Izvestiya, Physics of the Solid Earth最新文献

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.

Abstract—Numerical reconstructions of thermal history of the sedimentary cover in the region of the Dorado North well in the Mannar basin (Sri Lanka) and of the sedimentary blanket of the Ostaninskaya-438 well in the West Siberia Basin (Russia, Tomsk region), which were presented in (Premarathne et al., 2016; Isaev et al., 2021) are compared to the corresponding reconstructions for these areas using the GALO system for basin modeling. These examples show that using basin modeling systems with a given heat flow at the base of the sedimentary cover can produce an unrealistic thermal history of the basin, despite the fact that the calculated vitrinite reflectance matches the measured ones. The analysis of variations in basin tectonic subsidence incorporated in the GALO basin modeling system allows for an assessment of the amplitude and duration of thermal activation or stretching (crustal thinning) of the basin lithosphere. This approach avoids the challenge of setting the heat flow at relatively shallow basin depths. The constrained alternative model of basin thermal evolution, constructed in this way, is based on the same initial modeling database that is used in the basin modeling system with given heat flow at the base of sedimentary blanket; the only difference is the addition of the present Moho depth.

Abstract—The pseudo-Thellier method is numerically simulated based on a rigorous solution of kinetic equations for uniaxial randomly oriented noninteracting single-domain grains. Laboratory experiments have been performed to determine the relative paleointensity B_anc with thermoremanent magnetization (TRM) created in samples of igneous rocks in random fields B_rand; the domain structure of grains of these samples varies from single- to multi-domain. Both predicted and measured pseudo-Arai plots can be divided into two quasi linear segments, one in the relatively low-coercivity region B_c < 40–50 mT and the other at higher alternating field (AF) amplitudes. The determinations of relative paleointensity B_anc on TRM-bearing igneous rocks, estimated from low-coercivity segments of pseudo-Arai plots, give fairly good results with a linear correlation coefficient R = 0.8 between the true field B_rand and B_anc determined by the pseudo-Thellier method. It is shown that when thermal fluctuations for relatively small and magnetically soft particles (which corresponds to low blocking temperatures) are taken into account, a significant difference is observed between the coercive force B_cr of a grain and the actual field of its magnetization (demagnetization). The main conclusion of the study is that applying the pseudo-Thellier method to igneous rocks is promising. Further development of the methodological and practical aspects of this approach could yield interesting results, particularly when analyzing samples that are unstable to changes in magnetic minerals during the classical Thellier procedure.