Seismotectonic Deformation Research Articles

Retrospective Medium-Term Forecast of a Catastrophic Earthquake in Turkey in 2023 (02.06.2023, MW=7.7) Using the LURR Method

Variations of the LURR (load-unload response ratio) earthquake medium-term forecasr parameter in combination with changes in seismotectonic deformation modes (STD) for the East Anatolian fault region, where catastrophic earthquakes occurred in February 2023 (06.02.2003, MW=7.8, 06.02.2003, MW=7.6) are considered. The depth of the earthquake catalog for the LURR method calculations was equal to 23 years, and estimates of STD modes were possible received since 1976. Calculations have shown satisfactory results in detecting LURR anomalies before strong earthquakes. Almost half of the anomalies occurred in the one and a half year period before the doublet, and are unambiguously associated as precursors. The precursors were recorded by two series of LURR parameter anomalies in 2021 and 2022, and the calculation areas in which they were recorded compactly cover the East Anatolian fault, including the epicenters of the earthquakes on February 6, 2023. The results of calculations using the LURR method were compared with the reconstruction data using the STD method. As a result, it was possible to build the dynamics of the earthquake preparation process in its final part – from the appearance of the LURR anomaly to the earthquake. At the same time, the period before the appearance of anomalies (since the 1976) was also taken into account. It is shown that during the period of abnormal LURR behavior (the forecast period), the most significant changes in the geodynamic regime were observed, as well as a sharp increase in total seismic activity.

Not too old to rock: ESR and OSL dating reveal Quaternary activity of the Periadriatic Fault in the Alps

The Periadriatic Fault system (PAF) ranks among the largest post-collisional structures of the European Alps. Recent geodetic data suggest that a fraction of the Adria–Europe convergence is still being accommodated in the Eastern Alps. However, the historical seismicity records along the easternmost segment of the PAF are ambiguous, and instrumental records indicate that seismotectonic deformation is mostly concentrated in the adjacent Southern Alps and Dinarides. Both electron spin resonance (ESR) and optically stimulated luminescence (OSL) dating methods can be used to date coseismic slip (with a combined range covering a few decades to a couple of million years) in slowly deforming fault zones, such as the PAF. Since the saturation doses of the quartz ESR signals are larger than quartz and feldspar OSL, ESR enables establishing a maximum age of the last resetting event of the system, while OSL allows constraining their minimum age when the signal is in saturation. We collected fault gouge samples from three localities along the easternmost segment of the PAF. For ESR, we measured the signals from the Al center in quartz comparing the results from the single aliquot additive dose (SAAD) and single aliquot regenerative (SAR) dose protocols. For OSL, we recorded the infrared stimulated luminescence signal at 50°C (IR50) and post-infrared infrared-stimulated luminescence signal at 225 °C (pIRIR225). Our dating results indicate that the studied segment of the PAF system accommodated seismotectonic deformation during the Quaternary, with a maximum age for the last resetting event of the system ranging from 1075 ± 48 to 552 ± 26 ka (ESR SAR) and minimum ages in the range from 196 ± 12 to 281 ± 16 ka (saturation of pIRIR225). The obtained ages suggest that the studied segment of the PAF could be considered at least as a potentially active fault.Graphical abstract

SEISMICITY AND CRUSTAL SEISMOTECTONIC DEFORMATIONS OF THE ANATOLIAN PLATE (TURKEY)

The paper deals with the study of seismicity and the crustal stress-strain state of Turkey whose tectonics is caused by relative movements of the African, Aegean, Arabian, Anatolian, Black Sea and Eurasian plates. Seismotectonic deformations (STD) were calculated using the approaches proposed by Yu.V. Riznichenko and S.L. Yunga. The distribution of seismicity, average annual STD rate (STD intensity), seismogenic rupture concentration parameter and the Tsallis parameter was plotted from the earthquake catalog data analysis (more than 300000 events for 1900–2022). The representative part includes the events with М≥2.5. The distribution of the above-mentioned parameters was calculated for a 0–40 km layer wherein most of the earthquakes are located. Deep-focus earthquakes occur at a depth to 170 km. The maximum annual number of earthquakes (more than 90) was recorded in Balikesir Province. Seismicity and STD intensity analysis was made on the periods of 1997–2009 and 2010–2022 for the western and eastern parts of Turkey and for the destructive February 6, 2023 earthquake area. The number of earthquakes recorded in the western part of Turkey (75 %) largely exceeds that recorded in the eastern part (25 %). In the period 2010–2022, there was an increase in the number of earthquakes in the eastern part of Turkey relative to the period 1997–2009, which made up 38 % of the total number of earthquakes. The studies of STD direction are based on the earthquake focal mechanism data (807 events for 1976–2023). STD intensity in the February 6, 2023 earthquake area, with regard to the February 6, 2023 earthquakes, is 1.34⋅10–6 year–1, and the background intensity for the entire period of observation (1900–2022) is –10–10 year–1. The STD maps show the diversity of deformation settings in the study area. Turkey is largely dominated by the horizontal shear mode (eastern and central parts). The extension mode manifests itself in the southwestern part. The western part of Turkey and the southern part of the East Anatolian fault zone are characterized by transtension mode. The Lake Van area is characterized by transpression mode. The shortening axis direction changes from sublatitudinal in the west of Turkey to submeridional in the east. STD tensors served as a base for plotting the distributions of the Lode – Nadai coefficient με and the vertical component. Based on the seismic and GNSS data, a comparison was made between the shortening and elongation axes directions.

Сейсмотектонические деформации и сброшенные напряжения землетрясений Центрального Тянь-Шаня

Based on the seismic moment tensor (SMT) data of 270 earthquakes in the Central Tien Shan, which occurred from 1978 to 2021 and include 63 events from the Global Centroid Moment Tensor catalog and 207 events from the works of Aleksander D. Kostyuk and Naylya A. Sycheva, the focal parameters (seismotectonic deformations (STD), kinematic and dynamic parameters, source radius, and stress drop) were calculated. The STD calculation was based on the approaches proposed in the studies of Yuriy V. Riznichenko and Sergei L. Yunga. The area under consideration is characterized by such deformation modes as thrust, transpression, underpression, and oblique. The distribution of the Lode–Nadai coefficient was calculated and plotted. A significant part of the study area is characterized by simple compression deformation, dominated by simple compression and simple shear. To calculate the stress drop , the values of the scalar seismic moment M0, which are determined in the SMT calculation, and the source radii r, which are calculated on the basis of theoretical and experimental models of the dependence of the source radius on the moment magnitude, were used. The radii r and stress drops  were calculated for two models of earthquake sources: the Brune model and the Madariaga–Kaneko–Shearer model. A catalog of dynamic parameters was compiled. The comparison of the kinematic and dynamic parameters of earthquakes was carried out, and the relationship of the dropped stresses with the type of movement in the source, as well as with the Lode–Nadai coefficient, was established. The results obtained in the study can be useful for specialists in other fields of knowledge – geodesy, geology, and geophysics.

Сейсмотектонические деформации Алтае-Саянской горной области. Часть 1

Seismotectonic deformations (STD) of the Earth’s crust in the Altai-Sayan mountain region were studied. The STD calculation was performed on the basis of the approaches proposed in the works of Yu.V. Riznichenko and S.L. Yunga. Estimation of seismicity distribution and calculation of the average annual STD velocity (STD intensity) IƩ were made on the basis of the catalog of earthquakes that occurred in 1997–2020 (15 669 seismic events). Areas of manifestation of intense seismotectonic deformations and seismic activity are identified. A high level of seismicity and the average annual STD velocity (10–7 year–1) is noted in the areas where strong seismic events occurred (Chuya earthquake on September 27, 2003, Tuva earthquakes on December 27, 2011 and February 26, 2012). The study of STD directionality is based on data on the focal mechanisms of earthquake sources (591 events) that occurred from 1963 to 2021. The classification of STD modes was used to construct the STD map. According to the STD maps, the direction of the shortening axes was determined, which changes from west to east from northwest to northeast. The study area is characterized by a variety of deformation conditions: compression, transpression, strike-slip, transtension, tension, etc. Based on the averaged strain tensors, the distributions of the Lode–Nadai coefficient, angle of generalized plane strain, and vertical component are calculated and plotted. The zones where various modes of deformation, such as simple compression, the predominance of simple compression, shear, the predominance of simple tension and simple tension are manifested, are distinguished in the study area. Both uplift and subsidence of the Earth’s crust are noted in the study area depending on the deformation mode.

FOCAL MECHANISMS OF EARTHQUAKES IN THE SUBDUCTION ZONE OF THE WESTERN PACIFIC PLATE

Deformation features of the subducting Pacific lithospheric plate are considered according to the data on earthquake focal mechanisms. The territory includes the convergent boundaries between the Pacific Plate and the North American (in the Aleutian arc region), the Okhotsk, the Eurasian and the Philippine plates.It has been shown that the angle of subducting Pacific Plate in the Aleutian subduction zone affects the focal mechanisms of earthquakes that occurred in the upper, 35 km part of the oceanic plate in the zone of its bending. There occur normal-fault earthquakes at a steep-angle subduction and rare thrust earthquakes at a shallow-angle subduction. The azimuthal orientation of P-axes of the focal mechanism solutions in the upper (1–70 km) contact zone corresponds to the Pacific Plate displacement vector when the plate fragments are subducting west-northwestwards. There occurs a change in azimuthal orientation of the compression axes in the subducting plate at a depth of more than 70 km: the axes occupy different azimuthal sectors showing difference in the orientation of their slope, with the orientations of the T-axes become multidirectional.The calculation of seismotectonic deformations was carried out based on the data on focal mechanisms of 7768 earthquakes. It was revealed that the Exx and Ezz deformation fields are the most homogeneous at depths of 1–70 km. The pattern of seismotectonic deformations changes abruptly for deep parts of the subducting plate (105–200, 200–400, and 400–700 km), there are observed heterogeneous deformation fields Exx, Eyy and Еzz with alternating episodes of extension and shortening.There has been proposed the author’s scheme of the influence of the upper mantle convection structure on the geometry of the subducting plate (slab) as a potential catalyst for the processes responsible for the separation of seismic activity zones and the change of earthquake types with depth and in different parts of the extended subduction zone.

Reconstruction of seismotectonic deformations of Asia in different layers of the Earth’s crust

The calculation of seismotectonic deformations for different depth levels 1–15, 16–35, 36–70 km was performed according to the data of 1819 mechanisms of earthquake foci that occurred in Central Asia (φ = 25° – 60° N, λ=60° – 115° E) for the period from 1976 to the end of July 2020 with M>4.7. The orientation of the main axes of the strain tensor reconstructed from the mechanisms of earthquake foci with M>4.7 coincide at different depth levels with mainly submeridional and north-eastern shortening and varying elongation from sublatitude to north-western and near-vertical. The consistency of the orientation of the main axes of shortening and elongation reconstructed from seismological materials and from the published results of calculating GPS observations, is traced.

MUYAKAN EARTHQUAKE SEQUENCE in 2015 (Northern Baikal Region)

We present the results of studies of the seismic regime, focal mechanisms, and macroseismic data in the area of the largest Muyakan activation in 2015 (northern Baikal region). Due to the deployment of a network of temporary seismic stations, the number of registered earthquakes (KR≥3) increased significantly in 2015 and reached  30 thousand. Spatio-temporal development of the considered activation is characterized by stable low values of earthquake hypocenters and dividing the epicentral field into two clusters – eastern and north-western ones. Both clusters are connected with local stress-strain field (rift type and strike-slip, respectively), while the general regime of seismotectonic deformations of the crust in the activation area, calculated from the statistical analysis of 77 focal mechanisms of Muyakan earthquakes (KR≥9.2), demonstrates the predominance of submeri-dional horizontal extension. Macroseismic effects from the largest earthquakes of the Muyakan sequence were felt, predominantly, in Severomuysk settlement (=10–15 km, I=5). New data on strong motions, obtained from the records of the seismic station with the same name, have significantly complemented the database for the territory of the north-eastern flank of the Baikal rift zone. In general, the obtained results could be used to clarify the seismic hazard of the considered area and to improve the instrumental part of seismic scales.

SEISMOTECTONIC DEFORMATIONS IN THE PACIFIC AND OKHOTSK LITHOSPHERIC PLATES CONTACT ZONE

The seismotectonic deformations were determined in the Pacific and Okhotsk (Eurasian) lithospheric plates subduction zone based on 2458 mechanisms of earthquake foci data for 1977-2019. The deformation features of medium in different deep layers are shown. The deformation field uniformity in the depth range of 1-70 km and the deformation field inhomogeneity for the submerged plate deep parts (105-200, 200-400 and 400-700 km) are revealed. One of the deformations field change reasons is the influence of ascending and, especially, descending currents of thermogravitational convection in the upper mantle sublithospheric part, in particular, the convection structure influence on the subducting plate geometry

Finite-difference numerical analysis of faulting and accompanying seismicity near the Chuya and Kurai depressions, Gorny Altai, Russia

Numerical modeling of fault zone evolution and related seismicity can provide an insight into the process of large earthquake occurrences in a complicated fault system. In this paper, we develop a three-dimensional finite-difference numerical model of stress-strain evolution in and around the Chuya and Kurai depressions of Gorny Altai, Russia, to understand the fault zone evolution and the observed distribution of earthquakes in the region. Unlike in previous studies, the process of seismo-tectonic deformations of this region is addressed in a three-dimensional formulation with an improved model of rock massif behavior. A new geometrical model is designed, which is based on the seismotectonic, paleoseismological studies, and high-resolution Space-Radar-Topography-Mission data. The mathematical model applied here represents a set of partial differential equations, which are based on the fundamental conservation laws and constitutive equations for elastic and inelastic deformations. The initial stress state of the model is due to the action of gravity forces. The model is activated by assigning different displacement fields at the model boundaries – strike-slip and GPS-based displacements. The modeling results illustrate the stages of fault zone development and are in satisfactory agreement with the field observations in the case of GPS-based boundary conditions, which has not been modeled yet. Modeled seismic process is associated with the development of a fault zone resulting from the loss of strength in the subsurface points where the inelastic strain exceeds a certain threshold. The areas of high-degree of inelastic strain localization and the modeled fault zone represent an en-echelon system of dextral strike slips and various types of shear bands. The modeled seismic process obeys the Gutenberg-Richter (frequency-magnitude) law. The number of earthquakes in the attenuation part of the rock massif fracture process follows the Omori (aftershock decay) law.

Seismotectonic Deformation of Active Segments of the Junction Zone of the Kolyma–Omolon Superterrane and South Anui Suture (Southeastern Russia)

Our seismotectonic studies focus on active segments of the junction zone of the Kolyma–Omolon superterrane and the South Anui suture. The aim of our research is to identify features that show activation of suture zones and to determine the parameters of the stress–strain state of the crust in the study area. The analysis was based on the average seismotectonic deformation tensors, which were estimated for the main epicentral fields of Russia’s northeastern regions. New data are now available on the focal characteristics of moderate earthquakes, which can improve determination of the kinematic types of junctions of suture zones of the tectonic taxa located along the Arctic and Pacific continental margins. Seismotectonic crustal destruction regimes are determined for the active segments of the junction zone of the Kolyma–Omolon superterrane and the South Anui suture. These regimes are influenced by global geodynamic processes taking place at lithospheric plate margins, as well as by the dominant deformation fields of adjacent tectonic taxa. The seismotectonic analysis results suggest activation of the suture zones of the northwestern flank of the Kolyma–Omolon superterrane under stable north-eastward compression. The suture zones may extend into the Laptev Sea area, where they are conjugate with the structural elements of the South Anui suture (Novosibirsk–Svyatoi Nos segment). In the Anui–Chukotka segment of the suture, seismotectonic crustal destruction changes from compression to extension. This is due to the effect of deformation fields of active megazones of conjugated tectonic taxa of the Novosibirsk–Chukotka fold-and-thrust and Okhotsk–Chukotka active margin zones. For the tectonic taxa of the Arctic sector of Russia’s northeastern regions, a database has been consolidated, including the of seismotectonic crustal deformation parameters, which may be useful for various geodynamic reconstructions.

.RING-SHAPED SEISMICITY STRUCTURES IN VICINITY OF TOKYO: POSSIBLE PREPARATION FOR GREAT EARTHQUAKE

We have been studying some seismicity characteristics in the vicinity of Japanese capital, Tokyo. It was established that two pairs of ring-shaped seismicity structures at depths of 0–33 and 34–70 km have been formed here in 1976–2018. Ring-shaped structures, as in the other subduction zones form prior to large and great earthquakes. They are characterized by threshold magnitude values (Mt1 and Mt2 correspondingly) as well as big axes lengths (L and l). The first ring pair, located mainly to the south of Tokyo, intersects partly with the rupture zone of the Great Kanto earthquake of 1923 (Mw 7,9), and the second one is to the east of the city. Earlier we have found correlation dependences of parameters Mt1 and Mt2 on magnitudes Mw of the main events for the west of the Pacific. Using these dependences we estimated magnitudes of possible great earthquakes: Mw 7,9±0,1 and 8,1±0,1 for the two areas mentioned correspondingly. It is supposed that in the near years the great earthquake is most probable to the east of Tokyo, because a rate of seismo-tectonic deformation has increased sharply in the area of the ring structure during the last decade.

TO THE ESTIMATE OF STRESS-STRAIN STATE OF THE ROCK MASS IN THE NIZHNEKANSKY REGION

Practical geomechanics is based on an integrated approach, which assumes involving the results of geological, seismological, geophysical and other observations in order to increase the reliability of analytical solutions and to ensure the completeness and quality of interpretation of instrumental control data. The paper provides an example of the implementation of such an approach. When assessing the stress-strain state of the Nizhnekansky region, information on the geological characteristics of the object, as well as data on seismicity and seismotectonic deformations of the Earth’s crust in the Altai - Sayan region and Baikal rift zone were used. As a result of a systematic integrated analysis of geological and seismotectonic information, it was found that junction of the Siberian platform and the West Siberian plate in the area of Nizhnekansky granitoid massif should be related to a region with an average degree of tectonic activity. The territory of the right bank of the Yenisei is characterized by a regional compression field of near-latitudinal orientation. The results of instrumental stress control by hydraulic fracturing method in local zones of the rock mass at a depth of 260 m are presented. It is determined that the rock mass has a significant margin of safety with respect to the parameters of active stress field.

DEFORMATIONS IN THE MIDDLE AMERICA TRENCH ACCORDING TO EARTHQUAKE FOCAL MECHANISMS AND THEIR FEATURES IN THE AREA OF THE 2017 МW 8.2 CHIAPAS EARTHQUAKE, MEXICO

Seismotectonic deformations in the Middle America Trench and their features in the area of preparation of the Chiapas earthquake, М W =8.2, 08 September 2017, were determined using the data on 2244 focal mechanisms of earthquakes for the period of 1977–2017. The distribution of seismicity with depth was studied in detail. The decrease in the depth of the Benioff zone in the north-western subduction segments and the increase in the south-eastern segments is associated with the age of the subducting parts of the Cocos plate and the angle of their immersion. The latter mechanism can also explain the presence of earthquakes with normal focal mechanism on the oceanic uplift in the south-eastern segments of the subduction zone and their absence in the north-western ones. In general, the typical character of subduction deformations has a number of features in the Middle America Trench. The predominance of shortening by horizontal components and elongation by vertical ones at depths up to 35 km is replaced by the transitional type with mosaic distribution of deformations of different signs in the depth range of 36–70 km. Even lower, in the depth range of 70–105 km, the type of deformation changes to the opposite with respect to the upper horizon. The Chiapas earthquake occurred on the border of regions with different types of deformation, which indicates softening of the block’s medium to the west of the hypocenter and its hardening to the east. Such a state of the lithospheric medium may indicate the presence of a deformation shadow zone in the Chiapas earthquake preparation area.

Analysis of the seismic process of the Bishkek geodynamic test site (Northern Tien Shan)

Various characteristics of seismic process on the territory of Bishkek geodynamic proving ground are considered. Seismicity analysis is performed on the basis of earthquake catalogue, according to KNET network data. The catalog includes more than 10,000 seismic events that occurred from 1994 to 2019. To describe the energy distribution function of earthquakes, the Gutenberg - Richter law was used, as well as the position of nonequilibrium thermodynamics with the use of Tsallis statistics, which generalizes classical thermodynamics to the case of nonextensive systems. It is shown that the flow of earthquakes on the territory of the Bishkek geodynamic proving ground is a system with memory and long-range spatial correlations, and the study region itself is characterized as seismically active. The following seismic process characteristics are distributed in space and in time:KSRseismogenic fracture parameter, seismotectonic deformation intensity, seismic activity, Tsallis parameterqand constantsa, as well as a parameter characterizing the slope of the repeatability graph (b-value).

Geodynamics of Central Armenia Based on the Results of Hydrogeochemical Monitoring

Method for geophysical monitoring of the earth's crust has been introduced since 2000 aiming to study the earth's crust of Central Armenia. The method allows to track modern geodynamic processes of the region. The nature of time-space distribution of hydrogeodeformation processes of Central Armenia has been studied. The nature of space-time distribution of geodynamic intensity is determined. Anomalies of components of chemical composition of water have been recorded on stress-strain areas of Earth's crust. Types of seismotectonic deformation have been determined. The present work introduces the hydrogeochemical method of studying the geodynamic processes of the Earth's crust of Armenia. The method is based on hydrogeochemical observations of the chemical composition of mineral waters and their comparison with seismicity. The objective of the hydro geochemical method is to identify hydrogeochemical effects which mainly occur in the changes of macro-component and gas composition of waters related to geodynamic movements of the Earth's crust. The results of the applicaiton of the hydrogeochemical method in the central part of the region, confirmed the connection of the parameters of seismic events variations with the chemical composition of groundwater, as well as carbon dioxide (СО₂) dissolved in water. Stressed areas of the Earth's crust are observed according to the anomalies of components of chemical composition of water. Types of seismotectonic deformation are determined. Geochemical anomalies are most clearly observed in the macro-component composition of mineral water and gases. Seismic events are preceded by geochemical anomalies of components of water composition in relation to background values in percentage ratio. The hydrogeochemical method, combined with other methods, can serve as a reliable precursor to earthquakes and other geodynamic processes of the Earth's crust. The role of the hydrogeochemical method is also effective for short-term and operational prediction of tectonic movements of the Earth's crust (earthquakes, in particular).

Seismotectonic deformations of earth crust in Pamir and neighbor areas

We computed seismotectonic deformations (STD) of earth crust in Pamir and neighbor areas. We used ISC (International Seismological Centre, London) catalogue for average STD rate computations, including more than 25000 earthquakes that took place between 1934 and 2016. STD tensor axes’ directions were computed based on hypocenter focal mechanisms of 3049 earthquakes that took place between 1946 and 2018. We haveplotted maps showing distribution of STD intensity and number of earthquakes for various ranges of hypocenters depths, and map showing horizontal part of STD tensor. Finally we analyzed different deformation conditions in South Tien-Shan and Pamir.

Seismicity, Tectonics, and GPS Geodynamics of the Caucasus

The style of the seismotectonic deformation of the Earth’s crust in the Caucasus and its immediate surroundings corresponds to the thrust setting with a subhorizontal principal compression axis oriented north-northeast across the strike of the Caucasian structures and a subvertical principal extension axis, as established by the reconstruction of a representative set of focal mechanisms of earthquakes. Overall, this deformation style quite closely agrees with the notions developed in plate tectonics according to which the Caucasian segment of the Alpine–Indonesian mobile belt is experiencing strong transversal (across the strike) narrowing as a result of the convergence of the Arabian and Eurasian lithospheric plates. At the same time, the detailed geodetic measurements conducted in the territory of the Greater Caucasus established the GPS site displacements, testifying to the increase of its width. This widening cannot be attributed to the extension across the strike of this mountainous edifice because the focal mechanism solutions of earthquakes in this territory clearly indicate a setting of compressive stresses across the strike of the geological structures. We suggested interpreting this combination of the geodetic and seismological data by the active growth of the volume (and area) of layered rocks of the Greater Caucasus and the emergence of the setting of outward pressure probably as a result of the inflow of the additional mineral material carried by the ascending deep fluids.

The Traces and Chronology of the Strong Historical Earthquakes on Cape Zyuk, East Crimea

The results of studying the geological and archaeological traces of the strong earthquakes on Cape Zyuk where the ancient settlement existed from the turn of the 6th to the 5th centuries B.C. to the first-third–middle of the 6th century A.D. are presented. The detailed knowledge gained on this monument allowed us to compile the timeline of the strong earthquakes for the past 2500 years. The detection of the seismotectonic deformation of the Late Holocene sediments indicates that the rupture of the source of a strong earthquake at Cape Zyuk extended to the surface. The dating of this event is constrained by the upper age of the second half of the 4th century B.C. to the beginning of the third century B.C. The previous event is dated to before the turn of the 6th–5th centuries B.C. Besides these events, there were presumably another four earthquakes in 63 B.C., before the second half of the 4th century B.C., in the first third to the mid-6th century A.D., and in the 18th century. Presumably Cape Zyuk was struck by four or five strong earthquakes during the past 2500 years. The lack of information about the earthquakes between the 6th and 18th centuries, i.e., during more than a 1000-year period, can probably be related to both the long period of quiescence between seismic activations and to the incompleteness of the collected data.

Dynamics of the Zones of Strong Earthquake Epicenters in the Arctic–Asian Seismic Belt

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.