Том 54, № 10 (2018)

This is an outline of the main results of the study of dust devils (a type of atmospheric vortices) with a focus on the mechanism of vortex generation in an unstable stratified atmosphere. In the approximation of ideal hydrodynamics, a new nonlinear model of the generation of convective motions and dust devils in an unstable stratified atmosphere has been developed. Using nonlinear equations for internal gravity waves, the model of generation of convective cell plumes has been investigated in the axially symmetric approximation. It has been shown that, in a convectively unstable atmosphere with large-scale seed vorticity, the plumes extremely rapidly generate small-scale intense vertical vortices. The structure of radial, vertical, and toroidal velocity components in these vortices has been investigated. The structure of vertical vorticity and toroidal velocity in vortex areas that are limited by radius has been examined.

Analytic data on anomalies of the tree-ring structure of Siberian larch on the transect, passing through the Russian part of the Altai-Sayan Mountain Region from the west to the east along the top forest limit, are given for the first time. Four extreme events (1783–1785, 1788–1789, 1812–1814, and 1884) have been determined by a microscopic analysis of the anatomic structure of tree rings (identification of frost, light-colored, and missing rings and fluctuations in wood density). These were periods of strong cooling in almost the entire area of the Altai-Sayan Mountain Region. The data correspond to archived historical materials. A comparison of dates of extreme cold periods with data on volcanic eruptions, the emissions of which reached the stratosphere (the Volcanic Explosivity Index VEI ≥ 4), has shown that they coincide with periods of the awakening of volcanoes such as Laki (1783, VEI = 4), Asama (1783, VEI = 4), Etna (1787, VEI = 4), Soufriere (1812, VEI = 4), Awu (1812, VEI = 4), Suvanosedzima (1813, VEI = 4), and Krakatau (1883, VEI = 6). Nevertheless, the trees in the studied area did not respond to the large eruptions of the Tambora (1815, VEI = 7), Novarupta (1912, VEI = 6), and Pinatubo (1991, VEI = 6) volcanoes. This difference in the reaction of forest vegetation to strong volcanic eruptions of the 19th–20th centuries may be explained by changes in the direction and speed of atmospheric streams, the mosaic pattern of stratospheric aerosols in the north of Central Asia after the eruptions of some volcanoes, and the warmer climate in the 20th century (which reduced the sensitivity of trees at the top forest line in the Altai-Sayan Mountain Region to volcanic eruptions due to the upward shift of the temperature limit of forest development).

The occurrence time prediction of the strongest earthquakes is one of most topical tasks of seismology. Appearing in the recent years, new observation methods for precursors of different nature can open avenues to achieve success in the field of medium-term seismic forecast. One such method is to observe the Earth’s surface deformation using the Global Positioning System (GPS). Such a region is the territory of South-Western China, where in 2008 occurred the catastrophic Wenchuan earthquake, which caused very large destruction of infrastructure and huge human losses. This GPS system has been in operation since 1991 in the eastern part of the Qinghai–Tibet Plateau, the Sichuan Basin, and the Yunnan–Guizhou Plateau. The results of these observations have already been published and can be applied to study of the activity and segmentation of faults. Until 2004, the measurement network covering the Longmen Shan fault zone and the adjacent territory consisted of ten major points and some additional ones. The 1991–2001 data of GPS observations show that in the Longmen Shan fault zone was recorded offset to the northeast with a relatively low rate of 2.3 mm/year. As a result of studying the surface horizontal deformation using GPS observations, it was established that the focus area in 1999–2007 (prior to the strongest earthquake of 2008) was characterized by anomalously low rates of horizontal movements. This was probably related to the accumulation of stresses in the crust. It can be concluded retrospectively that the results of GPS observations could be considered as a medium-term precursor of the 2008 Wenchuan earthquake, which showed the location of the future seismic source position. The length of the zone of relatively weak horizontal displacements exceeded 250 km, which statistically correspond to a magnitude about 8 earthquake. The seismic rupture system (with a total length of ~240 km, originating during the 2008 Wenchuan earthquake) was confined to the NE-trending Longmen Shan fault zone, which occurs between the eastern margin of the Qinghai–Tibet Plateau and the northwestern part of the Sichuan Basin. Immediately after the Wenchuan event, the pattern of distribution of rates of horizontal movements has greatly changed. The horizontal deformations spanned most of the territory adjacent to the seismic fault zone, and the Longmen Shan Fault Zone exhibited the tectonic reduction of the surface at the expense of reversed movements of fault wings toward each other. The amplitudes of horizontal movements at equal distance on both sides of the branch of the Yingxiu–Beichuan main seismic rupture to the west are reduced slowly, and to the east – quickly. The vertical coseismic surface deformation, registered using satellite geodesy in the epicentral area of the seismic event, were mainly expressed in the submergence of the surface by different amounts in the southeastern wing of the Longmen Shan fault zone in the Sichuan Basin. It can be concluded on the basis of an analysis of the total seismic energy release during the earthquake that the period of 1991–2007 was an evident stage of seismic calm period prior to the strongest earthquake, whereas a period of seismic activity has been registered since 2008 (at the moment of the major shake) up to the present and may last several more years. The extremely low rate of horizontal displacements in the epicentral area of the preparing strongest earthquake can be considered as a middle-term precursor of its occurrence place.

In geophysical studies, particularly when searching for precursors of earthquakes, there are problems of investigating the geoelectric structure of the medium at the observation point and its changes over time. This paper develops an approach to solving these problems based on the long-term medium monitoring data using the vertical electrical sounding (VES) method. The sounding was carried out daily for 12 years (from April 1979 to May 1992) in the central part of the Garm research area using a stationary multielectrode array. The data are used to construct about 4000 individual VES curves, which are then used to construct 36 10-day average curves for solving the inverse problem within a horizontally layered model using the IPI package. Four-, five-, six-, and seven-layer models of the geoelectric section are constructed based on the interpretation of the solutions. These models are compared by different criteria of their quality. As a result, a four-layer model is selected, which can be considered the best in the sense of minimizing the residual of the solution of the inverse problem, a horizontally layered approximation of the real (average for the seasons of the year) geoelectric section. A comparison of the available geological and geophysical data with each other and with the results of solving the VES inverse problem shows that the four-layer model of the section is in good agreement with the data of geological (drilling, geological mapping), geoelectric (transient electromagnetic sounding (TEM), profile VES), and other studies performed at the observation point.