Izvestiya, Physics of the Solid Earth最新文献

Abstract—The authors’ software made it possible to perform a detailed identification of lineaments at various scale levels for the region of the Obruchev fault system of the western Baikal region. The identified lineaments significantly complement the mapped framework of faults and are consistent with the strike of fault structures of the corresponding rank. Based on the analysis of the relative specific density of lineaments of the local scale level, reflecting en echelon megafractures of large faults, heterogeneous damage zones of regional structures were established, which were divided into relatively homogeneous segments. For each identified segment and each structure as a whole, using the developed software Lineament Stress Calculator, a reconstruction of shear stress parameters was carried out on the basis of P.L. Hancock’s model. It has been proved earlier that the main features of the Early Paleozoic stage of the region development during accretion of the Olkhon terrane to the southern margin of the Siberian Craton were accompanied by activation of right-lateral strike-slip displacements along the SW–NE accretionary sutures and active metamorphism processes. The results confirm that the main faults of the SW–NE strike, subparallel to the marginal suture of the Siberian Platform, formed at the early stage of their development as right-lateral strike-slips with orientation of the compression axis of ≈90°. Second-order faults of the NW–SE orientation are defined as left-lateral strike-slips and were probably formed at that time as antithetical shears in relation to the main structures, having received their development during further structural rearrangements of the region.

Abstract—The results of 2D-calculations describing the formation of damage zone during the development of dynamic slip along a horizontal tectonic fault are presented. Different sliding behaviors are investigated, namely, the sub-Rayleigh sliding when rupture velocity V_r is no greater than the velocity of the Rayleigh wave in the medium and supershear when V_r is higher than the velocity of shear waves. The contribution of tensile and shear fracture mechanisms to the development of damage zone in the vicinity of a fault at different depths is considered. The degree of changes in the physical and mechanical properties of the rock massif at different distances from the fault is assessed. It is shown that at large depths, lithostatic stresses completely suppress tensile fracture, and rock fails exclusively due to shear deformation. At shallow depths, however, the tensile fracture mechanism becomes predominant. The stress release associated with the formation of tensile cracks sharply reduces the size of the shear fracture zone which is localized only in the immediate vicinity of the rupture plane. The increase in tensile strength leads to the enlargement of the shear fracture zone. The damage zone in supershear ruptures can have a complex, non-simply-connected structure. The change in the velocity of compression waves C_p by more than 15–20% is only observed in the immediate vicinity (within 10–20 m) of the sliding plane. At larger distances, a change in (frac{{dC}}{C}) is at most 10%. At shallow depths, tensile cracks may occur and propagate quite far from the sliding plane.

Abstract—The processes occurring during the interaction of crustal blocks in a subduction zone are reflected both in the features of the seismic regime and in the distribution of the major earthquake sources in the study area. In this study, we analyze the peculiarities of localization zones of the major earthquakes of the Kuril-Kamchatka arc based on two catalogs: the regional catalog of Kamchatka Branch, Federal Research Center, Geophysical Survey, Russian Academy of Sciences, and global international catalog of USGS NIEC of the US Geological Service for 1990–2024. Combination of catalogs based on a modified nearest neighbor method allowed us to remove duplicates—repeated earthquakes in initial catalogs—and to obtain a new unified catalog consisting of 52 574 earthquakes. The nearest neighbor method was applied to identify two subsets: independent and spatially and temporally clustered earthquakes, which were further used to analyze the density of seismic events. The obtained regularities were compared with the focal characteristics of the major earthquakes of the subduction zone. The proposed approach allowed us to identify localization zones of potential megaearthquake sources along the Kuril-Kamchatka arc.

Abstract—Monitoring of pore pressure or water level changes in observation wells shows significant variations both during the passage of P- and Rayleigh waves and during the passage of S- and Love waves. Recent borehole measurements have shown an azimuthal dependence of pore pressure variations on the stress orientation and strike direction of the fault zone. In the active fault zone, fracture-induced anisotropy corresponds to the preferred orientation of microcracks and other discontinuities in the medium. This paper is devoted to the development of a modified Skempton equation for a quantitative description of surface wave induced pore pressure variations in a reservoir, related to the orientation and principal values of the stress tensor and rock damage (fracturing). The developed relationships allow the azimuthal dependence of the pore pressure response to be described by a dimensionless parameter defined as the ratio of the amplitudes of the pressure variations caused by the shear component and the bulk strain. According to the proposed theoretical model, the maximum poroelastic response of the reservoir to the passage of a seismic wave is manifested in the case of subparallelism of the directions of predominant rock fracturing and maximum horizontal stress. Pore pressure monitoring data from the Arbuckle wastewater disposal reservoir (Oklahoma, USA) are used to verify the proposed theoretical model. It is shown that the observed diversity of pore pressure response in wells located in the vicinity of a fault zone intersecting the reservoir to the passage of seismic waves from seismic events at different distances is described with high accuracy by the developed model.

Abstract—Seismic interferometry method is used to extract detailed information about the dynamic processes and the properties of the inner core regions inaccessible to study by traditional methods. The method is based on cross-correlation time series analysis and applied to different data types. Cross-correlation analysis of seismic coda time window with a beginning three hours after a strong event and an end ten hours later is conducted for all possible pairs of more than 300 stations and six large earthquakes (for each separately) that occurred between 2013 and 2024. Synthetic cross-correlograms are calculated for models with different attenuation and an additional boundary in the inner core. Four different types of seismic interferometry analysis of the inner core have been carried out: global, regional, station latitude-dependent and calendar time-dependent. The study has demonstrated the stability of the PKIKPPKIKP wave on global correlograms, the possibility of its observation in regions with high and low density coverage by seismic stations, the dependence of the wave traveltime on the angle between the wave propagation direction and the Earth rotation axis, and the stationarity of the wave over a period from 2013 to 2024.

Abstract—Determining the properties of heterogeneous reservoirs from microseismic evolution data is an important problem in field development. Analyzing the propagation of microseismic events occurring during fluid injection/withdrawal provides valuable information about permeability and stress state of the reservoir. In this paper, we consider the inverse problem of determining reservoir filtration properties from microseismic event propagation data. For this, the influence of various geological factors on the distribution of microseismic event sources is investigated. Machine learning methods were used to identify correlations between geological model parameters and evolution of microseismicity. Due to the insufficient variability of in situ data, an artificial database of catalogs of microseismic events containing the coordinates of sources and their occurrence times was created to train the model. For this, numerical modeling of fluid injection and generation of microseismic events in synthetic models of permeable media with different geological structure was carried out. Thus, a comprehensive approach to the reconstruction of filtration properties of heterogeneous reservoirs from microseismicity evolution data using machine learning methods is proposed. This methodology can be applied to optimize field development, improve the efficiency of fluid recovery, and reduce the risks associated with the occurrence of undesirable anthropogenic seismic activity.

Abstract—In this study, we directly observed microcracks formed in a sample of rock under the action of uniaxial compressive load. Defects in the volume were detected by X-ray computed microtomography. A specific feature of the experiments is that a tomographic image of the sample was taken directly under mechanical load. Based on the analysis of tomographic slices, the fractal dimension and relative volume of microcracks were calculated at three stages of loading. Three-dimensional models of the defect structure were constructed to illustrate the change in the morphology of the main crack. Numerical experiments on the fracture of samples of heterogeneous materials were carried out using the discrete element model. The change in the fractal dimension of main cracks during their growth was investigated. Good agreement between the results of computer simulations and laboratory experiments has been established, which indicates the adequacy of the proposed model and allows in further studies to use it to study the behavior of local parameters that cannot be measured experimentally.

Abstract—The results of calculating the destruction, evaporation, and deceleration of stony meteoroids with sizes from 20 to 200 m in the Earth’s atmosphere are presented. The redistribution of thermal and kinetic energy between the condensed matter of the meteoroid, its vapors, and air is studied in detail. It is shown that when the size of the impactor is several tens of meters, the vaporized matter is not decelerated immediately, but flies along the trajectory for a long time, gradually transferring energy to the air. As a result, the main energy release in the atmosphere occurs at the stage of vapor jet deceleration, after the meteoroid and its fragments have completely vaporized.

Abstract—The description of foreshock and aftershock activation processes is of great significance in seismology both from practical and theoretical standpoints. An analogy between the mathematical expressions describing the seismicity patterns in the direct and inverse Omori–Utsu laws has been empirically established. Studies of the generalized vicinity of a large earthquake (LEGV, also abbreviated as GVLE) revealed an even closer analogy between the properties of foreshocks and aftershocks. This analogy also holds for the characteristics of the activation process, in particular, for the anomalous changes in the Gutenberg–Richter b-value. We propose a unifying model for the entire foreshock–aftershock process, which is described by kinetic equations with solutions in the form of strongly temporally localized maxima, called instantons by analogy with solitons for lozalized waves. A demonstrating example of an instanton solution is a graph of the time derivative of the logistic dependence describing a transient process. The rate of this process initially increases significantly, reaches a peak, and then asymptotically decreases to zero. The aim of this paper is to demonstrate effectiveness of the instanton model which generalizes the self-developing process (SDP) model but does not involve the formation of a physically unrealizable singularity typically simulating the explosive growth in the number of foreshocks and aftershocks in the vicinity of the main event. The new model is compared with empirical data from the earthquakes that occurred between 2003 and 2023 in the southern part of Sakhalin, an area with the best capabilities for seismicity recording. A reasonable consistency between theoretical and empirical time dependences is obtained both for the LEGV constructed for a region within 44.5°–50.5° N and 141.5°–143.5° E and for separate strong Sakhalin earthquakes.

Abstract—Some characteristics of seismicity in South Kamchatka are discussed. Parameters of the aftershock cloud of the August 17, 2024 large earthquake (M_w = 7.0) are studied. It is shown that ring-shaped seismicity structures in South Kamchatka have been formed in three depth ranges: 0–33, 34–70, and 71–110 km. As in other subduction zones, the structures are characterized in terms of limiting magnitude values—threshold magnitudes Mt1, Mt2, and Mt3, respectively, and lengths of major axes L1, L2, and L3. The epicenters of the August 17, 2024 earthquake and its strongest aftershocks fall in a shallow ring-shaped structure (Mt1 = 5.3), which supports the hypothesis of a preparation of a great earthquake in the South Kamchatka region. In the previous works, the correlation dependences of parameters Mt1 and Mt2 on the magnitudes M_w of large earthquakes have been constructed for the western Pacific (in the range M_w = 7.0–9.0). Using these dependencies, we estimated the magnitude of the great possible event in this region at M_w = 8.6 ± 0.2. The factors responsible for the formation of ring-shaped seismicity structures at different depths in the subduction zones are discussed.