The strongest earthquakes with magnitudes Mw 8–9 generate coseismic displacements of the Earth’s crust, covering entire regions of the world. These displacements can be recorded using observations provided by the independent geodetic GNSS networks. The data of these networks are processed using different algorithms and methods for analyzing satellite observations, methods for calculating the coseismic shift, and different implementations of the coordinate system. These factors lead to "inconsistency" of the combined displacement fields and the appearance of additional errors in the results of coseismic effects modeling. The paper proposes a method for combining the fields of coseismic displacements of the Earth's crust, obtained in the far-field zone from the source according to data from heterogeneous GNSS networks. The results of applying the proposed method are demonstrated by the example of combining the fields of coseismic displacements in China, South Korea and the south of the Far East of the Russian Federation, initiated by the catastrophic Tohoku earthquake on March 11, 2011, Mw 9.1, as well as the calculation and analysis of the unified field of coseismic deformations of the region under study.

The monograph is based on the textbook by T. K. Zlobin (Yuzhno-Sakhalinsk, Sakhalin State University, 2014), which was refined and supplemented significantly. The book presents modern concepts of geodynamical processes in the Earth’s core and its shells (mantle and crust, hydrosphere and atmosphere), up to the space phenomena, which are relevant to a variety of natural disasters: earthquakes, volcanic eruptions, landslides, avalanches, mudslides, tsunamis, storm surges. Tropical cyclones (typhoons, hurricanes, tornadoes), and falls of celestial objects have been characterized as well. Alongside the description of modern geodynamic processes, information is provided on the history of stars, the Sun and planets, the problem of the emergence of the Earth’s magnetic field, the inversion of magnetic poles, etc. The energy of geodynamic processes and natural disasters, their hierarchy and properties: fractality and quasi-periodicity, possible regime changes (bifurcations) have been considered. The monograph is assigned to geologists, geophysicists, specialists in adjacent fields of science, as well as for students and postgraduates studying modern geodynamic processes and related natural disasters.

The mechanisms of preparation and occurrence of the strongest deep-focus earthquakes with MW≥8, as well as their surface manifestations, remain insufficiently studied because of the lack of the relevant data. There are but three seismic events of this kind which have so far been instrumentally recorded. This paper describes the identification and analysis of the changes in the characteristics of modern crustal movement of the 2013, MW 8.3 Sea of Okhotsk deep-focus earthquake based on the data from long-term continuous geodetic-class GNSS stations in the Sea of Okhotsk region on the Kamchatka Peninsula, the Sakhalin Island, and the coast of the Sea of Okhotsk and the Sea of Japan. There has been found temporal stability of variations in the average annual geodetic site velocities. The coordinates of GNSS-stations do not show non-linear changes typical of strong shallow earthquakes in the initial post-seismic period. The Maxwell rheology for modeling of viscoelastic relaxation of the asthenosphere/upper mantle as a result of seismic impact allows for a first approximation to qualitatively and quantitatively reproduce the displacement patterns of GNSS-sites of the Kamchatka Peninsula observed in the initial postseismic period (2–3 years after the mainshock). After that, the model estimates of postseismic movements of the peninsula become systematically lower than the observed. The values calculated for the OKHT station motion on the western coast of the Sea of Okhotsk are in good agreement with those recorded for postseismic displacements over the entire measurement interval. The observed directions of the Sakhalin Island postseismic movements systematically deviate to the northeast from the model directions and are oriented almost orthogonally to the Kuril-Kamchatka Trench. Besides the viscoelastic relaxation process, another possible reason for this issue could be an enhanced viscous friction in the bottom of the subducting Pacific plate, leading to the intense deformation of the Sakhalin Island and the western coast of Kamchatka.

The May 27, 1995 Mw=7.0 Neftegorsk earthquake occurred in the north of Sakhalin Island, rupturing the Upper Piltun fault, a secondary feature of the main Hokkaido-Sakhalin regional fault zone. The fault geometry, coseismic slip model, and Coulomb stress changes in the earthquake focal area were calculated based on a finite fault modeling. We used near-field coseismic offsets at 24 points obtained by comparison between predating triangulation and GPS observations, which were collected before and after the earthquake. Our slip distribution model shows two major slip patches. Larger slip asperity (amplitude up to 6.36 m) was characterized by right-lateral strike-slip movements, which correspond to focal mechanism of the earthquake, whereas the northern segment has reverse fault mechanism with maximum slip of 2.64 m. The fault length and width, average slip and stress drop values are estimated at 78 km, 28 km, 1.91 m and 11.3 MPa, respectively. The estimated release moment is approximately 7.49×10 19 N∙m equal to Mw=7.2, which is larger than that reported by the USGS and GCMT but consistent with the values reported by other researchers. The coseismic Coulomb stress changes enhanced the stress by more than 10 MPa on the southern segment of the Gyrgylaninsky fault and middle section of the Hokkaido–Sakhalin fault. Seismic risks on the nearest faults cannot be ignored in the future despite the fact that the earthquake with a magnitude of 5.8 occurred in 2010 near the Gyrgylaninsky fault. The recent GPS rates in the surroundings of the Neftegorsk surface rupture mean that the recurrence interval for similar earthquakes may be more than a thousand years.

Современные проблемы ДЗЗ из космоса, 20(

An intraplate tsunamigenic earthquake with МW=7.5 occurred on March 25, 2020 southeast of the Paramushir Island (Kuril Islands) beneath the outer slope of the Kuril-Kamchatka Trench. Since 1900, this earthquake has been the largest event for an 800-km long oceanic slope and a 300-km long segment of the Kuril seismofocal zone located near the epicenter. Sub-horizontal compression stresses generated in the earthquake source region were oriented across the seismofocal zone. A type of motion is represented by reverse faulting along the both nodal planes.The compressive stress state in which there occurred the Paramushir earthquake reflects the present-day geodynamics in the subduction zone near the hypocenter. The paper shows that the earthquake occurrence is due to a strong mechanical contact surface between the Pacific and North American lithospheric plates in the subduction zone. The analysis of coseismic displacement of the nearest Global Navigation Satellite System (GNSS) station served as confirmation of the determination of fault plane solution of the earthquake. A seismogenerating motion occurred along the plane oriented to the southwest and dipping towards the trench. For Finite fault source models, there were calculated the increments of the Coulomb stress in the subduction zone. For the main fault plane, the increment of the Coulomb stress in the interpolate contact area propagates to a depth of ~30 km and reaches 1 bar.Coseismic stress increment in the subduction zone at the northern flank of the Kuril island arc, which has a high seismic potential at the present stage of the tectonic cycle, increases the likelihood of the largest interplate earthquake occurrence therein.

The network of geodynamic GNSS observations was deployed in 2006 throughout the Kuril island arc from Japan to Kamchatka. The network includes 11 stations of continuous and periodic registration. The article provides information on the organization of the network and its current status. The creation of the GNSS network provided extensive material for studying the modern geodynamic processes in the Kuril segment of the subduction zone of the North American (Okhotsk) and Pacific lithospheric plates. The performed observations made it possible to obtain the first information on the modern geodynamics of the region. The article presents an overview of the results of the previous years obtained by the authors together with other researchers. The source models of the largest seismic events are constructed on the basis of the instrumental data: the 2006 Mw 8.3 and 2007 Mw 8.1 Simushir earthquake doublet and the 2013 Mw 8.3 deep-focus Okhotsk earthquake. At the initial stage of the post-seismic process in the epicentral zone of the Simushir earthquakes, the dependence of the asthenosphere viscosity on the observed post-seismic displacement velocity of the Earth’s surface was found. The results obtained earlier were supplemented by new data on the changes in the geodynamic setting in the subduction zone. The dynamics of the transient decaying post-seismic process in the central part of the island arc is studied. Stress relaxation in the Earth’s crust at various stages of this process could be the trigger of powerful volcanic eruptions occurred in 2009–2019 on the central Kuril Islands. The seismic potential of various segments of the Kuril subduction zone has been clarified on the basis of the modeling of current mechanical coupling of lithospheric plates. It contributes to a more accurate assessment of the seismic hazard of the region together with other methods. The continuation of the GNSS observations on the Kuril Islands in the future will allow us to study in detail the features of the modern geodynamics of the region.

The strong earthquake with moment magnitude MW = 7.5 occurred on March 25, 2020, in the North Kurils to the southeast of the Paramushir Island. The hypocenter of the earthquake was located under the oceanic rise of deep-sea trench in the subducting Pacific lithospheric plate. This earthquake has been the strongest seismic event since 1900 for an area about 800 km long of the outer rise of the trench. It also was the strongest earthquake for the 300-kilometer long area of the Kuril-Kamchatka subduction zone adjacent to the epicenter. The article summarizes the data on the Paramushir earthquake. Tectonic position of the earthquake, source parameters, features of the aftershock process development, as well as coseismic displacement of the nearest continuous GNSS station are considered. The performed analysis did not allow us to clearly determine the rupture plane in the source. Nevertheless, the study of the features of the outer-rise earthquake is a matter of scientific interest, since the stress state of the bending area of the subducting Pacific lithospheric plate reflects the interplate interaction in the subduction zone.

Обсуждается проблема современной геодинамики Дальневосточного региона на основе мониторинга разномасштабных деформаций и сейсмичности в области сочленения Евразийской, Североамериканской, Тихоокеанской, Амурской и Охотской литосферных плит с применением современных методов космической геодезии и широкополосной сейсмологии. Дан краткий обзор этапов развития Единой сети геодинамических наблюдений ДВО РАН, основных результатов сейсмологических и GPS/ГЛОНАСС-наблюдений, полученных в рамках целевой комплексной программы научных исследований ДВО РАН «Современная геодинамика, активные геоструктуры и природные опасности Дальнего Востока России (2009–2013 гг.)» и проектов ДВО РАН 2014, 2018, 2019 гг., а также достигнутых позиций ДВО РАН в области геодинамики. The problem of the recent geodynamics of the Far East region is discussed based on monitoring of different-scale deformations and seismicity in the articulation of Eurasian, North American, Pacific, Amurian and Okhotsk lithospheric plates using modern methods of space geodesy and broadband seismology. We present a brief overview of the development stages of the Unified Network of Geodynamic Observations of the Far Eastern Branch of the Russian Academy of Sciences, the main results of seismological and GPS/GLONASS observations obtained within the framework of the Targeted Comprehensive Research Program of the Far Eastern Branch of the Russian Academy of Sciences for 2009–2013 «Recent geodynamics, active geological structures and natural hazards of the Far East of Russia», Projects of the Far Eastern Branch of the Russian Academy of Sciences (2014, 2018, 2019) and the achievements of FEB RAS in the field of geodynamics.

Based on an analysis of seismicity for the period of 1900–2018, the seismic potential of the Kuril–Kamchatka subduction zone is estimated, and the geometry of interplate coupling of the North American and Pacific lithospheric plates and the rate of seismic underthrusting of the latter beneath the former are specified. In order to identify areas of modern seismic deficits in the subduction zone, an approach based on the cumulative displacement of interplate earthquakes with Mw ≥ 7.0 is proposed. Together with other methods, such an approach contributes to a more accurate seismic hazard assessment of the region.

The 2006–2007 Simushir earthquakes started a new episode in the rupture history of the Kuril-Kamchatka subduction zone. This earthquake doublet terminated the seismic silence in the Central Kurils, which had lasted for almost a century. The analysis of seismologic, geologic and GPS data over the Kuril Islands region allows us to reveal the patterns of deformation of the lithosphere in the Kuril subduction zone, in particular, the peculiarities of accumulation and relaxation of elastic stresses during the seismic cycle. We analyzed > 9 years of continuous GPS observations on the Kuril Islands to determine the surface displacements caused by the geodynamic processes in the subduction zone. We used available GPS data to model the coseismic stress release and postseismic stress relaxation related to the 2006–2007 Simushir earthquakes. We showed that the duration of postseismic relaxation after the 2006 earthquake exceeds 10 years, preventing transition of the central Kurils to the interseismic stage and thus delaying the beginning of the new seismic cycle. The value of Maxwell viscosity of the asthenosphere found in this study (3 × 1017 Pa s) in the Kuril Island arc is substantially lower than the values determined for several other subduction zones. This contrast in viscosity agrees with Kogan et al. (J Geophys Res 118:3691–3706, 2013), who used shorter GPS time series than in our study. The results of our analysis show that multidirectional motions along the Kurils Islands are explained by the fact that segments of the island arc are at different stages of the seismic cycle.

In the northern Sakhalin Island, the tectonic activity of the fault zones is a potential threat to the industrial infrastructure of the petroleum fields. Recently, the background seismicity has increased at the Hokkaido‐Sakhalin fault that consists of several segments, including the Garomai active fault. In the studies of the regional deformation processes, it is important not only to analyze the seismic activity, but also to quantitatively assess the dynamics of deformation accumulation in the fault zones. In order to study the contemporary geodynamics of the Garomai fault, a local GPS/GLONASS network has been established in the area wherein trunk oil and gas pipelines are installed across the fault zone. Based on the annual periodic measurements taken in 2006–2016, we study the features of surface deformation and calculate the rates of displacements caused by the tectonic activity in the fault zone. During the survey period, no significant displacement of the fault wings was revealed. In the immediate vicinity of the fault zone, multidirectional horizontal displacements occur at a rate up to 1.6 mm/yr, and uplifting of the ground surface takes place at a rate of 3.4 mm/yr. This pattern of displacements is a reflection of local deformation processes in the fault zone. At the western wing of the fault, a maximum deformation rate amounts to 1110–6 per year. The fault is a boundary mark of a transition from lower deformation rates at the eastern wing to higher ones at the west wing. In contrast to the general regional compression setting that is typical of the northern Sakhalin Island, extension is currently dominant in the Garomai fault zone. The estimated rates of relative deformation in the vicinity of the Garomai fault give grounds to classify it as ‘hazardous’.

The earth surface deformation was modeled for the North, Central and South Sakhalin on the basis of de‐ formation velocities recorded by the GPS stations of the Sakhalin Geodynamical Network. A pattern of contemporary horizontal deformation is intricate in the vicinity of the main submeridional faults of the island. On the island surface, the dominant deformation regime is compression; however, the spatial distribution of deformation is heterogeneous. The horizontal compression is mainly sublatitudinal and SW‐NE‐trending. In addition to compression, there are zones of rather intense right‐lateral strike‐slip in the northern and central parts of the island, while stretching dominates in the south‐eastern parts. The regional geodynamic setting is reflected in the seismicity of the island. Recently, the seismic activity has been increased in the areas characterized by intensive surface deformation, while the areas of low deformation rates correlate with the zones of weak and sparse seismicity.

On August 14, 2016, at 11 h 15 min UTC, an earthquake with Mw = 5.8 occurred at ~9 km depth in the central part of Sakhalin, near its western coast. The shaking intensity in the epicentral zone was up to VII on the MSK-64 scale. Based on the aggregated seismotectonic data, we find that the slip occurred on the cutting fault joining two large regional fault zones of submeridional trends, the West Sakhalin and Central Sakhalin ones. By the method of waveform inversion we determine the seismic moment tensor and model the earthquake source. In the source, we reveal subhorizontal NE–SW-directed compressional stresses which agree with the contemporary character of deformations in the central part of the island. The slip type is a NW-dipping reverse fault with an insignificant strike-slip component. On the basis of reconstructed slips in the earthquake source, we calculate the coseismic deformations of the earth’s surface in the epicentral zone.

Abstract The Aleutian and Kuril‐Kamchatka arcs meet at a triple junction of the Pacific (PAC), Bering (BER), and North American (NAM) plates. We invert GPS observations from the westernmost Aleutian (Komandorsky) Islands and Kamchatka for the fault locking depth and block motion in the far western Aleutian transform boundary. Three boundary models were considered: (1) only the Aleutian thrust fault without a trench‐normal component, (2) only a strike‐slip fault in the back arc north of the Komandorsky Islands, and (3) a rigid Komandorsky sliver bounded by the Aleutian and back‐arc faults. Observed velocities prefer Model 3, with a secular westward sliver velocity of 51 mm/a relative to NAM (two thirds of the total PAC‐NAM motion). The observed velocities are ~10% slower because of elastic strain from boundary faults. The best fitting locking depth of faults bounding the sliver is 12 km, which is similar to depths observed in diverse tectonic environments.

1. University of Science and Technology of China, 2. Institute for Applied Mathematics of the Far Eastern Branch of the Russian Academy of Sciences, 3. Far Eastern Federal University, 4. University of California Berkeley, 5. Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences, 6. Institute of Marine Geology and Geophysics of the Far Eastern Branch of the Russian Academy of Sciences, 7. Pacific Geoscience Centre, Geological Survey of Canada