scholarly journals A three-dimensional radially anisotropic model of shear velocity in the whole mantle

2006 ◽  
Vol 167 (1) ◽  
pp. 361-379 ◽  
Author(s):  
Mark Panning ◽  
Barbara Romanowicz
Keyword(s):  
Three Dimensional ◽  
Shear Velocity ◽  
Anisotropic Model

scholarly journals Three-dimensional shear velocity structure of the Mauleon and Arzacq basins (Western Pyrenees)

2021 ◽  
Author(s):  
Maximilien Lehujeur ◽  
Sébastien Chevrot ◽  
Antonio Villaseñor ◽  
Emmanuel Masini ◽  
Nicolas Saspiturry ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Hanging Wall ◽  
Three Dimensional ◽  
Sedimentary Basins ◽  
Shear Velocity ◽  
Velocity Model ◽  
Tomographic Images ◽  
Reflection Seismic ◽  
Local Earthquake Tomography ◽  
Local Earthquake

We present a 3-D shear wave velocity model of the Mauleon and Arzacq basins from the surface down to 10~km depth. This model is obtained by inverting phase velocity maps for periods from 2 to 9~s measured on coherent surface wavefronts extracted from ambient seismic noise by matched filtering. This new model, which is found in good agreement with local earthquake tomography, reveals the architecture of the Mauleon and Arzacq basins which were poorly imaged by conventional reflection seismic data. Combining these new tomographic images with surface and subsurface geological information allows us to trace major orogenic structures from the basement to the surface. In the basin, the models are successfully imaging first-order folds and thrusts at kilometric scale. The velocity structure within the basement and its geometrical relationship with the base of inverted rift basins supports a progressive northward exhumation of deep crustal and mantle rocks in the hanging wall of north-vergent Pyrenean thrusts. Our tomographic models image in 3-D orogen-perpendicular structures responsible for crustal segmentation as the Saison and Barlanes transfer zones. We propose that these steep structures consist in tear faults that accommodate the deepening of the Mauleon basin basement from west to east. To the west, this basement made of former hyper-extended rift domains (including mantle rocks) is anomalously sampled within the hanging-wall of north-directed orogenic thrusts, explaining its shallow attitude and its best preservation in comparison to the eastern segment of the study area. Eastward, the vertical shift of the basement makes that the former Mauleon basin hyper-extended rift basement remained in a footwall situation in respect of orogenic thrust and was underthrust. The comparison of the tomographic models obtained with surface wave tomography and local earthquake tomography shows that each approach has its own advantages and shortcomings but also that they are very complementary in nature, which would suggest to combine them in joint inversions to further improve passive imaging of the shallow crust and sedimentary basins.

INFLUENCE OF STRUCTURAL DEFECTS ON NONEQUILIBRIUM CRITICAL BEHAVIOR OF THREE-DIMENSIONAL ANISOTROPIC HEISENBERG MODEL

2020 ◽  
Vol 25 (2) ◽  
pp. 13-23
Author(s):  
Vladimir Prudnikov ◽  
Pavel Prudnikov ◽  
Anton Demiyanenko ◽  
Yurii Kovalev
Keyword(s):  
Low Temperature ◽  
Critical Behavior ◽  
Easy Axis ◽  
Three Dimensional ◽  
Monte Carlo Study ◽  
Structural Defects ◽  
Anisotropic Model ◽  
Isotropic Model ◽  
Initial State ◽  
Initial States

The results of a Monte Carlo study of features of structural defects influence on nonequi-librium critical behavior of three-dimensional isotropic and anisotropic Heisenberg models are presented with their evolution from different initial states. It is shown that presence of defects changes characteristics of nonequilibrium critical behavior of anisotropic model with easy axis anisotropy type and evolution from both high-temperature and low-temperature initial states. Presence defects is relevant only for characteristics of nonequi-librium critical behavior of isotropic model with evolution from low-temperature initial state leading to superaging effects.

scholarly journals Three-Dimensional Anisotropic Inversions for Time-Domain Airborne Electromagnetic Data

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 218
Author(s):  
Yang Su ◽  
Changchun Yin ◽  
Yunhe Liu ◽  
Xiuyan Ren ◽  
Bo Zhang ◽  
...  
Keyword(s):  
Time Domain ◽  
Three Dimensional ◽  
Model Parameters ◽  
Anisotropic Model ◽  
Regularized Inversion ◽  
Earth Structures ◽  
Airborne Electromagnetic ◽  
Speed Up ◽  
The Time Domain ◽  
Airborne Electromagnetic Data

Rocks and ores in nature usually appear macro-anisotropic, especially in sedimentary areas with strong layering. This anisotropy will lead to false interpretation of electromagnetic (EM) data when inverted under the assumption of an isotropic earth. However, the time-domain (TD) airborne EM (AEM) inversion for an anisotropic model has not attracted much attention. To get reasonable inversion results from TD AEM data, we present in this paper the forward modeling and inversion methods based on a triaxial anisotropic model. We apply three-dimensional (3D) finite-difference on the secondary scattered electric field equation to calculate the frequency-domain (FD) EM responses, then we use the inverse Fourier transform and waveform convolution to obtain TD responses. For the regularized inversion, we calculate directly the sensitivities with respect to three diagonal conductivities and then use the Gauss–Newton (GN) optimization scheme to recover model parameters. To speed up the computation and to reduce the memory requirement, we adopt the moving footprint concept and separate the whole model into a series of small sub-models for the inversion. Finally, we compare our anisotropic inversion scheme with the isotropic one using both synthetic and field data. Numerical experiments show that the anisotropic inversion has inherent advantages over the isotropic ones, we can get more reasonable results for the anisotropic earth structures.

scholarly journals The Evolution of a Double Diffusive Magnetic Buoyancy Instability

2010 ◽  
Vol 6 (S271) ◽  
pp. 218-226
Author(s):  
Lara J. Silvers ◽  
Geoffrey M. Vasil ◽  
Nicholas H. Brummell ◽  
Michael R. E. Proctor
Keyword(s):  
Three Dimensional ◽  
Shear Velocity ◽  
Horizontal Magnetic Field ◽  
Field Gradients ◽  
Vertical Field ◽  
Magnetic Buoyancy ◽  
Interchange Instability ◽  
Upward Moving ◽  
Buoyancy Instability ◽  
Double Diffusive

AbstractRecently, Silvers et al. (2009b), using numerical simulations, confirmed the existence of a double diffusive magnetic buoyancy instability of a layer of horizontal magnetic field produced by the interaction of a shear velocity field with a weak vertical field. Here, we demonstrate the longer term nonlinear evolution of such an instability in the simulations. We find that a quasi two-dimensional interchange instability rides (or “surfs”) on the growing shear-induced background downstream field gradients. The region of activity expands since three-dimensional perturbations remain unstable in the wake of this upward-moving activity front, and so the three-dimensional nature becomes more noticeable with time.

Improving Stoneley-mode constraints on the structures near the core-mantle boundary

2020 ◽  
Author(s):  
Harry Matchette-Downes ◽  
Robert D. van der Hilst ◽  
Jingchen Ye ◽  
Jia Shi ◽  
Jiayuan Han ◽  
...  
Keyword(s):  
Material Properties ◽  
Three Dimensional ◽  
Normal Modes ◽  
Shear Velocity ◽  
Boundary Region ◽  
Earth Model ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
Special Cases

<p>Although observations of seismic normal modes provide constraints on the structure of the entire Earth, the core-mantle boundary region remains poorly understood. Stoneley modes should offer better constraints, because they are confined near to the fluid-solid interface, but this property also makes them difficult to detect. In this study, we use recently-developed finite-element approach to show that Stoneley modes can be excited and detected, but only in certain special cases. We first investigate the physical explanation for these cases. Next, we describe how they could be detected in seismic data, and the sensitivity of these data to the material properties. We illustrate this sensitivity by calculating the modes of a three-dimensional Earth model containing a large low-shear-velocity province (LLSVP). Finally, we present some preliminary observations. We hope that this new understanding will lead to new constraints on the material properties and morphology of the core-mantle boundary region. In turn, this information, especially the constraints on density, should help to answer questions about the Earth, for example in mantle convection (are LLSVPs thermally or chemically buoyant? Primordial or slab graveyards? Passive or active?) and core convection (does the outermost core have a stable stratification?).</p>

Three-dimensional small-angle neutron scattering of shear-induced phase separation in a dynamically asymmetric polymer mixture

2006 ◽  
Vol 39 (6) ◽  
pp. 878-888 ◽  
Author(s):  
Satoshi Koizumi ◽  
Jun-ichi Suzuki
Keyword(s):  
Phase Separation ◽  
Neutron Scattering ◽  
Temperature Region ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Three Dimensional ◽  
Shear Velocity ◽  
Intermediate Temperature ◽  
Polymer Mixture ◽  
Vinyl Methyl Ether

A polymer mixture of polystyrene (PS)/poly(vinyl methyl ether) (PVME) has been investigated by using a three-dimensional small-angle neutron scattering (3D-SANS) method. PS and PVME exhibit a large difference in the glass transition temperatureTg. Therefore, dynamical asymmetry is strongly enhanced in an intermediate temperature region between theTgvalues of neat PS and PVME. In the intermediate temperature region, a shear deformation was imposed on the polymer mixture to enhance the concentration fluctuations,i.e.shear-induced phase separation. By rotating the film specimen, which was rapidly quenched after deformation, 3D-SANS due to shear-induced phase separation was observed successfully. In theqx=qyplane of the sample coordinate system, whereqis a component of scattering vectorq, it was possible to observe SANS of `double-lobe' shape, with the minor axes of the lobes inclined towardsqx=qy, whereqx,qyandqz, denote the shear, velocity gradient and vorticity directions in reciprocal space, respectively. Abnormal `butterfly' scattering was observed in a section cut through the 3D-SANS in theqxqzplane. The 3D-SANS thus obtained is discussed in comparison with a model of dynamical coupling between stress and diffusion.

scholarly journals Three-Dimensional Velocity Distribution in Straight Smooth Channels Modeled by Modified Log-Law

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Shu-Qing Yang ◽  
Muhammad Zain Bin Riaz ◽  
Muttucumaru Sivakumar ◽  
Keith Enever ◽  
Nadeeka Sajeewani Miguntanna
Keyword(s):  
Velocity Distribution ◽  
Three Dimensional ◽  
Shear Velocity ◽  
Central Line ◽  
Channel Flows ◽  
Average Error ◽  
Measured Velocity ◽  
Rectangular Channels ◽  
Smooth Channel ◽  
Log Law

Time-average velocity distribution in steady and uniform channel flows is important for fundamental research and practical application as it is always three-dimensional (3D), regardless of channel geometry. However, its determination has predominantly been carried out by using complex numerical software, even for the simplest geometry such as rectangular channels. The log-law was developed initially for circular pipe flows, where a single shear velocity is used to normalize the velocity (u+) and its distance (y+). Tracy and Lester found that the performance of the log-law can be extended to express velocity profiles in rectangular channels when the global shear velocities (gRS)0.5 and (ghS)0.5 are used to normalize the measured velocity u and its distance y. This study extends this discovery from the channel central line to the corner regions, and its general form of log-law was found to be valid even in trapezoidal or triangular open channels or closed ducts. This modified log-law can produce good agreement with the measured velocity with an average error of less than 5%. Therefore, this study provides a simple and reliable tool for engineers and researchers to estimate the velocity contours in straight and smooth channel flows.

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