编号 1 (2023)

The use of a special technique for processing variations of the geomagnetic field at several mid-latitude observatories allowed us to identify a series of jerks over a 17-year period, from 2004 to 2020. To interpret the experimental results showing that jerks follow with a quasi period of 3‒4 years, a probable mechanism of the occurrence of rapid changes in the geomagnetic field caused by unstable processes in the Earth’s core is proposed.

During the construction of strategic facilities, micro zoning is required to determine the peak values of terrain acceleration due to possible earthquakes. The acceleration of the soil in this case strongly depends not only on the power of the earthquake, but also on the earthquake source mechanism and the geodynamic state of the terrain. The known dislocation models of a single dipole with a moment and a pair of dipoles without a moment of the earthquake source mechanism satisfactorily describe the observed effects of the quadrant stress distribution on the Earth’s surface during earthquakes. When carrying out calculations within the framework of the theory of elasticity, the actions of the dipoles are expressed through volumetric forces. There are two known models of replacing the moments with equivalent forces: one of them is based on the equilibrium equations for an infinitely elastic space (Landau and Lifshitz,1965; Maruyama,1963), and the other is based on the representation theorem for elastic bodies, by introducing a singular internal volume, at the boundary of which there are dislocations (Vvedenskaya, 1969; Aki and Richards, 1983). Although these models involve moment effects, they themselves are derived from the momentless theory of elasticity. In our work, we propose a double dipole effect without a moment based on the moment theory of elasticity. The proposed model of the earthquake source mechanism is applied to solve the problem of stress variations in the Earth’s crust in Central Asia using the example of a particular earthquake with a simplified orientation of the rupture plane. Stress variation is understood as the difference in stresses in problems with and without an earthquake mechanism. Static stresses are obtained by solving the inverse elasticity problem with partially unknown boundary conditions. The lithosphere is a prismatic body consisting of several homogeneous blocks, the upper surfaces of which correspond to the relief of Central Asia. Verification of the results of the numerical solution is carried out by comparing the obtained stresses with previously established empirical values. As a priori stresses for solving the inverse problem, we used the solution of the elastic plane problem, the boundary conditions in which correspond to the lateral compression of the lithosphere of the region of the Indian and Arabian plates on the one hand, and the Eurasian plate on the other hand. The obtained solutions of the problem were used to analyze the geodynamic state of Central Asia. Based on the results of laboratory experiments, the unambiguity of the conclusions about the geodynamic state of the Earth’s crust (compression, extension) according to the Lode-Nadai coefficient, which are currently used by many researchers, is questioned. It is shown, contrary to earlier statements, that the values μ_σ = +1 and μ_σ = –1 can correspond simultaneously to both tension and compression cases, depending on the spatial form (ellipsoid) of the stress state. Geodynamic analysis of the Earth’s crust is carried out according to the Anderson method.

To obtain realistic and correct estimates of seismic effects in the Baikal Rift Zone (BRZ), a ground motion prediction equation has been developed based on the records of local earthquakes (magnitudes m_b ~ 3.4–5.5, hypocentral distances R ~ 15–220 km) obtained by Ulan-Ude and Severomuisk seismic stations. At the first step, in our previous works, using stochastic simulation of the accelerograms of the recorded local earthquakes we estimated the regional parameters of radiation and propagation of seismic waves (stress drop in an earthquake source, quality function of the medium, geometrical spreading, wave attenuation at high frequencies, local site amplification, etc. These parameters were then used to generate a set of earthquake accelerograms over a wide range of magnitudes (M_w ~ 4.0–8.0) and distances (R ~ 1–200 km) on a rock site, and a ground motion prediction equation (GMPE) describing the dependence of peak ground accelerations (PGA) and peak ground velocities (PGV) on magnitude and distance are constructed. The obtained PGA estimates are compared with those estimated from GMPE recommended for BRZ by the international Global Earthquake Model (GEM) project. The scatter of the estimates obtained based on GEM GMPE indicates the relevance of developing the own GMPEs for Russian regions based on the records of local earthquakes. The GMPE derived in this work can be used for seismic hazard assessment in the BRZ eastern part and will be updated as new data are acquired.

The magnetic properties and mineralogy of titanomagnetite in the Red Sea pillow-basalt at different distances from the contact surface with water were studied. It was revealed that the composition of titanomagnetite in the pillow basalt changes from the crust deep into the pillow: the titanium content in titanomagnetite increases, while the magnesium and aluminum content decreases. Titanomagnetite in the surface layer of pillow basalt (0–2 cm) is single-phase oxidized, with a maximum oxidation degree of 0.13, and at more than 3 cm from the crust has stoichiometric composition. According to the increase in magnetic susceptibility from 0.2 up to 1.8 × 10^–2 SI, saturation magnetization from 0.026 to 0.895 A m²/kg and residual saturation magnetization from 0.014 to 0.296 A m²/kg, decrease in coercivity (H_c from 90 to 15 mT, H_cr from 153 to 20 mT), as well as by observations of electron and magnetic force microscopy, it is shown that the concentration of titanomagnetite in basalt and the grain size from single-domain state to pseudo-single-domain state increase with distance from the crust. The magnetic hardness of titanomagnetite grains was found to correlate with the maximum cooling rate of basalt. The NRM of basalt varies non-monotonically with distance from the pillow surface: up to a depth of about 3 cm its growth caused by the growth of titanomagnetite concentration was revealed, then a decrease caused by a decrease in the magnetic hardness of the grains. In spite of a rather strong variation of the magnetic properties in the 0–7 cm layer of pillow basalt, the experiments by the Thellier-Coe method for all layers showed close values of the geomagnetic field paleointensity (62.5–66.0 μT) with a high value of quality coefficient q (11–45). No regularity in the value of paleointensity with distance from the cushion surface was detected.