The present work studied the variations in ambient seismic noise within urban areas depending on the impact of anthropogenic factors: the operation of a thermal power plant (TPP), a hydroelectric dam, and road and rail transport. Frequency ranges of seismic radiation have been identified for various man-made sources. The discharge of steam at a TPP leads to an increase in the ambient seismic background noise level at frequencies from 6 to 18 Hz, while the calculated sound power level in the area of the Novo-Irkutsk TPP reaches 100–110 dB. An increase in water discharge at a hydroelectric dam leads to an increase in noise levels at frequencies from 0.1 to 40 Hz. Vehicle traffic produces ambient noise at frequencies from 5 to 15 Hz, with the noise level increasing by 1.3 times on weekdays compared to weekends. The decline in activity during the COVID-19 lockdown has led to a 1.13-time decrease in ambient seismic noise levels on weekdays and to a 1.09-time decrease on weekends in this frequency range 4–15 Hz. Trains passing in the near zone (several tens of meters) generate seismic wave radiation at frequencies from 5 to 30 Hz; an increase in the distance (up to a kilometer or more) provides a decomposition of the oscillation spectrum into two components: an increase in the range from 2 to 11 Hz with the maximum value attained at frequencies from 3 to 6 Hz and an increase at high frequencies – 32–45 Hz. Thus, each anthropogenic source is characterized by its own frequency range, which, together with the analysis of the recording form, makes it fairly easy to interpret an unknown source. The natural vibration frequencies of buildings are partially overlapped with the frequencies of seismic signals generated by road and rail transport and, to a lesser extent, by the operation of hydroelectric power plants, which can lead to the emergence of resonant vibrations and to a subsequent decrease in the strength and seismic resistance of buildings.
The first numerical 2D modeling has been performed of the effect of local crustal and lithospheric mantle decompaction on the surface relief and on the character of its temporal development by the example of the southern Sikhote-Alin. A numerical block model based on the current density model of the region made it possible to reveal the cumulative sequential effect of some anomalous crustal and upper mantle bodies and the shear effect along the Moho. The modeling has shown a probable relationship of the neotectonic movements, previously identified through the structurtal analysis, with the upper mantle decompaction and crustal granitization within the Sikhote-Alin orogenic belt. It is implied that the evolution of the current vertical movements within the southern part of the belt may be driven by: 1) relationship of the Mesozoic orogeny relief and its early-stage neotectonic development with the evolution of crustal and upper mantle density inhomogeneities; 2) the Sea of Japan opening with formation of the Tatar Straight trough and a synchronous occurrence of the Late Oligocene – Miocene basaltic volcanism.
The paper presents the results of the detailed geological structural studies of the Davenda-Klyuchevskoe ore cluster (Eastern Transbaikalia), including the Davenda Mo deposit, Klyuchevskoe gold ore deposit, and Borovoe ore occurrence. It has been found that the structure of the ore cluster is determined by a combination of heterochronous fault systems controlling magmatism and ore deposition. There are distinguished two main types of ore stockworks: linear (Davenda), confined to the North-Eastern fault system-1, and areal (Klyuchevskoe), formed at the intersection of the Shirotny, North-Western and North-Eastern-2 faults. It has been shown that the North-Eastern fault-1, initiated as early as during the consolidation of the Mongol-Okhotsk suture, controlled the intrusion of granitoids of the Amanan complex (159 Ma) and the subsequent formation of quartz-molybdenite veins. At the Klyuchevskoe deposit, there are distinguished three ore-controlling fault systems: Shirotny (right-lateral shear), North-Western (right-lateral shear) and the North-Eastern fault-2 (detachment). They formed during a short period about 150 Ma ago synchronously with the early stage of formation of the Amudzhikan-Sretensk complex and were accompanied by explosive processes which gave rise to the occurrence of complex brecciated ore bodies. Analysis has been made on the kinematic characteristics of faults and their relationships with dikes of different composition. The data obtained make it possible to update the structural-kinematic model of the ore cluster and to determine the relative age of mineralization.
Most of the existing stress field reconstruction methods involve fracture systems to determine the stress state in a small-volume geomedium. The principal stress axes orientations at a point can be reconstructed from a pair of conjugate fractures. Based on mathematical modeling of compression stress field in the shear zone, this article shows that even when only one of two conjugate fracture systems develops and another one does not or is not being formed at all, the shears of the existing system are formed at an angle to the local maximum compression axis. Therefore, when the compression failure point is in the linear part of the Mohr diagram, the formation of even one shear gives a lot of information concerning local principal stress axes orientations at the formation point. This information can be used under rather restricted conditions – with knowledge about the intermediate principal stress axis orientation and the considered-volume medium location at the moment of shear formation, but all this can be obtained, for example, in physical modeling. Successive formation of shears allows for accurate monitoring of the variations in principal axes orientations irrespective of whether the precise shear angle is known.
Presented here are the results of a comprehensive study of flysch successions common in the northern Abkhaz zone of the Greater Caucasus (Monastyrsky flysch). There have been micropaleontological analysis (nannoplankton), U-Pb dating of detrital zircons (LA-ICP-MS), and structural-kinematic studies. The fragment of the Monastyrsky flysch section, previously assigned to the Oligocene, has been dated back to the Miocene (or younger) epoch, its source areas have been identified, and an approach has been proposed for interpretation of flysch succession deformations, genetically related to the Monastyrsky fault. The Monastyrsky fault is paragenetically linked to the formation of the Vorontsov nappe and apparently remained active until recent times. The Vorontsov nappe, as well as the associated deformations, are not older than the Late Miocene. Study results of detrital zircons from sandy siltstones of the Miocene fragment of the Monastyrsky flysch have indicated that this flysch is not synorogenic with the Caucasus neoorogen. Most of the zircon grains from these rocks were most likely transported from platform-like structures northward of the Greater Caucasus orogen (ancient East European and young epi-Hercynian Scythian platforms) and their surrounding fold structures.
The key role of recent tectonics in the redistribution of the fresh groundwater resource base in the intensive water exchange zone is revealed. New approaches to the study of the conditions of formation and accumulation of groundwater in the upper hydrodynamic zone, as well as the assessment of their reserves and formation sources, were implemented through the integration of geomorphological and structural-hydrogeological criteria of water cut. A methodology is scientifically substantiated and hydrogeological criteria for searching for areas with localized fresh groundwater reserves in large depressions and elevations of the relief are developed. Based on a comprehensive hydrogeological and morphostructural analysis of the Irkutsk artesian basin of the second order (taking into account explored and evaluated deposits of fresh groundwater), the territory is detailed according to flow conditions, and high-performance collectors of the enclosing reservoirs are mapped (high filtration and transmissibility coefficients, renewable fresh groundwater reserves due to attracted resources – overflow from surface watercourses and reservoirs and natural resources – infiltration of atmospheric precipitation). The author outlines typical schemes of the formation of fresh groundwater deposits in the study area. Each scheme corresponds to deposits based on quantitative and qualitative characteristics, lithological and petrographic composition of water-bearing rocks, reservoir type and filtration indicators of production horizons, as well as the conditions of fresh groundwater formation. Deposits formed due to natural resources in positive direct and positive inverted morphostructures are distinguished. Based on the resources involved, deposits formed in positive direct, negative direct, and negative inverted morphostructures are distinguished. Within negative morphostructures (both direct and inverted), the production aquifers of fresh groundwater deposits are represented by pore-formation waters of loose Quaternary sediments. Within positive, straight morphostructures, fissure-formation and fissure-karst waters (outcrops of bedrock in which karst develops along fracture zones, forming a filtration field due to heterogeneous fracturing) of Jurassic and Paleozoic deposits are formed. Within positive, inverted morphostructures, fissure-formation waters of Jurassic deposits are formed.
The article discusses deep Earth crustal structure in the Baikal region, neighboring territory and Mongolia. The EIGEN-6C4 satellite gravity model-based Moho depth map was drawn for the territory with coordinates 43 to 61° N, 88 to 120° E. Gravity data interpretation was performed using seismic results obtained. The Bouguer EIGEN-6C4 model data interpretation was performed within the two-layer crust – mantle model with density diference 0.5·103 kg/m3. According to interpretation, Moho depth of the West Siberian Plate and Siberian Platform was estimated at 40–45 km with slight lateral variations, The depth decreases to 34–38 km near the Baikal basins. Strong lateral variations in Moho depth were obtained in mountainous areas south of the boundary going along the Main Sayan fault. The crustal thickness reaches 55–60 km in the area of active orogens (Mongolian Altai, Gobi Altai, Hangai) and decreases to 45 km in the Great Lakes Basin. The Stanovoi Range, Gobi Desert and Big Hingan have Moho depths ranging from 45 to 50 km. The southwesternmost part of the territory near Dzungaria, Tien Shan and Tuffan basin show the maximum drop of Moho from a depth of 40 km to 70 km. The Moho depth estimation error is from 2 to 4 km. The depths obtained for the Central Siberian Plateau and the Baikal basins generally correspond to the seismic data. The ground-based gravity data estimations do not contradict our results. The height anomalies of the quasigeoid model for the EIGEN-6C4 geopotential model relative to the WGS84 ellipsoid are found on the northwestern boundary of the Amur plate. The northern boundary of the Amur plate is clearly defined in the lateral distribution of the Bouguer anomalies and crustal thickness.
This paper presents the results of a comprehensive study of a catastrophic karst-suffosion sinkhole that occurred on September 19, 2024, in the Khadakhan-Melkhituy karst massif (Southern Angara region) and resulted in a human fatality. Using UAV‑derived data, the morphometric parameters of the sinkhole were determined (depth 9.7 m, volume 412 m³), and a comparison was made with historical monitoring data from the 1980s. Laboratory tests performed on samples collected from the sinkhole walls revealed that the 9.7‑m thick cover sequence consists of structurally unstable loess‑like loams and sandy loams, with anomalously high silt content (up to 84 %) and porosity (up to 64 %). The interaction between karst and suffosion processes plays a key role in the sinkhole formation. The long‑term (57‑year) backwater effect of the Bratsk Reservoir and its cyclic level fluctuations caused leaching of sulfate‑carbonate rocks, promoting mechanical removal of silt‑sized particles from the cover sequence by percolating water. A two-stage mechanism of karst-suffosion sinkhole development was identified: from the formation of a loosening zone above an ancient karst cavity to the instantaneous (brittle) roof collapse triggered by a technogenic factor – the weight of heavy agricultural machinery. The study of the reactivation of karst‑suffosion processes in the backwater zone of the Bratsk Reservoir contributes to the understanding of modern geodynamic processes and ground surface deformation mechanisms, including those induced by technogenesis.
The present paper deals with the use of a probabilistic spectral analysis in the study of statistical properties of the variations in Z-component of electromagnetic field during 14 days prior to the July 29, 2025, M 8.8 earthquake which struck off Kamchatka. Additional analysis has been made on similar data for 9 days after the event. The analysis showed persistent differences in the statistical structure of geomagnetic variations at four spatially spaced magnitovariational stations. The persistence of differences is evidenced by the fact that they re-arise during the variation of processing parameters (N1, M, h). The results obtained are consistent with the model of directed (anisotropic) effective current structure forming in the earthquake preparation zone. A simple geometric assessment based on the Biot – Savart – Laplace Law yields angular orientations comparable with an axial direction of seismic zone. The revealed differences do not correlate with the level of moderate geomagnetic activity of the period considered and may reflect large-scale anisotropy of magnetic response in the pre-seismic interval. The proposed approach is oriented at the analysis of statistical structure of geomagnetic variations and can be used to identify spatial features of strong earthquake preparation process. Further testing of the method on independent events is required to assess its practical applicability.
The modern geodynamics and seismicity of the Far Eastern region are largely determined by the interaction of the Eurasian, Pacific and North American plates, as well as by that of smaller Amurian and Okhotsk plates. Wellknown studies of the configuration and position of boundaries using geological methods are currently supplemented by the results of potential geophysical fields, seismology and space geodesy data interpretation. But despite the abundance of available information, there is ambiguity in location of interplate junction boundaries, particularly of the Amurian and Okhotsk plates, which makes it necessary to use new additional information about plate junction zones. The-past-twodecade deep seismic surveys along the reference geological and geophysical profiles make it possible to clarify the relationship between plate displacements and the deep structure of the Far East region. The comparison was made between the results of seismological and deep seismic sounding (DSS) (on the 1-SB and 3-DV reference geophysical profiles) and the existing geodynamic models in the Eurasian and Amurian lithospheric plates junction area. The confirmation has been provided for the ealier obtained seismic criteria of the boundaries in the Eurasian, Okhotsk and North American plates junction area, which involve a small crustal thickness (37–42 km), low boundary velocity along the Moho (7.85 to 8.0 km/s) and a reduced average (effective) velocity of longitudinal waves in the earth's crust (~6.3 km/s). The Eurasian and Amurian plates junction area along the 1-SB and 8-DV reference profiles is a wide stress zone with a maximum number of earthquakes, a maximum total released energy indicator and smaller hypocentral depths. The CDPM-based deep seismotomographic sections in this zone show an extremely heterogeneous middle crust, as well as poor reflections in the lower crust and in the Moho section.
The large Malo-Oinogor W-Mo deposit is located in the Zakamensk ore cluster of the Dzida ore district of the Western Transbaikalia. The W-Mo mineralization area is located within the Malo-Oinogor granite porphyry stock and surrounding metamorphic rocks of the Khasurta formation. The features of geological relationships with the surrounding rocks, as well as mineralogical-petrographic and geochemical features of the granite porphyries, indicate that the stock relates to the pre-ore stage and that the development of ore-bearing greisens occurred much later than the stock formation. The U-Pb (LA-ICP-MS) dating of zircons from granite porphyries of the Malo-Oinogor stock yielded an isotopic age of 310±2.5 Ma which does not correlate with the Mesozoic age of the granite porphyries from the Gudzhir intrusive complex, genetically associated with the W-Mo mineralization of the Dzhida ore district and, in particular, the Zakamensk ore cluster. The widespread occurrence of zircons, prone to lead loss, in the granite porphyry stock made it possibe to assess the probable threshold time of development of high-temperature hydrothermal metasomatism (132±6 Ma ago) in which U-Pb isotopic re-equilibration could take place. Within the margin of error this threshold time is comparable to the formation time of the Gudzhir ore-magmatic system (133–123 Ma). The formation of the Malo-Oinogor granite porphyry stock 310 Ma ago is due to the beginning of the formation of the Mongolian-Transbaikalian volcanoplutonic belt (PZ3–MZ1) during Mongol-Okhotsk orogeny which, in its turn, was related to the subduction of the Mongolian-Okhotsk paleooceanic plate beneath the southern margin of the Siberian continent. It is believed that W-Mo mineralization is related to hydrothermal activity, the source of which was the Early Cretaceous ore-bearing Gudzhir intrusive. The Gudzhir ore-magmatic system of the Zakamensk ore cluster was formed under tectonic extension during the Early Cretaceous Mongol-Okhotsk orogenic collapse. The arguments are presented for the fact that the Zakamensk ore cluster, to which the Malo-Oinogor W-Mo deposit is confied, is a promising area for the discovery of new deep rare metal reserves.
The Dzhida zone of the southern Baikal region comprises andesite-basalt and sedimentary-volcanic rocks of the Khokhyurt formation and the sandy-shale flyschoid Dzhida formation. This paper presents the results of lithogeochemical study of terrigenous deposits of the Khokhyurt and Dzhida formations, which demonstrate the evolution of terrigenous sedimentation during the geological development of the Dzhida guyot. Thin sandstone lenses of the Khokhyurt formation and turbidite sequences from the Dzhida formation contain mafic or intermediate clasts and fragments of carbonate rocks that composed the guyot caps. New geochemical data indicate that the flyschoid sequence from the Dzhida formation is similar in characteristics to the deposits of active rather than passive margins. Geochemical characteristics and highly fractionated REE patterns of sandstones suggest erosion of island-arc complexes that were contaminated with ancient crustal material during the early stages of their emplacement. Carbonate clasts of the Dzhida formation contain fragments of the Late Riphean and Early Cambrian carbonate formations, but lack the fragments of the Vendian formations that form the closely located margin of the Siberian craton. Nothing in the geochemical data suggests a direct supply of detrital material from the craton. The terrigenous strata of the Khokhyurt and Dzhida formations formed in deep-water fore-arc/back-arc basin settings on the active margin of the Paleo-Asian Ocean. The obtained data indicate that the Dzhida paleobasin was located at a considerable distance from the Siberian craton in the Late Precambrian and Early Paleozoic.
This study presents U-Pb dating results for zircon collected from the beaches of recreation zone "Peschanaya" (Sandy) on Lake Baikal. These beaches are formed exclusively by the erosion of Early Proterozoic rapakivi granites from the Primorsky Complex. Zircon from the granites yields a U-Pb age (ID-TIMS) of 1859±16 Ma, with an average U concentration of ~120 μg/g. Analysis of detrital zircon from the beaches of recreation zone "Peschanaya" was conducted using the ID-TIMS method on three aliquots and two in-situ methods – LA-ICP-MS and SHRIMP – on multiple (>600) individual grains. The new ID-TIMS and SHRIMP data are in complete agreement with each other, yielding ages of 1853.6±6.5 Ma and 1853.0±3.3 Ma, respectively. The LA-ICP-MS data, obtained in 7 Russian and 1 Chinese laboratory, are in general consistence with these results. Zircon from the beaches of the recreational zone "Peschanyа" is recommended as a secondary standard for U-Pb dating of early Precambrian samples.
The areal gravity survey conducted in Eastern Mongolia to investigate morphology and deep structure of the model Mesozoic granite massifs served as the basis for the field measurements using high-precision Scintrex Autograv CG-5 gravimeters in strict accordance with accepted methods for regional gravity surveys. The elevations of gravity stations were determined using Trimble 5700 GPS instrument, thus ensuring high accuracy of the vertical positioning and minimizing the errors in gravity anomaly calculations. The accuracy of the derived Bouguer gravity anomalies, together with the density of the observation network, fully meet the technical requirements for 1:100000 surveys, which ensures data reliability and validity. A detailed Bouguer anomaly map was prepared based on the processed data. Gravity field inversion enabled three-dimensional modeling of the granite massifs. Based on the derived geometry and dimensions of the bodies, as well as considerations of isostatic uplift, it is inferred that the development of positive relief landforms is associated with the upward displacement of granite bodies along the faults whose existence and activity in Eastern Mongolia have been theoretically and experimentally proved.
Studies have been made of the Abai alkaline rocks massif, located in the northeastern part of the ChingizTarbagatai zone of Eastern Kazakhstan. The Chingiz-Tarbagatai zone of Eastern Kazakhstan is located in the western part of the Central Asian Orogenic Belt (CAOB), the lithospheric evolution of which continued during the Paleozoic and was associated with the basin closure in the system of the Paleoasian Ocean. The 9 km² massif is characterized by an isometric shape with a clearly defined concentric zonal structure and represents a multiphase intrusion composed of several varieties of syenite. Potassium feldspar is the most prevalent mineral in syenite, while plagioclase, pyroxene (5 to 15 vol. %), and amphibole (5 to 20 vol. %) are less common. Most of the massif is composed of nepheline syenite rocks containing 5–10 vol. % of nepheline. Accessory minerals include apatite, zircon, and ilmenite. Studies of mineral composition and geochemical characteristics of the rocks revealed that the syenites formed during the evolution of a single magma melt composed of alkali-syenite or monzonite. This magma was formed probably as a result of primary alkaline-mafic magma differentiation. The U-Pb LA-ICP-MS dating of magmatic zircon grains for the first time yielded a relibale rock age estimate of 401–398 Ma, which corresponds to the Emsian stage of the Early Devonian. This refutes the previously accepted ideas about the Early Permian age of the massif and its intraplate geodynamic nature. When the data on the composition and age of the massif are compared with the data on the geological evolution of the region, it is apparent that the Abai syenite massif formation is related to the extensional processes in response to subduction of the Junggar-Balkhash oceanic lithosphere underneath the Chingiz-Tarbagatai zone.
When the maxima on the relative probability density curves of age of detrital zircons from the basal sandstones of the of the Riphean prototype (Ai and Bol’shoi Inzer formations, Southern Urals) are compared with the time intervals of formation of potential detrital zircon sources in the East European and Siberian cratons, ~1.7 Ga ago located immediately west and east of the area of accumulation of sediments originally comprising these formations, it is apparent that they are substantially similar to each other. This suggests that the detritus in the basal strata of the Riphean stratotype could be derived from rock complexes of both cratons. All of the aforesaid may represent an example of the so-called parallel tectonomagmatic evolution of cratons and draw the attention of researchers to the possibility of obtaining multivariate models for the formation of detrital zircon populations in sandstones based solely on U-Th-Pb isotopic dating of detrital zircons.
The results presented here concern the U-Pb (ID-TIMS) geochronological studies of garnet from ore-bearing skarns of the Granatovoe deposit (Irba ore field, Eastern Sayan). The studied garnet is represented by polychrome grains. It has been found that the studied garnet is similar in composition to andradite (98–100 %), though some of the parts of the marginal zones show the presence of a grossular component (no more than 5 %). On the boundary of the central zone composed of brown garnet and the periphery of the crystals, there is a zone made up of andradite-grossular garnet, where the aluminum content often exceeds the iron content. Polychrome zonation in garnets from magnetite skarns of the Granatovoe deposit reflects a complex combination of diffusion and infiltration metasomatism. High mobility of iron away from the contact in the early stages of skarn formation gave rise to primary brown andradite in the exoskarn zone. A subsequent increase in metasomatism intensity provided formation of high-aluminous garnet and its growth on early andradite. The granite-hosted molybdenite inclusions are a characteristic feature of the ore association and other iron ore deposits of the Eastern Sayan. Studies have been made of garnet fragments from concentrically zoned polychrome grains. It has been found that the central dark-colored zones of andradite composition are more enriched in uranium (25–29 ppm) than the outer light-colored zones which demonstrate a much lower uranium content (3.5 ppm) and a significant loss of radiogenic lead (Pbc/Pbt=0.67). A thermal effect on garnet during the late metasomatic processes caused diffusion of lead in the outer zones, while the U/Pb system remained almost unchanged in the central parts. The data obtained are the first "direct" age estimate of magnetite mineralization of the Irba ore field (503±6 Ma; MSWD=1.3). Age consistency between gabbroid volcanoplutonic complexes in other areas of the Altai-Sayan region suggests a simultaneous occurrence of the Early Paleozoic iron ore mineralization within the eastern segment of the Altai-Sayan folded region and gives grounds to recognize the iron-ore metallogenic epoch at the accretion-collision stage of the Altai-Sayan folded region development.
The 3-DV seismic profile data interpretation was used to obtain a geodynamic model for the deep structure of the southeastern margin of the Siberian craton and the South Verkhoyansk sector of the Verkhoyansk fold and thrust belt (VFTB). A determination has been made of the craton boundary, as well as of its reflection in the geological structure and geophysical fields. The model shows the mechanism of formation of thrust complexes on the craton margin and a compensatory underthrust beneath the craton of the lower crustal horizons of the fold-thrust belt, and explains the causes of abnormal RT-conditions reflected in the nature of the manifestation of metamorphism, magmatism, metallogeny and disjunctive tectonics. Using tectonic zoning, the parameters of the model are extended to the structures of the Southern Verkhoyanye and adjacent areas, which made it possible to determine the deep boundaries of the cratonic structures and their borders formed on the oceanic crust. The first are the margins of the Siberian craton and the Okhotsk terrane, the second are the adjacent VFTB structures. The boundary zone between the craton and the VFTB exhibited tectonomagmatic structures with high metallogenic potential. The obtained data make it possible to interpret the tectonic structure and development of the orogenic belt on the craton margin, and to relate the stages of its evolution to large Late Mesozoic geodynamic events in northeast Asia.
This article provides a geological, geophysical and geochemical description of the Dachnoye hydrothermal deposit (the central part of the Iturup Island, Kuril Islands), located in a zone of the modern tectonomagmatic activity. The results reported in the article describe the detailed thermal and geochemical studies within the deposit. This work presents the sublatitudinal geological and geothermal section of the deposit based on drilling and logging data. A statistical analysis of shallow-depth temperature survey of the deposit in an area of 6 km2 (over 1300 measurement points) allowed us to determine the sites where thermal mineral waters reach the surface and to characterize the tectonic features of the deposit area. Regarding the chemical composition of the waters, this area has a promising potential for balneological development.
