Volume 24, Nº 2 (2024)

An algorithm for identifying seismic generation zones or “seismic domains” using fuzzy logic has been developed and tested on the island of Sakhalin. Initial data were obtained from diagrams of the distribution of “weak” zones, relief elevation distribution skewness, and magnitude of recent area deformation for one year. These data were processed using a γ-operator in fuzzy logic with γ = 0.9, which allowed us to identify areas with high seismic activity. The areas where these active areas intersect with zones with increased compressive stress values, as determined by computer modeling, were considered to be seismic zones. It was shown that, if there are not enough source materials available, it is possible to exclude information about the recent deformation field from consideration and use an assumed grid of active faults for computer modeling. This approach may be useful when analyzing areas that have not been studied well.

The paper provides original data that shed light on the formation dynamics of Lake Chaika, which is situated in the central part of the Curonian Spit and is the only large water body in the sand spits of the southeastern Baltic. Based on the multi-proxy approach, incl. investigation of the lithological structure of the bottom sediment cores, loss-on-ignition analysis, diatom analysis, study of macrofossil remains, and radiocarbon dating, we revealed that Lake Chaika was formed already in historical time, around 200 years ago. Before this period, the lake kettle, presumably, has not submerged during the Littorina transgressions, enabling the terrestrial development of the ecosystems on the moraine protrusion. During the mid-late Holocene (6700–150 cal BP), this depression was occupied by the peat-forming fen and alder carr communities. The peat deposits are separated from the overlying layers of gyttja by the thin sand horizon. We consider it a time marker for the so-called “sand disaster”, which occurred on the territory of the Curonian Spit in the 18th century (≈1700–1800). The change in the hydrological regime of the lake launched the ecosystem shifts during the last two centuries: from the water body to a wetland and vice versa. It is stated eight formation phases of the lake’s ecosystem: the terrestrial development without wet habitats (8900–6700 cal BP), the period of alder carrs (6700–3400 calBP), the sedge fen period (3400–450 cal BP), the period of inundated forest (1500–1700 AD), the “sand disaster” period (1700–1800 AD), the period of eutrophic water body (1800–1900 AD), the period of terrestrialised wetland (1900–1950 AD), and the period of secondary development of eutrophic water body (after 1950 AD).

Native manifestations and deposits of precious metals of folded belts of surrounding of the North Asian and Sino-Korean cratons are of lesser resources and areas; that requires growth of research and technological potential for discoveries of the mineralizations. In Sikhote-Alin folded belt, which is typical example of boundary folded belts developed over a subduction zone, terranes of different age are described. Basements of these terranes are of accretion, island arc and turbidite origin, intruded by magmatic rocks and overlain by volcanic-sedimentary cover. Conducted researches consider area of island arc Kema terrane, which occupies large territories of the Strait of Tartary continental coast. Au-Ag deposits here are related to the origin and development of the active volcanic boundary. Genesis of the ore objects here is epithermal and related to intrusive and effusive complexes of Upper Cretaceous and Paleogene ages. Detailed field lithogeochemical surveys were held on a prospective Kolumbe site where Upper Jurassic–Lower Cretaceous siliceous and terrigenous rocks are intruded by Cretaceous granites of Tatibinski and Olginsky complexes. Research of the geochemical features was done using Principal Component Analysis, the effective method of dimensional reduction and data filtration. Implementation of that method in geochemical data analysis facilitates outlining of the associations of the elements by unifying them into principal components and discover their spacial distribution related to geological complexes of the research area. Determining of the number of principal components used explained variance covered by these components. Derived maps of the spatial distribution of principal components that include elements associations allowed to determine the locations of the local geochemical extrema. Grouping of elements into principal components made it possible to assume the staging in ore deposition in a prospective Kolumbe site. Conducted studies could invigorate further more detailed researches of the minerageny of the considered area.

Long-term calculations of the evolution of three-dimensional waves ranging from the early stage to energy stabilization were made on the basis of a two-dimensional phase-resolving model. The evolution of the main integral and spectral characteristics is analyzed along with the probability distribution for the elevation field and vertical velocity. The apparent property of self-similarity (i.e. the independence of the statistical structure of the field from the degree of wave development) for the wave field on the example of the first four moments for normalized fields of elevation and surface vertical velocity is shown. The conclusion is confirmed by the calculations with a three-dimensional model.

The paper is devoted to the study of the faults on Kunashir Island, focusing on their classification, morphology, kinematics, timing, and causes of formation, which are key to understanding the tectonic evolution of the area. The magma-supporting role of these faults is noted, contributing to the understanding of the distribution of volcanic and plutonic formations in the Great Kuril Ridge. The ore-controlling role of the faults was evaluated, which may contribute to the discovery of new mineral deposits. Additionally, studying these faults is important for improving the prediction of earthquakes and tsunamis. The research methodology includes an integrated approach that combines traditional geological observations with modern remote sensing methods, allowing us to detail the map of the Kunashir Island rupture faults. The results of the work confirm the presence of three systems of tectonic structures that differ in depth of emplacement, length, timing, kinematics, and causes of formation. The study contributes to our understanding of the complex geological structure of Kunashir Island and the entire island arc and provides a basis for further research in this area.