Izvestiya, Physics of the Solid Earth最新文献

Abstract—Previously, based on the construction and analysis of the generalized vicinity of a large earthquake (GVLE), the set of typical precursor signs of a large earthquake was identified and described in great detail. However, these typical features are rather rarely detected in the foreshock areas of individual large earthquakes. It was noted that the proportion of the events occurring in the foreshock regions where precursor signs are identified increases with the number of weak events in the vicinity of a given large earthquake. In this paper, a number of cases provided with more extensive seismicity data, it is checked how often the GVLE signs are detected when large sets of seismological data are considered. It is shown that in these cases, GVLE anomalies are detected in most cases. A proportion between the magnitudes of the target events and the completeness level of the catalogs to ensure highly probable identification of precursor GVLE anomalies is proposed. The problem of false alarms remains unresolved.

Abstract—The article discusses the results obtained from a detailed examination of the conditions for the preparation of hazardous earthquakes at different hierarchical levels: global, regional (Mongolia), and local (sections of the Baikal Rift Zone). Attention is paid to consideration of episodes of occurrence of instances of seismic activation in the vicinity of fault nodes of various scale levels, as well as geological and structural conditions that influence the modes of preparation of hazardous earthquake sources. study takes into account the linear dimensions and morphogenetic types of faults, their junction angles, specific features of the modern seismic regime, as well as information on seismic activity in the past. It has been established that due to the diverse conditions of dynamic interaction of faults at their junctions, strong earthquakes often occur in short time intervals and with their epicenters located close to each other. Such features complicate earthquake forecasting, since traditional ideas about the recurrence periods of earthquakes of a given magnitude are violated. Also, when forecasting earthquakes, additional problems arise concerning the estimates of the duration of earthquake expectation periods for short, medium and long time intervals. The authors have shown that in order to determine the duration of the waiting periods for hazardous earthquakes, it is currently possible to establish only probabilistic estimates of this parameter, linked to estimates of the predicted energy of upcoming events. To do this, it is necessary to conduct detailed observations of variations in the seismic regime of weak earthquakes at different crustal depths, and to record anomalous changes in the deformation regime and slip rate. It is also important to conduct geophysical observations of changes in parameters characteristic of the final stage of preparation of earthquake foci.

Abstract—The study constructs parametric mathematical models of the effective elastic properties of carbonate rocks with complex structure, represented by fine-grained organogenic-detrital limestones of the Moscovian with traces of dissolution. Such models make it possible to link parameters characterizing the composition and microstructure of rocks with their macroscopic elastic properties. With measurements of elastic wave velocities on representative rock samples, it is possible to estimate the parameters of their microstructure. However, the solution to such an inverse problem is usually ambiguous, necessitating the search for ways to reduce the domain of possible solutions. In order to solve this problem, this study uses measurements of elastic wave velocities (longitudinal and transverse) obtained on a representative sample of studied rocks in three states of fluid saturation: dry, water-saturated, and glycerin-saturated. Based on the results of measuring the mass of a sample between successive different fluid saturations and at the end of the measurement cycle, the following conclusion was drawn: as a result of repeated drying of the sample and saturation with the next liquid, its porosity did not change. As a result, it can be assumed that in each state of fluid saturation, the same structurally unaltered rock was studied. It is shown that the solution to the inverse problem for velocities obtained on a sample saturated with only one fluid leads to a large area of ambiguity in the solution for determining the parameters of the microstructure of the model, although the number of unknown parameters of the model is equal to the number of independent velocity measurements. Using data on sample velocities in other fluid saturation states to solve the inverse problem significantly reduces the uncertainty of the solution. Examples of the application of the constructed mathematical model of elastic properties of rocks to solve the problem of fluid substitution and influence of cracks on the elastic wave velocities of rocks are given.

Abstract—On January 22, 2024, an Mw = 7.0 earthquake occurred in the Southern Tien Shan in the Kyrgyzstan–China border region. The article presents an analysis of the previous regional seismicity based on homogeneous seismological data (global catalogs of earthquakes and focal mechanisms) and seismotectonic data (global database of active faults). The aftershock sequence is also studied based on regional data. It is shown that the source zone of the January 22, 2024 earthquake has partially filled the previously existing seismic gap and the gap in the active fault system. The aftershock series is intense, although without a pronounced strong aftershock. The focal mechanisms of the aftershocks practically coincide with the mechanism of the main shock. According to regional data, there is a deficit of strong aftershocks (mb ≥ 4.8). Whether this indicates that the seismic process is “completed” cannot be decided based on the data covering only a half-year observation period. The change in the number of aftershocks over time shows that a month and a half after the main shock, the decay of the aftershock process slowed down. This can be due both to the return of seismic activity to its long-term average level and to the stress redistribution in the focal area. As a rule, a seismotectonic basis for seismic hazard assessment is maps of active faults. In this case, a strong earthquake occurred in the region where there were no documented active faults; rather, earthquake faulting extended the pre-existing fault, on the edge of which a cluster of earthquake sources had previously been noted. The question arises: how reliable are seismic hazard assessments when their seismotectonic basis is the mapped active faults?

Abstract—The relationship between the Gutenberg–Richter parameters and the fractal dimension of a set of hypocenters is studied on a computer model of the Olami–Feder–Christensen cellular automaton (OFC) in spaces (on grids) of different dimensions. The modeling results are compared to the previous data of laboratory simulations of seismicity by fracturing of rock samples. Computer modeling in spaces of different dimensions has shown that the Gutenberg–Richter parameter (b-value) and the fractal dimension of the event set depend on the dimension of the space within which the fracture process develops, with both parameters increasing as dimensionality increases. In spaces of different dimensionalities, the stored elastic energy is released at rupture from regions that have different dimensionality. In the case of a three-dimensional (3D) space, the energy is released from a region of a certain volume, in the case of a two-dimensional (2D) space, from a region of a certain area. Given the same rupture size and the same critical elastic energy density, more energy is probably be released in the 3D (volumetric) case than in the 2D (areal) case. This can be assumed to be the reason why the power indices of the energy spectrum and fractal geometry of the fracture process differ in spaces of different dimensions. The results of the computer and laboratory modeling of seismicity also support the validity of the Aki formula stating direct proportion between the b-value and the fractal dimension. The substantiation of the validity of the Aki formula for fracture in spaces of different dimensionalities may be useful for the development of methods for a more meaningful and effective transition from seismic statistics to estimates of the physical parameters of the fracture process in regions with different types of fracture in different tectonic conditions.

Abstract—At the end of 2019, the automated seismological monitoring system of the Kola Branch, Federal Research Center Geophysical Survey, Russian Academy of Sciences, recorded an increase in weak seismicity localized in the northwestern part of Spitsbergen. The intensity of the seismic process reached several dozen events per day. Preliminary analysis of seismic event records visually revealed a high degree of similarity in their waveforms. To obtain the most complete catalog and spatiotemporal representation of the development of this seismic process, the cross-correlation detection method was used. The resulting catalog contains over 9000 seismic events in the magnitude range (ML) from –0.4 to 0.6. The localization of the epicenters showed that they were confined to the ablation zone of the Blomstrand glacier. Analysis of the resulting catalog showed that the sequence began and ended abruptly, with variations in the amplitudes of seismic events and times between their occurrence happening synchronously. Comparison of the results of seismic monitoring with satellite images obtained by the Santinel-2 research apparatus in the radio frequency range showed a relationship between this seismic sequence and large-scale movement of the terminal part of the Blomstrand glacier, accompanied by massive releases of ice material into the bay. At the same time, during the period of the active seismic process, no significant movements of the glacier front were observed, and large-scale movement of the glacier coincided with the end of seismic activation. Satellite data, as well as the periodicity in the occurrence of seismic events and the high similarity of their waveforms, may indicate manifestation of stick-slip motion of the glacier along the bed in the preparation for large-scale movement.

Abstract—The paper analyzes the evolution of the aftershock process, GNSS (GPS) site displacements, and gravity variations in the region of the November 15, 2006 and January 13, 2007 Simushir earthquakes. Postseismic creep and viscoelastic relaxation modeling with asthenospheric viscosity of 10¹⁹ Pa s is conducted. It is shown that the pattern of the GNSS site displacements, the growth of the gravity anomaly, which began five months after the earthquake of November 15, 2006, simultaneously with the propagation of the aftershock activity to a depth of 100 km, are mainly associated with the postseismic creep in a vast area including the segments of the subduction zone adjacent to the source region and the zone’s continuation to a depth of 100 km. Approximately 20% of the displacements are attributed to the action of viscoelastic relaxation. It is concluded that the features of many processes in the southern part of the Kuril Arc may be shaped by the direction of motion of the Pacific Plate which is not perpendicular to the oceanic trench in this region, and the so-called oblique subduction takes place. The emerging right-lateral shear component is realized not only in the back-arc basin, as it occurs, for example, in the Andaman Sea, but also at the plate contact itself. This leads to the formation of a zone of extension and destruction revealed by geophysical studies on the segment of the subduction zone from the Bussol Strait to the Diana Strait. On the edges of this segment, sharp changes are revealed in the depth to the acoustic basement top and the Moho which could not be detected in the destruction zone itself. This area has been a zone of seismic quiescence for a long time and hosted two largest events that occurred on November 15, 2006 and January 13, 2007. The postseismic creep model constructed in the work shows that in the region of extension and destruction, the displacements, along with the thrust component, also had a right-lateral shear component. To the north of this zone, in the region of Ketoy and Matua Islands, pure thrust displacements occurred; further north, the magnitude of the displacements decreases.

Abstract—The article discusses parametric effects in recent geodynamics, when anomalous deformation processes in fault zones occur in the setting of regional quasistatic stresses and are caused by fluctuations in the parameters of the medium inside the fault zones themselves, induced by small natural and man-made impacts. The results of physical modeling of parametric deformations under long-term (1 year) uniaxial quasistatic loading of rock samples are presented. Changes in Young’s modulus with periods of 0.03–0.3 years, accompanied by variations in the electrical potentials of rock samples, are revealed. Examples of the formation of parametric deformations induced in the fault zones by the process of preparation of a strong earthquake in Kamchatka are shown. Estimates of the influence of meteorological factors on local deformations of the ground surface are given. It is shown that in the case of linear loading , diurnal and annual temperature variations have the greatest influence. Under nonlinear parametric excitation of the processes in the fault zones, maximum deformations are caused by rainfall. The contribution of G.A. Sobolev to the development of studies of local deformations of the Earth’s surface induced by small natural impacts is noted.

Abstract—The article overviews the results of computer and laboratory experiments on the deformation of samples of various rocks. To identify defect evolution patterns, a model based on the discrete element method was used. In a laboratory experiment, the evolution of a microcrack system in samples (Westerly granite, Berea sandstone, metasandstone) was studied using two independent nondestructive methods: acoustic emission and X-ray computed microtomography). It is shown that the energy distribution of acoustic emission signals accompanying failure is not always approximated by a power function. An exponential form of the energy distribution of AE signals indicates a stable state of the deformed material. A power-law type of distribution indicates that the process of defect accumulation has reached a critical stage, leading to catastrophic failure.

Abstract—The paper presents the first section of a work devoted to laboratory studies of seismoelectric transformations in porous media. The main historical stages and current state of research into seismoelectric transformations and their place in the aggregate mechanoelectromagnetic phenomena in rocks are considered. An updated classification of seismoelectric effects is proposed, dividing effects by the type of primary influencing field, by the type of secondary changes, and the ratio of the frequencies of the primary and secondary fields. The data on the main publications for each effect are provided, and current relevant research areas are noted. The history of research into seismoelectric effects in the aggregate mechanoelectromagnetic phenomena at the Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, and the role of Corresponding Member G.A. Sobolev in these studies are described separately. The main problems associated with measuring the secondary electromagnetic field, primarily in laboratory experiments, are considered. Five of the most significant problems are identified, and various researchers’ methods for solving them are presented. It is shown that most of the solutions are incomplete and further research should be aimed at a comprehensive solution to these problems. The main problem is independent measurement of the magnetic and electrical components necessary for identifying the sources of the secondary electromagnetic field in the seismoelectric effect. It was proposed to use in the laboratory a contactless measurement of the magnetic effect of electric current, successfully tested earlier in the field. In this proposed method, subproblems have been formulated, the solution of which is necessary to obtain new data on the seismoelectric effect.