Crust In Area Research Articles

A proposed classification of the Earth's crustal areas by the level of geodynamic threat

It is accepted as a well-known fact that in different places on the Earth's crust, a similar anthropogenic impact causes a dissimilar response. Seismic zoning maps are not designed to predict such geodynamic hazards as rock bursts, induced earthquakes, reactivation of tectonic faults, etc., and therefore require careful adjustments in places of intense impact on the subsurface strata. In this regard, we consider the classification of the Earth's crustal areas according to the degree of geodynamic hazard, i.e. its potential geodynamic response to anthropogenic intervention. This classification is based on the concept that there exists a critically stressed layer within the Earth's crust. It is believed that such a critically stressed layer within the Earth's crust extends from the Earth's surface to a certain depth, and each point depends on the nature of the interaction between crustal blocks of different hierarchical levels.From this perspective, anthropogenic impact, such as mining operations, represents a direct impact upon the critically stressed zone. We recognize the hypothesis that the thicker the critical stressed rock layer, the stronger the response might be to anthropogenic intervention, as it has more accumulated energy. Four categories of geodynamic threat have been found and mapped. To verify this classification, the manifestations of the geodynamic hazards were studied. The intensity of geodynamic hazard increased from the first area to the fourth area. The phenomenon of large induced seismic events with hypocenters at great depths is explained on the basis of this theory, and could be associated with anthropogenic impacts from the surface directly on the regional zone of the critically stressed rock massif. The approach can be used to assess the geodynamic consequences of human exposure to the Earth's crust.

A Global Data Set of Present‐Day Oceanic Crustal Age and Seafloor Spreading Parameters

AbstractWe present an updated oceanic crustal age grid and a set of complementary grids including spreading rate, asymmetry, direction, and obliquity. Our data set is based on a selected set of magnetic anomaly identifications and the plate tectonic model of Müller et al. (2019, 10.1029/2018TC005462). We find the mean age of oceanic crust is 64.2 Myr, slightly older than previous estimates, mainly due to the inclusion of pockets of Mesozoic aged crust in the Atlantic and Mediterranean and improvements to the Jurassic Pacific triangle. This older crust is partly compensated by additional Cenozoic‐aged back‐arc basin crust not included in previous models. The distribution of spreading modes based on area of preserved crust is relatively equal between slow (20–55 mm/yr) and fast (75–180 mm/yr) spreading systems at 33% and 39%, respectively. Crust transitional between fast and slow, or intermediate systems (55–75 mm/yr), cover 20% of the preserved ocean floor with much smaller proportions of crust formed at ultraslow (5%) and super‐fast (3%) spreading systems. Slow and intermediate spreading systems exhibit the most stable behavior in terms of spreading asymmetry and obliquity, with the widest distribution of obliquities occurring at ultraslow spreading systems, consistent with present‐day observations. Our confidence grid provides a complementary resource for nonexperts to identify those parts of the age grid that are least well constrained. Our grids in 6, 2, and 1 arc min resolution as well as our python workflow, isopolate, used to compute our data sets are freely available in online repositories and on the GPlates data portal.

Microcontinents and Continental Fragments Associated With Subduction Systems

AbstractMicrocontinents and continental fragments are small pieces of continental crust that are surrounded by oceanic lithosphere. Although classically associated with passive margin formation, here we present several preserved microcontinents and continental fragments associated with subduction systems. They are located in the Coral Sea, South China Sea, central Mediterranean and Scotia Sea regions, and a “proto‐microcontinent,” in the Gulf of California. Reviewing the tectonic history of each region and interpreting a variety of geophysical data allows us to identify parameters controlling the formation of microcontinents and continental fragments in subduction settings. All these tectonic blocks experienced long, complex tectonic histories with an important role for developing inherited structures. They tend to form in back‐arc locations and separate from their parent continent by oblique or rotational kinematics. The separated continental pieces and associated marginal basins are generally small and their formation is quick (<50 Myr). Microcontinents and continental fragments formed close to large continental masses tend to form faster than those created in systems bordered by large oceanic plates. A common triggering mechanism for their formation is difficult to identify, but seems to be linked with rapid changes of complex subduction dynamics. The young ages of all contemporary pieces found in situ suggest that microcontinents and continental fragments in these settings are short lived. Although presently the amount of in‐situ subduction‐related microcontinents is meager (an area of 0.56% and 0.28% of global, non‐cratonic, continental crustal area and crustal volume, respectively), through time microcontinents contributed to terrane amalgamation and larger continent formation.

The tectonic architecture of wrinkle ridges on Mars

The geodynamic history of Mars is written largely in the form of its tectonic structures. A global population of compressional structures records a history of interior cooling and contraction, in combination with volcanic loading and flexure of the lithosphere. The most common of these structures are wrinkle ridges, interpreted as having formed by folding of near-surface layered volcanic materials above blind thrust faults. Topographic profiles of wrinkle ridges are found to dominantly fall into three classes: symmetric ridges, arch-style ridges characterized by broad convex upward backlimbs, and double ridges characterized by a broad arch and narrow ridge. A Monte Carlo boundary element model was used to constrain the underlying geometry of faults associated with the different ridge types. Symmetric ridges are pop-up structures formed between quasi-symmetric thrust and backthrust faults, in some cases above a horizontal décollement or low angle fault at depth. Arch-style ridges formed above a dominant primary thrust fault of near constant dip, with a secondary backthrust playing a lesser role in generating subtle inflections in the backlimb. Double ridges require two backthrust faults to localize strain within the narrow ridge at the ridge crest and to generate the secondary antiform on the backlimb. In these ridges, both the upper primary thrust and backthrust are contained within the layered volcanic materials, while the lower portions of the primary thrust can extend deep into the crust or upper mantle. A shallower depth of fault penetration in areas of thicker crust is consistent with the depth of faulting being limited by the brittle-ductile transition. Dips vary widely, but are typically steep in the upper faults and quite gentle in the lower faults. Thus, while wrinkle ridges do provide important records of tectonic and geodynamic processes on Mars as well as other bodies, the associated tectonic structures are more complex and varied than previously considered.

The crustal structure of the Eastern Subbasin of the South China Sea: constraints from receiver functions

SUMMARYThe crustal structure is a window to understand the tectonic evolution of an area. Through the first large-scale passive-source ocean bottom seismometer (OBS) array observation experiment in the Eastern Subbasin of the South China Sea (ESSCS), we calculated and obtained the respective receiver functions of these stations. As OBS works on the seafloor, where the working environment is different from that for its land-based counterpart, the effects of the sea-water layer and the oceanic low-velocity sediment layer on the seismic signals must be evaluated. Receiver functions’ synthetic test demonstrates the following: the presence of the sea-water layer produces a strong negative-amplitude phase (Pwp) in the receiver function, and the arrival time of this phase is delayed as the thickness of the sea-water layer increases; the presence of the low-velocity sediment layer produces a strong positive-amplitude phase (Pseds) which causes a delay in the arrival time of the Moho-related phases of the receiver function and makes them difficult to distinguish. On the basis of phase identification and synthetic tests, we estimate crustal thickness beneath each of the stations using two approaches. The first approach utilizes the observed arrival time of Moho phases, and the second approach finds the optimal crustal thickness by comparing the synthetic and observed receiver functions, which leads to more reliable results. The results of the second method show that the thickness of the sediment in the study area is mainly controlled by seafloor topography, the thickness of the crust in the seamount area is affected by the magma supply during the expansion stage and the post-spreading magmatism, and the crust in the flat basin is only affected by the magma supply during the expansion period. Moreover, the crust in the area affected by magmatic activity after the expansion stage is thicker than that in the area not affected.

Risk faults in stable crust of the eastern Bohemian Massif identified by integrating GNSS, levelling, geological, geomorphological and geophysical data

It is difficult to identify and assess the recently active faults, representing a risk factor for key human activities, in the areas of stable crust with slow tectonic deformation and reduced seismicity. We face the problem in the eastern Bohemian Massif (Central European Variscides) at a contact with the Eastern Alpine – Western Carpathian orogenic belt through building its integrated geodynamic model based on the long-term GNSS data cross-checked with the results from existing levelling, geological surveys, geophysical surveys, and a new geomorphological analysis. The model shows differently moving crustal blocks, determining the intervening boundary zones as the main risk regions, where weak earthquakes are also usually concentrated (primarily Diendorf–Čebín Tectonic Zone, Nectava–Konice Fault, Haná Faults, Bělá Fault and Bulhary Fault Shear Zone). The maximum horizontal GNSS differential velocities in the exposed Bohemian Massif reach up to 1.5–2.0 mm·yr−1. The up-thrusted segments of the Western Carpathians move individually ~2 mm·yr−1. The integration of a number of full-area datasets, corresponding to various dimensions and depth levels of crustal processes, allowed us to highlight the important fault zones as driving elements of regional geodynamics.

The crustal structure of the southern Davie Ridge offshore northern Mozambique – A wide-angle seismic and potential field study

Some of the oldest surviving oceanic basins in the world, the Mozambique and West Somali basins, were created during the breakup of Gondwana, starting around 180 Ma. Between the two basins, relative movements of West Gondwana and East Gondwana, including Madagascar, created a shear zone, the Davie Fracture Zone (DFZ) with a topographic elevation (Davie Ridge - DR) marking its centre. The crustal composition of the DFZ and DR is a subject of speculation and debate.In this study, we present seismic refraction data across the prominent topography of the southern DR. Ray tracing of the wide-angle data as well as additional seismic amplitude modelling and 2.5D density modelling constrain its crustal structure and architecture.The data indicate that in the Mozambique Channel the DR consists of fragments of continental crust with a thickness of 10 to 12 km. An oceanic crust indenter extends northward from the Mozambique Basin into the area between the DR and the East African margin at 16.5°S. Northeast of the DR, at 41.8°W/14.5°S, the Somali Basin is probably floored by 6 km thick oceanic crust. Hence, the continental DR separates oceanic crust of the Somali and Mozambique basins.The transitional crustal area at the central Mozambican margin is underlain by high velocity lower crust (HVLC). The HVLC has velocities up to 7.3 km/s and extents along the margin, vanishing northward between 16.5° and 14.5°S. At the Madagascan side of the DR, at 16.5°S, the highly intruded stretched continental crust is 9 km thick and possibly underlain with a smaller HVLC of 2.9 km thickness and an E-W extent of 120 km. The oceanic crust at 14.5°S represents the oldest part the Somali Basin, which formed after the initial NW-SE rifting between East and West Gondwana.

Geodynamics of Central Armenia Based on the Results of Hydrogeochemical Monitoring

Method for geophysical monitoring of the earth's crust has been introduced since 2000 aiming to study the earth's crust of Central Armenia. The method allows to track modern geodynamic processes of the region. The nature of time-space distribution of hydrogeodeformation processes of Central Armenia has been studied. The nature of space-time distribution of geodynamic intensity is determined. Anomalies of components of chemical composition of water have been recorded on stress-strain areas of Earth's crust. Types of seismotectonic deformation have been determined. The present work introduces the hydrogeochemical method of studying the geodynamic processes of the Earth's crust of Armenia. The method is based on hydrogeochemical observations of the chemical composition of mineral waters and their comparison with seismicity. The objective of the hydro geochemical method is to identify hydrogeochemical effects which mainly occur in the changes of macro-component and gas composition of waters related to geodynamic movements of the Earth's crust. The results of the applicaiton of the hydrogeochemical method in the central part of the region, confirmed the connection of the parameters of seismic events variations with the chemical composition of groundwater, as well as carbon dioxide (СО₂) dissolved in water. Stressed areas of the Earth's crust are observed according to the anomalies of components of chemical composition of water. Types of seismotectonic deformation are determined. Geochemical anomalies are most clearly observed in the macro-component composition of mineral water and gases. Seismic events are preceded by geochemical anomalies of components of water composition in relation to background values in percentage ratio. The hydrogeochemical method, combined with other methods, can serve as a reliable precursor to earthquakes and other geodynamic processes of the Earth's crust. The role of the hydrogeochemical method is also effective for short-term and operational prediction of tectonic movements of the Earth's crust (earthquakes, in particular).

A zircon petrochronologic view on granitoids and continental evolution

Temporal trends in granitoid chemistry and thermometry constrain major global changes in magmatism, tectonism or crustal thickness in the continents. Our study relies on zircon geochronology and trace element geochemistry on four new detrital rocks (two modern sediments and two Archean metasedimentary rocks) and a global compilation of published single zircon detrital chronology and trace chemistry data acquired on 5587 individual grains. Zircons of all ages from 4.4 Ga to present exist in this archive. Ti-in-zircon thermometry indicates that more than 98% of the grains with concordant U-Pb ages formed at temperatures exceeding 650°C. The great majority of these zircons formed in the 650–850°C range consistent with growth in intermediate to silicic magmas. Magmatic temperatures increased over time for the first 1.2 Ga of Earth's history after which they stayed constant before decreasing during the more recent past. U/Th<5 values in the overwhelming majority of grains are consistent with a magmatic origin. La/Yb, Sm/Yb and Eu/Eu* values are relatively constant throughout the history of the Earth suggesting that most granitoids formed at, or evolved from magmatic reservoirs located at depths of 35–45 km in the presence of amphibole, garnet and limited plagioclase. Such reservoirs are common today in hot deep crustal environments beneath some of the thicker island arcs and all continental arcs along subduction zones. Processes other than modern day style subduction may have contributed to the formation of granitoids in the early Earth but temperatures, depths and the presence of water arbitrated by the presence of amphibole were similar. These results also suggest that the thickness of continental crust in areas that produced granitoids was similar to today's global average throughout the 4.4 Ga time period covered by the zircon archive. There is no correlation between zircon chemistry over time and the assembly of supercontinents.

Gravity and Magnetic Constraints on the Crustal Structure of the Ceará Plateau, Brazilian Equatorial Margin

The Brazilian Equatorial Margin is a transform passive margin with long fracture zones and several seamounts, including the largest one, the Ceara Plateau. This is a complex and poorly recognized area, with few available geophysical data. Gravity and magnetic data from the Equant I Project, seismic published lines and other previous studies are used to make several models and analyses. We recognized gravity and magnetic anomalies related to a denser, magnetized basement, internally comprised of two magmatic highs. Through gravity and magnetic forward modeling, we estimated the basement surface between 800 and 6000 m and the Mohorovicic discontinuity about 22-23 km below the Ceara Plateau. We also present and discuss the position of the continent-ocean boundary 40 km away from the continental shelf, placing the plateau at the oceanic crust domain, and the area of the transitional crust, with an extension of 40-50 km, formed during the rifting phase of the Atlantic Ocean opening.

Nd isotope mapping of a Pinwarian-age composite arc belt in the Quebecia terrane of the central Grenville Province, Canada

There continues to be confusion in the geological community concerning the ages of crustal formation and crustal accretion within the central Grenville Province of Quebec. To clarify the geological history of crustal growth in the eastern part of the Quebecia terrane, sixty new Nd isotope analyses are presented from a 60,000 km2 area northwest of Baie Comeau. Most samples yield Pinwarian Nd model ages that suggest them to be derived from juvenile oceanic arc terranes. However, two large slivers with Paleoproterozoic TDM ages attest to the existence of hidden blocks of old crust, which divide the area of juvenile Pinwarian crust into a composite arc belt of smaller accreted terranes. The old crustal blocks probably do not reach the present surface, but represent an igneous crustal protolith of younger I-type magmatism. By comparison with a Mesozoic tectonic analogue, it is proposed that accreted juvenile arc crust with attached slivers of older crust were rifted away from an active margin to the west, and translated eastwards until blocked by the previously accreted Labradoria terrane. Although the Quebecia composite arc belt consists of over 95% of Pinwarian juvenile arc crust, the age of arc accretion was post-Pinwarian. The proposed oblique nature of the accretion process may explain the lack of a major collisional orogen at that time. This paper shows the usefulness of large-scale Nd isotope mapping of Precambrian crustal terranes to clarify complex processes of crustal formation and arc accretion.

The ratio of tectonic structure and modern movements of the crust in area of geodynamic proving ground in Bishkek

According to the various scale GPS measurements, the process of collision between India and Eurasia is still ongoing and is reflected on Central Asia territory. The maximum velocity of shortening on northern component between India and Asia is ∼35 mm/year; the longitudinal (east-west) extension of the Tien Shan is ∼20 mm/year. The maximum deformations of shortening ∼15 mm/year along the north coordinate operate in a narrow fault zone between the Pamir and Tien Shan. Not on all Cenozoic (neotectonic) faults occur modern movements of the earth’s crust, these faults may have separate segments of active at different times. The general kinematic tendencies of modern movements correlate well enough with the general kinematic structure of neotectonic faults. In the fault zones at distances from the first hundreds meters to the first kilometers, intense elastic changes in the baseline lengths up to 4 cm (strains of 10–4) can occur within a week and up to 3-5 months. Such high-frequency elastic events have a different character of manifestations and are 2-4 orders of magnitude greater level than stable many years’ residual deformations.

CHARACTERISTICS OF SELF‐SIMILARITY OF SEISMICITY AND THE FAULT NETWORK OF THE SIKHOTE ALIN OROGENIC BELT AND THE ADJACENT AREAS

We performed a comprehensive analysis of the characteristics of self‐similarity of seismicity and the fault network within the Sikhote Alin orogenic belt and the adjacent areas. It has been established that the main features of seismicity are controlled by the crustal earthquakes. Differentiation of the study area according to the density of earthquake epicenters and the fractal dimension of the epicentral field of earthquakes (De) shows that the most active crustal areas are linked to the Kharpi‐Kur‐Priamurye zone, the northern Bureya massif and the Mongol‐Okhotsk folded system. The analysis of the earthquake recurrence plot slope values reveals that the highest b‐values correlate with the areas of the highest seismic activity of the northern part of the Bureya massif and, to a less extent, of the Mongol‐Okhotsk folded system. The increased fractal dimension values for the fault network (Df) correlate with the folded systems (Sikhote Alin and Mongol‐Okhotsk), while the decreased values conform to the depressions and troughs (Middle Amur, Uda and Torom). A comparison of the fractal analysis results for the fault network with the recent stress‐strain data gives evidence of their general confineness to the contemporary areas of intense compression. The correspondence between the field of the parameter b‐value for the upper crustal earthquakes and the fractal dimension value for the fault network (Df) suggests a general consistency between the self‐similar earthquake magnitude (energy) distribution and the fractal distribution of the fault sizes. The analysis results demonstrate that the selfsimilarity parameters provide an important quantitative characteristic in seismotectonics and can be used for the neotectonic and geodynamic analyses.

A Global Plate Model Including Lithospheric Deformation Along Major Rifts and Orogens Since the Triassic

AbstractGlobal deep‐time plate motion models have traditionally followed a classical rigid plate approach, even though plate deformation is known to be significant. Here we present a global Mesozoic–Cenozoic deforming plate motion model that captures the progressive extension of all continental margins since the initiation of rifting within Pangea at ~240 Ma. The model also includes major failed continental rifts and compressional deformation along collision zones. The outlines and timing of regional deformation episodes are reconstructed from a wealth of published regional tectonic models and associated geological and geophysical data. We reconstruct absolute plate motions in a mantle reference frame with a joint global inversion using hot spot tracks for the last 80 million years and minimizing global trench migration velocities and net lithospheric rotation. In our optimized model, net rotation is consistently below 0.2°/Myr, and trench migration scatter is substantially reduced. Distributed plate deformation reaches a Mesozoic peak of 30 × 106 km2 in the Late Jurassic (~160–155 Ma), driven by a vast network of rift systems. After a mid‐Cretaceous drop in deformation, it reaches a high of 48 x 106 km2 in the Late Eocene (~35 Ma), driven by the progressive growth of plate collisions and the formation of new rift systems. About a third of the continental crustal area has been deformed since 240 Ma, partitioned roughly into 65% extension and 35% compression. This community plate model provides a framework for building detailed regional deforming plate networks and form a constraint for models of basin evolution and the plate‐mantle system.

Correlation of change in magnetotelluric parameters before and after Sikkim Himalayan earthquakes associated with stress variation

MT stations that were recorded before the moderate 5.3 Mw, 2006 Sikkim Himalaya earthquake had been reoccupied after 2007 (Mw 5.0) and 2011 (Mw 6.9) seismic activities. We analyzed the broadband MT data (0.001–1000 s) within the 60 km radius from epicenters location and within the focal depth range of 9–30 km. The observed change in apparent resistivity in the period range of 0.001–10 s has shown a considerable post-seismic decrease of the order 10–30%. The 2D geoelectric model constructed with post seismic acquired data also reveals the feature of a decrease in resistivity (C1). The relative change (decrease) of observed apparent resistivity ((Δρ/ρobs) after 2006, 2007 and 2011 earthquakes find a correlation with combined stress drop 11–18.2 MPa values estimated by Arms-Δσ approach. The correlation is further strengthened by a similar change in relative apparent resistivities ((Δρ/ρ2D_model) derived from 2D model with stress drop. Integrated stress drop values attribute to the accumulated apparent stresses (σa = 0.23 ∆σ) that reveals the area might be subjugated to 0.6–1.2 MPa stress before 2006, 1–1.5 MPa stress before 2007 and 1.7–2.9 MPa before 2011 earthquakes occurrence. Development of micro-cracks and generation of aqueous fluids is possible due to such stressed and slow rate of relentless thrust/shear environment within the area of crust. Therefore, resistivity could have been decreased with a fluid transition from compression to dilatancy zones at different depth levels before each earthquake and further decreased upon subsequent stress drops associated with strong ground motions. We interpreted that maximum stress might be dropped in dilatational zones oblique to the maximum compression stress directions along N200E, N-S and NNW-SSE before 2006, 2007 and 2011 earthquakes and resulted in a considerable decrease in apparent resistivity along E-W (TE-mode), i.e., ρyx component.

Kinematic model of the Midoceanic Gakkel ridge East areas development in the Eurasian basin of the Arctic ocean

The new map of linear magnetic anomalies axis for the mid-Arctic ridge east areas development in the Eurasian basin is made. The domestic geomagnetic investigations for the first time allow to determine paleomagnetic anomaly C25 and estimate the time of transfer rifting to spreading process as chrons С25r-С26n (57.656-59.237 ma). The eastablishing of Lomonosov ridge and Siberian margin splitting zone is made. The Euler pole for the splitting kinematic for first time calculated. The nocoinciding of conjugate isobaths related to process of sliding peripheral continental crust areas along lithosphere thrust plane for the first time is calculate.

Unsolved problems of the global tectonics and possibility of their solutions

The deep geological and geophysical studies of the continents and oceans have revealed a number of well-defined new regularities in the structure of the crust and upper mantle that do not find a clear explanation in the modern geodynamic concepts. The regularities are the following. The Earth is divided into two hemispheres with different structure of the lithosphere: the Pacific and Indo-Atlantic hemisphere. The Pacific hemisphere is surrounded by a ring of the tectonically active zones with high seismicity (Benioff Zones). The system of the mid-ocean ridges with approximately equal distances between them, 90°, is symmetrical relatively to the South Pole. The crust in the oceans is different in age and composition, it identified the remnants of an ancient (Archaean) crust and large areas of subcontinental crust. The continents are characterized by the large thickness of the lithosphere (more than 200 km), composed of the lower density depleted matter. Experimental data on petrophysical properties of the crust and upper mantle matter at high pressure and temperature, the data on deep xenoliths, geochemical studies of natural gases have showen a large role of deep energy-intensive fluids in the formation of the sialic crust and depleted mantle rocks. These data give possibility to explain the continents and oceans origin. The irregular in space the Earth degassing results in different lithosphere types formation: the thick granite-gneiss crust and the lower density depleted mantle of the continents were created in the areas of the higher deep fluids flows; in the areas of the lower fluids advection the primary oceanic crust was preserved and only some separate spots of the transition crust appeared. The lower density of the continental «roots» was the main factor in the formation of continents: the lower density lithosphere led to its emerging in respect to the oceanic lithosphere. Two hemispheres with different lithosphere structure were formed may be due to the elliptical form of the orbit, causing periodic changes of the planet accelerations. The structural symmetry of the global rift system relative to the planet poles gives possibility to explain its origin by the expansion of the planet.

Studying the sensitivity of GOCE gravity gradients to the crustal structure: case study of Central Europe

We discuss the determination of gravity gradients from the orbital ceiling to the depth of the Mohorovičić discontinuity (Moho) for Central Europe. Components of the Eötvös tensor were derived from “Heterogeneous gravity data combination for Earth interior and geophysical exploration research” project (“GOCE+”) by using the gridded data with a resolution of 0.2° per 0.2°. Gravity gradients to Moho boundary depth were modelled forward to the 255 km orbital height. We calculated gradient sensitivity using a 3D model divided into: sediments and consolidated crust including the precise location of the Moho boundary. To define tesseroids as mathematical model we need to set two parameters of the crust: density and thickness for each spherical layer separately. Altitudes for topography/bathymetry were derived from ETOPO1 model, sediments thickness from EuCRUST-07 model, and Moho boundary from Grad and Tiira (Geophys J Int 176(1):279–292, 2009. https://doi.org/10.1111/j.1365-246x.2008.03919.x) seismic map. For high latitudes, we noted the largest changes for the gradients towards the poles, with particular values of 689.07 mE (milli-eotvos) and 1138.19 mE for VXX and VZZ gradients, respectively. We obtained extreme values for the location of the deep and shallow areas of the crust (Alps, North-Eastern Poland and areas of seas) equal to − 3 E and + 1.5 E, respectively. Most of the gradients showed strong correlation with anomalies in crustal density of − 2.5 E for VZZ and + 1.5 E for VYY in the extreme cases. We showed that changes in crust density and thickness by respectively 50 kg/m3 and 10 km entail changes in gradient values by 15% for density and 10% for depths. Numerical analysis considering Preliminary Reference Earth Model (PREM) showed importance of density modeling for determination of gravity gradients.

Геоинформационное обеспечение проектирования геодезического мониторинга напряженно-деформированного состояния земной коры в районах освоения угольных месторождений

Геоинформационное обеспечение проектирования геодезического мониторинга напряженно-деформированного состояния земной коры в районах освоения угольных месторождений

Soil and Agrochemical Characteristics of the Svetloyar Irrigated Site in Volgograd Oblast

The agrochemical properties of humus-accumulative horizons of irrigated soils on the key site of the Svetloyar irrigation system in Volgograd oblast are analyzed. The field layout before the operation of the irrigation system and a long period of irrigation resulted in redistribution of the carbonate material. Its concentration in the upper part of the soil profile amounted 5–13%, which led to the formation of a dense soil crust and alfalfa crop failure areas (mortality spots). These sites are well detected on the materials of satellite imagery. In the over-45-year period of irrigated arable land exploitation, there has been a significant decrease in the humus content in comparison to arable, nonirrigated lands. The humus content in the soils of the key sites averaged 1.23% and approached the minimum acceptable level, according to (Metodicheskie…, 2003). The soil degradation is caused by the overall low level of farming culture and the long-term use of the surface irrigation method. The content of mobile phosphorus (20–102 mg/kg) and exchangeable potassium (316–806 mg/kg) varied widely from medium to very high levels in these soils.