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  • 1
    facet.materialart.12
    Earth dynamics : deformations and oscillations of the rotating Earth (2013)
    Cambridge : Cambridge University Press
    Details
    Call number: 9781107306189 (e-book)
    Description / Table of Contents: "The Earth is a dynamic system. Internal processes, together with external gravitational forces of the Sun, Moon and planets, displace the Earth's mass, impacting on its shape, rotation and gravitational field. Doug Smylie provides a rigorous overview of the dynamical behaviour of the solid Earth, explaining the theory and presenting methods for numerical implementation. Topics include advanced digital analysis, earthquake displacement fields, Free Core Nutations observed by the Very Long Baseline Interferometric technique, translational modes of the solid inner core observed by the superconducting gravimeters, and dynamics of the outer fluid core. This book is supported by freeware computer code, available online for students to implement the theory. Online materials also include a suite of graphics generated from the numerical analysis, combined with 100 graphic examples in the book to make this an ideal tool for researchers and graduate students in the fields of geodesy, seismology and solid earth geophysics"--
    Type of Medium: 12
    Pages: 1 Online-Ressource (XII, 543 Seiten) , Illustrationen
    Edition: Electronic reproduction. Ann Arbor, MI : ProQuest, 2015. Available via World Wide Web. Access may be limited to ProQuest affiliated libraries.
    ISBN: 9781107306189
    URL: Fulltext @ Ebook Central
    Language: English
    Note: Contents Preface and acknowledgments The book website www.cambridge.org/smylie 1 Introduction and theoretical background 1.1 Scalar, vector and tensor analysis 1.2 Separation of vector fields 1.3 Vector spherical harmonics 1.4 Elasticity theory 1.5 Linear algebraic systems 1.6 Interpolation and approximation 2 Time sequence and spectral analysis 2.1 Time domain analysis 2.2 Linear optimum Wiener filters 2.3 Frequency domain analysis 2.4 Fourier series and transforms 2.5 Power spectral density estimation 2.6 Maximum entropy spectral analysis 3 Earth deformations 3.1 Equilibrium equations 3.2 The reciprocal theorem of Betti 3.3 Radial equations: spheroidal and torsional 3.4 Dynamical equations 3.5 Solutions near the geocentre 3.6 Numerical integration of the radial equations 3.7 Fundamental, regular solutions in the inner core 4 Earth's rotation: observations and theory 4.1 Reference frames 4.2 Polar motion and wobble 4.3 The dynamics of polar motion and wobble 4.4 Nutation and motion of the celestial pole 5 Earth's figure and gravitation 5.1 Historical development 5.2 External gravity and figure 5.3 Equilibrium theory of the internal figure 5.4 Gravity coupling 6 Rotating fluids and the outer core 6.1 The inertial wave equation 6.2 Dynamics of the fluid outer core 6.3 Scaling of the core equations 6.4 Compressibility and density stratification 7 The subseisniic equation and boundary conditions 7.1 The subseismic wave equation 7.2 Deformation of the shell and inner core 8 Variational methods and core modes 8.1 A subseismic variational principle 8.2 Representation of the functional 8.3 Finite element support functions 8.4 Boundary conditions and constraints 8.5 Numerical implementation and results 8.6 Rotational splitting and viscosity 8.7 A viscosity profile for the outer core 9 Static deformations and dislocation theory 9.1 The elasticity theory of dislocations 9.2 The theory for realistic Earth models 9.3 Changes in the inertia tensor and the secular polar shift Appendix A Elementary results from vector analysis A.1 Vector identities A.2 Vector calculus identities A.3 Integral theorems Appendix B Properties of Legendre functions B.1 Recurrence relations B.2 Evaluation of Legendre functions Appendix C Numerical Earth models C.1 The Earth models References Fortran index Subject index
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  • 2
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    Continental flood basalts sample oxidized mantle sources (2024)
    In:  Lithos
    Details
    Publication Date: 2024-06-21
    Description: Large igneous provinces (LIP) are vast (0.2 to 〉1 Mkm3) outpourings of basaltic lava and voluminous intrusions of magmas that have had important environmental consequences, in many cases leading to immense greenhouse gas release and mass extinctions. Magmatic oxygen fugacity (fO2) influences the chemistry of volcanic gases and is an important parameter for examining the links between LIP eruptions and environmental change. To constrain the fO2 of LIP magmas, we report olivine elemental chemistry of 399 crystals from a set of fifteen olivine-rich LIP samples, spanning in age from the Proterozoic (∼1270 Ma) to the Miocene (∼17 Ma). Concentrations of V in olivine are used to show that mafic LIP lavas erupted at +1.20 ± 0.95 ΔFMQ, on average more oxidized than mid ocean ridge basalts (MORB) at −0.28 ± 0.28 ΔFMQ. Mafic LIP magmas show a much larger range than MORB, however. Additionally, fO2 shows a negative correlation with parental magma MgO content, with high MgO lavas approaching the MORB range. This correlation is likely due to sampling of a heterogeneous mixture of oxidized and reduced lithologies, as also sampled by ocean island basalts (OIB). Correlation between fO2 and isotopic ratios such as 143Nd/144Nd demonstrates that the oxidized endmember is geochemically enriched, and may result from subduction recycling of oxidized surficial materials. The high fO2 of primitive LIP magmas demonstrate that they largely emitted oxidized gases during eruption, and furthermore, that LIP magmas associated with mass extinctions have similar magmatic fO2 to those that are not. Global plate tectonic position, magnitude and duration of LIP volcanic eruptions and magmatic degassing, as well as interaction with sedimentary basins in the crust - but not mantle source fO2 - are likely to be the critical factors for whether a LIP was associated with a mass extinction.
    Language: English
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  • 3
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    Analysis of bridge displacement using GNSS time-series data (2023)
    In:  IOP Conference Series: Materials Science and Engineering
    Details
    Publication Date: 2024-06-21
    Description: Analysis and identifying the displacement characteristics play a key role in timely monitoring and detecting the physical responses of the bridge to ensure the safety of the human and structure. Many previous kinds of research used GNSS data to identify displacement and oscillation modelling of the bridge with different algorithms. This study uses GNSS time-series data to determine linear displacement and model oscillation of the bridge using a procedure including filtering outliers, linear regression, and sin function to identify amplitude in three directions, the plane displacement velocity, spatial displacement velocity, and vibration model of the bridge. The data in the research in the GNSS time-series data from three P5 GNSS receivers of the CHC brand on the Dachongyong bridge in Nanning, China with 1646 observations, at one-hour sample intervals in 68 consecutive days. The plane and spatial velocity of the three points DCQ01, DCQ02, and DCQ03 is 0.0181 mm/h, 0.0185 mm/h; 0.0114 mm/h, 0.0173 mm/h; and 0.0071 mm/h, 0.0082 mm/h respectively. The study results are significant in analyzing and identifying the bridge's displacement characteristics.
    Language: English
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  • 4
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    Anisotropic thermal conductivity of antigorite along slab subduction impacts seismicity of intermediate-depth earthquakes (2024)
    In:  Nature Communications
    Details
    Publication Date: 2024-06-21
    Description: Double seismic zones (DSZs) are a feature of some subducting slabs, where intermediate-depth earthquakes (~70–300 km) align along two separate planes. The upper seismic plane is generally attributed to dehydration embrittlement, whereas mechanisms forming the lower seismic plane are still debated. Thermal conductivity of slab minerals is expected to control the temperature evolution of subducting slabs, and therefore their seismicity. However, effects of the potential anisotropic thermal conductivity of layered serpentine minerals with crystal preferred orientation on slab’s thermal evolution remain poorly understood. Here we measure the lattice thermal conductivity of antigorite, a hydrous serpentine mineral, along its crystallographic b- and c-axis at relevant high pressure-temperature conditions of subduction. We find that antigorite’s thermal conductivity along the c-axis is ~3–4 folds smaller than the b-axis.Our numericalmodels further reveal thatwhen the lowthermal-conductivity c-axis is aligned normal to the slab dip, antigorite’s strongly anisotropic thermal conductivity enables heating at the top portion of the slab, facilitating dehydration embrittlement that causes the seismicity in the upper plane of DSZs. Potentially, the antigorite’s thermal insulating effect also hinders the dissipation of frictional heat inside shear zones, promoting thermal runaway along serpentinized faults that could trigger intermediatedepth earthquakes.
    Language: English
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  • 5
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    Boron sources of tourmaline-rich Nb-Y-F-pegmatites in south Norway: Implications for pegmatite melt origin (2024)
    In:  Precambrian Research
    Details
    Publication Date: 2024-06-21
    Description: Tourmaline is common in rare element pegmatites of the Nb-Y-F (NYF) type in the south-central part of the Proterozoic Sveconorwegian orogen in southern Norway. In the global context, however, tourmaline appears rare in this type of pegmatite. This study aims to explain the unusual tourmaline abundance in these pegmatites and the origin of boron (B) in the respective melts, and to raise awareness of tourmaline in NYF pegmatites generally. Tourmalines from six pegmatites in three Sveconorwegian lithotectonic units: Bamble, Kongsberg and Idefjorden, were investigated in terms of their mineral chemistry and δ11B values, in addition to bulk rock analyses of pegmatites and host rocks. Tourmalines in pegmatites from Bamble and Kongsberg record B isotopic compositions (δ11B = -1.0 to + 9.9 ‰) that are heavy relative to continental crust and mantle sources. In contrast, tourmaline in pegmatites and host rocks from Idefjorden have light B isotopic ratios (δ11B = -14.8 to −12.5 ‰) that are typical crustal values. We suggest that the latter melts were sourced from orthogneisses at depth. We relate the heavy B isotopic composition of Bamble and Kongsberg pegmatites to regional Na-metasomatism by fluids sourced from Mesoproterozoic shallow marine sediments. This is supported by previously published δ11B ratios from metasomatized Bamble host rocks. The spatial association of pegmatites with Na-metasomatism in the basement rocks suggests that metasomatism enhanced the fertility and B-concentration in the affected lithologies, favouring partial melting and the formation of tourmaline-bearing pegmatites. These findings contribute to understanding the petrogenesis of Sveconorwegian pegmatites but they also imply that B can play a greater role in the formation of NYF pegmatites than previously thought and that tourmaline has value as a petrogenetic tool in this type of pegmatites as well as in the Li-Cs-Ta (LCT) type to which is it is more commonly applied.
    Language: English
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  • 6
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    Convolution of individual and group identity: self-reliance increases polarisation in basic opinion model (2024)
    In:  Humanities and Social Sciences Communications
    Details
    Publication Date: 2024-06-21
    Description: Opinion formation within society follows complex dynamics. Towards its understanding, axiomatic theory can complement data analysis. To this end we propose an axiomatic model of opinion formation that aims to capture the interaction of individual conviction with social influence in a minimalist fashion. Despite only representing that (1) agents have an initial conviction with respect to a topic and are (2) influenced by their neighbours, the model shows emergence of opinion clusters from an initially unstructured state. Here, we show that increasing individual self-reliance makes agents more likely to align their socially influenced opinion with their inner conviction which concomitantly leads to increased polarisation. The opinion drift observed with increasing self-reliance may be a plausible analogue of polarisation trends in the real world. Modelling the basic traits of striving for individual versus group identity, we find a trade-off between individual fulfilment and societal cohesion. This finding from fundamental assumptions can serve as a building block to explain opinion polarisation.
    Language: English
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  • 7
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    Low carbon hydrogen in the European Union: A coherent regulatory framework (2024)
    Potsdam Institute for Climate Impact Research
    In:  Ariadne-Analyse
    Details
    Publication Date: 2024-06-21
    Description: Renewable hydrogen is necessary for the decarbonization of sectors that are difficult to electrify, such as industry and aviation, and as a storage medium for surplus electricity from renewable sources.
    Language: English
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  • 8
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    Hydrogeochemical characterization of water resources in the Pra Basin (Ghana) for quality assessment and water management (2024)
    Universität Potsdam
    Details
    Publication Date: 2024-06-20
    Description: Watershed management requires an understanding of key hydrochemical processes. The Pra Basin is one of the five major river basins in Ghana with a population of over 4.2 million people. Currently, water resources management faces challenges due to surface water pollution caused by the unregulated release of untreated household and industrial waste into aquatic ecosystems and illegal mining activities. This has increased the need for groundwater as the most reliable water supply. Our understanding of groundwater recharge mechanisms and chemical evolution in the basin has been inadequate, making effective management difficult. Therefore, the main objective of this work is to gain insight into the processes that determine the hydrogeochemical evolution of groundwater quality in the Pra Basin. The combined use of stable isotope, hydrochemistry, and water level data provides the basis for conceptualizing the chemical evolution of groundwater in the Pra Basin. For this purpose, the origin and evaporation rates of water infiltrating into the unsaturated zone were evaluated. In addition, Chloride Mass Balance (CMB) and Water Table Fluctuations (WTF) were considered to quantify groundwater recharge for the basin. Indices such as water quality index (WQI), sodium adsorption ratio (SAR), Wilcox diagram, and salinity (USSL) were used in this study to determine the quality of the resource for use as drinking water and for irrigation purposes. Due to the heterogeneity of the hydrochemical data, the statistical techniques of hierarchical cluster and factor analysis were applied to subdivide the data according to their spatial correlation. A conceptual hydrogeochemical model was developed and subsequently validated by applying combinatorial inverse and reaction pathway-based geochemical models to determine plausible mineral assemblages that control the chemical composition of the groundwater. The interactions between water and rock determine the groundwater quality in the Pra Basin. The results underline that the groundwater is of good quality and can be used for drinking water and irrigation purposes. It was demonstrated that there is a large groundwater potential to meet the entire Pra Basin’s current and future water demands. The main recharge area was identified as the northern zone, while the southern zone is the discharge area. The predominant influence of weathering of silicate minerals plays a key role in the chemical evolution of the groundwater. The work presented here provides fundamental insights into the hydrochemistry of the Pra Basin and provides data important to water managers for informed decision-making in planning and allocating water resources for various purposes. A novel inverse modelling approach was used in this study to identify different mineral compositions that determine the chemical evolution of groundwater in the Pra Basin. This modelling technique has the potential to simulate the composition of groundwater at the basin scale with large hydrochemical heterogeneity, using average water composition to represent established spatial groupings of water chemistry.
    Description: Die Bewirtschaftung von Wassereinzugsgebieten erfordert ein Verständnis der wichtigsten hydrochemischen Prozesse. Das Pra-Becken ist eines der fünf großen Flusseinzugsgebiete Ghanas mit einer Bevölkerung von über 4,2 Millionen Menschen. Die Bewirtschaftung der Wasserressourcen wird derzeit durch die Verschmutzung der Oberflächengewässer erschwert, die durch die unkontrollierte Einleitung von unbehandelten Haushalts- und Industrieabfällen in die aquatischen Ökosysteme und durch illegale Bergbauaktivitäten entsteht. Dies hat den Bedarf an Grundwasser als zuverlässigste Wasserversorgung erhöht. Unser Verständnis der Mechanismen der Grundwasserneubildung und der chemischen Entwicklung im Einzugsgebiet ist bislang unzureichend, was eine wirksame Bewirtschaftung erschwert. Daher ist das Hauptziel dieser Arbeit Einblicke in die Prozesse zu bekommen, welche die hydrogeochemische Entwicklung der Grundwasserqualität im Pra-Becken bestimmen. Die kombinierte Verwendung von Daten stabiler Isotope, der Hydrochemie und von Wasserständen bildet die Grundlage für die Konzeption der chemischen Entwicklung des Grundwassers im Pra-Becken. Dafür wurden die Herkunft und die Verdunstungsraten des in die ungesättigte Zone infiltrierenden Wassers bewertet. Darüber hinaus wurden die Chlorid-Massenbilanz und die Wasserspiegelschwankungen betrachtet, um die Grundwasserneubildung für das Einzugsgebiet zu quantifizieren. Indizes wie der Wasserqualitätsindex (WQI), das Natriumadsorptionsverhältnis (SAR), das Wilcox-Diagramm und der Salzgehalt (USSL) wurden in dieser Studie verwendet, um die Qualität der Ressource für die Verwendung als Trinkwasser und zu Bewässerungszwecken zu bestimmen. Aufgrund der Heterogenität der hydrochemischen Daten wurden die statistischen Verfahren der hierarchischen Cluster- und Faktorenanalyse angewandt, um die Daten entsprechend ihrer räumlichen Korrelation zu unterteilen. Ein konzeptionelles hydrogeochemisches Modell wurde entwickelt und anschließend durch Anwendung kombinatorischer inverser und reaktionspfadbasierter geochemischer Modelle validiert, um plausible mineralische Assemblagen zu bestimmen, welche die chemische Zusammensetzung des Grundwassers kontrollieren. Die Wechselwirkungen zwischen Wasser und Gestein bestimmen die Grundwasserqualität im Pra-Becken. Die Ergebnisse unterstreichen, dass das Grundwasser eine gute Qualität aufweist und als Trinkwasser und für Bewässerungszwecke genutzt werden kann. Es wurde nachgewiesen, dass ein großes Grundwasserpotenzial vorhanden ist, um den derzeitigen und künftigen Wasserbedarf des gesamten Pra-Beckens zu decken. Als Hauptneubildungsgebiet wurde die nördliche Zone im Gebiet identifiziert, während die südliche Zone das Abflussgebiet ist. Der vorherrschende Einfluss der Verwitterung von Silikatmineralen spielt bei der chemischen Entwicklung des Grundwassers eine zentrale Rolle. Die hier vorgestellte Arbeit gibt grundlegende Einblicke in die Hydrochemie des Pra-Beckens und liefert für das Wassermanagement wichtige Daten für eine fundierte Entscheidungsfindung bei der Planung und Zuweisung von Wasserressourcen für verschiedene Zwecke. Ein neuartiger Ansatz zur inversen Modellierungwurde in dieser Studie eingesetzt, um unterschiedliche Mineralzusammensetzungen zu ermitteln, welche die chemische Entwicklung des Grundwassers im Pra-Becken bestimmen. Diese Modellierungstechnik hat das Potenzial, die Zusammensetzung eines Grundwassers auf der Skala eines Beckens mit großer hydrochemischer Heterogenität zu simulieren, wobei die durchschnittliche Wasserzusammensetzung zur Darstellung der etablierten räumlichen Gruppierungen der Wasserchemie verwendet wird.
    Description: Watershed management requires an understanding of key hydrochemical processes. The Pra Basin is one of the five major river basins in Ghana with a population of over 4.2 million people. Currently, water resources management faces challenges due to surface water pollution caused by the unregulated release of untreated household and industrial waste into aquatic ecosystems and illegal mining activities. This has increased the need for groundwater as the most reliable water supply. Our understanding of groundwater recharge mechanisms and chemical evolution in the basin has been inadequate, making effective management difficult. Therefore, the main objective of this work is to gain insight into the processes that determine the hydrogeochemical evolution of groundwater quality in the Pra Basin. The combined use of stable isotope, hydrochemistry, and water level data provides the basis for conceptualizing the chemical evolution of groundwater in the Pra Basin. For this purpose, the origin and evaporation rates of water infiltrating into the unsaturated zone were evaluated. In addition, Chloride Mass Balance (CMB) and Water Table Fluctuations (WTF) were considered to quantify groundwater recharge for the basin. Indices such as water quality index (WQI), sodium adsorption ratio (SAR), Wilcox diagram, and salinity (USSL) were used in this study to determine the quality of the resource for use as drinking water and for irrigation purposes. Due to the heterogeneity of the hydrochemical data, the statistical techniques of hierarchical cluster and factor analysis were applied to subdivide the data according to their spatial correlation. A conceptual hydrogeochemical model was developed and subsequently validated by applying combinatorial inverse and reaction pathway-based geochemical models to determine plausible mineral assemblages that control the chemical composition of the groundwater. The interactions between water and rock determine the groundwater quality in the Pra Basin. The results underline that the groundwater is of good quality and can be used for drinking water and irrigation purposes. It was demonstrated that there is a large groundwater potential to meet the entire Pra Basin’s current and future water demands. The main recharge area was identified as the northern zone, while the southern zone is the discharge area. The predominant influence of weathering of silicate minerals plays a key role in the chemical evolution of the groundwater. The work presented here provides fundamental insights into the hydrochemistry of the Pra Basin and provides data important to water managers for informed decision-making in planning and allocating water resources for various purposes. A novel inverse modelling approach was used in this study to identify different mineral compositions that determine the chemical evolution of groundwater in the Pra Basin. This modelling technique has the potential to simulate the composition of groundwater at the basin scale with large hydrochemical heterogeneity, using average water composition to represent established spatial groupings of water chemistry.
    Language: English
    Type: info:eu-repo/semantics/doctoralThesis
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  • 9
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    Enhanced computational approaches for data-driven characterization of earthquake ground motion and rapid earthquake impact assessment (2024)
    Universität Potsdam
    Details
    Publication Date: 2024-06-20
    Description: Rapidly growing seismic and macroseismic databases and simplified access to advanced machine learning methods have in recent years opened up vast opportunities to address challenges in engineering and strong motion seismology from novel, datacentric perspectives. In this thesis, I explore the opportunities of such perspectives for the tasks of ground motion modeling and rapid earthquake impact assessment, tasks with major implications for long-term earthquake disaster mitigation. In my first study, I utilize the rich strong motion database from the Kanto basin, Japan, and apply the U-Net artificial neural network architecture to develop a deep learning based ground motion model. The operational prototype provides statistical estimates of expected ground shaking, given descriptions of a specific earthquake source, wave propagation paths, and geophysical site conditions. The U-Net interprets ground motion data in its spatial context, potentially taking into account, for example, the geological properties in the vicinity of observation sites. Predictions of ground motion intensity are thereby calibrated to individual observation sites and earthquake locations. The second study addresses the explicit incorporation of rupture forward directivity into ground motion modeling. Incorporation of this phenomenon, causing strong, pulse like ground shaking in the vicinity of earthquake sources, is usually associated with an intolerable increase in computational demand during probabilistic seismic hazard analysis (PSHA) calculations. I suggest an approach in which I utilize an artificial neural network to efficiently approximate the average, directivity-related adjustment to ground motion predictions for earthquake ruptures from the 2022 New Zealand National Seismic Hazard Model. The practical implementation in an actual PSHA calculation demonstrates the efficiency and operational readiness of my model. In a follow-up study, I present a proof of concept for an alternative strategy in which I target the generalizing applicability to ruptures other than those from the New Zealand National Seismic Hazard Model. In the third study, I address the usability of pseudo-intensity reports obtained from macroseismic observations by non-expert citizens for rapid impact assessment. I demonstrate that the statistical properties of pseudo-intensity collections describing the intensity of shaking are correlated with the societal impact of earthquakes. In a second step, I develop a probabilistic model that, within minutes of an event, quantifies the probability of an earthquake to cause considerable societal impact. Under certain conditions, such a quick and preliminary method might be useful to support decision makers in their efforts to organize auxiliary measures for earthquake disaster response while results from more elaborate impact assessment frameworks are not yet available. The application of machine learning methods to datasets that only partially reveal characteristics of Big Data, qualify the majority of results obtained in this thesis as explorative insights rather than ready-to-use solutions to real world problems. The practical usefulness of this work will be better assessed in the future by applying the approaches developed to growing and increasingly complex data sets.
    Description: Das rapide Wachstum seismischer und makroseismischer Datenbanken und der vereinfachte Zugang zu fortschrittlichen Methoden aus dem Bereich des maschinellen Lernens haben in den letzen Jahren die datenfokussierte Betrachtung von Fragestellungen in der Seismologie ermöglicht. In dieser Arbeit erforsche ich das Potenzial solcher Betrachtungsweisen im Hinblick auf die Modellierung erdbebenbedingter Bodenerschütterungen und der raschen Einschätzung von gesellschaftlichen Erdbebenauswirkungen, Disziplinen von erheblicher Bedeutung für den langfristigen Erdbebenkatastrophenschutz in seismisch aktiven Regionen. In meiner ersten Studie nutze ich die Vielzahl an Bodenbewegungsdaten aus der Kanto Region in Japan, sowie eine spezielle neuronale Netzwerkarchitektur (U-Net) um ein Bodenbewegungsmodell zu entwickeln. Der einsatzbereite Prototyp liefert auf Basis der Charakterisierung von Erdbebenherden, Wellenausbreitungspfaden und Bodenbeschaffenheiten statistische Schätzungen der zu erwartenden Bodenerschütterungen. Das U-Net interpretiert Bodenbewegungsdaten im räumlichen Kontext, sodass etwa die geologischen Beschaffenheiten in der Umgebung von Messstationen mit einbezogen werden können. Auch die absoluten Koordinaten von Erdbebenherden und Messstationen werden berücksichtigt. Die zweite Studie behandelt die explizite Berücksichtigung richtungsabhängiger Verstärkungseffekte in der Bodenbewegungsmodellierung. Obwohl solche Effekte starke, impulsartige Erschütterungen in der Nähe von Erdbebenherden erzeugen, die eine erhebliche seismische Beanspruchung von Gebäuden darstellen, wird deren explizite Modellierung in der seismischen Gefährdungsabschätzung aufgrund des nicht vertretbaren Rechenaufwandes ausgelassen. Mit meinem, auf einem neuronalen Netzwerk basierenden, Ansatz schlage ich eine Methode vor, umdieses Vorhaben effizient für Erdbebenszenarien aus dem neuseeländischen seismischen Gefährdungsmodell für 2022 (NSHM) umzusetzen. Die Implementierung in einer seismischen Gefährdungsrechnung unterstreicht die Praktikabilität meines Modells. In einer anschließenden Machbarkeitsstudie untersuche ich einen alternativen Ansatz der auf die Anwendbarkeit auf beliebige Erdbebeszenarien abzielt. Die abschließende dritte Studie befasst sich mit dem potenziellen Nutzen der von makroseismischen Beobachtungen abgeleiteten pseudo-Erschütterungsintensitäten für die rasche Abschätzung von gesellschaftlichen Erdbebenauswirkungen. Ich zeige, dass sich aus den Merkmalen solcher Daten Schlussfolgerungen über die gesellschaftlichen Folgen eines Erdbebens ableiten lassen. Basierend darauf formuliere ich ein statistisches Modell, welches innerhalb weniger Minuten nach einem Erdbeben die Wahrscheinlichkeit für das Auftreten beachtlicher gesellschaftlicher Auswirkungen liefert. Ich komme zu dem Schluss, dass ein solches Modell, unter bestimmten Bedingungen, hilfreich sein könnte, um EntscheidungsträgerInnen in ihren Bestrebungen Hilfsmaßnahmen zu organisieren zu unterstützen. Die Anwendung von Methoden des maschinellen Lernens auf Datensätze die sich nur begrenzt als Big Data charakterisieren lassen, qualifizieren die Mehrheit der Ergebnisse dieser Arbeit als explorative Einblicke und weniger als einsatzbereite Lösungen für praktische Fragestellungen. Der praktische Nutzen dieser Arbeit wird sich in erst in Zukunft an der Anwendung der erarbeiteten Ansätze auf wachsende und zunehmend komplexe Datensätze final abschätzen lassen.
    Language: English
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  • 10
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    Optical properties of (Mg,Fe)O at high pressure (2024)
    Universität Potsdam
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    Publication Date: 2024-06-20
    Description: Large parts of the Earth’s interior are inaccessible to direct observation, yet global geodynamic processes are governed by the physical material properties under extreme pressure and temperature conditions. It is therefore essential to investigate the deep Earth’s physical properties through in-situ laboratory experiments. With this goal in mind, the optical properties of mantle minerals at high pressure offer a unique way to determine a variety of physical properties, in a straight-forward, reproducible, and time-effective manner, thus providing valuable insights into the physical processes of the deep Earth. This thesis focusses on the system Mg-Fe-O, specifically on the optical properties of periclase (MgO) and its iron-bearing variant ferropericlase ((Mg,Fe)O), forming a major planetary building block. The primary objective is to establish links between physical material properties and optical properties. In particular the spin transition in ferropericlase, the second-most abundant phase of the lower mantle, is known to change the physical material properties. Although the spin transition region likely extends down to the core-mantle boundary, the ef-fects of the mixed-spin state, where both high- and low-spin state are present, remains poorly constrained. In the studies presented herein, we show how optical properties are linked to physical properties such as electrical conductivity, radiative thermal conductivity and viscosity. We also show how the optical properties reveal changes in the chemical bonding. Furthermore, we unveil how the chemical bonding, the optical and other physical properties are affected by the iron spin transition. We find opposing trends in the pres-sure dependence of the refractive index of MgO and (Mg,Fe)O. From 1 atm to ~140 GPa, the refractive index of MgO decreases by ~2.4% from 1.737 to 1.696 (±0.017). In contrast, the refractive index of (Mg0.87Fe0.13)O (Fp13) and (Mg0.76Fe0.24)O (Fp24) ferropericlase increases with pressure, likely because Fe Fe interactions between adjacent iron sites hinder a strong decrease of polarizability, as it is observed with increasing density in the case of pure MgO. An analysis of the index dispersion in MgO (decreasing by ~23% from 1 atm to ~103 GPa) reflects a widening of the band gap from ~7.4 eV at 1 atm to ~8.5 (±0.6) eV at ~103 GPa. The index dispersion (between 550 and 870 nm) of Fp13 reveals a decrease by a factor of ~3 over the spin transition range (~44–100 GPa). We show that the electrical band gap of ferropericlase significantly widens up to ~4.7 eV in the mixed spin region, equivalent to an increase by a factor of ~1.7. We propose that this is due to a lower electron mobility between adjacent Fe2+ sites of opposite spin, explaining the previously observed low electrical conductivity in the mixed spin region. From the study of absorbance spectra in Fp13, we show an increasing covalency of the Fe-O bond with pressure for high-spin ferropericlase, whereas in the low-spin state a trend to a more ionic nature of the Fe-O bond is observed, indicating a bond weakening effect of the spin transition. We found that the spin transition is ultimately caused by both an increase of the ligand field-splitting energy and a decreasing spin-pairing energy of high-spin Fe2+.
    Description: Geodynamische Prozesse werden von den physikalischen Materialeigenschaften unter den extremen Druck- und Temperaturbedingungen des Erdinneren gesteuert, gerade diese Areale sind aber faktisch nicht für direkte Beobachtungen zugänglich. Umso wichtiger ist es, die physikalischen Eigenschaften unter Bedingungen des Erdinneren zu untersuchen. Mit diesem Ziel vor Augen erlaubt das Studium der optischen Eigenschaften von Mineralen des Erdmantels, eine große Bandbreite an physikalischen Materialeigenschaften, in einer einfachen, reproduzierbaren und effizienten Art und Weise zu bestimmen. Dadurch bieten sich wichtige Einblicke in die physikalischen Prozessen des Erdinneren. Die vorliegende Arbeit konzentriert sich auf das System Mg-Fe-O, im Speziellen auf Periklas (MgO) und seine Eisen-haltige Variante Ferroperiklas ((Mg,Fe)O), ein wichtiger Baustein planetarer Körper. Das Hauptziel der Arbeit besteht darin Verbindungen zwischen optischen Eigenschaften und physikalischen Materialeigenschaften zu finden. Gerade der Spin-Übergang in Ferroperiklas, der zweithäufigsten Phase des unteren Erdmantels, ist dabei von Bedeutung, da damit Veränderungen in den physikalischen Materialeigenschaften einhergehen. Obwohl sich der Spinübergangsbereich vermutlich bis zur Kern-Mantel-Grenze erstreckt, sind die Auswirkungen des gemischten Spin-Zustandes, bei dem sowohl Hoch- als auch Tief-Spin präsent sind, nur unzureichend untersucht. Die hier vorgestellten Studien zeigen, wie optische Eigenschaften mit anderen wichtigen physikalischen Eigenschaften wie elektrischer und thermischer Leitfähigkeit, Viskosität oder auch mit der chemischen Bindung verbunden sind. Daraus lässt sich auch ableiten wie der Spin-Übergang in Ferroperiklas diese Eigenschaften beeinflusst. Von Raumbedingungen bis zu ~140 GPa sinkt der Brechungsindex von MgO um ~2.4 % von 1.737 auf 1.696 (±0.017). Im Gegensatz dazu steigt der Brechungsindex von (Mg0.87Fe0.13)O (Fp13) und (Mg0.76Fe0.24)O (Fp24) Ferroperiklas mit dem Druck an. Dies ist auf Fe-Fe Wechselwirkungen zwischen benachbarten Eisenpositionen zurückzuführen, die eine starke Verringerung der Polarisierbarkeit, wie im Falle von reinem MgO mit zunehmender Dichte, behindern. Eine Analyse der Dispersion des Brechungsindexes von MgO (Abnahme um ~23 % von 1 Atm zu ~103 GPa) offenbart eine Verbreiterung der Bandlücke von ~7.4 eV bei 1 Atm zu ~8.5 (±0.6) eV bei ~103 GPa. Die Messung der Dispersion (zwischen 550 und 870 nm) in Fp13 zeigt eine starke Abnahme über den Bereich des Spin-Überganges (~44–100 GPa) bis zu einem Faktor von ~3. Die Bandlücke nimmt in der Region des gemischten Spin-Zustandes signifikant auf bis zu ~4.7 eV zu (entspricht einer Zunahme um den Faktor ~1.7). Dies deutet auf eine Verringerung der Elektronen-Mobilität zwischen benachbarten Fe2+-Positionen mit unterschiedlichem Spin-Zustand hin, was die bereits in früheren Arbeiten beobachtete Abnahme der elektrischen Leitfähigkeit im Bereich des gemischten Spin-Zustandes erklärt. Absorptionsspektren an Fp13 zeigen eine Druck-bedingte Zunahme der Kovalenz der Fe-O Bindung für Ferroperiklas im Hoch-Spin Zustand, wohingegen Tief-Spin Ferroperiklas einen Trend zu einer mehr ionischen Fe-O Bindung auf-weist, was auf einen Bindungs-schwächenden Effekt des Spin-Wechsels hinweist. Der Übergang von Hoch- zu Tiefspin ist letztlich auf eine Zunahme der Ligandenfeldaufspaltungsenergie sowie eine abnehmende Spinpaarungsenergie von Hoch-Spin Fe2+ zurückzuführen.
    Language: English
    Type: info:eu-repo/semantics/doctoralThesis
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