Izvestiya, Physics of the Solid Earth最新文献

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.

Abstract—A theoretical formalism has been developed to calculate the electromagnetic fields generated in the atmosphere–ionosphere system by a finite-length underground horizontal current source. A numerical model with a realistic profile of the ionosphere in a vertical geomagnetic field has been constructed based on this theory. It is shown that the apparent impedance of the electromagnetic field produced by an underground source on the Earth surface is an order of magnitude higher than the Earth impedance; this can be used to discriminate perturbations from seismogenic sources. The presented results of numerical modeling allow us to relate perturbations created by a large-scale underground source in the magnetic field of the Earth surface and in the electric field in the ionosphere. Based on these model estimates, it is concluded that many of the ULF electric field perturbations detected in satellite data prior to earthquakes cannot be attributed to direct emission from seismogenic sources.

Elastic properties in the medium can affect piezomagnetic fields. In the paper, the heterogeneity effect of elastic properties on piezomagnetic fields has been investigated by constructing different dislocation models. The results show that the burial depth of the source and elastic properties in near-surface layer affect the heterogeneity effect significantly. However, the heterogeneity effect can be neglected when the dislocation source is buried under 5 km depth. When the dislocation reaches the surface, the heterogeneity effect mainly depends on the elastic properties in the near-surface layer. The smaller the elastic properties in the near-surface layer, the larger heterogeneity effect. The non-uniform slip model can reduce the heterogeneity effect.

Abstract—The effect of water saturation of the medium on the property of earthquakes to trigger other earthquake shocks (earthquake productivity) is studied using the long-term seismological observations and water inflow monitoring data in the Khibiny massif ore deposits. The analysis indicates that water saturation of the medium is a significant factor affecting the productivity of earthquakes.

Ground-based measurements of the vertical atmospheric electric field of the Earth sometimes show bay-like anomalies that precede some earthquakes. In some cases, these anomalies have even been accompanied by a change in the sign of the field under fair weather conditions. Possible causes of this phenomenon are typically attributed to anomalous changes in the electrical conductivity in the near-surface atmospheric layer, increased radon emission from the soil, etc. This paper proposes another mechanism of atmospheric electrical anomalies, which involves the entrainment of charged aerosols as well as light and heavy ions by air flows. Such flows can be produced due to small temperature anomalies observed before some seismic events. Theoretical analysis shows that anomalously strong electrical variations may occur even in the presence of weak air flows provided that they persist for a long time and a peculiar structure of the velocity field, which presumes vertical air circulation and particle exchange between different atmospheric layers. For this type of flows, an analytic solution is derived and spatial distributions of atmospheric electric perturbations are obtained. The results of calculations and estimates confirm that the proposed mechanism can explain the observation data.

We determined the velocity structure of the upper crust in the Jiaodong area using double difference seismic tomography, and found that the Jiaodong inland area near the surface (0–5 km) is mainly characterized by high-velocity anomaly, and there are several obvious low-velocity anomalies in the Bohai Sea. The Queshan metamorphic core complex shows obvious low-velocity anomaly at the depth of 5–15 km, and the southern part of the Linglong shows low-velocity anomaly at the depth of 10–20 km. It indicates the existence of significant mantle material upwelling and magmatic activity beneath metamorphic core complex. The Linglong and Queshan metamorphic core complex may be still in the process of uplift. The high-velocity anomaly of the Wulian-Yantai fault is likely closely related to the basic to ultrabasic rocks from the mantle. The basic to ultrabasic rocks upwelling along the Wulian-Yantai fault zone is segmented and mainly concentrated in the southern of the fault zone.

Abstract—The paper presents the results of applying the Discrete Perfect Set (DPS) topological filtering algorithm to analyze the spatial clustering of seismic epicenters in the Baikal region. The study in based on the earthquake data recorded by the seismic network of the Baikal Branch of the Geophysical Survey of the Russian Academy of Sciences in the region between (48° N, 58° N) and (99° E, 122° E) from 1964 to 2018. Clustering characteristics are obtained for (i) the recording period from 1989 to 2018 with different parameters of the DPS algorithm and four levels of the minimum energy class K_Р of seismic events and (ii) six nonoverlapping time intervals from 1964 to 2018 and seismic events of energy class K_Р ≥ 8.6 with fixed parameters of the DPS algorithm. The dynamics of the clustering parameters from 1964 to 2018 possibly characterizes the variability of seismicity in the region. Namely, the decrease in the linear size of the identified groups of epicenters from about a thousand km to tens km may indicate a significant change in seismic activity in the Baikal region at the end of the 1990s and the beginning of the 2000s compared to the period between 1964 and 1997.

For the first time, the ₂S₁ and ₃S₁ modes of the Earth’s free oscillations after the largest deep-focus earthquake in the Sea of Okhotsk on May 24, 2013 have been analyzed based on the method of maximum likelihood estimation (MLE). Data from 14 superconducting gravimeters of the IGETS network deployed in the central part of Europe are used. Estimates are obtained for the time of mode excitation relative to the earthquake origin time, degenerate frequencies, and mode splitting parameters.