Deep structure and seismotectonics of the Southern Sea of Okhotsk region along a profile from southern Sakhalin to the southern Kuril Islands

The results of deep seismic profiling through Southern Sakhalin, the southern Sea of Okhotsk, and the Southern Kuril Islands allowed the identification of deep fault zones, the hypocenter locations, the features of the stress state, and the types of seismic dislocations at the earthquake sources. The east side of the fault was upthrown relative to the west side beneath the southern part of the Tatar Strait and Sakhalin Island and led, as a result of multiple thrusting events along the fault over the geologic history, to the rise and 5-8 km displacement of the seismic boundaries. The true uplift of the Greater Kuril arc block was determined using the focal mechanism solutions. The seismoctectonics and present-day dynamics of the crustal blocks were estimated using a detailed joint analysis of the position of the structural boundaries at the seismic section and the seismotectonic movements according to the earthquake focal mechanisms.     

Deep structures in the Maritime Territory-Sea of Japan continental margin from seismic data

This paper discusses the results of interpreting seismic profiles on the Earth’s crust of the Maritime Territory and Sea of Japan performed during the 20th century by the Sakhalin Integrated Research Institute and by the Schmidt Joint Institute of Physics of the Earth, Russian Academy of Sciences. The seismic profiles confirmed the presence of structural features under the Maritime Territory and the Sea of Japan that were revealed previously from geological data, such as spreading zones, rifts, deep-seated faults, overthrusts, and subduction zones, suggesting an active type of continental margin in the Far East region. We assumed that a high occurrence of the asthenospheric layer enclosing magmatic chambers explains the high activity of tectonic processes in the Far Eastern continental margin. The identified system of rifts and spreading centers supports this assumption.     

欧亚大陆北部盆地发育历史——来自东西向跨洲剖面的证据

板块演化控制了盆地的形成与演化,盆地的性质和地质特征由其所处的板块构造单元决定.本文从大地构造背景角度出发,沿北纬60°±5°绘制了欧亚大陆东西向跨洲剖面,西起北海内伊湖—阿兰盆地,东至北鄂霍茨克盆地,全长为11000km.剖面将构造单元划分为不同级别(超大陆与构造域—板块与造山带—陆块与构造带—盆地与拱起),进而将构...     

Geophysical survey to estimate the 3D sliding surface and the 4D evolution of the water pressure on part of a deep seated landslide

Geophysical surveys were conducted on the very unstable front part of the La Clapière landslide in the French Alps (Alpes Maritimes). The electrical resistivity survey was carried out to obtain, for the first time on this deep-seated landslide, 3D information on the slipping surface and the vertical drained faults. Moreover, we planned to follow within time (6 months) the evolution of the saturated zones (presence of gravitational water) and their percolation into the shearing zones. Our 4D results showed the importance of the complex water channelization within the slope and relation to geological discontinuities.     

The Structure of the Sedimentary Cover of the Kandalaksha Gulf,White Sea,from Seismoacoustic Data

The geological structure of water areas adjacent to the White Sea biological research station of Moscow State University (Rugozero Bay and Great Salma Strait; both are parts of the Kandalaksha Gulf, White Sea) was studied for the first time based on the seismoacoustic data. The morphology of the top of the Achaean basement, the structure of the Quaternary sedimentary cover, and the bottom topography were investigated. The sequence of glacial deposits dated back to the last glaciation and the compound sequence consisting of glaciolacustrine, glacial-marine, and marine sediments are distinguished. The spatial locations and changes of their thicknesses are considered. It is shown that the recent bottom topography is controlled by predominantly NW- and NE-striking faults that run through the entire sedimentary sequence, including the Holocene sediments.     

Stable Isotope and Lithologic Evidence of Late-Glacial and Holocene Oceanography of the Northwestern Pacific and Its Marginal Seas

Stable isotopes, geochemical, lithological, and micropaleontological results from cores from the far northwest (FNW) Pacific and the Okhotsk and Bering seas are used to reconstruct the regional environment for the last glaciation, the deglacial transition, and the Holocene. δ¹⁸O records of planktonic foraminifera of the region show two “light” shifts during deglacial time, provoked by the freshening of the surface water and climate warming. These north Pacific terminal events (T1ANP and T1BNP) with ages of 12,500 and 9300 yr B.P., respectively, occur almost simultaneously with two episodes of accelerated glacier melting around the North Atlantic. Along with the isotopic shifts, the CaCO₃content in regional sediments increased abruptly (1A and 1B carbonate peaks), probably due to changes of productivity and pore water chemistry of surface sediments. Organic matter and opal concentration increased during the transition (between T1ANP and T1BNP events) in the sediments of the FNW Pacific and the southern part of the Bering Sea and opal content increased in the Holocene in the Bering and Okhotsk Seas. δ¹³C records of cores from the Okhotsk and Bering seas and the FNW Pacific do not contradict the hypothesis of increased intermediate water formation in the region during glaciation. During deglaciation, accumulation of the coarse terrigenous component decreased in sediments of the Bering Sea and the FNW Pacific before the T1ANP event, probably as a result of rising sea level and opening of the Bering Strait.     

Study of active faults: Theoretical and applied implications

Theoretical and applied implications of the study of active faults and their identification and parametrization are discussed. The term active fault is defined as a fault with displacements that occurred in the late Pleistocene and Holocene and are expected to resume in the future. The displaced young landforms, late Quaternary sediments, and man-made constructions are the main reference marks to recognize active faults and estimate their kinematics and intensity. Since the structural pattern and parameters of all active faults are referred to the same, geologically short time interval, they are important for the study of recent geodynamics and young tectogenesis on the global, regional, and local scales. The opportunities that are opened for such investigations are illustrated by verification of the real existence of the Okhotsk and Bering minor plates. With allowance for active faults, it is possible to make tectonic and geodynamic reconstructions of the past events more plausible. Natural hazards, primarily, earthquakes, are related to active faults. The geological and geomorphic assessment of the seismic potential of active fault zones is discussed with emphasis on the maximum possible magnitude of earthquakes (M _max) estimated from the segmentation of the active zones, the length of particular segments (L), the empirical relationships M _max/L for strong recent earthquakes, as well as the resumption periods of strong earthquakes and measurement of particular seismogenic offsets by trenching and other techniques, including archeoseismological methods. A question is posed about possible perennial variations in the stress-and-strain state of active zones, which are expressed on the scale of large seismoactive regions in oscillations of released seismic energy and should be taken into account by assessment of the seismic hazard.     

Interpretation of radon anomalies in seismotectonic and tectonic-gravitational settings: the south-eastern Crati graben (Northern Calabria, Italy)

The study area is located in the south-eastern part of the Crati valley (Northern Calabria, Italy), which is a graben bordered by N–S trending normal faults and crossed by NW–SE normal left-lateral faults. Numerous severe crustal earthquakes have affected the area in historical time. Present-day seismic activity is mainly related to the N–S faults located along the eastern border of the graben. In this area, much seismically induced deep-seated deformation has also been recognised.In the present paper, radon concentrations in soil gas have been measured and compared with (a) lithology, (b) Quaternary faults, (c) historical and instrumental seismicity, and (d) deep-seated deformation.The results highlight the following:

(a) There is no evidence of a strong correlation between lithology and the radon anomalies.

(b) A clear correlation between the N–S geometry of radon anomalies and the orientation of main fault systems has been recognised, except in the southernmost part of the area, where the radon concentrations are strongly affected by the superposition of the N–S and the NW–SE fault systems.

(c) Epicentral zones of instrumental and historical earthquakes correspond to the highest values of radon concentrations, probably indicating recent activated fault segments. In particular, high radon values occur in the zones struck by earthquakes in 1835, 1854, and 1870.

(d) Deep-seated gravitational deformation generally coincides with zones characterised by low radon concentrations.

In the studied area, the anisotropic distribution of radon concentrations is congruent with the presence of neotectonic features and deep-seated gravitational phenomena. The method used in this study could profitably contribute towards either seismic risk or deep-seated gravitational deformation analyses.     

Fault-block structures in the eastern margin of the Amur lithospheric plate,their seismicity,and fluid regimes

The results of long-term studies of the neotectonic processes and related phenomena such as the Earth’s interior degassing, the fluid discharge, and the high seismicity in the zone of interaction between the Amur and Okhotsk lithospheric plates at the transition between the Verkhnii and Srednii Amur regions were used for defining the separate structural blocks with different geodynamics and analyzing their relations with the seismic events during the periods of high seismic activity and quiescence. The heliometric and atmochemical studies in the Zeya-Bureya basin revealed zones of high permeability. Long-term observations of the fluid dynamics at the Konstantinovka mineral water deposit demonstrate a correlation between the variations in the water-soluble helium contents and the changes in the stress-deformed state of the blocks located up to 200 km away from regime observation sites.     

Deep structure of the southeastern part of the East European Platform

The results of CMP seismic data acquisition along regional deep profiles that cross large tectonic elements in the east of the East European Platform are considered. It has been established that the Zhiguli-Pugachev Arch and the Stavropol Depression (southern part of the Melekess Basin), as well as the Volga-Kama Anteclise and Pericaspian Syneclise, conjugate along reverse-thrust faults extending to the lower crust and Moho discontinuity. The position of the southeastern reverse-thrust boundary of the South Tatar Arch has been substantially specified in plan view and illustrated by seismic sections. Based on the results obtained, it is suggested that reverse-thrust faults of different orders are widespread in petroleum provinces in the east of the East European Platform, and this suggestion should be used in geological exploration. The CMP seismic data acquisition is efficient in studying the junction zones of large tectonic elements. It also provides insights into the deep structure of the Earth’s crust and its relationship to the structure and petroleum potential of the sedimentary cover and localization of oilfields. It is expedient to reprocess and integrate earlier seismic data in order to compile tectonic (tectonodynamic) regional maps on a new methodical basis.     

TECTONIC STRUCTURE AND OIL AND GAS POTENTIAL OF THE KOLKHIDA PLAIN AND ADJACENT REGIONS

Western Georgia is in the eastern part of the Riono-Black Sea intermontane oil and gas reservoir. Coastal Abkhaziya and the Colchis Plain is favorable for oil and gas prospecting as Mesozoic sediments are here overlain by a series of Tertiary and Quaternary rocks. From the Recent tectonic pattern, evolution, age, and composition of the present complexes the authors could outline three tectonic regions: Guri, Colchis and Abkhazsko-Megrel.

The geological pattern of the Colchis region has recently become better known. Borehole data indicate the presence of a heavy Cretaceous carbonate series (over 1, 000 m thick) overlain with sharp angular unconformity by Pliocene and Quaternary argillo-arenaceous sediments.

From data obtained by seismic prospecting, drill-hole exploration and geological survey the conclusion that all brachyanticlines in the Colchis region might be grouped into three anticlinal zones, namely northern-Colchis, central Colchis and southern Colchis. Within the northern Colchis zone three brachyanticlines (Ingur, Ochemchiri and Kodor) are distinguished. The same confinement of separate uplifts to the anticlinal zones may be observed in the Abkhazsko-Megrel and Guri regions, where an overall complex of Tertiary sediments is developed. In the area under discussion two structural layers are isolated: the lower Domeotic and the upper, consisting of Pliocene- Quaternary rocks. The lower layer is characterized by intermittent folding, the upper one -- by nearly horizontal bedding. The oil content of the Cretaceous sediments in Western Georgia is known from drilling data and abundant oil and gas occurrences. In this connection certain Colchis brachyanticlines are of great interest for oil and gas prospecting within the Cretaceous carbonate complex.     

Structure of terrestrial crust in southern Sakhalin and adjacent aquatoria

Recent deep seismic sounding and other data suggest presence of a deep rift which cuts across southern Sakhalin, Aniva Bay, La Perouse Strait, and Hokkaido Island, a suboceanic type of crust in the Sea of Okhotsk, and a continental one in Sakhalin. The density-velocities relationship determined here may account for the observed gravity anomalies as due primarily to variations in thickness of the crust (fig. 6), without resorting to other hypotheses.     

Main active faults and seismic activity along the Yangtze River Economic Belt: Based on remote sensing geological survey

The Yangtze River Economic Belt (YREB) spans three terrain steps in China and features diverse topography that is characterized by significant differences in geological structure and present-day crustal deformation. Active faults and seismic activity are important geological factors for the planning and development of the YREB. In this paper, the spatial distribution and activity of 165 active faults that exist along the YREB have been compiled from previous findings, using both remote-sensing data and geological survey results. The crustal stability of seven particularly noteworthy typical active fault zones and their potential effects on the crustal stability of the urban agglomerations are analyzed. The main active fault zones in the western YREB, together with the neighboring regional active faults, make up an arc fault block region comprising primarily of Sichuan-Yunnan and a “Sichuan-Yunnan arc rotational-shear active tectonic system” strong deformation region that features rotation, shear and extensional deformation. The active faults in the central-eastern YREB, with seven NE-NNE and seven NW-NWW active faults (the “7-longitudinal, 7-horizontal” pattern), macroscopically make up a “chessboard tectonic system” medium-weak deformation region in the geomechanical tectonic system. They are also the main geological constraints for the crustal stability of the YREB.     

Some interpretational aspects of time cross-sections based on seismic reflection data from the Sea of Okhotsk

The results of investigations in the Sea of Okhotsk by the seismic reflection method are considered with special attention paid to the acoustic anomalies. Two types of such anomalies are definable in the basin: local (“gas channel”) and areal (“turbid sequences”). It is shown that the acoustic anomalies distinguishable in the single channel seismic profiling (SCSP) records are characteristic of sediments with partial gas filling. Many local anomalies documented on the Sakhalin slope are spatially connected with zones of faulting. The simultaneous presence of acoustic anomalies and BSR in the upper part of the section serves as a reliable diagnostic feature of gas hydrates. The dispersion of the velocities in the wave packet characterizing the acoustic anomaly associated with the lower part of the sedimentary cover in the Kurile Basin points to the significant thickness of the gas-bearing sediments in the latter.     

Aspects of tectonics of Kamchatka

The tectonics of Kamchatka are reviewed in some detail and in several cases reinterpreted in light of recent geological and geophysical studies. Maps present major structural features and magnetic data, obtained by aerial survey. Recent work has confirmed four young phases of tectogenesis, accompanied by intrusions: 1) Late Cretaceous to early Paleogene (Laramian or Kamchatka phase), 2) early Miocene (Kuril phase), 3) late Miocene (Aleutian phase), and 4) late Pliocene (Sakhalin phase). These account for the young folded region that covers most of the Kamchatka Peninsula and the Koryak uplands to the northeast. Three structural-stratigraphic zones are recognized. The west zone is a marginal trough filled with coal- and oil-bearing strata, moderately folded. The central zone is an inner volcanic arc made up of volcanic rocks cut by granitoid rocks. The east zone consists of thick flysch with basic and ultrabasic igneous rocks characteristic of external folded arcs. In general, major synclinoria and anticlinoria have northeast strikes, and magnetic values in general correlate with the strike and composition of these belts. The meridionally oriented Central Massif of ancient rocks controlled the development of structures in nearby Tertiary and Cretaceous rocks. Deep faults also trend northeast and determined the position of volcanic and metallogenic zones, the ophiolite belts, and the chain of intrusive massifs. Geophysical work shows that the northern part of the Sea of Okhotsk is of platform type; it has recently been postulated that the Okhotsk massif is part of the Siberian platform.—W.D. Lowry     

Influencing factors and evaluation application of regional crustal stability in the Bohai Strait

Due to the extremely complex geological conditions in the Bohai Strait, active faults is very developed and earthquake activity occurs frequently. It is of great importance to evaluate the regional crustal stability for the planning and construction of the Trans-straits Passage. In this study, the authors carry out the evaluation by means of buffer analysis, topology analysis and overlay analysis based on ArcGIS software. The evaluation mainly analyzed six assessment factors of Bohai Strait including neotectonic activity, active faults distribution, seismicity, tectonic stress fields, Bouguer gravity anomaly and geological disasters. In brief, the crustal stability of the eastern North Yellow Sea Basin is best, while that of the Bohai Basin and southwest Bohai Strait is poor. Meanwhile, small and frequent earthquakes in the southern Strait and geological disasters developed in the northern and central Strait such as tidal ridge and shallow gas which may adversely impact on the Trans-straits Passage construction.     

Tectonics of the Devonian Complex of the Southern Sector of the Caspian Basin (Kazakhstan): A Set of Geological and Geophysical Methods

The paper presents a comprehensive analysis of new data for drilling and seismic survey of the oil and gas potential of deep-seated Paleozoic horizons of the Caspian Basin in Kazakhstan. The features of the development and occurrence of large Paleozoic uplifts and sedimentary strata promising for prospecting are specified. A set of geological and geophysical methods was applied, and magnetic and gravitational anomalies of potential fields were analyzed in the southern, southeastern, and eastern marginal parts of the southeastern sector of the Caspian Basin. This is supplemented with new data obtained by a set of reconnaissance methods, and the section attributed to the Paleozoic at depths up to 5.5–8.0 km and its Devonian–Lower Carboniferous sequence are specified. New data were obtained on the area of distribution and occurrence of Upper Devonian and Lower Carboniferous sediments, geological conditions and prerequisites were revealed that refined the trace of the pre-Devonian complex and of the Lower–Middle Devonian sediments. Analysis of the distribution of large local prospecting objects has confirmed the presence and development of megauplifts, which are zones of hypsometrically elevated Devonian–Lower Carboniferous sediments. In the contour of the megauplift, structural elements have developed that are less significant, but promising in terms of hydrocarbon content. Based on the results of studying and refining the distribution patterns of large Devonian‒Lower Carboniferous objects and identifying megauplifts, it is possible to optimize regional studies in the Caspian Basin for the period of 2020–2030.

     

Active faults in the Sea of Marmara, western Turkey, imaged by seismic reflection profiles

Turkey is moving westward relative to Eurasia, thereby accommodating the collision between Arabia and Eurasia. This motion is mostly taken up by strike-slip deformation along the North and East Anatolian Faults. The Sea of Marmara lies over the direct westward continuation of the North Anatolian Fault zone. Just east of the Sea of Marmara, the North Anatolian Fault splits into three strands, two of which continue into the sea. While the locations of the faults are well constrained on land, it has not yet been determined how the deformation is transferred across the Sea of Marmara, onto the faults on the west coast of Turkey. We present results from a seismic reflection survey undertaken to map the faults as they continue through the three deep Marmara Sea basins of Çlnarclk, Central Marmara and Tekirdag, in order to determine how the deformation is distributed across the Sea of Marmara, and how it is taken up on the western side of the sea. The data show active dipping faults with associated tilting of sedimentary layers, connecting the North Anatolian Fault to strike-slip faults that cut the Biga and Gallipoli Peninsulas.     

Partition geochemistry of hydrothermal precipitates from submarine hydrothermal fields in the Hellenic Volcanic Island Arc

The geochemical study of 5 sediment cores obtained from different shallow hydrothermal fields along the volcanic arc (Methana, Milos, Kos and Yali), revealed that the degree of rock hydrothermal alteration from one area to another is different and is influenced by the physical and geochemical properties of the hydrothermal venting fluids and the type of the rocks in the substrate. The submarine hydrothermal fields in the central Aegean Sea are linked with the Hellenic Volcanic Arc and imprint their hydrothermal influence on the local marine sediments. Hydrothermal venting fluids differ in pH, temperature, gas and metallic element content, intensity of gas and water flux, while rock substrate is variable in terms of thickness and chemistry of the marine sediments and the mineral deposits. The analytical results showed that the lowest values of Fe are observed in Palaeochori Bay (0.72%) and the highest values are found in Bros Thermi (2.72%). The highest Mn concentrations are found in Bros Thermi (407 ppm) and the lowest are found in Yali (29 ppm). Cu and Pb highest concentrations are found in Bros Thermi (21 ppm) and Thiafi Bay (16 ppm), and the lowest in Yali (1 ppm). Zn highest values are found in Bros Thermi (56 ppm) and the lowest values in Kephalos Bay (10 ppm). Finally, the Ca and Mg-richest layers are observed in Kephalos 7.5 and 0.98% respectively and the lowest are observed in Milos (0.01% for Ca) and Yali (0.12% for Mg). The hydrothermal activity presented variations with geological time and hydrothermal suspended particulate matter coming out from the vent outlets also influence the sediment geochemistry. As an example in Methana, high concentrations of Cu and Zn in SPM result in high levels of Cu and Zn in the sediments.     

断层研究在地震安全性评价和石油勘探工作中的对比分析

对比分析了地震安全性评价和石油勘探中,断层研究的内容和方法。两者研究内容都包括断层活动时代、位置、规模、产状、性质等,但地震安全性评价更关注断层在地表和浅层的状况,活动时代等;石油勘探更关注较深处断层的状况,能否形成断块圈闭是主要研究内容。研究方法都包括地质露头调查、重力、地磁、地震勘探、钻井等。