Izvestiya, Physics of the Solid Earth最新文献

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.

Abstract—Deep seismic surveys along profile 5-AP were carried out in the northeastern shelf zone of the Arctic from the Chukchi fold region on the continent to the deep North Chukchi Basin. To process the experimental material of this profile, mathematical modeling based on the time field method was used, as well as the method of migration of fields of refracted and reflected waves recorded at large distances from the source. As a result, with a high degree of reliability, it was possible not only to identify new features of the structure of the Earth’s crust and upper mantle of this region, but also to determine the rheological properties of the material making them up and the degree of its rigidity or plasticity. This made it possible to propose a new model of the possible geodynamic evolutionary history of this region.

The article studies the possibility and accuracy of correcting the coordinates of a moving object according to data of a modern satellite model of the Earth’s gravitational field. A software implementation of modeling the readings of strapdown inertial navigation systems (SINS) is presented. Based on an analysis of various sources and modeling of the route corresponding to a real marine scientific expedition, the optimal parameters of the SINS modules were obtained. An algorithm for refining the coordinate position of a moving object based on the coordinate descent method is proposed. Regression analysis was used to derive a formula for the relationship between the mean square error of the gravimetric map and the horizontal gradient of the gravity anomaly (GA). A number of experiments were carried out to refine the coordinate position in areas characterized by different GA gradients with modeling of the errors of the relative gravimeter and gravimetric map. As a result of experiments, it was found that it is possible to determine the coordinate position according to model gravity data with an accuracy of 100–1900 m in areas with “large” GA gradients (from 2 to 6 mGal/km) and from 100 to 6400 m in areas with “small” GA gradients (up to 2 mGal/km), depending on the type and magnitude of the errors.

Abstract—A three-dimensional geoelectric model of the tectonosphere has been constructed, containing typical geoelectric heterogeneities at three structural levels: uplift and subsidence of the roof of the basement, conductive prisms in the consolidated crust, and asthenospheric uplift in the upper mantle. Synthetic magnetotelluric data were calculated, and their sensitivity to geoelectric structures was analyzed. A two-dimensional smoothing inversion of synthetic data was performed along two perpendicular profiles. Despite significant three-dimensional effects, the obtained sections quite accurately reconstruct the position of the roof of the basement, obtain rough images of crustal structures, and poorly resolve the structure of the mantle. The influence of random noise of different levels on the inversion results is assessed. In the future, it is planned to perform three-dimensional inversion of synthetic data.

Abstract—The relationship between seismic intensity of ground shaking and soil conditions is analyzed using a large set of records obtained in the zones of strong earthquakes by KiK-net vertical arrays (Japan). The observed seismic intensity is compared in pairs of stations with different V_S30 soil characteristics, equidistant from the epicenter. In total, more than 1300 station pairs for 45 seismic events analyzed. For most pairs (more than 970), an inverse dependence of measured intensity on V_S30 is obtained (i.e., the necessary condition for applicability of seismic rigidity method (SRM) is fulfilled). However, for more than 350 pairs, the measured intensity was higher at the stations installed on denser soils. A probable cause is that nonlinear behavior of soft soils under strong motions and the resonance effects in the ground layers were neglected when using SRM. Besides, a large scatter is revealed in experimental estimates of seismic intensity as function of V_S30 at a fixed earthquake magnitude and hypocentral distance. The seismic intensity estimates from the Blake–Shebalin equations with coefficients for Kamchatka and the Kuril Islands proved to be inconsistent with observational data, which indicates rather low accuracy of intensity prediction based on soil conditions and the Blake–Shebalin equation. Improving outdated approaches in building codes has been a pressing issue for many years.

Abstract—The paper examines the possibility of occurrence of global geomagnetic disturbances during earthquakes, events that have been documented by observations and reported in numerous publications in leading Russian geophysical journals. Validation of the above phenomenon could become a significant discovery in geophysics. Therefore, these results require thorough verification. The comparison of the disturbances presented in the publications with the data from high-latitude magnetometer stations has shown that all the morphological features of the long-period disturbances (with quasi periods of 10–40 min) identify them as characteristic manifestations of the activation of the magnetospheric-ionospheric current system in the auroral latitudes. Thus, the detected disturbances represent a mid-latitude response to electrojet variations in the auroral region and are not related to seismic activity. The short-period disturbances (with a characteristic period less than 1 min) proved to be either a coseismic geomagnetic response to a surface seismic wave or a burst of Pc3 pulsations of magnetospheric origin, occasionally coinciding with the occurrence of a distant earthquake. This study clearly demonstrates that the identification of anomalous disturbances requires the efforts of both earthquake physics specialists and space weather experts.

Issues of the influence of rock composition and depth level of dynamic mobility on its geomechanical regime are considered with a number of natural examples from noncoeval terrigenous, metamorphic, and magmatic complexes and geostructural positions by studying fault gouge and films of slickensides. The features of rock material alteration in weakly lithified strata of the near-surface part of the crust and in consolidated rock and mineral varieties of a slightly deeper level in the transition zone from aseismic to seismogenic behavior of faults are assessed. The article demonstrates the consequences of mechanochemical alteration of rocks of different composition, changes in the thermodynamic parameters of metamorphic reactions, their volumetric effects and thermal energy orientation, as well as the influence of mineral-phase and structural-textural rearrangements on the mechanical instability of the displacement zone, its strengthening or weakening during dynamic development. The structural and material markers of stable, aseismic slip along the fault and unstable seismogenic displacement are characterized.

Abstract—We consider the algorithms for solving linear inverse problems of gravimetry in the framework of discrete potential theory in the local version. The main focus is on ways to find a discrete analog of the fundamental solution of the Laplace equation in Cartesian coordinates in a three-dimensional (3D) space. The grid analog of the fundamental solution of the Laplace equation is reconstructed at the nodes of a regular 3D grid using the matrix sweep method. A system of linear algebraic equations (SLAE) is then solved to find the distribution of gravitating masses at the nodes of the same grid from the values of the grid gravitational potential known on some subset of nodes.