Izvestiya, Physics of the Solid Earth最新文献

Abstract—In contrast to reversals, geomagnetic field excursions can occur at lower convection intensity in the Earth’s core. Since in such geodynamo regimes the magnetic field behavior is still quasi regular, a reduction in the dipole field during excursion may indicate a global failure in the dynamo process. As a consequence, it is possible that during the excursion, not only the dipole component, but also higher harmonics of the field decrease. This hypothesis is tested in a 3D (3D) dynamo model.

Abstract—This is our second paper concerning the study of earthquakes in Eastern Anatolia based on the information reported in the periodicals of the Russian Empire. We have made a systematic search of all the available Armenian, Georgian, and Russian language newspapers. This resulted in the first inventory of descriptions of the macroseismic effects from the June 29/July 12, 1900 earthquake, which were observed in 14 populated localities. Using these data, we determined the location of the epicenter and the magnitude of the earthquake. The macroseismic magnitude 5.9 precisely coincides with the instrumental magnitude reported in (Ambraseys and Finkel, 1987), while the epicenter location differs by 25 km. The epicenter location estimated in this work seems to be more reliable because its determination is based only on the original descriptions of the macroseismic effect.

Abstract—The manifestation of coast effect is studied based on magnetotelluric (MT) data from three profiles in the southern part of the Sikhote-Alin folded system (SAFS), which is bounded in the south and east by the Sea of Japan. It is shown that the coast effect barely distorts the MT apparent resistivity curves but is well pronounced in the behavior of the magnetovariational response functions. The analysis of the complex Wiese tipper and its real induction arrows in the northward and eastward directions has revealed the extent of the coast effect within the study area and the impact of the deep faults and conductive zones in the Earth’s crust and upper mantle on the manifestation of the effect. Three-dimensional (3D) numerical modeling is used to identify the key factors determining the behavior of the MT apparent resistivity curves subjected to coast effect for the conditions of the SAFS southern part and different geoelectric models.

Abstract—In 394 samples characterizing 266 stratigraphic levels in four Turonian–Santonian sections of the Southwestern Crimea, characteristic remanent magnetization components (ChRM) acquired at the stage of diagenesis are identified. The obtained data fix the record of the paleosecular geomagnetic variation of high amplitude (root mean square deviation S = 25.9° with a fixed cut-off angle of 45°, which is about twice as high as the model S for this latitude) in the sediments formed during ~5–6 Myr and is interpreted as anomalous behavior of the geomagnetic field in the Turonian, Coniacian, and Santonian.

For the eastern zone of the North Caucasus, including the Terek–Caspian trough, Dagestan wedge, and adjacent structures, with the maximum coverage of the data from the Federal network of seismological observations of the Geophysical Survey of the Russian Academy of Sciences (GS RAS), the regional frequency-dependent relations are determined using the Coda Wave Decay (CWD) method to estimate the seismic Q-factor of the Earth’s crust and upper mantle. In total, waveforms from 394 crustal earthquakes with source depths from 1 to 42 km and magnitudes М from 2.2 to 5.5 are analyzed using the Coda Q module of the SEISAN software package (Havskov et al., 2020). The seismic Q estimation technique using the single-scattering model is described in detail. Recommendations are given how to practically use the obtained estimates characterizing the wave properties of different-scale volumes of the fault-block geological environment to make attenuation corrections when calculating the source spectral parameters in the eastern zone of the North Caucasus. The results of the study will help to augment the information content of earthquake catalogs, in particular, with the data on energy characteristics of seismic events (universal moment magnitude values M_w) in the most seismically active regions of the Russian Federation.

Abstract—The study estimates the impact level of storm microseisms on long-term gravimetric measurements. The gravimetric measurements were conducted at the Zapolskoe, Obninsk, and Murmansk sites using CG-5 Autograv relative gravity meters. seismic measurements were conducted simultaneously with the gravimetric measurements at Zapolskoe. The analysis of these measurements has demonstrated the feasibility of using seismic data as control information to estimate the high-frequency noise component in gravimetric data. Additional seismic information was taken from the services of the Incorporated Research Institutions for Seismology. The analysis of these data established that the attenuation of the noise component in gravimetric measurements is consistent with the data from the modeled sensitive element of the gravimeter, which utilizes seismic series as an input. The first characterization of the storm-induced background noise in gravimetric measurements at the Murmansk site is obtained. Also, the possibility of predicting measurement errors based on meteorological forecasts is ascertained, which can aid in the planning of gravimetric work.

On January 8, 2022, an M6.9 earthquake occurred in Menyuan, Qinghai, which caused surface damage. In this paper, the line-of-sight (LOS) coseismic surface deformation field is obtained by the interferometric synthetic aperture radar (InSAR) of the Sentinel-1 satellite. Constrained by the InSAR surface deformation field, a Bayesian method based on sequential Monte Carlo sampling was used to invert the geometric parameters of seismogenic faults and the distribution of fault slip. Moment magnitude of the model is Mw6.6. The earthquake was determined to occur at a left-lateral strike-slip fault. Based on the historical strong earthquake dislocation model, the PSGRN/PSCMP program was used to calculate the Coulomb stress change at the epicenter of the 2022 Menyuan M6.9 earthquake caused by the surrounding historical strong earthquakes. The results show that the occurrence of the Gulang M8 earthquake in 1927, the Menyuan Mw5.7 in 1986 and the Menyuan Mw5.9 earthquake in 2016 caused a significant increase in Coulomb stress at the epicenter of the 2022 Menyuan earthquake. The coseismic and post-seismic Coulomb stress increases were greater than 0.01 MPa. Combined analysis of this result with regional tectonic stress, allows us to conclude that the 2022 Menyuan M6.9 earthquake occurred on the dynamic background of the continuous extrusion of the Indian plate towards the Eurasian plate, and the regional historical strong earthquake activity played a significant role in promoting it. The research results provide a theoretical basis for understanding the seismogenic background and dynamic mechanism of the 2022 Menyuan earthquake.

In recent theoretical studies of the authors, some estimates of the atmospheric disturbances related to inhomogeneities of the gravity field (IGF) have been obtained. The main attention was paid to dynamic effects: disturbances of the wind field under the influence of IGF. In this paper, attention is drawn to the fact that noticeable thermal effects of IGF can also exist in the surface layer of the atmosphere. These inhomogeneities, deforming the fields of pressure, air density, and air temperature, affect the temperature regime of the boundary layer and the heat exchange of air with the underlying surface. An analytical model designed to estimate the magnitudes of these effects is considered. Based on the proposed model, an analytical solution is found for a linear stationary two-dimensional problem for perturbations caused by one horizontal harmonic of the IGF in a semi-infinite stably stratified medium rotating around a vertical axis. The temperature of the lower boundary (underlying surface) was assumed to be fixed. It was also assumed for this boundary that the no-slip and no-flow conditions are satisfied. The attenuation of all disturbances with height was also assumed. The essential similarity parameters in this problem are analogues of the Rayleigh and Taylor numbers, in which the given horizontal scale of IGF serves a spatial scale. Analytical expressions are obtained for the profiles of temperature perturbations and amplitudes of deviations of vertical heat fluxes on the surface. The latter, along with amplitudes of gravity field inhomogeneities, depend most strongly on the background stratification of the medium. In highly anomalous regions, the amplitudes of heat flux deviations, according to the estimates obtained, may reach and even exceed 1 W/m², which gives grounds for taking into account the gravity field inhomogeneities in climatic calculations and numerical models of the atmosphere.

We investigate the contribution of gamma radiation of natural radionuclides constituting the Earth crust, radioactive emanations, and their decay product in the ground to the rate of production of ion pairs in the atmosphere against the background of ionization of the atmosphere by radioactive gases exhaled to the atmosphere from the ground and propagating together with their short-lived daughter products. The radon flux density to the atmosphere is estimated by three methods: the reservoir method, the integration of altitude profiles of volume activity of radon, based on gamma spectroscopic observations and the diffusion model. The distribution of the gamma radiation dose from the earth radionuclides in the soil and the atmosphere is calculated using Gleant4 software. The propagation of the radon isotopes and their decay products in the atmosphere is calculated simulated using large eddy simulation supplemented with kinematic simulation of subgrid flux of a passive scalar. It is shown that depending on the specific activity of radionuclides in the ground, the soil parameters, and the turbulent regime of the atmosphere, the total contribution of gamma radiation to the ion pair production rate in the atmospheric boundary layer is approximately from 1 to 20% and increases upon a decrease in the penetrability of the upper ground layer for radioactive emanations.