Three-dimensional Density Model Research Articles

Satellite observations and modeling of the plasmapause structure and dynamics

We investigated the structure and dynamics of the plasmapause using electron density data from the Arase (ERG) satellite between 2017 and 2019. By fitting the electron density profile to a hyperbolic function using the least-squares method, 1891 plasmapause events were identified. The hyperbolic function’s fitting parameters were used to estimate the plasmapause’s location and thickness. The plasmapause location and thickness were mapped onto the geomagnetic equator plane. We examined the dependence of the plasmapause location and thickness on the geomagnetic disturbance. The median plasmapause location on the geomagnetic equator plane was 32,089 km from Earth’s center. Plasmapause locations depend on geomagnetic disturbances that vary between four and six radii of the Earth.In contrast, the median plasmapause thickness obtained by fitting a hyperbolic function on the geomagnetic equator plane was 2472 km. The thickness changed from ∼1500 km at night to ∼ 3000 km during the daytime. The thickness was several times larger than the ring current H+ Larmor radius, suggesting an association with plasma instability in the plasmapause due to the penetration of magnetospheric electric fields.Additionally, we developed a three-dimensional empirical electron density model with historical effects associated with refilling the plasmasphere, plasmapause, and magnetosphere. The International Reference Ionosphere (IRI) model can be enhanced to incorporate the electron density model of the plasmasphere and estimate the total electron content (TECp) in the plasmasphere using the empirical model. Our analysis provides valuable insights into plasmapause and contributes to a better understanding of the inner magnetosphere.

Строение центральной части палеопротерозойского Лосевского террейна по данным плотностного моделирования

The results of detailed three-dimensional density modeling of the upper crust of the central part of the Losevsky terrane located in the northern part of the Voronezh crystal massif are considered. The distribution of absolute crustal density values of to a depth of 16 km was obtained as a result of the inversion of local anomalies of the gravitational field in the Bouguer reduction. The solution of the inverse problem of gravimetry was implemented within the framework of the initial model, which was formed using digital geological and geophysical data from the study area: the regional density model of the East European Platform lithosphere and its corresponding regional gravity field; the field of local gravity anomalies, representing the difference between the observed and regional fields of the lithosphere model; generalized information on the density of sedimentary cover rocks and the crystal basement; the thickness scheme of the «gravity-active» layer, obtained on the basis of statistical analysis of the anomalous field; geological and topographic information. Quantitative interpretation of the gravimetry data allowed us to obtain fundamentally new information about the geological structure of the upper crust of the study area. The reliability of the obtained results is confirmed by the consistency of a priori data and the correspondence of the total model (local plus regional) and observed gravitational fields.

Three-dimensional density model of the mantle beneath the Ukrainian shield

Purpose. Mantle density models are key tools for understanding the fundamental geological and physical processes occurring within the Earth and are essential to our scientific and applied understanding of the planet. Methodology. The tasks were solved by a complex research method, including analysis and generalization of literary and patent sources, analytical, experimental studies, using computer and mathematical modelling methods. Findings. One-dimensional models simplify the mantle density distribution by assuming that it is uniform only in the vertical direction. This limitation does not allow for horizontal variations in mantle density, which may be important on a regional scale. 3D models are more complex and require more data and computational resources, so their use may be limited. In this study, we present a quasi-three-dimensional model of mantle density beneath the Ukrainian Shield. This 3D model is obtained using a basic set of one-dimensional seismic tomographic velocity models calculated for 21 mantle domains in the depth range from 50 to 2,600 km. The process of converting the P-wave velocity model into a density model includes the following stages: 1) determining seismic boundaries in the mantle based on P-wave velocity curves for each mantle domain; 2) creating a synthetic mantle model beneath the Ukrainian Shield for the P,S-wave velocity curves; 3) solving the Adams-Williamson equation for each domain, considering polynomial corrections to extract heterogeneities during its solution; 4) analysing existing models by comparing the calculated gravitational potential at the central point of the Ukrainian Shield as the standard reference for selecting one of 5 reference models. Here, we focus on the final stages of constructing the mantle density model by: 1) balancing the mass of the upper and lower mantle for each domain when determining density using the Adams-Williamson equation and introducing polynomial corrections; 2) calculating densities for each of the 21 mantle domains and their 3D integration. Originality. The obtained mantle-density model of the Ukrainian Shield aligns well with the division of the mantle into three main layers: lithosphere, upper mantle, and lower mantle. Each of the mantle’s structural layers has its representation pattern in density heterogeneities. Anomalies of decreased density in the lithosphere of the Ukrainian Shield correlate with thermal anomalies, whereas anomalies of increased density correspond to tectonic zones dividing its megablocks. Practical value. Regions of increased density gradient are associated with mantle thrust faults, which in some cases can be boundaries between different petrological formations and serve as channels for magma ascent into the Earth’s crust at certain stages of geological development of the Ukrainian shield and, in turn, be sources of minerals.

Does Urbanization Affect the Carbon-Output Efficiency of Agriculture? Empirical Evidence from the Yellow River Basin

Purpose: Improving agricultural carbon-output efficiency is an important path to realize the “double carbon” goal in the Yellow River Basin. In the context of rapid urbanization development, it is significant to explore whether promoting urbanization will affect agricultural carbon-output efficiency. Methods: Based on panel data of 75 cities in the Yellow River Basin from 2000 to 2020, this paper uses the super-DEA model, three-dimensional kernel density model, and Markov chain model to measure and analyze the spatio-temporal evolution of agricultural carbon-output efficiency in the Yellow River Basin. The panel Tobit model is used on this basis to analyze the relationship between urbanization and carbon-output efficiency in agriculture. Results: The results show the following: (1) The level of agricultural carbon-output efficiency in the Yellow River Basin is low and has not reached an effective state, showing a slow downward trend in general where the agricultural carbon-output efficiency in the lower reaches is higher than that in the middle reaches, and the upper reaches has the lowest. (2) Agricultural carbon-output efficiency in the Yellow River Basin has a negative trend of transitioning to a low level overall and maintaining its original level, and it is difficult to realize the leapfrog transfer between states. Agricultural carbon-output efficiency has an obvious spatial spillover effect and “club convergence” phenomenon; the high-efficiency area has a positive driving effect on the neighborhood area, while the low-efficiency area has a negative impact on the neighborhood area. (3) The level of urbanization has a significant positive impact on the carbon-output efficiency of agriculture in the upper, middle, and lower reaches of the Yellow River Basin, which plays an important role in promoting the green development of agriculture.

Tracing the Iceland plume and North East Atlantic breakup in the lithosphere

Plumes are domains where hotter material rises through Earth´s mantle, heating also the moving lithospheric plates that may experience thinning or even continental breakup. In particular, the Iceland plume in the NE Atlantic (NEA) could have been instrumental in facilitating the breakup between Europe and Laurentia in the earliest Eocene. Here we present an open access three-dimensional density model of the NEA crust and uppermost mantle that is consistent with previously un-integrated available data. We propose that high-density anomalies in the crust represent the preserved modifications of the lithosphere in consequence of the plate’s journey over the hot mantle plume. Besides, low-density anomalies in the uppermost mantle would represent the present-day effect of the mantle plume and its interaction with the mid-ocean ridges. Overall, the model indicates that the presence of the plume together with the pre-existing crustal configuration controlled the timing, mechanisms and localization of the NEA breakup.

A Three-Dimensional Density Model of the Upper Crust at the Junction of the Losevo and Vorontsovka Terranes (Voronezh Crystalline Massif)

A Three-Dimensional Density Model of the Upper Crust at the Junction of the Losevo and Vorontsovka Terranes (Voronezh Crystalline Massif)

The use of INTEGRO GIS in the integrated geophysical study
 of the deep structure of oil and gas prospective regions (part 2)

This article continues a description of the methodological and technological aspects of the constructing physical-geological models of oil and gas promising regions with a help of the INTEGRO GIS tools. The methods are described on the materials of studying the deep structure of the Yenisei-Khatanga regional trough (YKRT).
 The first part of the article covered the stages of analysis of the spatial distributions of potential fields and integrated regional profile geophysical data. The present, second, part of the paper describes the process of the YKRT three-dimensional density model construction, which is based on the results of the previous analysis.

Three-dimensional density model of the sedimentary filling of the Carpathian-Pannonian region

The work is devoted to the construction and calculations of a three-dimensional density model of the sedimentary filling of the Carpathian-Pannonian region in order to obtain a more detailed map of the residual gravity field (stripped gravity map). This research was facilitated by and in-depth analysis of a large amount of data highlighting the density properties of Neogene-Quaternary deposits (the Pannonian Basin, the Transylvanian Depression, the Transcarpathian Trough), molasse deposits of the Carpathian Foredeep and flysch deposits of the Outer Carpathians in the Czech Republic, Slovakia, Poland, and Ukraine. Basic data for the construction of a three-dimensional density model of sedimentary deposits were obtained from laboratory studies of rock samples from drill core logging and deep exploratory wells, as well as rock samples taken from numerous outcrops in the research region. The average value of the density for molasse and flysch deposits of the Romanian part of the Carpathians was estimated based on the results of comparing the lithologic-stratigraphic complexes of these deposits in the adjacent areas of the eastern part of the Ukrainian Carpathians with similar ones in the Romanian Eastern Carpathians and the analysis of available data on the density of the Carpathian Foredeep and the Outer Flysch Carpathians for the Ukrainian part. The research method, which is a modification of geological reduction, has been applied in the work. Its essence consists of the sequential calculation and extraction of the three-dimensional gravity effect of sedimentary layers, the parameterization of which is better defined than those layers that lie deeper, from the anomalous gravity field. As a result, a residual gravity field is formed due to deep inhomogeneities associated with the consolidated part of the crust and the upper mantle. Calculations of gravity effects were carried out on a scale of 1:4,000,000 on a 10—10 km grid using the modern GMT-Auto. The detailed map of the residual (cleared of the effects of sedimentary layers) gravity field of the Carpathian-Pannonian region (stripped gravity map) is an effective tool in understanding the sources of the dominant gravity features of the studied region. Thus, the Pannonian Basin manifests itself as a general maximum with a number of local positive anomalies (more than 50 mGal), which are observed over small depressions filled with low-density thick sedimentary deposits: the Danube, Solnok, Makó, Békés Basins, and the Transcarpathian Trough. The phenomenon of positive and not negative values of the residual gravity field for these structures can be explained by the intrusion of the sedimentary cover of volcanic rocks, or the presence of high-density bodies with a special petrophysical composition (metamorphic complexes?) in the consolidated part of the crust. Another reason may be the effect of the regional background, which is due to the rise of Moho boundary in the Pannonian Basin to 24—26 km. The gravity minimum of the Western Carpathians, which on the map of the anomalous gravity field, consists of two parts (northern and southern), is reflected by one intense minimum, the southern one (-60 mGal). The northern part of this gravity minimum is practically leveled after calculations of the gravity effect of sedimentary filling, so it can be assumed that its source is low-density flysch and molasse deposits. The southern part of the gravity minimum of the Western Carpathians can be explained by the mass deficit in the consolidated part of the crust. Since the intensity of the gravity lows of the Eastern (-80 mGal) and Southern (-100 mGal) Carpathians remained high even after being cleared of the effect of the layer of sedimentary deposits, it can be assumed that they are due not only to the low values of the density of the sediments of the Outer Carpathians and the Carpathian Foredeep, but additionally also due to the gravity effect of deep inhomogeneities of the consolidated part of the crust (crustal root).

Constrained 3D gravity modelling of a multilayered aquifer system in an arid region: Case of Sebkhat El Bhira basin (Central Tunisia)

In arid regions, the significant and increasing demand for water has caused intensive exploitation of groundwater resources. The Sebkhat El Bhira basin, shared between Kairouan and Sidi Bouzid governorates in Central Tunisia, presents a multi-layer aquifer system composed of four main reservoirs: the sandy Mio-Plio-Quaternary (MPQ), the Paleogene, the Upper Cretaceous limestone and the Lower Cretaceous limestone, sand and dolomite reservoirs. The intensive exploitation of the shallower aquifer has led to a drawdown of the water table and a deterioration of water quality. The purpose of this work is to characterize the geometry of these potential reservoirs for sustainable water management, by applying geophysical methods.We used land gravity data covering 1387 Km2, twelve seismic reflection profiles with a total length of approximately 308 Km, two petroleum wells and 39 water wells.The processing of the gravity data shows the subdivision of Sebkhat El Bhira basin into four sub-basins and the identification of principal and minor lineaments oriented N-S, NE-SW, NNW-SSE, and E-W. The interpretation of reflection seismic lines allowed the identification of five main horizons: the bottom of MPQ, the bottom of Paleogene, the bottom of Upper Cretaceous, the bottom of Lower Cretaceous and the bottom of Jurassic (Top Triassic). For a better understanding of the subsurface structuring, we built twelve two-dimensional (2D) forward models of density. These latter are constrained in the area inside the plain by the converted time-to-depth seismic reflection data and wells. The interpolation of the 2D models allowed us to visualize the lateral and vertical thickness variations of each of the chrono-stratigraphic units and to produce a three-dimensional (3D) density model. The geophysical modelling allowed us to highlight the post-Jurassic tectonic and the Triassic halokinesis activities responsible for the actual subsurface geometry.The Triassic evaporites, in the study area, flow and rise through the fault's subvertical branches. It outcrops locally at the North-South Axis mountains range (NOSA). Inside the plain, the evaporitic uprising shows different schemes like diapir, wall and pillow. This Triassic halokinesis, with the tectonics, has shaped the deep morphology of the basin and managed the available space for the deposition of the overlying stratigraphic formations.The general structure of the potential aquifers is characterized by a depth which increases from the East to the West and towards the central part of the plain. Inside the basin, the structure of these aquifers is complex.

Uniformly strained anisotropic elastoplastic rods: Determination of elastoplastic constitutive relations and yield surface in terms of rod’s variables

This work presents a formulation for the elastoplastic deformation of the rod’s cross-section wherein the rod material can obey an arbitrary three-dimensional stored energy density model together with a rate-independent arbitrary phenomenological plasticity model. In order to do so, we impose a uniform strain field along the rod’s arc-length which reduces the three-dimensional nonlinear elastoplastic rod problem to just its cross-section. To solve this elastoplastic cross-sectional deformation problem, a three-dimensional elastoplastic moduli tensor is first derived along with a return map algorithm for the update of relevant internal variables at every point in the cross-section. A finite element formulation is then presented to solve the aforementioned cross-sectional problem. The elastoplastic stress resultants (internal contact force and moment in the rod’s cross-section) and elastoplastic stiffnesses (such as bending, twisting, extensional and shearing) of an elastically isotropic but plastically transversely-isotropic rod are then obtained numerically along with the warped state of the plastified cross-section. Several deformations (increment/decrement in combinations of extension, torsion, bending and shearing) are studied to observe the evolution of plasticity at each quadrature point in the rod’s cross-section. We observe that off-axis anisotropy during plasticity leads to unusual out-of-plane warping even during torsion of circular cross-sections. It also leads to coupling between various modes such as between bending and twisting. We also demonstrate that the rod’s various elastoplastic stiffnesses are not only dependent on the current strain state of the rod but also on the current direction of strain rate. Finally, we integrate the plastic work over the rod’s cross-section and use the criterion of limiting plastic work to obtain discrete points on the rod’s yield surface in terms of stress resultants. The obtained yield surface turns out to be different from the one obtained for purely isotropic material model.

Three-dimensional density model of the Tarasivka structure of the Golovanivsk suture zone of the Ukrainian Shield

For the first time, based on the data of three-dimensional density modeling, a diagram of the density distribution on the surface of the basement of the Tarasivka mafic-metamafic structure with an area of 2.5×5.5 km, extending to a depth of no more than 3—4 km, was constructed. The distribution of density to a depth of 5 km has been studied in detail, and the depths of occurrence of geological bodies have been determined. New in methodological terms is the use of a bypass step-like boundary from below, the form of representation of which is determined by the expected depth of occurrence of bodies with different densities. Thus, the depth of bodies with increased density near the basement surface is 2 km, of granitoids — 3 km, of undivided charnockites and enderbites — 4 km. It is shown that apogabbroids and aponorites with an average density of 2,80—2,90 g/cm3 (slightly altered rocks of mafic-metamafic composition), which form the central part of the Tarasivka mafic-metamafic structure, extend to a depth of 2 km without changing their angle fall, which is confirmed by seismic and electrical survey data. Based on the complex of available data, the selection and substantiation of the density of the host rocks of the charnockite-enderbite series, which are characterized by a density of 2,75—2,76 g/cm3 and form a ledge of about 1—2 km within the Tarasivka structure, were made. The marginal parts of the structure extend deeper than the central ones, which testifies against its synclinal structure. Along the latitudinal strike-slip fault, which passes through the central part, the Tarasivka structure is divided into two parts: the northern, less dense, and the compacted southern one. It is shown that in the eastern and northeastern parts of the structure, the fault zones are fragmented and compacted.In some of them, the density is 2,77 and 2,80 g/cm3 throughout the section, which can be explained by the intersection of high-density rocks by faults in such a places.The absence of supply channels and the shallow depth of the Tarasivka structure can be explained in two ways: either the channels of the mafic intrusion that forms the structure, most likely, have a small diameter (or diameters), that is why they cannot be fixed by gravimetry; or powerful strike-slip processes, which are fixed within the Golovanivsk suture zone, led to the formation of a detachment at a depth (modern) of 3—4 km, as a result of which the upper part of the Yatra block, together with the Tarasivka mafic-metamafic structure, moved quite strongly to the south, tearing it from root part. The last statement is considered the most probable.

Crustal thickness and structural pattern evaluation of Sinai Peninsula using three-dimensional density modeling with aeromagnetic and earthquake data

The Sinai Peninsula is a subplate located between the African and Arabian plates. It is an important subplate in the world; however, this region is poorly understood because of the shortage of geophysical data. Thus, this study focuses on built a three-dimensional (3D) high-resolution forward model of the crustal thickness with a new tectonic model and structural evaluation of the Sinai Peninsula to understand this area tectonically and determine its lithospheric and crustal thicknesses. Qualitative and quantitative interpretations of Bouguer gravity, reduced-to-the-pole (RTP) aeromagnetic, and earthquake data are explained to achieve the goals of this study. Two-dimensional (2D) interactive sequential modeling of gravity data is performed along with some well-selected profiles with existing crustal layer depth points from previous works in the studied region. Seventeen 2D models are constructed and used to determine the basement, Conrad (lower crust boundary), and Moho (upper mantle boundary) depths and to build a 3D model. Accuracy of the 3D built model is evaluated by extracting observed, calculated, and residual gravity anomaly maps. The results show that the basement rocks appear on the surface in the South of Sinai and deepen (down to 4.5 km) toward the North. The Conrad surface varies approximately from 16 km (in the northeast and southwest of Sinai) to 22.8 km (in the southeast). The Moho surface depth (i.e., crustal thickness) varies approximately from 28.8 to 34.2 km, and it deepens toward the northeastern and southwestern parts of Sinai. A tentative basement structure map is constructed from the horizontal gradient (H-gradient) filter and the 3D Euler deconvolution of the Bouguer gravity and RTP aeromagnetic data. Correlation between the geological background of the study area and the obtained results suggests that the Sinai Peninsula is tectonically active, mainly in its southern portion due to the tectonic movements along the Gulf of Suez and the Gulf of Aqaba. The crustal thickness increases southward and thins northward.

A Simplified Worldwide Ionospheric Model for Satellite Navigation

Ionospheric delay is one of the main sources of error in satellite positioning and navigation. Ionospheric broadcast parameters are required to correct for the ionospheric delay, especially in the case of massive single-frequency users. The well-known Klobuchar model has been providing the ionospheric delay corrections for GPS users during the last several decades. For Galileo users, a three-dimensional electron density model (NeQuick G) based on the NeQuick climatological model is used to correct for ionospheric delay. The recently completed Chinese BeiDou Satellite Navigation System (BDS) broadcasts two types of ionospheric models coefficients on different signals. In this article, we propose a simplified worldwide ionospheric model (SWIM) for satellite positioning. By comparison, our SWIM model has better performance than the Klobuchar model in terms of accuracy at both low and high solar activity, and is comparable to the NeQuick G and BDS ionospheric models. At the same time, the SWIM model has high efficiency because of the simple calculation process. It has great potential for ionospheric delay corrections in satellite navigation and positioning.

ТРЕХМЕРНАЯ ПЛОТНОСТНАЯ МОДЕЛЬ ВЕРХНЕЙ КОРЫ В ОБЛАСТИ СОЧЛЕНЕНИЯ ЛОСЕВСКОГО И ВОРОНЦОВСКОГО ТЕРРЕЙНОВ (ВОРОНЕЖСКИЙ КРИСТАЛЛИЧЕСКИЙ МАССИВ)

The results of detailed three-dimensional density modeling of the upper part of the Earth's crust for the area located in the northeastern part of the Voronezh crystalline massif in the area of the junction of the Losevsky and Vorontsovsky terranes are considered. The model obtained by solving the inverse gravimetry problem characterizes the density distribution of the rocks of the crystalline basement of the territory to a depth of 16 km. An important role in such constructions is given to the starting model of the studied environment, which was formed taking into account the available a priori geological and geophysical information: the regional density model of the East European Platform lithosphere and the gravity field, the data on the density of rocks of the sedimentary cover and the crystalline basement, estimates of the “gravity” layer thickness, the geological map of the crystalline basement, and the digital elevation models of the region. The three-dimensional density model allowed specifying the geological structure of the upper crust of the study area and tracing the deep continuation of the surface structures of the basement. The reliability of the obtained results is determined by the consistency of the accepted a priori data on the environment and the consistency of the model and observed gravity fields of the study area.

A new climatological electron density model for supporting space weather services

The ionosphere is the ionized part of the Earth’s atmosphere, ranging from about 60 km up to several Earth radii, whereas the upper part above about 1000 km height up to the plasmapause is usually called the plasmasphere. We present a new three-dimensional electron density model to support space weather services and mitigate propagation errors for trans-ionospheric signals. The model is developed by superposing the Neustrelitz Plasmasphere Model (NPSM) to an ionosphere model composed of separate F and E-layer distributions. It uses the Neustrelitz TEC model (NTCM), Neustrelitz Peak Density Model (NPDM), and the Neustrelitz Peak Height Model (NPHM) for the total electron content (TEC), peak ionization, and peak height information. These models describe the spatial and temporal variability of the key parameters as a function of local time, geographic/geomagnetic location, solar irradiation, and activity. The model is developed to calculate the electron concentration at any given location and time in the ionosphere for trans-ionospheric applications and named the Neustrelitz Electron Density Model (NEDM2020). A comprehensive validation study is conducted against electron density in-situ data from DMSP and Swarm, Van Allen Probes and ICON missions, and topside TEC data from COSMIC/FORMOSAT-3 mission, bottom side TEC data from TOPEX/Poseidon mission, and ground-based TEC data from International GNSS Service (IGS) covering both high and low solar activity conditions. Additionally, the model performance is compared with the 3D electron density model NeQuick2. Our investigation shows that the NEDM2020 performs better than the NeQuick2 compared with the in-situ data from Van Allen Probes and ICON satellites and TEC data from COSMIC and TOPEX/Poseidon missions. When compared with DMSP and IGS TEC data, both NEDM2020 and NeQuick2 perform very similarly.

Developing a lateral topographic density model for Brazil

Topographic density distribution models are used in many geodetic and geophysical problems. Due to the difficulty in developing a high-resolution three-dimensional density model, many studies are focusing on the development of lateral density models and, despite the existence of global models, it is understood that these are less detailed and need to be improved to be used in regional and local studies. In this context, this research develops a distribution model of the lateral density of topographic masses for Brazil (LTD_Brazil, with 30 arc-seconds grid spacing), associated with their uncertainties, considering more detailed information from geological maps and apparent density values of rock types. The model results indicated an average density of 2459 kg/m³, ranging from 1625 to 3400 kg/m³, with standard deviations ranging from 8 to 351 kg/m³. This average density value has great influence of large Phanerozoic sedimentary basins (Amazonas/Solimões/Acre, Alto Tapajós, Parecis, Parnaíba and Paraná basins) located in Brazil. Furthermore, comparing the LTD_Brazil with a global model (UNB_TopoDensT), it was possible to suggest that the differences (ranging from −500 to 600 kg/m3), more significant in metamorphic and igneous rocks regions, are associated with greater detail of the lithological units used and accuracy of the model.

Joint inversion of surface wave and gravity data reveals subbasin architecture of the Congo Basin

AbstractWe investigated the architecture of the greater Congo Basin, one of the largest and least-well-studied sedimentary basins on any continent. Seismograms from a large number of M > 4.5 earthquakes within and surrounding the African plate were used to make event-to-station Rayleigh wave group velocity measurements between periods of 5 and 100 s. Group velocities for discrete periods across the basin, obtained by inverting the event-station measurements, were jointly modeled with gravity data to obtain a three-dimensional S-wave and density model of the basin. The model corroborates the existence of two previously suggested subbasins, one to the north and one to the south, each ~8 km deep and separated by an east-west structural high. Our results favor a salt tectonics origin for the structural high but cannot rule out uplifted basement rock. The northern subbasin is offset to the west from the southern subbasin, consistent with previous studies suggesting sinistral motion along basement faults during periods of transpressional tectonics in late Neoproterozoic-early Paleozoic times.

ТРЕХМЕРНАЯ ПЛОТНОСТНАЯ МОДЕЛЬ ВЕРХНЕЙ КОРЫ В ОБЛАСТИ СОЧЛЕНЕНИЯ ЛОСЕВСКОГО И ДОНСКОГО ТЕРРЕЙНОВ (ВОРОНЕЖСКИЙ КРИСТАЛЛИЧЕСКИЙ МАССИВ)

The results of detailed three-dimensional density modeling of the upper crust of the area located in the southeastern part of the Voronezh crystalline massif at the junction of the Losevsky and Donskoy terranes and, partially, the Vorontsovsky terrane are presented. The resulting model was built based on the inversion of local anomalies of the gravity field into anomalous density values, taking into account all available geological and geophysical information. The field inversion was implemented within the framework of the starting model developed on the basis of the regional density model and corresponding gravitational field of the East European platform lithosphere, generalized information on the density of rocks of the sedimentary cover and crystalline basement, the thickness of the «gravitational» layer obtained by statistical analysis of the anomalous field, and geological data and topography. The resulting model shows density distribution of the crystalline basement rocks to a depth of 16 km, and provides thus fundamentally new information about the geological structure of the upper crust of the area. The model makes it possible to trace geological objects, which are most expressive in terms of density, at deep levels, and allows interpreting the relationship between the Losevsky and Donskoy terranes in the upper-middle crust. The consistency of the model and observed gravitational fields indicates the reliability of the obtained results.

ТРЕХМЕРНАЯ ПЛОТНОСТНАЯ МОДЕЛЬ ЗЕМНОЙ КОРЫ ТЕРРИТОРИИ РЕСПУБЛИКИ НИГЕР

The paper considers the results of calculation of the three-dimensional density model of the Earth’s crust for the territory of the Republic of Niger in conditions of incomplete initial geological and geophysical information. A brief description of the geological structure of the research region is given and the task of the study is formulated. The initial data set of density modeling is described, including: the anomalous gravity field, the initial model of the medium, the constraints on the desired solution, and the weight functions of redistribution of field incompatibilities. Inversion of the anomalous gravity field was performed in a three-dimensional formulation for a regular grid with a 25×25 km spacing in the plan and 14 layers of irregular vertical grid. The density model of the crystalline crust obtained by solving the inverse problem was combined with a priori data on the density of the upper mantle layer and the previously constructed layered model of the sedimentary cover of the region. The main features of the density model of the Earth’s crust are considered and its density heterogeneities are compared with the regional geological and tectonic data. The leading role of young structures of the West African rift System and their relationship with density inhomogeneities in the lower and middle crust of the territory of the Republic of Niger was noted.

Adaptation of the NeQuick2 model for GNSS wide-area ionospheric delay correction in China and the surrounding areas

As an empirical three-dimensional ionospheric electron density model, NeQuick2 can generally represent the temporal and spatial characterization of ionospheric Total Electron Content (TEC) at a global scale. However, mismodeling errors usually exist between NeQuick2 representation and actual state of short-term ionospheric variation in small scales. In this contribution, an adaptation method is proposed for the NeQuick2 model based on data ingestion with GNSS-derived ionospheric TEC data. The relationship between the background NeQuick2 Slant TEC (STEC) estimations and real STEC measurements can be properly modelled with a ‘scaling factor’ in a highly efficient manner. In order to verify the feasibility and usefulness of the algorithm, validation experiments are carried out with GNSS tracking stations in China and the surrounding areas under different levels of solar activity. The results show that the bias of NeQuick2 corrections after adaptation are mostly within 1.0 TECu, suggesting that the systematic bias of the original NeQuick2 model can be significantly reduced. In comparison with about 50%-70% STEC RMS errors corrected by the original NeQuick2 model, the NeQuick2 model after adaptation can generally correct about 80% − 90% STEC RMS errors, which is also better than the CODE final GIM product as it has smaller residual bias and uses fewer reference stations. Therefore, the proposed algorithm can be satisfactorily applied in wide area GNSS ionospheric corrections.