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.

Cameroon is made up of an extensive tectonic system that includes a geologically significant structure in Central Africa called the Cameroon Volcanic Line (CVL). In this study, a multi-phase approach was applied to identify new tectonic structures across the CVL using gravity data from the XGM2019e_2159 model, magnetic data from EMAG2, and topographic data from GMRT. First-order and second-order vertical derivatives of both magnetic and gravity data were used to filter geologic structures in the study areas. To understand the trend of the structures based on the potential field, edge enhancement of potential-field data using normalized statistics (standard deviation edge detection) and phase sym­metry were applied. Phase symmetry provides phase-based formulation that can detect ridges and valleys corresponding to geological structures regardless of anomaly strength, making it robust to noise and interpolation artifacts. For de­tailed analysis to delineate new and already existing lineaments, a 2D Laplacian terrain transformation of the topographic data was computed at various heights from 20 to 105 km. The gravitational and magnetic structures discovered were superimposed on the transformed topographic map and drawn out to identify the orientation and direction of the faults. The study further illustrates the occurrence of potential geologic features associated with gravity anomalies, magnetic anomalies, and the new lineaments identified in the area. These results highlight that the lineaments identified are mostly orientated SE-SW and act as evidence of the still continuing process of deformation of the CVL. This finding is essential for advanced regional tectonic modeling across the CVL.

The paper presents the results of the combined analysis of the rock-magnetic and granulometric parameters of the sediments of two Upper Quaternary cross-sections having different genesis, as well as different lithological and mineralogical compositions: Bely Yar-1 (aeolian sands, Tunka rift valley) and Tukhuren-Nur (lake clay sediments, East Sayan). Each of these cross-sections reveals horizons with anomalous contents of fine-grained single-domain and pseudo-single-domain magnetic particles. Negative (or insignificant) correlation was found between different-sized sedimentary and magnetic grains therein, while all other horizon cross-sections show positive correlation between these parameters. It has been found that magnetic parameters of the analyzed sediments were changed due to aeolian fine-grained ferromagnetic volcanic matter input. The paper proposes to interpret the presence of this type of ferromagnetic grains in the Quaternary strata as a universally applicable marker of volcanic events in this region. The geochronological data avalible on the studied sections make it possible to estimate the age of these markers and to reconstruct two types of recent volcanic activity in Southwest Pribaikalye dating back approximately to 27 kyr BP and to 12 kyr BP. The pre-Holocene eruptions therewith are recorded synchronously in the Jom-Bolok volcanic field of East Sayan and in the Tunka rift valley, thus suggesting a single stage of the Holocene volcanic activity in the southwestern Baikal rift zone.

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 purpose of this publication is to show the importance of lithological study of sediments of different age and genesis, and to ascertain sedimentary affiliation in order to correctly interpret sediment genesis and reconstruct paleogeographic and paleotectonic events. Use has been made of extensive factual material collected by the authors during many years in different areas of Eurasia, as well as of the data from numerous publications by I.V. Khvorova.

The article discusses examples of modern and ancient sedimentary environments, and the interrelations of facies and formations. The complex indicators of sedimentary environments shown here are terrigenous and volcanic-sedimentary deposits, carbonate accumulation, silicon accumulation, and glacial activity. The article also shows the difference between inland and ocean basins, as well as the structural features of their margins.

Considerable attention is paid to syn-collisional sedimentation. Previously it was assumed that chronological alternation in a vertical cross-section reflects the evolution of a structure. The mobilist approach implies that such alternation could be due to various reasons, including horizontal oceanic plate movement either from spreading to subduction or from high to low biological productivity zone and horizontal continental movement from one climatic zone to another.

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 paper presents the results for Jurassic terrigenous rocks of the Urman, Peshkov, Tyumen and Maksimoyar formations, encountered in Severo-Ketskaya 1 parametric well, that have been studied thoroughly to re­construct the paleogeographic evolution of the southeastern part of the West Siberian petroleum province. Petrographic analysis reveals two sandstone associations: quartz graywackes and arkosic sandstones of the Early – Middle Jurassic age and mesomictic sandstones of the Late Jurassic age. Plotting the samples on the Q–F–L (quartz – feldspar – lithic fragments) ternary diagram shows the upsection decrease in proportion of acidic volcanic clasts with increasing detritus removal from the eroded quartz-rich sediment. Detrital modes on the QFL Dickinson diagram indicate an evolution of teggigenous source areas from volcanic arc settings in the Early – Middle Jurassic to recycled orogens in the Late Jurassic, driven by the Late Jurassic – Early Cretaceous orogenic uplift within the Kolyvan-Tomsk and Ob-Zaisan fold belts. U-Pb dating of detrital zircons documents a provenance shift from predominantly local Early Paleozoic sources in the Early Jurassic to primarily distant Upper Paleozoic and Jurassic source areas in the Middle – Late Jurassic. This evolution re­flects the Mesozoic intracontinental orogeny along the southeastern margin of the West Siberian basin and the southern margin of the Siberian Platform, associated with the closure of the Paleo-Tethys and Mongol-Okhotsk oceans. The upsec­tion increase in Mesozoic and Paleoproterozoic zircon populations from Early to Late Jurassic is interpreted as a response to intensification of tectonic activity along the southern margin of the Siberian Platform, whereas the terrigenous material was transported in the Pra-Angara river system. The integrated dataset constrains the likely sediment source areas and improves paleogeographic reconstructions.

The present paper aims to improve a typification scheme of some granitoid complexes in the Urals. The objects of study are the Arakul Shikhan leucogranites (Middle Urals), forming a large dike among the ancient paleogneisses within the contours of the Arakul block, which is adjacent to the eastern boundary of the Main Uralian fault. The description has been provided for mineralogical and petrographic features of granites and for P-T conditions of granite generation, the data have been obtained on the content of petrogenic components (XRF) and admixture elements (ICP-MS), and an attempt has been made to perform U-Pb zircon dating (LA-ICP-MS). It has been shown that two-feldspar, two-mica, garnet-containing leucogranites of the Arakul Shikhan are comparable to S-granites by the combination of petrogeochemical features. The plagiogneiss of the host Arakul formation (PR₂?) were the main components of the substrate for melting of granites. The magma may have been generated during the melting of muscovite in the presence of fluid flowing at Т=680 °С and P=4–5 kbar, at the degree of partial melting of the substrate <20 %.

The preliminary U-Pb zircon age estimates allow confining the leucogranite intrusion to the period 277–255 Ma; the leucogranites emerged at the final stage of collision which formed the structure of the Uralian orogen. Although the latest edition of the geological map assigns the Arakul Shikhan granites to the III phase granites of the Uvildy-Kisegach complex (Р₁?), the comparison between the granites of these two areas showed that they differ principally in their mineralogical composition and geochemical features, thus not implying the Arakul Shikhan granites are part of the Uvildy-Kisegach complex.

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.

A new approach has been proposed for solving inverse tectonophysics problem of detecting the optimal stress state from the data on the geological or seismological indicators of fault displacements. Stress inversion from such data has so far been based on finding maximum value of optimization function which determines the maximum similarity between the directions of displacements along the fractures visible in the outcrops and the directions of shear stresses for the sought stress state (Wallace-Bott hypothesis). The evidence presented herein shows that this condition meets perfect plasticity theory rather than post-peak deformation behavior of brittle rocks. This implies that in case of insufficient representativeness of one of the families of conjugate fractures the orientation of fractures of the most representative family will be similar to the maximum shear stress areas, not to the shift planes.

A new kind of optimization function proposed here is based on energetic characteristics of brittle failure and fits into the known patterns. The optimization function obtained should be considered the maximum principle characterizing a linear stage of thermodynamic state of the deforming geomedium, approximated by elastic blocks with friction at their contact boundaries (block piecewise medium after M.A. Sadovsky)

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.