Based on the interseismic velocities of GNSS points, the horizontal deformations in Central Sakhalin were studied. The research area is characterized by the predominance of uniaxial compression conditions, however, the spatial distribution of deformations in the vicinity of the trans-regional lithospheric faults (Central-Sakhalin and Hokkaido-Sakhalin) is heterogeneous. The maximum reduction of the earth’s surface in the NW-SE direction occurs in the Hokkaido-Sakhalin fault zone. The area of intensive deformations of right-lateral slip and minimal dilatation rates is confined to the Central Sakhalin fault zone and its nearest surroundings. Overall, the kinematics of the region indicate the compression of the island at the rate of 2 mm/year and the right-lateral slip of 2.5 mm/year, which corresponds to the recent tectonic regime of the region. The right-lateral slip in the Central Sakhalin fault zone (1 mm/year) confirms its kinematics according to geological and geomorphological studies. Signs of a right-lateral slip in the Hokkaido-Sakhalin fault zone (~0.4 mm/year) appear only within the limits of their determination errors. Based on GNSS observations, the first estimates of secular vertical movements in the investigation area were obtained. The absolute vertical movements in Central Sakhalin are inherited in relation to neotectonic structures. West-Sakhalin and East-Sakhalin uplifts elevate at the rate of ~3 mm/year. A slight sinking of the earth’s surface occurs in Tym-Poronaysk depression.

The paper continues the series of annual brief reviews of the seismicity in the southern part of the Russian Far East, based on the data from the catalog of the “Yuzhno-Sakhalinsk” Regional Information Processing Center of the Sakhalin Branch of the Federal Research Center “Geophysical Survey of the Russian Academy of Sciences”. The main parameters of the seismicity of the studied area in 2024 are given: maps of earthquake epicenters and their maximum macroseismic effects, statistical estimate of the seismicity level SESL'09, Benioff graphs, and density maps of nominal elastic deformation. The information on some of the most significant and interesting for detailed study earthquakes is given. Seismicity of the south of the Russian Far East remains moderate in 2024, within the background level. At the same time, there is a reduced level of crustal and upper mantle seismicity (h ≤ 70 km). Almost all major earthquakes in 2024 occurred in the interval of deep earthquakes (h > 70 km). The strongest earthquake with Mw = 6.8 occurred in the middle part of the Kuril Island arc at the depth of h = 182 km.

The article discusses methodological issues of applying phase characteristics in determining the arrival time of seismic waves. The accuracy of earthquake location depends on the precision with which the arrival times of longitudinal, transverse, and surface waves can be determined. Determining the phase characteristics of seismic waves is crucial for locating nearby earthquakes, since these waves are different for distant earthquakes. Methods for determining the arrival times of seismic waves of various natures characterized by different frequencies are investigated based on the analysis of the phase characteristics of signals from seismic events . Theoretical underpinnings of this approach are considered, and the results of processing seismic data on determining the arrival times of wave packets of the corresponding elastic waves associated with earthquakes are presented.

The report presents the results of the fieldwork (July 2024) aimed at studying the traces of prehistoric ashfalls in the city of Kurilsk and nearby settlements: the villages of Kitovy, Rybaki, and Reydovo (Iturup, South Kuril Islands). The work was traditionally based on tephrostratigraphic studies, during which the sections of the soil-pyroclastic cover were studied. In total, more than 10 sections were studied. The materials obtained during the fieldwork, after carrying out radiocarbon dating and material composition studies, will be used in further regional studies on young volcanism of the South Kuril Islands, as well as in studies on assessing volcanic hazard and volcanic zoning.

The paper discusses the results of complex geological and geophysical studies of the deep structure of the seabed along the profiles “Magadan – Southern Kurils” (2-DV-M), “Shantar Islands – Northern Kurils” (1-OM) and “Cape Billings – Outer Continental Shelf Limits” (5-AR), carried out in 2006–2009 within the framework of the State program of expeditionary works on substantiation of national sovereignty over the continental shelf in the Sea of Okhotsk and East Siberian Sea. The main executors were the staff of the V.I. Il’ichev Pacific Oceanological Institute of FEB RAS and Federal State Unitary Scientific and Production Company (FSUSPC) Sevmorgeo. A special role was assigned to gas-geochemical studies with the purpose to establish regional background and anomalous gas fields to assess prospects for oil, gas and gas hydrates. As a result of complex geological and geophysical expeditions led by A.A. Merezhko (Sevmorgeo) in the Sea of Okhotsk, it was established that the enclave outside the 200-mile zone in the central part of the water area does not differ in geological structure from the adjacent parts and is a natural continuation of the framing geological structures of the basement. The evidence obtained was sufficient to successfully justify the application to the UN. On March 11, 2014, after careful consideration of the application and draft recommendations, the enclave of international waters in the Sea of Okhotsk was legally assigned to the Russian Federation. Studies in the East Siberian Sea have provided a huge amount of data on lithology, geochemistry and gas potential of bottom sediments in this area.

The distribution of tsunami deposits in the lacustrine-swamp sections on the Kasatka Bay coast is analyzed. The main objects were a swamp formed on the place of overgrown lagoon-type lake located behind dune ridge, and a low swampy isthmus between Oktyabrskoe and Srednee lakes. Five major events have been identified, run-up parameters and age have been determined on the base of radiocarbon dating and tephrostratigraphy. Diatom analysis data were used to confirm the marine origin of the sand. Established events are correlated with data on adjacent islands and the Eastern Hokkaido coast. A trace of only one strong historical tsunami was found, its deposits lie above marking volcanic ash Ta-a (1739) of the Tarumai Volcano, Hokkaido. The tsunami took place in the second half of the 18th century. Perhaps this is a trace of 1780 AD tsunami, the source was located near Urup Island. Four paleotsunamis are well compared in age with the megatsunamis of the region (17th, 13th centuries, 1.5; 2.3–2.4 ka), which most clearly manifested on the Eastern Hokkaido coasts and left sea sands and silts sheets in marshes of the Lesser Kuril Ridge and Kunashir Island. On Iturup, the thickness of tsunami deposits and wide of sand cover is much less. It has been suggested that the peat section of Iturup recorded the run-up values in the distal zone of the Late Holocene megatsunami, which had sources in the southernmost of the Kuril-Kamchatka Trench. Regional strong tsunamis occurred in the period of instrumental observations did not leave geological evidence in the studied sections.

The results of the study of long-wave motions with periods of more than 20 hours on the shelf of the southwest coast of Sakhalin Island using the time series of sea level fluctuations obtained in full-scale experiments with a discreteness of 1 s and a duration of 4 to 6 months are considered. Spectral analysis of the time series of sea level fluctuations for the period range from 8 to 200 hours revealed the presence of long-wave processes with periods from 26.1 to 46.7 hours, which significantly exceed the inertial period of 16.48 hours. Numerical modeling of shelf waves for exponentially convex profiles of the seabed, carried out using the dispersion relation of V.T. Buchwald and J. K. Adams for waves of the continental shelf, showed that the detected wave processes with periods from 31.2 h to 46.7 h are shelf waves. Their amplitudes increase during storms. The possibility of energy transferring from atmospheric disturbances to shelf waves, which contribute to the formation of sea level, is shown, that confirms the earlier made assumption. Using the calculation of the phase difference of the observed shelf waves at a distance of 12.4 km between Nevelsk and Gornazovodsk and determined by means of the theoretical model, it is shown that the second mode of the shelf wave with a frequency of 0.152 cycle/h is close to the theoretical one. It is shown for the wave with a period of 26.1 h recorded in Ilyinsky and Gornozavodsk for the distance between the points of 173.6 km, that this wave cannot be a shelf wave, but it is a Kelvin wave. This is confirmed by the calculated dispersion diagram, according to which the wavelength of about 689 km corresponds well to the phase difference for the distance Ilyinsky – Gornozavodsk. It is found that shelf waves, one of the generation mechanisms of which is the wind tension along the coast, have the different amplitudes in summer and winter, that is due to the seasonal direction of the offshore wind. In summer, the directions of shelf wave propagation and wind are opposite, which weakens the shelf waves.

The article presents the results of the composition analysis of 27 recent (surface) pollen assemblages collected in typical plant communities in the northern part of the Central Kamchatka Depression and on the surrounding slopes of the Sredinny Range and Klyuchevskaya Sopka volcano. Our data show that spore-pollen spectra reliably represent the composition of forest plant communities. However, the proportions of pollen in the spectra of some arboreal taxas does not always correspond to their role in plant communities The adequacy of the spectra for plant communities is confirmed by cluster analysis, according to which the most statistically similar spore-pollen spectra are formed in similar plant communities. Regional components of the spectra in surface samples distort the ratios of main taxa in plant communities, especially in the high altitudinal vegetation belt. The participation of coniferous tree pollen in the spectra is underestimated compared to their actual presence in plant communities. These features must be considered when interpreting fossil spore-pollen spectra. Our materials made it possible to identify taxa whose pollen is often found in the spectra of the subalpine and alpine zones: Alnus alnobetula, Liliaceae, Polygonaceae, Asteraceae, Saussurea and Sanguisorba. The strongest influence of local vegetation is observed in the spectra of swamps and coastal plant communities. The spectra of these communities usually contain pollen of Alnus hirsuta, Salix, and Populus, as well as Rosaceae, Cyperaceae, Comarum, Myrica, and Menyanthes, and spores of Polypodiaceae and Equisetum. Our materials will facilitate more reasonable reconstructions of Kamchatka vegetation based on the pollen analysis in the study of fossil pollen spectra of the Kamchatka Peninsula, as well as in the interpretation of pollen data from other mountainous regions.

The article continues to describe the results of the study of seismotectonic deformation (STD) of the Altai-Sayan Mountain region which were presented in previous Issue of «Geosystems of Transition Zones» journal. Given work presents the results of a STD study of two zones of the Altai-Sayan region: the Altai Mountains (the region of the Chuya earthquake) and the territory that includes the Academician Obruchev ridge, the southern part of the Eastern Sayan Mountains and the Southern Baikal region. The STD computation has been performed on the basis of the approaches proposed by well-known publications of Yu.V. Riznichenko and S.L. Yunga. The derivations on STD directions are based on focal mechanisms data (591 events) that occurred from 1963 to 2021). For the considered areas, a description of seismicity is given and STD maps are constructed. According to the STD maps, the directions of the axes of shortening and elongation are determined and the deformation modes is marked. The distributions of the Lode–Nadai coefficient, the angle of kind of the stressed state (the angle of the generalized plane deformation, the phase angle of STD tensor-deviator) and the vertical component (ZZ) have been constructed using the obtained averaged STD tensors for seismogenic layer of 0–35 km depths. The zone around Chuya earthquake source site is characterized by horizontal shear deformation, with a band of transpression (Chagan-Uzun block) passing though this zone. The territory, which includes Academician Obruchev ridge, the southern part of the Eastern Sayan Mountains and the Southern Baikal region is divided into two parts according to the deformation regime. The boundary runs along the Darkhat depression: the regimes of compression, transpression and horizontal shear occur in zones lying to the west of it; the regimes tension, transtension, and the transitional regime from vertical shear to tension occurs to the east. The Chagan-Uzun block and the Academician Obruchev ridge are uplifted, and the territory to the east of the Darkhat depression is lowered.