Geodynamic Observations Research Articles

Pliocene shorelines and the epeirogenic motion of continental margins: a target dataset for dynamic topography models

Abstract. Global mean sea level during the mid-Pliocene epoch (∼3 Ma), when CO2 and temperatures were above present levels, was notably higher than today due to reduced global ice sheet coverage. Nevertheless, the extent to which ice sheets responded to Pliocene warmth remains in question owing to high levels of uncertainty in proxy-based sea level reconstructions as well as solid Earth dynamic models that have been used to evaluate a limited number of data constraints. Here, we present a global dataset of 10 wave-cut scarps that formed by successive Pliocene sea level oscillations and which are observed today at elevations ranging from ∼6 to 109 m above sea level. The present-day elevations of these features have been identified using a combination of high-resolution digital elevation models and field mapping. Using the MATLAB interface TerraceM, we extrapolate the cliff and platform surfaces to determine the elevation of the scarp toe, which in most settings is buried under meters of talus. We correct the scarp-toe elevations for glacial isostatic adjustment and find that this process alone cannot explain observed differences in Pliocene paleo-shoreline elevations around the globe. We next determine the signal associated with mantle dynamic topography by back-advecting the present-day three-dimensional buoyancy structure of the mantle and calculating the difference in radial surface stresses over the last 3 Myr using the convection code ASPECT. We include a wide range of present-day mantle structures (buoyancy and viscosity) constrained by seismic tomography models, geodynamic observations, and rock mechanics laboratory experiments. Finally, we identify preferred dynamic topography change predictions based on their agreement with scarp elevations and use our most confident result to estimate a Pliocene global mean sea level based on one scarp from De Hoop, South Africa. This inference (11.6 ± 5.2 m) is a downward revision and may imply that ice sheets were relatively resistant to warm Pliocene climate conditions. We also conclude, however, that more targeted model development is needed to more reliably infer mid-Pliocene global mean sea level based on all scarps mapped in this study.

Экспериментальное исследование методики полевой оценки точности измерений ГНСС

The authors propose a field control of GNSS equipment precision characteristics methodology for recording sub-centimeter movements of the Earth`s surface at geodynamic observations of tectonically moderate areas activity. The factors influencing the accuracy of GNSS measurements are analyzed. The theoretical aspects of developing measuring equipment field control methods are presented. Testing of the devices was carried out in the course of surveys on the Nizhne-Kanskiy massif geodynamic range in Krasnoyarsk krai in 2020–2022. The experiment was made with two-system GNSS facilities of geodesic class (5 to 6 sets). The results show that the proposed methodology of the used tools accuracy characteristics field control enables detecting incorrect nominal parameters of measuring instruments. In this case the parameters of the receivers` antennas are well coordinated with each other. The exactness of control characteristics in plan is at the level of 1,3–2,5 mm, in height – 2,5 mm. It was revealed that the height of the actual phase center of Grant_G3T and MarAnt+ antennas differ from the manufacturer`s declared passport data

Results of Geodynamic Observations at the Zhanazhol Field, Kazakhstan

Results of Geodynamic Observations at the Zhanazhol Field, Kazakhstan

Bayesian Inference of Mantle Viscosity From Whole‐Mantle Density Models

AbstractThe long‐wavelength geoid is sensitive to Earth's mantle density structure as well as radial variations in mantle viscosity. We present a suite of inversions for the radial viscosity profile using whole‐mantle models that jointly constrain the variations in density, shear‐ and compressional‐wavespeeds using full‐spectrum tomography. We use a Bayesian approach to identify a collection of viscosity profiles compatible with the geoid, while enabling uncertainties to be quantified. Depending on tomographic model parameterization and data weighting, it is possible to obtain models with either positive‐ or negative‐buoyancy in the large low shear velocity provinces. We demonstrate that whole‐mantle density models in which density and VS variations are correlated imply an increase in viscosity below the transition zone, often near 1,000 km. Many solutions also contain a low‐viscosity channel below 650 km. Alternatively, models in which density is less‐correlated with VS—which better fit normal mode data—require a reduced viscosity region in the lower mantle. This feature appears in solutions because it reduces the sensitivity of the geoid to buoyancy variations in the lowermost mantle. The variability among the viscosity profiles obtained using different density models is indicative of the strong nonlinearities in modeling the geoid and the limited resolving power of the geoid kernels. We demonstrate that linearized analyses of model resolution do not adequately capture the posterior uncertainty on viscosity. Joint and iterative inversions of viscosity, wavespeeds, and density using seismic and geodynamic observations are required to reduce bias from prior assumptions on viscosity variation and scalings between material properties.

Використання геоінформаційних технологій для дослідження зсувних процесів

Виконано аналіз методів дослідження динаміки зсувних процесів. Проаналізовано причини виникнення зсувів, основними з яких є перезволоження ґрунту та збільшення навантаження на схил внаслідок забудови схилу та руху транспорту. Визначено роль рельєфу та його геоморфологічного стану у формуванні зсувів. Описано методи боротьби зі зсувами. Проаналізовано наявні методи спостережень на зсувних схилах, які забезпечують вирішення завдань із вивчення механізму та динаміки зсувного процесу. Виконано опис геодезичних методів дослідження зсувів, які передбачають створення геодезичної основи на зсувонебезпечних схилах, закріплення геодезичної основи спеціальними марками та періодичні вимірювання їх координат і висот високоточними електронними геодезичними приладами, ГНСС-приймачами. Запропоновано визначати просторово-часові характеристики зсувів геоінформаційними методами. За даними топографічного знімання з допомогою пакету програм Surfer створено тривимірну цифрову модель зсувного схилу та карту крутизни схилу. За даними зміщень геодезичних марок між двома циклами спостережень створено карти ізозміщень ґрунту по висоті та визначено межі зсуву. За геологічними даними складено карту ізопотужностей зсувного тіла, яка дає змогу визначити його об'єм. За даними повторних вимірювань створено карту швидкостей зсуву. Порівняння даних з різних циклів дає змогу проаналізувати динаміку зсувного процесу, розробити прогноз його розвитку та запроектувати відповідні протизсувні заходи. Запропоновано застосовувати геоінформаційні технології для створення просторово-часових моделей зсувних процесів. Розроблені карти є основою для створення інших геодинамічних карт: суміщених карт горизонтальних та вертикальних ізозміщень, карт прискорень ізозміщень та ін. Разом вони формують банк даних інформації, що дає змогу здійснювати ефективний моніторинг зсувних процесів.

The Sensitivity of Joint Inversions of Seismic and Geodynamic Data to Mantle Viscosity

AbstractSeismic tomography has revealed the existence of large‐scale velocity heterogeneities in the mantle. The interpretation of seismic velocity anomalies in terms of temperature and chemical composition is nonunique. We use geodynamic observations including gravity, plate motions, dynamic topography, and excess ellipticity of the core‐mantle boundary combined with seismic observations to investigate the thermo‐chemical structure of the mantle through joint inversions. An outstanding issue, however, is the physical connection between mantle density anomalies and the surface geodynamic observations, which requires knowledge of the mantle viscosity structure. Here we perform joint inversions assuming different viscosity profiles and examine the dependence of the results on the viscosity. We first assume that mantle heterogeneity is due to thermal variations, which places a constraint on the relation between seismic velocity and density, and we subsequently relax the constraint to allow for potential nonthermal effects. In all of our joint inversions, a nonthermal origin of density anomalies is required to explain the geodynamic data, though the amount varies with the assumed viscosity structure. A common observation is a high‐density chemical signal in the center of the large low‐shear‐velocity provinces at the base of the mantle resulting in a near neutral or slightly dense overall buoyancy there. Using the derived density models and their corresponding viscosity profiles, we also calculate instantaneous mantle flow fields. The predicted flow fields derived from joint inversions are generally similar but are quite different from flow fields using density models derived from a posteriori scaling of pure seismic tomography models.

Геодинамика территории Армении по результатам комплексных наблюдений

The geodynamics of the earth’s crust in the territory of Armenia is given according to seismic data, deformographic measurements, hydro geodynamic observations of the groundwater level, and geochemistry of mineral waters in the central part of the region. The map of the epicenters of earthquakes over the past three years includes stressed sections (concentration of earthquake epicenters) of the earth’s crust with increased activity geodynamic processes. Based on the results of the registration of deformations of two directions, the values of areal, volumetric, and vertical deformations are calculated. Variations in the water level in hydro geodynamic wells were obtained due to seismic events; the amplitudes of the variations depend on the magnitude of the earthquake, the distance from the epicenter, and the magnitude of the calculated deformation of the earth’s crust. The main components of the chemical composition of mineral waters (CL, HCO3, SO4, Mg), gas - CO2, and Ph in comparison with seismicity and other geodynamic processes of the earth’s crust.

Relamination of mafic subducting crust throughout Earth's history

Earth has likely cooled by several hundred degrees over its history, which has probably affected subduction dynamics and associated magmatism. Today, the process of compositional buoyancy driven upwelling, and subsequent underplating, of subducted materials (commonly referred to as “relamination”) is thought to play a role in the formation of continental crust. Given that Archean continental crust formation is best explained by the involvement of mafic material, we investigate the feasibility of mafic crust relamination under a wide range of conditions applicable to modern and early Earth subduction zones, to assess if such a process might have been viable in an early Earth setting.Our numerical parametric study illustrates that the hotter, thicker-crust conditions of the early Earth favour the upward relamination of mafic subducting crust. The amount of relaminating subducting crust is observed to vary significantly, with subduction convergence rate having the strongest control on the volume of relaminated material. Indeed, removal of the entire mafic crust from the subducting slab is possible for slow subduction (∼2 cm/yr) under Archean conditions. We also observe great variability in the depth at which this separation occurs (80–120 km), with events corresponding to shallower detachment being more voluminous, and that relaminating material has to remain metastably buoyant until this separation depth, which is supported by geological, geophysical and geodynamical observations. Furthermore, this relamination behaviour is commonly episodic with a typical repeat time of approximately 10 Myrs, similar to timescales of episodicity observed in the Archean rock record. We demonstrate that this relamination process can result in the heating of considerable quantities of mafic material (to temperatures in excess of 900 °C), which is then emplaced below the over-riding lithosphere. As such, our results have implications for Archean subduction zone magmatism, for continental crust formation in the early Earth, and provide a novel explanation for the secular evolution of continental crust.

Joint analysis of GOCE gravity gradients data of gravitational potential and of gravity with seismological and geodynamic observations to infer mantle properties

Joint analysis of the seismic velocities and geoid, gravity and gravity gradients are used to constrain the viscosity profile within the mantle as well as the lateral density variations. Recent ESA's Gravity field and steady-state Ocean Circulation Explorer measurements of the second-order derivatives of the Earth's gravity potential give new possibilities to determine these mantle properties. Using a simple mantle model and seismic tomography results, we investigate how the gravitational potential, the three components of the gravity vector and the gravity gradients can bring information on the radial viscosity profile and on the mantle mass anomalies. We start with lateral density variations in the Earth's mantle based either on slab history or deduced from seismic tomography. The main uncertainties are: for the latter case, the relationship between seismic velocity and density-the so-called density/velocity scaling factor-and for the former case, the variation with depth of the density contrast between the cold slabs and the surrounding mantle. We perform a Monte Carlo search for the viscosity and the density/velocity scaling factor profiles within the mantle, which allows to fit the observed geoid, gravity and gradients of gravity. We compute the posterior probability distribution of the unknown parameters, and find that the gravity gradients improve the estimate of the scaling factor within the upper mantle, because of their sensitivity to the masses within the upper mantle, whereas the geoid and the gravity better constrain the scaling factor in the lower mantle. In the upper mantle, it is less than 0.02 in the upper part and about 0.08-0.14 in the lower part, and it is significantly larger for depths greater than 1200 km (about 0.32-0.34). In any case, the density/velocity scaling factor between 670 and 1150 km depth is not well constrained. We show that the viscosity of the upper part of the mantle is strongly correlated with the viscosity of the lower part of the mantle and that the viscosity profile is characterized by a decrease in the lower part of the upper mantle (about 10 20-2 × 10 20 Pa s) and by an increase (about 10 23-2 × 10 23 Pa s) at the top of the lower mantle (between 670 and 1150 km).

Principali risultati conseguiti durante l'osservazione geodinamica, opportunamente estesa nel tempo, di grandi dighe di sbarramento, e loro giustificazioni teoriche

Are here examined — in their theoretical explanations — the results of systematic geodynamic observations (carried out by vibrometers, seismographs and clinographs), achieved on E.N.EL. big Dams. This investigation also, shows the great usefulness — being, indeed, a, necessity — of such observations. A period of fifteen years of clinographic records on the Val Gallina's Dam, include the Vajont's tragic event into a secular range phenomenon, particularly active — during the last geologic Era — in the Alpine orogenesis who, in special conditions, may be the cause (just like it happened) of anomalous local situations.

GyPSuM: A joint tomographic model of mantle density and seismic wave speeds

GyPSuM is a 3‐D model of mantle shear wave (S) speeds, compressional wave (P) speeds, and density. The model is developed through simultaneous inversion of seismic body wave travel times (P and S) and geodynamic observations while using realistic mineral physics parameters linking wave speeds and density. Geodynamic observations include the global free air gravity field, divergence of the tectonic plates, dynamic topography of the free surface, and the flow‐induced excess ellipticity of the core‐mantle boundary. GyPSuM is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution. Models of the density field from Earth's free oscillations have provided great insight into the density configuration of the mantle but are limited to very long wavelength solutions. Alternatively, scaling higher‐resolution seismic images to obtain density anomalies generates density fields that do not satisfy geodynamic observations. The current study provides a 3‐D density model for the mantle that directly satisfies geodynamic and seismic observations through a joint seismic‐geodynamic inversion process. Notable density field observations include high‐density piles at the base of superplume structures, supporting the general results of past normal mode studies. However, we find that these features are more localized and have lower amplitude than past studies would suggest. When we consider both fast and slow seismic anomalies in GyPSuM, we find that P and S wave speeds are strongly correlated throughout the mantle. However, we find a low correlation of fast S wave zones in the deep mantle (>1500 km depth) with the corresponding P wave anomalies, suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies. The cratonic lithosphere and D″ regions are shown to have strong compositional signatures. However, we argue that temperature variations are the primary cause of P wave speed, S wave speed, and density anomalies throughout most of the mantle.

High precision gravity measurements with the dual sphere superconducting gravimeter in Sutherland (South Africa)

Since March 2000, the reconstructed Dual Sphere Superconducting Gravimeter (SG) with two gravity sensors is continuously recording gravity data at the newly constructed South African Geodynamic Observatory Sutherland of GFZ (SAGOS). Additionally, meteorological sensors and a ground water table sensor were installed for estimation of gravity changes induced by the atmosphere and hydrosphere. The observatory is designed for high precision geodynamic observations of the Earth with space techniques and ground instruments. The Noise Magnitude characterising the quality of the site Sutherland is close and even smaller than the “New Low Noise Model” values at frequencies below 1 mHz. This result characterises the excellent quality of the site for the observation of weak gravity signals. For calibration of the SG gravity sensors, absolute gravity measurements have been carried out at SAGOS. The calibration factor could be fixed with an accuracy of 0.2%. Tidal amplitudes, amplitude factors and phase leads have been determined for Sutherland with high resolution and accuracy for the first time. After applying ocean loading correction for the main diurnal and semidiurnal waves, there are still discrepancies between the measured and model tidal parameters. These discrepancies have to be minimised by improving the models and data correction for non-tidal induced gravity effects. The maximal vertical surface shift caused by the earth tides and mass redistribution in the atmosphere during the time from March 27th 2000 to August 1st 2001 has been determined to 41.9 cm by using the Love numbers h2 and k2 derived from the tidal and deformation potential. The data of the earthquake near the coast of Peru on June 23rd 2001 have been analyzed for detection of the free oscillation modes of the Earth. Especially the long periodic modes 0S3, 2S1 and 0S2 are very well marked after this earthquake and less disturbed because of the low noise site. They confirm the model frequencies for these modes.

Some mineral physics constraints on the rheology and geothermal structure of Earth’s lower mantle

We explore the implications of recent mineral physics measurements of diffusion coefficients and melting temperatures of lower mantle materials on the rheological and geothermal structure of Earth’s lower mantle. We show that MgSiO 3 perovskite is significantly stronger than MgO periclase and therefore the rheology of the lower mantle depends strongly on the geometry of a weaker phase, periclase. We calculate viscosities of the lower mantle for two cases: (1) where periclase occurs as isolated grains and (2) where periclase occurs as continuous films, using mineral physics data and models of two-phase rheology. We find that the effective viscosity for the former is about ~10-1000 times higher than the latter. We therefore suggest that the rheology of the lower mantle is structureand hence strain-dependent, leading to weakening at large strains due to the formation of continuous films of periclase. Overall depth variation of viscosity depends not only on the pressure dependence of creep but also on the geothermal gradient. Both MgSiO 3 perovskite and periclase have relatively small activation energies (E* = gRT m with g = 10-14, where R is the gas constant and T m is melting temperature), and therefore the depth variation of viscosity is rather small, even for a nearly adiabatic temperature gradient. However, the geothermal gradients consistent with the geodynamical inference of nearly depth-independent viscosity are sensitive to the pressure dependence of viscosity which is only poorly understood. A superadiabatic gradient of up to ~0.6 K/km is also consistent with mineral physics and geodynamical observations.

Rotational Motion of Celestial Bodies in the Relativistic Framework

There are several important reasons to consider relativistic effects in rotational motion of celestial bodies. General Relativity is now recommended by the International Astronomical Union and International Union of Geodesy and Geophysics as a theoretical framework for modeling of high-precision observational data. On the other hand, various geodynamical observations provide data which are widely used for testing General Relativity itself.In Newtonian mechanics it is well known how to describe rotational motion of an extended body. In General Relativity this is a rather subtle issue. The concept of a precessing extended rigid body in general relativity encounters fundamental difficulties and cannot be introduced even in the first post-Newtonian approximation. From a practical point of view, however, the rotational motion of the Earth even at the Newtonian level is defined operationally through the time-dependence of geocentric quasi-inertial coordinates of observing sites. An analogous operational definition can be applied in general relativity. To this end, we need a set of physically adequate reference systems.

Laser strainmeters: New developments and earthquake prediction applications

Two novel laser strainmeters furnished with airfilled pressure-tight shielding pipe are considered to be an affordable tool for modern geodynamic observations. The thermal-to-strain coefficient of 1 · 10 −8 K −1 provides sufficient long-term instrument stability, while short-term sensitivity of ΔL/ L = 10 −11–10 −12 in the frequency band up to 1 kHz has been achieved. Experimental prototypes of the laser strainmeters have been tested at various sites and certain phenomena concerning earthquake prediction problems have been revealed.

Plans for VLBI and GPS monitoring network for geodesy and geodynamics in Canada

A newtork of VLBI and GPS sites in Canada will provide a framework for precise geodetic and geodynamic observations to study continent-wide crustal deformations, post-glacial uplift and plate tectonics. The VLBI component will consist of three permanent stations with a −3000-km baseline located on the geologically stable Canadian Shield as the principal calibration line; it will facilitate continuous monitoring of the earth's rotational dynamics and by means of collocated GPS receivers will serve to maintain the accuracy and the long-term stability of GPS satellite orbit computations. A mobile VLBI system will be used to establish fiducial points with a spacing of about 1000-km to provide a reference for high-precision regional GPS surveys. The unique Canadian VLBI data acquisition and processing system features time-domain multiplexing, a wave-front clock and 24 Mb/sec data recording on standard video cassettes. High-precision differential GPS positions with uniform spacing of about 500-km will complement the VLBI network; these will be reoccupied at regular intervals to facilitate construction of a strain map of Canada. Absolute gravity observations will be carried out at most VLBI and GPS sites to provide additional constraints for geophysical interpretation. ∗ ∗ Geological Survey of Canada Contribution Number 30286