Izvestiya, Physics of the Solid Earth最新文献

The article presents the results of studies of modern movements and deformations according to GNSS observations in the area of Avacha volcano in 2015–2023. Studies of Avacha volcano are particularly important, because it is an active volcano closest to the administrative center of Kamchatka Krai. Interesting features of the local geodynamics of the area were revealed. Horizontal and vertical displacements, dilatation, and full shear deformations, as well as characteristics of the deficit of “internal” displacements were analyzed. In the southern part of the network, there is an accumulation of compression deformation due to pressure from the subduction zone. In the vicinity of the volcanic crater, tensile strain accumulates in the absence of significant uplift. The characteristics of the internal displacement deficit show the response of the GNSS network to the M6.5 earthquake (April 3, 2023) All changes in the characteristics of crustal motions and deformations demonstrated about a 2-year cyclicity. In further observations it will be possible to evaluate the stability of this phenomenon. Also noteworthy is the need to expand the GNSS observation network to the northern slope and foot of Avacha volcano for more detailed geodetic monitoring of its state.

The objective of the study was to assess the influence of the relief, defined in the form of a system of steep scarps, on the apparent resistivity curves and the parameters of geoelectric sections determined from them during magnetotelluric observations. It was solved using three-dimensional mathematical modeling of magnetotelluric fields using the finite difference method and the Maxwellf program. The dependences of the curves and the results of their one-dimensional inversion on the parameters of the blocks that make up the two- and three-dimensional models were analyzed. The distortions that shift the invariant curves of apparent resistivity calculated on the steps of the staircase model from the MTS curves measured on the plane ground-air boundary were estimated. In this case, the geoelectric parameters of the blocks located under the plane boundary are equal to those specified under the model with relief. The problem of constructing geoelectric models in conditions of stepwise changes in terrain can be solved using three-dimensional mathematical modeling of apparent resistivity curves, adjusted by normalizing coefficients that take into account the transition to a 3D model with a plane ground–air boundary. However, they depend on the period of variations. For this reason, it is more appropriate to evaluate the use of 3D inversion programs that include terrain topography in the initial 3D models. Before carrying out this procedure, it is necessary to know what shifts the apparent resistivity curves may have if the influence of the relief on them and the deviations obtained during their inversion of the geoelectric parameters of the sections from the test models are not taken into account.

Based on data from nuclear explosions along the Quartz profile, which crosses the Pre-Ural trough with the Urals and the West Siberian plate and is part of the Altai-Sayan fold region to the southeast, the structure of the lithospheric mantle and asthenosphere has been studied. A two-dimensional seismic model of the upper mantle has been constructed using the ray tracing method of the propagation of refracted–refracted and reflected longitudinal waves in a directly spherical approximation of the Earth’s shape. Regional structural-velocity heterogeneities of the two-layer mantle lithosphere with decreasing thickness toward the fold region and correspondingly increasing thickness of the asthenosphere were discovered. Particular attention is drawn to localization of a mantle heterogeneity corresponding to the location of the Koltogorsk–Urengoy rift graben. The distribution of residual mantle Bouguer gravity anomalies (recalculated to the base of the earth’s crust) shows a clear zoning corresponding to seismic inhomogeneities with a weak dependence on the Moho depth.

The characteristics of radiation and propagation of seismic waves in the Ural region are refined based on stochastic modeling of the records of local earthquakes. These characteristics correspond to transient characteristics from areas of stable continental seismicity to seismically active regions with crustal seismicity. A ground motion prediction equation (GMPE) describing the dependence of peak ground accelerations (PGA), peak ground velocities (PGV), and acceleration response spectrum amplitudes (SA) on rock soil on magnitude and distance is constructed for the Ural region. The GMPE is applicable in a wide range of magnitudes (M_W ~ 4–6.5) and distances (1–250 km) and can be used in seismic hazard assessment for the design and construction of earthquake-resistant structures in the Ural region. To account for the epistemic uncertainty of the estimates of seismic impacts in probabilistic seismic hazard analysis and construct a logic tree, five alternative modern GMPEs from other regions are selected: a global model for crustal seismicity, two models developed for the mountain regions of the Swiss and French Alps, and two models for regions of stable continental seismicity—eastern North America and Great Britain. These models are tested using the array of synthetic ground motion parameters. The equation for the Swiss Alps proved to be the closest to the GMPE developed for the Urals.

The article presents information on the development of a network of broadband seismic stations in the central East European Platform. Three new seismic stations have been installed: Udomlya (UDO), Borok (BROK), and Vladimir (VLD). Their recording capabilities were analyzed. It is shown that the use of data from new stations allows for successful detection and location of both teleseismic and local seismic events of various genesis. The location capabilities and quality of the data of the new seismic stations will further make it possible to characterize the structure of the Earth’s crust and upper mantle of the Fennoscandia and Volga–Uralia megablocks near their collision zone.

More than 30 years ago, the existence of a regular quasi-cyclic regime of seismicity was revealed at a qualitative level for the eastern regions of the North Caucasus (Dagestan and Chechnya) on an area of 300 × 300 km for the period 1800–1985. The regularity was that the level of seismicity during one cycle lasting 10–30 years decreased from the peak event (magnitude 5.0–6.5) to the background values, followed by a rapid increase in seismicity (during 2–3 years) until the next peak event. This hypothetical phenomenon was rigorously analyzed by us in a formalized way on the data of an extended catalog, including the year of 2022. The obtained result confirmed the existence of a regular quasi-cyclical change in the level of seismicity in the eastern part of the North Caucasus as a natural phenomenon. The revealed pattern can be used for medium-term prediction of seismicity and for testing seismicity models of the region.

Based on an archeomagnetic study of four ceramic fragments from two cultural layers of the multilayer archeological site Ivanovskoe III, the age of the ceramics is proposed based on the correlation with the VADM reference curve for the central part of the Russian Plain. For two ceramic fragments from the first cultural layer, the age of the Late Bronze Age, determined typologically and by the radiocarbon method, is consistent with the age determined by correlation with the VADM reference archeomagnetic data. Radiocarbon dates from undecomposed wood found in the peat layer beneath the second cultural layer have a wide range of values. Comparison with the graph of the VADM dependence on age for the central part of the Russian Plain allows us to state that one of the ceramic fragments found in the second cultural layer has a Neolithic age. For the second ceramic fragment from the second cultural layer, low VADM values were obtained, uncharacteristic of either the Late Bronze Age or the Developed Neolithic. A distinctive feature of samples with low VADM determinations is that they contain thermally unstable maghemite. The age of the second ceramic fragment may correspond to the Early Neolithic as a result of mixing of layers due to the economic activity of people who repeatedly inhabited this area.