Izvestiya, Physics of the Solid Earth最新文献

Abstract—We study the records of ground motion vertical velocity in the vicinity of broadband seismic stations on the west coast of South America and in the adjacent region of the Pacific Ocean, where the M_w 8.8 earthquake occurred on February 27, 2010. Starting from 2009, asymmetric seismic pulses lasting several hundred seconds have been detected in records of some stations. These pulses occurred under quiet weather conditions and low geomagnetic activity. It is believed that the earthquake was preceded by tectonic movements in the oceanic and continental lithosphere.

The geological efficiency of seismic exploration and, as a result, the reliability of structural constructions in areas of intense tectonic dislocations (normal, reverse and thrust faults) is significantly reduced. At the same time, it is in such areas, that the presence of lithostratigraphic complexes contrasting in density or magnetic properties in the section and the abundance of subvertical boundaries provide prerequisites for the successful use of potential field methods (gravity exploration, magnetic exploration) to verify and supplement the structural interpretation of seismic exploration data. The paper presents the technology of complex interpretation of magnetic and seismic exploration data, tested on one of the objects of the Pechora Sea. In the course of the research, the connection of local magnetic anomalies with the seismic structural plan was established, which made it possible to identify and trace a magnetically active complex in the sedimentary strata with parameters typical of volcanogenic sedimentary rocks, weakly contrasting in seismic records. As a result of 3D modeling, the morphology of the roof and the base of the magnetic layer were determined, and the three-dimensional distribution of magnetization was calculated. It is proved that the sources of local magnetic field anomalies, a priori considered as isolated intrusive massifs, are associated with the distribution of magnetization within a single stratified volcanogenic-sedimentary strata. The obtained result was used in the construction of an updated geological and geophysical model. The developed technology is recommended as one of the promising approaches for building seismomagnetic models in similar physical and geological situations.

Abstract—The subsidence of the Earth’s surface, calculated from the theoretical model of a shear trough above a longwall developed by pillar and room caving are compared with displacements that can be estimated from trough monitoring using satellite images acquired from a single and two orbits. It is shown that the transverse and longitudinal axes of the trough do not shift when subsidence is calculated using data from descending and ascending orbits together. The maximum subsidence magnitude is determined almost without error. Errors in the reconstruction of the trough geometry appear where there is a significant northern displacement component, which, due to the characteristics of satellite radar imaging, is usually neglected. For the north‒south and west‒east trending troughs, these are their northern and southern boundaries; and for a trough trending from northwest to southeast, these are its northernmost and southernmost corners. In the maps of displacements in the direction towards the satellite (Line-of-Sight displacements, LOS), as well as in the subvertical displacement maps U_subv calculated using images from a single orbit, assuming that horizontal surface displacements are much smaller than vertical ones, the subsiding and uplifting areas are always shifted towards the satellite. Namely, in the displacement maps based on satellite images acquired from ascending and descending orbits these areas are always shifted to the west and east, respectively. The displacement magnitude is 50–60 m. The displacement direction of the longitudinal and transverse axes of the trough in the maps of subvertical displacements U_subv depends on their strike. The displacements of the trough axes relative to their real ground position should be taken into account when estimating the location of a shear trough from the maps U_subv of subvertical displacements derived from images from one orbit. In these maps, the maximum subsidence magnitude is approximately 10% larger than the displacements calculated from the trough model.

Modelling of the movements at the interface of the Amur and Okhotsk plates within the Sakhalin Island was performed using repeated satellite measurements on the Sakhalin Island and the nearest continental zone for the period of 2016–2021, as well as previously published data. When modelling fault-block kinematics, well-known relations were used to calculate reverse movements for buried rectangular dislocations in an elastic medium, which were implemented in the TDEFNODE software package. In the process of modelling the movements, the measured horizontal components of GNSS (Global Navigation Satellite System) velocities, the boundary and the mutual kinematics of the Amur and Okhotsk plates relative to the North American Plate according to the NNR-MORVEL56 model were used as the input data. This approach revealed persistent deviations in the direction of the simulated displacements of the Earth’s surface from the observed ones, which can be explained by the discrepancy between the a priori specified kinematics of the blocks and the observed movements. To eliminate the systematic discrepancy, it was necessary to allow the possibility of updating the mutual kinematics of the blocks. The repeated calculations, with the same input data but in a problem formulation that allowed refinement of block kinematics, led to suppression of systematic discrepancies between the model and measured displacements while retaining the random scatter. The movement parameters of the Amur and Okhotsk plates, which were refined during the modelling, show typical slight differences from the movement parameters of the corresponding large lithospheric plates (the Eurasian and North American plates), from which they are separated into independent blocks in modern constructions. The calculated locking coefficients in the Sakhalin segment of the interplate boundary reach maximal values at depths of 20–30 km. The obtained locking pattern at the plate interface is compared with the sources of the largest earthquakes in the last 30 years in the considered area, viz., Neftegorsk (May 27, 1995) and Uglegorsk (April 4, 2000) earthquakes, which are found to be associated with zones of maximal locking and a high locking gradient, both in the dip and strike directions.

Abstract— Long-term (1962‒2020) observations of air temperature and atmospheric pressure at two weather stations in the region of Petropavlovsk-Kamchatsky, Kamchatka Krai, are analyzed to examine the hypotheses about a connection between increased and decreased meteorological parameter values and their contrasting changes with a final stage of preparation of local Kamchatka earthquakes with magnitudes 5.2‒8.3, which occurred at epicentral distances of 22–440 km and caused perceptible shaking with intensity I_MSK-64 ≥ 4–5. To identify meteorological anomalies, we used an empirical method comparing daily mean air temperatures and atmospheric pressures with daily averages of their annual seasonal-mean functions and a formalized method estimating the minimum normalized entropy En, the logarithm of the curtosis coefficient logκ, and the autoregressive measure of nonstationarity Q² of the time series of air temperature and atmospheric pressure in a moving time window with a length of 112 days shifted by one day. Various types of meteoanomalies before earthquakes were studied on time intervals of seven and 30 days. The correlation between the detected anomalies and subsequent earthquakes was evaluated from the ratio of reliability and validity of the conditional meteorological precursor. It is found that the manifestation of various types of meteorological anomalies before earthquakes is mainly of a random nature. The lack of a pronounced correlation between air temperature increases and subsequent earthquakes casts doubt on the reality of the mechanism of generation of thermal surface anomalies before earthquakes in the lithosphere‒atmosphere‒ionosphere‒magnetosphere coupling (LAIMC) model for the study region. The methods used for meteorological data analysis can be applied in seismic forecasting in the region of the Petropavlovsk-Yelizovo agglomeration, Kamchatka Krai, for diagnosing weather-dependent anomalies in the changes of the ground-based observation data.

Abstract—A complex of archaeomagnetic and rock magnetic studies is conducted to compare the archaeomagnetic intensity determined by the Thellier–Coe and Wilson methods with the known “true” value of the geomagnetic field during the firing of the ceramic samples manufactured on February 21, 2017 in the town of Myshkin (Yaroslavl oblast, Russia). The results obtained show two different values of archaeomagnetic intensity corresponding to two temperature intervals. The archaeomagnetic intensity estimated from the low-temperature interval (~150–350°C) are approximately 13 μT lower than the true value, while the values obtained in the interval of ~350–600°C are fairly close to the “true” ones. The cause of the phenomenon is likely due to the presence of small magnetic grains in the ceramic under study, which are close in size to superparamagnetic ones and can resume their growth upon heating and reaching a particle size in a single-domain state. The results of rock magnetic studies suggest that thermoremanent magnetization in the studied ceramics is carried by grains of oxidized magnetite, hematite, and possibly ε-Fe₂O_3.

When studying the fault tectonics of the Vychegodskii trough, we detected an area of high concentrations of soil radon, confined to the zone of the Vychegda–Lokchim fault. To localize the radon anomaly, we carried measurements of the volumetric radon activity out over a network of observation points. Air sampling at each point was performed from the wellhead with a depth of 0.5 m and a diameter of 0.1 m. Based on the data obtained, an intense radon anomaly was contoured. At different times, the anomaly changed in the size, shape, and intensity, but its center always remained fixed. According to areal observations, in the central part of the 2 × 2-km anomaly, the radon concentration reached 3800–4800 Bq/m³. The results of continuous daily monitoring in the center of the anomaly showed that the of radon concentration is subject to daily dynamics, which directly depends on meteorological parameters, namely on temperature and humidity. At night, with a decrease in temperature and an increase in air humidity, the level of radon increased to 6000–8000 Bq/m³ on average, in rare cases up to 10 000–12 000 Bq/m³. In the daytime, with an increase in temperature, a decrease in the volumetric radon activity was noted. In addition to the daily dynamics, seasonal variability of the radon field was observed. In autumn, the radon concentration is lower than in summer, which is associated with short-term precipitation and, as a result, the filling of the pore space with water. The Archean–Early Proterozoic basement composed of gneisses, amphibolites, quartzites, and migmatites at a depth of 2 km is considered as the main source of radon. Due to the fact that the anomaly is located in the zone controlled by the Vychegda–Lokchim fault, the latter is considered the main pathway for fluid transport to the surface.

Abstract—The geodynamics of Northern Eurasia has been analyzed based on repeated coordinate solutions for GNSS stations throughout the Russian Federation territory from 2015 to the present. Two sources of data were used for this purpose: observations at the stations of the Russian Fundamental Astro-Geodetic Network (FAGN) and stations of the International GNSS Service (IGS) with permanent satellite tracking. This data set allowed one to estimate correctness of the block kinematics of the Eurasian plate in three tectonic plate motion models: NUVEL-1A, NNR-MORVEL-56, and ITRF2014. The analysis of the misfits between the observed and model velocities has shown that these misfits have a systematic component in the vicinity of the East European Platform, which differs for each of three models. In addition to analyzing the block kinematics of the Eurasian Plate, we also evaluated its internal stability. For this purpose, we calculated the areal deformations of Northern Eurasia using the finite element method. To this end, the processing results of two original datasets were complemented by the results for the observation data from the global dataset of the Nevada Geodetic Laboratory. Besides interplate boundary deformations, which are consistent with existing ideas of the geodynamics of Northern Eurasia, the strain field analysis also revealed intraplate deformations distributed consistently with the configuration of the Northern Eurasia cratons.

Abstract—As part of the international collaboration of several research groups from Russia, France, and Germany, 77 temporary seismic stations were installed in the summer of 2015 for one-year period to conduct a detailed study of the deep structure of the Earth’s crust and upper mantle in the region of the Klyuchevskoi Volcano Group (KVG), Kamchatka Peninsula. One of the results of the KISS experiment (Klyuchevskoi Investigation –Seismic Structure of an extraordinary volcanic system) was the final catalog based on the joint data from the temporary stations and the permanent network of the Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences (KB GS RAS). The catalog comprises 2136 events, including 560 for which the permanent network catalog lacked sufficient data for correct processing. The catalog in .xlsx format and the station bulletin in .isf format are presented in the supplementary material to the paper. A comparative analysis is performed of joint solutions of two catalogs, one obtained solely from the data of the KB GS RAS permanent network stations and another from a denser seismic network integrated with KISS stations.

Abstract—To describe secular geomagnetic variation on geological timescales, statistical models have been widely used in recent decades. Currently, the most popular among these is the TK03 model (Tauxe and Kent, 2004). As other statistical models, TK03 numerically characterizes the amplitude of secular geomagnetic variation and the shape of the distribution of paleomagnetic directions which are thought to directly reflect the directions of the geomagnetic field on the considered interval of geological time. For this purpose, three main parameters are used: the scatter S_b (or S) of the virtual geomagnetic poles, the elongation E of the distribution of paleomagnetic directions, and the elongation direction ({{D}_{{{{V}_{2}}}}}) of the distribution of paleomagnetic directions. The correct use of these parameters to describe paleosecular variation requires the fulfillment of certain, sometimes rather strict conditions. These conditions for parameters S_b and E were considered in a number of previous publications, while the limits and conditions of application of ({{D}_{{{{V}_{2}}}}}) have not been studied in detail so far. The results of mathematical modeling presented in this paper allow us to evaluate the stability of the calculated parameter values as a function of sampling latitude, the number of samples used to determine this parameter, the length of the time series from which this parameter is estimated, as well as the inclination shallowing and the degree of averaging if ({{D}_{{{{V}_{2}}}}}) is estimated from sedimentary rocks. We also consider the extent to which the ({{D}_{{{{V}_{2}}}}}) parameter can be sensitive to the presence and characteristics of the equatorial dipole component in the total geomagnetic field.