Information on the strong Ilin-Tass (Abyi) earthquake recorded on February 14, 2013, in Northeastern Yakutia with Мw.=6.7 is provided. It arose to the Chersky seismotectonic zone (SZCH), which is part of the Arctic-Asian seismic belt that separates the Eurasian and North American lithospheric plates in Northeast Asia. The intensity of the shock at the epicenter corresponded to 9. The instrumental and macroseismic data, the focal mechanism, and the seismotectonic situation in the epicenter region are analyzed. The interconnections of the earthquake with the large regional Ilin-Tass fault are established. It is concluded that the occurrence of the Ilin-Tass (Abyi) earthquake occurred as a result of thrust displacements along the mentioned fault during the collision of the Eurasian and North American plates under compression conditions.

Magnetic exploration is the most informational and economical method of prospecting and exploration of iron-ore deposits. In rough-terrain and remote areas without any infrastructure, problems associated with ground-based methods can be avoided by using modern unmanned technologies that allow conducting geophysical surveys in a more efficient way. An unmanned aeromagnetic survey complex (aerial vehicle, UAV) Geoscan 401 was used to assess the possibility of using UAVs for aeromagnetic surveying of iron-ore deposits. Our experimental study was conducted in the well-studied area of the largest iron-ore deposit of South Yakutia. The UAV capacities were confirmed by comparing the aeromagnetic survey data with the available data obtained by ground magnetic exploration of the study area. By analysing magnetic fields, we established that the anomalies detected by the ground and aeromagnetic surveys were fully identical. Furthermore, a weak anomaly was discovered in the northeastern part of the study area (it was not reflected in the magnetic field from the ground survey data). Recalculation of the vertical gradient of the magnetic field shows that the anomaly is caused by a blind ore body. Its upper edge is located at a depth of 200–250 m from the day surface. In calculations for a data array without gradient intervals, a mean square error (MSE) amounts to 1.01 nT. An absolute error in the heights of the working and control flights did not exceed 1.5 m. Both the preliminary and control measurements were performed very efficiently. Profiles for UAV surveys were spaced by 100 m. A 1.0 km2 site was covered by one flight within approximately 20 minutes. The Geoskan-401 UAV is useful for obtaining orthophotos, topographic maps and 3D models of the surveyed territory as required for further studies consistent with the magnetic surveys. The aeromagnetic surveys were followed by trenching to verify the newly discovered anomalies. Based on the results of this experimental study, the forecast resources of the Sutam deposit should be increased by almost 250–350 million tons, i.e. plus 15 % to the previously explored and approved reserves of the Sutam field.

The results of the interpretation of seismological, geologic–structural, seismotectonic and macroseismic data obtained for the focal zone of the strong Ulakhan-Chistay earthquake (Ms=5.7), which occurred January 20, 2013 in the Chersky seismotectonic zone , on the Eurasia-North America lithospheric plates boundary, are presented. The shock occurred in the zone of a large Ulakhan fault, which is visible in satellite images and can be seen in the topography between the Indigirka and Kolyma Rivers at a distance of 1,500 km. Statistics of seismic observations in the last century and at the beginning of this century show that in the zone of influence of the Ulakhan fault within the crust (~ 35 km thick) at a depth of 7-30 km, more than 14 thousand local events were noted. The epicentral intensity of more than ten of them reached 6–8 on the Russian scale (MSK-64). In addition to high seismicity, additional geodynamic indicators of the reactivation of the Ulakhan fault in modern time were identified, in particular, high heat flux, icing processes, paleo-and modern seismic dislocations, etc.The macro effects of this event on an area of 300 thousand square kilometers were studied in three Arctic regions of Yakutia and in the south of the Magadan region and its epicenter is located by the proximity to the well-preserved paleoseismodislocation Uryun – Takh – Takh, which arose more than a thousand years ago and is clearly visible in the search sistem of Google. As a result, a structural-dynamic model of the Ulakhan fault zone is proposed, explaining the occurrence of the Ulakhan – Chistay earthquake on the basis of the kinematic scheme of the Omulevsky block, which is undergoing extrusion by a collision between the Eurasian and North American lithospheric plates in Northeast Asia.

––The first comprehensive seismotectonic study was performed in the Olenek and Vilyui areas of the Yakutian kimberlite province, which was aimed at elucidating the geodynamic activity of neotectonic structures of the Siberian craton and assessing the environmental hazard of groups of kimberlite fields. Based on the degree of activity and trend of geodynamic processes, we have developed regional principles for the classification of neotectonic structures of the Siberian craton and its fold-thrust framing with the rationale for their differentiation into classes. The active segments of the Verkhoyansk and Baikal–Patom fold–thrust belts are analyzed, which have a dynamic effect on the mode of tectonic deformations of the adjacent sections of the Siberian Platform, where groups of kimberlite fields are localized. The revealed patterns of seismotectonic destruction processes made it possible to establish the intensity and types of the Earth’s crust stresses and strains in the reactivation zones of the marginal sutures of the Siberian craton. Applying mathematical statistics methods permitted a quantitative analysis of the geodynamic parameters of the geologic environment in the Olenek and Vilyui areas of the Yakutian kimberlite province, based on the significant factors responsible for activation of the recent structures as manifestations of a single stress accumulation/discharge process in the Earth’s crust. Using the set of seismotectonic data, we have differentiated the activation zones according to the stress–strain intensity in the Earth’s crust and have assessed the potential environmental hazard of groups of kimberlite fields in the Yakutian diamondiferous province.

Quantitative estimates of present-day lateral ground surface displacement rates in southern Yakutia were obtained during recent years by setting up the first (and the only so far) stations of continuous GPS observation at the town of Neryungri (NRG) and at the town of Chul’man (CHL3). Both stations are in the southern margin of the Eurasian plate, near the system of active structures that separate it from the Amur plate. For an estimate of relative displacement we chose a period of joint operation at these two GPS stations, viz., from June 29, 2015 to December 1, 2016. The rate of displacement at Neryungri as calculated for a 5-year term (between October 27, 2011 and October 1, 2016) was 21.83 ± 0.73 mm/yr in the east–west direction and 12.26 ± 0.25 mm/yr in the north–south direction based on the ITRF2014 frame. The resulting values are little different from the theoretical rates of motion for the Eurasian plate at this point. The difference between measured rates and those for the well-known kinematic model for the Eurasian plate as developed in this study is |0.5| mm/yr for the east component and |1.0| mm/yr for the north component; these values are in agreement with results of other authors (Kreemer et al., 2014; Ashurkov et al., 2016). The accuracy of determination for the rates of lateral ground motion at CHL3 should enhanced by making measurements synchronously with the NRG2 station.

This paper presents seismogeodynamic analysis of modern structures located in the Lena river delta. These structures are key elements in the tectonic evolution of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates. The geological structure of the Lena river delta is predetermined by the junction of the ancient Siberian platform and the Mesozoic Laptev Sea plate. These two large geoblocks of the crust, which differ in age, are separated by a fragment of the Kharaulakh segment of the Verkhoyansk fold system. In our study aimed to reveal regularities in seismotectonic destruction of the crust, we analyzed the geological and geophysical data on the crustal structure, active faults, modern structural plan, dynamic characteristics of the modern relief, and hydrological features characterizing of the flow redistribution in the Lena riverbed. A system of active faults identified in the Lena river delta shows a contrasting kinematic plan of the junction zone of the main geostructures. According to the analysis results, shear faulting is a dominant factor of impact on the morphologic features and seismogeodynamic activation of the modern structures. A regional right-lateral strike-slip fault of the sublatitudinal strike is traced as a major structural boundary that cuts the Lena river delta into several geodynamic segments. Seismotectonic destruction of the crust in the segments differs in types (transpression, transtension and compression). The above-mentioned fault is not only the main element of the kinematic plan of the newest structures in the Lena river delta – it controls the general structural pattern and seismotectonic parameters of active fault zones in the entire northern sector of the Verkhoyansk marginal suture. The seismogeodynamic analysis results obtained in our study provide a reliable basis for estimating potential seismic hazard of the modern structures in the Lena river delta and updating the available seismic zoning maps of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates.

Our comprehensive study of the Russian Arctic region aims to clarify the features and types of seismotectonic deformation of the crust in the Arctic–Asian Seismic Belt, specifically in the zones of strong earthquakes in the Laptev Sea Segment, the Kharaulakh Segment, and the Chersky Seismotectonic Zone. We have analyzed modern tectonic structures and active fault systems, as well as tectonic stress fields reconstructed by tectonophysical analysis of the Late Cenozoic faults and folds. The investigated neotectonic structures are ranked with respect to the regional classification principles. Changes in the crustal stress–strain state in the lithospheric plate boundaries between the Eurasian, North American, and Okhotsk Sea Plates are analyzed, and regularities of such changes are discovered. A set of models has been constructed for the studied segments of plate boundaries with account of the dynamics of the regional geological structures. The models can give a framework for the assessment of potential seismic risks of seismogenerating structures in the Russian Arctic region.

For a quantitative assessment of the current horizontal velocity of the surface displacement of the crust in southern Yakutia in recent years, was organized the first and only points of permanent GPS observations in the city of Neryungri (NRG) and the city of Chulman (CHL3). Both points of observation are located within the southern margin of the Eurasian plate, near the system of active structures separating it from the Amur plate. To estimate the relative displacement, the period of joint operation of these two GPS points was chosen, namely from June 29, 2015 to December 1, 2016. The rate of displacement of the point in Neryungri, calculated for a 5-year period (from 27.10.2011 to 01.10.2016), was 21.83±0.73 mm/year in the East-West direction and 12.26±0.25 mm/year in the North-South direction in the international reference basis ITRF2014. The obtained values differ slightly from the theoretical values of the velocity of the Eurasian lithospheric plate at the specified point. The difference of the measured velocities with velocities according to the known kinematic model of the Eurasian plate obtained in this paper is |0.5| mm/year for the Eastern component and |1.0| mm/year for the Northern one and corresponds to the assessment of other authors [Kreemer et al., 2014]. To improve the accuracy of determining the speed of horizontal displacements of the earth's crust at the station CHL3, it is necessary to continue measurements synchronous with the station NRG2.

Для количественной оценки современных горизонтальных скоростей смещения поверхности земной коры в Южной Якутии в последние годы были организованы первые и пока единственные пункты постоянных GPS наблюдений в г. Нерюнгри (NRG) и в г. Чульман (CHL3). Оба пункта наблюдений располагаются в пределах южной окраины Евразийской плиты, вблизи системы активных структур, отделяющих ее от Амурской плиты. Для оценки относительного смещения был выбран период совместной работы этих двух GPS пунктов, а именно с 29 июня 2015 по 1 декабря 2016 гг. Скорость смещения пункта в г. Нерюнгри, рассчитанная за 5-летний период (с 27.10.2011 г. по 01.10.2016 г.), составила 21.83±0.73 мм/год в направлении восток–запад и 12.26±0.25 мм/год в направлении север–юг в международной отсчетной основе ITRF2014. Полученные значения незначительно отличаются от теоретических значений скорости движения Евразийской литосферной плиты в указанной точке. Разность измеренных скоростей со скоростями согласно известной кинематической модели Евразийской плиты, полученной в данной работе, составляет |0.5| мм/год для восточной компоненты и |1.0| мм/год – для северной и соответствует оценке других авторов [Kreemer et al., 2014]. Для повышения точности определения скорости горизонтальных смещений земной коры на станции СHL3 необходимо продолжить синхронные со станцией NRG2 измерения.

Research objective - determination of the quantitative indicators of seismic wave attenuation on the area of geotechnical landscapes with contrasting properties and the forecast of the seismic intensity impact within the area of study of the linear engineering structure in conditions of permafrost zone. During the research tasks were performed: study of the geotechnical structure of the area, registration of the microseismic disturbance, acceleration graph of the industrial explosions and powerful man-caused sources of the seismic waves. Main hypothesis of the study - contrast saving of the seismic properties of for-mation from geotechnical landscapes of rooted slopes and above floodplain river terrac-es in conditions of the permafrost zone. During the research complex of geophysical and seismological researches was performed, drawing of the geotechnical section confirmed by the drilling data. Results of the study confirmed main hypothesis - major difference of seismic properties of frost soils foundations for joint landscapes has been established.

Our research of the modern structures of Siberian Craton aims to reveal regional regularities in the seismotectonic destruction of the Earth’s crust and to clarify the dynamics of the formation of the focal zones of strong earthquakes. Analysis of activated structures and marginal suture zones located in the study area was based on structural and geophysical data, the modern structural plan, and the quantitative characteristics of modern and recent tectonic movements, active faults, and tectonic stress fields identified by tectonophysical analysis of deformation and seismological parameters. Unambiguous correlation between the seismic activity level of modern structures and the rates of modern and recent tectonic movements were not determined in our study. The most active structures of the Siberian Craton located in zones of the dynamic influence of marginal sutures are contrasted against the gradient field of modern vertical tectonic movements and characterized by the mosaic field of the mean and low rates of modern movements. The kinematics of seismotectonic deformation and levels of seismic activation of suture zones of the Siberian Craton are governed by global geodynamic processes taking place at the boundaries between the Eurasian, North American and Amur lithospheric plates. The activated structures in the northern regions of Siberian platform, which are characterized by the highest rates of modern movements, are heterogeneous. Both fluid processes and glacioisostatic movements may have influenced the dynamics of the formation of these high-gradient deformation zones. In seismotectonic studies aimed at determining levels of the potential seismic hazard of modern structures, we find it important to take into account errors in geodetic data and ensure more correct reference to the rates of tectonic movements at the neotectonic stage. In order to correctly assess the degree of geodynamic activity of modern structures, special consideration should be given to the fluid-geodynamic factor that controls most geodynamic processes, including tectonic stress accumulation, the formation of earthquake focal zones, and the intensity of seismic events.

Complex research to determine the stress–strain state of the Earth’s crust and the types of seismotectonic destruction for the northeastern sector of the Russian Arctic was conducted. The principles of regional ranking of neotectonic structures were developed according to the activity of geodynamic processes, and argumentation for their class differentiation is presented. The structural-tectonic position, the parameters of the deep structure, the system of active faults, and the tectonic stress fields, calculated on the basis of both tectonophysical analysis of discontinuous and folded late Cenozoic deformations and seismological data, were analyzed. This complex of investigations made it possible to determine the directions of the main axes of deformations of the stress–strain state of the Earth’s crust and to reveal the regularity in the change of tectonic regimes.

Impulse loads, arising due to the high natural seismicity of the South Yakutia region, exercise both direct and indirect effects on the upper part of the Earth's crust during industrial explosions. The direct effects result from nonlinear displacements caused by the blast wave and the subsequent formation of new disturbances. The indirect effects arise due to the activation of structural elements along geological contacts, leading to the emergence of technogenic seismicity foci. The foci of induced seismicity are either confined to the blast points, or located along the tectonic structures crossing quarry fields. The technogenic impact on the geological environment transforms the independent local seismic process, since explosions trigger a chain of local seismic events. The near-surface layers of the Earth's crust become activated in the area of dynamic influence of active faults. Under the influence of explosions, both the number of seismic events and the average level of released energy alter. Impulse loads on the geological environment lead to a spatial redistribution of the foci of low-energy (K <7) earthquakes. The main form of the geodynamic development of seismogenic faults is the movement of their sides in the form of mutual “slippage”. Seismic events are manifested only when the aforementioned form of deformation is impossible or difficult to develop, in other words, when the stress-state areas of the Earth's crust develop. Therefore, the shaking impact of blasts can be considered as a factor contributing to the predominance of aseismic forms of fault motion in the form of smooth slippage of their sides. In conclusion, the impact of industrial blasts can not only activate faults around the mining area, but also have an unloading effect on the foci of seismic hazard forming in the interior, i.e. the redistribution of earthquake energy in terms of reducing earthquake energy class.

Seismotectonic deformation and crustal stress pattern have been studied comprehensively in major seismogenic structures of the Kharaulakh sector of the Verkhoyansk fold system and adjacent parts of the Chersky seismotectonic zone. The study focuses on neotectonic structures, deep structure, and systems of active faults, as well as tectonic stress fields inferred by tectonophysical analysis of Late Cenozoic faults and folds. The results, along with geological and geophysical data, reveal main strain directions and structural patterns of crustal stress and strain in the Arctic segment of the Eurasia-North America plate boundary. The area is a junction of mid-ocean and continental structures evolving in a mixed setting of extension, compression, and their various combinations. The rotation pole of the two plates is presumably located near Buor-Khaya Bay. In this case, extension is expected to act currently upon the neotectonic structures north of the bay and compression to control those in the south and southeast. This inference is consistent with the identified zoning of stress and strain in the Kharaulakh sector. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.