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No 5 (2025)
Articles
Tectonic position and seismotectonic manifestations of the March 28, 2025 Mandalay earthquake MW = 7.7 (Myanmar)
Abstract
The March 28, 2025 Mandalay Earthquake, with a magnitude Mw = 7.7 and its epicenter near the city of Mandalay, occurred within the zone of the major N‒S trending active right-lateral Sagaing fault. The earthquake generated a seismic rupture zone that extended mainly southward from the epicenter along this fault. Using radar interferometry and sub-pixel correlation of satellite imagery, the authors determined the parameters of the rupture zone. Its length is ~ 460 km, with right-lateral displacement reaching the maximum observed amplitude of 5.8 m. Given the hypocenter depth of 10 km, the seismic ruptures can be considered the surface expression of the earthquake source. The Sagaing Fault is associated with the ophiolite belt of Myanmar, which represents relicts of the Meso-Tethys paleo-ocean, displaced by Cenozoic tectonic movements. In northern Myanmar, where the Mandalay earthquake occurred, the ophiolite belt functions as the magmatic component of the submeridional northern segment of the Sunda island arc, beneath which the Indian Plate is subducting in a north-northeast direction. While the subduction surface is gently dipping near the front of the Sunda Plate, it experiences steep subduction further to the east. The Sagaing Fault lies above the eastern flank of the region of steep Indian Plate subduction. Beneath the region lies a mantle plume that reduces lithospheric thickness and causes softening of the lower crust. We suggest that the increased extent of the rupture zone of the Mandalay earthquake is due to the plasticity of the ophiolitic substrate, which facilitates rock slip, while the shallow depth of the hypocenter is related to the softening of the lower crust and upper mantle under the influence of the mantle plume. The significance of these factors is confirmed by comparing the Mandalay earthquake with the strongest earthquakes in Eastern Anatolia over the past 80 years, which occurred under similar tectonic conditions. These factors are supposed to be taken into account when assessing seismic impacts of major earthquakes
3-22
Stages of deformation and formation of the middle-late paleozoic collision structures of the paleocontinental sector of the southern urals
Abstract
The article presents the results of structural studies in the areas of distribution of folded structural complexes that formed the main structural-formational zones of the paleocontinental sector of the Southern Urals. The sequence of formation of meso-structural parageneses of these complexes is considered, the Middle-Late Paleozoic structural evolution of the study region is determined. Structural evidence of the previously assumed existence of the united Sakmara‒Krakinsky allochthon is obtained. The four stages of deformation, which are distinguished in the Hercynian deformation history of the Southern Urals region, are established. At the first stage of deformation (D1), the formation of F1 folds of southeastern and (rarely ‒ northwestern) vergence occurred. Stage D1 is associated with the oblique left-lateral collision of the Magnitogorsk island arc with the margin of the Baltica paleocontinent. The second stage of deformation (D2) is marked by the formation of F2 folds and associated thrusts of western and southwestern vergence. Stage D2 is associated with the movement of the Sakmara‒Krakinsky allochthon in the western direction. At the third stage of deformation (D3), the formation of F3 folds and co-folded thrusts of eastern and northeastern vergence occurred. Stage D3 is due to the processes of retrostriation, which occurred under conditions of sublatitudinal compression directed from east to west, when the package of allochthonous plates did not shift to the west. At the final stage of deformation, left-lateral folds with steeply dipping hinges were formed, which corresponds to post-collisional strike-slip movements. That stage completed the main phase of structural evolution of the Southern Urals region.
23-55
Relationship between local and regional stress fields of the Altai–Sayan folded region: results of structural-paragenetic and cataclastic methods of fault analysis
Abstract
Based on results of structural studies using the structural-paragenetic and cataclastic methods of disjunctive deformation analysis of the Altai‒Sayan and Western Sayan region that formed Altai‒Sayan folded area, a complex structure of the stress field of the latest stage was revealed. The lateral structural heterogeneities of the region determibe sihnificant variations in the stress field with the prevalence of a general shear deformation setting. In the study region, the submeridional direction of maximum horizontal compression is most clearly expressed. The manifestation of compression transversely and longitudinally to local and regional structures in which the orientation of the Paleozoic structural plan significally dominate, was also established. We consider the reason for the complex tectonics and geodynamics of the Altai‒Sayan folded area is in the activation of the Paleozoic disjunctive structures of the Alpine stage.
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Evolution of the Du Toit–Andrew Bain–Marion–Prince Edward transform fault system (Indian Ocean): Physical modeling of structural and kinematic changes in the late Cretaceous–Paleocene
Abstract
The Du Toit–Andrew Bain–Marion–Prince Edward transform fault system separates two parts of the Southwest Indian Ridge that differ in structure and development. The change in the extension direction significantly affected the structure of the transform faults, when in the period 69–52 Ma it was successively subjected to transtension and transpression, which led to the formation of multiple bends in its fault zones. A physical modeling method was used to identify the conditions of structural changes and the evolution of the transform fault during this period. It was experimentally shown that a complex structural pattern could only form under a certain combination of conditions, the most important of which are (i) the angle of inclination of the transform fault system to the direction of extension, (ii) the length of the fault segments, (iii) the ratio of the length of the fault segments to the length of the spreading segments. The experimental results suggest the development of passive trace bends as a transtensional duplex, which is confirmed by the long existence of the structure and its self-development. Almost identical results were obtained under transtensional conditions, in which the multitransform system gradually transforms into a single oblique transform fault under the influence of a gradual decrease in intertransform spreading segments. The possibility of formation intertransform ridges observed within the passive traces of the Andrew Bain fault, which remained as a result of the rotation of lithospheric blocks, was shown in two experimental series. Sharp structural and kinematic changes in the fault zone may be the result of a major regional tectonic reorganization during the collision of the paleocontinents of India and Eurasia.
75-91
Determining locations of possible earthquakes in the western Tien Shan using artificial neural network and a mathematical model of tectonic processes
Abstract
In this paper, we developed a numerical model of the stress state of the earth’s crust of the Western Tien Shan microplate to use as additional features for machine learning. An alternative to the deep learning models could be a neural network based on the Kolmogorov‒Arnold (KAN) general approximation theorem. What distinguishes KAN from existing machine learning networks is its interpretability, i.e. the ability to explain the “logic” of the model’s operation and high accuracy in complex physical processes. KANs differs from existing machine learning networks in its high interpretation and accuracy in complex physical processes. Unlike conventional networks, KAN neural network requires only one or two layers to obtain a solution to the problem, which significantly reduces the computing power. Using the KANs algorithm, we have built for the first time a neural network for classification and regression applied to the medium-term earthquake prediction in the Western Tien Shan microplate. The results obtained allowed us to predict the locations of possible earthquakes with a magnitude of 5 > M < 6 in environs of the city Tashkent (the Capital of Republic of Uzbekistan). The performed retrospective analysis of strong earthquakes that occurred in 2024 within the West Tien Shan microplate showed that the developed model predicts the locations of earthquakes with a magnitude of M < 6 with an accuracy of geographic coordinates of ±0.1° N, ±0.1° E and a magnitude of ΔM = ±0.4.
92-106