Lithospheric Plates Research Articles

Tomographic Imaging of the Plate Geometry Beneath the Arunachal Himalaya and Burmese Subduction Zones

AbstractWe present 3‐D P and S‐wave velocity perturbation maps of the upper‐mantle beneath eastern Himalaya and Burmese subduction zones at 2° × 2° lateral resolution, using teleseismic travel‐time tomography. Collated waveforms of 5,727 teleseismic earthquakes recorded at 273 seismic stations generated an accurate data set of 86,570 P‐arrival and 85,227 S‐arrival times using multichannel cross‐correlation. Tomograms enabled imaging of the structural features down to 1,000 km depth. The subducting Indian lithospheric plate extends up to Bangong‐Nujiang Suture Zone, overturns and descends steeply beyond 200 km below the Himalayan arc. A southward plunging detached slab can be traced beyond 600 km. Results reveal no evidence for the detachment of a S‐E deflecting Indian lithospheric slab below the Burmese arc. The geometry of the slab mimics regional seismicity (up to 200 km) followed by a deeper aseismic zone related to petrological changes. No gaps are seen between the northward and eastward subducting Indian plate, hence confining the eastward escape of Tibetan‐lithospheric material between the Eastern Himalayan Syntaxis and Sichuan Basin.

The role of plate geometry and boundary type in global plate ductility and mantle convection

This paper tracks the role of plates in plate tectonics and mantle convection. Geometric and morphologic plate analyses are based on paleoreconstructions, beginning at 200 Ma, large-scale volcanic events, APWPs, and geoid data. Plates organize themselves to form a space-fitting geometry with a minimum perimeter/area (P/A) ratio (i.e., SA/V in three-dimensions) and a coordination number close to 5. Plates are either broken and subducted in order to remove plates with high P/A ratios or combined with other plates to reduce the total perimeter in the lithospheric plate mosaic. Various permutations of breaking and/or combining of high P/A plates are applied throughout earth's history to reduce the global P/A ratio. During this process, plates change their shape and/or size, which aids plate mobility to ultimately reach a stable geometry. Plates can only move with a suitable geometry and the global pattern keeps adjusting to reach a stable geometry. The lithospheric plates follow a pattern of ‘punctuated steady state’, where the global geometry cycles between ‘ductile’ periods, when the plates are moving to reach a new steady state geometry, to more static, or stable, periods, when the plates are relatively immobile and connected by a stable network of compressional stresses. Here, the Bénard-Marangoni theory is used to explain plate patterns in terms of surface tension because it allows for convection to be driven by temperature dependent surface tension. Mantle flow drives the temperature gradient at the surface, which results in a surface tension gradient. So, temperature dependent buoyancy and surface tension both play a role in convection. This suggests that there is feedback between the plates and the mantle, so neither is entirely passive.

Relationships of Surface Geological and Geophysical Characteristics with the Deep Structure of the Mid-Atlantic Ridge According to Seismic Tomography Data

—A retrospective analysis of seismic tomography models with different levels of detail along the Mid-Atlantic Ridge (MAR) has shown that mantle inhomogeneities depicted by variations of seismic waves velocities in low-detail models look larger than their true sizes determined by more detailed modern models. They also confirm that there are two different types of upwelling in the Atlantic mantle: active plume, which has an impulsive character, and passive axial, which occurs as a response to spatial appearance during the drift of lithospheric plates. The structure of mantle velocity and density inhomogeneities, determined by low-frequency gravity anomalies and their reductions, has a consistent interpretation based on the thermal state of the mantle. Detailed models of the velocities under the MAR can serve as a basis for comparison with the geochemical characteristics of basalts. The decomposition of a single axial tomographic anomaly in detailed models into a chain of vertical lenses under slow spreading conditions corresponds to geochemical data on discrete manifestations of different basalt associations along the MAR. The attribute δ(Vp/Vs) section along the MAR in the mantle above ~700 km contains cold lenses with a thickness of 200–300 km, which are spatially related to the following structural and tectonic phenomena: transform faults with maximum lateral rift displacement; geochemical segmentation of the MAR; modulation of the total lengths of transform faults with increased values above the “cold” lenses; asymmetry features of the half-spreading rates, which decreases to zero above the cold lenses and reaches maximum values between the cold lenses. The cold mantle lenses at an average depth of ~500 km and the corresponding lithospheric geophysical characteristics reflect the background conditions, and areas above hot segments are disturbances that occur when plume branches interfere with the MAR. Inhomogeneous spreading rates can lead to movements of blocks inside large plates and tectonic deformations of the intraplate space. Along the 4 Ma isochron in the Northern Hemisphere, the half-spreading rates on the eastern flank of the MAR exceed the half-spreading rates on the western flank. In the Southern Hemisphere, the pattern is reversed, which indicates the possible influence of the Earth’s rotation effects on geodynamic processes along the MAR. Against the general trend, there are local inversion zones from the western predominance of increased rates to the eastern and, conversely, in the Northern and Southern hemispheres. The main demarcation faults of the Atlantic differ in seismic events by their maximum energy release and are located near the “cold” mantle lenses and the contrasting lateral transition to the hot regions. The distribution of the total seismic moment in the depth intervals of 0‒13 and 13‒35 km also has less intense extremes near the branches of plumes with a predominantly crustal position of the hypocenters. The seismicity along the main MAR space associated with standard basalt magmatism has a background character and does not significantly contribute to the total released seismic moment compared to shear zones.

Treatment of Liquefiable Soils by the Ballasted Column Technique: Case of Martil River Bridge in the North of Morocco

The seismic activity in northern Morocco is largely due to an intense tectonic activity Plio-Quaternary and current generated by the approach of the two lithospheric plates Africa-Eurasia. Certainly, the liquefaction of soils is a phenomenon that presents a potential risk and a major challenge for the construction of foundations of engineering structures. The objective of this work is the realization of test plates to decide on adequate treatment in a soil liquefiable. For our case during the construction of a double bridge on a liquefiable soil and in a seismic zone, we were confronted with two technical problems, on the one hand the choice of the method of treatment of the soil in place and on the other hand the verification of this improvement by the results of the CPT tests (Cone Penetration Test) carried out before and after the densification of the soil. Many types of liquefaction remediation methods have been developed. However, for our case, the results indicate the effectiveness of the vibrocompaction method in improving the in-place soil compared to the dry method in eliminating the risk of soil liquefaction. It should be noted that the wet columns were lowered to 22m/TN, and the dry columns were stopped at varying depths between 2 and 14m/TN, and the results of the CPT (Cone Penetration Test) confirm the effectiveness of vibrocompaction and that the bridge foundations are protected against the phenomenon of soil liquefaction.

Особенности сейсмического процесса в западной части Алеутской субдукционной зоны и их возможная связь с климатическими изменениями в Арктике

In the second half of the XX century, there was a pronounced increase in the average annual temperature in the troposphere surface layer of the Russian Arctic region, which led to a scaling-up in the risks of natural disasters associated with the cryolithosphere degradation. Modern integrated studies of the Arctic have revealed a significant influence of geodynamic processes on the permafrost state. Previously, a seismogenic-trigger mechanism of the occurrence of climate warming phases in the Arctic proved to be possible due to strong mechanical disturbances of the marginal region of the Arctic lithosphere, caused by major earthquakes in the Aleutian subduction zone. The authors discuss the features of the seismic cycle in the Aleutian subduction zone, characterized the presence of a pronounced tangential component of the convergence vector of lithospheric plates. The study shows that the orientation of the plate convergence vector relative to subduction zone axis can have a significant impact on the preparation and occurrence of major earthquakes in subduction zones. In particular, the analysis of the seismic activity occurring in the western part of the Aleutian island arc showed that the seismic cycles here are shorter than in the eastern part of the arc. The authors revealed that major earthquakes, repeated in the same areas of the western part of the Aleutian subduction zone, differ both in magnitude and foci length. Taking into account the oblique subduction setting, the authors propose a keyboard model for the generation of major subduction-associated earthquakes as a mechanism potentially capable to explain the reduction in the seismic cycle duration and noticeable differences in the spatial extent and the foci localization of seismic events with similar magnitudes observed in the same segment of the western half of the Aleutian subduction zone.

The behavior of zeolites wairakite and phillipsite at high P-T parameters

In situ investigation of mineral behavior in water medium at simultaneously high P-T parameters can be applied to modelling of mineral transformation processes in lithospheric plates. The behavior of zeolites wairakite and phillipsite under the P-T conditions of «cold» slab subduction, corresponding to the start of oceanic plate diving or ocean floor near geothermal sources, was studied by in situ Raman spectroscopy. During compression in water medium, phillipsite initial phase is stable up to T = 350 °C, P = 1.7 GPa and with further increase of P-T parameters, phillipsite undergoes amorphization and partially dissolves in water. Wairakite compressed in water medium has a polymorphic transformation at T ≈ 300 °C and P ≈ 0.4 GPa. At 300–450 °C and P = 1 GPa the Raman spectrum almost disappears due to the amorphization of wairakite. Zeolite wairakite partially dissolves, and other zeolite phillipsite grows out of the fluid at T = 450 °C and P = 1 GPa. This transformation indicates the higher stability of phillipsite in comparison to wairakite. The in situ observed high P-T stability of phillipsite, which does not transform to other zeolites, and its formation from wairakite may indicate ф possible widespread distribution of this zeolite in marine sediments.By using the plane-wave pseudo-potential method, ab initio DFT calculations of Raman and FTIR spectra of wairakite were carried out. Comparing theoretical and experimental spectra, interpretation of the vibrational spectra of both zeolites was suggested.

The relationship of strong earthquakes, volcanoes and typhoons in the Philippine plate region as a result of the mutual influence of geospheres

The Philippine lithospheric plate is located at the intersection of the zones of intense influence of geosystems responsible for the evolution of the Earth’s outer shells, and is one of the most dangerous regions of the globe. The study of temporal variations of natural disasters at the end of the 20th — beginning of the 21st century is based on lies the premise of the relationship of strong earthquakes, volcanic eruptions and tropical atmospheric eddies in areas of complex high instability of geospheres.

On integral equations of cracks of a new type

For the first time, the paper develops a new type of crack modeling method that allows describing them in environments of complex rheologies. It is based on a new universal modeling method previously published by the authors, used in boundary value problems for systems of partial differential equations. The advantage of the method is the possibility of avoiding the need to solve complex boundary value problems for systems of partial differential equations by replacing them with separate differential equations, among which the Helmholtz equations are the simplest. Namely, with the help of combinations of solutions of boundary value problems for this equation, it is possible to describe the behavior of complex solutions of multicomponent boundary value problems. In this paper, for the first time, the method is applied to a mixed boundary value problem for cracks of a new type. Cracks of a new type, complementing the Griffiths cracks, were discovered during the study of fractures of lithospheric plates that converge at the ends during oncoming traffic along the Conrad boundary. In the course of the study, Kirchhoff plates were adopted as models of lithospheric plates. The method developed in the published article is aimed at the possibility of describing models of approaching objects similar to lithospheric plates in the form of deformable plates of more complex rheologies. In particular, it can be thermoelectroelastic plates or other rheology. In the process of solving problems using Kirchhoff models for lithospheric plates, there was a problem of calculating some functionals that needed to be determined. This method demonstrates an approach that eliminates this drawback. The derivation of integral equations of cracks of a new type, the method of their solution and the approach to application in more complex rheologies is given.

МОДЕЛЬ ГЛУБИННОГО СТРОЕНИЯ ЮЖНОЙ КАМЧАТКИ ПО РЕЗУЛЬТАТАМ ПЛОТНОСТНОГО 3D-МОДЕЛИРОВАНИЯ И КОМПЛЕКСУ ГЕОЛОГО-ГЕОФИЗИЧЕСКИХ ДАННЫХ

In the south of Kamchatka, a number of deep geophysical studies have been conducted along the profile lines. The aim of the research was to study the lithosphere in the zone of present-day volcanism and active seismicity. Geological and geophysical models of the Earth's crust and upper mantle were constructed along the profiles. The results were obtained as part of two-dimensional modeling of geophysical fields. But the analysis of materials shows that the territory is characterized by a complex geological structure, which is reflected in three-dimensional distribution of gravitating masses. For the first time, the article presents the results of volumetric density modeling covering the territory of southern Kamchatka, including areas covered by the Sea of Okhotsk and the Pacific Ocean. The model is based on the technology of three-dimensional imaging of 2D modeling results obtained along the grid of intersecting profiles. The 3D modeling generated isodensity surfaces that enclose regions with layers of high density (≥ 3.33 g/cm3). Thus, the surface identified beneath the ocean is interpreted as a fragment of the top of the subducting plate and the surface under the peninsula is identified as the top of the paleosubduction zone. A subhorizontal high-gradient zone (3.0–3.3 g/cm3) is recognized in the density structures that intersect the 3D model, which is identified with the Moho boundary. A model of subduction interaction between oceanic and continental lithospheric plates is proposed. The two-dimensional model shows the formation of a transitional layer between the Moho boundary of the overhanging lithospheric plate and the top of the paleosubduction zone. In the transition layer, a low-density zone is distinguished, where individual areas of maximum low-density are associated with melting chambers. Conditions are shown for the formation of the crust block with abundant basic-ultrabasic intrusions and the diorite-granodiorite intrusive massif. All ore occurrences and gold deposits of the Karymshinsky ore cluster are located within the contours of projection onto the ground surface of the deep high-gradient zone that encloses the low-density zone. Ore occurrences are genetically related to the zones of crustal weakness where epithermal deposits are formed in closed hydrothermal systems. Based on the analogy, it is possible to prognosticate gold occurrences in other areas of the projection of the high-gradient zone.

Геодинамические GNSS наблюдения на Курильских островах

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.

ГЕОДИНАМІКА

The purpose of the work is the analysis and geological-tectonic interpretation of the anomalous gravity field of the Ukrainian Carpathians and adjacent territories, as well as the construction of a density model of the Earth's crust and upper mantle according to the international PANCAKE seismic profile. The need to build a density model along the PANCAKE profile is due to the significant interest of a number of geologists and geophysicists in the results of seismic research along this profile. It is also caused by certain discrepancies in the seismological models of different authors. The gravity modeling technique, used in the work, includes the analysis of geological-geophysical maps and models. They are related to the geological-tectonic structure of the research region, to the creation of the initial structural part of the model and to the determination of the densities of strata and blocks of the model. The geometry and densities of the model are refined by the selection method, which is based on the interactive solution of the direct problem of gravimetric and the analysis of the reasons for the inconsistency of the calculated gravity field and Bouguer anomalies. A qualitative correspondence of the density model to the tectonic interpretation of the seismic section along the PANCAKE profile was achieved by using the methods of gravity modeling. The modelling results confirm the four-layer structure of the Earth's crust: the sedimentary cover, the upper, middle, and lower parts of the crust, which differ significantly in density. There is also evidence of the difference of the ALCAPA lithospheric plate, Flysch Carpathians and Precambrian Craton in Earth's crust and upper mantle structure. The ALCAPA plate is characterized by a small thickness (up to 29 km) and a low density of the Earth's crust. The density of the ALCAPA upper mantle is lower (3.20-3.21×103 kg/m3) compared to the upper mantle under the Ukrainian Carpathians and the East European Craton (3.28-3.30×103 kg/m3). This may be related to a change of a mantle composition and increased heat flow under ALCAPA. The Ukrainian fragment of the East European craton in the PANCAKE profile zone is characterized by a typical thickness of the crust (~41-45 km). The upper part of the crystalline crust, in contrast to the middle (2.86-2.90×103 kg/m3) and the lower part (2.98-3.10×103 kg/m3), is characterized by a lower density and greater differentiation in horizontal direction and with depth (from 2.66×103 kg/m3 to 2.86×103 kg/m3). The complex transition zone (subduction zone, Carpathian Orogen) between the ALCAPA microplate and the East European Craton causes an intense negative Bouguer anomaly – the Carpathian gravity minimum, which reaches -90×10-5 m/s2. It has a complex nature: Neogene and Paleogene-Cretaceous flysch rocks low density (≤2.50×103 kg/m3) of the Boryslav-Pokuttia cover, the main huge Precarpathian sub-vertical fault (>4 km) on the extreme southwestern slope of the platform (relatively local factors) and significant deepening of the MOHO surface under the Carpathian structure (regional factor). According to our density model, the depth of the MOHO under the front of the Carpathian thrust reaches 56 km.

ПОТЕНЦИАЛЬНАЯ НЕФТЕГАЗОНОСНОСТЬ ЗАПАДНО-КАМЧАТСКОГО ПОБЕРЕЖЬЯ И ЕЕ СВЯЗЬ СО СТРУКТУРНО-ТЕКТОНИЧЕСКИМ СТРОЕНИЕМ ОХОТОМОРСКОГО РЕГИОНА ПО ГЕОФИЗИЧЕСКИМ ДАННЫМ

This article describes the peculiarities of the deep structure of sedimentary depressions of the West Kamchatka coast and the adjacent offshore areas of the Okhotsk Sea shelf, manifested in the observed potential fields, as well as in their transformations. To reveal geophysical regularities reflecting the structure of the deepest part of the crystalline basement within the analyzed objects, a pseudo gravity field calculated on the basis of analytical approximation was used. The regional and local components of the decomposition of the observed potential fields, calculated by two-dimensional adaptive energy filtering and presumably associated with different-depth structural-tectonic objects, were analyzed. On the basis of comparison of the investigated Pustoretsky depression with the «reference» Kolpakovskaya depression, which includes known gas-condensate fields (West Kamchatka oil-and-gas bearing region), conclusions about the similarity of their formation conditions and subsequent evolution were made. A regional geophysical model of the Pustoretsky depression has been compiled, which makes it possible to reasonably assume its formation in the zone of Cenozoic subduction processes caused by the interaction of lithospheric plates.

Review of the main Black Sea rifting phase in the Cretaceous and implications for the evolution of the Black Sea lithosphere

The Black Sea is a deep marine basin formed by lithosphere extension and active rifting in a back-arc tectonic setting, by general consensus, in the Cretaceous. Its present structural architecture, however, is mainly defined by compressional tectonics during the Cenozoic when large scale “basin inversion” reactivated extensional fault systems formed in the Cretaceous. Rifting during the Cretaceous is usually taken to represent the main process forming the present-day basin (that is, producing crustal thinning and concomitant subsidence prior to its modification during Cenozoic inversion). Rifting at this time took place within continental lithosphere that had been accreted to and, by the Cretaceous, formed part of the Eurasian lithospheric plate. The precise history of how and when pre-Cretaceous aged tectonic domains were accreted to Eurasia forming the continental lithosphere underlying the Black Sea is poorly known. A critical issue to the tectono-thermal evolution of the Black Sea basin with important implications for paleogeography and sedimentary depositional environments is the degree of crust (and lithosphere) thinning during Cretaceous rifting and whether oceanic or “sub-oceanic” crust was formed at that time. The main focus of this paper, in order to illuminate this issue, is on kinematic observations related to the Cretaceous (Albian-Cenomanian) rifting phase, including subsidence analysis, as well as the immediate post-rift sedimentation and stratigraphy. The results suggest that rifting during the Cretaceous was insufficient in its own right to reveal exhumed mantle or to promote ocean crust formation beneath the deep basins of the Black Sea. It is concluded that an important contribution to observed present-day crustal and lithosphere architecture of the Black Sea area are legacy extensional tectonic events affecting the area in pre-Cretaceous times, with implications for the Late Palaeozoic-Mesozoic paleogeography and paleotectonic evolution of this area.

Changes in the properties of the statistics of physical and biophysical fields as earthquake precursor

This article discusses the precursors of earthquakes associated with changes in the statistics of physical and biophysical fields, which may contain information about the preparation of the expected seismic event. The approach used is associated with the study of the change in the entropy of the measured fields, which occurs as a result of the activation of the processes of fractures of the lithospheric plates immediately before the earthquake. As a result of the calculations, it was possible to identify the phenomena of processes with a high degree of determinism that arise in a short period of time before a seismic event. These phenomena correspond to the statistics obtained for both physical and biophysical fields and are valid up to large, up to several thousand kilometres, distances from the point of the corresponding measurements.

Lithospheric plate tectonics and mass extinctions of biological species

The merging of lithospheric plates and the formation of supercontinents are considered to be the main causes of global species extinctions within the Earth’s biosphere. Under those conditions, the factor of geographic isolation is diminished and interspecies competition is accelerated, allowing for the survival of the best-adapted species. The divergence of lithospheric plates triggers a new spurt of speciation that surpasses the previous one, as it involves the participation of the winning species.

Temperature distribution in a subduction zone

A model of the thermal and hydrodynamic structure of the subduction zone is proposed. This model includes free convection flows in the asthenospheric layer and layer C (mantle transition zone). Temperature profiles in the subducting lithospheric plate, as well as in the continental limb of the subduction zone, are presented. The heat flux due to friction at the contact between the subducting plate and the continental limb significantly affects the heat transfer and, consequently, the temperature field formation in the subduction zone. The temperature level in the crustal layer of the submerging plate implies that there is no melting in the crustal layer.

Geodynamic risks of developing rockburst-hazardous deposits in the Far Eastern region

Geodynamic activity of the Earth’s crust depends on the parameters of the movement of lithospheric plates and stress fields, both inherited in aseismic areas and modified in seismic active ones. Geomechanical processes occur in rock mass under the influence of various natural (endogenous and exogenous) and man-made (anthropogenic) factors. The degree of influence of these factors on the change in the energy saturation of blocks of various ranks will depend on various factors. In the geological environment of natural and man-made systems, there are dynamic phenomena of various energy levels from acoustic noise (microseismic) to rockburst and mining-induced earthquakes, that is, there is always a geodynamic risk in the geological environment of natural and man-made systems, especially in mining ones. The conditions of the geodynamic risks occurrence at specific deposits are considered on the example of rockburst hazardous deposits in the Far Eastern region of the Russian Federation. The influence of natural seismic activity on the realization of mining-induced seismicity is shown.

What Is the Impact of Tectonic Plate Movement on Country Size? A Long-Term Forecast

The Earth’s surface is under permanent alteration with the area of some nations growing or shrinking due to natural or man-made processes, for example sea level change. Here, based on the NUVEL 1A model, we forecast (in 10, 25, and 50 years) the changes in area for countries that are located on the border of the major tectonic plates. In the analysis we identify countries that are projected to gain or lose land due to the tectonic plate movement only. Over the next 50 years, the global balance of area gains (0.4 km2) and losses (12.7 km2) is negative. Thus, due to the movements of lithospheric plates, the land surface of the Earth will decrease by 12 km2 in 50 years. Overall, the changes are not that spectacular, as in the case of changes in sea/water levels, but in some smaller countries, projected losses exceed a few thousand square metres a year, e.g., in Nepal the losses exceed 10,000 m2 year−1. Methodologically, this paper finds itself between metric analysis and essay, trying to provoke useful academic discussion and incite educators’ interests to illustrate to students the tectonic movement and its force. Limitations of the used model have been discussed in the methodology section.

COMPARISON OF MODERN GEODYNAMIC MODES OF FRAMING OF THE EUROASIAN LITHOSPHERIC PLATE

The purpose of the work is to analyze the modern geodynamic mode of framing of the Eurasian lithospheric plate to determine the types of deformations in the structures of spreading, subduction and rift genesis and favorable conditions for oil and gas formation at certain stages of structure development. The authors have analyzed the Arctic spreading zone, the Kamchatka subduction zone, the southwestern part of Eurasia and the Baikal rift system. The author's development of calculation of slip vectors of rock masses in foci of earthquakes and methods of tensor analysis of mechanics of fractured media were used in the work. Differences and similarities between the Arctic spreading zone, the Kamchatka subduction zone, the southwestern part of Eurasia and the Baikal rift system are shown. All of the above structures have a complex layered-block structure. That is, in a layered-block medium in layers, and in individual blocks and in time, the stress-strain state of the lithosphere changes, which directly depends on the direction of the axes of compressive stresses

Subsurface structure of the martian Elysium Rise revealed by gravitational field separation

The Elysium Rise in the Martian northern hemisphere is the second largest volcanic province on Mars. To understand the volcanic activity in the Elysium Rise, the gravitational characteristics of this area were studied using the Bouguer gravity data derived from Goddard Mars Model-3 (GMM-3). The Bouguer gravity anomaly in the Elysium Rise was separated into regional fields and residual fields and the subsurface density profiles were obtained by a three-dimensional density inversion. The different anomaly features of the large volcanoes in the Elysium Rise were exhibited by the separation and density inversion results. Elysium Mons is characterized by a positive residual gravity anomaly surrounded by an annular negative anomaly, which possibly results from the volcano loading on a lithosphere plate. Albor Tholus has a positive gravity anomaly but with no obvious annular negative anomalies, which may result from the relatively small mass deficit generated by the eruption of Albor Tholus, unlike the Elysium Mons. In addition, the residual field shows prominent positive gravity anomalies with 150 km wide, centred at 157.2°E, 12.1°N, which could possibly be a hidden impact crater with an untraceable surface morphology or topography. Our study reveals the subsurface mass source distributions and structures of the Elysium volcanoes, providing a new method to understand the tectonic framework of the Martian subsurface through the study of gravity.