Showing papers on "Slab published in 2000"
TL;DR: Seismic tomography models of the three-dimensional upper mantle velocity structure of the Mediterranean-Carpathian region provide a better understanding of the lithospheric processes governing its geodynamical evolution.
Abstract: Seismic tomography models of the three-dimensional upper mantle velocity structure of the Mediterranean-Carpathian region provide a better understanding of the lithospheric processes governing its geodynamical evolution. Slab detachment, in particular lateral migration of this process along the plate boundary, is a key element in the lithospheric dynamics of the region during the last 20 to 30 million years. It strongly affects arc and trench migration, and causes along-strike variations in vertical motions, stress fields, and magmatism. In a terminal-stage subduction zone, involving collision and suturing, slab detachment is the natural last stage in the gravitational settling of subducted lithosphere.
1,492 citations
TL;DR: The cause and geodynamic impact of fiat subduction are investigated in this article, where the authors conclude that the buoyancy of thickened oceanic crust of moderate to young age and a delay in the basalt to eclogite transition due to the cool thermal structure of two overlapping lithospheres is the main cause of the fast deformation of the Peru fiat slab segment.
Abstract: The cause and geodynamic impact of fiat subduction are investigated. First, the 1500 km long Peru fiat slab segment is examined. Earthquake hypocenter data image two morphologic highs in the subducting Nazca Plate which correlate with the posi- tions of subducted oceanic plateaus. Travel time tomo- graphic images confirm the three-dimensional slab ge- ometry and suggest a lithospheric tear may bound the NW edge of the fiat slab segment, with possible slab de- tachment occurring down dip as well. Other fiat slab re- gions worldwide are discussed: central Chile, Ecuador, NW Colombia, Costa Rica, Mexico, southern Alaska, SW Japan, and western New Guinea. Flat subduction is shown to be a widespread phenomenon, occuring in 10% of modern convergent margins. in nearly all these cases, as a spatial and temporal correlation is observed between subducting oceanic plateaus and fiat subduc- tion, we conclude that fiat subduction is caused pri- marily by (1) the buoyancy of thickened oceanic crust of moderate to young age and (2) a delay in the basalt to eclogite transition due to the cool thermal structure of two overlapping lithospheres. A statistical analysis of seismicity along the entire length of the Andes demon- strates that seismic energy release in the upper plate at a distance of 250-800 km from the trench is on aver- age 3-5 times greater above fiat slab segments than for adjacent steep slab segments. We propose this is due to higher interplate coupling and the cold, strong rhe- ology of the overriding lithosphere which thus enables stress and deformation to be transmitted hundreds of kilometers into the heart of the upper plate.
673 citations
Abstract: Analytic properties of the reflection coefficient of a multilayer metal-backed slab are considered. The result is a new form of the dispersion relationship, which characterizes the integral of the reflectance over wavelength in terms of the total thickness and averaged static permeability of the slab. The relation may be transformed to an inequality, which produces the least thickness to bandwidth ratio achievable for a physically realizable radar absorber. The particular cases of broad-band and narrow-band absorbers are discussed. The least thickness of a 10-dB broad-band dielectric radar absorber is shown to be 1/17 of the largest operating wavelength. The discussion also involves the results of a numerical study.
608 citations
TL;DR: In this paper, local and regional geochemical trends are observed in all the segments of the arc, regardless of the intensity of the slab signature, indicating that marine stratigraphy controls some geochemical characteristics of the lavas.
Abstract: The sedimentary section (at DSDP Site 495) on the subducting Cocos Plate has large stratigraphic changes in incompatible elements and element ratios, the result of early carbonate deposition followed by late hemipelagic deposition. Lavas from Central America define both local and regional geochemical trends that reflect the strong influence of the two Cocos Plate sediment units. Element ratios with large stratigraphic variations on the Cocos Plate (e.g. Ba/Th, U/La) define local variations within individual volcanic centers in Central America, indicating that marine stratigraphy controls some geochemical characteristics of the lavas. These local trends can be explained by changing the proportions of hemipelagic sediment input into the magma generation process. These local trends are observed in all the segments of the arc, regardless of the intensity of the slab signature. Regional variations are most clearly seen in element ratios that are nearly constant through the Cocos Plate sediment stratigraphy (e.g. Ba/La, U/Th), suggesting that regional variations reflect differences in the intensity of the flux from the subducting slab. The slab signal is strongest in Nicaragua and along the volcanic front. The signal decreases to the northwest and southeast of Nicaragua and toward the back arc. The large slab signature in the lavas from western Nicaragua occurs in the area with the thinnest continental crust and steepest dip of the slab. The mass flux of incompatible elements into the system is easily estimated, except for elements, like Pb, that have high and variable abundances in the basaltic oceanic crust section. The mass flux of elements out of the system depends on eruption rates, which are variable along the arc and only approximately known. Comparison of input and output fluxes for five different segments of the arc reveals that some elements (K, B, Cs, and Rb) are very efficiently delivered to the volcanoes from the subducted slab. Other elements (Sr, Ba, and U) are returned to the surface with moderate efficiency, whereas some elements (REEs) may come mostly from the mantle wedge with minor slab contribution. The relative order of recycling efficiencies of incompatible elements implies that a hydrous fluid dominates the transfer of material from the slab to mantle.
317 citations
TL;DR: In this article, the frequency band structure of an infinite photonic crystal and the transmission, reflection and absorption coefficients of light by a slab of this crystal are calculated using a new version of a program.
258 citations
TL;DR: A three-dimensional spherical computer model of mantle convection is used to show that seismic images of the subducted Farallon plate provide strong evidence for a Mesozoic period of low-angle subduction under North America.
Abstract: The high-resolution seismic imaging of subducted oceanic slabs1,2 has become a powerful tool for reconstructing palaeogeography3. The images can now be interpreted quantitatively by comparison with models of the general circulation of the Earth's mantle4. Here we use a three-dimensional spherical computer model of mantle convection5,6 to show that seismic images of the subducted Farallon plate provide strong evidence for a Mesozoic period of low-angle subduction under North America. Such a period of low-angle subduction has been invoked independently to explain Rocky Mountain uplift far inland from the plate boundary during the Laramide orogeny7. The computer simulations also allow us to locate the largely unknown Kula–Farallon spreading plate boundary, the location of which is important for inferring the trajectories of ‘suspect’ terrain across the Pacific basin8.
187 citations
TL;DR: In this paper, the phase change problem is divided into sub-problems and solved progressively, with special emphasis on minimizing the rising of junction temperatures due to thermal transient effects, and quasi-steady state solutions are obtained both for the melt depth and the evolution of surface temperature as functions of time and Biot number.
148 citations
TL;DR: In this paper, a series of cyclic tests on shear connections with floor slabs were conducted to evaluate the strength, stiffness, and ductility of these connections under cyclic loading.
Abstract: The problems with welded moment connections in the Northridge earthquake of 1994 gave researchers incentive to examine the actual contribution of the simple, or shear, connections to the lateral resistance of welded steel moment-frame buildings With the composite action of the floor slab, these connections may have more lateral resistance than traditionally assumed; thus, they may be used in the repair or retrofit of damaged welded steel moment-frame buildings or used more actively in new construction To evaluate these possibilities, and to establish the strength, stiffness, and ductility of these connections under cyclic loading, two series of eight full-scale, cyclic tests on shear connections with floor slabs were planned The first test series has demonstrated the cyclic behavior of the simple connections and has shown that these “pinned” connections have significant moment capacities, both on their own and with the contribution of the floor slab This paper summarizes the results of the first eight
141 citations
TL;DR: In this paper, a modified weighted slab technique along with recent values of the relevant cross sections was employed to compute primary to secondary ratios including B/C and Sub-Fe/Fe for different galactic propagation models.
Abstract: In an attempt to understand the source and propagation of galactic cosmic rays we have employed the Modified Weighted Slab technique along with recent values of the relevant cross sections to compute primary to secondary ratios including B/C and Sub-Fe/Fe for different galactic propagation models. The models that we have considered are the disk-halo diffusion model, the dynamical halo wind model, the turbulent diffusion model and a model with minimal reacceleration. The modified weighted slab technique will be briefly discussed and a more detailed description of the models will be given. We will also discuss the impact that the various models have on the problem of anisotropy at high energy and discuss what properties of a particular model bear on this issue.
138 citations
TL;DR: In this article, a quasi-three-level laser design with the pump light incident from the slab edge is presented. But the design does not address the problem of thermal distortion and power scaling.
Abstract: We present a novel design for a quasi-three-level laser. The design uses a slab laser configuration with the pump light incident from the slab edge. This allows a lower threshold and better power scaling than a conventional face-pumped slab. We present an analytic description of pumping optimization, thermal distortion, and power scaling. Several point designs illustrating power scaling are also described.
132 citations
TL;DR: In this paper, the distribution of Nb and Ta among the continental crust, the depleted mantle and subducted slabs and mass balance of bulk-silicate-earth require that a significant mass of deeply-subducted oceanic slabs is hidden in the lower mantle.
TL;DR: In this paper, the effectiveness of using the reduced beam section and welded haunch for seismic rehabilitation of pre-Northridge steel moment connections was investigated through cyclic testing of six full-scale specimens.
Abstract: The effectiveness of using the reduced beam section (RBS) and welded haunch for seismic rehabilitation of pre-Northridge steel moment connections was investigated through cyclic testing of six full-scale specimens—three of them incorporated lightweight concrete slabs. Test results showed that, unless the low-toughness E70T-4 groove weld was replaced by notch-tough weld metal, introducing RBS to the beam bottom flange alone could not prevent brittle fracture in the groove weld of the top flange. The presence of a concrete slab or removing steel backing only improved the cyclic performance slightly. Although two RBS specimens with weld replacement performed well, a new type of ductile fracture along the “k” line of the beam was observed. With E70T-4 groove welds in place, however, the welded haunch specimens performed better than the RBS specimens. No brittle fracture occurred when the slab was present. The composite slab only increased the beam positive flexural strength by about 10%.
TL;DR: In this article, a slab of semiconductor material is placed between two photonic bandgap (PBG) mirrors, and waveguide modes at frequencies out of the PBG can be obtained.
Abstract: We show that by placing a slab of semiconductor material between two photonic bandgap (PBG) mirrors, waveguide modes at frequencies out of the PBG can be obtained. These modes are similar to the modes of a conventional dielectric slab waveguide. Using these modes, we can obtain very good coupling between a PBG waveguide and a dielectric slab waveguide with similar slab properties. We discuss the properties of these slab modes and outline the guideline for the optimization of the PBG waveguides based on these properties.
TL;DR: In this article, it was found that the composite flooring system, comprising lightweight concrete, anti-crack mesh reinforcement and steel deck, had a greater inherent fire resistance than suggested by current codified design methods.
TL;DR: In this paper, the authors consider the mechanism of viscous Rayleigh-Taylor-type removal of gravitationally unstable lithosphere and explore alternate styles of deep lithospheric deformation during tectonic convergence.
Abstract: In studying orogenic processes, the mechanism of viscous Rayleigh-Taylor–type removal of gravitationally unstable lithosphere is often invoked to explain the behavior of the mantle lithosphere. Using numerical models, we consider this mechanism and explore alternate styles of deep lithospheric deformation during tectonic convergence. The numerical experiments incorporate a mix of viscous and plastic rheologies to model the mechanical evolution of the lithosphere-asthenosphere system. Our results suggest that there are a number of deformational modes of the model mantle lithosphere: (1) a dripping or Rayleigh-Taylor–type instability; (2) an asymmetric underthrusting or subduction; (3) symmetric, ablative plate consumption; (4) slab breakoff, the failure and detachment of the strong lithosphere; and (5) mixed modes with combinations of these processes. The development of the modes is controlled by the rate of convergence associated with the background tectonic regime, the density field, and the rheology of the mantle lithosphere. It is important to determine whether these modes occur in the Earth beneath collisional orogens.
TL;DR: In this article, the directional emission intensities emerging from a parallel plane slab or semi-transparent media in which is imposed a variable spatial refractive index, have been determined by a curved ray-tracing method determining the trajectories of radiation propagation and integrating the radiative transfer equation on each of these trajectories.
Abstract: The directional emission intensities emerging from a parallel plane slab or semi-transparent media in which is imposed a variable spatial refractive index, have been determined by a curved ray-tracing method determining the trajectories of radiation propagation and integrating the radiative transfer equation on each of these trajectories. Cases of linear and sinusoidal refractive indexes are examined, for both isothermal and non-isothermal situations, which display significant differences from the case of a constant refractive index.
TL;DR: In this article, the authors show that 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 ∼7.5×105 and Os abundances that are 100-600 times higher than mid ocean ridge basalts.
TL;DR: In this article, an analytical-Ritz method is developed to study the vibratory characteristics of the elastic thin plate placed into a rectangular hole and connected to the rigid bottom slab of a rectangular container filled with fluid having a free surface.
01 Jan 2000
TL;DR: In this paper, the authors determined whether shear wave splitting observed in subduction zone back arc regions can be quantitatively modeled with flow in the back arc mantle driven by the motions of the subducting slab and the upper back arc plate.
Abstract: The goal of this study is to determine whether shear wave splitting observed in subduction zone back arc regions, the Tonga subduction zone in particular, can be quantitatively modeled with flow in the back arc mantle driven by the motions of the subducting slab and the upper back arc plate. We calculated two-dimensional mantle flow models using known Tonga plate motions as boundary conditions and assuming a range of uniform and variable viscosity structures. Shear wave splitting was predicted for the anisotropy due to lattice preferred orien- tation (LPO) of olivine and orthopyroxene in the flow model finite strain fields. The predicted shear wave splitting provides a good match to the fast directions (parallel to the azimuth of subducting plate motion) and splitting times (0.5-1.5 s) observed in Tonga, both for models where LPO anisotropy develops everywhere above 410 km and for models where LPO anisotropy is confined to regions of relatively high stress. If LPO anisotropy does develop over the entire upper 410 km of the mantle, the strength of anistropy induced by a given amount of shear strain must be relatively weak (-4% for shear strains of 1.5, with a maximum value of-6% for very large strains). The splitting observations are comparably fit by a wide range of different viscosity models. Anisotropy due to melt-filled cracks aligned by stresses in the back arc flow models predicts fast directions roughly normal to observed values and thus cannot alone explain the observed splitting.
TL;DR: In this paper, the authors determined whether shear wave splitting observed in subduction zone back arc regions can be quantitatively modeled with flow in the back arc mantle driven by the motions of the subducting slab and the upper back arc plate.
Abstract: The goal of this study is to determine whether shear wave splitting observed in subduction zone back arc regions, the Tonga subduction zone in particular, can be quantitatively modeled with flow in the back arc mantle driven by the motions of the subducting slab and the upper back arc plate. We calculated two-dimensional mantle flow models using known Tonga plate motions as boundary conditions and assuming a range of uniform and variable viscosity structures. Shear wave splitting was predicted for the anisotropy due to lattice preferred orientation (LPO) of olivine and orthopyroxene in the flow model finite strain fields. The predicted shear wave splitting provides a good match to the fast directions (parallel to the azimuth of subducting plate motion) and splitting times (0.5–1.5 s) observed in Tonga, both for models where LPO anisotropy develops everywhere above 410 km and for models where LPO anisotropy is confined to regions of relatively high stress. If LPO anisotropy does develop over the entire upper 410 km of the mantle, the strength of anistropy induced by a given amount of shear strain must be relatively weak (∼4% for shear strains of 1.5, with a maximum value of ∼6% for very large strains). The splitting observations are comparably fit by a wide range of different viscosity models. Anisotropy due to melt-filled cracks aligned by stresses in the back arc flow models predicts fast directions roughly normal to observed values and thus cannot alone explain the observed splitting.
TL;DR: In this paper, the authors used in situ microphotography and observations of texture to complement strength measurements from shear frame tests to monitor the evolution of persistent weak layers, such as buried surface hoar.
Abstract: Buried layers of surface hoar are the failure plane for many slab avalanches, including fatal human-triggered avalanches in various mountain regions. These layers may persist as weak layers in the snow cover for weeks or months. It is therefore essential for operational avalanche forecasters to monitor the evolution of persistent weak layers, such as buried surface hoar. Traditional grain-shape observations of isolated grains with a magnifier and crystal screen do not show bonding that is decisive for strength. In this study we used in situ microphotography and observations of texture to complement strength measurements from shear frame tests. Buried layers of surface hoar consist of crystals most of which extend from the layer below to the layer above, and may exhibit a columnar or truss-like structure. Observations and measurements show that texture and crystal size change little over periods of up to several months during which the snowpack remains dry. Under these conditions, layer thickness decreases while density and strength increase. Based on field measurements, we argue that the increase in strength is primarily due to penetration of the surface-hoar crystals into the adjacent layers, especially at the bottom of the buried surface-hoar layer, where bonding is critical. The weak bonding at the bottom implies that shear failure occurs at the lower interface rather than within the weak layer. On slopes, we find that surface-hoar crystals that were initially surface-normal are tilted downslope faster than predicted by published shear strain rates for settled snow, indicating that shear strain is concentrated in these layers. The characteristic texture of buried surface hoar (columnar or truss-like) permits collapsing at the time of fracture. The gravitational energy released by the displacement of the slab may contribute to the extensive fracture propagation associated with buried surface-hoar layers.
TL;DR: In this article, the upper mantle discontinuities in a 30×20° large region at the active continental margin of the Japan subduction zone and neighboring areas, using P-to-S converted phases from teleseismic records of permanent broadband stations, were detected within ± 10 km of its global average position.
TL;DR: In this paper, an advanced nonlinear finite-element (FE) program was developed for the analysis of general composite structures of steel and reinforced concrete, including composite space trusses.
Abstract: This paper presents an advanced nonlinear finite-element (FE) program developed for the analysis of general composite structures of steel and reinforced concrete, including composite space trusses. The elements used to represent the concrete slab and steel beam actions are described, and in particular the ability to model ribbed composite slabs of reinforced concrete on profiled steel sheeting is demonstrated. Attention is drawn to the usefulness of the layering technique in determining local stress redistributions associated with progressive through-depth cracking and yielding in the slab and steel beam elements. Concrete is represented as a nonlinear elastic isotropic material before cracking and nonlinear orthotropic thereafter, while steel is taken to be initially elastic with strain-hardening capabilities after yielding. All material models are empirical in origin. A specialized stub element with empirical nonlinear shear force-slip relationships is used at the concrete slab–steel beam interface to p...
TL;DR: In this article, the effectiveness of a floating slab track system to stationary harmonic loads and moving harmonic loads is investigated by using the receptance method, and the results show that the floating slab tracker system is effective in reducing the forces transmitted at frequencies above the designed frequency compared to the fixed slab tracker.
TL;DR: In this paper, three-dimensional analysis is performed for the turbulent reactive flow and radiative heat transfer in the walking-beam-type slab reheating furnace by FLUENT.
Abstract: Three-dimensional analysis is performed for the turbulent reactive flow and radiative heat transfer in the walking-beam-type slab reheating furnace by FLUENT. A simplified burner is validated against the results of the actual burner with the detailed grid resolution to avoid an excessive number of grids. The predicted temperature distribution in the furnace and global energy flow fractions are in reasonable agreement with available data. Distribution of the heat flux to the slabs, velocity vectors, and all major scalar variables in the furnace also are predicted. This study shows that three-dimensional analysis may be a useful tool to understand quantitatively the complicated combustion and heat transfer characteristics in the furnace.
TL;DR: In this paper, a method of analysis for continuous composite beams based on a specific kinematic model of the cross section is proposed, which allows the introduction of a constitutive relationship for bond between reinforcing bars and concrete in the theoretical analysis; thus, the tension stiffening effect in the negative bending moment regions can be computed, and actual mechanical behavior of reinforcing bars of the slab can be analyzed.
Abstract: Negative bending moments arise near the intermediate supports in continuous beams; thus, when steel-concrete composite beams are considered, tensile stresses act on the concrete slab. As a result the structural response generally becomes nonlinear due to two main effects: the slip at the slab-profile interface and cracking in the concrete slab. In the present paper a method of analysis for continuous composite beams based on a specific kinematic model of the cross section is proposed. The main feature of the model is the capability to take into account the slip at the slab-profile interface and the slip at the concrete-reinforcement interface. This approach allows the introduction of a constitutive relationship for bond between reinforcing bars and concrete in the theoretical analysis; thus, the tension stiffening effect in the negative bending moment regions can be computed, and the actual mechanical behavior of reinforcing bars of the slab can be analyzed. The results of numerical analyses are compared ...
TL;DR: In this paper, the authors present designs and test results for several technologies involving cold-formed sections in composite construction, including self-drilling screwed cold formed shear connectors, and built-up sections bolted to precast concrete planks.
TL;DR: In this paper, the Nonsberg ultramafic metamorphic rocks were used to study the evolution of peridotites and pyroxenites in a subducting continental slab.
TL;DR: In this paper, the authors show that slow velocity anomalies exist in the mantle wedge and extend to the forearc region down to the subducting Philippine Sea slab under northern Kyushu.
Abstract: Seismic tomography shows that slow velocity anomalies exist in the mantle wedge and extend to the forearc region down to the subducting Philippine Sea slab under northern Kyushu. We also conducted numerical simulations with petrologic data to estimate the fluid distribution in the mantle wedge. The seismic and simulation results indicate that regimes of melting and magmatism in a subduction zone with a young slab are different from those with old slabs. Dehydration and melting occur beneath the arc and forearc above a young (and warm) slab such as in northern Kyushu (≤ 26 Ma), while fluids (aqueous solution and melt) occur mainly beneath the back arc above old slabs.
TL;DR: In this article, the effects of placing steel fiber-reinforced concrete (SFRC) in the slab and the concentration of slab reinforcement around the column were investigated on the punching shear capacity, negative moment cracking, and stiffness of the two-way slab specimens.
Abstract: Six two-way slab-column specimens, designed to fail in punching shear, were tested. The parameters investigated were the placement of steel fiber-reinforced concrete (SFRC) in the slab and the concentration of slab reinforcement around the column. The effects of these parameters on the punching shear capacity, negative moment cracking, and stiffness of the two-way slab specimens were investigated. Currently, there is no beneficial effect in the 1995 American Concrete Institute Code for using FRC or concentrated slab reinforcement near the column in the calculation for the punching shear resistance. The beneficial effects of concentrating the slab reinforcement near the column and of using FRC are demonstrated.