ГЕОДИНАМИЧЕСКАЯ АКТИВНОСТЬ НОВЕЙШИХ СТРУКТУР И ПОЛЯ ТЕКТОНИЧЕСКИХ НАПРЯЖЕНИЙ СЕВЕРО-ВОСТОКА АЗИИ

Based on the analysis of changes in the stress-strain state of the crust at the boundary of the Eurasian and North American tectonic plates, we develop a dynamic model of the main seismogenerating structures inNortheast Asia. We have established a regularity in changes of geodynamic regimes within the interplate boundary between the Kolyma-Chukotka crustal plate and the Eurasian, North American and Pacific tectonic plates: spreading in the Gakkel Ridge area; rifting in the Laptev Sea shelf; a mixture of tectonic stress types in the Kharaulakh segment; transpression in the Chersky seismotectonic zone, in the segment from the Komandor to the Aleutian Islands, and in the Koryak segment; and crustal stretching in the Chukotka segment.Анализ изменений напряженно-деформированного состояния земной коры, проведенный вдоль границы Евразийской и Североамериканской литосферных плит, позволил обосновать динамическую модель главных сейсмогенерирующих структур территории северо-востока Азии. В пределах единой межплитной границы, отделяющей Колымо-Чукотскую коровую плиту от Евразийской, Североамериканской и Тихоокеанской литосферных плит, наблюдается закономерная смена геодинамических режимов: спрединг хребта Гаккеля; рифтогенез на шельфе моря Лаптевых; смешанное поле тектонических напряжений в Хараулахском сегменте; транспрессия в сейсмотектонической зоне Черского, на участке от Командорских до Алеутских островов и в Корякском сегменте; растяжение в Чукотском сегменте

Digital topographic analysis and lineament interpretation south of the Lena Delta, North Siberia: Landscape expression of its tectonic activity

This study applies semi-automated techniques to analyze the landforms, morphostructure, and geology of the Kharaulakh and Chekanovsky sectors, south of the Lena Delta, northern Siberia. High-resolution data, including TanDEM-X 30 m spatial resolution Digital Elevation Models (DEM), 2 m spatial resolution ArcticDEM Digital Surface Models (DSM), and Sentinel-2 satellite imagery, serve as the basis for the analysis. Digital terrain classification and identification of tectonic lineaments are performed using the Benthic Terrain Modeler (BTM) and Linear Extraction (LINE) algorithm, respectively. Additionally, a hypsometric analysis is conducted to assess areas of potential neotectonic activity. 873 lineaments are identified, primarily in NE-SW and E-W orientations. NW-SE lineaments perpendicular to the lithological and fold belt strikes in the Kharaulakh Ridge suggest inheritance from original depositional settings or later compressional tectonics, now appearing as valleys and weak zones facilitating erosion and river incision. Longer N-S or NNW-SSE lineaments in the Kharaulakh Sector are associated with thrust sheets of the Verkhoyansk fold-and-thrust belt and Cenozoic graben structures linked to the formation of the Laptev Sea Rift System and ongoing regional deformation. The Chekanovsky Sector, marked by epiplatform blocks and hills, presents a dissected plateau with steep valleys. Here, high hypsometric integral values are attributed to compression and uplift near the southwestern boundary of the Laptev Sea Microplate

ТЕКТОНИЧЕСКИЕ НАПРЯЖЕНИЯ В СТРУКТУРАХ СЕВЕРНОГО ПРИОХОТЬЯ (МАГАДАНСКАЯ ОБЛАСТЬ) ПО ГЕОЛОГИЧЕСКИМ ДАННЫМ

Tectonic fracturing of the Mesozoic and Cenozoic structures was studied in the Northern Priokhotie (Magadan region). The cataclastic analysis method and the statistical method of fracture density analysis were used to reconstruct their state of stress. It is revealed that the folded structures of the Arman’-Viliga synclinorium are subjected to horizontal shearing; the axis of maximum compression is sublatitudinal (azimuth 67°, angle 12°); extension is submeridional (azimuth 161°, angle 19°). In the Uda-Murgal volcanic arc, horizontal extension with shear takes place; the compression axis is directed to NW (azimuth 259°, angle 29°), and the extension axis to NE (azimuth 152°, angle 26°). In the Okhotsk-Chukotka volcanogenic belt, volcanic structures are in the field of varying tectonic stresses, from predominant horizontal extension to horizontal shear. The Cenozoic intermontane depressions of the Miocene – Pliocene ages are subjected to horizontal shear; the compression axis is directed to NE (azimuth 214°, angle 29°), and the extension axis to NW (azimuth 121°, angle 4°). The results of the comparative analysis of the stress states in the above-mentioned areas reliably show that the diversity of the stress state types is statistically related to the structural positions of the studies sites. Such diversity cannot be explained by an influence of active faults, or by any consecutive superposition of deformations at different stages, despite the fact that the deformations have complicated the observed pattern of the stress states. We conclude that each subsequent geodynamic stage only introduced additional elements into the previous structure, but did not completely transform it.Представлены результаты изучения тектонической трещиноватости в структурах мезозойского и кайнозойского возраста Северного Приохотья (Магаданская область). Напряженные состояния в изучаемых структурах восстанавливались методом катакластического анализа и статистическим методом анализа плотности трещиноватости. Было установлено, что складчатым структурам Армано-Вилигинского синклинория свойственны четко выраженные напряженные состояния типа горизонтального сдвига с осью максимального сжатия в субширотном направлении (аз. 67°, угол 12°) и растяжения в субмеридиональном направлении (аз. 161°, угол 19°). Структуры Удско-Мургальской вулканической дуги обладают напряженными состояниями типа горизонтального растяжения со сдвигом с осью сжатия в северо-западном направлении (аз. 259°, угол 29°) и осью растяжения – в северо-восточном (аз. 152°, угол 26°). Вулканоструктуры Охотско-Чукотского вулканогенного пояса характеризуются изменчивым полем тектонических напряжений с вариациями геодинамического типа от преобладающего горизонтального растяжения до горизонтального сдвига. Кайнозойским межгорным впадинам миоцен-плиоценового возраста присущи напряженные состояния типа горизонтального сдвига с осью сжатия в северо-восточном направлении (аз. 214°, угол 29°) и осью растяжения в северо-западном направлении (аз. 121°, угол 4°). Выполненный сравнительный анализ напряженных состояний показывает, что их разнообразие статистически достоверно связано со структурным положением и не может быть объяснено влиянием активных разломов территории или последовательным наложением разных этапов деформаций на территории, закономерно осложняющим наблюдаемую картину разнообразия напряженных состояний. Таким образом, каждый последующий геодинамический этап вносил в предшествующую структуру только дополнительные элементы, но не преобразовывал ее полностью

ГЛУБИННОЕ СТРОЕНИЕ И МОДЕЛЬ ФОРМИРОВАНИЯ КОНТИНЕНТАЛЬНОЙ КОРЫ ВЕРХОЯНСКОГО СКЛАДЧАТО-НАДВИГОВОГО ПОЯСА В ПОЗДНЕМ МЕЗОЗОЕ

The article considers the geological framework of a large orogenic structure in northeastern Eurasia - the Verkhoyansk fold-and-thrust belt (VFTB), formed in the Late Mesozoic on the eastern margin of the Siberian craton. Zoning of geopotential fields and the authors' interpretation of frequency-energetic characteristics along the 3-DV reference geo-physical profile provided the basis for modeling the deep structure of the VFTB and adjacent structures of the Siberian craton. There were identified structural zones of different geodynamic nature: the outer zone of the fold belt, underlain by the dropped margin of the craton; the inner zone of the VFTB with the oceanic crust at the base; the rear-zone structures formed by the Verkhoyansk complex in the subduction zone of the Uyandina-Yasachnaya island arc. In the Earth's crust of the VFTB there are distinguished two layers of approximately equal thickness: the lower one comprises a duplex system of complexes of the oceanic crust, and the upper one is built up by formations of the Verkhoyansk terrigenous complex, which have also undergone folding and duplexing. In parallel with thrusting of the upper terrigenous layer over the craton in the zone of collision between the VFTB structures and the Siberian craton margin there also occurred subduction of the lower layer of the VFTB under its margin. This led to an increase in thickness of the craton's crust by 5-10 km from below. The development of the Uyandina-Yasachnaya island arc system comprises two stages associated with blocking of the subduction zone and its transition towards the Oimyakon Ocean, which increased its area and complicated the structure. The paleosubduction zones and blocking structures are well-traced on the deep sections of reference seismic profiles.Рассмотрено строение крупной орогенной структуры северо-востока Евразии - Верхоянского складчато-надвигового пояса (ВСНП), образованного в позднем мезозое на восточной окраине Сибирского кратона. На основе районирования геопотенциальных полей, совместно с авторской интерпретацией частотно-энергетических характеристик по опорному геофизическому профилю 3-ДВ, построена модель глубинного строения ВСНП и прилегающих структур Сибирского кратона. Выделены структурные зоны, имеющие различную геодинамическую природу: внешняя зона складчатого пояса, подстилаемая опущенной окраиной кратона, внутренняя зона ВСНП с корой океанического типа в основании и структуры тыловой зоны, сформированные верхоянским комплексом в зоне субдукции Уяндино-Ясачненской островной дуги. В земной коре ВСНП выделяются два слоя примерно равной мощности: нижний сложен дуплекс-системой из комплексов океанической коры, а верхний - образованиями верхоянского терригенного комплекса, также подвергшимися складчатости и дуплексированию. В зоне столкновения структур ВСНП с окраиной Сибирского кратона, наряду с надвиганием верхнего терригенного слоя на кратон, происходило и пододвигание нижнего слоя коры ВСНП под его окраину. Это привело к наращиванию земной коры кратона снизу на 5-10 км. В развитии Уяндино-Ясачненской островодужной системы выделены два этапа, связанные с блокировкой зоны субдукции и перескоком ее в сторону Оймяконского океана, что увеличило ее площадь и усложнило строение. Следы зон палеосубдукции и блокирующих структур хорошо читаются на глубинных разрезах опорных сейсмических профилей

СЕЙСМОГЕОЛОГИЧЕСКИЕ, СЕЙСМОЛОГИЧЕСКИЕ И ИНЖЕНЕРНО-СЕЙСМОЛОГИЧЕСКИЕ ИССЛЕДОВАНИЯ ЛАБОРАТОРИИ ИНЖЕНЕРНОЙ СЕЙСМОЛОГИИ И СЕЙСМОГЕОЛОГИИ ИЗК СО РАН

The article presents recent results of seismogeological, seismological and engineering seismological studies conducted by the Laboratory. Specific features of seismicity in regions of Russia are reviewed. Space-and-time and energy patterns of seismicity and the state of stresses of the lithosphere are analysed. It is forecasted how foundations of buildings and structures located in the Baikal rift zone may be affected by potential strong earthquakes.   Представляются в обобщенном виде результаты исследований, полученные за последние годы сотрудниками лаборатории по вопросам сейсмологии, сейсмогеологии и инженерной сейсмологии. Рассмотрены особенности проявления сейсмичности в различных регионах России, проведен анализ пространственно-временной и энергетической структуры сейсмичности и напряженно-деформированного состояния литосферы. Дается прогноз сейсмических воздействий сильных землетрясений на основания сооружений в различных районах БРЗ.    

New Perspectives in the Definition/Evaluation of Seismic Hazard through Analysis of the Environmental Effects Induced by Earthquakes

The devastating effects caused by the recent catastrophic earthquakes that took place all over the world from Japan, New Zealand, to Chile, as well as those occurring in the Mediterranean basin, have once again shown that ground motion, although a serious source of direct damage, is not the only parameter to be considered, with most damage being the result of coseismic geological effects that are directly connected to the earthquake source or caused by ground shaking. The primary environmental effects induced by earthquakes as well as the secondary effects (sensu Environmental Seismic Intensity - ESI 2007 scale) must be considered for a more correct and complete evaluation of seismic hazards, at both regional and local scales. This Special Issue aims to collect all contributions that, using different methodologies, integrate new data produced with multi-disciplinary and innovative methods. These methodologies are essential for the identification and characterization of seismically active areas, and for the development of new hazard models, obtained using different survey techniques. The topic attracted a lot of interest, 19 peer-reviewed articles were collected; moreover, different areas of the world have been analyzed through these methodologies: Italy, USA, Spain, Australia, Ecuador, Guatemala, South Korea, Kyrgyzstan, Mongolia, Russia, China, Japan, and Nepal

Fluvial and permafrost history of the lower Lena River, north‐eastern Siberia, over late Quaternary time

Arctic warming and permafrost thaw visibly expose changes in the landscape of the Lena River delta, the largest Arctic delta. Determining the past and modern river regime of thick deltaic deposits shaping the Lena River mouth in north-eastern Siberia is critical for understanding the history of delta formation and carbon sequestration. Using a 65 m long sediment core from the delta apex a set of sedimentological techniques is applied to aid reconstructing the Lena River history. The analysis includes: (i) grain-size measurements and the determination of the bedload composition; (ii) X-ray fluorescence, X-ray diffractometry, and magnetic susceptibility measurements and heavy mineral analysis for tracking mineral change; (iii) pH, electrical conductivity, ionic concentrations, and the δ18O and δD stable isotope composition from ground ice for reconstructing permafrost formation. In addition; (iv) total and dissolved organic carbon is assessed. Chronology is based on; (vi) radiocarbon dating of organic material (accelerator mass spectrometry and conventional) and is complemented by two infrared – optically stimulated luminescence dates. The record stretches back approximately to Marine Isotope Stage 7. It holds periods from traction, over saltation, to suspension load sedimentation. Minerogenic signals do not indicate provenance change over time. They rather reflect the change from high energy to a lower energy regime after Last Glacial Maximum time parallel to the fining-up grain-size trend. A prominent minimum in the ground ice stable isotope record at early Holocene highlights that a river arm migration and an associated refreeze of the underlying river talik has altered the isotopic composition at that time. Fluvial re-routing might be explained by internal dynamics in the Lena River lowland or due to a tectonic movement, since the study area is placed in a zone of seismic activity. At the southern Laptev Sea margin onshore continental compressional patterns are bordering offshore extensional normal faults

Thermokarst and thermal erosion: Degradation of Siberian ice-rich permafrost

Current climate warming is affecting arctic regions at a faster rate than the rest of the world. This has profound effects on permafrost that underlies most of the arctic land area. Permafrost thawing can lead to the liberation of considerable amounts of greenhouse gases as well as to significant changes in the geomorphology, hydrology, and ecology of the corresponding landscapes, which may in turn act as a positive feedback to the climate system. Vast areas of the east Siberian lowlands, which are underlain by permafrost of the Yedoma-type Ice Complex, are particularly sensitive to climate warming because of the high ice content of these permafrost deposits. Thermokarst and thermal erosion are two major types of permafrost degradation in periglacial landscapes. The associated landforms are prominent indicators of climate-induced environmental variations on the regional scale. Thermokarst lakes and basins (alasses) as well as thermo-erosional valleys are widely distributed in the coastal lowlands adjacent to the Laptev Sea. This thesis investigates the spatial distribution and morphometric properties of these degradational features to reconstruct their evolutionary conditions during the Holocene and to deduce information on the potential impact of future permafrost degradation under the projected climate warming. The methodological approach is a combination of remote sensing, geoinformation, and field investigations, which integrates analyses on local to regional spatial scales. Thermokarst and thermal erosion have affected the study region to a great extent. In the Ice Complex area of the Lena River Delta, thermokarst basins cover a much larger area than do present thermokarst lakes on Yedoma uplands (20.0 and 2.2 %, respectively), which indicates that the conditions for large-area thermokarst development were more suitable in the past. This is supported by the reconstruction of the development of an individual alas in the Lena River Delta, which reveals a prolonged phase of high thermokarst activity since the Pleistocene/Holocene transition that created a large and deep basin. After the drainage of the primary thermokarst lake during the mid-Holocene, permafrost aggradation and degradation have occurred in parallel and in shorter alternating stages within the alas, resulting in a complex thermokarst landscape. Though more dynamic than during the first phase, late Holocene thermokarst activity in the alas was not capable of degrading large portions of Pleistocene Ice Complex deposits and substantially altering the Yedoma relief. Further thermokarst development in existing alasses is restricted to thin layers of Holocene ice-rich alas sediments, because the Ice Complex deposits underneath the large primary thermokarst lakes have thawed completely and the underlying deposits are ice-poor fluvial sands. Thermokarst processes on undisturbed Yedoma uplands have the highest impact on the alteration of Ice Complex deposits, but will be limited to smaller areal extents in the future because of the reduced availability of large undisturbed upland surfaces with poor drainage. On Kurungnakh Island in the central Lena River Delta, the area of Yedoma uplands available for future thermokarst development amounts to only 33.7 %. The increasing proximity of newly developing thermokarst lakes on Yedoma uplands to existing degradational features and other topographic lows decreases the possibility for thermokarst lakes to reach large sizes before drainage occurs. Drainage of thermokarst lakes due to thermal erosion is common in the study region, but thermo-erosional valleys also provide water to thermokarst lakes and alasses. Besides these direct hydrological interactions between thermokarst and thermal erosion on the local scale, an interdependence between both processes exists on the regional scale. A regional analysis of extensive networks of thermo-erosional valleys in three lowland regions of the Laptev Sea with a total study area of 5,800 km² found that these features are more common in areas with higher slopes and relief gradients, whereas thermokarst development is more pronounced in flat lowlands with lower relief gradients. The combined results of this thesis highlight the need for comprehensive analyses of both, thermokarst and thermal erosion, in order to assess past and future impacts and feedbacks of the degradation of ice-rich permafrost on hydrology and climate of a certain region

Mesozoic tectonic history and geochronology of the Kular Dome, Russia and Bendeleben Mountains, Seward Peninsula, Alaska

The tectonic history responsible for formation of the major basins of the Arctic and movement of landmasses surrounding these basins remains unclear despite multidisciplinary efforts. Most studies focus on one of four potential movement pathways of the Arctic Alaska-Chukotka microplate during the Mesozoic and the relationship between this movement and formation of the Amerasian Basin. Due to difficulty in access and harsh climate of the Arctic Ocean, most geological studies focus on landmasses surrounding the Amerasian Basin. For this reason, we have conducted research in the Kular Dome of northern Russia and the Bendeleben Mountain Range of the Seward Peninsula, Alaska in an attempt to better constrain timing of emplacement of plutons in these areas and their associated tectonic conditions. For both areas, U-Pb zircon crystallization geochronology was performed on several samples collected from plutons responsible for gneiss dome formation during the Mesozoic. Dating of these plutons in tandem with field observation and thin section analysis of deformation suggests an extensional emplacement setting for both areas during the Middle to Late Cretaceous.;In the Kular Dome, intrusion of the Kular pluton occurred from approximately 111-103 Ma along with extensional development of the nearby Yana fault, which was previously interpreted as a regional suture between deposits of the Kolyma-Omolon superterrane and passive-margin sequences of the Verkhoyansk Fold-Thrust Belt. Evidence for extensional emplacement of the Kular pluton includes top-down shear around mantled porphyroblasts plunging along gentle foliation away from the pluton and abundant low-offset normal faults in the area. The Kular Dome also falls into a north-south oriented belt of Late Cretaceous plutons interpreted to have been emplaced under regional extensional conditions based on geochemical discrimination diagrams.;Detrital zircon geochronology was also performed on seven samples collected from Triassic sandstones and Jurassic greywackes near the Kular Dome and compared to results from previously studied surrounding regions in Russia and the Arctic Alaska-Chukotka microplate in order to better define the relationship between the Arctic Alaska-Chukotka microplate and northern Russia during the Mesozoic. Results suggest that though the Chukotkan portion of the Arctic Alaska-Chukotka microplate was separated from the Kular Dome area during the Triassic, by the Tithonian it shared similar source regions for detrital zircon populations. Based on detrital zircon data from Chukotka, the Kular Dome, and the In\u27Yali Debin area, a new tectonic model for the formation of the Amerasian Basin and structures within is proposed. In this new model, Chukotka separated from and moved independently of the North Slope of Alaska during the Late Triassic-Early Jurassic, experiencing strike-slip emplacement along the northern coast of paleo-Russia and closed the South Anyui Ocean via transpression to form the South Anyui suture.;Geochronologic and geochemical results from the Bendeleben and Windy Creek plutons of the southeastern Seward Peninsula were also studied to better describe Arctic tectonic conditions during the Late Mesozoic. In this area, six samples were collected from the multiple lithologies seen within the Bendeleben and Windy Creek plutons and were also dated by zircon U-Pb geochronology and analyzed for their major and trace element geochemistry. Results suggest that the Bendeleben and Windy Creek plutons were emplaced during multiple extensionally driven pulses of magmatism above a southward-retreating, northward-subducting slab causing extension in the overlying crust from about 104 Ma to 83 Ma. The magma chamber at depth was experiencing continuous replenishment and liquid segregation causing stratification of the Bendeleben pluton. Magmas of the felsic cap, which now form the outer region of the Bendeleben pluton, were emplaced first, followed by subsequent intrusion of younger, mafic magma from below. Evidence for north-south directed extension during emplacement of the Bendeleben pluton was in the form of consistent east-west dike orientation in the Seward Peninsula, top-down shear in mantled garnet porphyroblasts from country rock surrounding the Bendeleben pluton, gentle foliation dip away from the pluton and stretching lineations around the pluton. Discrimination diagrams based on Rb, Nb and Y concentrations from bulk rock samples supports a collisional or volcanic arc province and is consistent with emplacement in an extensional environment above a subducting plate