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Deformation
Kinds of Deformation Terms modified by Deformation Selected AbstractsMATERIAL AND CONSTRUCTION CHANGES INFLUENCE ON A TIRE DYNAMIC DEFORMATIONEXPERIMENTAL TECHNIQUES, Issue 3 2009M. Mokry First page of article [source] TIMING AND MODES OF DEFORMATION IN THE WESTERN SICILIAN THRUST SYSTEM, SOUTHERN ITALYJOURNAL OF PETROLEUM GEOLOGY, Issue 2 2001L. Tortorici Imbricate units in the western Sicilian fold-and-thrust belt originated on the southern continental margin of Neotethys, and were deformed during the Neogene-Recent in response to convergence between the African and European Plates. Neogene-Pleistocene synorogenic sediments, deposited in flexural foredeeps and satellite piggy-back basins, contain a record of the belt's evolution. Progressive migration of the thrust front southwards into the foreland has been documented, beginning in the Tortonian and continuing to the present-day particularly in western parts of the belt. In the eastern part, activity on Quaternary strike-slip fault zones has produced asymmetric flower structures and other interference structures. In this paper, we present two regional sections across the western Sicilian foreland-thrust belt system. These structural cross-sections extend down as far as the top of the Hercynian basement and integrate our field observations with previously-acquired well log, magnetic and seismic data. We show that complex interactions between the foreland-migrating thrust belt, which developed between the Late Miocene and the Pleistocene, and Pleistocene strike-slip faults led to the development of structural traps which constitute potential targets for hydrocarbon exploration. [source] 3-D DYNAMIC OPTICAL TECHNIQUES TO MODEL FOOD MECHANICAL DEFORMATIONJOURNAL OF TEXTURE STUDIES, Issue 4 2010MURIEL JACQUOT ABSTRACT Finding new instrumental rheological parameters that better describe sensory textures can improve correlation between rheological and sensory measurements of food. Two optical three-dimensional (3-D) techniques commonly used in mechanical engineering field were studied. These techniques have never been used in food science. Digital image correlation and Breuckmann scanning systems were successful to distinguish gelatin gels and soft cheeses varying in firmness and viscoelastic properties. These two systems were coupled with a universal testing machine to provide information regarding 3-D displacements and surface deformation of sample. Mathematical models were developed to determine surface displacement profiles of samples from their firmness and viscoelastic properties. Three parameters were obtained to describe surface displacement profiles linked to samples textural properties. These parameters may be useful to develop models predicting accurately food sensory texture from instrumental measurements. PRACTICAL APPLICATIONS Finding new instrumental rheological parameters that better describe sensory textures to improve correlation between rheological and sensory measurements of food. [source] RHEOLOGY AND MICROSTRUCTURE OF WHEAT DOUGH DEVELOPED WITH CONTROLLED DEFORMATIONJOURNAL OF TEXTURE STUDIES, Issue 1 2000EMILY J. SCHLUENTZ ABSTRACT Undeveloped wheat dough samples were strained in shear and extensional flow between parallel plates to produce a controlled level of development. Dough made in a standard Farinograph, considered developed dough, was used for comparison. Scanning electron microscopy images of deformed dough were subjected to numerical image processing to characterize the protein matrix present. Results were compared to dynamic rheological properties to evaluate the influence of strain deformation on the formation of microstructure. Viscoelastic moduli of wheat dough showed that developed dough had the greatest amount of structure formation, followed by extensionally-strained and shear-strained samples, respectively. Undeveloped dough showed the lowest levels of structure development. Image analysis indicated statistically significant differences between protein matrices in developed and undeveloped samples; however, results were not significantly different between shear- and extension-ally-strained samples. [source] Deformation by examples: a density flow approachCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2 2007Hoi-Chau Leung Abstract In this article, a shape transformation technique is introduced for deforming objects based on a given deformation example. The example consists of two reference shapes representing two different states of an object. The reference shapes are assumed to morph from one state to the other. The evolution between the two reference shapes determines the shape transformation function. Any given objects can then be deformed by the same transformation. A continuous 4D Radial Basis Function is used to construct a density flow field (an extension of the optical flow in computer vision) representing the shape transformation of the example in 3-space. Objects embedded in the density flow field are deformed by moving vertices of the objects along the density flow vectors. Additional parameters are introduced to control the process of the deformation. This provides explicit control on the shape of the object obtained in the deformation process. Copyright © 2007 John Wiley & Sons, Ltd. [source] ProcDef: Local-to-global Deformation for Skeleton-free Character AnimationCOMPUTER GRAPHICS FORUM, Issue 7 2009Takashi Ijiri Abstract Animations of characters with flexible bodies such as jellyfish, snails, and, hearts are difficult to design using traditional skeleton-based approaches. A standard approach is keyframing, but adjusting the shape of the flexible body for each key frame is tedious. In addition, the character cannot dynamically adjust its motion to respond to the environment or user input. This paper introduces a new procedural deformation framework (ProcDef) for designing and driving animations of such flexible objects. Our approach is to synthesize global motions procedurally by integrating local deformations. ProcDef provides an efficient design scheme for local deformation patterns; the user can control the orientation and magnitude of local deformations as well as the propagation of deformation signals by specifying line charts and volumetric fields. We also present a fast and robust deformation algorithm based on shape-matching dynamics and show some example animations to illustrate the feasibility of our framework. [source] Optimizing Structure Preserving Embedded Deformation for Resizing Images and Vector ArtCOMPUTER GRAPHICS FORUM, Issue 7 2009Qi-xing Huang Abstract Smart deformation and warping tools play an important part in modern day geometric modeling systems. They allow existing content to be stretched or scaled while preserving visually salient information. To date, these techniques have primarily focused on preserving local shape details, not taking into account important global structures such as symmetry and line features. In this work we present a novel framework that can be used to preserve the global structure in images and vector art. Such structures include symmetries and the spatial relations in shapes and line features in an image. Central to our method is a new formulation of preserving structure as an optimization problem. We use novel optimization strategies to achieve the interactive performance required by modern day modeling applications. We demonstrate the effectiveness of our framework by performing structure preservation deformation of images and complex vector art at interactive rates. [source] Energy-Based Image DeformationCOMPUTER GRAPHICS FORUM, Issue 5 2009Z. Karni Abstract We present a general approach to shape deformation based on energy minimization, and applications of this approach to the problems of image resizing and 2D shape deformation. Our deformation energy generalizes that found in the prior art, while still admitting an efficient algorithm for its optimization. The key advantage of our energy function is the flexibility with which the set of "legal transformations" may be expressed; these transformations are the ones which are not considered to be distorting. This flexibility allows us to pose the problems of image resizing and 2D shape deformation in a natural way and generate minimally distorted results. It also allows us to strongly reduce undesirable foldovers or self-intersections. Results of both algorithms demonstrate the effectiveness of our approach. [source] Direct Visualization of Deformation in VolumesCOMPUTER GRAPHICS FORUM, Issue 3 2009Stef Busking Abstract Deformation is a topic of interest in many disciplines. In particular in medical research, deformations of surfaces and even entire volumetric structures are of interest. Clear visualization of such deformations can lead to important insight into growth processes and progression of disease. We present new techniques for direct focus+context visualization of deformation fields representing transformations between pairs of volumetric datasets. Typically, such fields are computed by performing a non-rigid registration between two data volumes. Our visualization is based on direct volume rendering and uses the GPU to compute and interactively visualize features of these deformation fields in real-time. We integrate visualization of the deformation field with visualization of the scalar volume affected by the deformations. Furthermore, we present a novel use of texturing in volume rendered visualizations to show additional properties of the vector field on surfaces in the volume. [source] Control of Feature-point-driven Facial Animation Using a Hypothetical FaceCOMPUTER GRAPHICS FORUM, Issue 4 2001Ming-Shing Su A new approach to the generation of a feature-point-driven facial animation is presented. In the proposed approach, a hypothetical face is used to control the animation of a face model. The hypothetical face is constructed by connecting some predefined facial feature points to create a net so that each facet of the net is represented by a Coon's surface. Deformation of the face model is controlled by changing the shape of the hypothetical face, which is performed by changing the locations of feature points and their tangents. Experimental results show that this hypothetical-face-based method can generate facial expressions which are visually almost identical to those of a real face. [source] Local Dysfunction and Asymmetrical Deformation of Mitral Annular Geometry in Ischemic Mitral Regurgitation: A Novel Computerized 3D Echocardiographic AnalysisECHOCARDIOGRAPHY, Issue 4 2008Masao Daimon M.D. Objective: Most studies of the pathogenesis of functional mitral regurgitation (MR) have focused on alterations in ventricular function and geometry. We used a novel 3D echocardiographic method to assess abnormalities in mitral annular (MA) geometry and motion in patients with ischemic MR (IMR) and compared these data to those obtained from normal subjects and from patients with MR caused by dilated cardiomyopathy (DMR). Methods: Real time 3D echo was performed in 12 normal subjects, 25 with IMR, and 14 with DMR. Eight points along the saddle-shaped MA were identified using our software at systole and diastole. From these eight points, four annular diameters at each cardiac phase were determined. Annular motion was assessed by measuring local displacement (LD) of a given point between systole and diastole. Results: Annular motion was different between groups: IMR had smaller LD in posterior MA segments than did normals (2.6 ± 1.1 vs 4.8 ± 1.9 mm, P < 0.01), while DMR had globally reduced LD. In IMR systolic MA dilatation was striking in the anterior,posterior (diameter; IMR vs controls, 28.3 ± 3.5 vs 22.5 ± 2.2 mm, P< 0.05) and anterolateral,posteromedial (31.7 ± 3.5 vs 25.1 ± 2.2 mm, P < 0.05) directions; in IMR, systolic MA diameters in these two directions correlated with MR severity(P = 0.02). MA dilatation occurred globally in DMR. Conclusion: This novel 3D echo method demonstrated that MA motion and dilatation were asymmetric in IMR and symmetric in DMR. These differences in MA geometry and motion may aid in the development of distinct new therapies for IMR and DMR. [source] Involvement of the thalamocortical network in TLE with and without mesiotemporal sclerosisEPILEPSIA, Issue 8 2010Susanne G. Mueller Summary Purpose:, The thalamus plays an important role in seizure propagation in temporal lobe epilepsy (TLE). This study investigated how structural abnormalities in the focus, ipsilateral thalamus and extrafocal cortical structures relate to each other in TLE with mesiotemporal sclerosis (TLE-MTS) and without hippocampal sclerosis (TLE-no). Methods:, T1 and high-resolution T2 images were acquired on a 4T magnet in 29 controls, 15 TLE-MTS cases, and 14 TLE-no. Thalamus volumes were obtained by warping a labeled atlas onto each subject's brain. Deformation-based morphometry was used to identify regions of thalamic volume loss and FreeSurfer for cortical thickness measurements. CA1 volumes were obtained from high-resolution T2 images. Multiple regression analysis and correlation analyses for voxel- and vertex-based analyses were performed in SPM2 and FreeSurfer. Results:, TLE-MTS had bilateral volume loss in the anterior thalamus, which was correlated with CA1 volume and cortical thinning in the mesiotemporal lobe. TLE-no had less severe volume loss in the dorsal lateral nucleus, which was correlated with thinning in the mesiotemporal region but not with extratemporal thinning. Discussion:, The findings suggest that seizure propagation from the presumed epileptogenic focus or regions close to it into the thalamus occurs in TLE-MTS and TLE-no and results in circumscribed neuronal loss in the thalamus. However, seizure spread beyond the thalamus seems not to be responsible for the extensive extratemporal cortical abnormalities in TLE. [source] Bulk Nanostructured Functional Materials By Severe Plastic Deformation,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Michael Zehetbauer Since severe plastic deformation (SPD) has demonstrated its capability of producing bulk nanomaterials with highly advanced mechanical properties, research is increasingly focusing on the question as to whether functional nanomaterials can be achieved by SPD and in bulk shape, too. This paper presents promising results of reaching functional properties in SPD-processed bulk nanocrystalline magnetic alloys, bulk shape memory nanoalloys, as well as nanometals and alloys for hydrogen storage, and also reports on problems with other functional properties, like those of thermoelectricity, occurring in non-metallic nanomaterials. [source] Optimization of the Magnetic Properties of FePd Alloys by Severe Plastic Deformation,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Abdelahad Chbihi Abstract A FePd alloy was nanostructured by severe plastic deformation following two different routes: ordered and disordered states were processed by high pressure torsion (HPT). A grain size in a range of 50 to 150,nm is obtained in both cases. Severe plastic deformation induces some significant disordering of the long range ordered L10 phase. However, transmission electron microscopy (TEM) data clearly show that few ordered nanocrystals remain in the deformed state. The deformed materials were annealed to achieve nanostructured long range ordered alloys. The transformation proceeds via a first order transition characterized by the nucleation of numerous ordered domains along grain boundaries. The influence of the annealing conditions (temperature and time) on the coercivity was studied for both routes. It is demonstrated that starting with the disorder state prior to HPT and annealing at low temperature (400,°C) leads to the highest coercivity (about 1.8,kOe). [source] Consolidation of Particles by Severe Plastic Deformation: Mechanism and Applications in Processing Bulk Ultrafine and Nanostructured Alloys and Composites,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Kenong Xia Severe plastic deformation (SPD) can be used to consolidate particles into bulk ultrafine and nanostructured materials. SPD consolidation relies on plastic deformation of individual particles, rather than diffusion, to achieve bonding and thus can be carried out at much lower temperatures. Using examples of consolidation of Al particles by back pressure equal channel angular pressing (BP-ECAP), it is demonstrated that full consolidation is achieved when the particles are sheared to disrupt the surface oxide layer whereas consolidation is impossible or incomplete in the case of particles sliding over each other. The effects of particle characteristics such as size, shape, strength and surface condition, as well as processing parameters including temperature and back pressure, are discussed to shed light on the mechanism of SPD consolidation. Potential applications of SPD in powder consolidation and processing of bulk ultrafine and nanostructured materials are discussed. [source] Enhanced Strength and Ductility of Ultrafine-Grained Ti Processed by Severe Plastic Deformation,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Irina Semenova This work deals with the study of strength and ductility in ultrafine-grained (UFG) Ti Grade 4 produced by equal channel angular pressing (ECAP) in combination with subsequent thermomechanical treatments. We found that additional annealing of UFG Ti resulted in unusual enhancement of strength and ductility, which is associated with not only small grain size but also with a grain boundary structure. The origin of this phenomenon is investigated using the results of transmission electron microscopy and atom probe tomography. The innovation potential of UFG Ti for medical use is considered. [source] A New Technique for Severe Plastic Deformation: The Cone,Cone MethodADVANCED ENGINEERING MATERIALS, Issue 12 2009Olivier Bouaziz Abstract A new technique for producing ultrafine grained materials by severe plastic deformation is proposed. The principle and possible design of this technique, referred to as "cone,cone method," are outlined and the first results of numerical simulations that demonstrate its feasibility are reported. These results give promise with regard to achieving very large plastic strains and the concomitant grain refinement in sheet products. [source] Transition of Failure Mode and Enhanced Plastic Deformation of Metallic Glass by Multiaxial Confinement,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Fu-Fa Wu Multiple shear bands are formed in a confined metallic-glass specimen under small-punch loading. The intersecting of shear bands and the formation of profuse secondary shear bands are promoted under this confinement; accordingly, the failure mode changes from catastrophic fracture to stable multiple shear banding. Multiaxial confinement is an effective method to stabilize shear banding and further enhance the mechanical performance, especially the plastic deformation capability of metallic glass. These results present a simple step for making shear banding more stable and exploiting the shear-deformation capability of metallic glasses, leading to the toughening of brittle metallic glasses and potentially broadening their applications. [source] In situ Investigation of Structural Changes during Deformation and Fracture of Polymers by Synchrotron SAXS and WAXS,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Konrad Schneider By simultaneous mechanical characterisation and synchrotron wide-angle x-ray scattering (WAXS) and small-angle x-ray scattering (SAXS), it is possible to characterise on-line local changes in a polymer's structure with a rather-high time and space resolution, together with the mechanical properties. In this contribution, we discuss the experimental requirements for such investigations as well as three examples. The evolution of structural features during tensile deformation of a polyethylene copolymer, as depicted by WAXS (top) and SAXS (bottom) are shown in the figure. The deformation leads to a martensitic transformation from the orthorhombic to monoclinic system and the formation of nanocavities. [source] The Effect of the Superconducting Transition on Plastic Deformation of Ultrafine-Grained Aluminum,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2009Yuri Estrin Abstract In this paper, the mechanical behavior of ultrafine- and coarse-grained Al at a record low temperature of 0.52,K is presented. It is demonstrated that grain refinement by equal channel angular pressing leads to increased flow stress and to a change in the strain hardening behavior of Al at this temperature. Special emphasis is placed on the effect of the superconducting transition on the mechanical behavior in the different microstructural conditions. It is shown that the magnitude of the stress jump associated with the transition correlates with the strain hardening behavior which, in turn, is related to the microstructure of the material. [source] Suppression of Premature Fracture of Silicon under Three-Point Bending: Role of Nanoscale Localized Deformation of Metallic Multilayered Coating,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2009Yuan-Ping Li Brittle single crystal Si with and without Au/Cu multilayer coating was investigated via three-point bending test. Load-bearing capacity of the Si coated with the Au/Cu multilayer is improved evidently compared with the bare Si. Especially the nanoscale plastic deformation of the multilayer was observed to be effective in delaying instable crack propagation within the Si. That would shed significant light in toughening methods of brittle materials. [source] Analysis of Superplastic Deformation of AZ31 Magnesium Alloy,ADVANCED ENGINEERING MATERIALS, Issue 9 2007K. Abu-Farha AZ31 is a magnesium alloy possessing good mechanical properties, which makes it particularly attractive for automotive applications. Yet, in order to advance the utilization of this alloy, a broad database of its superplastic behavior is needed. This work presents the results of a comprehensive study on the elevated temperature superplastic behavior of the AZ31 magnesium alloy. Flow stress, fracture strain and strain sensitivity index maps were constructed over a wide range of strain rates, covering temperatures between 325 and 450 °C. [source] The Characterization of Local Deformation and Fracture Properties , a Tool for Advanced Materials Design,ADVANCED ENGINEERING MATERIALS, Issue 11 2006O. Kolednik Novel experimental techniques have been recently developed to measure local deformation and fracture properties. The techniques comprise quantitative fracture surface analysis and in-situ loading experiments in combination with digital image analysis. Examples are presented, demonstrating how these methods can be used to investigate the damage evolution in materials, to improve tools for the numerical simulation, and for the design of more fracture resistant materials and components. [source] Commercialization of Nanostructured Metals Produced by Severe Plastic Deformation ProcessingADVANCED ENGINEERING MATERIALS, Issue 5 2003T.C. Lowe Abstract The promise of nanotechnology is increasingly being realized as governments, universities, public and private research laboratories, and the various industrial sectors devote resources to this emerging area. Estimates for the economic impact of nanotechnology on existing global markets exceed 700 billion by the year 2008. Nanomaterials are projected to be one of the earliest components of nanotechnology to appear in commercial applications. Amongst the emerging new nanomaterials, bulk nanostructured metals produced by severe plastic deformation (SPD) have shown promise in a wide range of application areas. In this paper, we overview developments in severe plastic deformation technology, emphasizing progress since the international workshop "Investigations and Applications of Severe Plastic Deformation" held 2,8 August 1999 in Moscow, Russia. Then, we overview some of principal areas of application for SPD metals and alloys. [source] Influence of Deformation on Recrystallization of an Yttrium Oxide Dispersion-Strengthened Iron Alloy (PM2000),ADVANCED ENGINEERING MATERIALS, Issue 4 2003C. Capdevila Montes A two-fold effect of non-uniform deformation of the yttria-strengthened Fe alloy PM2000 has been revealed by analysis of the microstructure: Firstly, recrystallization temperature decreases, in accordance with the hypothesis that anything that makes the original microstructure more heterogeneous will encourage recrystallization; and secondly, the increase in number and density of recrystallization nuclei leads to fine grain structures which are more 3D isotropic. [source] Factors affecting fluid flow in strike,slip fault systems: coupled deformation and fluid flow modelling with application to the western Mount Isa Inlier, AustraliaGEOFLUIDS (ELECTRONIC), Issue 1 2009A. FORD Abstract Deformation and focused fluid flow within a mineralized system are critical in the genesis of hydrothermal ore deposits. Dilation and integrated fluid flux due to coupled deformation and fluid flow in simple strike,slip fault geometries were examined using finite difference analysis in three dimensions. A series of generic fault bend and fault jog geometries consistent with those seen in the western Mount Isa Inlier were modelled in order to understand how fault geometry parameters influence the dilation and integrated fluid flux. Fault dip, fault width, bend/jog angle, and length were varied, and a cross-cutting fault and contrasting rock types were included. The results demonstrate that low fault dips, the presence of contrasts in rock type, and wide faults produce highest dilation and integrated fluid flux values. Increasing fault bend lengths and angles increases dilation and integrated fluid flux, but increasing fault jog length or angle has the opposite effect. There is minimal difference between the outputs from the releasing and restraining fault bend and jog geometries. Model characteristics producing greater fluid flows and/or gradients can be used in a predictive capacity in order to focus exploration on regions with more favorable fault geometries, provided that the mineralized rocks had Mohr,Coulomb rheologies similar to the ones used in the models. [source] Fluid injection and surface deformation at the KTB location: modelling of expected tilt effectsGEOFLUIDS (ELECTRONIC), Issue 1 2005T. JAHR Abstract This investigation is indented to explore the relationship between changes in pore fluid pressure and deformation of the land surface induced by a large-scale injection experiment at the KTB site. Deformation will be monitored by ASKANIA borehole tiltmeters at five locations. During the year 2003, a network of borehole tiltmeters was installed, data transmission links established and tested, and recording of tilt data started. Our first main interest was to receive data sets of all stations well before the injection experiment to start in May 2004, to be able to evaluate local site effects. Thus, the separation of injection-induced effects will be more reliable. Principal 3D numerical modelling (poro-elastic modelling and investigations, using the finite element method, FEM) of poro-elastic behaviour showed that significant tilt amplitudes can be expected during controlled fluid injection. Observed deformation will be investigated within the framework of the fluid flow behaviour and resulting deformation. Two models have been used: a coupled hydro geomechanical finite element model (abaqus) and, as a first step, also a multi-layered poro-elastic crust (poel). With the numerical model two effects can be quantified: (i) the deformation of the upper crust (tilt measurements) and (ii) the spatial distribution and the changes of material properties in the KTB area. The main aim of the project is to improve the knowledge of coupled geomechanic,hydraulic processes and to quantify important parameters. Thus, the understanding of fracture-dominated changes of the hydrogeological parameters will be enhanced, geomechanical parameter changes and the heterogeneity of the parameter field quantified. In addition, the induced stress field variation can be explained, which is believed to be mainly responsible for the increase of local seismic activity. Here, we introduce the tiltmeter array at the KTB site, the modelling for a poro-elastic crust and the preliminary FEM modelling. [source] Deformation during exhumation of medium- and high-grade metamorphic rocks in the Variscan chain in northern Sardinia (Italy)GEOLOGICAL JOURNAL, Issue 3 2009Rodolfo Carosi Abstract The Anglona and SW Gallura regions represent key places to investigate the tectonic evolution of medium- and high-grade metamorphic rocks cropping out in northern Sardinia (Italy). From south to north we distinguish two different metamorphic complexes recording similar deformation histories but different metamorphic evolution: the Medium Grade Metamorphic Complex (MGMC) and the High Grade Metamorphic Complex (HGMC). After the initial collisional stage (D1 deformation phase), both complexes were affected by three contractional deformational phases (D2, D3 and D4) followed by later extensional tectonics. The D2 deformation phase was the most significant event producing an important deformation partitioning that produced localized shearing and folding domains at the boundary between the two metamorphic complexes. We highlight the presence of two previously undocumented systems of shear belts with different kinematics but analogous orientation in the axial zone of Sardinia. They became active at the boundary between the MGMC and HGMC from the beginning of D2. They formed a transpressive regime responsible for the exhumation of the medium- and high-grade metamorphic rocks, and overall represent a change from orthogonal to orogen-parallel tectonic transport. Copyright © 2008 John Wiley & Sons, Ltd. [source] Subducted slabs and lateral viscosity variations: effects on the long-wavelength geoidGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2009Nicola Tosi SUMMARY The characteristic broad local maxima exhibited by the long-wavelength geoid over subduction zones are investigated with a numerical model of mantle flow. In a spherical axisymmetric geometry, a synthetic model of buoyancy driven subduction is used to test the effects on the geoid caused by the depth of penetration of the lithosphere into the mantle, by the viscosity stratification and by lateral viscosity variations (LVV) in the lithosphere, upper and lower mantle. The presence of anomalous slab density in the lower mantle guarantees geoid amplitudes comparable with the observations, favouring the picture of slabs that penetrate the transition zone and sink into the deep mantle. The viscosity of the lower mantle controls the long-wavelength geoid to the first order, ensuring a clear positive signal when it is at least 30-times greater than the upper-mantle viscosity. The presence of LVV in the lithosphere, in the form of weak plate margins, helps to increase the contribution of the surface topography, causing a pronounced reduction of the geoid. Localized LVV associated with the cold slab play a secondary role if they are in the upper mantle. On the other hand, highly viscous slabs in the lower mantle exert a large influence on the geoid. They cause its amplitude to increase dramatically, way beyond the values typically observed over subduction zones. Long-wavelength flow becomes less vigorous as the slab viscosity increases. Deformation in the upper mantle becomes more localized and power is transferred to short wavelengths, causing the long-wavelength surface topography to diminish and the total geoid to increase. Slabs may be then weakened in the lower mantle or retain their high viscosity while other mechanisms act to lower the geoid. It is shown that a phase change from perovskite to post-perovskite above the core,mantle boundary can cause the geoid to reduce significantly, thereby helping to reconcile models and observations. [source] Deformation and stress change associated with plate interaction at subduction zones: a kinematic modellingGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2000Shaorong Zhao The interseismic deformation associated with plate coupling at a subduction zone is commonly simulated by the steady-slip model in which a reverse dip-slip is imposed on the down-dip extension of the locked plate interface, or by the backslip model in which a normal slip is imposed on the locked plate interface. It is found that these two models, although totally different in principle, produce similar patterns for the vertical deformation at a subduction zone. This suggests that it is almost impossible to distinguish between these two models by analysing only the interseismic vertical deformation observed at a subduction zone. The steady-slip model cannot correctly predict the horizontal deformation associated with plate coupling at a subduction zone, a fact that is proved by both the numerical modelling in this study and the GPS (Global Positioning System) observations near the Nankai trough, southwest Japan. It is therefore inadequate to simulate the effect of the plate coupling at a subduction zone by the steady-slip model. It is also revealed that the unphysical assumption inherent in the backslip model of imposing a normal slip on the locked plate interface makes it impossible to predict correctly the horizontal motion of the subducted plate and the stress change within the overthrust zone associated with the plate coupling during interseismic stages. If the analysis made in this work is proved to be correct, some of the previous studies on interpreting the interseismic deformation observed at several subduction zones based on these two models might need substantial revision. On the basis of the investigations on plate interaction at subduction zones made using the finite element method and the kinematic/mechanical conditions of the plate coupling implied by the present plate tectonics, a synthesized model is proposed to simulate the kinematic effect of the plate interaction during interseismic stages. A numerical analysis shows that the proposed model, designed to simulate the motion of a subducted slab, can correctly produce the deformation and the main pattern of stress concentration associated with plate coupling at a subduction zone. The validity of the synthesized model is examined and partially verified by analysing the horizontal deformation observed by GPS near the Nankai trough, southwest Japan. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||