Earth's Interior Research Articles

Earth's core-mantle boundary shaped by crystalizing a hydrous terrestrial magma ocean

Enigmatic anomalous structures of Earth's lowermost mantle may have been incubated at the hydrous magma ocean of the Hadean eon.

Layered construction process with the material point method

This paper presents a novel procedure to simulate layered construction processes with the material point method (MPM), a method suitable for modelling large deformations. For the first time, the paper provides the MPM with the capability of modelling the behaviour of earth structures from their construction until the eventual post-failure behaviour in an integrated manner without requiring, as currently done, the use of other numerical tools for the construction simulation. In addition, the proposed methodology includes the option of simulating the engineering practice of compensating settlements that occurred during construction, to match the designed geometry. This option, typically neglected in alternative numerical methods, is implemented by filling the computational elements of the layers that become empty by adding new material points.The construction process proposed and its numerical implementation into an open-source code are described in detail. The validation is carried out by modelling an elastic oedometric column with varying number of layers and by comparing it with analytical solutions and finite element-based results. The construction of a soil embankment in dry, saturated, and partially saturated conditions is also simulated. It shows the capability of the method to capture the excess pore water pressures that may develop.

K- and Na-rich davemaoite inclusion in diamond is not inherited from deeply subducted oceanic crusts

Deep potassium (K) and sodium (Na) cycles can affect the physiochemical properties and geodynamic processes of the Earth's interior, to some extent. Recently reported natural K- and Na-rich davemaoite inclusion in superdeep diamond (Tschauner et al., 2021), which is still controversial (Walter et al. 2022a; Tschauner et al., 2022), motivated us to reinvestigate the recycling and partitioning behaviours of K and Na in the subducting oceanic crust under deep-mantle P-T conditions. In this study, we experimentally determined the partitioning of Na and K, as well as other major elements, in a natural phengite-rich eclogite system under 5–30 GPa and 850–1550 °C, relevant to P-T conditions from the deep upper mantle to the uppermost lower mantle. We found that the produced davemaoite with the perovskite structure contained minimal amounts of other elements, including K and Na. Therefore, we conclude that K- and Na-rich davemaoite inclusion in the superdeep diamond cannot be inherited from deeply subducted oceanic crusts. In addition, our experimental results further support previous arguments overestimating the K and Na, and other elemental contents in natural davemaoite, which may further indicate that the reported diamond “inclusion” with abnormally high heteroatoms (Tschauner et al., 2021) is not a davemaoite from the lower mantle (Walter et al. 2022a). Finally, we combined the high-pressure phase relationship in the upper continental crust, oceanic basalt, and pyrolite systems from previous studies, and constructed a geodynamical model for the deep K and Na cycles along with the subduction of the oceanic slabs into the uppermost lower mantle.

EARTHQUAKE PREDICTION USING ARTIFICIAL INTELLIGENCE IN THE FERGHANA DEPRESSION (UZBEKISTAN)

Solving the problem of predicting earthquakes faces difficulties of both theoretical and practical nature. The reason is that the occurrence of earthquakes depends on many factors, which give rise to various anomalies that are used as precursors. However, because of the complexity of the earthquake process and the unavailability of much information about the detailed structure of the Earth's crust, a small number of them can accurately indicate future seismic events. The results of the application of machine learning and deep learning give hope for the possibility of obtaining more accurate information about future strong earthquakes if disparate factors are combined. To determine the most important signs of an earthquake and determine the spatial location of strong earthquakes in a specific seismically active territory of Uzbekistan, namely, in the Fergana depression, the Cora 3, Cora 4, random forest algorithms of machine learning and LSTM, ANN architectures of deep learning were implemented.

Seismic Tomography 2024

ABSTRACT Seismic tomography is the most abundant source of information about the internal structure of the Earth at scales ranging from a few meters to thousands of kilometers. It constrains the properties of active volcanoes, earthquake fault zones, deep reservoirs and storage sites, glaciers and ice sheets, or the entire globe. It contributes to outstanding societal problems related to natural hazards, resource exploration, underground storage, and many more. The recent advances in seismic tomography are being translated to nondestructive testing, medical ultrasound, and helioseismology. Nearly 50 yr after its first successful applications, this article offers a snapshot of modern seismic tomography. Focused on major challenges and particularly promising research directions, it is intended to guide both Earth science professionals and early-career scientists. The individual contributions by the coauthors provide diverse perspectives on topics that may at first seem disconnected but are closely tied together by a few coherent threads: multiparameter inversion for properties related to dynamic processes, data quality, and geographic coverage, uncertainty quantification that is useful for geologic interpretation, new formulations of tomographic inverse problems that address concrete geologic questions more directly, and the presentation and quantitative comparison of tomographic models. It remains to be seen which of these problems will be considered solved, solved to some extent, or practically unsolvable over the next decade.

Electronic Structure Calculations of Rare-Earth-Doped Magnesium Oxide Based on Density Functional Theory

In this paper, the electronic structures of rare earth (Nd, Er)-doped MgO were investigated using density functional theory (DFT), with Hubbard on-site corrections (Ueff) applied to rare earth elements. Li was considered a co-dopant. Defect complexes were involved, instead of a single dopant atom, in the supercell. The splitting and distribution of the 4f ground states of Nd and Er dopants in the band gap changed by co-doping Li. The calculation results provide insights into the influences of Li on the optical properties of rare-earth-doped MgO.

In situ investigation of the atomic structure of carbonate-silicate liquids at high pressure-temperature and spectroscopic characterization of the recovered quenched glasses

Carbonate-silicate melts that originate in Earth's interior are described as transitional melts which possess compositions intermediate between carbonatitic and basaltic end members. The covariation of key oxides between carbonatite and basalt (e.g., 10–35 wt% SiO2 and 40–10 wt% CO2, respectively) is expected to have a strong effect on liquid properties. However, due to their paucity both in the record of terrestrial rocks and as quenched glasses, their molecular structure has remained poorly explored to date. We investigated the atomic structure of a synthetic carbonate-silicate liquid with chemical composition within the CaO-MgO-Al2O3-SiO2-FeO-Na2O-ClO−-CO2 oxide system having 18.28 wt% SiO2 and 22.54 wt% CO2 using multi-angle energy dispersive X-ray diffraction at pressures (P) and temperatures (T) of 1.4 GPa/1815 °C, 2.6 GPa/1865 °C, 4.3 GPa/1990 °C, 4.4 GPa/1950 °C. The results show that the intermediate range ordering of the structure decreases with an increase of both P and T. Based on this study, the carbonate-silicate magmas at upper mantle P-T conditions are expected to increase their viscosities during their ascent through the mantle as a result of increasing intermediate range ordering upon cooling and decompression. Additionally, spectroscopic measurements were carried out on the quenched glasses at ambient pressure using micro-Raman as well as micro-FTIR in reflection and transmission modes in the mid infrared range. High pressure investigation using micro-FTIR was also conducted. The distribution of Qn species obtained by deconvolution of the Raman spectra within the aluminosilicate region confirms the depolymerized nature of the quenched glasses as inferred by the low viscosities of the corresponding liquids; peculiar characteristics of the C vibrations would suggest a distorted environment surrounding the network modifying CO32− anion. No evidence of molecular CO2 was detected. Notably, we find evidence of both dissolved molecular CO and CO linked to a metal cation forming carbonyl complexes in the quenched glasses at P-T-fo2 conditions compatible with a hot Archean upper mantle. This suggests a role for carbonate-silicate magmas as carriers of reduced gaseous C-O-H species towards the early atmosphere along with the mobilization of PGE-elements.

Achieving excellent strength-ductility combination of Al-aided Mg-Gd-Al-Zr-Zn alloys fabricated by cold metal transfer-based wire-arc directed energy deposition via uniform equiaxed grains and multiple precipitates

Limited ductility consistently poses a challenge for high-strength Mg-RE (rare earth) structures prepared by additive manufacturing. Particularly following heat treatment, while the strength of the Mg-RE alloy experiences a substantial increase, there is a noteworthy decrease in its ductility. Herein, a novel Mg-Gd-Al-Zr-Zn thin wall was successfully fabricated by cold metal transfer-based wire-arc directed energy deposition (CMT-WA-DED) and Al alloying. The microstructural evolution and mechanical properties of deposited and heat-treatment alloys were elucidated systematically. By adding Al element, Al2Gd and Al-Zr phases with thermal stability were precipitated in the deposited alloy. During the solidification or heat treatment stage, Al2Gd and Al-Zr phases could pin grain boundaries to restrict grain growth. The as-deposited alloys exhibited fully equiaxed grains at different heights and orientations. Thus, the thin wall exhibited good isotropic performance. After the heat treatment, the grain size only slightly grew and no abnormal grain growth was observed. Various morphologies of β precipitation phases were discovered along grain boundaries and within the grains. Additionally, a high density of β' and β1 phases within the grains and β phases along the grain boundary played pivotal roles in enhancing the mechanical strength of the Mg-Gd-Al-Zr-Zn alloy. The alloys exhibited an excellent combination of strength and ductility with ultimate tensile strength of 340 ± 7 MPa, yield strength of 212 ± 5 MPa, and elongation of 12.7 ± 0.9%. This work provides theoretical and practical reference value for the Mg-RE structures obtaining an excellent combination of strength and ductility prepared by additive manufacturing.

A matching pursuit approach to the geophysical inverse problem of seismic travel time tomography under the ray theory approximation

Summary Seismic travel time tomography is a geophysical imaging method to infer the 3-D interior structure of the solid Earth. Most commonly formulated as a linearized inverse problem, it maps differences between observed and expected wave travel times to interior regions where waves propagate faster or slower than the expected average. The Earth’s interior is typically parametrized by a single kind of localized basis function. Here we present an alternative approach that uses matching pursuits on large dictionaries of basis functions. Within the past decade the (Learning) Inverse Problem Matching Pursuits ((L)IPMPs) have been developed. They combine global and local trial functions. An approximation is built in a so-called best basis, chosen iteratively from an intentionally overcomplete set or dictionary. In each iteration, the choice for the next best basis element reduces the Tikhonov–Phillips functional. This is in contrast to classical methods that use either global or local basis functions. The LIPMPs have proven their applicability in inverse problems like the downward continuation of the gravitational potential as well as the MEG-/EEG-problem from medical imaging. Here, we remodel the Learning Regularized Functional Matching Pursuit (LRFMP), which is one of the LIPMPs, for travel time tomography in a ray theoretical setting. In particular, we introduce the operator, some possible trial functions and the regularization. We show a numerical proof of concept for artificial travel time delays obtained from a contrived model for velocity differences. The corresponding code is available online.

Investigating ANU and ICE-6G Ice Model Relative Sea Level Misfits to Determine Viscosity Constraints since the Last Glacial Maximum

Abstract Glacial isostatic adjustment (GIA) incorporates glacial rebound and gravitational potential to calculate sea level rise. However, many ice models struggle to accurately represent these effects in relative sea level (RSL) predictions. Two widely used ice models that incorporate GIA effects, ANU and ICE-6G, require further analysis to gauge their validity. In this thesis, we compare the model predictions of RSL of the ANU and ICE-6G models against six distinct RSL field datasets using a semi-analytic GIA model. To predict RSL, a GIA model requires an ice model and models of the Earth’s mantle viscosity, density, and elastic structure. While mantle density and elastic structures are reliably constructed from seismology studies, mantle viscosity is not well constrained. We developed 864 simulated mantle viscosity models to run with the ANU and ICE-6G ice models to obtain the predicted RSL data. We analyzed the Root Mean Square (RMS) misfits of the simulated test RSL outputs against the observed RSL field data. We showed that RMS demonstrates error quality of field data is critically important to the GIA modeling process. We also showed the strengths and weaknesses of each ice model through further RMS analysis. Lay Summary Sea level change is not only a critical aspect of our climate’s response, but also a novel gateway to understanding the structure of the Earth’s mantle. This understanding is made possible by studying sea level changes over long timescales, such as since the Last Glacial Maximum. The Earth’s crust responds to increased (or decreased) weight of ice on its surface by deforming (or rebounding) and reaching a new equilibrium state over thousands of years. The response time and altered geometryof the crust give information about mantle viscosity. Observations and calculations of sea level over time geospatially constrain historical ice models, creating an opportunity to determine the most appropriate viscosity. This research identified two widely used ice models (ANU and ICE-6G) to reconstruct present day sea level, combined with varying values for the Earth’s upper and lower mantle. Findings were then compared with observations to identify minimum misfits—calculations that are closest to observation values. By understanding the factors that influence these discrepancies, the researchers hope to improve the accuracy of future models and predictions of sea level changes. For the full text and references, please visit https://scholar.colorado.edu/concern/undergraduate_honors_theses/z603qz79c.

The thermal equation of state of the magma Ocean

As the protolunar disk formed by the giant impact with the incoming asteroid Theia started to cool, the Earth condensed in its center as a molten planet. The outer layer, rich in lithophile oxides, formed the magma ocean, whose dynamical behavior heavily influenced the entire evolution of the early Earth. Here, we employ first-principles molecular dynamics simulations to characterize the magma ocean in its initial stage. We compute the compressibility and the viscosity of the molten pyrolite, which best approximates the bulk silicate Earth composition. With an extensive set of calculations, we span the entire relevant pressure-temperature range. We provide a detailed analysis of the athermal and thermal equations of state in various formulations. We obtain a linear temperature dependence for the bulk modulus using the 4th order Birch-Murnaghan equation of state. We show that the liquid silicate accommodates compression by the collapse of the second Si-O coordination sphere, whose corresponding coordination number passes from about 24 at the surface of the magma ocean to about 40 at its deepest point. We found that pyrolite melts have a very low viscosity, about one order of magnitude lower than that of molten basalt. We also propose a revised position of the critical point of the bulk silicate Earth, which lies around 6000 K and 1.1–1.2 kbars.

Proterozoic crustal evolution of the granitoids from the northern margin of the Chotanagpur Gneissic Complex (CGC), Bihar

Since the Proterozoic, considerable expansion of the continental crust has taken place. A significant amount of granitic plutons were deposited on the earth’s crust during this time. The dynamic structure of the earth plays a close role in the genesis of granites and related rocks. Information about the formation and development of the continental crust can be understood from the study of these rocks. The emplacement of large scale anorthosite massif in shield areas was another process that contributed to the Proterozoic expansion of the continental (Mukherjee, et al.,, 2005). One of the primary sources of information regarding the formation and evolution of the continents over geological time is the genesis of granite. Enclaves of supracrustal meta-sediments intrude the Chotanagpur Gneissic Complex (CGC), which is primarily composed of granites, granitoid gneisses, and migmatites exhibiting a wide range of structure, texture, and mineralogy variations.The granitic plutons exposed in the northern fringe of the Chotanagpur Gneissic Complex, CGC, and the associated anorthosites of the Barabar Anorthosite Complex along the northen margin of Bihar holds information about the various magmatic episodes that have taken place in that area millions of years ago.

Modulation of evapotranspiration and stream runoff by weathered bedrock in arid and semi-arid mountains

Earth's Critical Zone exhibits remarkable heterogeneity and complexity. Hence, further investigation is required to examine the composition of Earth's Critical Zone as well as the diverse eco-hydrological patterns they exhibit under varying climatic and geological circumstances. This exploration should primarily be conducted through the investigation and experiments of the hillslope unit, where the topography and weathered bedrock are representative, with particular emphasis on semi-arid regions where water resources serve as the primary limiting factor. Here, we have determined that the structure of the weathering profile displays systematic variation across the topography and heterogeneous landscape on uninterrupted slopes. Differences in the structure of the subsurface critical zone led to differences in its water storage capacity at the same time. Runoff in alpine shrubs and forests was dominated by subsurface runoff, and grassland was dominated by surface runoff. In the alpine shrub immediately adjacent to the watershed, an estimated quantity of 129 mm of water is stored within the unsaturated zone of the soil, serving as exchange water to replenish moisture in the underlying bedrock. In contrast to alpine shrubs, an estimated quantity of 62.7 mm of water originates from the unsaturated zone of soil and weathered bedrock in the forest. However, approximately 21.1 mm of moisture is unavailable to plants. The soil water storage in grasslands exhibits a decline throughout the growing season, with a subsequent augmentation occurring solely after substantial precipitation events exceeding 20 mm. In wet years, dynamic storage predominantly manifests as groundwater saturation throughout the entire ground and high subsurface runoff. In dry years, the limited runoff response indicates that the catchment's dynamic water storage primarily comprises “indirect” water storage, which predominantly resides within the soil, saprolite, and weathered rock below the “field capacity”, subsequently being released into the atmosphere through evapotranspiration.

Revising palaeoelevation estimates for the Tibetan Plateau by integrating latitude, paleogeographic and paleotemperature data

Quantifying the palaeoelevation of the Tibetan Plateau (TP) is important for investigations of deep earth dynamics, surface uplift, and climate evolution. In particular, high precision palaeogeographic data can provide a more comprehensive understanding of the processes and mechanisms of TP uplift and can help refine palaeoclimate simulations. As a whole, there are complex physical and chemical interactions between the six concentric layers of the Earth. In this study, we used published palaeogeographic and palaeotemperature data to revise the evolution of the TP elevation for six time intervals of the Cenozoic according to the time nodes of key changes in each layer. We then revised the palaeoelevations using palaeotemperature data and linear and polynomial regression models. Our revised palaeoelevation results solve the problems of the low resolution of palaeotemperature data and the low accuracy of palaeogeographic data, and they enable us to fine tune the palaeoelevation data for the studied intervals. Our findings contribute to reconstructions of the palaeogeomorphology and palaeoelevation of the TP and provide supporting data for future studies of the TP system on long timescales.

Geothermal resource potentials estimation from the interpretation of aeromagnetic data over parts of Southwestern Nigeria

In a bid to explore unconventional electricity generation sources and reduce effects of fossil fuels, this study evaluates geothermal resource potentials over parts of Southwestern Nigeria, precisely depth to the bottom of magnetic source (DBMS), heat flow, geothermal gradient and their relationships. Regional-residual anomaly separation was conducted, and spectral analysis was applied on the residual anomaly component of 14 aeromagnetic data sheets. Depth to the bottom of magnetic source varies between 1.87 and 6.26 km, with average value of 3.50 km, heat flow varies between 23.18 and 77.38 mWm−2, with average value of 43.79 mWm−2, while geothermal gradient varies between 9.27 and 30.95 oC/km with average value of 17.52 oC/km. Northcentral region has the highest heat flow (77.4 mWm−2), followed by Northeast (68.3 mWm−2), Southwest has the least (< 40.0 mWm−2) while Southeast has values in between the extremes. A comparison between the average heat flow and that of ‘thermally stable’ continental regions of the world (60 or 65) mW/m2 gives 72.98 or 67.37% respectively. The estimated heat is probably from mantle plumes, radioactive sources or heat generated from pressures within basements that are overlaid by thick thermally insulated sediments, hence hot magmatic fluid flows into fractured basement and cause hydrothermal alterations of surrounding rocks. Since most geodynamic operations depends on thermal structure of the earth’s crust, the result of this study has undoubtedly contributed significantly to the body of existing thermal knowledge and closed the information gap regarding crustal temperature distribution at depth in Southwest part of Nigeria and Nigeria in general.

Iron alloys of volatile elements in the deep Earth's interior.

Investigations into the compositional model of the Earth, particularly the atypical concentrations of volatile elements within the silicate portion of the early Earth, have attracted significant interest due to their pivotal role in elucidating the planet's evolution and dynamics. To understand the behavior of such volatile elements, an established 'volatility trend' has been used to explain the observed depletion of certain volatile elements. However, elements such as Se and Br remain notably over-depleted in the silicate Earth. Here we show the results from first-principles simulations that explore the potential for these elements to integrate into hcp-Fe through the formation of substitutional alloys, long presumed to be predominant constituents of the Earth's core. Based on our findings, the thermodynamic stability of these alloys suggests that these volatile elements might indeed be partially sequestered within the Earth's core. We suggest potential reservoirs for volatile elements within the deep Earth, augmenting our understanding of the deep Earth's composition.

On the Stability of Mantle‐Sensitive P‐Wave Interference During a Secondary Microseismic Event

AbstractBody wave extraction from oceanic secondary microseismic sources with seismic interferometry provides alternative information to better constrain the Earth's structure. However, sources' spatiotemporal variations raise concerns about travel time measurement robustness. Therefore, we study the cross‐correlations’ stability during a single oceanic event. This study focuses on 3 days of data and three seismic arrays' combinations between 8 and 11 December 2014 during storm Alexandra, a “weather bomb” event in southern Greenland. We use the WAVEWATCH III hindcast to model P‐wave noise sources and assess the impact of short‐term source variations on cross‐correlations. Model‐based cross‐correlations compared to data show coherent delays to reference 3D Earth models (∼0–3 s) confirming the robustness of the source model which could explain minor travel time variations (≤1 s).

Imaging the top of the Earth's inner core: a present-day flow model.

Despite considerable progress in seismology, mineral physics, geodynamics, paleomagnetism, and mathematical geophysics, Earth's inner core structure and evolution remain enigmatic. One of the most significant issues is its thermal history and the current thermal state. Several hypotheses involving a thermally-convecting inner core have been proposed: a simple, high-viscosity, translational mode, or a classical, lower-viscosity, plume-style convection. Here, we use state-of-the-art seismic imaging to probe the outermost shell of the inner core for its isotropic compressional speed and compare it with recently developed attenuation maps. The pattern emerging in the resulting tomograms is interpreted with recent data on the viscosity of iron as the inner core surface manifestation of a thermally-driven flow, with a positive correlation among compressional speed and attenuation and temperature. Although the outer-core convection controls the heat flux across the inner core boundary, the internally driven inner-core convection is a plausible model that explains a range of observations for the inner core, including distinct anisotropy in the innermost inner core.

Deep carbon recycling viewed from global plate tectonics

Abstract Plate tectonics plays an essential role in the redistribution of life-essential volatile elements between Earth's interior and surface, whereby our planet has been well tuned to maintain enduring habitability over much of its history. Here we present an overview of deep carbon recycling in the regime of modern plate tectonics, with a special focus on convergent plate margins for assessing global carbon mass balance. The up-to-date flux compilation implies approximate balance between deep carbon outflux and subduction carbon influx within uncertainty but remarkably limited return of carbon to convecting mantle. If correct, carbon would gradually accumulate in the lithosphere over time by (i) massive subsurface carbon storage occurring primarily in continental lithosphere from convergent margins to continental interior and (ii) persistent surface carbon sinks to seafloors sustained by high-flux deep CO2 emissions to the atmosphere. Further assessment of global carbon mass balance requires updates on fluxes of subduction-driven carbon recycling paths and reduction in uncertainty of deep carbon outflux. From a global plate tectonics point of view, we particularly emphasize that continental reworking is an important mechanism for remobilizing geologically sequestered carbon in continental crust and sub-continental lithospheric mantle. In light of recent advances, future research is suggested to focus on a better understanding of the reservoirs, fluxes, mechanisms, and climatic effects of deep carbon recycling following an integrated methodology of observation, experiment, and numerical modeling, with the aim of decoding the self-regulating Earth system and its habitability from the deep carbon recycling perspective.

Quantification and Optimization of Compaction Energy Used in Earth Construction: Case of Static and Dynamic Compaction

Earth construction is a sustainable and environmentally friendly approach to building. In addition to their good thermal performance, earth materials are abundant, inexpensive, and readily available, reducing the need for resource-intensive materials like concrete and steel. Regarding the construction process of earth structures, which is based on compaction, there is often a difference between the laboratory compaction process and the onsite one. The energy consumed onsite to produce earth structures is still approximative and uncontrolled, which affects considerably the mechanical performances of earth walls. Then, the investigation of the optimal compaction energy is necessary. To optimize the on-site compaction energy used in rammed earth (RE), an experimental study is carried out to compare the dynamic compaction usually applied to produce RE walls to the static compaction using a mechanical press. By considering increasing dynamic and static energies, the physical and mechanical properties are analyzed for each case. The obtained results show that RE walls can be replaced by prefabricated pressed earth blocks where the compaction energy is reduced by 60% and the compressive strength is enhanced by 70% using static compaction, thus achieving 4 MPa without stabilization. This solution allows to reduce the execution time and to control the quality of earth buildings.