Tensor-guided fitting of subduction slab depths

USGS Publications Warehouse

Bazargani, Farhad; Hayes, Gavin P.

2013-01-01

Geophysical measurements are often acquired at scattered locations in space. Therefore, interpolating or fitting the sparsely sampled data as a uniform function of space (a procedure commonly known as gridding) is a ubiquitous problem in geophysics. Most gridding methods require a model of spatial correlation for data. This spatial correlation model can often be inferred from some sort of secondary information, which may also be sparsely sampled in space. In this paper, we present a new method to model the geometry of a subducting slab in which we use a data‐fitting approach to address the problem. Earthquakes and active‐source seismic surveys provide estimates of depths of subducting slabs but only at scattered locations. In addition to estimates of depths from earthquake locations, focal mechanisms of subduction zone earthquakes also provide estimates of the strikes of the subducting slab on which they occur. We use these spatially sparse strike samples and the Earth’s curved surface geometry to infer a model for spatial correlation that guides a blended neighbor interpolation of slab depths. We then modify the interpolation method to account for the uncertainties associated with the depth estimates.

Imaging the Peruvian flat slab with Rayliegh wave tomography

NASA Astrophysics Data System (ADS)

Knezevic Antonijevic, Sanja

In subduction zones the oceanic plates descend at a broad range of dip angles. A "flat slab" is an oceanic plate that starts to subduct steeply, but bends at 100 km depth and continues almost horizontally for several hundred kilometers. This unusual slab geometry has been linked to various geologic features, including the cessation of arc volcanism, basement core uplifts removed far from subducting margins, and the formation of high plateaus. Despite the prevalence of flat slabs worldwide since the Proterozoic, questions on how flat slabs form, persist, and re-steepen remains a topic of ongoing research. Even less clear is how this phenomenon relates to unusual features observed at the surface. To better understand the causes and consequences of slab flattening I focus on the Peruvian flat slab. This is not only the biggest flat slab region today, but due to the oblique angle at which the Nazca Plate subducts under the South American Plate, it also provides unique opportunity to get insights into the temporal evolution of the flat slab. Using ambient noise and earthquake-generated Rayleigh waves recorded at several contemporary dense seismic networks, I was able to perform unprecedentedly high resolution imaging of the subduction zone in southern Peru. Surprisingly, instead of imaging a vast flat slab region as expected, I found that the flat slab tears and re-steepens north of the subducting Nazca Ridge. The change in slab geometry is associated with variations in the slab's internal strain along strike, as inferred from slab-related anisotropy. Based on newly-discovered features I discuss the critical role of the subducting ridges in the formation and longevity of flat slabs. The slab tear created a new mantle pathway between the torn slab and the flat slab remnant to the east, and is possibly linked to the profound low velocity anomaly located under the eastern corner of the flat slab. Finally, I re-evaluate the connection between slab flattening and volcanic patterns at the surface. These findings have important implications for all present-day and paleo-flat slab regions, such as the one proposed for the western United States during the Laramide orogeny 80-55 Ma.

Recommendations for design, construction, and maintenance of bridge approach slabs.

DOT National Transportation Integrated Search

2012-09-01

Settlement and heave related movements of bridge approach slabs relative to bridge decks create a bump in : the roadway. Several problems arise from these bumps, which include poor riding conditions, potential : vehicle damage, loss of vehicle contro...

Assessment of Design Tools and Criteria for Urban Rail Track Structures : Volume 2. At-Grade Slab Track.

DOT National Transportation Integrated Search

1974-04-01

This report presents the results of a critical review of the technical factors which govern the design and performance of at-grade slab track for urban rail systems. The assessment of current design practices is based on a review of the literature an...

Comment on: Diffusion through a slab

NASA Astrophysics Data System (ADS)

Gieseler, U. D. J.; Kirk, J. G.

1997-05-01

Mahan [J. Math. Phys. 36, 6758 (1995)] has calculated the transmission coefficient and angular distribution of particles which enter a thick slab at normal incidence and which diffuse in the slab with linear anisotropic, non-absorbing, scattering. Using orthogonality relations derived by McCormick and Kuščer [J. Math. Phys. 6, 1939 (1965); 7, 2036 (1966)] for the eigenfunctions of the problem, this calculation is generalized to a boundary condition with particle input at arbitrary angles. It is also shown how to use the orthogonality relations to relax in a simple way the restriction to a thick slab.

Green's function integral equation method for propagation of electromagnetic waves in an anisotropic dielectric-magnetic slab

NASA Astrophysics Data System (ADS)

Shu, Weixing; Lv, Xiaofang; Luo, Hailu; Wen, Shuangchun

2010-08-01

We extend the Green's function integral method to investigate the propagation of electromagnetic waves through an anisotropic dielectric-magnetic slab. From a microscopic perspective, we analyze the interaction of wave with the slab and derive the propagation characteristics by self-consistent analyses. Applying the results, we find an alternative explanation to the general mechanism for the photon tunneling. The results are confirmed by numerical simulations and disclose the underlying physics of wave propagation through slab. The method extended is applicable to other problems of propagation in dielectric-magnetic materials, including metamaterials.

Field demonstration of new bridge approach slab designs and performance.

DOT National Transportation Integrated Search

2014-06-01

The Louisiana Department of Transportation and Development (DOTD) has initiated a major effort to minimize the bridge end bump problem associated : with differential settlement. As a result, a new design for the approach slab was proposed, which requ...

Constraints on the Locations of Volcanic Arcs (August Love Medal Lecture)

NASA Astrophysics Data System (ADS)

England, Philip

2010-05-01

Partial melting of the mantle in subduction zones is a leading mechanism of chemical differentiation of the Earth. Whereas the broad outlines of Earth's other major system of partial melting - the oceanic ridges - seem clear, the greater dynamic and thermodynamic complexities of subduction zones obscure fundamental aspects of the system, in particular the conditions under which melting initiates and the pathways by which the melt travels towards the Earth's surface. The vast majority of studies of these problems rest on interrogation of petrological and/or geochemical data on rocks erupted at the volcanic arcs, but this approach has resulted in the co-existence of mutually incompatible explanations for the locations of the volcanic arcs. An alternative to the complexity of petrological and geochemical argument is to focus on the geometrical simplicity of volcanic arcs. The observations (i) that the fronts to volcanic arcs fit small circles to within about 10 km and (ii) that the depth to the slab beneath the arc fronts correlates negatively with the descent speed of the slab provide a strong clue to the melting processes occurring at depth. Localized release of fluids by reactions taking place near the top of the slab are incapable of explaining this correlation. However, scaling analysis based on the physics of heat transfer in the wedge shows that such a correlation is predicted if the location of the arcs is controlled by a temperature-critical process taking place in the mantle wedge above the slab. Numerical experiments using realistic physical properties for the mantle in subduction zones support the scaling analysis and, when combined with the observed positions of the arcs, strongly imply that the arcs are localized above the places where the mantle wedge reaches a critical temperature of ~1250o-1300oC. Therefore, despite the importance of hydrous fluids for the overall magmatic budget in subduction zones, it is melting in the region above the anhydrous solidus that determines the location of the arcs. Heat carried by magma rising from this region is sufficient to modify the thermal structure of the wedge and determine the pathway through which both wet and dry melts reach the surface.

Alternative and cost-effective bridge approach slabs.

DOT National Transportation Integrated Search

2010-10-01

The primary objectives of the proposed project are to investigate the causes for any bumps at the end of the bridge approach slab : and to develop remedial measures or alternative designs for a replacement. It is clear that the problem stems from geo...

Field demonstration of new bridge approach slab designs and performance : [tech summary].

DOT National Transportation Integrated Search

2014-06-01

The Louisiana Department of Transportation and Development (DOTD) has launched a major e ort to solve : the bridge bump problem by changing the design of approach slabs where di erential settlement is expected. : The objective is to nd a fe...

Analysis of Fan Waves in a Laboratory Model Simulating the Propagation of Shear Ruptures in Rocks

NASA Astrophysics Data System (ADS)

Tarasov, B. G.; Sadovskii, V. M.; Sadovskaya, O. V.

2017-12-01

The fan-shaped mechanism of rotational motion transmission in a system of elastically bonded slabs on flat surface, simulating the propagation of shear ruptures in super brittle rocks, is analyzed. Such ruptures appear in the Earth's crust at seismogenic depths. They propagate due to the nucleation of oblique tensile microcracks, leading to the formation of a fan domino-structure in the rupture head. A laboratory physical model was created which demonstrates the process of fan-structure wave propagation. Equations of the dynamics of rotational motion of slabs as a mechanical system with a finite number of degrees of freedom are obtained. Based on the Merson method of solving the Cauchy problem for systems of ordinary differential equations, the computational algorithm taking into account contact interaction of slabs is developed. Within the framework of a simplified mathematical model of dynamic behavior of a fan-shaped system in the approximation of a continuous medium, the approximate estimates of the length of a fan depending on the velocity of its motion are obtained. It is shown that in the absence of friction a fan can move with any velocity that does not exceed the critical value, which depends on the size, the moment of inertia of slabs, the initial angle and the elasticity coefficient of bonds. In the presence of friction a fan stops. On the basis of discrete and continuous models, the main qualitative features of the behavior of a fan-structure moving under the action of applied tangential forces, whose values in a laboratory physical model are regulated by a change in the inclination angle of the rupture plane, are analyzed. Comparison of computations and laboratory measurements and observations shows good correspondence between the results.

Elimination of deck joints using a corrosion resistant FRP approach

NASA Astrophysics Data System (ADS)

Aleti, Ashok Reddy

The research presented herein describes the development of durable link slabs for jointless bridge decks based on using FRP grid for reinforcement. Specifically, the ductility of the FRP material was utilized to accommodate bridge deck deformations imposed by girder deflection, temperature variations, and concrete shrinkage. It would also provide a solution to a number of deterioration problems associated with bridge deck joints. The design concept of the link slabs was then examined to form the basis of design for FRP grid link slabs. Improved design of FRP grid link slab/concrete deck slab interface was confirmed in the numerical analysis. The mechanical properties between the FRP grid and concrete were evaluated. The behavior of the link slab was investigated and confirmed for durability. The results indicated that the technique would allow simultaneous achievement of structural need (lower flexural stiffness of the link slab approaching the behavior of a hinge) and durability need of the link slab. Also, the development length results confirm that the bond between the FRP grid and the concrete was highly improved. The overall investigation supports the contention that durable jointless concrete bridge decks may be designed and constructed with FRP grid link slabs. It is recommended that the link slab technique be used during new construction of the bridge decks and in repair and retrofit of the bridge decks.

Development of concrete mix proportions for minimizing/eliminating shrinkage cracks in slabs and high performance grouts : final report.

DOT National Transportation Integrated Search

2017-02-01

The two focus areas of this research address longstanding problems of (1) cracking of concrete slabs due to creep and shrinkage and (2) high performance compositions for grouting and joining precast concrete structural elements. Cracking of bridge de...

Free Energy Minimization by Simulated Annealing with Applications to Lithospheric Slabs and Mantle Plumes

NASA Astrophysics Data System (ADS)

Bina, C. R.

An optimization algorithm based upon the method of simulated annealing is of utility in calculating equilibrium phase assemblages as functions of pressure, temperature, and chemical composi tion. Operating by analogy to the statistical mechanics of the chemical system, it is applicable both to problems of strict chemical equilibrium and to problems involving metastability. The method reproduces known phase diagrams and illustrates the expected thermal deflection of phase transitions in thermal models of subducting lithospheric slabs and buoyant mantle plumes. It reveals temperature-induced changes in phase transition sharpness and the stability of Fe-rich γ phase within an α+γ field in cold slab thermal models, and it suggests that transitions such as the possible breakdown of silicate perovskite to mixed oxides can amplify velocity anomalies.

Hydration-reduced lattice thermal conductivity of olivine in Earth's upper mantle.

PubMed

Chang, Yun-Yuan; Hsieh, Wen-Pin; Tan, Eh; Chen, Jiuhua

2017-04-18

Earth's water cycle enables the incorporation of water (hydration) in mantle minerals that can influence the physical properties of the mantle. Lattice thermal conductivity of mantle minerals is critical for controlling the temperature profile and dynamics of the mantle and subducting slabs. However, the effect of hydration on lattice thermal conductivity remains poorly understood and has often been assumed to be negligible. Here we have precisely measured the lattice thermal conductivity of hydrous San Carlos olivine (Mg 0.9 Fe 0.1 ) 2 SiO 4 (Fo90) up to 15 gigapascals using an ultrafast optical pump-probe technique. The thermal conductivity of hydrous Fo90 with ∼7,000 wt ppm water is significantly suppressed at pressures above ∼5 gigapascals, and is approximately 2 times smaller than the nominally anhydrous Fo90 at mantle transition zone pressures, demonstrating the critical influence of hydration on the lattice thermal conductivity of olivine in this region. Modeling the thermal structure of a subducting slab with our results shows that the hydration-reduced thermal conductivity in hydrated oceanic crust further decreases the temperature at the cold, dry center of the subducting slab. Therefore, the olivine-wadsleyite transformation rate in the slab with hydrated oceanic crust is much slower than that with dry oceanic crust after the slab sinks into the transition zone, extending the metastable olivine to a greater depth. The hydration-reduced thermal conductivity could enable hydrous minerals to survive in deeper mantle and enhance water transportation to the transition zone.

A Numerical Method for Obtaining Monoenergetic Neutron Flux Distributions and Transmissions in Multiple-Region Slabs

NASA Technical Reports Server (NTRS)

Schneider, Harold

1959-01-01

This method is investigated for semi-infinite multiple-slab configurations of arbitrary width, composition, and source distribution. Isotropic scattering in the laboratory system is assumed. Isotropic scattering implies that the fraction of neutrons scattered in the i(sup th) volume element or subregion that will make their next collision in the j(sup th) volume element or subregion is the same for all collisions. These so-called "transfer probabilities" between subregions are calculated and used to obtain successive-collision densities from which the flux and transmission probabilities directly follow. For a thick slab with little or no absorption, a successive-collisions technique proves impractical because an unreasonably large number of collisions must be followed in order to obtain the flux. Here the appropriate integral equation is converted into a set of linear simultaneous algebraic equations that are solved for the average total flux in each subregion. When ordinary diffusion theory applies with satisfactory precision in a portion of the multiple-slab configuration, the problem is solved by ordinary diffusion theory, but the flux is plotted only in the region of validity. The angular distribution of neutrons entering the remaining portion is determined from the known diffusion flux and the remaining region is solved by higher order theory. Several procedures for applying the numerical method are presented and discussed. To illustrate the calculational procedure, a symmetrical slab ia vacuum is worked by the numerical, Monte Carlo, and P(sub 3) spherical harmonics methods. In addition, an unsymmetrical double-slab problem is solved by the numerical and Monte Carlo methods. The numerical approach proved faster and more accurate in these examples. Adaptation of the method to anisotropic scattering in slabs is indicated, although no example is included in this paper.

Geometrical optics of dense aerosols: forming dense plasma slabs.

PubMed

Hay, Michael J; Valeo, Ernest J; Fisch, Nathaniel J

2013-11-01

Assembling a freestanding, sharp-edged slab of homogeneous material that is much denser than gas, but much more rarefied than a solid, is an outstanding technological challenge. The solution may lie in focusing a dense aerosol to assume this geometry. However, whereas the geometrical optics of dilute aerosols is a well-developed field, the dense aerosol limit is mostly unexplored. Yet controlling the geometrical optics of dense aerosols is necessary in preparing such a material slab. Focusing dense aerosols is shown here to be possible, but the finite particle density reduces the effective Stokes number of the flow, a critical result for controlled focusing.

Laser beat wave excitation of terahertz radiation in a plasma slab

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chauhan, Santosh; Parashar, Jetendra, E-mail: j.p.parashar@gmail.com

2014-10-15

Terahertz (THz) radiation generation by nonlinear mixing of lasers, obliquely incident on a plasma slab is investigated. Two cases are considered: (i) electron density profile is parabolic but density peak is below the critical density corresponding to the beat frequency, (ii) plasma boundaries are sharp and density is uniform. In both cases, nonlinearity arises through the ponderomotive force that gives rise to electron drift at the beat frequency. In the case of inhomogeneous plasma, non zero curl of the nonlinear current density gives rise to electromagnetic THz generation. In case of uniform plasma, the sharp density variation at the plasmamore » boundaries leads to radiation generation. In a slab width of less than a terahertz wavelength, plasma density one fourth of terahertz critical density, laser intensities ∼10{sup 17 }W/cm{sup 2} at 1 μm, one obtains the THz intensity ∼1 GW/cm{sup 2} at 3 THz radiation frequency.« less

Research on Soft Reduction Amount Distribution to Eliminate Typical Inter-dendritic Crack in Continuous Casting Slab of X70 Pipeline Steel by Numerical Model

NASA Astrophysics Data System (ADS)

Liu, Ke; Wang, Chang; Liu, Guo-liang; Ding, Ning; Sun, Qi-song; Tian, Zhi-hong

2017-04-01

To investigate the formation of one kind of typical inter-dendritic crack around triple point region in continuous casting(CC) slab during the operation of soft reduction, fully coupled 3D thermo-mechanical finite element models was developed, also plant trials were carried out in a domestic continuous casting machine. Three possible types of soft reduction amount distribution (SRAD) in the soft reduction region were analyzed. The relationship between the typical inter-dendritic cracks and soft reduction conditions is presented and demonstrated in production practice. Considering the critical strain of internal crack formation, a critical tolerance for the soft reduction amount distribution and related casing parameters have been proposed for better contribution of soft reduction to the internal quality of slabs. The typical inter-dendritic crack around the triple point region had been eliminated effectively through the application of proposed suggestions for continuous casting of X70 pipeline steel in industrial practice.

High-quality slab-based intermixing method for fusion rendering of multiple medical objects.

PubMed

Kim, Dong-Joon; Kim, Bohyoung; Lee, Jeongjin; Shin, Juneseuk; Kim, Kyoung Won; Shin, Yeong-Gil

2016-01-01

The visualization of multiple 3D objects has been increasingly required for recent applications in medical fields. Due to the heterogeneity in data representation or data configuration, it is difficult to efficiently render multiple medical objects in high quality. In this paper, we present a novel intermixing scheme for fusion rendering of multiple medical objects while preserving the real-time performance. First, we present an in-slab visibility interpolation method for the representation of subdivided slabs. Second, we introduce virtual zSlab, which extends an infinitely thin boundary (such as polygonal objects) into a slab with a finite thickness. Finally, based on virtual zSlab and in-slab visibility interpolation, we propose a slab-based visibility intermixing method with the newly proposed rendering pipeline. Experimental results demonstrate that the proposed method delivers more effective multiple-object renderings in terms of rendering quality, compared to conventional approaches. And proposed intermixing scheme provides high-quality intermixing results for the visualization of intersecting and overlapping surfaces by resolving aliasing and z-fighting problems. Moreover, two case studies are presented that apply the proposed method to the real clinical applications. These case studies manifest that the proposed method has the outstanding advantages of the rendering independency and reusability. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Review of Punching Shear Behaviour of Flat Slabs Reinforced with FRP Bars

NASA Astrophysics Data System (ADS)

Mohamed, Osama A.; Khattab, Rania

2017-10-01

Using Fibre Reinforced Polymer (FRP) bars to reinforce two-way concrete slabs can extend the service life, reduce maintenance cost and improve-life cycle cost efficiency. FRP reinforcing bars are more environmentally friendly alternatives to traditional reinforcing steel. Shear behaviour of reinforced concrete structural members is a complex phenomenon that relies on the development of internal load-carrying mechanisms, the magnitude and combination of which is still a subject of research. Many building codes and design standards provide design formulas for estimation of punching shear capacity of FRP reinforced flat slabs. Building code formulas take into account the effects of the axial stiffness of main reinforcement bars, the ratio of the perimeter of the critical section to the slab effective depth, and the slab thickness on the punching shear capacity of two-way slabs reinforced with FRP bars or grids. The goal of this paper is to compare experimental data published in the literature to the equations offered by building codes for the estimation of punching shear capacity of concrete flat slabs reinforced with FRP bars. Emphasis in this paper is on two North American codes, namely, ACI 440.1R-15 and CSA S806-12. The experimental data covered in this paper include flat slabs reinforced with GFRP, BFRP, and CFRP bars. Both ACI 440.1R-15 and CSA S806-12 are shown to be in good agreement with test results in terms of predicting the punching shear capacity.

Viscous Dissipation and Criticality of Subducting Slabs

NASA Astrophysics Data System (ADS)

Riedel, Mike; Karato, Shun; Yuen, Dave

2016-04-01

Rheology of subducting lithosphere appears to be complicated. In the shallow part, deformation is largely accomodated by brittle failure, whereas at greater depth, at higher confining pressures, ductile creep is expected to control slab strength. The amount of viscous dissipation ΔQ during subduction at greater depth, as constrained by experimental rock mechanics, can be estimated on the basis of a simple bending moment equation [1,2] 2ɛ˙0(z) ∫ +h/2 2 M (z) = h ṡ -h/2 4μ(y,z)y dy , (1) for a complex multi-phase rheology in the mantle transition zone, including the effects of a metastable phase transition as well as the pressure, temperature, grain-size and stress dependency of the relevant creep mechanisms; μ is here the effective viscosity and ɛ˙0(z) is a (reference) strain rate. Numerical analysis shows that the maximum bending moment, Mcrit, that can be sustained by a slab is of the order of 1019 Nm per m according to Mcrit˜=σp ∗h2/4, where σp is the Peierl's stress limit of slab materials and h is the slab thickness. Near Mcrit, the amount of viscous dissipation grows strongly as a consequence of a lattice instability of mantle minerals (dislocation glide in olivine), suggesting that thermo-mechanical instabilities become prone to occur at places where a critical shear-heating rate is exceeded, see figure. This implies that the lithosphere behaves in such cases like a perfectly plastic solid [3]. Recently available detailed data related to deep seismicity [4,5] seems to provide support to our conclusion. It shows, e.g., that thermal shear instabilities, and not transformational faulting, is likely the dominating mechanism for deep-focus earthquakes at the bottom of the transition zone, in accordance with this suggested "deep criticality" model. These new findings are therefore briefly outlined and possible implications are discussed. References [1] Riedel, M. R., Karato, S., Yuen, D. A. Criticality of Subducting Slabs. University of Minnesota Supercomputing Institute Research Report, UMSI 99/129: 21 pages, 1999. [2] Karato, S., Riedel, M. R., Yuen, D. A. Rheological structure and deformation of subducted slabs in the mantle transition zone: implications for mantle circulation and deep earthquakes. Physics of the Earth and Planetary Interiors, 127, doi:10.1016/S0031-9201(01)00223-0, 2001. [3] Buffett, B. A., Becker, T. W., Bending stress and dissipation in subducted lithosphere. Journal of Geophysical Research, 117, doi:10.1029/2012JB009205, 2012. [4] Zhan, Z., Kanamori, H., Tsai, V. C., Helmberger, D. V., Wei, S., Rupture complexity of the 1994 Bolivia and 2013 Sea of Okhotsk deep earthquakes. Earth and Planetary Science Letters, 385, doi:10.1016/j.epsl.2013.10.028, 2014. [5] Meng, L., Ampuero, J.-P., Bürgmann, R., The 2013 Okhotsk deep-focus earthquake: Rupture beyond the metastable olivine wedge and thermally controlled rise time near the edge of a slab. Geophys. Res. Lett., 41, doi:10.1002/2014GL059968, 2014.

Nanoscale Properties of Rocks and Subduction Zone Rheology: Inferences for the Mechanisms of Deep Earthquakes

NASA Astrophysics Data System (ADS)

Riedel, M. R.

2007-12-01

Grain boundaries are the key for the understanding of mineral reaction kinetics. More generally, nanometer scale processes involved in breaking and establishing bonds at reaction sites determine how and at which rate bulk rock properties change in response to external tectonic forcing and possibly feed back into various geodynamic processes. A particular problem is the effects of grain-boundary energy on the kinetics of the olivine-spinel phase transformation in subducting slabs. Slab rheology is affected in many ways by this (metastable) mineral phase change. Sluggish kinetics due to metastable hindrance is likely to cause particular difficulties, because of possible strong non-linear feedback loops between strain-rate and change of creep properties during transformation. In order to get these nanoscale properties included into thermo-mechanical models, reliable kinetic data is required. The measurement of grain-boundary energies is, however, a rather difficult problem. Conventional methods of grain boundary surface tension measurement include (a) equilibrium angles at triple junction (b) rotating ball method (c) thermal groove method, and others (Gottstein & Shvindlerman, 1999). Here I suggest a new method that allows for the derivation of grain-boundary energies for an isochemical phase transformation based on experimental (in-situ) kinetic data in combination with a corresponding dynamic scaling law (Riedel and Karato, 1997). The application of this method to the olivine-spinel phase transformation in subducting slabs provides a solution to the extrapolation problem of measured kinetic data: Any kinetic phase boundary measured at the laboratory time scale can be "scaled" to the correct critical isotherm at subduction zones, under experimentelly "forbidden" conditions (Liou et al., 2000). Consequences for the metastability hypothesis that relates deep seismicity with olivine metastability are derived and discussed. References: Gottstein G, Shvindlerman LS (1999) Grain Boundary Migration in Metals, CRC Press, 385 pp., New York. Riedel MR, Karato S (1997) Grain-Size Evolution in Subducted Oceanic Lithosphere Associated with the Olivine- Spinel Transformation and Its Effects on Rheology. EPSL 148: 27-43. Liou JG, Hacker BR, Zhang RY (2000) Into the forbidden zone. Science 287, 1215-1216.

An analytical approach for the Propagation Saw Test

NASA Astrophysics Data System (ADS)

Benedetti, Lorenzo; Fischer, Jan-Thomas; Gaume, Johan

2016-04-01

The Propagation Saw Test (PST) [1, 2] is an experimental in-situ technique that has been introduced to assess crack propagation propensity in weak snowpack layers buried below cohesive snow slabs. This test attracted the interest of a large number of practitioners, being relatively easy to perform and providing useful insights for the evaluation of snow instability. The PST procedure requires isolating a snow column of 30 centimeters of width and -at least-1 meter in the downslope direction. Then, once the stratigraphy is known (e.g. from a manual snow profile), a saw is used to cut a weak layer which could fail, potentially leading to the release of a slab avalanche. If the length of the saw cut reaches the so-called critical crack length, the onset of crack propagation occurs. Furthermore, depending on snow properties, the crack in the weak layer can initiate the fracture and detachment of the overlying slab. Statistical studies over a large set of field data confirmed the relevance of the PST, highlighting the positive correlation between test results and the likelihood of avalanche release [3]. Recent works provided key information on the conditions for the onset of crack propagation [4] and on the evolution of slab displacement during the test [5]. In addition, experimental studies [6] and simplified models [7] focused on the qualitative description of snowpack properties leading to different failure types, namely full propagation or fracture arrest (with or without slab fracture). However, beside current numerical studies utilizing discrete elements methods [8], only little attention has been devoted to a detailed analytical description of the PST able to give a comprehensive mechanical framework of the sequence of processes involved in the test. Consequently, this work aims to give a quantitative tool for an exhaustive interpretation of the PST, stressing the attention on important parameters that influence the test outcomes. First, starting from a pure mechanical point of view, a broad phenomenology of the main failure types of the PST is outlined. Then, the Euler-Bernoulli beam theory is applied to the test setup, allowing an easy description of the snowpack stress state in the quasi-static regime. We assume an elastic-perfectly brittle model as constitutive law for the snow slab. Besides, considering the weak layer as a rigid bed of crystals with an a priori inclination, a local instability problem is formulated in order to take into account the combined effect of compressive and shear loading. As a result, the onset of slab and weak layer fracture is described in terms of cut length, slab dimensions and the main mechanical parameters. A condition on the possible propagation of the crack is proposed as well. References [1] C. Sigrist and J. Schweizer, "Critical energy release rates of weak snowpack layers determined in field experiments", Geophysical Research Letters, Volume 34, L03502, 2007. [2] D. Gauthier and B. Jamieson, "Evaluation of a prototype field test for fracture and failure propagation propensity in weak snowpack layers". Cold Regions Science and Technology, Volume 51, Issue 2, Pages 87-97, 2008. [3] R. Simenhois and K.W. Birkeland. "The extended column test: Test effectiveness, spatial variability, and comparison with the propagation saw test." Cold Regions Science and Technology, Volume 59, Issue 23, Pages 210-216, 2009. [4] J. Heierli, P. Gumbsch, M. Zaiser, "Anticrack Nucleation as Triggering Mecchanism for Snow Slab Avalanches", Science, Volume 321, Pages 240-243, 2008. [5] A. van Herwijnen, J. Schweizer, J. Heierli, "Measurement of the deformation field associated with fracture propagation in weak snowpack layers", Journal of Geophysical Research, Volume 115, F03042, 2010. [6] K. W. Birkeland, A. van Herwijnen, E. Knoff, M. Staples, E. Bair, R. Simenhois, "The role of slabs and weak layers in fracture arrest", Proceedings of the International Snow Science Workshop, Banff, 2014. [7] J. Schweizer, B. Reuter, A. van Herwijnen, B. Jamieson, "On how the tensile strength of the slab affects crack propagation propensity", Proceedings of the International Snow Science Workshop, Banff, 2014. [8] J. Gaume, A. van Herwijnen, G. Chambon, K. W. Birkeland, J. Schweizer. "Modeling of crack propagation in weak snowpack layers using the discrete element method", The Cryosphere, Volume 9, Pages 1915-1932, 2015.

Dynamic triggering of deep earthquakes within a fossil slab

NASA Astrophysics Data System (ADS)

Cai, Chen; Wiens, Douglas A.

2016-09-01

The 9 November 2009 Mw 7.3 Fiji deep earthquake is the largest event in a region west of the Tonga slab defined by scattered seismicity and velocity anomalies. The main shock rupture was compact, but the aftershocks were distributed along a linear feature at distances of up to 126 km. The aftershocks and some background seismicity define a sharp northern boundary to the zone of outboard earthquakes, extending westward toward the Vitiaz deep earthquake cluster. The northern earthquake lineament is geometrically similar to tectonic reconstructions of the relict Vitiaz subduction zone at 8-10 Ma, suggesting the earthquakes are occurring in the final portion of the slab subducted at the now inactive Vitiaz trench. A Coulomb stress change calculation suggests many of the aftershocks were dynamically triggered. We propose that fossil slabs contain material that is too warm for earthquake nucleation but may be near the critical stress susceptible to dynamic triggering.

Hydration-reduced lattice thermal conductivity of olivine in Earth’s upper mantle

PubMed Central

Chang, Yun-Yuan; Hsieh, Wen-Pin; Tan, Eh; Chen, Jiuhua

2017-01-01

Earth’s water cycle enables the incorporation of water (hydration) in mantle minerals that can influence the physical properties of the mantle. Lattice thermal conductivity of mantle minerals is critical for controlling the temperature profile and dynamics of the mantle and subducting slabs. However, the effect of hydration on lattice thermal conductivity remains poorly understood and has often been assumed to be negligible. Here we have precisely measured the lattice thermal conductivity of hydrous San Carlos olivine (Mg0.9Fe0.1)2SiO4 (Fo90) up to 15 gigapascals using an ultrafast optical pump−probe technique. The thermal conductivity of hydrous Fo90 with ∼7,000 wt ppm water is significantly suppressed at pressures above ∼5 gigapascals, and is approximately 2 times smaller than the nominally anhydrous Fo90 at mantle transition zone pressures, demonstrating the critical influence of hydration on the lattice thermal conductivity of olivine in this region. Modeling the thermal structure of a subducting slab with our results shows that the hydration-reduced thermal conductivity in hydrated oceanic crust further decreases the temperature at the cold, dry center of the subducting slab. Therefore, the olivine−wadsleyite transformation rate in the slab with hydrated oceanic crust is much slower than that with dry oceanic crust after the slab sinks into the transition zone, extending the metastable olivine to a greater depth. The hydration-reduced thermal conductivity could enable hydrous minerals to survive in deeper mantle and enhance water transportation to the transition zone. PMID:28377520

The significance of slab-crusted lava flows for understanding controls on flow emplacement at Mount Etna, Sicily

NASA Astrophysics Data System (ADS)

Guest, John E.; Stofan, Ellen R.

2005-04-01

Slab-crusted flows on Mount Etna, Sicily are defined here as those whose crust has ridden on the flow core without significant disruption or deformation and have a high length to width ratio. They typically erupt from ephemeral boccas as late-stage products on dominantly aa flow fields, such as that of the 1983 eruption on Mount Etna. Slab-crusted flows tend to inflate mainly as they approach and after they reach the maximum length of slab-crust formation, the flow interior acting as a preferential pathway for injecting lava under a stable crust. Coalescence of vesicles under successive crusts causes separation between core and crust giving a new cooling surface within the flow, on which ropy surfaces (and occasionally aa textures) of limited areal extent may develop. Slab-crusted flows tend to form at ephemeral boccas together with other surface textural types including toes, ropy pahoehoe sheets and aa flows. This suggests that, on Etna, slab-crusted flows form from lava of the same rheological properties as both aa and pahoehoe textured flows. They do not represent a transition between aa and pahoehoe as argued for toothpaste flows in Hawaii. We conclude that slab-crusted flows on Etna owe their morphology to a relatively high critical ratio of effusion rate to advance rate, related to vent cross-sectional area and the slope over which the flow forms.

Meteorological variables associated with deep slab avalanches on persistent weak layers

USGS Publications Warehouse

Marienthal, Alex; Hendrikx, Jordy; Birkeland, Karl; Irvine, Kathryn M.

2014-01-01

Deep slab avalanches are a particularly challenging avalanche forecasting problem. These avalanches are typically difficult to trigger, yet when they are triggered they tend to propagate far and result in large and destructive avalanches. For this work we define deep slab avalanches as those that fail on persistent weak layers deeper than 0.9m (3 feet), and that occur after February 1st. We utilized a 44-year record of avalanche control and meteorological data from Bridger Bowl Ski Area to test the usefulness of meteorological variables for predicting deep slab avalanches. As in previous studies, we used data from the days preceding deep slab cycles, but we also considered meteorological metrics over the early months of the season. We utilized classification trees for our analyses. Our results showed warmer temperatures in the prior twenty-four hours and more loading over the seven days before days with deep slab avalanches on persistent weak layers. In line with previous research, extended periods of above freezing temperatures led to days with deep wet slab avalanches on persistent weak layers. Seasons with either dry or wet avalanches on deep persistent weak layers typically had drier early months, and often had some significant snow depth prior to those dry months. This paper provides insights for ski patrollers, guides, and avalanche forecasters who struggle to forecast deep slab avalanches on persistent weak layers late in the season.

Pitch angle scattering in three-dimensional "critical balance" MHD turbulence.

NASA Astrophysics Data System (ADS)

Forman, Miriam; Oughton, Sean; Horbury, Tim

2004-11-01

We calculated the dependence of the quasi-linear particle pitch angle scattering coefficient in general 3-dimensional turbulence axi-symmetric about the mean magnetic field. We integrate over the power spectrum tensor of the turbulence in terms of the scalar functions E, F, C, and H of the wavevector k, as described by Oughton, et al. for incompressible MHD. The application to a "slab+ 2.5D" model is trivial, and reproduces Bieber, et al.'s extremely important previous result that the 2.5D part does not do any pitch-angle scattering. However, the "slab + 2D" is a highly idealized model. One wonders how its two parts are related to actual turbulence, as observed in space or in simulations, and to the calculation of the particle scattering. Here we update the "slab + 2D" model to a more realistic distribution in k-space, specifically a modification of the inertial-range "critical balance" form introduced by Goldreich and Sridhar, and developed further by Cho, Lazarian and Vishniac. We apply the 3D quasi-linear method to calculate D and the spatial diffusion coefficient parallel to the local mean magnetic field, in the "critical balance" anisotropic turbulence. We thank the International Space Science Institute (Bern, Switzerland) for support of this work.

Subduction of Young Lithosphere at Critical Thermal Ages (10-20 Ma): Incites From Thermal Models and the Trans-Mexican Subduction System with Emphasis on the Importance of Slab Travel Times

NASA Astrophysics Data System (ADS)

Grose, C. J.

2007-12-01

The Trans-Mexican Volcanic Belt (TMVB) is a system where the age range of subducting plates is typically thought of as critical in their relation to lithospheric thermal structure (~10-20 Ma). I refer to this age range as "critical" because it is in this range where thermal lithospheres begin to rapidly decrease their correlative influence on the thermal state of the subduction system above the crust/mantle wedge interface for most systems. After ~20 Ma the cool upper portion of downgoing lithosphere becomes sufficiently thick so that crustal reheating and corresponding heat flow in the time between trench subduction and the zone of melt generation, due to the accumulation of conductive and frictional heating, behaves somewhat similarly with little regard to age. Typical slab travel times are on the order of 1.5-2.5 My. However, low dip angles and flat-slab behavior in the Eastern end of the TMVB facilitates anomalously long travel times exceeding 6.5 My! Here I show that while the influence of plate age is clearly significant in determining the holistic thermal geodynamics of subduction systems, the influence can be dampened or enhanced by auxiliary factors. I present thermal modeling cases using a solution for the conduction of heat into an evolving semi-infinite half-space with variable boundary conditions. Preliminary results indicate that extraordinary slab travel times and flat-slab behavior, mantle wedge advection regimes, and plate age thermally enhance and dampen each other. Geochemically, the TMVB shows consistent along-arc changes in light element abundance systematics (B/Be, Li/Yb, Be/Zr). Moderately elevated B/Be (Easterly increases from ~4 to ~12 ppm B/Be) observed in the eastern shallow subduction region is thought to correlate with subduction of an older, cooler portion of the slab. However, greater slab travel times in the Eastern TVMB should simultaneously act to warm the slab and depreciate these values which may partly explain the minimal consistency and magnitude of the TMVB along-arc variations. Li/Yb has a more impressive range of correlative along-arc variation, argued to be the result of greater extents of melting in the east. This can be explained by increased dehydration melting (due to a cooler slab and longer H20 residence times in the slab), a warmer slab affect, or changes in the mean depth of amphibole and garnet crystallization. While elevated B and B/Be values in the eastern TMVB correlate with increased hydration melting, it is likely that the affect is dampened by the positive thermal affects of greater travel times. Comparison to arc rocks in subduction further to the east in Central America, particularly Guatemala, whose B abundance and B/Be ratios are much more elevated (20-70 ppm B/Be) and show convergence on those in the Eastern TMVB. I suggest that the minimal range of B/Be variation seen in the TMVB arc is a result of the extraordinary slab travel times associated with shallow subduction in the eastern TMVB. Furthermore, similar to the B/Be data, the depleted Li/Yb (relative to the rifting region encompassing the Jalisco block) of the Eastern end also continues to converge on values represented in the Central American arc, indicating that the strong variations seen in the TMVB are primarily due to crystallization instead of extents of melting. Thermal modeling results presented here show that sources aside from plate age are capable and likely have influenced the systematic correlations observed in the TMVB and this hypothesis is consistent with the LREE data.

Electromagnetic scattering from two-dimensional thick material junctions

NASA Technical Reports Server (NTRS)

Ricoy, M. A.; Volakis, John L.

1990-01-01

The problem of the plane wave diffraction is examined by an arbitrary symmetric two dimensional junction, where Generalized Impedance Boundary Conditions (GIBCs) and Generalized Sheet Transition Conditions (GSTCs) are employed to simulate the slabs. GIBCs and GSTCs are constructed for multilayer planar slabs of arbitrary thickness and the resulting GIBC/GSTC reflection coefficients are compared with exact counterparts to evaluate the GIBCs/GSTCs. The plane wave diffraction by a multilayer material slab recessed in a perfectly conducting ground plane is formulated and solved via the Generalized Scattering Matrix Formulation (GDMF) in conjunction with the dual integral equation approach. Various scattering patterns are computed and validated with exact results where possible. The diffraction by a material discontinuity in a thick dielectric/ferrite slab is considered by modelling the constituent slabs with GSTCs. A non-unique solution in terms of unknown constants is obtained, and these constants are evaluated for the recessed slab geometry by comparison with the solution obtained therein. Several other simplified cases are also presented and discussed. An eigenfunction expansion method is introduced to determine the unknown solution constants in the general case. This procedure is applied to the non-unique solution in terms of unknown constants; and scattering patterns are presented for various slab junctions and compared with alternative results where possible.

Reasonable Temperature Schedules for Cold or Hot Charging of Continuously Cast Steel Slabs

NASA Astrophysics Data System (ADS)

Li, Yang; Chen, Xin; Liu, Ke; Wang, Jing; Wen, Jin; Zhang, Jiaquan

2013-12-01

Some continuously cast steel slabs are sensitive to transverse fracture problems during transportation or handling away from their storage state, while some steel slabs are sensitive to surface transverse cracks during the following rolling process in a certain hot charging temperature range. It is revealed that the investigated steel slabs with high fracture tendency under room cooling condition always contain pearlite transformation delayed elements, which lead to the internal brittle bainitic structure formation, while some microalloyed steels exhibit high surface crack susceptibility to hot charging temperatures due to carbonitride precipitation. According to the calculated internal cooling rates and CCT diagrams, the slabs with high fracture tendency during cold charging should be slowly cooled after cutting to length from hot strand or charged to the reheating furnace directly above their bainite formation temperatures. Based on a thermodynamic calculation for carbonitride precipitation in austenite, the sensitive hot charging temperature range of related steels was revealed for the determination of reasonable temperature schedules.

Focusing fluids towards the arc: the role of rheology and reactions

NASA Astrophysics Data System (ADS)

Wilson, C. R.; Spiegelman, M. W.

2014-12-01

Aqueous fluids released from the down-going slab in subduction zones are generally thought to be the cause of arc volcanism. However there is a significant discrepancy between the consistent location of the volcanic front with respect to intermediate depth earthquakes (e.g. 100+/-40 km; England et al., GJI, 2004, Syracuse & Abers, G-cubed, 2006) and the large depth range over which dehydration reactions are predicted to occur in the slab (e.g. 80-250 km; van Keken et al., JGR, 2011). By coupling the fluid flow to the solid rheology through compaction pressure, recent numerical models (Wilson et al., EPSL, 2014) demonstrated a number of focusing mechanisms that can be invoked to explain this apparent discrepancy. Most notable among these were permeability channels within the slab. These were shown to be highly effective in transporting fluid from deeper fluid sources along the slab towards the shallowest source. In the presence of these channels the majority of the fluid is released into the mantle wedge far shallower and closer to the arc than it was originally generated. While observations consistent with free fluids in the slab have been reported (e.g. Shiina et al., GRL, 2013), it is possible that changing the rheology and reactivity of the slab can change the efficiency of in-slab transport. We present a series of simplified model problems of fluid flow within the slab and mantle wedge demonstrating the potential effect of these processes on fluid flux. In particular, pseudo-1D models show that if fluids can efficiently rehydrate slab minerals, then these reactions can shut down fluid pathways within the slab, resulting in deeper release of fluid into the mantle wedge. However, the behavior in full subduction zone models remains to be determined.

Evidences of a Stalled-slab Beneath the Coast Ranges, California, From Seismicity and Converted Phases

NASA Astrophysics Data System (ADS)

Cao, A.; Liu, K. H.; Gao, S. S.

2001-12-01

In spite of numerous geophysical studies, the existence and geometry of a stalled slab beneath the Coast Ranges remains vague. In this study we use the distribution of mantle earthquakes and P-to-S converted phases from tilt interfaces to address the problem. Based on the CNSS catalog, in the period between 01/1960 and 04/2001, there were about 450 earthquakes occurred at depth larger than 35 km in the vicinity of the Coast Ranges. When plotted along east-west cross-sections, those earthquakes show a clear slab-like image, similar to the upper part of classic Benioff zones along subducting oceanic slabs. One of such cross-sections, which has a width of 20 km and a latitude of 39N, is located in the so-called 'slabless window' suggested by several previous geologic and geophysic studies, implying the existence of a stalled-slab along the cross-section. The mantle earthquakes can be explained as the result of stress concentration caused by heterogeneities in elastic properties associated with the cold slab, and of changes in mineralogical phases in the upper-most mantle in and around the slab. The existence of the slab is supported by clear azimuthal variations of the amplitude and arrival time of P-to-S converted phases from a tilt interface at about 70 km depth recorded by a broadband seismic station in the area. Our analysis shows that the converted phase is probably from a subducted oceanic lithosphere dipping to the east. The strike of the slab is approximately parallel to the Coast Ranges.

Cartwheel projections of segmented pulmonary vasculature for the detection of pulmonary embolism

NASA Astrophysics Data System (ADS)

Kiraly, Atilla P.; Naidich, David P.; Novak, Carol L.

2005-04-01

Pulmonary embolism (PE) detection via contrast-enhanced computed tomography (CT) images is an increasingly important topic of research. Accurate identification of PE is of critical importance in determining the need for further treatment. However, current multi-slice CT scanners provide datasets typically containing 600 or more images per patient, making it desirable to have a visualization method to help radiologists focus directly on potential candidates that might otherwise have been overlooked. This is especially important when assessing the ability of CT to identify smaller, sub-segmental emboli. We propose a cartwheel projection approach to PE visualization that computes slab projections of the original data aided by vessel segmentation. Previous research on slab visualization for PE has utilized the entire volumetric dataset, requiring thin slabs and necessitating the use of maximum intensity projection (MIP). Our use of segmentation within the projection computation allows the use of thicker slabs than previous methods, as well as the ability to employ visualization variations that are only possible with segmentation. Following automatic segmentation of the pulmonary vessels, slabs may be rotated around the X-, Y- or Z-axis. These slabs are rendered by preferentially using voxels within the lung vessels. This effectively eliminates distracting information not relevant to diagnosis, lessening both the chance of overlooking a subtle embolus and minimizing time on spent evaluating false positives. The ability to employ thicker slabs means fewer images need to be evaluated, yielding a more efficient workflow.

The linear Boltzmann equation in slab geometry - Development and verification of a reliable and efficient solution

NASA Technical Reports Server (NTRS)

Stamnes, K.; Lie-Svendsen, O.; Rees, M. H.

1991-01-01

The linear Boltzmann equation can be cast in a form mathematically identical to the radiation-transport equation. A multigroup procedure is used to reduce the energy (or velocity) dependence of the transport equation to a series of one-speed problems. Each of these one-speed problems is equivalent to the monochromatic radiative-transfer problem, and existing software is used to solve this problem in slab geometry. The numerical code conserves particles in elastic collisions. Generic examples are provided to illustrate the applicability of this approach. Although this formalism can, in principle, be applied to a variety of test particle or linearized gas dynamics problems, it is particularly well-suited to study the thermalization of suprathermal particles interacting with a background medium when the thermal motion of the background cannot be ignored. Extensions of the formalism to include external forces and spherical geometry are also feasible.

Exceptional points of resonant states on a periodic slab

NASA Astrophysics Data System (ADS)

Abdrabou, Amgad; Lu, Ya Yan

2018-06-01

A special kind of degeneracy, known as exceptional points (EPs), for resonant states on a dielectric periodic slab are investigated. Due to their unique properties, EPs have found important applications in lasing, sensing, unidirectional operations, etc. In general, EPs may appear in non-Hermitian eigenvalue problems, including those related to -parity-time-symmetric systems and those for open dielectric structures (due to the existence of radiation loss). In this paper, we study EPs on a simple periodic structure: a slab with a periodic array of gaps. By using an efficient numerical method, we calculate the EPs and study their dependence on geometric parameters. Analytic results are obtained for the limit as the periodic slab approaches a uniform one. Our work provides a simple platform for further studies concerning EPs on dielectric periodic structures, their unusual properties, and applications.

Slab2 - Updated Subduction Zone Geometries and Modeling Tools

NASA Astrophysics Data System (ADS)

Moore, G.; Hayes, G. P.; Portner, D. E.; Furtney, M.; Flamme, H. E.; Hearne, M. G.

2017-12-01

The U.S. Geological Survey database of global subduction zone geometries (Slab1.0), is a highly utilized dataset that has been applied to a wide range of geophysical problems. In 2017, these models have been improved and expanded upon as part of the Slab2 modeling effort. With a new data driven approach that can be applied to a broader range of tectonic settings and geophysical data sets, we have generated a model set that will serve as a more comprehensive, reliable, and reproducible resource for three-dimensional slab geometries at all of the world's convergent margins. The newly developed framework of Slab2 is guided by: (1) a large integrated dataset, consisting of a variety of geophysical sources (e.g., earthquake hypocenters, moment tensors, active-source seismic survey images of the shallow slab, tomography models, receiver functions, bathymetry, trench ages, and sediment thickness information); (2) a dynamic filtering scheme aimed at constraining incorporated seismicity to only slab related events; (3) a 3-D data interpolation approach which captures both high resolution shallow geometries and instances of slab rollback and overlap at depth; and (4) an algorithm which incorporates uncertainties of contributing datasets to identify the most probable surface depth over the extent of each subduction zone. Further layers will also be added to the base geometry dataset, such as historic moment release, earthquake tectonic providence, and interface coupling. Along with access to several queryable data formats, all components have been wrapped into an open source library in Python, such that suites of updated models can be released as further data becomes available. This presentation will discuss the extent of Slab2 development, as well as the current availability of the model and modeling tools.

Focusing Fluids towards the Arc: the Role of Rehydration Reactions and Rheology

NASA Astrophysics Data System (ADS)

Wilson, C. R.; Spiegelman, M. W.; Van Keken, P. E.; Hacker, B. R.

2015-12-01

Aqueous fluids released from the down-going slab in subduction zones are generally thought to be the cause of arc volcanism. However there is a significant discrepancy between the consistent location of the volcanic front with respect to intermediate depth earthquakes (e.g. 100+/-40 km; England et al., GJI, 2004, Syracuse & Abers, G-cubed, 2006) and the large depth range over which dehydration reactions are predicted to occur in the slab (e.g. 80-250 km; van Keken et al., JGR, 2011).By coupling the fluid flow to the solid rheology through compaction pressure, recent numerical models (Wilson et al., EPSL, 2014) demonstrated a number of focusing mechanisms that can be invoked to explain this apparent discrepancy. Most notable among these were permeability channels within the slab. These were shown to be highly effective in transporting fluid from deeper fluid sources along the slab towards the shallowest source. In the presence of these channels the majority of the fluid is released into the mantle wedge far shallower and closer to the arc than it was originally generated.While observations consistent with free fluids in the slab have been reported (e.g. Shiina et al., GRL, 2013), it is possible that changing the reactivity and rheology of the slab can change the efficiency of in-slab transport (e.g. Wada et al., EPSL, 2012, Faccenda et al., G3, 2012). We present a series of simplified model problems of fluid flow within the slab and mantle wedge demonstrating the potential effect of these processes on fluid flux. In particular, pseudo-1D models show that if fluids can efficiently rehydrate slab minerals, then these reactions can shut down fluid pathways within the slab, resulting in deeper release of fluid into the mantle wedge. We will expand these results to consider the effects of rehydration in 2-D calculations. In addition, our previous models have considered only the simplest rheologies and geometries for the slab. We will also discuss new results that investigate simple visco-plastic models for the slab that limit the stresses and maximum viscosities in the slab for more realistic slab geometries. Despite these additional complexities, the robust observation of the location of the volcanic front with respect to intermediate depth earthquakes provides a clear test for evaluating subduction zone models.

Seismic Behaviour of Masonry Vault-Slab Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chesi, Claudio; Butti, Ferdinando; Ferrari, Marco

2008-07-08

Spandrel walls typically play a structural role in masonry buildings, transferring load from a slab to the supporting vault. Some indications are given in the literature on the behaviour of spandrels under the effect of vertical loads, but little attention is given to the effect coming from lateral forces acting on the building. An opportunity to investigate this problem has come from the need of analyzing a monumental building which was damaged by the Nov. 24, 2004 Val Sabbia earthquake in the north of Italy. The finite element model set up for the analysis of the vault-spandrel-slab system is presentedmore » and the structural role resulting for the spandrels is discussed.« less

Analysis of Slabs-on-Grade for a Variety of Loading and Support Conditions.

DTIC Science & Technology

1984-12-01

applications, namely "- the problem of a slab-on-grade, as encountered in the analysis and design of rigid pavements. - ". This is one of the few...proper design and construction methods are adhered to. There are several additional reasons, entirely due to recent developments, that warrant the...conservative designs led to almost imperceptible pavement deformations, thus warranting the term "rigid pavements". Modern-day analytical techniques

Narrow-linewidth, quasi-continuous-wave ASE source based on a multiple-pass Nd:YAG zigzag slab amplifier configuration.

PubMed

Chen, Xiaoming; Lu, Yanhua; Hu, Hao; Tong, Lixin; Zhang, Lei; Yu, Yi; Wang, Juntao; Ren, Huaijin; Xu, Liu

2018-03-05

We present investigations into a narrow-linewidth, quasi-continuous-wave pulsed all-solid-state amplified spontaneous emission (ASE) source by use of a novel multiple-pass zigzag slab amplifier. The SE fluorescence emitted from a Nd:YAG slab active medium acts as the seed and is amplified back and forth 8 times through the same slab. Thanks to the angular multiplexing nature of the zigzag slab, high-intensity 1064-nm ASE output can be produced without unwanted self-lasing in this configuration. Experimentally, the output energy, optical conversion efficiency, pulse dynamics, spectral property, and beam quality of the ASE source are studied when the Nd:YAG slab end-pumped by two high-brightness laser diode arrays. The maximum single pulse energy of 347 mJ is generated with an optical efficiency of ~5.9% and a beam quality of 3.5/17 in the thickness/width direction of the slab. As expected, smooth pulses without relaxing spikes and continuous spectra are achieved. Moreover, the spectral width of the ASE source narrows versus the pump energy, getting a 3-dB linewidth of as narrow as 20 pm (i.e. 5.3 GHz). Via the sum frequency generation, high-intensity, smooth-pulse, and narrow-linewidth ASE sources are preferred for solving the major problem of saturation of the mesospheric sodium atoms and can create a much brighter sodium guide star to meet the needs of adaptive imaging applications in astronomy.

An elastic dimpling instability with Kosterlitz-Thouless character and a precursor role in creasing

NASA Astrophysics Data System (ADS)

Engstrom, Tyler; Paulsen, Joseph; Schwarz, Jennifer

Creasing instability, also known as sulcification, occurs in a variety of quasi-2d elastic systems subject to compressive plane strain, and has been proposed as a mechanism of brain folding. While the dynamics of pre-existing creases can be understood in terms of crack propagation, a detailed critical phenomena picture of the instability is lacking. We show that surface dimpling is an equilibrium phase transition, and can be described in a language of quasi-particle excitations conceptualized as ``ghost fibers'' within the shear lag model. Tension-compression pairs (dipoles) of ghost fibers are energetically favorable at low strains, and the pairs unbind at a critical compressive plane strain, analogously to vortices in the Kosterlitz-Thouless transition. This dimpling transition bears strong resemblance to the creasing instability. We argue that zero-length creases are ghost fibers, which are a special case of ``ghost slabs''. Critical strain of a ghost slab increases linearly with its length, and is independent of both shear modulus and system thickness.

Surface correlation effects in two-band strongly correlated slabs.

PubMed

Esfahani, D Nasr; Covaci, L; Peeters, F M

2014-02-19

Using an extension of the Gutzwiller approximation for an inhomogeneous system, we study the two-band Hubbard model with unequal band widths for a slab geometry. The aim is to investigate the mutual effect of individual bands on the spatial distribution of quasi-particle weight and charge density, especially near the surface of the slab. The main effect of the difference in band width is the presence of two different length scales corresponding to the quasi-particle profile of each band. This is enhanced in the vicinity of the critical interaction of the narrow band where an orbitally selective Mott transition occurs and a surface dead layer forms for the narrow band. For the doped case, two different regimes of charge transfer between the surface and the bulk of the slab are revealed. The charge transfer from surface/center to center/surface depends on both the doping level and the average relative charge accumulated in each band. Such effects could also be of importance when describing the accumulation of charges at the interface between structures made of multi-band strongly correlated materials.

A fluid model simulation of a simplified plasma limiter based on spectral-element time-domain method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qian, Cheng; Ding, Dazhi, E-mail: dzding@njust.edu.cn; Fan, Zhenhong

2015-03-15

A simplified plasma limiter prototype is proposed and the fluid model coupled with Maxwell's equations is established to describe the operating mechanism of plasma limiter. A three-dimensional (3-D) simplified sandwich structure plasma limiter model is analyzed with the spectral-element time-domain (SETD) method. The field breakdown threshold of air and argon at different frequency is predicted and compared with the experimental data and there is a good agreement between them for gas microwave breakdown discharge problems. Numerical results demonstrate that the two-layer plasma limiter (plasma-slab-plasma) has better protective characteristics than a one-layer plasma limiter (slab-plasma-slab) with the same length of gasmore » chamber.« less

Length-scales of Slab-induced Asthenospheric Deformation from Geodynamic Modeling, Mantle Deformation Fabric, and Synthetic Shear Wave Splitting

NASA Astrophysics Data System (ADS)

Jadamec, M. A.; MacDougall, J.; Fischer, K. M.

2017-12-01

The viscosity structure of the Earth's interior is critically important, because it places a first order constraint on plate motion and mantle flow rates. Geodynamic models using a composite viscosity based on experimentally derived flow laws for olivine aggregates show that lateral viscosity variations emerge in the upper mantle due to the subduction dynamics. However, the length-scale of this transition is still not well understood. Two-dimensional numerical models of subduction are presented that investigate the effect of initial slab dip, maximum yield stress (slab strength), and viscosity formulation (Newtonian versus composite) on the emergent lateral viscosity variations in the upper-mantle and magnitude of slab-driven mantle flow velocity. Significant viscosity reductions occur in regions of large flow velocity gradients due to the weakening effect of the dislocation creep deformation mechanism. The dynamic reductions in asthenospheric viscosity (less than 1018 Pa s) occur within approximately 500 km from driving force of the slab, with peak flow velocities occurring in models with a lower yield stress (weaker slab) and higher stress exponent. This leads to a sharper definition of the rheological base of the lithosphere and implies lateral variability in tractions along the base of the lithosphere. As the dislocation creep mechanism also leads to mantle deformation fabric, we then examine the spatial variation in the LPO development in the asthenosphere and calculate synthetic shear wave splitting. The models show that olivine LPO fabric in the asthenosphere generally increases in alignment strength with increased proximity to the slab, but can be transient and spatially variable on small length scales. The vertical flow fields surrounding the slab tip can produce shear-wave splitting variations with back-azimuth that deviate from the predictions of uniform trench-normal anisotropy, a result that bears on the interpretation of complexity in shear-wave splitting observed in real subduction zones.

Solution of the radiative transfer equation for Rayleigh scattering using the infinite medium Green's function

NASA Astrophysics Data System (ADS)

Biçer, M.; Kaşkaş, A.

2018-03-01

The infinite medium Green's function is used to solve the half-space albedo, slab albedo and Milne problems for the unpolarized Rayleigh scattering case; these problems are the most classical problems of radiative transfer theory. The numerical results are obtained and are compared with previous ones.

Numerical Modelling of Foundation Slabs with use of Schur Complement Method

NASA Astrophysics Data System (ADS)

Koktan, Jiří; Brožovský, Jiří

2017-10-01

The paper discusses numerical modelling of foundation slabs with use of advanced numerical approaches, which are suitable for parallel processing. The solution is based on the Finite Element Method with the slab-type elements. The subsoil is modelled with use of Winklertype contact model (as an alternative a multi-parameter model can be used). The proposed modelling approach uses the Schur Complement method to speed-up the computations of the problem. The method is based on a special division of the analyzed model to several substructures. It adds some complexity to the numerical procedures, especially when subsoil models are used inside the finite element method solution. In other hand, this method makes possible a fast solution of large models but it introduces further problems to the process. Thus, the main aim of this paper is to verify that such method can be successfully used for this type of problem. The most suitable finite elements will be discussed, there will be also discussion related to finite element mesh and limitations of its construction for such problem. The core approaches of the implementation of the Schur Complement Method for this type of the problem will be also presented. The proposed approach was implemented in the form of a computer program, which will be also briefly introduced. There will be also presented results of example computations, which prove the speed-up of the solution - there will be shown important speed-up of solution even in the case of on-parallel processing and the ability of bypass size limitations of numerical models with use of the discussed approach.

Influence of field dependent critical current density on flux profiles in high Tc superconductors

NASA Technical Reports Server (NTRS)

Takacs, S.

1990-01-01

The field distribution for superconducting cylinders and slabs with field dependent critical current densities in combined DC and AC magnetic fields and the corresponding magnetic fluxes are calculated. It is shown that all features of experimental magnetic-field profile measurements can be explained in the framework of field dependent critical current density. Even the quantitative agreement between the experimental and theoretical results using Kim's model is very good.

Tomographic imaging of subducted lithosphere below northwest Pacific island arcs

USGS Publications Warehouse

Van Der Hilst, R.; Engdahl, R.; Spakman, W.; Nolet, G.

1991-01-01

The seismic tomography problem does not have a unique solution, and published tomographic images have been equivocal with regard to the deep structure of subducting slabs. An improved tomographic method, using a more realistic background Earth model and surf ace-reflected as well as direct seismic phases, shows that slabs beneath the Japan and Izu Bonin island arcs are deflected at the boundary between upper and lower mantle, whereas those beneath the northern Kuril and Mariana arcs sink into the lower mantle.

An exact solution for the solidification of a liquid slab of binary mixture

NASA Technical Reports Server (NTRS)

Antar, B. N.; Collins, F. G.; Aumalia, A. E.

1986-01-01

The time dependent temperature and concentration profiles of a one dimensional finite slab of a binary liquid alloy is investigated during solidification. The governing equations are reduced to a set of coupled, nonlinear initial value problems using the method outlined by Meyer. Two methods will be used to solve these equations. The first method uses a Runge-Kutta-Fehlberg integrator to solve the equations numerically. The second method comprises of finding closed form solutions of the equations.

Zigzag laser with reduced optical distortion

DOEpatents

Albrecht, G.F.; Comaskey, B.; Sutton, S.B.

1994-04-19

The architecture of the present invention has been driven by the need to solve the beam quality problems inherent in Brewster's angle tipped slab lasers. The entrance and exit faces of a solid state slab laser are cut perpendicular with respect to the pump face, thus intrinsically eliminating distortion caused by the unpumped Brewster's angled faces. For a given zigzag angle, the residual distortions inherent in the remaining unpumped or lightly pumped ends may be reduced further by tailoring the pump intensity at these ends. 11 figures.

Zigzag laser with reduced optical distortion

DOEpatents

Albrecht, Georg F.; Comaskey, Brian; Sutton, Steven B.

1994-01-01

The architecture of the present invention has been driven by the need to solve the beam quality problems inherent in Brewster's angle tipped slab lasers. The entrance and exit faces of a solid state slab laser are cut perpendicular with respect to the pump face, thus intrinsically eliminating distortion caused by the unpumped Brewster's angled faces. For a given zigzag angle, the residual distortions inherent in the remaining unpumped or lightly pumped ends may be reduced further by tailoring the pump intensity at these ends.

Zinc isotope evidence for sulfate-rich fluid transfer across subduction zones.

PubMed

Pons, Marie-Laure; Debret, Baptiste; Bouilhol, Pierre; Delacour, Adélie; Williams, Helen

2016-12-16

Subduction zones modulate the chemical evolution of the Earth's mantle. Water and volatile elements in the slab are released as fluids into the mantle wedge and this process is widely considered to result in the oxidation of the sub-arc mantle. However, the chemical composition and speciation of these fluids, which is critical for the mobility of economically important elements, remain poorly constrained. Sulfur has the potential to act both as oxidizing agent and transport medium. Here we use zinc stable isotopes (δ 66 Zn) in subducted Alpine serpentinites to decipher the chemical properties of slab-derived fluids. We show that the progressive decrease in δ 66 Zn with metamorphic grade is correlated with a decrease in sulfur content. As existing theoretical work predicts that Zn-SO 4 2- complexes preferentially incorporate heavy δ 66 Zn, our results provide strong evidence for the release of oxidized, sulfate-rich, slab serpentinite-derived fluids to the mantle wedge.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuzmina, M.G.

The polarized radiation transfer problems for slabs of weakly anisotropic optically active media are considered as the perturbations of the corresponding problems for isotropic ones. The perturbation method is developed for the integral transport equation and the estimate for the total perturbation of the solution due to the anisotropy of the medium is obtained.

Evolution of a Directional Wave Spectrum in a 3D Marginal Ice Zone with Random Floe Size Distribution

NASA Astrophysics Data System (ADS)

Montiel, F.; Squire, V. A.

2013-12-01

A new ocean wave/sea-ice interaction model is proposed that simulates how a directional wave spectrum evolves as it travels through a realistic marginal ice zone (MIZ), where wave/ice dynamics are entirely governed by coherent conservative wave scattering effects. Field experiments conducted by Wadhams et al. (1986) in the Greenland Sea generated important data on wave attenuation in the MIZ and, particularly, on whether the wave spectrum spreads directionally or collimates with distance from the ice edge. The data suggest that angular isotropy, arising from multiple scattering by ice floes, occurs close to the edge and thenceforth dominates wave propagation throughout the MIZ. Although several attempts have been made to replicate this finding theoretically, including by the use of numerical models, none have confronted this problem in a 3D MIZ with fully randomised floe distribution properties. We construct such a model by subdividing the discontinuous ice cover into adjacent infinite slabs of finite width parallel to the ice edge. Each slab contains an arbitrary (but finite) number of circular ice floes with randomly distributed properties. Ice floes are modeled as thin elastic plates with uniform thickness and finite draught. We consider a directional wave spectrum with harmonic time dependence incident on the MIZ from the open ocean, defined as a continuous superposition of plane waves traveling at different angles. The scattering problem within each slab is then solved using Graf's interaction theory for an arbitrary incident directional plane wave spectrum. Using an appropriate integral representation of the Hankel function of the first kind (see Cincotti et al., 1993), we map the outgoing circular wave field from each floe on the slab boundaries into a directional spectrum of plane waves, which characterizes the slab reflected and transmitted fields. Discretizing the angular spectrum, we can obtain a scattering matrix for each slab. Standard recursive techniques are then used to solve the problem for the full MIZ. Wave attenuation data are obtained using ensemble averaging and preliminary comparisons with field experiment data will be given in the presentation. The model also offers important insights in regards to the spreading of the directional wave spectrum as it penetrates deeper into the MIZ. Cincotti, G., Gori, F., Santarsiero, M., Frezza, F., Furno, F., and Schettini, G. (1993). Plane wave expansion of cylindrical functions. Opt. Commun., 95(4):192-198. Wadhams, P., Squire, V. A., Ewing, J. A., and Pascal, R. W. (1986). The effect of the marginal ice zone on the directional wave spectrum of the ocean. J. Phys. Oceanogr., 16:358-376.

Excitation of the Uller-Zenneck electromagnetic surface waves in the prism-coupled configuration

NASA Astrophysics Data System (ADS)

Rasheed, Mehran; Faryad, Muhammad

2017-08-01

A configuration to excite the Uller-Zenneck surface electromagnetic waves at the planar interfaces of homogeneous and isotropic dielectric materials is proposed and theoretically analyzed. The Uller-Zenneck waves are surface waves that can exist at the planar interface of two dissimilar dielectric materials of which at least one is a lossy dielectric material. In this paper, a slab of a lossy dielectric material was taken with lossless dielectric materials on both sides. A canonical boundary-value problem was set up and solved to find the possible Uller-Zenneck waves and waveguide modes. The Uller-Zenneck waves guided by the slab of the lossy dielectric material were found to be either symmetric or antisymmetric and transmuted into waveguide modes when the thickness of that slab was increased. A prism-coupled configuration was then successfully devised to excite the Uller-Zenneck waves. The results showed that the Uller-Zenneck waves are excited at the same angle of incidence for any thickness of the slab of the lossy dielectric material, whereas the waveguide modes can be excited when the slab is sufficiently thick. The excitation of Uller-Zenneck waves at the planar interfaces with homogeneous and all-dielectric materials can usher in new avenues for the applications for electromagnetic surface waves.

Determination and prioritization of MoDOT geotechnical related problems with emphasis on effectiveness of design for bridge approach slabs and pavement edge drains

DOT National Transportation Integrated Search

2003-01-01

Surveys, interviews and site visits were used to identify, observe and document geotechnical-related problems in Missouri DOT infrastructure. Documented issues were evaluated and prioritized. Additional attention was focused on Pavement Edge Drains a...

Two-dimensional radiative transfer. I - Planar geometry. [in stellar atmospheres

NASA Technical Reports Server (NTRS)

Mihalas, D.; Auer, L. H.; Mihalas, B. R.

1978-01-01

Differential-equation methods for solving the transfer equation in two-dimensional planar geometries are developed. One method, which uses a Hermitian integration formula on ray segments through grid points, proves to be extremely well suited to velocity-dependent problems. An efficient elimination scheme is developed for which the computing time scales linearly with the number of angles and frequencies; problems with large velocity amplitudes can thus be treated accurately. A very accurate and efficient method for performing a formal solution is also presented. A discussion is given of several examples of periodic media and free-standing slabs, both in static cases and with velocity fields. For the free-standing slabs, two-dimensional transport effects are significant near boundaries, but no important effects were found in any of the periodic cases studied.

Infrastructure design integration to optimize structures and minimize groundwater impacts. Case of a bottom slab and groundwater by-pass integration in La Sagrera railway station, Spain.

NASA Astrophysics Data System (ADS)

Serrano Juan, Alejandro; Vázquez-Suñè, Enric; Pujades, Estanislao; Velasco, Violeta; Criollo, Rotman; Jurado, Anna

2016-04-01

Underground constructions search the most efficient solutions to increase safety, reduce impacts in both underground construction (such as bottom slab water pressures) and groundwater (such as groundwater barrier effect), reduce future maintenance processes and ensure that everything is implemented by the minimum cost. Even being all the previous solutions directly related to groundwater, independent solutions are usually designed to independently deal with each problem. This paper shows how with a groundwater by-pass design that enables the groundwater flow through the structure it is possible to provide an homogeneous distribution of the water pressures under the bottom slab and reduce the barrier effect produced by the structure. The new integrated design has been applied to the largest infrastructure of Barcelona: La Sagrera railway station. Through a hydrogeological model has been possible to test the project and the integrated designs in three different scenarios. This new solution resolves the barrier effect produced by the structure and optimizes the bottom slab, reducing considerably the costs and increasing safety during the construction phase.

Photon migration through a turbid slab described by a model based on diffusion approximation. II. Comparison with Monte Carlo results.

PubMed

Martelli, F; Contini, D; Taddeucci, A; Zaccanti, G

1997-07-01

In our companion paper we presented a model to describe photon migration through a diffusing slab. The model, developed for a homogeneous slab, is based on the diffusion approximation and is able to take into account reflection at the boundaries resulting from the refractive index mismatch. In this paper the predictions of the model are compared with solutions of the radiative transfer equation obtained by Monte Carlo simulations in order to determine the applicability limits of the approximated theory in different physical conditions. A fitting procedure, carried out with the optical properties as fitting parameters, is used to check the application of the model to the inverse problem. The results show that significant errors can be made if the effect of the refractive index mismatch is not properly taken into account. Errors are more important when measurements of transmittance are used. The effects of using a receiver with a limited angular field of view and the angular distribution of the radiation that emerges from the slab have also been investigated.

Problem of image superresolution with a negative-refractive-index slab.

PubMed

Nieto-Vesperinas, Manuel

2004-04-01

By means of the angular spectrum representation of wave fields, a discussion is given on the propagation and restoration of the wave-front structure in a slab of a left-handed medium (or negative-index medium) whose surface impedance matches that of vacuum, namely, one whose effective optical parameters are n = epsilon = mu = -1. This restoration was previously discussed [Phys. Rev. Lett. 85, 3866 (2000)] in regard to whether it may yield superresolved images. The divergence of the wave field in the slab, and its equivalence with that of the inverse diffraction propagator in free space, is addressed. Further, the existence of absorption, its regularization of this divergence, and the trade-off of a resulting limited superresolution are analyzed in detail in terms of its effect on the evanescent components of the wave field and hence on the transfer function width.

Coupling intensity and isostatic competition between subducting slab and overriding plate control trench motions and tectonics of the overriding plate

NASA Astrophysics Data System (ADS)

Wu, G.; Moresi, L. N.

2017-12-01

Trench motions not only reflect tectonic regimes on the overriding plate but also shed light on the competition between subducting slab and overriding plate, however, major controls over trench advance or retreat and their consequences are still illusive. We use 2D thermo-mechanical experiments to study the problem. We find that the coupling intensity particularly in the uppermost 200 km and the isostatic competition between subducting slab and overriding plate largely determine trench motion and tectonics of in the overriding plate. Coupling intensity is the result of many contributing factors, including frictional coefficient of brittle part of the subducting interface and the viscosity of the ductile part, thermal regime and rheology of the overriding plate, and water contents and magmatic activity in the subducting slab and overriding plate. In this study, we are not concerned with the dynamic evolution of individual controlling parameter but simply use effective media. For instance, we impose simple model parameters such as frictional coefficient and vary the temperature and strain-rate dependent viscosity of the weak layer between the subducting slab and overriding plate. In the coupled end-member case, strong coupling leads to strong corner flow, depth-dependent compression/extension, and mantle return flow on the overriding plate side. It results in fast trench retreat, broad overriding plate extension, and even slab breakoff. In the decoupled end-member case, weak coupling causes much weaker response on the overriding plate side compared with the coupled end-member case, and the subducting slab can be largely viewed as a conveyer belt. We find that the isostatic competition between the subducting slab and overriding plate also has a major control over trench motion, and may better be viewed in 3D models. This is consistent with the findings in previous 3D studies that trench motion is most pronounced close to the slab edge. Here we propose that the differential subduction and isostatic differences along strike are the major cause of complex trench behavior and tectonic variations in the overriding plate. Finally, our models must be placed in a reference frame outside our modeled domain when used in global scale.

Rotational flow in tapered slab rocket motors

NASA Astrophysics Data System (ADS)

Saad, Tony; Sams, Oliver C.; Majdalani, Joseph

2006-10-01

Internal flow modeling is a requisite for obtaining critical parameters in the design and fabrication of modern solid rocket motors. In this work, the analytical formulation of internal flows particular to motors with tapered sidewalls is pursued. The analysis employs the vorticity-streamfunction approach to treat this problem assuming steady, incompressible, inviscid, and nonreactive flow conditions. The resulting solution is rotational following the analyses presented by Culick for a cylindrical motor. In an extension to Culick's work, Clayton has recently managed to incorporate the effect of tapered walls. Here, an approach similar to that of Clayton is applied to a slab motor in which the chamber is modeled as a rectangular channel with tapered sidewalls. The solutions are shown to be reducible, at leading order, to Taylor's inviscid profile in a porous channel. The analysis also captures the generation of vorticity at the surface of the propellant and its transport along the streamlines. It is from the axial pressure gradient that the proper form of the vorticity is ascertained. Regular perturbations are then used to solve the vorticity equation that prescribes the mean flow motion. Subsequently, numerical simulations via a finite volume solver are carried out to gain further confidence in the analytical approximations. In illustrating the effects of the taper on flow conditions, comparisons of total pressure and velocity profiles in tapered and nontapered chambers are entertained. Finally, a comparison with the axisymmetric flow analog is presented.

2-dimensional triplicated waveform modeling of the mantle transition zone beneath Northeast Asia

NASA Astrophysics Data System (ADS)

Lai, Y.; Chen, L.; Wang, T.

2017-12-01

The Mantle Transition Zone (MTZ) of Northeast Asia has long been investigated by geoscientists for its critical importance where the subducted Pacific slab is stagnant above the 660km discontinuity, accompanied by complicated mantle processes. Taking advantages of the frequent occurrent deep earthquakes in subduction zone and dense seismic arrays in Northeast China, we successfully constructed the fine-scale P and SH velocity structure of a narrow azimuthal fan area based on 2-Dimensional (2D) triplicated waveform modeling for three deep close earthquakes, in which the triplicated waveforms are very sensitive to MTZ velocity structure in general, particularly the morphology of the stagnant slab in Northeast Asia. In our 2D triplication study, for the first time, we show a quite consistent feature of a high velocity layer for both Vp and Vs with the thickness of 140km and the length of 1200km just atop the 660km discontinuity, the western edge of the stagnant slab intersect with the North-South Gravity Lineament in China and has the subducting age of 30 Ma. Compared with a quite normal Vp, the Shear wave velocity reduction of -0.5% in the slab and -2.5% in the upper MTZ is required to reconcile the SH waves featured by the broad BOD. The high Vp/Vs ratio beneath Northeast Asia may imply a water-rich MTZ with the H2O content of 0.1-0.3 wt%. Particularly, a low velocity anomaly of about 150km wide was detected in the overall high-velocity stagnant slab by both P and SH triplicated waveform modeling, with the velocity anomaly value of -1% and -3%, respectively. The gap/window in the stagnant slab may provide a passage for hot deeper mantle materials to penetrate through the thick slab and feed the surface Changbaishan volcano. We also speculate that the existence of such a gap can be the manifestation of the original heterogeneity in the subducted slab and will further exacerbatethe impending gravitational instability and speed up mantle avalanche.

Geometrical Optics of Dense Aerosols

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hay, Michael J.; Valeo, Ernest J.; Fisch, Nathaniel J.

2013-04-24

Assembling a free-standing, sharp-edged slab of homogeneous material that is much denser than gas, but much more rare ed than a solid, is an outstanding technological challenge. The solution may lie in focusing a dense aerosol to assume this geometry. However, whereas the geometrical optics of dilute aerosols is a well-developed fi eld, the dense aerosol limit is mostly unexplored. Yet controlling the geometrical optics of dense aerosols is necessary in preparing such a material slab. Focusing dense aerosols is shown here to be possible, but the nite particle density reduces the eff ective Stokes number of the flow, amore » critical result for controlled focusing. __________________________________________________« less

A tale of two arcs? Plate tectonics of the Izu-Bonin-Mariana (IBM) arc using subducted slab constraints

NASA Astrophysics Data System (ADS)

Wu, J. E.; Suppe, J.; Renqi, L.; Kanda, R. V. S.

2014-12-01

Published plate reconstructions typically show the Izu-Bonin Marianas arc (IBM) forming as a result of long-lived ~50 Ma Pacific subduction beneath the Philippine Sea. These reconstructions rely on the critical assumption that the Philippine Sea was continuously coupled to the Pacific during the lifetime of the IBM arc. Because of this assumption, significant (up to 1500 km) Pacific trench retreat is required to accommodate the 2000 km of Philippine Sea/IBM northward motion since the Eocene that is constrained by paleomagnetic data. In this study, we have mapped subducted slabs of mantle lithosphere from MITP08 global seismic tomography (Li et al., 2008) and restored them to a model Earth surface to constrain plate tectonic reconstructions. Here we present two subducted slab constraints that call into question current IBM arc reconstructions: 1) The northern and central Marianas slabs form a sub-vertical 'slab wall' down to maximum 1500 km depths in the lower mantle. This slab geometry is best explained by a near-stationary Marianas trench that has remained +/- 250 km E-W of its present-day position since ~45 Ma, and does not support any significant Pacific slab retreat. 2) A vanished ocean is revealed by an extensive swath of sub-horizontal slabs at 700 to 1000 km depths in the lower mantle below present-day Philippine Sea to Papua New Guinea. We call this vanished ocean the 'East Asian Sea'. When placed in an Eocene plate reconstruction, the East Asian Sea fits west of the reconstructed Marianas Pacific trench position and north of the Philippine Sea plate. This implies that the Philippine Sea and Pacific were not adjacent at IBM initiation, but were in fact separated by a lost ocean. Here we propose a new IBM arc reconstruction constrained by subducted slabs mapped under East Asia. At ~50 Ma, the present-day IBM arc initiated at equatorial latitudes from East Asian Sea subduction below the Philippine Sea. A separate arc was formed from Pacific subduction below the East Asian Sea. The Philippine Sea plate moved northwards, overrunning the East Asian Sea and the two arcs collided between 15 to 20 Ma. From 15 Ma to the present, IBM arc magmatism was produced by Pacific subduction beneath the Philippine Sea.

Big mantle wedge, anisotropy, slabs and earthquakes beneath the Japan Sea

NASA Astrophysics Data System (ADS)

Zhao, Dapeng

2017-09-01

The Japan Sea is a part of the western Pacific trench-arc-backarc system and has a complex bathymetry and intense seismic activities in the crust and upper mantle. Local seismic tomography revealed strong lateral heterogeneities in the crust and uppermost mantle beneath the eastern margin of the Japan Sea, which was determined using P and S wave arrival times of suboceanic earthquakes relocated precisely with sP depth phases. Ambient-noise tomography revealed a thin crust and a thin lithosphere beneath the Japan Sea and significant low-velocity (low-V) anomalies in the shallow mantle beneath the western and eastern margins of the Japan Sea. Observations with ocean-bottom seismometers and electromagnetometers revealed low-V and high-conductivity anomalies at depths of 200-300 km in the big mantle wedge (BMW) above the subducting Pacific slab, and the anomalies are connected with the low-V zone in the normal mantle wedge beneath NE Japan, suggesting that both shallow and deep slab dehydrations occur and contribute to the arc and back-arc magmatism. The Pacific slab has a simple geometry beneath the Japan Sea, and earthquakes occur actively in the slab down to a depth of ∼600 km beneath the NE Asian margin. Teleseismic P and S wave tomography has revealed that the Philippine Sea plate has subducted aseismically down to the mantle transition zone (MTZ, 410-660 km) depths beneath the southern Japan Sea and the Tsushima Strait, and a slab window is revealed within the aseismic Philippine Sea slab. Seismic anisotropy tomography revealed a NW-SE fast-velocity direction in the BMW, which reflects corner flows induced by the fast deep subduction of the Pacific slab. Large deep earthquakes (M > 7.0; depth > 500 km) occur frequently beneath the Japan Sea western margin, which may be related to the formation of the Changbai and Ulleung intraplate volcanoes. A metastable olivine wedge is revealed within the cold core of the Pacific slab at the MTZ depth, which may be related to the deep seismicity. However, many of these results are still preliminary, due to the lack of seismic stations in the Japan Sea. The key to resolving these critical geoscientific issues is seismic instrumentation in the Japan Sea, for which international cooperation of geoscience communities in the East Asian countries is necessary.

The temporal evolution of a subducting plate in the lower mantle

NASA Astrophysics Data System (ADS)

Loiselet, C.; Grujic, D.; Braun, J.; Fullsack, P.; Thieulot, C.; Yamato, P.

2009-04-01

It is now widely accepted that some subducting slabs may cross the lower/upper mantle boundary to ground below the 660 km discontinuity. Indeed, geophysical data underline long and narrow traces of fast materials, associated with subducting slabs, from the upper mantle transition zone to mid-mantle depths that are visible beneath North and South America and southern Asia (Li et al, 2008). Furthermore, seismic tomography data (Van der Hilst et al., 1997; Karason and van der Hilst, 2000, 2001) show a large variety of slab geometries and of mantle flow patterns around subducting plate boundaries (e.g. the slab geometry in the lower mantle in the Tonga subduction zone). However, seismic tomography does not elucidate the temporal evolution of the slab behaviour and geometry during its descent through the upper and lower mantle. In this work, we therefore propose to study the deformation of a thin plate (slab) falling in a viscous fluid (mantle) by means of both analogue and numerical modelling. The combination of both analogue and numerical experiments provides important insights into the shape and attitude evolution of subducting slabs. Models bring information into the controls exerted by the rheology of the slab and the mantle and other physical parameters such as the density contrast between the slab and the surrounding mantle, on the rate at which this deformation takes place. We show that in function of a viscosity ratios between the plate and the surrounding fluid, the plate will acquire a characteristic shape. For the isoviscous case, the plate shape tends toward a bubble with long tails: a "jellyfish" form. The time necessary for the plate to acquire this shape is a function of the viscosity and density contrast between the slab and the mantle. To complete our approach, we have developed a semi-analytical model based on the solution of the Hadamar-Rybinski equations for the problem of a dense, yet isoviscous and thus deforming sphere. This model helps to better describe flow processes around the downgoing plate and, simultaneously, to characterize its deformation. In this way, we were able to calculate the velocities in the mantle, the forces exerted by the fluid on the plate, and the dissipated energy in the surrounding fluid. Experimental results will be correlated with geophysical data.

The Temporal Evolution Of A Subducting Plate In The Lower Mantle

NASA Astrophysics Data System (ADS)

Loiselet, C.; Grujic, D.; Fullsack, P.; Thieulot, C.; Yamato, P.; Braun, J.

2008-12-01

It is now widely accepted that some subducting slabs may cross the lower/upper mantle boundary to ground below the 660 km discontinuity. Indeed, geophysical data underline long and narrow traces of fast materials, associated with subducting slabs, from the upper mantle transition zone to mid-mantle depths that are visible beneath North and South America and southern Asia (Li et al, 2008). Furthermore, seismic tomography data (Van der Hilst et al., 1997; Karason and van der Hilst, 2000, 2001)) show a large variety of slab geometries and of mantle flow patterns around subducting plate boundaries (e.g. the slab geometry in the lower mantle in the Tonga subduction zone). However, seismic tomography does not elucidate the temporal evolution of the slab behaviour and geometry during its descent through the upper and lower mantle. In this work, we therefore propose to study the deformation of a thin plate (slab) falling in a viscous fluid (mantle). The combination of both analogue and numerical experiments provides important insights into the shape and attitude evolution of subducting slabs. Models bring information into the controls exerted by the rheology of the slab and the mantle and other physical parameters such as the density contrast between the slab and the surrounding mantle, on the rate at which this deformation takes place. We show that in function of a viscosity ratios between the plate and the surrounding fluid, the plate will acquire a characteristic shape. For the isoviscous case, the plate shape tends toward a bubble with long tails: a jellyfish form. The time necessary for the plate to acquire this shape is a function of the viscosity and density contrast between the slab and the mantle. To complete our approach, we have developed a semi-analytical model based on the solution of the Hadamar-Rybinski equations for the problem of a dense, yet isoviscous and thus deforming sphere. This model helps to better describe flow processes around the downgoing plate and, simultaneously, to characterize its deformation. In this way, we were able to calculate the velocities in the mantle, the forces exerted by the fluid on the plate, and the dissipated energy in the surrounding fluid. Experimental results will be correlated with geophysical data.

Impulsively Generated Wave Trains in Coronal Structures. II. Effects of Transverse Structuring on Sausage Waves in Pressurelesss Slabs

NASA Astrophysics Data System (ADS)

Li, Bo; Guo, Ming-Zhe; Yu, Hui; Chen, Shao-Xia

2018-03-01

Impulsively generated sausage wave trains in coronal structures are important for interpreting a substantial number of observations of quasi-periodic signals with quasi-periods of order seconds. We have previously shown that the Morlet spectra of these wave trains in coronal tubes depend crucially on the dispersive properties of trapped sausage waves, the existence of cutoff axial wavenumbers, and the monotonicity of the dependence of the axial group speed on the axial wavenumber in particular. This study examines the difference a slab geometry may introduce, for which purpose we conduct a comprehensive eigenmode analysis, both analytically and numerically, on trapped sausage modes in coronal slabs with a considerable number of density profiles. For the profile descriptions examined, coronal slabs can trap sausage waves with longer axial wavelengths, and the group speed approaches the internal Alfvén speed more rapidly at large wavenumbers in the cylindrical case. However, common to both geometries, cutoff wavenumbers exist only when the density profile falls sufficiently rapidly at distances far from coronal structures. Likewise, the monotonicity of the group speed curves depends critically on the profile steepness right at the structure axis. Furthermore, the Morlet spectra of the wave trains are shaped by the group speed curves for coronal slabs and tubes alike. Consequently, we conclude that these spectra have the potential for inferring the subresolution density structuring inside coronal structures, although their detection requires an instrumental cadence of better than ∼1 s.

Phantom Preparation and Optical Property Determination

NASA Astrophysics Data System (ADS)

He, Di; He, Jie; Mao, Heng

2018-12-01

Tissue-like optical phantoms are important in testing new imaging algorithms. Homogeneous optical phantoms with determined optical properties are the first step of making a proper heterogeneous phantom for multi-modality imaging. Typical recipes for such phantoms consist of epoxy resin, hardener, India ink and titanium oxide. By altering the concentration of India ink and titanium oxide, we are able to get multiple homogeneous phantoms with different absorption and scattering coefficients by carefully mixing all the ingredients. After fabricating the phantoms, we need to find their individual optical properties including the absorption and scattering coefficients. This is achieved by solving diffusion equation of each phantom as a homogeneous slab under canonical illumination. We solve the diffusion equation of homogeneous slab in frequency domain and get the formula for theoretical measurements. Under our steady-state diffused optical tomography (DOT) imaging system, we are able to obtain the real distribution of the incident light produced by a laser. With this source distribution we got and the formula we derived, numerical experiments show how measurements change while varying the value of absorption and scattering coefficients. Then we notice that the measurements alone will not be enough for us to get unique optical properties for steady-state DOT problem. Thus in order to determine the optical properties of a homogeneous slab we want to fix one of the coefficients first and use optimization methods to find another one. Then by assemble multiple homogeneous slab phantoms with different optical properties, we are able to obtain a heterogeneous phantom suitable for testing multi-modality imaging algorithms. In this paper, we describe how to make phantoms, derive a formula to solve the diffusion equation, demonstrate the non-uniqueness of steady-state DOT problem by analysing some numerical results of our formula, and finally propose a possible way to determine optical properties for homogeneous slab for our future work.

A generalized Poisson and Poisson-Boltzmann solver for electrostatic environments.

PubMed

Fisicaro, G; Genovese, L; Andreussi, O; Marzari, N; Goedecker, S

2016-01-07

The computational study of chemical reactions in complex, wet environments is critical for applications in many fields. It is often essential to study chemical reactions in the presence of applied electrochemical potentials, taking into account the non-trivial electrostatic screening coming from the solvent and the electrolytes. As a consequence, the electrostatic potential has to be found by solving the generalized Poisson and the Poisson-Boltzmann equations for neutral and ionic solutions, respectively. In the present work, solvers for both problems have been developed. A preconditioned conjugate gradient method has been implemented for the solution of the generalized Poisson equation and the linear regime of the Poisson-Boltzmann, allowing to solve iteratively the minimization problem with some ten iterations of the ordinary Poisson equation solver. In addition, a self-consistent procedure enables us to solve the non-linear Poisson-Boltzmann problem. Both solvers exhibit very high accuracy and parallel efficiency and allow for the treatment of periodic, free, and slab boundary conditions. The solver has been integrated into the BigDFT and Quantum-ESPRESSO electronic-structure packages and will be released as an independent program, suitable for integration in other codes.

A generalized Poisson and Poisson-Boltzmann solver for electrostatic environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fisicaro, G., E-mail: giuseppe.fisicaro@unibas.ch; Goedecker, S.; Genovese, L.

2016-01-07

The computational study of chemical reactions in complex, wet environments is critical for applications in many fields. It is often essential to study chemical reactions in the presence of applied electrochemical potentials, taking into account the non-trivial electrostatic screening coming from the solvent and the electrolytes. As a consequence, the electrostatic potential has to be found by solving the generalized Poisson and the Poisson-Boltzmann equations for neutral and ionic solutions, respectively. In the present work, solvers for both problems have been developed. A preconditioned conjugate gradient method has been implemented for the solution of the generalized Poisson equation and themore » linear regime of the Poisson-Boltzmann, allowing to solve iteratively the minimization problem with some ten iterations of the ordinary Poisson equation solver. In addition, a self-consistent procedure enables us to solve the non-linear Poisson-Boltzmann problem. Both solvers exhibit very high accuracy and parallel efficiency and allow for the treatment of periodic, free, and slab boundary conditions. The solver has been integrated into the BigDFT and Quantum-ESPRESSO electronic-structure packages and will be released as an independent program, suitable for integration in other codes.« less

3D Numerical modelling of topography development associated with curved subduction zones

NASA Astrophysics Data System (ADS)

Munch, Jessica; Ueda, Kosuke; Burg, Jean-Pierre; May, Dave; Gerya, Taras

2017-04-01

Curved subduction zones, also called oroclines, are geological features found in various places on Earth. They occur in diverse geodynamic settings: 1) single slab subduction in oceanic domain (e.g. Sandwich trench in the Southern Atlantic); 2) single slab subduction in continental domain, (e.g. Gibraltar-Alboran orocline in the Western Mediterranean) 3); multi-slab subduction (e.g. Caribbean orocline in the South-East of the Gulf of Mexico). These systems present various curvatures, lengths (few hundreds to thousands of km) and ages (less than 35 Ma for Gibraltar Alboran orocline, up to 100 Ma for the Caribbean). Recent studies suggested that the formation of curved subduction systems depends on slab properties (age, length, etc) and may be linked with processes such as retreating subduction and delamination. Plume induced subduction initiation has been proposed for the Caribbean. All of these processes involve deep mechanisms such as mantle and slab dynamics. However, subduction zones always generate topography (trenches, uplifts, etc), which is likely to be influenced by surface processes. Hence, surface processes may also influence the evolution of subduction zones. We focus on different kinds of subduction systems initiated by plume-lithosphere interactions (single slab subduction/multi-slab subduction) and scrutinize their surface expression. We use numerical modeling to examine large-scale subduction initiation and three-dimensional slab retreat. We perform two kinds of simulations: 1) large scale subduction initiation with the 3D-thermomechanical code I3ELVIS (Gerya and Yuen, 2007) in an oceanic domain and 2) large scale subduction initiation in oceanic domain using I3ELVIS coupled with a robust new surface processes model (SPM). One to several retreating slabs form in the absence of surface processes, when the conditions for subduction initiation are reached (c.f. Gerya et al., 2015), and ridges occur in the middle of the extensional domain opened by slab retreat. Topography associated with slab retreat is curved. Coupling I3ELVIS with SPM yields more accurate topography of the curved subduction zone. This allows balancing the relative importance of surface and deep processes in the evolution of curved subduction zones and the development of their related topography. References: Gerya, T. V., & Yuen, D. A. (2007). Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems. Physics of the Earth and Planetary Interiors, 163(1), 83-105. Gerya, T. V., Stern, R. J., Baes, M., Sobolev, S. V., & Whattam, S. A. (2015). Plate tectonics on the Earth triggered by plume-induced subduction initiation. Nature, 527(7577), 221-225.

Computational procedure for finite difference solution of one-dimensional heat conduction problems reduces computer time

NASA Technical Reports Server (NTRS)

Iida, H. T.

1966-01-01

Computational procedure reduces the numerical effort whenever the method of finite differences is used to solve ablation problems for which the surface recession is large relative to the initial slab thickness. The number of numerical operations required for a given maximum space mesh size is reduced.

Solar-pumped solid state Nd lasers

NASA Technical Reports Server (NTRS)

Williams, M. D.; Zapata, L.

1985-01-01

Solid state neodymium lasers are considered candidates for space-based polar-pumped laser for continuous power transmission. Laser performance for three different slab laser configurations has been computed to show the excellent power capability of such systems if heat problems can be solved. Ideas involving geometries and materials are offered as potential solutions to the heat problem.

A classical Perron method for existence of smooth solutions to boundary value and obstacle problems for degenerate-elliptic operators via holomorphic maps

NASA Astrophysics Data System (ADS)

Feehan, Paul M. N.

2017-09-01

We prove existence of solutions to boundary value problems and obstacle problems for degenerate-elliptic, linear, second-order partial differential operators with partial Dirichlet boundary conditions using a new version of the Perron method. The elliptic operators considered have a degeneracy along a portion of the domain boundary which is similar to the degeneracy of a model linear operator identified by Daskalopoulos and Hamilton [9] in their study of the porous medium equation or the degeneracy of the Heston operator [21] in mathematical finance. Existence of a solution to the partial Dirichlet problem on a half-ball, where the operator becomes degenerate on the flat boundary and a Dirichlet condition is only imposed on the spherical boundary, provides the key additional ingredient required for our Perron method. Surprisingly, proving existence of a solution to this partial Dirichlet problem with ;mixed; boundary conditions on a half-ball is more challenging than one might expect. Due to the difficulty in developing a global Schauder estimate and due to compatibility conditions arising where the ;degenerate; and ;non-degenerate boundaries; touch, one cannot directly apply the continuity or approximate solution methods. However, in dimension two, there is a holomorphic map from the half-disk onto the infinite strip in the complex plane and one can extend this definition to higher dimensions to give a diffeomorphism from the half-ball onto the infinite ;slab;. The solution to the partial Dirichlet problem on the half-ball can thus be converted to a partial Dirichlet problem on the slab, albeit for an operator which now has exponentially growing coefficients. The required Schauder regularity theory and existence of a solution to the partial Dirichlet problem on the slab can nevertheless be obtained using previous work of the author and C. Pop [16]. Our Perron method relies on weak and strong maximum principles for degenerate-elliptic operators, concepts of continuous subsolutions and supersolutions for boundary value and obstacle problems for degenerate-elliptic operators, and maximum and comparison principle estimates previously developed by the author [13].

Automatic low-order aberration compensator for solid-state slab lasers

NASA Astrophysics Data System (ADS)

Yu, Xin; Dong, Lizhi; Lai, Boheng; Yang, Ping; Kong, Qingfeng; Yang, Kangjian; Liu, Yong; Tang, Guomao; Xu, Bing

2016-09-01

Slab geometry is a promising architecture for power scaling of solid-state lasers. By propagating the laser beams along zigzag path in the gain medium, the thermal effects can be well compensated. However, in the non-zigzag direction, the thermal effects are not compensated. Among the overall aberrations in the slab lasers, the major contributors are two low-order aberrations: astigmatism and defocus, which can range up to over 100 microns (peak to valley), leading to detracted beam quality. Another problem with slab lasers is that the output beams are generally in a rectangular aperture with high aspect ratio (normally 1:10), where square beams are favorable for many applications. In order to solve these problems, we propose an automatic low-order aberration compensation system. This system is composed of three lenses fixed on a motorized rail, one is a spherical lens and the others are cylindrical lenses. Astigmatism and defocus can be compensated by merely adjusting the distances between the lenses. Two wave-front sensors are employed in this compensation system, one is used for detecting the initial parameters of the beams, and the other one is used for detecting the remaining aberrations after correction. The adjustments of the three lenses are directly calculated based on beam parameters using ray tracing method. The initial size of the beam is 3.2mm by 26mm, and peak to valley(PV) value of the wave-front is 33.07λ(λ=1064nm). After correction, the dimension becomes 40mm by 40mm, and peak to valley (PV) value of the wave-front is less than 2 microns.

Zinc isotope evidence for sulfate-rich fluid transfer across subduction zones

PubMed Central

Pons, Marie-Laure; Debret, Baptiste; Bouilhol, Pierre; Delacour, Adélie; Williams, Helen

2016-01-01

Subduction zones modulate the chemical evolution of the Earth's mantle. Water and volatile elements in the slab are released as fluids into the mantle wedge and this process is widely considered to result in the oxidation of the sub-arc mantle. However, the chemical composition and speciation of these fluids, which is critical for the mobility of economically important elements, remain poorly constrained. Sulfur has the potential to act both as oxidizing agent and transport medium. Here we use zinc stable isotopes (δ66Zn) in subducted Alpine serpentinites to decipher the chemical properties of slab-derived fluids. We show that the progressive decrease in δ66Zn with metamorphic grade is correlated with a decrease in sulfur content. As existing theoretical work predicts that Zn-SO42− complexes preferentially incorporate heavy δ66Zn, our results provide strong evidence for the release of oxidized, sulfate-rich, slab serpentinite-derived fluids to the mantle wedge. PMID:27982033

Multiple Bloch surface waves in visible region of light at the interfaces between rugate filter/rugate filter and rugate filter/dielectric slab/rugate filter

NASA Astrophysics Data System (ADS)

Ullah Manzoor, Habib; Manzoor, Tareq; Hussain, Masroor; Manzoor, Sanaullah; Nazar, Kashif

2018-04-01

Surface electromagnetic waves are the solution of Maxwell’s frequency domain equations at the interface of two dissimilar materials. In this article, two canonical boundary-value problems have been formulated to analyze the multiplicity of electromagnetic surface waves at the interface between two dissimilar materials in the visible region of light. In the first problem, the interface between two semi-infinite rugate filters having symmetric refractive index profiles is considered and in the second problem, to enhance the multiplicity of surface electromagnetic waves, a homogeneous dielectric slab of 400 nm is included between two semi-infinite symmetric rugate filters. Numerical results show that multiple Bloch surface waves of different phase speeds, different polarization states, different degrees of localization and different field profiles are propagated at the interface between two semi-infinite rugate filters. Having two interfaces when a homogeneous dielectric layer is placed between two semi-infinite rugate filters has increased the multiplicity of electromagnetic surface waves.

Negotiating Multicollinearity with Spike-and-Slab Priors.

PubMed

Ročková, Veronika; George, Edward I

2014-08-01

In multiple regression under the normal linear model, the presence of multicollinearity is well known to lead to unreliable and unstable maximum likelihood estimates. This can be particularly troublesome for the problem of variable selection where it becomes more difficult to distinguish between subset models. Here we show how adding a spike-and-slab prior mitigates this difficulty by filtering the likelihood surface into a posterior distribution that allocates the relevant likelihood information to each of the subset model modes. For identification of promising high posterior models in this setting, we consider three EM algorithms, the fast closed form EMVS version of Rockova and George (2014) and two new versions designed for variants of the spike-and-slab formulation. For a multimodal posterior under multicollinearity, we compare the regions of convergence of these three algorithms. Deterministic annealing versions of the EMVS algorithm are seen to substantially mitigate this multimodality. A single simple running example is used for illustration throughout.

Oxide-cladding aluminum nitride photonic crystal slab: Design and investigation of material dispersion and fabrication induced disorder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Melo, E. G., E-mail: emerdemelo@usp.br; Alvarado, M. A.; Carreño, M. N. P.

2016-01-14

Photonic crystal slabs with a lower-index material surrounding the core layer are an attractive choice to circumvent the drawbacks in the fabrication of membranes suspended in air. In this work we propose a photonic crystal (PhC) slab structure composed of a triangular pattern of air holes in a multilayer thin film of aluminum nitride embedded in silicon dioxide layers designed for operating around 450 nm wavelengths. We show the design of an ideal structure and analyze the effects of material dispersion based on a first-order correction perturbation theory approach using dielectric functions obtained by experimental measurements of the thin film materials.more » Numerical methods were used to investigate the effects of fabrication induced disorder of typical nanofabrication processes on the bandgap size and spectral response of the proposed device. Deviation in holes radii and positions were introduced in the proposed PhC slab model with a Gaussian distribution profile. Impacts of slope in holes sidewalls that might result from the dry etching of AlN were also evaluated. The results show that for operation at the midgap frequency, slope in holes sidewalls is more critical than displacements in holes sizes and positions.« less

Complex dynamics induced by strong confinement - From tracer diffusion in strongly heterogeneous media to glassy relaxation of dense fluids in narrow slits

NASA Astrophysics Data System (ADS)

Mandal, Suvendu; Spanner-Denzer, Markus; Leitmann, Sebastian; Franosch, Thomas

2017-08-01

We provide an overview of recent advances of the complex dynamics of particles in strong confinements. The first paradigm is the Lorentz model where tracers explore a quenched disordered host structure. Such systems naturally occur as limiting cases of binary glass-forming systems if the dynamics of one component is much faster than the other. For a certain critical density of the host structure the tracers undergo a localization transition which constitutes a critical phenomenon. A series of predictions in the vicinity of the transition have been elaborated and tested versus computer simulations. Analytical progress is achieved for small obstacle densities. The second paradigm is a dense strongly interacting liquid confined to a narrow slab. Then the glass transition depends nonmonotonically on the separation of the plates due to an interplay of local packing and layering. Very small slab widths allow to address certain features of the statics and dynamics analytically.

Wave propagation in media having negative permittivity and permeability.

PubMed

Ziolkowski, R W; Heyman, E

2001-11-01

Wave propagation in a double negative (DNG) medium, i.e., a medium having negative permittivity and negative permeability, is studied both analytically and numerically. The choices of the square root that leads to the index of refraction and the wave impedance in a DNG medium are determined by imposing analyticity in the complex frequency domain, and the corresponding wave properties associated with each choice are presented. These monochromatic concepts are then tested critically via a one-dimensional finite difference time domain (FDTD) simulation of the propagation of a causal, pulsed plane wave in a matched, lossy Drude model DNG medium. The causal responses of different spectral regimes of the medium with positive or negative refractive indices are studied by varying the carrier frequency of narrowband pulse excitations. The smooth transition of the phenomena associated with a DNG medium from its early-time nondispersive behavior to its late-time monochromatic response is explored with wideband pulse excitations. These FDTD results show conclusively that the square root choice leading to a negative index of refraction and positive wave impedance is the correct one, and that this choice is consistent with the overall causality of the response. An analytical, exact frequency domain solution to the scattering of a wave from a DNG slab is also given and is used to characterize several physical effects. This solution is independent of the choice of the square roots for the index of refraction and the wave impedance, and thus avoids any controversy that may arise in connection with the signs of these constituents. The DNG slab solution is used to critically examine the perfect lens concept suggested recently by Pendry. It is shown that the perfect lens effect exists only under the special case of a DNG medium with epsilon(omega)=mu(omega)=-1 that is both lossless and nondispersive. Otherwise, the closed form solutions for the field structure reveal that the DNG slab converts an incident spherical wave into a localized beam field whose parameters depend on the values of epsilon and mu. This beam field is characterized with a paraxial approximation of the exact DNG slab solution. These monochromatic concepts are again explored numerically via a causal two-dimensional FDTD simulation of the scattering of a pulsed cylindrical wave by a matched, lossy Drude model DNG slab. These FDTD results demonstrate conclusively that the monochromatic electromagnetic power flow through the DNG slab is channeled into beams rather then being focused and, hence, the Pendry perfect lens effect is not realizable with any realistic metamaterial.

Wood Performance in Doorways of Single-Family Houses

Treesearch

Thomas W. Popham; Rodney C. DeGroot; Ronald W. Howe

1978-01-01

Front doors and door frames in 175 new houses with slab-on-ground foundations were examined for moisture and decay problems in three Mississippi counties that border the Gulf of Mexico during summer 1973. Defects were often the result of building techniques of particular developers. No special problem was detected that would cause frames or doors to have excessively...

Deformation of olivine during phase transformation to wadsleyite

NASA Astrophysics Data System (ADS)

Mohiuddin, A.; Girard, J.; Karato, S. I.

2017-12-01

The strength of subducting slabs in the transition zone is critical in controlling the style of mantle convection. However, rheological properties of a subducted slab are elusive: low temperatures of a slab would make slabs strong, but in many regions there is evidence of intense deformation of slabs in the transition zone. One potential cause of intense deformation of subducting slabs is grain size reduction and accompanied microstructural changes during phase transformation of olivine to its higher-pressure polymorphs. There have been no experimental studies to quantify the influence of grain-size evolution. In addition to grain size reduction, distribution of small grains during phase transformation governs the degree of weakening during phase transformation (for e.g. load bearing framework vs. inter-connected layered framework). We conducted laboratory studies on the size and spatial distribution of new grains of wadsleyite after the transformation from olivine. Our results under static conditions show that an interconnected microstructure develops during the initial stage of phase transformation and that the grain size of the interconnected phase (wadsleyite) depends on the temperature at which the phase transformation occurs (smaller grains at lower temperatures). Development of an interconnected microstructure may lead to strain localization in the weaker phase, i.e. the fine-grained interconnected network accommodates most of the strain and therefore weakening of the entire composite. We will test this model through a series of two synchrotron in-situ deformation experiments: (i) Olivine aggregate will be deformed during slow pressure increase from deep upper mantle pressure ( 10 GPa) to transition zone pressure ( 15 GPa) at a given temperature simulating the deformation of a slab penetrating into the transition zone (ii) olivine is partially transformed to wadsleyite in a multi anvil apparatus at Yale and will be deformed within the stability field where olivine and wadsleyite coexist. We will use the Rotational Drickamer Apparatus (RDA) at a synchrotron facility (Argonne National Lab, 6-BM-B beamline, white beam and x-ray radiography) and characterize the stresses acting on olivine and wadsleyite during such simulations. We plan to present our preliminary results.

Teleseismic P and S wave attenuation constraints on temperature and melt of the upper mantle in the Alaska Subduction Zone.

NASA Astrophysics Data System (ADS)

Soto Castaneda, R. A.; Abers, G. A.; Eilon, Z.; Christensen, D. H.

2017-12-01

Recent broadband deployments in Alaska provide an excellent opportunity to advance our understanding of the Alaska-Aleutians subduction system, with implications for subduction processes worldwide. Seismic attenuation, measured from teleseismic body waves, provides a strong constraint on thermal structure as well as an indirect indication of ground shaking expected from large intermediate-depth earthquakes. We measure P and S wave attenuation from pairwise amplitude and phase spectral ratios for teleseisms recorded at 204 Transportable Array, Alaska Regional, and Alaska Volcano Observatory, SALMON (Southern Alaska Lithosphere & Mantle Observation Network) and WVLF (Wrangell Volcanics & subducting Lithosphere Fate) stations in central Alaska. The spectral ratios are inverted in a least squares sense for differential t* (path-averaged attenuation operator) and travel time anomalies at every station. Our preliminary results indicate a zone of low attenuation across the forearc and strong attenuation beneath arc and backarc in the Cook Inlet-Kenai region where the Aleutian-Yakutat slab subducts, similar to other subduction zones. This attenuation differential is observed in both the volcanic Cook Inlet segment and amagmatic Denali segments of the Aleutian subduction zone. By comparison, preliminary results for the Wrangell-St. Elias region past the eastern edge of the Aleutian slab show strong attenuation beneath the Wrangell Volcanic Field, as well as much further south than in the Cook Inlet-Kenai region. This pattern of attenuation seems to indicate a short slab fragment in the east of the subduction zone, though the picture is complex. Results also suggest the slab may focus or transmit energy with minimal attenuation, adding to the complexity. To image the critical transition between the Alaska-Aleutian slab and the region to its east, we plan to incorporate new broadband data from the WVLF array, an ongoing deployment of 37 PASSCAL instruments installed in 2016. These stations have 10-20 km spacing, spanning the edge of the subducting slab, and so will provide a zone of increased resolution in the region where slab behavior is poorly understood. We will discuss these data in the context of enigmatic Wrangell volcanism and its relationship to the eastern end of the Alaska-Aleutian Wadati-Benioff zone.

Dynamics of inductors for heating of the metal under deformation

NASA Astrophysics Data System (ADS)

Zimin, L. S.; Yeghiazaryan, A. S.; Protsenko, A. N.

2018-01-01

Current issues of creating powerful systems for hot sheet rolling with induction heating application in mechanical engineering and metallurgy were discussed. Electrodynamical and vibroacoustic problems occurring due to the induction heating of objects with complex shapes, particularly the slabs heating prior to rolling, were analysed. The numerical mathematical model using the method of related contours and the principle of virtual displacements is recommended for electrodynamical calculations. For the numerical solution of the vibrational problem, it is reasonable to use the finite element method (FEM). In general, for calculating the distribution forces, the law of Biot-Savart-Laplace method providing the determination of the current density of the skin layer in slab was used. The form of the optimal design of the inductor based on maximum hardness was synthesized while researching the vibrodynamic model of the system "inductor-metal" which provided allowable sound level meeting all established sanitary standards.

Two algorithms for neural-network design and training with application to channel equalization.

PubMed

Sweatman, C Z; Mulgrew, B; Gibson, G J

1998-01-01

We describe two algorithms for designing and training neural-network classifiers. The first, the linear programming slab algorithm (LPSA), is motivated by the problem of reconstructing digital signals corrupted by passage through a dispersive channel and by additive noise. It constructs a multilayer perceptron (MLP) to separate two disjoint sets by using linear programming methods to identify network parameters. The second, the perceptron learning slab algorithm (PLSA), avoids the computational costs of linear programming by using an error-correction approach to identify parameters. Both algorithms operate in highly constrained parameter spaces and are able to exploit symmetry in the classification problem. Using these algorithms, we develop a number of procedures for the adaptive equalization of a complex linear 4-quadrature amplitude modulation (QAM) channel, and compare their performance in a simulation study. Results are given for both stationary and time-varying channels, the latter based on the COST 207 GSM propagation model.

Fokker-Planck-Based Acceleration for SN Equations with Highly Forward Peaked Scattering in Slab Geometry

NASA Astrophysics Data System (ADS)

Patel, Japan

Short mean free paths are characteristic of charged particles. High energy charged particles often have highly forward peaked scattering cross sections. Transport problems involving such charged particles are also highly optically thick. When problems simultaneously have forward peaked scattering and high optical thickness, their solution, using standard iterative methods, becomes very inefficient. In this dissertation, we explore Fokker-Planck-based acceleration for solving such problems.

The Theory of Nearly Incompressible Magnetohydrodynamic Turbulence: Homogeneous Description

NASA Astrophysics Data System (ADS)

Zank, G. P.; Adhikari, L.; Hunana, P.; Shiota, D.; Bruno, R.; Telloni, D.; Avinash, K.

2017-09-01

The theory of nearly incompressible magnetohydrodynamics (NI MHD) was developed to understand the apparent incompressibility of the solar wind and other plasma environments, particularly the relationship of density fluctuations to incompressible manifestations of turbulence in the solar wind and interstellar medium. Of interest was the identification of distinct leading-order incompressible descriptions for plasma beta β ≫ 1 and β ∼ 1 or ≪ 1 environments. In the first case, the “dimensionality” of the MHD description is 3D whereas for the latter two, there is a collapse of dimensionality in that the leading-order incompressible MHD description is 2D in a plane orthogonal to the large-scale or mean magnetic field. Despite the success of NI MHD in describing fluctuations in a low-frequency plasma environment such as the solar wind, a basic turbulence description has not been developed. Here, we rewrite the NI MHD system in terms of Elsässer variables. We discuss the distinction that emerges between the three cases. However, we focus on the β ∼ 1 or ≪ 1 regimes since these are appropriate to the solar wind and solar corona. In both cases, the leading-order turbulence model describes 2D turbulence and the higher-order description corresponds to slab turbulence, which forms a minority component. The Elsäasser β ∼ 1 or ≪ 1 formulation exhibits the nonlinear couplings between 2D and slab components very clearly, and shows that slab fluctuations respond in a passive scalar sense to the turbulently evolving majority 2D component fluctuations. The coupling of 2D and slab fluctuations through the β ∼ 1 or ≪ 1 NI MHD description leads to a very natural emergence of the “Goldreich-Sridhar” critical balance scaling parameter, although now with a different interpretation. Specifically, the critical balance parameter shows that the energy flux in wave number space is a consequence of the intensity of Alfvén wave sweeping versus passive scalar convection by leading-order 2D Elsässer fluctuations, with critical balance being achieved when Alfvén wave sweeping balances passive scalar convection by leading-order 2D Elsässer fluctuations. Besides yielding predictions of 2D and slab spectra for Elsässer fluctuations, NI MHD shows that density fluctuations are advected by the majority or dominant incompressible velocity fluctuations. In the case of β ∼ 1 or ≪ 1, the density spectrum is Kolmogorov in the perpendicular wave number, thus providing a possible explanation for the observed extended Kolmogorov-like power law spectrum for electron density fluctuations in the interstellar medium.

Integrating surface and mantle constraints for palaeo-ocean evolution: a tour of the Arctic and adjacent regions (Arne Richter Award for Outstanding Young Scientists Lecture)

NASA Astrophysics Data System (ADS)

Shephard, Grace E.

2016-04-01

Plate tectonic reconstructions heavily rely on absolute motions derived from hotspot trails or palaeomagnetic data and ocean-floor magnetic anomaies and fracture-zone geometries to constrain the detailed history of ocean basins. However, as oceanic lithosphere is progressively recycled into the mantle, kinematic data regarding the history of these now extinct-oceans is lost. In order to better understand their evolution, novel workflows, which integrate a wide range of complementary yet independent geological and geophysical datasets from both the surface and deep mantle, must be utilised. In particular, the emergence of time-dependent, semi or self-consistent geodynamic models of ever-increasing temporal and spatial resolution are revealing some critical constraints on the evolution and fate of oceanic slabs. The tectonic evolution of the circum-Arctic is no exception; since the breakup of Pangea, this enigmatic region has seen major plate reorganizations and the opening and closure of several ocean basins. At the surface, a myriad of potential kinematic scenarios including polarity, timing, geometry and location of subduction have emerged, including for systems along continental margins and intra-oceanic settings. Furthermore, recent work has reignited a debate about the origins of 'anchor' slabs, such as the Farallon and Mongol-Okhotsk slabs, which have been used to refine absolute plate motions. Moving to the mantle, seismic tomography models reveal a region peppered with inferred slabs, however assumptions about their affinities and subduction location, timing, geometry and polarity are often made in isolation. Here, by integrating regional plate reconstructions with insights from seismic tomography, satellite derived gravity gradients, slab sinking rates and geochemistry, I explore some Mesozoic examples from the palaeo-Arctic, northern Panthalassa and western margin of North America, including evidence for a discrete and previously undescribed slab under present-day Greenland. While regional in focus, the methods and insights described have global applications and illustrate the power of an integrated approach.

Evaluation of joint sealant materials : interim report No. 1.

DOT National Transportation Integrated Search

1972-03-01

This report illustrates some of the problems caused by ineffectively sealed joints and points to the great need for properly sealing joints in both concrete pavements and structures. : The principles of design including slab lengths, joint dimensions...

Technological aspects of lift-slab method in high-rise-building construction.

NASA Astrophysics Data System (ADS)

Gaidukov, Pavel V.; Pugach, Evgeny M.

2018-03-01

The utilization efficiency of slab lifting technology for high-rise-building construction is regarded in the present article. The main problem of the article is organizing technology abilities indication, which proves the method application possibility. There is the comparing of lifting technologies and sequential concrete-frame extension, as follows: the first one: the parameters are defined, and the second one: the organizational model is executed. This model defines borders of the usage methods, as well. There is the mathematic model creating, which describes boundary conditions of the present technologies usage. This model allows to predict construction efficiency for different stored-number buildings.

Automatic low-order aberrations compensator for a conduction-cooled end-pumped solid-state zigzag slab laser

NASA Astrophysics Data System (ADS)

Yu, Xin; Dong, Lizhi; Lai, Boheng; Yang, Ping; Wang, Shuai; Wang, Xun; Liu, Yong; Tang, Guomao; Xu, Bing

2017-11-01

In order to solve the problem of large low-order aberrations with solid-state zigzag slab lasers, an automatic compensator has been developed in this paper. In this compensator, three lenses are mounted on a motorized rail, whose positions can be obtained using ray tracing method based on the beam parameters detected by a wave-front sensor. The initial peak to valley (PV) values of the wave-front range up to several tens of microns. Both simulated and experimental results show that the PV values of the wave-front can be reduced to around 1 . 6 μm with the proposed automatic compensator.

Scattering by a slab containing randomly located cylinders: comparison between radiative transfer and electromagnetic simulation.

PubMed

Roux, L; Mareschal, P; Vukadinovic, N; Thibaud, J B; Greffet, J J

2001-02-01

This study is devoted to the examination of scattering of waves by a slab containing randomly located cylinders. For the first time to our knowledge, the complete transmission problem has been solved numerically. We have compared the radiative transfer theory with a numerical solution of the wave equation. We discuss the coherent effects, such as forward-scattering dip and backscattering enhancement. It is seen that the radiative transfer equation can be used with great accuracy even for optically thin systems whose geometric thickness is comparable with the wavelength. We have also shown the presence of dependent scattering.

Detecting metastable olivine wedge beneath Japan Sea with deep earthquake coda wave interferometry

NASA Astrophysics Data System (ADS)

Shen, Z.; Zhan, Z.

2017-12-01

It has been hypothesized for decades that the lower-pressure olivine phase would kinetically persist in the interior of slab into the transition zone, forming a low-velocity "Metastable Olivine Wedge" (MOW). MOW, if exists, would play a critical role in generating deep earthquakes and parachuting subducted slabs with its buoyancy. However, seismic evidences for MOW are still controversial, and it is suggested that MOW can only be detected using broadband waveforms given the wavefront healing effects for travel times. On the other hand, broadband waveforms are often complicated by shallow heterogeneities. Here we propose a new method using the source-side interferometry of deep earthquake coda to detect MOW. In this method, deep earthquakes are turned into virtual sensors with the reciprocity theorem, and the transient strain from one earthquake to the other is estimated by cross-correlating the coda from the deep earthquake pair at the same stations. This approach effectively isolates near-source structure from complicated shallow structures, hence provide finer resolution to deep slab structures. We apply this method to Japan subduction zone with Hi-Net data, and our preliminary result does not support a large MOW model (100km thick at 410km) as suggested by several previous studies. Metastable olivine at small scales or distributed in an incoherent manner in deep slabs may still be possible.

Seismicity pattern: an indicator of source region of volcanism at convergent plate margins

NASA Astrophysics Data System (ADS)

Špičák, Aleš; Hanuš, Václav; Vaněk, Jiří

2004-04-01

The results of detailed investigation into the geometry of distribution of earthquakes around and below the volcanoes Korovin, Cleveland, Makushin, Yake-Dake, Oshima, Lewotobi, Fuego, Sangay, Nisyros and Montagne Pelée at convergent plate margins are presented. The ISC hypocentral determinations for the period 1964-1999, based on data of global seismic network and relocated by Engdahl, van der Hilst and Buland, have been used. The aim of this study has been to contribute to the solution of the problem of location of source regions of primary magma for calc-alkaline volcanoes spatially and genetically related to the process of subduction. Several specific features of seismicity pattern were revealed in this context. (i) A clear occurrence of the intermediate-depth aseismic gap (IDAG) in the Wadati-Benioff zone (WBZ) below all investigated active volcanoes. We interpret this part of the subducted slab, which does not contain any teleseismically recorded earthquake with magnitude greater than 4.0, as a partially melted domain of oceanic lithosphere and as a possible source of primary magma for calc-alkaline volcanoes. (ii) A set of earthquakes in the shape of a seismically active column (SAC) seems to exists in the continental wedge below volcanoes Korovin, Makushin and Sangay. The seismically active columns probably reach from the Earth surface down to the aseismic gap in the Wadati-Benioff zone. This points to the possibility that the upper mantle overlying the subducted slab does not contain large melted domains, displays an intense fracturing and is not likely to represent the site of magma generation. (iii) In the continental wedge below the volcanoes Cleveland, Fuego, Nisyros, Yake-Dake, Oshima and Lewotobi, shallow seismicity occurs down to the depth of 50 km. The domain without any earthquakes between the shallow seismically active column and the aseismic gap in the Wadati-Benioff zone in the depth range of 50-100 km does not exclude the melting of the mantle also above the slab. (iv) Any earthquake does not exist in the lithospheric wedge below the volcano Montagne Pelée. The source of primary magma could be located in the subducted slab as well as in the overlying mantle wedge. (v) Frequent aftershock sequences accompanying stronger earthquakes in the seismically active columns indicate high fracturing of the wedge below active volcanoes. (vi) The elongated shape of clusters of epicentres of earthquakes of seismically active columns, as well as stable parameters of the available fault plane solutions, seem to reflect the existence of dominant deeply rooted fracture zones below volcanoes. These facts also favour the location of primary magma in the subducting slab rather than in the overlying wedge. We suppose that melts advancing from the slab toward the Earth surface may trigger the observed earthquakes in the continental wedge that is critically pre-stressed by the process of subduction. However, for definitive conclusions it will be necessary to explain the occurrence of earthquake clusters below some volcanoes and the lack of seismicity below others, taking into account the uncertainty of focal depth determination from global seismological data in some regions.

Scaling up spike-and-slab models for unsupervised feature learning.

PubMed

Goodfellow, Ian J; Courville, Aaron; Bengio, Yoshua

2013-08-01

We describe the use of two spike-and-slab models for modeling real-valued data, with an emphasis on their applications to object recognition. The first model, which we call spike-and-slab sparse coding (S3C), is a preexisting model for which we introduce a faster approximate inference algorithm. We introduce a deep variant of S3C, which we call the partially directed deep Boltzmann machine (PD-DBM) and extend our S3C inference algorithm for use on this model. We describe learning procedures for each. We demonstrate that our inference procedure for S3C enables scaling the model to unprecedented large problem sizes, and demonstrate that using S3C as a feature extractor results in very good object recognition performance, particularly when the number of labeled examples is low. We show that the PD-DBM generates better samples than its shallow counterpart, and that unlike DBMs or DBNs, the PD-DBM may be trained successfully without greedy layerwise training.

Negotiating Multicollinearity with Spike-and-Slab Priors

PubMed Central

Ročková, Veronika

2014-01-01

In multiple regression under the normal linear model, the presence of multicollinearity is well known to lead to unreliable and unstable maximum likelihood estimates. This can be particularly troublesome for the problem of variable selection where it becomes more difficult to distinguish between subset models. Here we show how adding a spike-and-slab prior mitigates this difficulty by filtering the likelihood surface into a posterior distribution that allocates the relevant likelihood information to each of the subset model modes. For identification of promising high posterior models in this setting, we consider three EM algorithms, the fast closed form EMVS version of Rockova and George (2014) and two new versions designed for variants of the spike-and-slab formulation. For a multimodal posterior under multicollinearity, we compare the regions of convergence of these three algorithms. Deterministic annealing versions of the EMVS algorithm are seen to substantially mitigate this multimodality. A single simple running example is used for illustration throughout. PMID:25419004

Cretaceous subduction in the Pyrenees: Iberian plate-kinematics in a mantle reference frame

NASA Astrophysics Data System (ADS)

Vissers, Reinoud; van Hinsbergen, Douwe; van der Meer, Douwe; Spakman, Wim

2016-04-01

During the Cretaceous, Iberia was a microplate separated from Laurasia and Gondwana by ridges and transforms, and by a convergent margin to its northeast along which the Pyrenean fold-thrust belt developed. As a microplate, Iberia underwent a well-defined but ill-understood Albian-Aptian ~ 35° counterclockwise rotation relative to Eurasia. Three competing kinematic scenarios for Iberian motion in the late Mesozoic are all compatible with the Pyrenean geological record and comprise (1) transtensional eastward motion of Iberia versus Eurasia, (2) strike-slip motion followed by orthogonal extension and (3) scissor-style opening of the Bay of Biscay coupled with subduction in the Pyrenean realm. The last scenario is the only one consistent with paleomagnetic and ocean floor anomaly constraints showing Iberia's rotation, but is criticized because the upper mantle below the Pyrenees contains no evidence for a subducted slab. Here we show that when taking absolute plate motions into account, Aptian oceanic subduction in the Pyrenees followed by Albian slab break-off should leave a slab remnant in the present-day mid-mantle below NW Africa instead of below the Pyrenees. Mantle tomography shows a positive seismic velocity anomaly that matches the predicted position and dimension of such a slab remnant between 1900 and 1500 km depth below Reggane in Southern Algeria. Seismic tomographic imaging of the mantle structure therefore does not falsify the Pyrenean subduction hypothesis, and provides no basis to discard marine magnetic and paleomagnetic constraints on Iberia's kinematic history. Slab break-off explains the well-dated Albian-Cenomanian high-temperature metamorphism in the Pyrenees that hitherto has been interpreted as an expression of continental break-up and hyperextension. We suspect that subduction in the Pyrenees may have played a key role in driving the rapid Aptian rotation of the Iberian microplate.

The Ophiolite Problem, Is It Really a Problem?

NASA Astrophysics Data System (ADS)

Casey, J. F.; Dewey, J. F.

2009-12-01

Ophiolites and ophiolite complexes have been recognized as having an oceanic affinity or origin since the classic work of Ian Gass in the 1950’s on the Troodos Complex. A problem has been that the term ophiolite has included a very diverse range of meanings from obscure slivers of mafic and ultramafic rocks of doubtful origin in orogenic belts to large obducted slabs with the full range (Coleman, 1972), from base to top, of lherzolite/ariegite, harzburgite, dunite, gabbro, sheeted dyke complex, pillow basalts, and sediments, commonly with a two-pyroxene mafic granulite as a thin aureole attached to the base of the complex. Large obducted ophiolite slabs are mainly early Ordovician and mid-Cretaceous. The principal enigma of these obducted slabs is that they clearly must have been generated by some form of organized sea-floor spreading/plate-accretion, such as may be envisioned for the oceanic ridges, yet the volcanics commonly have arc affinity (Miyashiro) with boninites (high-temperature/low-pressure, high Mg and Si andesites), which suggest a forearc origin. Our model hinges on the PT conditions under which boninites form. Many ophiolites have complexly-deformed associated assemblages that suggest fracture zone/transform geology, which in turn has led to models involving the nucleation of subduction zones on fracture zones/transforms. Hitherto, arc-related sea-floor-spreading has been considered to be either pre-arc (fore-arc boninites) or post-arc (classic Karig-style back arc basins that split arcs). We propose a new model with syn-arc boninites that involves a stable ridge/trench/trench triple junction, the ridge being between the two upper plates. The direction of subduction must be oblique with a different sense in the two subduction zones and the oblique subduction cannot be partitioned into trench orthogonal and parallel strike-slip components. As the ridge spreads, new oceanic lithosphere is created within the forearc, the arc and fore-arc lengthen significantly, and a syn-arc ophiolite complex is generated that ages along arc-strike; a distinctive diachronous boninite/arc volcanic stratigraphy develops. Dikes in the ophiolite are oblique to the trench as are magnetic anomalies in the “back-arc” basin. Boninites and high-mg andesites are generated in the fore-arc under the aqueous, low pressure/high temperature, regime at the ridge above the dehydrating slab or where a ridge subducts beneath the forearc. The mafic protolith, garnet/two pyroxene, aureole is generated in and sliced from the subducting slab and attached to the base of the overriding lithosphere at about 1000°C, ten to twelve million years from the ridge axis, where the SSZ ophiolite is about ten to twelve kilometers thick, at which thickness of the ophiolite is buffered by the subducting slab. Obduction of the SSZ ophiolite with its subjacent aureole occurs whenever the oceanic arc attempts subduction of a stable continental margin.

Assessment of mitigating embankment settlement with pile-supported approach slabs : final report.

DOT National Transportation Integrated Search

1999-12-01

Problems involving highway bridge approach settlement have been observed at many sites in Louisiana. In southeastern Louisiana, where subsoil settlement potential is the greatest, the bridge structures are usually lengthened in order to reduce the he...

Assessment of mitigating embankment settlement with pile-supported approach slabs : summary report.

DOT National Transportation Integrated Search

1999-12-01

Problems involving highway bridge approach settlement have been observed at many sites in Louisiana. In southeastern Louisiana, where subsoil settlement potential is the greatest, the bridge structures are usually lengthened in order to reduce the he...

Characterizing wet slab and glide slab avalanche occurrence along the Going-to-the-Sun Road, Glacier National Park, Montana, USA

USGS Publications Warehouse

Peitzsch, Erich H.; Hendrikx, Jordy; Fagre, Daniel B.; Reardon, Blase

2010-01-01

Wet slab and glide slab snow avalanches are dangerous and yet can be particularly difficult to predict. Both wet slab and glide slab avalanches are thought to depend upon free water moving through the snowpack but are driven by different processes. In Glacier National Park, Montana, both types of avalanches can occur in the same year and affect the Going-to-the-Sun Road (GTSR). Both wet slab and glide slab avalanches along the GTSR from 2003-2010 are investigated. Meteorological data from two high-elevation weather stations and one SNOTEL site are used in conjunction with an avalanche database and snowpit profiles. These data were used to characterize years when only glide slab avalanches occurred and those years when both glide slab and wet slab avalanches occurred. Results of 168 glide slab and 57 wet slab avalanches along the GTSR suggest both types of avalanche occurrence depend on sustained warming periods with intense solar radiation (or rain on snow) to produce free water in the snowpack. Differences in temperature and net radiation metrics between wet slab and glide slab avalanches emerge as one moves from one day to seven days prior to avalanche occurrence. On average, a more rapid warming precedes wet slab avalanche occurrence. Glide slab and wet slab avalanches require a similar amount of net radiation. Wet slab avalanches do not occur every year, while glide slab avalanches occur annually. These results aim to enhance understanding of the required meteorological conditions for wet slab and glide slab avalanches and aid in improved wet snow avalanche forecasting.

Applied approach slab settlement research, design/construction : final report.

DOT National Transportation Integrated Search

2013-08-01

Approach embankment settlement is a pervasive problem in Oklahoma and many other states. The bump and/or abrupt slope change poses a danger to traffic and can cause increased dynamic loads on the bridge. Frequent and costly maintenance may be needed ...

ONR Far East Scientific Information Bulletin. Volume 14, Number 4, October-December 1989

DTIC Science & Technology

1989-12-01

methods. said by Greenlaw, "the breadth first search problem is easier than the depth first prob- Keynote and Invited Speeches lem." Another fruitful ...circuit design problems taken as a warning that logic alone is not with reasonable efficiency. likely to be a fruitful approach to problem solving. In...width on test slabs cantly affect the mechanical properties. The were detected with good reliability. Lee et addition of 0.3 wt. % Mo produced an al

In situ seismic anisotropy around deep earthquakes in Japan subduction slabs using Japan Meteorological Agency moment tensors

NASA Astrophysics Data System (ADS)

Li, J.; Zheng, Y.; Thomsen, L.

2017-12-01

Knowing the in situ seismic anisotropy around deep earthquakes in slabs is important in understanding deep-earthquake mechanism as it may provide critically needed information about the rock fabric where deep earthquakes occur. It has been recognized for about 50 years that many deep earthquakes are not double-couple (DC) events. Previously we showed that in situ anisotropy around deep earthquakes could explain such observed non-DC events. Traditionally, the shear wave splitting method has been used to infer such anisotropy around deep earthquakes but this is challenging because it will need many crossing ray paths for the method to localize the anisotropic region (Long 2013). In this abstract, we adopt the same procedure to obtain anisotropy in the Pacific slab under Japan using moment tensors provided by the Japan Meteorological Agency using the F-net data. We directly probe the in situ anisotropy within the subducting slabs using the radiation patterns (represented by the moment tensors) of deep earthquakes (with depth greater than 60 km). By assuming a group of shear dislocation events embedded in a common tilted transversely isotropic (TTI) medium, we used the moment tensors as our input data to invert for the anisotropy in Mariana-Japan-Kuril subducting zone. The TTI medium is characterized by the P and S wave velocities along the symmetry axis (described by two free angles) and three Thomsen parameters. We divided the deep earthquake events into 9 groups by their spatial proximity using the k-means clustering method (Hartigan and Wong 1979). These 9 groups include 2 intermediate-depth groups (depth from 60 km to 300 km) and 7 deep-focus groups (depth greater than 300 km). Our inversion results show that the inverted TTI symmetry axes are perpendicular to the slab interface for two intermediate-depth groups (consistent with dehydration metamorphic reactions) and parallel to the slab interface for 7 deep-focus group. The shear wave anisotropy is best resolved by our inversion algorithm with a typical value of around 28% (ranging from 25% to 41%). Our inverted anisotropy provides direct information of stress and rock fabric inside the subducting slab and may help explain the mechanisms of deep earthquakes.

Tracing Geophysical Indicators of Fluid-Induced Serpentinization in the Pampean Flat Slab Subduction Region of Chile

NASA Astrophysics Data System (ADS)

Bourke, J. R.; Nikulin, A.; Park, J. J.

2016-12-01

An activity gap in the Andean volcanic arc in the Pampean section of the subduction zone in Chile ( 28°-33°S) marks a section of flat-slab subduction. Past studies connected this change in geometry to the collision and subduction of the Juan Fernandez Ridge and the resulting migration of both the thrust front and magmatism eastward to the Sierras Pampeanas. The fate of fluids released from the subducting Nazca slab remains uncertain and the degree of their interaction with the basal layer of the continental lithosphere is poorly understood. We present initial results of a receiver-function investigation and forward-modeling effort at station GO03 operated by the Chilean National Seismic Network. Receiver function analysis of 75 well-recorded teleseismic earthquake events recorded at GO03 allow us to constrain the position of the subducting Nazca slab and to address the physical properties of the interplate contact zone. Critically, our analysis indicates presence of a highly-anisotropic zone of low velocities directly above the subucting Nazca slab. We point out a remarkable similarity in geophysical characteristics between the observed seismic anomaly at GO03 and a volume of proposed serpentinization in an area of sub-horizontal subduction above the Juan de Fuca slab in Cascadia. This interpretation is further supported by forward-modeling receiver functions at GO03 relying on a velocity model that incorporates a serpentinized interplate region. The newly-identified low-velocity highly-anisotropic layer may extend beyond the GO03 area and act as a mineral reservoir that captures and, possibly, transports fluids derived from the dehydrating Nazca Plate as it subducts below South America. It is likely that there is a relationship between this feature and the lack of volcanic activity in the Pampean flat slab region. Figure Caption: A) Backazimuth sweep of receiver functions recorded at station GO03 with predicted phase arrivals plotted for 55 km, 65 km, 75 km and 85 km. B) Depth-migrated receiver functions for station GO03 relying on AK-135 velocity model and local seismicity (Mw>4.5) plotted within 15km of a 100km profile centered on GO03 along the dominant direction of subduction (74°).

Distance-Dependent Sign Reversal in the Casimir-Lifshitz Torque

NASA Astrophysics Data System (ADS)

Thiyam, Priyadarshini; Parashar, Prachi; Shajesh, K. V.; Malyi, Oleksandr I.; Boström, Mathias; Milton, Kimball A.; Brevik, Iver; Persson, Clas

2018-03-01

The Casimir-Lifshitz torque between two biaxially polarizable anisotropic planar slabs is shown to exhibit a nontrivial sign reversal in its rotational sense. The critical distance ac between the slabs that marks this reversal is characterized by the frequency ωc˜c /2 ac at which the in-planar polarizabilities along the two principal axes are equal. The two materials seek to align their principal axes of polarizabilities in one direction below ac, while above ac their axes try to align rotated perpendicular relative to their previous minimum energy orientation. The sign reversal disappears in the nonretarded limit. Our perturbative result, derived for the case when the differences in the relative polarizabilities are small, matches excellently with the exact theory for uniaxial materials. We illustrate our results for black phosphorus and phosphorene.

The effect of a realistic thermal diffusivity on numerical model of a subducting slab

NASA Astrophysics Data System (ADS)

Maierova, P.; Steinle-Neumann, G.; Cadek, O.

2010-12-01

A number of numerical studies of subducting slab assume simplified (constant or only depth-dependent) models of thermal conductivity. The available mineral physics data indicate, however, that thermal diffusivity is strongly temperature- and pressure-dependent and may also vary among different mantle materials. In the present study, we examine the influence of realistic thermal properties of mantle materials on the thermal state of the upper mantle and the dynamics of subducting slabs. On the basis of the data published in mineral physics literature we compile analytical relationships that approximate the pressure and temperature dependence of thermal diffusivity for major mineral phases of the mantle (olivine, wadsleyite, ringwoodite, garnet, clinopyroxenes, stishovite and perovskite). We propose a simplified composition of mineral assemblages predominating in the subducting slab and the surrounding mantle (pyrolite, mid-ocean ridge basalt, harzburgite) and we estimate their thermal diffusivity using the Hashin-Shtrikman bounds. The resulting complex formula for the diffusivity of each aggregate is then approximated by a simpler analytical relationship that is used in our numerical model as an input parameter. For the numerical modeling we use the Elmer software (open source finite element software for multiphysical problems, see http://www.csc.fi/english/pages/elmer). We set up a 2D Cartesian thermo-mechanical steady-state model of a subducting slab. The model is partly kinematic as the flow is driven by a boundary condition on velocity that is prescribed on the top of the subducting lithospheric plate. Reology of the material is non-linear and is coupled with the thermal equation. Using the realistic relationship for thermal diffusivity of mantle materials, we compute the thermal and flow fields for different input velocity and age of the subducting plate and we compare the results against the models assuming a constant thermal diffusivity. The importance of the realistic description of thermal properties in models of subducted slabs is discussed.

A multigroup radiation diffusion test problem: Comparison of code results with analytic solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shestakov, A I; Harte, J A; Bolstad, J H

2006-12-21

We consider a 1D, slab-symmetric test problem for the multigroup radiation diffusion and matter energy balance equations. The test simulates diffusion of energy from a hot central region. Opacities vary with the cube of the frequency and radiation emission is given by a Wien spectrum. We compare results from two LLNL codes, Raptor and Lasnex, with tabular data that define the analytic solution.

Sculpting Ceramic Heads.

ERIC Educational Resources Information Center

Sapiro, Maurice

1983-01-01

Clay sculpture is difficult to produce because of the requirements of kiln firing. The problems can be overcome by modeling the original manikin head and making a plaster mold, pressing molding slabs of clay into the plaster mold to form the hollow clay armature, and sculpting on the armature. (IS)

Radiative heat transfer and nonequilibrium Casimir-Lifshitz force in many-body systems with planar geometry

NASA Astrophysics Data System (ADS)

Latella, Ivan; Ben-Abdallah, Philippe; Biehs, Svend-Age; Antezza, Mauro; Messina, Riccardo

2017-05-01

A general theory of photon-mediated energy and momentum transfer in N -body planar systems out of thermal equilibrium is introduced. It is based on the combination of the scattering theory and the fluctuational-electrodynamics approach in many-body systems. By making a Landauer-like formulation of the heat transfer problem, explicit formulas for the energy transmission coefficients between two distinct slabs as well as the self-coupling coefficients are derived and expressed in terms of the reflection and transmission coefficients of the single bodies. We also show how to calculate local equilibrium temperatures in such systems. An analogous formulation is introduced to quantify momentum transfer coefficients describing Casimir-Lifshitz forces out of thermal equilibrium. Forces at thermal equilibrium are readily obtained as a particular case. As an illustration of this general theoretical framework, we show on three-body systems how the presence of a fourth slab can impact equilibrium temperatures in heat-transfer problems and equilibrium positions resulting from the forces acting on the system.

Subduction zone seismicity and the thermo-mechanical evolution of downgoing lithosphere

NASA Astrophysics Data System (ADS)

Wortel, M. J. R.; Vlaar, N. J.

1988-09-01

In this paper we discuss characteristic features of subduction zone seismicity at depths between about 100 km and 700 km, with emphasis on the role of temperature and rheology in controlling the deformation of, and the seismic energy release in downgoing lithosphere. This is done in two steps. After a brief review of earlier developments, we first show that the depth distribution of hypocentres at depths between 100 km and 700 km in subducted lithosphere can be explained by a model in which seismic activity is confined to those parts of the slab which have temperatures below a depth-dependent critical value T cr. Second, the variation of seismic energy release (frequency of events, magnitude) with depth is addressed by inferring a rheological evolution from the slab's thermal evolution and by combining this with models for the system of forces acting on the subducting lithosphere. It is found that considerable stress concentration occurs in a reheating slab in the depth range of 400 to 650 700 km: the slab weakens, but the stress level strongly increases. On the basis of this stress concentration a model is formulated for earthquake generation within subducting slabs. The model predicts a maximum depth of seismic activity in the depth range of 635 to 760 km and, for deep earthquake zones, a relative maximum in seismic energy release near the maximum depth of earthquakes. From our modelling it follows that, whereas such a maximum is indeed likely to develop in deep earthquake zones, zones with a maximum depth around 300 km (such as the Aleutians) are expected to exhibit a smooth decay in seismic energy release with depth. This is in excellent agreement with observational data. In conclusion, the incoroporation of both depth-dependent forces and depth-dependent rheology provides new insight into the generation of intermediate and deep earthquakes and into the variation of seismic activity with depth. Our results imply that no barrier to slab penetration at a depth of 650 700 km is required to explain the maximum depth of seismic activity and the pattern of seismic energy release in deep earthquake zones.

Dynamics of double-polarity subduction: application to the Western Mediterranean

NASA Astrophysics Data System (ADS)

Peral, Mireia; Zlotnik, Sergio; Fernandez, Manel; Vergés, Jaume; Jiménez-Munt, Ivone; Torne, Montserrat

2016-04-01

The evolution of the Western Mediterranean is a highly debated question by geologists and geophysicists. Even though most scientists agree in considering slab roll-back to be the driving mechanism of the tectonic evolution of this area, there is still no consensus about the initial setup and its time evolution. A recent model suggests a lateral change in subduction polarity of the Ligurian-Thetys oceanic domain to explain the formation and evolution of the Betic-Rif orogenic system and the associated Alboran back-arc basin. Such geodynamic scenario is also proposed for different converging regions. The aim of this study is to analyze the dynamic evolution of a double-polarity subduction process and its consequences in order to test the physical feasibility of this interaction and provide geometries and evolutions comparable to those proposed for the Western Mediterranean. The 3D numerical model is carried out via the Underworld framework. Tectonic plate behavior is described by equations of fluid dynamics in the presence of several different phases. Underworld solves a non-linear Stokes flow problem using Finite Elements combined with particle-in-cell approach, thus the discretization combines a standard Eulerian Finite Element mesh with Lagrangian particles to track the location of the phases. The final model consists of two oceanic plates with viscoplastic rheology subducting into the upper mantle in opposite direction and the problem is driven by Rayleigh-Taylor instability. We study the influence of the boundary conditions in the model evolution, and the slab deformation produced by the proximity between both plates. Moreover the case of asymmetric friction on the lateral sides of slabs is also considered. Simulations of single subduction models are used as a reference, to compare results and understand the influence of the second plate. We observe slight differences in the trench retreat velocity and the slab morphology near the contact area when plates are spaced less than 100 km.

Effects of shape and size of agar gels on heating uniformity during pulsed microwave treatment.

PubMed

Soto-Reyes, Nohemí; Temis-Pérez, Ana L; López-Malo, Aurelio; Rojas-Laguna, Roberto; Sosa-Morales, María Elena

2015-05-01

Model gel systems with different shape (sphere, cylinder, and slab) and size (180 and 290 g) were prepared with agar (5%) and sucrose (5%). Dielectric constant (ε'), loss factor (ε"), thermophysical properties, and temperature distribution of the model system were measured. Each agar model system was immersed and suspended in water, and then, heated in a microwave oven with intermittent heating until the core temperature reached 50 °C. The ε' and ε" of agar gels decreased when frequency increased. The density and thermal conductivity values of the agar gels were 1033 kg/m(3) and 0.55 W/m °C, respectively. The temperature distribution of sphere, cylinder, and slab was different when similar power doses were applied. The slab reached 50 °C in less time (10 min) and showed a more uniform heating than spheres and cylinders in both sizes. Agar model systems of 180 g heated faster than those of 290 g. The coldest point was the center of the model systems in all studied cases. Shape and size are critical food factors that affect the heating uniformity during microwave heating processes. © 2015 Institute of Food Technologists®

Ponderomotive force on solitary structures created during radiation pressure acceleration of thin foils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tripathi, Vipin K.; Sharma, Anamika

2013-05-15

We estimate the ponderomotive force on an expanded inhomogeneous electron density profile, created in the later phase of laser irradiated diamond like ultrathin foil. When ions are uniformly distributed along the plasma slab and electron density obeys the Poisson's equation with space charge potential equal to negative of ponderomotive potential, φ=−φ{sub p}=−(mc{sup 2}/e)(γ−1), where γ=(1+|a|{sup 2}){sup 1/2}, and |a| is the normalized local laser amplitude inside the slab; the net ponderomotive force on the slab per unit area is demonstrated analytically to be equal to radiation pressure force for both overdense and underdense plasmas. In case electron density is takenmore » to be frozen as a Gaussian profile with peak density close to relativistic critical density, the ponderomotive force has non-monotonic spatial variation and sums up on all electrons per unit area to equal radiation pressure force at all laser intensities. The same result is obtained for the case of Gaussian ion density profile and self consistent electron density profile, obeying Poisson's equation with φ=−φ{sub p}.« less

Origins of ultralow velocity zones through slab-derived metallic melt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jiachao; Li, Jie; Hrubiak, Rostislav

2016-05-03

Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron-carbon system crosses the current geotherm near Earth’s core-mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce themore » seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich post-bridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth’s core-mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle.« less

Origins of ultralow velocity zones through slab-derived metallic melt

PubMed Central

Liu, Jiachao; Li, Jie; Smith, Jesse S.

2016-01-01

Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron−carbon system crosses the current geotherm near Earth’s core−mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce the seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich postbridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth's core−mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle. PMID:27143719

Innovative discharge geometries for diffusion-cooled gas lasers

NASA Astrophysics Data System (ADS)

Lapucci, Antonio

2004-09-01

Large area, narrow discharge gap, diffusion cooled gas lasers are nowadays a well established technology for the construction of industrial laser sources. Successful examples exist both with the slab (Rofin-Sinar) or coaxial (Trumpf) geometry. The main physical properties and the associated technical problems of the transverse large area RF discharge, adopted for the excitation of high power diffusion cooled gas lasers, are reviewed here. The main problems of this technology are related to the maintenance of a uniform and stable plasma excitation between closely spaced large-area electrodes at high power-density loading. Some practical solutions such as distributed resonance of the discharge channel proved successful in the case of square or rectangular cross-sections but hardly applicable to geometries such as that of coaxial electrodes. In this paper we present some solutions, adopted by our group, for the development of slab and annular CO2 lasers and for CO2 laser arrays with linear or circular symmetry. We will also briefly mention the difficulties encountered in the extraction of a good quality beam from an active medium with such a cross section. A problem that has also seen some interesting solutions.

Constraints of subducted slab geometries on trench migration and subduction velocities: flat slabs and slab curtains in the mantle under Asia

NASA Astrophysics Data System (ADS)

Wu, J. E.; Suppe, J.; Renqi, L.; Lin, C.; Kanda, R. V.

2013-12-01

The past locations, shapes and polarity of subduction trenches provide first-order constraints for plate tectonic reconstructions. Analogue and numerical models of subduction zones suggest that relative subducting (Vs) and overriding (Vor) plate velocities may strongly influence final subducted slab geometries. Here we have mapped the 3D geometries of subducted slabs in the upper and lower mantle of Asia from global seismic tomography. We have incorporated these slabs into plate tectonic models, which allows us to infer the subducting and overriding plate velocities. We describe two distinct slab geometry styles, ';flat slabs' and ';slab curtains', and show their implications for paleo-trench positions and subduction geometries in plate tectonic reconstructions. When compared to analogue and numerical models, the mapped slab styles show similarities to modeled slabs that occupy very different locations within Vs:Vor parameter space. ';Flat slabs' include large swaths of sub-horizontal slabs in the lower mantle that underlie the well-known northward paths of India and Australia from Eastern Gondwana, viewed in a moving hotspot reference. At India the flat slabs account for a significant proportion of the predicted lost Ceno-Tethys Ocean since ~100 Ma, whereas at Australia they record the existence of a major 8000km by 2500-3000km ocean that existed at ~43 Ma between East Asia, the Pacific and Australia. Plate reconstructions incorporating the slab constraints imply these flat slab geometries were generated when continent overran oceanic lithosphere to produce rapid trench retreat, or in other words, when subducting and overriding velocities were equal (i.e. Vs ~ Vor). ';Slab curtains' include subvertical Pacific slabs near the Izu-Bonin and Marianas trenches that extend from the surface down to 1500 km in the lower mantle and are 400 to 500 km thick. Reconstructed slab lengths were assessed from tomographic volumes calculated at serial cross-sections. The ';slab curtain' geometry and restored slab lengths indicate a nearly stationary Pacific trench since ~43 Ma. In contrast to the flat slabs, here the reconstructed subduction zone had large subducting plate velocities relative to very small overriding plate velocities (i.e. Vs >> Vor). In addition to flat slabs and slab curtains, we also find other less widespread local subduction settings that lie at other locations in Vs:Vor parameter space or involved other processes. Slabs were mapped using Gocad software. Mapped slabs were restored to a spherical model Earth surface by two approaches: unfolding (i.e. piecewise flattening) to minimize shape and area distortions, and by evaluated mapped slab volumes. Gplates software was used to integrate the mapped slabs with plate tectonic reconstructions.

Ionic Graphitization of Ultrathin Films of Ionic Compounds.

PubMed

Kvashnin, A G; Pashkin, E Y; Yakobson, B I; Sorokin, P B

2016-07-21

On the basis of ab initio density functional calculations, we performed a comprehensive investigation of the general graphitization tendency in rocksalt-type structures. In this paper, we determine the critical slab thickness for a range of ionic cubic crystal systems, below which a spontaneous conversion from a cubic to a layered graphitic-like structure occurs. This conversion is driven by surface energy reduction. Using only fundamental parameters of the compounds such as the Allen electronegativity and ionic radius of the metal atom, we also develop an analytical relation to estimate the critical number of layers.

The dynamics of double slab subduction

NASA Astrophysics Data System (ADS)

Holt, A. F.; Royden, L. H.; Becker, T. W.

2017-04-01

We use numerical models to investigate the dynamics of two interacting slabs with parallel trenches. Cases considered are: a single slab reference, outward dipping slabs (out-dip), inward dipping slabs (in-dip) and slabs dipping in the same direction (same-dip). Where trenches converge over time (same-dip and out-dip systems), large positive dynamic pressures in the asthenosphere are generated beneath the middle plate and large trench-normal extensional forces are transmitted through the middle plate. This results in slabs that dip away from the middle plate at depth, independent of trench geometry. The single slab, the front slab in the same-dip case and both out-dip slabs undergo trench retreat and exhibit stable subduction. However, slabs within the other double subduction systems tend to completely overturn at the base of the upper mantle, and exhibit either trench advance (rear slab in same-dip), or near-stationary trenches (in-dip). For all slabs, the net slab-normal dynamic pressure at 330 km depth is nearly equal to the slab-normal force induced by slab buoyancy. For double subduction, the net outward force on the slabs due to dynamic pressure from the asthenosphere is effectively counterbalanced by the net extensional force transmitted through the middle plate. Thus, dynamic pressure at depth, interplate coupling and lithospheric stresses are closely linked and their effects cannot be isolated. Our results provide insights into both the temporal evolution of double slab systems on Earth and, more generally, how the various components of subduction systems, from mantle flow/pressure to interplate coupling, are dynamically linked.

Evaluation of the telegrapher's equation and multiple-flux theories for calculating the transmittance and reflectance of a diffuse absorbing slab.

PubMed

Kong, Steven H; Shore, Joel D

2007-03-01

We study the propagation of light through a medium containing isotropic scattering and absorption centers. With a Monte Carlo simulation serving as the benchmark solution to the radiative transfer problem of light propagating through a turbid slab, we compare the transmission and reflection density computed from the telegrapher's equation, the diffusion equation, and multiple-flux theories such as the Kubelka-Munk and four-flux theories. Results are presented for both normally incident light and diffusely incident light. We find that we can always obtain very good results from the telegrapher's equation provided that two parameters that appear in the solution are set appropriately. We also find an interesting connection between certain solutions of the telegrapher's equation and solutions of the Kubelka-Munk and four-flux theories with a small modification to how the phenomenological parameters in those theories are traditionally related to the optical scattering and absorption coefficients of the slab. Finally, we briefly explore how well the theories can be extended to the case of anisotropic scattering by multiplying the scattering coefficient by a simple correction factor.

Behaviour of reinforced concrete slabs with steel fibers

NASA Astrophysics Data System (ADS)

Baarimah, A. O.; Syed Mohsin, S. M.

2017-11-01

This paper investigates the potential effect of steel fiber added into reinforced concrete slabs. Four-point bending test is conducted on six slabs to investigate the structural behaviour of the slabs by considering two different parameters; (i) thickness of slab (ii) volume fraction of steel fiber. The experimental work consists of six slabs, in which three slabs are designed in accordance to Eurocode 2 to fulfil shear capacity characteristic, whereas, the other three slabs are designed with 17% less thickness, intended to fail in shear. Both series of slabs are added with steel fiber with a volume fraction of Vf = 0%, Vf = 1% and Vf = 2% in order to study the effect and potential of fiber to compensate the loss in shear capacity. The slab with Vf = 0% steel fiber and no reduction in thickness is taken as the control slab. The experimental result suggests promising improvement of the load carrying capacity (up to 32%) and ductility (up to 87%) as well as delayed in crack propagation for the slabs with Vf = 2%. In addition, it is observed that addition of fibers compensates the reduction in the slab thickness as well as changes the failure mode of the slab from brittle to a more ductile manner.

Slab-pull and slab-push earthquakes in the Mexican, Chilean and Peruvian subduction zones

NASA Astrophysics Data System (ADS)

Lemoine, A.; Madariaga, R.; Campos, J.

2002-09-01

We studied intermediate depth earthquakes in the Chile, Peru and Mexican subduction zones, paying special attention to slab-push (down-dip compression) and slab-pull (down-dip extension) mechanisms. Although, slab-push events are relatively rare in comparison with slab-pull earthquakes, quite a few have occurred recently. In Peru, a couple slab-push events occurred in 1991 and one slab-pull together with several slab-push events occurred in 1970 near Chimbote. In Mexico, several slab-push and slab-pull events occurred near Zihuatanejo below the fault zone of the 1985 Michoacan event. In central Chile, a large M=7.1 slab-push event occurred in October 1997 that followed a series of four shallow Mw>6 thrust earthquakes on the plate interface. We used teleseismic body waveform inversion of a number of Mw>5.9 slab-push and slab-pull earthquakes in order to obtain accurate mechanisms, depths and source time functions. We used a master event method in order to get relative locations. We discussed the occurrence of the relatively rare slab-push events in the three subduction zones. Were they due to the geometry of the subduction that produces flexure inside the downgoing slab, or were they produced by stress transfer during the earthquake cycle? Stress transfer can not explain the occurence of several compressional and extensional intraplate intermediate depth earthquakes in central Chile, central Mexico and central Peru. It seemed that the heterogeneity of the stress field produced by complex slab geometry has an important influence on intraplate intermediate depth earthquakes.

Intra-slab COH fluid fluxes evidenced by fluid-mediated decarbonation of lawsonite eclogite-facies altered oceanic metabasalts

NASA Astrophysics Data System (ADS)

Vitale Brovarone, Alberto; Chu, Xu; Martin, Laure; Ague, Jay J.; Monié, Patrick; Groppo, Chiara; Martinez, Isabelle; Chaduteau, Carine

2018-04-01

The interplay between the processes controlling the mobility of H2O and C-bearing species during subduction zone metamorphism exerts a critical control on plate tectonics and global volatile recycling. Here we present the first study on fresh, carbonate-bearing, lawsonite eclogite-facies metabasalts from Alpine Corsica, France, which reached the critical depths at which important devolatilization reactions occur in subducting slabs. The studied samples indicate that the evolution of oceanic crustal sequences subducted under present-day thermal regimes is dominated by localized fluid-rock interactions that are strongly controlled by the nature and extent of inherited (sub)seafloor hydrothermal processes, and by the possibility of deep fluids to be channelized along inherited or newly-formed discontinuities. Fluid channelization along inherited discontinuities controlled local rehydration and dehydration/decarbonation reactions and the stability of carbonate and silicate minerals at the blueschist-eclogite transition. Fluid-mediated decarbonation was driven by upward, up-temperature fluid flow in the inverted geothermal gradient of a subducting oceanic slab, a process that has not been documented in natural samples to date. We estimate that the observed fluid-rock reactions released 20-60 kg CO2 per m3 of rock (i.e. 0.7-2.1 wt% CO2), which is in line with the values predicted from decarbonation of metabasalts in open systems at these depths. Conversely, the estimated time-integrated fluid fluxes (20-50 t/m2) indicate that the amount of carbon transported by channelized fluid flow within the volcanic part of subducting oceanic plates is potentially much higher than previous numerical estimates, testifying to the percolation of C-bearing fluids resulting from devolatilization/dissolution processes operative in large reservoirs.

Effect of rheological approximations on slab detachment in 3D numerical simulations of continental collision

NASA Astrophysics Data System (ADS)

Pusok, Adina E.; Kaus, Boris; Popov, Anton

2017-04-01

It is commonly accepted that slab detachment results from the development of extensional stresses within the subducting slab. Subduction slowdown due to arrival of buoyant continental material at the trench is considered to cause such stress build up in the slab. Following slab detachment, slab pull partially or completely loses its strength and hot asthenosphere may flow through the slab window, which can have major consequences for continental collision. The dynamics of slab detachment has been extensively studied in 2D (i.e. analytical and numerical), but 3D models of slab detachment during continental collision remain largely unexplored. Some of the previous 3D models have investigated the role of an asymmetric margin on the propagation of slab detachment (van Hunen and Allen, 2011), the impact of slab detachment on the curvature of orogenic belts (Capitanio and Replumaz, 2013), the role of the collision rate on slab detachment depth (Li et al., 2013) or the effect of along-trench variations on slab detachment (Duretz et al., 2014). However, rheology of mantle and lithosphere is known to have a major influence on the dynamics of subduction. Here, we explore a range of different rheological approximations to understand their sensitivity on the possible scenarios. We employ the code LaMEM (Kaus et al., 2016) to perform 3D simulations of subduction/continental collision in an integrated lithospheric and upper-mantle scale model. The models exhibit a wide range of behaviours depending on the rheological law employed: from linear, to temperature-dependent visco-elasto-plastic rheology that takes into account both diffusion and dislocation creep. For example, we find that slab dynamics varies drastically between end member models: in viscous approximations, slab detachment is slow, dominated by viscous thinning, while for a non-linear visco-elasto-plastic rheology, slab detachment is relatively fast, dominated by plastic breaking and inducing strong mantle flow in the slab window. Moreover, in models of viscous approximation, slab break-off starts in the slab interior due tot the nature of slab necking, while in models of non-linear visco-elasto-plastic rheology, slab tear will first occur at the edges of the continental collision.

Phase accumulation tracking algorithm for effective index retrieval of fishnet metamaterials and other resonant guided wave networks

NASA Astrophysics Data System (ADS)

Feigenbaum, Eyal; Hiszpanski, Anna M.

2017-07-01

A phase accumulation tracking (PAT) algorithm is proposed and demonstrated for the retrieval of the effective index of fishnet metamaterials (FMMs) in order to avoid the multi-branch uncertainty problem. This algorithm tracks the phase and amplitude of the dominant propagation mode across the FMM slab. The suggested PAT algorithm applies to resonant guided wave networks having only one mode that carries the light between the two slab ends, where the FMM is one example of this metamaterials sub-class. The effective index is a net effect of positive and negative accumulated phase in the alternating FMM metal and dielectric layers, with a negative effective index occurring when negative phase accumulation dominates.

TM surface wave diffraction by a truncated dielectric slab recessed in a perfectly conducting surface. [considering flush mounted space shuttle antenna

NASA Technical Reports Server (NTRS)

Pathak, P. H.; Kouyoumjian, R. G.

1974-01-01

The diffraction of a TM sub o surface wave by a terminated dielectric slab which is flush mounted in a perfectly conducting surface is studied. The incident surface wave gives rise to waves reflected and diffracted by the termination; these reflected and diffracted fields may be expressed in terms of the geometrical theory of diffraction by introducing surface wave reflection and diffraction coefficients which are associated with the termination. In this investigation, the surface wave reflection and diffraction coefficients have been deduced from a formally exact solution to this canonical problem. The solution is obtained by a combination of the generalized scattering matrix technique and function theoretic methods.

Nonlinear saturation of the slab ITG instability and zonal flow generation with fully kinetic ions

NASA Astrophysics Data System (ADS)

Miecnikowski, Matthew T.; Sturdevant, Benjamin J.; Chen, Yang; Parker, Scott E.

2018-05-01

Fully kinetic turbulence models are of interest for their potential to validate or replace gyrokinetic models in plasma regimes where the gyrokinetic expansion parameters are marginal. Here, we demonstrate fully kinetic ion capability by simulating the growth and nonlinear saturation of the ion-temperature-gradient instability in shearless slab geometry assuming adiabatic electrons and including zonal flow dynamics. The ion trajectories are integrated using the Lorentz force, and the cyclotron motion is fully resolved. Linear growth and nonlinear saturation characteristics show excellent agreement with analogous gyrokinetic simulations across a wide range of parameters. The fully kinetic simulation accurately reproduces the nonlinearly generated zonal flow. This work demonstrates nonlinear capability, resolution of weak gradient drive, and zonal flow physics, which are critical aspects of modeling plasma turbulence with full ion dynamics.

Optical device for thermal diffusivity determination in liquids by reflection of a thermal wave

NASA Astrophysics Data System (ADS)

Sánchez-Pérez, C.; De León-Hernández, A.; García-Cadena, C.

2017-08-01

In this work, we present a device for determination of the thermal diffusivity using the oblique reflection of a thermal wave within a solid slab that is in contact with the medium to be characterized. By using the reflection near a critical angle under the assumption that thermal waves obey Snell's law of refraction with the square root of the thermal diffusivities, the unknown thermal diffusivity is obtained by simple formulae. Experimentally, the sensor response is measured using the photothermal beam deflection technique within a slab that results in a compact device with no contact of the laser probing beam with the sample. We describe the theoretical basis and provide experimental results to validate the proposed method. We determine the thermal diffusivity of tridistilled water and glycerin solutions with an error of less than 0.5%.

Numerical and theoretical evaluations of AC losses for single and infinite numbers of superconductor strips with direct and alternating transport currents in external AC magnetic field

NASA Astrophysics Data System (ADS)

Kajikawa, K.; Funaki, K.; Shikimachi, K.; Hirano, N.; Nagaya, S.

2010-11-01

AC losses in a superconductor strip are numerically evaluated by means of a finite element method formulated with a current vector potential. The expressions of AC losses in an infinite slab that corresponds to a simple model of infinitely stacked strips are also derived theoretically. It is assumed that the voltage-current characteristics of the superconductors are represented by Bean's critical state model. The typical operation pattern of a Superconducting Magnetic Energy Storage (SMES) coil with direct and alternating transport currents in an external AC magnetic field is taken into account as the electromagnetic environment for both the single strip and the infinite slab. By using the obtained results of AC losses, the influences of the transport currents on the total losses are discussed quantitatively.

Lateral restoring force on a magnet levitated above a superconductor

NASA Technical Reports Server (NTRS)

Davis, L. C.

1990-01-01

The lateral restoring force on a magnet levitated above a superconductor is calculated as a function of displacement from its original position at rest using Bean's critical-state model to describe flux pinning. The force is linear for small displacements and saturates at large displacements. In the absence of edge effects the force always attracts the magnet to its original position. Thus it is a restoring force that contributes to the stability of the levitated magnet. In the case of a thick superconductor slab, the origin of the force is a magnetic dipole layer consisting of positive and negative supercurrents induced on the trailing side of the magnet. The qualitative behavior is consistent with experiments reported to date. Effects due to the finite thickness of the superconductor slab and the granular nature of high-Tc materials are also considered.

The rideability of a deflected bridge approach slab (LTRC project 02-2GT continuation : phase II) : [tech summary].

DOT National Transportation Integrated Search

2014-10-01

DOTD has made attempts to use the standard international roughness index (IRI) to index bridge bumps. However, it was : discovered that IRI has problems indexing localized roughness. A research e ort was undertaken to investigate if there might : ...

Slab interactions in 3-D subduction settings: The Philippine Sea Plate region

NASA Astrophysics Data System (ADS)

Holt, Adam F.; Royden, Leigh H.; Becker, Thorsten W.; Faccenna, Claudio

2018-05-01

The importance of slab-slab interactions is manifested in the kinematics and geometry of the Philippine Sea Plate and western Pacific subduction zones, and such interactions offer a dynamic basis for the first-order observations in this complex subduction setting. The westward subduction of the Pacific Sea Plate changes, along-strike, from single slab subduction beneath Japan, to a double-subduction setting where Pacific subduction beneath the Philippine Sea Plate occurs in tandem with westward subduction of the Philippine Sea Plate beneath Eurasia. Our 3-D numerical models show that there are fundamental differences between single slab systems and double slab systems where both subduction systems have the same vergence. We find that the observed kinematics and slab geometry of the Pacific-Philippine subduction can be understood by considering an along-strike transition from single to double subduction, and is largely independent from the detailed geometry of the Philippine Sea Plate. Important first order features include the relatively shallow slab dip, retreating/stationary trenches, and rapid subduction for single slab systems (Pacific Plate subducting under Japan), and front slabs within a double slab system (Philippine Sea Plate subducting at Ryukyu). In contrast, steep to overturned slab dips, advancing trench motion, and slower subduction occurs for rear slabs in a double slab setting (Pacific subducting at the Izu-Bonin-Mariana). This happens because of a relative build-up of pressure in the asthenosphere beneath the Philippine Sea Plate, where the asthenosphere is constrained between the converging Ryukyu and Izu-Bonin-Mariana slabs. When weak back-arc regions are included, slab-slab convergence rates slow and the middle (Philippine) plate extends, which leads to reduced pressure build up and reduced slab-slab coupling. Models without back-arcs, or with back-arc viscosities that are reduced by a factor of five, produce kinematics compatible with present-day observations.

Casimir forces on a bi-anisotropic absorbing magneto-dielectric slab between two parallel conducting plates

NASA Astrophysics Data System (ADS)

Amooshahi, Majid; Shoughi, Ali

2018-05-01

A fully canonical quantization of electromagnetic field in the presence of a bi-anisotropic absorbing magneto-dielectric slab is demonstrated. The electric and the magnetic polarization densities of the magneto-dielectric slab are defined in terms of the dynamical variables modeling the slab and the coupling tensors that couple the electromagnetic field to the slab. The four susceptibility tensors of the bi-anisotropic magneto-dielectric slab are expressed in terms of the coupling tensors that couple an electromagnetic field to the slab. It is shown that the four susceptibility tensors of the bi-anisotropic magneto-dielectric slab satisfy Kramers-Kronig relations. The Maxwell’s equations are exactly solved in the presence of the bi-anisotropic magneto-dielectric slab. The tangential and the normal components of the Casimir forces exerted on the bi-anisotropic magnet-dielectric slab exactly are calculated in the vacuum state and thermal state of the total system. It is shown that the tangential components of the Casimir forces vanish when the bi-anisotropic slab is converted to an isotropic slab.

Collaborative sparse priors for multi-view ATR

NASA Astrophysics Data System (ADS)

Li, Xuelu; Monga, Vishal

2018-04-01

Recent work has seen a surge of sparse representation based classification (SRC) methods applied to automatic target recognition problems. While traditional SRC approaches used l0 or l1 norm to quantify sparsity, spike and slab priors have established themselves as the gold standard for providing general tunable sparse structures on vectors. In this work, we employ collaborative spike and slab priors that can be applied to matrices to encourage sparsity for the problem of multi-view ATR. That is, target images captured from multiple views are expanded in terms of a training dictionary multiplied with a coefficient matrix. Ideally, for a test image set comprising of multiple views of a target, coefficients corresponding to its identifying class are expected to be active, while others should be zero, i.e. the coefficient matrix is naturally sparse. We develop a new approach to solve the optimization problem that estimates the sparse coefficient matrix jointly with the sparsity inducing parameters in the collaborative prior. ATR problems are investigated on the mid-wave infrared (MWIR) database made available by the US Army Night Vision and Electronic Sensors Directorate, which has a rich collection of views. Experimental results show that the proposed joint prior and coefficient estimation method (JPCEM) can: 1.) enable improved accuracy when multiple views vs. a single one are invoked, and 2.) outperform state of the art alternatives particularly when training imagery is limited.

Tomography of the subducting Pacific slab and the 2015 Bonin deepest earthquake (Mw 7.9).

PubMed

Zhao, Dapeng; Fujisawa, Moeto; Toyokuni, Genti

2017-03-15

On 30 May 2015 an isolated deep earthquake (~670 km, Mw 7.9) occurred to the west of the Bonin Islands. To clarify its causal mechanism and its relationship to the subducting Pacific slab, we determined a detailed P-wave tomography of the deep earthquake source zone using a large number of arrival-time data. Our results show that this large deep event occurred within the subducting Pacific slab which is penetrating into the lower mantle. In the Izu-Bonin region, the Pacific slab is split at ~28° north latitude, i.e., slightly north of the 2015 deep event hypocenter. In the north the slab becomes stagnant in the mantle transition zone, whereas in the south the slab is directly penetrating into the lower mantle. This deep earthquake was caused by joint effects of several factors, including the Pacific slab's fast deep subduction, slab tearing, slab thermal variation, stress changes and phase transformations in the slab, and complex interactions between the slab and the ambient mantle.

Tomographic imaging of the effects of Peruvian flat slab subduction on the Nazca slab and surrounding mantle under central and southern Peru

NASA Astrophysics Data System (ADS)

Scire, A. C.; Zandt, G.; Beck, S. L.; Bishop, B.; Biryol, C. B.; Wagner, L. S.; Long, M. D.; Minaya, E.; Tavera, H.

2014-12-01

The modern central Peruvian Andes are dominated by a laterally extensive region of flat slab subduction. The Peruvian flat slab extends for ~1500 km along the strike of the Andes, correlating with the subduction of the Nazca Ridge in the south and the theorized Inca Plateau in the north. We have used data from the CAUGHT and PULSE experiments for finite frequency teleseismic P- and S-wave tomography to image the Nazca slab in the upper mantle below 95 km depth under central Peru between 10°S and 18°S as well as the surrounding mantle. Since the slab inboard of the subducting Nazca Ridge is mostly aseismic, our results provide important constraints on the geometry of the subducting Nazca slab in this region. Our images of the Nazca slab suggest that steepening of the slab inboard of the subducting Nazca Ridge locally occurs ~100 km further inland than was indicated in previous studies. The region where we have imaged the steepening of the Nazca slab inboard of the Nazca Ridge correlates with the location of the Fitzcarrald Arch, a long wavelength upper plate topographic feature which has been suggested to be a consequence of ridge subduction. When the slab steepens inboard of the flat slab region, it does so at a very steep (~70°) angle. The transition from the Peruvian flat slab to the more normally dipping slab south of 16°S below Bolivia is characterized by an abrupt bending of the slab anomaly in the mantle in response to the shift from flat to normal subduction. The slab anomaly appears to be intact south of the Nazca Ridge with no evidence for tearing of the slab in response to the abrupt change in slab dip. A potential tear in the slab is inferred from an observed offset in the slab anomaly north of the Nazca Ridge extending subparallel to the ridge axis between 130 and 300 km depth. A high amplitude (-5-6%) slow S-wave velocity anomaly is observed below the projection of the Nazca Ridge. This anomaly appears to be laterally confined to the mantle directly below projection of the Nazca Ridge but descends to ~300 km depth in the mantle. This sub-slab slow anomaly may correlate with vertical mantle flow induced by movement of material through the inferred tear in the slab north of the Nazca Ridge or alternately may represent a long-lived feature of the sub-slab mantle possibly associated with the development of the Nazca Ridge at the Easter Island hot spot.

New seismic observation on the lithosphere and slab subduction beneath the Indo-Myanmar block: Implications for continent oblique subduction and transition to oceanic slab subduction

NASA Astrophysics Data System (ADS)

Jiang, M.; He, Y.; Zheng, T.; Mon, C. T.; Thant, M.; Hou, G.; Ai, Y.; Chen, Q. F.; Sein, K.

2017-12-01

The Indo-Myanmar block locates to the southern and southeastern of the Eastern Himalayan Syntax (EHS) and marks a torsional boundary of the collision between the Indian and Eurasian plates. There are two fundamental questions concerned on the tectonics of Indo-Myanmar block since the Cenozoic time. One is whether and how the oblique subduction is active in the deep; the other is where and how the transition from oceanic subduction and continental subduction operates. However, the two problems are still under heated debate mainly because the image of deep structure beneath this region is still blurring. Since June, 2016, we have executed the China-Myanmar Geophysical Survey in the Myanmar Orogen (CMGSMO) and deployed the first portable seismic array in Myanmar in cooperation with Myanmar Geosciences Society (MGS). This array contains 70 stations with a dense-deployed main profile across the Indo-Myanmar Range, Central Basin and Shan State Plateau along latitude of 22° and a 2-D network covering the Indo-Myanmar Range and the western part of the Central Basin. Based on the seismic data collected by the new array, we conducted the studies on the lithospheric structure using the routine surface wave tomography and receiver function CCP stacking. The preliminary results of surface wave tomography displayed a remarkable high seismic velocity fabric in the uppermost of mantle beneath the Indo-Myanmar Range and Central Basin, which was interpreted as the subducted slab eastward. Particularly, we found a low velocity bulk within the high-velocity slab, which was likely to be a slab window due to the slab tearing. The preliminary results of receiver function CCP stacking showed the obvious variations of the lithospheric structures from the Indo-Myanmar Range to the Central Basin and Shan State Plateau. The lithospheric structure beneath the Indo-Myanmar Range is more complex than that beneath the Central Basin and Shan State Plateau. Our resultant high-resolution images will provide important constrains for establishing the tectonic framework of Indian plate eastward subduction. This study is supported by the National Natural Science Foundation of China (grants 41490612, 41274002).

Research on Crack Formation in Gypsum Partitions with Doorway by Means of FEM and Fracture Mechanics

NASA Astrophysics Data System (ADS)

Kania, Tomasz; Stawiski, Bohdan

2017-10-01

Cracking damage in non-loadbearing internal partition walls is a serious problem that frequently occurs in new buildings within the short term after putting them into service or even before completion of construction. Damage in partition walls is sometimes so great that they cannot be accepted by their occupiers. This problem was illustrated by the example of damage in a gypsum partition wall with doorway attributed to deflection of the slabs beneath and above it. In searching for the deflection which causes damage in masonry walls, fracture mechanics applied to the Finite Element Method (FEM) have been used. For a description of gypsum behaviour, the smeared cracking material model has been selected, where stresses are transferred across the narrowly opened crack until its width reaches the ultimate value. Cracks in the Finite Element models overlapped the real damage observed in the buildings. In order to avoid cracks under the deflection of large floor slabs, the model of a wall with reinforcement in the doorstep zone and a 40 mm thick elastic junction between the partition and ceiling has been analysed.

Simplifying the exploration of volumetric images: development of a 3D user interface for the radiologist's workplace.

PubMed

Teistler, M; Breiman, R S; Lison, T; Bott, O J; Pretschner, D P; Aziz, A; Nowinski, W L

2008-10-01

Volumetric imaging (computed tomography and magnetic resonance imaging) provides increased diagnostic detail but is associated with the problem of navigation through large amounts of data. In an attempt to overcome this problem, a novel 3D navigation tool has been designed and developed that is based on an alternative input device. A 3D mouse allows for simultaneous definition of position and orientation of orthogonal or oblique multiplanar reformatted images or slabs, which are presented within a virtual 3D scene together with the volume-rendered data set and additionally as 2D images. Slabs are visualized with maximum intensity projection, average intensity projection, or standard volume rendering technique. A prototype has been implemented based on PC technology that has been tested by several radiologists. It has shown to be easily understandable and usable after a very short learning phase. Our solution may help to fully exploit the diagnostic potential of volumetric imaging by allowing for a more efficient reading process compared to currently deployed solutions based on conventional mouse and keyboard.

Reconstruction of 3D Shapes of Opaque Cumulus Clouds from Airborne Multiangle Imaging: A Proof-of-Concept

NASA Astrophysics Data System (ADS)

Davis, A. B.; Bal, G.; Chen, J.

2015-12-01

Operational remote sensing of microphysical and optical cloud properties is invariably predicated on the assumption of plane-parallel slab geometry for the targeted cloud. The sole benefit of this often-questionable assumption about the cloud is that it leads to one-dimensional (1D) radiative transfer (RT)---a textbook, computationally tractable model. We present new results as evidence that, thanks to converging advances in 3D RT, inverse problem theory, algorithm implementation, and computer hardware, we are at the dawn of a new era in cloud remote sensing where we can finally go beyond the plane-parallel paradigm. Granted, the plane-parallel/1D RT assumption is reasonable for spatially extended stratiform cloud layers, as well as the smoothly distributed background aerosol layers. However, these 1D RT-friendly scenarios exclude cases that are critically important for climate physics. 1D RT---whence operational cloud remote sensing---fails catastrophically for cumuliform clouds that have fully 3D outer shapes and internal structures driven by shallow or deep convection. For these situations, the first order of business in a robust characterization by remote sensing is to abandon the slab geometry framework and determine the 3D geometry of the cloud, as a first step toward bone fide 3D cloud tomography. With this specific goal in mind, we deliver a proof-of-concept for an entirely new kind of remote sensing applicable to 3D clouds. It is based on highly simplified 3D RT and exploits multi-angular suites of cloud images at high spatial resolution. Airborne sensors like AirMSPI readily acquire such data. The key element of the reconstruction algorithm is a sophisticated solution of the nonlinear inverse problem via linearization of the forward model and an iteration scheme supported, where necessary, by adaptive regularization. Currently, the demo uses a 2D setting to show how either vertical profiles or horizontal slices of the cloud can be accurately reconstructed. Extension to 3D volumes is straightforward but the next challenge is to accommodate images at lower spatial resolution, e.g., from MISR/Terra. G. Bal, J. Chen, and A.B. Davis (2015). Reconstruction of cloud geometry from multi-angle images, Inverse Problems in Imaging (submitted).

Analysis, testing and verification of the behavior of composite pavements under Florida conditions using a heavy vehicle simulator

NASA Astrophysics Data System (ADS)

Tapia Gutierrez, Patricio Enrique

Whitetopping (WT) is a rehabilitation method to resurface deteriorated asphalt pavements. While some of these composite pavements have performed very well carrying heavy load, other have shown poor performance with early cracking. With the objective of analyzing the applicability of WT pavements under Florida conditions, a total of nine full-scale WT test sections were constructed and tested using a Heavy Vehicle Simulator (HVS) in the APT facility at the FDOT Material Research Park. The test sections were instrumented to monitor both strain and temperature. A 3-D finite element model was developed to analyze the WT test sections. The model was calibrated and verified using measured FWD deflections and HVS load-induced strains from the test sections. The model was then used to evaluate the potential performance of these test sections under critical temperature-load condition in Florida. Six of the WT pavement test sections had a bonded concrete-asphalt interface by milling, cleaning and spraying with water the asphalt surface. This method produced excellent bonding at the interface, with shear strength of 195 to 220 psi. Three of the test sections were intended to have an unbonded concrete-asphalt interface by applying a debonding agent in the asphalt surface. However, shear strengths between 119 and 135 psi and a careful analysis of the strain and the temperature data indicated a partial bond condition. The computer model was able to satisfactorily model the behavior of the composite pavement by mainly considering material properties from standard laboratory tests and calibrating the spring elements used to model the interface. Reasonable matches between the measured and the calculated strains were achieved when a temperature-dependent AC elastic modulus was included in the analytical model. The expected numbers of repetitions of the 24-kip single axle loads at critical thermal condition were computed for the nine test sections based on maximum tensile stresses and fatigue theory. The results showed that 4" slabs can be used for heavy loads only for low-volume traffic. To withstand the critical load without fear of fatigue failure, 6" slabs and 8" slabs would be needed for joint spacings of 4' and 6', respectively.

The Electromagnetic Field for a PEC Wedge Over a Grounded Dielectric Slab: 1. Formulation and Validation

NASA Astrophysics Data System (ADS)

Daniele, Vito G.; Lombardi, Guido; Zich, Rodolfo S.

2017-12-01

Complex scattering problems are often made by composite structures where wedges and penetrable substrates may interact at near field. In this paper (Part 1) together with its companion paper (Part 2) we study the canonical problem constituted of a Perfectly Electrically Conducting (PEC) wedge lying on a grounded dielectric slab with a comprehensive mathematical model based on the application of the Generalized Wiener-Hopf Technique (GWHT) with the help of equivalent circuital representations for linear homogenous regions (angular and layered regions). The proposed procedure is valid for the general case, and the papers focus on E-polarization. The solution is obtained using analytical and semianalytical approaches that reduce the Wiener-Hopf factorization to integral equations. Several numerical test cases validate the proposed method. The scope of Part 1 is to present the method and its validation applied to the problem. The companion paper Part 2 focuses on the properties of the solution, and it presents physical and engineering insights as Geometrical Theory of Diffraction (GTD)/Uniform Theory of Diffraction(UTD) coefficients, total far fields, modal fields, and excitation of surface and leaky waves for different kinds of source. The structure is of interest in antenna technologies and electromagnetic compatibility (tip on a substrate with guiding and antenna properties).

The transformation of weak saturated soils using piles-drains for improving its mechanical properties

NASA Astrophysics Data System (ADS)

Ter-Martirosyan, Z. G.; Ter-Martirosyan, A. Z.; Sidorov, V. V.

2018-04-01

In practice of increased responsibility structures design there are often weak saturated clayey soils with low characteristics of deformability and strength take place on the construction site. In these cases, foundations using piles-drains of sandy or coarse material are recommended by norms, which is able to bear the load and to accelerate the consolidation process. The presented solutions include an analytical solution of the interaction problem between piles and slab raft foundation with the surrounding soil of the base with the possibility of extension of pile shaft. The closed-form solutions to determine the stresses in pile shaft and in the soil under the foundation slab are obtained. The article presents the results of large scale tests in the pilot area construction of major energy facilities in Russia.

Research on Vibration Test in Urban Indoor Substation

NASA Astrophysics Data System (ADS)

Ma, Yuchao; Mo, Juan; Xu, Jin; Fan, Baozhen

2018-01-01

The problem of vibration and noise of urban indoor substations has becoming more and more socially concerned.The urban indoor substation of 110kV and its conjoined buildings were taken as the research object and the vibration tests of the transformer and each floor slab were respectively carried out.The sound vibration characteristics and sound transmission rules of the urban indoor substation were obtained through the time-frequency analysis and coherence analysis of the test data. The vibration spectrum of transformer body was mainly 100Hz together with its multiplying factors and the vibration characteristics of the floor slab were basically the same as those of the transformer body. it is crucial to control the vibration and noise transmission in the equipment floor of the urban indoor substation.

Benchmark study for charge deposition by high energy electrons in thick slabs

NASA Technical Reports Server (NTRS)

Jun, I.

2002-01-01

The charge deposition profiles created when highenergy (1, 10, and 100 MeV) electrons impinge ona thick slab of elemental aluminum, copper, andtungsten are presented in this paper. The chargedeposition profiles were computed using existing representative Monte Carlo codes: TIGER3.0 (1D module of ITS3.0) and MCNP version 4B. The results showed that TIGER3.0 and MCNP4B agree very well (within 20% of each other) in the majority of the problem geometry. The TIGER results were considered to be accurate based on previous studies. Thus, it was demonstrated that MCNP, with its powerful geometry capability and flexible source and tally options, could be used in calculations of electron charging in high energy electron-rich space radiation environments.

Highly selective and compact tunable MOEMS photonic crystal Fabry-Perot filter.

PubMed

Boutami, S; Ben Bakir, B; Leclercq, J-L; Letartre, X; Rojo-Romeo, P; Garrigues, M; Viktorovitch, P; Sagnes, I; Legratiet, L; Strassner, M

2006-04-17

The authors report a compact and highly selective tunable filter using a Fabry-Perot resonator combining a bottom micromachined 3-pair-InP/air-gap Bragg reflector with a top photonic crystal slab mirror. It is based on the coupling between radiated vertical cavity modes and waveguided modes of the photonic crystal. The full-width at half maximum (FWHM) of the resonance, as measured by microreflectivity experiments, is close to 1.5nm (around 1.55 microm). The presence of the photonic crystal slab mirror results in a very compact resonator, with a limited number of layers. The demonstrator was tuned over a 20nm range for a 4V tuning voltage, the FWHM being kept below 2.5nm. Bending of membranes is a critical issue, and better results (FWHM=0.5nm) should be obtained on the same structure if this technological point is fixed.

How mantle slabs drive plate tectonics.

PubMed

Conrad, Clinton P; Lithgow-Bertelloni, Carolina

2002-10-04

The gravitational pull of subducted slabs is thought to drive the motions of Earth's tectonic plates, but the coupling between slabs and plates is not well established. If a slab is mechanically attached to a subducting plate, it can exert a direct pull on the plate. Alternatively, a detached slab may drive a plate by exciting flow in the mantle that exerts a shear traction on the base of the plate. From the geologic history of subduction, we estimated the relative importance of "pull" versus "suction" for the present-day plates. Observed plate motions are best predicted if slabs in the upper mantle are attached to plates and generate slab pull forces that account for about half of the total driving force on plates. Slabs in the lower mantle are supported by viscous mantle forces and drive plates through slab suction.

Plate tectonic reconstruction of the northeast Eurasian margin and Alaska since 50 Ma using subducted slab constraints

NASA Astrophysics Data System (ADS)

Wu, J. E.; Suppe, J.; Chen, Y. W.

2016-12-01

Seismic tomographic studies have revealed a swath of flat slab anomalies in the mantle transition zone at 410 to 660 km depths under Japan, Korea and NE China that continue northwards at deeper depths under the Russian Far East. These slab anomalies are remarkable because they appear to be continuous from their western edge far inland (>2000 km) under the NE Eurasian margin to the present-day NW Pacific subduction zones, which suggests they are Pacific slabs that were subducted in the Cenozoic. Other studies have proposed that some of these slabs were subducted at an ancient subduction zone during the Mesozoic or earlier. Here we discuss the fate of these slabs and their implications for the plate tectonic reconstruction of the NW Pacific margin along NE Asia and Alaska. We present both new and recently published slab mapping (Wu et al., 2016; JGR Solid Earth) including 30 major and minor slabs mapped in 3D from MITP08 global seismic tomography. We unfolded our mapped slabs to a spherical Earth model to estimate their pre-subduction size, shape and locations. The slab constraints were input into GPlates software to constrain a new regional NW Pacific plate tectonic reconstruction in the Cenozoic. Mapped slabs included the Marianas, Izu-Bonin, Japan and Kuril slabs, the Philippine Sea slabs and Aleutian slabs under the Bering Sea. Our mapped western Pacific slabs between the southernmost Izu-Bonin trench and the western Aleutians had unfolded E-W lengths of 3400 to 4900 km. Our plate model shows that these slabs are best reconstructed as Pacific slabs that were subducted in the Cenozoic and account for fast Pacific subduction along the NE Eurasian margin since plate reorganization at 50 Ma. Our mapped northern Kuril slab edge near the western Aleutians and a southern edge at the southernmost Izu-Bonin trench are roughly east-west and consistent with the orientations of Pacific absolute motions since 50 Ma. We interpret these long E-W slab edges as STEP fault-type transforms (i.e. lithospheric tears that progressively formed during subduction). We further discuss our plate model against the opening of the NW Pacific marginal basins in the Cenozoic, including the Japan Sea, Kuril Basin and Okhotsk Sea.

Stress regime in the Philippine Sea slab beneath Kanto, Japan

NASA Astrophysics Data System (ADS)

Nakajima, Junichi; Hasegawa, Akira; Hirose, Fuyuki

2011-08-01

We determine the focal mechanisms of earthquakes within the Philippine Sea slab beneath the Tokyo metropolitan area, and perform stress tensor inversions to investigate the detailed stress field within the slab. The results show a characteristic spatial variation in earthquake-generating stress. Slab stress in northeastern part of the PHS slab is characterized by down-dip tension (DDT), except for the uppermost tip of the seismic portion of the slab where down-dip compression (DDC) stress is dominant. We interpret that DDT is caused by the net slab pull and DDC is attributable to local resistance to subduction at the tip of the slab. In southwestern part of the PHS slab, σ1 and σ3 are generally rotated oblique to the dip of the slab, suggesting that earthquakes occur under stress conditions of neither DDC nor DDT. The rotations in σ1 and σ3 may be related to stress accumulation by the slip deficit along the asperity of the 1923 Kanto earthquake (M7.9).

Bridge approach slabs for Missouri DOT field evaluation of alternative and cost efficient bridge approach slabs.

DOT National Transportation Integrated Search

2013-05-01

Based on a recent study on cost efficient alternative bridge approach slab (BAS) designs (Thiagarajan et : al. 2010) has recommended three new BAS designs for possible implementation by MoDOT namely a) 20 feet cast-inplace : slab with sleeper slab (C...

Investigation of sub-slab pressure field extension in specified granular fill materials incorporating a sump-based soil depressurisation system for radon mitigation.

PubMed

Hung, Le Chi; Goggins, Jamie; Fuente, Marta; Foley, Mark

2018-05-14

Design of bearing layers (granular fill material layers) is important for a house with a soil depressurisation (SD) system for indoor radon mitigation. These layers should not only satisfy the bearing capacity and serviceability criteria but should also provide a sufficient degree of the air permeability for the system. Previous studies have shown that a critical parameter for a SD system is the sub-slab pressure field extension in the bearing layers, but this issue has not been systematically investigated. A series of two-dimensional computational fluid dynamic simulations that investigate the behaviour of the sub-slab pressure field extension developed in a SD system is presented in this paper. The SD system considered in this paper consists of a granular fill material layer and a radon sump. The granular fill materials are 'T1 Struc' and 'T2 Perm', which are standard materials for building in the Republic of Ireland. Different conditions, which might be encountered in a practical situation, were examined. The results show that the air permeability and thickness of the granular fill materials are the two key factors which affect the sub slab pressure field extension (SPFE) significantly. Furthermore, the air permeability of native soil is found to be a fundamental factor for the SPFE so that it should be well understood when designing a SD system. Therefore, these factors should be considered sufficiently in each practical situation. Finally, a significant improvement of the pressure field extension can be achieved by ensuring air tightness of the SD system. Copyright © 2018 Elsevier B.V. All rights reserved.

The Relationship between Ionospheric Slab Thickness and the Peak Density Height, hmF2

NASA Astrophysics Data System (ADS)

Meehan, J.; Sojka, J. J.

2017-12-01

The electron density profile is one of the most critical elements in the ionospheric modeling-related applications today. Ionosphere parameters, hmF2, the height of the peak density layer, and slab thickness, the ratio of the total electron content, TEC, to the peak density value, NmF2, are generally obtained from any global sounding observation network and are easily incorporated into models, theoretical or empirical, as numerical representations. Slab thickness is a convenient one-parameter summary of the electron density profile and can relate a variety of elements of interest that effect the overall electron profile shape, such as the neutral and ionospheric temperatures and gradients, the ionospheric composition, and dynamics. Using ISR data from the 2002 Millstone Hill ISR data campaign, we found, for the first time, slab thickness to be correlated to hmF2. For this, we introduce a new ionospheric index, k, which ultimately relates electron density parameters and can be a very useful tool for describing the topside ionosphere shape. Our study is an initial one location, one season, 30-day study, and future work is needed to verify the robustness of our claim. Generally, the ionospheric profile shape, requires knowledge of several ionospheric parameters: electron, ion and neutral temperatures, ion composition, electric fields, and neutral winds, and is dependent upon seasons, local time, location, and the level of solar and geomagnetic activity; however, with this new index, only readily-available, ionospheric density information is needed. Such information, as used in this study, is obtained from a bottomside electron density profile provided by an ionosonde, and TEC data provided by a local, collocated GPS receiver.

Tomography of the subducting Pacific slab and the 2015 Bonin deepest earthquake (Mw 7.9)

PubMed Central

Zhao, Dapeng; Fujisawa, Moeto; Toyokuni, Genti

2017-01-01

On 30 May 2015 an isolated deep earthquake (~670 km, Mw 7.9) occurred to the west of the Bonin Islands. To clarify its causal mechanism and its relationship to the subducting Pacific slab, we determined a detailed P-wave tomography of the deep earthquake source zone using a large number of arrival-time data. Our results show that this large deep event occurred within the subducting Pacific slab which is penetrating into the lower mantle. In the Izu-Bonin region, the Pacific slab is split at ~28° north latitude, i.e., slightly north of the 2015 deep event hypocenter. In the north the slab becomes stagnant in the mantle transition zone, whereas in the south the slab is directly penetrating into the lower mantle. This deep earthquake was caused by joint effects of several factors, including the Pacific slab’s fast deep subduction, slab tearing, slab thermal variation, stress changes and phase transformations in the slab, and complex interactions between the slab and the ambient mantle. PMID:28295018

Tomography of the subducting Pacific slab and the 2015 Bonin deepest earthquake (Mw 7.9)

NASA Astrophysics Data System (ADS)

Zhao, Dapeng; Fujisawa, Moeto; Toyokuni, Genti

2017-03-01

On 30 May 2015 an isolated deep earthquake (~670 km, Mw 7.9) occurred to the west of the Bonin Islands. To clarify its causal mechanism and its relationship to the subducting Pacific slab, we determined a detailed P-wave tomography of the deep earthquake source zone using a large number of arrival-time data. Our results show that this large deep event occurred within the subducting Pacific slab which is penetrating into the lower mantle. In the Izu-Bonin region, the Pacific slab is split at ~28° north latitude, i.e., slightly north of the 2015 deep event hypocenter. In the north the slab becomes stagnant in the mantle transition zone, whereas in the south the slab is directly penetrating into the lower mantle. This deep earthquake was caused by joint effects of several factors, including the Pacific slab’s fast deep subduction, slab tearing, slab thermal variation, stress changes and phase transformations in the slab, and complex interactions between the slab and the ambient mantle.

Resolving the crustal composition paradox by 3.8 billion years of slab failure magmatism and collisional recycling of continental crust

NASA Astrophysics Data System (ADS)

Hildebrand, Robert S.; Whalen, Joseph B.; Bowring, Samuel A.

2018-06-01

In the standard paradigm, continental crust is formed mainly by arc magmatism, but because the compositions of magma rising from the mantle are basaltic and continental crust is estimated to contain about 60% SiO2 and much less MgO than basalt, the two do not match. To resolve this paradox, most researchers argue that large amounts of magmatic fractionation produce residual cumulates at the base of the crust, which because arcs are inferred to have magmatically thickened crust, form eclogites that ultimately founder and sink into the mantle. Not only are there problems with the contrasting bulk compositions, but the standard model also fails because prior to collision most modern arcs do not have thick crust, as documented by their eruption close to sea level, and in cases of ancient arc sequences, their intercalation with marine sedimentary rocks. Our study of Cretaceous batholiths in the North American Cordillera resolves the crustal composition paradox because we find that most are not arc-derived as commonly believed; but instead formed during the waning stages of collision and consequent slab failure. Because the batholiths typically have silica contents >60% and are derived directly from the mantle, we argue that they are the missing link in the formation of continental crust. Slab failure magmas worldwide are compositionally similar to tonalite-trondhjemite-granodiorite suites as old as 3.8 Ga, which points to their collective formation by slab failure and long-lived plate tectonics. Our model also provides (1) an alternative solution to interpret compiled detrital zircon arrays, because episodic peaks that coincide with periods of supercontinent amalgamation are easily interpreted to represent collisions with formation of new crust by slab failure; and (2) that models of early whole-earth differentiation are more reasonable than those invoking progressive growth of continental crust.

Secondary Fire Analysis.

DTIC Science & Technology

1981-09-01

of wood frame and brick veneer, slab on grade construction), killed 33, injured more than 1,000, derailed a train, destroyed 4,000 cars, uprooted most... of a nuclear detonation) in or near structures, with emphasis on critical facil- ities and industries. Assessment of the potential for secondary fires...and/or 517 East Dayshore, Redwood City, CA 94063 DistI pial (DETACHABLE SUMMARY) SECONDARY FIRE ANALYSIS This report presents the results of a

Experimental sensitivity analysis of subsoil-slab behaviour regarding degree of fibre-concrete slab reinforcement

NASA Astrophysics Data System (ADS)

Hrubesova, E.; Lahuta, H.; Mohyla, M.; Quang, T. B.; Phi, N. D.

2018-04-01

The paper is focused on the sensitivity analysis of behaviour of the subsoil – foundation system as regards the variant properties of fibre-concrete slab resulting into different relative stiffness of the whole cooperating system. The character of slab and its properties are very important for the character of external load transfer, but the character of subsoil cannot be neglected either because it determines the stress-strain behaviour of the all system and consequently the bearing capacity of structure. The sensitivity analysis was carried out based on experimental results, which include both the stress values in soil below the foundation structure and settlements of structure, characterized by different quantity of fibres in it. Flat dynamometers GEOKON were used for the stress measurements below the observed slab, the strains inside slab were registered by tensometers, the settlements were monitored geodetically. The paper is focused on the comparison of soil stresses below the slab for different quantity of fibres in structure. The results obtained from the experimental stand can contribute to more objective knowledge of soil – slab interaction, to the evaluation of real carrying capacity of the slab, to the calibration of corresponding numerical models, to the optimization of quantity of fibres in the slab, and finally, to higher safety and more economical design of slab.

Tomographic Signatures of Ridge Subduction Along Western North America: Implications for Northern Cordillera Plate Tectonics Since the Cretaceous

NASA Astrophysics Data System (ADS)

Lin, Y. A.; Wu, J.

2017-12-01

A number of northern Cordillera plate reconstructions have predicted subduction of the Kula-Farallon ridge and possibly other ridges along western North America after the late Mesozoic. The timing and location of these predicted ridge subduction events have been controversial, with implications for rapid northward terrane motions (i.e. the Baja-British Columbia hypothesis). In contrast, Sigloch and Mihalynuk (2013) proposed an archipelago-style plate model that placed one or several Jurassic-Cretaceous ocean basins between the Farallon plate and western North America, which apparently would preclude any sustained Kula-Farallon ridge subduction along western North America. In this study we test the viability of these models by mapping and unfolding subducted slabs from MITP08 tomography (Li et al., 2008) between Alaska and California within the upper 1500 km mantle. Our aim was to locate significant slab gaps that might be related to ancient ridge subduction `slab windows'. Tomographic velocities were extracted and displayed on our mapped slabs following the methods of Wu et al. (2016) to assist with the identification of slab gaps or windows. Near Alaska, we mapped the Aleutian slab and a detached slab that was previously identified as the `K slab' by Sigloch and Mihalynuk (2013). When unfolded these slabs apparently account for Pacific-Kula convergence towards Alaska since the late Cretaceous. We did not find evidence for a ridge subduction-related slab gap under the Alaskan region. Between northern Canada to California, we mapped the Juan de Fuca slab and several detached slabs at 1000 to 1500 km depths that were previously identified by Sigloch and Mihalynuk (2013). The velocity perturbations within our mapped slabs revealed slower P-wavespeed `slab gaps' under southernmost Alaska, Yukon, and British Columbia between the mapped Kula and Juan de Fuca plate. We did not find evidence of the hypothesized Resurrection plate. We compare our mapped slab gaps to predicted slab window geometries from previous studies and discuss their implications for plate tectonic reconstructions of the northern Cordillera and surrounding area.

Dense and Dry Mantle Between the Continental Crust and the Oceanic Slab: Folding, Faulting and Tearing in the Slab in the Pampean Flat Slab, Southern Central Andes Evidenced by 3D Body Wave Tomography Along the 2015 Illapel, Chile Earthquake Rupture Area

NASA Astrophysics Data System (ADS)

Comte, D.; Farías, M.; Roecker, S. W.; Brandon, M. T.

2017-12-01

The 2015 Illapel interplate earthquake Mw 8.4 generated a large amount of aftershocks that was recorded by the Chile-Illapel Aftershock Experiment (CHILLAX) during a year after the mainshock. Using this database, along with previous seismological campaigns, an improved 3D body wave tomographic image was obtained, allowing us to visualize first-order lithospheric discontinuities. This new analysis confirms not only the presence of this dense block, but also that the Benioff zone extends with a 30° dip even below the 100 km depth, where the Nazca plate has been interpreted to be flat. Recent results of seismic anisotropy show that the oceanic plate has been detached at depths greater than 300 km. We propose that: i) The dry, cold mantle beneath the continental crust is an entrapped mantle, cooled by the slab flattening, while the western part would be hydrated by slab-derived fluid; ii) The Nazca plate would be faulted and is now subducting with a normal dip beneath the flattened slab segment. Considering that the slab segment is detached from deeper part of the subducted plate, slab pull on the flat segment would be reduced, decreasing its eastward advance. In the western side, the flat segment of the slab has been observed to be slightly folded. We propose that the current normal subduction is related to the slab break-off resulting from the loss of a slab-pull force, producing the accretion of the slab beneath the dry and cold mantle. Considering that the flat slab segment does not occur at depths shallower than 100 km, rollback of the slab is not expected. In turn, suction forces would have induced the shortening in the flat segment considering its eastward slowing down due to slab break-off, thus producing a breakthrough faulting. This proposition implies that the underplated flat slab segment, along with the overlying dense and dry mantle may be delaminated by gravitional instabilities and ablative subduction effects.

Multi-Dimensional, Non-Pyrolyzing Ablation Test Problems

NASA Technical Reports Server (NTRS)

Risch, Tim; Kostyk, Chris

2016-01-01

Non-pyrolyzingcarbonaceous materials represent a class of candidate material for hypersonic vehicle components providing both structural and thermal protection system capabilities. Two problems relevant to this technology are presented. The first considers the one-dimensional ablation of a carbon material subject to convective heating. The second considers two-dimensional conduction in a rectangular block subject to radiative heating. Surface thermochemistry for both problems includes finite-rate surface kinetics at low temperatures, diffusion limited ablation at intermediate temperatures, and vaporization at high temperatures. The first problem requires the solution of both the steady-state thermal profile with respect to the ablating surface and the transient thermal history for a one-dimensional ablating planar slab with temperature-dependent material properties. The slab front face is convectively heated and also reradiates to a room temperature environment. The back face is adiabatic. The steady-state temperature profile and steady-state mass loss rate should be predicted. Time-dependent front and back face temperature, surface recession and recession rate along with the final temperature profile should be predicted for the time-dependent solution. The second problem requires the solution for the transient temperature history for an ablating, two-dimensional rectangular solid with anisotropic, temperature-dependent thermal properties. The front face is radiatively heated, convectively cooled, and also reradiates to a room temperature environment. The back face and sidewalls are adiabatic. The solution should include the following 9 items: final surface recession profile, time-dependent temperature history of both the front face and back face at both the centerline and sidewall, as well as the time-dependent surface recession and recession rate on the front face at both the centerline and sidewall. The results of the problems from all submitters will be collected, summarized, and presented at a later conference.

Long-life slab replacement concrete.

DOT National Transportation Integrated Search

2015-03-01

This research was initiated following reports of high incidence of cracking on FDOT concrete pavement replacement : slab projects. Field slabs were instrumented for data acquisition from high-early-strength concrete pavement : replacement slabs place...

Manipulation of enhanced absorption with tilted hexagonal boron nitride slabs

NASA Astrophysics Data System (ADS)

Wu, Xiaohu; Fu, Ceji

2018-04-01

The wavevector of electromagnetic wave propagation in a hexagonal boron nitride (hBN) slab can be controlled by tilting its optical axis. This property can be used to manipulate the absorption in a hBN slab. By carefully analyzing the dependence of the absorptivity of a thin hBN slab on the tilted angle of its optical axis, we propose a structure that can realize great absorptivity enhancement in a band by stacking hBN slabs of different tilted angles. Our numerical results show that the absorptivity of a structure made of 91 stacked hBN slabs can be achieved higher than 0.94 in the wavenumber range from 1367 to 1580 cm-1 when the tilted angles of the slabs are properly arranged. The strong absorption is attributed to the combination of impedance matching at the slab interfaces and enlarged wavevectors in the slabs. This work reveals a novel way to realize strong absorption with anisotropic materials for applications in areas such as thermal radiative energy harvesting and conversion.

Subducted Slab Dynamics: Toward Understanding the Causes of Slab Stagnation

NASA Astrophysics Data System (ADS)

King, S. D.; Frost, D. J.; Rubie, D. C.

2013-12-01

The evolution and dynamics of subducted slabs are controlled by a number of factors, including rheology and composition. The correlation of the transformations from olivine to wadslayite and ringwoodite to perovskite plus magnesiowüstite with the seismic velocity discontinuities at 410 and 660 km depth, along with the density changes have been extensively investigated in terms of their impact on slab dynamics. Owing to the relatively smaller changes in density extending over a broader depth range, the impact of the pyroxene-garnet system has received less attention. Recent experimental work has found that the majorite component in garnet--a product of the transition from pyroxene into garnet--is one of the slowest-diffusing components in Earth's mantle. At the relatively low temperatures of the slab, this slow diffusion inhibits the dissolution of pyroxene into garnet, so that the slab remains buoyant relative to the ambient mantle and stagnates. We present dynamic subduction calculations that illustrate the effect of the non-equilibrium pyroxene to garnet transition on slab dynamics. If the transition between equilibrium and non-equilibrium behavior is below 1000 K, we find no impact on slab dynamics. If the transition occurs at 1200 K, it is enough to cause the slab to thicken and stagnate in the transition zone for an extended period of time. Our analysis suggests that cold slabs should be more likely to stagnate in the transition zone and we will compare a global compilation of slab geometries with slab thermal structure to evaluate.

Effective Process Design for the Production of HIC-Resistant Linepipe Steels

NASA Astrophysics Data System (ADS)

Nieto, J.; Elías, T.; López, G.; Campos, G.; López, F.; Garcia, R.; De, Amar K.

2013-09-01

Production of slabs for sour service applications requires stringent control in slab internal quality and secondary processing so as to guarantee resistance against hydrogen-induced cracking (HIC). ArcelorMittal Steelmaking facility at Lazaro Cardenas, Mexico had recently implemented key steelmaking and casting processing technologies for production of sound, centerline free slabs for catering to the growing API Linepipe and off-shore market for sour service applications. State-of-the-art steelmaking with use of residual-free Direct-reduced Iron and continuous casting facilities with dynamic soft reduction were introduced for the production of slabs with ultra clean centerline. Introduction of controlled cooling of slabs for atomic hydrogen control well below 2 ppm has enabled production of slabs suitable for excellent HIC-resistant plate processing. Substantial tonnages of slabs were produced for production of API X52-X65 grade plates and pipes for sour service. Stringent quality control at each stage of steelmaking, casting, and slab inspection ensured slabs with excellent internal quality suitable for HIC resistance to be guaranteed in final product (Plates & Pipes). Details of production steps which resulted in successful HIC-resistant slab production have been described in this article.

0-6722 : spread prestressed concrete slab beam bridges.

DOT National Transportation Integrated Search

2014-08-01

The Texas Department of Transportation uses : precast prestressed concrete slab beam bridges for : shorter-span bridges of approximately 3050 ft in : length. Conventional slab beam bridges have slab : beams placed immediately adjacent to one anoth...

MC 2 -3: Multigroup Cross Section Generation Code for Fast Reactor Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Changho; Yang, Won Sik

This paper presents the methods and performance of the MC2 -3 code, which is a multigroup cross-section generation code for fast reactor analysis, developed to improve the resonance self-shielding and spectrum calculation methods of MC2 -2 and to simplify the current multistep schemes generating region-dependent broad-group cross sections. Using the basic neutron data from ENDF/B data files, MC2 -3 solves the consistent P1 multigroup transport equation to determine the fundamental mode spectra for use in generating multigroup neutron cross sections. A homogeneous medium or a heterogeneous slab or cylindrical unit cell problem is solved in ultrafine (2082) or hyperfine (~400more » 000) group levels. In the resolved resonance range, pointwise cross sections are reconstructed with Doppler broadening at specified temperatures. The pointwise cross sections are directly used in the hyperfine group calculation, whereas for the ultrafine group calculation, self-shielded cross sections are prepared by numerical integration of the pointwise cross sections based upon the narrow resonance approximation. For both the hyperfine and ultrafine group calculations, unresolved resonances are self-shielded using the analytic resonance integral method. The ultrafine group calculation can also be performed for a two-dimensional whole-core problem to generate region-dependent broad-group cross sections. Verification tests have been performed using the benchmark problems for various fast critical experiments including Los Alamos National Laboratory critical assemblies; Zero-Power Reactor, Zero-Power Physics Reactor, and Bundesamt für Strahlenschutz experiments; Monju start-up core; and Advanced Burner Test Reactor. Verification and validation results with ENDF/B-VII.0 data indicated that eigenvalues from MC2 -3/DIF3D agreed well with Monte Carlo N-Particle5 MCNP5 or VIM Monte Carlo solutions within 200 pcm and regionwise one-group fluxes were in good agreement with Monte Carlo solutions.« less

Flowing Air-Water Cooled Slab Nd: Glass Laser

NASA Astrophysics Data System (ADS)

Lu, Baida; Cai, Bangwei; Liao, Y.; Xu, Shifa; Xin, Z.

1989-03-01

A zig-zag optical path slab geometry Nd: glass laser cooled through flowing air-water is developed by us. Theoretical studies on temperature distribution of slab and rod configurations in the unsteady state clarify the advantages of the slab geometry laser. The slab design and processing are also reported. In our experiments main laser output characteristics, e. g. laser efficiency, polarization, far-field divergence angle as well as resonator misalignment are investigated. The slab phosphate glass laser in combination with a crossed Porro-prism resonator demonstrates a good laser performance.

Distribution of slab-derived fluids around the edge of the Philippine Sea Plate from Central to Northeast Japan

NASA Astrophysics Data System (ADS)

Nakamura, Hitomi; Iwamori, Hikaru; Ishizuka, Osamu; Nishizawa, Tatsuji

2018-01-01

Marginal parts of a plate and subducting slab can play important roles in geodynamics. This is because in areas where a plate interacts with other plates or with the mantle thermal, geochemical, and mechanical interactions are expected. The Philippine Sea (PHS) slab that subducts beneath the Japan arcs has such an edge. To examine the relationship between arc magmatism and the slab edge in the transition zone from Northeast Japan to Central Japan, we investigated isotopic systematics of the regional volcanic rocks, incorporating data from literature and new data for five isotopic ratios of Sr, Nd, and Pb. The new data included major element compositions of 22 samples from the back-arc area, and 5 isotopic ratios for 6 samples selected from Pleistocene to early Quaternary epochs. Consequently, several findings were determined based on the spatial variation of the isotopic ratios and the estimated amount of slab-derived fluid: (1) the amount of fluid derived from the two subducting slabs (i.e., the Pacific slab and the PHS slab) decreases northward from a significantly high value ( 5 wt% fluid added to the source mantle), away from the seismically determined edge of the PHS slab; (2) the proportion of the PHS component in the total slab-derived fluid also decays northward; and (3) the PHS component spreads to the north beyond the seismically determined edge of the PHS slab. These observations strongly suggest that the existence of an aseismic PHS slab beneath southernmost parts of Northeast Japan delivers the PHS component to the arc magmatism. As was indicated by previous geodynamical studies, subduction of the PHS and PAC slabs may generate suction force towards the corner of mantle wedge, which might account for the large amount of fluid near the seismically determined slab edge as described in (1) above.

Investigating Different Patterns of Slab Deformation in the Lower Mantle

NASA Astrophysics Data System (ADS)

Zhang, J.; McNamara, A. K.

2017-12-01

The geometry of slabs within the upper mantle have been relatively well-imaged by tomography and regional seismic studies; however, the style of slab deformation in the lower mantle remains poorly understood. Although tomography models reveal that the lower mantle beneath paleo-subduction regions are faster-than-average, the resolution is not high enough to resolve how slabs are actually deforming there. Slabs have long been hypothesized as viscous, tabular sheets that subduct at the surface, descend through the mantle, and impinge on the core-mantle boundary (CMB). Geodynamical studies have shown a wide range of possible deformational behaviors, ranging from stiff, buckling slabs to more-ductile masses of accumulating slab material undergoing pure shear. Of particular interest is how rheology and 3D spherical geometry control the shape and deformational style of slabs as they descend deeper into the mantle. We performed high resolution 3D spherical calculations to explore slab deformation in deep mantle as a function of slab strength. In our model, kinematic velocity boundary conditions are imposed on the surface to simulate a moving plate which guides the formation of a subducting slab. In addition, a viscosity jump at the transition zone is applied. We find that although a slab subducts as a large tabular sheet from the surface, it doesn't always maintain such geometry. Instead, it typically breaks apart into a few smaller and narrower sheets which can even turn into cylindrical-shaped downwelling after subducting into deep mantle. Since seismic anisotropy is hypothesized to originate from crystal preferred orientation (CPO) in a slab when it impinges on the CMB and is predicted with significant help of time-dependent deformation information from the geodynamic models, our findings on lower mantle slab deformation patterns may enhance the understanding towards the cause of characteristic patterns of predicted seismic anisotropy.

Preface: Deep Slab and Mantle Dynamics

NASA Astrophysics Data System (ADS)

Suetsugu, Daisuke; Bina, Craig R.; Inoue, Toru; Wiens, Douglas A.

2010-11-01

We are pleased to publish this special issue of the journal Physics of the Earth and Planetary Interiors entitled "Deep Slab and Mantle Dynamics". This issue is an outgrowth of the international symposium "Deep Slab and Mantle Dynamics", which was held on February 25-27, 2009, in Kyoto, Japan. This symposium was organized by the "Stagnant Slab Project" (SSP) research group to present the results of the 5-year project and to facilitate intensive discussion with well-known international researchers in related fields. The SSP and the symposium were supported by a Grant-in-Aid for Scientific Research (16075101) from the Ministry of Education, Culture, Sports, Science and Technology of the Japanese Government. In the symposium, key issues discussed by participants included: transportation of water into the deep mantle and its role in slab-related dynamics; observational and experimental constraints on deep slab properties and the slab environment; modeling of slab stagnation to constrain its mechanisms in comparison with observational and experimental data; observational, experimental and modeling constraints on the fate of stagnant slabs; eventual accumulation of stagnant slabs on the core-mantle boundary and its geodynamic implications. This special issue is a collection of papers presented in the symposium and other papers related to the subject of the symposium. The collected papers provide an overview of the wide range of multidisciplinary studies of mantle dynamics, particularly in the context of subduction, stagnation, and the fate of deep slabs.

Spread prestressed concrete slab beam bridges.

DOT National Transportation Integrated Search

2015-04-01

TxDOT uses prestressed slab beam bridges for short-span bridges ranging from approximately 3050 ft in : length. These bridges have precast, pretensioned slab beams placed immediately adjacent to one another : with a cast-in-place slab made composi...

Strength and Stiffness Analysis by the Finite-Difference Method of a Concrete Floor Slab Reinforced with Composite Rods During a Fire

NASA Astrophysics Data System (ADS)

Shirko, A. V.; Kamlyuk, A. N.; Drobysh, A. S.; Spiglazov, A. V.

2017-05-01

A strength and stiffness comparative analysis has been made of a concrete slab reinforced with composite-reinforcement rods and a slab reinforced with steel rods. The stress-strain state has been assessed for both versions of reinforcement of the slab. The stress-strain state was determined under the action of only static load and with subsequent application of temperature fields, i.e., under standard-fire conditions. It has been shown that the fire resistance of the slab with a composite reinforcement turns out to be 1.6 higher as far as the bearing capacity is concerned, than the fire resistance of the slab with a steel reinforcement, although the initial deflection due to the action of only static load for the slab reinforced with composite rods exceeds six to seven times the deflection of the slab reinforced with steel rods.

Modeling Slab-Slab Interactions: Dynamics of Outward Dipping Double-Sided Subduction Systems

NASA Astrophysics Data System (ADS)

Király, Ágnes; Holt, Adam F.; Funiciello, Francesca; Faccenna, Claudio; Capitanio, Fabio A.

2018-03-01

Slab-slab interaction is a characteristic feature of tectonically complex areas. Outward dipping double-sided subduction is one of these complex cases, which has several examples on Earth, most notably the Molucca Sea and Adriatic Sea. This study focuses on developing a framework for linking plate kinematics and slab interactions in an outward dipping subduction geometry. We used analog and numerical models to better understand the underlying subduction dynamics. Compared to a single subduction model, double-sided subduction exhibits more time-dependent and vigorous toroidal flow cells that are elongated (i.e., not circular). Because both the Molucca and Adriatic Sea exhibit an asymmetric subduction configuration, we also examine the role that asymmetry plays in the dynamics of outward dipping double-sided subduction. We introduce asymmetry in two ways; with variable initial depths for the two slabs ("geometric" asymmetry), and with variable buoyancy within the subducting plate ("mechanical" asymmetry). Relative to the symmetric case, we probe how asymmetry affects the overall slab kinematics, whether asymmetric behavior intensifies or equilibrates as subduction proceeds. While initial geometric asymmetry disappears once the slabs are anchored to the 660 km discontinuity, the mechanical asymmetry can cause more permanent differences between the two subduction zones. In the most extreme case, the partly continental slab stops subducting due to the unequal slab pull force. The results show that the slab-slab interaction is most effective when the two trenches are closer than 10-8 cm in the laboratory, which is 600-480 km when scaled to the Earth.

Experimental and finite element study of ultimate strength of continuous composite concrete slabs with steel decking

NASA Astrophysics Data System (ADS)

Gholamhoseini, Alireza

2018-03-01

Composite one-way concrete slabs with profiled steel decking as permanent formwork are commonly used in the construction industry. The steel decking supports the wet concrete of a cast in situ reinforced or post-tensioned concrete slab and, after the concrete sets, acts as external reinforcement. In this type of slab, longitudinal shear failure between the concrete and the steel decking is the most common type of failure at the ultimate load stage. Design codes require the experimental evaluation of the ultimate load capacity and longitudinal shear strength of each type of steel decking using full-scale tests on simple-span slabs. There is also no procedure in current design codes to evaluate the ultimate load capacity and longitudinal shear strength of continuous composite slabs and this is often assessed experimentally by full-scale tests. This paper presents the results of three full-scale tests up to failure on continuous composite concrete slabs cast with trapezoidal steel decking profile (KF70) that is widely used in Australia. Slab specimens were tested in four-point bending at each span with shear spans of span/4. The longitudinal shear failure of each slab is evaluated and the measured mid-span deflection, the end slip and the mid-span steel and concrete strains are also presented and discussed. Redistribution of bending moment in each slab is presented and discussed. A finite element model is proposed and verified by experimental data using interface element to model the bond properties between steel decking and concrete slab and investigate the ultimate strength of continuous composite concrete slabs.

An imbalance in the deep water cycle at subduction zones: The potential importance of the fore-arc mantle

NASA Astrophysics Data System (ADS)

Ribeiro, Julia M.; Lee, Cin-Ty A.

2017-12-01

The depth of slab dehydration is thought to be controlled by the thermal state of the downgoing slab: cold slabs are thought to mostly dehydrate beneath the arc front while warmer slabs should mostly dehydrate beneath the fore-arc. Cold subduction zone lavas are thus predicted to have interacted with greater extent of water-rich fluids released from the downgoing slab, and should thus display higher water content and be elevated in slab-fluid proxies (i.e., high Ba/Th, H2O/Ce, Rb/Th, etc.) compared to hot subduction zone lavas. Arc lavas, however, display similar slab-fluid signatures regardless of the thermal state of the slab, suggesting more complexity to volatile cycling in subduction zones. Here, we explore whether the serpentinized fore-arc mantle may be an important fluid reservoir in subduction zones and whether it can contribute to arc magma generation by being dragged down with the slab. Using simple mass balance and fluid dynamics calculations, we show that the dragged-down fore-arc mantle could provide enough water (∼7-78% of the total water injected at the trenches) to account for the water outfluxes released beneath the volcanic arc. Hence, we propose that the water captured by arc magmas may not all derive directly from the slab, but a significant component may be indirectly slab-derived via dehydration of dragged-down fore-arc serpentinites. Fore-arc serpentinite dehydration, if universal, could be a process that explains the similar geochemical fingerprint (i.e., in slab fluid proxies) of arc magmas.

Deformation of the Tonga Slab: Evidence for Interaction with a Small-scale Secondary Plume in the Transition Zone

NASA Astrophysics Data System (ADS)

Billen, M. I.; Bikoba, J. Z.; Tarlow, S.

2015-12-01

Magali I. Billen and John Z. BikobaThe Tonga Slab is the most seismically active subduction zone providing a uniquely detailed picture of the internal deformation of the slab, with apparent warping and folding, from the surface through the transition zone. Here, we investigate the dynamical origin of a irregular feature in the seismicity within the transition zone located at 21-28oS, using 3D visualization and analysis of the seismicity and compression/tension (P/T) axis from the moment tensor solutions to characterize the geometry of, and the orientation of forces acting on, the slab. This irregular feature can be described as narrow region of upward deflection of the slab, with a gap in seismicity beyond (down-dip of) the deflected region, and flanked by two narrow V-shaped gaps in seismicity suggestive of tearing of the slab. The P/T axis show a dominate down-dip orientation of the P axis above the deflection point, which rotate to a nearly vertical orientation within the central region of the deflected slab. The adjacent attached regions (down-dip of the two flanking slab gaps) also have rotated and more heterogeneous P/T axis orientations. In contrast, the adjacent section of the slab to the north of 21oS has continuous seismicity throughout the transition zone, with a roughly uniform planar shape, and generally down-dip orientation of the P axis. We explore three possible hypothesis for the observed deformation including: 1) deflection due to a buoyant metastable olivine wedge, 2) a buckling feature in the slab as previously proposed by Myhill (GJI., 2013), and interaction with a small-scale, secondary plume upwelling below the slab. If the newly-observed gaps in seismicity indicate physical gaps or significant thinning of the slab, then these observations are not consistent with the buckling hypothesis. The lack of significant along-strike variation in slab age or subduction rate also suggests that a localized region of metastable olivine is unlikely. Therefore, we test the third hypothesis using a simple 3D geodynamical model of a planar dipping slab overlying a localized buoyant upwelling (radius < 150 km). We present comparisons of the observations to the model predictions for the subsequent deformation of the slab and orientations of principal stress axis within the slab.

Flexural performance of steel fiber reinforced concrete (SFRC) ribbed slab with various topping thicknesses

NASA Astrophysics Data System (ADS)

Rahman, Fadhillah Abdul; Bakar, Afidah Abu; Hashim, Mohd Hisbany Mohd; Ahmad, Hazrina

2017-11-01

Ribbed slab provides lighter slab than an equivalent solid slab which helps in reducing the weight with its voids. However, in order to overcome the drawbacks in the construction process, the application of steel fibre reinforcement concrete (SFRC) is seen as an alternative material to be used in the slab. This study is performed to investigate the behaviour of SFRC as the main material in ribbed slab, omitting the conventional reinforcements, under four-point bending test. Three equivalent samples of ribbed slabs were prepared for this study with variations in the topping thickness of 100, 75 and 50 mm. The flexural strength of ribbed slab with 100 mm topping shows similar loading carrying capacity with the 75mm topping while 50 mm gave the lowest ultimate loading. First cracks for all slabs occurred at the topping. The cracks began from the external ribs and propagates toward the internal rib. Incorporation of steel fibres help in giving a longer deflection softening than a sudden brittle failure, thus proves its ability to increase energy absorption capacity and improving cracking behaviour.

South-American plate advance and forced Andean trench retreat as drivers for transient flat subduction episodes.

PubMed

Schepers, Gerben; van Hinsbergen, Douwe J J; Spakman, Wim; Kosters, Martha E; Boschman, Lydian M; McQuarrie, Nadine

2017-05-16

At two trench segments below the Andes, the Nazca Plate is subducting sub-horizontally over ∼200-300 km, thought to result from a combination of buoyant oceanic-plateau subduction and hydrodynamic mantle-wedge suction. Whether the actual conditions for both processes to work in concert existed is uncertain. Here we infer from a tectonic reconstruction of the Andes constructed in a mantle reference frame that the Nazca slab has retreated at ∼2 cm per year since ∼50 Ma. In the flat slab portions, no rollback has occurred since their formation at ∼12 Ma, generating 'horse-shoe' slab geometries. We propose that, in concert with other drivers, an overpressured sub-slab mantle supporting the weight of the slab in an advancing upper plate-motion setting can locally impede rollback and maintain flat slabs until slab tearing releases the overpressure. Tear subduction re-establishes a continuous slab and allows the process to recur, providing a mechanism for the transient character of flat slabs.

How to measure slab-off and reverse slab prism in spectacle lenses.

PubMed

Christoff, Alexander; Guyton, David L

2007-08-01

It is well known that new spectacle lenses for the correction of anisometropia can induce diplopia with reading. The difference in the powers of the lenses induces a net prismatic effect that can cause double vision through off-center areas of the lenses. This is particularly bothersome when patients try to read, often noting vertical double vision in attempted downgaze, especially through multifocal add segments. This induced prismatic effect can be compensated at one level of downgaze by the use of slab-off or reverse slab prism. Typically the slab-off correction is ground into the stronger minus, or weaker plus lens. Reverse slab is ground into the weaker minus, or stronger plus, lens. Unfortunately, determining the amount of slab-off prism already incorporated into spectacle lenses is nonintuitive and inconvenient. This usually requires the use of a lens clock, which is not widely accessible to many ophthalmology practices. A simple technique, described in the past but poorly known, is illustrated here for quickly measuring slab-off and reverse slab prism prescription lenses in the clinic with a common manual lens meter.

Metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere

NASA Astrophysics Data System (ADS)

Kirby, Stephen H.; Stein, Seth; Okal, Emile A.; Rubie, David C.

1996-05-01

Earth's deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km. This depth interval closely brackets the mantle transition zone, characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher-pressure phases. Deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal, thermodynamic, and mechanical ferment inside slabs. Numerical simulations of reaction rates show that the olivine → spinel transformation should be kinetically hindered in old, cold slabs descending into the transition zone. Thus wedge-shaped zones of metastable peridotite probably persist to depths of more than 600 km. Laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting. This instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser, finer-grained phase. Hence in cold slabs, such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite. It is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs. This consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features. It explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone, where minerals in downgoing slabs should transform to spinel and ilmenite structures. The onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab. Even if a slab penetrates into the lower mantle, earthquakes should cease at depths near 700 km, because the seismogenic phase transformations in the slab are completed or can no longer occur. Substantial metastability is expected only in old, cold slabs, consistent with the observed restriction of deep earthquakes to those settings. Earthquakes should be restricted to the cold cores of slabs, as in any model in which the seismicity is temperature controlled, via the distribution of metastability. However, the geometries of recent large deep earthquakes pose a challenge for any such models. Transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics, including focal mechanisms indicating localized shear failure rather than implosive deformation, are so similar to those of shallow earthquakes. Finally, metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab. Such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and/or are detached from subducting slabs. Metastability in downgoing slabs could have considerable geodynamic significance. Metastable wedges would reduce the negative buoyancy of slabs, decrease the driving force for subduction, and influence the state of stress in slabs. Heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage, causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity. Because wedge formation should occur only for fast subducting slabs, it may act as a "parachute" and contribute to regulating plate speeds. Wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge transforms to denser spinel, favoring the subsequent sinking of the slab into the lower mantle.

Rotation-invariant neural pattern recognition system with application to coin recognition.

PubMed

Fukumi, M; Omatu, S; Takeda, F; Kosaka, T

1992-01-01

In pattern recognition, it is often necessary to deal with problems to classify a transformed pattern. A neural pattern recognition system which is insensitive to rotation of input pattern by various degrees is proposed. The system consists of a fixed invariance network with many slabs and a trainable multilayered network. The system was used in a rotation-invariant coin recognition problem to distinguish between a 500 yen coin and a 500 won coin. The results show that the approach works well for variable rotation pattern recognition.

Temperature field for radiative tomato peeling

NASA Astrophysics Data System (ADS)

Cuccurullo, G.; Giordano, L.

2017-01-01

Nowadays peeling of tomatoes is performed by using steam or lye, which are expensive and polluting techniques, thus sustainable alternatives are searched for dry peeling and, among that, radiative heating seems to be a fairly promising method. This paper aims to speed up the prediction of surface temperatures useful for realizing dry-peeling, thus a 1D-analytical model for the unsteady temperature field in a rotating tomato exposed to a radiative heating source is presented. Since only short times are of interest for the problem at hand, the model involves a semi-infinite slab cooled by convective heat transfer while heated by a pulsating heat source. The model being linear, the solution is derived following the Laplace Transform method. A 3D finite element model of the rotating tomato is introduced as well in order to validate the analytical solution. A satisfactory agreement is attained. Therefore, two different ways to predict the onset of the peeling conditions are available which can be of help for proper design of peeling plants. Particular attention is paid to study surface temperature uniformity, that being a critical parameter for realizing an easy tomato peeling.

Dimensional stability of concrete slabs on grade.

DOT National Transportation Integrated Search

2012-10-01

Drying shrinkage is one of the major causes of cracking in concrete slabs on grade. The moisture : difference between the top and bottom surface of the slabs causes a dimensional or shrinkage gradient : to develop through the depth of the slabs...

On Heat Transfer through a Solid Slab Heated Uniformly and Periodically: Determination of Thermal Properties

ERIC Educational Resources Information Center

Rojas-Trigos, J. B.; Bermejo-Arenas, J. A.; Marin, E.

2012-01-01

In this paper, some heat transfer characteristics through a sample that is uniformly heated on one of its surfaces by a power density modulated by a periodical square wave are discussed. The solution of this problem has two contributions, comprising a transient term and an oscillatory term, superposed to it. The analytical solution is compared to…

Application of Advanced Sensor Technology to DoD Soil Vapor Intrusion Problems

DTIC Science & Technology

2012-10-01

19 Figure 10. Photographs of: a) Layton , Utah, ASU SERDP project study house and b) basement...relative to sub-slab; line). ..................... 24 Figure 18. Spatial distributions of TCE in Layton , Utah, house without VI and emplaced indoor...technical advice and use of ASU’s Strategic Environmental Research and Development Program (SERDP) VI study house in Layton , Utah, is very

Thermal buoyancy on Venus - Underthrusting vs subduction

NASA Technical Reports Server (NTRS)

Burt, Jeffrey D.; Head, James W.

1992-01-01

The thermal and buoyancy consequences of the subduction endmember are modeled in an attempt to evaluate the conditions distinguishing underthrusting and subduction. Thermal changes in slabs subducting into the Venusian mantle with a range of initial geotherms are used to predict density changes and, thus, slab buoyancy. Based on a model for subduction-induced mantle flow, it is then argued that the angle of the slab dip helps differentiate between underthrusting and subduction. Mantle flow applies torques to the slab which, in combination with torques due to slab buoyancy, act to change the angle of slab dip.

Tectonic evolution of the Mexico flat slab and patterns of intraslab seismicity.

NASA Astrophysics Data System (ADS)

Moresi, L. N.; Sandiford, D.

2017-12-01

The Cocos plate slab is horizontal for about 250 km beneath the Guerrero region of southern Mexico. Analogous morphologies can spontaneously develop in subduction models, through the presence of a low-viscosity mantle wedge. The Mw 7.1 Puebla earthquake appears to have ruptured the inboard corner of the Mexican flat slab; likely in close proximity to the mantle wedge corner. In addition to the historical seismic record, the Puebla earthquake provides a valuable constraint through which to assess geodynamic models for flat slab evolution. Slab deformation predicted by the "weak wedge" model is consistent with past seismicity in the both the upper plate and slab. Below the flat section, the slab is anomalously warm relative to its depth; the lack of seismicity in the deeper part of the slab fits the global pattern of temperature-controlled slab seismicity. This has implications for understanding the deeper structure of the slab, including the seismic hazard from source regions downdip of the Puebla rupture (epicenters closer to Mexico City). While historical seismicity provides a deformation pattern consistent with the weak wedge model , the Puebla earthquake is somewhat anomalous. The earthquake source mechanism is consistent with stress orientations in our models, however it maps to a region of relatively low deviatoric stress.

Field evaluation of alternative and cost efficient bridge approach slabs.

DOT National Transportation Integrated Search

2013-11-01

Based on a recent study on cost efficient alternative bridge approach slab (BAS) designs (Thiagarajan et al. 2010) has recommended : three new BAS designs for possible implementation by MoDOT namely a) 20 feet cast-inplace slab with sleeper slab (CIP...

Cenozoic tectonics of western North America controlled by evolving width of Farallon slab.

PubMed

Schellart, W P; Stegman, D R; Farrington, R J; Freeman, J; Moresi, L

2010-07-16

Subduction of oceanic lithosphere occurs through two modes: subducting plate motion and trench migration. Using a global subduction zone data set and three-dimensional numerical subduction models, we show that slab width (W) controls these modes and the partitioning of subduction between them. Subducting plate velocity scales with W(2/3), whereas trench velocity scales with 1/W. These findings explain the Cenozoic slowdown of the Farallon plate and the decrease in subduction partitioning by its decreasing slab width. The change from Sevier-Laramide orogenesis to Basin and Range extension in North America is also explained by slab width; shortening occurred during wide-slab subduction and overriding-plate-driven trench retreat, whereas extension occurred during intermediate to narrow-slab subduction and slab-driven trench retreat.

Physical and Clinical Evaluation of Hip Spica Cast applied with Three-slab Technique using Fibreglass Material

PubMed Central

Bitar, KM; Ferdhany, ME; Saw, A

2016-01-01

Introduction: Hip spica casting is an important component of treatment for developmental dysplasia of the hip (DDH) and popular treatment method for femur fractures in children. Breakage at the hip region is a relatively common problem of this cast. We have developed a three-slab technique of hip spica application using fibreglass as the cast material. The purpose of this review was to evaluate the physical durability of the spica cast and skin complications with its use. Methodology: A retrospective review of children with various conditions requiring hip spica immobilisation which was applied using our method. Study duration was from 1st of January 2014 until 31st December 2015. Our main outcomes were cast breakage and skin complications. For children with hip instability, the first cast would be changed after one month, and the second cast about two months later. Results: Twenty-one children were included, with an average age of 2.2 years. The most common indication for spica immobilisation was developmental dysplasia of the hip. One child had skin irritation after spica application. No spica breakage was noted. Conclusion: This study showed that the three-slab method of hip spica cast application using fibreglass material was durable and safe with low risk of skin complications. PMID:28553442

Subducting Slabs: Jellyfishes in the Earth's Mantle

NASA Astrophysics Data System (ADS)

Loiselet, C.; Braun, J.; Husson, L.; Le Carlier de Veslud, C.; Thieulot, C.; Yamato, P.; Grujic, D.

2010-12-01

The constantly improving resolution of geophysical data, seismic tomography and seismicity in particular, shows that the lithosphere does not subduct as a slab of uniform thickness but is rather thinned in the upper mantle and thickened around the transition zone between the upper and lower mantle. This observation has traditionally been interpreted as evidence for the buckling and piling of slabs at the boundary between the upper and lower mantle, where a strong contrast in viscosity may exist and cause resistance to the penetration of slabs into the lower mantle. The distribution and character of seismicity reveal, however, that slabs undergo vertical extension in the upper mantle and compression near the transition zone. In this paper, we demonstrate that during the subduction process, the shape of low viscosity slabs (1 to 100 times more viscous than the surrounding mantle) evolves toward an inverted plume shape that we coin jellyfish. Results of a 3D numerical model show that the leading tip of slabs deform toward a rounded head skirted by lateral tentacles that emerge from the sides of the jellyfish head. The head is linked to the body of the subducting slab by a thin tail. A complete parametric study reveals that subducting slabs may achieve a variety of shapes, in good agreement with the diversity of natural slab shapes evidenced by seismic tomography. Our work also suggests that the slab to mantle viscosity ratio in the Earth is most likely to be lower than 100. However, the sensitivity of slab shapes to upper and lower mantle viscosities and densities, which remain poorly constrained by independent evidence, precludes any systematic deciphering of the observations.

Subducting slabs: Jellyfishes in the Earth's mantle

NASA Astrophysics Data System (ADS)

Loiselet, Christelle; Braun, Jean; Husson, Laurent; Le Carlier de Veslud, Christian; Thieulot, Cedric; Yamato, Philippe; Grujic, Djordje

2010-08-01

The constantly improving resolution of geophysical data, seismic tomography and seismicity in particular, shows that the lithosphere does not subduct as a slab of uniform thickness but is rather thinned in the upper mantle and thickened around the transition zone between the upper and lower mantle. This observation has traditionally been interpreted as evidence for the buckling and piling of slabs at the boundary between the upper and lower mantle, where a strong contrast in viscosity may exist and cause resistance to the penetration of slabs into the lower mantle. The distribution and character of seismicity reveal, however, that slabs undergo vertical extension in the upper mantle and compression near the transition zone. In this paper, we demonstrate that during the subduction process, the shape of low viscosity slabs (1 to 100 times more viscous than the surrounding mantle) evolves toward an inverted plume shape that we coin jellyfish. Results of a 3D numerical model show that the leading tip of slabs deform toward a rounded head skirted by lateral tentacles that emerge from the sides of the jellyfish head. The head is linked to the body of the subducting slab by a thin tail. A complete parametric study reveals that subducting slabs may achieve a variety of shapes, in good agreement with the diversity of natural slab shapes evidenced by seismic tomography. Our work also suggests that the slab to mantle viscosity ratio in the Earth is most likely to be lower than 100. However, the sensitivity of slab shapes to upper and lower mantle viscosities and densities, which remain poorly constrained by independent evidence, precludes any systematic deciphering of the observations.

Slab edge interaction with a back-arc spreading center: 3D instantaneous mantle flow models of Vanuatu, SW Pacific

NASA Astrophysics Data System (ADS)

McLean, K. A.; Jadamec, M.; Durance-Sie, P. M.; Moresi, L. N.

2011-12-01

The Vanuatu area of the south-west Pacific is a dynamic region of high heat-flow and strain-rate, dominated by ongoing plate boundary processes. At the southern termination of the Vanuatu arc the curved geometry of the New Hebrides trench juxtaposes the slab edge perpendicular to its back-arc spreading center. While existing 3D subduction models have demonstrated the importance of mantle flow around a slab edge, the nature of interaction between back-arc upwelling and circum-slab edge mantle flow is not well understood. We use 3D instantaneous numerical models of a Newtonian mantle rheology to test the effect of the slab edge and back-arc upwelling on the mantle flow vector field beneath southern Vanuatu. These high-resolution models simulate temperature-dependent buoyancy-driven deformation of the lithosphere and mantle for a realistic slab geometry. Model results show a small but significant component of vertical mantle flow velocity associated with the slab edge and back-arc spreading center. We also see strain-rate and dynamic topography commensurate with surface observations. Mantle flow by toroidal-type motion brings hotter mantle material from behind the slab into the mantle wedge, elevating geothermal gradients in the slab edge vicinity. The implications of moderate vertical displacement of this hot mantle material at the slab edge are wide-ranging, and such a tectonic framework might aid interpretation of a number of surface observations. For example, induced decompression partial-melting in the mantle wedge and/or slab, and thermal erosion of the slab may contribute to the diverse magma compositions from this region.

Peculiarities of field penetration in the presence of cross-flux interaction

NASA Astrophysics Data System (ADS)

Berseth, V.; Buzdin, A. I.; Indenbom, M. V.; Benoit, W.

1996-02-01

The attractive core interaction between two orthogonal vortex lattices in alayered superconductor is calculated. When one of these lattices is moving, this interaction gives rise to a drag force acting on the other one. Considering a moving in-plane flux lattice, the effect of the drag force on the perpendicular flux is modelled through a modification of the bulk critical current for this field component. The new critical current depends on the direction of motion of both parallel and perpendicular vortices. The results are derived within the critical-state model for the infinite slab and for the thin strip. For this latter geometry, computations are made with the help of a new numerical method simulating flux penetration in the critical state. The new predicted qualitative phenomena (like the formation of a vortex-free region between two zones of opposite flux in the flat geometry) can be directly verified by the magneto-optic technique.

Metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere

USGS Publications Warehouse

Kirby, S.H.; Stein, S.; Okal, E.A.; Rubie, David C.

1996-01-01

Earth's deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km. This depth interval closely brackets the mantle transition zone, characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher-pressure phases. Deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal, thermodynamic, and mechanical ferment inside slabs. Numerical simulations of reaction rates show that the olivine ??? spinel transformation should be kinetically hindered in old, cold slabs descending into the transition zone. Thus wedge-shaped zones of metastable peridotite probably persist to depths of more than 600 km. Laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting. This instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser, finer-grained phase. Hence in cold slabs, such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite. It is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs. This consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features. It explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone, where minerals in downgoing slabs should transform to spinel and ilmenite structures. The onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab. Even if a slab penetrates into the lower mantle, earthquakes should cease at depths near 700 km, because the seismogenic phase transformations in the slab are completed or can no longer occur. Substantial metastability is expected only in old, cold slabs, consistent with the observed restriction of deep earthquakes to those settings. Earthquakes should be restricted to the cold cores of slabs, as in any model in which the seismicity is temperature controlled, via the distribution of metastability. However, the geometries of recent large deep earthquakes pose a challenge for any such models. Transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics, including focal mechanisms indicating localized shear failure rather than implosive deformation, are so similar to those of shallow earthquakes. Finally, metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab. Such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and/or are detached from subducting slabs. Metastability in downgoing slabs could have considerable geodynamic significance. Metastable wedges would reduce the negative buoyancy of slabs, decrease the driving force for subduction, and influence the state of stress in slabs. Heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage, causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity. Because wedge formation should occur only for fast subducting slabs, it may act as a "parachute" and contribute to regulating plate speeds. Wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge tra

Aseismic deep subduction of the Philippine Sea plate and slab window

NASA Astrophysics Data System (ADS)

Huang, Zhouchuan; Zhao, Dapeng; Hasegawa, Akira; Umino, Norihito; Park, Jung-Ho; Kang, Ik-Bum

2013-10-01

We have made great efforts to collect and combine a large number of high-quality data from local earthquakes and teleseismic events recorded by the dense seismic networks in both South Korea and West Japan. This is the first time that a large number of Korean and Japanese seismic data sets are analyzed jointly. As a result, a high-resolution 3-D P-wave velocity model down to 700-km depth is determined, which clearly shows that the Philippine Sea (PHS) plate has subducted aseismically down to ˜460 km depth under the Japan Sea, Tsushima Strait and East China Sea. The aseismic PHS slab is visible in two areas: one is under the Japan Sea off western Honshu, and the other is under East China Sea off western Kyushu. However, the aseismic PHS slab is not visible between the two areas, where a slab window has formed. The slab window is located beneath the center of the present study region where many teleseismic rays crisscross. Detailed synthetic tests were conducted, which indicate that both the aseismic PHS slab and the slab window are robust features. Using the teleseismic data recorded by the Japanese stations alone, the aseismic PHS slab and the slab window were also revealed (Zhao et al., 2012), though the ray paths in the Japanese data set crisscross less well offshore. The slab window may be caused by the subducted Kyushu-Palau Ridge and Kinan Seamount Chain where the PHS slab may be segmented. Hot mantle upwelling is revealed in the big mantle wedge above the Pacific slab under the present study region, which may have facilitated the formation of the PHS slab window. These novel findings may shed new light on the subduction history of the PHS plate and the dynamic evolution of the Japan subduction zone.

Accelerated slab replacement using temporary precast panels and self-consolidating concrete : [summary].

DOT National Transportation Integrated Search

2016-06-01

Researchers at Florida State University demonstrated the feasibility of using precast reinforced concrete panels to temporarily fill slab removal pits. The precast slabs can be driven on so traffic lanes can be open during the day, and new slab casti...

Production of High Quality Die Steels from Large ESR Slab Ingots

NASA Astrophysics Data System (ADS)

Geng, Xin; Jiang, Zhou-hua; Li, Hua-bing; Liu, Fu-bin; Li, Xing

With the rapid development of manufacture industry in China, die steels are in great need of large slab ingot of high quality and large tonnage, such as P20, WSM718R and so on. Solidification structure and size of large slab ingots produced with conventional methods are not satisfied. However, large slab ingots manufactured by ESR process have a good solidification structure and enough section size. In the present research, the new slab ESR process was used to produce the die steels large slab ingots with the maximum size of 980×2000×3200mm. The compact and sound ingot can be manufactured by the slab ESR process. The ultra-heavy plates with the maximum thickness of 410 mm can be obtained after rolling the 49 tons ingots. Due to reducing the cogging and forging process, the ESR for large slab ingots process can increase greatly the yield and production efficiency, and evidently cut off product costs.

Age of the Subducting Philippine Sea Slab and Mechanism of Low-Frequency Earthquakes

NASA Astrophysics Data System (ADS)

Hua, Yuanyuan; Zhao, Dapeng; Xu, Yixian; Liu, Xin

2018-03-01

Nonvolcanic low-frequency earthquakes (LFEs) usually occur in young and warm subduction zones under condition of near-lithostatic pore fluid pressure. However, the relation between the LFEs and the subducting slab age has never been documented so far. Here we estimate the lithospheric age of the subducting Philippine Sea (PHS) slab beneath the Nankai arc by linking seismic tomography and a plate reconstruction model. Our results show that the LFEs in SW Japan take place in young parts ( 17-26 Myr) of the PHS slab. However, no LFE occurs beneath the Kii channel where the PHS slab is very young ( 15 Myr) and thin ( 29 km), forming an LFE gap there. According to the present results and previous works, we think that the LFE gap at the Kii channel is caused by joint effects of several factors, including the youngest slab age, high temperature, low fluid content, high permeability of the overlying plate, a slab tear, and hot upwelling flow below the PHS slab.

Atlas of the underworld: Slab remnants in the mantle, their sinking history, and a new outlook on lower mantle viscosity

NASA Astrophysics Data System (ADS)

van der Meer, Douwe G.; van Hinsbergen, Douwe J. J.; Spakman, Wim

2018-01-01

Across the entire mantle we interpret 94 positive seismic wave-speed anomalies as subducted lithosphere and associate these slabs with their geological record. We document this as the Atlas of the Underworld, also accessible online at www.atlas-of-the-underworld.org, a compilation comprising subduction systems active in the past 300 Myr. Deeper slabs are correlated to older geological records, assuming no relative horizontal motions between adjacent slabs following break-off, using knowledge of global plate circuits, but without assuming a mantle reference frame. The longest actively subducting slabs identified reach the depth of 2500 km and some slabs have impinged on Large Low Shear Velocity Provinces in the deepest mantle. Anomously fast sinking of some slabs occurs in regions affected by long-term plume rising. We conclude that slab remnants eventually sink from the upper mantle to the core-mantle boundary. The range in subduction-age versus - depth in the lower mantle is largely inherited from the upper mantle history of subduction. We find a significant depth variation in average sinking speed of slabs. At the top of the lower mantle average slab sinking speeds are between 10 and 40 mm/yr, followed by a deceleration to 10-15 mm/yr down to depths around 1600-1700 km. In this interval, in situ time-stationary sinking rates suggest deceleration from 20 to 30 mm/yr to 4-8 mm/yr, increasing to 12-15 mm/yr below 2000 km. This corroborates the existence of a slab deceleration zone but we do not observe long-term (> 60 My) slab stagnation, excluding long-term stagnation due to compositional effects. Conversion of slab sinking profiles to viscosity profiles shows the general trend that mantle viscosity increases in the slab deceleration zone below which viscosity slowly decreases in the deep mantle. This is at variance with most published viscosity profiles that are derived from different observations, but agrees qualitatively with recent viscosity profiles suggested from material experiments.

The atomic arrangement of iimoriite-(Y), Y2(SiO4)(CO3)

USGS Publications Warehouse

Hughes, J.M.; Foord, E.E.; Jai-Nhuknan, J.; Bell, J.M.

1996-01-01

Iimoriite-(Y) from Bokan Mountain, Prince of Wales Island, Alaska has been studied using single-crystal X-ray-diffraction techniques. The mineral, ideally Y2(SiO4)(CO3), crystallizes in space group P1, with a 6.5495(13), b 6.6291(14), c 6.4395(11)A??, ?? 116.364(15), ?? 92.556(15) and ?? 95.506(17)??. The atomic arrangement has been solved and refined to an R value of 0.019. The arrangement of atoms consists of alternating (011) slabs of orthosilicate groups and carbonate groups, with no sharing of oxygen atoms between anionic complexes in adjacent slabs. Y1 atoms separate adjacent tetrahedra along [100] within the orthosilicate slab, and Y2 atoms separate adjacent carbonate groups along [100] within the carbonate slab. Adjacent orthosilicate and carbonate slabs are linked in (100) by bonding Y atoms from each slab to oxygen atoms of adjacent slabs, in the form of YO8 polyhedra. The Y1 atoms exist in Y12O14 dimers in the orthosilicate slab, and the Y2 atoms exist in continuous [011] ribbons of edge-sharing Y2O8 polyhedra in the carbonate slab.

Geologic signature of early Tertiary ridge subduction in Alaska

USGS Publications Warehouse

Bradley, Dwight C.; Kusky, Timothy M.; Haeussler, Peter J.; Goldfarb, Richard J.; Miller, Marti L.; Dumoulin, Julie A.; Nelson, Steven W.; Karl, Susan M.

2003-01-01

A mid-Paleocene to early Eocene encounter between an oceanic spreading center and a subduction zone produced a wide range of geologic features in Alaska. The most striking effects are seen in the accretionary prism (Chugach–Prince William terrane), where 61 to 50 Ma near-trench granitic to gabbroic plutons were intruded into accreted trench sediments that had been deposited only a few million years earlier. This short time interval also saw the genesis of ophiolites, some of which contain syngenetic massive sulfide deposits; the rapid burial of these ophiolites beneath trench turbidites, followed immediately by obduction; anomalous high-T, low-P, near-trench metamorphism; intense ductile deformation; motion on transverse strike-slip and normal faults; gold mineralization; and uplift of the accretionary prism above sea level. The magmatic arc experienced a brief flare-up followed by quiescence. In the Alaskan interior, 100 to 600 km landward of the paleotrench, several Paleocene to Eocene sedimentary basins underwent episodes of extensional subsidence, accompanied by bimodal volcanism. Even as far as 1000 km inboard of the paleotrench, the ancestral Brooks Range and its foreland basin experienced a pulse of uplift that followed about 40 million years of quiescence.All of these events - but most especially those in the accretionary prism - can be attributed with varying degrees of confidence to the subduction of an oceanic spreading center. In this model, the ophiolites and allied ore deposits were produced at the soon-to-be subducted ridge. Near-trench magmatism, metamorphism, deformation, and gold mineralization took place in the accretionary prism above a slab window, where hot asthenosphere welled up into the gap between the two subducted, but still diverging, plates. Deformation took place as the critically tapered accretionary prism adjusted its shape to changes in the bathymetry of the incoming plate, changes in the convergence direction before and after ridge subduction, and changes in the strength of the prism as it was heated and then cooled. In this model, events in the Alaskan interior would have taken place above more distal, deeper parts of the slab window. Extensional (or transtensional) basin subsidence was driven by the two subducting plates that each exerted different tractions on the upper plate. The magmatic lull along the arc presumably marks a time when hydrated lithosphere was not being subducted beneath the arc axis. The absence of a subducting slab also may explain uplift of the Brooks Range and North Slope: Geodynamic models predict that longwavelength uplift of this magnitude will take place far inboard from Andean-type margins when a subducting slab is absent. Precise correlations between events in the accretionary prism and the Alaskan interior are hampered, however, by palinspastic problems. During and since the early Tertiary, margin-parallel strike-slip faulting has offset the near-trench plutonic belt - i.e., the very basis for locating the triple junction and slab window - from its backstop, by an amount that remains controversial.Near-trench magmatism began at 61 Ma at Sanak Island in the west but not until 51 Ma at Baranof Island, 2200 km to the east. A west-to-east age progression suggests migration of a trench-ridge-trench triple junction, which we term the Sanak-Baranof triple junction. Most workers have held that the subducted ridge separated the Kula and Farallon plates. As a possible alternative, we suggest that the ridge may have separated the Kula plate from another oceanic plate to the east, which we have termed the Resurrection plate.

A slab expression in the Gibraltar arc?

NASA Astrophysics Data System (ADS)

Nijholt, Nicolai; Govers, Rob; Wortel, Rinus

2017-04-01

The present-day geodynamic setting of the Gibraltar arc region results from several Myrs of subduction rollback in the overall (oblique) convergence of Africa and Iberia. As for most rollback settings in a convergence zone, the interaction of these two components is complex and distinctly non-stationary. Gibraltar slab rollback is considered to have stalled, or at least diminished largely in magnitude, since the late Miocene/early Pliocene, suggesting that the effect of the slab on present-day surface motions is negligible. However, GPS measurements indicate that the Gibraltar arc region has an anomalous motion with respect to both Iberia and Africa, i.e., the Gibraltar arc region does not move as part of the rigid Iberian, or the rigid African plate. A key question is whether this surface motion is an expression of the Gibraltar slab. Seismic activity in the Gibraltar region is diffuse and considerable in magnitude, making it a region of high seismic risk. Unlike the North African margin to the east, where thrust earthquakes dominate the focal mechanism tables, a complex pattern is observed with thrust, normal and strike-slip earthquakes in a region stretching between the northern Moroccan Atlas across the Gibraltar arc and Alboran Sea (with the Trans-Alboran Shear Zone) to the Betics of southern Spain. Even though no large mega-thrust earthquakes have been observed in recent history, slab rollback may not have completely ceased. However, since no activity has been observed in the accretionary wedge, probably since the Pliocene, it is likely that the subduction interface is locked. In this study, we perform a series of numerical models in which we combine the relative plate convergence, variable magnitude of friction on fault segments, regional variations in gravitational potential energy and slab pull of the Gibraltar slab. We seek to reproduce the GPS velocities and slip sense on regional faults and thereby determine whether the Gibraltar slab has an effect on surface motion. Slab shape and slab continuity to the surface, allowing slab pull to be transfered to the surface lithosphere, are key factors controlling the force balance in the region. We explore slab geometries with or without continuity at the Betics (with a slab window between the known subduction interface and a possible Betics connection) and/or continental material attached to the slab (which lowers the slab pull magnitude). Through our methodology, we are able to study which slab shape of those proposed in the literature best fits the surface data.

Multi-region relaxed magnetohydrodynamics in plasmas with slowly changing boundaries -- Resonant response of a plasma slab

DOE PAGES

Dewar, R. L.; Hudson, S. R.; Bhattacharjee, A.; ...

2017-04-03

The adiabatic limit of a recently proposed dynamical extension of Taylor relaxation, multi-region relaxed magnetohydrodynamics (MRxMHD), is summarized, with special attention to the appropriate definition of a relative magnetic helicity. The formalism is illustrated using a simple two-region, sheared-magnetic-field model similar to the Hahm-Kulsrud-Taylor (HKT) rippled-boundary slab model. In MRxMHD, a linear Grad-Shafranov equation applies, even at finite ripple amplitude. The adiabatic switching on of boundary ripple excites a shielding current sheet opposing reconnection at a resonant surface. The perturbed magnetic field as a function of ripple amplitude is calculated by invoking the conservation of magnetic helicity in the twomore » regions separated by the current sheet. Here, at low ripple amplitude, "half islands" appear on each side of the current sheet, locking the rotational transform at the resonant value. Beyond a critical amplitude, these islands disappear and the rotational transform develops a discontinuity across the current sheet. Published by AIP Publishing.« less

Multi-region relaxed magnetohydrodynamics in plasmas with slowly changing boundaries -- Resonant response of a plasma slab

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dewar, R. L.; Hudson, S. R.; Bhattacharjee, A.

The adiabatic limit of a recently proposed dynamical extension of Taylor relaxation, multi-region relaxed magnetohydrodynamics (MRxMHD), is summarized, with special attention to the appropriate definition of a relative magnetic helicity. The formalism is illustrated using a simple two-region, sheared-magnetic-field model similar to the Hahm-Kulsrud-Taylor (HKT) rippled-boundary slab model. In MRxMHD, a linear Grad-Shafranov equation applies, even at finite ripple amplitude. The adiabatic switching on of boundary ripple excites a shielding current sheet opposing reconnection at a resonant surface. The perturbed magnetic field as a function of ripple amplitude is calculated by invoking the conservation of magnetic helicity in the twomore » regions separated by the current sheet. Here, at low ripple amplitude, "half islands" appear on each side of the current sheet, locking the rotational transform at the resonant value. Beyond a critical amplitude, these islands disappear and the rotational transform develops a discontinuity across the current sheet. Published by AIP Publishing.« less

Refining the Tonga Slab Geometry Using Slab Phases of Seismic Waves

NASA Astrophysics Data System (ADS)

Alongi, T.; Wei, S. S.; Blackman, D. K.

2017-12-01

Although the Tonga subducting slab geometry has been previously mapped by earthquake distribution, its detailed morphology is poorly constrained. The uncertainties of the slab surface relative to earthquakes can be translated into large errors in predicted temperature of hypocenters that is considered as a chief control of intermediate-depth seismicity. Seismic waves converted at the interface between the slab crust and the overlying mantle wedge can provide additional constraints on the location of the slab surface. A PS phase converted at the slab interface is observable in the horizontal components, whereas an SP converted phase can be seen in the vertical component. In this study, we analyze PS and SP phases in the seismic dataset of the 2009-2010 Ridge2000 Lau Spreading Center project, which consisted of 50 ocean bottom seismographs (OBSs) and 17 island-based seismic stations deployed in Fiji, Tonga, and the Lau Basin for about one year. More than 1,000 PS arrivals from local events were manually picked, predominantly with a 1-3 Hz filter. Next, the PS-P differential travel times will be inverted to determine improved depths of the slab surface relative to the local earthquakes and the receiving stations. The refined slab geometry will allow us to assess the thermal structure and dehydration reactions of the Tonga slab, lending further insight into the mechanisms of intermediate-depth seismicity.

Seismicity and structure of Nazca Plate subduction zone in southern Peru

NASA Astrophysics Data System (ADS)

Lim, H.; Kim, Y.; Clayton, R. W.; Thurber, C. H.

2016-12-01

We define subducting plate geometries in the Nazca subduction zone by (re)locating intra-slab earthquakes in southern Peru (2-18°S) and taking previously published converted phase analysis results, to clarify the slab geometry and inferred relationships to the seismicity. We also provide both P- and S-wave velocities of the subducting Nazca Plate and mantle wedge portions close to the slab using double-difference tomography (Zhang and Thurber, 2003) to understand upper plate volcanism and subduction process. A total of 492 regional earthquakes from August 2008 to February 2013 recorded from the dense seismic array (PeruSE, 2013) are selected for the relocation and tomography. The relocated seismicity shows a smooth contortion in the slab-dip transition zone for 400 km between the shallow (25°)-to-flat dipping interface in the north and 40°-dipping interface in the south. We find a significant slab-dip difference (up to 10°) between our results and previously published slab models along the profile region sampling the normal-dip slab at depth (>100 km). Robust features in both P- and S-wave tomography inversions are dipping low-velocity slabs down to 100 km transitioning to higher-velocities at 100-140 km in both flat slab and dipping slab regions. Differences in the velocities of the mantle wedge between the two regions may indicate different hydration states in the wedge.

Development of an Improved Crack Propagation Model for Corrosion-Induced Cover Cracking in RC Structures

NASA Astrophysics Data System (ADS)

Hilyati, S.; Nizam, Z. M.; Zurisman, M. A. A.; Azhar, A. T. S.

2017-06-01

During the last two decades, reinforced concrete (RC) has been extensively used in most of the world as one of the common construction material due to its advantages and durability. However, RC structures exposed to marine environments are subjected to chloride attack. Chlorides from seawater penetrate into RC structures are not only causing severe corrosion problems but also affect the durability and serviceability of such structures. This paper investigates the influence of transverse reinforcement and spacing of reinforcing bars on concrete cover cracking of two-way RC slab specimens using accelerated corrosion tests. The experimental program involved the testing of four RC slab specimens and was generally designed to observe the crack width and the time of crack to propagate. An improved model for predicting the timing of crack propagation based on the experimental data was then developed.

Implications of slab mineralogy for subduction dynamics

NASA Astrophysics Data System (ADS)

Bina, Craig R.; Stein, Seth; Marton, Frederic C.; Van Ark, Emily M.

2001-12-01

Phase relations among mantle minerals are perturbed by the thermal environment of subducting slabs, both under equilibrium and disequilibrium (metastable) conditions. Such perturbations yield anomalies not only in seismic velocities but also in density. The buoyancy forces arising from these density anomalies may exert several important effects. They contribute to the stress field within the slab, in a fashion consistent with observed patterns of seismicity. They may affect subduction rates, both by inducing time-dependent velocity changes under equilibrium conditions and by imposing velocity limits through a thermal feedback loop under disequilibrium conditions. They may affect slab morphology, possibly inhibiting penetration of slabs into the lower mantle and allowing temporary stagnation of deflected or detached slabs. Latent heat release from phase transitions under disequilibrium conditions in slabs can yield isobaric superheating, which may generate adiabatic shear instabilities capable of triggering deep seismicity.

Image transfer properties by photonic crystal slab with negative refractive index

NASA Astrophysics Data System (ADS)

Chen, Hongbo; Chen, Xiaoshuang; Zhou, Renlong; Lu, Wei

2008-04-01

We have studied the properties of image transferred by photonic crystal (PhC) slab with negative refractive index n=-1 and confirmed the negative refractive phonomenon, but not found the saturated image properties as expected. It is found that real images will not be formed when the source distance larger than the thickness of PhC, and the transferred images are virtual images. Furthermore, comparing the quality of images transferred by a PhC slab and a cascaded stack of photonic crystal slab (CSPS), we found that the transferred images are distorted in both situations. The image resolution is good along the direction parallel to the slab interface, but bad along the direction normal to the slab interface. Simulation results show that the image formed by a CSPS is no better than a PhC slab.

Geometry of slab, intraslab stress field and its tectonic implication in the Nankai trough, Japan

NASA Astrophysics Data System (ADS)

Xu, J.; Kono, Y.

2002-07-01

The characteristics of geometry of slabs and the intraslab stress field in the Nankai subduction zone, Japan, were analyzed based on highly accurate hypocentral data and focal mechanism solutions. The results suggest that the shallow seismic zone of the Philippine Sea slab subducts with dip angels between 10 and 22 degrees beneath Shikoku and the Kii peninsula, and between 11 and 40 degrees beneath Kyushu. Two types of seismogenic stress field exist within the slab. The stress field of down-dip compression type can be seen in the slab beneath Shikoku and the Kii peninsula, where the horizontal component of regional compression stress is NNW. On the other hand the stress field of down-dip extension type within the slab is dominant in the region from western Shikoku to Kyushu, where the direction of horizontal compressive stress is near WWN. The existence of the two types of stress field is related to the differences of slab geometry and slab age of the subduciton zone. These properties imply that slab beneath Kyushu (40 Ma) probably is older than that beneath Shikoku and the Kii peninsula (11-20 Ma). The young slab of the oceanic Philippine Sea plate subducts with a shallow angle beneath the Eurasian plate in Shikoku and the Kii peninsula. The subduction has encountered strong resistance there, resulting in a down-dip compression stress field. The down-dip extension stress field may be related to the older slab of the Philippine Sea plate which subducts beneath Kyushu with a steeper dip angle.

Water-induced convection in the Earth's mantle transition zone

NASA Astrophysics Data System (ADS)

Richard, Guillaume C.; Bercovici, David

2009-01-01

Water enters the Earth's mantle by subduction of oceanic lithosphere. Most of this water immediately returns to the atmosphere through arc volcanism, but a part of it is expected as deep as the mantle transition zone (410-660 km depth). There, slabs can be deflected and linger before sinking into the lower mantle. Because it lowers the density and viscosity of the transition zone minerals (i.e., wadsleyite and ringwoodite), water is likely to affect the dynamics of the transition zone mantle overlying stagnant slabs. The consequences of water exchange between a floating slab and the transition zone are investigated. In particular, we focus on the possible onset of small-scale convection despite the adverse thermal gradient (i.e., mantle is cooled from below by the slab). The competition between thermal and hydrous effects on the density and thus on the convective stability of the top layer of the slab is examined numerically, including water-dependent density and viscosity and temperature-dependent water solubility. For plausible initial water content in a slab (≥0.5 wt %), an episode of convection is likely to occur after a relatively short time delay (5-20 Ma) after the slab enters the transition zone. However, water induced rheological weakening is seen to be a controlling parameter for the onset time of convection. Moreover, small-scale convection above a stagnant slab greatly enhances the rate of slab dehydration. Small-scale convection also facilitates heating of the slab, which in itself may prolong the residence time of the slab in the transition zone.

Slab stagnation and buckling in the mantle transition zone: Rheology, phase transition, trench migration, and seismic structure

NASA Astrophysics Data System (ADS)

Bina, Craig; Cizkova, Hana

2014-05-01

Subducting slabs may exhibit buckling instabilities and consequent folding behavior in the mantle transition zone for various combinations of dynamical parameters, accompanied by temporal variations in dip angle, plate velocity, and trench retreat. Parameters governing such behavior include both viscous forces (slab and mantle rheology) and buoyancy forces (slab thermal structure and mineral phase relations). 2D numerical experiments show that many parameter sets lead to slab deflection at the base of the transition zone, typically accompanied by quasi-periodic oscillations (consistent with previous scaling analyses) in largely anticorrelated plate and rollback velocities, resulting in undulating stagnant slabs as buckle folds accumulate subhorizontally atop the lower mantle. Slab interactions with mantle phase transitions are important components of this process (Bina and Kawakatsu, 2010; Čížková and Bina, 2013). For terrestrial parameter sets, trench retreat is found to be nearly ubiquitous, and trench advance is quite rare - due to both rheological structure and ridge-push effects (Čížková and Bina, 2013). Recent analyses of global plate motions indicate that significant trench advance is also rare on Earth, being largely restricted to the Izu-Bonin arc (Matthews et al., 2013). Consequently, we explore the conditions necessary for terrestrial trench advance through dynamical models involving the unusual geometry associated with the Philippine Sea region. Detailed images of buckled stagnant slabs are difficult to resolve due to smoothing effects inherent in seismic tomography, but velocity structures computed for compositionally layered slabs, using laboratory data on relevant mineral assemblages, can be spatially low-pass filtered for comparison with tomographic images of corresponding resolution. When applied to P-wave velocity anomalies from stagnant slab material beneath northeast China, model slabs which undulate due to compound buckling fit observations better than a flat-lying slab (Zhang et al., 2013). Earthquake hypocentral distributions and focal mechanisms may provide clearer insights into slab buckling, as they appear to vary systematically across regions of slab stagnation (Fukao and Obayashi, 2013). Stress fields computed from our dynamical models may help to illuminate such observations. References: Bina, C.R., and H. Kawakatsu, Buoyancy, bending, and seismic visibility in deep slab stagnation, Phys. Earth Planet. Inter., 183, 330-340, 2010. Čížková, H., and C.R. Bina, Effects of mantle and subduction-interface rheologies on slab stagnation and trench rollback, Earth Planet. Sci. Lett., 379, 95-103, 2013. Fukao, Y., and M. Obayashi, Deepest hypocentral distributions associated with stagnant slabs and penetrated slabs, Fall Meeting Abstracts, AGU, DI14A-01, 2013. Li, Z.-H., and N.M. Ribe, Dynamics of free subduction from 3-D boundary element modeling, J. Geophys. Res., 117, B06408. Matthews, D.C., L. Zheng, and R.G. Gordon, Do trenches advance? Fall Meeting Abstracts, AGU, T43D-2682, 2013. Zhang, Y., Y. Wang, Y. Wu, C. Bina, Z. Jin, and S. Dong, Phase transitions of harzburgite and buckled slab under eastern China, Geochem. Geophys. Geosys., 14, 1182-1199, 2013.

Polymer impregnated bridge slabs : interim report, condition of slabs after three years of service life.

DOT National Transportation Integrated Search

1983-01-01

The condition of six concrete bridge slabs that had been in service for three years was evaluated. The top 2 in. of the four slabs that had been impregnated to a depth of about 1 in. with a methyl methacrylate and trimethylolpropane trimethacrylate m...

Nonimaging concentrators for diode-pumped slab lasers

NASA Astrophysics Data System (ADS)

Lacovara, Philip; Gleckman, Philip L.; Holman, Robert L.; Winston, Roland

1991-10-01

Diode-pumped slab lasers require concentrators for high-average power operation. We detail the properties of diode lasers and slab lasers which set the concentration requirements and the concentrator design methodologies that are used, and describe some concentrator designs used in high-average power slab lasers at Lincoln Laboratory.

Field demonstration of new bridge approach slab designs and performance : [research project capsule].

DOT National Transportation Integrated Search

2008-10-01

A normal bridge approach slab in Louisiana is a reinforced concrete slab. It connects : the bridge deck to the adjacent paved roadway. Its intended functions are: : 1. To span the void that may develop below the slab due to soil erosion or : embankme...

Earthquake location in island arcs

USGS Publications Warehouse

Engdahl, E.R.; Dewey, J.W.; Fujita, K.

1982-01-01

A comprehensive data set of selected teleseismic P-wave arrivals and local-network P- and S-wave arrivals from large earthquakes occurring at all depths within a small section of the central Aleutians is used to examine the general problem of earthquake location in island arcs. Reference hypocenters for this special data set are determined for shallow earthquakes from local-network data and for deep earthquakes from combined local and teleseismic data by joint inversion for structure and location. The high-velocity lithospheric slab beneath the central Aleutians may displace hypocenters that are located using spherically symmetric Earth models; the amount of displacement depends on the position of the earthquakes with respect to the slab and on whether local or teleseismic data are used to locate the earthquakes. Hypocenters for trench and intermediate-depth events appear to be minimally biased by the effects of slab structure on rays to teleseismic stations. However, locations of intermediate-depth events based on only local data are systematically displaced southwards, the magnitude of the displacement being proportional to depth. Shallow-focus events along the main thrust zone, although well located using only local-network data, are severely shifted northwards and deeper, with displacements as large as 50 km, by slab effects on teleseismic travel times. Hypocenters determined by a method that utilizes seismic ray tracing through a three-dimensional velocity model of the subduction zone, derived by thermal modeling, are compared to results obtained by the method of joint hypocenter determination (JHD) that formally assumes a laterally homogeneous velocity model over the source region and treats all raypath anomalies as constant station corrections to the travel-time curve. The ray-tracing method has the theoretical advantage that it accounts for variations in travel-time anomalies within a group of events distributed over a sizable region of a dipping, high-velocity lithospheric slab. In application, JHD has the practical advantage that it does not require the specification of a theoretical velocity model for the slab. Considering earthquakes within a 260 km long by 60 km wide section of the Aleutian main thrust zone, our results suggest that the theoretical velocity structure of the slab is presently not sufficiently well known that accurate locations can be obtained independently of locally recorded data. Using a locally recorded earthquake as a calibration event, JHD gave excellent results over the entire section of the main thrust zone here studied, without showing a strong effect that might be attributed to spatially varying source-station anomalies. We also calibrated the ray-tracing method using locally recorded data and obtained results generally similar to those obtained by JHD. ?? 1982.

INTERIOR OVERVIEW OF CONTINUOUS CASTER WITH NO. 12 LADLE. MOLTEN ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

INTERIOR OVERVIEW OF CONTINUOUS CASTER WITH NO. 12 LADLE. MOLTEN STEEL IS POURED FROM LADLE THROUGH SHROUD TO TUNDISH. FROM TUNDISH STEEL ENTERS MOLD THROUGH SHROUD AND FORMATION OF SLAB SHELL BEGINS. AS SLAB PROGRESSES THROUGH CONTAINMENT SECTION IT IS COOLED WITH AIR MIST SPRAYS AND CONTINUES SOLIDIFICATION. UPON EXITING THE MACHINE THE SLABS ARE CUT TO DESIRED LENGTH AND IDENTIFIED. THE SLABS ARE STACKED, REMOVED FROM MACHINE AND PREPARED FOR SHIPMENT TO HOT STRIP MILL. CASTER HAS ABILITY TO PRODUCE SINGLE OR TWIN CASTS. SINGLE SLABS PRODUCED MAY BE UP TO 102 INCHES; DOUBLE SLABS UP TO 49 INCHES. - U.S. Steel, Fairfield Works, Continuous Caster, Fairfield, Jefferson County, AL

Flexural strength and behaviour of SFRSCC ribbed slab under four point bending

NASA Astrophysics Data System (ADS)

Ahmad, Hazrina; Hashim, Mohd Hisbany Mohd; Bakar, Afidah Abu; Hamzah, Siti Hawa; Rahman, Fadhillah Abdul

2017-11-01

An experimental investigation was carried out to study the ultimate strength and behaviour of SFRSCC ribbed slab under four point bending. Comparison was been made between ribbed slab that was fully reinforced with steel fibres (SFWS) with conventionally reinforced concrete ribbed slab (CS and CRC). The volume fraction of the 35 mm hooked end steel fibres used in the mix was 1% (80 kg/m3) with the aspect ratio of 65. Three full scale slab samples with the dimension of 2.8 x 1.2 m with 0.2 m thickness was constructed for the purpose of this study. The slab samples was loaded until failure in a four point bending test. As a whole, based on the results, it can be concluded that the performance of the steel fiber reinforced samples (SFWS) was found to be almost equivalent to the conventionally reinforced concrete ribbed slab sample (CRC).

TESTING OF INDOOR RADON REDUCTION TECHNIQUES IN CENTRAL OHIO HOUSES: PHASE 2 (WINTER 1988-1989)

EPA Science Inventory

The report gives results of tests of developmental indoor radon reduction techniques in nine slab-on-grade and four crawl-space houses near Dayton. Ohio. he slab-on-grade tests indicated that, when there is a good layer of aggregate under the slab, the sub-slab ventilation (SSV) ...

A review of the geodynamic evolution of flat slab subduction in Mexico, Peru, and Chile

NASA Astrophysics Data System (ADS)

Constantin Manea, Vlad; Manea, Marina; Ferrari, Luca; Orozco, María Teresa; Wong Valenzuela, Raul; Husker, Allen Leroy; Kostoglodovc, Vlad; Ionescu, Constantin

2017-04-01

Subducting plates around the globe display a large variability in terms of slab geometry, including regions where smooth and little variation in subduction parameters is observed. While the vast majority of subduction slabs plunge into the mantle at different, but positive dip angles, the end-member case of flat-slab subduction seems to strongly defy this rule and move horizontally several hundreds of kilometers before diving into the surrounding hotter mantle. By employing a comparative assessment for the Mexican, Peruvian and Chilean flat-slab subduction zones we find a series of parameters that apparently facilitate slab flattening. Among them, trench roll-back, as well as strong variations and discontinuities in the structure of oceanic and overriding plates seem to be the most important. However, we were not able to find the necessary and sufficient conditions that provide an explanation for the formation of flat slabs in all three subduction zones. In order to unravel the origin of flat-slab subduction, it is probably necessary a numerical approach that considers also the influence of surrounding plates, and their corresponding geometries, on 3D subduction dynamics.

A review of the geodynamic evolution of flat slab subduction in Mexico, Peru, and Chile

NASA Astrophysics Data System (ADS)

Manea, V. C.; Manea, M.; Ferrari, L.; Orozco-Esquivel, T.; Valenzuela, R. W.; Husker, A.; Kostoglodov, V.

2017-01-01

Subducting plates around the globe display a large variability in terms of slab geometry, including regions where smooth and little variation in subduction parameters is observed. While the vast majority of subduction slabs plunge into the mantle at different, but positive dip angles, the end-member case of flat-slab subduction seems to strongly defy this rule and move horizontally several hundreds of kilometers before diving into the surrounding hotter mantle. By employing a comparative assessment for the Mexican, Peruvian and Chilean flat-slab subduction zones we find a series of parameters that apparently facilitate slab flattening. Among them, trench roll-back, as well as strong variations and discontinuities in the structure of oceanic and overriding plates seem to be the most important. However, we were not able to find the necessary and sufficient conditions that provide an explanation for the formation of flat slabs in all three subduction zones. In order to unravel the origin of flat-slab subduction, it is probably necessary a numerical approach that considers also the influence of surrounding plates, and their corresponding geometries, on 3D subduction dynamics.

3-D Transient Heat Transfer Analysis of Slab Heating Characteristics in a Reheating Furnace in Hot Strip Mills

NASA Astrophysics Data System (ADS)

Jang, J. Y.; Lee, Y. W.; Lin, C. N.; Wang, C. H.

2016-05-01

A three-dimensional mathematical transient heat transfer model for the prediction of temperature distribution within the slab has been developed by considering the thermal radiation in the walking-beam-type reheating furnace chamber. The steel slabs are heated up through the non-firing, preheating, 1st-heating, 2nd-heating, and soaking zones in the furnace, respectively, where the furnace wall temperature is function of time. Comparison with the in-situ experimental data from Steel Company in Taiwan shows that the present heat transfer model works well for the prediction of thermal behavior of the slab in the reheating furnace. The effects of different skid button height (H=60mm, 90mm, and 120mm) and different gap distance between two slabs (S=50mm, 75mm, and 100mm) on the slab skid mark formation and temperature profiles are investigated. It is found that the skid mark severity decreases with an increase in the skid button height. The effect of gap distance is important only for the slab edge planes, while it is insignificant for the slab central planes.

Effect of kenaf fiber in reinforced concrete slab

NASA Astrophysics Data System (ADS)

Syed Mohsin, S. M.; Baarimah, A. O.; Jokhio, G. A.

2018-04-01

The effect of kenaf fibers in reinforced concrete slab with different thickness is discusses and presented in this paper. Kenaf fiber is a type of natural fiber and is added in the reinforced concrete slab to improve the structure strength and ductility. For this study, three types of mixtures were prepared with fiber volume fraction of 0%, 1% and 2%, respectively. The design compressive strength considered was 20 MPa. Six cubes were prepared to be tested at 7th and 28th day. A total of six reinforced concrete slab with two variances of thickness were also prepared and tested under four-point bending test. The differences in the thickness is to study the potential of kenaf fiber to serve as part of shear reinforcement in reinforced concrete slab that was design to fail in shear. It was observed that, addition of kenaf fiber in reinforced concrete slab improves the flexural strength and ductility of the reinforced concrete slab. In the slab with reduction in thickness, the mode of failure change from brittle to ductile with the inclusion of kenaf fiber.

Closure behavior of spherical void in slab during hot rolling process

NASA Astrophysics Data System (ADS)

Cheng, Rong; Zhang, Jiongming; Wang, Bo

2018-04-01

The mechanical properties of steels are heavily deteriorated by voids. The influence of voids on the product quality should be eliminated through rolling processes. The study on the void closure during hot rolling processes is necessary. In present work, the closure behavior of voids at the center of a slab at 800 °C during hot rolling processes has been simulated with a 3D finite element model. The shape of the void and the plastic strain distribution of the slab are obtained by this model. The void decreases along the slab thickness direction and spreads along the rolling direction but hardly changes along the strip width direction. The relationship between closure behavior of voids and the plastic strain at the center of the slab is analyzed. The effects of rolling reduction, slab thickness and roller diameter on the closure behavior of voids are discussed. The larger reduction, thinner slab and larger roller diameter all improve the closure of voids during hot rolling processes. Experimental results of the closure behavior of a void in the slab during hot rolling process mostly agree with the simulation results..

Early Earth slab stagnation

NASA Astrophysics Data System (ADS)

Agrusta, R.; Van Hunen, J.

2016-12-01

At present day, the Earth's mantle exhibits a combination of stagnant and penetrating slabs within the transition zone, indicating a intermittent convection mode between layered and whole-mantle convection. Isoviscous thermal convection calculations show that in a hotter Earth, the natural mode of convection was dominated by double-layered convection, which may imply that slabs were more prone to stagnate in the transition zone. Today, slab penetration is to a large extent controlled by trench mobility for a plausible range of lower mantle viscosity and Clapeyron slope of the mantle phase transitions. Trench mobility is, in turn, governed by slab strength and density and upper plate forcing. In this study, we systematically investigate the slab-transition zone internation in the Early Earth, using 2D self-consistent numerical subduction models. Early Earth's higher mantle temperature facilitates decoupling between the plates and the underlying asthenosphere, and may result in slab sinking almost without trench retreat. Such behaviour together with a low resistance of a weak lower mantle may allow slabs to penetrate. The ability of slab to sink into the lower mantle throughout Earth's history may have important implications for Earth's evolution: it would provide efficient mass and heat flux through the transition zone therefore provide an efficient way to cool and mix the Earth's mantle.

Degradation and mechanism of the mechanics and durability of reinforced concrete slab in a marine environment

NASA Astrophysics Data System (ADS)

Wu, Sheng-xing; Liu, Guan-guo; Bian, Han-bing; Lv, Wei-bo; Jiang, Jian-hua

2016-04-01

An experimental research was conducted to determine the corrosion and bearing capacity of a reinforced concrete (RC) slab at different ages in a marine environment. Results show that the development of corrosion-induced cracks on a slab in a marine environment can be divided into three stages according to crack morphology at the bottom of the slab. In the first stage, cracks appear. In the second stage, cracks develop from the edges to the middle of the slab. In the third stage, longitudinal and transverse corrosion-induced cracks coexist. The corrosion ratio of reinforcements nonlinearly increases with the age, and the relationship between the corrosion ratio of the reinforcements and the corrosion-induced crack width of the concrete is established. The flexural capacity of the corroded RC slab nonlinearly decreases with the age, and the model for the bearing capacity factor of the corroded RC slab is established. The mid-span deflection of the corroded RC slab that corresponds to the yield of the reinforcements linearly increases with the increase in corrosion ratio. Finally, the mechanisms of corrosion morphology and the degradation of the mechanical properties of an RC slab in a marine environment are discussed on the basis of the basic theories of steel corrosion in concrete and concrete structure design.

Meteorological variables to aid forecasting deep slab avalanches on persistent weak layers

USGS Publications Warehouse

Marienthal, Alex; Hendrikx, Jordy; Birkeland, Karl; Irvine, Kathryn M.

2015-01-01

Deep slab avalanches are particularly challenging to forecast. These avalanches are difficult to trigger, yet when they release they tend to propagate far and can result in large and destructive avalanches. We utilized a 44-year record of avalanche control and meteorological data from Bridger Bowl ski area in southwest Montana to test the usefulness of meteorological variables for predicting seasons and days with deep slab avalanches. We defined deep slab avalanches as those that failed on persistent weak layers deeper than 0.9 m, and that occurred after February 1st. Previous studies often used meteorological variables from days prior to avalanches, but we also considered meteorological variables over the early months of the season. We used classification trees and random forests for our analyses. Our results showed seasons with either dry or wet deep slabs on persistent weak layers typically had less precipitation from November through January than seasons without deep slabs on persistent weak layers. Days with deep slab avalanches on persistent weak layers often had warmer minimum 24-hour air temperatures, and more precipitation over the prior seven days, than days without deep slabs on persistent weak layers. Days with deep wet slab avalanches on persistent weak layers were typically preceded by three days of above freezing air temperatures. Seasonal and daily meteorological variables were found useful to aid forecasting dry and wet deep slab avalanches on persistent weak layers, and should be used in combination with continuous observation of the snowpack and avalanche activity.

Earthquakes and strain in subhorizontal slabs

NASA Astrophysics Data System (ADS)

Brudzinski, Michael R.; Chen, Wang-Ping

2005-08-01

Using an extensive database of fault plane solutions and precise locations of hypocenters, we show that the classic patterns of downdip extension (DDE) or downdip compression (DDC) in subduction zones deteriorate when the dip of the slab is less than about 20°. This result is depth-independent, demonstrated by both intermediate-focus (depths from 70 to 300 km) and deep-focus (depths greater than 300 km) earthquakes. The absence of pattern in seismic strain in subhorizontal slabs also occurs locally over scales of about 10 km, as evident from a detailed analysis of a large (Mw 7.1) earthquake sequence beneath Fiji. Following the paradigm that a uniform strain of DDE/DDC results from sinking of the cold, dense slab as it encounters resistance from the highly viscous mantle at depth, breakdown of DDE/DDC in subhorizontal slabs reflects waning negative buoyancy ("slab pull") in the downdip direction. Our results place a constraint on the magnitude of slab pull that is required to dominate over localized sources of stress and to align seismic strain release in dipping slabs. Under the condition of a vanishing slab pull, eliminating the only obvious source of regional stress, the abundance of earthquakes in subhorizontal slabs indicates that a locally variable source of stress is both necessary and sufficient to sustain the accumulation of elastic strain required to generate intermediate- and deep-focus seismicity. Evidence is growing that the process of seismogenesis under high pressures, including localized sources of stress, is tied to the presence of petrologic anomalies.

Depth to the Juan De Fuca slab beneath the Cascadia subduction margin - a 3-D model for sorting earthquakes

USGS Publications Warehouse

McCrory, Patricia A.; Blair, J. Luke; Oppenheimer, David H.; Walter, Stephen R.

2004-01-01

We present an updated model of the Juan de Fuca slab beneath southern British Columbia, Washington, Oregon, and northern California, and use this model to separate earthquakes occurring above and below the slab surface. The model is based on depth contours previously published by Fluck and others (1997). Our model attempts to rectify a number of shortcomings in the original model and update it with new work. The most significant improvements include (1) a gridded slab surface in geo-referenced (ArcGIS) format, (2) continuation of the slab surface to its full northern and southern edges, (3) extension of the slab surface from 50-km depth down to 110-km beneath the Cascade arc volcanoes, and (4) revision of the slab shape based on new seismic-reflection and seismic-refraction studies. We have used this surface to sort earthquakes and present some general observations and interpretations of seismicity patterns revealed by our analysis. For example, deep earthquakes within the Juan de Fuca Plate beneath western Washington define a linear trend that may mark a tear within the subducting plate Also earthquakes associated with the northern stands of the San Andreas Fault abruptly terminate at the inferred southern boundary of the Juan de Fuca slab. In addition, we provide files of earthquakes above and below the slab surface and a 3-D animation or fly-through showing a shaded-relief map with plate boundaries, the slab surface, and hypocenters for use as a visualization tool.

Unusually deep Bonin earthquake of 30 May 2015: A precursory signal to slab penetration?

NASA Astrophysics Data System (ADS)

Obayashi, Masayuki; Fukao, Yoshio; Yoshimitsu, Junko

2017-02-01

An M7.9 earthquake occurred on 30 May 2015 at an unusual depth of 680 km downward and away from the well-defined Wadati-Benioff (WB) zone of the southern Bonin arc. To the north (northern Bonin), the subducted slab is stagnant above the upper-lower mantle boundary at 660-km depth, where the WB zone bends forward to sub-horizontal. To the south (northern Mariana), it penetrates the boundary, where the WB zone extends near-vertically down to the boundary. Thus, the southern Bonin slab can be regarded as being in a transitional state from slab stagnation to penetration. The transition is shown to happen rapidly within the northern half of the southern Bonin slab where the heel part of the shoe-like configured stagnant slab hits the significantly depressed 660-km discontinuity. The mainshock and aftershocks took place in this heel part where they are sub-vertically aligned in approximate parallel to their maximum compressional axes. Here, the dips of the compressional axes of WB zone earthquakes change rapidly across the thickness of the slab from the eastern to western side and along the strike of the slab from the northern to southern side, suggesting rapid switching of the downdip compression axis in the shoe-shaped slab. Elastic deformation associated with the WB zone seismicity is calculated by viewing it as an integral part of the slab deformation process. With this deformation, the heel part is deepened relative to the arch part and is compressed sub-vertically and stretched sub-horizontally, a tendency consistent with the idea of progressive decent of the heel part in which near-vertical compressional stress is progressively accumulated to generate isolated shocks like the 2015 event and eventually to initiate slab penetration.

Slab stagnation and detachment under northeast China

NASA Astrophysics Data System (ADS)

Honda, Satoru

2016-03-01

Results of tomography models around the Japanese Islands show the existence of a gap between the horizontally lying (stagnant) slab extending under northeastern China and the fast seismic velocity anomaly in the lower mantle. A simple conversion from the fast velocity anomaly to the low-temperature anomaly shows a similar feature. This feature appears to be inconsistent with the results of numerical simulations on the interaction between the slab and phase transitions with temperature-dependent viscosity. Such numerical models predict a continuous slab throughout the mantle. I extend previous analyses of the tomography model and model calculations to infer the origins of the gap beneath northeastern China. Results of numerical simulations that take the geologic history of the subduction zone into account suggest two possible origins for the gap: (1) the opening of the Japan Sea led to a breaking off of the otherwise continuous subducting slab, or (2) the western edge of the stagnant slab is the previous subducted ridge, which was the plate boundary between the extinct Izanagi and the Pacific plates. Origin (2) suggesting the present horizontally lying slab has accumulated since the ridge subduction, is preferable for explaining the present length of the horizontally lying slab in the upper mantle. Numerical models of origin (1) predict a stagnant slab in the upper mantle that is too short, and a narrow or non-existent gap. Preferred models require rather stronger flow resistance of the 660-km phase change than expected from current estimates of the phase transition property. Future detailed estimates of the amount of the subducted Izanagi plate and the present stagnant slab would be useful to constrain models. A systematic along-arc variation of the slab morphology from the northeast Japan to Kurile arcs is also recognized, and its understanding may constrain the 3D mantle flow there.

The 2017 Mw = 8.2 Tehuantepec earthquake: a slab bending or slab pull rupture?

NASA Astrophysics Data System (ADS)

Duputel, Z.; Gombert, B.; Simons, M.; Fielding, E. J.; Rivera, L. A.; Bekaert, D. P.; Jiang, J.; Liang, C.; Moore, A. W.; Liu, Z.

2017-12-01

On September 8th 2017, a regionally destructive Mw 8.2 intra-slab earthquake struck Mexico in the Gulf of Tehuantepec. While large intermediate depth intra-slab earthquakes are a major hazard, we have only a limited knowledge of the strain budgets within subducting slabs. Several mechanisms have been proposed to explain intraplate earthquakes in subduction zones. Bending stresses might cause the occurrence of seismic events located at depths where the slab dip changes abruptly. However, an alternative explanation is needed if the ruptures are found to propagate through the entire lithosphere. Depending on the coupling of the subduction interface, intraplate earthquakes occurring updip or downdip of the locked zone could also be caused by the negative buoyancy of the sinking slab (i.e., slab pull). The increasing availability of near-fault data provides a unique opportunity to better constrain the seismogenic behavior of large intra-slab earthquakes. Teleseismic analyses of the 2017 Tehuantepec earthquake lead to contrasting statements about the depth extent of the rupture: while most of long period centroid moment tensor inversions yield fairly large centroid depths (>40 km), some finite-fault models suggest much shallower slip concentrated at depths less than 30 km. In this study, we analyze GPS, InSAR, tsunami and seismological data to constrain the earthquake location, fault geometry and slip distribution. We use a Bayesian approach devoid of significant spatial smoothing to characterize the range of allowable rupture depths. In addition, to cope with potential artifacts in centroid depth estimates due to unmodeled lateral heterogeneities, we also analyze long-period seismological data using a full 3D Earth model. Preliminary results suggest a fairly deep rupture consistent with a slab-pull process breaking a significant proportion of the lithosphere and potentially reflecting at least local detachment of the slab.

Untangling Slab Dynamics Using 3-D Numerical and Analytical Models

NASA Astrophysics Data System (ADS)

Holt, A. F.; Royden, L.; Becker, T. W.

2016-12-01

Increasingly sophisticated numerical models have enabled us to make significant strides in identifying the key controls on how subducting slabs deform. For example, 3-D models have demonstrated that subducting plate width, and the related strength of toroidal flow around the plate edge, exerts a strong control on both the curvature and the rate of migration of the trench. However, the results of numerical subduction models can be difficult to interpret, and many first order dynamics issues remain at least partially unresolved. Such issues include the dominant controls on trench migration, the interdependence of asthenospheric pressure and slab dynamics, and how nearby slabs influence each other's dynamics. We augment 3-D, dynamically evolving finite element models with simple, analytical force-balance models to distill the physics associated with subduction into more manageable parts. We demonstrate that for single, isolated subducting slabs much of the complexity of our fully numerical models can be encapsulated by simple analytical expressions. Rates of subduction and slab dip correlate strongly with the asthenospheric pressure difference across the subducting slab. For double subduction, an additional slab gives rise to more complex mantle pressure and flow fields, and significantly extends the range of plate kinematics (e.g., convergence rate, trench migration rate) beyond those present in single slab models. Despite these additional complexities, we show that much of the dynamics of such multi-slab systems can be understood using the physics illuminated by our single slab study, and that a force-balance method can be used to relate intra-plate stress to viscous pressure in the asthenosphere and coupling forces at plate boundaries. This method has promise for rapid modeling of large systems of subduction zones on a global scale.

Equilibrium properties of simple metal thin films in the self-compressed stabilized jellium model.

PubMed

Mahmoodi, T; Payami, M

2009-07-01

In this work, we have applied the self-compressed stabilized jellium model to predict the equilibrium properties of isolated thin Al, Na and Cs slabs. To make a direct correspondence to atomic slabs, we have considered only those L values that correspond to n-layered atomic slabs with 2≤n≤20, for surface indices (100), (110), and (111). The calculations are based on the density functional theory and self-consistent solution of the Kohn-Sham equations in the local density approximation. Our results show that firstly, the quantum size effects are significant for slabs with sizes smaller than or near to the Fermi wavelength of the valence electrons λ(F), and secondly, some slabs expand while others contract with respect to the bulk spacings. Based on the results, we propose a criterion for realization of significant quantum size effects that lead to expansion of some thin slabs. For more justification of the criterion, we have tested it on Li slabs for 2≤n≤6. We have compared our Al results with those obtained from using all-electron or pseudo-potential first-principles calculations. This comparison shows excellent agreements for Al(100) work functions, and qualitatively good agreements for the other work functions and surface energies. These agreements justify the way we have used the self-compressed stabilized jellium model for the correct description of the properties of simple metal slab systems. On the other hand, our results for the work functions and surface energies of large- n slabs are in good agreement with those obtained from applying the stabilized jellium model for semi-infinite systems. In addition, we have performed the slab calculations in the presence of surface corrugation for selected Al slabs and have shown that the results are worsened.

Seismicity and structure of Nazca Plate subduction zone in southern Peru

NASA Astrophysics Data System (ADS)

Lim, H.; Kim, Y.; Clayton, R. W.

2015-12-01

We image the Nazca plate subduction zone system by detecting and (re)locating intra-slab earthquakes in southern Peru. Dense seismic arrays (PeruSE, 2013) were deployed along four lines to target geophysical characterization of the subduction system in the transition zone between flat and normal dipping segments of the Nazca plate (2-15°S). The arc volcanism is absent near the flat slab segment, and currently, the correlation between the location of the active volcanic front and corresponding slab depth is neither clear nor consistent between previously published models from seismicity. We detect 620 local earthquakes from August 2008 to February 2013 by manually picking 6559 and 4145 arrival times for P- and S-phases, respectively. We observe that the S-phase data is helpful to reduce the trade-off between origin time and depth of deeper earthquakes (>100 km). Earthquake locations are relocated to constrain the Nazca slab-mantle interface in the slab-dip transition zone using 7322 measurements of differential times of nearby earthquake pairs by waveform cross-correlation. We also employ the double-difference tomography (Zhang and Thurber, 2003) to further improve earthquake source locations and the spatial resolution of the velocity structure simultaneously. The relocated hypocenters clearly delineate the dipping Wadati-Benioff zone in the slab-dip transition zone between the shallow- (25°) to-flat dipping slab segment in the north and the normal (40°) dipping segment in the south. The intermediate-depth seismicity in the flat slab region stops at a depth of ~100 km and a horizontal distance of ~400 km from the trench. We find a significant slab-dip difference (up to 10°) between our relocated seismicity and previously published slab models along the profile region sampling the normal-dip slab at depth (>100 km).

Upper mantle anisotropy beneath Peru from SKS splitting: Constraints on flat slab dynamics and interaction with the Nazca Ridge

NASA Astrophysics Data System (ADS)

Eakin, Caroline M.; Long, Maureen D.; Wagner, Lara S.; Beck, Susan L.; Tavera, Hernando

2015-02-01

The Peruvian flat slab is by far the largest region of flat subduction in the world today, but aspects of its structure and dynamics remain poorly understood. In particular, questions remain over whether the relatively narrow Nazca Ridge subducting beneath southern Peru provides dynamic support for the flat slab or it is just a passive feature. We investigate the dynamics and interaction of the Nazca Ridge and the flat slab system by studying upper mantle seismic anisotropy across southern Peru. We analyze shear wave splitting of SKS, sSKS, and PKS phases at 49 stations distributed across the area, primarily from the PerU Lithosphere and Slab Experiment (PULSE). We observe distinct spatial variations in anisotropic structure along strike, most notably a sharp transition from coherent splitting in the north to pervasive null (non-split) arrivals in the south, with the transition coinciding with the northern limit of the Nazca Ridge. For both anisotropic domains there is evidence for complex and multi-layered anisotropy. To the north of the ridge our *KS splitting measurements likely reflect trench-normal mantle flow beneath the flat slab. This signal is then modified by shallower anisotropic layers, most likely in the supra-slab mantle, but also potentially from within the slab. To the south the sub-slab mantle is similarly anisotropic, with a trench-oblique fast direction, but widespread nulls appear to reflect dramatic heterogeneity in anisotropic structure above the flat slab. Overall the regional anisotropic structure, and thus the pattern of deformation, appears to be closely tied to the location of the Nazca Ridge, which further suggests that the ridge plays a key role in the mantle dynamics of the Peruvian flat slab system.

Slab anisotropy from subduction zone guided waves in Taiwan

NASA Astrophysics Data System (ADS)

Chen, K. H.; Tseng, Y. L.; Hu, J. C.

2014-12-01

Frozen-in anisotropic structure in the oceanic lithosphere and faulting/hydration in the upper layer of the slab are expected to play an important role in anisotropic signature of the subducted slab. Over the past several decades, despite the advances in characterizing anisotropy using shear wave splitting method and its developments, the character of slab anisotropy remains poorly understood. In this study we investigate the slab anisotropy using subduction zone guided waves characterized by long path length in the slab. In the southernmost Ryukyu subduction zone, seismic waves from events deeper than 100 km offshore northern Taiwan reveal wave guide behavior: (1) a low-frequency (< 1 Hz) first arrival recognized on vertical and radial components but not transverse component (2) large, sustained high-frequency (3-10 Hz) signal in P and S wave trains. The depth dependent high-frequency content (3-10Hz) confirms the association with a waveguide effect in the subducting slab rather than localized site amplification effects. Using the selected subduction zone guided wave events, we further analyzed the shear wave splitting for intermediate-depth earthquakes in different frequency bands, to provide the statistically meaningful shear wave splitting parameters. We determine shear wave splitting parameters from the 34 PSP guided events that are deeper than 100 km with ray path traveling along the subducted slab. From shear wave splitting analysis, the slab and crust effects reveal consistent polarization pattern of fast directions of EN-WS and delay time of 0.13 - 0.27 sec. This implies that slab anisotropy is stronger than the crust effect (<0.1 s) but weaker than the mantle wedge and sub-slab mantle effect (0.3-1.3 s) in Taiwan.

Mantle flow influence on subduction evolution

NASA Astrophysics Data System (ADS)

Chertova, Maria V.; Spakman, Wim; Steinberger, Bernhard

2018-05-01

The impact of remotely forced mantle flow on regional subduction evolution is largely unexplored. Here we investigate this by means of 3D thermo-mechanical numerical modeling using a regional modeling domain. We start with simplified models consisting of a 600 km (or 1400 km) wide subducting plate surrounded by other plates. Mantle inflow of ∼3 cm/yr is prescribed during 25 Myr of slab evolution on a subset of the domain boundaries while the other side boundaries are open. Our experiments show that the influence of imposed mantle flow on subduction evolution is the least for trench-perpendicular mantle inflow from either the back or front of the slab leading to 10-50 km changes in slab morphology and trench position while no strong slab dip changes were observed, as compared to a reference model with no imposed mantle inflow. In experiments with trench-oblique mantle inflow we notice larger effects of slab bending and slab translation of the order of 100-200 km. Lastly, we investigate how subduction in the western Mediterranean region is influenced by remotely excited mantle flow that is computed by back-advection of a temperature and density model scaled from a global seismic tomography model. After 35 Myr of subduction evolution we find 10-50 km changes in slab position and slab morphology and a slight change in overall slab tilt. Our study shows that remotely forced mantle flow leads to secondary effects on slab evolution as compared to slab buoyancy and plate motion. Still these secondary effects occur on scales, 10-50 km, typical for the large-scale deformation of the overlying crust and thus may still be of large importance for understanding geological evolution.

Non-traditional shape GFRP rebars for concrete reinforcement

NASA Astrophysics Data System (ADS)

Claure, Guillermo G.

The use of glass-fiber-reinforced-polymer (GFRP) composites as internal reinforcement (rebars) for concrete structures has proven to be an alternative to traditional steel reinforcement due to significant advantages such as magnetic transparency and, most importantly, corrosion resistance equating to durability and structural life extension. In recent years, the number of projects specifying GFRP reinforcement has increased dramatically leading the construction industry towards more sustainable practices. Typically, GFRP rebars are similar to their steel counterparts having external deformations or surface enhancements designed to develop bond to concrete, as well as having solid circular cross-sections; but lately, the worldwide composites industry has taken advantage of the pultrusion process developing GFRP rebars with non-traditional cross-sectional shapes destined to optimize their mechanical, physical, and environmental attributes. Recently, circular GFRP rebars with a hollow-core have also become available. They offer advantages such as a larger surface area for improved bond, and the use of the effective cross-sectional area that is engaged to carry load since fibers at the center of a solid cross-section are generally not fully engaged. For a complete understanding of GFRP rebar physical properties, a study on material characterization regarding a quantitative cross-sectional area analysis of different GFRP rebars was undertaken with a sample population of 190 GFRP specimens with rebar denomination ranging from #2 to #6 and with different cross-sectional shapes and surface deformations manufactured by five pultruders from around the world. The water displacement method was applied as a feasible and reliable way to conduct the investigation. In addition to developing a repeatable protocol for measuring cross-sectional area, the objectives of establishing critical statistical information related to the test methodology and recommending improvements to existing provisions and standards allowing for a consistent universal norm for all GFRP rebars were reached. This dissertation also presents an evaluation of the structural behavior of reinforced concrete (RC) beams and slabs using the new type of GFRP rebar consisting of a non-traditional hollow-core shape compared to "traditional" solid round rebars with equivalent cross-sectional areas within the framework of two studies, respectively. To validate the design assumptions following ACI 440.1R design guidelines, two conditions were investigated: under-reinforced (failure controlled by rupture of GFRP rebar); and, over-reinforced (failure controlled by crushing of concrete). For comparison, a cyclic three-point bending load test matrix was developed: for beams, 3 under-reinforced and 3 over-reinforced with hollow-core and solid GFRP rebars, respectively, making a total of 12 RC specimens; for slabs, 3 under-reinforced and 3 over-reinforced with hollow-core and 2 types of solid GFRP rebars, respectively, making a total of 18 RC slabs. The studies on GFRP RC beams and slabs concluded that the hollow-core GFRP rebars were as effective as their solid counterpart and ACI 440.1R design guidelines were applicable to predict their performance. It was shown that final design may be controlled by the permissible deflections as governing parameter for elements under service conditions. Also, a final study with a test matrix containing six extra specimens was generated for post-fire residual strength evaluation of fire-exposed GFRP RC slabs along with temperature gradient in the slabs and dynamic mechanical analysis (DMA) investigation on GFRP samples extracted from the fire-exposed slabs. In this study, the ability of GFRP RC slabs to retain structural integrity during a standards fire exposure as well as determining the residual structural capacity were investigated. The residual strength evaluation of the fire-exposed slabs showed a range of results varying between +/- 10%, of the virgin slabs. And, 19 mm (0.75 in.) cover with normal weight concrete was shown to be adequate to provide the necessary fire protection to the GFRP rebars preventing irreversible damage for two-hour fire rated GFRP RC slabs subjected to service loads; also, from the DMA and glass transition temperature of samples extracted from the GFRP rebars, it is inferred that the resin had undergone a post curing phase.

The upper crust laid on its side: tectonic implications of steeply tilted crustal slabs for extension in the basin and range

USGS Publications Warehouse

Howard, Keith A.

2005-01-01

Tilted slabs expose as much as the top 8–15 km of the upper crust in many parts of the Basin and Range province. Exposures of now-recumbent crustal sections in these slabs allow analysis of pre-tilt depth variations in dike swarms, plutons, and thermal history. Before tilting the slabs were panels between moderately dipping, active Tertiary normal faults. The slabs and their bounding normal faults were tilted to piggyback positions on deeper footwalls that warped up isostatically beneath them during tectonic unloading. Stratal dips within the slabs are commonly tilted to vertical or even slightly overturned, especially in the southern Basin and Range where the thin stratified cover overlies similarly tilted basement granite and gneiss. Some homoclinal recumbent slabs of basement rock display faults that splay upward into forced folds in overlying cover sequences, which thereby exhibit shallower dips. The 15-km maximum exposed paleodepth for the slabs represents the base of the brittle upper crust, as it coincides with the depth of the modern base of the seismogenic zone and the maximum focal depths of large normal-fault earthquakes in the Basin and Range. Many upended slabs accompany metamorphic core complexes, but not all core complexes have corresponding thick recumbent hanging-wall slabs. The Ruby Mountains core complex, for example, preserves only scraps of upper-plate rocks as domed-up extensional klippen, and most of the thick crustal section that originally overlay the uplifted metamorphic core now must reside below little-tilted hanging-wall blocks in the Elko-Carlin area to the west. The Whipple and Catalina Mountains core complexes in contrast are footwall to large recumbent hanging-wall slabs of basement rock exposing 8-15 km paleodepths that originally roofed the metamorphic cores; the exposed paleodepths require that a footwall rolled up beneath the slabs.

Numerical modeling of Farallon Plate flat-slab subduction: Influence of lithosphere structure and rheology on slab dynamics

NASA Astrophysics Data System (ADS)

Liu, X.; Currie, C. A.

2017-12-01

The subducted Farallon plate is believed to have evolved to a flat geometry underneath North America plate during Late Cretaceous, triggering Laramide deformation within the continental interior. However, the mechanism that caused the oceanic slab to flatten and the factors that control the flat-slab depth remain uncertain. In this work, we use 2D thermal-mechanical models using the SOPALE code to study the subduction dynamics from 90 Ma to 50 Ma. During this period, an oceanic plateau (Shatsky Conjugate) is inferred to have subducted beneath western North America and interacted with the continental lithosphere, including areas of thicker lithosphere such as the Colorado Plateau and Wyoming Craton. Based on seismic tomography and plate reconstruction data sets, we built a set of models to examine the influence of the structure and rheology of the oceanic and continental plates on slab dynamics. Models include a 600 km wide oceanic plateau consisting of 18 km thick crust and a 36 km thick underlying harzburgite layer, and we ran a series of model experiments to test different continental thicknesses (80 km, 120 km, & 180 km) and continental mantle lithosphere strengths (approximating conditions from wet olivine to dry olivine). Consistent with earlier studies, we find that creation of a long flat slab requires a buoyant oceanic plateau (i.e., non-eclogitized crust) and trenchward motion of the continent. In addition, our models demonstrate the upper plate has an important control on slab dynamics. A flat slab requires either a thin continent or, if the continent is thick, its mantle lithosphere must be relatively weak so that it can be displaced by the flattening slab. The depth of the flat slab is mainly controlled by two factors: (1) the continental thickness and (2) the strength of the continental mantle lithosphere. For the same initial lithosphere thickness (120 km), a shallower flat slab ( 90 km depth) occurs for the weakest mantle lithosphere ( wet olivine) compared to 120 km depth for strong ( dry) mantle lithosphere because the flat slab removes the lowermost weak lithosphere. Moreover, an even deeper slab ( 130 km) can be found underneath the weakest but thicker continental lithosphere (180 km). Future models will focus on how the flat slab may induce hydration and deformation for the overriding continental plate.

Vertical slab sinking and westward subduction offshore of Mesozoic North America

NASA Astrophysics Data System (ADS)

Sigloch, Karin; Mihalynuk, Mitchell G.

2013-04-01

Subducted slabs in the mantle, as imaged by seismic tomography, preserve a record of ancient subduction zones. Ongoing debate concerns how direct this link is. How long ago did each parcel of slab subduct, and where was the trench located relative to the imaged slab position? Resolving these questions will benefit paleogeographic reconstructions, and restrict the range of plausible rheologies for mantle convection simulations. We investigate one of the largest and best-constrained Mesozoic slab complexes, the "Farallon" in the transition zone and lower mantle beneath North America. We quantitatively integrate observations from whole-mantle P-wave tomography, global plate reconstructions, and land geological evidence from the North American Cordillera. These three data sets permit us to test the simplest conceivable hypothesis for linking slabs to paleo-trenches: that each parcel of slab sank only vertically shortly after entering the trench That is, we test whether within the limits of tomographic resolution, all slab material lies directly below the location where it subducted beneath its corresponding arc. Crucially and in contrast to previous studies, we do not accept or impose an Andean-style west coast trench (Farallon-beneath-continent subduction) since Jurassic times, as this scenario is inconsistent with many geological observations. Slab geometry alone suggests that trenches started out as intra-oceanic because tomography images massive, linear slab "walls" in the lower mantle, extending almost vertically from about 800 km to 2000+ km depth. Such steep geometries would be expected from slabs sinking vertically beneath trenches that were quasi-stationary over many tens of millions of years. Intra-oceanic trenches west of Mesozoic North America could have been stationary, whereas a coastal Farallon trench could not, because the continent moved westward continuously as the Atlantic opened. Overlap of North American west-coast positions, as reconstructed in a hotspot reference frame, with elongate slab walls predicts where and when the intra-oceanic trenches would have been overridden by the westward-moving continent. Land geology plays the role of a validating data set: trench override is predicted to coincide with accretion of buoyant arc terranes, deformation of the continental margin and slab window volcanism. We find excellent agreement between predicted and observed accretion episodes, validating both vertical sinking (within observational uncertainties of a few hundred kilometers laterally), and westward subduction beneath an archipelago of island arcs west of Jura-Cretaceous North America. Amalgamation of the arcs with North America occurred as the intervening ocean crust was consumed. Implied slab sinking rates are of 10±2 mm/a, uniformly for three different slab walls. We conclude that the hypothesis of essentially vertical slab sinking produces a self-consistent model that explains first-order observations of 200 Ma - 50 Ma Cordilleran geology. By contrast, the standard scenario of a continental Farallon trench requires massive amounts of slab to be laterally displaced by 1000+ km after subduction, and offers no explanation for a long series of Cretaceous terrane accretions.

DESIGN AND TESTING OF SUB-SLAB DEPRESSURIZATION FOR RADON MITIGATION IN NORTH FLORIDA HOUSES - PART I. PERFORMANCE AND DURABILITY - VOLUME 2. DATA APPENDICES

EPA Science Inventory

The report gives results of a demonstration/research project to evaluate sub-slab depressurization (SSD) techniques for radon mitigation in North Florida where the housing stock is primarily slab-on-grade and the sub-slab medium typically consists of native soil and sand. Objecti...

DESIGN AND TESTING OF SUB-SLAB DEPRESSURIZATION FOR RADON MITIGATION IN NORTH FLORIDA HOUSES - PART I. PERFORMANCE AND DURABILITY - VOLUME 1. TECHNICAL REPORT

EPA Science Inventory

The report gives results of a demonstration/research project to evaluate sub-slab depressurization (SSD) techniques for radon mitigation in North Florida where the housing stock is primarily slab-on-grade and the sub-slab medium typically consists of native soil and sand. Objecti...

Analysis of surface wave propagation in a grounded dielectric slab covered by a resistive sheet

NASA Technical Reports Server (NTRS)

Shively, David G.

1992-01-01

Both parallel and perpendicular polarized surface waves are known to propagate on lossless and lossy grounded dielectric slabs. Surface wave propagation on a grounded dielectric slab covered with a resistive sheet is considered. Both parallel and perpendicular polarizations are examined. Transcendental equations are derived for each polarization and are solved using iterative techniques. Attenuation and phase velocity are shown for representative geometries. The results are applicable to both a grounded slab with a resistive sheet and an ungrounded slab covered on each side with a resistive sheet.

Drug release from slabs and the effects of surface roughness.

PubMed

Kalosakas, George; Martini, Dimitra

2015-12-30

We discuss diffusion-controlled drug release from slabs or thin films. Analytical and numerical results are presented for slabs with flat surfaces, having a uniform thickness. Then, considering slabs with rough surfaces, the influence of a non-uniform slab thickness on release kinetics is numerically investigated. The numerical release profiles are obtained using Monte Carlo simulations. Release kinetics is quantified through the stretched exponential (or Weibull) function and the resulting dependence of the two parameters of this function on the thickness of the slab, for flat surfaces, and the amplitude of surface fluctuations (or the degree of thickness variability) in case of roughness. We find that a higher surface roughness leads to a faster drug release. Copyright © 2015 Elsevier B.V. All rights reserved.

Metasomatism, Fluid Overpressure and Brecciation at the Slab-Mantle Interface: Insights from the Livingstone Fault, New Zealand

NASA Astrophysics Data System (ADS)

Tarling, M.; Smith, S. A. F.; Scott, J.

2017-12-01

Juxtaposition of mantle peridotite and serpentinite against quartzofeldspathic and mafic schists occurs along the shallow slab-mantle interface in some subduction zones. This part of the subduction interface has been invoked as a possible source region of episodic tremor and slow slip, yet geological observations of fault zone structures and chemical reactions pertinent to this region are quite rare. The >1000 km long Livingstone Fault in New Zealand is a superbly exposed fault zone that provides a suitable analogue (both in terms of scale and the rock types involved) for the shallow slab-mantle interface. The fault is characterized by a foliated and highly sheared serpentinite mélange tens to several hundreds of meters wide that separates (partially serpentinised) peridotites from quartzofeldspathic schists. Talc- and tremolite-forming metasomatic reactions occurred along the margins of the mélange and around entrained pods due to mixing of serpentinite with silica- and calcium-rich fluids derived from the adjacent quartzofeldspathic schist. The metasomatic reactions generated significant volumes of water at the melange-schist contact that became trapped between the two relatively impermeable fault zone lithologies. On the schist side of the contact, brittle faulting was promoted by the formation of a laterally-continuous silicified zone up to tens of metres wide. On the melange side, a zone up to tens of metres wide of `crackle-breccias' containing veined stockworks of tremolite indicates periodic increases of pore pressure sufficient to cause hydraulic fracture of serpentinite. The crackle-breccias are multi-generational indicating that this process was episodic. Sr and Nd isotope data and permeability calculations suggest that the episodic brecciation process was critical to the transfer of fluids across the melange. Our observations suggest that fluid-producing metasomatic reactions along the shallow slab-mantle interface may contribute to the tremor signal by triggering brecciation events and promoting brittle failure in serpentinite and schist.

Rise of Earth's atmospheric oxygen controlled by efficient subduction of organic carbon

NASA Astrophysics Data System (ADS)

Duncan, Megan S.; Dasgupta, Rajdeep

2017-04-01

The net flux of carbon between the Earth's interior and exterior, which is critical for redox evolution and planetary habitability, relies heavily on the extent of carbon subduction. While the fate of carbonates during subduction has been studied, little is known about how organic carbon is transferred from the Earth's surface to the interior, although organic carbon sequestration is related to sources of oxygen in the surface environment. Here we use high pressure-temperature experiments to determine the capacity of rhyolitic melts to carry carbon under graphite-saturated conditions in a subducting slab, and thus to constrain the subduction efficiency of organic carbon, the remnants of life, through time. We use our experimental data and a thermodynamic model of CO2 dissolution in slab melts to quantify organic carbon mobility as a function of slab parameters. We show that the subduction of graphitized organic carbon, and the graphite and diamond formed by reduction of carbonates with depth, remained efficient even in ancient, hotter subduction zones where oxidized carbon subduction probably remained limited. We suggest that immobilization of organic carbon in subduction zones and deep sequestration in the mantle facilitated the rise (~103-5 fold) and maintenance of atmospheric oxygen since the Palaeoproterozoic and is causally linked to the Great Oxidation Event. Our modelling shows that episodic recycling of organic carbon before the Great Oxidation Event may also explain occasional whiffs of atmospheric oxygen observed in the Archaean.

Experimental investigation of dynamic performance of a prototype hybrid tuned mass damper under human excitation

NASA Astrophysics Data System (ADS)

Noormohammadi, Nima; Reynolds, Paul

2013-04-01

Current sport stadia designs focus mainly on maximizing audience capacity and providing a clear view for all spectators. Hence, incorporation of one or more cantilevered tiers is typical in these designs. However, employing such cantilevered tiers, usually with relatively low damping and natural frequencies, can make grandstands more susceptible to excitation by human activities. This is caused by the coincidence between the activity frequencies (and their lowest three harmonics) and the structural natural frequencies hence raising the possibility of resonant vibration. This can be both a vibration serviceability and a safety issue. Past solutions to deal with observed or anticipated vibration serviceability problems have been mainly passive methods, such as tuned mass dampers (TMDs). These techniques have exhibited problems such as lack of performance and offtuning caused by human-structure interaction. To address this issue, research is currently underway to investigate the possible application of hybrid TMDs (HTMDs), which are a combination of active and passive control, to improve the vibration serviceability of such structures under human excitation. The work presented here shows a comparative experimental investigation of a passive TMD and a prototype HTMD applied on a slab strip structure. The most effective control algorithm to enhance the performance of the HTMD and also deal with the off-tuning problem is investigated. The laboratory structure used here is an in-situ cast simply-supported post-tensioned slab strip excited by forces from a range of human activities.

The study of the transition regime between slab and mixed slab-toroidal electron temperature gradient modes in a basic experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balbaky, Abed; Sokolov, Vladimir; Sen, Amiya K.

2015-05-15

Electron temperature gradient (ETG) modes are suspected sources of anomalous electron thermal transport in magnetically confined plasmas as in tokamaks. Prior work in the Columbia Linear Machine (CLM) has been able to produce and identify slab ETG modes in a slab geometry [Wei et al., Phys. Plasmas 17, 042108 (2010)]. Now by modifying CLM to introduce curvature to the confining axial magnetic field, we have excited mixed slab-toroidal modes. Linear theory predicts a transition between slab and toroidal ETG modes when (k{sub ∥}R{sub c})/(k{sub y}ρ) ∼1 [J. Kim and W. Horton, Phys. Fluids B 3, 1167 (1991)]. We observe changesmore » in the mode amplitude for levels of curvature R{sub c}{sup −1}≪(k{sub ∥,slab})/(k{sub ⊥}ρ) , which may be explained by reductions in k{sub ∥} in the transition from slab to mixed slab-toroidal modes, as also predicted by theory. We present mode amplitude scaling as a function of magnetic field curvature. Over the range of curvature available in CLM experimentally we find a modest increase in saturated ETG potential fluctuations (∼1.5×), and a substantial increase in the power density of individual mode peaks (∼4–5×)« less

Deep Subducction in a Compressible Mantle: Observations and Theory

NASA Astrophysics Data System (ADS)

King, S. D.

2017-12-01

Our understanding of slab dynamics is primarily based on the results of numerical models of subduction. In such models coherent, cold slabs are clearly visible from the surface of the Earth to the core mantle boundary. In contrast, fast seismic anomalies associated with cold subducted slabs are difficult to identify below 1500-2000 km in tomographic models of Earth's mantle. One explanation for this has been the resolution, or lack thereof, of seismic tomography in the mid-mantle region; however in this work I will explore the impact of compressibility on the dynamics of subducting slabs, specifically shear heating of the slab and latent heat of phase transformations. Most geodynamic models of subduction have used an incompressible formulation, thus because subducted slabs are assumed to be cold and stiff, the primary means of thermal equilibration is conduction. With an assumed sinking velocity of approximately 0.1 m/yr, a subducted slab reaches the core-mantle boundary in approximately 30 Myrs—too fast for significant conductive cooling of the downgoing slab. In this work I consider a whole-mantle geometry and include both phase transformations with associated latent heat and density changes from the olivine-wadsleyite-ringwoodite-bridgmanite system and the pyroxene-garnet system. The goal of this work is to understand both the eventual fate and thermal evolution of slabs beneath the transition zone.

Extraordinary wavelength reduction in terahertz graphene-cladded photonic crystal slabs

PubMed Central

Williamson, Ian A. D.; Mousavi, S. Hossein; Wang, Zheng

2016-01-01

Photonic crystal slabs have been widely used in nanophotonics for light confinement, dispersion engineering, nonlinearity enhancement, and other unusual effects arising from their structural periodicity. Sub-micron device sizes and mode volumes are routine for silicon-based photonic crystal slabs, however spectrally they are limited to operate in the near infrared. Here, we show that two single-layer graphene sheets allow silicon photonic crystal slabs with submicron periodicity to operate in the terahertz regime, with an extreme 100× wavelength reduction from graphene’s large kinetic inductance. The atomically thin graphene further leads to excellent out-of-plane confinement, and consequently photonic-crystal-slab band structures that closely resemble those of ideal two-dimensional photonic crystals, with broad band gaps even when the slab thickness approaches zero. The overall photonic band structure not only scales with the graphene Fermi level, but more importantly scales to lower frequencies with reduced slab thickness. Just like ideal 2D photonic crystals, graphene-cladded photonic crystal slabs confine light along line defects, forming waveguides with the propagation lengths on the order of tens of lattice constants. The proposed structure opens up the possibility to dramatically reduce the size of terahertz photonic systems by orders of magnitude. PMID:27143314

Demountable externally anchored low-stress magnet system and related method

DOEpatents

Powell, James; Hsieh, Shih-Yung; Lehner, John R.

1981-01-01

Toroidal field coils are interlaced with other toroidal structures and are operated under supercooled conditions. To facilitate demounting the toroidal field coils, which are supercooled, they are made in the form of connected segments constituting coils of polygonal form. The segments may be rectilinear in form, but some may also be U-shaped or L-shaped. The segments are detachable from one another and are supported in load relieving manner. Power devices are used to displace the segments to facilitate removal of the coils from the aforesaid toroidal structures and to provide for the accommodation of dimensional changes and stresses due to thermal and magnetic conditions. The segments are formed of spaced parallel conductive slabs with the slabs of one segment being interdigitated with the slabs of the adjacent segment. The interdigitated slabs may be soldered together or slidingly engaged. The slabs are shaped to accommodate superconductors and to provide passages for a cooling medium. The slabs are moreover separated by insulator slabs with which they form a coil structure which is jacketed.

Modified creep and shrinkage prediction model B3 for serviceability limit state analysis of composite slabs

NASA Astrophysics Data System (ADS)

Gholamhoseini, Alireza

2016-03-01

Relatively little research has been reported on the time-dependent in-service behavior of composite concrete slabs with profiled steel decking as permanent formwork and little guidance is available for calculating long-term deflections. The drying shrinkage profile through the thickness of a composite slab is greatly affected by the impermeable steel deck at the slab soffit, and this has only recently been quantified. This paper presents the results of long-term laboratory tests on composite slabs subjected to both drying shrinkage and sustained loads. Based on laboratory measurements, a design model for the shrinkage strain profile through the thickness of a slab is proposed. The design model is based on some modifications to an existing creep and shrinkage prediction model B3. In addition, an analytical model is developed to calculate the time-dependent deflection of composite slabs taking into account the time-dependent effects of creep and shrinkage. The calculated deflections are shown to be in good agreement with the experimental measurements.

Revisiting Yasinsky and Henry`s benchmark using modern nodal codes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feltus, M.A.; Becker, M.W.

1995-12-31

The numerical experiments analyzed by Yasinsky and Henry are quite trivial by comparison with today`s standards because they used the finite difference code WIGLE for their benchmark. Also, this problem is a simple slab (one-dimensional) case with no feedback mechanisms. This research attempts to obtain STAR (Ref. 2) and NEM (Ref. 3) code results in order to produce a more modern kinetics benchmark with results comparable WIGLE.

Leaky unstable modes and electromagnetic radiation amplification by an anisotropic plasma slab

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vagin, K. Yu., E-mail: vagin@sci.lebedev.ru; Uryupin, S. A., E-mail: uryupin@sci.lebedev.ru

2015-09-15

The interaction between electromagnetic radiation and a photoionized plasma slab with an anisotropic electron velocity distribution is studied. It is shown that the fields of leaky modes are amplified due to the development of aperiodic instability in the slab, which leads to an increase in both the reflected and transmitted fields. The transmitted field can significantly increase only if the slab thickness does not exceed the ratio of the speed of light to the electron plasma frequency, whereas there is no upper bound on the slab thickness for the reflected signal to be amplified.

High energy efficient solid state laser sources. [slab geometry laser sources

NASA Technical Reports Server (NTRS)

Byer, R. L.

1983-01-01

Slab glass performance studies demonstate 18 J of output at 2 Hz with 2.3% wall plug efficiency. The goal is to achieve 10 J per pulse at 10 Hz and 3% wall plug efficiency during the next annual period. The slab concept was extended to Nd:YAG and to Nd:GGG. To date over 80 W of CW output power at 2% efficiency was generated in slab Nd:YAG. A multiplexed slab Nd:YAG pre-amplifier was invented and a Nd:YAG oscillator was demonstrated with 100kHz linewidth for eventual use in wind velocity measurements.

MULTIPLE SETS OF TWIN SLABS ON THE RUN OUT. THE ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

MULTIPLE SETS OF TWIN SLABS ON THE RUN OUT. THE RUN OUT INCLUDES THE TRAVELING TORCH WHICH CUTS SLABS TO DESIRED LENGTH, AN IDENTIFICATION SYSTEM TO INDICATE HEAT NUMBER AND TRACE IDENTITY OF EVERY SLAB, AND A DEBURRING DEVICE TO SMOOTH SLABS. AT LEFT OF ROLLS IS THE DUMMY BAR. DUMMY BAR IS INSERTED UP THROUGH CONTAINMENT SECTION INTO MOLD PRIOR TO START OF CAST. WHEN STEEL IS INTRODUCED INTO MOLD IT CONNECTS WITH BAR AS CAST BEGINS, AT RUN OUT DUMMY BAR DISCONNECTS AND IS STORED. - U.S. Steel, Fairfield Works, Continuous Caster, Fairfield, Jefferson County, AL

MULTIPLE SETS OF TWIN SLABS ON THE RUN OUT. THE ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

MULTIPLE SETS OF TWIN SLABS ON THE RUN OUT. THE RUN OUT INCLUDES THE TRAVELING TORCH WHICH CUTS SLABS TO DESIRED LENGTH, AN IDENTIFICATION SYSTEM TO INDICATE HEAT NUMBER AND TRACE IDENTITY OF EVERY SLAB, AND A DEBURRING DEVICE TO SMOOTH SLABS. AT LEFT OF ROLLS IS THE DUMMY BAR. DUMMY BAR IS INSERTED UP THROUGH CONTAINMENT SECTION INTO MOLD PRIOR TO START OF CAST. WHEN STEEL IS INTRODUCED INTO MOLD IT CONNECTS WITH BAR AS CAST BEGINS, AT RUN OUT DUMMY BAR DISCONNECTS AND IS STORED - U.S. Steel, Fairfield Works, Continuous Caster, Fairfield, Jefferson County, AL

Cause Analysis on the Void under Slabs of Cement Concrete Pavement

NASA Astrophysics Data System (ADS)

Wen, Li; Zhu, Guo Xin; Baozhu

2017-06-01

This paper made a systematic analysis on the influence of the construction, environment, water and loads on the void beneath road slabs, and also introduced the formation process of structural void and pumping void, and summarizes the deep reasons for the bottom of the cement concrete pavement. Based on the analysis above, this paper has found out the evolution law of the void under slabs which claimed that the void usually appeared in the slab corners and then the cross joint, resulting void in the four sides with the void area under the front slab larger than the rear one.

Shear Wave Velocities in the Pampean Flat Slab Region from Rayleigh Wave Tomography: Implications for Crustal Composition and Upper Mantle Hydration

NASA Astrophysics Data System (ADS)

Porter, R. C.; Gilbert, H. J.; Zandt, G.; Beck, S. L.; Warren, L. M.; Calkins, J. A.; Alvarado, P. M.; Anderson, M. L.

2011-12-01

The Pampean flat slab region, located in Chile and western Argentina between 29° and 34° S, is characterized by the subducting Nazca plate assuming a sub-horizontal geometry for ~300 km laterally before resuming a more "normal" angle of subduction. The onset of flat slab subduction is associated with the cessation of regional arc related volcanism and the migration of deformation inboard from the high Andes into the thin-skinned Precordillera and thick-skinned Sierras Pampeanas. Developing a better understanding of this region's geology is of particular importance, as it is an ideal area to study flat slab subduction and serves as a modern analogue to Laramide flat slab subduction in the western US. To study the crustal and mantle structure in the region, we combine ambient noise tomography and ballistic surface wave tomography to produce a regional 3D shear wave velocity model that encompasses flat slab subduction in the north and normal subduction geometry in the south, allowing for a comparison of the two. Results from this work show that shear velocities within the upper crust are largely determined by composition, with sedimentary basins and areas with active volcanism exhibiting slower velocities than basement cored uplifts and other bedrock exposures. Though surface waves are not particularly sensitive to the depth of sharp velocity contrasts, we observe an eastward increase in shear velocity at depth that correlates with an eastward decrease in crustal thickness. In both the slab and overlying mantle, we observe significant variations in shear wave velocity. North of 32° S, where flat slab subduction is occurring, the Nazca plate contains low-velocity zones (LVZs) beneath the high Andes and Precordillera that are not present in the east beneath the Sierras Pampeanas. An opposite transition is observed in the overlying mantle, which changes from fast in the west to slow in the east. Both of these observations are consistent with an initially hydrated slab dehydrating and releasing water into the overlying mantle. Within this region we also observe a LVZ immediately above the slab as the subduction angle steepens. This zone potentially represents asthenosphere or hydrated lithospheric mantle. South of 32° S, where subduction is occurring at a more normal angle, the slab is visible as a high-velocity body with a low-velocity mantle wedge present beneath the arc and back arc. The variations in slab and upper mantle shear velocities are consistent with a hydrated flat slab and the presence of a LVZ above the flat slab as it steepens suggests that water is being transported to a significant depth or that an asthenospheric wedge is present between the slab and cratonic lithosphere.

Pacific slab beneath northeast China revealed by regional and teleseismic waveform modeling

NASA Astrophysics Data System (ADS)

WANG, X.; Chen, Q. F.; Wei, S.

2015-12-01

Accurate velocity and geometry of the slab is essential for better understanding of the thermal, chemical structure of the mantle earth, as well as geodynamics. Recent tomography studies show similar morphology of the subducting Pacific slab beneath northeast China, which was stagnant in the mantle transition zone with thickness of more than 200km and an average velocity perturbation of ~1.5% [Fukao and Obayashi, 2013]. Meanwhile, waveform-modeling studies reveal that the Pacific slab beneath Japan and Kuril Island has velocity perturbation up to 5% and thickness up to 90km [Chen et al., 2007; Zhan et al., 2014]. These discrepancies are probably caused by the smoothing and limited data coverage in the tomographic inversions. Here we adopted 1D and 2D waveform modeling methods to study the fine structure of Pacific slab beneath northeast China using dense regional permanent and temporary broadband seismic records. The residual S- and P-wave travel time, difference between data and 1D synthetics, shows significant difference between the eastern and western stations. S-wave travel time residuals indicate 5-10s earlier arrivals for stations whose ray path lies within the slab, compared with those out of the slab. Teleseimic waveforms were used to rule out the major contribution of the possible low velocity structure above 200km. Furthermore, we use 2D finite-difference waveform modeling to confirm the velocity perturbation and geometry of the slab. Our result shows that the velocity perturbation in the slab is significantly higher than those reported in travel-time tomography studies. ReferencesChen, M., J. Tromp, D. Helmberger, and H. Kanamori (2007), Waveform modeling of the slab beneath Japan, J. Geophys. Res.-Solid Earth, 112(B2), 19, doi:10.1029/2006jb004394.Fukao, Y., and M. Obayashi (2013), Subducted slabs stagnant above, penetrating through, and trapped below the 660 km discontinuity, J. Geophys. Res.-Solid Earth, 118(11), 5920-5938, doi:10.1002/2013jb010466.Zhan, Z. W., D. V. Helmberger, and D. Z. Li (2014), Imaging subducted slab structure beneath the Sea of Okhotsk with teleseismic waveforms, Phys. Earth Planet. Inter., 232, 30-35, doi:10.1016/j.pepi.2014.03.008.

Present-day stress field in subduction zones: Insights from 3D viscoelastic models and data

NASA Astrophysics Data System (ADS)

Petricca, Patrizio; Carminati, Eugenio

2016-01-01

3D viscoelastic FE models were performed to investigate the impact of geometry and kinematics on the lithospheric stress in convergent margins. Generic geometries were designed in order to resemble natural subduction. Our model predictions mirror the results of previous 2D models concerning the effects of lithosphere-mantle relative flow on stress regimes, and allow a better understanding of the lateral variability of the stress field. In particular, in both upper and lower plates, stress axes orientations depend on the adopted geometry and axes rotations occur following the trench shape. Generally stress axes are oriented perpendicular or parallel to the trench, with the exception of the slab lateral tips where rotations occur. Overall compression results in the upper plate when convergence rate is faster than mantle flow rate, suggesting a major role for convergence. In the slab, along-strike tension occurs at intermediate and deeper depths (> 100 km) in case of mantle flow sustaining the sinking lithosphere and slab convex geometry facing mantle flow or in case of opposing mantle flow and slab concave geometry facing mantle flow. Along-strike compression is predicted in case of sustaining mantle flow and concave slabs or in case of opposing mantle flow and convex slabs. The slab stress field is thus controlled by the direction of impact of mantle flow onto the slab and by slab longitudinal curvature. Slab pull produces not only tension in the bending region of subducted plate but also compression where upper and lower plates are coupled. A qualitative comparison between results and data in selected subductions indicates good match for South America, Mariana and Tonga-Kermadec subductions. Discrepancies, as for Sumatra-Java, emerge due to missing geometric (e.g., occurrence of fault systems and local changes in the orientation of plate boundaries) and rheological (e.g., plasticity associated with slab bending, anisotropy) complexities in the models.

Slab detachment during continental collision: Influence of crustal rheology and interaction with lithospheric delamination

NASA Astrophysics Data System (ADS)

Duretz, T.; Gerya, T. V.

2013-08-01

Collision between continents can lead to the subduction of continental material. If the crust remains coupled to the downgoing slab, a large buoyancy force is generated. This force slows down convergence and promotes slab detachment. If the crust resists to subduction, it may decouple from the downgoing slab and be subjected to buoyant extrusion. We employ two-dimensional thermo-mechanical modelling to study the importance of crustal rheology on the evolution of subduction-collision systems. We propose simple quantifications of the mechanical decoupling between lithospheric levels (σ*) and the potential for buoyant extrusion of the crust (ξ*). The modelling results indicate that a variable crustal rheological structure results in slab detachment, delamination, or the combination of both mechanisms. A strong crust provides coupling at the Moho (low σ*) and remains coherent during subduction (low ξ). It promotes deep subduction of the crust (180 km) and slab detachment. Exhumation occurs in coherent manners via eduction and thrusting. Slab detachment triggers the development of topography (> 4.5 km) close to the suture. A contrasting style of collision occurs using a weak crustal rheology. Mechanical decoupling at the Moho (high σ*) promotes the extrusion of the crust (high ξ), disabling slab detachment. Ongoing shortening leads to buckling of the crust and development of topography on the lower plate. Collisions involving rheologically layered crust allow decoupling at mid-crustal depths. This structure favours both the extrusion of upper crust and the subduction of the lower crust. Such collisions are successively affected by delamination and slab detachment. Topography develops together with the buoyant extrusion of crust onto the foreland and is further amplified by slab detachment. Our results suggest that the occurrence of both delamination (Apennines) and slab detachment (Himalayas) in orogens may indicate differences in the initial crustal structure of subducting continental plates in these regions.

Tearing, segmentation, and backstepping of subduction in the Aegean: New insights from seismicity

NASA Astrophysics Data System (ADS)

Bocchini, G. M.; Brüstle, A.; Becker, D.; Meier, T.; van Keken, P. E.; Ruscic, M.; Papadopoulos, G. A.; Rische, M.; Friederich, W.

2018-06-01

This study revisits subduction processes at the Hellenic Subduction Zone (HSZ) including tearing, segmentation, and backstepping, by refining the geometry of the Nubian slab down to 150-180 km depth using well-located hypocentres from global and local seismicity catalogues. At the western termination of the HSZ, the Kefalonia Transform Fault marks the transition between oceanic and continental lithosphere subducting to the south and to the north of it, respectively. A discontinuity is suggested to exist between the two slabs at shallow depths. The Kefalonia Transform Fault is interpreted as an active Subduction-Transform-Edge-Propagator-fault formed as consequence of faster trench retreat induced by the subduction of oceanic lithosphere to the south of it. A model reconstructing the evolution of the subduction system in the area of Peloponnese since 34 Ma, involving the backstepping of the subduction to the back-side of Adria, provides seismological evidence that supports the single-slab model for the HSZ and suggests the correlation between the downdip limit of the seismicity to the amount of subducted oceanic lithosphere. In the area of Rhodes, earthquake hypocentres indicate the presence of a NW dipping subducting slab that rules out the presence of a NE-SW striking Subduction-Transform-Edge-Propagator-fault in the Pliny-Strabo trenches region. Earthquake hypocentres also allow refining the slab tear beneath southwestern Anatolia down to 150-180 km depth. Furthermore, the distribution of microseismicity shows a first-order slab segmentation in the region between Crete and Karpathos, with a less steep and laterally wider slab segment to the west and a steeper and narrower slab segment to the east. Thermal models indicate the presence of a colder slab beneath the southeastern Aegean that leads to deepening of the intermediate-depth seismicity. Slab segmentation affects the upper plate deformation that is stronger above the eastern slab segment and the seismicity along the interplate seismogenic zone.

A dynamic model for slab development associated with the 2015 Mw 7.9 Bonin Islands deep earthquak

NASA Astrophysics Data System (ADS)

Zhan, Z.; Yang, T.; Gurnis, M.

2016-12-01

The 680 km deep May 30, 2015 Mw 7.9 Bonin Islands earthquake is isolated from the nearest earthquakes by more than 150 km. The geodynamic context leading to this isolated deep event is unclear. Tomographic models and seismicity indicate that the morphology of the west-dipping Pacific slab changes rapidly along the strike of the Izu-Bonin-Mariana trench. To the north, the Izu-Bonin section of the Pacific slab lies horizontally above the 660 km discontinuity and extends more than 500 km westward. Several degrees south, the Mariana section dips vertically and penetrates directly into the lower mantle. The observed slab morphology is consistent with plate reconstructions suggesting that the northern section of the IBM trench retreated rapidly since the late Eocene while the southern section of the IBM trench was relatively stable during the same period. We suggest that the location of the isolated 2015 Bonin Islands deep earthquake can be explained by the buckling of the Pacific slab beneath the Bonin Islands. We use geodynamic models to investigate the slab morphology, temperature and stress regimes under different trench motion histories. Models confirm previous results that the slab often lies horizontally within the transition zone when the trench retreats, but buckles when the trench position becomes fixed with respect to the lower mantle. We show that a slab-buckling model is consistent with the observed deep earthquake P-axis directions (assumed to be the axis of principal compressional stress) regionally. The influences of various physical parameters on slab morphology, temperature and stress regime are investigated. In the models investigated, the horizontal width of the buckled slab is no more than 400 km.

Vibration Analysis of Beam and Block Precast Slab System due to Human Vibrations

NASA Astrophysics Data System (ADS)

Chik, T. N. T.; Kamil, M. R. H.; Yusoff, N. A.

2018-04-01

Beam and block precast slabs system are very efficient which generally give maximum structural performance where their voids based on the design of the unit soffit block allow a significant reduction of the whole slab self-weight. Initially for some combinations of components or the joint connection of the structural slab, this structural system may be susceptible to excessive vibrations that could effects the performance and also serviceability. Dynamic forces are excited from people walking and jumping which produced vibrations to the slab system in the buildings. Few studies concluded that human induced vibration on precast slabs system may be harmful to structural performance and mitigate the human comfort level. This study will investigate the vibration analysis of beam and block precast slab by using finite element method at the school building. Human activities which are excited from jumping and walking will induce the vibrations signal to the building. Laser Doppler Vibrometer (LDV) was used to measure the dynamic responses of slab towards the vibration sources. Five different points were assigned specifically where each of location will determine the behaviour of the entire slabs. The finite element analyses were developed in ABAQUS software and the data was further processed in MATLAB ModalV to assess the vibration criteria. The results indicated that the beam and block precast systems adequate enough to the vibration serviceability and human comfort criteria. The overall vibration level obtained was fell under VC-E curve which it is generally under the maximum permissible level of vibrations. The vibration level on the slab is acceptable within the limit that have been used by Gordon.

Mantle plumes in the vicinity of subduction zones

NASA Astrophysics Data System (ADS)

Mériaux, C. A.; Mériaux, A.-S.; Schellart, W. P.; Duarte, J. C.; Duarte, S. S.; Chen, Z.

2016-11-01

We present three-dimensional deep-mantle laboratory models of a compositional plume within the vicinity of a buoyancy-driven subducting plate with a fixed trailing edge. We modelled front plumes (in the mantle wedge), rear plumes (beneath the subducting plate) and side plumes with slab/plume systems of buoyancy flux ratio spanning a range from 2 to 100 that overlaps the ratios in nature of 0.2-100. This study shows that 1) rising side and front plumes can be dragged over thousands of kilometres into the mantle wedge, 2) flattening of rear plumes in the trench-normal direction can be initiated 700 km away from the trench, and a plume material layer of lesser density and viscosity can ultimately almost entirely underlay a retreating slab after slab/plume impact, 3) while side and rear plumes are not tilted until they reach ∼600 km depth, front plumes can be tilted at increasing depths as their plume buoyancy is lessened, and rise at a slower rate when subjected to a slab-induced downwelling, 4) rear plumes whose buoyancy flux is close to that of a slab, can retard subduction until the slab is 600 km long, and 5) slab-plume interaction can lead to a diversity of spatial plume material distributions into the mantle wedge. We discuss natural slab/plume systems of the Cascadia/Bowie-Cobb, and Nazca/San Felix-Juan Fernandez systems on the basis of our experiments and each geodynamic context and assess the influence of slab downwelling at depths for the starting plumes of Java, Coral Sea and East Solomon. Overall, this study shows how slab/plume interactions can result in a variety of geological, geophysical and geochemical signatures.

The influence of rheological weakening and yield stress on the interaction of slabs with the 670 km discontinuity

NASA Astrophysics Data System (ADS)

Čížková, Hana; van Hunen, Jeroen; van den Berg, Arie P.; Vlaar, Nico J.

2002-06-01

Results of high resolution seismic tomography showing subducting slabs deflected in the transition zone and thickened in the lower mantle seem to call for slab material weaker than inferred from mineral physics deformation mechanisms. A possible mechanism suggested by several authors could be the weakening due to grain size reduction, which should occur in the cold portion of fast slabs after an exothermic phase transition at a depth of 400 km. Since the amount of weakening as well as the rate of subsequent strengthening due to the grain growth are not precisely known, we present here a parametric study of slab behavior in the transition zone and upper part of the lower mantle. We simulate a subducting slab in a two-dimensional (2-D) Cartesian box in the numerical model with composite rheology including diffusion creep, dislocation creep and a general stress limiting rheology approximating Peierl's creep. We concentrate on two rheologic effects: the dynamic effect of slab weakening due to grain size reduction at the phase boundary and the effect of yield stress of stress limiting rheology. The effect of trench migration on slab deformation is also included in our study. Results show that the slab ability to penetrate into the lower mantle is not significantly affected by a trench retreat in the absence of grain size weakening. However, in case of a 4 cm/yr trench retreat, grain size weakening provides a viable mechanism to deflect the slab in the transition zone, provided that stress limiting deformation mechanism would limit the effective viscosity outside the areas of grain size weakening to about 1024 Pa s.

Constraining Slab Breakoff Induced Magmatism through Numerical Modelling

NASA Astrophysics Data System (ADS)

Freeburn, R.; Van Hunen, J.; Maunder, B. L.; Magni, V.; Bouilhol, P.

2015-12-01

Post-collisional magmatism is markedly different in nature and composition than pre-collisional magmas. This is widely interpreted to mark a change in the thermal structure of the system due to the loss of the oceanic slab (slab breakoff), allowing a different source to melt. Early modelling studies suggest that when breakoff takes place at depths shallower than the overriding lithosphere, magmatism occurs through both the decompression of upwelling asthenopshere into the slab window and the thermal perturbation of the overriding lithosphere (Davies & von Blanckenburg, 1995; van de Zedde & Wortel, 2001). Interpretations of geochemical data which invoke slab breakoff as a means of generating magmatism mostly assume these shallow depths. However more recent modelling results suggest that slab breakoff is likely to occur deeper (e.g. Andrews & Billen, 2009; Duretz et al., 2011; van Hunen & Allen, 2011). Here we test the extent to which slab breakoff is a viable mechanism for generating melting in post-collisional settings. Using 2-D numerical models we conduct a parametric study, producing models displaying a range of dynamics with breakoff depths ranging from 150 - 300 km. Key models are further analysed to assess the extent of melting. We consider the mantle wedge above the slab to be hydrated, and compute the melt fraction by using a simple parameterised solidus. Our models show that breakoff at shallow depths can generate a short-lived (< 3 Myr) pulse of mantle melting, through the hydration of hotter, undepleted asthenosphere flowing in from behind the detached slab. However, our results do not display the widespread, prolonged style of magmatism, observed in many post-collisional areas, suggesting that this magmatism may be generated via alternative mechanisms. This further implies that using magmatic observations to constrain slab breakoff is not straightforward.

Imaging the slab structure in the Alpine region by high-resolution P-wave tomography

NASA Astrophysics Data System (ADS)

Guillot, Stéphane; Zhao, Liang; Paul, Anne; Malusà, Marco G.; Xu, Xiaobing; Zheng, Tianyu; Solarino, stefano; Schwartz, Stéphane; Dumont, Thierry; Salimbeni, Simone; Aubert, Coralie; Pondrelli, Silvia; Wang, Qingchen; Zhu, Rixiang

2017-04-01

Based upon a finite-frequency inversion of traveltimes, we computed a new high-resolution tomography model using P-wave data from 527 broadband seismic stations, both from permanent networks and temporary experiments (Zhao et al., 2016). This model provides an improved image of the slab structure in the Alpine region, and fundamental pin-points for the analysis of Cenozoic magmatism, (U)HP metamorphism and Alpine topography. Our results document the lateral continuity of the European slab from the Western to the Central Alps, and the down-dip slab continuity beneath the Central Alps, ruling out the hypothesis of slab breakoff to explain Cenozoic Alpine magmatism. A low velocity anomaly is observed in the upper mantle beneath the core of the Western Alps, pointing to dynamic topography effects (Malusà et al., this meeting). A NE-dipping Adriatic slab, consistent with Dinaric subduction, is possibly observed beneath the Eastern Alps, whereas the laterally continuous Adriatic slab of the Northern Apennines shows major gaps at the boundary with the Southern Apennines, and becomes near vertical in the Alps-Apennines transition zone. Tear faults accommodating opposite-dipping subductions during Alpine convergence may represent reactivated lithospheric faults inherited from Tethyan extension. Our results suggest that the interpretations of previous tomography results that include successive slab breakoffs along the Alpine-Zagros-Himalaya orogenic belt might be proficiently reconsidered. Malusà M.G. et alii (2017) On the potential asthenospheric linkage between Apenninic slab rollback and Alpine topographic uplift: insights from P wave tomography and seismic anisotropy analysis. EGU 2017. Zhao L. et alii (2016), Continuity of the Alpine slab unraveled by high-resolution P wave tomography. J. Geophys. Res., doi:10.1002/2016JB013310.

Kinematic variables and water transport control the formation and location of arc volcanoes.

PubMed

Grove, T L; Till, C B; Lev, E; Chatterjee, N; Médard, E

2009-06-04

The processes that give rise to arc magmas at convergent plate margins have long been a subject of scientific research and debate. A consensus has developed that the mantle wedge overlying the subducting slab and fluids and/or melts from the subducting slab itself are involved in the melting process. However, the role of kinematic variables such as slab dip and convergence rate in the formation of arc magmas is still unclear. The depth to the top of the subducting slab beneath volcanic arcs, usually approximately 110 +/- 20 km, was previously thought to be constant among arcs. Recent studies revealed that the depth of intermediate-depth earthquakes underneath volcanic arcs, presumably marking the slab-wedge interface, varies systematically between approximately 60 and 173 km and correlates with slab dip and convergence rate. Water-rich magmas (over 4-6 wt% H(2)O) are found in subduction zones with very different subduction parameters, including those with a shallow-dipping slab (north Japan), or steeply dipping slab (Marianas). Here we propose a simple model to address how kinematic parameters of plate subduction relate to the location of mantle melting at subduction zones. We demonstrate that the location of arc volcanoes is controlled by a combination of conditions: melting in the wedge is induced at the overlap of regions in the wedge that are hotter than the melting curve (solidus) of vapour-saturated peridotite and regions where hydrous minerals both in the wedge and in the subducting slab break down. These two limits for melt generation, when combined with the kinematic parameters of slab dip and convergence rate, provide independent constraints on the thermal structure of the wedge and accurately predict the location of mantle wedge melting and the position of arc volcanoes.

Long-life slab replacement concrete : [summary].

DOT National Transportation Integrated Search

2015-04-01

Concrete slab replacement projects in Florida have demonstrated a high incidence of : replacement slab cracking. Causes of cracking have not been reliably determined. University of South Florida researchers : sought to identify the factors or : param...

Experimental validation of systematically designed acoustic hyperbolic meta material slab exhibiting negative refraction

NASA Astrophysics Data System (ADS)

Christiansen, Rasmus E.; Sigmund, Ole

2016-09-01

This Letter reports on the experimental validation of a two-dimensional acoustic hyperbolic metamaterial slab optimized to exhibit negative refractive behavior. The slab was designed using a topology optimization based systematic design method allowing for tailoring the refractive behavior. The experimental results confirm the predicted refractive capability as well as the predicted transmission at an interface. The study simultaneously provides an estimate of the attenuation inside the slab stemming from the boundary layer effects—insight which can be utilized in the further design of the metamaterial slabs. The capability of tailoring the refractive behavior opens possibilities for different applications. For instance, a slab exhibiting zero refraction across a wide angular range is capable of funneling acoustic energy through it, while a material exhibiting the negative refractive behavior across a wide angular range provides lensing and collimating capabilities.

Electromagnetic Tunneling and Resonances in Pseudochiral Omega Slabs

PubMed Central

Razzaz, Faroq; Alkanhal, Majeed A. S.

2017-01-01

This paper presents theoretical investigation of the electromagnetic wave tunneling and anomalous transmission around the trapped modes in a pseudochiral omega slab. The dispersion relation, the conditions of the trapped modes, and the evanescent wave coupling and tunneling in two different reciprocal pseudochiral omega slab structures are derived. The Berreman’s matrix method is applied to obtain the transmission coefficients across the pseudochiral omega slab. When the structure is perturbed, a resonance phenomenon is detected around the trapped modes. This resonance results in transmission anomalies (total transmission and total reflection) and dramatic field amplifications around the trapped modes. The number of the discrete trapped modes and then the resonance frequencies are prescribed by the parameters of the pseudochiral omega slab such as the value of the omega parameter and its orientation and the slab thickness. PMID:28165058

Overturned Alboran slab beneath westernmost Mediterranean

NASA Astrophysics Data System (ADS)

Sun, D.; Miller, M. S.

2017-12-01

The geological evolution of the westernmost Mediterranean holds an important piece of the puzzle of how whole western Mediterranean evolved due to the convergence of Africa with Eurasia. The idea of continuous slab roll back acting a prominent force in this region is strongly supported by tomographic images with near vertical high velocity structure connecting the surface beneath the Alboran domain [Spakman and Wortel, 2004; Bezada et al., 2013]. However, the slab shape, width, and sharpness of its edges are not well resolved. Here, we use the waveforms recorded from the PICASSO (XB) array and IberArray (IA) for the deep 2010 earthquake beneath Granada to study the detailed Alboran slab structure. We found: (1) A low velocity structure (7 km thickness, δVs = -20%) surrounding the earthquake to explain the second arrivals observed in many stations at Spain. (2) A thin low velocity layer sits on the bottom of the high velocity slab-like structure to explain the high frequency second arrivals and long coda after the P and S arrivals on stations in the Rif Mountains of Morocco. The most feasible explanation of the low velocity structure is the dehydrated surface of the slab lithosphere extending from the 600 km to the shallow mantle. However, such geometry is contradictory with our observation, which the low velocity layer is at the bottom of the slab. We proposed that the Albora slab had undergone significant "roll-over" movement, which overturned the slab surface.

Juan de Fuca slab geometry and its relation to Wadati-Benioff zone seismicity

USGS Publications Warehouse

McCrory, Patricia A.; Blair, J. Luke; Waldhause, Felix; Oppenheimer, David H.

2012-01-01

A new model of the subducted Juan de Fuca plate beneath western North America allows first-order correlations between the occurrence of Wadati-Benioff zone earthquakes and slab geometry, temperature, and hydration state. The geo-referenced 3D model, constructed from weighted control points, integrates depth information from earthquake locations and regional seismic velocity studies. We use the model to separate earthquakes that occur in the Cascadia forearc from those that occur within the underlying Juan de Fuca plate and thereby reveal previously obscured details regarding the spatial distribution of earthquakes. Seismicity within the slab is most prevalent where the slab is warped beneath northwestern California and western Washington suggesting that slab flexure, in addition to expected metamorphic dehydration processes, promotes earthquake occurrence within the subducted oceanic plate. Earthquake patterns beneath western Vancouver Island are consistent with slab dehydration processes. Conversely, the lack of slab earthquakes beneath western Oregon is consistent with an anhydrous slab. Double-differenced relocated seismicity resolves a double seismic zone within the slab beneath northwestern California that strongly constrains the location of the plate interface and delineates a cluster of seismicity 10 km above the surface that includes the 1992 M7.1 Mendocino earthquake. We infer that this earthquake ruptured a surface within the Cascadia accretionary margin above the Juan de Fuca plate. We further speculate that this earthquake is associated with a detached fragment of former Farallon plate. Other subsurface tectonic elements within the forearc may have the potential to generate similar damaging earthquakes.

In situ Raman spectroscopic investigation of the structure of subduction-zone fluids

USGS Publications Warehouse

Mibe, Kenji; Chou, I.-Ming; Bassett, William A.

2008-01-01

In situ Raman spectra of synthetic subduction-zone fluids (KAlSi3O8-H2O system) were measured to 900?? and 2.3 GPa using a hydrothermal diamond-anvil cell. The structures of aqueous fluid and hydrous melt become closer when conditions approach the second critical endpoint. Almost no three-dimensional network was observed in the supercritical fluid above 2 GPa although a large amount of silicate component is dissolved, suggesting that the physical and chemical properties of these phases change drastically at around the second critical endpoint. Our experimental results indicate that the fluids released from a subducting slab change from aqueous fluid to supercritical fluid with increasing depth under the volcanic arcs. Copyright 2008 by the American Geophysical Union.

Finite-Size Effects on the Behavior of the Susceptibility in van der Waals Films Bounded by Strongly Absorbing Substrates

NASA Technical Reports Server (NTRS)

Dantchev, Daniel; Rudnick, Joseph; Barmatz, M.

2007-01-01

We study critical point finite-size effects in the case of the susceptibility of a film in which interactions are characterized by a van der Waals-type power law tail. The geometry is appropriate to a slab-like system with two bounding surfaces. Boundary conditions are consistent with surfaces that both prefer the same phase in the low temperature, or broken symmetry, state. We take into account both interactions within the system and interactions between the constituents of the system and the material surrounding it. Specific predictions are made with respect to the behavior of 3He and 4He films in the vicinity of their respective liquid-vapor critical points.

Injected polyurethane slab jacking : interim report

DOT National Transportation Integrated Search

2000-09-01

Conventional methods for raising in-place concrete slabs to align roadway sections or to counteract subsidence requires pressure-injecting grout under the slab. As other transportation organizations have had success with the URETEK Method, which util...

Injected polyurethane slab jacking : final report.

DOT National Transportation Integrated Search

2002-06-01

Conventional methods for raising in-place concrete slabs to align roadway sections or to counteract subsidence requires pressure-injecting grout under the slab. As other transportation organizations have had success with the URETEK Method, which util...

van der Waals torque and force between anisotropic topological insulator slabs

NASA Astrophysics Data System (ADS)

Lu, Bing-Sui

2018-01-01

We investigate the character of the van der Waals (vdW) torque and force between two coplanar and dielectrically anisotropic topological insulator (TI) slabs separated by a vacuum gap in the nonretardation regime, where the optic axes of the slabs are each perpendicular to the normal direction to the slab-gap interface and also generally differently oriented from each other. We find that in addition to the magnetoelectric coupling strength, the anisotropy can also influence the sign of the vdW force, viz., a repulsive vdW force can become attractive if the anisotropy is increased sufficiently. In addition, the vdW force oscillates as a function of the angular difference between the optic axes of the TI slabs, being most repulsive/least attractive (least repulsive/most attractive) for angular differences that are integer (half-integer) multiples of π . Our third finding is that the vdW torque for TI slabs is generally weaker than that for ordinary dielectric slabs. Our work provides an instance in which the vector potential appears in a calculation of the vdW interaction for which the limit is nonretarded or static.

Anomalous deepening of a belt of intraslab earthquakes in the Pacific slab crust under Kanto, central Japan: Possible anomalous thermal shielding, dehydration reactions, and seismicity caused by shallower cold slab material

USGS Publications Warehouse

Hasegawa, A.; Nakajima, J.; Kita, S.; Okada, T.; Matsuzawa, T.; Kirby, S.H.

2007-01-01

A belt of intraslab seismicity in the Pacific slab crust parallel to iso-depth contours of the plate interface has been found beneath Hokkaido and Tohoku. Hypocenter relocations have shown that this seismic belt does not run parallel to but obliquely to the iso-depth contours beneath Kanto, deepening toward the north from ???100 km to ???140 km depth. The depth limit of the contact zone with the overlying Philippine Sea slab is located close to and parallel to this obliquely oriented seismic belt, suggesting that the deepening of the seismic belt there is caused by the contact with the overlying slab. The contact with this cold slab hinders the heating of the Pacific slab crust by hot mantle wedge, which would cause delay of eclogite-forming phase transformations and hence deepening of the seismic belt there. The depth limit of the subducting low-velocity crust also deepens toward the north, supporting this idea. Copyright 2007 by the American Geophysical Union.

Comparison of discrete ordinate and Monte Carlo simulations of polarized radiative transfer in two coupled slabs with different refractive indices.

PubMed

Cohen, D; Stamnes, S; Tanikawa, T; Sommersten, E R; Stamnes, J J; Lotsberg, J K; Stamnes, K

2013-04-22

A comparison is presented of two different methods for polarized radiative transfer in coupled media consisting of two adjacent slabs with different refractive indices, each slab being a stratified medium with no change in optical properties except in the direction of stratification. One of the methods is based on solving the integro-differential radiative transfer equation for the two coupled slabs using the discrete ordinate approximation. The other method is based on probabilistic and statistical concepts and simulates the propagation of polarized light using the Monte Carlo approach. The emphasis is on non-Rayleigh scattering for particles in the Mie regime. Comparisons with benchmark results available for a slab with constant refractive index show that both methods reproduce these benchmark results when the refractive index is set to be the same in the two slabs. Computed results for test cases with coupling (different refractive indices in the two slabs) show that the two methods produce essentially identical results for identical input in terms of absorption and scattering coefficients and scattering phase matrices.

Seismic evidence for hydration of the Central American slab: Guatemala through Costa Rica

NASA Astrophysics Data System (ADS)

Syracuse, E. M.; Thurber, C. H.

2011-12-01

The Central American subduction zone exhibits a wide variability in along-arc slab hydration as indicated by geochemical studies. These studies generally show maximum slab contributions to magma beneath Nicaragua and minimum contributions beneath Costa Rica, while intermediate slab fluid contributions are found beneath El Salvador and Guatemala. Geophysical studies suggest strong slab serpentinization and fluid release beneath Nicaragua, and little serpentinization beneath Costa Rica, but the remainder of the subduction zone is poorly characterized seismically. To obtain an integrated seismic model for the Central American subduction zone, we combine 250,000 local seismic arrivals and 1,000,000 differential arrivals for 6,500 shallow and intermediate-depth earthquakes from the International Seismic Centre, the Central American Seismic Center, and the temporary PASSCAL TUCAN array. Using this dataset, we invert for Vp, Vs, and hypocenters using a variable-mesh double-difference tomography algorithm. By observing low-Vp areas within the normally high-Vp slab, we identify portions of the slab that are likely to contain serpentinized mantle, and thus contribute to higher degrees of melting and higher volatile components observable in arc lavas.

Too much slab waving in South America? Wet plumes as an alternative to flat slab steepening as the cause of back arc large volcanic provinces

NASA Astrophysics Data System (ADS)

Booker, J. R.; Burd, A. I.

2013-12-01

A widely held view is that the Nazca Slab under western S. America acts like a tattered flag waving in the wind: It is segmented and the dip angle of segments flap up and down with time. There are presently two flat segments - one under Peru and the other, the "Pampean" flat slab (centered around 31S) under central Chile and Argentina. Both are correlated with subduction of buoyant crust of oceanic aseismic ridges, complete cessation of Andean arc volcanism and very thick crust. It has been argued that the waxing and waning of flat subduction is responsible for much of the time variations in tectonics and volcanism up to 800 km east of the S. American coast for at least 100 MA. For instance, the back arc Payenia igneous plateau (35-38S) and the Somuncura igneous plateau (40.5-43S) are both thought to follow from the steepening of flat slabs at about 2 and 27 MA. Each flat slab existed for more than 5 MA. However, the case for the existence of these flat slabs rests heavily on volcanism with "arc signature" hundreds of km east of the modern volcanic arc at a time when an asthenospheric wedge would be in its final stages of being squeezed out of the space between the slab and the lithosphere. Arc signature can be summarized as the geochemical consequence of mantle melting in the presence of water. If there is a source of water in the mantle other than a shallow slab, the strongest argument for a flat slab dissolves. We have found two electrically conductive plumes rising from below 350 km near the top of the Mantle Transition Zone (MTZ). One passes through a window in the Pampean flat slab but does not penetrate the lithosphere. The other rises under Payenia. The maximum resistivity at the core of these plumes is less than 10 Ohm-m. Partial melt can explain such low resistivity, but will not be buoyant and rise from below 350 km. We propose that the low resistivity is more likely due to water and that we are seeing "wet plumes" that have been proposed to explain volcanism in SW Japan and in mainland China. Wet plumes are an MTZ instability triggered by a subducted slab that has stagnated in the MTZ. Their rise is driven by the lower density of hydrous minerals and their melting at the base of the lithosphere can produce the same geochemical consequences as a shallow slab. Seismic tomography of the MTZ beneath S. America supports stagnant slabs beneath our plumes. We conclude, therefore that many of the flat slabs proposed in S. America may not have existed.

Follow up of injected polyurethane slab jacking.

DOT National Transportation Integrated Search

2003-08-01

GLENN JACKSON BRIDGE FOLLOW-UP REPORT The elevation monitoring in the report entitled Injected Polyurethane Slab Jacking (Soltesz 2000) is continued in this current report. The elevations of the concrete slabs are being monitored to see if polyuretha...

16. 'Concrete Bridge Over Salt River, Port Kenyon, Humboldt County, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

16. 'Concrete Bridge Over Salt River, Port Kenyon, Humboldt County, California, A.J. Logan, County Surveyor, H.J. Brunnier, Consulting Engineer, March 7, 1919,' showing detail of floor beam at central pier, half section of cantilever slab at end of bridge, floor beam end panels, slab reinforcing, plan of slab reinforcing, diagram of slab bars, typical floor girder. - Salt River Bridge, Spanning Salt River at Dillon Road, Ferndale, Humboldt County, CA

Imaging performance of an isotropic negative dielectric constant slab.

PubMed

Shivanand; Liu, Huikan; Webb, Kevin J

2008-11-01

The influence of material and thickness on the subwavelength imaging performance of a negative dielectric constant slab is studied. Resonance in the plane-wave transfer function produces a high spatial frequency ripple that could be useful in fabricating periodic structures. A cost function based on the plane-wave transfer function provides a useful metric to evaluate the planar slab lens performance, and using this, the optimal slab dielectric constant can be determined.

Regional body-wave tomography of the Peruvian flat slab

NASA Astrophysics Data System (ADS)

Young, Bissett E.

Local travel time data were used to create three dimensional tomography models of Vp and Vs above the flat slab in southern Peru, where the Nazca plate subducts subhorizontally beneath the continental lithosphere. The Peruvian flat slab segment corresponds to a gap in the volcanic arc and far-field thick-skinned deformation in the Eastern Cordillera. Despite ongoing research, there is little consensus on the causes and consequences of flat slab subduction. We present results from regional body-wave tomography which show high S-wave velocities above the slab for a region that coincides with the location of the Nazca ridge, a bathymetric high subducting at ~15°S. We propose that fast S-wave arrivals can be explained by mantle anisotropy. We attribute low Vs observed in the mantle north of the ridge to the presence of hydrous phases, resulting from the depth dependent dehydration of amphibole in an area where the slab is deeper.

Mantle flow through a tear in the Nazca slab inferred from shear wave splitting

NASA Astrophysics Data System (ADS)

Lynner, Colton; Anderson, Megan L.; Portner, Daniel E.; Beck, Susan L.; Gilbert, Hersh

2017-07-01

A tear in the subducting Nazca slab is located between the end of the Pampean flat slab and normally subducting oceanic lithosphere. Tomographic studies suggest mantle material flows through this opening. The best way to probe this hypothesis is through observations of seismic anisotropy, such as shear wave splitting. We examine patterns of shear wave splitting using data from two seismic deployments in Argentina that lay updip of the slab tear. We observe a simple pattern of plate-motion-parallel fast splitting directions, indicative of plate-motion-parallel mantle flow, beneath the majority of the stations. Our observed splitting contrasts previous observations to the north and south of the flat slab region. Since plate-motion-parallel splitting occurs only coincidentally with the slab tear, we propose mantle material flows through the opening resulting in Nazca plate-motion-parallel flow in both the subslab mantle and mantle wedge.

Numerical analysis of the shifting slabs applied in a wireless power transfer system to enhance magnetic coupling

NASA Astrophysics Data System (ADS)

Dong, Yayun; Yang, Xijun; Jin, Nan; Li, Wenwen; Yao, Chen; Tang, Houjun

2017-05-01

Shifting medium is a kind of metamaterial, which can optically shift a space or an object a certain distance away from its original position. Based on the shifting medium, we propose a concise pair of shifting slabs covering the transmitting or receiving coil in a two-coil wireless power transfer system to decrease the equivalent distance between the coils. The electromagnetic parameters of the shifting slabs are calculated by transformation optics. Numerical simulations validate that the shifting slabs can approximately shift the electromagnetic fields generated by the covered coil; thus, the magnetic coupling and the efficiency of the system are enhanced while remaining the physical transmission distance unchanged. We also verify the advantages of the shifting slabs over the magnetic superlens. Finally, we provide two methods to fabricate shifting slabs based on split-ring resonators.

Dislocation-free strained silicon-on-silicon by in-place bonding

NASA Astrophysics Data System (ADS)

Cohen, G. M.; Mooney, P. M.; Paruchuri, V. K.; Hovel, H. J.

2005-06-01

In-place bonding is a technique where silicon-on-insulator (SOI) slabs are bonded by hydrophobic attraction to the underlying silicon substrate when the buried oxide is undercut in dilute HF. The bonding between the exposed surfaces of the SOI slab and the substrate propagates simultaneously with the buried oxide etching. As a result, the slabs maintain their registration and are referred to as "bonded in-place". We report the fabrication of dislocation-free strained silicon slabs from pseudomorphic trilayer Si/SiGe/SOI by in-place bonding. Removal of the buried oxide allows the compressively strained SiGe film to relax elastically and induce tensile strain in the top and bottom silicon films. The slabs remain bonded to the substrate by van der Waals forces when the wafer is dried. Subsequent annealing forms a covalent bond such that when the upper Si and the SiGe layer are removed, the bonded silicon slab remains strained.

Thermal, Petrologic, and Structural Conditions for the September 2017 M=8.2 and M=7.1 intra-slab earthquakes in Mexico

NASA Astrophysics Data System (ADS)

Wang, K.; Gao, X.; Rogers, G. C.

2017-12-01

The M=8.2 Tehuantepec and M=7.1 Puebla earthquakes of September 2017 are similar to the 1999 Oaxaca (M=7.5, Mexico), 2001 Geiyo (M=6.7, Nankai), and 2001 Nisqually (M=6.8, Cascadia) earthquakes. All these events are normal-faulting events in the 40-60 km depth range within young and warm subducting slabs. They all ruptured the mantle part of the slab. To investigate the thermal and petrologic conditions of these earthquakes, we have developed finite element thermal models in the areas of the two September events. Along the northern transect for the M=7.1 event, where the age of the incoming plate is 13.5 Ma, the slab geometry is well constrained by previous receiver function and earthquake location studies. Two available hypocenter locations of the main shock fall within or at the lower boundary of our model-predicted zone of serpentine (antigorite) stability in the slab mantle. Along the southern transect for the M=8.2 event, where the age of the incoming plate is 25.5 Ma, the slab geometry is less well known, and we have considered two published geometrical models. Several available hypocenter locations of the main shock are within or below the serpentine stability zone, depending on which slab geometry is assumed. Most of the rupture zone is shallower than the hypocenter. The model results support the following hypothesis. The two September earthquakes probably ruptured pre-existing normal faults that extended into the oceanic mantle and had been locally hydrated prior to and during the beginning phase of subduction. The earthquakes may have initiated at the dehydration boundary of antigorite or chlorite, facilitated by elevated pore fluid pressure (dehydration embrittlement). Most of the rupture was in the uppermost mantle part of the slab but may have involved parts of the slab crust. That large intra-slab earthquakes of this type tend to involve mantle rupture has been explained as due to the structural condition caused by warm-slab metamorphism (Wang et al., 2004): The upper crust of the slab is too fragmented due to metamorphic densification, but hydrated deep-cutting faults can produce large earthquakes in the more coherent mantle and lower crust. Wang, K., J. F. Cassidy, I. Wada, and A. J. Smith (2004), Effects of metamorphic crustal densification on earthquake size in warm slabs, Geophys. Res. Lett., 31, L01605, doi:10.1029/2003GL018644.

Four-Pass Coupler for Laser-Diode-Pumped Solid-State Laser

NASA Technical Reports Server (NTRS)

Coyle, Donald B.

2008-01-01

A four-pass optical coupler affords increased (in comparison with related prior two-pass optical couplers) utilization of light generated by a laser diode in side pumping of a solid-state laser slab. The original application for which this coupler was conceived involves a neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal slab, which, when pumped by a row of laser diodes at a wavelength of 809 nm, lases at a wavelength of 1,064 nm. Heretofore, typically, a thin laser slab has been pumped in two passes, the second pass occurring by virtue of reflection of pump light from a highly reflective thin film on the side opposite the side through which the pump light enters. In two-pass pumping, a Nd:YAG slab having a thickness of 2 mm (which is typical) absorbs about 84 percent of the 809-nm pump light power, leaving about 16 percent of the pump light power to travel back toward the laser diodes. This unused power can cause localized heating of the laser diodes, thereby reducing their lifetimes. Moreover, if the slab is thinner than 2 mm, then even more unused power travels back toward the laser diodes. The four-pass optical coupler captures most of this unused pump light and sends it back to the laser slab for two more passes. As a result, the slab absorbs more pump light, as though it were twice as thick. The gain and laser cavity beam quality of a smaller laser slab in conjunction with this optical coupler can thus be made comparable to those of a larger two-pass-pumped laser slab.

A seismological constraint on the age of a subducting slab: the Huatung basin offshore Taiwan

NASA Astrophysics Data System (ADS)

Chang, Y.; Kuo, B.

2010-12-01

At the northwestern corner of the Philippine basin, collision and subduction are taking place simultaneously as the Philippine Sea plate is obliquely subducting beneath the Ryukyu trench and NE Taiwan. What is engaging in these processes is the Huatung basin (HB) lithosphere, a small piece of oceanic lithosphere which, unlike the rest of the Philippine Sea plate, is controversial in its age and structure. Because certain ages of lithosphere correspond to certain overall velocity structures, we examine how old the subducting slab of the HB has to be to satisfy seismological observations. We select from broadband seismic networks on Taiwan a rough linear array that points to the events in the Kuril trench region, rendering a slab dipping towards the upcoming P wave field. The slab thus defocuses seismic energy and produces an amplitude low along the array with magnitude and spread controlled by the age of the slab. We employ a 2D finite-difference waveform technique and experimented with 2 types of slab models with various ages: a simplistic conduction model and a high-resolution slab-wedge convection model. The older and thicker the slab, the more widely the predicted amplitude low spreads. Comparison with the observations indicates that the best slab ages fall into 20-50 Ma. This is at odds with the 125 Ma Ar-Ar dating model. Now the issue is not how to make the chronologically old lithosphere seismologically young, but why those basaltic rock samples dated to be old are located on the HB.

Impact of Mantle Wind on Subducting Plate Geometry and Interplate Pressure: Insights From Physical Modelling.

NASA Astrophysics Data System (ADS)

Boutelier, D.; Cruden, A. R.

2005-12-01

New physical models of subduction investigate the impact of large-scale mantle flow on the structure of the subducted slab and deformation of the downgoing and overriding plates. The experiments comprise two lithospheric plates made of highly filled silicone polymer resting on a model asthenosphere of low viscosity transparent silicone polymer. Subduction is driven by a piston that pushes the subducting plate at constant rate, a slab-pull force due to the relative density of the slab, and a basal drag force exerted by flow in the model asthenosphere. Large-scale mantle flow is imposed by a second piston moving at constant rate in a tunnel at the bottom of the experiment tank. Passive markers in the mantle track the evolution of flow during the experiment. Slab structure is recorded by side pictures of the experiment while horizontal deformation is studied via passive marker grids on top of both plates. The initial mantle flow direction beneath the overriding plate can be sub-horizontal or sub-vertical. In both cases, as the slab penetrates the mantle, the mantle flow pattern changes to accommodate the subducting high viscosity lithosphere. As the slab continues to descend, the imposed flow produces either over- or under-pressure on the lower surface of the slab depending on the initial mantle flow pattern (sub-horizontal or sub-vertical respectively). Over-pressure imposed on the slab lower surface promotes shallow dip subduction while under-pressure tends to steepen the slab. These effects resemble those observed in previous experiments when the overriding plate moves horizontally with respect to a static asthenosphere. Our experiments also demonstrate that a strong vertical drag force (due to relatively fast downward mantle flow) exerted on the slab results in a decrease in strain rate in both the downgoing and overriding plates, suggesting a decrease in interplate pressure. Furthermore, with an increase in drag force deformation in the downgoing plate can switch from compression to extension. The density contrast between the downgoing plate and asthenosphere is varied from 0% to ~2% in order to investigate the relative contributions of mantle flow and slab pull force on the geometry of the slab and tectonic regime (compressional or extensional).

Using thermal and compositional modeling to assess the role of water in Alaskan flat slab subduction

NASA Astrophysics Data System (ADS)

Robinson, S. E.; Porter, R. C.; Hoisch, T. D.

2017-12-01

Although plate tectonic theory is well established in the geosciences, the mechanisms and details of various plate-tectonics related phenomena are not always well understood. In some ( 10%) convergent plate boundaries, subduction of downgoing oceanic plates is characterized by low angle geometries and is termed "flat slab subduction." The mechanism(s) driving this form of subduction are not well understood. The goal of this study is to explore the role that water plays in these flat slab subduction settings. This is important for a better understanding of the behavior of these systems and for assessing volcanic hazards associated with subduction and slab rollback. In southern Alaska, the Pacific Plate is subducting beneath the North American plate at a shallow angle. This low-angle subduction within the region is often attributed to the subduction of the Yakutat block, a terrane accreting to the south-central coast of Alaska. This flat slab region is bounded by the Aleution arc to the west and the strike-slip Queen Charlotte fault to the east. Temperature and compositional models for a 500-km transect across this subduction zone in Alaska were run for ten million years (the length of time that flat slab subduction has been ongoing in Alaska) and allow for interpretation of present-day conditions at depth. This allows for an evaluation of two hypotheses regarding the role of water in flat-slab regions: (1) slab hydration and dehydration help control slab buoyancy which influences whether flat slab subduction will be maintained or ended. (2) slab hydration/dehydration of the overlying lithosphere impacts deformation within the upper plate as water encourages plate deformation. Preliminary results from thermal modeling using Thermod8 show that cooling of the mantle to 500 °C is predicted down to 100 km depth at 10 million years after the onset of low-angle subduction (representing present-day). Results from compositional modeling in Perple_X show the maximum amount of water that can be held in the system assuming crustal (basalt and metabasalt) and mantle (peridotite) compositions. These models will be compared with seismic velocity models created from EarthScope Transportable Array data in the region in order to determine amounts of serpentinite and other water-bearing rocks within the flat slab subduction system.

ICANT, a code for the self-consistent computation of ICRH antenna coupling

NASA Astrophysics Data System (ADS)

Pécoul, S.; Heuraux, S.; Koch, R.; Leclert, G.

1996-02-01

The code deals with 3D antenna structures (finite length antennae) that are used to launch electromagnetic waves into tokamak plasmas. The antenna radiation problem is solved using a finite boundary element technique combined with a spectral solution of the interior problem. The slab approximation is used, and periodicity in y and z directions is introduced to account for toroidal geometry. We present results for various types of antennae radiating in vacuum: antenna with a finite Faraday screen and ideal Faraday screen, antenna with side limiters and phased antenna arrays. The results (radiated power, current profile) obtained are very close to analytical solutions when available.

Microwave Quantitative NDE Technique for Dielectric Slab Thickness Estimation Using the Music Algorithm

NASA Astrophysics Data System (ADS)

Abou-Khousa, M. A.; Zoughi, R.

2007-03-01

Non-invasive monitoring of dielectric slab thickness is of great interest in various industrial applications. This paper focuses on estimating the thickness of dielectric slabs, and consequently monitoring their variations, utilizing wideband microwave signals and the MUtiple SIgnal Characterization (MUSIC) algorithm. The performance of the proposed approach is assessed by validating simulation results with laboratory experiments. The results clearly indicate the utility of this overall approach for accurate dielectric slab thickness evaluation.

Tottori earthquakes and Daisen volcano: Effects of fluids, slab melting and hot mantle upwelling

NASA Astrophysics Data System (ADS)

Zhao, Dapeng; Liu, Xin; Hua, Yuanyuan

2018-03-01

We investigate the 3-D seismic structure of source areas of the 6 October 2000 Western Tottori earthquake (M 7.3) and the 21 October 2016 Central Tottori earthquake (M 6.6) which occurred near the Daisen volcano in SW Japan. The two large events took place in a high-velocity zone in the upper crust, whereas low-velocity (low-V) and high Poisson's ratio (high-σ) anomalies are revealed in the lower crust and upper mantle. Low-frequency micro-earthquakes (M 0.0-2.1) occur in or around the low-V and high-σ zones, which reflect upward migration of magmatic fluids from the upper mantle to the crust under the Daisen volcano. The nucleation of the Tottori earthquakes may be affected by the ascending fluids. The flat subducting Philippine Sea (PHS) slab has a younger lithosphere age and so a higher temperature beneath the Daisen and Tottori area, facilitating the PHS slab melting. It is also possible that a PHS slab window has formed along the extinct Shikoku Basin spreading ridge beneath SW Japan, and mantle materials below the PHS slab may ascend to the shallow area through the slab window. These results suggest that the Daisen adakite magma was affected by the PHS slab melting and upwelling flow in the upper mantle above the subducting Pacific slab.

A dipping, thick Farallon slab below central United States

NASA Astrophysics Data System (ADS)

Sun, D.; Gurnis, M.; Saleeby, J.; Helmberger, D. V.

2015-12-01

It has been hypothesized that much of the Laramide orogeny was caused by dynamic effects induced by an extensive flat slab during a period of plateau subduction. A particularly thick block containing the Shatsky Rise conjugate, now in the mid-mantle, left a distinctive deformation footprint from southern California to Denver, Colorado. Thus mid-mantle, relic slabs can provide fundamental information about past subduction and the history of plate tectonics if properly imaged. Here we find clear evidence for a northeastward dipping (35° dip), slab-like, but fat (up to 400-500 km thick) seismic anomaly within the top of the lower mantle below the central United States. Using a deep focus earthquake below Spain with direct seismic paths that propagate along the top and bottom of the anomaly, we find that the observed, stacked seismic waveforms recorded with the dense USArray show multi-pathing indicative of sharp top and bottom surfaces. Plate tectonic reconstructions in which the slab is migrated back in time suggest strong coupling of the slab to North America. In combination with the reconstructions, we interpret the structure as arising from eastward dipping Farallon subduction at the western margin of North America during the Cretaceous, in contrast with recent interpretations. The slab could have been fattened through a combination of pure shear thickening during flat-slab subduction and a folding instability during penetration into the lower mantle.

Connecting the surface to the deep: Flat-slab subduction dynamics and the evolution of western Amazonia

NASA Astrophysics Data System (ADS)

Eakin, C. M.

2017-12-01

Plate tectonics is primarily driven by the subduction of cold dense oceanic slabs. It has yet to be fully understood however how variations in slab morphology and buoyancy influence the surrounding mantle dynamics, and what difference if any is seen at the surface. An excellent natural laboratory to answer such questions is found along the Andean margin where the world's largest flat slab is presently subducting beneath much of Peru. Following the deployment of broadband seismic arrays across the region, mantle flow both beneath and above the flat-slab is investigated using targeted shear-wave splitting techniques that detect seismic anisotropy and the pattern of mantle deformation. The along strike change in slab dip angle and buoyancy content is found to exert a strong control over the surrounding mantle flow field. Modeling of the induced mantle flow, and the dynamic topography at the surface that results, predicts a wave of dynamic subsidence that propagates away from the trench as the flat slab develops. This is found to correlate well with the record of widespread sediment deposition across western Amazonia during the Miocene. A combination of uplift, flexure and dynamic topography during slab flattening is proposed to explain the overall landscape evolution of the region and the subsequent configuration of the transcontinental Amazon drainage system we see today.

Subduction and volatile recycling in Earth's mantle

NASA Technical Reports Server (NTRS)

King, S. D.; Ita, J. J.; Staudigel, H.

1994-01-01

The subduction of water and other volatiles into the mantle from oceanic sediments and altered oceanic crust is the major source of volatile recycling in the mantle. Until now, the geotherms that have been used to estimate the amount of volatiles that are recycled at subduction zones have been produced using the hypothesis that the slab is rigid and undergoes no internal deformation. On the other hand, most fluid dynamical mantle flow calculations assume that the slab has no greater strength than the surrounding mantle. Both of these views are inconsistent with laboratory work on the deformation of mantle minerals at high pressures. We consider the effects of the strength of the slab using two-dimensional calculations of a slab-like thermal downwelling with an endothermic phase change. Because the rheology and composition of subducting slabs are uncertain, we consider a range of Clapeyron slopes which bound current laboratory estimates of the spinel to perovskite plus magnesiowustite phase transition and simple temperature-dependent rheologies based on an Arrhenius law diffusion mechanism. In uniform viscosity convection models, subducted material piles up above the phase change until the pile becomes gravitationally unstable and sinks into the lower mantle (the avalanche). Strong slabs moderate the 'catastrophic' effects of the instabilities seen in many constant-viscosity convection calculations; however, even in the strongest slabs we consider, there is some retardation of the slab descent due to the presence of the phase change.

A quantitative study of ramped radio frequency, magnetization transfer, and slab thickness in three-dimensional time-of-flight magnetic resonance angiography in a patient population.

PubMed

Goodrich, K C; Blatter, D D; Parker, D L; Du, Y P; Meyer, K J; Bernstein, M A

1996-06-01

The authors compare the effectiveness of various magnetic resonance (MR) angiography acquisition strategies in enhancing the visibility of small intracranial vessels. Blood vessel contrast-to-noise ratio (CNR) in time-of-flight MR angiography was studied as a function of vessel size and several selectable imaging parameters. Contrast-to-noise measurements were made on 257 vessel segments ranging in size from 0.3 mm to 4.2 mm in patients who recently had undergone intraarterial cerebral angiography. Imaging parameters studied included magnetization transfer, spatially variable radio frequency (RF) pulse profile (ramped RF), and imaging slab thickness. The combination of thin slabs (16 slices/slab), ramped RF, and magnetization transfer resulted in the highest CNR for all but the smallest vessel sizes. The smallest vessels (< 0.5 mm) had the highest CNR, using the thick slab (64 slices/slab) with ramped RF and magnetization transfer. Magnetization transfer always improved vessel CNR, but the improvement diminished as the slab thickness was reduced. The CNR increased with a decrease in slab thickness for all but the smallest vessel sizes. Overall, the results provide a quantitative demonstration that inflow enhancement of blood is reduced for small vessels. Thus, whereas magnetization transfer is important at all vessel sizes, it becomes the primary factor in improving the visibility of the smallest vessels.

Quantum confinement effects on electronic photomobilities at nanostructured semiconductor surfaces: Si(111) without and with adsorbed Ag clusters

NASA Astrophysics Data System (ADS)

Hembree, Robert H.; Vazhappilly, Tijo; Micha, David A.

2017-12-01

The conductivity of holes and electrons photoexcited in Si slabs is affected by the slab thickness and by adsorbates. The mobilities of those charged carriers depend on how many layers compose the slab, and this has important scientific and technical consequences for the understanding of photovoltaic materials. A previously developed general computational procedure combining density matrix and electronic band structure treatments has been applied to extensive calculations of mobilities of photoexcited electrons and holes at Si(111) nanostructured surfaces with varying slab thickness and for varying photon energies, to investigate the expected change in mobility magnitudes as the slab thickness is increased. Results have been obtained with and without adsorbed silver clusters for comparison of their optical and photovoltaic properties. Band states were generated using a modified ab initio density functional treatment with the PBE exchange and correlation density functionals and with periodic boundary conditions for large atomic supercells. An energy gap correction was applied to the unoccupied orbital energies of each band structure by running more accurate HSE hybrid functional calculations for a Si(111) slab. Photoexcited state populations for slabs with 6, 8, 10, and 12 layers were generated using a steady state reduced density matrix including dissipative effects due to energy exchange with excitons and phonons in the medium. Mobilities have been calculated from the derivatives of voltage-driven electronic energies with respect to electronic momentum, for each energy band and for the average over bands. Results show two clear trends: (a) adding Ag increases the hole photomobilities and (b) decreasing the slab thickness increases hole photomobilities. The increased hole populations in 6- and 8-layer systems and the large increase in hole mobility for these thinner slabs can be interpreted as a quantum confinement effect of hole orbitals. As the slab thickness increases to ten and twelve layers, the effect of silver adsorbates decreases leading to smaller relative enhancements to the conduction electron and hole mobilities, but the addition of the silver nanoclusters still increases the absorbance of light and the mobility of holes compared to their mobilities in the pure Si slabs.

Numerical simulations of water transport in subduction zone: Influences of serpentinized layer in oceanic slabs on subduction dynamics

NASA Astrophysics Data System (ADS)

Nakao, A.; Hikaru, I.; Nakakuki, T.; Suzuki, Y.; Nakamura, H.

2017-12-01

Water liberated from subducting oceanic slabs can affect the subduction dynamics such as mantle wedge flows and plate motion (e.g., Gerya & Meilick, 2011; Horiuchi & Iwamori, 2016; Nakao et al., 2016). However, how water liberated from the slabs, in particular a hydrated part within the oceanic lithosphere (e.g., Fujie et al., 2013), is transported and affects the subduction dynamics has not been fully understood. In order to clarify the roles of water in subduction dynamics, we conducted 2-D dynamical simulations of water transport and mantle convection without imposing the geometry and velocity of subducting slabs. Using the simulations with various thicknesses (0-20 km) of a partially serpentinized layer (hereafter referred to as "SL") underlaying the altered oceanic basalt crust (AOC) in the subducting oceanic lithosphere, we estimate the subduction rate, back-arc spreading, trench migration, and slab geometry. The simulations show that the plate motion significantly changes depending on the amount of liberated water. When the SL is absent (0 km thick), the AOC mostly dehydrates at shallow depths (< 70 km). In this case, the plate subducts slowly, the trench is stationary, and the slab penetrates the 660-km boundary. If the SL is 7.5 km in thickness, it dehydrates at a greater depth compared to AOC, and more water enters the mantle wedge and the back-arc region. The liberated water reduces the viscosity of mantle wedge, and consequently, the subduction rate increases, the trench migrates seaward, and the slab stagnates on the 660-km. If the SL is 20 km in thickness, the upper SL releases much water into the mantle wedge and the back-arc region, whereas the lower SL does not dehydrate because of water uptake by phase A and phase D. In this case, because buoyancy of the subducting slab increases, the subduction is slow, back-arc spreading is weakened, and the slab penetrates the 660-km. Our results imply that the observed variety of subducting slabs reflects different amounts of water liberated from and within the slabs.

Using the MDCT thick slab MinIP method for the follow-up of pulmonary emphysema.

PubMed

Lan, Hai; Nishitani, Hiromu; Nishihara, Sadamitsu; Ueno, Junji; Takao, Shoichiro; Iwamoto, Seiji; Kawanaka, Takashi; Mahmut, Mawlan; Qingge, Si

2011-08-01

The purpose of this study was to evaluate the usefulness of thick slab minimum intensity projection (MinIP) as a follow-up method in patients with pulmonary emphysema. This method was used to determine the presence or absence of changes over time in the lung field based on multi-detector-row CT (MDCT) data. Among patients diagnosed with pulmonary emphysema who underwent 16-MDCT (slice thickness, 1 mm) twice at an interval of 6 months or more, 12 patients without changes in the lung field and 14 with clear changes in the lung field were selected as subjects. An image interpretation experiment was performed by five image interpreters. Pulmonary emphysema was followed up using two types of thick slab MinIP (thick slab MinIP 1 and 2) and multi-planar reformation (MPR), and the results of image interpretation were evaluated by receiver operating characteristic (ROC) analysis. In addition, the time required for image interpretation was compared among the three follow-up methods. The area under the ROC curve (Az) was 0.794 for thick slab MinIP 1, 0.778 for the thick slab MinIP 2, and 0.759 for MPR, showing no significant differences among the three methods. Individual differences in each item were significantly more marked for MPR than for thick slab MinIP. The time required for image interpretation was around 18 seconds for thick slab MinIP 1, 11 seconds for thick slab MinIP 2, and approximately 127 seconds for MPR, showing significant differences among the three methods. There were no significant differences in the results of image interpretation regarding the presence or absence of changes in the lung fields between thick slab MinIP and MPR. However, thick slab MinIP showed a shorter image interpretation time and smaller individual differences in the results among image interpreters than MPR, suggesting the usefulness of this method for determining the presence or absence of changes with time in the lung fields of patients with pulmonary emphysema.

Investigation of approach slab and its settlement for roads and bridges.

DOT National Transportation Integrated Search

2014-01-01

Approach slabs serve as a transitional system between an approach road and a bridge. Settlement of bridge approach slabs and their : supporting backfill has been experienced by more than ten Departments of Transportation throughout the United States....

Precast concrete replacement slabs for bridge decks.

DOT National Transportation Integrated Search

1982-01-01

The report illustrates and evaluates the first use in Virginia of precast concrete replacement slabs for bridge decks. It shows that a bridge deck can be replaced with the precast slabs while traffic is maintained in the adjacent traffic lane. The qu...

On reducing bumps at pavement-bridge interface.

DOT National Transportation Integrated Search

2010-12-21

This report contains the causes and long-term solutions to the bumps at bridge/approach slab and/or approach slab/pavement interface. A research was conducted on both structural and geotechnical aspects of an approach slab. : A 3-D finite element ana...

Instabilities of convection patterns in a shear-thinning fluid between plates of finite conductivity

NASA Astrophysics Data System (ADS)

Varé, Thomas; Nouar, Chérif; Métivier, Christel

2017-10-01

Rayleigh-Bénard convection in a horizontal layer of a non-Newtonian fluid between slabs of arbitrary thickness and finite thermal conductivity is considered. The first part of the paper deals with the primary bifurcation and the relative stability of convective patterns at threshold. Weakly nonlinear analysis combined with Stuart-Landau equation is used. The competition between squares and rolls, as a function of the shear-thinning degree of the fluid, the slabs' thickness, and the ratio of the thermal conductivity of the slabs to that of the fluid is investigated. Computations of heat transfer coefficients are in agreement with the maximum heat transfer principle. The second part of the paper concerns the stability of the convective patterns toward spatial perturbations and the determination of the band width of the stable wave number in the neighborhood of the critical Rayleigh number. The approach used is based on the Ginzburg-Landau equations. The study of rolls stability shows that: (i) for low shear-thinning effects, the band of stable wave numbers is bounded by zigzag instability and cross-roll instability. Furthermore, the marginal cross-roll stability boundary enlarges with increasing shear-thinning properties; (ii) for high shear-thinning effects, Eckhaus instability becomes more dangerous than cross-roll instability. For square patterns, the wave number selection is always restricted by zigzag instability and by "rectangular Eckhaus" instability. In addition, the width of the stable wave number decreases with increasing shear-thinning effects. Numerical simulations of the planform evolution are also presented to illustrate the different instabilities considered in the paper.

Bulldozing of Basal Continental Mantle Lithosphere During Flat-Slab Subduction

NASA Astrophysics Data System (ADS)

Axen, G. J.; van Wijk, J.; Currie, C. A.

2017-12-01

Flat-slab subduction occurs along 10% of subduction margins, forming magmatic gaps and causing inland migration of upper-plate deformation. We suggest that basal continental mantle lithosphere (CML) can be bulldozed ahead of the flat portion of horizontally-subducted oceanic lithosphere, forming a growing and advancing keel of thickened CML. This process fills the asthenospheric mantle wedge with CML, precluding melting. The bulldozed CML keel may transmit tectonic stresses ahead of the flat slab itself, causing upper-plate deformation ahead of the slab hinge. We designed 2-D numerical models after the North American Laramide orogeny, with subduction of a thick, buoyant oceanic plateau (conjugate Shatsky Rise) and with the continent advancing trenchward over the initial slab hinge. This results in slab-flattening, and removal of CML material. In our models, the thickness of the CML layer removed by this process depends on overriding plate rheology and is up to 25 km. The removed material is bulldozed ahead of the hinge and may fill up the asthenospheric wedge. Low-density (depleted) CML favors formation of bulldozed keels, which increase in width as CML strength decreases. Regular-density and/or stronger CML forms smaller bulldozed keels that are more likely to sink with the slab as eclogitization and densification proceed. When the flat slab rolls back, it leaves a step in the CML at the farthest extent of the slab. Relics of this step may remain below North America or may have dripped off. We interpret an upper-mantle fast-velocity anomaly below SE New Mexico and W Texas as a drip/keel, and the step in lithosphere thickness in southwestern Colorado as a fossil step, caused by the removal of the CML layer. Our model predicts that the Laramide bulldozed CML keel may have aided in stress transmission that caused basement uplifts as far as NE Wyoming and subsurface folds even farther N and E. Modern examples may exist in South American flat slab segments.

Regional body wave tomography of the Peruvian flat slab

NASA Astrophysics Data System (ADS)

Young, B. E.; Wagner, L. S.; Knezevic Antonijevic, S.; Kumar, A.; Beck, S. L.; Long, M. D.; Tavera, H.

2013-12-01

Local travel time data from the PerU Lithosphere and Slab Experiment (PULSE) were used to create three dimensional tomographic models of Vp and Vs above the flat slab in southern Peru. In the flat slab subduction regions of Peru and central Chile/Argentina, the Nazca plate subducts normally to a depth of ~100 km and then bends and progresses subhorizontally for several hundreds of kilometers before it resumes steep subduction. The Peruvian flat slab segment, located between 3°S and 15°S, corresponds to a gap in the volcanic arc and far-field thick-skinned deformation in the Eastern Cordillera. Despite ongoing research, there is still little consensus on the causes and consequences of flat slab subduction. In western North American, it has been suggested that flat subduction may have been responsible for the formation of the Rocky Mountains and ignimbrite flare-up during the Laramide orogeny. Preliminary tomography results show high shear wave velocities above the slab for a region that coincides with the location of the Nazca ridge, a 200 km wide bathymetric high that is currently subducting at ~15°S. Meanwhile, P wave velocities appear to be relatively normal. North of the ridge location, shear wave velocities can be separated into sublinear high (near the coast) and low (inland) velocity zones oriented approximately parallel to the trench. This geometry corresponds well with the organization of geotectonic and morphological terrains in Peru. High shear wave velocities above the slab are consistent with results from the 2000-2002 CHARGE deployment in central Chile/Argentina. This could indicate the presence of silica enriched, dry continental lithosphere, or it may be due to the presence of an anisotropic layer of hydrous phases directly above the slab. Future comparisons with results from Rayleigh wave tomography aim to address the role of anisotropy in observed shear wave velocities above flat slabs.

Usage of digital image correlation in assessment of behavior of block element pavement structure

NASA Astrophysics Data System (ADS)

Grygierek, M.; Grzesik, B.; Rokitowski, P.; Rusin, T.

2018-05-01

In diagnostics of existing road pavement structures deflection measurements have fundamental meaning, because of ability to assess present stiffness (bearing capacity) of whole layered construction. During test loading the reaction of pavement structure to applied load is measured in central point or in a few points located along a straight on a 1.5 ÷ 1.8 m distance (i.e. Falling Weight Deflectometer) in similar spacing equal to 20 ÷ 30 cm. Typical measuring techniques are productive and precise enough for most common pavement structures such as flexible, semi-rigid and rigid. It should be noted that in experimental research as well as in pavements in complex stress state, measurement techniques allowing observation of pavement deformation in 3D would have been very helpful. A great example of that type of pavements is a block element pavement structure consisting of i.e. paving blocks or stone slabs. Due to high stiffness and confined ability of cooperation of surrounding block elements, in that type of pavements fatigue life is strongly connected with displacement distribution. Unfortunately, typical deflection measurement methods forefend displacement observations and rotation of single block elements like paving blocks or slabs. Another difficult problem is to carry out unmistakable analysis of cooperation between neighboring elements. For more precise observations of displacements state of block element pavements under a wheel load a Digital Image Correlation (DIC) was used. Application of this method for assessment of behavior of stone slabs pavement under a traffic load enabled the monitoring of deformations distribution and encouraged to formulate conclusions about the initiation mechanism and development of damages in this type of pavement structures. Results shown in this article were obtained in field tests executed on an exploited pavement structure with a surface course made of granite slabs with dimensions 0.5x1.0x0.14 m.

Thermal Lens Measurement in Diode-Pumped Nd:YAG Zig-Zag Slab

NASA Technical Reports Server (NTRS)

Smoak, M. C.; Kay, R. B.; Coyle, D. B.; Hopf, D.

1998-01-01

A major advantage that solid state zig-zag slab lasers have over conventional rod-based designs is that a much weaker thermal lens is produced in the slab when side-pumped with Quasi-CW laser diode arrays, particularly if the pump radiation is kept well away from the Brewster-cut ends. This paper reports on a rather strong thermal lens produced when diode pump radiation is collimated into a narrow portion of the zig-zag slab. The collimation of multi-bar pump packages to increase brightness and improve overlap is a direct consequence of designs which seek to maximize performance and efficiency. Our slab design employed a 8.1 cm x 2.5 mm x 5 mm slab with opposing Brewster end faces. It was pumped through the 2.5 mm direction by seven laser diode array packages, each housing four 6OW diode bars, 1 cm in width. The pump face, anti-reflection (AR) coated at 809 nm, was 6.8 cm in width and the 8.1 cm opposing side, high-reflection (HR) coated at 809 nm, reflected the unabsorbed pump beam for a second pass through the slab.

Eelgrass slabs, a soilless culture substrate that inhibits adhesion of fungi and oomycetes and enhances antioxidant activity in tomato.

PubMed

Meot-Duros, Laetitia; Le Floch, Gaëtan; Meot, Benoit; Letousey, Patricia; Jacob, Bruno; Barbier, Georges

2011-10-26

Composed of a marine plant, Zostera sp., eelgrass slabs are a novel organic substrate for soilless cultures used in tomato production. The benefit of using eelgrass slabs for growing tomatoes was assessed by comparing it with coconut fiber slabs in regard to contamination by Pythium spp. and to the antioxidant properties of tomato fruits. First, tomato root contamination by Pythium spp. was studied by direct plate counting, and a molecular comparison of fungal and oomycete communities was conducted using PCR-DHPLC. Second, the antioxidant properties of tomato fruits were analyzed by measuring total phenol and carotenoid contents and by evaluating radical scavenging activity. Compared to plants grown on coconut fiber slabs, those on eelgrass slabs presented a lower rate of Pythium spp. root contamination. Moreover, culture on eelgrass slabs produced fruits with better radical scavenging activity and higher total phenol content compared to controls. Carotenoid content was not affected by the type of substrate. This study highlights the value of detrital leaves of Zostera sp. as a substrate for soilless culture that reduces root contamination and also promotes the production of tomato fruits with better nutritional value.

Slab dragging and the recent geodynamic evolution of the western Mediterranean plate boundary region

NASA Astrophysics Data System (ADS)

Spakman, Wim; Chertova, Maria V.; van den Berg, Arie P.; Thieulot, Cedric; van Hinsbergen, Douwe J. J.

2016-04-01

The Tortonian-Present geodynamic evolution of the plate boundary between North Africa and Iberia is characterized by first-order enigmas. This concerns, e.g., the diffuse tectonic activity of the plate boundary; the crustal thickening below the Rif; the closing of the northern Moroccan marine gateways prior to the Messinian Salinity Crisis; crustal extension of the central to eastern Betics; the origin and sense of motion of the large left-lateral Trans Alboran Shear Zone (TASZ) and Eastern Betic Shear Zone (EBSZ); and lithosphere delamination of the North African continental edge. Many explanations have been given for each of these seemingly disparate tectonic features, which invariably have been addressed in the plate tectonic context of the NW-SE relative plate convergence between the major plates since the Tortonian, mostly independently from each other. Usually there is no clear role for the subducted slab underlying the region, except for presumed rollback, either to SW or to the W, depending on the type of observations that require explanation. Here we integrate the dynamic role of the slab with the NW-SE relative plate convergence by 3-D numerical modelling of the slab evolution constrained by absolute plate motions (Chertova et al., JGR,2014 & Gcubed 2014). By combining observations and predictions from seismology, geology, and geodesy, with our numerical 3-D slab-mantle dynamics modelling, we developed a new and promising geodynamic framework that provides explanations of all noted tectonic enigmas in a coherent and connected way. From the Tortonian until today, we propose that mantle-resisted slab dragging combines with the NW-SE plate convergence across the (largely) unbroken plate boundary to drive the crustal deformation of the region. Slab dragging is the lateral transport, pushing or pulling, of slab through the mantle by the absolute motion of the subducting plate (Chertova et al., Gcubed, 2014). Because the slab is connected to both the Iberian and African lithosphere, both plates are dragging the slab by their shared ~NNE component of absolute plate motion, which in fact is invisible in the relative plate convergence frame that is usually adopted. Slab dragging induces mantle resistance that, we demonstrate by numerical modelling, leads in the region to differential lateral motion between the slab and African plate driving indentation of the Africa continental lithosphere leading to crustal shortening explaining the closure of Moroccan seaways and the thickening of the Rif crust. The differential motion also explains the TASZ and the transition from western Betics shortening to eastern Betics extension, both still active today. During Miocene westward slab rollback mantle-resisted slab dragging also provided the driving force of edge delamination of African lithosphere, we propose. These explanations of geological features are fully corroborates by an analysis of the GPS motion field in terms of the strain- and rotation rate fields using the method of Spakman and Nyst (2002), and the predicted crustal flow field. In particular, we derive from the GPS and geological data that the direction of African absolute motion is ~NNE and that the slab experiences at present negligible rollback.

Development Length for Headed Bars in Slab-Column Joints of RC Slab Bridges

DOT National Transportation Integrated Search

2015-12-04

In accordance with the Caltrans Seismic Design Criteria, the superstructure in a slab bridge should remain essentially elastic and only the pile extensions/columns are permitted to develop inelastic deformations during a seismic event. Hence, the lon...

Polymer-impregnated bridge slabs : performance over 10 years.

DOT National Transportation Integrated Search

1990-01-01

This report presents the results of a study to evaluate the performance over a 10-year period of slabs that were impregnated to a depth of about 1 in with a monomer that was subsequently polymerized (shallow polymer impregnation). The slabs were used...

Determination of interaction between bridge concrete approach slab and embankment settlement.

DOT National Transportation Integrated Search

2005-07-01

The main objective of this research is to correlate the deformation and internal force of the approach slab with the approach embankment settlements and the approach slab parameters such as length and thickness. Finite element analysis was carried ou...

Precast alternative for flat slab bridges : final report.

DOT National Transportation Integrated Search

2013-10-26

The cast-in-place (CIP) concrete slab bridge and the hollow core flat slab bridge are two very common bridge types utilized by the : South Carolina Department of Transportation (SCDOT). The CIP bridge is durable but has a long construction time while...

Imaging hydration and dehydration across the Cascadia subduction zone (Invited)

NASA Astrophysics Data System (ADS)

Abers, G. A.; Van Keken, P. E.; Hacker, B. R.; Mann, M. E.; Crosbie, K.; Creager, K.

2017-12-01

Arc volcanoes and exhumed forearc metamorphic rocks show clear evidence for upward transport of slab-derived fluids, but geophysical measurements rarely image features that could constrain the mode of this fluid transport. The hottest subduction zones such as Cascadia pose a particular challenge, as the depths where hydrous minerals are stable seaward of trenches is limited, and much of the water is expected to depart the slab before reaching sub-arc depths. Here we improve our understanding of this problem by developing a new thermal model for central Cascadia, leveraging new results several onshore and offshore geophysical investigations, notably the iMUSH project (Imaging Magma Under mount St. Helens), to evaluate constraints on the fluid flux. Offshore onshore heat flow measurements require a cold forearc and preclude detectable shear heating. Several puzzles emerge. The first is that Mount St. Helens overlies a continuous subducting plate which has an upper surface only 65-70 km deep beneath the volcano, imaged by migrated scattered P coda. This location, together with heat flow observations and inferences from the strength of the upper plate Moho, place the volcano over a cold forearc mantle wedge that is substantially hydrated. It is unclear how the wide range of magmas at Mount St. Helens could emerge in this setting since many have mantle origin. A second puzzle is that a large velocity step, about 10% in Vs, is seen along the slab Moho to depths exceeding 90 km where thermal models predict the subducting crust is in eclogite facies; eclogite and peridotite should have nearly indistinguishable Vs. Possibly a gabbroic oceanic crust persists metastably well below the arc, or perhaps the interface represents a deeper hydration front rather than petrologic Moho. A third puzzle is the persistent indication of H2O in arc magmas here despite almost certain dehydration of subducting sediments and upper oceanic crust. This indicates substantial H2O delivered by hydrated mantle lithosphere despite seismic evidence offshore for very little hydration. Perhaps the subducting lower crust carries more H2O than previously thought, or H2O transports structurally downward into the slab after subduction commences. Overall, substantial evidence exists for lateral transport of hydrous fluids in their path from slab to surface.

Steady fall of isothermal, resistive-viscous, compressible fluid across magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Low, B. C., E-mail: low@ucar.edu; Egan, A. K., E-mail: andrea.egan@colorado.edu

This is a basic MHD study of the steady fall of an infinite, vertical slab of isothermal, resistive-viscous, compressible fluid across a dipped magnetic field in uniform gravity. This double-diffusion steady flow in unbounded space poses a nonlinear but numerically tractable, one-dimensional (1D) free-boundary problem, assuming constant coefficients of resistivity and viscosity. The steady flow is determined by a dimensionless number μ{sub 1} proportional to the triple product of the two diffusion coefficients and the square of the linear total mass. For a sufficiently large μ{sub 1}, the Lorentz, viscous, fluid-pressure, and gravitational forces pack and collimate the fluid intomore » a steady flow of a finite width defined by the two zero-pressure free-boundaries of the slab with vacuum. The viscous force is essential in this collimation effect. The study conjectures that in the regime μ{sub 1}→0, the 1D steady state exists only for μ{sub 1}∈Ω, a spectrum of an infinite number of discrete values, including μ{sub 1} = 0 that corresponds to two steady states, the classical zero-resistivity static slab of Kippenhahn and Schlüter [R. Kippenhahn and A. Schlüter, Z. Astrophys. 43, 36 (1957)] and its recent generalization [B. C. Low et al., Astrophys. J. 755, 34 (2012)] to admit an inviscid resistive flow. The pair of zero-pressure boundaries of each of the μ{sub 1}→0 steady-state slabs are located at infinity. Computational evidence suggests that the Ω steady-states are densely distributed around μ{sub 1} = 0, as an accumulation point, but are sparsely separated by open intervals of μ{sub 1}-values for which the slab must be either time-dependent or spatially multi-dimensional. The widths of these intervals are vanishingly small as μ{sub 1}→0. This topological structure of physical states is similar to that described by Landau and Liftshitz [L. D. Landau and E. M. Lifshitz, Fluid Mechanics (Addison-Wesley, Reading, MA, 1959)] to explain the onset of hydrodynamic turbulence. The implications of this MHD study are discussed, with an interest in the prominences in the solar atmosphere and the interstellar clouds in the Galaxy.« less

Imaging the transition from Aleutian subduction to Yakutat collision in central Alaska, with local earthquakes and active source data

USGS Publications Warehouse

Eberhart-Phillips, D.; Christensen, D.H.; Brocher, T.M.; Hansen, R.; Ruppert, N.A.; Haeussler, Peter J.; Abers, G.A.

2006-01-01

In southern and central Alaska the subduction and active volcanism of the Aleutian subduction zone give way to a broad plate boundary zone with mountain building and strike-slip faulting, where the Yakutat terrane joins the subducting Pacific plate. The interplay of these tectonic elements can be best understood by considering the entire region in three dimensions. We image three-dimensional seismic velocity using abundant local earthquakes, supplemented by active source data. Crustal low-velocity correlates with basins. The Denali fault zone is a dominant feature with a change in crustal thickness across the fault. A relatively high-velocity subducted slab and a low-velocity mantle wedge are observed, and high Vp/Vs beneath the active volcanic systems, which indicates focusing of partial melt. North of Cook Inlet, the subducted Yakutat slab is characterized by a thick low-velocity, high-Vp/Vs, crust. High-velocity material above the Yakutat slab may represent a residual older slab, which inhibits vertical flow of Yakutat subduction fluids. Alternate lateral flow allows Yakutat subduction fluids to contribute to Cook Inlet volcanism and the Wrangell volcanic field. The apparent northeast edge of the subducted Yakutat slab is southwest of the Wrangell volcanics, which have adakitic composition consistent with melting of this Yakutat slab edge. In the mantle, the Yakutat slab is subducting with the Pacific plate, while at shallower depths the Yakutat slab overthrusts the shallow Pacific plate along the Transition fault. This region of crustal doubling within the shallow slab is associated with extremely strong plate coupling and the primary asperity of the Mw 9.2 great 1964 earthquake. Copyright 2006 by the American Geophysical Union.

Visualizing Three-dimensional Slab Geometries with ShowEarthModel

NASA Astrophysics Data System (ADS)

Chang, B.; Jadamec, M. A.; Fischer, K. M.; Kreylos, O.; Yikilmaz, M. B.

2017-12-01

Seismic data that characterize the morphology of modern subducted slabs on Earth suggest that a two-dimensional paradigm is no longer adequate to describe the subduction process. Here we demonstrate the effect of data exploration of three-dimensional (3D) global slab geometries with the open source program ShowEarthModel. ShowEarthModel was designed specifically to support data exploration, by focusing on interactivity and real-time response using the Vrui toolkit. Sixteen movies are presented that explore the 3D complexity of modern subduction zones on Earth. The first movie provides a guided tour through the Earth's major subduction zones, comparing the global slab geometry data sets of Gudmundsson and Sambridge (1998), Syracuse and Abers (2006), and Hayes et al. (2012). Fifteen regional movies explore the individual subduction zones and regions intersecting slabs, using the Hayes et al. (2012) slab geometry models where available and the Engdahl and Villasenor (2002) global earthquake data set. Viewing the subduction zones in this way provides an improved conceptualization of the 3D morphology within a given subduction zone as well as the 3D spatial relations between the intersecting slabs. This approach provides a powerful tool for rendering earth properties and broadening capabilities in both Earth Science research and education by allowing for whole earth visualization. The 3D characterization of global slab geometries is placed in the context of 3D slab-driven mantle flow and observations of shear wave splitting in subduction zones. These visualizations contribute to the paradigm shift from a 2D to 3D subduction framework by facilitating the conceptualization of the modern subduction system on Earth in 3D space.

MAGNETIC FIELD LINE RANDOM WALK FOR DISTURBED FLUX SURFACES: TRAPPING EFFECTS AND MULTIPLE ROUTES TO BOHM DIFFUSION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghilea, M. C.; Ruffolo, D.; Sonsrettee, W.

2011-11-01

The magnetic field line random walk (FLRW) is important for the transport of energetic particles in many astrophysical situations. While all authors agree on the quasilinear diffusion of field lines for fluctuations that mainly vary parallel to a large-scale field, for the opposite case of fluctuations that mainly vary in the perpendicular directions, there has been an apparent conflict between concepts of Bohm diffusion and percolation/trapping effects. Here computer simulation and non-perturbative analytic techniques are used to re-examine the FLRW in magnetic turbulence with slab and two-dimensional (2D) components, in which 2D flux surfaces are disturbed by the slab fluctuations.more » Previous non-perturbative theories for D{sub perpendicular}, based on Corrsin's hypothesis, have identified a slab contribution with quasilinear behavior and a 2D contribution due to Bohm diffusion with diffusive decorrelation (DD), combined in a quadratic formula. Here we present analytic theories for other routes to Bohm diffusion, with random ballistic decorrelation (RBD) either due to the 2D component itself (for a weak slab contribution) or the total fluctuation field (for a strong slab contribution), combined in a direct sum with the slab contribution. Computer simulations confirm the applicability of RBD routes for weak or strong slab contributions, while the DD route applies for a moderate slab contribution. For a very low slab contribution, interesting trapping effects are found, including a depressed diffusion coefficient and subdiffusive behavior. Thus quasilinear, Bohm, and trapping behaviors are all found in the same system, together with an overall viewpoint to explain these behaviors.« less

Plate tectonic reconstruction of South and East Asia since 43 Ma using seismic tomographic constraints: role of the subducted ';East Asia Sea' (Invited)

NASA Astrophysics Data System (ADS)

Wu, J. E.; Suppe, J.; Renqi, L.; Kanda, R. V.

2013-12-01

Lithosphere that subducts at convergent plate boundaries provides a potentially decipherable plate tectonic record. In this study we use global seismic tomography to map subducted slabs in the upper and lower mantle under South and East Asia to constrain plate reconstructions. The mapped slabs include the Pacific, the Indian Ocean and Banda Sea, the Molucca Sea, Celebes Sea, the Philippine Sea and Eurasia, New Guinea and other lower mantle detached slabs. The mapped slabs were restored to the earth surface and used with Gplates software to constrain a globally-consistent, fully animated plate reconstruction of South and East Asia. Three principal slab elements dominate possible plate reconstructions: [1] The mapped Pacific slabs near the Izu-Bonin and the Marianas trenches form a subvertical slab curtain or wall extending down to 1500 km in the lower mantle. The ';slab curtain' geometry and restored slabs lengths indicate that the Pacific subduction zone has remained fixed within +/- 250 km of its present position since ~43 Ma. In contrast, the Tonga Pacific slab curtain records at least 1000 km trench rollback associated with expansion of back-arc basins. [2] West of the Pacific slab curtain, a set of flat slabs exist in the lower mantle and record a major 8000km by 2500-3000km ocean that existed at ~43 Ma. This now-subducted ocean, which we call the ';East Asian Sea', existed between the Ryukyu Asian margin and the Lord Howe hotspot, present-day eastern Australia, and fills a major gap in Cenozoic plate reconstructions between Indo-Australia, the Pacific Ocean and Asia. [3] An observed ';picture puzzle' fit between the restored edges of the Philippine Sea, Molucca Sea and Indian Ocean slabs suggests that the Philippine Sea was once part of a larger Indo-Australian Ocean. Previous models of Philippine Sea plate motions are in conflict with the location of the East Asian Sea lithosphere. Using the mapped slab constraints, we propose the following 43 Ma to 0 plate tectonic reconstruction. At ~43 Ma a major plate reorganization occurred in South and East Asia marked by Indian Ocean Wharton ridge extinction, initiation of Pacific Ocean WNW motions and the rapid northward motion of the Australian plate. The Philippine Sea and Molucca Sea were clustered at the northern margin of Australia, northwest of New Guinea. During the mid-Cenozoic these plates moved NNE with Australia, accommodated by N-S transforms at the eastern margin of Sundaland. The East Asian Sea was subducted under the northward-moving Philippine Sea and Australia plates, and the expanding Melanesian and Shikoku-Parece Vela backarc basins. At ~20 to 25 Ma the Philippine Sea and Molucca Sea were fragmented from Indo-Australia and began to have a westward component of motion due to partial Pacific capture. Around 1-2 Ma the Philippine Sea was more fully captured by the Pacific and now has rapid Pacific-like northwestward motions.

TRUST. I. A 3D externally illuminated slab benchmark for dust radiative transfer

NASA Astrophysics Data System (ADS)

Gordon, K. D.; Baes, M.; Bianchi, S.; Camps, P.; Juvela, M.; Kuiper, R.; Lunttila, T.; Misselt, K. A.; Natale, G.; Robitaille, T.; Steinacker, J.

2017-07-01

Context. The radiative transport of photons through arbitrary three-dimensional (3D) structures of dust is a challenging problem due to the anisotropic scattering of dust grains and strong coupling between different spatial regions. The radiative transfer problem in 3D is solved using Monte Carlo or Ray Tracing techniques as no full analytic solution exists for the true 3D structures. Aims: We provide the first 3D dust radiative transfer benchmark composed of a slab of dust with uniform density externally illuminated by a star. This simple 3D benchmark is explicitly formulated to provide tests of the different components of the radiative transfer problem including dust absorption, scattering, and emission. Methods: The details of the external star, the slab itself, and the dust properties are provided. This benchmark includes models with a range of dust optical depths fully probing cases that are optically thin at all wavelengths to optically thick at most wavelengths. The dust properties adopted are characteristic of the diffuse Milky Way interstellar medium. This benchmark includes solutions for the full dust emission including single photon (stochastic) heating as well as two simplifying approximations: One where all grains are considered in equilibrium with the radiation field and one where the emission is from a single effective grain with size-distribution-averaged properties. A total of six Monte Carlo codes and one Ray Tracing code provide solutions to this benchmark. Results: The solution to this benchmark is given as global spectral energy distributions (SEDs) and images at select diagnostic wavelengths from the ultraviolet through the infrared. Comparison of the results revealed that the global SEDs are consistent on average to a few percent for all but the scattered stellar flux at very high optical depths. The image results are consistent within 10%, again except for the stellar scattered flux at very high optical depths. The lack of agreement between different codes of the scattered flux at high optical depths is quantified for the first time. Convergence tests using one of the Monte Carlo codes illustrate the sensitivity of the solutions to various model parameters. Conclusions: We provide the first 3D dust radiative transfer benchmark and validate the accuracy of this benchmark through comparisons between multiple independent codes and detailed convergence tests.

Experimental study of a VBG-based Tm : YLF slab laser at different output coupler parameters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, X M; Ding, Y; Dai, T Y

2015-04-30

The performance of a Tm : YLF slab laser is studied at different output coupler parameters. Use is made of a 20-mm-long a-cut slab crystal doped with 2.5 at. % thulium ions. With a volume Bragg grating and a Fabry – Perot etalon, the selected output wavelength of this Tm : YLF slab laser is 1908 nm. For the optimised output coupler with a transmission of 20% and a radius of curvature of 300 mm, the output power exceeds 74.1 W and the slope efficiency with respect to the absorbed pump power reaches 48.4%. In addition, the beam quality ofmore » the Tm : YLF slab laser is improved. (lasers)« less

Novel Approach for Modeling of Nonuniform Slag Layers and Air Gap in Continuous Casting Mold

NASA Astrophysics Data System (ADS)

Wang, Xudong; Kong, Lingwei; Yao, Man; Zhang, Xiaobing

2017-02-01

Various kinds of surface defects on the continuous casting slab usually originate from nonuniform heat transfer and mechanical behavior, especially during the initial solidification inside the mold. In this article, a model-coupled inverse heat transfer problem incorporating the effect of slag layers and air gap is developed to study the nonuniform distribution of liquid slag, solid slag, and air gap layers. The model considers not only the formation and evolution of slag layers and air gap but also the temperatures in the mold copper as measured by thermocouples. The simulation results from the model and the measured temperatures from experiments are shown to be in good agreement with each other. At the casting speed of 0.65 m/min, the liquid slag film disappears and transforms into solid slag entirely at about 400 mm away from meniscus, and an air gap begins to form. Until the mold exit, the maximum thickness of the solid slag layer and air gap gradually increases to 1.34 and 0.056 mm, respectively. The results illustrate that the magnitude and nonuniform distribution of the slag layers and air gap along the cross direction, correlating with heat flux between the shell and mold, eventually determine the temperature profiles of the mold hot face and slab surface. The proposed model may provide a convenient approach for analyzing nonuniform heat transfer and mechanical behaviors between the mold and slab in the real casting process.

Accelerated slab replacement using temporary precast panels and self-consolidating concrete.

DOT National Transportation Integrated Search

2016-06-06

Slab replacement is the main activity in any concrete pavement rehabilitation project. According to a survey of industry and FDOT, contractor productivity in slab replacements has been very low, ranging between 25 to 50 cu. yds. The low number of sla...

Studies on Punching Shear Resistance of Two Way Slab Specimens with Partial Replacement of Cement by GGBS with Different Edge Conditions

NASA Astrophysics Data System (ADS)

Nemani, Ravi Dakshina Murthy; Rao, M. V. S.; Grandhe, Veera Venkata Satya Naranyana

2016-09-01

The present work is an effort to quantify the punching shear load resistance effect on two way simply supported slab specimens with replacement of cement by Ground Granulated Blast Furnace Slag (GGBS) with different edge conditions at various replacement levels and evaluate its efficiency. GGBS replacement has emerged as a major alternative to conventional concrete and has rapidly drawn the concrete industry attention due to its cement savings, cost savings, environmental and socio-economic benefits. The two way slab specimens were subjected to punching shear load by in house fabricated apparatus. The slab specimens were cast using M30 grade concrete with HYSD bars. The cement was partially replaced with GGBS at different percentages i.e., 0 to 30 % at regular intervals of 10 %. The test results indicate that the two way slab specimens with partial replacement of cement by GGBS exhibit high resistance against punching shear when compared with conventional concretes slab specimens.

Farallon slab detachment and deformation of the Magdalena Shelf, southern Baja California

USGS Publications Warehouse

Brothers, Daniel S.; Harding, Alistair J.; Gonzalez-Fernandez, Antonio; Holbrook, W.S. Steven; Kent, Graham M.; Driscoll, Neal W.; Fletcher, John M.; Lizarralde, Daniel; Umhoefer, Paul J.; Axen, Gary

2012-01-01

Subduction of the Farallon plate beneath northwestern Mexico stalled by ~12 Ma when the Pacific-Farallon spreading-ridge approached the subduction zone. Coupling between remnant slab and the overriding North American plate played an important role in the capture of the Baja California (BC) microplate by the Pacific Plate. Active-source seismic reflection and wide-angle seismic refraction profiles across southwestern BC (~24.5°N) are used to image the extent of remnant slab and study its impact on the overriding plate. We infer that the hot, buoyant slab detached ~40 km landward of the fossil trench. Isostatic rebound following slab detachment uplifted the margin and exposed the Magdalena Shelf to wave-base erosion. Subsequent cooling, subsidence and transtensional opening along the shelf (starting ~8 Ma) starved the fossil trench of terrigenous sediment input. Slab detachment and the resultant rebound of the margin provide a mechanism for rapid uplift and exhumation of forearc subduction complexes.

Printable Single-Crystal Silicon Micro/Nanoscale Ribbons, Platelets and Bars Generated from Bulk Wafers

DTIC Science & Technology

2007-08-28

enables high yield integration onto wafers, glass plates, plastic sheets, rubber slabs or other surfaces. As one application example, bottom gate thin... EPDMS 1m2Si ESi 1m2PDMS 23 is the critical strain for buck- ling, epre is the degree of prestrain, k0 and A0 are...Young’s modulus of Si and PDMS. The following values were used to yield the calcualted value of it (i.e., 84 lm): ESi = 160 GPa, EPDMS = 2 MPa, mPDMS

Dynamic Linkages Between the Transition Zone & Surface Plate Motions in 2D Models of Subduction

NASA Astrophysics Data System (ADS)

Arredondo, K.; Billen, M. I.

2013-12-01

While slab pull is considered the dominant force controlling plate motion and speed, its magnitude is controlled by slab behavior in the mantle, where tomographic studies show a wide range of possibilities from direct penetration to folding, or stagnation directly above the lower mantle (e.g. Fukao et al., 2009). Geodynamic studies have investigated various parameters, such as plate age and two phase transitions, to recreate observed behavior (e.g. Běhounková and Cízková, 2008). However, past geodynamic models have left out known slab characteristics that may have a large impact on slab behavior and our understanding of subduction processes. Mineral experiments and seismic observations have indicated the existence of additional phase transitions in the mantle transition zone that may produce buoyancy forces large enough to affect the descent of a subducting slab (e.g. Ricard et al., 2005). The current study systematically tests different common assumptions used in geodynamic models: kinematic versus free-slip boundary conditions, the effects of adiabatic heating, viscous dissipation and latent heat, compositional layering and a more complete suite of phase transitions. Final models have a complete energy equation, with eclogite, harzburgite and pyrolite lithosphere compositional layers, and seven composition-dependent phase transitions within the olivine, pyroxene and garnet polymorph minerals. Results show important feedback loops between different assumptions and new behavior from the most complete models. Kinematic models show slab weakening or breaking above the 660 km boundary and between compositional layers. The behavior in dynamic models with a free-moving trench and overriding plate is compared to the more commonly found kinematic models. The new behavior may have important implications for the depth distribution of deep earthquakes within the slab. Though the thermodynamic parameters of certain phase transitions may be uncertain, their presence and feedback to other added processes remain important, which could encourage mineralogical research into multiphase systems. Feedback from the compositionally complex slab to the dynamic trench may improve understanding on the mechanics of slab behavior in the upper and lower mantle and surface behavior of the subducting and overriding plates. Běhounková, M., and H. Cízková, Long-wavelength character of subducted slabs in the lower mantle, Earth and Planetary Science Letters, 275, 43-53, 2008. Fukao, Y., M. Obayashi, T. Nakakuki, and the Deep Slab Project Group, Stagnant slab: A review, Annual Reviews of Earth and Planetary Science, 37, 19-46, 2009. Ricard, Y., E. Mattern, and J. Matas, Synthetic tomographic images of slabs from mineral physics, in Earth's Deep Mantle: Structure, Composition, and Evolution, Geophysical Monograph Series, vol. 160, American Geophysical Union, 2005.

Array-Based Receiver Function Analysis of the Subducting Juan de Fuca Plate Beneath the Mount St. Helens Region and its Implications for Subduction Geometry and Metamorphism

NASA Astrophysics Data System (ADS)

Mann, M. E.; Abers, G. A.; Creager, K. C.; Ulberg, C. W.; Crosbie, K.

2017-12-01

Mount St. Helens (MSH) is unusual as a prolific arc volcano located 50 km towards the forearc of the main Cascade arc. The iMUSH (imaging Magma Under mount St. Helens) broadband deployment featured 70 seismometers at 10-km spacing in a 50-km radius around MSH, spanning a sufficient width for testing along-strike variation in subsurface geometry as well as deep controls on volcanism in the Cascade arc. Previous estimates of the geometry of the subducting Juan de Fuca (JdF) slab are extrapolated to MSH from several hundred km to the north and south. We analyze both P-to-S receiver functions and 2-D Born migrations of the full data set to locate the upper plate Moho and the dip and depth of the subducting slab. The strongest coherent phase off the subducting slab is the primary reverberation (Ppxs; topside P-to-S reflection) from the Moho of the subducting JdF plate, as indicated by its polarity and spatial pattern. Migration images show a dipping low velocity layer at depths less than 50 km that we interpret as the subducting JdF crust. Its disappearance beyond 50 km depth may indicate dehydration of subducting crust or disruption of high fluid pressures along the megathrust. The lower boundary of the low velocity zone, the JdF Moho, persists in the migration image to depths of at least 90 km and is imaged at 74 km beneath MSH, dipping 23 degrees. The slab surface is 68 km beneath MSH and 85 km beneath Mount Adams volcano to the east. The JdF Moho exhibits 10% velocity contrasts as deep as 85 km, an observation difficult to reconcile with simple models of crustal eclogitization. The geometry and thickness of the JdF crust and upper plate Moho is consistent with similar transects of Cascadia and does not vary along strike beneath iMUSH, indicating a continuous slab with no major disruption. The upper plate Moho is clear on the east side of the array but it disappears west of MSH, a feature we interpret as a result of both serpentinization of the mantle wedge and a westward increase in wavespeed of the continental crust. The seismically-imaged surface of the subducting JdF slab at 68 km beneath MSH is the shallowest yet documented beneath an arc volcano. Combined with the inference of serpentinization in the mantle wedge, this geometry presents a problem in that vertical mantle melt migration seems unfeasible, yet mantle melts contribute to erupted MSH magmas.

Low electrical resistivity associated with plunging of the Nazca flat slab beneath Argentina.

PubMed

Booker, John R; Favetto, Alicia; Pomposiello, M Cristina

2004-05-27

Beneath much of the Andes, oceanic lithosphere descends eastward into the mantle at an angle of about 30 degrees (ref. 1). A partially molten region is thought to form in a wedge between this descending slab and the overlying continental lithosphere as volatiles given off by the slab lower the melting temperature of mantle material. This wedge is the ultimate source for magma erupted at the active volcanoes that characterize the Andean margin. But between 28 degrees and 33 degrees S the subducted Nazca plate appears to be anomalously buoyant, as it levels out at about 100 km depth and extends nearly horizontally under the continent. Above this 'flat slab', volcanic activity in the main Andean Cordillera terminated about 9 million years ago as the flattening slab presumably squeezed out the mantle wedge. But it is unknown where slab volatiles go once this happens, and why the flat slab finally rolls over to descend steeply into the mantle 600 km further eastward. Here we present results from a magnetotelluric profile in central Argentina, from which we infer enhanced electrical conductivity along the eastern side of the plunging slab, indicative of the presence of partial melt. This conductivity structure may imply that partial melting occurs to at least 250 km and perhaps to more than 400 km depth, or that melt is supplied from the 410 km discontinuity, consistent with the transition-zone 'water-filter' model of Bercovici and Karato.

Analysis of prestressed concrete slab-and-beam structures

NASA Astrophysics Data System (ADS)

Sapountzakis, E. J.; Katsikadelis, J. T.

In this paper a solution to the problem of prestressed concrete slab-and-beam structures including creep and shrinkage effect is presented. The adopted model takes into account the resulting inplane forces and deformations of the plate as well as the axial forces and deformations of the beam, due to combined response of the system. The analysis consists in isolating the beams from the plate by sections parallel to the lower outer surface of the plate. The forces at the interface, which produce lateral deflection and inplane deformation to the plate and lateral deflection and axial deformation to the beam, are established using continuity conditions at the interface. The influence of creep and shrinkage effect relative with the time of the casting and the time of the loading of the plate and the beams is taken into account. The estimation of the prestressing axial force of the beams is accomplished iteratively. Both instant (e.g. friction, slip of anchorage) and time dependent losses are encountered. The solution of the arising plate and beam problems, which are nonlinearly coupled, is achieved using the analog equation method (AEM). The adopted model, compared with those ignoring the inplane forces and deformations, describes better the actual response of the plate-beams system and permits the evaluation of the shear forces at the interfaces, the knowledge of which is very important in the design of prefabricated ribbed plates.

Effects of the symmetry axis orientation of a TI overburden on seismic images

NASA Astrophysics Data System (ADS)

Chang, Chih-Hsiung; Chang, Young-Fo; Tseng, Cheng-Wei

2017-07-01

In active tectonic regions, the primary formations are often tilted and subjected to the processes of folding and/or faulting. Dipping formations may be categorised as tilted transverse isotropy (TTI). While carrying out hydrocarbon exploration in areas of orogenic structures, mispositioning and defocusing effects in apparent reflections are often caused by the tilted transverse isotropy of the overburden. In this study, scaled physical modelling was carried out to demonstrate the behaviours of seismic wave propagation and imaging problems incurred by transverse isotropic (TI) overburdens that possess different orientations of the symmetry axis. To facilitate our objectives, zero-offset reflections were acquired from four stratum-fault models to image the same structures that were overlain by a TI (phenolite) slab. The symmetry axis of the TI slab was vertical, tilted or horizontal. In response to the symmetry axis orientations, spatial shifts and asymmetrical diffraction patterns in apparent reflections were observed in the acquired profiles. Given the different orientations of the symmetry axis, numerical manipulations showed that the imaged events could be well described by theoretical ray paths computed by the trial-and-error ray method and Fermat's principle (TERF) method. In addition, outputs of image restoration show that the imaging problems, i.e. spatial shift in the apparent reflections, can be properly handled by the ray-based anisotropic 2D Kirchhoff time migration (RAKTM) method.

Parameter retrieval of chiral metamaterials based on the state-space approach.

PubMed

Zarifi, Davoud; Soleimani, Mohammad; Abdolali, Ali

2013-08-01

This paper deals with the introduction of an approach for the electromagnetic characterization of homogeneous chiral layers. The proposed method is based on the state-space approach and properties of a 4×4 state transition matrix. Based on this, first, the forward problem analysis through the state-space method is reviewed and properties of the state transition matrix of a chiral layer are presented and proved as two theorems. The formulation of a proposed electromagnetic characterization method is then presented. In this method, scattering data for a linearly polarized plane wave incident normally on a homogeneous chiral slab are combined with properties of a state transition matrix and provide a powerful characterization method. The main difference with respect to other well-established retrieval procedures based on the use of the scattering parameters relies on the direct computation of the transfer matrix of the slab as opposed to the conventional calculation of the propagation constant and impedance of the modes supported by the medium. The proposed approach allows avoiding nonlinearity of the problem but requires getting enough equations to fulfill the task which was provided by considering some properties of the state transition matrix. To demonstrate the applicability and validity of the method, the constitutive parameters of two well-known dispersive chiral metamaterial structures at microwave frequencies are retrieved. The results show that the proposed method is robust and reliable.

ENGINEERING DESIGN CRITERIA FOR SUB-SLAB DEPRESSURIZATION SYSTEMS IN LOW-PERMEABILTY SOLIDS

EPA Science Inventory

The report describes the development of engineering design criteria for the successful design, installation, and operation of sub-slab depressurization systems, based on radon (Rn) mitigation experience on 14 slab-on-grade houses in South Central Florida. The Florida houses are c...

Shear wave splitting and shear wave splitting tomography of the southern Puna plateau

NASA Astrophysics Data System (ADS)

Calixto, Frank J.; Robinson, Danielle; Sandvol, Eric; Kay, Suzanne; Abt, David; Fischer, Karen; Heit, Ben; Yuan, Xiaohui; Comte, Diana; Alvarado, Patricia

2014-11-01

We have investigated the seismic anisotropy beneath the Central Andean southern Puna plateau by applying shear wave splitting analysis and shear wave splitting tomography to local S waves and teleseismic SKS, SKKS and PKS phases. Overall, a very complex pattern of fast directions throughout the southern Puna plateau region and a circular pattern of fast directions around the region of the giant Cerro Galan ignimbrite complex are observed. In general, teleseismic lag times are much greater than those for local events which are interpreted to reflect a significant amount of sub and inner slab anisotropy. The complex pattern observed from shear wave splitting analysis alone is the result of a complex 3-D anisotropic structure under the southern Puna plateau. Our application of shear wave splitting tomography provides a 3-D model of anisotropy in the southern Puna plateau that shows different patterns depending on the driving mechanism of upper-mantle flow and seismic anisotropy. The trench parallel a-axes in the continental lithosphere above the slab east of 68W may be related to deformation of the overriding continental lithosphere since it is under compressive stresses which are orthogonal to the trench. The more complex pattern below the Cerro Galan ignimbrite complex and above the slab is interpreted to reflect delamination of continental lithosphere and upwelling of hot asthenosphere. The a-axes beneath the Cerro Galan, Cerro Blanco and Carachi Pampa volcanic centres at 100 km depth show some weak evidence for vertically orientated fast directions, which could be due to vertical asthenospheric flow around a delaminated block. Additionally, our splitting tomographic model shows that there is a significant amount of seismic anisotropy beneath the slab. The subslab mantle west of 68W shows roughly trench parallel horizontal a-axes that are probably driven by slab roll back and the relatively small coupling between the Nazca slab and the underlying mantle. In contrast, the subslab region (i.e. depths greater than 200 km) east of 68W shows a circular pattern of a-axes centred on a region with small strength of anisotropy (Cerro Galan and its eastern edge) which suggest the dominant mechanism is a combination of slab roll back and flow driven by an overlying abnormally heated slab or possibly a slab gap. There seems to be some evidence for vertical flow below the slab at depths of 200-400 km driven by the abnormally heated slab or slab gap. This cannot be resolved by the tomographic inversion due to the lack of ray crossings in the subslab mantle.

Tomography of the subducting Cocos plate in central Mexico using data from the installation of a prototype wireless seismic network: Images of a truncated slab

NASA Astrophysics Data System (ADS)

Husker, Allen Leroy, Jr.

The central Mexican subduction zone exhibits an oblique strike of the volcanic arc, the Trans-Mexican Volcanic Belt (TMVB), with respect to the trench, flat-slab subduction, and has no Wadati-Benioff zone. The oblique strike of the TMVB is explained by the changing rate of subduction at the trench. The shape of the slab beyond the flat slab section has been unknown until now due to a lack of seismicity, but inferred by the position of the volcanic arc. Here we use data from the Middle America Seismic Experiment (MASE) to image the slab both with tomography and inverting for a slab temperature model. MASE is a collaboration between the Center for Embedded Networked Sensing (CENS) at UCLA, the Universidad Nacional Autonoma de Mexico (UNAM), and the California Institute of Technology (CIT). The data used in this study was from the MASE seismic network. It consisted of 100 seismic stations running, in a line, every 5-6 km from Acapulco, north through TMVB, and to almost the Gulf of Mexico. Half of the seismic stations were the typical standalone style station. These stations were visited once a month to change memory disks and for maintenance. The other 50 stations were developed to send data wirelessly through the network to a base station where the data is linked to the Internet. The 50 stations, called the Wirelessly Linked Seismological Network (WiLSoN), utilize standard Internet tools and protocols to make it both robust and portable to other systems. WiLSoN is described and compared to the standalone stations. The time to permit and install WiLSoN was double that of the standalone network. However, the benefits of WiLSoN included near real-time data and knowledge of system health as compared to only once a month visits to collect data from the standalone stations. However, the data collected from the standalone sites was more complete than that collected from WiLSoN. The lack of data completeness is attributed to the development of both software and hardware for WiLSoN during the MASE experiment. The MASE data is used to perform a 2D P-wave tomography of the subducting Cocos plate. A seismicity study by Pardo and Suarez (1995) mapped a flat Cocos slab under the North America plate to 190 km inland. Our tomography shows the slab subduction continues from 250 km inland at a much steeper angle of 75°. The slab stops somewhere between 450 km and 550 km depth under the northern Trans-Mexican Volcanic Belt. The Farallon plate, from which the Cocos plate presumably broke, is not seen. P-wave travel times are also inverted for a 2D temperature model of the Cocos slab under Mexico. The temperature model from Davies and Stevenson (1992) is found to have unrealistic values in the case of a thin slab, so the diffusion equation is solved with their initial conditions to correct their solution to remove this limitation. The dipping portion of the slab begins 230 km inland, dip at an angle of 74 degrees from the surface, extend to 500 km depth, and have a thickness of 40 km. The model is extended to 21/2D by assuming the slab is infinite along its width. The strike of the slab is then solved for with the full 3D rays found from ray tracing through the iasp91 model. The strike of the dipping slab is found to be 108° clockwise from north, very similar to the strike of the TMVB. A model of the tectonic history is presented that combines those proposed by Ferrari (2004) and Gorbatov and Fukao (2005). At 25 Ma the volcanic arc moved inland marking the beginning of flat-slab subduction. At the same time a tear between the Cocos and Farallon initiated. The torsion from the tear squeezed the Cocos plate causing a flat-slab geometry. At 12.5 Ma another tear propagated along the flat Cocos slab removing the torsion causing uplift. The removal of the uplift caused the upper portion of the Cocos slab to sink and start rolling back until it reached the position where it is imaged in this study. The lack of a Wadati-Benioff zone is due to no deeper slab end which would normally elevate the deviatoric stress to levels that generate earthquakes.

DEVELOPMENT OF A SUB-SLAB AIR SAMPLING PROTOCOL TO SUPPORT ASSESSMENT OF VAPOR INTRUSION

EPA Science Inventory

The primary purpose of this research effort is to develop a methodology for sub-slab sampling to support the EPA guidance and vapor intrusion investigations after vapor intrusion has been established at a site. Methodologies for sub-slab air sampling are currently lacking in ref...

Possibility of sidewall collapse of underground structures due to loss of lateral support under internal blast loading.

DOT National Transportation Integrated Search

2014-03-01

For some immersed tube tunnels, the horizontal slab contributes to the structural integrity. If a train running on the slab were subjected to an explosion, which then failed a large area of the horizontal slab, the sidewall might yield under the late...

Slab track field test and demonstration program for shared freight and high-speed passenger service

DOT National Transportation Integrated Search

2010-08-01

Two types of slab tracks were installed on the High Tonnage Loop at the Facility for Accelerated Service Testing. Direct fixation slab track (DFST) and independent dual block track (IDBT) were installed into a 5-degree curve with 4-inch superelevatio...

Field evaluation of corrosion inhibitors for concrete. Interim report 1, Evaluation of exposure slabs repaired with corrosion inhibitors.

DOT National Transportation Integrated Search

1998-01-01

One hundred and fifty-six exposure slabs have been constructed with and without a variety of combinations of corrosion inhibiting admixtures and topically applied inhibitors. To accelerate corrosion one hundred and thirty-six of the slabs were constr...

Face pumping of thin, solid-state slab lasers with laser diodes.

PubMed

Faulstich, A; Baker, H J; Hall, D R

1996-04-15

A new technique for face pumping of slab lasers uses transfer of light from 10 quasi-cw laser diode bars through a slotted mirror into a rectangular, highly ref lective pump chamber, giving efficient multipass pumping of a thin Nd:glass slab laser. A slope efficiency of 28% and a maximum pulse energy of 65 mJ have been obtained, and gain and loss measurements with thickness t = 0.45-1.04 mm have confirmed the 1/t scaling of gain in thin slabs and the high efficiency of pump light transfer.

Comparison of Slab and Cylinder Expansion Test Geometries for PBX 9501

NASA Astrophysics Data System (ADS)

Jackson, Scott; Anderson, Eric; Aslam, Tariq; Whitley, Von

2017-06-01

The slab expansion test or ``sandwich test'' is the two-dimensional analog of the axisymmetric cylinder expansion test. The test consists of a high-aspect-ratio rectangular cuboid of high explosive with the two large sides confined by a thin metal confiner. Analysis of the confiner motion after the passage of the detonation yields the detonation product isentrope, which is a specialized form of the product equation of state. The slab expansion geometry inherently exhibits a lower product expansion rate and lower plastic work on the confiner than the cylinder expansion geometry. The slab geometry does, however, have a shorter test time. We review recent slab and cylinder expansion data with PBX 9501, the associated equation of state analysis, and the advantages of each geometry for different applications.

Geochemical evidence for mélange melting in global arcs

PubMed Central

Nielsen, Sune G.; Marschall, Horst R.

2017-01-01

In subduction zones, sediments and hydrothermally altered oceanic crust, which together form part of the subducting slab, contribute to the chemical composition of lavas erupted at the surface to form volcanic arcs. Transport of this material from the slab to the overlying mantle wedge is thought to involve discreet melts and fluids that are released from various portions of the slab. We use a meta-analysis of geochemical data from eight globally representative arcs to show that melts and fluids from individual slab components cannot be responsible for the formation of arc lavas. Instead, the data are compatible with models that first invoke physical mixing of slab components and the mantle wedge, widely referred to as high-pressure mélange, before arc magmas are generated. PMID:28435882

Asymptotic behavior of exact exchange potential of slabs

NASA Astrophysics Data System (ADS)

Engel, E.

2014-06-01

In this contribution the exact exchange potential vx of density functional theory is examined for slabs such as graphene, for which one has a Bravais lattice in the x-y directions, while the electrons are confined to the finite region -L≤z≤L in the z direction. It is demonstrated analytically that the exact vx behaves as -e2/z for z ≫L. This result extends the corresponding statement of Horowitz, Proetto, and Rigamonti [Phys. Rev. Lett. 97, 026802 (2006), 10.1103/PhysRevLett.97.026802] for jellium slabs to slabs with arbitrary periodic density distributions. Application of the exact exchange to a Si(111) slab (within the Krieger-Li-Iafrate approximation) indicates that the corrugation of the exact vx is more pronounced than that of the local density approximation for vx.

Optical bistability and multistability in a defect slab doped by GaAs/AlGaAs multiple quantum wells

NASA Astrophysics Data System (ADS)

Seyyed, Hossein Asadpour; G, Solookinejad; M, Panahi; E Ahmadi, Sangachin

2016-05-01

We proposed a new model for controlling the optical bistability (OB) and optical multistability (OM) in a defect slab doped with four-level GaAs/AlGaAs multiple quantum wells with 15 periods of 17.5 nm GaAs wells and 15-nm Al0.3 Ga0.7As barriers. The effects of biexciton energy renormalization, exciton spin relaxation, and thickness of the slab on the OB and OM properties of the defect slab were theoretically investigated. We found that the transition from OB to OM or vice versa is possible by adjusting the controllable parameters in a lab. Moreover, the transmission, reflection, and absorption properties of the weak probe light through the slab were also discussed in detail.

Frequency-selective near-field radiative heat transfer between photonic crystal slabs: a computational approach for arbitrary geometries and materials.

PubMed

Rodriguez, Alejandro W; Ilic, Ognjen; Bermel, Peter; Celanovic, Ivan; Joannopoulos, John D; Soljačić, Marin; Johnson, Steven G

2011-09-09

We demonstrate the possibility of achieving enhanced frequency-selective near-field radiative heat transfer between patterned (photonic-crystal) slabs at designable frequencies and separations, exploiting a general numerical approach for computing heat transfer in arbitrary geometries and materials based on the finite-difference time-domain method. Our simulations reveal a tradeoff between selectivity and near-field enhancement as the slab-slab separation decreases, with the patterned heat transfer eventually reducing to the unpatterned result multiplied by a fill factor (described by a standard proximity approximation). We also find that heat transfer can be further enhanced at selective frequencies when the slabs are brought into a glide-symmetric configuration, a consequence of the degeneracies associated with the nonsymmorphic symmetry group.

Geochemical evidence for mélange melting in global arcs.

PubMed

Nielsen, Sune G; Marschall, Horst R

2017-04-01

In subduction zones, sediments and hydrothermally altered oceanic crust, which together form part of the subducting slab, contribute to the chemical composition of lavas erupted at the surface to form volcanic arcs. Transport of this material from the slab to the overlying mantle wedge is thought to involve discreet melts and fluids that are released from various portions of the slab. We use a meta-analysis of geochemical data from eight globally representative arcs to show that melts and fluids from individual slab components cannot be responsible for the formation of arc lavas. Instead, the data are compatible with models that first invoke physical mixing of slab components and the mantle wedge, widely referred to as high-pressure mélange, before arc magmas are generated.

Electrically Conductive Plumes Rising From the Mantle Transition Zone in the Andean Back-Arc of Argentina from 30 to 40° South

NASA Astrophysics Data System (ADS)

Booker, J. R.; Burd, A. I.; Mackie, R.

2011-12-01

Three-dimensional interpretation of a large number of magnetotelluric sites in the Andean back arc of Argentina reveals at least two near-vertical conductive structures that extend from near the top of the mantle transition zone to the base of the lithosphere. Both are of limited horizontal extent. One is near the eastern-most extent of the Nazca flat-slab. It penetrates the most reasonable down-dip extension of the seismogenic subducted slab and suggests that the slab may not extend much deeper than about 200 km. The other is south of the flat-slab region and just east of the large Payun-Matru basaltic volcanic province. It arises roughly where the subducted slab would meet the transition zone if the slab extends linearly down from where it is seismogenic. It is tempting to conclude that both structures are partially molten plumes arising from the transition zone or deeper. The flat-slab plume has not penetrated the compressive lithosphere of the Sierras Pampeanas. The Payunia plume would logically seem connected to the geologically recent OIB-like volcanism near Payun Matru, but the shallow mantle structure beneath the area of most recent activity seems better explained by a connection to the Andean volcanism to the west.

Trench motion-controlled slab morphology and stress variations: Implications for the isolated 2015 Bonin Islands deep earthquake

NASA Astrophysics Data System (ADS)

Yang, Ting; Gurnis, Michael; Zhan, Zhongwen

2017-07-01

The subducted old and cold Pacific Plate beneath the young Philippine Sea Plate at the Izu-Bonin trench over the Cenozoic hosts regional deep earthquakes. We investigate slab morphology and stress regimes under different trench motion histories with mantle convection models. Viscosity, temperature, and deviatoric stress are inherently heterogeneous within the slab, which we link to the occurrence of isolated earthquakes. Models expand on previous suggestions that observed slab morphology variations along the Izu-Bonin subduction zone, exhibited as shallow slab dip angles in the north and steeper dip angles in the south, are mainly due to variations in the rate of trench retreat from the north (where it is fast) to the south (where it is slow). Geodynamic models consistent with the regional plate tectonics, including oceanic plate age, plate convergence rate, and trench motion history, reproduce the seismologically observed principal stress direction and slab morphology. We suggest that the isolated 680 km deep, 30 May 2015 Mw 7.9 Bonin Islands earthquake, which lies east of the well-defined Benioff zone and has its principal compressional stress direction oriented toward the tip of the previously defined Benioff zone, can be explained by Pacific slab buckling in response to the slow trench retreat.

MOBILE GAMMA IRRADIATORS FOR FRUIT PRODUCE (Engineering Materials)

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

1963-10-31

Mobile irradiators used for the radiopasteurization of strawberries, grapes, peaches, tomatoes, and lemons are described. The irradiators are mounted on trailers and each irradiator, including the trailer, weighs 70 to 80 tons. Radiatton doses range from 100,000 to 200,000 rads. Minimum production is 500 lb of fruit per hour. Drawings are included for four types of irradiators: the single-slab twopass, double-slab one-pass, single-slab four-pass, and line-source rotary. In the single-slab two-pass system, the packages make two passes in front of the source. The length of the packages is parallel to the direction of travel. The packages are irradiated on eachmore » side. This system is light in weight, has low capital cost, and is simple to fabricate. The double-slab one- pass system is the same as the above except the source strength is doubled and irradiation time is cut in half. The same arrangement is used in the single-slab four-pass system that is used in the singleslab two-pass system except the packages make two passes on each side of the source. The rotary system combines a linear and rotary motion to provide high dosage. It uses a small Co/sup 60/ source but costs more than a single-slab twopass system. (F.E.S.)« less

Development of a Rolling Process Design Tool for Use in Improving Hot Roll Slab Recovery (Quarterly Report: Q3-FY03)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Couch, R; Wang, P

2003-07-31

In this quarter, an FEM simulation has been performed to compare the shape of the deformed slab after the 8th reduction pass with the experimental metrology data provided by Alcoa Technical Center (ATC). Also, a bug in the thermal contact algorithm used in parallel processing have been identified and corrected for consistent thermal solutions between the rollers and the slab. The overall shape of the slab at the end of the 8th pass is shown in Figure 1. Comparison of the sectional views at the center plane along the length of the slab for both experiment and simulation, shows thatmore » the curvature at the slab mouth at the centerline is slightly higher than the experimental result as shown in Figure 2. We are currently focusing on tuning the parameter values used in the simulation and a more complete parametric study for validation is underway. Also, unexpected fracture occurred along the surface of the slab in the 9th pass as shown in Figure 3. We believe that the reason is due to previously noted inadequacies in the fracture model at low strain rates and high stress triaxiality. We are expecting to receive a modified fracture model based on additional experiment shortly from Alcoa.« less

An evaluation of controlled permeability formwork for long-term durability of structural concrete elements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suryavanshi, A.K.; Swamy, R.N.

1997-07-01

The long-term performance of a concrete slab (CPF slab) exposed to chloride ingress and atmospheric carbonation from the surface generated by controlled permeability formwork (CPF) is investigated. The results are compared with a similar slab exposed to long-term chloride ingress and atmospheric carbonation from the cast face (Control slab). Techniques such as X-ray diffraction (XRD) and differential thermal analyses (DTA) were employed to determine the resistance against carbonation while, mercury porosimetry was used for investigating the pore size distribution at the surface of the slabs. Amount of acid soluble chlorides was determined by using Volhard`s method. The CPF employed atmore » the bottom of the mould was not fully effective in its intended purpose of generating a permanent and dense impermeable concrete layer adjacent to it when the design water-cement (w/c) ration of the concrete mix was 0.60. This resulted in an almost similar extent of carbonation at the surface for both CPF and control slabs as shown by XRD and DTA studies. Similarly, there were no significant differences in the amount of chlorides and their depths of penetration for both CPF and control slabs, although the former was marginally superior in chloride penetration resistance at the surface.« less

Subduction zone evolution and low viscosity wedges and channels

NASA Astrophysics Data System (ADS)

Manea, Vlad; Gurnis, Michael

2007-12-01

Dehydration of subducting lithosphere likely transports fluid into the mantle wedge where the viscosity is decreased. Such a decrease in viscosity could form a low viscosity wedge (LVW) or a low viscosity channel (LVC) on top of the subducting slab. Using numerical models, we investigate the influence of low viscosity wedges and channels on subduction zone structure. Slab dip changes substantially with the viscosity reduction within the LVWs and LVCs. For models with or without trench rollback, overthickening of slabs is greatly reduced by LVWs or LVCs. Two divergent evolutionary pathways have been found depending on the maximum depth extent of the LVW and wedge viscosity. Assuming a viscosity contrast of 0.1 with background asthenosphere, models with a LVW that extends down to 400 km depth show a steeply dipping slab, while models with an LVW that extends to much shallower depth, such as 200 km, can produce slabs that are flat lying beneath the overriding plate. There is a narrow range of mantle viscosities that produces flat slabs (5 to10 × 10 19 Pa s) and the slab flattening process is enhanced by trench rollback. Slab can be decoupled from the overriding plate with a LVC if the thickness is at least a few 10 s of km, the viscosity reduction is at least a factor of two and the depth extent of the LVC is several hundred km. These models have important implications for the geochemical and spatial evolution of volcanic arcs and the state of stress within the overriding plate. The models explain the poor correlation between traditional geodynamic controls, subducting plate age and convergence rates, on slab dip. We predict that when volcanic arcs change their distance from the trench, they could be preceded by changes in arc chemistry. We predict that there could be a larger volatile input into the wedge when arcs migrate toward the trench and visa-versa. The transition of a subduction zone into the flat-lying regime could be preceded by changes in the volatile budget such that the dehydration front moves to shallower depths. Our flat-slab models shed some light on puzzling flat subduction systems, like in Central Mexico, where there is no deformation within the overriding plate above the flat segment. The lack of in-plane compression in Central Mexico suggests the presence of a low viscosity shear zone above the flat slab.

Lawsonite Microstructures and Fabric Development at the Slab-Mantle Interface

NASA Astrophysics Data System (ADS)

Fornash, K.; Whitney, D.; Teyssier, C. P.; Seaton, N. C.

2016-12-01

Lawsonite is of critical importance to element and water cycling in subduction zones because it has a high H2O content, is stable at high pressures, and is a significant reservoir for trace elements in HP/LT rocks. In addition, the presence, abundance, and crystallographic orientation of lawsonite can affect the deformation and rheological behavior of subducted oceanic crust and sediments, and may influence the seismic properties of subducted slabs. The scarcity of unaltered lawsonite in HP/LT rocks exhumed to the Earth's surface, particularly in eclogite, however, has prevented an understanding of the deformation behavior of lawsonite and the factors controlling the development of fabrics in lawsonite, which are important for understanding the effects of lawsonite on the physical properties of subducted slabs. One of the few places in the world with unaltered lawsonite in eclogite and blueschist facies rocks is the Sivrihisar Massif, Turkey, which contains a coherent sequence of lawsonite-bearing metabasaltic and metasedimentary rocks that were metamorphosed and deformed at the slab-mantle interface (45 - 80 km), and therefore provide an opportunity to systematically compare lawsonite fabrics in rocks with different modal amounts of rheologically significant minerals (e.g., glaucophane, omphacite, quartz), integrated with information about lawsonite crystal size, compositional zoning patterns, shape, and twinning. Studies to date of lawsonite CPO from natural lawsonite-bearing rocks have resulted in two patterns: one is characterized by a concentration of [001] axes parallel to lineation and the other is characterized by a concentration of [001] axes perpendicular to foliation. We have documented the first type in metabasalt and the second in quartzite, but other researchers have documented both types in metabasalt. Regardless of variations in lawsonite CPO or rock type, omphacite and glaucophane CPO remain consistent. Quartz c-axis patterns vary in eclogite- and blueschist-facies quartzite, although lawsonite CPO in quartzite does not vary. Samples in which lawsonite is polycrystalline or occurs as aggregates, tends to yield more diffuse patterns. Ongoing research investigates the controls on lawsonite CPO, and their consequences for subduction processes.

Crustal inheritance and arc magmatism: Magnetotelluric constraints from the Washington Cascades on top-down control

NASA Astrophysics Data System (ADS)

Bedrosian, P.; Peacock, J.; Bowles-martinez, E.; Schultz, A.; Hill, G.

2017-12-01

Worldwide, arc volcanism occurs along relatively narrow magmatic arcs, the locations of which are considered to mark the onset of dehydration reactions within the subducting slab. This `bottom-up' approach, in which the location of arc volcanism reflects where fluids and melt are generated, explains first-order differences in trench-to-arc distance and is consistent with known variations in the thermal structure and geometry of subducting slabs. At a finer scale, arc segmentation, magmatic gaps, and anomalous forearc and backarc magmatism are also frequently interpreted in terms of variations in slab geometry, composition, or thermal structure.The role of inherited crustal structure in controlling faulting and deformation is well documented; less well examined is the role of crustal structure in controlling magmatism. While the source distribution of melt and subduction fluids is critical to determining the location of arc magmatism, we argue that crustal structure provides `top-down' control on patterns or seismicity and deformation as well as the channeling and ascent of arc magmas. We present evidence within the Washington Cascades based upon correlation between a new three-dimensional resistivity model, potential-field data, seismicity, and Quaternary volcanism. We image a mid-Tertiary batholith, intruded within an Eocene crustal suture zone, and extending throughout much of the crustal column. This and neighboring plutons are interpreted to channel crustal fluids and melt along their margins within steeply dipping zones of marine to transitional metasedimentary rock. Mount St. Helens is interpreted to be fed by fluids and melt generated further east at greater slab depths, migrating laterally (underplating?) beneath the Spirit Lake batholith, and ascending through metasedimentary rocks within the brittle crust. At a regional scale, we argue that this concealed suture zone controls present-day deformation and seismicity as well as the distribution of forearc magmatism. More generally, our results highlight the control that inherited crustal structure has on both the location and style of arc magmatism. We also address divergent interpretations of the Southern Washington Cascades Conductor, which we show results from limited data density and modeling assumptions in previous studies.

Building characteristics associated with moisture related problems in 8,918 Swedish dwellings.

PubMed

Hägerhed-Engman, Linda; Bornehag, Carl-Gustaf; Sundell, Jan

2009-08-01

Moisture problems in buildings have in a number of studies been shown to increase the risk for respiratory symptoms. The study Dampness in Buildings and Health (DBH) was initiated with the aim to identify health relevant exposures related to dampness in buildings. A questionnaire study about home environment with a focus on dampness problems and health was conducted in one county of Sweden (8,918 homes, response rate 79%). Building characteristics that were associated with one or more of the dampness indicators were for single-family houses, older houses, flat-roofed houses built in the 1960s and 1970s, houses with a concrete slab on the ground that were built before 1983. Moreover, tenancy and earlier renovation due to mould or moisture problems was strongly associated with dampness. A perception of dry air was associated with window-pane condensation, e.g. humid indoor air.

Switches in subduction polarity, slab tearing and the opening of slab gaps along the Alpine chain - a view from the bottom up

NASA Astrophysics Data System (ADS)

Handy, M. R.; Ustaszewski, K. M.; Kissling, E. H.

2013-12-01

Kinematic reconstructions of the Alpine orogen from Late Cretaceous to present time reveal that slab tearing and switches of subduction polarity are related to two slab gaps presently imaged as low-velocity anomalies at the transition of the Eastern and Central Alps, and beneath the northern Dinarides. A lithosphere-scale transfer fault at the Alps-Dinarides join (ADT) linked S-directed subduction of the oceanic part of the European plate in the Alps with N-directed subduction of the continental part of the Adriatic plate in the Dinarides in Late Cretaceous to Paleogene time. Transfer faulting in the Dinarides was initially situated along a suture zone, then jumped westward no later than 40 Ma as thrusting and subduction affected more external units of the Alps and Dinarides. Late Eocene Alpine collision led to a slowing of Adria-Europe convergence and initial rupturing of the European and Adriatic slabs in Eocene-Oligocene time, when most of the oceanic lithosphere broke off. This thermally preconditioned the lithosphere for a radical reorganization of slabs and mantle flow in the Alpine domain beginning in early Miocene time. This included the onset of Carpathian rollback subduction, as well as counterclockwise rotation and N-ward subduction of Adriatic continental lithosphere into the space beneath the Eastern Alps that was vacated by foundering and renewed tearing of the European slab in Oligocene-early Miocene time. Our plate reconstructions indicate that this tear nucleated at the tip of a subducted sliver of European continental lithosphere coinciding with the present location of the narrow slab gap between the Eastern and Central Alps. This tear then propagated horizontally to the NE along the subducted boundary of the European margin and the Carpathian embayment of the Alpine Tethyan ocean. The surface response to slab tearing included peneplainization and uplift of part of the Eastern Alps. Transfer faulting along the ADT gave way to back-arc extension and strike-slip faulting behind the retreating Carpathian orogeny no later than 23 Ma. Continued NW-motion of the Adriatic microplate in Oligocene-Miocene time opened a gap along the former ADT which filled with upwelling asthenosphere. We speculate that this thermally eroded the Miocene slab beneath the northern Dinarides, giving rise to the present slab gap there. The forces governing motion of the Adriatic microplate changed both with time and the nature of the subducting lithosphere. From 84-35 Ma, the NW-retreat of the down-going European plate facilitated the independent motion of Adria at 1-2 cm/a with respect to Europe. Adria's motion may have been driven partly by suction behind this European slab which comprised mostly old oceanic lithosphere. With the onset of Alpine collision at c. 35 Ma, the slabs became gravitationally unstable and ruptured. N-ward subduction of a fragment of Adriatic continental lithosphere beneath the Eastern Alps in Miocene time was probably initiated by push from Africa and possibly enhanced by neutral to negative buoyancy of the slab itself which included dense lower crust of the Adriatic continental margin.

Kinematic Thermal Model for Tonga Descending Slab: A Case Study on the Influence of Velocity Boundary Layers

NASA Astrophysics Data System (ADS)

Zhang, K.; Wei, D.

2009-12-01

Within the core of a colder slab (e.g., the Tonga slab), the existence of metastable olivine (MO), extending deeper than the 410 km, has several important implications for understanding both the mechanism of deep earthquakes (>300 km) and the slab dynamics. The effect of subduction kinematics on the slab thermal structure has been widely investigated by prescribing Constant Velocity field for the subducting Slab (CVS-model), which may result in artificial computational interferences along the slab interfaces by accelerating the heating of subducting slabs. For the purpose of moderating the CVS effect and investigating the influence of metastable phase transformations on deep seismicity, we construct a 2-dimensional finite element thermal model for a 120 Ma-old 50° dipping oceanic lithosphere descending at 10 cm/yr with Velocity Boundary Layers (VBL-model), within which the velocities decrease from v to zero with the distance to the interface. The density anomalies for the VBL-model show significant variations (~100 kg/m3) at depths of both ~230 and ~410 km, whereas CVS-model shows anomalies above ~410 km. Thus, the VBL-model result is in better agreement with our knowledge of the subducting evolution that the density anomalies are primarily controlled by the conductive cooling and the phase transitions for the shallow depths of the slab and the transition zone, respectively. The VBL-model pressure anomalies also indicate that the negative buoyancy force causes the downdip tensional (DDT) earthquakes occurring above depth of ~230 km. At depths >410 km, the zonal distributed pressures of the VBL-model show negative and positive anomalies within the core and the outermost portion of slab, respectively, whereas the CVS-model produces negative pressure anomalies. The seismicity shows that down-dip compressional (DDC) and DDT deep earthquakes occur along the lower and upper interfaces of Tonga slab, whereas the P- and T-axes for the earthquakes in-between portion are interchangeable. The VBL model rather than CVS model produces MO wedge extending to depth as the deepest (>660 km) earthquakes. If there really exists MO at depths >660 km, these deepest earthquakes will be in agreement with the suggestion that the MO associated transformational faulting can occur for the exothermic Ol-Sp transition but not for the endothermic Sp-Pv+Mw change (Green, 2007), otherwise, other mechanisms should be responsible for them. Therefore, the phase boundaries are important for the buoyancy and stresses within slabs (e.g. Bina, 2001) and the VBL-model is more credible. Moreover, VBL-model results also indicate that MO within the transition zone in Tonga increases the positive buoyancy force acting on the slab and facilitates slab stagnation at 660 km depth, in agreement with the tomographic (van der Hilst et al., 1995) and seismological observations (Chen and Brudzinski, 2001). As the subducting materials accumulated over 660 km, the MO begins to transform to Sp and deepest earthquakes occur. If Sp further transforms to Pv+Mw, the flattened ‘slab’ would penetrate the 660 km due to the density increment of Sp transformation.

Reconstructing the Alps-Carpathians-Dinarides as a key to understanding switches in subduction polarity, slab gaps and surface motion

NASA Astrophysics Data System (ADS)

Handy, Mark R.; Ustaszewski, Kamil; Kissling, Eduard

2015-01-01

Palinspastic map reconstructions and plate motion studies reveal that switches in subduction polarity and the opening of slab gaps beneath the Alps and Dinarides were triggered by slab tearing and involved widespread intracrustal and crust-mantle decoupling during Adria-Europe collision. In particular, the switch from south-directed European subduction to north-directed "wrong-way" Adriatic subduction beneath the Eastern Alps was preconditioned by two slab-tearing events that were continuous in Cenozoic time: (1) late Eocene to early Oligocene rupturing of the oppositely dipping European and Adriatic slabs; these ruptures nucleated along a trench-trench transfer fault connecting the Alps and Dinarides; (2) Oligocene to Miocene steepening and tearing of the remaining European slab under the Eastern Alps and western Carpathians, while subduction of European lithosphere continued beneath the Western and Central Alps. Following the first event, post-late Eocene NW motion of the Adriatic Plate with respect to Europe opened a gap along the Alps-Dinarides transfer fault which was filled with upwelling asthenosphere. The resulting thermal erosion of the lithosphere led to the present slab gap beneath the northern Dinarides. This upwelling also weakened the upper plate of the easternmost part of the Alpine orogen and induced widespread crust-mantle decoupling, thus facilitating Pannonian extension and roll-back subduction of the Carpathian oceanic embayment. The second slab-tearing event triggered uplift and peneplainization in the Eastern Alps while opening a second slab gap, still present between the Eastern and Central Alps, that was partly filled by northward counterclockwise subduction of previously unsubducted Adriatic continental lithosphere. In Miocene time, Adriatic subduction thus jumped westward from the Dinarides into the heart of the Alpine orogen, where northward indentation and wedging of Adriatic crust led to rapid exhumation and orogen-parallel escape of decoupled Eastern Alpine crust toward the Pannonian Basin. The plate reconstructions presented here suggest that Miocene subduction and indentation of Adriatic lithosphere in the Eastern Alps were driven primarily by the northward push of the African Plate and possibly enhanced by neutral buoyancy of the slab itself, which included dense lower crust of the Adriatic continental margin.

The Effect of Slab Holes on the Surrounding Mantle Flow Field and the Surface from a Multi-Disciplinary Approach

NASA Astrophysics Data System (ADS)

Portner, D. E.; Kiraly, A.; Makushkina, A.; Parks, B. H.; Ghosh, T.; Haynie, K. L.; Metcalf, K.; Manga, M.; O'Farrell, K. A.; Moresi, L. N.; Jadamec, M. A.; Stern, R. J.

2017-12-01

Large-scale detachment of subducting slabs can have a significant geologic footprint by altering the slab-driven mantle flow field as hot subslab mantle can flow upward through the newly developed opening in the slab. The resulting increase in heat and vertical motion in the mantle wedge may contribute to volcanism and broad surface uplift. Recent geodynamic modeling results show that smaller tears and holes are similarly likely to form in many settings, such as where oceanic ridges or continental fragments subduct. High-resolution seismic tomography models are imaging an increasing number of these gaps and tears ranging in size from tens to hundreds of km in size, many of which occur proximal to alkali volcanism. Here we investigate the role of such gaps on the subduction-induced mantle flow field and related surface response. In particular, we address the relationships between slab hole size, depth, and distance from the slab edge and the magnitude of dynamic response of the mantle using analog experiments and numerical simulations. In the laboratory models, the subduction system is simplified to a two-layered Newtonian viscous sheet model. Our setup consists of a tank filled with glucose syrup and a plate made from silicon putty to model the upper mantle and subducting lithosphere, respectively. In each experiment, we pre-cut a rectangular hole with variable width into the silicon putty plate. Additionally, we perform a series of complementary numerical models using the Underworld geophysical modeling code to calculate the more detailed instantaneous mantle flow perturbation induced by the slab hole. Together, these results imply a strong effect of hole size on mantle flow. Similarly, the depth of the slab hole influences near-surface flow, with significant surface flow alteration when the hole is near the trench and diminishing surface deformation as the hole is dragged deeper into the mantle. The inferred consequence of the dependence of vertical mantle flux on slab hole position and size is that the induced surface response can vary based on slab hole parameters.

Unusually Deep Bonin Earthquake (M7.9) of May 30, 2015 Suggests that Stagnant Slab Transforms into Penetration Stage

NASA Astrophysics Data System (ADS)

Obayashi, M.; Fukao, Y.; Yoshimitsu, J.

2015-12-01

A great shock occurred at an unusual depth of 678 km far away from the well-defined Wadati-Benioff zone of the Izu-Bonin arc (Fig.1). To the north of this region the slab is stagnant above the 660 km discontinuity and to the south it penetrates the discontinuity (Fig.2). Thus, the slab in this region can be viewed as in a transitional state from the stagnant to penetrating slab. Here, the steeply dipping part of the slab bends sharply to horizontal and the great shock happened at the lowest corner of this bending. The CMT indicates a pure normal faulting with the trench-normal near horizontal tensional axis and the near vertical compressional axis (Fig.1). We suggest that this mechanism reflects a transitional state of slab deformation from the bending-dominant mode to the penetration-dominant mode. The mechanism is consistent with either of these two two modes. We show that the mechanism is also consistent with the resultant stress field generated by many deep shocks occurring along the Wadati-Benioff zone. The calculated stress field changes rapidly along a trench-normal profile at a depth of 680 km and becomes similar to that generated by the great shock at points near the hypocenter (Fig.3). Thus, the stress field due to the Wadati-Benioff zone earthquakes works to enhance the occurrence of deep shocks of the type of the 2015 great shock, which represents slab deformation associated with the transition from stagnant to penetrating slab.

Plume-stagnant slab-lithosphere interactions: Origin of the late Cenozoic intra-plate basalts on the East Eurasia margin

NASA Astrophysics Data System (ADS)

Kimura, Jun-Ichi; Sakuyama, Tetsuya; Miyazaki, Takashi; Vaglarov, Bogdan S.; Fukao, Yoshio; Stern, Robert J.

2018-02-01

Intra-plate basalts of 35-0 Ma in East Eurasia formed in a broad backarc region above the stagnant Pacific Plate slab in the mantle transition zone. These basalts show regional-scale variations in Nd-Hf isotopes. The basalts with the most radiogenic Nd-Hf center on the Shandong Peninsula with intermediate Nd-Hf at Hainan and Datong. The least radiogenic basalts occur in the perimeters underlain by the thick continental lithosphere. Shandong basalts possess isotopic signatures of the young igneous oceanic crust of the subducted Pacific Plate. Hainan and Datong basalts have isotopic signatures of recycled subduction materials with billions of years of storage in the mantle. The perimeter basalts have isotopic signatures similar to pyroxenite xenoliths from the subcontinental lithospheric mantle beneath East Eurasia. Hainan basalts exhibit the highest mantle potential temperature (Tp), while the Shandong basalts have the lowest Tp. We infer that a deep high-Tp plume interacted with the subducted Pacific Plate slab in the mantle transition zone to form a local low-Tp plume by entraining colder igneous oceanic lithosphere. We infer that the subducted Izanagi Plate slab, once a part of the Pacific Plate mosaic, broke off from the Pacific Plate slab at 35 Ma to sink into the lower mantle. The sinking Izanagi slab triggered the plume that interacted with the stagnant Pacific slab and caused subcontinental lithospheric melting. This coincided with formation of the western Pacific backarc marginal basins due to Pacific Plate slab rollback and stagnation.

The intermediate-depth Tonga double-seismic zone and relationship to slab thermal structure

NASA Astrophysics Data System (ADS)

Wei, S. S.; Wiens, D.; Van Keken, P. E.; Adams, A. N.; Cai, C.

2015-12-01

We used data from the ocean bottom seismographs and island-based stations deployed in the Tonga-Fiji area from 2009 to 2010 to investigate the seismicity of the Tonga subducting slab. We relocated 785 events from the Reviewed ISC Bulletin with local array data, 379 newly detected intermediate-depth events, as well as 1976-2012 events with Global Centroid-Moment-Tensor (CMT) solutions. The events were relocated with both local and teleseismic P, pP, and S arrivals using a hypocentroidal decomposition relative location algorithm. The results show a double-seismic zone (DSZ) with a separation of about 30 km along the Tonga slab within a depth range of about 70 - 300 km. The upper plane is more seismically active and characterized by downdip compressional stress whereas the lower plane is characterized by downdip tensional stress, consistent with the slab unbending model. Accordingly, focal mechanisms of the earthquakes along the surface of the slab show downdip extension above the depth of 80 km, but turn to compression below it, coinciding with the change of the slab dip angle from 30˚ to 60˚ at the same depth. The lower limit of the DSZ beneath Tonga is significantly deeper than that in Japan and Mariana (about 200 km), implying the importance of thermal variations in controlling the DSZ. Since the Tonga slab, with the fastest subduction rate, is cooler than other slabs, thermally controlled processes such as dehydration embrittlement can occur at greater depths, resulting in a deeper depth extent of the DSZ.

P-wave attenuation in the Pacific slab beneath northeastern Japan revealed by the spectral ratio of intraslab earthquakes

NASA Astrophysics Data System (ADS)

Shiina, Takahiro; Nakajima, Junichi; Matsuzawa, Toru

2018-05-01

We investigate P-wave attenuation, Qp-1, in the Pacific slab beneath northeastern (NE) Japan, adopting for the first time the spectral ratio technique for intraslab earthquakes. When seismograms of two earthquakes are recorded at a station and their ray paths to the station are largely overlapped, station-dependent amplification and structural effects on the overlapped rays can be canceled out from the ratio of the spectral amplitudes of the seismograms. Therefore, adopting the spectral ratio technique for intraslab earthquakes has a great advantage for the precise evaluation of Qp-1 in the slab because the structural effects above the slab, including the high-attenuation mantle wedge, are removed. For estimating the intraslab Qp-1, we determined corner frequency of the intraslab earthquakes using the S-coda wave spectral ratio as the first step. Then, we evaluated the inter-event path attenuation, Δt*, from the ratio of the spectral amplitudes of P waves. The obtained result shows that P-wave attenuation in the Pacific slab marks Qp-1 of 0.0015 (Qp of ∼670) at depths of 50-250 km. This indicates that the P-wave attenuation in the Pacific slab is weaker than that in the mantle wedge. The relatively high-Qp-1 is correlated with the distributions of intraslab earthquakes, suggesting that the P-wave amplitude is more attenuated around active seismicity zones in the slab. Therefore, our observations likely indicate the presence of fractures, hydrous minerals, and dehydrated fluid around seismogenic zones in the slab at intermediate depths.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sackett, S.J.

JASON solves general electrostatics problems having either slab or cylindrical symmetry. More specifically, it solves the self-adjoint elliptic equation, div . (KgradV) - ..gamma..V + rho = 0 in an aritrary two-dimensional domain. For electrostatics, V is the electrostatic potential, K is the dielectric tensor, and rho is the free-charge density. The parameter ..gamma.. is identically zero for electrostatics but may have a positive nonzero value in other cases (e.g., capillary surface problems with gravity loading). The system of algebraic equations used in JASON is generated by the finite element method. Four-node quadrilateral elements are used for most of themore » mesh. Triangular elements, however, are occasionally used on boundaries to avoid severe mesh distortions. 15 figures. (RWR)« less

Comptonization in Ultra-Strong Magnetic Fields: Numerical Solution to the Radiative Transfer Problem

NASA Technical Reports Server (NTRS)

Ceccobello, C.; Farinelli, R.; Titarchuk, L.

2014-01-01

We consider the radiative transfer problem in a plane-parallel slab of thermal electrons in the presence of an ultra-strong magnetic field (B approximately greater than B(sub c) approx. = 4.4 x 10(exp 13) G). Under these conditions, the magnetic field behaves like a birefringent medium for the propagating photons, and the electromagnetic radiation is split into two polarization modes, ordinary and extraordinary, that have different cross-sections. When the optical depth of the slab is large, the ordinary-mode photons are strongly Comptonized and the photon field is dominated by an isotropic component. Aims. The radiative transfer problem in strong magnetic fields presents many mathematical issues and analytical or numerical solutions can be obtained only under some given approximations. We investigate this problem both from the analytical and numerical point of view, provide a test of the previous analytical estimates, and extend these results with numerical techniques. Methods. We consider here the case of low temperature black-body photons propagating in a sub-relativistic temperature plasma, which allows us to deal with a semi-Fokker-Planck approximation of the radiative transfer equation. The problem can then be treated with the variable separation method, and we use a numerical technique to find solutions to the eigenvalue problem in the case of a singular kernel of the space operator. The singularity of the space kernel is the result of the strong angular dependence of the electron cross-section in the presence of a strong magnetic field. Results. We provide the numerical solution obtained for eigenvalues and eigenfunctions of the space operator, and the emerging Comptonization spectrum of the ordinary-mode photons for any eigenvalue of the space equation and for energies significantly lesser than the cyclotron energy, which is on the order of MeV for the intensity of the magnetic field here considered. Conclusions. We derived the specific intensity of the ordinary photons, under the approximation of large angle and large optical depth. These assumptions allow the equation to be treated using a diffusion-like approximation.

The slab geometry laser. I - Theory

NASA Technical Reports Server (NTRS)

Eggleston, J. M.; Kane, T. J.; Kuhn, K.; Byer, R. L.; Unternahrer, J.

1984-01-01

Slab geometry solid-state lasers offer significant performance improvements over conventional rod-geometry lasers. A detailed theoretical description of the thermal, stress, and beam-propagation characteristics of a slab laser is presented. The analysis includes consideration of the effects of the zig-zag optical path, which eliminates thermal and stress focusing and reduces residual birefringence.

Time-to-Corrosion of Reinforcing Steel in Concrete Slabs, Vol. 4: Galvanized Reinforcing Steel

DOT National Transportation Integrated Search

1981-12-01

Four-ft. by 5-ft. by 6-inch (1.2m x 1.5m x 0.15m) reinforced concrete slabs were fabricated, cured and subjected to 7 years of daily salting at an outdoor exposure yard. Subsequently, the slabs were modified and instrumented to allow direct measureme...

Collision-induced light scattering in a thin xenon layer between graphite slabs - MD study.

PubMed

Dawid, A; Górny, K; Wojcieszyk, D; Dendzik, Z; Gburski, Z

2014-08-14

The collision-induced light scattering many-body correlation functions and their spectra in thin xenon layer located between two parallel graphite slabs have been investigated by molecular dynamics computer simulations. The results have been obtained at three different distances (densities) between graphite slabs. Our simulations show the increased intensity of the interaction-induced light scattering spectra at low frequencies for xenon atoms in confined space, in comparison to the bulk xenon sample. Moreover, we show substantial dependence of the interaction-induced light scattering correlation functions of xenon on the distances between graphite slabs. The dynamics of xenon atoms in a confined space was also investigated by calculating the mean square displacement functions and related diffusion coefficients. The structural property of confined xenon layer was studied by calculating the density profile, perpendicular to the graphite slabs. Building of a fluid phase of xenon in the innermost part of the slot was observed. The nonlinear dependence of xenon diffusion coefficient on the separation distance between graphite slabs has been found. Copyright © 2014. Published by Elsevier B.V.

Fossil slabs attached to unsubducted fragments of the Farallon plate.

PubMed

Wang, Yun; Forsyth, Donald W; Rau, Christina J; Carriero, Nina; Schmandt, Brandon; Gaherty, James B; Savage, Brian

2013-04-02

As the Pacific-Farallon spreading center approached North America, the Farallon plate fragmented into a number of small plates. Some of the microplate fragments ceased subducting before the spreading center reached the trench. Most tectonic models have assumed that the subducting oceanic slab detached from these microplates close to the trench, but recent seismic tomography studies have revealed a high-velocity anomaly beneath Baja California that appears to be a fossil slab still attached to the Guadalupe and Magdalena microplates. Here, using surface wave tomography, we establish the lateral extent of this fossil slab and show that it is correlated with the distribution of high-Mg andesites thought to derive from partial melting of the subducted oceanic crust. We also reinterpret the high seismic velocity anomaly beneath the southern central valley of California as another fossil slab extending to a depth of 200 km or more that is attached to the former Monterey microplate. The existence of these fossil slabs may force a reexamination of models of the tectonic evolution of western North America over the last 30 My.

Parametric performance of circumferentially grooved heat pipes with homogeneous and graded-porosity slab wicks at cryogenic temperatures

NASA Technical Reports Server (NTRS)

Groll, M.; Pittman, R. B.; Eninger, J. E.

1975-01-01

A recently developed, potentially high-performance nonarterial wick has been extensively tested. This slab wick has an axially varying porosity which can be tailored to match the local stress imposed on the wick. The purpose of the tests was to establish the usefulness of the graded-porosity slab wick at cryogenic temperatures between 110 K and 260 K, with methane and ethane as working fluids. For comparison, a homogeneous (i.e., uniform porosity) slab wick was also tested. The tests included: (1) maximum heat pipe performance as a function of fluid inventory, (2) maximum performance as a function of operating temperature, (3) maximum performance as a function of evaporator elevation, and (4) influence of slab wick orientation on performance. The experimental data was compared with theoretical predictions obtained with the computer program GRADE.

Parametric performance of circumferentially grooved heat pipes with homogeneous and graded-porosity slab wicks at cryogenic temperatures. [methane and ethane working fluids

NASA Technical Reports Server (NTRS)

Groll, M.; Pittman, R. B.; Eninger, J. E.

1976-01-01

A recently developed, potentially high-performance nonarterial wick was extensively tested. This slab wick has an axially varying porosity which can be tailored to match the local stress imposed on the wick. The purpose of the tests was to establish the usefulness of the graded-porosity slab wick at cryogenic temperatures between 110 and 260 K, with methane and ethane as working fluids. For comparison, a homogeneous (i.e., uniform porosity) slab wick was also tested. The tests included: maximum heat pipe performance as a function of fluid inventory, maximum performance as a function of operating temperature, maximum performance as a function of evaporator elevation, and influence of slab wick orientation on performance. The experimental data were compared with theoretical predictions obtained with the GRADE computer program.

Avalanche weak layer shear fracture parameters from the cohesive crack model

NASA Astrophysics Data System (ADS)

McClung, David

2014-05-01

Dry slab avalanches release by mode II shear fracture within thin weak layers under cohesive snow slabs. The important fracture parameters include: nominal shear strength, mode II fracture toughness and mode II fracture energy. Alpine snow is not an elastic material unless the rate of deformation is very high. For natural avalanche release, it would not be possible that the fracture parameters can be considered as from classical fracture mechanics from an elastic framework. The strong rate dependence of alpine snow implies that it is a quasi-brittle material (Bažant et al., 2003) with an important size effect on nominal shear strength. Further, the rate of deformation for release of an avalanche is unknown, so it is not possible to calculate the fracture parameters for avalanche release from any model which requires the effective elastic modulus. The cohesive crack model does not require the modulus to be known to estimate the fracture energy. In this paper, the cohesive crack model was used to calculate the mode II fracture energy as a function of a brittleness number and nominal shear strength values calculated from slab avalanche fracture line data (60 with natural triggers; 191 with a mix of triggers). The brittleness number models the ratio of the approximate peak value of shear strength to nominal shear strength. A high brittleness number (> 10) represents large size relative to fracture process zone (FPZ) size and the implications of LEFM (Linear Elastic Fracture Mechanics). A low brittleness number (e.g. 0.1) represents small sample size and primarily plastic response. An intermediate value (e.g. 5) implies non-linear fracture mechanics with intermediate relative size. The calculations also implied effective values for the modulus and the critical shear fracture toughness as functions of the brittleness number. The results showed that the effective mode II fracture energy may vary by two orders of magnitude for alpine snow with median values ranging from 0.08 N/m (non-linear) to 0.18 N/m (LEFM) for median slab density around 200 kg/m3. Schulson and Duval (2009) estimated the fracture energy of solid ice (mode I) to be about 0.22-1 N/m which yields rough theoretical limits of about 0.05- 0.2 N/m for density 200 kg/m3 when the ice volume fraction is accounted for. Mode I results from lab tests (Sigrist, 2006) gave 0.1 N/m (200 kg/m3). The median effective mode II shear fracture toughness was calculated between 0.31 to 0.35 kPa(m)1/2 for the avalanche data. All the fracture energy results are much lower than previously calculated from propagation saw tests (PST) results for a weak layer collapse model (1.3 N/m) (Schweizer et al., 2011). The differences are related to model assumptions and estimates of the effective slab modulus. The calculations in this paper apply to quasi-static deformation and mode II weak layer fracture whereas the weak layer collapse model is more appropriate for dynamic conditions which follow fracture initiation (McClung and Borstad, 2012). References: Bažant, Z.P. et al. (2003) Size effect law and fracture mechanics of the triggering of dry snow slab avalanches, J. Geophys. Res. 108(B2): 2119, doi:10.1029/2002JB))1884.2003. McClung, D.M. and C.P. Borstad (2012) Deformation and energy of dry snow slabs prior to fracture propagation, J. Glaciol. 58(209), 2012 doi:10.3189/2012JoG11J009. Schulson, E.M and P. Duval (2009) Creep and fracture of ice, Cambridge University Press, 401 pp. Schweizer, J. et al. (2011) Measurements of weak layer fracture energy, Cold Reg. Sci. and Tech. 69: 139-144. Sigrist, C. (2006) Measurement of fracture mechanical properties of snow and application to dry snow slab avalanche release, Ph.D thesis: 16736, ETH, Zuerich: 139 pp.

Numerical models of the magmatic processes induced by slab breakoff

NASA Astrophysics Data System (ADS)

Freeburn, Rebecca; Bouilhol, Pierre; Maunder, Ben; Magni, Valentina; van Hunen, Jeroen

2017-11-01

After the onset of continental collision, magmatism often persists for tens of millions of years, albeit with a different composition, in reduced volumes, and with a more episodic nature and more widespread spatial distribution, compared to normal arc magmatism. Kinematic modelling studies have suggested that slab breakoff can account for this post-collisional magmatism through the formation of a slab window and subsequent heating of the overriding plate and decompression melting of upwelling asthenosphere, particularly if breakoff occurs at depths shallower than the overriding plate. To constrain the nature of any melting and the geodynamic conditions required, we numerically model the collision of two continental plates following a period of oceanic subduction. A thermodynamic database is used to determine the (de)hydration reactions and occurrence of melt throughout this process. We investigate melting conditions within a parameter space designed to generate a wide range of breakoff depths, timings and collisional styles. Under most circumstances, slab breakoff occurs deeper than the depth extent of the overriding plate; too deep to generate any decompressional melting of dry upwelling asthenosphere or thermal perturbation within the overriding plate. Even if slab breakoff is very shallow, the hot mantle inflow into the slab window is not sustained long enough to sufficiently heat the hydrated overriding plate to cause significant magmatism. Instead, for relatively fast, shallow breakoff we observe melting of asthenosphere above the detached slab through the release of water from the tip of the heating detached slab. Melting of the subducted continental crust during necking and breakoff is a more common feature and may be a more reliable indicator of the occurrence of breakoff. We suggest that magmatism from slab breakoff alone is unable to explain several of the characteristics of post-collisional magmatism, and that additional geodynamical processes need to be considered when interpreting magmatic observations.

Does slab-window opening cause uplift of the overriding plate? A case study from the Gulf of California

NASA Astrophysics Data System (ADS)

Mark, Chris; Chew, David; Gupta, Sanjeev

2017-11-01

Complete subduction of an oceanic plate results in slab-window opening. A key uncertainty in this process is whether the higher heat flux and asthenospheric upwelling conventionally associated with slab-window opening generate a detectable topographic signature in the overriding plate. We focus on the Baja California Peninsula, which incorporates the western margin of the Gulf of California rift. The topography and tectonics of the rift flank along the peninsula are strongly bimodal. North of the Puertecitos accommodation zone, the primary drainage divide attains a mean elevation of ca. 1600 m above sea level (asl), above an asthenospheric slab-window opened by Pacific-Farallon spreading ridge subduction along this section of the trench at ca. 17-15 Ma. To the south, mean topography decreases abruptly to ca. 800 m asl (excluding the structurally distinct Los Cabos block at the southern tip of the peninsula), above fragments of the oceanic Farallon slab which stalled following slab tear-off at ca. 15-14 Ma. Along the peninsula, a low-relief surface established atop Miocene subduction-related volcaniclastic units has been incised by a west-draining canyon network in response to uplift. These canyons exhibit cut-and-fill relationships with widespread post-subduction lavas. Here, we utilise LANDSAT and digital elevation model (DEM) data, integrated with previously published K-Ar and 40Ar/39Ar lava crystallisation ages, to constrain the onset of rift flank uplift to ca. 9-5 Ma later than slab-window formation in the north and ca. 11-10 Ma later in the south. These greatly exceed response time estimates of ca. 2 Ma or less for uplift triggered by slab-window opening. Instead, uplift timing of the high-elevation northern region is consistent with lower-lithospheric erosion driven by rift-related convective upwelling. To the south, stalled slab fragments likely inhibited convective return flow, preventing lithospheric erosion and limiting uplift to the isostatic response to crustal unloading during rifting.

Thermal evolution of flattening slab and formation of wet plume: Insight into intraplate volcanism in East Asia

NASA Astrophysics Data System (ADS)

He, L.

2016-12-01

Geophysical observations imply the intraplate volcanism in East Asia is related to dehydration of slab stagnating in the transition zone. To better understand the dynamics of such process, a thermochemical mantle convection model is constructed to simulate numerically the thermal evolution of slab and the transportation of water in the process of subduction. Equation of water transfer is explicitly included, and water effects on density and viscosity are considered. Modeling results indicate that behavior of water transport relates closely to the transient thermal state and viscosities both of the slab and the surrounding mantle. Generally, initiation of wet plume is mainly influenced by the viscosity of the wet layer in the uppermost slab, whereas the horizontal distance of water transport and its ascending rate is affected strongly by the viscosity of the big mantle wedge. Whether water can be carried successfully by slab into the mantle transition zone and trigger wet plume at the surface of flattening slab depends on the viscosity contrast between wet layer and surrounding mantle. The complex fluid flow superposed by corner flow and free thermal convection controls the water transport pattern in the upper mantle. Modeling results together with previous modeling infer three stages of water circulation in the big mantle wedge: 1) water is brought into the mantle transition zone by downward subducting slab when water layer viscosity is much higher than the wedge viscosity, otherwise water is released at shallow depth near wedge tip; 2) wet plume generates from surface of warm flattening slab if containing water, which arrives at the lithospheric base and induces melting; and 3) water spreads all over the big mantle wedge, mantle convection within the big mantle wedge becomes more active, leading to upwelling of asthenosphere and erosion of the overriding continental lithosphere. Wet plume from the flattening Pacific Plate can explain the intraplate Cenozoic volcanoes in East Asia.

Slab rupture and delamination under the Betics and Rif constrained from receiver functions

NASA Astrophysics Data System (ADS)

Mancilla, Flor de Lis; Booth-Rea, Guillermo; Stich, Daniel; Pérez-Peña, José Vicente; Morales, José; Azañón, José Miguel; Martin, Rosa; Giaconia, Flavio

2015-11-01

We map the lithospheric structure under the westernmost Mediterranean convergent setting interpreting P-receiver functions obtained from a dense seismic network. No orogenic root occurs under the eastern and great part of the central Betics. However, the subducted South Iberian continental lithosphere is found beneath the western Betics where the Iberian Moho reaches depths of approximately 65 km, dipping gently towards the SE. Meanwhile, at the Rif, strong crustal and lithospheric thickness contrasts occur across the Nekor NW-SE sinistral fault that overlies the region of present slab tearing. East of the Nekor fault there is no orogenic root and the crust has been thinned to approximately 22 km, whilst to the west the crust reaches 55 km thickness and the Maghrebian continental lithosphere is attached to the lithospheric slab imaged by tomography under the Alboran basin. These data suggest that subduction rollback under the Alboran and Algerian basins, together with continental slab tearing or detachment producing edge delamination under the Betics and Rif have been the main tectonic mechanisms driving extension, magmatism and regional uplift in the westernmost Mediterranean since the Late Miocene until present. The surface expression of edge-delamination and slab tearing is marked by regional uplift, denudation of HP rocks in elongated core-complex type domes, late Miocene volcanism in the Eastern Betics and Rif, and by large NE-SW strike-slip transfer faults like the Alpujarras, Crevillente, Torcal or Nekor faults that accommodate strong gradients in crustal displacements. The Iberian slab is still attached to the oceanic slab imaged under the Alboran basin at the western Betics where intermediate depth seismicity, recent dextral strike-slip faulting and folding, could reflect slab tearing. Meanwhile, active faulting and differential GPS-measured displacements would mark slab tearing beneath the Rif coinciding with the trace of the sinistral Nekor fault.

Slab Geometry and Stress State of the Southwestern Colombia Subduction Zone

NASA Astrophysics Data System (ADS)

Chang, Ying

A high rate of intermediate-depth earthquakes is concentrates in the Cauca cluster (3.5°N-5.5°N) and isolated from nearby seismicity in the southwestern Colombia subduction zone. Previously-studied nests of intermediate-depth earthquakes show that a high seismicity rate is often associated with a slab tear, detachment, or contortion. The cause of the less-studied Cauca cluster is unknown. To investigate the cause, we image the slab geometry using precise relative locations of intermediate-depth earthquakes. We use the earthquake catalog produced and seismic waveforms recorded by the Colombian National Seismic Network from January 2010 to March 2014. We calculate the focal mechanisms to examine whether the earthquakes reactivate pre-existing faults or form new fractures. The focal mechanisms are inverted for the intraslab stress field to check the stress guide hypothesis and to evaluate the stress orientations with regard to the change in the slab geometry. The earthquake relocations indicate that the Cauca segment has a continuous 20 km thick seismic zone and increases in dip angle from north to south. Two 40-km-tall fingers of earthquakes extend out of the slab and into the mantle wedge. Different from the previously-studied nests, the Cauca cluster does not correspond to slab contortions or tearing. The cluster may be associated with a high amount of dehydrated fluid. The determined focal mechanisms of 69 earthquakes have various types and variably-oriented nodal planes, corresponding to the reactivation of pre-existing faults and the formation of new fractures. The results of stress inversion show that the extensional axis in the northern Cauca segment is in the plane of the slab and 25° from the downdip direction, and the southern part has along-strike extension. The compression is subnormal to the plane of the slab. The stress field supports the stress guide hypothesis and shows a consistent rotation with increase in slab dip angle.

Self-Sustained Mode-3 Tear Controls Dynamics of Narrow Retreating Subduction Zones

NASA Astrophysics Data System (ADS)

Munch, J.; Gerya, T.; Ueda, K.

2017-12-01

The Caribbean oroclinal basin exhibits several narrow retreating slabs in an oceanic domain. The slabs show a curved shape associated to a bent topography (trench). We propose that the curvature of the topography depends on slab retreat mechanisms following mode-3 tearing at the edges of the slab (out of the plane fracture propagation). While first-order characteristics have been principally reproduced in self-sustained subduction initiation models (Gerya et al., 2015, Nature, 527, 221-225), the relevant observations have not been quantified and the exact mechanism is not understood. In this work, we study the long-term 3D evolution of narrowing oceanic subduction zones during retreat, and investigate the link between mode-3 tear and orocline formation. Numerical experiments are carried out with a thermo-mechanical 3D finite-difference code. To allow the observation of developing topography, the precise location of the internal surface and its evolution by material diffusion is tracked. Retreating subduction is facilitated via a strong age contrast between a young lithosphere window enclosed by shear zones and the surrounding lithosphere. By varying the length and thickness of the shear zones and location of the age transition, the influence of these parameters on the tearing process and the development of topography is assessed. Experiments trigger subduction initiation and slab retreat via fracture zone collapse and spontaneous paired mode-3 tear propagation within the oceanic plate interior. Narrow retreating subducting slabs form as a natural result of the spontaneous paired tearing process. A curved trench forms along with slab retreat. Topography evolution and tearing trajectory appear to be dependent on the initial shear zones and young window dimensions. We also note a strong narrowing of the slab during the retreat (several tens of kilometers over 800 km of retreat). Overall, results indicate that narrowing of retreating slabs is a self-consistent consequence of tear propagation dynamics. This plate tearing mechanism may control dynamics of other narrow retreating subduction zones worldwide.

Endocytic Machinery Protein SlaB Is Dispensable for Polarity Establishment but Necessary for Polarity Maintenance in Hyphal Tip Cells of Aspergillus nidulans▿†

PubMed Central

Hervás-Aguilar, América; Peñalva, Miguel A.

2010-01-01

The Aspergillus nidulans endocytic internalization protein SlaB is essential, in agreement with the key role in apical extension attributed to endocytosis. We constructed, by gene replacement, a nitrate-inducible, ammonium-repressible slaB1 allele for conditional SlaB expression. Video microscopy showed that repressed slaB1 cells are able to establish but unable to maintain a stable polarity axis, arresting growth with budding-yeast-like morphology shortly after initially normal germ tube emergence. Using green fluorescent protein (GFP)-tagged secretory v-SNARE SynA, which continuously recycles to the plasma membrane after being efficiently endocytosed, we establish that SlaB is crucial for endocytosis, although it is dispensable for the anterograde traffic of SynA and of the t-SNARE Pep12 to the plasma and vacuolar membrane, respectively. By confocal microscopy, repressed slaB1 germlings show deep plasma membrane invaginations. Ammonium-to-nitrate medium shift experiments demonstrated reversibility of the null polarity maintenance phenotype and correlation of normal apical extension with resumption of SynA endocytosis. In contrast, SlaB downregulation in hyphae that had progressed far beyond germ tube emergence led to marked polarity maintenance defects correlating with deficient SynA endocytosis. Thus, the strict correlation between abolishment of endocytosis and disability of polarity maintenance that we report here supports the view that hyphal growth requires coupling of secretion and endocytosis. However, downregulated slaB1 cells form F-actin clumps containing the actin-binding protein AbpA, and thus F-actin misregulation cannot be completely disregarded as a possible contributor to defective apical extension. Latrunculin B treatment of SlaB-downregulated tips reduced the formation of AbpA clumps without promoting growth and revealed the formation of cortical “comets” of AbpA. PMID:20693304

An exact plane-stress solution for a class of problems in orthotropic elasticity

NASA Technical Reports Server (NTRS)

Erb, D. A.; Cooper, P. A.; Weisshaar, T. A.

1982-01-01

An exact solution for the stress field within a rectangular slab of orthotropic material is found using a two dimensional Fourier series formulation. The material is required to be in plane stress, with general stress boundary conditions, and the principle axes of the material must be parallel to the sides of the rectangle. Two load cases similar to those encountered in materials testing are investigated using the solution. The solution method has potential uses in stress analysis of composite structures.

Propagation of diffuse light in a turbid medium with multiple spherical inhomogeneities.

PubMed

Pustovit, Vitaliy N; Markel, Vadim A

2004-01-01

We develop a fast and accurate solver for the forward problem of diffusion tomography in the case of several spherical inhomogeneities. The approach allows one to take into account multiple scattering of diffuse waves between different inhomogeneities. Theoretical results are illustrated with numerical examples; excellent numerical convergence and efficiency are demonstrated. The method is generalized for the case of additional planar diffuse-nondiffuse interfaces and is therefore applicable to the half-space and slab imaging geometries.

Interaction of an ion bunch with a plasma slab

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krasovitskiy, V. B., E-mail: krasovit@mail.ru; Turikov, V. A.

2016-11-15

Charge neutralization of a short ion bunch passing through a plasma slab is studied by means of numerical simulation. It is shown that a fraction of plasma electrons are trapped by the bunch under the action of the collective charge separation field. The accelerated electrons generated in this process excite beam−plasma instability, thereby violating the trapping conditions. The process of electron trapping is also strongly affected by the high-frequency electric field caused by plasma oscillations at the slab boundaries. It is examined how the degree of charge neutralization depends on the parameters of the bunch and plasma slab.

Light-assisted templated self assembly using photonic crystal slabs.

PubMed

Mejia, Camilo A; Dutt, Avik; Povinelli, Michelle L

2011-06-06

We explore a technique which we term light-assisted templated self-assembly. We calculate the optical forces on colloidal particles over a photonic crystal slab. We show that exciting a guided resonance mode of the slab yields a resonantly-enhanced, attractive optical force. We calculate the lateral optical forces above the slab and predict that stably trapped periodic patterns of particles are dependent on wavelength and polarization. Tuning the wavelength or polarization of the light source may thus allow the formation and reconfiguration of patterns. We expect that this technique may be used to design all-optically reconfigurable photonic devices.

Seismic anisotropy and mantle flow below subducting slabs

NASA Astrophysics Data System (ADS)

Walpole, Jack; Wookey, James; Kendall, J.-Michael; Masters, T.-Guy

2017-05-01

Subduction is integral to mantle convection and plate tectonics, yet the role of the subslab mantle in this process is poorly understood. Some propose that decoupling from the slab permits widespread trench parallel flow in the subslab mantle, although the geodynamical feasibility of this has been questioned. Here, we use the source-side shear wave splitting technique to probe anisotropy beneath subducting slabs, enabling us to test petrofabric models and constrain the geometry of mantle fow. Our global dataset contains 6369 high quality measurements - spanning ∼ 40 , 000 km of subduction zone trenches - over the complete range of available source depths (4 to 687 km) - and a large range of angles in the slab reference frame. We find that anisotropy in the subslab mantle is well characterised by tilted transverse isotropy with a slow-symmetry-axis pointing normal to the plane of the slab. This appears incompatible with purely trench-parallel flow models. On the other hand it is compatible with the idea that the asthenosphere is tilted and entrained during subduction. Trench parallel measurements are most commonly associated with shallow events (source depth < 50 km) - suggesting a separate region of anisotropy in the lithospheric slab. This may correspond to the shape preferred orientation of cracks, fractures, and faults opened by slab bending. Meanwhile the deepest events probe the upper lower mantle where splitting is found to be consistent with deformed bridgmanite.

En face OCT in Stargardt disease.

PubMed

Sodi, Andrea; Mucciolo, Dario Pasquale; Cipollini, Francesca; Murro, Vittoria; Caporossi, Orsola; Virgili, Gianni; Rizzo, Stanislao

2016-09-01

To evaluate the structural features of the macular region by enface OCT imaging in patients with clinical diagnosis of Stargardt disease, confirmed by the detection of ABCA4 mutations. Thirty-two STGD patients were included in the study for a total of 64 eyes. All patients received a comprehensive ophthalmological examination, color fundus photography, fundus auto-fluorescence imaging and OCT. Five OCT scans were considered: ILM and RPE scans (both automatically obtained from the instrument), above-RPE slab, photoreceptor slab and sub-RPE slab (these last three manually obtained). ILM scans showed evident radial folds on the retinal surface in 8/64 eyes (12.5 %). In 6 of the 7 patients, these vitreo-retinal interface abnormalities were unilateral. The photoreceptor slab showed some macular alterations ranging from dis-homogeneous, hypo-reflective abnormalities (7/64 eyes, 11 %) to a homogeneous, well-defined, roundish, hypo-reflective area (17/64 eyes, 27 %) in all the eyes. The sub-RPE slab showed a centrally evident, hyper-reflective abnormality in 58/64 eyes (90.6 %). Superimposing the sub-RPE slab over the images corresponding to the photoreceptor slab, the area of the photoreceptor atrophy sharply exceeded that of the RPE atrophy (44/46 eyes, 96 %). Enface OCT proved to be a clinically useful tool for the management of STGD patients, illustrating in vivo the structural abnormalities of the different retinal layers.

On the consistency of tomographically imaged lower mantle slabs

NASA Astrophysics Data System (ADS)

Shephard, Grace E.; Matthews, Kara J.; Hosseini, Kasra; Domeier, Mathew

2017-04-01

Over the last few decades numerous seismic tomography models have been published, each constructed with choices of data input, parameterization and reference model. The broader geoscience community is increasingly utilizing these models, or a selection thereof, to interpret Earth's mantle structure and processes. It follows that seismically identified remnants of subducted slabs have been used to validate, test or refine relative plate motions, absolute plate reference frames, and mantle sinking rates. With an increasing number of models to include, or exclude, the question arises - how robust is a given positive seismic anomaly, inferred to be a slab, across a given suite of tomography models? Here we generate a series of "vote maps" for the lower mantle by comparing 14 seismic tomography models, including 7 s-wave and 7 p-wave. Considerations include the retention or removal of the mean, the use of a consistent or variable reference model, the statistical value which defines the slab "contour", and the effect of depth interpolation. Preliminary results will be presented that address the depth, location and degree of agreement between seismic tomography models, both for the 14 combined, and between the p-waves and s-waves. The analysis also permits a broader discussion of slab volumes and subduction flux. And whilst the location and geometry of slabs, matches some the documented regions of long-lived subduction, other features do not, illustrating the importance of a robust approach to slab identification.

A Physical Model to Study the Effects of Nozzle Design on Dispersed Two-Phase Flows in a Slab Mold Casting Ultra-Low-Carbon Steels

NASA Astrophysics Data System (ADS)

Salazar-Campoy, María M.; Morales, R. D.; Nájera-Bastida, A.; Calderón-Ramos, Ismael; Cedillo-Hernández, Valentín; Delgado-Pureco, J. C.

2018-04-01

The effects of nozzle design on dispersed, two-phase flows of the steel-argon system in a slab mold are studied using a water-air model with particle image velocimetry and ultrasound probe velocimetry techniques. Three nozzle designs were tested with the same bore size and different port geometries, including square (S), special bottom design with square ports (U), and circular (C). The meniscus velocities of the liquid increase two- or threefold in two-phase flows regarding one-phase flows using low flow rates of the gas phase. This effect is due to the dragging effects on bubbles by the liquid jets forming two-way coupled flows. Liquid velocities (primary phase) along the narrow face of the mold also are higher for two-phase flows. Flows using nozzle U are less dependent on the effects of the secondary phase (air). The smallest bubble sizes are obtained using nozzle U, which confirms that bubble breakup is dependent on the strain rates of the fluid and dissipation of kinetic energy in the nozzle bottom and port edges. Through dimensionless analysis, it was found that the bubble sizes are inversely proportional to the dissipation rate of the turbulent kinetic energy, ɛ 0.4. A simple expression involving ɛ, surface tension, and density of metal is derived to scale up bubble sizes in water to bubble sizes in steel with different degrees of deoxidation. The validity of water-air models to study steel-argon flows is discussed. Prior works related with experiments to model argon bubbling in steel slab molds under nonwetting conditions are critically reviewed.

Translational Response of Toe-Restrained Retaining Walls to Earthquake Ground Motions Using CorpsWallSlip (CWSlip)

DTIC Science & Technology

2007-06-01

corresponding software developed for the translational response of rock- founded retaining walls buttressed at their toe by a reinforced concrete slab...by a Reinforced Concrete Slab ...........................................................................................................32 2.1...2.5 New translational analysis model of a wall retaining a partially submerged backfill and buttressed by a reinforced concrete slab

Sensor4PRI: A Sensor Platform for the Protection of Railway Infrastructures

PubMed Central

Cañete, Eduardo; Chen, Jaime; Díaz, Manuel; Llopis, Luis; Rubio, Bartolomé

2015-01-01

Wireless Sensor Networks constitute pervasive and distributed computing systems and are potentially one of the most important technologies of this century. They have been specifically identified as a good candidate to become an integral part of the protection of critical infrastructures. In this paper we focus on railway infrastructure protection and we present the details of a sensor platform designed to be integrated into a slab track system in order to carry out both installation and maintenance monitoring activities. In the installation phase, the platform helps operators to install the slab tracks in the right position. In the maintenance phase, the platform collects information about the structural health and behavior of the infrastructure when a train travels along it and relays the readings to a base station. The base station uses trains as data mules to upload the information to the internet. The use of a train as a data mule is especially suitable for collecting information from remote or inaccessible places which do not have a direct connection to the internet and require less network infrastructure. The overall aim of the system is to deploy a permanent economically viable monitoring system to improve the safety of railway infrastructures. PMID:25734648

Seismic tomographic constraints on plate-tectonic reconstruction of Nazca subduction under South America since late Cretaceous (~80 Ma)

NASA Astrophysics Data System (ADS)

Chen, Yi-Wei; Wu, Jonny; Suppe, John; Liu, Han-Fang

2016-04-01

Our understanding of the global plate tectonics is based mainly on seafloor spreading and hotspot data obtained from the present earth surface, which records the growth of present ocean basins. However, in convergent tectonic settings vast amounts of lithosphere has been lost to subduction, contributing to increasing uncertainty in plate reconstruction with age. However, subducted lithosphere imaged in seismic tomography provides important information. By analyzing subducted slabs we identify the loci of subduction and assess the size and shape of subducted slabs, giving better constrained global plate tectonic models. The Andean margin of South America is a classic example of continuous subduction up to the present day, providing an opportunity to test the global plate prediction that ~24×10e6 km2 (4.7% of earth surface) lithosphere has been subducted since ~80 Ma. In this study, we used 10 different global seismic tomographies and Benioff zone seismicity under South America. To identify slabs, we first compared all data sets in horizontal slices and found the subducted Nazca slab is the most obvious structure between the surface and 750 km depth, well imaged between 10°N and 30°S. The bottom of the subducted Nazca slab reaches its greatest depth at 1400 km at 3°N (Carnegie Andes) and gradually shallows towards the south with 900 km minimum depth at 30°S (Pampean Andes). To assess the undeformed length of subducted slab, we used a refined cross-sectional area unfolding method from Wu et al. (in prep.) in the MITP08 seismic tomography (Li et al., 2008). Having cut spherical-Earth tomographic profiles that parallel to the Nazca-South America convergence direction, we measured slab areas as a function of depth based on edges defined by steep velocity gradients, calculating the raw length of the slab by the area and dividing an assumed initial thickness of oceanic lithosphere of 100km. Slab areas were corrected for density based on the PREM Earth model (Dziewonski and Anderson, 1981). We found the unfolded length of the Nazca slab is 7000km at 5°N and gradually decreases to 4700 km at 30°S, with total area of ~24×10e6 km2. Finally, we imported our unfolded Nazca slab into Gplates software to reconstruct its tectonic evolution, using the Seton et al. (2012) and Gibbons et al. (2015) global plate model. We find that our unfolded base of the Nazca slab fits tightly against South America at ~80 Ma if the pre-deformed South America margin of McQuarrie (2002) is used. This close fit implies a plate reorganization at the South American margin, marking the beginning of Nazca subduction at ~80 Ma. This observation is in agreement with a beginning of Andian magmatism ~80 Ma, following a 80-100 Ma hiatus in magmatism (Haschke et al., 2002). This result illustrates the importance of subducted-slab constraints in convergent plate-tectonic reconstruction. Our study also provides tracers for mantle flow yielding Nazca slab sinking rates between 1.2 cm/yr and 1.6 cm/yr, which are similar to other global results.

A Detailed 3D Seismic Velocity Structure of the Subducting Pacific Slab Beneath Hokkaido, Tohoku and Kanto, Japan, by Double-Difference Tomography

NASA Astrophysics Data System (ADS)

Tsuji, Y.; Nakajima, J.; Kita, S.; Okada, T.; Matsuzawa, T.; Hasegawa, A.

2007-12-01

Three-dimensional heterogeneous structure beneath northeastern (NE) Japan has been investigated by previous studies and an inclined seismic low-velocity zone is imaged in the mantle wedge sub-parallel to the down-dip direction of the subducting slab (Zhao et al., 1992, Nakajima et al., 2001). However, the heterogeneous structure within the slab has not been well studied even though it is very important to understand the whole process of water transportation from the slab to the surface. Here we show a detailed 3D seismic velocity structure within the subducted Pacific slab around Japan and propose a water-transportation path from the slab to the mantle wedge. In this study, we estimated 3D velocity structure within the Pacific slab by the double-difference tomography (Zhang and Thurber, 2003). We divided the study area, from Hokkaido to Kanto, into 6 areas due to the limitation of memory and computation time. In each area, arrival-time data of 7,500-17,000 events recorded at 70-170 stations were used in the analysis. The total number of absolute travel-time data was about 140,000-312,000 for P wave and 123,000-268,000 for S wave, and differential data were about 736,000-1,920,000 for P wave and 644,000-1,488,000 for S wave. Horizontal and vertical grid separations are 10-25 km and 6.5 km, respectively. RMS residuals of travel times for P wave decreased from 0.23s to 0.09s and for S wave from 0.35s to 0.13s. The obtained results are as follows: (1) a remarkable low-Vs zone exists in the uppermost part of the subducting slab, (2) it extends down to a depth of about 80 km, (3) the termination of this low-Vs zone almost corresponds to the "seismic belt" recently detected in the upper plane of the double seismic zone (Kita et al.,2006; Hasegawa et al., 2007), (4) at depths deeper than 80 km, a low-Vs and high-Vp/Vs zone is apparently distributed in the mantle wedge, immediately above the slab crust. We consider that these features reflect water-transportation processes from the slab to the mantle wedge. A low- Vs zone in the uppermost part of the subducting slab corresponds to the hydrous oceanic crust since its absolute velocity is about 4.0 km/s, comparable to that expected for the oceanic crust (Hacker et al., 2003). Dehydration reactions occur in the oceanic crust as temperature and pressure increase, and a relatively large amount of water is released at depths of about 80-100 km. The water generated by dehydration reactions could migrate upward and react peridotite at the base of the mantle wedge, forming a thin-serpentine layer there. Then, the layer is dragged by the subducting slab to deeper depths (e.g. Iwamori, 1998). Such water-transportation processes from the slab to the mantle wedge are partly constrained by a recent receiver function analysis (Kawakatsu and Watada, 2007). We further found an along-arc variation of the termination depth of the low-velocity oceanic crust, suggesting the along-arc variation in the amount of fluids released from the slab.

Magmatic and Seismic Evidence for the Neogene Evolution of the Subducting Slab and Crustal and Mantle Lithosphere under the Central Andes

NASA Astrophysics Data System (ADS)

Kay, S. M.; Sandvol, E. A.

2017-12-01

Geophysical models coupled with the distribution, chemistry and age of magmatic rocks provide powerful tools for reconstructing the thermal and material balance and deformational history of the Central Andean crust and lithosphere in time and space. Two examples are given. In the first, a model for changing slab geometry, delamination (foundering) of the crust and mantle and forearc subduction erosion beneath the southern Puna plateau comes from studies of Miocene to Recent magmatic rocks linked with seismic studies. The distribution and chemistry (e.g., Sm/Yb, La/Ta, Ba/La, isotopes) of the volcanic rocks support an 18-7 Ma period of slab shallowing, followed by slab steepening and forearc subduction erosion linked with backarc crustal and lithospheric delamination and eruption of large ignimbrites. Support for delamination comes from seismic attenuation and Vs tomographic images that reveal an 100 km wide high velocity anomaly associated with an irregular shear wave splitting pattern, which is interpreted as a delaminated block above a nearly aseismic segment of the subducting slab at a depth of 150-200 km (Calixto et al., 2013, 2014; Liang et al. 2014). This block underlies the < 7 Ma giant Cerro Galan dacitic ignimbrites and bordering mafic flows and glassy andesites and dacites to the east. The characteristics of the flows support equilibration of basaltic magmas at > 1350°C at 2 Gpa followed by fractionation and mixing with melts of garnet-pyroxene-amphibole bearing crust (Risse et al., 2013). In accord, the lavas are over a region where receiver functions indicate a lithosphere-asthenosphere boundary at 60-80 km and a regionally thin 45-55 km thick crust with a low Vp/Vs (< 1.70) ratio (Heit et al., 2014). Calculations of crustal loss and gain allow up to 10% of the southern Puna lower crust to have been lost in the last 10 Ma. A second region where the characteristics of the magmatic rocks provide clues to the timing of slab shallowing and proposed slab tears (e.g., Lynner et al, 2017) is over and on the margins of the Chilean flat-slab). In this case, shallowing of the slab as the trench normal portion of the Juan Fernandez Ridge began to subduct at 11-10 Ma correlates well with the magmatic and deformational history. If the magmatism on the margins of the flat slab corresponds to slab tears, these tears also began at 10 Ma.

Along-strike slab segmentation under Greece from a 500 km long teleseismic receiver-function swath profile : control on large earthquakes, upper plate motion, and surface morphology

NASA Astrophysics Data System (ADS)

Sachpazi, M.; Laigle, M.; Diaz, J.; Gesret, A.; Charalampakis, M.; Kissling, E. H.; Hirn, A.

2010-12-01

Observations from teleseismic converted waves recorded at 100 sites in Greece from Crete to North Aegean in a 500 km swath along the slab strike during the EU project “Thales was right” allow imaging its top in 3D. Multiscale analysis brings high-resolution to interface imaging at depth which resolved for the first time a thin, oceanic, crust for the slab under southern Greece. This first indication of its large negative buoyancy suggests its roll-back and is consistent with the upper plate trenchward motion with the highest velocities there, as shown by GPS. With respect to up to now subduction zone surveys with receivers deployed along the presumed dip to get a cross-section of the downgoing slab, our swath was instead perpendicular, that is along strike. This was in order to track down lateral changes in slab attitude along the subduction zone, that is a possible segmentation. The expected subduction strike at shallow depth, as approximated by a line from SW of Crete to W of the Ionian Islands is about N 135°E. Instead, the slab top is found along an almost N-S line at several places, at 60-70 km depth. However the slab depth contours deviate from it in-between. Their broad correspondance with the Aegean coastline or extensional domain suggests a possible control on surface morphology, and on upper plate deformation as mirrored in the topography of its crust-mantle boundary. Indeed, this first image recovered with such a high lateral resolution reveals that several slab segments can be defined dipping N 60°E, that is with a N 160 °E strike, and that these are juxtaposed through domains of strong localized variations along-strike that suggest warping or tearing of the slab. Apart their strong bearing on geodynamic reconstructions, and the continental/oceanic nature of the slab fragments, these 3D images reach the high-resolution for their discussion with respect to major earthquakes. The attitude of the slab, the dip of its upper part and its buoyancy force enter the balance controlling the degree of seismic coupling, of the seismogenic interplate fault, as well as its along dip extent as discussed earlier for the Ionian Islands. The segmented nature revealed at depth suggests a possible segmentation of the shallower interplate seismogenic zone. The precise location of the stronger intermediate-depth earthquakes occurred during the deployment appears also related to this deep structural and tectonic control.

A Reply to the Comment on "Assessing Discrepancies Between Previous Plate Kinematic Models of Mesozoic Iberia and Their Constraints" by Barnett-Moore Et Al.

NASA Astrophysics Data System (ADS)

Barnett-Moore, N.; Font, E.; Neres, M.

2017-12-01

We welcome the comments of van Hinsbergen et al. (2017) on the recent efforts of Barnett-Moore et al. (2016). Specifically, van Hinsbergen et al. (2017) raise concerns about two of the major conclusions made by Barnett-Moore et al. (2016). First, Barnett-Moore et al. (2016) choose to negate the Cretaceous Iberian paleomagnetic database as a viable plate kinematic constraint on the plate motions of Mesozoic Iberia. This conclusion, criticized by van Hinsbergen et al. (2017), was based on citing the previous efforts of Neres et al. (2012, 2013), which exposed several shortcomings, elaborated on below, within this data set. Second, van Hinsbergen et al. (2017) criticize Barnett-Moore et al. (2016) for dismissing mantle tomographic interpretations in support of a preserved Cretaceous Pyrenean "subducted slab" beneath northern Africa. Below, we have addressed each of these major criticisms from van Hinsbergen et al. (2017) in a two-section layout, similar to their comment above.

Geological features of Subduction Transfer Edge Propagator (STEP) faults, examples from the Betics and Rif

NASA Astrophysics Data System (ADS)

Booth-Rea, Guillermo; Pérez-Peña, Vicente; Azañón, José Miguel; de Lis Mancilla, Flor; Morales, Jose; Stich, Daniel; Giaconia, Flavio

2014-05-01

Most of the geological features of the Betics and Rif have resulted from slab tearing, edge delamination and punctual slab breakoff events between offset STEP faults. New P-reciever function data of the deep structure under the Betics and Rif have helped to map the deep boundaries of slab tearing and rupture in the area. Linking surface geological features with the deep structure shows that STEP faulting under the Betics occurred along ENE-WSW segments offset towards the south, probably do to the westward narrowing of the Tethys slab. The surface expression of STEP faulting at the Betics consists of ENE-WSW dextral strike-slip fault segments like the Crevillente, Alpujarras or Torcal faults that are interrupted by basins and elongated extensional domes were exhumed HP middle crust occurs. Exhumation of deep crust erases the effects of strike-slip faulting in the overlying brittle crust. Slab tearing affected the eastern Betics during the Tortonian to Messinian, producing the Fortuna and Lorca basins, and later propagated westward generating the end-Messinian to Pleistocene Guadix-Baza basins and the Granada Pliocene-Pleistocene depocentre. At present slab tearing is occurring beneath the Málaga depression, where the Torcal dextral strike-slip fault ends in a region of active distributed shortening and where intermediate depth seismicity occurs. STEP fault migration has occurred at average rates between 2 and 4 cm/yr since the late Miocene, producing a wave of alternating uplift-subsidence pulses. These initiate with uplift related to slab flexure, subsidence related to slab-pull, followed by uplift after rupture and ending with thermal subsidence. This "yo-yo" type tectonic evolution leads to the generation of endorheic basins that later evolve to exhorheic when they are uplifted and captured above the region where asthenospheric upwelling occurs.

Signature of slab fragmentation beneath Anatolia from full-waveform tomography

NASA Astrophysics Data System (ADS)

Govers, Rob; Fichtner, Andreas

2016-09-01

When oceanic basins close after a long period of convergence and subduction, continental collision and mountain building is a common consequence. Slab segmentation is expected to have been relatively common just prior to closure of other oceans in the geological past, and may explain some of the complexity that geologists have documented in the Tibetan plateau also. We focus on the eastern Mediterranean basin, which is the last remainder of a once hemispherical neo-Tethys ocean that has nearly disappeared due to convergence of the India and Africa/Arabia plates with the Eurasia plate. We present new results of full-waveform tomography that allow us to image both the crust and upper mantle in great detail. We show that a major discontinuity exists between western Anatolia lithosphere and the region to the east of it. Also, the correlation of geological features and the crustal velocities is substantially stronger in the west than in the east. We interpret these observations as the imprint in the overriding plate of fragmentation of the neo-Tethys slab below it. This north-dipping slab may have fragmented following the Eocene (about 35 million years ago) arrival of a continental promontory (Central Anatolian Core Complex) at the subduction contact. From the Eocene through the Miocene, slab roll-back ensued in the Aegean and west Anatolia, while the Cyprus-Bitlis slab subducted horizontally beneath central and east Anatolia. Following collision of Arabia (about 16 million years ago), the Cyprus-Bitlis slab steepened, exposing the crust of central and east Anatolia to high temperature, and resulting in the velocity structure that we image today. Slab fragmentation thus was a major driver of the evolution of the overriding plate as collision unfolded.

Seismic probing of continental subduction zones

NASA Astrophysics Data System (ADS)

Zhao, Liang; Xu, Xiaobing; Malusà, Marco G.

2017-09-01

High-resolution images of Earth's interior provide pivotal information for the understanding of a range of geodynamic processes, including continental subduction and exhumation of ultrahigh-pressure (UHP) metamorphic rocks. Here we present a synthesis of available global seismic observations on continental subduction zones, and selected examples of seismic probing from the European Alps, the Himalaya-Tibet and the Qinling-Dabie orogenic belts. Our synthesis and examples show that slabs recognized beneath exhumed continental UHP terranes generally have shallow dip angles (<45°) at depths <100 km, to become much steeper at depths >100 km. Slabs underlined by a clear high velocity anomaly from Earth's surface to the mantle are generally Cenozoic in age. Some of these slabs are continuous, whereas other continental subduction zones are located above discontinuous high velocity anomalies possibly suggesting slab breakoff. The density of seismic stations and the quality of recordings are of primary importance to get high-resolution images of the upper mantle to be used as a starting point to provide reliable geodynamic interpretations. In some cases, areas previously indicated as possible site of slab breakoff, such as the European Alps, have been later proven to be located above a continuous slab by using higher quality travel time data from denser seismic arrays. Discriminating between oceanic and continental slabs can be challenging, but valuable information can be provided by combining teleseismic tomography and receiver function analysis. The upper mantle beneath most continental UHP terranes generally shows complex seismic anisotropy patterns that are potentially preserved even in pre-Cenozoic subduction zones. These patterns can be used to provide information on continental slabs that are no longer highlighted by a clear high-velocity anomaly.

Exact exchange plane-wave-pseudopotential calculations for slabs: Extending the width of the vacuum

NASA Astrophysics Data System (ADS)

Engel, Eberhard

2018-04-01

Standard plane-wave pseudopotential (PWPP) calculations for slabs such as graphene become extremely demanding, as soon as the exact exchange (EXX) of density functional theory is applied. Even if the Krieger-Li-Iafrate (KLI) approximation for the EXX potential is utilized, such EXX-PWPP calculations suffer from the fact that an accurate representation of the occupied states throughout the complete vacuum between the replicas of the slab is required. In this contribution, a robust and efficient extension scheme for the PWPP states is introduced, which ensures the correct exponential decay of the slab states in the vacuum for standard cutoff energies and therefore facilitates EXX-PWPP calculations for very wide vacua and rather thick slabs. Using this scheme, it is explicitly verified that the Slater component of the EXX/KLI potential decays as -1 /z over an extended region sufficiently far from the surface (assumed to be perpendicular to the z direction) and from the middle of the vacuum, thus reproducing the asymptotic behavior of the exact EXX potential of a single slab. The calculations also reveal that the orbital-shift component of the EXX/KLI potential is quite sizable in the asymptotic region. In spite of the long-range exchange potential, the replicas of the slab decouple rather quickly with increasing width of the vacuum. Relying on the identity of the work function with the Fermi energy obtained with a suitably normalized total potential, the present EXX/KLI calculations predict work functions for both graphene and the Si(111) surface which are substantially larger than the corresponding experimental data. Together with the size of the orbital-shift potential in the asymptotic region, the very large EXX/KLI work functions indicate a failure of the KLI approximation for nonmetallic slabs.

Buoyant subduction on Venus: Implications for subduction around coronae

NASA Astrophysics Data System (ADS)

Burt, J. D.; Head, J. W.

1993-03-01

Potentially low lithospheric densities, caused by high Venus surface and perhaps mantle temperatures, could inhibit the development of negative buoyancy-driven subduction and a global system of plate tectonics/crustal recycling on that planet. No evidence for a global plate tectonic system was found so far, however, specific features strongly resembling terrestrial subduction zones in planform and topographic cross-section were described, including trenches around large coronae and chasmata in eastern Aphrodite Terra. The cause for the absence, or an altered expression, of plate tectonics on Venus remains to be found. Slab buoyancy may play a role in this difference, with higher lithospheric temperatures and a tendency toward positive buoyancy acting to oppose the descent of slabs and favoring under thrusting instead. The effect of slab buoyancy on subduction was explored and the conditions which would lead to under thrusting versus those allowing the formation of trenches and self-perpetuating subduction were defined. Applying a finite element code to assess the effects of buoyant forces on slabs subducting into a viscous mantle, it was found that mantle flow induced by horizontal motion of the convergent lithosphere greatly influences subduction angle, while buoyancy forces produce a lesser effect. Induced mantle flow tends to decrease subduction angle to near an under thrusting position when the subducting lithosphere converges on a stationary overriding lithosphere. When the overriding lithosphere is in motion, as in the case of an expanding corona, subduction angles are expected to increase. An initial stage involved estimating the changes in slab buoyancy due to slab healing and pressurization over the course of subduction. Modeling a slab, descending at a fixed angle and heated by conduction, radioactivity, and the heat released in phase changes, slab material density changes due to changing temperature, phase, and pressure were derived.

[Evaluation of Slavic continuity for electrocardiograph (ECG)-gated non-helical scan using multi detector-row computed tomography with 64 data acquisition system].

PubMed

Shiotani, Masataka; Ogawa, Masato; Watanabe, Ryo; Shinohara, Tamotsu

2012-01-01

Multi detector-row computed tomography with 64 data acquisition systems are widely used for coronary CT angiography with an electrocardiograph (ECG) gated helical scan (HS). Step and shoot with ECG gated non-helical scan (snap shot pulse: SSP) could reduce exposure dose but banding artifact-like discontinuity was observed between adjacent slabs on volume rendering (VR) and curved planner reconstruction (CPR). Therefore, we investigated the factors that influence continuity of VR and CPR images by calculating image properties of Z-axis direction of slab. The observer performance studies were performed for evaluating continuity of simulated blood vessels of VR and CPR images at simulated heart rates: 50, 55, 57 and 60 beat per minute (bpm). As a result, the value of SD at both slab edges in SSP were 20.5% lower than middle part of slab and differences of value of SD were up to 4.4 between adjacent slab edges. Slice thickness of both slab edges were 20.3% thinner than that of the peripheral part of slab. At the border of the adjacent slab, the position of the simulated blood vessel was shifted. VR images of SSP at 57 bpm was indicated as the highest score and HS was significantly superior to SSP at 55 and 60 bpm (p<0.05). In CPR images, there were no significant differences at all simulated heart rates. In conclusion, we considered that VR images of SSP were influenced heart rates except 57 bpm (resonance case) and there was little difference of visibility for discontinuity of both CPR images obtained by SSP and HS.

Wet plume atop of the flattening slab: Insight into intraplate volcanism in East Asia

NASA Astrophysics Data System (ADS)

He, Lijuan

2017-08-01

Geophysical observations imply the intraplate volcanism in East Asia is related to dehydration of slab stagnating in the transition zone. To better understand the dynamics of such process, a thermochemical mantle convection model is constructed to simulate numerically the thermal evolution of slab and the transportation of water in the process of slab downgoing, flattening and stagnation. Equation of water transfer is included, and water effects on density and viscosity are considered. Model results indicate the warming of slab by surrounding mantle is rather slow. Water could be successfully dragged into the transition zone if the reference viscosity of the hydrous layer (with initial water of 2 wt%) is higher than 1017 Pa s and that of mantle is 1021 Pa s. Wet plumes could then originate in the flat-lying part of the slab, relatively far from the trench. Generally, the viscosity of the hydrous layer governs the initiation of wet plume, whereas the viscosity of the overlying mantle wedge controls the activity of the ascending wet plumes - they are more active in the weaker wedge. The complex fluid flow superposed by corner flow and free thermal convection influences greatly the water transport pattern in the upper mantle. Modeling results together with previous modeling infer three stages of water circulation in the big mantle wedge: 1) water is brought into the mantle transition zone by downward subducting slab under some specific thermo-rheological conditions, otherwise water is released at shallow depth near wedge tip; 2) wet plume generates from surface of the flattening slab warmed by surrounding mantle, and 3) water spreads over the big mantle wedge. Wet plume from the flattening Pacific Plate arrives at the lithospheric base and induces melting, which can explain the intraplate Cenozoic volcanoes in East Asia.

Upper Mantle Velocity Structure beneath the Northeastern Philippine Sea Constrained by Waveform Modeling of P Triplicated Phases

NASA Astrophysics Data System (ADS)

Cho, S.; Rhie, J.; Lee, S. H.; Kim, S.; Kang, T. S.

2017-12-01

A study on the detailed velocity structures of the stagnant Pacific slab is important to understand the complex processes happening in the upper mantle. Although waveform modeling of P triplicated phases can reveal the detailed velocity structures especially for the discontinuities, the regions where the method can be applied are limited due to uneven distribution of earthquakes and stations. In this study, we used waveforms generated by two deep earthquakes near Izu-Bonin Trench and recorded by stations in South Korea. These event-station pairs are appropriate to study the upper mantle structures beneath the northeastern Philippine Sea, where no previous results by triplicated waveform modeling have been reported. In this region, the subducting Pacific slab seems to hit the 660 km discontinuity and become stagnant. We applied the reflectivity method to calculate waveforms and found the best fitting model by trial-and-error and manual inspection. In general, our best model is similar to M3.11, which is widely accepted 1D model for the regions where the stagnant slab exists and the 660 km discontinuity is depressed by the slab. The most noticeable feature of our model is that P wave velocities of inside and above the slab are considerably higher and lower than ones for M3.11, respectively. This specific velocity model is necessary to explain arrivals of two distinct phases identified in observed waveforms; one refracts inside the slab and the other reflects on the upper boundary of the slab. To understand the cause of the differences between our model and M3.11, further studies including thermal and mechanical modelling of the slab in this region will be recommended.

On the role of subducting oceanic plateaus in the development of shallow flat subduction

NASA Astrophysics Data System (ADS)

van Hunen, Jeroen; van den Berg, Arie P.; Vlaar, Nico J.

2002-08-01

Oceanic plateaus, aseismic ridges or seamount chains all have a thickened crust and their subduction has been proposed as a possible mechanism to explain the occurrence of flat subduction and related absence of arc magmatism below Peru, Central Chile and at the Nankai Trough (Japan). Their extra compositional buoyancy could prohibit the slab from sinking into the mantle. With a numerical thermochemical convection model, we simulated the subduction of an oceanic lithosphere that contains an oceanic crustal plateau of 18-km thickness. With a systematic variation, we examined the required physical parameters to obtain shallow flat subduction. Metastability of the basaltic crust in the eclogite stability field is of crucial importance for the slab to remain buoyant throughout the subduction process. In a 44-Ma-old subducting plate, basalt must be able to survive a temperature of 600-700 °C to keep the plate buoyant sufficiently long to cause a flat-slab segment. We found that the maximum yield stress in the slab must be limited to about 600 MPa to allow for the necessary bending to the horizontal. Young slabs show flat subduction for larger parameter ranges than old slabs, since they are less gravitationally unstable and show less resistance against bending. Hydrous weakening of the mantle wedge area and lowermost continent are required to allow for the necessary deformation of a change in subduction style from steep to flat. The maximum flat slab extent is about 300 km, which is sufficient to explain the observed shallow flat subduction near the Nankai Trough (Japan). However, additional mechanisms, such as active overthrusting by an overriding continental plate, need to be invoked to explain the flat-slab segments up to 500 km long below Peru and Central Chile.

THE IMPLICIT CONTRIBUTION OF SLAB MODES TO THE PERPENDICULAR DIFFUSION COEFFICIENT OF PARTICLES INTERACTING WITH TWO-COMPONENT TURBULENCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shalchi, A., E-mail: andreasm4@yahoo.com

2016-10-20

We explore the transport of energetic particles in two-component turbulence in which the stochastic magnetic field is assumed to be a superposition of slab and two-dimensional modes. It is known that in magnetostatic slab turbulence, the motion of particles across the mean magnetic field is subdiffusive. If a two-dimensional component is added, diffusion is recovered. It was also shown before that in two-component turbulence, the slab modes do not explicitly contribute to the perpendicular diffusion coefficient. In the current paper, the implicit contribution of slab modes is explored and it is shown that this contribution leads to a reduction ofmore » the perpendicular diffusion coefficient. This effect improves the agreement between simulations and analytical theory. Furthermore, the obtained results are relevant for investigations of diffusive shock acceleration.« less

Seismic evidence for rotating mantle flow around subducting slab edge associated with oceanic microplate capture

NASA Astrophysics Data System (ADS)

Mosher, Stephen G.; Audet, Pascal; L'Heureux, Ivan

2014-07-01

Tectonic plate reorganization at a subduction zone edge is a fundamental process that controls oceanic plate fragmentation and capture. However, the various factors responsible for these processes remain elusive. We characterize seismic anisotropy of the upper mantle in the Explorer region at the northern limit of the Cascadia subduction zone from teleseismic shear wave splitting measurements. Our results show that the mantle flow field beneath the Explorer slab is rotating anticlockwise from the convergence-parallel motion between the Juan de Fuca and the North America plates, re-aligning itself with the transcurrent motion between the Pacific and North America plates. We propose that oceanic microplate fragmentation is driven by slab stretching, thus reorganizing the mantle flow around the slab edge and further contributing to slab weakening and increase in buoyancy, eventually leading to cessation of subduction and microplate capture.

Transverse shifts of a light beam reflected from a uniaxially anisotropic chiral slab

NASA Astrophysics Data System (ADS)

Xu, Guoding; Li, Jun; Xiao, Yuting; Mao, Hongmin; Sun, Jian; Pan, Tao

2015-01-01

We study for the first time the transverse shifts of a Gaussian beam reflected from a uniaxially anisotropic chiral (UAC) slab, where the chirality appears only in one direction and the host medium is a uniaxial crystal or an electric plasma. The results indicate that the transverse shifts are closely related to the propagation behaviors of the eigenwaves in the slab. Specifically, when one or both of the eigenwaves are totally reflected at the second interface of the slab, the spatial transverse shift becomes resonances but is not enhanced; when one eigenwave is totally reflected at the first interface and the other is transmitted at the second interface, the larger and negative transverse shifts can be obtained. The propagation behaviors of the eigenwaves in the UAC slab provide more abundant information about the transverse shifts than in a single interface structure.

Causes of Early-Age Thermal Cracking of Concrete Foundation Slabs and their Reinforcement to Control the Cracking

NASA Astrophysics Data System (ADS)

Bilčík, Juraj; Sonnenschein, Róbert; Gažovičová, Natália

2017-09-01

This paper focuses on the causes and consequences of early-age cracking of mass concrete foundation slabs due to restrained volume changes. Considering the importance of water leaking through cracks in terms of the serviceability, durability and environmental impact of watertight concrete structures, emphasis is placed on the effect of temperature loads on foundation slabs. Foundation slabs are usually restrained to some degree externally or internally. To evaluate the effect of external restraints on foundation slabs, friction and interaction models are introduced. The reinforcement of concrete cannot prevent the initiation of cracking, but when cracking has occurred, it may act to reduce the spacing and width of cracks. According to EN 1992-1-1, results of calculating crack widths with local variations included in National Annexes (NAs) vary considerably. A comparison of the required reinforcement areas according to different NAs is presented.

Surface imprint of toroidal flow at retreating slab edges: The first geodetic evidence in the Calabrian subduction system

NASA Astrophysics Data System (ADS)

Palano, M.; Piromallo, C.; Chiarabba, C.

2017-01-01

Dense GPS observations can help Earth scientists to capture the surface imprint of mantle toroidal flow at slab edges. We document this process in the Calabrian subduction system, where the Ionian slab rollback took place during the past 30 Ma, following a stepwise process driven by migration of lithospheric tearing. We found rotation rates of 1.29°/Ma (counterclockwise) and 1.74°/Ma (clockwise), for poles located close to the northern and southern slab edges, respectively. These small-scale, opposite rotations occur along complex sets of active faults representing the present-day lithospheric expression of the tearing processes affecting the southeastward retreating Ionian slab at both edges. The observed rotations are likely still young and the process more immature at the northern tear, where it is unable to reorient mantle fabric and therefore is unseen by SKS splitting.

Analytical and numerical treatment of resistive drift instability in a plasma slab

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mirnov, V. V., E-mail: vvmirnov@wisc.edu; Sauppe, J. P.; Hegna, C. C.

An analytic approach combining the effect of equilibrium diamagnetic flows and the finite ionsound gyroradius associated with electron−ion decoupling and kinetic Alfvén wave dispersion is derived to study resistive drift instabilities in a plasma slab. Linear numerical computations using the NIMROD code are performed with cold ions and hot electrons in a plasma slab with a doubly periodic box bounded by two perfectly conducting walls. A linearly unstable resistive drift mode is observed in computations with a growth rate that is consistent with the analytic dispersion relation. The resistive drift mode is expected to be suppressed by magnetic shear inmore » unbounded domains, but the mode is observed in numerical computations with and without magnetic shear. In the slab model, the finite slab thickness and the perfectly conducting boundary conditions are likely to account for the lack of suppression.« less

Comparison of various contact algorithms for poroelastic tissues.

PubMed

Galbusera, Fabio; Bashkuev, Maxim; Wilke, Hans-Joachim; Shirazi-Adl, Aboulfazl; Schmidt, Hendrik

2014-01-01

Capabilities of the commercial finite element package ABAQUS in simulating frictionless contact between two saturated porous structures were evaluated and compared with those of an open source code, FEBio. In ABAQUS, both the default contact implementation and another algorithm based on an iterative approach requiring script programming were considered. Test simulations included a patch test of two cylindrical slabs in a gapless contact and confined compression conditions; a confined compression test of a porous cylindrical slab with a spherical porous indenter; and finally two unconfined compression tests of soft tissues mimicking diarthrodial joints. The patch test showed almost identical results for all algorithms. On the contrary, the confined and unconfined compression tests demonstrated large differences related to distinct physical and boundary conditions considered in each of the three contact algorithms investigated in this study. In general, contact with non-uniform gaps between fluid-filled porous structures could be effectively simulated with either ABAQUS or FEBio. The user should be aware of the parameter definitions, assumptions and limitations in each case, and take into consideration the physics and boundary conditions of the problem of interest when searching for the most appropriate model.

Numerical study of coupled turbulent flow and solidification for steel slab casters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aboutalebi, M.R.; Hasan, M.; Guthrie, R.I.L.

1995-09-01

A two-dimensional numerical modeling study was undertaken to account for coupled turbulent flow and heat transfer with solidification in the mold and submold regions of a steel slab coaster. Liquid steel is introduced into a water-cooled mold through a bifurcated submerged entry nozzle. Turbulence phenomena in the melt pool of the caster were accounted for, using a modified version of the low-Reynolds-number {kappa}-{epsilon} turbulence model of Launder and Sharma. The mushy region solidification, in the presence of turbulence, was taken into account by modifying the standard enthalpy-porosity technique, which is presently popular for modeling solidification problems. Thermocapillary and buoyancy effectsmore » have been considered in this model to evaluate the influences of the liquid surface tension gradient at the meniscus surface, and natural convection on flow patterns in the liquid pool. Parametric studies were carried out to evaluate the effects of typical variables, such as inlet superheat and casting speed, on the fluid flow and heat transfer results. The numerical predictions were compared with available experimental data.« less

A fictitious domain method for fluid/solid interaction applied to the plate folding over the 660 Km depth boundary.

NASA Astrophysics Data System (ADS)

Cerpa, Nestor; Hassani, Riad; Gerbault, Muriel

2014-05-01

A large variety of geodynamical problems involve a mechanical system where a competent body is embedded in a more deformable medium, and hence they can be viewed as belonging to the field of solid/fluid interaction.The lithosphere/asthenosphere interaction in subduction zones is among those kind of problems which are generally difficult to tackle numerically since the immersed (solid) body can be geometrically complex and the surrounding (fluid) medium can thus undergo large deformation. Our work presents a new numerical approach for the study of subduction zones. The lithosphere is modeled as a Maxwell viscoelastic body sinking in the viscous asthenosphere. Both domains are discretized by the Finite Element Method (FEM) and we use a staggered coupling method. The interaction is provided by a non-matching interface method called the Fictitious Domain Method (FDM). We have validated this method with some 2-D benchmarks and examples. Through this numerical coupling method we aim at studying the effect of mantle viscosity on the cyclicity of slab folding on the 660 km depth discontinuity approximated as an impenetrable barrier. Depending on the kinematics condition imposed to the overriding and subducting plates, analog and numerical models have previously shown that cyclicity occurs. The viscosity of the asthenosphere (taken as an isoviscous or a double viscosity-layer fluid) impacts on folding cyclicity and consequently on the slab's dip as well as the stress regime of the overriding plate. In particular, applying far-field plate velocities corresponding to those of the South-American and Nazca plates at present, (4.3 cm/yr and 2.9 cm/yr respectively), we obtain periodic slab folding which is consistent with magmatism and sedimentalogical records. These data report cycles in orogenic growth of the order of 30-40 Myrs, a period that we reproduce when the mantle viscosity ranges in between 3 and 5 x 1020 Pa.s. Moreover, we reproduce episodic development of horizontal subduction induced by cyclic folding and, hence, propose a new explanation for episodes of flat subduction under the South-American plate. We show also preliminary results of 3-D subduction.

Tomography and Dynamics of Western-Pacific Subduction Zones

NASA Astrophysics Data System (ADS)

Zhao, D.

2012-01-01

We review the significant recent results of multiscale seismic tomography of the Western-Pacific subduction zones and discuss their implications for seismotectonics, magmatism, and subduction dynamics, with an emphasis on the Japan Islands. Many important new findings are obtained due to technical advances in tomography, such as the handling of complex-shaped velocity discontinuities, the use of various later phases, the joint inversion of local and teleseismic data, tomographic imaging outside a seismic network, and P-wave anisotropy tomography. Prominent low-velocity (low-V) and high-attenuation (low-Q) zones are revealed in the crust and uppermost mantle beneath active arc and back-arc volcanoes and they extend to the deeper portion of the mantle wedge, indicating that the low-V/low-Q zones form the sources of arc magmatism and volcanism, and the arc magmatic system is related to deep processes such as convective circulation in the mantle wedge and dehydration reactions in the subducting slab. Seismic anisotropy seems to exist in all portions of the Northeast Japan subduction zone, including the upper and lower crust, the mantle wedge and the subducting Pacific slab. Multilayer anisotropies with different orientations may have caused the apparently weak shear-wave splitting observed so far, whereas recent results show a greater effect of crustal anisotropy than previously thought. Deep subduction of the Philippine Sea slab and deep dehydration of the Pacific slab are revealed beneath Southwest Japan. Significant structural heterogeneities are imaged in the source areas of large earthquakes in the crust, subducting slab and interplate megathrust zone, which may reflect fluids and/or magma originating from slab dehydration that affected the rupture nucleation of large earthquakes. These results suggest that large earthquakes do not strike anywhere, but in only anomalous areas that may be detected with geophysical methods. The occurrence of deep earthquakes under the Japan Sea and the East Asia margin may be related to a metastable olivine wedge in the subducting Pacific slab. The Pacific slab becomes stagnant in the mantle transition zone under East Asia, and a big mantle wedge (BMW) has formed above the stagnant slab. Convective circulations and fluid and magmatic processes in the BMW may have caused intraplate volcanism (e.g., Changbai and Wudalianchi), reactivation of the North China craton, large earthquakes, and other active tectonics in East Asia. Deep subduction and dehydration of continental plates (such as the Eurasian plate, Indian plate and Burma microplate) are also found, which have caused intraplate magmatism (e.g., Tengchong) and geothermal anomalies above the subducted continental plates. Under Kamchatka, the subducting Pacific slab shortens toward the north and terminates near the Aleutian-Kamchatka junction. The slab loss was induced by friction with the surrounding asthenosphere, as the Pacific plate rotated clockwise 30 Ma ago, and then it was enlarged by the slab-edge pinch-off by the asthenospheric flow. The stagnant slab finally collapses down to the bottom of the mantle, which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle. Suggestions are also made for future directions of the seismological research of subduction zones.

42. PRESSING A SLAB OF CLAY ONTO A MOSAIC MOLD. ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

42. PRESSING A SLAB OF CLAY ONTO A MOSAIC MOLD. THE MOLD, WHICH HAS A RAISED DESIGN, LEAVES AND OUTLINE IN THE SLAB, THE PIECES THUS DEFINED, ARE THEN CUT APART TO BE FIRED SEPARATELY AND REASSEMBLED. - Moravian Pottery & Tile Works, Southwest side of State Route 313 (Swamp Road), Northwest of East Court Street, Doylestown, Bucks County, PA

Experiment study on RC frame retrofitted by the external structure

NASA Astrophysics Data System (ADS)

Liu, Chunyang; Shi, Junji; Hiroshi, Kuramoto; Taguchi, Takashi; Kamiya, Takashi

2016-09-01

A new retrofitting method is proposed herein for reinforced concrete (RC) structures through attachment of an external structure. The external structure consists of a fiber concrete encased steel frame, connection slab and transverse beams. The external structure is connected to the existing structure through a connection slab and transverse beams. Pseudostatic experiments were carried out on one unretrofitted specimen and three retrofitted frame specimens. The characteristics, including failure mode, crack pattern, hysteresis loops behavior, relationship of strain and displacement of the concrete slab, are demonstrated. The results show that the load carrying capacity is obviously increased, and the extension length of the slab and the number of columns within the external frame are important influence factors on the working performance of the existing structure. In addition, the displacement difference between the existing structure and the outer structure was caused mainly by three factors: shear deformation of the slab, extraction of transverse beams, and drift of the conjunction part between the slab and the existing frame. Furthermore, the total deformation determined by the first two factors accounted for approximately 80% of the damage, therefore these factors should be carefully considered in engineering practice to enhance the effects of this new retrofitting method.

Evaluation of the deflected mode of the monolithic span pieces and preassembled slabs combined action

NASA Astrophysics Data System (ADS)

Roshchina, Svetlana; Ezzi, Hisham; Shishov, Ivan; Lukin, Mikhail; Sergeev, Michael

2017-10-01

In single-story industrial buildings, the cost of roof covering comprises 40-55% of the total cost of the buildings. Therefore, research, development and application of new structural forms of reinforced concrete rafter structures, that allow to reduce material consumption and reduce the sub-assembly weight of structures, are the main tasks in the field of improving the existing generic solutions. The article suggests a method for estimating the relieving effect in the rafter structure as the result of combined deformation of the roof slabs with the end arrises. Calculated and experimental method for determining the stress and strain state of the rafter structure upper belt and the roof slabs with regard to their rigid connection has been proposed. A model of a highly effective roof structure providing a significant reduction in the construction height of the roofing and the cubic content of the building at the same time allowing to include the end arrises and a part of the slabs shelves with the help of the monolithic concrete has been proposed. The proposed prefabricated monolithic concrete rafter structure and its rigid connection with ribbed slabs allows to reduce the consumption of the prestressed slabs reinforcement by 50%.

The double seismic zone in downgoing slabs and the viscosity of the mesosphere

NASA Technical Reports Server (NTRS)

Sleep, N. H.

1979-01-01

The seismic zone beneath several island arcs between about 100 and 200 km depth consists of an upper zone having down-dip compression and a lower zone having down-dip tension. Several numerical models of the Aleutian arc were computed to test the hypothesis that these double seismic zones are due to sagging of the slab under its own weight. This sagging occurs because the asthenosphere (between about 100 and 200 km) provides little support or resistance to the slab, which is supported from below by the more viscous mesosphere and from above by the lithosphere. The viscosity of the mesosphere was constrained to the interval between 0.25 x 10 to the 22nd and 0.5 x 10 to the 22nd P by noting that the slab would have mainly down-dip compression at higher viscosities and mainly down-dip tension at lower viscosities. The deviatoric stress in the slab and the fault plane between the slab and the island arc is about 200-300 bars (expressed as shear stress). The models were calibrated to the observed depth and gravity anomalies in the trench.

Hydrodynamic electron flow in a Weyl semimetal slab: Role of Chern-Simons terms

NASA Astrophysics Data System (ADS)

Gorbar, E. V.; Miransky, V. A.; Shovkovy, I. A.; Sukhachov, P. O.

2018-05-01

The hydrodynamic flow of the chiral electron fluid in a Weyl semimetal slab of finite thickness is studied by using the consistent hydrodynamic theory. The latter includes viscous, anomalous, and vortical effects, as well as accounts for dynamical electromagnetism. The energy and momentum separations between the Weyl nodes are taken into account via the topological Chern-Simons contributions in the electric current and charge densities in Maxwell's equations. When an external electric field is applied parallel to the slab, it is found that the electron fluid velocity has a nonuniform profile determined by the viscosity and the no-slip boundary conditions. Most remarkably, the fluid velocity field develops a nonzero component across the slab that gradually dissipates when approaching the surfaces. This abnormal component of the flow arises due to the anomalous Hall voltage induced by the topological Chern-Simons current. Another signature feature of the hydrodynamics in Weyl semimetals is a strong modification of the anomalous Hall current along the slab in the direction perpendicular to the applied electric field. Additionally, it is found that the topological current induces an electric potential difference between the surfaces of the slab that is strongly affected by the hydrodynamic flow.

Analysis and design of composite slab by varying different parameters

NASA Astrophysics Data System (ADS)

Lambe, Kedar; Siddh, Sharda

2018-03-01

Composite deck slabs are in demand because of its faster, lighter and economical construction work. Composite slab consists of cold formed deck profiled sheet and concrete either lightweight or normal. Investigation of shear behaviour of the composite slab is very complex. Shear bond strength depends on the various parameter such as a shape of sheeting, a thickness of the sheet, type of embossment and its frequency of use, shear stiffener or intermediate stiffener, type of load, an arrangement of load, length of shear span, the thickness of concrete and support friction etc. In present study finite element analysis is carried out with ABAQUS 6.13, a simply supported composite slab is considered for the investigation of the shear bond behaviour of the composite slab by considering variation in three different parameters, the shape of a sheet, thickness of sheet and shear span. Different shear spans of two different shape of cold formed deck profiled sheet i.e. with intermediate stiffeners and without intermediate stiffeners are considered with two different thicknesses (0.8 mm and 1.2 mm) for simulation. In present work, simulation of models has done for static loading with 20 mm mesh size is considered.

Bend Faulting at the Edge of a Flat Slab: The 2017 Mw7.1 Puebla-Morelos, Mexico Earthquake

NASA Astrophysics Data System (ADS)

Melgar, Diego; Pérez-Campos, Xyoli; Ramirez-Guzman, Leonardo; Spica, Zack; Espíndola, Victor Hugo; Hammond, William C.; Cabral-Cano, Enrique

2018-03-01

We present results of a slip model from joint inversion of strong motion and static Global Positioning System data for the Mw7.1 Puebla-Morelos earthquake. We find that the earthquake nucleates at the bottom of the oceanic crust or within the oceanic mantle with most of the moment release occurring within the oceanic mantle. Given its location at the edge of the flat slab, the earthquake is likely the result of bending stresses occurring at the transition from flat slab subduction to steeply dipping subduction. The event strikes obliquely to the slab, we find a good agreement between the seafloor fabric offshore the source region and the strike of the earthquake. We argue that the event likely reactivated a fault first created during seafloor formation. We hypothesize that large bending-related events at the edge of the flat slab are more likely in areas of low misalignment between the seafloor fabric and the slab strike where reactivation of preexisting structures is favored. This hypothesis predicts decreased likelihood of bending-related events northwest of the 2017 source region but also suggests that they should be more likely southeast of the 2017 source region.

Slab Geometry and Segmentation on Seismogenic Subduction Zone; Insight from gravity gradients

NASA Astrophysics Data System (ADS)

Saraswati, A. T.; Mazzotti, S.; Cattin, R.; Cadio, C.

2017-12-01

Slab geometry is a key parameter to improve seismic hazard assessment in subduction zones. In many cases, information about structures beneath subduction are obtained from geophysical dedicated studies, including geodetic and seismic measurements. However, due to the lack of global information, both geometry and segmentation in seismogenic zone of many subductions remain badly-constrained. Here we propose an alternative approach based on satellite gravity observations. The GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission enables to probe Earth deep mass structures from gravity gradients, which are more sensitive to spatial structure geometry and directional properties than classical gravitational data. Gravity gradients forward modeling of modeled slab is performed by using horizontal and vertical gravity gradient components to better determine slab geophysical model rather than vertical gradient only. Using polyhedron method, topography correction on gravity gradient signal is undertaken to enhance the anomaly signal of lithospheric structures. Afterward, we compare residual gravity gradients with the calculated signals associated with slab geometry. In this preliminary study, straightforward models are used to better understand the characteristic of gravity gradient signals due to deep mass sources. We pay a special attention to the delineation of slab borders and dip angle variations.

Simulating the effect of slab features on vapor intrusion of crack entry

PubMed Central

Yao, Yijun; Pennell, Kelly G.; Suuberg, Eric M.

2012-01-01

In vapor intrusion screening models, a most widely employed assumption in simulating the entry of contaminant into a building is that of a crack in the building foundation slab. Some modelers employed a perimeter crack hypothesis while others chose not to identify the crack type. However, few studies have systematically investigated the influence on vapor intrusion predictions of slab crack features, such as the shape and distribution of slab cracks and related to this overall building foundation footprint size. In this paper, predictions from a three-dimensional model of vapor intrusion are used to compare the contaminant mass flow rates into buildings with different foundation slab crack features. The simulations show that the contaminant mass flow rate into the building does not change much for different assumed slab crack shapes and locations, and the foundation footprint size does not play a significant role in determining contaminant mass flow rate through a unit area of crack. Moreover, the simulation helped reveal the distribution of subslab contaminant soil vapor concentration beneath the foundation, and the results suggest that in most cases involving no biodegradation, the variation in subslab concentration should not exceed an order of magnitude, and is often significantly less than this. PMID:23359620

Seismogenesis of dual subduction beneath Kanto, central Japan controlled by fluid release.

PubMed

Ji, Yingfeng; Yoshioka, Shoichi; Manea, Vlad C; Manea, Marina

2017-12-04

Dual subduction represents an unusual case of subduction where one oceanic plate subducts on top of another, creating a highly complex tectonic setting. Because of the complex interaction between the two subducted plates, the origin of seismicity in such region is still not fully understood. Here we investigate the thermal structure of dual subduction beneath Kanto, central Japan formed as a consequence of a unique case of triple trench junction. Using high-resolution three-dimensional thermo-mechanical models tailored for the specific dual subduction settings beneath Kanto, we show that, compared with single-plate subduction systems, subduction of double slabs produces a strong variation of mantle flow, thermal and fluid release pattern that strongly controls the regional seismicity distribution. Here the deepening of seismicity in the Pacific slab located under the Philippine Sea slab is explained by delaying at greater depths (~150 km depth) of the eclogitization front in this region. On the other hand, the shallower seismicity observed in the Philippine Sea slab is related to a young and warm plate subduction and probably to the presence of a hot mantle flow traveling underneath the slab and then moving upward on top of the slab.

Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes

NASA Astrophysics Data System (ADS)

Hasegawa, Akira; Nakajima, Junichi

2017-12-01

We review studies of intermediate-depth seismicity and seismic imaging of the interior of subducting slabs in relation to slab metamorphism and their implications for the genesis of intermediate-depth earthquakes. Intermediate-depth events form a double seismic zone in the depth range of c. 40-180 km, which occur only at locations where hydrous minerals are present, and are particularly concentrated along dehydration reaction boundaries. Recent studies have revealed detailed spatial distributions of these events and a close relationship with slab metamorphism. Pressure-temperature paths of the crust for cold slabs encounter facies boundaries with large H2O production rates and positive total volume change, which are expected to cause highly active seismicity near the facies boundaries. A belt of upper-plane seismicity in the crust nearly parallel to 80-90 km depth contours of the slab surface has been detected in the cold Pacific slab beneath eastern Japan, and is probably caused by slab crust dehydration with a large H2O production rate. A seismic low-velocity layer in the slab crust persists down to the depth of this upper-plane seismic belt, which provides evidence for phase transformation of dehydration at this depth. Similar low-velocity subducting crust closely related with intraslab seismicity has been detected in several other subduction zones. Seismic tomography studies in NE Japan and northern Chile also revealed the presence of a P-wave low-velocity layer along the lower plane of a double seismic zone. However, in contrast to predictions based on the serpentinized mantle, S-wave velocity along this layer is not low. Seismic anisotropy and pore aspect ratio may play a role in generating this unique structure. Although further validation is required, observations of these distinct low P-wave velocities along the lower seismic plane suggest the presence of hydrated rocks or fluids within that layer. These observations support the hypothesis that dehydration-derived H2O causes intermediate-depth intraslab earthquakes. However, it is possible that dual mechanisms generate these earthquakes; the initiation of earthquake rupture may be caused by local excess pore pressure from H2O, and subsequent ruptures may propagate through thermal shear instability. In either case, slab-derived H2O plays an important role in generating intermediate-depth events.

Reconciling the geological history of western Turkey with plate circuits and mantle tomography

NASA Astrophysics Data System (ADS)

Kaymakci, N.; van Hinsbergen, D. J.; Spakman, W.; Torsvik, T. H.

2010-12-01

We place the geological history since Cretaceous times in western Turkey in a context of convergence, subduction, collision and slab break-off. To this end, we compare the west Anatolian geological history with amounts of Africa-Europe convergence calculated from the Atlantic plate circuit, and the seismic tomography images of the west Anatolian mantle structure. Western Turkish geology reflects the convergence between the Sakarya continent (here treated as Eurasia) in the north and Africa in the south, with the Anatolide-Tauride Block (ATB) between two strands of the Neotethyan ocean. Convergence between the Sakarya and the ATB started at least ~95-90Myr ago, marked by ages of metamorphic soles of ophiolites that form the highest structural unit below Sakarya. These are underlain by high-pressure, low-temperature metamorphic rocks of the Tavsanli and Afyon zones, and the Ören Unit, which in turn are underlain by the Menderes Massif derived from the ATB. Underthrusting of the ATB below Sakarya was since ~50Ma, associated with high-temperature metamorphism and widespread granitic magmatism. Thrusting in the Menderes Massif continued until 35 Ma, after which there is no record of accretion in western Turkey. Plate circuits show that since 90 Ma, ~1400 km of Africa-Europe convergence occurred, of which ~700 km since 50 Ma and ~450 km since 35Ma. Seismic tomography shows that the African slab under western Turkey is decoupled from the African Plate. This detached slab is a single, coherent body, representing the lithosphere consumed since 90 Ma. There was no subduction re-initiation after slab break-off. ATB collision with Europe therefore did not immediately lead to slab break-off but instead to delamination of subducting lithospheric mantle from accreting ATB crust, while staying attached to the African Plate. This led to asthenospheric inflow below the ATB crust, high-temperature metamorphism and felsic magmatism. Slab break-off in western Turkey probably occurred ~15 Myr ago, after which overriding plate compression and rotation accommodated ongoing Africa-Europe convergence. Slab break-off was accommodated along a vertical NE trending subduction transform edge propagator (STEP) fault zone, accelerating southwestward slab retreat of the Aegean slab. The SE Aegean slab edge may have existed already since early Miocene times or before, but started to rapidly roll back along the southeastern Aegean STEP in middle Miocene times, penetrating the Aegean region in the Pliocene.

Subduction and dehydration of slow-spread oceanic lithosphere

NASA Astrophysics Data System (ADS)

Paulatto, M.; Laigle, M.; Galve, A.; Charvis, P.

2016-12-01

Water transported by subducting slabs affects the dynamics of subduction zones and is a major gateway in the global geochemical water cycle. During subduction much of the water stored in the slab is released via pore fluid escape and through metamorphic reactions that depend on the thermal regime. The most notable are eclogitization of hydrated basalt and gabbro and breakdown of serpentinite. Most constraints to date have been obtained at Pacific subduction zones, and have contributed to a model of slab dehydration applicable to normal fast-spread oceanic lithosphere with a mafic crust. Slow-spread crust however, is heterogeneous in thickness and composition and has a different water distribution than fast-spread crust. We use P-wave traveltimes from several active source seismic experiments and P- and S-wave traveltimes from shallow and intermediate depth (< 160 km) local earthquakes recorded on a vast amphibious array of OBSs and land seismometers to recover the 3D Vp and Vp/Vs structure of the central Lesser Antilles subduction zone from the surface to 160 km depth. This slab was formed by slow accretion at the Mid-Atlantic ridge and represents the global slow accretion rate end-member. We image the dipping low-Vp layer at the top of the slab corresponding to the hydrated slab crust penetrating to about 100 km depth. High Vp/Vs ratio on the slab top and in the forearc crust is interpreted as evidence of elevated fluid content either as free fluids or as bound water in hydrated minerals. A local minimum in Vp is observed on the slab top at 50 km depth, and forms an elongated trench-parallel anomaly. This anomaly is interrupted at the projection of the Marathon fracture zone. We suggest that this is the result of lateral variations in slab crust composition from normal mafic oceanic crust to tectonized oceanic crust consisting to a large extent of serpentinized peridotite near the fracture zone. Slab regions with normal mafic oceanic crust likely undergo eclogitization, resulting in voluminous water release over a narrow depth range. Serpentinized ultramafic crust, in contrast, may release water at a more constant rate. We infer that subduction of slow-spread lithosphere may result in heterogeneous water transport and release at subduction zones with implications for seismicity, magma generation and the geochemical budget.

Gaps, tears and seismic anisotropy around the subducting slabs of the Antilles

NASA Astrophysics Data System (ADS)

Schlaphorst, David; Kendall, J.-Michael; Baptie, Brian; Latchman, Joan L.; Tait, Steve

2017-02-01

Seismic anisotropy in and beneath the subducting slabs of the Antilles is investigated using observations of shear-wave splitting. We use a combination of teleseismic and local events recorded at three-component broadband seismic stations on every major island in the area to map anisotropy in the crust, the mantle wedge and the slab/sub-slab mantle. To date this is the most comprehensive study of anisotropy in this region, involving 52 stations from 8 seismic networks. Local event delay times (0.21 ± 0.12 s) do not increase with depth, indicating a crustal origin in anisotropy and an isotropic mantle wedge. Teleseismic delay times are much larger (1.34 ± 0.47 s), with fast shear-wave polarisations that are predominantly parallel to trend of the arc. These observations can be interpreted three ways: (1) the presence of pre-existing anisotropy in the subducting slab; (2) anisotropy due to sub-slab mantle flow around the eastern margin of the nearly stationary Caribbean plate; (3) some combination of both mechanisms. However, there are two notable variations in the trench-parallel pattern of anisotropy - trench-perpendicular alignment is observed in narrow regions east of Puerto Rico and south of Martinique. These observations support previously proposed ideas of eastward sublithospheric mantle flow through gaps in the slab. Furthermore, the pattern of anisotropy south of Martinique, near Saint Lucia is consistent with a previously proposed location for the boundary between the North and South American plates.

Comparative evaluation of enamel remineralization potential of processed cheese, calcium phosphate-based synthetic agent, and a fluoride-containing toothpaste: An in situ study.

PubMed

Grewal, Navneet; Gumber, Samita; Kaur, Nirapjeet

2017-01-01

Enamel remineralization potential of variety of products has been established, but there is a lack of evidence of comparison of remineralization potential of natural versus synthetic products. The aim of this study was to compare the enamel remineralization potential of saliva, cheese, casein phosphopeptide-amorphous calcium phosphate (CPP-ACP)-based synthetic agent, and fluoride toothpaste. In situ study was carried out on sixty individuals who wore an intraoral appliance containing demineralized enamel slabs for each agent. One out of six slabs was kept as a control so as to record the baseline values (neither subjected to demineralization nor remineralization). Experimental agents were applied on the designated enamel slabs on day 1, 4, 7, and 10 with a crossover wash out period of 7 days. Quantitative values of mineral content of slab were measured using energy dispersive X-ray and qualitative changes in surface topography of slab were seen under scanning electron microscope at ×20K magnification. Highly significant changes from baseline values were seen in calcium and phosphorus content of slabs treated with cheese and CPP-ACP-based agent whereas levels of fluoride were significantly higher in enamel slabs treated with fluoride-containing toothpaste. Cheese is an organic, economical, and user-friendly option over prescribed synthetic agents. A synergistic effect of fluoride-containing toothpaste with intake of cheese could be a good enamel remineralization protocol.

Subduction Thermal Regime, Slab Dehydration, and Seismicity Distribution Beneath Hikurangi Based on 3-D Simulations

NASA Astrophysics Data System (ADS)

Suenaga, Nobuaki; Ji, Yingfeng; Yoshioka, Shoichi; Feng, Deshan

2018-04-01

The downdip limit of seismogenic interfaces inferred from the subduction thermal regime by thermal models has been suggested to relate to the faulting instability caused by the brittle failure regime in various plate convergent systems. However, the featured three-dimensional thermal state, especially along the horizontal (trench-parallel) direction of a subducted oceanic plate, remains poorly constrained. To robustly investigate and further map the horizontal (trench-parallel) distribution of the subduction regime and subsequently induced slab dewatering in a descending plate beneath a convergent margin, we construct a regional thermal model that incorporates an up-to-date three-dimensional slab geometry and the MORVEL plate velocity to simulate the plate subduction history in Hikurangi. Our calculations suggest an identified thrust zone featuring remarkable slab dehydration near the Taupo volcanic arc in the North Island distributed in the Kapiti, Manawatu, and Raukumara region. The calculated average subduction-associated slab dehydration of 0.09 to 0.12 wt%/km is greater than the dehydration in other portions of the descending slab and possibly contributes to an along-arc variation in the interplate pore fluid pressure. A large-scale slab dehydration (>0.05 wt%/km) and a high thermal gradient (>4 °C/km) are also identified in the Kapiti, Manawatu, and Raukumara region and are associated with frequent deep slow slip events. An intraslab dehydration that exceeds 0.2 wt%/km beneath Manawatu near the source region of tectonic tremors suggests an unknown relationship in the genesis of slow earthquakes.

Effects of a semi-infinite stratification on the Rayleigh-Taylor instability in an interface with surface tension

NASA Astrophysics Data System (ADS)

de Andrea González, Ángel; González-Gutiérrez, Leo M.

2017-09-01

The Rayleigh-Taylor instability (RTI) in an infinite slab where a constant density lower fluid is initially separated from an upper stratified fluid is discussed in linear regime. The upper fluid is of increasing exponential density and surface tension is considered between both of them. It was found useful to study stability by using the initial value problem approach (IVP), so that we ensure the inclusion of certain continuum modes, otherwise neglected. This methodology includes the branch cut in the complex plane, consequently, in addition to discrete modes (surface RTI modes), a set of continuum modes (internal RTI modes) also appears. As a result, the usual information given by the normal mode method is now complete. Furthermore, a new role is found for surface tension: to transform surface RTI modes (discrete spectrum) into internal RTI modes belonging to a continuous spectrum at a critical wavenumber. As a consequence, the cut-off wavenumber disappears: i.e. the growth rate of the RTI surface mode does not decay to zero at the cut-off wavenumber, as previous researchers used to believe. Finally, we found that, due to the continuum, the asymptotic behavior of the perturbation with respect to time is slower than the exponential when only the continuous spectrum exists.

Lessons to be learned from rehabilitation of concrete structures in bleach plants in pulp and paper mills

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nixon, R.

The deterioration of concrete structures due to chloride induced reinforcing steel corrosion such as in elevated concrete floor slabs, columns, and beams in bleach plants is a constant and growing problem within the pulp and paper industry. In general, the condition analysis methods used for assessing the extent of bleach plant concrete degradation include physical testing of drilled concrete core samples, chloride ion concentration testing, half-cell potential measurements, and physical sounding of concrete surfaces, i.e. chain drag for topside surfaces and hammer sounding of soffit surfaces. While this paper does not promote any vastly different evaluative methods, it does sharemore » learnings relative to interpreting the data provided by these typical test methods. It further offers some recommendations on how to improve the use of these typical evaluation techniques and offers some other test methods which should be considered as valuable additions for such evaluations. One of the most common methods which has been used in the past for large scale bleach plant concrete restoration has been the application of site dry mixed shotcrete for rebuilding the soffits of floor slabs and the faces of columns and beams. More often than not, bulk mixed dry shotcrete repairs have not been cost-effective because they prematurely failed due to excessive hydration related shrinkage cracking, lack of sufficient adhesion to the parent concrete substrate or other problems related to poor durability or construction practice.« less

Current Practices on Nighttime Pavement Construction Asphaltic Concrete.

DTIC Science & Technology

1982-07-01

repair: None g. Slab removals and replacements: None. h. Other ( mudjacking , asphalt underseal): None. i. Heater scarifying: None. j. Milling: None. k...g. Slab removals and replacements: None. h. Other ( mudjacking , asphalt underseal): None. i. Heater scarifying: None. j. Milling was performed...None e. "D" line cracking repair - None f. Spall repair - None g. Slab removals and replacements - None h. Other ( mudjacking , asphalt underseal) - None

Anomalous refraction of a low divergence monochromatic light beam in a transparent slab.

PubMed

Lequime, Michel; Amra, Claude

2018-04-01

An exact formulation for the propagation of a monochromatic wave packet impinging on a transparent, homogeneous, isotropic, and parallel slab at oblique incidence is given. Approximate formulas are derived for low divergence light beams. These formulas show the presence of anomalous refraction phenomena at any slab thickness, including negative refraction and flat lensing effects, induced by reflection at the rear face.

Re-Os isotopic systematics of primitive lavas from the Lassen region of the Cascade arc, California

USGS Publications Warehouse

Borg, L.E.; Brandon, A.D.; Clynne, M.A.; Walker, R.J.

2000-01-01

Rhenium-osmium isotopic systematics of primitive calc-alkaline lavas from the Lassen region appear to be controlled by mantle wedge processes. Lavas with a large proportion of slab component have relatively low Re and Os abundances, and have radiogenic Os and mid ocean ridge basalt-like Sr and Pb isotopic compositions. Lavas with a small proportion of slab component have higher Re and Os elemental abundances and display mantle-like Os, Sr, Nd, and Pb isotopic compositions. Assimilation with fractional crystallization can only generate the Re-Os systematics of the Lassen lavas from a common parent if the distribution coefficient for Re in sulfide is ~40-1100 times higher than most published estimates and if most incompatible element abundances decrease during differentiation. High Re/Os ratios in mid ocean ridge basalts makes subducted oceanic crust a potential source of radiogenic Os in volcanic arcs. The slab beneath the southernmost Cascades is estimated to have 187Os/188Os ratios as high as 1.4. Mixing between a slab component and mantle wedge peridotite can generate the Os isotopic systematics of the Lassen lavas provided the slab component has a Sr/Os ratio of ~7.5X105 and Os abundances that are 100-600 times higher than mid ocean ridge basalts. For this model to be correct, Os must be readily mobilized and concentrated in the slab component, perhaps as a result of high water and HCl fugacities in this subduction environment. Another possible mechanism to account for the correlation between the magnitude of the subduction geochemical signature and Os isotopic composition involves increasing the stability of an Os-bearing phase in mantle wedge peridotites as a result of fluxing with the slab component. Melting of such a source could yield low Os magmas that are more susceptible to crustal contamination, and hence have more radiogenic Os isotopic compositions, than magmas derived from sources with a smaller contribution from the slab. Thus, the addition of the slab component to the mantle wedge appears to result in either the direct or indirect addition of radiogenic Os to arc magmas. (C) 2000 Elsevier Science B.V. All rights reserved.

ICANT, a code for the self-consistent computation of ICRH antenna coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pecoul, S.; Heuraux, S.; Koch, R.

1996-02-01

The code deals with 3D antenna structures (finite length antennae) that are used to launch electromagnetic waves into tokamak plasmas. The antenna radiation problem is solved using a finite boundary element technique combined with a spectral solution of the interior problem. The slab approximation is used, and periodicity in {ital y} and {ital z} directions is introduced to account for toroidal geometry. We present results for various types of antennae radiating in vacuum: antenna with a finite Faraday screen and ideal Faraday screen, antenna with side limiters and phased antenna arrays. The results (radiated power, current profile) obtained are verymore » close to analytical solutions when available. {copyright} {ital 1996 American Institute of Physics.}« less

Continental and oceanic crustal structure of the Pampean flat slab region, western Argentina, using receiver function analysis: new high-resolution results

NASA Astrophysics Data System (ADS)

Gans, Christine R.; Beck, Susan L.; Zandt, George; Gilbert, Hersh; Alvarado, Patricia; Anderson, Megan; Linkimer, Lepolt

2011-07-01

The Pampean flat slab of central Chile and Argentina (30°-32°S) has strongly influenced Cenozoic tectonics in western Argentina, which contains both the thick-skinned, basement-cored uplifts of the Sierras Pampeanas and the thin-skinned Andean Precordillera fold and thrust belt. In this region of South America, the Nazca Plate is subducting nearly horizontally beneath the South American Plate at ˜100 km depth. To gain a better understanding of the deeper structure of this region, including the transition from flat to 'normal' subduction to the south, three IRIS-PASSCAL arrays of broad-band seismic stations have been deployed in central Argentina. Using the dense SIEMBRA array, combined with the broader CHARGE and ESP arrays, the flat slab is imaged for the first time in 3-D detail using receiver function (RF) analysis. A distinct pair of RF arrivals consisting of a negative pulse that marks the top of the oceanic crust, followed by a positive pulse, which indicates the base of the oceanic crust, can be used to map the slab's structure. Depths to Moho and oceanic crustal thicknesses estimated from RF results provide new, more detailed regional maps. An improved depth to continental Moho map shows depths of more than 70 km in the main Cordillera and ˜50 km in the western Sierras Pampeanas, that shallow to ˜35 km in the eastern Sierras Pampeanas. Depth to Moho contours roughly follow terrane boundaries. Offshore, the hotspot seamount chain of the Juan Fernández Ridge (JFR) is thought to create overthickened oceanic crust, providing a mechanism for flat slab subduction. By comparing synthetic RFs, based on various structures, to the observed RF signal we determine that the thickness of the oceanic crust at the top of the slab averages at least ˜13-19 km, supporting the idea of a moderately overthickened crust to provide the additional buoyancy for the slab to remain flat. The overthickened region is broader than the area directly aligned with the path of the JFR, however, and indicates, along with the slab earthquake locations, that the flat slab area is wider than the JFR volcanic chain observed in the offshore bathymetry. Further, RFs indicate that the subducted oceanic crust in the region directly along the path of the subducted ridge is broken by trench-parallel faults. One explanation for these faults is that they are older structures within the oceanic crust that were created when the slab subducted. Alternatively, it is possible that faults formed recently from tectonic underplating caused by increased interplate coupling in the flat slab region.

Trench dynamics: Effects of dynamically migrating trench on subducting slab morphology and characteristics of subduction zones systems

NASA Astrophysics Data System (ADS)

Yoshida, Masaki

2017-07-01

Understanding the mechanisms of trench migration (retreat or advance) is crucial to characterizing the driving forces of Earth's tectonics plates, the origins of subducting slab morphologies in the deep mantle, and identifying the characteristics of subduction zones systems, which are among the fundamental issues of solid Earth science. A series of numerical simulations of mantle convection, focusing on plate subduction in a three-dimensional (3-D) regional spherical shell coordinate system, was performed to examine subduction zone characteristics, including geodynamic relationships among trench migration, back-arc stress, and slab morphology. The results show that a subducting slab tends to deflect around the base of the mantle transition zone and form a sub-horizontal slab because its front edge (its 'toe') is subject to resistance from the highly viscous lower mantle. As the sub-horizontal slab starts to penetrate into the lower mantle from its 'heel,' the toe of the slab is drawn into the lower mantle. The results for models with dynamically migrating trenches suggest that trench retreat is the dynamically self-consistent phenomenon in trench migration. The reason for this is that the strong lateral mantle flow that is generated as a sequence of events leading from corner flow at the subduction initiation to return flow of the formation of a sub-horizontal slab in the shallower part of mantle wedge produces the retreat of the subducting slab. In fact, a 'mantle suction force,' which is generated in the mantle wedge to fill space left by the retreating subducting plate, is enhanced by the subsequent trench retreat. Even when upwelling flow with significant positive buoyancy originates just above a mantle phase boundary at a depth of 410 km (as inferred from independent seismic tomographic, geodynamic, geochemical, and mineral physics), reaches the base of the overriding plate, and the overriding plate is slightly thinned, lithospheric stress tends to be compressed above the upwelling flow. The reason for this is that the strong lateral mantle flow originating from the upwelling flow generates resistance drag force at the base of the overriding plates. This situation may apply to a case of East Asia, under which the typical morphology of sub-horizontal slabs can be seen by seismic tomography. The strong lateral velocity observed in the shallower mantle wedge in the present numerical simulation may account for both the compressional subduction tectonics and back arc compression in the Japan-Kuril-Kamchatka, Aleutian, and South Chile trenches, as well as for weak plate-slab coupling, strong seismic coupling, and the possibility of great earthquakes along these trenches.

Thermal structure and geodynamics of subduction zones

NASA Astrophysics Data System (ADS)

Wada, Ikuko

The thermal structure of subduction zones depends on the age-controlled thermal state of the subducting slab and mantle wedge flow. Observations indicate that the shallow part of the forearc mantle wedge is stagnant and the slab-mantle interface is weakened. In this dissertation, the role of the interface strength in controlling mantle wedge flow, thermal structure, and a wide range of subduction zone processes is investigated through two-dimensional finite-element modelling and a global synthesis of geological and geophysical observations. The model reveals that the strong temperature-dependence of the mantle strength always results in full slab-mantle decoupling along the weakened part of the interface and hence complete stagnation of the overlying mantle. The interface immediately downdip of the zone of decoupling is fully coupled, and the overlying mantle is driven to flow at a rate compatible with the subduction rate. The sharpness of the transition from decoupling to coupling depends on the rheology assumed and increases with the nonlinearity of the flow system. This bimodal behaviour of the wedge flow gives rise to a strong thermal contrast between the cold stagnant and hot flowing parts of the mantle wedge. The maximum depth of decoupling (MDD) thus dictates the thermal regime of the forearc. Observed surface heat flow patterns and petrologically and geochemically estimated mantle wedge temperatures beneath the volcanic arc require an MDD of 70--80 km in most, if not all, subduction zones regardless of their thermal regime of the slab. The common MDD of 70--80 km explains the observed systematic variations of the petrologic, seismological, and volcanic processes with the thermal state of the slab and thus explains the rich diversity of subduction zones in a unified fashion. Models for warm-slab subduction zones such as Cascadia and Nankai predict shallow dehydration of the slab beneath the cold stagnant part of the mantle wedge, which provides ample fluid for mantle wedge serpentinization in the forearc but little fluid for melt generation beneath the arc. In contrast, models for colder-slab subduction zones such as NE Japan and Kamchatka predict deeper dehydration, which provides greater fluid supply for melt generation beneath the arc and allows deeper occurrence of intraslab earthquakes but less fluid for forearc mantle wedge serpentinization. The common MDD also explains the intriguing uniform configuration of subduction zones, that is, the volcanic arc always tends to be situated where the slab is at about 100 km depth. The sudden onset of mantle wedge flow downdip of the common MDD overshadows the thermal effect of the slab, and the resultant thermal field and slab dehydration control the location of the volcanic arc. The recognition of the fundamental importance of the MDD has important implications to the study of geodynamics and earthquake hazard in subduction zones.

Deformation in the mantle wedge associated with Laramide flat-slab subduction

NASA Astrophysics Data System (ADS)

Behr, W. M.; Smith, D.

2013-12-01

Early Tertiary crustal deformation preserved ~1500 km from the plate boundary in the western U.S. is considered by most to be related to a narrow segment of shallow Farallon-slab subduction, similar to the modern Pampean flat-slab of the central Andes. Evidence that the slab shallowed enough to penetrate several hundred kilometers inboard of the plate boundary includes a) shearing off of lithosphere and underplating of schists derived from the accretionary wedge beneath the volcanic arc; b) a cessation of arc magmatism and eastward sweeping of the magmatic front; and c) mid-Tertiary eruptions as far east as the Four Corners region of serpentinized ultramafic microbreccia (SUM) sourced from very cold, hydrated mantle lithosphere. Included within the SUM diatremes are eclogites interpreted to represent fragments of the slab itself and/or remnants of older rock from the mantle wedge metasomatized and recrystallized to eclogite along the top of the slab. Also included within the SUM diatremes are deformed peridotites that represent pieces of the variably hydrated mantle wedge as well as tectonically eroded and entrained fragments of the plate interface. These include weakly deformed to strongly foliated tectonites, spectacularly sheared mylonites and ultramylonites, and cataclasites, formed at temperatures ranging from 500-650°C. Some of the deformed samples contain hydrous minerals, including antigorite, chlorite, and/or tremolite/pargasite that were formed in-situ prior to or during deformation. We investigate the rheological and seismic properties of the peridotite samples using detailed microstructural and petrological analyses. Initial EBSD data indicate that an antigorite-bearing mylonite exhibits a B-type olivine LPO, whereas an ultramylonite that lacks hydrous minerals exhibits an A-type olivine LPO. This is consistent with experimental data that indicate B-type LPOs form under hydrous conditions; and it suggests that these rocks record a transition from trench-parallel to trench-perpendicular seismic anisotropy, as commonly observed in the mantle wedge above active subduction zones. We also show that the deformation within these sheared peridotites can be used to estimate the magnitude of shear stress along the contact between the Farallon slab and the overlying North American lithosphere. Shear stresses along the plate interface were moderate to high (~40 MPa), allowing a strong degree of interplate coupling, consistent with the stress transfer required to deform the upper plate and produce the basement-cored uplifts characteristic of the Laramide orogeny (e.g. the Rocky Mountains). These results place important natural constraints on flat-slab subduction mechanics. Schematic representation of Laramide flat-slab subduction (modified from Humphreys et al., 2003, Int. Geo. Rev.). The mantle inclusions examined here are sourced from the mantle wedge above the slab and from a serpentinite melange along the slab interface.

Machine Learning and Inverse Problem in Geodynamics

NASA Astrophysics Data System (ADS)

Shahnas, M. H.; Yuen, D. A.; Pysklywec, R.

2017-12-01

During the past few decades numerical modeling and traditional HPC have been widely deployed in many diverse fields for problem solutions. However, in recent years the rapid emergence of machine learning (ML), a subfield of the artificial intelligence (AI), in many fields of sciences, engineering, and finance seems to mark a turning point in the replacement of traditional modeling procedures with artificial intelligence-based techniques. The study of the circulation in the interior of Earth relies on the study of high pressure mineral physics, geochemistry, and petrology where the number of the mantle parameters is large and the thermoelastic parameters are highly pressure- and temperature-dependent. More complexity arises from the fact that many of these parameters that are incorporated in the numerical models as input parameters are not yet well established. In such complex systems the application of machine learning algorithms can play a valuable role. Our focus in this study is the application of supervised machine learning (SML) algorithms in predicting mantle properties with the emphasis on SML techniques in solving the inverse problem. As a sample problem we focus on the spin transition in ferropericlase and perovskite that may cause slab and plume stagnation at mid-mantle depths. The degree of the stagnation depends on the degree of negative density anomaly at the spin transition zone. The training and testing samples for the machine learning models are produced by the numerical convection models with known magnitudes of density anomaly (as the class labels of the samples). The volume fractions of the stagnated slabs and plumes which can be considered as measures for the degree of stagnation are assigned as sample features. The machine learning models can determine the magnitude of the spin transition-induced density anomalies that can cause flow stagnation at mid-mantle depths. Employing support vector machine (SVM) algorithms we show that SML techniques can successfully predict the magnitude of the mantle density anomalies and can also be used in characterizing mantle flow patterns. The technique can be extended to more complex problems in mantle dynamics by employing deep learning algorithms for estimation of mantle properties such as viscosity, elastic parameters, and thermal and chemical anomalies.

Ray trace visualization of negative refraction of light in two-dimensional air-bridged silicon photonic crystal slabs at 1.55 microm.

PubMed

Gan, Lin; Liu, Ya-Zhao; Li, Jiang-Yan; Zhang, Ze-Bo; Zhang, Dao-Zhong; Li, Zhi-Yuan

2009-06-08

We demonstrate design, fabrication, and ray trace observation of negative refraction of near-infrared light in a two-dimensional square lattice of air holes etched into an air-bridged silicon slab. Special surface morphologies are designed to reduce the impedance mismatch when light refracts from a homogeneous silicon slab into the photonic crystal slab. We clearly observed negative refraction of infrared light for TE-like modes in a broad wavelength range by using scanning near-field optical microscopy technology. The experimental results are in good agreement with finite-difference time-domain simulations. The results indicate the designed photonic crystal structure can serve as polarization beam splitter.

Spatially dispersive finite-difference time-domain analysis of sub-wavelength imaging by the wire medium slabs

NASA Astrophysics Data System (ADS)

Zhao, Yan; Belov, Pavel A.; Hao, Yang

2006-06-01

In this paper, a spatially dispersive finite-difference time-domain (FDTD) method to model wire media is developed and validated. Sub-wavelength imaging properties of the finite wire medium slabs are examined. It is demonstrated that the slab with its thickness equal to an integer number of half-wavelengths is capable of transporting images with sub-wavelength resolution from one interface of the slab to another. It is also shown that the operation of such transmission devices is not sensitive to their transverse dimensions, which can be made even comparable to the wavelength. In this case, the edge diffractions are negligible and do not disturb the image formation.

Rayleigh-Taylor instability in accelerated elastic-solid slabs

NASA Astrophysics Data System (ADS)

Piriz, S. A.; Piriz, A. R.; Tahir, N. A.

2017-12-01

We develop the linear theory for the asymptotic growth of the incompressible Rayleigh-Taylor instability of an accelerated solid slab of density ρ2, shear modulus G , and thickness h , placed over a semi-infinite ideal fluid of density ρ1<ρ2 . It extends previous results for Atwood number AT=1 [B. J. Plohr and D. H. Sharp, Z. Angew. Math. Phys. 49, 786 (1998), 10.1007/s000330050121] to arbitrary values of AT and unveil the singular feature of an instability threshold below which the slab is stable for any perturbation wavelength. As a consequence, an accelerated elastic-solid slab is stable if ρ2g h /G ≤2 (1 -AT) /AT .

Experimental and numerical investigation of slabs on ground subjected to concentrated loads

NASA Astrophysics Data System (ADS)

Øverli, Jan

2014-09-01

An experimental program is presented where a slab on ground is subjected to concentrated loading at the centre, the edges and at the corners. Analytical solutions for the ultimate load capacity fit well with the results obtained in the tests. The non-linear behaviour of the slab is captured by performing nonlinear finite element analyses. The soil is modelled as a no-tension bedding and a smeared crack approach is employed for the concrete. Through a parametric study, the finite element model has been used to assess the influence of subgrade stiffness and shrinkage. The results indicate that drying shrinkage can cause severe cracking in slabs on grade.

Software Analytical Instrument for Assessment of the Process of Casting Slabs

NASA Astrophysics Data System (ADS)

Franěk, Zdeněk; Kavička, František; Štětina, Josef; Masarik, Miloš

2010-06-01

The paper describes the original proposal of ways of solution and function of the program equipment for assessment of the process of casting slabs. The program system LITIOS was developed and implemented in EVRAZ Vitkovice Steel Ostrava on the equipment of continuous casting of steel (further only ECC). This program system works on the data warehouse of technological parameters of casting and quality parameters of slabs. It enables an ECC technologist to analyze the course of casting melt and with using statistics methods to set the influence of single technological parameters on the duality of final slabs. The system also enables long term monitoring and optimization of the production.

The relationship between plate velocity and trench viscosity in Newtonian and power-law subduction calculations

NASA Technical Reports Server (NTRS)

King, Scott D.; Hager, Bradford H.

1990-01-01

The relationship between oceanic trench viscosity and oceanic plate velocity is studied using a Newtonian rheology by varying the viscosity at the trench. The plate velocity is a function of the trench viscosity for fixed Rayleigh number and plate/slab viscosity. Slab velocities for non-Newtonian rheology calculations are significantly different from slab velocities from Newtonian rheology calculations at the same effective Rayleigh number. Both models give reasonable strain rates for the slab when compared with estimates of seismic strain rate. Non-Newtonian rheology eliminates the need for imposed weak zones and provides a self-consistent fluid dynamical mechanism for subduction in numerical convection models.

Displacement monitoring of switch track and its slab on a bridge of high speed railway by FBG

NASA Astrophysics Data System (ADS)

Li, Weilai; Li, He; Cheng, Jian; Huang, Xiaomei; Pan, Jianjun; Zhou, Ciming; Yang, Minghong

2011-05-01

In a 350km/h high speed railway line, there is a seamless switch with ballastless slabs built on a bridge. 54 Fiber Bragg Grating detecting cells are employed to monitor the displacement of track and slab. The cell is of extending function of measurement range, up to 50mm displacement, and is of good linearity. Protecting methods for cells and fiber are adopted to keep them surviving from the harsh conditions. The results show that in 75 days, the displacement of the track and sleeper slab was 8-9mm, and the displacement is of high correlation with daily environmental temperature change.

Precise hypocenter distribution and earthquake generating and stress in and around the upper-plane seismic belt in the subducting Pacific slab beneath NE Japan

NASA Astrophysics Data System (ADS)

Kita, S.; Okada, T.; Nakajima, J.; Matsuzawa, T.; Uchida, N.; Hasegawa, A.

2007-12-01

1. Introduction We found an intraslab seismic belt (upper-plane seismic belt) in the upper plane of the double seismic zone within the Pacific slab, running interface at depths of 70-100km beneath the forearc area. The location of the deeper limits of this belt appears to correspond to one of the facies boundaries (from jadeite lawsonite blueschist to lawsonite amphibole eclogite) in the oceanic crust [Kita et al., 2006, GRL]. In this study, we precisely relocated intraslab earthquakes by using travel time differences calculated by the waveform cross-spectrum analysis to obtain more detailed distribution of the upper plane-seismic belt within the Pacific slab beneath NE Japan. We also discuss the stress field in the slab by examining focal mechanisms of the earthquakes. 2. Data and Method We relocated events at depths of 50-00 km for the period from March 2003 to November 2006 from the JMA earthquake catalog. We applied the double-difference hypocenter location method (DDLM) by Waldhauser and Ellsworth (2000) to the arrival time data of the events. We use relative earthquake arrival times determined both by the waveform cross-spectrum analysis and by the catalog-picking data. We also determine focal mechanisms using the P wave polarity. 3. Spatial distribution of relocated hypocenters In the upper portion of the slab crust, seismicity is very active and distributed relatively homogeneously at depths of about 70-100km parallel to the volcanic front, where the upper-plane seismic belt has been found. In the lower portion of slab crust and/or the uppermost portion of the slab mantle, seismicity is spatially very limited to some small areas (each size is about 20 x 20km) at depths around 65km. Two of them correspond to the aftershock area of the 2003 Miyagi (M7.1) intraslab earthquake and that of the 1987 Iwaizumi (M6.6) intraslab earthquake, respectively. Based on the dehydration embrittelment hypothesis, the difference of the spatial distribution of the seismicity in the slab should correspond to the difference of the spatial distribution of the hydrated minerals and their dehydration reactions. In the upper slab crust, the upper-plane seismic belt is found because the hydrated minerals could be distributed homogeneously and the dehydration reaction (from jadeite lawsonite blueschist to lawsonite amphibole eclogite [Hacker et al., 2003b]) occurs perhaps largely at depth of 70-100km. Our result also suggests that in the lower portion of the slab crust and/or the uppermost portion of the slab mantle, the hydrated minerals could be inhomogeneously distributed and the seismicity occurs at depths around 65km, where another dehydration reaction may exist. 4. Characteristics of the focal mechanisms We examined the stress distribution within the slab by using focal mechanisms of the upper plane, interplane and lower plane events. From the plate interface to about 20 km below it, downdip-compressional (DC) type events are dominant. Below 20km from the plate interface, downdip-tensional (DT) type events are dominant. Many of interplane events have DC type focal mechanisms because of their locations in the uppermost portions of the slab mantle. These results indicate that the stress neutral plane from the DC type to DT type could be located at depth of about 20km from the plate interface.

Compositional mantle layering revealed by slab stagnation at ~1000-km depth

PubMed Central

Ballmer, Maxim D.; Schmerr, Nicholas C.; Nakagawa, Takashi; Ritsema, Jeroen

2015-01-01

Improved constraints on lower-mantle composition are fundamental to understand the accretion, differentiation, and thermochemical evolution of our planet. Cosmochemical arguments indicate that lower-mantle rocks may be enriched in Si relative to upper-mantle pyrolite, whereas seismic tomography images suggest whole-mantle convection and hence appear to imply efficient mantle mixing. This study reconciles cosmochemical and geophysical constraints using the stagnation of some slab segments at ~1000-km depth as the key observation. Through numerical modeling of subduction, we show that lower-mantle enrichment in intrinsically dense basaltic lithologies can render slabs neutrally buoyant in the uppermost lower mantle. Slab stagnation (at depths of ~660 and ~1000 km) and unimpeded slab sinking to great depths can coexist if the basalt fraction is ~8% higher in the lower mantle than in the upper mantle, equivalent to a lower-mantle Mg/Si of ~1.18. Global-scale geodynamic models demonstrate that such a moderate compositional gradient across the mantle can persist can in the presence of whole-mantle convection. PMID:26824060

Cattle cruelty and risks of meat contamination at Akinyele cattle market and slaughter slab in Oyo State, Nigeria.

PubMed

Adeyemo, Olanike K; Adeyemi, Isaac G; Awosanya, Emmanuel J

2009-12-01

Cattle transported to the government-run cattle market and slaughter slab in Akinyele, Oyo State, Nigeria on their final voyage are facing a disturbingly cruel, filthy and unsafe environment that is also raising the risk of contamination of meat sold for human consumption. This report gives a picture of what the cattle have to go through before they are slaughtered. This study also reveals cattle awaiting slaughter in abysmal health conditions, cows pulled with extreme force towards lairage and slaughter slab. Equally disturbing is the filthy situation inside the abattoir where the risk of contamination of meat is significant. Also, poor meat handling, transportation and sales practices subject meat to contamination leading to poor quality and exposure of human consumers to health risk. Development of hygienic slaughter slab operations, improved transportation system for both livestock and meat is therefore recommended; not only for Akinyele, but all abattoirs and slaughter slabs in Nigeria.

Discussion on the installation checking method of precast composite floor slab with lattice girders

NASA Astrophysics Data System (ADS)

Chen, Li; Jin, Xing; Wang, Yahui; Zhou, Hele; Gu, Jianing

2018-03-01

Based on the installation checking requirements of China’s current standards and the international norms for prefabricated structural precast components, it proposed an installation checking method for precast composite floor slab with lattice girders. By taking an equivalent composite beam consisted of a single lattice girder and the precast concrete slab as the checking object, compression instability stress of upper chords and yield stress of slab distribution reinforcement at the maximum positive moment, tensile yield stress of upper chords, slab normal section normal compression stress and shear instability stress of diagonal bars at the maximum negative moment were checked. And the bending stress and deflection of support beams, strength and compression stability bearing capacity of the vertical support, shear bearing capacity of the bolt and compression bearing capacity of steel tube wall at the bolt were checked at the same time. Every different checking object was given a specific load value and load combination. Application of installation checking method was given and testified by example.

Potential application of a homogeneous and anisotropic slab as an angle insensitive absorbing material

NASA Astrophysics Data System (ADS)

Wang, Fang; Liu, Chang; Liu, Xiaoning; Niu, Tiaoming; Wang, Jing; Mei, Zhonglei; Qin, Jiayong

2017-06-01

In this paper, a flat and incident angle independence absorbing material is proposed and numerically verified in the optical spectrum. A homogeneous and anisotropic dielectric slab as a non-reflecting layer is first reviewed, and a feasible realization strategy of the slab is then given by using layered isotropic materials. When the loss components of the constitutive materials are not zero, the slab will work as an angle insensitive absorbing layer, and the absorption rate augments with increase of the losses. As the numerical verifications, the field distributions of a metallic cylinder and a triangular metallic object individually covered by the designed absorbing layer are demonstrated. The simulation results show that the designed absorbing layer can efficiently absorb the incident waves with the property of incident angle independence at the operation frequency. This homogeneous slab can be used in one and two dimensional situations for the realization of an invisibility cloak, a carpet cloak and even a skin cloak, if it is used to conformally cover target objects.

Thermodiffusion in concrete slab as a driving force of indoor radon entry.

PubMed

Minkin, L

2001-02-01

The core of the hypotheses considered is that there is an additional strong driving force-the thermodiffusion of radon and soil air in concrete and soils, which can cause an intensive indoor radon entry. A vertical thermogradient in the slab causes thermodiffusion air flux through concrete into the house. The proof of this concept is based on consideration of concrete slab as a micro-porous system having a pore-size distribution that mostly pertains to Knudsen's region and a transition zone of pore sizes. The Knudsen's theory for a transition zone is developed, which is consistent with the known experimental data of thermodiffusion. Calculated thermodiffusion air flux across a concrete slab under thermogradient 80 K m(-1) approximately ranges 1 x 10(-7)-1 x 10(-6) kg x m(-2) x s(-1). The calculated typical radon-bearing advective air velocity in soil due to thermogradient in the slab is about 1 x 10(-6) m x s(-1).

Enhancement of specific absorption rate in lossy dielectric objects using a slab of left-handed material.

PubMed

Zhao, Lei; Cui, Tie Jun

2005-12-01

An enhancement of the specific absorption rate (SAR) inside a lossy dielectric object has been investigated theoretically based on a slab of left-handed medium (LHM). In order to make an accurate analysis of SAR distribution, a proper Green's function involved in the LHM slab is proposed, from which an integral equation for the electric field inside the dielectric object is derived. Such an integral equation has been solved accurately and efficiently using the conjugate gradient method and the fast Fourier transform. We have made a lot of numerical experiments on the SAR distributions inside the dielectric object excited by a line source with and without the LHM slab. Numerical experiments show that SAR can be enhanced tremendously when the LHM slab is involved due to the proper usage of strong surface waves, which will be helpful in the potential biomedical applications for hyperthermia. The physical insight for such a phenomenon has also been discussed.

Oceanic slab melting and mantle metasomatism.

PubMed

Scaillet, B; Prouteau, G

2001-01-01

Modern plate tectonic brings down oceanic crust along subduction zones where it either dehydrates or melts. Those hydrous fluids or melts migrate into the overlying mantle wedge trigerring its melting which produces arc magmas and thus additional continental crust. Nowadays, melting seems to be restricted to cases of young (< 50 Ma) subducted plates. Slab melts are silicic and strongly sodic (trondhjemitic). They are produced at low temperatures (< 1000 degrees C) and under water excess conditions. Their interaction with mantle peridotite produces hydrous metasomatic phases such as amphibole and phlogopite that can be more or less sodium rich. Upon interaction the slab melt becomes less silicic (dacitic to andesitic), and Mg, Ni and Cr richer. Virtually all exposed slab melts display geochemical evidence of ingestion of mantle material. Modern slab melts are thus unlike Archean Trondhjemite-Tonalite-Granodiorite rocks (TTG), which suggests that both types of magmas were generated via different petrogenetic pathways which may imply an Archean tectonic model of crust production different from that of the present-day, subduction-related, one.

Microwave Semiconductor Research - Materials, Devices, Circuits.

DTIC Science & Technology

1982-04-30

34, C.L. Tang and J-M. Halbout, invited talk, SPIE Technical Symposium, Los Angeles, CA (January, 1982). 3. "Observation of light induced refractive index ... index slab its desirable dispersive properties. The relatively poor dispersion characteristics of the uniform dielectric slab can be attributed to the...34, January 1982. 2. H. Zmuda completed his M.S. program. Thesis: "Simplified Dispersion Analysis of the Multistep and Graded Index Dielectric Slab Waveguide

Direct electronic communication at bio-interfaces assisted by layered-metal-hydroxide slab arrays with controlled nano-micro structures.

PubMed

An, Zhe; He, Jing

2011-10-28

The electronic transfer (eT) at bio-interfaces has been achieved by orientating 2D inorganic slabs in a regular arrangement with the slab ab-planes vertical to the electrode substrate. The eT rate is effectively promoted by tuning the nano-micro scale structures of perpendicular LDH arrays. This journal is © The Royal Society of Chemistry 2011

Mid-Mantle Interaction Between the Big, Active Samoan Plume and the Tonga-Kermadec Slabs

NASA Astrophysics Data System (ADS)

Chang, S. J.; Ferreira, A. M. G.; Faccenda, M.

2015-12-01

Mantle plumes play an efficient role in transferring heat from the core-mantle boundary to the surface, where they significantly influence plate tectonics. It is well known that, upon impinging on the lithosphere at spreading ridges or intra-oceanic settings, mantle plumes generate hotspots, Large Igneous Provinces and considerable dynamic topography. However, it is still poorly understood which is the active role of mantle plumes on subducting slabs. Here we show that the stagnancy and fastest trench retreat of the Tonga slab in Southwestern Pacific are consistent with an interaction with the big Samoan plume and the Hikurangi plateau. Our findings are based on comparisons between 3-D anisotropic tomography images and 3-D petrological-thermo-mechanical models, which show complex mantle flow around the slab and intense deformation and anisotropy in the transition zone, explaining several unique features in the Fiji-Tonga area self-consistently. We also found that horizontally polarized shear waves (SH) are faster than vertically polarized shear waves (SV) in the mid mantle beneath the Tonga slab, which may indicate a dominant dislocation creep mechanism during the slab-plume interaction. We propose possible slip systems of bridgmanite in the lower mantle that reconcile the observed seismic anisotropy with thermo-mechanical calculations.

Plate interface rheological switches during subduction infancy: Control on slab penetration and metamorphic sole formation

NASA Astrophysics Data System (ADS)

Agard, P.; Yamato, P.; Soret, M.; Prigent, C.; Guillot, S.; Plunder, A.; Dubacq, B.; Chauvet, A.; Monié, P.

2016-10-01

Subduction infancy corresponds to the first few million years following subduction initiation, when slabs start their descent into the mantle. It coincides with the transient (yet systematic) transfer of material from the top of the slab to the upper plate, as witnessed by metamorphic soles welded beneath obducted ophiolites. Combining structure-lithology-pressure-temperature-time data from metamorphic soles with flow laws derived from experimental rock mechanics, this study highlights two main successive rheological switches across the subduction interface (mantle wedge vs. basalts, then mantle wedge vs. sediments; at ∼800 °C and ∼600 °C, respectively), during which interplate mechanical coupling is maximized by the existence of transiently similar rheologies across the plate contact. We propose that these rheological switches hinder slab penetration and are responsible for slicing the top of the slab and welding crustal pieces (high- then low-temperature metamorphic soles) to the base of the mantle wedge during subduction infancy. This mechanism has implications for the rheological properties of the crust and mantle (and for transient episodes of accretion/exhumation of HP-LT rocks in mature subduction systems) and highlights the role of fluids in enabling subduction to overcome the early resistance to slab penetration.

Slab melting beneath the Cascade Arc driven by dehydration of altered oceanic peridotite

NASA Astrophysics Data System (ADS)

Walowski, K. J.; Wallace, P. J.; Hauri, E. H.; Wada, I.; Clynne, M. A.

2015-05-01

Water is returned to Earth’s interior at subduction zones. However, the processes and pathways by which water leaves the subducting plate and causes melting beneath volcanic arcs are complex; the source of the water--subducting sediment, altered oceanic crust, or hydrated mantle in the downgoing plate--is debated; and the role of slab temperature is unclear. Here we analyse the hydrogen-isotope and trace-element signature of melt inclusions in ash samples from the Cascade Arc, where young, hot lithosphere subducts. Comparing these data with published analyses, we find that fluids in the Cascade magmas are sourced from deeper parts of the subducting slab--hydrated mantle peridotite in the slab interior--compared with fluids in magmas from the Marianas Arc, where older, colder lithosphere subducts. We use geodynamic modelling to show that, in the hotter subduction zone, the upper crust of the subducting slab rapidly dehydrates at shallow depths. With continued subduction, fluids released from the deeper plate interior migrate into the dehydrated parts, causing those to melt. These melts in turn migrate into the overlying mantle wedge, where they trigger further melting. Our results provide a physical model to explain melting of the subducted plate and mass transfer from the slab to the mantle beneath arcs where relatively young oceanic lithosphere is subducted.

Sub-wavelength grating mode transformers in silicon slab waveguides.

PubMed

Bock, Przemek J; Cheben, Pavel; Schmid, Jens H; Delâge, André; Xu, Dan-Xia; Janz, Siegfried; Hall, Trevor J

2009-10-12

We report on several new types of sub-wavelength grating (SWG) gradient index structures for efficient mode coupling in high index contrast slab waveguides. Using a SWG, an adiabatic transition is achieved at the interface between silicon-on-insulator waveguides of different geometries. The SWG transition region minimizes both fundamental mode mismatch loss and coupling to higher order modes. By creating the gradient effective index region in the direction of propagation, we demonstrate that efficient vertical mode transformation can be achieved between slab waveguides of different core thickness. The structures which we propose can be fabricated by a single etch step. Using 3D finite-difference time-domain simulations we study the loss, polarization dependence and the higher order mode excitation for two types (triangular and triangular-transverse) of SWG transition regions between silicon-on-insulator slab waveguides of different core thicknesses. We demonstrate two solutions to reduce the polarization dependent loss of these structures. Finally, we propose an implementation of SWG structures to reduce loss and higher order mode excitation between a slab waveguide and a phase array of an array waveguide grating (AWG). Compared to a conventional AWG, the loss is reduced from -1.4 dB to < -0.2 dB at the slab-array interface.

Water transportation ability of flat-lying slabs in the mantle transition zone and implications for craton destruction

NASA Astrophysics Data System (ADS)

Wang, Zhensheng; Kusky, Timothy M.; Capitanio, Fabio A.

2018-01-01

Water transported by deep subduction to the mantle transition zone (MTZ) that is eventually released and migrates upwards is invoked as a likely cause for hydroweakening and cratonic lithosphere destruction. The destruction of the North China Craton (NCC) during the Mesozoic has been proposed to be related to hydroweakening. However, the source of water related to large-scale craton destruction in the NCC is poorly constrained. Some suggest that the water was mainly released from a flat-lying (or stagnating) slab in the MTZ, whereas others posit that most water was released from a previously existing strongly hydrous MTZ then perturbed by the stagnating subduction in the MTZ layer. In this study, we use numerical modeling to evaluate the water carrying ability of flat-lying slabs in the MTZ with different slab ages and water contents to simulate its maximum value and discuss its potential role on large-scale hydroweakening and craton destruction. Our results reveal that a single flat-lying slab in the MTZ cannot provide enough water for large-scale cratonic lithosphere hydroweakening and thinning. Water estimates invoked for craton destruction as experienced by the NCC can only be the result of long-term piling of multiple slabs in the MTZ or penetrating deeper into the lower mantle.

Slab temperature controls on the Tonga double seismic zone and slab mantle dehydration

PubMed Central

Wei, S. Shawn; Wiens, Douglas A.; van Keken, Peter E.; Cai, Chen

2017-01-01

Double seismic zones are two-layered distributions of intermediate-depth earthquakes that provide insight into the thermomechanical state of subducting slabs. We present new precise hypocenters of intermediate-depth earthquakes in the Tonga subduction zone obtained using data from local island–based, ocean-bottom, and global seismographs. The results show a downdip compressional upper plane and a downdip tensional lower plane with a separation of about 30 km. The double seismic zone in Tonga extends to a depth of about 300 km, deeper than in any other subduction system. This is due to the lower slab temperatures resulting from faster subduction, as indicated by a global trend toward deeper double seismic zones in colder slabs. In addition, a line of high seismicity in the upper plane is observed at a depth of 160 to 280 km, which shallows southward as the convergence rate decreases. Thermal modeling shows that the earthquakes in this “seismic belt” occur at various pressures but at a nearly constant temperature, highlighting the important role of temperature in triggering intermediate-depth earthquakes. This seismic belt may correspond to regions where the subducting mantle first reaches a temperature of ~500°C, implying that metamorphic dehydration of mantle minerals in the slab provides water to enhance faulting. PMID:28097220

van der Waals torque and force between dielectrically anisotropic layered media.

PubMed

Lu, Bing-Sui; Podgornik, Rudolf

2016-07-28

We analyse van der Waals interactions between a pair of dielectrically anisotropic plane-layered media interacting across a dielectrically isotropic solvent medium. We develop a general formalism based on transfer matrices to investigate the van der Waals torque and force in the limit of weak birefringence and dielectric matching between the ordinary axes of the anisotropic layers and the solvent. We apply this formalism to study the following systems: (i) a pair of single anisotropic layers, (ii) a single anisotropic layer interacting with a multilayered slab consisting of alternating anisotropic and isotropic layers, and (iii) a pair of multilayered slabs each consisting of alternating anisotropic and isotropic layers, looking at the cases where the optic axes lie parallel and/or perpendicular to the plane of the layers. For the first case, the optic axes of the oppositely facing anisotropic layers of the two interacting slabs generally possess an angular mismatch, and within each multilayered slab the optic axes may either be the same or undergo constant angular increments across the anisotropic layers. In particular, we examine how the behaviors of the van der Waals torque and force can be "tuned" by adjusting the layer thicknesses, the relative angular increment within each slab, and the angular mismatch between the slabs.