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Brune S.,German Research Center for Geosciences | Popov A.A.,Johannes Gutenberg University Mainz | Sobolev S.V.,German Research Center for Geosciences | Sobolev S.V.,Schmidt Institute of Physics of the Earth
Tectonophysics | Year: 2013

The arrival of a plume head at Earth's continental lithosphere is often considered to be an important factor for continental break-up. However, the impact of plume impingement on strength and duration of a rift remains unclear. In this study, we quantify the mechanical and thermal influence of a plume (i.e. lithosphere erosion) on continental break-up. To do that we apply the three-dimensional numerical code SLIM3D that features realistic elasto-visco-plastic rheology. We model the thermo-mechanical response of a segment of Earth's lithosphere that is affected both by extension as well as plume-related lithosphere erosion in order to evaluate the influence on the overall force budget. We find that lithosphere erosion leads to a moderate lithospheric strength reduction of several TN/m. In a force-limited environment, however, this strength reduction may have strong influence on the timing of continental break-up, or it may even control whether continental break-up takes place at all. Additional reduction of the lithospheric strength is likely due to the massive emplacement of dikes that follows intensive melting within the plume head. © 2013 Elsevier B.V.

Ghasemi M.F.,Schmidt Institute of Physics of the Earth | Bayuk I.O.,Schmidt Institute of Physics of the Earth | Alkhimenkov Y.,Delft University
7th EAGE Saint Petersburg International Conference and Exhibition: Understanding the Harmony of the Earth's Resources Through Integration of Geosciences | Year: 2016

Geomechanical modeling is of great importance for different tasks of prospecting geophysics. This modeling requires knowledge on geomechanical characteristics including the static moduli (Young modulus and Poisson coefficient), the uniaxial compression strength and internal friction angle. The only way to get reliable geomechanical parameters is laboratory tests providing "stress-strain" curves. However, this way is time consuming and should be performed for many representative samples of all stratigraphic units penetrated by a well. Many empirical relations exist that allow one to relate the dynamic moduli provided by logging with the geomechanical parameters. However these relations work only locally. In this work we propose an approach based on classification of rocks with respect to their macrostructure controlling the both dynamic moduli and geomechanical characteristics. The microstructure is described by the rock's model parameters inverted from the experimental data with the help of the Rock Physics modeling. This makes it possible to group different rocks into classes with respect to the model parameters. As a result this allows one to find relations between the dynamic elastic parameters measured in field and geomechanical and other physical parameters (not measured) for different rock groups via the rock microstructure parameters specific of each rock group.

Marinin A.V.,Schmidt Institute of Physics of the Earth | Saintot A.,Ruhr University Bochum
Comptes Rendus - Geoscience | Year: 2012

Two groups of researchers have used the same datasets in order to determine paleostress regimes and the corresponding tectonic phases in the northwestern-Greater Caucasus fold-and-thrust belt. The kinematic indicators were inverted by both groups to determine the magnitude and orientation of the tectonic stresses. The Russian group's method is based on the " structural pattern" that developed under a single stress-strain state in a given rock volume. The French group used a fault slip data inversion. Stress fields reconstructed by both groups show similarities. Because the methods are independent, the paleostress fields may reflect natural processes. The best-expressed paleostress field is a NE-SW compression related to the Late Eocene folding and thrusting event. A stress field that may correspond to the latest tectonic phase of the northwestern-Greater Caucasus is characterized by a NNW-SSE striking pressure axis. Other paleostress fields that span from Late Cretaceous to present-day are also reconstructed by both groups. © 2012 Académie des sciences.

Petrunin A.G.,Helmholtz Center Potsdam | Rogozhina I.,Helmholtz Center Potsdam | Vaughan A.P.M.,Trinity College Dublin | Vaughan A.P.M.,British Antarctic Survey | And 6 more authors.
Nature Geoscience | Year: 2013

At the Earth's surface, heat fluxes from the interior are generally insignificant compared with those from the Sun and atmosphere, except in areas permanently blanketed by ice. Modelling studies show that geothermal heat flux influences the internal thermal structure of ice sheets and the distribution of basal melt water, and it should be taken into account in planning deep ice drilling campaigns and climate reconstructions. Here we use a coupled ice-lithosphere model driven by climate and show that the oldest and thickest part of the Greenland Ice Sheet is strongly influenced by heat flow from the deep Earth. We find that the geothermal heat flux in central Greenland increases from west to east due to thinning of the lithosphere, which is only about 25-66% as thick as is typical for terrains of early Proterozoic age. Complex interactions between geothermal heat flow and glaciation-induced thermal perturbations in the upper crust over glacial cycles lead to strong regional variations in basal ice conditions, with areas of rapid basal melting adjoining areas of extremely cold basal ice. Our findings demonstrate the role that the structure of the solid Earth plays in the dynamics of surface processes. © 2013 Macmillan Publishers Limited. All rights reserved.

Galybin A.N.,Schmidt Institute of Physics of the Earth
Engineering Analysis with Boundary Elements | Year: 2016

This paper presents a system of integral equations for the determination of contact stresses on a part of the boundary of elastic half-space by measured data of displacements on the rest of the stress-free boundary. Inverse problems like this are refereed to as conditionally ill-posed with pronounced dependence of the solution from small perturbations in measured data. The 3D problem formulation is based on spatial harmonic functions. It is proposed to use a Trefftz-type method for the sought harmonic functions based on the radial basis functions to solve the system of integral equations. A synthetic example is presented to illustrate the proposed approach. © 2016 Published by Elsevier Ltd.

Yagova N.,Schmidt Institute of Physics of the Earth | Heilig B.,Tihany Geophysical Observatory MFGI | Fedorov E.,Schmidt Institute of Physics of the Earth
Annales Geophysicae | Year: 2015

We analyze Pc2-3 pulsations recorded by the CHAMP (CHAllenging Minisatellite Payload) satellite in the F layer of the Earth's ionosphere, on the ground, and in the magnetosphere during quiet geomagnetic conditions. The spectra of Pc2-3 pulsations recorded in the F layer are enriched with frequencies above 50 mHz in comparison to the ground Pc2-3 spectra. These frequencies are higher than the fundamental harmonics of the field line resonances in the magnetosphere. High quality signals with dominant frequencies 70-200 mHz are a regular phenomenon in the F layer and in the magnetosphere. The mean latitude of the maximum Pc2-3 occurrence rate lies at L ≈ 3.5 in the F layer, i.e., inside the plasmasphere. Day-to-day variations of the L value of the CHAMP Pc2-3 occurrence rate maximum follow the plasmapause day-to-day variations. Polarization and amplitude of Pc2-3s in the magnetosphere, in the ionosphere, and on the ground allow us to suggest that they are generated as fast magnetosonic (FMS) waves in the outer magnetosphere and are partly converted into shear Alfven waves near the plasmapause. The observed ground-to-ionosphere amplitude ratio during the night is interpreted as a result of the Alfven wave transmission through the ionosphere. The problem of wave transmission through the ionosphere is solved theoretically by means of a numerical solution of the full-wave equation for the Alfven wave reflection from and transmission through a horizontally stratified ionosphere. The best agreement between the calculated and measured values of the ground-to-ionosphere amplitude ratio is found for k Combining double low line 5 × 10−3 km'1, i.e., the observed ground-to-ionosphere amplitude ratio corresponds to a wave spatial scale which could provide a Doppler shift within a few percent of the apparent frequency of the Pc2-3 pulsations as recorded by a low-orbiting spacecraft.

Kaban M.K.,Helmholtz Center Potsdam | Kaban M.K.,Schmidt Institute of Physics of the Earth | Petrunin A.G.,Helmholtz Center Potsdam | Petrunin A.G.,Schmidt Institute of Physics of the Earth | And 2 more authors.
Surveys in Geophysics | Year: 2014

A joint effect of weak zones, dividing lithospheric plates, and lateral viscosity variations (LVV) in the whole mantle on the observed geoid is investigated by a new numerical approach. This technique is based on the substantially revised method introduced by Zhang and Christensen (Geophys J Int 114:531–547, 1993) for solving the Navier–Stokes–Poisson equations in the spectral domain with strong LVV. Weak plate boundaries (WPB) are introduced based on an integrated global model of plate boundary deformations GSRM (Kreemer et al. in Geophys J Int 154:8–34, 2003). The effect of WPB on the geoid is significant and reaches −40 to 70 m with RMS ~20 m. The peaks are observed over large subduction zones in South America and the southwestern Pacific in agreement with previous studies. The positive geoid anomaly in South America could be explained largely by a dynamic effect of decoupling of the Nazca and South American plates. The negative changes of the geoid mostly relate to mid-oceanic ridges. The amplitude of the effect depends on the viscosity contrasts at WPB compared with the plate viscosity until its value reaches the limit of 2.5–3 orders of magnitude. This value might be considered as a level at which the plates are effectively decoupled. The effect of WPB exceeds the effect of LVV in the whole mantle and generally does not correlate with it. However, inclusion of LVV reduces the geoid perturbations due to WPB by about 10 m. Therefore, it is important to consider all factors together. The geoid changes mainly result from changes of the dynamic topography, which are about −300 to +500 m. The obtained results show that including WPB may significantly improve the reliability of instantaneous global dynamic models. © 2014, Springer Science+Business Media Dordrecht.

Akopian S.T.,Schmidt Institute of Physics of the Earth
Geophysical Journal International | Year: 2015

A concept of seismic system (SS), which is responsible for the preparation of an ensemble of strong earthquakes, is considered as an open dissipative system exchanging energy and entropy with the environment. Open dissipative SS allow one to describe the equilibrium and non-equilibrium states of SS, and the lithosphere evolution under different plate tectonic settings on the basis of seismostatistics. Several new seismic parameters ('seismic temperature', 'seismic time', dissipation function, efficiency, inelastic energy, dynamical probability) are defined and proposed for better understanding and describing the dynamical processes. The Sakhalin SS is considered to illustrate the behaviour of proposed parameters. By analogy to Liouville's equation in thermodynamics, it is shown that there is no criterion of instability in the domain where the Gutenberg-Richter law is true. In the proposed approach, the instability origination and the formation of seismogenic structures in the lithosphere are based on the energy versus information entropy power law; the existence of 'time arrow' also proceeds from such a dependence. Application of energy and trajectory diagrams enables to describe the preparation of strong earthquakes within an ensemble in terms of slow and fast timescales. These diagrams help perform the spatiotemporal-energy monitoring of the instability origination in the lithosphere. It is shown that the information entropy parameter can serve as a measure of the unknown external energy flow into the system (this energy is supplied for the elastic radiation energy in the earthquake sources and for inelastic processes in the system volume). The property of the ensemble of strong earthquakes is periodically to restore the SS equilibrium state that enables to describe the SS energy balance. The results offer possibilities to estimate the fraction of inelastic energy released by the SS medium during the preparation and occurrence of seismic catastrophes. The construction of phase diagrams and 'entropy funnels' in the virtual space (with time, energy and entropy coordinates) can provide new opportunities for the visualization of undetectable processes leading to disastrous earthquakes. © The Author 2015. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Popov A.A.,Helmholtz Center Potsdam | Popov A.A.,Johannes Gutenberg University Mainz | Sobolev S.V.,Helmholtz Center Potsdam | Sobolev S.V.,Schmidt Institute of Physics of the Earth | Zoback M.D.,Stanford University
Geochemistry, Geophysics, Geosystems | Year: 2012

We present a three-dimensional finite element thermomechanical model idealizing the complex deformation processes associated with evolution of the San Andreas Fault system (SAFS) in northern and central California over the past 20 Myr. More specifically, we investigate the mechanisms responsible for the eastward (landward) migration of the San Andreas plate boundary over time, a process that has largely determined the evolution and present structure of SAFS. Two possible mechanisms had been previously suggested. One mechanism suggests that the Pacific plate first cools and captures uprising mantle in the slab window, subsequently causing accretion of the continental crustal blocks. An alternative scenario attributes accretion to the capture of plate fragments (microplates) stalled in the ceased Farallon-North America subduction zone. Here we test both these scenarios numerically using a recently developed lithospheric-scale code, SLIM3D, that employs free surface, nonlinear temperature- and stress-dependent elastoviscoplastic rheology and allows for self-generation of faults. Modeling suggests that microplate capture is the primary driving mechanism for the eastward migration of the plate boundary, while the slab window cooling mechanism alone is incapable of explaining this phenomenon. We also show that the system evolves to the present day structure of SAFS only if the coefficient of friction at mature faults is low (0.08 for the best fit model). Thus, our model provides an independent constraint supporting the "weak fault in a strong crust" hypothesis for SAFS. © 2012. American Geophysical Union. All Rights Reserved.

Petrunin A.G.,Helmholtz Center Potsdam | Kaban M.K.,Helmholtz Center Potsdam | Rogozhina I.,Helmholtz Center Potsdam | Trubitsyn V.,Schmidt Institute of Physics of the Earth
Geochemistry, Geophysics, Geosystems | Year: 2013

The observed geoid, dynamic topography, and surface plate velocities are controlled by various factors such as density and viscosity variations in the Earth's mantle and strength of the lithosphere. Previous studies have shown that the geoid signal cannot be resolved in details within the framework of a simplified model of the mantle flow considering only radial viscosity variations. Thus, a modeling technique handling both radial and lateral variations of viscosity and other parameters should be used. The spectral method provides a high-accuracy semianalytical solution of the Navier-Stokes and Poisson equations when viscosity is only depth (radially) dependent. In this study, we present the numerical approach, built up on the substantially revised method originally proposed by Zhang and Christensen (1993), for solving the Navier-Stokes equation in the spectral domain with lateral variations of viscosity (LVV). This approach incorporates a number of numerical algorithms providing efficient calculations of the instantaneous Stokes flow in the sphere and taking into account the effects of LVV, self gravitation, and compressibility. In contrast to the traditionally used propagator method, our approach suggests a continuous integration over depth without introducing internal interfaces. Various numerical tests have been employed to test accuracy and efficiency of the proposed technique. Benchmarking of the code shows its ability to solve the mantle convection problems implying strong LVV with high resolution. © 2013. American Geophysical Union. All Rights Reserved.

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