth-based calibration of the rheology was performed. The Love numbers of the Earth were calculated at ten tidal frequencies for two viscosity distributions and for 1530 different combinations of the parameters α and ζ. The comparison of the model values with the observed ones allowed us to determine a set of values for α and ζ that are suitable for describing the inelasticity of the Earth’s mantle.

In this study, we consider in detail the July 13, 2023, earthquake that occurred on the shelf of the eastern Laptev Sea (Belkov–Svyatoi Nos rift). On the one hand, our interest in this event is due to the location of its epicenter, to the east of which there is a sharp decrease in seismic activity. Conversely, detailed common depth point (CDP) data on the structure of the upper crust are available for its epicentral zone, making it possible to analyze the seismotectonic position of the earthquake source. Focal parameters in the instantaneous point source approximation are calculated from surface waves recorded at teleseismic distances. As a result, we have obtained a scalar seismic moment (M₀ = 9.8 × 10¹⁶ N m), corresponding moment magnitude (M_w = 5.3), source depth (h = 8 km), and focal mechanism (a normal fault along a gently dipping nodal plane with a NW–SE strike). Our results are compared with data from seismological agencies. It has been shown that differences between them are most likely caused by various initial data, including their different frequency ranges. Our estimates agree better with the available geological and geophysical information on the tectonics of the study area. Taking into account the data on strike, dip, and penetration depth of faults and our source parameter values, we have concluded that the July 13, 2023, earthquake could have been associated with a major listric normal fault on the western slope of the Belkov–Svyatoi Nos rift.

A new of fundamental approach to solving inverse geophysics problems using the linear integral representation method and discrete gravity potential theories is proposed. This approach makes it possible to reconstruct the masses, which can be regarded as arbitrary distributed points in two- and three-dimensional network spaces.

Linear sequences of earthquake epicenters (“chains”) related in space and time are studied. A new approach to understanding earthquake chains as a special kind of group (clustered) events is proposed. It is believed that clusters of group earthquakes with pronounced spatial anisotropy potentially represent the desired chains. Such chains are given the physical meaning of markers of activated tectonic faults. A formalized algorithm for the allocation of linear sequences of earthquake epicenters based on the proposed approach has been developed. The search for chains is conducted in the catalog of group earthquakes. Previously, single earthquakes (i.e., not included in clusters) are removed from seismicity. For this, a previously developed algorithm was used, focused on the selection of any interrelated events, and not only (mainly) aftershock and/or foreshock series (Descherevsky et al., 2016a). The proposed method of isolating earthquake chains has been successfully tested on earthquake catalogs of Garm, Iran and central Turkey. Chain maps are provided, and summary statistics of the chain field are discussed. As a rule, these chains can be compared with various tectonic disturbances, but a significant part of them are not tied to known structures. For the Garm district, the continuity of the results obtained with previously performed studies is shown. Like almost any method of analyzing seismic data, the earthquake chain algorithm has a significant number of configurable parameters. Within certain limits, you can vary the criteria for allocating group events, the minimum number of events in the chain and its minimum length, as well as the required level of straightness of the chain. However, all these settings primarily affect the total number of chains found in the catalog, and their location and orientation (azimuths) they almost do not depend on the algorithm settings. This allows us to consider the proposed analysis method as a fundamentally new way of extracting and visualizing information about the spatial and temporal organization of seismicity. A more detailed study of both the structure of earthquake chains and its changes over time in various seismically active regions of the world can contribute to a better understanding of the dynamics of the seismotectonic process.

Abstract—This paper examines the construction of an aftershock activity area in conditions of natural and mining-induced seismicity based after the data on the first aftershocks. The study area is apatite–nepheline deposits located in the southern part of the Khibiny massif. A significant number of variants of aftershock regions were investigated that differ in shape, location, and orientation. The size of the area has been determined by scaling based on physical and statistical characteristics calculated from both the main shock and the first aftershocks. The criterion based on an error diagram has been used to quantitatively compare a large number of different variants. As a result, the optimal area type has been selected, which showing the best results of the quantitative test based on seismicity data on the study area for 1996–2022. The technique can be used to predict the area of aftershock activity distribution at the Khibiny massif deposits after a natural–mining-induced earthquake based on operational processing data.

The article presents the results of an express radon survey on the territory of the Timan Ridge. The study objects were kimberlite pipes and local anomalies of the Middle Timan similar to them in the magnetic field. In the course of the study, the maps of the magnetic field of different scales were used to identify and sort magnetic anomalies similar to those of pipe-like bodies. Magnetic anomalies were distinguished using such qualitative characteristics as location, shape, size, sign, intensity, and gradient. Magnetometric and radon surveys were carried out to study the explosion pipes and magnetic anomalies. The magnetometric observations were conducted along a profile network in order to detect and determine the contour of the anomaly. The method of radiometric studies consisted in crossing the magnetic anomaly with a profile passing through three observation points—center, edge, and beyond the contour. The radiometric measurements within the Umbinskaya, Srednenskaya, Vodorazdelnaya and the Verkhnemezenskaya series of explosion pipes revealed the elevated values of volumetric radon activity (VRA) above the pipes. Thus, radon survey can be used as an additional search criterion included in the complex of geophysical works. Based on morphological variations in the magnetic field, several sites were distinguished in different tectonic structures of Middle Timan, within which radiometric studies of 68 magnetic anomalies were carried out. Moreover, 23 of the considered anomalies were characterized by the elevated VRA values. These anomalies, in turn, were divided into two promising categories that are of interest for further study. The first category includes anomalies with VRA values more than 1000 Bq/m³, the second category includes anomalies with VRA values from 450 to 1000 Bq/m³. This scatter of VRA values is associated, first of all, with the geological and tectonic position of the structure. The identified promising anomalies are very close in morphology to the pipe type, and geologically they can be caused by small intrusive bodies or explosion pipes. However, not only explosion pipes can be characterized by high VRA values, but this is also typical of individual magnetic anomalies caused by dikes and sills of basic, ultrabasic, and alkaline composition, as well as rocks enriched in radioelements. When setting tasks for studying magnetic anomalies aimed at searching for explosion pipes, the first step is to sort out such anomalies according to their location in the studied tectonic structures, morphology, and intensity.

The ₁S₁ Slichter mode is the longest-period mode of the Earth’s free oscillations, caused by oscillations of the Earth’s inner solid core relative to the outer liquid core. In this paper, the search for and estimation of the Slichter mode from the IEGTS superconducting gravimeter network data after the 2011 Tohoku earthquake are performed. In the course of the work, the theoretical calculation of the Slichter mode splitting parameters for the PREM model was made. The mode was estimated using an original algorithm based on the maximum likelihood method. The algorithm uses optimal data integration obtained from all 21 records of 16 gravimeters, which can significantly increase the signal-to-noise ratio at the output of the detection system. Three most probable estimates of the degenerate frequency of the mode and its splitting parameters were obtained, what allows one to conclude that the Slichter mode was highly likely to be observed after the Tohoku earthquake. The differences in density between the inner and outer cores of the Earth corresponding to the periods of the mode were determined.

The Klyuchevskoy group of volcanoes is a unique research object, also from a seismological point of view. Classical high-frequency and long-period earthquakes of varying depths are being observed here, and the installation of temporary stations as part of the KISS project has made it possible to apply new methods to classify the observed seismicity. Two methods for determining seismic moments are used in the study. The spectral ratio method is used for the first time, which makes it possible to estimate the seismic moments of source spectra for the magnitude range M_w = 1–3. An independent assessment of seismic moments is also performed using a spectral method based on the level of low-frequency plateau of the amplitude displacement spectrum of body waves, and relation with the local magnitude is studied.

The traditional field of research has been enriched by discovering and applying several unique approaches for extracting relevant information from a time series of Solid Earth tides for a specific location. This study focused on the impactful Mw 9.1 megathrust earthquake of December 26, 2004, in Sumatra-Andaman, which spans 13 earthquakes within a 75-kilometer radius from 1991 to 2021. Employing the univariate singular spectrum analysis (SSA) on Solid Earth tides (SET), a significant anomalous variation in the sixth component of empirical orthogonal functions (EOF) is identified. It is noted that the eigenvalue corresponding to this component exhibits a correlation with earthquake magnitude. Further, this study is extended to a broader spatial region to perform in-depth spatio-temporal analysis exclusively for the December 26, 2004 earthquake, by expanding spatial analysis to latitudes 2° to 5° N and longitudes 94° to 98° E through a sliding window method. A spatio-temporal analysis from 1995 to 2004 reveals distinct patterns preceding higher magnitude earthquakes, offering valuable insights for long-term forecasting. It has been correlated with foreshocks that occur to the same spatiotemporal extent. In a nutshell, singular spectrum analysis SSA of Solid Earth Tides emerges as a promising precursor for long-term earthquake magnitude prediction. Also, EOF alone is insufficient for accurately forecasting the magnitude, as the results show an inverse relationship with magnitude. Finally, it might be combined with other parameters like foreshocks for reliable earthquake forecasting.