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Nº 4 (2025)
Articles
On the Relationship Between RTL and B-Value Anomalies of Seismicity
Resumo
The article, prepared for the issue of the journal dedicated to the memory of G.A. Sobolev, reflects the history of the creation and presents a description of the physical foundations of the RTL technique for identifying prognostic anomalies of seismicity, proposed by G.A. Sobolev in 1995. From the standpoint of the concept of avalanche-unstable fracturing formation (AUF), physical ideas about the nature of the patterns of precursor anomalies of the RTL and Gutenberg-Richter b-value are discussed. The previously obtained results of comparing the manifestations of RTL and GRP anomalies in a number of regions related to different tectonic types are summarized: subduction zones, rift and shear zones. Issues related to RTL and b-value calculation methods are also discussed. The manifestations of the considered anomalies in regions related to different tectonic types have both common patterns and demonstrate regional differences. In shear zones, the sequence (stage) of the onset of seismic quiescence (RTL parameter) and changes in the energy “spectrum” of seismicity (b-value) turned out to be the opposite to the stage found in subduction zones and the rift zone. At the same time, in all regions, regardless of their tectonic type, the same stages of formation of anomalies of b-value and seismicity activation are observed: activation begins later than the decrease in b-value. This corresponds to the scenario following from the AUF concept, thus confirming the effectiveness of this concept in tectonically different regions.
Fizika zemli. 2025;(4):4-20
4-20
South Tien Shan Earthquake on January 22, 2024, Mw = 7.0: Filling a Seismic Gap?
Resumo
On January 22, 2024, an earthquake with Mw = 7.0 occurred in the Southern Tien Shan in the Kyrgyzstan-China border region. The article presents an analysis of the previous seismicity of the region based on homogeneous seismological (global earthquake and focal mechanisms catalogues) and seismotectonic data (active fault global database). The aftershock sequence is also studied using regional data. It is shown that the focal area of the earthquake on January 22, 2024 partially filled the previously existing seismic gap and the gap in the active fault system. The aftershock sequence is intense, although without a pronounced strong aftershock. The aftershock mechanisms are almost identical with the main shock mechanism. According to regional data, there is a deficit of strong aftershocks (mb ≥ 4.8). Whether this indicates the “incompleteness” of the seismic process or not, cannot be assessed based on just six months of data. The change in the number of aftershocks over time shows that after a month and a half after the main shock, the decay of the aftershock process slowed down. This may be due to both seismic activities reaching a long-term level and the redistribution of stresses in the focal area. As a rule, active fault maps serve as a seismotectonic basis for assessing seismic hazard. In this case, a strong earthquake occurred where no documented active faults were noted — it rather extended an existing fault, on the edge of which a cluster of earthquake foci had previously been noted. The question arises as to how reliable are seismic hazard assessments, the seismotectonic basis of which are mapped active faults.
Fizika zemli. 2025;(4):21-34
21-34
Systematic earthquake forecast
Resumo
A computer-based method for systematic earthquake forecasting is discussed. The forecast is calculated regularly and over a fixed time interval. The result is a map of the alarm zone where the epicenters of target earthquakes are expected. A forecast is considered successful if all the epicenters of target earthquakes within the given interval fall into the alarm zone. The minimum alarm area method is used to train the forecast. The method optimizes the probability of a successful forecast with a limited alarm zone. This method also estimates the probability of success for the next forecast interval and explains the alarm zone using logical implication and a list of previous earthquakes with similar precursor values. An example of systematic forecast of Kamchatka earthquakes is presented.
Fizika zemli. 2025;(4):35-49
35-49
Typical Precursor Anomalies of the 6 February 2023 Kahramanmaraş, Türkiye, Doublet, Mw 7.8 and Mw 7.6 and the 2004 Sumatra-Andaman and the 2011 Tohoku-Oki Mw 9.0+ Mega Earthquakes
Resumo
Previously, as a result of constructing and analyzing the generalized vicinity of a large earthquake (GVLE), a system of typical predictive features of a large earthquake was identified and described in high detail. However, these typical features are only relatively rarely detected in the foreshock zones of individual large earthquakes. It was noted that the proportion of events in the foreshock zones of which predictive GVLE features are identified increases with the number of weak events in the vicinity of a given large earthquake. Using the example of cases better provided with seismic data, it is checked how often GVLE features are detected with large volumes of seismological data. It is shown that in these cases GVLE anomalies are recorded quite systematically. A relationship is proposed between the magnitudes of target earthquakes and the completeness of the catalog used, when the identification of GVLE predictive features is possible with a high probability. The unresolved problem of false alarms is noted.
Fizika zemli. 2025;(4):50-62
50-62
Geodynamic manifestations of the seismic process in the area of the Simushir earthquakes on November 15, 2006 and January 13, 2007
Resumo
The study analyzes the development of the aftershock process, displacements at GNSS (GPS) stations, and time variations of the gravity field in the area of the Simushir earthquakes on November 15, 2006 and January 13, 2007. A simulation of the post-seismic creep and the viscoelastic relaxation process with an asthenospheric viscosity of 1019 Pa·s has been performed. It is shown that the nature of the displacements at GNSS stations, the growth of the gravity anomaly, which began 5 months after the earthquake of November 15, 2006, simultaneously with the advance of aftershock activity to a depth of 100 km, are mainly associated with postseismic creep in a vast area, including areas of the subduction zone adjacent to the focal zone and its 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 occurring in the southern part of the Kuril Arc may be related to the fact that the direction of the Pacific plate movement here is not perpendicular to the oceanic trench; the so-called oblique subduction takes place. The emerging component of the right-lateral strike-slip 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 an extension and destruction zone, revealed by geophysical work in the area of the subduction zone from the Bussol Strait to the Diana Strait. Sharp changes in the depth of the acoustic basement and the Moho boundary were recorded at the edges of this zone, Moho was not recorded in the destruction zone itself. This area has been a seismic quiescence for a long time and two strong events occurred in it on November 15, 2006 and January 13, 2007. The postseismic creep model constructed in this study shows that in the area of extension and destruction, the displacements, along with the thrust component, also had a right-lateral strike-slip component. To the north of this zone, in the area of the Ketoy and Matua Islands, purely thrust displacements occurred, further to the north the magnitude of the displacements decreases.
Fizika zemli. 2025;(4):63-79
63-79
Observations of the Blomstrand Glacier Activation in the North of West Spitsbergen Island Based on Data from a Single Seismic Station
Resumo
At the end of 2019, the automated seismological monitoring system of the Kola Branch of the FRC UGS RAS recorded an increase in weak seismicity localized in the northwestern part of West Spitsbergen Island. The intensity of the seismic process reached several dozens of events per day. A preliminary analysis of the records of seismic events visually revealed a high degree of similarity in their waveforms. To obtain the most complete catalogue and spatial-temporal representation of the development of this seismic process, the cross-correlation detection method was used. The resulting final catalogue contains over 9,000 seismic events in the magnitude range (ML) from –0.4 to 0.6. The localization of the epicenters showed that they are confined to the ablation zone of the Blomstrand Glacier. Analysis of the resulting catalogue showed that the sequence began and ended abruptly, with variations in the amplitudes of seismic events and the times between their occurrence taking place simultaneously. Comparison of the seismic monitoring results with satellite images obtained by the Santinel-2 research apparatus in the radio frequency range showed a connection between this seismic sequence and a large-scale movement of the terminal part of the Blomstrand Glacier, accompanied by massive emissions of ice material into the bay. At the same time, during the period of 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 the manifestation of the phenomenon of stick-slip motion of the glacier along the bed in the process of preparing for a large-scale movement.
Fizika zemli. 2025;(4):80-92
80-92
Seismo-electromagnetic and seismo-ionospheric phenomena: from the earliest works of G.A. Sobolev to the present day
Resumo
The review examines seismo-electromagnetic and seismo-ionospheric phenomena, the potential of which for earthquake forecasting and exploration geophysics was anticipated by the remarkable Russian geophysicist G.A. Sobolev. His works inspired geophysicists around the world to work in these areas, and to date they have developed rapidly. The areas of research that modern geophysics owes much to G.A. Sobolev include the study of the relationship between seismic and electromagnetic noise and vibrations, the electromagnetic response to rock loading, disturbances of electrotelluric fields at the stage of preparation for a seismic event, anomalies on radio paths and disturbances of the ionosphere before strong earthquakes, and trigger phenomena in geophysics. The development of ideas in the course of later studies proved the general value of G.A. Sobolev’s earliest ideas. The current state of work in these areas and the problems that researchers face are considered.
Fizika zemli. 2025;(4):93-114
93-114
Laboratory Studies of Seismoelectric Conversions in Porous Media. I. Retrospective and Perspective
Resumo
The paper presents the first part of the work devoted to laboratory studies of seismoelectric conversions in porous media. The main historical stages and the current state of research into seismoelectric transformations, their place in the aggregate of mechanoelectromagnetic phenomena in rocks are considered. An updated classification of seismoelectric effects is proposed, dividing the effects by the type of the primary acting field, by the type of secondary changes, by the ratio of the frequencies of the primary and secondary fields. Data on the main publications on each effect are provided, and current relevant research areas are noted. The history of research into seismoelectric conversions in totality of mechanoelectromagnetic phenomena at the Institute of Physics of the Earth of the Russian Academy of Sciences and the role of Corresponding Member of the RAS Sobolev G.A. in these works are separately described. The main problems associated with measuring the secondary electromagnetic field, primarily in laboratory experiments, are considered. Five most significant problems are identified, and ways of solving them by various researchers are given. It is shown that most of the solutions are incomplete and that further research should be aimed at a comprehensive solution to these problems. Primary task is the separated measurement of magnetic and electric components necessary to identify sources of the secondary electromagnetic field in seismoelectric conversions. It is proposed to use contactless measurement of magnetic action of electric current in the laboratory, which was previously successfully tested in the field study. Within the framework of this proposal, subtasks are formulated, the solution of which is necessary to obtain new data on the seismoelectric effect.
Fizika zemli. 2025;(4):115-133
115-133
Effect of direct heating on cracking process in the uniaxially compressed sample
Resumo
A suggestion was made in a number of published papers that the effect of electromagnetic exposure on the seismic regime in natural conditions or on the crack formation process in laboratory experiments can be explained by the role of Joule heating when electric current passes through fluid-saturated rocks. Heating of the fluid in the pore space can lead to an increase in the fluid pressure in the pores and cracks, which in turn can stimulate additional cracking of the solid skeleton and a decrease in the strength of the rock. In this paper, in order to identify the role of the thermal factor on the crack formation process in rocks, the results of direct heating of artificial sandstone samples under uniaxial compression are presented. The samples were taken from the same batch that was previously studied in experiments on the effect of electric current passing through a sample on the characteristics of acoustic emission and on the process of its destruction. In the presented experiments, the heat flux was supplied to the opposite side faces of the sample using Peltier elements, which are a reverse thermoelectric converter. The heat flux density on the sample surface reached almost 104 W/m2; the local temperature of the outer surface of the sample near the heating element increased during the heating process by 10-15°C depending on the duration of the current being turned on. Experiments have shown that even with such significant heat fluxes, the effect of heating is manifested only at loads close to destructive (Kp ≥ 0.95-0.97). The effect of heating was manifested in the fact that the crack formation process in the sample intensified, and the sample itself gradually passed into a overcritical state and, eventually, was destroyed. At lower loads, direct heating of the sample does not have a noticeable effect on the crack formation process.
Fizika zemli. 2025;(4):134-143
134-143
Experimental study of a porous medium destruction during a pressure drop
Resumo
A number of negative consequences are associated with a pore pressure drop in permeable fluid-saturated rocks: sudden coal outbursts, destruction of the borehole surrounding rock in oil producing wells, methane emissions as a result of permafrost degradation, etc. The article discusses the results of a series of model laboratory experiments to study the destruction of a porous fluid-saturated material of low strength during a rapid pressure release at its boundary. The pressure release rate, strength properties of the material, presence of gas and position of the boundary between gas and liquid were varied. The conditions for the formation of microcracks and permeability growth with repeated cycles of pressurre growth-release were found. It was found that with an increase in the pressure release rate, the number of formed cracks and the depth of destruction increase. Numerical modeling of the formation of macrocracks during pressure release in gas-filled samples was carried out.
Fizika zemli. 2025;(4):144-158
144-158
Role of microstructure consideration in modeling the effective elastic properties of limestones
Resumo
The work is devoted to the construction of parametric mathematical models of effective elastic properties of carbonate rocks of complex structure, which are represented by fine-grained organogenic-detrital limestones of the Moscow stage with traces of dissolution. Such models make it possible to link the parameters characterizing the composition and microstructure of rocks with their macroscopic elastic properties. Having measurements of the velocities of elastic waves 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, which leads to the need to find ways to reduce the area of possible solutions. In this work, in order to solve this problem, we use measurements of the elastic wave velocities (longitudinal and transverse), obtained on a representative sample of the studied rocks in three states of fluid saturation — dry, water-saturated and saturated with glycerol. Based on the results of measuring the sample mass between successive different fluid saturations and at the end of the measurement cycle, the following assumption was made: as a result of repeated drying of the sample and saturation with the next fluid, its porosity did not change. Thus, it can be stated that in each state of fluid saturation, the same structurally unaltered rock was studied. It is shown that solving the inverse problem using velocities obtained on a sample saturated with only one fluid leads to an extensive area of ambiguity in the solution for determining the parameters of the microstructure of the model, despite the fact that the number of unknown parameters of the model is equal to the number of independent velocity measurements. Using data on sample velocities in other states of fluid saturation to solve the inverse problem significantly reduces the uncertainty of the solution. Examples of application of the constructed mathematical model of rock elastic properties to solving the problem of the fluid substitution and the influence of cracks on the elastic wave velocities are shown.
Fizika zemli. 2025;(4):159-177
159-177
Features of energy distributions of acoustic emission signals during rock deformation: Laboratory experiment and computer simulation
Resumo
The paper gives an overview of the results of computer and laboratory experiments on the deformation of various rock samples. A model based on the discrete element method was used to identify the regularities of defect evolution. In the laboratory experiment, the evolution of the microcrack system in samples (Westerly granite, Berea sandstone, metasandstone) was investigated using two independent nondestructive methods: acoustic emission and X-ray computed microtomography. It is shown that the energy distribution of acoustic emission signals accompanying destruction is not always approximated by a power function. The exponential type of the energy distribution of AE signals indicates a stable state of deformed material. The power type of distribution indicates that the process of defect accumulation has reached a critical stage leading to catastrophic failure.
Fizika zemli. 2025;(4):178-186
178-186
On the relationship between Gutenberg-Richter b-value and the fractal dimension of seismicity according to computer and laboratory modeling data in spaces of different dimensions
Resumo
A study was conducted on the relationship between the Gutenberg–Richter b-value and the fractal dimension of a set of hypocenters based on a computer model of the Olami–Feder–Christensen (OFC) cellular automaton in spaces (on grids) of different dimensions. The results of the computer modeling were compared with previously obtained data from laboratory modeling of seismicity the rock samles destruction. Computer modeling in spaces of different dimensions has shown that the Gutenberg–Richter b-value and the fractal dimension of the set of events depend on the dimension of the space in which the failure develops, increasing with increasing dimension. In spaces of different dimensions, the accumulated elastic energy is released during the formation of a rupture of the medium from domain of different dimensions. In the case of three-dimensional space — from an area of a certain volume, in the case of two-dimensional space — from an domain of a certain area. With the same size of the rupture and the same critical density of elastic energy in the three-dimensional (volumetric) case, more energy is probably released than in the two-dimensional (areal) case. It can be assumed that this is associated with the difference in the indices of the energy spectrum and fractal geometry of the destruction process in spaces of different dimensions. The results of computer and laboratory modeling of seismicity also confirmed the validity of the Aki formula (direct proportionality of the Gutenberg–Richter b-value and fractal dimension). The justification of the implementation of the Aki formula for destruction in spaces of different dimensions 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 failure process in areas with different types of destruction under different tectonic conditions.
Fizika zemli. 2025;(4):187-198
187-198
On the role of the sliding surface macrostructure in the origin and development of dynamic instability in the upper part of the Earth’s crust
Resumo
The heterogeneous structure of the future rupture surface plays an important role at all stages of the evolution of dynamic instability processes in rock massifs. The presence of heterogeneities leads to the appearance of stress concentration areas on large-scale irregularities (asperities) and relatively unloaded areas of the interface with radically different frictional properties. The influence of the interaction of such zones may be more complex than just stress concentration. According to published data from geodetic and seismological observations, with certain structures of the fault zone structure, various slip modes along the fault can be observed — from slow slip events to supershear ruptures. The article presents the results of laboratory experiments on the shear of meter-scale rock blocks, the contact between which contained zones of increased strength, which have the property of velocity weakening. In order to compare the results of laboratory experiments with the effects observed in nature, a database containing rupture models for more than 150 earthquakes in different regions of the world was used. A joint analysis of the results of laboratory experiments and seismological observations showed that the development of a rupture occurs according to several scenarios determined by the mutual arrangement of asperity zones. Information on the location of such areas, for use in numerical modeling of the deformation process of a specific region of the crust, can be obtained from the results of satellite and seismological observations. For areas of preparation of relatively small earthquakes, where geodetic observations are ineffective, the necessary information can be obtained using observations of microseismicity.
Fizika zemli. 2025;(4):199-215
199-215
Parametric effects in recent geodynamics
Resumo
Parametric effects in recent geodynamics are discussed, when anomalous deformation processes in fault zones occur in a setting of regional quasi-static 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 quasi-static loading of rock samples is shown. Changes in Young’s modulus with periods of 0.03 — 0.3 years, which are accompanied by variations in the electrical potentials of rock samples, are revealed. Examples of the formation of parametric deformations in fault zones induced by the preparation process of a strong earthquake in Kamchatka are presented. Estimates of the influence of meteorological factors on local deformations of the earth’s surface are given. It is shown that with a linear effect, daily and annual temperature changes have the greatest influence. With nonlinear effect, parametric excitation of processes in 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 minor natural impacts is noted.
Fizika zemli. 2025;(4):216-236
216-236
Seismogeological Conditions of Preparation of Dangerous Earthquakes in Fault Nodes
Resumo
The article discusses the results obtained in a detailed examination of the conditions for the preparation of dangerous earthquakes at different hierarchical levels — global, regional (Mongolia) and local (sections of the Baikal rift zone). Attention is paid to the episodes of seismic activation acts in the vicinity of fault nodes of different scale levels, as well as geological and structural conditions affecting the preparation modes of foci of dangerous earthquakes. The linear dimensions and morphogenetic types of faults, their articulation angles, features of the modern seismic regime, as well as information on seismic activity in the past were taken into account. It was established that due to the variety of conditions for the dynamic interaction of faults at their articulation sites, strong earthquakes often occur at short time intervals and close locations of their epicenters. Such features complicate the forecast of earthquakes, since traditional ideas about the recurrence periods of earthquakes of the corresponding magnitude are violated. Also, when forecasting earthquakes, additional problems arise concerning the estimates of the duration of the waiting periods for earthquakes for short, medium and long-time intervals. The authors have shown that in order to determine the duration of the waiting periods for dangerous earthquakes, it is currently possible to establish only probabilistic estimates of this parameter, associated with estimates of the predicted energy of upcoming events. For this purpose, it is necessary to conduct detailed observations of variations in the seismic regime of weak earthquakes at different depths of the earth’s crust, to record anomalous changes in the deformation regime and slip velocity. It is also important to conduct geophysical observations of changes in parameters characteristic of the final stage of preparation of earthquake foci.
Fizika zemli. 2025;(4):237-252
237-252