Search

Glacial isostatic adjustment is largely governed by the rheological properties of the Earth's mantle. Large mass redistributions in the ocean–cryosphere system and the subsequent response of the viscoelastic Earth have led to dramatic sea level changes in the past. This process is ongoing, and in order to understand and predict current and future sea level changes, the knowledge of mantle properties such as viscosity is essential. In this study, we present a method to obtain estimates of mantle viscosities by the assimilation of relative sea level rates of change into a viscoelastic model of the lithosphere and mantle. We set up a particle filter with probabilistic resampling. In an identical twin experiment, we show that mantle viscosities can be recovered in a glacial isostatic adjustment model of a simple three-layer Earth structure consisting of an elastic lithosphere and two mantle layers of different viscosity. We investigate the ensemble behaviour on different parameters in the following three set-ups: (1) global observations data set since last glacial maximum with different ensemble initialisations and observation uncertainties, (2) regional observations from Fennoscandia or Laurentide/Greenland only, and (3) limiting the observation period to 10 ka until the present. We show that the recovery is successful in all cases if the target parameter values are properly sampled by the initial ensemble probability distribution. This even includes cases in which the target viscosity values are located far in the tail of the initial ensemble probability distribution. Experiments show that the method is successful if enough near-field observations are available. This makes it work best for a period after substantial deglaciation until the present when the number of sea level indicators is relatively high.

In this article, a 3-D finite-difference time-domain (FDTD) method is proposed for rigorous modeling and fast calculation of ultralow frequency geomagnetic storm electromagnetic fields (GS-EMFs). The proposed FDTD approach enables modeling of large-scale and complex 3-D earth structure (e.g., multilayer ground and earth curvature). Unlike conventional FDTD methods, the proposed FDTD method does not require extensive computational resources when dealing with ultralow frequency problems. In this article, the ground surface GS-EMFs produced by an electrojet (line current and sheet current sources) are compared with those obtained using the classical 1-D approaches for case of uniform and horizontally stratified ground. The effect of horizontally vertically multilayer ground and earth curvature on the GS-EMFs is evaluated by the proposed FDTD method. The presented results fully support the adequacy and efficiency of the proposed FDTD method for modeling of large-scale and complex 3-D earth structures for calculation of GS-EMFs.

Objective. The study is aimed at determining the dependence of the average error in calculating the epicenter coordinates of an earthquake on errors in measuring the velocities of seismic waves for various methods of seismic event localization. Error distribution investigation for the method for determining the earthquake hypocenter coordinates using the Cassinian oval. Methods. The problem was solved using statistical methods: methods of frequency and regression analyzes, means comparison method, and uniform search method. Results. A relationship between the accuracy of measuring the velocities of seismic waves when determining the coordinates of an earthquake epicenter were established for four different earthquake hypocenter coordinates calculation methods. A method for determining the earthquake hypocenter coordinates using the fourth-order figure of the Cassinian oval was proposed. The error distribution density of the Cassinian oval method was compared with the ones of other methods. Conclusion. The results obtained make it possible to choose one or another method for calculating the hypocenter coordinates depending on the specific area in which a seismic event occurred and the locations of seismic sensors.

The Bouguer correction of the gravity data of a thin-layered material is a classic topic of research that has been extensively investigated in the field of geodesy. In the case of a flat Earth model, the Bouguer slab formula $$2\pi G h$$ is often utilized, where $$h$$ denotes the height, $$\rho$$ denotes the density of the thin layer, and $$G$$ denotes the gravitational constant. In the case of a spherical thin layer, the effect of gravity is usually expressed by $$4\pi G\rho h$$ . Another Bouguer correction formula also exists, expressed by the spherical harmonics for an arbitrary inhomogeneous layer on the Earth’s surface, i.e., $$2\pi G\rho \sum [1 + 1/\left( {2n + 1} \right)]h_{{nm}} Y_{{nm}}$$ , where the thickness is expressed by spherical harmonic series $$Y_{{nm}}$$ with coefficient $$h_{{nm}}$$ . This implies that the geometric character of the thin layer exerts a significant influence on the Bouguer correction. To investigate the relationship between the three cases, we review and re-derive the three Bouguer correction formulae in detail using Newton's formula and the “Love numbers” mathematical framework, and thoroughly discuss the differences and relations between them from a mathematical and geodetic point of view. After that, we use different formulae and discuss three applications case by case. Finally, we give some suggestions for the use of the Bouguer correction formula in general.

This study is focused on the analysis of data of the long-term latitude observations and the Global Navigation Satellite System (GNSS). The latitude observations include small-amplitude periodic and random harmonics as noise components of different nature and duration. These harmonics are a source of valuable information on seismology, geodynamic processes, and Earth structure in the telescope vicinity. The value of observations carried out at a certain observatory is in their reliability, homogeneity, uniqueness, and long-term series. The latitude observations are reduced to build a diagram of temporal variations in the mean latitude of an observational site on a long-time interval. In this paper, we analyze a curve of the nonpolar oscillations (free of components induced by the pole motion) of the mean latitude. We compare the periodic components of secular variations in the mean latitude and the GNSS observations. Geodynamic parameters of the dynamics of the Earth’s crust relative to tectonic faults on the Tatarstan territory have been determined from the GNSS data; also, from the analysis of the astronomical latitude variations anomalously deviating from the predictive model, the correlation with seismic processes has been shown.

SUMMARYThe Pacific Coast of Central North America is a geodynamically complex region which has been subject to various geophysical processes operating on different timescales. Glacial isostatic adjustment (GIA), the ongoing deformational response of the solid Earth to past deglaciation, is an important geodynamic process in this region. In this study, we apply earth models with 3-D structure to determine if the inclusion of lateral structure can explain the poor performance of 1-D models in this region. Three different approaches are used to construct 3-D models of the Earth structure. For the first approach, we adopt an optimal 1-D viscosity structure from previous work and add lateral variations based on four global seismic shear wave velocity anomalies and two global lithosphere thickness models. The results based on these models indicate that the addition of lateral structure significantly impacts modelled RSL changes, but the data-model fits are not improved. The global seismic models are limited in spatial resolution and so two other approaches were considered to produce higher resolution models of 3-D structure: inserting a regional seismic model into two of the global seismic models and, explicitly incorporating regional structure of the Cascadia subduction zone and vicinity, that is the subducting slab, the overlying mantle wedge and the plate boundary interface. The results associated with these higher resolution models do not reveal any clear improvement in satisfying the RSL observations, suggesting that our estimates of lateral structure are inaccurate and/or the data-model misfits are primarily due to limitations in the adopted ice-loading history. The different realizations of 3-D Earth structure gives useful insight to uncertainty associated with this aspect of the GIA model. Our results indicate that improving constraints on the deglacial history of the southwest sector of the Cordilleran ice sheet is an important step towards developing more accurate of GIA models for this region.

The selection of geosynthetic reinforcements in the design of geosynthetic-reinforced soil (GRS) retaining walls has been based on the requirement on the long-term strength. However, the mobilized loads in the reinforcements are related to both the reinforcement stiffness and soil deformation, and the desired factor of safety may not exist in the earth structure if they are not properly considered. Therefore, it is also important to take into account the long-term reinforcement stiffness when designing GRS retaining walls. In this study, a simplistic analytical method is proposed to determine the required reinforcement stiffness with given factor of safety on the backfill soil. The method takes into account soil-reinforcement interaction, nonlinear stress-strain behavior of soil, and soil dilatancy. The reinforcement strains predicted by the proposed method were compared to those analyzed by validated nonlinear Finite Element analyses, and close agreement was obtained.

Analyses of glacial isostatic adjustment (GIA) and deglacial relative sea-level (RSL) change in the Russian Arctic deliver important insights into the Earth's viscosity structure and the deglaciation history of the Eurasian ice sheet complex. Here, we validate the 1D GIA models ICE-6G_C (VM5a) and ICE-7G_NA (VM7) and select new 3D GIA models in the Russian Arctic against a quality-controlled deglacial RSL database of >500 sea-level data points from 24 regions. Both 1D models correspond to the RSL data along the southern coast of the Barents Sea and Franz Josef Land from ∼11 ka BP to present but show notable misfits (>50 m at 10 ka BP) with the White Sea data. We find 3D model predictions of deglacial RSL resolve most of the misfits with the observed data for the White Sea while retaining comparable fits in other regions of the Russian Arctic. Our results further reveal: (a) RSL in the western Russian Arctic is sensitive to elastic lithosphere with lateral thickness variation and 3D viscosity structure in the upper mantle; and (b) RSL in the whole Russian Arctic is less sensitive to 3D viscosity structure in the lower mantle compared to the upper mantle. The 3D models reveal a compromise in the upper mantle between the background viscosity and scaling factor to best fit the RSL data, which needs to be considered in future 3D GIA studies. Ministry of Education (MOE) National Research Foundation (NRF) Published version Tanghua Li, Timothy A. Shaw, and Benjamin P. Horton are supported by the Singapore Ministry of Education Academic Research Fund MOE2019 -T3-1-004, MOE2018-T2-1-030 and MOE-T2EP50120-0007, the National Research Foundation Singapore, and the Singapore Ministry of Education, under the Research Centers of Excellence initia- tive. The research of W. Richard Peltier at Toronto is supported by NSERC discov- ery Grant A9627. The work of Alisa Baranskaya was supported by the Russian Science Foundation Grant 22-77-10,031; she used equipment and facilities obtained within the State Budget Theme АААА- А16-116032810055-0. The FE calcula- tion was performed with the ABAQUS package from Hibbitt, Karlsson and Sorensen Inc. This research is conducted in part using the research computing facilities and/or advisory services offered by Information Technology Services, the University of Hong Kong. The authors acknowledge HOLSEA and PALSEA, working groups of the International Union for Quaternary Sciences (INQUA) and Past Global Changes (PAGES), which in turn received support from the Swiss Academy of Sciences and the Chinese Academy of Sciences. This article is a contribution to International Geoscience Program (IGCP) Project 639, “Sea-Level Changes from Minutes to Millennia.” We express our gratitude to Muhammad Hadi Ikhsan for support with the graphics. This work is Earth Observatory of Singapore contribution 435.

Observations of teleseismic earthquakes using broadband seismometers on the Ross Ice Shelf (RIS) must contend with environmental and structural processes that do not exist for land-sited seismometers. Important considerations are: (1) a broadband, multi-mode ambient wavefield excited by ocean gravity wave interactions with the ice shelf; (2) body wave reverberations produced by seismic impedance contrasts at the ice/water and water/seafloor interfaces and (3) decoupling of the solid Earth horizontal wavefield by the sub-shelf water column. We analyze seasonal and geographic variations in signal-to-noise ratios for teleseismic P-wave (0.5–2.0 s), S-wave (10–15 s) and surface wave (13–25 s) arrivals relative to the RIS noise field. We use ice and water layer reverberations generated by teleseismic P-waves to accurately estimate the sub-station thicknesses of these layers. We present observations consistent with the theoretically predicted transition of the water column from compressible to incompressible mechanics, relevant for vertically incident solid Earth waves with periods longer than 3 s. Finally, we observe symmetric-mode Lamb waves generated by teleseismic S-waves incident on the grounding zones. Despite their complexity, we conclude that teleseismic coda can be utilized for passive imaging of sub-shelf Earth structure, although longer deployments relative to conventional land-sited seismometers will be necessary to acquire adequate data.

The input parameters for the hardening law for the elasto-plastic constitutive model of unsaturated soils are generally fitting parameters that control the degree of hardening response and cannot easily be determined without the results of experimental tests in which the changes in suction, water content, and volume are measured or controlled. However, it is next to impossible to complete such precise experimental tests on all the geomaterials comprising the earth structure to be analysed, such as an embankment. It is important, therefore, to establish a method for determining these parameters from more easily attainable data on the material. This paper presents a practical method for estimating the input parameters related to hardening/softening due to desaturation/saturation in the elasto-plastic constitutive model proposed by Ohno et al. (2007a) from a compaction curve, which is frequently obtained and widely used in engineering practice. In the proposed method, the input parameters are estimated by simultaneously solving three theoretical equations, each of which holds for a different point, indicating the statically compacted state on the dry side of the compaction curve, while the approximately represented compaction curve is used instead of a hand-drawn one. The paper demonstrates that the proposed method enables the estimation of the input parameter values within a range small enough so as not to affect the results of the simulation, irrespective of the way in which the points on the represented compaction curve are selected. The validity of the estimated parameters is verified and then discussed through a series of static compaction test simulations.

This paper proposes a technique to approximate a multi-layer earth structure by a homogeneous conductivity soil in ground return impedance calculations. An equivalent real-valued conductivity parameter is obtained, which can be used with reasonable accuracy in a simpler expression or in commonly available EMTP software, such as the Line Constants routine of the Alternative Transients Program (ATP). Several actual soil models are evaluated at frequencies ranging from 1 Hz to 2 MHz. Results show that the proposed method is accurate for modeling most power system problems, from steady-state conditions to transients commonly verified in electrical systems. The proposed expression is easy to use and introduces a considerable performance gain in terms of floating-point operations, compared to the analytical formulation of the general multi-layer soil structure.

Borehole conductivity logs provide an in situ measurement of the electrical conductivity of the subsurface. Despite the measurements being a proxy for the true earth structure, they are often used as ground truth when inferring subsurface electrical conductivity boundaries between lithologies. Borehole conductivity measurements are therefore commonly used to plan and benchmark electromagnetic (EM) surveys and to establish the credibility of a given inversion technique. A consequence of the diffusion physics of EM prospecting is that not all subsurface features present in a conductivity log can be resolved by an EM system, nor can they be recovered by a subsequent inversion. Quantification of the ability of an EM system to determine layer boundaries in the subsurface is therefore an issue meriting investigation. We have developed a reversible-jump Markov chain Monte Carlo (RJMCMC) method to segment borehole conductivity logs at the scale recoverable by a given EM system as the foundation for an objective comparison between the inversion results and conductivity logs. A common consequence of RJMCMC inversions for EM problems is that few layers are required to fit the data. Similarly, we find that a borehole log blocked at the scale sensed by an EM system consists of a limited number of segments. Segmentation of borehole conductivity logs is determined by the physics of EM prospecting and by factors such as base frequency, number of gates, system geometry, and noise levels. For a survey line intersecting a borehole near Carnarvon, Western Australia, we see that different inversion schemes result in images of the subsurface that are consistent with a borehole conductivity log segmented according to the mechanics of the EM system and accounting for the physics of EM prospecting.

Investigations of hydraulically induced micro-seismicity are typically connected with magma injections, exploitation of geothermal fields and salt mines. Our study examines the seismicity and seismic sources in a peri-platform region with long salt production history. In addition, a very large site for extraction of aggregates and limestone is presented in the area. Increased seismicity in the region has been observed for several decades as during the study period of the last 12 years, more than 1000 events with magnitude $$M < 4.3$$ have been registered. To study the complex seismic sources concentrated in such small area spatial distribution of seismicity and fault plane solutions are analyzed together with available geological and geophysical data, in order to connect registered earthquakes swarms with geological structures. Results show that several faults are outlined from geological information and confirmed by interpretation of geophysical data. Very different focal mechanisms calculated for the 13 earthquakes in the near region of the salt production site cannot propose a dominant fault mechanism and confirm the complexity of the seismic sources in the area. Our results suppose that activation of some of these structures is more likely due to water injected in the salt dome as part of the production process, which changes the stress equilibrium in the Earth crust.

The information of earth structure is curial for designing the grounding system and evaluating the transmission line parameters. In order to obtain the earth structure using the measured data, an efficient algorithm for the parameter estimation of a horizontally multilayered soil by using a novel integration method is proposed. In the proposed algorithm, an adaptive iteration process will terminate till the predefined error reaches the requirement, where the earth parameters, such as the layer depth, layer resistivity, and layer number, are adjusted accordingly with the help of the Levenberg-Marquardt algorithm. In each iteration, the key is to evaluate the apparent resistivity and its partial derivatives with respect to soil parameters, which are expressed in the form of general Sommerfeld integral (GSI). In this paper, the GSI is divided into two parts. The first part with an infinite upper limit is integrated along a novel complex integration path instead of the conventional real axis path, which makes the evaluation of the GSI highly efficient due to the fast damping property of the transformed kernel. The second part with the finite integral interval is calculated using the cubic spline technique to have a semi-analytic expression, which can avoid evaluating the oscillatory kernel. In comparison with the results in the published literatures, numerical examples show that the proposed soil parameters estimation approach can reach good accuracy, and is robust and efficient. The reason is simple as the GSIs are calculated by using the well-designed and sophisticated approach. With extensive numerical experiments, the proposed algorithm is believed to be a capable and applicable candidate in engineering to invert the information of the earth structure.

As is well known, Greece has a significant number of earthquakes each year. Ιn recent years, several earthquakes have occurred in Greece. For this scope, a methodology was used to determine the source parameters. This methodology is based on minimizing the difference between the observed and the synthetic waveforms, using the method Source Parameters Calculation—SPCa [1]. The source parameters, using the proposed methodology, are calculated by comparing observed seismograms and synthetic by inverting data. The synthetics are calculated using the reflectivity method (Kennett, 1983) as implemented by Randall et al. (1994) for a given earth structure. This study includes inversion results for the strongest events that occurred in Greece from 2008 to 2014. For the same events calculated the main fault plane, using the method of Hypocenter Centroid-plot (HC-plot) [2] [3]. This methodology is a simple geometrical method based on the combination between the hypocentral position and the two possible fault planes.

Over the past decade(s), more and more Earth-like exoplanets are being detected, which raises questions about their ability to sustain life. Despite these exciting developments, we have only begun to develop an understanding of what shaped our own planet to its unique habitable state. In particular, our knowledge of Earth’s interior structure, and how it has evolved through billions of years, remains limited. Earth’s mantle is a 2890 km-thick shell which lies between Earth’s dense core and its outer layer, the crust, representing more than 80% of our planet’s volume. It hosts “mantle convection”, responsible for the transfer of mass and heat in Earth’s interior, and is therefore crucial for the evolution of our planet. As we are limited in terms of natural data on Earth’s deep interior and its history, detailed studies rely on the exploration of computational ex- periments of planetary dynamics: geodynamic modelling. This thesis presents novel geodynamic studies that aim to bring us closer towards an integrated view on the dynamics of our planet’s deep interior. The work presented in this thesis focuses on the feedbacks between the composition and physical properties of mantle rocks, the flow patterns of these materials, and long-term planetary evolution. In four different parts (I-IV), this thesis guides you through my search for a recipe of the deep Earth. In the first part (I) I explore the effect of the presence of ancient, deep-Earth materials (that formed during our planet’s earliest history) on the long-term evolution of our planet. I assess what types of rock reservoirs of distinct compositions potentially lie deep beneath our feet, and what they reveal about our planet’s history. Ultimately, a new style of mantle convection is proposed for the Earth, which integrates a variety of observations and previously- proposed views of our planet’s internal structure. In the second part of this thesis (II) I present the first-ever mantle convection models in 3D geometry that explicitly address the evolution of multiple types of mantle reservoirs in Earth-like planets. I show how my previously-made predictions for Earth’s mantle remain valid in 3D geometry, thereby providing an important step towards integrating recent theories of Earth’s mantle structure into a more realistic framework. For the third part of this thesis (III), I implemented a new numerical tool in the geodynamic code that projects micro-scale rock deformation behaviour to global-scale mantle dynamics, in order to facilitate linking results from laboratory experiments on deep-Earth materials to global- scale geodynamic computer models. I use this numerical tool to assess whether the deformation history of mantle rocks influences mantle flow patterns, and, through it, the dynamic evolution of our planet. Importantly, I show that history-dependent weakening of mantle materials mostly affects the style of heat transfer from the deep interior to the surface. The impact of these models is significant, as previously-unexplained observations of the deep Earth can potentially be explained. These findings further raise the possibility of mantle rocks behaving, on large and long-time scales, akin to “rigid" rocks that we can see at our planet’s surface. Finally, in the last part of this thesis (IV), I put the work in a broader scientific context and discuss their relevance to Earth and other rocky (exo)planets, with a special focus on our neighbouring planet Venus. The ensemble of this thesis work emphasises the feedbacks between the spatial distribution of distinct deep-Earth materials, the physical properties of those materials, and the style of man- tle convection, and their combined effects on our planet’s long-term evolution. The thesis results and new, publicly available geodynamical techniques present fundamental progress to the un- derstanding of the evolution of the Earth and other rocky bodies, and even for the necessities for a habitable planet.

Seismology focuses on the study of earthquakes and associated phenomena to characterize seismic sources and Earth structure, which both are of immediate relevance to society. This article is composed of two independent views on the state of the integrated, coordinated, open, networked (ICON) principles (Goldman et al., 2021, https://doi.org/10.1029/2021eo153180) in seismology and reflects on the opportunities and challenges of adopting them from a different angle. Each perspective focuses on a different topic. Section 1 deals with the integration of multiscale and multidisciplinary observations, focusing on integrated and open approaches, whereas Section 2 discusses computing and open-source algorithms, reflecting coordinated, networked, and open principles. In the past century, seismology has benefited from two co-existing technological advancements—The emergence of new, more capable sensory systems and affordable and distributed computing infrastructure. Integrating multiple observations is a crucial strategy to improve the understanding of earthquake hazards. However, current efforts in making big datasets available and manageable lack coherence, which makes it challenging to implement initiatives that span different communities. Building on ongoing advancements in computing, machine learning algorithms have been revolutionizing the way of seismic data processing and interpretation. A community-driven approach to code management offers open and networked opportunities for young scholars to learn and contribute to a more sustainable approach to seismology. Investing in new sensors, more capable computing infrastructure, and open-source algorithms following the ICON principles will enable new discoveries across the Earth sciences.

The study of the Earth structure and geodynamic is one of constitutive purposes of Earth sciences. The aim of our article is to describe Ross superplume that was discovered in the southwestern part of the Pacific Ocean near and under the western margin of Antarctica. This plume was not mentioned in seismic tomographic literature and in catalogs. Ross superplume was detected by gravimetric tomography method that was developed by Rudolf Greku in Institute of Geological Sciences, National Academy of Sciences of Ukraine. Authours used gravitomography data to describe the complex geometry of the superplume, evidences of the segmental collapse of the Paleo-Pacific slab (one of them to a depth of 4800 km), and its location within the pre-existing geothermal convective flow, under the influence of which the southwestern part of the Pacific Ocean, West Antarctica and the western part of East Antarctica are still located. Main conclusions. Combined effect of such factors as presence of geothermal interpolar flux and enter of slab into the outer liquid core within this flux led to formation of superplume. Two different parts of Ross superplume were formed in different structural-density conditions of lithospheric lower-mantle: the southern part was formed near and under the Antarctic obduction margin; the northern part was formed beneath the oceanic lithosphere. Ross superplume formation happened simultaneously with the 100 Ma event of the global reorganization of lithospheric structures, which drivers are poorly understood yet. We suppose that trigger of this event was explosive formation of Ross superplume. Our results were interpreted using available open literature data about this region and they do not contradict existing understanding of geodynamic history of the region.