Showing papers on "Slab published in 1984"

The interaction of a subducting lithospheric slab with a chemical or phase boundary

Abstract: We have used a finite element model of time-dependent convection to determine the conditions for penetration of the subducted plate into the lower mantle. A temperature-dependent and non-Newtonian rheology is applied to achieve platelike behavior of the upper and sinking thermal boundary layer of convection. The 650-km discontinuity is taken as either a chemical or phase boundary or as a combination of both. It is represented by a marker chain which effects additional buoyancy when distorted out of its equilibrium position. When the compositional density contrast is greater than about 5%, the descending slab is deflected sidewards at the boundary and two-layer convection prevails. A resulting depression of the boundary in the range of 50–200 km should be detectable with seismic methods. Below 5% density difference the slab plunges several hundred kilometers into the lower mantle, and below 2% it will probably not stop before reaching the core-mantle boundary and extensive mixing would be expected. With a pure phase change a negative Clapeyron slope of about −6 MPa/K (−60 bar/K) is required to establish a type of “leaky” double-layer convection. A more moderate slope can aid a small compositional density difference to prevent slab penetration into the lower mantle. With the present uncertainties about the physical nature of the 650-km discontinuity, a variety of convective styles appears possible on dynamical grounds.

Slab penetration into the lower mantle

Abstract: To investigate whether or not lithospheric slabs descending along subducting margins penetrate below the 670-km seismic discontinuity, we have analyzed 4040 P and PKIKP travel times from 14 intermediate- and deep-focus earthquakes in the northwestern Pacific and obtained estimates of the near-source anomaly as a function of position on the lower focal hemisphere. Station and ellipticity corrections are applied, and any component of the anomaly explicable by hypocenter mislocation is removed by orthogonalization of the residual vector with respect to the location parameters; the resulting residual sphere is smoothed and interpolated by a stochastic filtering scheme to average out observational errors and the effects of small-scale heterogeneities far from the source. The smoothed residual spheres for six Sea of Okhotsk earthquakes deeper than 500 km are dominated by NE-SW trending troughs of negative anomalies having strikes and dips similar to the seismic zone at these depths; the troughs are bounded on the NW and SE by parallel ridges of positive anomalies, with peak-to-trough amplitudes averaging about 1.5 s. As the focal depth decreases, the pattern translates to the NW, so that for hypocenters near 200 km the negative trough has been replaced by a positive ridge. The axis of the anomaly pattern for two Sea of Japan deep-focus earthquakes is rotated counterclockwise from Okhotsk, consistent with the nearly N-S strike of the Japan seismic zone. These correlations, and the fact that one nearby earthquake not within a subduction zone shows very little anomaly, suggest that the residual sphere anomalies are caused primarily by slab heterogeneity. Forward modeling experiments corroborate this conclusion. The thermal disturbance of the mantle is calculated for an assumed flow field by a finite difference algorithm, and from it a model of P velocity heterogeneity is constructed; theoretical travel time residuals are computed by tracing rays through this three-dimensional structure, and the event is relocated and the residual sphere smoothed using the same station set and by the same algorithm applied to the observations. To obtain a good fit to the deep-focus Okhotsk data requires penetration by the Kuril-Kamchatka slab to depths of at least 900–1000 km. Penetration to much greater depths is consistent with the data. This conclusion agrees with the S wave results of Jordan (1977); it implies the circulation of at least some upper mantle material into the deep mantle and argues against a rigorously stratified upper mantle/lower mantle convective system.

Laramide crustal thickening event in the Rocky Mountain Foreland and Great Plains

Abstract: The Rocky Mountain foreland and Great Plains of the western United States were formerly part of a continental platform, adjusted by erosion and deposition in Cambrian through Jurassic time to near mean sea level, and therefore to a near-uniform crustal thickness of approximately 33 km. Today the region stands at regional elevations up to 2 km, isostatically supported by a crust exceeding 50 km in thickness. Reasonable estimates of Tertiary sedimentation and Laramide strain do not account for more than 15% of the implied thickening. However, from approximately 70-40 m.y. B.P., this region was underlain by a horizontally-subducting slab of Farallon plate lithosphere moving northeast; this slab could have been the cause of the thickening. Finite-difference thermal models with specified kinematics show only a temporary cooling of the base of the North American lithosphere by this slab. The excess weight of the slab would have depressed the region; plate-bending calculations show a quantitative agreement of predicted depression with upper Cretaceous isopachs. Since depression by this slab lasted until the Eocene at least, the latest-Cretaceous regression was probably caused by a Laramide crustal thickening event. The Farallon slab might have caused crustal thickening in two ways. Its excess weight would have drawn in ductile lower crust from surrounding regions. However, calculations show that this effect is too slow, too local, and too reversible to explain most of the crustal thickening. Therefore it seems likely that ductile lower crust was transported from SW to NE by shear stresses which the Farallon plate exerted on the base of the North American lithosphere. A preliminary finite-element calculation based on this hypothesis shows the correct general pattern of crustal thickening. An unexpected but encouraging result is that predicted principal compression directions are orthogonal to many Laramide basement uplifts.

Preventing Progressive Collapse of Slab Structures

Abstract: The response of slab structures after initial failure is investigated in order to determine a means of preventing progressive collapse. Analytical models for predicting the post‐failure response of slabs are presented and the predictions are compared with experimental results. These analytical models along with an experimental investigation enabled the development of simple design and detailing guidelines for bottom slab reinforcement which is capable of hanging the slab from the columns after initial failures due to punching shear and flexure.

Continuous chewing gum method

Abstract: A method for continuously forming wide, thin chewing gum slabs suitable for forming sheets and bands ready for packaging in an automatic wrapping machine is disclosed. The method involves compounding a chewing gum paste; extruding the formed gum paste as a wide thin slab through a die mounted on the discharge end of the extruder; cooling the extruded gum paste slab; and passing the gum paste slab through no more than two sets of calender rolls.

Shallow-Buried RC Box-Type Structures

Abstract: A method for the analysis of reinforced concrete (RC) box‐type structures under the effects of severe dynamic loading conditions is presented. The method incorporates theoretical and experimental evaluations of RC slab behavior into a simplified structural model. The effects of dynamic loadings conditions on material properties, flexure, thrust, and shear are considered for model development and analysis. The method is illustrated by example, and comparisons to experimental data are presented.

Selective Freezing of a Dilute Salt Solution on a Cold Ice Surface

Abstract: The growth of a solid-liquid, two-phase region during selective freezing of a dilute, eutectic-forming, salt solution over a subcooled ice slab is investigated experimentally and theoretically. The morphology of the two-phase region and the kinetics of the solid-liquid interface observed for a NaCl-H/sub 2/O system are described photographically. The motion of the two-phase, liquidus front, recorded by a telescopic device that amplifies the local phenomena of the two-phase region is presented along with the measured transient temperature distribution of the system. Based on the assumption that the solution element of the two-phase region is in local thermodynamic equilibrium with the solid phase, a similarity model is developed to predict the dependence of the freezing rate on various controlling parameters of the system. Transient heat conduction in the ice slab is also included in the model to study the effect of the wall. Comparison is made between the analytical and the experimental results and found to be good.

The response of a confined gas to a thermal disturbance: rapid boundary heating

Abstract: An inert compressible gas confined between infinite parallel planar walls is subjected to significant heat addition at the boundaries. The wall temperature is increased during an interval which is scaled by the acoustic time of the container, defined as the passage time of an acoustic wave across the slab. On this time scale heat transfer to the gas occurs in thin conductive boundary layers adjacent to the walls. Temperature increases in these layers cause the gas to expand such that a finite velocity exists at the boundary-layer edge. This mechanical effect, which is like a time-varying piston motion, induces a planar linear acoustic field in the basically adiabatic core of the slab. A spatially homogeneous pressure rise and a bulk velocity field evolve in the core as the result of repeated passage of weak compression waves through the gas. Eventually the thickness of the conduction boundary layers is a significant fraction of the slab width. This occurs on the condition time scale of the slab which is typically a factor of 106 larger than the acoustic time. The further evolution of the thermomechanical response of the gas is dominated by a conductive-convective balance throughout the slab. The evolving spatially-dependent temperature distribution is affected by the homogeneous pressure rise (compressive heating) and by the deformation process occurring in the confined gas. Superimposed on this relatively slowly-varying conduction-dominated field is an acoustic field which is the descendent of that generated on the shorter time scale. The short-time-scale acoustic waves are distorted as they propagate through a slowly-varying inhomogeneous gas in a finite space. Solutions are developed in terms of asymptotic expansions valid when the ratio of the acoustic to conduction time scales is small. The results provide an explicit expression for the piston analogy of boundary heat addition.

Iterative approach to the frequency-domain solution of the inverse-scattering problem for an inhomogeneous lossless dielectric slab

Abstract: A previously developed time-domain iterative inverse-scattering method is generalized to the problem of reconstructing the susceptibility of an inhomogeneous lossless dielectric slab from frequency-domain reflection data. In subsequent iteration steps, approximations for the electric field inside the slab and the unknown susceptibility profile are obtained by alternately solving an approximate direct-scattering problem and an approximate inverse-scattering problem. Numerical results are presented and discussed.

Flexure of the continental lithosphere beneath Apennine and Carpathian foredeep basins

Abstract: The preservation of foredeep basins after an associated mountain belt has been greatly reduced by erosion suggests that an additional load must act on the subducted slab's lithosphere independently of topography. This hypothesis is presently tested for the case of young orogenic belts, through the construction of transects through the Apennine and outer Carpathian thrust belts of the Mediterranean region. A simple elastic model is used to show that the topographic loads present along the transects are not sufficient to cause the observed plate deflection, suggesting that an additional load or downward force is acting on the plate to generate the plate deflection observed. It is proposed that this extra load is due either to the negative buoyancy contrast between the subducted slab and the asthenosphere, or to the crustal structure's modification by backarc rifling in the hinterland.

Composite floor system

Abstract: A novel composite floor system is described, together with a specific metallic reinforcing and support section for use in the floor system. The system comprises a concrete slab and a metallic reinforcing and support section mechanically embedded in the slab. The support section comprises an elongated unitary strip having a substantially flat central web portion containing a plurality of spaced holes, a pair of substantially flat leg portions extending away from the sides of said web and an edge flange extending outwardly from the outer end of each leg portion, with at least the leg portions and the edge flanges being embedded in the concrete with the web adjacent the face of the slab. Support bolts are mounted within the web portion holes and extend outwardly from the slab. These bolts can be used to support a formwork for the pouring of the concrete slab.

Evidence for a 180-km-long subducted slab beneath northern California

Abstract: We present new seismic data for subduction of a 180-km-long segment of the Gorda plate beneath Cape Mendocino in northern California. The inclined seismic zone dips ∼10 to 11° in the direction S68°E for a length of 120 km to depths of 30 to 35 km, then steepens in dip to 25° and plunges to depths of at least 60 km. P -wave focal mechanisms of two earthquakes at depths of 30 and 58 km are consistent with downdip tension and imply that these events resulted from stresses within the slab and not from Gorda-North American plate interaction.

Analysis of Composite Beams with Web Openings

Abstract: The ultimate strength is derived for a composite beam comprising a ribbed slab and steel section with a large rectangular web opening. Shearing force is assumed to be carried in both the steel section and the slab at the opening, and the method accounts for partial shear connection. Good agreement is demonstrated with maximum loads measured in tests. Comparison with a more detailed theory presented elsewhere shows good agreement over the full range of moment‐to‐shear ratio. Caution is recommended when applying the theory to cases differing substantially from the parameters of the test beams.

Composite slab incorporating a sheet of marble or similar natural stone, for the formation of facings for building, interior decoration and the like

Abstract: A composite facing slab comprises a sheet of natural stone, such as marble, and a protective layer constituted by a sheet of transparent glass. The latter is fixed to the face of the stone sheet intended to remain visible with the interpositioning of an interlayer of transparent thermoplastics material which can adhere to both the sheets and fills the surface defects (pores, cavities, cracks and the like) of the stone sheet.

Method for positioning and stabilizing a concrete slab

Abstract: A method of lifting and stabilizing a concrete slab having an opening therein in which a plate is attached to the top surface of the slab, the plate having an opening coinciding with the opening in the slab, a hydraulic jack having a downwardly extending piston is removeably secured to the plate and a series of tubular shafts are forced downwardly through the opening in the plate and the slab to penetrate the earth beneath the slab and apply lifting force. When the slab has been lifted to the desired elevation, grout, such as a concrete slurry, can be injected below the slab so that the slab is stabilized in the selected elevational position. After the plate is removed the hole in the slab is filled.

Lead Isotopes and Andean Magmagenesis

Abstract: Late Cenozoic volcanics from the northern and southern Andes have restricted Pb isotope compositions which appear unrelated to rock type or basement age. Although regional differences in 2°6Pb/204Pb exist between the two areas, the uniform enrichment in 207Pb and 208Pb in the lavas is likely to be due to Pb leached from sediments and the altered igneous rocks of the subducted slab, which have with time been well mixed into the mantle wedge above the slab.

Finite element modeling of deformations of the lithosphere at an arc-arc junction

Abstract: The stress-field near an arc-arc junction shows an anomalous state against the expectation from the relative motion of converging plates. The Hokkaido corner is a typical example of such anomalous regions, where the compressional axes (P-axes) derived from focal mechanism of earthquakes in the continental lithosphere lie parallel to the strike of trench axes. In order to explain this anomalous state of stress, a three-dimensional finite element method is employed to model the configuration of the Pacific plate subducting beneath the Hokkaido corner. Several types of plate driving forces are taken into consideration: (1) a negative buoyancy due to the density contrast between the subducted lithosphere and the surrounding asthenosphere, (2) a negative buoyancy which might act on the lid of the Sea of Japan to simulate a presumed subduction of the "Japan Sea plate, " (3) a northwestward compressive force generated by the movement of the Pacific plate, (4) a northwestward compressive force due to the flow in the asthenosphere, (5) an eastward compressive force expected from the movement of Eurasia or the assumed "Japan Sea plate, " (6) a drag force exerted at the edge of the subducted slab in the model space, (7) thermal stresses arising in the subducted slab which are caused by the contact with a hot asthenosphere. We calculate the displacements and stresses in the crust and upper mantle around this region, due to these forces under the assumption of viscoelastic rheology, compare them with the observations, and evaluate their relative importance. It is concluded that a negative buoyancy exerted on the descending slab could yield the observed anomalous stress field and that all of the compressive forces under consideration might not play an important role. However, downwarping of crustal vertical movements is predominant over the whole region under consideration in the case of a negative buoyancy acting on the subducted Pacific slab. Other sources such as thermal stresses might be required, which yield upward motions and preserve the trend of P-axes. An anomalous wedge zone which might exist above the subducted slab on the landward side of the junction would have some effects on the generation of the complex stress field.

End clamp for gel slab plate assembly

Abstract: A novel device for clamping together a sandwich-type gel slab plate assembly includes an elongate housing having a recess on one side and two movable bars placed parallel to each other inside the recess. Due to a series of angled parallel surface segments on the lateral edges of the bars and one side wall of the recess, a vertical force against one bar translates into a lateral force against the other, urging the latter toward the other side wall of the recess, clamping the plates in between with even force along the entire length.

Continuous rolling method and apparatus

Abstract: A method and apparatus for rolling strip in line with a continuous caster is disclosed. A slab capable of being coiled say 1.5 inches or less, is passed through an in-line furnace to homogenize temperature and is thereafter coiled in one of two vertically aligned coilers in either side of the pass line. The slab is then payed off into a rolling mill while a subsequent slab is coiled in the other of the two coiler furnaces.

A radiating device with an improved microstrip structure and its application to an adaptable antenna

Abstract: The invention concerns radiating elements of the microstrip type. Dielectrics (not shown) separate a lower metal coating or earth plane (PM), an intermediate metal slab (P11) and an upper metal slab (P12). Slab (P12) is connected to slab (P11) via short circuit pins (CC12), and slab (P11) is connected to the ground plane via short circuit pins (CC11). A coaxial cable has a screening (CB12) electrically connected to the ground plane (PM), whilst its core (CA12) passes through the dielectrics and without contact with either the ground plane or with the intermediate slab (P11), comes to be connected to the upper slab (P12). Of reduced size, and with a wide angular spread, such an element is capable of operating simultaneously on two frequencies with a very narrow band. It readily facilitates impedance matching at the power level. It is particularly worthwhile for the making of adaptable antennae, with a hemispherical cover, and capable of working in circular polarisation. In a further embodiment (Figs 11 and 12) individual coaxial feeds are connected to the top and intermediate slabs. Four units successively displaced by 90 DEG provide circular polarisation.

Heating Pattern in a Multi-Layered Material Exposed to Microwaves (Short Papers)

Abstract: The electromagnetic-induced heating pattern in a multiIayered slab material exposed to uniform plane microwaves is studied. A general expression taking into account the multiple reflections at the interfaces is derived for the power dissipated per unit volume in the medium. A numerical method is developed for solving the heat transport equation describing the temperature distribution in this material. A steady, as well as a transient solution is obtained for either a Dirichlet- or a Neumann-type of boundary condition. The effect on the temperature distribution of a cooling fluid circulating inside the slab is considered. The method is applied to the special case of a three-layered material having characteristics similar to those of a biological structure. The possibility of achieving a preferential heating of one of the layers by, means of standing waves created with the aid of a flat reflector is demonstrated.

Package for coiled products and method of production thereof

Abstract: A package for products to be coiled such as ropes, hoses, cables, flexible tubing and similar kinds of products which are available by the yard coiled into a ring-shaped bundle (1). The package according to the invention comprises a supporting carrying construction (2) mounted on one side of the ring-shaped bundle (1). The supporting construction (2) can comprise an inner annular flat slab (3) the inside diameter of which essentially corresponds to the inside diameter of the ring-shaped bundle (1), and an outer (4) flat slab engaging the inner slab (3). The outer slab has a circular opening, the diameter of which is somewhat smaller than the outside diameter of the inner slab (3). The inner slab (3) is disposed concentrically with the circular opening of the outer slab (4) which it overlaps. To the outer slab (45) and the inner slab (3) a number of flexible bands (5) are fixed which extend outwards from the outer slab and inwards from the inner slab and which are of such length, that the bands (5A, 5B) after having been bent over the ring-shaped bundle (1) and fixed to one another, surround and retain the ring-shaped bundle (1) in coorporation with the supporting construction (2). The invention alo relates to a method for manufacturing said package. According to the method the supporting construction (2) is disposed at one end of a rotatable coiling matrix perpendicularly to the rotation axis thereof. The product to be coiled is coiled on the matrix in close proximity to the supporting construction, and when a sufficient length has been coiled, the free ends (5A, 5B) of the band (5) are bent around the ring-shaped bundle thus formed and are clamped at one another on the opposite side of the bundle. The ring-shaped bundle can then be removed from the matrix as a package ready for delivery.