Study of fractured reservoirs during geological exploration in the north-eastern part of the Sakhalin Island

During a geological fieldworks in the northeast of Sakhalin Island in order to study the siliceous deposits of the Pilskaya formation and to develop a technique for locating oil deposits in unconventional fractured reservoirs, natural outcrops of Cenozoic deposits on the Schmidt Peninsula and in the Pogranichny depression were studied. Samples were taken for analytical studies (geomechanical, geochemical, lithological, etc.), structural forms (folds, minor faults, slickensides, tension gashes, joints, shear fractures), which are indicators of tectonic deformations of the rock massive, were studied. It is shown that the intensity of fracturing strongly depends on the lithology, the position of the observation point relative to disjunctive and/or plicative structures. The direction of the joints varies depending on the position relative to the elements of the local folds and on the position of the block (with a small-block structure). According to the results of field observations it is shown, that the zone of intense dislocations has an extremely insignificant thickness usually the first tens of meters. An extremely nonuniformity of the stress field in the vicinity of the Pogranichniy depression is noted, which is reflected in the nature of the dipping planes, structural patterns and parageneses. In the northern part of the syncline, numerous flowing oil shows associated with open fracturing are identified, which obviously indicates the extension regime that continues up to this day.

Development of Solontsovskie Lakes as indicator of humidity within Central Sikhote-Alin in the Late Holocene

The stages of development of small Solontsovskie (Shanduyskie) Lakes located in the middle mountains of the Central Sikhote-Alin within large landslides, formed on the slopes of the paleovolcano, are identified on the basis of complex study of the sediment section of the Nizhnee Lake. The ecological-taxonomic composition of the diatom flora, the botanical composition of peat have been analyzed, and the tendencies of lacustrine sedimentation depending on the different scale of hydroclimatic changes in the Late Holocene have been established. The age model is based on 6 radiocarbon dates. The temporary resolution for the reconstructions is 30–60 years. A comparison of the development of Nizhnee and Izyubrinye Solontsi Lakes was carried out, the stages of watering and shallowing of lakes were identified on the basis of their dynamics, which made it possible to restore the change in moisture in the middle mountains. Organogenic deposits in lacustrine basins accumulated at high rates (up to 1.7–1.9 mm/ year). The most detailed data were obtained for the last 2.6 thousand cal. yr BP based on the study of the sediment section of the Nizhnee Lake, which responded more sensitively to changing climatic conditions. Frequent changes in diatom assemblages and peat-forming plants indicate unstable hydroclimatic conditions with varying degrees of watering and drainage up to complete overgrowth of water bodies. According to the data of diatom analysis, a successive change in the trophicity of the lake was traced. A frequent change of sphagnum mosses of different sections with different trophic preferences was established. The main reason for the change in the hydrological regime of the lakes was variations in precipitation during the short-term climatic changes. The correlation of the identified paleoclimatic events with global data has been carried out. Cooling periods, as a rule, were accompanied by a decrease in moisture, but the Little Ice Age was wet due to an increase in precipitation.

Concerning the theory of LURR based deterministic earthquake prediction

This paper considers theoretical aspects of a trigger effect of earth tides on earthquake initiation under the LURR approach. The growth of Coulomb stress, which appears resulting from this phenomenon, is shown to occur not for all regimes of stress state acting in the studied region. Its greatest increase corresponds to the regime of the horizontal extension and shear associated with the faults with kinematics of the normal and strike-slip faults. The low level of additional Coulomb stress for the horizontal compression regime allows asserting the low probability of the trigger effect for the faults with kinematics of the reverse faults. It is noted, that there is also an indirect factor in the form of additional pressure caused by the sea tides in addition to the main factor of the earth tides effect on deformations in the solid earth for island arcs and coastal areas of the continental crust. This is an additional vertical pressure for the ocean floor, and a lateral pressure for the crust of island arcs and coastal areas of the continents. Indirect factors significantly complicate the effect of earth tides on the Earth’s crust, completely neutralizing the influence of the direct factor in some cases.

Pliocene adakite-like accent of andesites and dacites from the Orlov volcanic field (Sakhalin Island)

Adakite-like geochemical signature (high Sr/Y ratio at a low Y concentration) is recognized in andesites and dacites, associated with intraplate basalts in the Orlov volcanic field of Sakhalin Island. These rocks denote the final (Pliocene) accent of intraplate volcanism in the Lesogorsk zone, which began in the Middle Miocene in an area of its junction with the Chekhov zone of the preceded (Oligocene-Early Miocene) suprasubduction one. The adakite-like accent was related to the Sakhalin folding phase that accompanied the general structural reorganization in the back-side region in the Japan arc system. Such a geological environment differed from the one of classical adakites generation resulted from melting of a young slab in the Aleutian island arc. It is supposed, that the Sakhalin adakite-like magmas were produced in deep-seated sources of the crust-mantle transition displayed in the Sakhalin-Hokkaido-Japan Sea zone of hot transtension due to drastic change of tectonic deformations from the thin crust of the South Tatar Basin to the thicker one of its northeastern extremity.

Geological evolution of the northern Mid Kuril trough based on seismic facies analysis

The model of geological evolution of an interarc basin, which is the north-east ending of Mid Kuril trough located on the continental slope of Kuril-Kamchatka trench, was constructed. Seismic facies analysis was first applied to define sedimentation conditions in a deep water trench. The analysis was based on the 2D CDP reflection seismic data obtained by Dalmorneftegeophysica JSC in 2014. According to the modeling results, the basin began to form in the Late Cretaceous and passed several stages. Initial subsidence of a local crust area of the incipient basin changed over to its further separation from the adjacent waters of the Sea of Okhotsk and Pacific Ocean by various volcanic formations framing its contour. The basin waters and the Pacific Ocean waters merged as a result of subsidence and submersion of volcanic structures on the east basin framing at the final stage during the Oligocene-Middle Miocene. This subsidence is directly related to the global processes associated with Kuril-Kamchatka ocean trench appearance such as inherent crust subsidence along valley bottom line accompanied by increase in inclination angle of its flanks. It was concluded that the trench origination time approximately corresponds to the Oligocene-Middle Miocene boundary.

The March 25, 2020 MW 7.5 Paramushir earthquake

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.

Activation of the Sarychev Peak volcano in 2020–2021 (Matua Isl., the Central Kuril Islands)

This publication, based on remote sensing data, examines the features of the effusive eruption of the Sarychev Peak volcano (Matua Isl., the Central Kuril Islands), which took place from December 2020 till February 2021. On the basis of the analysis of the Sentinel satellite data, it was established that starting from December 2020, the crater of the Sarychev Peak volcano began to fill with lava. As of January 18, 2021, it was completely filled, then lava outpouring through a fissure in the north-northwest part began. A lava flow (length 2 km, width 80–90 m) descended along the bottom of the valley, which cuts the northwestern slope of the volcanic cone. The outpouring of lava was completed by February 7, 2021. The effusive eruption of the Sarychev Peak volcano in 2020–2021 is atypical for the modern stage of eruptive history, characterized mainly by explosive and explosive-effusive type of eruptions.

On the unusual distribution of modified Amur River water in the Aniva Bay (Sakhalin) in November 2001

In addition to the distribution of modified water of the Amur River runoff in the Aniva Bay, remote from its mouth, according to the data from 2012–2013 (Shevchenko G.V., Chastikov V.N. Distribution of the Amur waters in the eastern part of the Aniva Bay in late autumn. Meteorology and Hydrology, 2021, no. 1), the materials of the oceanological survey carried out in this basin in mid-November 2001 are presented. It is shown that desalinated water entered the bay in an unusually wide stream in the upper 30-meter layer and occupied a vast area, almost to the middle of the bay. At the same time, the differences in salinity with local waters were less than usual. The most probable reason for such specific features of oceanological conditions in 2001 was an increase (by about 30% in comparison with the usual values) of the wind of west-northwest rhumb of an offshore character. The obtained results show that the influence of this water can manifest itself not only near the eastern coast of the bay, as was demonstrated in the mentioned article, but also at a distance of more than 30 km from it. Accordingly, abrupt decreases in salinity can affect the marine biota not only of the coastal complex, but also inhabiting the central part of the bay.

Fundamental for self-developing processes model and problems of its application to earthquakes prediction in the Far East region

Seismic activation in the period of foreshocks (prior to the mainshock) described by the model of self-developing processes (SDP) is possibly a manifestation of explosive instability of low frequency straining waves in metastable medium. To highlight so nontrivial relationship of continuous wave motions and discrete seismic events flow is a goal of this narrative. Thus, the rationale of the SDP model (the equation, in reality) has been modified, which is of importance in relevance with the article by the Malyshevs in the current issue (A.I. Malyshev, L.K. Malysheva. Precedent-extrapolation estimate of the seismic hazard in the Sakhalin and South Kurils region) which is to improve the seismic hazard estimates by means of this model. A new way to reveal the very beginning of blow-up regime after quasi-stationary one is proposed.

Peculiarities of anomalous gas-geochemical fields in the East Deryugin graben of the Sea of Okhotsk

This paper presents the research data on methane distribution in the area of the most noticeable gas discharges in the Deryugin Basin of the Sea of Okhotsk. In the East Deryugin graben, a unique methane seep is known, which spatially coincides with the local authigenic barite-carbonate mineralization. The question of the source nature, which is associated with the methane emission in the studied area, is considered.