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.

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.

Plate deformation at depth under northern California: Slab gap or stretched slab?

USGS Publications Warehouse

ten Brink, Uri S.; Shimizu, N.; Molzer, P.C.

1999-01-01

Plate kinematic interpretations for northern California predict a gap in the underlying subducted slab caused by the northward migration of the Pacific-North America-Juan de Fuca triple junction. However, large-scale decompression melting and asthenospheric upwelling to the base of the overlying plate within the postulated gap are not supported by geophysical and geochemical observations. We suggest a model for the interaction between the three plates which is compatible with the observations. In this 'slab stretch' model the Juan de Fuca plate under coastal northern California deforms by stretching and thinning to fill the geometrical gap formed in the wake of the northward migrating Mendocino triple junction. The stretching is in response to boundary forces acting on the plate. The thinning results in an elevated geothermal gradient, which may be roughly equivalent to a 4 Ma oceanic lithosphere, still much cooler than that inferred by the slab gap model. We show that reequilibration of this geothermal gradient under 20-30 km thick overlying plate can explain the minor Neogene volcanic activity, its chemical composition, and the heat flow. In contrast to northern California, geochemical and geophysical consequences of a 'true' slab gap can be observed in the California Inner Continental Borderland offshore Los Angeles, where local asthenospheric upwelling probably took place during the Miocene as a result of horizontal extension and rotation of the overlying plate. The elevated heat flow in central California can be explained by thermal reequilibration of the stalled Monterey microplate under the Coast Ranges, rather than by a slab gap or viscous shear heating in the mantle.

Plexus structure imaging with thin slab MR neurography: rotating frames, fly-throughs, and composite projections

NASA Astrophysics Data System (ADS)

Raphael, David T.; McIntee, Diane; Tsuruda, Jay S.; Colletti, Patrick; Tatevossian, Raymond; Frazier, James

2006-03-01

We explored multiple image processing approaches by which to display the segmented adult brachial plexus in a three-dimensional manner. Magnetic resonance neurography (MRN) 1.5-Tesla scans with STIR sequences, which preferentially highlight nerves, were performed in adult volunteers to generate high-resolution raw images. Using multiple software programs, the raw MRN images were then manipulated so as to achieve segmentation of plexus neurovascular structures, which were incorporated into three different visualization schemes: rotating upper thoracic girdle skeletal frames, dynamic fly-throughs parallel to the clavicle, and thin slab volume-rendered composite projections.

Comparison of analytic and iterative digital tomosynthesis reconstructions for thin slab objects

NASA Astrophysics Data System (ADS)

Yun, J.; Kim, D. W.; Ha, S.; Kim, H. K.

2017-11-01

For digital x-ray tomosynthesis of thin slab objects, we compare the tomographic imaging performances obtained from the filtered backprojection (FBP) and simultaneous algebraic reconstruction (SART) algorithms. The imaging performance includes the in-plane molulation-transfer function (MTF), the signal difference-to-noise ratio (SDNR), and the out-of-plane blur artifact or artifact-spread function (ASF). The MTF is measured using a thin tungsten-wire phantom, and the SDNR and the ASF are measured using a thin aluminum-disc phantom embedded in a plastic cylinder. The FBP shows a better MTF performance than the SART. On the contrary, the SART outperforms the FBP with regard to the SDNR and ASF performances. Detailed experimental results and their analysis results are described in this paper. For a more proper use of digital tomosynthesis technique, this study suggests to use a reconstuction algorithm suitable for application-specific purposes.

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.

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.

Analysis of Wave Propagation in Stratified Structures Using Circuit Analogues, with Application to Electromagnetic Absorbers

ERIC Educational Resources Information Center

Sjoberg, Daniel

2008-01-01

This paper presents an overview of how circuit models can be used for analysing wave propagation in stratified structures. Relatively complex structures can be analysed using models which are accessible to undergraduate students. Homogeneous slabs are modelled as transmission lines, and thin sheets between the slabs are modelled as lumped…

Waveform inversion for 3-D S-velocity structure of D'' beneath the Northern Pacific: possible evidence for a remnant slab and a passive plume

NASA Astrophysics Data System (ADS)

Suzuki, Yuki; Kawai, Kenji; Geller, Robert J.; Borgeaud, Anselme F. E.; Konishi, Kensuke

2016-12-01

We conduct waveform inversion to infer the three-dimensional (3-D) S-velocity structure in the lowermost 400 km of the mantle (the D'' region) beneath the Northern Pacific region. Our dataset consists of about 20,000 transverse component broadband body-wave seismograms observed at North American stations for 131 intermediate and deep earthquakes which occurred beneath the western Pacific subduction region. We use S, ScS, and other phases that arrive between them. Resolution tests indicate that our methods and dataset can resolve the velocity structure in the target region with a horizontal scale of about 150 km and a vertical scale of about 50 km. The 3-D S-velocity model obtained in this study shows three prominent features: (1) prominent sheet-like lateral high-velocity anomalies up to ˜3% faster than the Preliminary Reference Earth Model (PREM) with a thickness of ˜200 km, whose lower boundary is ˜150 km above the core-mantle boundary (CMB). (2) A prominent low-velocity anomaly block located to the west of the Kamchatka peninsula, which is ˜2.5% slower than PREM, immediately above the CMB beneath the high-velocity anomalies. (3) A relatively thin (˜300 km) low-velocity structure continuous from the low-velocity anomaly "(2)" to at least 400 km above the CMB. We also detect a continuous low-velocity anomaly from the east of the Kamchatka peninsula at an altitude of 50 km above the CMB to the far east of the Kuril islands at an altitude of 400 km above the CMB. We interpret these features respectively as: (1) remnants of slab material where the bridgmanite to Mg-post-perovskite phase transition may have occurred within the slab, (2, 3) large amounts of hot and less dense materials beneath the cold Kula or Pacific slab remnants just above the CMB which ascend and form a passive plume upwelling at the edge of the slab remnants.[Figure not available: see fulltext.

Stress distribution calculations through a snow slab of varying elastic modulus; comparison with stability evaluation in the field

NASA Astrophysics Data System (ADS)

Swinkels, Laura; Borstad, Chris

2017-04-01

Field observations are the main tools for assessing the snow stability concerning dry snow slab avalanche release. Often, theoretical studies cannot directly be translated into useful information for avalanche recreationists and forecasters in the field, and vice versa; field observations are not always objective and quantifiable for theoretical studies. Moreover, numerical models often simplify the snowpack and generally use an isotropic single layer slab which is not representative of the real-life situation. The aim of this study is to investigate the stress distribution in a snowpack with an elastic modulus that continuously varies with depth. The focus lies on the difference between a slab with a gradient in hardness and a slab with isotropic hardness and the effect on the calculated maximum stress and the stability evaluation in the field. Approximately 20 different snow pits were evaluated in the mountains around Tromsø, Norway and Longyearbyen, Svalbard. In addition to the standard snowpack observations, the hardness was measured using a thin-blade gauge. Extended column tests were executed for stability evaluation. Measurements from the field were used as input for stress calculations for each snow pit using a line load solution for a sloping half space with a non-homogeneous elastic modulus. The hardness measurements were used to calculate the elastic modulus and a power law relation was fit through the modulus in the slab. The calculated shear stress was compared to the estimated stability and character of the specific snowpack The results show that the approach used for this study improves the calculation of stress at a given depth, although many assumptions and simplifications were still needed. Comparison with the snow profiles indicate that calculated stresses correlate well with the observed snowpack properties and stability. The calculated shear stresses can be introduced in the standard stability index and give a better indication for the snowpack stability. Further research is required to delimit the stresses needed for propagation of a weak layer fracture.

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.

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

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

Digital x-ray tomosynthesis with interpolated projection data for thin slab objects

NASA Astrophysics Data System (ADS)

Ha, S.; Yun, J.; Kim, H. K.

2017-11-01

In relation with a thin slab-object inspection, we propose a digital tomosynthesis reconstruction with fewer numbers of measured projections in combinations with additional virtual projections, which are produced by interpolating the measured projections. Hence we can reconstruct tomographic images with less few-view artifacts. The projection interpolation assumes that variations in cone-beam ray path-lengths through an object are negligible and the object is rigid. The interpolation is performed in the projection-space domain. Pixel values in the interpolated projection are the weighted sum of pixel values of the measured projections considering their projection angles. The experimental simulation shows that the proposed method can enhance the contrast-to-noise performance in reconstructed images while sacrificing the spatial resolving power.

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.

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.

Improved Nazca slab structure from teleseismic P-wave tomography along the Andean margin

NASA Astrophysics Data System (ADS)

Portner, D. E.; Beck, S. L.; Scire, A. C.; Zandt, G.

2017-12-01

South America marks the longest continuous ocean-continent subduction zone. As such, there is significant along-strike variability in the subducting Nazca slab structure and the tectonics of the South American margin. Most notably two gaps in the otherwise continuous volcanic arc are correlated with regions of flat slab subduction, indicating that the structure of the Nazca slab plays a controlling role in South American tectonics. Traditionally in subduction zones, our knowledge of slab structure is defined by Wadati-Benioff zone earthquakes. While this method allows for the determination of large-scale variations in Nazca slab structure such as regions of flat slab subduction, a scarcity of intermediate-depth earthquakes hinders our ability to observe the smaller-scale structural variations in the slab that may be critical to our understanding of the geologic record. We use an updated, larger dataset for finite-frequency teleseismic P-wave tomography including relative arrival times from >700 seismic stations along the Andean margin to image the detailed Nazca slab structure throughout the upper mantle and uppermost lower mantle between latitudes 5°S and 45°S. Our results show prominent variations in slab character along the margin. Slab dip varies significantly, from sub-vertical inboard of the Peruvian flat slab segment to 30° dip south of the Pampean flat slab, while the slab's velocity anomaly amplitude changes dramatically near the Pampean flat slab region. High slab velocities north of the Pampean region relative to the south indicate variable slab thermal structures that correspond roughly with the locations of deep (>500 km depth) earthquakes that also occur exclusively north of the Pampean region. Additionally, a wider regional footprint increases our sampling of the upper-lower mantle boundary, improving constraints on the slab's interaction with the 660 km discontinuity along strike. We see that the Nazca slab appears to penetrate into the lower mantle along the majority of the margin.

Thin polymer etalon arrays for high-resolution photoacoustic imaging

PubMed Central

Hou, Yang; Huang, Sheng-Wen; Ashkenazi, Shai; Witte, Russell; O’Donnell, Matthew

2009-01-01

Thin polymer etalons are demonstrated as high-frequency ultrasound sensors for three-dimensional (3-D) high-resolution photoacoustic imaging. The etalon, a Fabry-Perot optical resonator, consists of a thin polymer slab sandwiched between two gold layers. It is probed with a scanning continuous-wave (CW) laser for ultrasound array detection. Detection bandwidth of a 20-μm-diam array element exceeds 50 MHz, and the ultrasound sensitivity is comparable to polyvinylidene fluoride (PVDF) equivalents of similar size. In a typical photoacoustic imaging setup, a pulsed laser beam illuminates the imaging target, where optical energy is absorbed and acoustic waves are generated through the thermoelastic effect. An ultrasound detection array is formed by scanning the probing laser beam on the etalon surface in either a 1-D or a 2-D configuration, which produces 2-D or 3-D images, respectively. Axial and lateral resolutions have been demonstrated to be better than 20 μm. Detailed characterizations of the optical and acoustical properties of the etalon, as well as photoacoustic imaging results, suggest that thin polymer etalon arrays can be used as ultrasound detectors for 3-D high-resolution photoacoustic imaging applications. PMID:19123679

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.

Integrated waveguide and nanostructured sensor platform for surface-enhanced Raman spectroscopy

NASA Astrophysics Data System (ADS)

Pearce, Stuart J.; Pollard, Michael E.; Oo, SweZin; Chen, Ruiqi; Kalsi, Sumit; Charlton, Martin D. B.

2014-01-01

Limitations of current sensors include large dimensions, sometimes limited sensitivity and inherent single-parameter measurement capability. Surface-enhanced Raman spectroscopy can be utilized for environment and pharmaceutical applications with the intensity of the Raman scattering enhanced by a factor of 10. By fabricating and characterizing an integrated optical waveguide beneath a nanostructured precious metal coated surface a new surface-enhanced Raman spectroscopy sensing arrangement can be achieved. Nanostructured sensors can provide both multiparameter and high-resolution sensing. Using the slab waveguide core to interrogate the nanostructures at the base allows for the emission to reach discrete sensing areas effectively and should provide ideal parameters for maximum Raman interactions. Thin slab waveguide films of silicon oxynitride were etched and gold coated to create localized nanostructured sensing areas of various pitch, diameter, and shape. These were interrogated using a Ti:Sapphire laser tuned to 785-nm end coupled into the slab waveguide. The nanostructured sensors vertically projected a Raman signal, which was used to actively detect a thin layer of benzyl mercaptan attached to the sensors.

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...

Metamaterials with gradient negative index of refraction.

PubMed

Pinchuk, Anatoliy O; Schatz, George C

2007-10-01

We propose a new metamaterial with a gradient negative index of refraction, which can focus a collimated beam of light coming from a distant object. A slab of the negative refractive index metamaterial has a focal length that can be tuned by changing the gradient of the negative refractive index. A thin metal film pierced with holes of appropriate size or spacing between them can be used as a metamaterial with the gradient negative index of refraction. We use finite-difference time-domain calculations to show the focusing of a plane electromagnetic wave passing through a system of equidistantly spaced holes in a metal slab with decreasing diameters toward the edges of the slab.

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.

Relocation of Intermediate-depth Seismicity in the Relic Alboran Slab: Clustering and Relationship to Tearing and Dehydration Embrittlement.

NASA Astrophysics Data System (ADS)

Sun, M.; Bezada, M.

2017-12-01

Intermediate-depth seismicity outside active subduction zones is rare. However, there is a well-known occurrence of such events in a N-S elongated volume between Spain and Morocco, within what most researchers consider to be the relic Alboran slab. Partial subduction of, and tearing from the adjoining continental lithosphere have been suggested in this area. We investigate whether dehydration embrittlement or shear instability is more consistent with the Alboran intermediate depth seismicity by considering their location relative to the expected thermal structure and expected areas of high strain rate associated with thinning or tearing of the slab. We use a dense temporary seismograph deployment in Spain and Morocco to relocate 65 intermediate-depth events occurring between 2010 and 2013 in this region. The relocation procedure is realized by a grid-search approach that minimizes the normalized misfit between the picked times and travel times calculated using a regional 3D velocity model. Results indicate that, compared with catalog results, hypocenters after relocation are more concentrated in space; they tend to shift southward and eastward while no systematic shift in depth is observed. Relocated hypocenters concentrate at a depth range between 50-100 km and along a narrow longitude range around 4.5W. Investigation of the earthquake density distribution indicates these earthquakes concentrate into several clusters. One such cluster sits above the spain-arm of the Alboran slab and beneath the Spain continental lithosphere, indicating that it is likely associated to the thinning process of the Alboran slab. The other four clusters all lie within the interior of the slab. Interestingly, two of them are near the middle of the subducted lithosphere and the other two lie near its base. This observation seems at odds with expectations based on the two leading hypotheses for enabling brittle failure at intermediate depths.

Angular sensitivities of scintillator slab configurations for location of gamma ray bursts

NASA Technical Reports Server (NTRS)

Gregory, J. C.

1976-01-01

Thin flat scintillator slabs are a useful means of measuring the angular location of gamma ray fluxes of astronomical interest. A statistical estimate of position error was made of two scintillator systems suitable for gamma ray burst location from a balloon or satellite platform. A single rotating scintillator with associated flux monitor is compared with a pair of stationary orthogonal scintillators. Position error for a strong burst is of the order of a few arcmin if systematic errors are ignored.

Continuity diaphragm for skewed continuous span precast prestressed concrete girder bridges : technical summary report.

DOT National Transportation Integrated Search

2004-03-01

Most highway bridges are built as cast-in-place : reinforced concrete slabs and prestressed concrete : girders. The shear connectors on the top of the girders : assure composite action between the slabs and : girders. The design guidelines for bridge...

Assessment of the Uretek process on continuously reinforced concrete pavement, jointed concrete pavement, and bridge approach slabs : technical assistance report.

DOT National Transportation Integrated Search

2004-12-01

This study evaluates the rehabilitation method utilizing the injection of Uretek (polyurethane) into the pavement structures on continuously reinforced concrete pavement (CRCP), jointed concrete pavement (JCP), and bridge approach slabs. The polyuret...

The Hikurangi Plateau: Tectonic Ricochet and Accretion

NASA Astrophysics Data System (ADS)

Willis, David; Moresi, Louis; Betts, Peter; Whittaker, Joanne

2015-04-01

80 million years between interactions with different subduction systems provided time for the Hikurangi Plateau and Pacific Ocean lithosphere to cool, densify and strengthen. Neogene subduction of the Hikurangi Plateau occurring orthogonal to its Cretaceous predecessor, provides a unique opportunity to explore how changes to the physical properties of oceanic lithosphere affect subduction dynamics. We used Underworld to build mechanically consistent collision models to understand the dynamics of the two Hikurangi collisions. The Hikurangi Plateau is a ~112 Ma, 15km thick oceanic plateau that has been entrained by subduction zones immediately preceding the final break-up of Eastern Gondwana and currently within the active Hikurangi Margin. We explore why attempted subduction of the plateau has resulted in vastly different dynamics on two separate occasions. Slab break-off occured during the collision with Gondwana, currently there is apparent subduction of the plateau underneath New Zealand. At ~100Ma the young, hot Hikurangi Plateau, positively buoyant with respect to the underlying mantle, impacted a Gondwana Margin under rapid extension after the subduction of an mid-ocean ridge 10-15Ma earlier. Modelling of plateaus within young oceanic crust indicates that subduction of the thickened crust was unlikely to occur. Frontal accretion of the plateau and accompanying slab break-off is expected to have occured rapidly after its arrival. The weak, young slab was susceptible to lateral propagation of the ~1500 km window opened by the collision, and break-off would have progressed along the subduction zone inhibiting the "step-back" of the trench seen in older plates. Slab break-off coincided with a world-wide reorganisation of plate velocites, and orogenic collapse along the Gondwana margin characterised by rapid extension and thinning of the over-riding continental plate from ~60 to 30km. Following extension, Zealandia migrated to the NW until the Miocene allowing the oceanic crust time to densify and strengthen. At ~23Ma, the inception of the Hikurangi Subduction Zone drove the scissor rotation of the Australian and Pacific Plates creating displacement along the Alpine Fault. The Hikurangi Plateau was once again drawn into the subduction system, this time with subduction occurring orthogonal to the Cretaceous suture. The northern margin of the plateau has begun to subduct, but towards the southern terminus, the trench appears to be pinned. The result of the locked subduction zone is the asymmetric roll-back of the Hikurangi-Kermadec-Tonga subduction system around the point where the trench transitions from roll-back to shortening. The oceanic Pacific lithosphere is now signficantly negatively buoyant while the thickened lithosphere of the plateau maintains a slight positive buoyancy. The oceanic crust provides sufficient slab pull to drive subduction of the northern plateau, aided by the thin ~500km width of the plateaus subducting front. The increased strength profile of the older subducting lithosphere allows buoyancy forces to be transmitted to the over-riding plate, allowing continued convergence and hindering slab-breakoff.

Theoretical description and design of nanomaterial slab waveguides: application to compensation of optical diffraction.

PubMed

Kivijärvi, Ville; Nyman, Markus; Shevchenko, Andriy; Kaivola, Matti

2018-04-02

Planar optical waveguides made of designable spatially dispersive nanomaterials can offer new capabilities for nanophotonic components. As an example, a thin slab waveguide can be designed to compensate for optical diffraction and provide divergence-free propagation for strongly focused optical beams. Optical signals in such waveguides can be transferred in narrow channels formed by the light itself. We introduce here a theoretical method for characterization and design of nanostructured waveguides taking into account their inherent spatial dispersion and anisotropy. Using the method, we design a diffraction-compensating slab waveguide that contains only a single layer of silver nanorods. The waveguide shows low propagation loss and broadband diffraction compensation, potentially allowing transfer of optical information at a THz rate.

The Influence of Vanadium Microalloying on the Production of Thin Slab Casting and Direct Rolled Steel Strip

NASA Astrophysics Data System (ADS)

Li, Yu; Milbourn, David

Vanadium microalloying is highly effective in high strength strip steels produced by thin slab casting and direct rolled process. Because of the high solubility of V(C,N) in austenite, vanadium is likely to remain in solution during casting, equalisation and rolling. Vanadium microalloyed steels have better hot ductility and are less prone to transverse cracking than niobium containing steels. Despite a coarse as-cast austenite grain size before rolling, significant grain refinement can be achieved in vanadium microalloyed steels by repeated recrystallization during rolling, resulting in a fine uniform ferrite microstructure in final strip. Almost all vanadium present in microalloyed steels is available to precipitate in ferrite as very fine particles, contributing to precipitation strengthening. Vanadium microalloyed steels show less sensitivity to rolling process variables and exhibit excellent combination of strength and toughness.

Long range surface plasmons on asymmetric suspended thin film structures for biosensing applications.

PubMed

Min, Qiao; Chen, Chengkun; Berini, Pierre; Gordon, Reuven

2010-08-30

We show that long-range surface plasmons (LRSPs) are supported in a physically asymmetric thin film structure, consisting of a low refractive index medium on a metal slab, supported by a high refractive index dielectric layer (membrane) over air, as a suspended waveguide. For design purposes, an analytic formulation is derived in 1D yielding a transcendental equation that ensures symmetry of the transverse fields of the LRSP within the metal slab by constraining its thicknesses and that of the membrane. Results from the formulation are in quantitative agreement with transfer matrix calculations for a candidate slab waveguide consisting of an H(2)O-Au-SiO(2)-air structure. Biosensor-relevant figures of merit are compared for the asymmetric and symmetric structures, and it is found that the asymmetric structure actually improves performance, despite higher losses. The finite difference method is also used to analyse metal stripes providing 2D confinement on the structure, and additional constraints for non-radiative LRSP guiding thereon are discussed. These results are promising for sensors that operate with an aqueous solution that would otherwise require a low refractive index-matched substrate for the LRSP.

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.

Origin of back-arc basins and effects of western Pacific subduction systems on eastern China geology

NASA Astrophysics Data System (ADS)

Niu, Y.

2013-12-01

Assuming that subduction initiation is a consequence of lateral compositional buoyancy contrast within the lithosphere [1], and recognizing that subduction initiation within normal oceanic lithosphere is unlikely [1], we can assert that passive continental margins that are locations of the largest compositional buoyancy contrast within the lithosphere are the loci of future subduction zones [1]. We hypothesize that western Pacific back-arc basins were developed as and evolved from rifting at passive continental margins in response to initiation and continuation of subduction zones. This hypothesis can be tested by demonstrating that intra-oceanic island arcs must have basement of continental origin. The geology of the Islands of Japan supports this. The highly depleted forearc peridotites (sub-continental lithosphere material) from Tonga and Mariana offer independent lines of evidence for the hypothesis [1]. The origin and evolution of the Okinawa Trough (back-arc basin) and Ryukyu Arc/Trench systems represents the modern example of subduction initiation and back-arc basin formation along a (Chinese) continental margin. The observation why back-arc basins exit behind some subduction zones (e.g., western Pacific) but not others (e.g., in South America) depends on how the overlying plate responds to subduction, slab-rollback and trench retreat. In the western Pacific, trench retreat towards east results in the development of extension in the upper Eurasian plate and formation of back-arc basins. In the case of South America, where no back-arc basins form because trench retreat related extension is focused at the 'weakest' South Mid-Atlantic Ridge. It is thus conceptually correct that the South Atlantic is equivalent to a huge 'back-arc basin' although its origin may be different. Given the negative Clayperon slope of the Perovskite-ringwoodite phase transition at the 660 km mantle seismic discontinuity (660-D), slab penetration across the 660-D is difficult and trench retreat in the western Pacific readily result in the horizontal stagnation of the Pacific plate in the transition zone beneath eastern Asian continent [2]. Dehydration of this slab supplies water, which rises and results in 'basal hydration weakening' of the eastern China lithosphere and its thinning by converting it into weak material of asthenospheric property [3]. We note the proposal that multiple subduction zones with more water (i.e., subduction of the South China Block beneath the North China Craton, NCC; subduction of the Siberian/Mongolian block beneath the NCC) all contribute to the lithosphere thinning beneath the NCC [4]. However, 'South China-NCC' and 'Siberian/Mongolian-NCC' represent two collisional tectonics involving no trench retreat, causing no transition-zone slab stagnation, supplying no water, and thus contributing little to lithosphere thinning beneath the NCC. Furthermore, lithosphere thinning happened to the entire eastern China, not just limited to the NCC, emphasizing the effects of the western Pacific subduction system on eastern China geology. References: [1] Niu et al., 2003, Journal of Petrology, 44, 851-866. [2] Kárason & van der Hilst, R., 2000, Geophysical Monograph, 121, 277-288. [3] Niu, 2005, Geological Journal of China Universities, 11, 9-46. [4] Windley et al., 2010, American Journal of Science, 310, 1250-1293.

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.

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.

[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.

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.

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.

Infiltration of Slag Film into the Grooves on a Continuous Casting Mold

NASA Astrophysics Data System (ADS)

Cho, Jung-Wook; Jeong, Hee-Tae

2013-02-01

An analytical model is developed to clarify the slag film infiltration into grooves on a copper mold during the continuous casting of steel slabs. A grooved-type casting mold was applied to investigate the infiltration of slag film into the grooves of a pitch of 0.8 mm, width of 0.7 mm, and depth of 0.6 mm at the vicinity of a meniscus. The plant trial tests were carried out at a casting speed of 5.5 m min-1. The slag film captured at a commercial thin slab casting plant showed that both the overall and the liquid film thickness were decreased exponentially as the distance from the meniscus increases. In contrast, the infiltration of slag film into the grooves had been increased with increasing distance from the meniscus. A theoretic model has been derived based on the measured profile of slag film thickness to calculate the infiltration of slag film into the grooves. It successfully reproduces the empirical observation that infiltration ratio increased sharply along casting direction, about 80 pct at 50 mm and 95 pct at 150 mm below the meniscus. In the model calculation, the infiltration of slag film increases with increasing groove width and/or surface tension of the slag. The effect of groove depth is negligible when the width to depth ratio of the groove is larger than unity. It is expected that the developed model for slag film infiltration in this study will be widely utilized to optimize the design of groove dimensions in continuous casting molds.

Self-stressed sandwich bridge decks.

DOT National Transportation Integrated Search

1971-01-01

Proposed is an entirely new type of bridge deck, consisting of an unreinforced lightweight concrete slab made of expanding cement sandwiched between two thin plates of steel. The expanding core serves to prestress the panel. Laboratory tests were con...

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

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.

Performance assessment of Wisconsin's whitetopping and ultra thin whitetopping projects.

DOT National Transportation Integrated Search

2010-03-01

Whitetopping overlay is a concrete overlay on the prepared existing hot mix asphalt (HMA) pavement to : improve both the structural and functional capability. Its a relatively new rehabilitation technology for : deteriorated HMA. If the slab thick...

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.

Two-dimensional models for the optical response of thin films

NASA Astrophysics Data System (ADS)

Li, Yilei; Heinz, Tony F.

2018-04-01

In this work, we present a systematic study of 2D optical models for the response of thin layers of material under excitation by normally incident light. The treatment, within the framework of classical optics, analyzes a thin film supported by a semi-infinite substrate, with both the thin layer and the substrate assumed to exhibit local, isotropic linear response. Starting from the conventional three-dimensional (3D) slab model of the system, we derive a two-dimensional (2D) sheet model for the thin film in which the optical response is described by a sheet optical conductivity. We develop criteria for the applicability of this 2D sheet model for a layer with an optical thickness far smaller than the wavelength of the light. We examine in detail atomically thin semi-metallic and semiconductor van-der-Waals layers and ultrathin metal films as representative examples. Excellent agreement of the 2D sheet model with the 3D slab model is demonstrated over a broad spectral range from the radio frequency limit to the near ultraviolet. A linearized version of system response for the 2D model is also presented for the case where the influence of the optically thin layer is sufficiently weak. Analytical expressions for the applicability and accuracy of the different optical models are derived, and the appropriateness of the linearized treatment for the materials is considered. We discuss the advantages, as well as limitations, of these models for the purpose of deducing the optical response function of the thin layer from experiment. We generalize the theory to take into account in-plane anisotropy, layered thin film structures, and more general substrates. Implications of the 2D model for the transmission of light by the thin film and for the implementation of half- and totally absorbing layers are discussed.

Epitaxial Hexagonal Ferrites for Millimeter Wave Tunable Filters.

DTIC Science & Technology

1982-12-13

form of thin films or slabs, the LPE format should be particularly suitable. Another potential advantage of the LPE format is that the insulating...flux (solvent). In effect, this emulates the successful LPE garnet (YIG) technology which employs this flux. In contrast to garnets , Pb atoms can be...member for a workshop entitled "Application of Garnet and Ferrite Thin Films to Microwave Devices." The principal investigator also attended the 6th

High-Temperature Creep Behaviour and Positive Effect on Straightening Deformation of Q345c Continuous Casting Slab

NASA Astrophysics Data System (ADS)

Guo, Long; Zhang, Xingzhong

2018-03-01

Mechanical and creep properties of Q345c continuous casting slab subjected to uniaxial tensile tests at high temperature were considered in this paper. The minimum creep strain rate and creep rupture life equations whose parameters are calculated by inverse-estimation using the regression analysis were derived based on experimental data. The minimum creep strain rate under constant stress increases with the increase of the temperature from 1000 °C to 1200 °C. A new casting machine curve with the aim of fully using high-temperature creep behaviour is proposed in this paper. The basic arc segment is cancelled in the new curve so that length of the straightening area can be extended and time of creep behaviour can be increased significantly. For the new casting machine curve, the maximum straightening strain rate at the slab surface is less than the minimum creep strain rate. So slab straightening deformation based on the steel creep behaviour at high temperature can be carried out in the process of Q345c steel continuous casting. The effect of creep property at high temperature on slab straightening deformation is positive. It is helpful for the design of new casting machine and improvement of old casting machine.

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.

Slab replacement maturity guidelines : [summary].

DOT National Transportation Integrated Search

2014-04-01

Concrete sets in hours at moderate temperatures, : but the bonds that make concrete strong continue : to mature over days to years. However, for : replacement concrete slabs on highways, it is : crucial that concrete develop enough strength : within ...

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.

Characterization of the punching shear capacity of thin ultra-high performance concrete slabs.

DOT National Transportation Integrated Search

2005-01-01

Ultra-high performance concrete (UHPC) is a relatively new type of concrete that exhibits mechanical properties that are far superior to those of conventional concrete and in some cases rival those of steel. The main characteristics that distinguish ...

Creating a Driven, Collapsed Radiative Shock in the Laboratory

NASA Astrophysics Data System (ADS)

Reighard, Amy

2006-10-01

We report details of the first experimental campaign to create a driven, planar, radiatively collapsed in laboratory experiment. Radiation hydrodynamics experiments are challenging to realize in a laboratory setting, requiring high temperatures in a system of sufficient extent. The Omega laser at ˜10^15 W/cm^2 drives a thin slab of low-Z material at >100 km/s gas via laser ablation pressure. This slab initially shocks, then continues driving a shock through a cylindrical volume of Xe gas at 6 mg/cc. Simulations predict a collapsed layer in which the density reaches ˜45 times initial density. Side-on x-ray backlighting was the principal diagnostic. We have successfully imaged shocks with average velocities between 95-205 km/sec, with measured thicknesses of 45-150 μm in experiments lasting up to 20 ns and spanning up 2.5 mm in extent. Comparison of the shock position as a function of time from these experiments to 1D radiation hydrodynamic simulation results show some discrepancy, which will be explored. Optical depth before and behind the shock is important for meaningful comparison to these astrophysical systems. This shock is optically thin to emitted radiation in the unshocked region and optically thick to radiation in the shocked, dense region. We compare this system to collapsed shocks in astrophysical systems with similar optical depth profiles. An experiment using a Thomson scattering diagnostic across the shock front is also discussed. This research was sponsored by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Research Grants DE-FG52-03NA00064, DE-FG53-2005-NA26014, and other grants and contracts.

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.

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.

Air slab-correction for Γ-ray attenuation measurements

NASA Astrophysics Data System (ADS)

Mann, Kulwinder Singh

2017-12-01

Gamma (γ)-ray shielding behaviour (GSB) of a material can be ascertained from its linear attenuation coefficient (μ, cm-1). Narrow-beam transmission geometry is required for μ-measurement. In such measurements, a thin slab of the material has to insert between point-isotropic γ-ray source and detector assembly. The accuracy in measurements requires that sample's optical thickness (OT) remain below 0.5 mean free path (mfp). Sometimes it is very difficult to produce thin slab of sample (absorber), on the other hand for thick absorber, i.e. OT >0.5 mfp, the influence of the air displaced by it cannot be ignored during μ-measurements. Thus, for a thick sample, correction factor has been suggested which compensates the air present in the transmission geometry. The correction factor has been named as an air slab-correction (ASC). Six samples of low-Z engineering materials (cement-black, clay, red-mud, lime-stone, cement-white and plaster-of-paris) have been selected for investigating the effect of ASC on μ-measurements at three γ-ray energies (661.66, 1173.24, 1332.50 keV). The measurements have been made using point-isotropic γ-ray sources (Cs-137 and Co-60), NaI(Tl) detector and multi-channel-analyser coupled with a personal computer. Theoretical values of μ have been computed using a GRIC2-toolkit (standardized computer programme). Elemental compositions of the samples were measured with Wavelength Dispersive X-ray Fluorescence (WDXRF) analyser. Inter-comparison of measured and computed μ-values, suggested that the application of ASC helps in precise μ-measurement for thick samples of low-Z materials. Thus, this hitherto widely ignored ASC factor is recommended to use in similar γ-ray measurements.

Capillary sample introduction of polymerase chain reaction (PCR) products separated in ultrathin slab gels.

PubMed

Bullard, K M; Hietpas, P B; Ewing, A G

1998-01-01

Polymerase chain reaction (PCR) amplified short tandem repeat (STR) samples from the HUMVWF locus have been analyzed using a unique sample introduction and separation technique. A single capillary is used to transfer samples onto an ultrathin slab gel (57 microm thin). This ultrathin nondenaturing polyacrylamide gel is used to separate the amplified fragments, and laser-induced fluorescence with ethidium bromide is used for detection. The feasibility of performing STR analysis using this system has been investigated by examining the reproducibility for repeated samples. Reproducibility is examined by comparing the migration of the 14 and 17 HUMVWF alleles on three consecutive separations on the ultrathin slab gel. Using one locus, separations match in migration time with the two alleles 42 s apart for each of the three consecutive separations. This technique shows potential to increase sample throughput in STR analysis techniques although separation resolution still needs to be improved.

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.

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.

Trench-parallel spreading ridge subduction and its consequences for the geological evolution of the overriding plate: Insights from analogue models and comparison with the Neogene subduction beneath Patagonia

NASA Astrophysics Data System (ADS)

Salze, Méline; Martinod, Joseph; Guillaume, Benjamin; Kermarrec, Jean-Jacques; Ghiglione, Matias C.; Sue, Christian

2018-07-01

A series of 3-D asthenospheric-scale analogue models have been conducted in the laboratory in order to simulate the arrival of a spreading ridge at the trench and understand its effect on plate kinematics, slab geometry, and on the deformation of the overriding plate. These models are made of a two-layered linearly viscous system simulating the lithosphere and asthenosphere. We reproduce the progressive decrease in thickness of the oceanic lithosphere at the trench. We measure plate kinematics, slab geometry and upper plate deformation. Our experiments reveal that the subduction of a thinning plate beneath a freely moving overriding continent favors a decrease of the subduction velocity and an increase of the oceanic slab dip. When the upper plate motion is imposed by lateral boundary conditions, the evolution of the subducting plate geometry largely differs depending on the velocity of the overriding plate: the larger its trenchward velocity, the smaller the superficial dip of the oceanic slab. A slab flattening episode may occur resulting from the combined effect of the subduction of an increasingly thinner plate and the trenchward motion of a fast overriding plate. Slab flattening would be marked by an increase of the distance between the trench and the volcanic arc in nature. This phenomenon may explain the reported Neogene eastward motion of the volcanic arc in the Southern Patagonia that occurred prior to the subduction of the Chile Ridge.

Use of precast slabs for pavement rehabilitation on I-66.

DOT National Transportation Integrated Search

2012-06-01

Highway agencies continuously strive to expedite pavement construction and repairs and to evaluate materials and : methods to provide long-lasting pavements. As part of this effort, agencies have used precast concrete slabs for more than 10 : years w...

Spiral Microstrip Antenna with Resistance

NASA Technical Reports Server (NTRS)

Shively, David G. (Inventor)

1998-01-01

A spiral microstrip antenna having resistor elements embedded in each of the spiral arms is provided. The antenna is constructed using a conductive back plane as a base. The back plane supports a dielectric slab having a thickness between one-sixteenth and one-quarter of an inch. A square spiral, having either two or four arms, is attached to the dielectric slab. Each arm of the spiral has resistor elements thereby dissipating an excess energy not already emitted through radiation. The entire configuration provides a thin, flat, high gain, wide bandwidth antenna which requires no underlying cavity. The configuration allows the antenna to be mounted conformably on an aircraft surface.

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.

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.

Spontaneous emission in semiconductor laser amplifiers

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

Arnaud, J.; Coste, F.; Fesqueet, J.

1985-06-01

In a mode matched configuration, spontaneous emission in semiconductor laser amplifiers is enhanced by a factor which is larger than unity but which is significantly smaller than the K-factor calculated by Petermann. Using thin-slab model, we find that in typical situations, the factor is about K/2.

Bias of air void system data from fly ash concretes.

DOT National Transportation Integrated Search

1983-01-01

Hollow censopheres of fly ash may have walls so thin that they will appear to be air voids when they appear on a polished slab prepared for air void determination by ASTM C457. Therefore the following precautions are recommended. 1. The operator of t...

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.

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.

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.

On the potential asthenospheric linkage between Apenninic slab rollback and Alpine topographic uplift: insights from P wave tomography and seismic anisotropy analysis

NASA Astrophysics Data System (ADS)

Malusa', Marco Giovanni; Salimbeni, Simone; Zhao, Liang; Guillot, Stéphane; Pondrelli, Silvia; Margheriti, Lucia; Paul, Anne; Solarino, Stefano; Aubert, Coralie; Dumont, Thierry; Schwartz, Stéphane; Wang, Qingchen; Xu, Xiaobing; Zheng, Tianyu; Zhu, Rixiang

2017-04-01

The role of surface and deep-seated processes in controlling the topography of complex plate-boundary areas is a highly debated issue. In the Western Alps, which include the highest summits in Europe, factors controlling topographic uplift still remain poorly understood. In the absence of active convergence, recent works have suggested a potential linkage between slab breakoff and fast uplift, but this hypothesis is ruled out by the down-dip continuity of the Alpine slab documented by recent tomographic images of the upper mantle beneath the Alpine region (Zhao et al. 2016). In order to shed light on this issue, we use a densely spaced array of temporary broadband seismic stations and previously published observations to analyze the seismic anisotropy pattern along the transition zone between the Alps and the Apennines, within the framework of the upper mantle structure unveiled by P wave tomography. Our results show a continuous trend of anisotropy fast axes near-parallel to the western alpine arc, possibly due to an asthenospheric counterflow triggered by the eastward retreat of the Apenninic slab. This trend is located in correspondence of a low velocity anomaly in the European upper mantle, and beneath the Western Alps region characterized by the highest uplift rates, which may suggest a potential impact of mantle dynamics on Alpine topography. We propose that the progressive rollback of the Apenninic slab induced a suction effect and an asthenospheric counterflow at the rear of the unbroken Alpine slab and around its southern tip, as well as an asthenospheric upwelling, mirrored by low P wave velocities, which may have favored the topographic uplift of the Alpine belt from the Mt Blanc to the Ligurian coast. Zhao L. et al., 2016. Continuity of the Alpine slab unraveled by high-resolution P wave tomography. J. Geophys. Res., doi:10.1002/2016JB013310.

Evaluation of performance and maximum length of continuous decks in bridges : part 2.

DOT National Transportation Integrated Search

2012-08-01

Field experimental measurements and analytical studies showed that the link-slab reinforcement : experiences almost no axial load due to thermal and gravity loading. One of the fundamental : reasons for the low loads in the link-slab reinforcement is...

Revealing topological Dirac fermions at the surface of strained HgTe thin films via quantum Hall transport spectroscopy

NASA Astrophysics Data System (ADS)

Thomas, C.; Crauste, O.; Haas, B.; Jouneau, P.-H.; Bäuerle, C.; Lévy, L. P.; Orignac, E.; Carpentier, D.; Ballet, P.; Meunier, T.

2017-12-01

We demonstrate evidences of electronic transport via topological Dirac surface states in a thin film of strained HgTe. At high perpendicular magnetic fields, we show that the electron transport reaches the quantum Hall regime with vanishing resistance. Furthermore, quantum Hall transport spectroscopy reveals energy splittings of relativistic Landau levels specific to coupled Dirac surface states. This study provides insights in the quantum Hall effect of topological insulator (TI) slabs, in the crossover regime between two- and three-dimensional TIs, and in the relevance of thin TI films to explore circuit functionalities in spintronics and quantum nanoelectronics.

Late Paleozoic-Early Mesozoic tectonic evolution of the Paleo-Asian Ocean: geochronological and geochemical evidence from granitoids in the northern margin of Alxa, Western China

NASA Astrophysics Data System (ADS)

Sha, Xin; Wang, Jinrong; Chen, Wanfeng; Liu, Zheng; Zhai, Xinwei; Ma, Jinlong; Wang, Shuhua

2018-03-01

The Paleo-Asian Ocean (Southern Mongolian Ocean) ophiolitic belts and massive granitoids are exposed in the Alxa block, in response to oceanic subduction processes. In this work, we report petrographic, geochemical, and zircon U-Pb age data of some granitoid intrusions from the northern Alxa. Zircon U-Pb dating for the quartz diorite, tonalite, monzogranite, and biotite granite yielded weighted mean 206Pb/238U ages of 302±9.2 Ma, 246.5±4.6 Ma, 235±4.4 Ma, and 229.5±5.6 Ma, respectively. The quartz diorites ( 302 Ma) exhibit geochemical similarities to adakites, likely derived from partial melting of the initially subducted Chaganchulu back-arc oceanic slab. The tonalites ( 246.5 Ma) display geochemical affinities of I-type granites. They were probably derived by fractional crystallization of the modified lithospheric mantle-derived basaltic magmas in a volcanic arc setting. The monzogranites ( 235 Ma) are characterized by low Al2O3, but high Y and Yb with notably negative Eu anomalies. In contrast, the biotite granites ( 229.5 Ma) show high Al2O3 but low Y and Yb with steep HREE patterns and the absence of negative Eu anomalies. Elemental data suggested that the biotite granites were likely derived from a thickened lower crust, but the monzogranites originated from a thin crust. Our data suggested that the initial subduction of the Chaganchulu oceanic slab towards the Alxa block occurred at 302 Ma. This subduction process continued to the Early Triassic ( 246 Ma) and the basin was finally closed before the Middle Triassic ( 235 Ma). Subsequently, the break-off of the subducted slab triggered asthenosphere upwelling (240-230 Ma).

Probing the liquid crystal alignment interface and switching dynamics in a slab waveguide architecture

NASA Astrophysics Data System (ADS)

Gotjen, Henry G.; Kolacz, Jakub; Myers, Jason D.; Frantz, Jesse A.; Bekele, Robel Y.; Naciri, Jawad; Spillmann, Christopher M.

2018-02-01

A non-mechanical refractive laser beam steering device has been developed to provide continuous, two-dimensional steering of infrared beams. The technology implements a dielectric slab waveguide architecture with a liquid crystal (LC) cladding. With voltage control, the birefringence of the LC can be leveraged to tune the effective index of the waveguide under an electrode. With a clever prism electrode design a beam coupled into the waveguide can be deflected continuously in two dimensions as it is coupled out into free space. The optical interaction with LC in this beamsteerer is unique from typical LC applications: only the thin layer of LC (100s of nm) near the alignment interface interacts with the beam's evanescent field. Whereas most LC interactions take place over short path lengths (microns) in the bulk of the material, here we can interrogate the behavior of LC near the alignment interface over long path lengths (centimeters). In this work the beamsteerer is leveraged as a tool to study the behavior of LC near the alignment layer in contrast to the bulk material. We find that scattering is substantially decreased near the alignment interface due to the influence of the surface anchoring energy to suppress thermal fluctuations. By tracking the position of the deflected beam with a high speed camera, we measure response times of the LC near the interface in off-to-on switching ( ms) and on-to-off switching ( 100ms). Combined, this work will provide a path for improved alignment techniques, greater optical throughput, and faster response times in this unique approach to non-mechanical beamsteering.

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.

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.

Vibrated and self-compacting fibre reinforced concrete: experimental investigation on the fibre orientation

NASA Astrophysics Data System (ADS)

Conforti, A.; Plizzari, G. A.; Zerbino, R.

2017-09-01

In addition to the fibre type and content, the residual properties of fibre reinforced concrete are influenced by fibre orientation. Consequently, the performance fibre reinforced concrete can be affected by its fresh properties (workability, flowing capacity) and by casting and compaction processes adopted. This paper focuses on the study of the orientation of steel or macro-synthetic fibres in two materials characterized by very different fresh properties: vibrated and self-compacting concrete. Four rectangular slabs 1800 mm long, 925 mm wide and 100 mm high were produced changing concrete and fibre type. From each slab, eighteen small prisms (550 mm long) were firstly cut either orthogonal or parallel to casting direction and, secondly, notched and tested in bending according to EN 14651. Experimental results showed that the toughness properties of a thin slab significantly varies both in vibrated and self-compacting concrete, even if in case of self-compacting concrete this variation resulted higher. Steel fibres led to greater variability of results compared to polymer one, underlining a different fibre orientation. A discussion on the relative residual capacity measured on the prisms sawn from the slabs and the parameters obtained from standard specimens is performed.

In Situ Observation of Rock Spalling in the Deep Tunnels of the China Jinping Underground Laboratory (2400 m Depth)

NASA Astrophysics Data System (ADS)

Feng, Xia-Ting; Xu, Hong; Qiu, Shi-Li; Li, Shao-Jun; Yang, Cheng-Xiang; Guo, Hao-Sen; Cheng, Yuan; Gao, Yao-Hui

2018-04-01

To study rock spalling in deep tunnels at China Jinping Underground Laboratory Phase II (CJPL-II), photogrammetry method and digital borehole camera were used to quantify key features of rock spalling including orientation, thickness of slabs and the depth of spalling. The failure mechanism was analysed through scanning electron microscope and numerical simulation based on FLAC3D. Observation results clearly showed the process of rock spalling failure: a typical spalling pattern around D-shaped tunnels after top-heading and bottom bench were discovered. The orientation and thickness of the slabs were obtained. The slabs were parallel to the excavated surfaces of the tunnel and were related to the shape of the tunnel surface and orientation of the principal stress. The slabs were alternately thick and thin, and they gradually increased in thickness from the sidewall inwards. The form and mechanism of spalling at different locations in the tunnels, as influenced by stress state and excavation, were analysed. The result of this study was helpful to those rethinking the engineering design, including the excavation and support of tunnels, or caverns, at high risk of spalling.

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.

Glacitectonic deformation around the retreating margin of the last Irish ice sheet

NASA Astrophysics Data System (ADS)

Knight, J.

2008-12-01

Evidence for ice-marginal glacitectonic shunting and deformation of bedrock slabs is described from three sites around the west coast of Ireland. These sites (Brandon Bay, County Kerry; Pigeon Point, County Mayo; Inishcrone, County Sligo) are all locations where the late Devensian ice margin retreated on land and was confined to within limestone bedrock embayments. At these sites, flat-lying bedrock slabs (< 8 m long) have been dissociated from rockhead and moved seaward (in the direction of ice flow) by glacitectonic shunting. At all of the sites, bedrock slabs have been variously stacked, rotated, deformed into open folds, and brecciated. Separating the bedrock slabs is either a thin layer (< 20 cm) of brecciated and mylonitised cemented bedrock that shows internal folding; or a thicker (< 50 cm) normally-graded diamicton with a fine matrix. Together, the presence of these features suggests oscillation of a polythermal and clean basal ice margin that was strongly associated with basal freeze-on and the presence of proglacial permafrost. Subglacial sediment-laden meltwater was focused from behind the ice margin and through permafrost taliks. It is suggested that hydrofracturing under high hydraulic pressure, and through a frozen-bed ice margin, forced sediment injection into bedrock fractures and bedding planes and away from the ice margin, and that bedrock slabs were moved in part by hydraulic lift as well as thrust-style ice-marginal tectonics. The presence of a mosaic of warm and frozen ice-bed patches, in combination with strong geologic control and meltwater generation from behind the ice margin, can help explain formation of these unusual bedrock slab features.

Coarse mesh and one-cell block inversion based diffusion synthetic acceleration

NASA Astrophysics Data System (ADS)

Kim, Kang-Seog

DSA (Diffusion Synthetic Acceleration) has been developed to accelerate the SN transport iteration. We have developed solution techniques for the diffusion equations of FLBLD (Fully Lumped Bilinear Discontinuous), SCB (Simple Comer Balance) and UCB (Upstream Corner Balance) modified 4-step DSA in x-y geometry. Our first multi-level method includes a block Gauss-Seidel iteration for the discontinuous diffusion equation, uses the continuous diffusion equation derived from the asymptotic analysis, and avoids void cell calculation. We implemented this multi-level procedure and performed model problem calculations. The results showed that the FLBLD, SCB and UCB modified 4-step DSA schemes with this multi-level technique are unconditionally stable and rapidly convergent. We suggested a simplified multi-level technique for FLBLD, SCB and UCB modified 4-step DSA. This new procedure does not include iterations on the diffusion calculation or the residual calculation. Fourier analysis results showed that this new procedure was as rapidly convergent as conventional modified 4-step DSA. We developed new DSA procedures coupled with 1-CI (Cell Block Inversion) transport which can be easily parallelized. We showed that 1-CI based DSA schemes preceded by SI (Source Iteration) are efficient and rapidly convergent for LD (Linear Discontinuous) and LLD (Lumped Linear Discontinuous) in slab geometry and for BLD (Bilinear Discontinuous) and FLBLD in x-y geometry. For 1-CI based DSA without SI in slab geometry, the results showed that this procedure is very efficient and effective for all cases. We also showed that 1-CI based DSA in x-y geometry was not effective for thin mesh spacings, but is effective and rapidly convergent for intermediate and thick mesh spacings. We demonstrated that the diffusion equation discretized on a coarse mesh could be employed to accelerate the transport equation. Our results showed that coarse mesh DSA is unconditionally stable and is as rapidly convergent as fine mesh DSA in slab geometry. For x-y geometry our coarse mesh DSA is very effective for thin and intermediate mesh spacings independent of the scattering ratio, but is not effective for purely scattering problems and high aspect ratio zoning. However, if the scattering ratio is less than about 0.95, this procedure is very effective for all mesh spacing.

The Solnhofen Limestone: A stony heritage of many uses

NASA Astrophysics Data System (ADS)

Kölbl-Ebert, Martina; Kramar, Sabina; Cooper, Barry J.

2016-04-01

High above the valley of the River Altmühl (Bavaria, Germany), between Solnhofen to the west and Kelheim to the east, numerous quarries give access to thinly plated limestone from the Upper Jurassic, some 150 million years before the present. The main quarry areas lie around the town of Eichstätt and between the villages of Solnhofen, Langenaltheim and Mörnsheim. Here limestone slabs have been quarried for several hundred years, some even in Roman times. Solnhofen Limestone is famous worldwide; not only because it is a beautiful building stone of high quality, but also because of the exceptionally well-preserved fossils it contains -among them the early bird Archaeopteryx. The quarry industry between Solnhofen and Eichstätt has shaped a cultural landscape, with old and new quarries sunk into the plain and numerous spoil heaps rising above it, for the rock is not all economically useful. But many of the spoil heaps and the old quarries are environmentally protected as they provide a habitat for some rare plants and animals. It is not necessary to cut the Solnhofen Limestone with a saw: it is split by hand into thin and even slabs or sheets which are used for flagstones and wall covers, which since centuries are sold world-wide. Locally it also serves as roof tiles for traditional houses. Thick slabs of especially fine quality may be found near Solnhofen and Mörnsheim and are used for lithography printing.

Quantum resonances of Landau damping in the electromagnetic response of metallic nanoslabs.

PubMed

Castillo-López, S G; Makarov, N M; Pérez-Rodríguez, F

2018-05-15

The resonant quantization of Landau damping in far-infrared absorption spectra of metal nano-thin films is predicted within the Kubo formalism. Specifically, it is found that the discretization of the electromagnetic and electron wave numbers inside a metal nanoslab produces quantum nonlocal resonances well-resolved at slab thicknesses smaller than the electromagnetic skin depth. Landau damping manifests itself precisely as such resonances, tracing the spectral curve obtained within the semiclassical Boltzmann approach. For slab thicknesses much greater than the skin depth, the classical regime emerges. Here the results of the quantum model and the Boltzmann approach coincide. Our analytical study is in perfect agreement with corresponding numerical simulations.

Lithosphere thickness in the Gulf of California region

NASA Astrophysics Data System (ADS)

Fernández, Alejandra; Pérez-Campos, Xyoli

2017-11-01

The Gulf of California has a long tectonic history. Before the subduction of the Guadalupe and Magdalena plates ceased, extension of the Gulf began to the east, at the Basin and Range province. Later, it was focused west of the Sierra Madre Occidental and the opening of the Gulf started. Currently, the Gulf rifting has different characteristics to the north than to the south. In this study, we analyze the lithosphere thickness in the Gulf of California region by means of P-wave and S-wave receiver functions. We grouped our lithosphere-thickness estimates into five froups: 1) North of the Gulf, with a thin lithosphere ( 50 km) related to the extension observed in the Salton Through region; 2) the northwestern part of Baja California, with a thicker lithosphere ( 80 km), thinning towards the Gulf due to the extension and opening processes ( 65 km); 3) central Baja California, with no converted phase corresponding to the lithosphere-asthenosphere boundary but evidence of the presence of a slab remnant; 4) the southern Baja California peninsula, showing a shallow lithosphere-astenosphere boundary (LAB) (< 55 km) and a lithosphere thinning towards the Gulf; and 5) the eastern Gulf margin with lithosphere thinning towards the south. These groups can be further assembled into three regions: A) The northernmost Gulf, where both margins of the Gulf show a relatively constant lithosphere thickness, consistent with an old basement in Sonora and the presence of the Peninsular Ranges batholith in northern Baja California, thinning up towards the axis of the rift in the northernmost Gulf. B) Central and southern Gulf, where the lithosphere thickness in this region ranges from 40 to 55 km, which is consistent with the presence of a younger crust. C) Central Baja California peninsula, where LAB is not detected; but there is evidence of a slab remnant.

Anisotropic contribution to the van der Waals and the Casimir-Polder energies for CO2 and CH4 molecules near surfaces and thin films

NASA Astrophysics Data System (ADS)

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

2015-11-01

In order to understand why carbon dioxide (CO2) and methane (CH4) molecules interact differently with surfaces, we investigate the Casimir-Polder energy of a linearly polarizable CO2 molecule and an isotropically polarizable CH4 molecule in front of an atomically thin gold film and an amorphous silica slab. We quantitatively analyze how the anisotropy in the polarizability of the molecule influences the van der Waals contribution to the binding energy of the molecule.

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.

Difference of the seismic structure between the Hyuga-nada and the Nankai seismogenic segments

NASA Astrophysics Data System (ADS)

Yamamoto, Y.; Obana, K.; Takahashi, T.; Nakanishi, A.; Kodaira, S.; Kaneda, Y.

2010-12-01

In the Nankai Trough, three major seismogenic zones of megathrust earthquake exist (Tokai, Tonankai and Nankai earthquake regions). The Hyuga-nada region was distinguished from these seismogenic zones because of the lack of megathrust earthquake. In the Hyuga-nada region, interplate earthquakes of M~7 occur repeatedly at intervals of about 20 years whereas no megathrust (M > 8) earthquakes had been recognized up to now. However, recent studies show the possibility of simultaneous rupture of the Tokai, Tonankai, Nankai and Hyuga-nada segments was also pointed out [e.g., Hori et al., 2009 AOGS]. To understand the possibility of seismic linkage of Nankai and Hyuga-nada segments, Japan Agency for Marine-Earth Science and Technology has been carried out a wide-angle active source survey and local seismic observation in the western end of the Nankai seismogenic zone, as a part of Research concerning Interaction Between the Tokai, Tonankai and Nankai Earthquakes' funded by Ministry of Education, Culture, Sports, Science and Technology, Japan. Nakanishi et al [2009, AGU] showed that subducting Philippine Sea Plate can be divided into three zones and there is the zone of the thin oceanic crust of the subducting Philippine Sea Plate between Nankai segment and Kyushu-Palau Ridge segment by analyzing of the active source survey. Deep structure of the subducting slab is also important to consider the possibility of the seismic linkage and the location of the boundary among three zones described above. To obtain the deep seismic image, we performed a three-dimensional seismic tomography using the local seismic data recorded on 158 ocean bottom seismographs and 105 land seismic stations. From these data, we could detect 1141 earthquakes in the Hyuga-nada region. From the result of hypocenter relocation, microseismicity near the trough axis is active on the western part of the ‘thin oceanic crust’, whereas inactive on the eastern part. Besides, velocity structure of the uppermost part of the subducting slab mantle shows spatial heterogeneities. In the thin oceanic crust zone, high velocity slab mantle is imaged from near the trough to coastline. On the other hands, there is low velocity zone in the slab mantle near the trough axis in the Kyusyu-Palau Ridge segment. This low velocity zone may be related to the location of the eastern end of subducted Kyusyu-Palau Ridge.

Experimental study of the continuous casting slab solidification microstructure by the dendrite etching method

NASA Astrophysics Data System (ADS)

Yang, X. G.; Xu, Q. T.; Wu, C. L.; Chen, Y. S.

2017-12-01

The relationship between the microstructure of the continuous casting slab (CCS) and quality defects of the steel products, as well as evolution and characteristics of the fine equiaxed, columnar, equiaxed zones and crossed dendrites of CCS were systematically investigated in this study. Different microstructures of various CCS samples were revealed. The dendrite etching method was proved to be quite efficient for the analysis of solidified morphologies, which are essential to estimate the material characteristics, especially the CCS microstructure defects.

The effect of averaging adjacent planes for artifact reduction in matrix inversion tomosynthesis

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

Godfrey, Devon J.; Page McAdams, H.; Dobbins, James T. III

2013-02-15

Purpose: Matrix inversion tomosynthesis (MITS) uses linear systems theory and knowledge of the imaging geometry to remove tomographic blur that is present in conventional backprojection tomosynthesis reconstructions, leaving in-plane detail rendered clearly. The use of partial-pixel interpolation during the backprojection process introduces imprecision in the MITS modeling of tomographic blur, and creates low-contrast artifacts in some MITS planes. This paper examines the use of MITS slabs, created by averaging several adjacent MITS planes, as a method for suppressing partial-pixel artifacts. Methods: Human chest tomosynthesis projection data, acquired as part of an IRB-approved pilot study, were used to generate MITS planes,more » three-plane MITS slabs (MITSa3), five-plane MITS slabs (MITSa5), and seven-plane MITS slabs (MITSa7). These were qualitatively examined for partial-pixel artifacts and the visibility of normal and abnormal anatomy. Additionally, small (5 mm) subtle pulmonary nodules were simulated and digitally superimposed upon human chest tomosynthesis projection images, and their visibility was qualitatively assessed in the different reconstruction techniques. Simulated images of a thin wire were used to generate modulation transfer function (MTF) and slice-sensitivity profile curves for the different MITS and MITS slab techniques, and these were examined for indications of partial-pixel artifacts and frequency response uniformity. Finally, mean-subtracted, exposure-normalized noise power spectra (ENNPS) estimates were computed and compared for MITS and MITS slab reconstructions, generated from 10 sets of tomosynthesis projection data of an acrylic slab. The simulated in-plane MTF response of each technique was also combined with the square root of the ENNPS estimate to yield stochastic signal-to-noise ratio (SNR) information about the different reconstruction techniques. Results: For scan angles of 20 Degree-Sign and 5 mm plane separation, seven MITS planes must be averaged to sufficiently remove partial-pixel artifacts. MITSa7 does appear to subtly reduce the contrast of high-frequency 'edge' information, but the removal of partial-pixel artifacts makes the appearance of low-contrast, fine-detail anatomy even more conspicuous in MITSa7 slices. MITSa7 also appears to render simulated subtle 5 mm pulmonary nodules with greater visibility than MITS alone, in both the open lung and regions overlying the mediastinum. Finally, the MITSa7 technique reduces stochastic image variance, though the in-plane stochastic SNR (for very thin objects which do not span multiple MITS planes) is only improved at spatial frequencies between 0.05 and 0.20 cycles/mm. Conclusions: The MITSa7 method is an improvement over traditional single-plane MITS for thoracic imaging and the pulmonary nodule detection task, and thus the authors plan to use the MITSa7 approach for all future MITS research at the authors' institution.« less

The effect of averaging adjacent planes for artifact reduction in matrix inversion tomosynthesis.

PubMed

Godfrey, Devon J; McAdams, H Page; Dobbins, James T

2013-02-01

Matrix inversion tomosynthesis (MITS) uses linear systems theory and knowledge of the imaging geometry to remove tomographic blur that is present in conventional backprojection tomosynthesis reconstructions, leaving in-plane detail rendered clearly. The use of partial-pixel interpolation during the backprojection process introduces imprecision in the MITS modeling of tomographic blur, and creates low-contrast artifacts in some MITS planes. This paper examines the use of MITS slabs, created by averaging several adjacent MITS planes, as a method for suppressing partial-pixel artifacts. Human chest tomosynthesis projection data, acquired as part of an IRB-approved pilot study, were used to generate MITS planes, three-plane MITS slabs (MITSa3), five-plane MITS slabs (MITSa5), and seven-plane MITS slabs (MITSa7). These were qualitatively examined for partial-pixel artifacts and the visibility of normal and abnormal anatomy. Additionally, small (5 mm) subtle pulmonary nodules were simulated and digitally superimposed upon human chest tomosynthesis projection images, and their visibility was qualitatively assessed in the different reconstruction techniques. Simulated images of a thin wire were used to generate modulation transfer function (MTF) and slice-sensitivity profile curves for the different MITS and MITS slab techniques, and these were examined for indications of partial-pixel artifacts and frequency response uniformity. Finally, mean-subtracted, exposure-normalized noise power spectra (ENNPS) estimates were computed and compared for MITS and MITS slab reconstructions, generated from 10 sets of tomosynthesis projection data of an acrylic slab. The simulated in-plane MTF response of each technique was also combined with the square root of the ENNPS estimate to yield stochastic signal-to-noise ratio (SNR) information about the different reconstruction techniques. For scan angles of 20° and 5 mm plane separation, seven MITS planes must be averaged to sufficiently remove partial-pixel artifacts. MITSa7 does appear to subtly reduce the contrast of high-frequency "edge" information, but the removal of partial-pixel artifacts makes the appearance of low-contrast, fine-detail anatomy even more conspicuous in MITSa7 slices. MITSa7 also appears to render simulated subtle 5 mm pulmonary nodules with greater visibility than MITS alone, in both the open lung and regions overlying the mediastinum. Finally, the MITSa7 technique reduces stochastic image variance, though the in-plane stochastic SNR (for very thin objects which do not span multiple MITS planes) is only improved at spatial frequencies between 0.05 and 0.20 cycles∕mm. The MITSa7 method is an improvement over traditional single-plane MITS for thoracic imaging and the pulmonary nodule detection task, and thus the authors plan to use the MITSa7 approach for all future MITS research at the authors' institution.

A Thermal Paradox: Which Gets Warmer?

ERIC Educational Resources Information Center

Salazar, Agustin; Apinaniz, Estibaliz; Mendioroz, Arantza; Oleaga, Alberto

2010-01-01

In this paper we address a common misconception concerning the thermal behaviour of matter, namely that the front surface of a very thin plate, uniformly illuminated by a constant light beam, reaches a higher temperature than the front surface of a very thick slab made out of the same material. We present analytical solutions for the temperature…

Method and apparatus for powering an electrodeless lamp with reduced radio frequency interference

DOEpatents

Simpson, James E.

1999-01-01

An electrodeless lamp waveguide structure includes tuned absorbers for spurious RF signals. A lamp waveguide with an integral frequency selective attenuation includes resonant absorbers positioned within the waveguide to absorb spurious out-of-band RF energy. The absorbers have a negligible effect on energy at the selected frequency used to excite plasma in the lamp. In a first embodiment, one or more thin slabs of lossy magnetic material are affixed to the sidewalls of the waveguide at approximately one quarter wavelength of the spurious signal from an end wall of the waveguide. The positioning of the lossy material optimizes absorption of power from the spurious signal. In a second embodiment, one or more thin slabs of lossy magnetic material are used in conjunction with band rejection waveguide filter elements. In a third embodiment, one or more microstrip filter elements are tuned to the frequency of the spurious signal and positioned within the waveguide to couple and absorb the spurious signal's energy. All three embodiments absorb negligible energy at the selected frequency and so do not significantly diminish the energy efficiency of the lamp.

Method and apparatus for powering an electrodeless lamp with reduced radio frequency interference

DOEpatents

Simpson, J.E.

1999-06-08

An electrodeless lamp waveguide structure includes tuned absorbers for spurious RF signals. A lamp waveguide with an integral frequency selective attenuation includes resonant absorbers positioned within the waveguide to absorb spurious out-of-band RF energy. The absorbers have a negligible effect on energy at the selected frequency used to excite plasma in the lamp. In a first embodiment, one or more thin slabs of lossy magnetic material are affixed to the sidewalls of the waveguide at approximately one quarter wavelength of the spurious signal from an end wall of the waveguide. The positioning of the lossy material optimizes absorption of power from the spurious signal. In a second embodiment, one or more thin slabs of lossy magnetic material are used in conjunction with band rejection waveguide filter elements. In a third embodiment, one or more microstrip filter elements are tuned to the frequency of the spurious signal and positioned within the waveguide to couple and absorb the spurious signal's energy. All three embodiments absorb negligible energy at the selected frequency and so do not significantly diminish the energy efficiency of the lamp. 18 figs.

SMALL-SCALE SOLAR WIND TURBULENCE DUE TO NONLINEAR ALFVÉN WAVES

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

Kumar, Sanjay; Moon, Y.-J.; Sharma, R. P., E-mail: sanjaykumar@khu.ac.kr

We present an evolution of wave localization and magnetic power spectra in solar wind plasma using kinetic Alfvén waves (AWs) and fast AWs. We use a two-fluid model to derive the dynamical equations of these wave modes and then numerically solve these nonlinear dynamical equations to analyze the power spectra and wave localization at different times. The ponderomotive force associated with the kinetic AW (or pump) is responsible for the wave localization, and these thin slabs (or sheets) become more chaotic as the system evolves with time until the modulational instability (or oscillating two-stream instability) saturates. From our numerical results,more » we notice a steepening of the spectra from the inertial range (k{sup −1.67}) to the dispersion range (k{sup −3.0}). The steepening of the spectra could be described as the energy transference from longer to smaller scales. The formation of complex magnetic thin slabs and the change of the spectral index may be considered to be the main reason for the charged particles acceleration in solar wind plasma.« less

Buckling and stretching of thin viscous sheets

NASA Astrophysics Data System (ADS)

O'Kiely, Doireann; Breward, Chris; Griffiths, Ian; Howell, Peter; Lange, Ulrich

2016-11-01

Thin glass sheets are used in smartphone, battery and semiconductor technology, and may be manufactured by producing a relatively thick glass slab and subsequently redrawing it to a required thickness. The resulting sheets commonly possess undesired centerline ripples and thick edges. We present a mathematical model in which a viscous sheet undergoes redraw in the direction of gravity, and show that, in a sufficiently strong gravitational field, buckling is driven by compression in a region near the bottom of the sheet, and limited by viscous resistance to stretching of the sheet. We use asymptotic analysis in the thin-sheet, low-Reynolds-number limit to determine the centerline profile and growth rate of such a viscous sheet.

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.

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.

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.

High-resolution Imaging of the Philippine Sea Plate subducting beneath Central Japan

NASA Astrophysics Data System (ADS)

Padhy, S.; Furumura, T.

2016-12-01

Thermal models predict that the oceanic crust of the young (<20 Ma) and warmer Philippine-sea plate (PHP) is more prone to melting. Deriving a high-resolution image of the PHP, including slab melting and other features of the subduction zone, is a key to understand the basics of earthquake occurrence and origin of magma in complex subduction zone like central Japan, where both the PHP and Pacific (PAC) Plates subduct. To this purpose, we analyzed high-resolution waveforms of moderate sized (M 4-6), intermediate-to-deep (>150 km) PAC earthquakes occurring in central Japan and conducted numerical simulation to derive a fine-scale PHP model, which is not constrained in earlier studies. Observations show spindle-shaped seismograms with strong converted phases and extended coda with very slow decay from a group of PAC events occurring in northern part of central Japan and recorded by high-sensitivity seismograph network (Hi-net) stations in the region. We investigate the mechanism of propagation of these anomalous waveforms using the finite difference method (FDM) simulation of wave propagation through the subduction zone. We examine the effects on waveform changes of major subduction zone features, such as the melting of oceanic crust in PHP, serpentinized mantle wedge, hydrated layer on the PAC due to slab dehydration, and anomaly in upper mantle between the PAC and PHP. Simulation results show that the waveform anomaly is primarily explained by strong scattering and absorption of high-frequency energy by the low-velocity anomalous mantle structure, with a strong coda excitation yielding spindle-shaped waveforms. The data are secondarily explained by melting of PHP in the basaltic crust. The location of the mantle anomaly is tightly constrained by the observation and evidence of PAC thinning in the region; these localized low-velocity structures aid in ascending the slab-derived fluids around the slab thinning. We expect that the results of this study will enhance our present understanding on the mechanism of intermediate to deep earthquakes in the region.

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.

High skew link slab bridge system with deck sliding over backwall or backwall sliding over abutments : part II.

DOT National Transportation Integrated Search

2011-09-30

A new bridge design and construction trend to help improve durability and rideability is to remove expansion joints over piers and abutments. One approach to achieve this is to make the deck continuous over the piers by means of a link slab while the...

High skew link slab bridge system with deck sliding over backwall or backwall sliding over abutments : part I.

DOT National Transportation Integrated Search

2011-09-30

A new bridge design and construction trend to help improve durability and rideability is to remove expansion : joints over piers and abutments. One approach to achieve this is to make the deck continuous over the piers by : means of a link slab while...

Why does continental convergence stop

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

Hynes, A.

1985-01-01

Convergence between India and Asia slowed at 45 Ma when they collided, but continues today. This requires that substantial proportions of the Indian and/or Asian lithospheric mantle are still being subducted. The resulting slab-pull is probably comparable with that from complete lithospheric slabs and may promote continued continental convergence even after collision. Since descending lithospheric slabs are present at all collision zones at the time of collision such continued convergence may be general after continental collisions. It may cease only when there is a major (global) plate reorganization which results in new forces on the convergent continents that may counteractmore » the slab-pull. These inferences may be tested on the late Paleozoic collision between Gondwanaland and Laurasia. This is generally considered to have been complete by mid-Permian time (250 Ma). However, this may be only the time of docking of Gondwanaland with North America, not that of the cessation of convergence. Paleomagnetic polar-wander paths for the Gondwanide continents exhibit consistently greater latitudinal shifts from 250 Ma to 200 Ma than those of Laurasia when corrected for post-Triassic drift, suggesting that convergence continued through late Permian well into the Triassic. It may have been accommodated by crustal thickening under what is now the US Coastal Plain, or by strike-slip faulting. Convergence may have ceased only when Pangea began to fragment again, in which case the cause for its cessation may be related to the cause of continental fragmentation.« less

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

Equilibrium Slab Models of Lyman-Alpha Clouds

NASA Technical Reports Server (NTRS)

Charlton, Jane C.; Salpeter, Edwin E.; Hogan, Craig J.

1993-01-01

We model the L(sub y(alpha)) clouds as slabs of hydrogen with an ionizing extragalactic radiation field incident from both sides. In general, the equilibrium configuration of a slab at redshift z approx. less than 5 is determined by a balance of the gas pressure, gravity (including the effects of a dark matter halo), and the pressure exerted by the inter-galactic medium, P(sub ext). These models have been used to make predictions of the number of slabs as a function of the neutral hydrogen column density, N(sub H). A break in the curve is predicted at the transition between regimes where gravity and pressure are the dominant confining forces, with a less rapid decrease at larger N(sub H). The transition from optically thin to optically thick slabs leads to a gap in the distribution, whose location is governed largely by the spectrum of ionizing radiation. There are certain parallels between lines of sight through the outer HI disk of spiral galaxy with increasing radius, and the progression from damped, to Lyman limit, to forest clouds. We discuss briefly the possibility that at least some of the observed low z forest clouds may be a separate population, associated with galaxies, as suggested by the observations of Bahcall et al. This population could dominate the forest at present if the dark matter attached to galaxies should lead to gravity confinement for this disk population, while the isolated clouds remain pressure confined. The formalism developed in this paper will allow a more detailed study. We also discuss a more general parameter study of the equilibrium configuration of slabs, including mock gravity and L(sub y(alpha)) photon trapping.

Quantitative evaluation of the oral biofilm-removing capacity of a dental water jet using an electron-probe microanalyzer.

PubMed

Kato, Kazuo; Tamura, Kiyomi; Nakagaki, Haruo

2012-01-01

This study was conducted to evaluate the oral biofilm-removing capacity of a dental water jet (DWJ) by measuring biofilm thickness using an electron-probe microanalyzer (EPMA). Thirty consenting subjects wore in situ plaque-generating devices, which consisted of a pair of 4mm(2) enamel slabs attached to the upper molars for 2 days. Each device removed from the mouth was clamped, and one of the slab surfaces was treated with the DWJ, irrigating it for 5s. The devices were randomly assigned to three different pressure settings of 707, 350 or 102kPa. Another slab with no treatment served as a control. Each slab was freeze-dried, sputter-coated with platinum, and examined using secondary-electron imaging. The slabs were then embedded in methacrylate and cross-sectioned in the centre. Their surfaces were polished, coated with carbon, and examined using backscattered electron compositional (COMPO) imaging. The area between the enamel and the outer biofilm surface, indicated by a thin platinum layer, was measured by COMPO imaging to calculate the average thickness of the biofilm on the specimen. The removal capacity of biofilm by irrigation was estimated using a reduced rate of biofilm thickness, which was calculated from the differences between a pair of treated and control slabs. The reduced rates were 85.5% at 707kPa, 85.1% at 350kPa and 63.4% at 102kPa, indicating that biofilm thickness was significantly reduced at every pressure setting. The results suggest that irrigation using a DWJ would be an effective means of plaque control. Copyright © 2011 Elsevier Ltd. All rights reserved.

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.

The dynamic history of the Trans-Mexican Volcanic Belt and the Mexico subduction zone

NASA Astrophysics Data System (ADS)

Ferrari, Luca; Orozco-Esquivel, Teresa; Manea, Vlad; Manea, Marina

2012-02-01

The Trans-Mexican Volcanic Belt (TMVB) is a 1000 km long Neogene continental arc showing a large variation in composition and volcanic style, and an intra-arc extensional tectonics. It overlies the Rivera and Cocos slabs, which display marked changes in geometry. Geophysical studies indicate that lithospheric mantle is very thin or absent beneath the forearc and arc, the fluids from the slab are released in a 40 to 100 km wide belt beneath the frontal part of the arc, and the lower crust beneath the arc is partially molten. East of 101°W the TMVB is built on a Precambrian to Paleozoic crust with thickness of 50-55 km. West of 101°W the TMVB is underlain by Jurassic to Cenozoic marine and continental arcs with a 35-40 km thick crust. The evolution of the TMVB occurred in four stages: 1) from ~ 20 to 10 Ma the initial andesitic arc moved inland showing progressively drier melting and, eventually, slab melting, suggesting flattening of the subducted slab; 2) since ~ 11 Ma a pulse of mafic volcanism migrated from west to east reaching the Gulf of Mexico by 7 Ma. This mafic lavas marks the lateral propagation of a slab tear, triggered by cessation of subduction beneath Baja California; 3) thereafter, the volcanic front started moving trenchward, with a marked phase of silicic volcanism between 7.5 and 3 Ma, local emplacement of small volume intraplate-like basalts since 5 Ma, and development of extensional faulting. These features are related to slab rollback, enhancing asthenophere flux into the mantle wedge and promoting partial melting of the crust; 4) the modern arc consists of a frontal belt dominated by flux and slab melting, and a rear belt characterized by more differentiated rocks or by mafic lavas with little or no evidence of subduction fluids but higher asthenosphere fingerprint.

Diffusive Propagation of Exciton-Polaritons through Thin Crystal Slabs

PubMed Central

Zaitsev, D. A.; Il’ynskaya, N. D.; Koudinov, A. V.; Poletaev, N. K.; Nikitina, E. V.; Egorov, A. Yu.; Kavokin, A. V.; Seisyan, R. P.

2015-01-01

If light beam propagates through matter containing point impurity centers, the amount of energy absorbed by the media is expected to be either independent of the impurity concentration N or proportional to N, corresponding to the intrinsic absorption or impurity absorption, respectively. Comparative studies of the resonant transmission of light in the vicinity of exciton resonances measured for 15 few-micron GaAs crystal slabs with different values of N, reveal a surprising tendency. While N spans almost five decimal orders of magnitude, the normalized spectrally-integrated absorption of light scales with the impurity concentration as N1/6. We show analytically that this dependence is a signature of the diffusive mechanism of propagation of exciton-polaritons in a semiconductor. PMID:26088555

Spiral microstrip antenna with resistance

NASA Technical Reports Server (NTRS)

Shively, David G. (Inventor)

1994-01-01

The present invention relates to microstrip antennas, and more particularly to wide bandwidth spiral antennas with resistive loading. A spiral microstrip antenna having resistor element embedded in each of the spiral arms is provided. The antenna is constructed using a conductive back plane as a base. The back plane supports a dielectric slab having a thickness between one-sixteenth and one-quarter of an inch. A square spiral, having either two or four arms, is attached to the dielectric slab. Each arm of the spiral has resistor elements thereby dissipating an excess energy not already emitted through radiation. The entire configuration provides a thin, flat, high gain, wide bandwidth antenna which requires no underlying cavity. The configuration allows the antenna to be mounted conformably on an aircraft surface.

Mechanism of Macrosegregation Formation in Continuous Casting Slab: A Numerical Simulation Study

NASA Astrophysics Data System (ADS)

Jiang, Dongbin; Wang, Weiling; Luo, Sen; Ji, Cheng; Zhu, Miaoyong

2017-12-01

Solidified shell bulging is supposed to be the main reason for slab center segregation, while the influence of thermal shrinkage rarely has been considered. In this article, a thermal shrinkage model coupled with the multiphase solidification model is developed to investigate the effect of the thermal shrinkage, solidification shrinkage, grain sedimentation, and thermal flow on solute transport in the continuous casting slab. In this model, the initial equiaxed grains contract freely with the temperature decrease, while the coherent equiaxed grains and columnar phase move directionally toward the slab surface. The results demonstrate that the center positive segregation accompanied by negative segregation in the periphery zone is mainly caused by thermal shrinkage. During the solidification process, liquid phase first transports toward the slab surface to compensate for thermal shrinkage, which is similar to the case considering solidification shrinkage, and then it moves opposite to the slab center near the solidification end. It is attributed to the sharp decrease of center temperature and the intensive contract of solid phase, which cause the enriched liquid to be squeezed out. With the effect of grain sedimentation and thermal flow, the negative segregation at the external arc side (zone A1) and the positive segregation near the columnar-to-equiaxed transition at the inner arc side (position B1) come into being. Besides, it is found that the grain sedimentation and thermal flow only influence solute transport before equiaxed grains impinge with each other, while the solidification and thermal shrinkage still affect solute redistribution in the later stage.

Crustal and mantle shear velocity structure of Costa Rica and Nicaragua from ambient noise and teleseismic Rayleigh wave tomography

NASA Astrophysics Data System (ADS)

Harmon, Nicholas; de la Cruz, Mariela Salas; Rychert, Catherine Ann; Abers, Geoffrey; Fischer, Karen

2013-11-01

The Costa Rica-Nicaragua subduction zone shows systematic along strike variation in arc chemistry, geology, tectonics and seismic velocity and attenuation, presenting global extremes within a few hundred kilometres. In this study, we use teleseismic and ambient noise derived surface wave tomography to produce a 3-D shear velocity model of the region. We use the 48 stations of the TUCAN array, and up to 94 events for the teleseismic Rayleigh wave inversion, and 18 months of continuous data for cross correlation to estimate Green's functions from ambient noise. In the shallow crust (0-15 km) we observe low-shear velocities directly beneath the arc volcanoes (<3 km s-1) and higher velocities in the backarc of Nicaragua. The anomalies below the volcanoes are likely caused by heated crust, intruded by magma. We estimate crustal thickness by picking the depth to the 4 km s-1 velocity contour. We infer >40-km-thick crust beneath the Costa Rican arc and the Nicaraguan Highlands, thinned crust (˜20 km) beneath the Nicaraguan Depression, and increasing crustal thickness in the backarc region, consistent with receiver function studies. The region of thinned, seismically slow and likely weakened crust beneath the arc in Nicaragua is not localizing deformation associated with oblique subduction. At mantle depths (55-120 km depth) we observe lower shear velocities (up to 3 per cent) beneath the Nicaraguan arc and backarc than beneath Costa Rica. Our low-shear velocity anomaly beneath Nicaragua is in the same location as a low-shear velocity anomaly and displaced towards the backarc from the high VP/VS anomaly observed in body wave tomography. The lower shear velocity beneath Nicaragua may indicate higher melt content in the mantle perhaps due to higher volatile flux from the slab or higher temperature. Finally, we observe a linear high-velocity region at depths >120 km parallel to the trench, which is consistent with the subducting slab.

Real-time absorption and scattering characterization of slab-shaped turbid samples obtained by a combination of angular and spatially resolved measurements.

PubMed

Dam, Jan S; Yavari, Nazila; Sørensen, Søren; Andersson-Engels, Stefan

2005-07-10

We present a fast and accurate method for real-time determination of the absorption coefficient, the scattering coefficient, and the anisotropy factor of thin turbid samples by using simple continuous-wave noncoherent light sources. The three optical properties are extracted from recordings of angularly resolved transmittance in addition to spatially resolved diffuse reflectance and transmittance. The applied multivariate calibration and prediction techniques are based on multiple polynomial regression in combination with a Newton--Raphson algorithm. The numerical test results based on Monte Carlo simulations showed mean prediction errors of approximately 0.5% for all three optical properties within ranges typical for biological media. Preliminary experimental results are also presented yielding errors of approximately 5%. Thus the presented methods show a substantial potential for simultaneous absorption and scattering characterization of turbid media.

Over 10-watt pico-second diffraction-limited output from a Nd:YVO4 slab amplifier with a phase conjugate mirror.

PubMed

Ojima, Yasukuni; Nawata, Kouji; Omatsu, Takashige

2005-10-31

We have produced a high beam quality pico-second laser based on a continuous-wave diode pumped Nd:YVO4 slab amplifier with a photorefractive phase conjugate mirror. 12.8W diffraction-limited output with a pulse width of 8.7ps was obtained.

Fabrication and characterization of a planar gradient-index, plasma-enhanced chemical vapor deposition lens.

PubMed

Beltrami, D R; Love, J D; Durandet, A; Samo, A; Cogswell, C J

1997-10-01

A thin, one-dimensional, gradient-index slab lens with a parabolic profile was designed and fabricated in fluorine-doped silica by use of plasma-enhanced chemical vapor deposition in a Helicon plasma reactor. The refractive-index profile of the fabricated lens was determined by the application of an inversion technique to the values of modal effective index measured with a prism coupler. The periodic refocusing property of the lens and the independence of the wavelength were measured with the fluorescence of a specially doped, thin polymer layer spin-coated onto the surface of the lens.

Aseismic Slip of a Thin Slab Due to a Fluid Source

NASA Astrophysics Data System (ADS)

Aubin, P. W.; Viesca, R. C.

2017-12-01

We explore the effects of an increase of pore pressure on the frictional interface along the base of a thin slab. The thin slab approximation corresponds to a layer overriding a substrate in which variations along the layer's length occur over distances much greater than the layer thickness. We consider deformation that may be in-plane or anti-plane, but approximately uniform in depth, such that spatial variations of displacement (and hence, slip) occur only along one direction parallel to the interface. Such a thin-sheet model may well represent the deformation of landslides and glacial ice streams, and also serves as a first-pass for fault systems, which, while better represented by elastic half-spaces in frictional contact, nonetheless show qualitatively similar behavior. We consider that the friction coefficient at the layer's interface remains (approximately) constant, and that aseismic slip is initiated by a (line) source of fluid at constant pressure, with one-dimensional diffusion parallel to the interface. As posed, the problem yields a self-similar expansion of slip, whose extent grows proportionally to (α * t)^(1/2) (where α is the hydraulic diffusivity) and can either lag behind or outpace the fluid diffusion front. The problem is controlled by a single parameter, accounting for the friction coefficient and the initial (pre-injection) states of stress and pore pressure. The problem solution consists of the self-similar slip profile and the coefficient of proportionality for the crack-front motion. Within the problem parameter range, two end-member scenarios result: one in which the initial level of shear stress on the interface is close to the value of the pre-injection strength (critically stressed) or another in which fluid pressure is just enough to induce slip (marginally pressurized). For the critically stressed and marginally pressurized cases, the aseismic slip front lies far ahead or far behind, respectively, the fluid diffusion front. We find closed-form solutions for both end-members, and in the former case, via matched asymptotics. These solutions provide a basis to solve the general problem, which we also solve numerically for comparison. The solutions also provide a starting point for examining the progression of slip and locking following the shutoff of the fluid source.

A New Predictive Model of Centerline Segregation in Continuous Cast Steel Slabs by Using Multivariate Adaptive Regression Splines Approach

PubMed Central

García Nieto, Paulino José; González Suárez, Victor Manuel; Álvarez Antón, Juan Carlos; Mayo Bayón, Ricardo; Sirgo Blanco, José Ángel; Díaz Fernández, Ana María

2015-01-01

The aim of this study was to obtain a predictive model able to perform an early detection of central segregation severity in continuous cast steel slabs. Segregation in steel cast products is an internal defect that can be very harmful when slabs are rolled in heavy plate mills. In this research work, the central segregation was studied with success using the data mining methodology based on multivariate adaptive regression splines (MARS) technique. For this purpose, the most important physical-chemical parameters are considered. The results of the present study are two-fold. In the first place, the significance of each physical-chemical variable on the segregation is presented through the model. Second, a model for forecasting segregation is obtained. Regression with optimal hyperparameters was performed and coefficients of determination equal to 0.93 for continuity factor estimation and 0.95 for average width were obtained when the MARS technique was applied to the experimental dataset, respectively. The agreement between experimental data and the model confirmed the good performance of the latter.

An ab-initio coupled mode theory for near field radiative thermal transfer.

PubMed

Chalabi, Hamidreza; Hasman, Erez; Brongersma, Mark L

2014-12-01

We investigate the thermal transfer between finite-thickness planar slabs which support surface phonon polariton modes (SPhPs). The thickness-dependent dispersion of SPhPs in such layered materials provides a unique opportunity to manipulate and enhance the near field thermal transfer. The key accomplishment of this paper is the development of an ab-initio coupled mode theory that accurately describes all of its thermal transfer properties. We illustrate how the coupled mode parameters can be obtained in a direct fashion from the dispersion relation of the relevant modes of the system. This is illustrated for the specific case of a semi-infinite SiC substrate placed in close proximity to a thin slab of SiC. This is a system that exhibits rich physics in terms of its thermal transfer properties, despite the seemingly simple geometry. This includes a universal scaling behavior of the thermal conductance with the slab thickness and spacing. The work highlights and further increases the value of coupled mode theories in rapidly calculating and intuitively understanding near-field transfer.

Size and Velocity Characteristics of Droplets Generated by Thin Steel Slab Continuous Casting Secondary Cooling Air-Mist Nozzles

NASA Astrophysics Data System (ADS)

Minchaca M, J. I.; Castillejos E, A. H.; Acosta G, F. A.

2011-06-01

Direct spray impingement of high temperature surfaces, 1473 K to 973 K (1200 °C to 700 °C), plays a critical role in the secondary cooling of continuously cast thin steel slabs. It is known that the spray parameters affecting the local heat flux are the water impact flux w as well as the droplet velocity and size. However, few works have been done to characterize the last two parameters in the case of dense mists ( i.e., mists with w in the range of 2 to 90 L/m2s). This makes it difficult to rationalize how the nozzle type and its operating conditions must be selected to control the cooling process. In the present study, particle/droplet image analysis was used to determine the droplet size and velocity distributions simultaneously at various locations along the major axis of the mist cross section at a distance where the steel strand would stand. The measurements were carried out at room temperature for two standard commercial air-assisted nozzles of fan-discharge type operating over a broad range of conditions of practical interest. To achieve statistically meaningful samples, at least 6000 drops were analyzed at each location. Measuring the droplet size revealed that the number and volume frequency distributions were fitted satisfactorily by the respective log-normal and Nukiyama-Tanasawa distributions. The correlation of the parameters of the distribution functions with the water- and air-nozzle pressures allowed for reasonable estimation of the mean values of the size of the droplets generated. The ensemble of measurements across the mist axis showed that the relationship between the droplet velocity and the diameter exhibited a weak positive correlation. Additionally, increasing the water flow rate at constant air pressure caused a decrease in the proportion of the water volume made of finer droplets, whereas the volume proportion of faster droplets augmented until the water flow reached a certain value, after which it decreased. Diminishing the air-to-water flow rates ratio, particularly below 10, resulted in mists of bigger and slower droplets with low impinging Weber numbers. However, increasing the air pressure maintaining a constant water flow rate caused a greater proportion of finer and faster drops with Weber numbers greater than 80, which suggests an increased probability of wet drop contact with a hot surface that would intensify heat extraction.

Organic Thin Films for Photonics Applications. Volume 14

DTIC Science & Technology

1997-01-01

progress of the polymer optical fiber (POF) and related photonics polymer for high-speed telecommunication is reviewed. The high-bandwidth perfluorinated ...silicon. In the waveguide spectrometry studies described above, ab- sorption was measured on slab waveguides where fabrication imperfections are... compound in scries I[//| and II|//| , we have determined in solution: - the ground-state dipole /{ using capacitive measurements - the static

Refractory Inclusion Size Distribution and Fabric Measured in a Large Slab of the Allende CV3 Chondrite

NASA Technical Reports Server (NTRS)

Srinivasan, P.; Simon, Justin I.; Cuzzi, J. N.

2013-01-01

Aggregate textures of chondrites reflect accretion of early-formed particles in the solar nebula. Explanations for the size and density variations of particle populations found among chondrites are debated. Differences could have risen out of formation in different locations in the nebula, and/or they could have been caused by a sorting process [1]. Many ideas on the cause of chondrule sorting have been proposed; some including sorting by mass [2,3], by X-winds [4], turbulent concentration [5], and by photophoresis [6]. However, few similar studies have been conducted for Ca-, Al-rich inclusions (CAIs). These particles are known to have formed early, and their distribution could attest to the early stages of Solar System (ESS) history. Unfortunately, CAIs are not as common in chondrites as chondrules are, reducing the usefulness of studies restricted to a few thin sections. Furthermore, the largest sizes of CAIs are generally much larger than chondrules, and therefore rarely present in most studied chondrite thin sections. This study attempts to perform a more representative sampling of the CAI population in the Allende chondrite by investigating a two decimeter-sized slab.

Common-path conoscopic interferometry for enhanced picosecond ultrasound detection

NASA Astrophysics Data System (ADS)

Liu, Liwang; Guillet, Yannick; Audoin, Bertrand

2018-05-01

We report on a common-path implementation of conoscopic interferometry in picosecond pump-probe reflectometry for simple and efficient detection of picosecond ultrasounds. The interferometric configuration proposed here is greatly simplified, involving only the insertion of a birefringent crystal in a standard reflectometry setup. Our approach is demonstrated by the optical detection of coherent acoustic phonons propagating through thin metal films under two representative geometries, one a particular case where the crystal slab is part of a sample as substrate of a metal film, and the other a more general case where the crystal slab is independent of the sample as part of the detection system. We first illustrate the former with a 300 nm thin film of polycrystalline titanium, deposited by physical vapor deposition on top of a 1 mm-thick uniaxial (0001) sapphire crystal. A signal-to-noise ratio (SNR) enhancement of more than 15 dB is achieved compared to conventional reflectometry. Next, the general case is demonstrated with a 900 nm-tungsten film sputtered on a silicon wafer substrate. More echoes can be discriminated by using the reported approach compared to standard reflectometry, which confirms the improvement in SNR and suggests broad applications for the reported method.

Lithospheric structure of Iberia and Morocco using finite-frequency Rayleigh wave tomography from earthquakes and seismic ambient noise

NASA Astrophysics Data System (ADS)

Palomeras, I.; Villaseñor, A.; Thurner, S.; Levander, A.; Gallart, J.; Harnafi, M.

2017-05-01

We present a new 3-D shear velocity model of the western Mediterranean from the Pyrenees, Spain, to the Atlas Mountains, Morocco, and the estimated crustal and lithospheric thickness. The velocity model shows different crustal and lithospheric velocities for the Variscan provinces, those which have been affected by Alpine deformation, and those which are actively deforming. The Iberian Massif has detectable differences in crustal thickness that can be related to the evolution of the Variscan orogen in Iberia. Areas affected by Alpine deformation have generally lower velocities in the upper and lower crust than the Iberian Massif. Beneath the Gibraltar Strait and surrounding areas, the crustal thickness is greater than 50 km, below which a high-velocity anomaly (>4.5 km/s) is mapped to depths greater than 200 km. We identify this as a subducted remnant of the NeoTethys plate referred to as the Alboran and western Mediterranean slab. Beneath the adjacent Betic and Rif Mountains, the Alboran slab is still attached to the base of the crust, depressing it, and ultimately delaminating the lower crust and mantle lithosphere as the slab sinks. Under the adjacent continents, the Alboran slab is surrounded by low upper mantle shear wave velocities (Vs < 4.3) that we interpret as asthenosphere that has replaced the continental margin lithosphere which was viscously removed by Alboran plate subduction. The southernmost part of the model features an anomalously thin lithosphere beneath the Atlas Mountains that could be related to lateral flow induced by the Alboran slab.

­­New Finite-Frequency Teleseismic P-wave Tomography of the Anatolian Sub-continent and the Fate of the Subducted Cyprean Slab

NASA Astrophysics Data System (ADS)

Portner, D. E.; Biryol, C. B.; Delph, J. R.; Beck, S. L.; Zandt, G.; Özacar, A.; Sandvol, E. A.; Turkelli, N.

2016-12-01

The eastern Mediterranean region is characterized by active subduction of Tethyan lithosphere beneath the Anatolian sub-continent at the Aegean and Cyprean trenches. The subduction system is historically characterized by slab roll-back, detachment, and slab settling in the mantle transition zone. Prior mantle tomography studies reveal segmentation of the subducted Tethyan lithosphere, which is thought to have a strong control on surface volcanism and uplift across Anatolia. However, tomographic resolution, particularly in central Anatolia, has been limited, thus making detailed delineations of the subducted slab segments difficult. To improve resolution, we combine two years of seismic data from the recent Continental Dynamics - Central Anatolia Tectonics (CD-CAT) seismic deployment and Turkey's national seismic network ( 33,000 residuals) to 33,000 travel time residuals from Biryol et al. (2011, GJI) in a new finite-frequency teleseismic P-wave tomographic inversion. Our new images reveal with detail a complicated geometry of fast velocity anomalies associated with subducted Tethyan lithosphere. At shallow depths, slow velocities separate the fast anomalies connected to the Aegean and Cyprean trenches. The fast anomaly connected to the Cyprean trench has an arcuate shape in map view, following the trace of the Central Taurus Mountains. This anomaly is separated from a high-amplitude block to the north that appears to dip sub-vertically throughout the upper mantle (200-660 km depth). Other blocks of fast material that may represent subducted Tethyan lithosphere appear down-dip of the vertical block. Additionally, our images indicate that some of the fast velocity anomalies previously seen to flatten in the mantle transition zone may continue into the lower mantle. Thus, our new images provide a more detailed picture of the fate of the Cyprean slab and suggest that some of the fast anomalies associated with the slab continue into the lower mantle, bringing to question the traditional view of a slab graveyard in the mantle transition zone in this region.

Mantle Response to Collision, Slab Breakoff & Lithospheric Tearing in Anatolian Orogenic Belts, and Cenozoic Geodynamics of the Aegean-Eastern Mediterranean Region

NASA Astrophysics Data System (ADS)

Dilek, Yildirim; Altunkaynak, Safak

2010-05-01

The geochemical and temporal evolution of the Cenozoic magmatism in the Aegean, Western Anatolian and peri-Arabian regions shows that plate tectonic events, mantle dynamics, and magmatism were closely linked in space and time. The mantle responded to collision-driven crustal thickening, slab breakoff, delamination, and lithospheric tearing swiftly, within geologically short time scales (few million years). This geodynamic continuum resulted in lateral mantle flow, whole-sale extension and accompanying magmatism that in turn caused the collapse of tectonically and magmatically weakened orogenic crust. Initial stages of post-collisional magmatism (~45 Ma) thermally weakened the orogenic crust in Tethyan continental collision zones, giving way into large-scale extension and lower crustal exhumation via core complex formation starting around 25-23 Ma. Slab breakoff was the most common driving force for the early stages of post-collisional magmatism in the Tethyan mountain belts in the eastern Mediterranean region. Magmatic rocks produced at this stage are represented by calc-alkaline-shoshonitic to transitional (in composition) igneous suites. Subsequent lithospheric delamination or partial convective removal of the sub-continental lithospheric mantle in collision-induced, overthickened orogenic lithosphere caused decompressional melting of the upwelling asthenosphere that in turn resulted in alkaline basaltic magmatism (<12 Ma). Attendant crustal extension and widespread thinning of the lithosphere facilitated rapid ascent of basaltic (OIB) magmas without much residence time in the crust and hence the eruption of relatively uncontaminated, asthenosphere-derived magmas at the surface (i.e. Kula lavas in SW Anatolia). Subduction of the Tethyan mantle lithosphere northward beneath Eurasia was nearly continuous since the latest Cretaceous, only temporarily punctuated by the collisional accretion of several ribbon continents (i.e. Pelagonia, Sakarya, Tauride-South Armenian) to the southern margin of Eurasia, and by related slab breakoff events. Exhumation of middle to lower crustal rocks and the formation of extensional metamorphic domes occurred in the backarc region of this progressively southward-migrated trench and the Tethyan (Afro-Arabian) slab throughout the Cenozoic. Thus, slab retreat played a major role in the Cenozoic geodynamic evolution of the Aegean and Western Anatolian regions. However, the subducting African lithospheric slab beneath the Aegean-Western Anatolian region is delimited to the east by a subduction-transform edge propagator (STEP) fault, which corresponds to the sharp cusp between the Hellenic and Cyprus trenches whose surface expression is marked by the Isparta Angle in the Western Taurides. This lithospheric tear in the downgoing African plate allowed the mantle to rise beneath SW Anatolia, inducing decompressional melting of shallow asthenosphere and producing linearly distributed alkaline magmatism younging in the direction of tear propagation (southward). The N-S-trending potassic and ultra-potassic volcanic fields stretching from the Kirka and Afyon-Suhut region (~17 Ma) in the north to the Isparta-Gölcük area (4.6 Ma-Recent) in the south are the result of this melting of the sub-slab (asthenospheric) mantle, which was metasomatized by recent subduction events in the region. Asthenospheric low velocities detected through Pn tomographic imaging in this region support the existence of shallow asthenosphere beneath the Isparta Angle at present. These observations suggest that currently there is no active subduction underneath much of Western Anatolia.

Extensive decarbonation of continuously hydrated subducting slabs

NASA Astrophysics Data System (ADS)

Arzilli, Fabio; Burton, Mike; La Spina, Giuseppe; Macpherson, Colin G.

2017-04-01

CO2 release from subducting slabs is a key element of Earth's carbon cycle, consigning slab carbon either to mantle burial or recycling to the surface through arc volcanism, however, what controls subducted carbon's fate is poorly understood. Fluids mobilized by devolatilization of subducting slabs play a fundamental role in the melting of mantle wedges and in global geochemical cycles [1]. The effect of such fluids on decarbonation in subducting lithologies has been investigated recently [2-5], but several thermodynamic models [2-3], and experimental studies [6] suggest that carbon-bearing phases are stable at sub-arc depths (80-140 km; 2.6-4.5 GPa), implying that this carbon can be carried to mantle depths of >140 km. This is inconsistent with observations of voluminous CO2 release from arc volcanoes [7-10], located above slabs that are at 2.6-4.5 GPa pressure. The aim of this study is to re-evaluate the role of metamorphic decarbonation, showing if decarbonation reactions could be feasible at sub-arc depths combined with a continuous hydration scenario. We used the PerpleX software combined with a custom-designed algorithm to simulate a pervasive fluid infiltration characterized by "continuous hydration" combined with a distillation model, in which is possible to remove CO2 when decarbonation occurs, to obtain an open-system scenario. This is performed by repeatedly flushing the sediment with pure H2O at 0.5, 1.0 or 5 wt.% until no further decarbonation occurs. Here we show that continuous hydrated of sediment veneers on subducting slabs by H2O released from oceanic crust and serpentinised mantle lithosphere [11-13], produces extensive slab decarbonation over a narrow, sub-arc pressure range, even for low temperature subduction pathways. This explains the location of CO2-rich volcanism, quantitatively links the sedimentary composition of slab material to the degree of decarbonation and greatly increases estimates for the magnitude of carbon flux through the arc in subduction zones. [1] Hilton, D.R. et al. (2002) Rev. Mineral. Geochem. 47, 319-370. [2] Gorman, P.J. et al. (2006) Geochem. Geophys. Geosyst. 7. [3] Kerrick, D.M. and Connolly, J.A.D. (2001) Nature 411, 293-296. [4] Cook-Kollars, J. et al. (2014) Chem. Geol. 386, 31-48. [5] Collins, N.C. et al. (2015) Chem. Geol. 412, 132-150. [6] Poli, S. et al. (2009) Earth Planet. Sci. Lett. 278, 350-360. [7] Sano, Y. and Williams, S.N. (1996) Geophys. Res. Lett. 23, 2749-2752. [8] Marty, B. and Tolstikhin, I.N. (1998) Chem. Geol. 145, 233-248. [9] Wallace, P.J. (2005) J. Volcanol. Geoth. Res. 140, 217-240. [10] Burton, M.R. et al. (2013) Rev. Mineral. Geochem. 75, 323-354. [11] Ulmer, P. and Trommsdorff, V. (1995) Science 268, 858-861. [12] Schmidt, M.W. and Poli, S. (1998) Earth Planet. Sci. Lett. 163, 361-379. [13] van Keken, P. E. et al. (2011) J. Geophys. Res. 116.

Photonic crystals for improving light absorption in organic solar cells

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

Duché, D., E-mail: david.duche@im2np.fr; Le Rouzo, J.; Masclaux, C.

2015-02-07

We theoretically and experimentally study the structuration of organic solar cells in the shape of photonic crystal slabs. By taking advantage of the optical properties of photonic crystals slabs, we show the possibility to couple Bloch modes with very low group velocities in the active layer of the cells. These Bloch modes, also called slow Bloch modes (SBMs), allow increasing the lifetime of photons within the active layer. Finally, we present experimental demonstration performed by using nanoimprint to directly pattern the standard poly-3-hexylthiophène:[6,6]-phenyl-C61-butiryc acid methyl ester organic semiconductor blend in thin film form in the shape of a photonic crystalmore » able to couple SBMs. In agreement with the model, optical characterizations will demonstrate significant photonic absorption gains.« 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.

Assessment of doses caused by electrons in thin layers of tissue-equivalent materials, using MCNP.

PubMed

Heide, Bernd

2013-10-01

Absorbed doses caused by electron irradiation were calculated with Monte Carlo N-Particle transport code (MCNP) for thin layers of tissue-equivalent materials. The layers were so thin that the calculation of energy deposition was on the border of the scope of MCNP. Therefore, in this article application of three different methods of calculation of energy deposition is discussed. This was done by means of two scenarios: in the first one, electrons were emitted from the centre of a sphere of water and also recorded in that sphere; and in the second, an irradiation with the PTB Secondary Standard BSS2 was modelled, where electrons were emitted from an (90)Sr/(90)Y area source and recorded inside a cuboid phantom made of tissue-equivalent material. The speed and accuracy of the different methods were of interest. While a significant difference in accuracy was visible for one method in the first scenario, the difference in accuracy of the three methods was insignificant for the second one. Considerable differences in speed were found for both scenarios. In order to demonstrate the need for calculating the dose in thin small zones, a third scenario was constructed and simulated as well. The third scenario was nearly equal to the second one, but a pike of lead was assumed to be inside the phantom in addition. A dose enhancement (caused by the pike of lead) of ∼113 % was recorded for a thin hollow cylinder at a depth of 0.007 cm, which the basal-skin layer is referred to in particular. Dose enhancements between 68 and 88 % were found for a slab with a radius of 0.09 cm for all depths. All dose enhancements were hardly noticeable for a slab with a cross-sectional area of 1 cm(2), which is usually applied to operational radiation protection.

X-radiography of trace fossils in limestones and dolostones from the Jurassic Smackover Formation, south Alabama

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

Esposito, R.A.; Castleman, S.P.; King, D.T. Jr.

X-radiography has been useful in studying biogenic sedimentary structures in unconsolidated sediments but the technique has not been applied often to the study of hard carbonate rock. The authors have applied x-radiography to the study of the lower part of the Smackover to enhance the complete petrologic description of the rock. The lower Smackover has many dense micrite intervals and intervals of monotonous, thin graded beds. Parts of the lower Smackover is also dolomitized. None of the above rocks contains significant amount of skeletal debris and trace fossils are not generally obvious in an etched slab of core. In limestone,more » they have detected well-preserved trace fossils by x-radiography, however. The dolostones show no traces using our method. In limestones, the traces are marked by minute amounts of finely divided iron sulfides. This causes a slight density difference resulting in greater x-ray absorption. They recognize two main trace-fossil types: a Thalassinoides best seen in slabs cut parallel to bedding and a Zoophycos best seen in slabs cut perpendicular to bedding. The technique requires a slab cut 8 mm thick with parallel flat surfaces and a medical x-ray unit using accelerating voltages of 66 kV and 10 mas. Traces are most successfully imaged on industrial-quality films.« less

Strategies to reduce mass and photons transfer limitations in heterogeneous photocatalytic processes: Hexavalent chromium reduction studies.

PubMed

Marinho, Belisa A; Cristóvão, Raquel O; Djellabi, Ridha; Caseiro, Ana; Miranda, Sandra M; Loureiro, José M; Boaventura, Rui A R; Dias, Madalena M; Lopes, José Carlos B; Vilar, Vítor J P

2018-07-01

The current work presents different approaches to overcome mass and photon transfer limitations in heterogeneous photocatalytic processes applied to the reduction of hexavalent chromium to its trivalent form in the presence of a sacrificial agent. Two reactor designs were tested, a monolithic tubular photoreactor (MTP) and a micro-meso-structured photoreactor (NETmix), both presenting a high catalyst surface area per reaction liquid volume. In order to reduce photon transfer limitations, the tubular photoreactor was packed with transparent cellulose acetate monolithic structures (CAM) coated with the catalyst by a dip-coating method. For the NETmix reactor, a thin film of photocatalyst was uniformly deposited on the front glass slab (GS) or on the network of channels and chambers imprinted in the back stainless steel slab (SSS) using a spray system. The reaction rate for the NETmix photoreactor was evaluated for two illumination sources, solar light or UVA-LEDs, using the NETmix with the front glass slab or/and back stainless steel slab coated with TiO 2 -P25. The reusability of the photocatalytic films on the NETmix walls was also evaluated for three consecutive cycles using fresh Cr(VI) solutions. The catalyst reactivity in combination with the NETmix-SSS photoreactor is almost 70 times superior to one obtained with the MTP. Copyright © 2018 Elsevier Ltd. All rights reserved.

Seismic constraints of thinning and fragmenting continental lithosphere beneath the Korean Peninsula

NASA Astrophysics Data System (ADS)

Kim, S.; Tauzin, B.; Tkalcic, H.; Rhie, J.

2017-12-01

Modification of the continental lithosphere is still an enigmatic process. The Korean Peninsula (KP) is one of ideal place to depict the process by interactions with subducting oceanic slabs. We detect a significant thickness change (>50 km) of the continental lithosphere beneath the KP that is confirmed by two independent approaches: (1) 3D imaging using ambient noise analysis and (2) receiver function CCP stacking. A series of transdimensional and hierarchical Bayesian joint inversions is performed to obtain a high-resolution 3D model from different types of surface wave dispersion data. For the stacking of receiver function waveforms, the coda waveforms of crustal multi-modes (PpPs and PpSs) are combined together to better image the lithosphere-asthenosphere boundary. We estimate the relatively deeper rooted lithosphere (>100 km) in the southwestern part of the KP compared to shallower surrounding regions. The lithospheric structure is underlain by lower velocity anomalies (Vs<4.1 km/s), which extends from back-arc regions near subducting slabs horizontally and connects to low velocity anomalies in the deeper upper mantle vertically. The imaged features clearly show that the effect of the oceanic slab subduction is a key factor controlling the modification process. We further examine the implication for the occurrence of intraplate volcanoes and the relationship to the mantle transition zone heterogeneities due to stagnant slabs in the northeast Asia.

3-D Shear Velocity Structure of Costa Rica and Nicaragua from Teleseismic and Ambient Noise Rayleigh Wave Tomography

NASA Astrophysics Data System (ADS)

Harmon, N.; Salas, M.; Rychert, C. A.; Fischer, K. M.; Abers, G. A.

2012-12-01

The Costa Rica-Nicaragua subduction zone shows systematic along strike variation in arc chemistry, geology and seismic velocity and attenuation, presenting global extremes within a few hundred kilometres. In this study we use teleseismic and ambient noise derived surface wave tomography to produce a 3-D shear velocity model of the region. We use the 48 stations of the TUCAN array, and up to 96 events for the teleseismic Rayleigh wave inversion, and 20 months of continuous data for cross correlation to estimate Green's functions from ambient noise. In the shallow crust (0-15 km) we observe low shear velocities directly beneath the arc volcanos (< 3 km/s) with higher velocities in the back arc of Nicaragua. The anomalies are likely caused by heated crust, possibly intruded by magma. We observe > 40 km thick crust beneath the Costa Rican arc and the Nicaraguan Highlands, with thinned crust (~20 km) beneath the Nicaraguan Depression, with increasing crustal thickness in the back arc region. At mantle depths (55-120 km depth) we observe lower shear velocities (~2%) beneath the Nicaraguan arc and back arc relative to Costa Rica. This is well-correlated with a Vp/Vs anomaly beneath Nicaragua. The lower shear velocity beneath Nicaragua may indicate higher melt content in the mantle perhaps due to higher volatile flux from the slab. Finally, we observe a linear high velocity region at depths > 120 km parallel to the trench, which is consistent with the subducting slab.

3-D S-velocity structure in the lowermost mantle beneath the Northern Pacific

NASA Astrophysics Data System (ADS)

Suzuki, Y.; Kawai, K.; Geller, R. J.; Borgeaud, A. F. E.; Konishi, K.

2017-12-01

We previously (Suzuki et al., EPS, 2016) reported the results of waveform inversion to infer the three-dimensional (3-D) S-velocity structure in the lowermost 400 km of the mantle (the Dʺ region) beneath the Northern Pacific region. Our dataset consists of about 20,000 transverse component broadband body-wave seismograms observed at North American stations (mainly USArray) for 131 intermediate and deep earthquakes which occurred beneath the western Pacific subduction region. Synthetic resolution tests indicate that our methods and dataset can resolve the velocity structure in the target region with a horizontal scale of about 150 km and a vertical scale of about 50 km. The 3-D S-velocity model obtained in that study shows three prominent features: (i) horizontal high-velocity anomalies up to about 3 per cent faster than the Preliminary Reference Earth Model (PREM) with a thickness of a few hundred km and a lower boundary which is at most about 150 km above the core-mantle boundary (CMB), (ii) low-velocity anomalies about 2.5 per cent slower than PREM beneath the high-velocity anomalies at the base of the lower mantle, (iii) a thin (about 150 km) low-velocity structure continuous from the base of the low-velocity zone to at least 400 km above the CMB. We interpret these features respectively as: (i) remnants of slab material where the Mg-perovskite to Mg-post-perovskite phase transition could have occurred within the slab, (ii, iii) large amounts of hot and less dense materials beneath the cold Kula or Pacific slab remnants immediately above the CMB which ascend and form a passive plume upwelling at the edge of the slab remnants. Since our initial work we subsequently conducted waveform inversion using both the transverse- and radial-component horizontal waveform data to infer the isotropic shear velocity structure in the lowermost mantle beneath the Northern Pacific in more detail. We also compute partial derivatives with respect to the 5 independent elastic constants (A, C, F, L, N) of a transversely isotropy (TI) medium, and conduct a synthetic resolution test to examine the ability of our methods and dataset to resolve the anisotropic structure in this region using two-component waveform data.

Twin-belt continuous caster with containment and cooling of the exiting cast product for enabling high-speed casting of molten-center product

DOEpatents

Dykes, Charles D.; Daniel, Sabah S.; Wood, J. F. Barry

1990-02-20

In continuously casting molten metal into cast product by a twin-belt machine, it is desirable to achieve dramatic increases in speed (linear feet per minute) at which cast product exits the machine, particularly in installations where steel cast product is intended to feed a downstream regular rolling mill (as distinct from a planetary mill) operating in tandem with the twin-belt caster. Such high-speed casting produces product with a relatively thin shell and molten interior, and the shell tends to bulge outwardly due to metallostatic head pressure of the molten center. A number of cooperative features enable high-speed, twin-belt casting: (1) Each casting belt is slidably supported adjacent to the caster exit pulley for bulge control and enhanced cooling of cast product. (2) Lateral skew steering of each belt provides an effective increase in moving mold length plus a continuity of heat transfer not obtained with prior art belt steering apparatus. (3) The exiting slab is contained and supported downstream from the casting machine to prevent bulging of the shell of the cast product, and (4) spray cooling is incorporated in the exit containment apparatus for secondary cooling of cast product.

First-principles study on the bulk and (1 1 1) surface half-metallicity of KS and RbS in CsCl structure

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

Li, Lei; Lei, Gang; Gao, Qiang

2015-08-15

Graphical abstract: Spin-polarized total and atomic DOS at S-(1 1 1) terminated slab and bulk in CsCl-type RbS. - Highlights: • The half metallic properties of CsCl-type RbS and KS have been studied. • The RbS's and KS's (1 1 1) slabs have been investigated. • Surface energy of RbS's and KS's (1 1 1) slabs are calculated. - Abstract: The electronic and magnetic properties of RbS and KS in CsCl structure have been investigated by using the full-potential local-orbital minimum-basis method. Calculating the relation between the total energies and lattice parameters for RbS and KS, we find out thatmore » the equilibrium lattice parameters are 4.02 Å and 3.84 Å for RbS and KS, respectively. According to our calculations in generalized gradient approximation approximation, both RbS and KS are half-metallic ferromagnets with the magnetic moments of 1 μ{sub B} per formula unit, and band gap of 4.287 eV for RbS and 4.395 eV for KS. We also have studied the electronic and magnetic properties of (1 1 1) surfaces of RbS and KS, and have found out that the half-metallicity of their bulk is preserved in all of those surfaces. Finally, through the calculations of formation energy of RbS and KS, it is found that their thin films are stable in the equilibrium conditions, and the Rb-terminated (1 1 1) slab of RbS and the K-terminated (1 1 1) slab of KS are more stable than their S-terminated (1 1 1) slabs. All of the above properties lead the compounds of RbS and KS in CsCl structure to be promising candidates for spintronic applications.« less

Thermal State, Slab Metamorphism, and Interface Seismicity in the Cascadia Subduction Zone Based On 3-D Modeling

NASA Astrophysics Data System (ADS)

Ji, Yingfeng; Yoshioka, Shoichi; Banay, Yuval A.

2017-09-01

Giant earthquakes have repeatedly ruptured the Cascadia subduction zone, and similar earthquakes will likely also occur there in the near future. We employ a 3-D time-dependent thermomechanical model that incorporates an up-to-date description of the slab geometry to study the Cascadia subduction thrust. Results show a distinct band of 3-D slab dehydration that extends from Vancouver Island to the Seattle Basin and farther southward to the Klamath Mountains in northern California, where episodic tremors cluster. This distribution appears to include a region of increased dehydration in northern Cascadia. The phenomenon of heterogeneous megathrust seismicity associated with oblique subduction suggests that the presence of fluid-rich interfaces generated by slab dehydration favors megathrust seismogenesis in the northern part of this zone. The thin, relatively weakly metamorphosed Explorer, Juan de Fuca, and Gorda Plates are associated with an anomalous lack of thrust earthquakes, and metamorphism that occurs at temperatures of 500-700°C near the Moho discontinuity may represent a key factor in explaining the presence of the associated episodic tremor and slip (ETS), which requires a young oceanic plate to subduct at a small dip angle, as is the case in Cascadia and southwestern Japan. The 3-D intraslab dehydration distribution suggests that the metamorphosed plate environment is more complex than had previously been believed, despite the existence of channeling vein networks. Slab amphibolization and eclogitization near the continental Moho depth is thus inferred to account for the resultant overpressurization at the interface, facilitating the generation of ETS and the occurrence of small to medium thrust earthquakes beneath Cascadia.

A geochemical and geochronological section through the Eastern Aegean

NASA Astrophysics Data System (ADS)

Boehm, Katharina; Kuiper, Klaudia; Vroon, Pieter; Wijbrans, Jan

2017-04-01

The convergence of Africa and Eurasia and the subduction of a oceanic lithosphere of narrow basins between Gondwana terranes has controlled the geological evolution of the Eastern Mediterranean region since the Cretaceous. This resulted in back-arc extension and lithospheric thinning caused by slab roll-back together with the westward extrusion of Anatolia, in the southwards retreat and stepwise development of the subduction system and also in a low velocity seismic anomaly gap between the Cyprus and Hellenic slab and other slab segments. However, the exact timing of all these events in the Eastern Mediterranean region is still a matter of debate, and the purpose of this study is therefore to disentangle when terrains collided and slab detached in the last 30Ma. In a N-S transect magmatic rocks of the Aegean plate are studied, including volcanics from the islands Nisyros, Kos, Patmos, Chios, Lesbos and Samothraki. Major- and trace elements as well as Sr-Nd-Hf-Pb-O isotopes are used to interpret the different features of the Aegean subduction zone. With this geochemical approach the extend of upwelling hot asthenospheric material from the slab tear can be traced in the recent to Eocene volcanic rocks. The volcanic rocks give a wide scatter in classification diagrams and pose for example the question how the sodium rich volcanic products of Patmos can be explained. On the other hand Chios seems to play a key role around 15 Ma years in a phase of relatively low volcanic activity. To get a reliable timeline of the subduction in the Aegean since the Eocene we are aiming to tie our chemical and isotopic data to parallel obtained geochronological ages. New 40Ar/39Ar data will allow us to get the needed resolution for this time span and material.

Bound exciton and free exciton states in GaSe thin slab.

PubMed

Wei, Chengrong; Chen, Xi; Li, Dian; Su, Huimin; He, Hongtao; Dai, Jun-Feng

2016-09-22

The photoluminescence (PL) and absorption experiments have been performed in GaSe slab with incident light polarized perpendicular to c-axis of sample at 10 K. An obvious energy difference of about 34 meV between exciton absorption peak and PL peak (the highest energy peak) is observed. By studying the temperature dependence of PL and absorption spectra, we attribute it to energy difference between free exciton and bound exciton states, where main exciton absorption peak comes from free exciton absorption, and PL peak is attributed to recombination of bound exciton at 10 K. This strong bound exciton effect is stable up to 50 K. Moreover, the temperature dependence of integrated PL intensity and PL lifetime reveals that a non-radiative process, with activation energy extracted as 0.5 meV, dominates PL emission.

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.

Extensive decarbonation of continuously hydrated subducting slabs

NASA Astrophysics Data System (ADS)

Arzilli, F.; Burton, M. R.; La Spina, G.; Macpherson, C.

2016-12-01

CO2 release from subducting slabs is a key element of Earth's carbon cycle, consigning slab carbon either to mantle burial or recycling to the surface through arc volcanism, however, what controls subducted carbon's fate is poorly understood. Fluids mobilized by devolatilization of subducting slabs play a fundamental role in the melting of mantle wedges and in global geochemical cycles [1]. The effect of such fluids on decarbonation in subducting lithologies has been investigated recently [2-5] but mechanisms of carbon transfer from the slab to wedge are poorly understood [2-6]. Several thermodynamic models [2-3], and experimental studies [6] suggest that carbon-bearing phases are stable at sub-arc depths (80-140 km; 2.6-4.5 GPa), implying that this carbon can be subducted to mantle depths of >140 km. This is inconsistent with observations of voluminous CO2 release from arc volcanoes [7-10], located above slabs that are at 2.6-4.5 GPa pressure. Here, we show that continuous hydrated of sediment veneers on subducting slabs by H2O released from oceanic crust and serpentinised mantle lithosphere [11-13], produces extensive slab decarbonation over a narrow, sub-arc pressure range, even for low temperature subduction pathways. This explains the location of CO2-rich volcanism, quantitatively links the sedimentary composition of slab material to the degree of decarbonation and greatly increases estimates for the magnitude of carbon flux through the arc in subduction zones. [1] Hilton, D.R. et al. (2002) Rev. Mineral. Geochem. 47, 319-370. [2] Gorman, P.J. et al. (2006) Geochem. Geophys. Geosyst. 7. [3] Kerrick, D.M. and Connolly, J.A.D. (2001) Nature 411, 293-296. [4] Cook-Kollars, J. et al. (2014) Chem. Geol. 386, 31-48. [5] Collins, N.C. et al. (2015) Chem. Geol. 412, 132-150. [6] Poli, S. et al. (2009) Earth Planet. Sci. Lett. 278, 350-360. [7] Sano, Y. and Williams, S.N. (1996) Geophys. Res. Lett. 23, 2749-2752. [8] Marty, B. and Tolstikhin, I.N. (1998) Chem. Geol. 145, 233-248. [9] Wallace, P.J. (2005) J. Volcanol. Geoth. Res. 140, 217-240. [10] Burton, M.R. et al. (2013) Rev. Mineral. Geochem. 75, 323-354. [11] Ulmer, P. and Trommsdorff, V. (1995) Science 268, 858-861. [12] Schmidt, M.W. and Poli, S. (1998) Earth Planet. Sci. Lett. 163, 361-379. [13] van Keken, P. E. et al. (2011) J. Geophys. Res. 116.

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.

Mid-Infrared Spectroscopy Platform Based on GaAs/AlGaAs Thin-Film Waveguides and Quantum Cascade Lasers.

PubMed

Sieger, Markus; Haas, Julian; Jetter, Michael; Michler, Peter; Godejohann, Matthias; Mizaikoff, Boris

2016-03-01

The performance and versatility of GaAs/AlGaAs thin-film waveguide technology in combination with quantum cascade lasers for mid-infrared spectroscopy in comparison to conventional FTIR spectroscopy is presented. Infrared radiation is provided by a quantum cascade laser (QCL) spectrometer comprising four tunable QCLs providing a wavelength range of 5-11 μm (1925-885 cm(-1)) within a single collimated beam. Epitaxially grown GaAs slab waveguides serve as optical transducer for tailored evanescent field absorption analysis. A modular waveguide mounting accessory specifically designed for on-chip thin-film GaAs waveguides is presented serving as a flexible analytical platform in lieu of conventional attenuated total reflection (ATR) crystals uniquely facilitating macroscopic handling and alignment of such microscopic waveguide structures in real-world application scenarios.

Synthesis, Characterization and Cold Workability of Cast Copper-Magnesium-Tin Alloys

NASA Astrophysics Data System (ADS)

Bravo Bénard, Agustín Eduardo; Martínez Hernández, David; González Reyes, José Gonzalo; Ortiz Prado, Armando; Schouwenaars Franssens, Rafael

2014-02-01

The use of Mg as an alloying element in copper alloys has largely been overlooked in scientific literature and technological applications. Its supposed tribological compatibility with iron makes it an interesting option to replace Pb in tribological alloys. This work describes the casting process of high-quality thin slabs of Cu-Mg-Sn alloys with different compositions by means of conventional methods. The resulting phases were analyzed using X-ray diffraction, scanning electron microscopy, optical microscopy, and energy dispersive X-ray spectroscopy techniques. Typical dendritic α-Cu, eutectic Cu2Mg(Sn) and eutectoid non-equilibrium microstructures were found. Tensile tests and Vickers microhardness show the excellent hardening capability of Mg as compared to other copper alloys in the as-cast condition. For some of the slabs and compositions, cold rolling reductions of over 95 pct have been easily achieved. Other compositions and slabs have failed during the deformation process. Failure analysis after cold rolling reveals that one cause for brittleness is the presence of casting defects such as microshrinkage and inclusions, which can be eliminated. However, for high Mg contents, a high volume fraction of the intermetallic phase provides a contiguous path for crack propagation through the connected interdendritic regions.

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

Detection and reconstruction of solidification cracks - Laser ultrasonic measurements during the continuous casting process of aluminum

NASA Astrophysics Data System (ADS)

Mitter, Thomas; Grün, Hubert; Roither, Jürgen; Betz, Andreas; Bozorgi, Salar; Reitinger, Bernhard; Burgholzer, Peter

2014-05-01

In the continuous casting process the avoidance and rapid detection of occurring solidification cracks in the slab is a crucial issue, in particular for the maintenance of a high quality level in further production processes. Due to the elevated temperatures of the slab surface a remote sensing non-destructive tool for quality inspection is required, which is also applicable for the harsh industrial environment. In this work the application of laser ultrasound (LUS) technique during the continuous casting process in industrial environment is shown. The proof of principle of the detection of the centered solidification cracks is shown by pulse-echo measurements with laser ultrasonic equipment for inline quality inspection. Preliminary examinations in the lab of different casted samples have shown the distinguishability of slabs with and without any solidification cracks. Furthermore the damping of the bulk wave has been used for the prediction of the dimension of the crack. With an adapted "synthetic aperture focusing technique" (SAFT) algorithm the image reconstruction of multiple measurements at different positions around the circumference has provided enough information for the estimation of the localization and extension of the centered solidification cracks. Subsequent first measurements using this laser ultrasonic setup during the continuous casting of aluminum were carried out and showed the proof of principle in an industrial environment with elevated temperatures, dust, cooling water and vibrations.

Field verification for the effectiveness of continuity diaphragms for skewed continuous P/C P/S concrete girder bridges : tech summary.

DOT National Transportation Integrated Search

2009-10-01

The majority of highway bridges are built as cast-in-place reinforced concrete slabs and prestressed concrete : girders. The simple-span precast, prestressed concrete girders made continuous through cast-in-place decks : and diaphragms have been wide...

Seismic evidence of the lithosphere-asthenosphere boundary beneath Izu-Bonin area

NASA Astrophysics Data System (ADS)

Cui, H.; Gao, Y.; Zhou, Y.

2016-12-01

The lithosphere-asthenosphere boundary (LAB), separating the rigid lithosphere and the ductile asthenosphere layers, is the seismic discontinuity with the negative velocity contrast of the Earth's interior [Fischer et al., 2010]. The LAB has been also termed the Gutenberg (G) discontinuity that defines the top of the low velocity zone in the upper mantle [Gutenberg, 1959; Revenaugh and Jordan, 1991]. The seismic velocity, viscosity, resistivity and other physical parameters change rapidly with the depths across the boundary [Eaton et al., 2009]. Seismic detections on the LAB in subduction zone regions are of great help to understand the interactions between the lithosphere and asthenosphere layers and the geodynamic processes related with the slab subductions. In this study, the vertical broadband waveforms are collected from three deep earthquake events occurring from 2000 to 2014 with the focal depths of 400 600 km beneath the Izu-Bonin area. The waveform data is processed with the linear slant stack method [Zang and Zhou, 2002] to obtain the vespagrams in the relative travel-time to slowness domain and the stacked waveforms. The sP precursors reflected on the LAB (sLABP), which have the negative polarities with the amplitude ratios of 0.17 0.21 relative to the sP phases, are successfully extracted. Based on the one-dimensional modified velocity model (IASP91-IB), we obtain the distributions for six reflected points of the sLABP phases near the source region. Our results reveal that the LAB depths range between 58 and 65 km beneath the Izu-Bonin Arc, with the average depth of 62 km and the small topography of 7 km. Compared with the results of the tectonic stable areas in Philippine Sea [Kawakatsu et al., 2009; Kumar and Kawakatsu, 2011], the oceanic lithosphere beneath the Izu-Bonin Arc shows the obvious thinning phenomena. We infer that the lithospheric thinning is closely related with the partial melting, which is caused by the volatiles continuously released from the subducted western Pacific slab in deep Earth, and the strong erosions of the small-scale mantle convection in the back-arc mantle wedge.

Response of a grounded dielectric slab to an impulse line source using leaky modes

NASA Technical Reports Server (NTRS)

Duffy, Dean G.

1994-01-01

This paper describes how expansions in leaky (or improper) modes may be used to represent the continuous spectrum in an open radiating waveguide. The technique requires a thorough knowledge of the life history of the improper modes as they migrate from improper to proper Riemann surfaces. The method is illustrated by finding the electric field resulting from an impulsively forced current located in the free space above a grounded dielectric slab.

Extending Alaska's plate boundary: tectonic tremor generated by Yakutat subduction

USGS Publications Warehouse

Wech, Aaron G.

2016-01-01

The tectonics of the eastern end of the Alaska-Aleutian subduction zone are complicated by the inclusion of the Yakutat microplate, which is colliding into and subducting beneath continental North America at near-Pacific-plate rates. The interaction among these plates at depth is not well understood, and further east, even less is known about the plate boundary or the source of Wrangell volcanism. The drop-off in Wadati-Benioff zone (WBZ) seismicity could signal the end of the plate boundary, the start of aseismic subduction, or a tear in the downgoing plate. Further compounding the issue is the possible presence of the Wrangell slab, which is faintly outlined by an anemic, eastward-dipping WBZ beneath the Wrangell volcanoes. In this study, I performed a search for tectonic tremor to map slow, plate-boundary slip in south-central Alaska. I identified ∼11,000 tremor epicenters, which continue 85 km east of the inferred Pacific plate edge marked by WBZ seismicity. The tremor zone coincides with the edges of the downgoing Yakutat terrane, and tremors transition from periodic to continuous behavior as they near the aseismic Wrangell slab. I interpret tremor to mark slow, semicontinuous slip occurring at the interface between the Yakutat and North America plates. The slow slip region lengthens the megathrust interface beyond the WBZ and may provide evidence for a connection between the Yakutat slab and the aseismic Wrangell slab.

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.

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).

Slab narrowing in the Central Mediterranean: the Calabro-Ionian subduction zone as imaged by high resolution seismic tomography.

PubMed

Scarfì, L; Barberi, G; Barreca, G; Cannavò, F; Koulakov, I; Patanè, D

2018-03-26

A detailed 3D image of the Calabro-Ionian subduction system in the central Mediterranean was obtained by means of a seismic tomography, exploiting a large dataset of local earthquakes and computing algorithms able to build a dense grid of measure nodes. Results show that the slab is continuous below the southern sector of the Calabro-Peloritan Arc, but the deformation processes developing at its edges are leading to its progressive narrowing, influencing tectonics and magmatism at the surface, and with possible stress concentration in the tip zones. In the southwest, the deformation occurring at a free slab edge lead to propagation of a vertical lithospheric tear in the overriding plate, which extends along a NW-SE fault system (Aeolian-Tindari-Letojanni) up to about 30 km into the Ionian Sea; further southeast, the lithosphere appears only flexed and not broken yet. In the northeast, the slab seems to break progressively, parallel to the trench. Finally, northwest of Mt. Etna, the tomography highlights low V P that can be related to an upwelling of deep mantle material likely flowing laterally through a window opened by the complete slab detachment.

On the forces that drive and resist deformation of the south-central Mediterranean: a mechanical model study

NASA Astrophysics Data System (ADS)

Nijholt, Nicolai; Govers, Rob; Wortel, Rinus

2018-04-01

The geodynamics of the Mediterranean comprises a transitional setting in which slab rollback and plate convergence compete to shape the region. In the central Mediterranean, where the balance of driving and resisting forces changes continuously and rapidly since the Miocene, both kinematic and seismo-tectonic observations display a strong variation in deformation style and, therefore possibly, lithospheric forces. We aim to understand the current kinematics in southern Italy and Sicily in terms of lithospheric forces that cause them. The strong regional variation of geodetic velocities appears to prohibit such simple explanation. We use mechanical models to quantify the deformation resulting from large-scale Africa-Eurasia convergence, ESE retreat of the Calabrian subduction zone, pull by the Aegean slab, and regional variations in gravitational potential energy (topography). A key model element is the resistance to slip on major regional fault zones. We show that geodetic velocities, seismicity and sense of slip on regional faults can be understood to result from lithospheric forces. Our most important new finding is that regional variations in resistive tractions are required to fit the observations, with notably very low tractions on the Calabrian subduction contact, and a buildup towards a significant earthquake in the Calabrian fore-arc. We also find that the Calabrian net slab pull force is strongly reduced (compared to the value possible in view of the slab's dimensions) and that trench suction tractions are negligible. Such very small contributions to the present-day force balance in the south-central Mediterranean suggest that the Calabrian arc is now further transitioning towards a setting dominated by Africa-Eurasia plate convergence, whereas during the past 30 Myrs slab retreat continually was the dominant factor.

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.

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

Numerical modeling of the thin shallow solar dynamo

NASA Astrophysics Data System (ADS)

O'Bryan, J. B.; Jarboe, T. R.

2017-10-01

Nonlinear, numerical computation with the NIMROD code is used to explore and validate the thin shallow solar dynamo model [T.R. Jarboe et al. 2017], which explains the observed global temporal evolution (e.g. magnetic field reversal) and local surface structures (e.g. sunspots) of the sun. The key feature of this model is the presence and magnetic self-organization of global magnetic structures (GMS) lying just below the surface of the sun, which resemble 1D radial Taylor states of size comparable to the supergranule convection cells. First, we seek to validate the thin shallow solar dynamo model by reproducing the 11 year timescale for reversal of the solar magnetic field. Then, we seek to model formation of GMS from convection zone turbulence. Our computations simulate a slab covering a radial depth 3Mm and include differential rotation and gravity. Density, temperature, and resistivity profiles are taken from the Christensen-Dalsgaard model.

The effect of dynamic topography and gravity on lithospheric effective elastic thickness estimation: a case study

NASA Astrophysics Data System (ADS)

Bai, Yongliang; Dong, Dongdong; Kirby, Jon F.; Williams, Simon E.; Wang, Zhenjie

2018-04-01

Lithospheric effective elastic thickness (Te), a proxy for plate strength, is helpful for the understanding of subduction characteristics. Affected by curvature, faulting and magma activity, lithospheric strength near trenches should be weakened but some regional inversion studies have shown much higher Te values along some trenches than in their surroundings. In order to improve Te estimation accuracy, here we discuss the long-wavelength effect of dynamic topography and gravity on Te estimation by taking the Izu-Bonin-Mariana (IBM) Trench as a case study area. We estimate the long-wavelength influence of the density and negative buoyancy of the subducting slab on observed gravity anomalies and seafloor topography. The residual topography and gravity are used to map Te using the fan-wavelet coherence method. Maps of Te, both with and without the effects of dynamic topography and slab gravity anomaly, contain a band of high-Te values along the IBM Trench, though these values and their errors are lower when slab effects are accounted for. Nevertheless, tests show that the Te map is relatively insensitive to the choice of slab-density modelling method, even though the dynamic topography and slab-induced gravity anomaly vary considerably when the slab density is modelled by different methods. The continued presence of a high-Te band along the trench after application of dynamic corrections shows that, before using 2D inversion methods to estimate Te variations in subduction zones, there are other factors that should be considered besides the slab dynamic effects on the overriding plate.

The effect of dynamic topography and gravity on lithospheric effective elastic thickness estimation: a case study

NASA Astrophysics Data System (ADS)

Bai, Yongliang; Dong, Dongdong; Kirby, Jon F.; Williams, Simon E.; Wang, Zhenjie

2018-07-01

Lithospheric effective elastic thickness (Te), a proxy for plIate strength, is helpful for the understanding of subduction characteristics. Affected by curvature, faulting and magma activity, lithospheric strength near trenches should be weakened but some regional inversion studies have shown much higher Te values along some trenches than in their surroundings. In order to improve Te-estimation accuracy, here we discuss the long-wavelength effect of dynamic topography and gravity on Te estimation by taking the Izu-Bonin-Mariana (IBM) Trench as a case study area. We estimate the long-wavelength influence of the density and negative buoyancy of the subducting slab on observed gravity anomalies and seafloor topography. The residual topography and gravity are used to map Te using the fan-wavelet coherence method. Maps of Te, both with and without the effects of dynamic topography and slab gravity anomaly, contain a band of high-Te values along the IBM Trench, though these values and their errors are lower when slab effects are accounted for. Nevertheless, tests show that the Te map is relatively insensitive to the choice of slab-density modelling method, even though the dynamic topography and slab-induced gravity anomaly vary considerably when the slab density is modelled by different methods. The continued presence of a high-Te band along the trench after application of dynamic corrections shows that, before using 2-D inversion methods to estimate Te variations in subduction zones, there are other factors that should be considered besides the slab dynamic effects on the overriding plate.

Attenuation of Slab determined from T-wave generation by deep earthquakes

NASA Astrophysics Data System (ADS)

Huang, J.; Ni, S.

2006-05-01

T-wave are seismically generated acoustic waves that propagate over great distance in the ocean sound channel (SOFAR). Because of the high attenuation in both the upper mantle and the ocean crust, T wave is rarely observed for earthquakes deeper than 80 km. However some deep earthquakes deeper than 80km indeed generate apparent T-waves if the subducted slab is continuous Okal et al. (1997) . We studied the deep earthquakes in the Fiji/Tonga region, where the subducted lithosphere is old and thus with small attenuation. After analyzing 33 earthquakes with the depth from 10 Km to 650 Km in Fiji/Tonga, we observed and modeled obvious T-phases from these earthquakes observed at station RAR. We used the T-wave generated by deep earthquakes to compute the quality factor of the Fiji/Tonga slab. The method used in this study is followed the equation (1) by [Groot-Hedlin et al,2001][1]. A=A0/(1+(Ω0/Ω)2)×exp(-LΩ/Qv)×Ωn where the A is the amplitude computed by the practicable data, amplitude depending on the earthquakes, and A0 is the inherent frequency related with the earthquake's half duration, L is the length of ray path that P wave or S travel in the slab, and the V is the velocity of P-wave. In this study, we fix the n=2, by assuming the T- wave scattering points in the Fiji/Tonga island arc having the same attribution as the continental shelf. After some computing and careful analysis, we determined the quality factor of the Fiji/Tonga to be around 1000, Such result is consistent with results from the traditional P,S-wave data[Roth & Wiens,1999][2] . Okal et al. (1997) pointed out that the slab in the part of central South America was also a continuous slab, by modeling apparent T-waves from the great 1994 Bolivian deep earthquake in relation to channeling of S wave energy propagating upward through the slab[3]. [1]Catherine D. de Groot-Hedlin, John A. Orcutt, excitation of T-phases by seafloor scattering, J. Acoust. Soc, 109,1944-1954,2001. [2]Erich G.Roth and Douglas A.Wiens, Leroy M.Dorman, Seismic attenuation tomography of the Tonga-Fiji region using phase pair methods, Geophys. Res.,104,4795-4809,1999. [3]Emile A.Okal and Jacques Talandier, T waves from the great 1994 Bolivian deep earthquake in relation to channeling of S wave energy up the slab, J.Geophys. Res.,102(12):27421-27437,1997.

The Two Subduction Zones of the Southern Caribbean: Lithosphere Tearing and Continental Margin Recycling in the East, Flat Slab Subduction and Laramide-Style Uplifts in the West

NASA Astrophysics Data System (ADS)

Levander, A.; Bezada, M. J.; Niu, F.; Schmitz, M.

2015-12-01

The southern Caribbean plate boundary is a complex strike-slip fault system bounded by oppositely vergent subduction zones, the Antilles subduction zone in the east, and a currently locked Caribbean-South American subduction zone in the west (Bilham and Mencin, 2013). Finite-frequency teleseismic P-wave tomography images both the Atlanic (ATL) and the Caribbean (CAR) plates subducting steeply in opposite directions to transition zone depths under northern South America. Ps receiver functions show a depressed 660 discontinuity and thickened transition zone associated with each subducting plate. In the east the oceanic (ATL) part of the South American (SA) plate subducts westward beneath the CAR, initiating the El Pilar-San Sebastian strike slip system, a subduction-transform edge propagator (STEP) fault (Govers and Wortel, 2005). The point at which the ATL tears away from SA as it descends into the mantle is evidenced by the Paria cluster seismicity at depths of 60-110 km (Russo et al, 1993). Body wave tomography and lithosphere-asthenosphere boundary (LAB) thickness determined from Sp and Ps receiver functions and Rayleigh waves suggest that the descending ATL also viscously removes the bottom third to half of the SA continental margin lithospheric mantle as it descends. This has left thinned continental lithosphere under northern SA in the wake of the eastward migrating Antilles subduction zone. The thinned lithosphere occupies ~70% of the length of the El Pilar-San Sebastian fault system, from ~64oW to ~69oW, and extends inland several hundred kilometers. In northwestern SA the CAR subducts east-southeast at low angle under northern Colombia and western Venezuela. The subducting CAR is at least 200 km wide, extending from northernmost Colombia as far south as the Bucaramanga nest seismicity. The CAR descends steeply under Lake Maracaibo and the Merida Andes. This flat slab is associated with three Neogene basement cored, Laramide-style uplifts: the Santa Marta block, the Perija Range, and the Merida Andes (Kellogg and Bonini, 1982). The steep descent of the CAR under Maracaibo implies that the CAR plate is torn somewhere between the Merida Andes and the Caribbean Sea, where it forms the ocean floor. An upcoming broadband seismic experiment will examine the CAR flat slab and the suspected slab tear in detail.

Late Cretaceous - recent lithosphere scale evolution of Turkey: linking the crustal surface evolution to the structure of the mantle

NASA Astrophysics Data System (ADS)

Bartol, J.; Govers, R. M. A.; Wortel, M. J. R.

2015-12-01

Central Anatolia (Central Turkey) possesses all the characteristics of a plateau. It experienced a period of rapid and substantial uplift (late Miocene, ˜8 Ma) while significant crustal shortening did not occur. Similar to other plateaus, the presence of volcanic ash and tuff within the sediments suggest that uplift was preceded by widespread volcanism (˜14-9Ma). The lithospheric context of these events is, however, unknown. For the Eastern Anatolian plateau, similar events have been attributed to southward retread followed by slab break-off of the northern Neotethys slab. Recent tomographic results indicate that this northern Neotethys slab extended beneath both the Eastern and Central Anatolian plateau prior to late Miocene delamination and possibly even beneath western Anatolia prior to the Eocene (?). We propose a new lithospheric scenario for the regional evolution for the Aegean-Anatolia-Near East region that combines a recent compilation of surface geology data with the structure of the upper mantle imaged with tomography. In our new scenario for the evolution of the Aegean-Anatolia-Near East region, a single continuous subduction zone south of the Pontides (Izmir - Ankara - Erzincan crustal suture zone) accommodated the Africa - Eurasia convergence until the end of the late Cretaceous. In the Late Cretaceous - Eocene the northern Neotethys Ocean closed followed by Anatolide - Taurides (south) and Pontides (north) continental collision along the Izmir - Ankara - Erzincan crustal suture zone. While the trench jumped to the south of Anatolide - Taurides terrane, subduction continued beneath the Izmir-Ankara-Erzincan suture where the northern Neotethys slab continued to sink into the deeper mantle. In the early Miocene (˜20-15Ma), the northern Neotethys slab started to retreat southward towards the trench, resulting in delamination of the lithospheric mantle. The last part of (early Miocene - recent) our scenario is testable. We use a coupled thermal-flexural model of the lithosphere. Model results show that delamination can explain the average present-day long-wavelength topography of the Central Anatolian plateau. For the Eastern Anatolian plateau, delamination explains half the present-day elevation: the other half resulted from crustal thickening.

3D lithospheric mapping of the Iberian Peninsula and surrounding Atlantic and Mediterranean margins from 3D joint inversion of potential field and elevation data.

NASA Astrophysics Data System (ADS)

Torne, Montserrat; Zeyen, Hermann; Jimenez-Munt, Ivone; Fernandez, Manel; Vergés, Jaume

2017-04-01

We investigate the lithospheric density structure of the Iberian Peninsula and the surrounding Atlantic and Mediterranean margins from a 3D joint inversion of free-air, geoid and elevation data, based on a Bayesian approach. In addition, the crustal structure has been further constrained by incorporating about 750 Moho values from DSS investigations and RF analysis covering the entire region. Our preliminary results shows a significant lithospheric deformation along the plate boundaries, the Bay of Biscay-Pyrenees to the North and the Azores-Gibraltar to the south, where the CMB and LAB are located at depths more than 45 and 150 km, respectively. Noteworthy is the arcuate lithospheric thickening located at the westernmost end of the Gibraltar Arc system showing the presence of the NW-to-Westward retreated Gibraltar Arc slab that has given rise to the formation of the Betics-Rif Alpine belt system and the back arc Alboran basin. To the west, the stable-slightly deformed Iberian massif shows a quasi-flat CMB and LAB topography (30 to 32 km and about 110 km, respectively). The crust and mantle lithosphere thin towards the Mediterranean and Atlantic margins, with the exception of its northern margin where lithospheric thickening extends offshore to the Gulf of Biscay. In the western Mediterranean the SE-Neogene slab retreat has resulted in a significant thinning of the crust and mantle lithosphere. Thin lithosphere is also observed in the Tagus-Horseshoe abyssal plain region where the LAB shallows to less than 90 km. This work has been funded by the Spanish projects MITE (CGL2014-59516-P) and WEME-CSIC project 201330E11.

A rapid method to map the crustal and lithospheric thickness using elevation, geoid anomaly and thermal analysis. Application to the Gibraltar Arc System, Atlas Mountains and adjacent zones

NASA Astrophysics Data System (ADS)

Fullea, J.; Fernàndez, M.; Zeyen, H.; Vergés, J.

2007-02-01

We present a method based on the combination of elevation and geoid anomaly data together with thermal field to map crustal and lithospheric thickness. The main assumptions are local isostasy and a four-layered model composed of crust, lithospheric mantle, sea water and the asthenosphere. We consider a linear density gradient for the crust and a temperature dependent density for the lithospheric mantle. We perform sensitivity tests to evaluate the effect of the variation of the model parameters and the influence of RMS error of elevation and geoid anomaly databases. The application of this method to the Gibraltar Arc System, Atlas Mountains and adjacent zones reveals the presence of a lithospheric thinning zone, SW-NE oriented. This zone affects the High and Middle Atlas and extends from the Canary Islands to the eastern Alboran Basin and is probably linked with a similarly trending zone of thick lithosphere constituting the western Betics, eastern Rif, Rharb Basin, and Gulf of Cadiz. A number of different, even mutually opposite, geodynamic models have been proposed to explain the origin and evolution of the study area. Our results suggest that a plausible slab-retreating model should incorporate tear and asymmetric roll-back of the subducting slab to fit the present-day observed lithosphere geometry. In this context, the lithospheric thinning would be caused by lateral asthenospheric flow. An alternative mechanism responsible for lithospheric thinning is the presence of a hot magmatic reservoir derived from a deep ancient plume centred in the Canary Island, and extending as far as Central Europe.

The Quaternary calc-alkaline volcanism of the Patagonian Andes close to the Chile triple junction: geochemistry and petrogenesis of volcanic rocks from the Cay and Maca volcanoes (˜45°S, Chile)

NASA Astrophysics Data System (ADS)

D'Orazio, M.; Innocenti, F.; Manetti, P.; Tamponi, M.; Tonarini, S.; González-Ferrán, O.; Lahsen, A.; Omarini, R.

2003-08-01

Major- and trace-element, Sr-Nd isotopes, and mineral chemistry data were obtained for a collection of volcanic rock samples erupted by the Cay and Maca Quaternary volcanoes, Patagonian Andes (˜45°S, Chile). Cay and Maca are two large, adjacent stratovolcanoes that rise from the Chiloe block at the southern end of the southern volcanic zone (SVZ) of the Andes. Samples from the two volcanoes are typical medium-K, calc-alkaline rocks that form two roughly continuous, largely overlapping series from subalkaline basalt to dacite. The overall geochemistry of the samples studied is very similar to that observed for most volcanoes from the southern SVZ. The narrow range of Sr-Nd isotope compositions ( 87Sr/ 86Sr=0.70389-0.70431 and 143Nd/ 144Nd=0.51277-0.51284) and the major- and trace-element distributions indicate that the Cay and Maca magmas differentiated by crystal fractionation without significant contribution by crustal contamination. This is in accordance with the thin (<30 km), relatively young (Paleozoic or more recent) continental crust beneath the volcanoes. The nature of the subduction-derived materials involved in the genesis of the Cay and Maca magmas is investigated by means of the relative concentration of fluid mobile (e.g. Ba) and fluid immobile (e.g. Nb, Ta, Zr, Y) elements and other relevant trace-element ratios (e.g. Sr/Y). The results indicate that small amounts (<1 wt%) of both subducted sediments and slab-released fluids were added to the mantle sources of the Cay and Maca volcanoes and that, despite the very young age (<10 Ma) of the oceanic lithosphere subducted beneath the volcanoes, slab melts were not involved in the magma genesis. Notwithstanding the proximity of the Cay and Maca magma sources to the northern edge of the slab window generated by the subduction of the Chile ridge under the South American plate, we did not find any geochemical evidence for a contribution of a subslab asthenospheric mantle. However, this mantle has been used to explain the peculiar geochemical features (e.g. the mild alkalinity and relatively low ratios between large ion lithophile and high field strength elements) of the Hudson volcano, which is located even closer to the slab window than the Cay and Maca volcanoes are.

The Sapphire (0001) Surface, Clean and with d-metal Overlayers: Density Functional - LDA Results

NASA Astrophysics Data System (ADS)

Verdozzi, C.; Jennison, D. R.; Schultz, P. A.; Sears, M. P.

1998-03-01

Previous theoretical work for the a-Al2O3(0001) surface mostly used very thin slabs, and limited theoretical information is available on the binding of metal overlayers. Also, no systematic information is available about the dependence of the metal-ceramic interaction on metal coverage. We present here results using the local density approximation for the structural and electronic properties of the a-Al2O3(0001) surface, with and without d-metal overlayers Pt, Ag, Cu, and with sufficiently thick slabs to find the bottom of the unusually large and deep surface relaxation in this material. Our thick slab site-optimized calculations are performed for 1, 2/3 and 1/3 monolayer (ML) coverage. The adhesion energy and the nature of the interfacial bond vary greatly with metal coverage and can be understood in terms of the relative roles of the surface Madelung potential and the strength of the lateral metal-metal bond. Our study should in principle succeed in bracketing the phenomenology of adhesion and wetting at least for the right-most part of the d-metal periodic table. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000. Corresponding author: claudio@sandia.gov.

Electron beam transport in heterogeneous slab media from MeV down to eV.

PubMed

Yousfi, M; Leger, J; Loiseau, J F; Held, B; Eichwald, O; Defoort, B; Dupillier, J M

2006-01-01

An optimized Monte Carlo method based on the null collision technique and on the treatment of individual interactions is used for the simulation of the electron transport in multilayer materials from high energies (MeV or several hundred of keV) down to low cutoff energies (between 1 and 10 eV). In order to better understand the electron transport and the energy deposition at the interface in the composite application framework, two layer materials are considered (carbon and polystyrene with densities of 1.7 g cm(-3) and 1.06 g cm(-3), respectively) under two slab or three slab configurations as, e.g. a thin layer of carbon sandwiched between two polystyrene layers. The electron-matter cross-sections (electron-carbon and electron-polystyrene) used in the case of pure material (carbon and polystyrene) as well as our Monte-Carlo code have been first validated. The boundary interface layer is considered without any mean free path truncation and with a rigorous treatment of the backscattered and also the forward scattered electrons from one layer to another. The large effect of the choice of a low cutoff energy and the dissociation process consideration are also clearly shown in the heterogeneous multi-layer media more particularly on the secondary electron emission, inelastic collision number and energy spectra.

Model Fe-Al Steel with Exceptional Resistance to High Temperature Coarsening. Part II: Experimental Validation and Applications

NASA Astrophysics Data System (ADS)

Zhou, Tihe; Zhang, Peng; O'Malley, Ronald J.; Zurob, Hatem S.; Subramanian, Mani

2015-01-01

In order to achieve a fine uniform grain-size distribution using the process of thin slab casting and directing rolling (TSCDR), it is necessary to control the grain-size prior to the onset of thermomechanical processing. In the companion paper, Model Fe- Al Steel with Exceptional Resistance to High Temperature Coarsening. Part I: Coarsening Mechanism and Particle Pinning Effects, a new steel composition which uses a small volume fraction of austenite particles to pin the growth of delta-ferrite grains at high temperature was proposed and grain growth was studied in reheated samples. This paper will focus on the development of a simple laboratory-scale setup to simulate thin-slab casting of the newly developed steel and demonstrate the potential for grain size control under industrial conditions. Steel bars with different diameters are briefly dipped into the molten steel to create a shell of solidified material. These are then cooled down to room temperature at different cooling rates. During cooling, the austenite particles nucleate along the delta-ferrite grain boundaries and greatly retard grain growth. With decreasing temperature, more austenite particles precipitate, and grain growth can be completely arrested in the holding furnace. Additional applications of the model alloy are discussed including grain-size control in the heat affected zone in welds and grain-growth resistance at high temperature.

Putting the slab back: First steps of creating a synthetic seismic section of subducted lithosphere

NASA Astrophysics Data System (ADS)

Zertani, S.; John, T.; Tilmann, F. J.; Leiss, B.; Labrousse, L.; Andersen, T. B.

2016-12-01

Imaging subducted lithosphere is a difficult task which is usually tackled with geophysical methods. To date, the most promising method is receiver function imaging (RF), which concentrates on first order conversions from p- to s-waves at boundaries (e.g. lithological and structural) with contrasting seismic velocities. The resolution is high for the upper parts of the subducting material. However, in greater depths (40-80 km) the visualization of the subducted slab becomes increasingly blurry, until the slab cannot be distinguished from Earth's mantle anymore, rendering a visualization impossible. This blurry zone is thought to occur due to advancing eclogitization of the subducting slab. However, it is not well understood how micro- to macro-scale structures related to progressive eclogitization affect RF signals. The island of Holsnoy in the Bergen Arcs of western Norway represents a partially eclogitized formerly subducted block of lower crust and serves as an analogue to the aforementioned blurry zone in RF images. This eclogitization can be observed in static fluid induced eclogitization patches or fingers, but is mainly present in localized shear zones of variable sizes (mm to 100s of meters). We mapped the area to gain a better understanding of the geometries of such shear zones, which could possibly function as seismic reflectors. Further, we calculated seismic velocities from thermodynamic modelling on the basis of XRF whole rock analysis and compared these results to velocities calculated from a combination of thin section information, EMPA and physical mineral properties (Voigt-Reuss-Hill averaging). Both methods yield consistent results for p- and s-wave velocities of eclogites and granulites from Holsnoy. In combination with X-ray measurements to identify the microtextures of the characteristic samples to incorporate seismic anisotropy caused by e.g. foliation or lineation, these seismic velocities are used as an input for seismic models to reconstruct the progressive eclogitization of a subducting slab as seen in many RF-images (i.e. blurry zone).

Sustainability assessment of a lightweight biomimetic ceiling structure.

PubMed

Antony, Florian; Grießhammer, Rainer; Speck, Thomas; Speck, Olga

2014-03-01

An intensive and continuous debate centres on the question of whether biomimetics has a specific potential to contribute to sustainability. In the context of a case study, the objective of this paper is to contribute to this debate by presenting the first systematic approach to assess the sustainability of a complex biomimetic product. The object of inquiry is a lecture hall's ribbed slab. Based on criteria suggested by the Association of German Engineers (VDI), it has been verified that the slab has been correctly defined as biomimetic. Moreover, a systematic comparative product sustainability assessment has been carefully carried out. For purposes of comparison, estimated static calculations have been performed for conceivable current state-of-the-art lightweight ceiling structures. Alternative options are a hollow article slab and a pre-stressed flat slab. Besides a detailed benefit analysis and a discussion of social effects, their costs have also been compared. A particularly detailed life cycle assessment on the respective environmental impacts has also been performed. Results show that the biomimetic ribbed slab built in the 1960s is able to keep up with the current state-of-the-art lightweight solutions in terms of sustainability. These promising results encourage a systematic search for a broad range of sustainable biomimetic solutions.

Slab melting beneath the Cascades Arc driven by dehydration of altered oceanic peridotite

USGS Publications Warehouse

Walowski, Kristina J; Wallace, Paul J.; Hauri, E.H.; Wada, I.; Clynne, Michael A.

2015-01-01

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.

Density structure and geometry of the Costa Rican subduction zone from 3-D gravity modeling and local earthquake data

NASA Astrophysics Data System (ADS)

Lücke, O. H.; Arroyo, I. G.

2015-07-01

The eastern part of the oceanic Cocos Plate presents a heterogeneous crustal structure due to diverse origins and ages as well as plate-hot spot interactions which originated the Cocos Ridge, a structure that converges with the Caribbean Plate in southeastern Costa Rica. The complex structure of the oceanic plate directly influences the dynamics and geometry of the subduction zone along the Middle American Trench. In this paper an integrated interpretation of the slab geometry is presented based on three-dimensional density modeling of combined satellite and surface gravity data, constrained by available geophysical and geological data and seismological information obtained from local networks. The results show the continuation of steep subduction geometry from the Nicaraguan margin into Northwestern Costa Rica, followed by a moderate dipping slab under the Central Cordillera toward the end of the Central American Volcanic Arc. To the southeast end of the volcanic arc, our preferred model shows a steep, coherent slab that extends up to the landward projection of the Panama Fracture Zone. Overall, a gradual change in the depth of the intraplate seismicity is observed, reaching 220 km in the northwestern part, and becoming progressively shallower toward the southeast, where it reaches a terminal depth of 75 km. The changes in the terminal depth of the observed seismicity correlate with the increased density in the modeled slab. The absence of intermediate depth intraplate seismicity in the southeastern section and the higher densities for the subducted slab in this area, support a model in which dehydration reactions in the subducted slab cease at a shallower depth, originating an anhydrous and thus aseismic slab.

Density structure and geometry of the Costa Rican subduction zone from 3-D gravity modeling and local earthquake data

NASA Astrophysics Data System (ADS)

Lücke, O. H.; Arroyo, I. G.

2015-10-01

The eastern part of the oceanic Cocos Plate presents a heterogeneous crustal structure due to diverse origins and ages as well as plate-hot spot interactions which originated the Cocos Ridge, a structure that converges with the Caribbean Plate in southeastern Costa Rica. The complex structure of the oceanic plate directly influences the dynamics and geometry of the subduction zone along the Middle American Trench. In this paper an integrated interpretation of the slab geometry in Costa Rica is presented based on 3-D density modeling of combined satellite and surface gravity data, constrained by available geophysical and geological data and seismological information obtained from local networks. The results show the continuation of steep subduction geometry from the Nicaraguan margin into northwestern Costa Rica, followed by a moderate dipping slab under the Central Cordillera toward the end of the Central American Volcanic Arc. Contrary to commonly assumed, to the southeast end of the volcanic arc, our preferred model shows a steep, coherent slab that extends up to the landward projection of the Panama Fracture Zone. Overall, a gradual change in the depth of the intraplate seismicity is observed, reaching 220 km in the northwestern part, and becoming progressively shallower toward the southeast, where it reaches a maximum depth of 75 km. The changes in the terminal depth of the observed seismicity correlate with the increased density in the modeled slab. The absence of intermediate depth (> 75 km) intraplate seismicity in the southeastern section and the higher densities for the subducted slab in this area, support a model in which dehydration reactions in the subducted slab cease at a shallower depth, originating an anhydrous and thus aseismic slab.

Slab1.0: A three-dimensional model of global subduction zone geometries

NASA Astrophysics Data System (ADS)

Hayes, Gavin P.; Wald, David J.; Johnson, Rebecca L.

2012-01-01

We describe and present a new model of global subduction zone geometries, called Slab1.0. An extension of previous efforts to constrain the two-dimensional non-planar geometry of subduction zones around the focus of large earthquakes, Slab1.0 describes the detailed, non-planar, three-dimensional geometry of approximately 85% of subduction zones worldwide. While the model focuses on the detailed form of each slab from their trenches through the seismogenic zone, where it combines data sets from active source and passive seismology, it also continues to the limits of their seismic extent in the upper-mid mantle, providing a uniform approach to the definition of the entire seismically active slab geometry. Examples are shown for two well-constrained global locations; models for many other regions are available and can be freely downloaded in several formats from our new Slab1.0 website, http://on.doi.gov/d9ARbS. We describe improvements in our two-dimensional geometry constraint inversion, including the use of `average' active source seismic data profiles in the shallow trench regions where data are otherwise lacking, derived from the interpolation between other active source seismic data along-strike in the same subduction zone. We include several analyses of the uncertainty and robustness of our three-dimensional interpolation methods. In addition, we use the filtered, subduction-related earthquake data sets compiled to build Slab1.0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far, concluding that the width of these seismogenic zones is on average 30% larger than previous studies have suggested.

Thermo-Physical Properties of B2O3-Containing Mold Flux for High Carbon Steels in Thin Slab Continuous Casters: Structure, Viscosity, Crystallization, and Wettability

NASA Astrophysics Data System (ADS)

Park, Jun-Yong; Kim, Gi Hyun; Kim, Jong Bae; Park, Sewoong; Sohn, Il

2016-08-01

The effect of B2O3 on the thermo-physical properties of commercial mold fluxes, including the viscosity, crystallization behavior, and wettability, was investigated. Viscosity was measured using the rotating spindle method, and CCT (continuous cooling transformation) diagrams were obtained to investigate the crystallization behavior at various cooling rates using CLSM (confocal laser scanning microscope). The wettability of the fluxes was determined by measuring the contact angles at 1573 K (1300 °C) using the digital images generated by the sessile drop method and were used to calculate the surface tension, interfacial tension, and work of adhesion for Flux A (existing flux) and B (modified flux). These thermo-physical properties were correlated with the structural analysis obtained using FT-IR (Fourier transform-infrared), Raman and MAS-NMR (magic angle spin-nuclear magnetic resonance) spectroscopy. In addition, DTA (differential thermal analysis) was performed on the samples to measure the liquidus temperatures. Higher B2O3 concentrations resulted in lower liquidus temperatures, consequently decreasing the viscosity, the break temperature, and the crystallization temperature. However, B2O3 addition accelerated crystal growth owing to the higher diffusion kinetics of the cations, which also reduced the size of the liquid/solid co-existing region.

Crustal structure in the Falcón Basin area, northwestern Venezuela, from seismic and gravimetric evidence

NASA Astrophysics Data System (ADS)

Bezada, Maximiliano J.; Schmitz, Michael; Jácome, María Inés; Rodríguez, Josmat; Audemard, Franck; Izarra, Carlos; The Bolivar Active Seismic Working Group

2008-05-01

The Falcón Basin in northwestern Venezuela has a complex geological history driven by the interactions between the South American and Caribbean plates. Igneous intrusive bodies that outcrop along the axis of the basin have been associated with crustal thinning, and gravity modeling has shown evidence for a significantly thinned crust beneath the basin. In this study, crustal scale seismic refraction/wide-angle reflection data derived from onshore/offshore active seismic experiments are interpreted and forward-modeled to generate a P-wave velocity model for a ˜450 km long profile. The final model shows thinning of the crust beneath the Falcón Basin where depth to Moho decreases to 27 km from a value of 40 km about 100 km to the south. A deeper reflected phase on the offshore section is interpreted to be derived from the downgoing Caribbean slab. Velocity values were converted to density and the resulting gravimetric response was shown to be consistent with the regional gravity anomaly. The crustal thinning proposed here supports a rift origin for the Falcón Basin.

Multiple stationary solutions of an irradiated slab

NASA Astrophysics Data System (ADS)

Taylor, P. D.; Feltham, D. L.

2005-04-01

A mathematical model describing the heat budget of an irradiated medium is introduced. The one-dimensional form of the equations and boundary conditions are presented and analysed. Heat transport at one face of the slab occurs by absorption (and reflection) of an incoming beam of short-wave radiation with a fraction of this radiation penetrating into the body of the slab, a diffusive heat flux in the slab and a prescribed incoming heat flux term. The other face of the slab is immersed in its own melt and is considered to be a free surface. Here, temperature continuity is prescribed and evolution of the surface is determined by a Stefan condition. These boundary conditions are flexible enough to describe a range of situations such as a laser shining on an opaque medium, or the natural environment of polar sea ice or lake ice. A two-stream radiation model is used which replaces the simple Beer's law of radiation attenuation frequently used for semi-infinite domains. The stationary solutions of the governing equations are sought and it is found that there exists two possible stationary solutions for a given set of boundary conditions and a range of parameter choices. It is found that the existence of two stationary solutions is a direct result of the model of radiation absorption, due to its effect on the albedo of the medium. A linear stability analysis and numerical calculations indicate that where two stationary solutions exist, the solution corresponding to a larger thickness is always stable and the solution corresponding to a smaller thickness is unstable. Numerical simulations reveal that when there are two solutions, if the slab is thinner than the smaller stationary thickness it will melt completely, whereas if the slab is thicker than the smaller stationary thickness it will evolve toward the larger stationary thickness. These results indicate that other mechanisms (e.g. wave-induced agglomeration of crystals) are necessary to grow a slab from zero initial thickness in the parameter regime that yields two stationary solutions.

A possible mechanism for earthquakes found in the mantle wedge of the Nazca subduction zone

NASA Astrophysics Data System (ADS)

Warren, L. M.; Chang, Y.; Prieto, G. A.

2017-12-01

Beneath Colombia, the Cauca cluster of intermediate-depth earthquakes extends for 200 km along the trench (3.5°N-5.5°N, 77.0°W-75.3°W) and, with 58 earthquakes per year with local magnitude ML >= 2.5, has a higher rate of seismicity than the subduction zone immediately to the north or south. By precisely locating 433 cluster earthquakes from 1/2010-3/2014 with data from the Colombian National Seismic Network, we found that the earthquakes are located both in a continuous Nazca plate subducting at an angle of 33°-43° and in the overlying mantle wedge. The mantle wedge earthquakes (12% of the earthquakes) form two isolated 40-km-tall columns extending perpendicular to the subducting slab. Using waveform inversion, we computed focal mechanisms for 69 of the larger earthquakes. The focal mechanisms are variable, but the intraslab earthquakes are generally consistent with an in-slab extensional stress axis oriented 25° counterclockwise from the down-dip direction. We suggest that the observed mantle wedge earthquakes are the result of hydrofracture in a relatively cool mantle wedge. This segment of the Nazca Plate is currently subducting at a normal angle, but Wagner et al. (2017) suggested that a flat slab slowly developed in the region between 9-5.9 Ma and persisted until 4 Ma. During flat slab subduction, the overlying mantle wedge typically cools because it is cut off from mantle corner flow. After hydrous minerals in the slab dehydrate, the dehydrated fluid is expelled from the slab and migrates through the mantle wedge. If a cool mantle wedge remains today, fluid dehydrated from the slab may generate earthquakes by hydrofracture, with the mantle wedge earthquakes representing fluid migration pathways. Dahm's (2000) model of water-filled fracture propagation in the mantle wedge shows hydrofractures propagating normal to the subducting slab and extending tens of km into the mantle wedge, as we observe.

Hidden symmetries in plasmonic gratings

NASA Astrophysics Data System (ADS)

Huidobro, P. A.; Chang, Y. H.; Kraft, M.; Pendry, J. B.

2017-04-01

Plasmonic gratings constitute a paradigmatic instance of the wide range of applications enabled by plasmonics. While subwavelength metal gratings find applications in optical biosensing and photovoltaics, atomically thin gratings achieved by periodically doping a graphene monolayer perform as metasurfaces for the control of terahertz radiation. In this paper we show how these two instances of plasmonic gratings inherit their spectral properties from an underlying slab with translational symmetry. We develop an analytical formalism to accurately derive the mode spectrum of the gratings that provides a great physical insight.

The estimation of galactic cosmic ray penetration and dose rates

NASA Technical Reports Server (NTRS)

Burrell, M. O.; Wright, J. J.

1972-01-01

This study is concerned with approximation methods that can be readily applied to estimate the absorbed dose rate from cosmic rays in rads - tissue or rems inside simple geometries of aluminum. The present work is limited to finding the dose rate at the center of spherical shells or behind plane slabs. The dose rate is calculated at tissue-point detectors or for thin layers of tissue. This study considers cosmic-rays dose rates for both free-space and earth-orbiting missions.

Emission properties of body-centered cubic elemental metal photocathodes

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

Li, Tuo; Rickman, Benjamin L., E-mail: brickm2@uic.edu; Schroeder, W. Andreas

2015-04-07

A first principles analysis of photoemission is developed to explain the lower than expected rms transverse electron momentum measured using the solenoid scan technique for the body-centered cubic Group Vb (V, Nb, and Ta) and Group VIb (Cr, Mo, and W) metallic photocathodes. The density functional theory based analysis elucidates the fundamental role that the electronic band structure (and its dispersion) plays in determining the emission properties of solid-state photocathodes and includes evaluation of work function anisotropy using a thin-slab method.

Demonstration of pulse controlled all-optical switch/modulator.

PubMed

Akin, Osman; Dinleyici, M S

2014-03-15

An all-optical pulse controlled switch/modulator based on evanescent coupling between a polymer slab waveguide and a single mode fiber is demonstrated. Very fast all-optical modulation/switching is achieved via Kerr effect of the nonlinear polymer placed in the evanescent region of the optical fiber. Local refractive index perturbation (Δn=-1.45612×10(-5)) on the thin film leads to 0.374 nW power modulation at the fiber output, which results in a switching efficiency of ≈1.5%.

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.

Neogene subduction beneath Java, Indonesia: Slab tearing and changes in magmatism

NASA Astrophysics Data System (ADS)

Cottam, Michael; Hall, Robert; Cross, Lanu; Clements, Benjamin; Spakman, Wim

2010-05-01

Java is a Neogene calc-alkaline volcanic island arc formed by the northwards subduction of the Indo-Australian Plate beneath Sundaland, the continental core of SE Asia. The island has a complex history of volcanism and displays unusual subduction characteristics. These characteristics are consistent with the subduction of a hole in the down going slab that was formed by the arrival of a buoyant oceanic plateau at the trench. Subduction beneath Java began in the Eocene. However, the position and character of the calc-alkaline arc has changed over time. An older Paleogene arc ceased activity in the Early Miocene. Volcanic activity resumed in the Late Miocene producing a younger arc to the north of the older arc, and continues to the present day. An episode of Late Miocene thrusting at about 7 Ma is observed throughout Java and appears to be linked to northward movement of the arc. Arc rocks display typical calc-alkaline characteristics and reflect melting of the mantle wedge and subducted sediments associated with high fluid fluxes. Between West Java and Bali the present arc-trench gap is unusually wide at about 300 km. Seismicity identifies subducted Indian Ocean lithosphere that dips north at about 20° between the trench and the arc and then dips more steeply at about 60-70° from 100 to 600 km depth. In East Java there is gap in seismicity between about 250 and 500 km. Seismic tomography shows that this gap is not an aseismic section of the subduction zone but a hole in the slab. East Java is also unusual in the presence of K-rich volcanoes, now inactive, to the north of the calc-alkaline volcanoes of the active arc. In contrast to the calc-alkaline volcanism of the main arc, these K-rich melts imply lower fluid fluxes and a different mantle source. We suggest that all these observations can be explained by the tearing of the subducting slab when a buoyant oceanic plateau arrived at the trench south of East Java at about 8 Ma. With the slab unable to subduct, continued convergence caused contractional deformation and thrusting in Java. The slab then broke in front of the plateau. The trench stepped back to the south by about 150 km and subduction resumed behind the plateau, causing a hole to develop in the subducting slab. As the hole passed beneath the arc, and fluid flux declined, normal calc-alkaline volcanism ceased. With the mantle wedge melt component ‘switched off' K-rich melts, produced from a deeper mantle component that remained undiluted, dominated arc volcanism. As the hole got deeper K-rich volcanism ceased. Normal, calc-alkaline, arc activity resumed when the untorn slab following the hole was subducted.

Tomography reveals buoyant asthenosphere accumulating beneath the Juan de Fuca plate

NASA Astrophysics Data System (ADS)

Hawley, William B.; Allen, Richard M.; Richards, Mark A.

2016-09-01

The boundary between Earth’s strong lithospheric plates and the underlying mantle asthenosphere corresponds to an abrupt seismic velocity decrease and electrical conductivity increase with depth, perhaps indicating a thin, weak layer that may strongly influence plate motion dynamics. The behavior of such a layer at subduction zones remains unexplored. We present a tomographic model, derived from on- and offshore seismic experiments, that reveals a strong low-velocity feature beneath the subducting Juan de Fuca slab along the entire Cascadia subduction zone. Through simple geodynamic arguments, we propose that this low-velocity feature is the accumulation of material from a thin, weak, buoyant layer present beneath the entire oceanic lithosphere. The presence of this feature could have major implications for our understanding of the asthenosphere and subduction zone dynamics.

Theory of Earth

NASA Astrophysics Data System (ADS)

Anderson, D. L.

2014-12-01

Earth is an isolated, cooling planet that obeys the 2nd law. Interior dynamics is driven from the top, by cold sinking slabs. High-resolution broad-band seismology and geodesy has confirmed that mantle flow is characterized by narrow downwellings and ~20 broad slowly rising updrafts. The low-velocity zone (LVZ) consists of a hot melange of sheared peridotite intruded with aligned melt-rich lamellae that are tapped by intraplate volcanoes. The high temperature is a simple consequence of the thermal overshoot common in large bodies of convecting fluids. The transition zone consists of ancient eclogite layers that are displaced upwards by slabs to become broad passive, and cool, ridge feeding updrafts of ambient mantle. The physics that is overlooked in canonical models of mantle dynamics and geochemistry includes; the 2nd law, convective overshoots, subadiabaticity, wave-melt interactions, Archimedes' principle, and kinetics (rapid transitions allow stress-waves to interact with melting and phase changes, creating LVZs; sluggish transitions in cold slabs keep eclogite in the TZ where it warms up by extracting heat from mantle below 650 km, creating the appearance of slab penetration). Canonical chemical geodynamic models are the exact opposite of physics and thermodynamic based models and of the real Earth. A model that results from inverting the assumptions regarding initial and boundary conditions (hot origin, secular cooling, no external power sources, cooling internal boundaries, broad passive upwellings, adiabaticity and whole-mantle convection not imposed, layering and self-organization allowed) results in a thick refractory-yet-fertile surface layer, with ancient xenoliths and cratons at the top and a hot overshoot at the base, and a thin mobile D" layer that is an unlikely plume generation zone. Accounting for the physics that is overlooked, or violated (2nd law), in canonical models, plus modern seismology, undermines the assumptions and conclusions of these models.

Advances in Surface Plasmon Resonance Imaging enable quantitative measurement of laterally heterogeneous coatings of nanoscale thickness

NASA Astrophysics Data System (ADS)

Raegen, Adam; Reiter, Kyle; Clarke, Anthony; Lipkowski, Jacek; Dutcher, John

2013-03-01

The Surface Plasmon Resonance (SPR) phenomenon is routinely exploited to qualitatively probe changes to the optical properties of nanoscale coatings on thin metallic surfaces, for use in probes and sensors. Unfortunately, extracting truly quantitative information is usually limited to a select few cases - uniform absorption/desorption of small biomolecules and films, in which a continuous ``slab'' model is a good approximation. We present advancements in the SPR technique that expand the number of cases for which the technique can provide meaningful results. Use of a custom, angle-scanning SPR imaging system, together with a refined data analysis method, allow for quantitative kinetic measurements of laterally heterogeneous systems. We first demonstrate the directionally heterogeneous nature of the SPR phenomenon using a directionally ordered sample, then show how this allows for the calculation of the average coverage of a heterogeneous sample. Finally, the degradation of cellulose microfibrils and bundles of microfibrils due to the action of cellulolytic enzymes will be presented as an excellent example of the capabilities of the SPR imaging system.

Miocene-Recent sediment flux in the south-central Alaskan fore-arc basin governed by flat-slab subduction

NASA Astrophysics Data System (ADS)

Finzel, Emily S.; Enkelmann, Eva

2017-04-01

The Cook Inlet in south-central Alaska contains the early Oligocene to Recent stratigraphic record of a fore-arc basin adjacent to a shallowly subducting oceanic plateau. Our new measured stratigraphic sections and detrital zircon U-Pb geochronology and Hf isotopes from Neogene strata and modern rivers illustrate the effects of flat-slab subduction on the depositional environments, provenance, and subsidence in fore-arc sedimentary systems. During the middle Miocene, fluvial systems emerged from the eastern, western, and northern margins of the basin. The axis of maximum subsidence was near the center of the basin, suggesting equal contributions from subsidence drivers on both margins. By the late Miocene, the axis of maximum subsidence had shifted westward and fluvial systems originating on the eastern margin of the basin above the flat-slab traversed the entire width of the basin. These mud-dominated systems reflect increased sediment flux from recycling of accretionary prism strata. Fluvial systems with headwaters above the flat-slab region continued to cross the basin during Pliocene time, but a change to sandstone-dominated strata with abundant volcanogenic grains signals a reactivation of the volcanic arc. The axis of maximum basin subsidence during late Miocene to Pliocene time is parallel to the strike of the subducting slab. Our data suggest that the character and strike-orientation of the down-going slab may provide a fundamental control on the nature of depositional systems, location of dominant provenance regions, and areas of maximum subsidence in fore-arc basins.

60-nm-thick basic photonic components and Bragg gratings on the silicon-on-insulator platform.

PubMed

Zou, Zhi; Zhou, Linjie; Li, Xinwan; Chen, Jianping

2015-08-10

We demonstrate integrated basic photonic components and Bragg gratings using 60-nm-thick silicon-on-insulator strip waveguides. The ultra-thin waveguides exhibit a propagation loss of 0.61 dB/cm and a bending loss of approximately 0.015 dB/180° with a 30 μm bending radius (including two straight-bend waveguide junctions). Basic structures based on the ultra-thin waveguides, including micro-ring resonators, 1 × 2 MMI couplers, and Mach-Zehnder interferometers are realized. Upon thinning-down, the waveguide effective refractive index is reduced, making the fabrication of Bragg gratings possible using the standard 248-nm deep ultra-violet (DUV) photolithography process. The Bragg grating exhibits a stopband width of 1 nm and an extinction ratio of 35 dB, which is practically applicable as an optical filter or a delay line. The transmission spectrum can be thermally tuned via an integrated resistive micro-heater formed by a heavily doped silicon slab beside the waveguide.

Thin-film magnetless Faraday rotators for compact heterogeneous integrated optical isolators

NASA Astrophysics Data System (ADS)

Karki, Dolendra; Stenger, Vincent; Pollick, Andrea; Levy, Miguel

2017-06-01

This report describes the fabrication, characterization, and transfer of ultra-compact thin-film magnetless Faraday rotators to silicon photonic substrates. Thin films of magnetization latching bismuth-substituted rare-earth iron garnets were produced from commercially available materials by mechanical lapping, dice polishing, and crystal-ion-slicing. Eleven- μ m -thick films were shown to retain the 45 ° Faraday rotation of the bulk material to within 2 ° at 1.55 μ m wavelength without re-poling. Anti-reflection coated films evince 0.09 dB insertion loses and better than -20 dB extinction ratios. Lower extinction ratios than the bulk are ascribed to multimode propagation. Significantly larger extinction ratios are predicted for single-mode waveguides. Faraday rotation, extinction ratios, and insertion loss tests on He-ion implanted slab waveguides of the same material yielded similar results. The work culminated with bond alignment and transfer of 7 μ m -thick crystal-ion-sliced 50 × 480 μ m 2 films onto silicon photonic substrates.

Wave propagation through an inhomogeneous slab sandwiched by the piezoelectric and the piezomagnetic half spaces.

PubMed

Jiao, Fengyu; Wei, Peijun; Li, Li

2017-01-01

Wave propagation through a gradient slab sandwiched by the piezoelectric and the piezomagnetic half spaces are studied in this paper. First, the secular equations in the transverse isotropic piezoelectric/piezomagnetic half spaces are derived from the general dynamic equation. Then, the state vectors at piezoelectric and piezomagnetic half spaces are related to the amplitudes of various possible waves. The state transfer equation of the functionally graded slab is derived from the equations of motion by the reduction of order, and the transfer matrix of the functionally gradient slab is obtained by solving the state transfer equation with the spatial-varying coefficient. Finally, the continuous interface conditions are used to lead to the resultant algebraic equations. The algebraic equations are solved to obtain the amplitude ratios of various waves which are further used to obtain the energy reflection and transmission coefficients of various waves. The numerical results are shown graphically and are validated by the energy conservation law. Based on the numerical results on the fives of gradient profiles, the influences of the graded slab on the wave propagation are discussed. It is found that the reflection and transmission coefficients are obviously dependent upon the gradient profile. The various surface waves are more sensitive to the gradient profile than the bulk waves. Copyright © 2016 Elsevier B.V. All rights reserved.

Characteristics of nonlinear imaging of broadband laser stacked by chirped pulses

NASA Astrophysics Data System (ADS)

Wang, Youwen; You, Kaiming; Chen, Liezun; Lu, Shizhuan; Dai, Zhiping; Ling, Xiaohui

2014-11-01

Nanosecond-level pulses of specific shape is usually generated by stacking chirped pulses for high-power inertial confinement fusion driver, in which nonlinear imaging of scatterers may damage precious optical elements. We present a numerical study of the characteristics of nonlinear imaging of scatterers in broadband laser stacked by chirped pulses to disclose the dependence of location and intensity of images on the parameters of the stacked pulse. It is shown that, for sub-nanosecond long sub-pulses with chirp or transform-limited sub-pulses, the time-mean intensity and location of images through normally dispersive and anomalously dispersive self-focusing medium slab are almost identical; While for picosecond-level short sub-pulses with chirp, the time-mean intensity of images for weak normal dispersion is slightly higher than that for weak anomalous dispersion through a thin nonlinear slab; the result is opposite to that for strong dispersion in a thick nonlinear slab; Furthermore, for given time delay between neighboring sub-pulses, the time-mean intensity of images varies periodically with chirp of the sub-pulse increasing; for a given pulse width of sub-pulse, the time-mean intensity of images decreases with the time delay between neighboring sub-pulses increasing; additionally, there is a little difference in the time-mean intensity of images of the laser stacked by different numbers of sub-pulses. Finally, the obtained results are also given physical explanations.

Thick-skinned tectonics closing the Rifian Corridor

NASA Astrophysics Data System (ADS)

Capella, Walter; Matenco, Liviu; Dmitrieva, Evelina; Roest, Wilmer M. J.; Hessels, Suzanne; Hssain, Mohamed; Chakor-Alami, Abdelwahid; Sierro, Francisco J.; Krijgsman, Wout

2017-07-01

Tectonic processes in the Gibraltar region are associated with Africa-Iberia convergence and the formation of the Betic-Rif orogenic system. The Late Miocene shortening recorded in the Rif orogen resulted in gradual shallowing and eventual closure of the Rifian Corridor, a narrow marine gateway connecting the Atlantic Ocean with the Mediterranean Sea. This closure is associated with paleoenvironmental changes that ultimately led to the Mediterranean Messinian Salinity Crisis. Here we present a structural analysis based on a combination of field kinematic data and interpretation of reflection seismic lines acquired for petroleum exploration to understand the deformational phases associated with the closure of the Rifian Corridor. We show the succession of three Late Miocene to present day events, an initial thin-skinned nappe thrusting, followed by regional subsidence and continued by thick-skinned contraction. The transition from in sequence thin-skinned tectonics during subduction to thick-skinned contraction during continental collision resulted in significant acceleration of tectonic uplift and associated exhumation. This is related to a change in the regional deformation linked to plate convergence, but possibly also coupled with deep lithospheric or dynamic topography processes. Such a mechanism is also common for other Mediterranean orogens during late stages of slab retreat, where accelerated tectonics resulted in rapid sedimentation and associated basins evolution. We conclude that the thick-skinned contraction in the Rif orogeny initiated in the late Tortonian, has created a cumulative uplift in the order of 1 km, and provided high enough uplift rates to close the Rifian Corridor.

Recent Developments in Ground-Borne Noise and Vibration Control

NASA Astrophysics Data System (ADS)

Nelson, J. T.

1996-05-01

Vibration control provisions available to the transit designer include (among others) precision straightened rail, ballast mats, floating slabs and very soft direct fixation fasteners, in addition to rail grinding, wheel truing, and continuous welded rail. Recently, the Los Angeles Metro has developed specifications for a soft resilient direct fixation fastener to fit the same base dimensions as the standard direct fixation fastener. In San Francisco, low resonance frequency (8 Hz) floating slabs have been constructed to mitigate predicted ground vibration impacts at nearby residential structures. In Atlanta, low resonance frequency loading slabs have been constructed to maintain a low vibration environment in a medical building planned to be built over the subway structure. In Portland and Pasadena, ballast mats have been recommended to control light rail transit ground vibration impacts on housing located at typically 35 feet from the alignment. Each of these provisions are briefly described in view of recent applications at U.S. transit systems.

Responsivity boosting in FIR TiN LEKIDs using phonon recycling: simulations and array design

NASA Astrophysics Data System (ADS)

Fyhrie, Adalyn; McKenney, Christopher; Glenn, Jason; LeDuc, Henry G.; Gao, Jiansong; Day, Peter; Zmuidzinas, Jonas

2016-07-01

To characterize further the cosmic star formation history at high redshifts, a large-area survey by a cryogenic 4-6 meter class telescope with a focal plane populated by tens of thousands of far-infrared (FIR, 30-300 μm) detectors with broadband detector noise equivalent powers (NEPs) on the order of 3×10-9 W/√ Hz is needed. Ideal detectors for such a surveyor do not yet exist. As a demonstration of one technique for approaching the ultra-low NEPs required by this surveyor, we present the design of an array of 96 350 µm KIDs that utilize phonon recycling to boost responsivity. Our KID array is fabricated with TiN deposited on a silicon-on-insulator (SOI) wafer, which is a 2 μm thick layer of silicon bonded to a thicker slab of silicon by a thin oxide layer. The backside thick slab is etched away underneath the absorbers so that the inductors are suspended on just the 2 μm membrane. The intent is that quasiparticle recombination phonons are trapped in the thin membrane, thereby increasing their likelihood of being re-absorbed by the KID to break additional Cooper pairs and boost responsivity. We also present a Monte-Carlo simulation that predicts the amount of signal boost expected from phonon recycling given different detector geometries and illumination strategies. For our current array geometry, the simulation predicts a measurable 50% boost in responsivity.

KINK AND SAUSAGE MODES IN NONUNIFORM MAGNETIC SLABS WITH CONTINUOUS TRANSVERSE DENSITY DISTRIBUTIONS

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

Yu, Hui; Li, Bo; Chen, Shao-Xia

2015-11-20

We examine the influence of a continuous density structuring transverse to coronal slabs on the dispersive properties of fundamental standing kink and sausage modes supported therein. We derive generic dispersion relations (DRs) governing linear fast waves in pressureless straight slabs with general transverse density distributions, and focus on cases where the density inhomogeneity takes place in a layer of arbitrary width and in arbitrary form. The physical relevance of the solutions to the DRs is demonstrated by the corresponding time-dependent computations. For all profiles examined, the lowest order kink modes are trapped regardless of longitudinal wavenumber k. A continuous density distribution introducesmore » a difference to their periods of ≲13% when k is the observed range relative to the case where the density profile takes a step function form. Sausage modes and other branches of kink modes are leaky at small k, and their periods and damping times are heavily influenced by how the transverse density profile is prescribed, in particular the length scale. These modes have sufficiently high quality to be observable only for physical parameters representative of flare loops. We conclude that while the simpler DR pertinent to a step function profile can be used for the lowest order kink modes, the detailed information on the transverse density structuring needs to be incorporated into studies of sausage modes and higher order kink modes.« less

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.

Electron transport in ultra-thin films and ballistic electron emission microscopy

NASA Astrophysics Data System (ADS)

Claveau, Y.; Di Matteo, S.; de Andres, P. L.; Flores, F.

2017-03-01

We have developed a calculation scheme for the elastic electron current in ultra-thin epitaxial heterostructures. Our model uses a Keldysh’s non-equilibrium Green’s function formalism and a layer-by-layer construction of the epitaxial film. Such an approach is appropriate to describe the current in a ballistic electron emission microscope (BEEM) where the metal base layer is ultra-thin and generalizes a previous one based on a decimation technique appropriated for thick slabs. This formalism allows a full quantum mechanical description of the transmission across the epitaxial heterostructure interface, including multiple scattering via the Dyson equation, which is deemed a crucial ingredient to describe interfaces of ultra-thin layers properly in the future. We introduce a theoretical formulation needed for ultra-thin layers and we compare with results obtained for thick Au(1 1 1) metal layers. An interesting effect takes place for a width of about ten layers: a BEEM current can propagate via the center of the reciprocal space (\\overlineΓ ) along the Au(1 1 1) direction. We associate this current to a coherent interference finite-width effect that cannot be found using a decimation technique. Finally, we have tested the validity of the handy semiclassical formalism to describe the BEEM current.

Geodynamic Evolution of Subduction to Collision to Escape in Central Anatolia From Surface to Mantle - Results From the CD-CAT Project

NASA Astrophysics Data System (ADS)

Darin, Michael

2017-04-01

Despite significant progress toward understanding the kinematics of modern tectonic escape in Anatolia, considerable uncertainty remains regarding the dynamics of the transition from collision to escape. Because of the relatively small size of the Anatolia microplate, regional-scale studies spanning the plate margins and interior are well-suited to investigate the driving forces and space-time evolution of this unique tectonic transition in collisional orogens. CD-CAT (Continental Dynamics-Central Anatolia Tectonics) is a five-year (2011-2016) project funded by the National Science Foundation (USA) designed to explore the surface-to-mantle dynamics of Anatolia during the Cenozoic subduction-collision-escape transition in central Anatolia. Our approach integrates results from a diversity of methods including: structural, stratigraphic, and geomorphic analyses; magnetostratigraphy; low-temperature thermochronometry; Ar/Ar geochronology; geochemistry; passive seismic experiments (71 stations over two years); magnetotellurics; and numerical modeling. The principal results from this project include: recognition of a margin-wide magmatic lull from 40-20 Ma, followed by a southwestward migration of the initiation of magmatism toward and within the Central Anatolia Volcanic Province (CAVP); an early Miocene switch from contraction/transpression to extension/transtension in the Kırşehir and Niǧde Massifs, while contraction changed to late Miocene strike-slip deformation east of the Central Anatolian fault zone (CAFZ); rain shadow development due to uplift of the central Taurides 11-5 Ma; thin to absent lithospheric mantle beneath central Anatolia; the lack of an Arabia slab shallower than 800 km depth; and a change in the Cyprus slab from horizontal beneath the central Taurides and apparently fragmented beneath the CAVP, to very steeply dipping beneath the eastern Isparta Angle. The CAFZ lies along part of the Inner Tauride Suture (ITS) and represents a fundamental inherited lithosphere-scale structure that has accommodated contrasting magnitudes and styles of deformation to the east and west since Arabia collision. The coincidence of a similarly NNE-oriented lower plate boundary (Africa COB) or STEP fault between the Cyprus and Arabia slabs may have amplified the role of the CAFZ in controlling differential upper plate deformation. These findings support the following tectonic scenario: the first stage involved late Eocene to early Miocene horizontal subduction of the Afro-Arabia slab from central Anatolia to the Zagros, culminating in the final suturing of the Taurides and Pontides in Anatolia. The second stage occurred during the Miocene and involved the segmentation of the downgoing slab at the longitude of the CAFZ to form the Arabia slab in the east and the Cyprus slab in the west. North of Arabia, early Miocene rollback and foundering of the Arabia slab resulted in widespread volcanism, slab delamination beneath the eastern Taurides and eventual break-off and rapid sinking into the lower mantle starting at 15-10 Ma. North of Cyprus, initial rollback, steepening and breakup of the Cyprus slab are recorded by early Miocene upper plate extension and exhumation, followed by middle Miocene voluminous CAVP magmatism and uplift of the southern Taurides margin. The final stage involved a transition from diffuse to localized strain along transcurrent structures that have facilitated the westward escape of Anatolia since the latest Miocene-Pliocene.

A numerical investigation of continental collision styles

NASA Astrophysics Data System (ADS)

Ghazian, Reza Khabbaz; Buiter, Susanne J. H.

2013-06-01

Continental collision after closure of an ocean can lead to different deformation styles: subduction of continental crust and lithosphere, lithospheric thickening, folding of the unsubducted continents, Rayleigh-Taylor (RT) instabilities and/or slab break-off. We use 2-D thermomechanical models of oceanic subduction followed by continental collision to investigate the sensitivity of these collision styles to driving velocity, crustal and lithospheric temperature, continental rheology and the initial density difference between the oceanic lithosphere and the asthenosphere. We find that these parameters influence the collision system, but that driving velocity, rheology and lithospheric (rather than Moho and mantle) temperature can be classified as important controls, whereas reasonable variations in the initial density contrast between oceanic lithosphere and asthenosphere are not necessarily important. Stable continental subduction occurs over a relatively large range of values of driving velocity and lithospheric temperature. Fast and cold systems are more likely to show folding, whereas slow and warm systems can experience RT-type dripping. Our results show that a continent with a strong upper crust can experience subduction of the entire crust and is more likely to fold. Accretion of the upper crust at the trench is feasible when the upper crust has a moderate to weak strength, whereas the entire crust can be scraped-off in the case of a weak lower crust. We also illustrate that weakening of the lithospheric mantle promotes RT-type of dripping in a collision system. We use a dynamic collision model, in which collision is driven by slab pull only, to illustrate that adjacent plates can play an important role in continental collision systems. In dynamic collision models, exhumation of subducted continental material and sediments is triggered by slab retreat and opening of a subduction channel, which allows upward flow of buoyant materials. Exhumation continues after slab break-off by reverse motion of the subducting plate (`eduction') caused by the reduced slab pull. We illustrate how a simple force balance of slab pull, slab push, slab bending, viscous resistance and buoyancy can explain the different collision styles caused by variations in velocity, temperature, rheology, density differences and the interaction with adjacent plates.

Along-strike Translation of a Fossil Slab Beneath California (Invited)

NASA Astrophysics Data System (ADS)

Forsyth, D. W.

2013-12-01

There are three places where subduction ceased before a spreading ridge was consumed at a trench, leaving behind remnant microplates that were incorporated into the non-subducting oceanic plate. In the cases of the Phoenix plate off the Antarctic peninsula and the Guadalupe and Magdalena microplates off Baja California, fossil slabs still attached to the microplates have been traced into the asthenosphere using seismological techniques. Apparently deep subducting plates can tear off from the surface plate leaving behind fossil pieces of young oceanic lithosphere extending 100 km or more into the asthenosphere. The young slab fragments may be close to neutral buoyancy with their asthenospheric surroundings. In the case of the Monterey microplate off central California, now part of the Pacific plate, oceanic crust has been traced beneath the continental margin using active source seismology. Nicholson et al. (1994) suggested that the translation of the Monterey microplate under North America dragged bits of the overriding plate with it, causing the rotation of the Transverse Ranges in southern California. They also suggested that the San Andreas initiated as a low angle fault between the overriding North American plate and the subducted Monterey plate. There is a gap in coastal, post-subduction volcanic activity opposite the microplate, perhaps because a slab window never formed. A steeply dipping seismic anomaly, the Isabella anomaly, also lies opposite the microplate, probably indicating the continuation of the Monterey slab deep into the asthenosphere. Between the Isabella anomaly and the surface remnants of the Monterey microplate lies the aseismic, creeping section of the San Andreas fault, which we speculate may be caused by the migration of fluids from the subducted plate. The Monterey case differs from the Phoenix and Guadalupe cases in that the hypothesized fossil slab lies beneath the North American plate, which is translating relative to the Pacific/Monterey plate. We have shown that the fossil slab could translate with the Monterey plate with reasonable viscosity contrast with the surrounding asthenosphere.

Imaging the complex Farallon subduction system with USArray derived joint inversion of body waves and surface waves

NASA Astrophysics Data System (ADS)

Porritt, R. W.; Allen, R. M.; Pollitz, F. F.; Hung, S.

2012-12-01

The 150 million year history of subduction of the Farallon plate is being well elucidated by the passage of USArray. In this study, we use body wave relative delay times to generate independent P, SV, and SH relative velocity models for the USArray footprint. In addition, we use Rayleigh wave phase velocities derived from teleseismic earthquakes and ambient seismic noise to constrain the lithospheric structure where body waves have limited crossing ray information to form the SV-joint velocity model. The model volume contains a complex series of high velocities mostly along a planar front representing the remnants of the Farallon plate system. This feature has significant lateral and radial extent; beginning off the western coast of the US and terminating east of the model resolution, which goes to the Mississippi river. The bottom of the slab is well imaged through the mantle transition zone to at least 1000km. However, low velocity anomalies within this plane show the slab is far from a continuous sheet. Low velocities break up the slab into several major provinces, relating to different ages of orogens and an episode of flat slab subduction. Additionally, high velocities are often imaged well above the trace of the top of the slab with similar anomaly amplitude and dip as the main slab. While many of these anomalies have been interpreted as mantle drips, the similarity to the slab suggests a possible subduction origin for the features. However, the relatively shallow depths of these features require some mechanism of differentiation to develop neutral buoyancy. The prevalence of these high velocities, such as the Siletzia Curtain, Isabella Anomaly, Nevada Anomaly, and a newly imaged feature under southwest Texas, suggests a differentiation mechanism is fairly common among plates subducting under North America allowing for the observation of widespread shallow high velocity anomalies.

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.

Reconciling the geological history of western Turkey with plate circuits and mantle tomography

NASA Astrophysics Data System (ADS)

van Hinsbergen, Douwe J. J.; Kaymakci, Nuretdin; Spakman, Wim; Torsvik, Trond H.

2010-09-01

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 ~ 95-90 Myr 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 Tavşanlı 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 ~ 50 Ma, 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 35 Ma. 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.

Tomographic Imaging of the Lesser Antilles Subducted Slab and its Significance for Estimating the Age and Amount of Eastward Motion of the Overriding Caribbean Plate

NASA Astrophysics Data System (ADS)

Mann, P.; Chen, Y. W.; Wu, J.; Suppe, J.

2017-12-01

The idea of a Pacific-derived and eastward-transported Caribbean and Scotia plates was first proposed by J. Tuzo Wilson in 1966. Wilson proposed that the motion of these two, small plates was analogous to "ice rafting" observed on frozen lakes and oceans when a narrow ( 50 m) strip of ice is forced over a lower plate of ice. In the Caribbean the upper plate corresponds to the 750 km-long, north-south length of the Lesser Antilles volcanic arc ranging in thickness from 20-30 km while its subducting plate is Atlantic Cretaceous oceanic crust of 8-10 km thickness and subducting at an angle of 45º to a depth of 300 km into the mantle. We estimated the length of the Lesser Antilles slab from MIT P-wave global tomography (MITP08; Li et al., 2008) and compared to published transects from Utrecht UUP-07 global tomography (van Bentham et al., 2013). The measured slab lengths vary from 1550 km (Utrecht) to 1250 km (MIT). We then unfolded both slabs to the Earth's surface, and used GPlates to restore the leading edge of the Caribbean plate at the time of the Lesser Antilles slab's initial subduction. The Middle Eocene (49 Ma) reconstruction realigns the proto-Lesser Antilles arc and leading edge of the Caribbean plate in a continuous arc with older arc rocks in Cuba. During this Middle Eocene period of abrupt tectonic transition, the Cuban arc segment was terminated on its northeastward path by collision with the Bahama carbonate platform with subsequent reorientation onto its present, east-west path into the central Atlantic Ocean from 49-0 Ma. This collision/plate reorientation event is independently recorded by: 1) a poorly defined Greater Antilles slab seen on tomography that is aligned with the Cuban arc; 2) identical initiation ages of 49 Ma for the Cayman trough pull-apart and the Lesser Antilles slab; and 3) similarity in lengths for the length of the subducted, Lesser Antilles slab ( 1250-1550 km) and the length of the Cayman trough pull-apart basin ( 1100 km). East-west-trending, velocity anomalies observed at depths of 0-550 km, near the centerline of the subducted Lesser Antilles slab, and extending 1000 km west beneath the Caribbean plate appear to be downdip extensions of orthogonally-subducted, Central Atlantic fracture ones that have allowed the mantle to rise through an east-west-trending slab tear.

XAS Study at Mo and Co K-Edges of the Sulfidation of a CoMo / Al2O3 Hydrotreating Catalyst

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

Pichon, C.; Gandubert, A. D.; Legens, C.

2007-02-02

Because of its impact on environment, the removal of sulfur is an indispensable step, called hydrotreatment, in the refining of petroleum. One of the most commonly used hydrotreating catalysts is CoMo-type catalyst which is composed of molybdenum disulfide slabs promoted by cobalt atoms (CoMoS phase) and well dispersed on a high specific area alumina. As far as the highest sulfur content allowed in gasoline and diesel is continually decreasing, more and more efficient and active hydrotreating catalysts are required. In order to optimize the reactivity of the CoMo-type catalyst in hydrotreatment, a better understanding of the processes used to producemore » the active phase (CoMoS slabs) of the catalyst is necessary. The study reported here deals with the sulfiding mechanism of the slabs and the influence of temperature on the phenomenon. Ex situ X-ray absorption spectroscopy (XANES and EXAFS) was used to study the evolution of the structure of CoMo-type catalyst sulfided at various temperatures (from 293 to 873 K). XAS analysis was performed at both molybdenum and cobalt K-edges to obtain a cross-characterization of the sulfidation of the slabs. It evidenced the formation of various compounds, including two molybdenum oxides, MoS3 (or MoS3-like compound) and Co9S8, at specific steps of the sulfiding process. It showed the role of intermediate played by MoS3 (or MoS3-like compound) during the formation of the slabs and the competition between the appearance of promoted slabs (CoMoS phase) and Co9S8. At last, it leaded to the proposal of a mechanism for the sulfidation of the catalyst.« less

Seismicity Structure of the Downgoing Nazca Slab in Northern Chile

NASA Astrophysics Data System (ADS)

Sippl, C.; Schurr, B.

2017-12-01

We applied an automatized earthquake detection and location algorithm to 8 years of continuous seismic data from the IPOC network in Northern Chile, located in the forearc between about 18.5°S and 24°S. The resulting seismicity catalog contains more than 113k double-difference relocated earthquake hypocenters and features a completeness magnitude around 2.8. Despite the occurrence of two megathrust earthquakes with vigorous aftershock seismicity in the studied time period (the 2007 Tocopilla and the 2014 Iquique earthquakes), >60% of the retrieved seismicity is located in a highly active band of intermediate-depth earthquakes (80-120 km deep) within the downgoing Nazca slab.We obtain a triple seismic zone in the updip part of the slab, with the three parallel dipping planes corresponding to the plate interface, the oceanic Moho (ca. 8 km below the interface) and a third band in the mantle lithosphere 26-28 km beneath the slab top. The plate interface seismicity terminates abruptly at a depth of 55 km. At about 80-90 km depth, the remaining two planes of seismicity then merge into the single, 20 km thick cluster of vigorous seismicity mentioned above, which terminates at 120 km depth. This cluster is located directly beneath the volcanic arc and shows a pronounced kink in the slab dipping angle. Intra-slab seismicity is most likely related to metamorphic dehydration reactions, hence our high-resolution earthquake distribution can be considered a map of metamorphic reactions (although a possibly incomplete one, since not all reactions necessarily invoke seismicity). By correlating this distribution with isotherms from thermal models as well as geophysical imaging results from previous studies, we attempt to get a glimpse at the processes that produce the different patches of intraslab seismicity at intermediate depths.

A field experiment on the controls of sediment transport on bedrock erosion

NASA Astrophysics Data System (ADS)

Beer, A. R.; Turowski, J. M.; Fritschi, B.; Rieke-Zapp, D.; Campana, L.; Lavé, J.

2012-12-01

The earth`s surface is naturally shaped by interactions of physical and chemical processes. In mountainous regions with steep topography river incision fundamentally controls the geomorphic evolution of the whole landscape. There, erosion of exposed bedrock sections by fluvial sediment transport is an important mechanism forming mountain river channels. The links between bedload transport and bedrock erosion has been firmly established using laboratory experiments. However, there are only few field datasets linking discharge, sediment transport, impact energy and erosion that can be used for process understanding and model evaluation. To fill this gap, a new measuring setup has been commissioned to raise an appropriate simultaneous dataset of hydraulics, sediment transport and bedrock erosion at high temporal and spatial resolution. Two natural stone slabs were installed flush with the streambed of the Erlenbach, a gauged stream in the Swiss Pre-Alps. They are mounted upon force sensors recording vertical pressure und downstream shear caused by passing sediment particles. The sediment transport rates can be assessed using geophone plates and an automated moving basket system taking short-term sediment samples. These devices are located directly downstream of the stone slabs. Bedrock erosion rates are measured continuously with erosion sensors at sub-millimeter accuracy at three points on each slab. In addition, the whole slab topography is surveyed with photogrammetry and a structured-light 3D scanner after individual flood events. Since the installation in 2011, slab bedrock erosion has been observed during several transport events. We discuss the relation between hydraulics, bedload transport, resulting pressure forces on the stone slabs and erosion rates. The aim of the study is the derivation of an empirical process law for fluvial bedrock erosion driven by moving sediment particles.

Lithospheric structure of an incipient rift basin: Results from receiver function analysis of Bransfield Strait, NW Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Biryol, C. Berk; Lee, Stephen J.; Lees, Jonathan M.; Shore, Michael J.

2018-06-01

Bransfield Basin (BB), located northwest of the Antarctic Peninsula (AP) and southeast of the South Shetland Islands (SSI), is the most active section of the Antarctic continental margin. The region has long been (50 Ma) a convergent plate boundary where the Phoenix plate was subducting beneath the Antarctic Plate and is characterized by long-lived arc magmatism and accretion. However, the collision of the Antarctic-Phoenix spreading center with the subduction front near SSI (ca. 4 Ma) gave way to the opening of slab windows and dramatic decrease in the subduction rate of the Phoenix plate beneath AP and SSI. Consequently, the Phoenix slab began to rollback slowly along the South Shetland Trench (SST), giving way to slow extension in the back-arc region and rifting along the BB. Although there is consensus on the factors that control the current deformation and extension of the BB, the origin of the BB and the tectonic configuration of the basin are still unclear. Most of the controversy stems from uncertainties regarding the crustal thickness of the BB. Hence, we computed teleseismic receiver functions for 10 broadband stations in the region that belong to existing permanent and temporary deployments in order obtain robust constraints on the lithospheric structure and crustal thickness of the BB, as well as the AP and SSI. Our results indicate that the crust is thinning from 30 km to 26 km from the AP towards the South Shetland trench and Central BB showing the asymmetrical character of the rift basin. The crustal thickness and Vp/Vs variations are less pronounced along the AP but very significant across the SSB indicating the lithospheric scale segmentation of the South Shetland Block (SSB) and the incipient rift basin under the control of the opening of slab window and the roll-back of stalled Phoenix slab. High Vp/Vs ratios (∼1.9) beneath BB and SSI, agree well with the nascent rift character of BB, the presence of a steep Phoenix slab and consequently a wider mantle wedge characterized by the presence of underplating partial melts beneath SSI and BB.

Tomography reveals buoyant asthenosphere accumulating beneath the Juan de Fuca plate.

PubMed

Hawley, William B; Allen, Richard M; Richards, Mark A

2016-09-23

The boundary between Earth's strong lithospheric plates and the underlying mantle asthenosphere corresponds to an abrupt seismic velocity decrease and electrical conductivity increase with depth, perhaps indicating a thin, weak layer that may strongly influence plate motion dynamics. The behavior of such a layer at subduction zones remains unexplored. We present a tomographic model, derived from on- and offshore seismic experiments, that reveals a strong low-velocity feature beneath the subducting Juan de Fuca slab along the entire Cascadia subduction zone. Through simple geodynamic arguments, we propose that this low-velocity feature is the accumulation of material from a thin, weak, buoyant layer present beneath the entire oceanic lithosphere. The presence of this feature could have major implications for our understanding of the asthenosphere and subduction zone dynamics. Copyright © 2016, American Association for the Advancement of Science.

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

Enhancement of the transverse magneto-optical Kerr effect via resonant tunneling in trilayers containing magneto-optical metals

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

Girón-Sedas, J. A.; Centro de Investigación e Innovación en Bioinformática y Fotónica - CIBioFI, AA 25360 Cali; Mejía-Salazar, J. R., E-mail: jrmejia3146@gmail.com

We propose a way to enhance the transverse magneto-optical Kerr effect, by the excitation of resonant tunneling modes, in subwavelength trilayer structures featuring a dielectric slab sandwiched between two magneto-optical metallic layers. Depending on the magneto-optical layer widths, the proposed system may exhibit an extraordinary transverse magneto-optical Kerr effect, which makes it very attractive for the design and engineering of thin-film magneto-optical-based devices for future photonic circuits or fiber optical-communication systems.

SKS splitting results in central Italy and Dinaric region inside the AlpArray-CASE project

NASA Astrophysics Data System (ADS)

Salimbeni, S.; Prevolnik, S.; Pondrelli, S.; Molinari, I.; Stipcevic, J.; Kissling, E.; Šipka, V.; Herak, M.

2017-12-01

In the framework of the AlpArray project (AlpArray Seismic Network, 2015), the complementary "Central Adriatic Seismic Experiment" (CASE; AlpArray Seismic Network, 2016) was established as collaboration between ETH Zürich, University of Zagreb, INGV and Republic Hydrometeorological Service of Republic of Srpska. The CASE project consists of 9 temporary stations, installed in October 2016, located in Bosnia and Herzegovina, Croatia and Italy. Temporary broadband seismic stations, with the permanent stations present in the region shared by the Croatian Seismological Service and INGV, make an almost continuous transect cutting the Central-Southern Appenines, the central Adriatic region, central External Dinarides and finishing at the eastern margin of the Internal Dinarides. The presence of the the Apenninic and Dinarides slabs, verging in opposite directions and plunging along the opposite sides of the Adriatic plate, make this area a peculiar spot to understand the complex dynamic of the region. Various tomographic images (e.g. Bijwaard and Spakman, 2000; Piromallo and Morelli, 2003) shows not continuous slabs under the Appenines and the Dinarides, suggesting the presence of slab-gaps right beneath the region covered by the CASE experiment. Here we present the preliminary results of the SKS splitting analysis performed on the data recorded by the temporary and permanent seismic stations included in the CASE project. The new results, in combination with previous interpretation, will provide clues about how Northern and Southern Apennines are connected at depth, how the slab rollback of the Apennines thrust belt acted and if and how the Apennines are in relation with the Dinaric region. Together with the measurements from previous studies and from the AlpArray project, our new data will support the mapping of the seismic anisotropy deformation pattern from Western Alps to Pannonian region.

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.

Role of rheology in reconstructing slab morphology in global mantle models

NASA Astrophysics Data System (ADS)

Bello, Léa; Coltice, Nicolas; Tackley, Paul; Müller, Dietmar

2015-04-01

Reconstructing the 3D structure of the Earth's mantle has been a challenge for geodynamicists for about 40 years. Although numerical models and computational capabilities have incredibly progressed, parameterizations used for modeling convection forced by plate motions are far from being Earth-like. Among the set of parameters, rheology is fundamental because it defines in a non-linear way the dynamics of slabs and plumes, and the organization of the lithosphere. Previous studies have employed diverse viscosity laws, most of them being temperature and depth dependent with relatively small viscosity contrasts. In this study, we evaluate the role of the temperature dependence of viscosity (variations up to 6 orders of magnitude) on reconstructing slab evolution in 3D spherical models of convection driven by plate history models. We also investigate the importance of pseudo-plasticity in such models. We show that strong temperature dependence of viscosity combined with pseudo-plasticity produce laterally and vertically continuous slabs, and flat subduction where trench retreat is fast (North, Central and South America). Moreover, pseudo-plasticity allows a consistent coupling between imposed plate motions and global convection, which is not possible with temperature-dependent viscosity only. However, even our most sophisticated model is not able to reproduce unambiguously stagnant slabs probably because of the simplicity of material properties we use here. The differences between models employing different viscosity laws are very large, larger than the differences between two models with the same rheology but using two different plate reconstructions or initial conditions.

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.

Artifacts in slab average-intensity-projection images reformatted from JPEG 2000 compressed thin-section abdominal CT data sets.

PubMed

Kim, Bohyoung; Lee, Kyoung Ho; Kim, Kil Joong; Mantiuk, Rafal; Kim, Hye-ri; Kim, Young Hoon

2008-06-01

The objective of our study was to assess the effects of compressing source thin-section abdominal CT images on final transverse average-intensity-projection (AIP) images. At reversible, 4:1, 6:1, 8:1, 10:1, and 15:1 Joint Photographic Experts Group (JPEG) 2000 compressions, we compared the artifacts in 20 matching compressed thin sections (0.67 mm), compressed thick sections (5 mm), and AIP images (5 mm) reformatted from the compressed thin sections. The artifacts were quantitatively measured with peak signal-to-noise ratio (PSNR) and a perceptual quality metric (High Dynamic Range Visual Difference Predictor [HDR-VDP]). By comparing the compressed and original images, three radiologists independently graded the artifacts as 0 (none, indistinguishable), 1 (barely perceptible), 2 (subtle), or 3 (significant). Friedman tests and exact tests for paired proportions were used. At irreversible compressions, the artifacts tended to increase in the order of AIP, thick-section, and thin-section images in terms of PSNR (p < 0.0001), HDR-VDP (p < 0.0001), and the readers' grading (p < 0.01 at 6:1 or higher compressions). At 6:1 and 8:1, distinguishable pairs (grades 1-3) tended to increase in the order of AIP, thick-section, and thin-section images. Visually lossless threshold for the compression varied between images but decreased in the order of AIP, thick-section, and thin-section images (p < 0.0001). Compression artifacts in thin sections are significantly attenuated in AIP images. On the premise that thin sections are typically reviewed using an AIP technique, it is justifiable to compress them to a compression level currently accepted for thick sections.

Reduction of Bridge Deck Cracking through Alternative Material Usage

DOT National Transportation Integrated Search

2017-12-01

ODOT routinely deploys a large number of continuous span structural slab bridges. Despite being designed to strictly satisfy all the relevant AASHTO and ODOT BDM requirements, many such bridge decks show transverse cracks, with widths greater than th...

S-to-P Conversions from Mid-mantle Slow Scatterers in Slab Regions: Observations of Deep/Stagnated Oceanic Crust?

NASA Astrophysics Data System (ADS)

He, Xiaobo; Zheng, Yixian

2018-02-01

The fate of a subducted slab is a key ingredient in the context of plate tectonics, yet it remains enigmatic especially in terms of its crustal component. In this study, our efforts are devoted to resolve slab-related structures in the mid-mantle below eastern Indonesia, the Izu-Bonin region, and the Peru area by employing seismic array analysing techniques on high-frequency waveform data from F-net in Japan and the Alaska regional network and the USArray in North America. A pronounced arrival after the direct P wave is observed in the recordings of four deep earthquakes (depths greater than 400 km) from three subduction systems including the Philippines, the Izu-Bonin, and the Peru. This later arrival displays a slightly lower slowness compared to the direct P wave and its back-azimuth deviates somewhat from the great-circle direction. We explain it as an S-to-P conversion at a deep scatterer below the sources in the source region. In total, five scatterers are seen at depths ranging from 930 to 1500 km. Those scatterers appear to be characterised by an 7 km-thick low-velocity layer compared to the ambient mantle. Combined evidence from published mineral physical analysis suggests that past subducted oceanic crust, possibly fragmented, is most likely responsible for these thin-layer compositional heterogeneities trapped in the mid-mantle beneath the study regions. Our observations give a clue to the potential fate of subducted oceanic crust.

Observation of reflected electrons driven quasi- longitudinal (QL) whistlers in large laboratory plasma

NASA Astrophysics Data System (ADS)

Sanyasi, A. K.; Awasthi, L. M.; Srivastava, P. K.; Mattoo, S. K.; Sharma, D.; Singh, R.; Paikaray, R.; Kaw, P. K.

2017-10-01

This paper reports experimental and theoretical investigations on plasma turbulence in the source plasma of a Large Volume Plasma Device. It is shown that a highly asymmetrical localized thin rectangular slab of strong plasma turbulence is excited by loss cone instability. The position of the slab coincides with the injection line of the primary ionizing energetic electrons. Outside the slab, in the core, the turbulence is weaker by a factor of 30 . The plasma turbulence consists of oblique [ θ=tan-1(k⊥/k||)≈87 ° ] Quasi-Longitudinal (QL) electromagnetic whistlers in a broad band of 40 kHz

Delta-Ferrite Distribution in a Continuous Casting Slab of Fe-Cr-Mn Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Chen, Chao; Cheng, Guoguang

2017-10-01

The delta-ferrite distribution in a continuous casting slab of Fe-Cr-Mn stainless steel grade (200 series J4) was analyzed. The results showed that the ferrite fraction was less than 3 pct. The "M" type distribution was observed in the thickness direction. For the distribution at the centerline, the maximum ferrite content was found in the triangular zone of the macrostructure. In addition, in this zone, the carbon and sulfur were severely segregated. Furthermore, an equilibrium solidification calculation by Thermo-Calc® software indicates that the solidification mode of the composition in this triangular zone is the same as the solidification mode of the averaged composition, i.e., the FA (ferrite-austenite) mode. None of the nickel-chromium equivalent formulas combined with the Schaeffler-type diagram could predict the ferrite fraction of the Cr-Mn stainless steel grade in a reasonable manner. The authors propose that more attention should be paid to the development of prediction models for the ferrite fraction of stainless steels under continuous casting conditions.

Automatic detection of pulmonary nodules at spiral CT: first clinical experience with a computer-aided diagnosis system

NASA Astrophysics Data System (ADS)

Wormanns, Dag; Fiebich, Martin; Wietholt, Christian; Diederich, Stefan; Heindel, Walter

2000-06-01

We evaluated the practical application of a Computer-Aided Diagnosis (CAD) system for viewing spiral computed tomography (CT) of the chest low-dose screening examinations which includes an automatic detection of pulmonary nodules. A UNIX- based CAD system was developed including a detection algorithm for pulmonary nodules and a user interface providing an original axial image, the same image with nodules highlighted, a thin-slab MIP, and a cine mode. As yet, 26 CT examinations with 1625 images were reviewed in a clinical setting and reported by an experienced radiologist using both the CAD system and hardcopies. The CT studies exhibited 19 nodules found on the hardcopies in consensus reporting of 2 experienced radiologists. Viewing with the CAD system was more time consuming than using hardcopies (4.16 vs. 2.92 min) due to analyzing MIP and cine mode. The algorithm detected 49% (18/37) pulmonary nodules larger than 5 mm and 30% (21/70) of all nodules. It produced an average of 6.3 false positive findings per CT study. Most of the missed nodules were adjacent to the pleura. However, the program detected 6 nodules missed by the radiologists. Automatic nodule detection increases the radiologists's awareness of pulmonary lesions. Simultaneous display of axial image and thin-slab MIP makes the radiologist more confident in diagnosis of smaller pulmonary nodules. The CAD system improves the detection of pulmonary nodules at spiral CT. Lack of sensitivity and specificity is still an issue to be addressed but does not prevent practical use.

The subresolution DaTSCAN phantom: a cost-effective, flexible alternative to traditional phantom technology.

PubMed

Taylor, Jonathan C; Vennart, Nicholas; Negus, Ian; Holmes, Robin; Bandmann, Oliver; Lo, Christine; Fenner, John

2018-03-01

The Alderson striatal phantom is frequently used to assess I-FP-CIT (Ioflupane) image quality and to test semi-quantification software. However, its design is associated with a number of limitations, in particular: unrealistic image appearances and inflexibility. A new physical phantom approach is proposed on the basis of subresolution phantom technology. The design incorporates thin slabs of attenuating material generated through additive manufacturing, and paper sheets with radioactive ink patterns printed on their surface, created with a conventional inkjet printer. The paper sheets and attenuating slabs are interleaved before scanning. Use of thin layers ensures that they cannot be individually resolved on reconstructed images. An investigation was carried out to demonstrate the performance of such a phantom in producing simplified I-FP-CIT uptake patterns. Single photon emission computed tomography imaging was carried out on an assembled phantom designed to mimic a healthy patient. Striatal binding ratio results and linear striatal dimensions were calculated from the reconstructed data and compared with that of 22 clinical patients without evidence of Parkinsonian syndrome, determined from clinical follow-up. Striatal binding ratio results for the fully assembled phantom were: 3.1, 3.3, 2.9 and 2.6 for the right caudate, left caudate, right putamen and right caudate, respectively. All were within two SDs of results derived from a cohort of clinical patients. Medial-lateral and anterior-posterior dimensions of the simulated striata were also within the range of values seen in clinical data. This work provides the foundation for the generation of a range of more clinically realistic, physical phantoms.

The feeder system of the Toba supervolcano from the slab to the shallow reservoir

PubMed Central

Koulakov, Ivan; Kasatkina, Ekaterina; Shapiro, Nikolai M.; Jaupart, Claude; Vasilevsky, Alexander; El Khrepy, Sami; Al-Arifi, Nassir; Smirnov, Sergey

2016-01-01

The Toba Caldera has been the site of several large explosive eruptions in the recent geological past, including the world's largest Pleistocene eruption 74,000 years ago. The major cause of this particular behaviour may be the subduction of the fluid-rich Investigator Fracture Zone directly beneath the continental crust of Sumatra and possible tear of the slab. Here we show a new seismic tomography model, which clearly reveals a complex multilevel plumbing system beneath Toba. Large amounts of volatiles originate in the subducting slab at a depth of ∼150 km, migrate upward and cause active melting in the mantle wedge. The volatile-rich basic magmas accumulate at the base of the crust in a ∼50,000 km3 reservoir. The overheated volatiles continue ascending through the crust and cause melting of the upper crust rocks. This leads to the formation of a shallow crustal reservoir that is directly responsible for the supereruptions. PMID:27433784

Slab-plume interaction beneath the Pacific Northwest

NASA Astrophysics Data System (ADS)

Obrebski, Mathias; Allen, Richard M.; Xue, Mei; Hung, Shu-Huei

2010-07-01

The Pacific Northwest has undergone complex plate reorganization and intense tectono-volcanic activity to the east during the Cenozoic (last 65 Ma). Here we show new high-resolution tomographic images obtained using shear and compressional data from the ongoing USArray deployment that demonstrate first that there is a continuous, whole-mantle plume beneath the Yellowstone Snake River Plain (YSRP) and second, that the subducting Juan de Fuca (JdF) slab is fragmented and even absent beneath Oregon. The analysis of the geometry of our tomographic models suggests that the arrival and emplacement of the large Yellowstone plume had a substantial impact on the nearby Cascadia subduction zone, promoting the tearing and weakening of the JdF slab. This interpretation also explains several intriguing geophysical properties of the Cascadia trench that contrast with most other subduction zones, such as the absence of deep seismicity and the trench-normal fast direction of mantle anisotropy. The DNA velocity models are available for download and slicing at http://dna.berkeley.edu.

Water Adsorption on Clean and Defective Anatase TiO2 (001) Nanotube Surfaces: A Surface Science Approach.

PubMed

Kenmoe, Stephane; Lisovski, Oleg; Piskunov, Sergei; Bocharov, Dmitry; Zhukovskii, Yuri F; Spohr, Eckhard

2018-05-31

We use ab initio molecular dynamics simulations to study the adsorption of thin water films with 1 and 2 ML coverage on anatase TiO 2 (001) nanotubes. The nanotubes are modeled as 2D slabs, which consist of partially constrained and partially relaxed structural motifs from nanotubes. The effect of anion doping on the adsorption is investigated by substituting O atoms with N and S impurities on the nanotube slab surface. Due to strain-induced curvature effects, water adsorbs molecularly on defect-free surfaces via weak bonds on Ti sites and H bonds to surface oxygens. While the introduction of an S atom weakens the interaction of the surface with water, which adsorbs molecularly, the presence of an N impurity renders the surface more reactive to water, with a proton transfer from the water film and the formation of an NH group at the N site. At 2 ML coverage, a further surface-assisted proton transfer takes place in the water film, resulting in the formation of an OH - group and an NH 2 + cationic site on the surface.

Detection of nanoscale embedded layers using laboratory specular X-ray diffraction

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

Beekman, Matt, E-mail: matt.beekman@oit.edu; Rodriguez, Gabriel; Atkins, Ryan

Unusual specular X-ray diffraction patterns have been observed from certain thin film intergrowths of metal monochalcogenide (MX) and transition metal dichalcogenide (TX{sub 2}) structures. These patterns exhibit selective “splitting” or broadening of selected (00l) diffraction peaks, while other (00l) reflections remain relatively unaffected [Atkins et al., Chem. Mater. 24, 4594 (2012)]. Using a simplified optical model in the kinematic approximation, we illustrate that these peculiar and somewhat counterintuitive diffraction features can be understood in terms of additional layers of one of the intergrowth components, MX or TX{sub 2}, interleaved between otherwise “ideal” regions of MX-TX{sub 2} intergrowth. The interpretation ismore » in agreement with scanning transmission electron microscope imaging, which reveals the presence of such stacking “defects” in films prepared from non-ideal precursors. In principle, the effect can be employed as a simple, non-destructive laboratory probe to detect and characterize ultrathin layers of one material, e.g., 2-dimensional crystals, embedded between two slabs of a second material, effectively using the two slabs as a highly sensitive interferometer of their separation distance.« less

Optimal width of quasicrystalline slabs of dielectric cylinders to microwave radiation transmission contrast

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

Andueza, Ángel; Sevilla, Joaquín; Smart Cities Institute, Universidad Pública de Navarra, 31006 Pamplona

2016-08-28

Light confinement induced by resonant states in aperiodic photonic structures is interesting for many applications. A particular case of these resonances can be found in 2D quasicrystalline arrangements of dielectric cylinders. These systems present a rather isotropic band gap as well as isolated in-gap photonic states (as a result of spatially localized resonances). These states are built by high symmetry polygonal clusters that can be regarded as photonic molecules. In this paper, we study the transmission properties of a slab of glass cylinders arranged in approximants of the decagonal quasicrystalline structure. In particular, we investigate the influence of the slabmore » width in the transmission contrast between the states and the gap. The study is both experimental and numerical in the microwave regime. We find that the best transmission contrast is found for a width of around three times the radiation wavelength. The transmission in the band gap region is mediated by the resonances of the photonic molecules. If the samples are thin enough, they become transparent except around a resonance of the photonic molecule which reflects the incoming light.« less

3-D electrical structure across the Yadong-Gulu rift revealed by magnetotelluric data: New insights on the extension of the upper crust and the geometry of the underthrusting Indian lithospheric slab in southern Tibet

NASA Astrophysics Data System (ADS)

Wang, Gang; Wei, Wenbo; Ye, Gaofeng; Jin, Sheng; Jing, Jianen; Zhang, Letian; Dong, Hao; Xie, Chengliang; Omisore, Busayo O.; Guo, Zeqiu

2017-09-01

The approximately north-south trending Cenozoic Yadong-Gulu rift (YGR) in the eastern Lhasa block is an ideal location to investigate the extensional kinematic mechanism of the upper crust and the deformation characteristics of the Indian lithospheric slab in southern Tibet. The magnetotelluric (MT) method has been widely used in probing subsurface structures at lithospheric scale and is sensitive to high electrically conductive body (conductor). A three-dimensional (3-D) inversion of MT data was conducted to derive the east-west electrical structures across the northern segment of the YGR. The result reveals that the conductors in the middle crust are not continuous in the east-west direction. The deep conductor underneath the YGR is interpreted to result from the tearing of the Indian lithospheric slab. The upper crust to the east of the YGR is significantly intruded by underlying conductors. Based on the features of the 3-D inversion result from this study and other geophysical observations, the formation of the YGR is most likely caused by tearing of the Indian lithospheric slab through the pull of mid-lower crustal conductors that have locally weak strength beneath the YGR.

Dynamic analysis of slab track on multi-layered transversely isotropic saturated soils subjected to train loads

NASA Astrophysics Data System (ADS)

Zhan, Yongxiang; Yao, Hailin; Lu, Zheng; Yu, Dongming

2014-12-01

The dynamic responses of a slab track on transversely isotropic saturated soils subjected to moving train loads are investigated by a semi-analytical approach. The track model is described as an upper Euler beam to simulate the rails and a lower Euler beam to model the slab. Rail pads between the rails and slab are represented by a continuous layer of springs and dashpots. A series of point loads are formulated to describe the moving train loads. The governing equations of track-ground systems are solved using the double Fourier transform, and the dynamic responses in the time domain are obtained by the inverse Fourier transform. The results show that a train load with high velocity will generate a larger response in transversely isotropic saturated soil than the lower velocity load, and special attention should be paid on the pore pressure in the vicinity of the ground surface. The anisotropic parameters of a surface soil layer will have greater influence on the displacement and excess pore water pressure than those of the subsoil layer. The traditional design method taking ground soil as homogeneous isotropic soil is unsafe for the case of RE < 1 and RG < 1, so a transversely isotropic foundation model is of great significance to the design for high train velocities.

Wave propagation through a flexoelectric piezoelectric slab sandwiched by two piezoelectric half-spaces.

PubMed

Jiao, Fengyu; Wei, Peijun; Li, Yueqiu

2018-01-01

Reflection and transmission of plane waves through a flexoelectric piezoelectric slab sandwiched by two piezoelectric half-spaces are studied in this paper. The secular equations in the flexoelectric piezoelectric material are first derived from the general governing equation. Different from the classical piezoelectric medium, there are five kinds of coupled elastic waves in the piezoelectric material with the microstructure effects taken into consideration. The state vectors are obtained by the summation of contributions from all possible partial waves. The state transfer equation of flexoelectric piezoelectric slab is derived from the motion equation by the reduction of order, and the transfer matrix of flexoelectric piezoelectric slab is obtained by solving the state transfer equation. By using the continuous conditions at the interface and the approach of partition matrix, we get the resultant algebraic equations in term of the transfer matrix from which the reflection and transmission coefficients can be calculated. The amplitude ratios and further the energy flux ratios of various waves are evaluated numerically. The numerical results are shown graphically and are validated by the energy conservation law. Based on these numerical results, the influences of two characteristic lengths of microstructure and the flexoelectric coefficients on the wave propagation are discussed. Copyright © 2017 Elsevier B.V. All rights reserved.

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.

Close or not so close? Provenance studies of megalithic monuments from Alentejo (Portugal)

NASA Astrophysics Data System (ADS)

Boaventura, R.; Moita, P.

2012-04-01

There has been a significant amount of studies about megalithic tombs conducted in the Alentejo region. However the geological provenance of monoliths used in the construction of those tombs usually was not a priority among researchers with rare exceptions (Dehn, Kalb and Vortisch, 1991; Boaventura, 2000). Recent studies of dolmens (Oliveira, 1997 and 2006; Gonçalves, 2003) refer only to a brief characterization of rocks, such as "granite or schist slabs", highlighting certain types if the geological stratum is identical or not to the stone blocks. On the other hand, when the type of raw material appears to be similar with the bedrock, it is common and empirically assumed its local provenance. With the aim of testing and expand the knowledge about the provenance of the slabs used in the construction of megalithic tombs, several lithic samples from dolmen slabs and outcrops in their surroundings were collected for analysis and comparison. The samples were characterized by petrographic studies in thin section as well with a geochemical analyses performed by XRF that gives major elements as well some trace elements. The dolmens tested for this project are located roughly between the northeast to west of the town of Monforte (Upper region of Alentejo, Portugal) and are named, from south to north, as Serrinha, Rabuje group (1 to 5), Geodésico de Besteiros 3 and Velho. The field work and petrographic studies revealed that the slabs are constituted mainly by several types of granitoids (gnaissic, red, white, tonalitic), amphibolites and mottled schist shale. The comparison of chemical analyses between slabs and selected outcrops revealed that the provenances are in most of the cases from the nearby geological stratum. In fact, major elements (e.g. MgO, SiO2, CaO) as well trace elements (e.g. Sr, Y, Zr, Nb) compositions are similar on slab samples and in rocks from the outcrops. If in terms of major elements a similarity was already expectable, or easier to obtain, the trace elements (namely immobile elements such as Y or Nb) compositions corroborated that slabs and geological bedrock were alike. The capstone slab that covers the dolmen of Rabuje 1 group does not belong to the nearby geological stratum. Nevertheless, a probable matching source-outcrop was located sampled and characterized in terms of geochemistry and petrograpphy and compared with the megalithic capstone. This work allowed a better characterization of the rocks used in megalithic tombs as well as corroborat a pragmatic attitude of Neolithic populations in the search of the appropriate slabs for construction as proposed previously (Boaventura, 2000). When available, the megalithic stones were likely collected from the nearby stratum and therefore the distances traveled were small (in situ or less than 1-2 km). Nevertheless, when the type of stone needed was not available in the vicinity (e.g fracturing provided only smaller stones) it would be necessary to travel longer distances, up to 8 km (Boaventura, 2000), as in the case of the dolmen of Rabuje 1. Boaventura, R. (2000) - A geologia das Antas de Rabuje (Monforte, Alentejo), Revista Portuguesa de Arquelogia.Vol. 3;2.pp-15-23. Dehn, W. Kalb, P. and Vortich, W. (1991) - Geologisch-Petrographische Untersuchungen an Megalithgräbern Portugals. Madrider Mitteilungen, 32, p. 1-28. Oliveira, J. (1997) - Monumentos megalíticos da bacia hidrográfica do Rio Sever. Ibn Maruan. Castelo de Vide. Special Edition. Oliveira, J. (2006) - Património arqueológico da Coudelaria de Alter e as primeiras comunidades agropastoris. [Évora]: Colibri.

The hydrological cycle response to cirrus cloud thinning

NASA Astrophysics Data System (ADS)

Kristjánsson, Jón Egill; Muri, Helene; Schmidt, Hauke

2015-12-01

Recent multimodel studies have shown that if one attempts to cancel increasing CO2 concentrations by reducing absorbed solar radiation, the hydrological cycle will weaken if global temperature is kept unchanged. Using a global climate model, we investigate the hydrological cycle response to "cirrus cloud thinning (CCT)," which is a proposed climate engineering technique that seeks to enhance outgoing longwave radiation. Investigations of the "fast response" in experiments with fixed sea surface temperatures reveal that CCT causes a significant enhancement of the latent heat flux and precipitation. This is due to enhanced radiative cooling of the troposphere, which is opposite to the effect of increased CO2 concentrations. By combining CCT with CO2 increase in multidecadal simulations with a slab ocean, we demonstrate a systematic enhancement of the hydrological cycle due to CCT. This leads to enhanced moisture availability in low-latitude land regions and a strengthening of the Indian monsoon.

Microwave inversion of leaf area and inclination angle distributions from backscattered data

NASA Technical Reports Server (NTRS)

Lang, R. H.; Saleh, H. A.

1985-01-01

The backscattering coefficient from a slab of thin randomly oriented dielectric disks over a flat lossy ground is used to reconstruct the inclination angle and area distributions of the disks. The disks are employed to model a leafy agricultural crop, such as soybeans, in the L-band microwave region of the spectrum. The distorted Born approximation, along with a thin disk approximation, is used to obtain a relationship between the horizontal-like polarized backscattering coefficient and the joint probability density of disk inclination angle and disk radius. Assuming large skin depth reduces the relationship to a linear Fredholm integral equation of the first kind. Due to the ill-posed nature of this equation, a Phillips-Twomey regularization method with a second difference smoothing condition is used to find the inversion. Results are obtained in the presence of 1 and 10 percent noise for both leaf inclination angle and leaf radius densities.

Collapsing Radiative Shocks in Xenon Gas on the Omega Laser

NASA Astrophysics Data System (ADS)

Reighard, A. B.; Glendinning, S. G.; Knauer, J.; Bouquet, S.; Koenig, M.

2005-10-01

A number of astrophysical systems involve radiative shocks that collapse spatially in response to energy lost through radiation, producing thin shells believed to be Vishniac unstable. We report experiments intended to study such collapsing shocks. The Omega laser drives a thin slab of material at >100 km/s through Xe gas. Simulations predict a collapsed layer in which the density reaches 45 times initial density. X-ray backlighting techniques have yielded images of a collapsed shock compressed to <1/25 its initial thickness (45 μm) at a speed of ˜100 km/s when the shock has traveled 1.3 mm. Optical depth before and behind the shock is important for comparison to astrophysical systems. This research was sponsored by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Research Grants DE-FG52-03NA00064, DE-FG53-2005-NA26014, and other grants and contracts.

Random vibration analysis of train-bridge under track irregularities and traveling seismic waves using train-slab track-bridge interaction model

NASA Astrophysics Data System (ADS)

Zeng, Zhi-Ping; Zhao, Yan-Gang; Xu, Wen-Tao; Yu, Zhi-Wu; Chen, Ling-Kun; Lou, Ping

2015-04-01

The frequent use of bridges in high-speed railway lines greatly increases the probability that trains are running on bridges when earthquakes occur. This paper investigates the random vibrations of a high-speed train traversing a slab track on a continuous girder bridge subjected to track irregularities and traveling seismic waves by the pseudo-excitation method (PEM). To derive the equations of motion of the train-slab track-bridge interaction system, the multibody dynamics and finite element method models are used for the train and the track and bridge, respectively. By assuming track irregularities to be fully coherent random excitations with time lags between different wheels and seismic accelerations to be uniformly modulated, non-stationary random excitations with time lags between different foundations, the random load vectors of the equations of motion are transformed into a series of deterministic pseudo-excitations based on PEM and the wheel-rail contact relationship. A computer code is developed to obtain the time-dependent random responses of the entire system. As a case study, the random vibration characteristics of an ICE-3 high-speed train traversing a seven-span continuous girder bridge simultaneously excited by track irregularities and traveling seismic waves are analyzed. The influence of train speed and seismic wave propagation velocity on the random vibration characteristics of the bridge and train are discussed.

46 CFR 164.013-7 - Marking.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 6 2011-10-01 2011-10-01 false Marking. 164.013-7 Section 164.013-7 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL MATERIALS Foam, Unicellular Polyethylene (Buoyant, Slab, Slitted Trigonal Pattern...

46 CFR 164.013-7 - Marking.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 6 2010-10-01 2010-10-01 false Marking. 164.013-7 Section 164.013-7 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL MATERIALS Foam, Unicellular Polyethylene (Buoyant, Slab, Slitted Trigonal Pattern...

Experimental investigation of heat transfer and pressure drop characteristics of water and glycol-water mixture in multi-port serpentine microchannel slab heat exchangers

NASA Astrophysics Data System (ADS)

Khan, Md Mesbah-ul Ghani

Microchannels have several advantages over traditional large tubes. Heat transfer using microchannels recently have attracted significant research and industrial design interests. Open literatures leave with question on the applicability of classical macroscale theory in microchannels. Better understanding of heat transfer in various microchannel geometries and building experimental database are continuously urged. The purpose of this study is to contribute the findings and data to this emerging area through carefully designed and well controlled experimental works. The commercially important glycol-water mixture heat transfer fluid and multiport slab serpentine heat exchangers are encountered in heating and cooling areas, e.g. in automotive, aircraft, and HVAC industries. For a given heat duty, the large diameter tubes experience turbulent flow whereas the narrow channels face laminar flow and often developing flow. Study of low Reynolds number developing glycol-water mixture laminar flow in serpentine microchannel heat exchanger with parallel multi-port slab is not available in the open literature. Current research therefore experimentally investigates glycol-water mixture and water in simultaneously developing laminar flows. Three multiport microchannel heat exchangers; straight and serpentine slabs, are used for each fluid. Friction factors of glycol-water mixture and water flows in straight slabs are higher than conventional fully developed laminar flow. If a comprehensive pressure balance is introduced, the results are well compared with conventional Poiseuille theory. Similar results are found in serpentine slab. The pressure drop for the straight core is the highest, manifolds are the intermediate, and serpentine is the least; which are beneficial for heat exchangers. The heat transfer results in serpentine slab for glycol-water mixture and water are higher and could not be compared with conventional fully developed and developing flow correlations. New heat transfer correlations are therefore developed in current study. The experimental data are compared with improved scheme of modified Wilson Plot Technique and numerical simulation having the same geometries and operating conditions. Very good agreements in results were found in all cases. The presence of adiabatic serpentine bend in multi-port flat slab heat exchanger enhances more heat transfer with less pressure drop penalty as compared to the initial entrance condition caused by the inlet manifold.

The Cause of the Cauca, Colombia, Cluster of Intermediate-Depth Earthquakes From Earthquake Relocation and Focal Mechanisms

NASA Astrophysics Data System (ADS)

Warren, L. M.; Chang, Y.; Prieto, G. A.

2016-12-01

In subducting slabs, a high seismicity rate in a concentrated volume (an earthquake cluster) is often associated with geometric complexities such as slab detachment, tearing, or contortions. The intermediate-depth Cauca, Colombia, cluster (3.5°N-5.5°N), in contrast, appears to be located in a slab without such complexities. However, previous constraints on the slab geometry are based on global data. We use regional data to investigate the cause of the Cauca cluster by estimating its geometry from earthquake relocations and stress regime from focal mechanism calculations and stress inversions. The Cauca segment of the Nazca Plate is characterized by relatively sparse seismicity away from the cluster and a narrow volcanic arc. To the northeast of the Cauca cluster, six active volcanoes are concentrated within an 80-km along-trench distance and are isolated 180 km from the rest of the northern Andes volcanic arc. The Colombian National Seismic Network, from Jan 2010 to Mar 2014, reports 433 earthquakes in the cluster at depths of 50-200 km with local magnitudes ranging from 2.0-4.7. Earthquake relocations show a continuous 20-km-thick seismic zone dipping at 33°-43°, with the angle increasing to the south. In addition, earthquakes locate in two columns that extend normal to the slab and into the mantle wedge. The focal mechanisms show various types, including down-dip extension, strike slip, and trench-parallel compression, but are consistent with a predominantly down-dip extensional stress field. The maximum and intermediate stress axes are interchangeable because of their similar magnitudes. The down-dip extensional stress regime may expel dehydrated fluid from the slab into the mantle wedge. As the fluid moves through the mantle wedge, it may generate hydrofractures and the observed mantle-wedge earthquakes. The fluid in the mantle wedge may be transported along the trench, from the steeper southern section to the more shallowly-dipping northern section, and cause the volcanoes to the northeast of the Cauca cluster. The Cauca cluster, unlike most clusters, is not associated with a complex slab geometry. Instead, its high seismicity rate may result from a high dehydration rate in the slab and conditions that promote fluid migration into and earthquakes in the mantle wedge.

The Last Word

NASA Astrophysics Data System (ADS)

Anderson, D. L.

2014-12-01

Earth is an isolated, cooling planet, that obeys the 2nd law of thermodynamics. Interior dynamics is driven from the top, by cold sinking slabs. High-resolution broad-band seismology and geodesy have confirmed that mantle flow is characterized by narrow downwellings and ~20 broad slowly rising updrafts. The low-velocity zone (LVZ) consists of a hot melange of sheared peridotite intruded with aligned melt-rich lamellae that are tapped by intraplate volcanoes. The high temperature is a simple consequence of the thermal overshoot common in large bodies of convecting fluids. The transition zone consists of ancient eclogite layers that are displaced upwards by slabs to become broad, passive, cool ridge-feeding updrafts of ambient mantle. The physics that is overlooked in canonical models of mantle dynamics and geochemistry includes; the 2nd law of thermodynamics, convective overshoots, subadiabaticity, wave-melt interactions, Archimedes principle, and kinetics. Rapid transitions allow stress-waves to interact with melting and phase changes, creating LVZs; sluggish transitions in cold slabs keep eclogite in the transition zone where it warms up by extracting heat from mantle below 650 km, creating the appearance of slab penetration. Canonical chemical geodynamic models are the exact opposite of physics- and thermodynamic-based models and of the real Earth. A model that results from inverting the assumptions regarding initial and boundary conditions (hot origin, secular cooling, no external power sources, cooling internal boundaries, broad passive upwellings, adiabaticity and whole-mantle convection not imposed, layering and self-organization allowed) results in a thick refractory-yet-fertile surface layer, with ancient xenoliths and cratons at the top and a hot overshoot at the base. A thin mobile D" layer results, that is an unlikely plume-generation zone. Accounting for the physics that is overlooked or violated (the 2nd law of thermodynamics) in canonical models, plus modern seismology, undermines the assumptions and conclusions of these models.

Rock-avalanche and ocean-resurge deposits in the late Eocene Chesapeake Bay impact structure: Evidence from the ICDP-USGS Eyreville cores, Virginia, USA

USGS Publications Warehouse

Gohn, G.S.; Powars, D.S.; Dypvik, H.; Edwards, L.E.

2009-01-01

An unusually thick section of sedimentary breccias dominated by target-sediment clasts is a distinctive feature of the late Eocene Chesapeake Bay impact structure. A cored 1766-m-deep section recovered from the central part of this marine-target structure by the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) drilling project contains 678 m of these breccias and associated sediments and an intervening 275-m-thick granite slab. Two sedimentary breccia units consist almost entirely of Cretaceous nonmarine sediments derived from the lower part of the target sediment layer. These sediments are present as coherent clasts and as autoclastic matrix between the clasts. Primary (Cretaceous) sedimentary structures are well preserved in some clasts, and liquefaction and fluidization structures produced at the site of deposition occur in the clasts and matrix. These sedimentary breccias are interpreted as one or more rock avalanches from the upper part of the transient-cavity wall. The little-deformed, unshocked granite slab probably was transported as part of an extremely large slide or avalanche. Water-saturated Cretaceous quartz sand below the slab was transported into the seafloor crater prior to, or concurrently with, the granite slab. Two sedimentary breccia units consist of polymict diamictons that contain cobbles, boulders, and blocks of Cretaceous nonmarine target sediments and less common shocked-rock and melt ejecta in an unsorted, unstratified, muddy, fossiliferous, glauconitic quartz matrix. Much of the matrix material was derived from Upper Cretaceous and Paleogene marine target sediments. These units are interpreted as the deposits of debris flows initiated by the resurge of ocean water into the seafloor crater. Interlayering of avalanche and debris-flow units indicates a partial temporal overlap of the earlier avalanche and later resurge processes. A thin unit of stratified turbidite deposits and overlying laminated fine-grained deposits at the top of the section represents the transition to normal shelf sedimentation. ?? 2009 The Geological Society of America.

On the Heat Transfer through a Solid Slab Heated Uniformly and Continuously on One of Its Surfaces

ERIC Educational Resources Information Center

Marin, E.; Lara-Bernal, A.; Calderon, A.; Delgado-Vasallo, O.

2011-01-01

Some peculiarities of the heat transfer through a sample that is heated by the superficial absorption of light energy under continuous uniform illumination are discussed. We explain, using a different approach to that presented in a recent article published in this journal (Salazar "et al" 2010 "Eur. J. Phys." 31 1053-9), that the front surface of…

A Hybrid Fiber/Solid-State Regenerative Amplifier with Tunable Pulse Widths for Satellite Laser Ranging

NASA Technical Reports Server (NTRS)

Coyle, Barry; Poulios, Demetrios

2013-01-01

A fiber/solid-state hybrid seeded regenerative amplifier, capable of achieving high output energy with tunable pulse widths, has been developed for satellite laser ranging applications. The regenerative amplifier cavity uses a pair of Nd:YAG zigzag slabs oriented orthogonally to one another in order to make thermal lensing effects symmetrical and simplify optical correction schemes. The seed laser used is a fiber-coupled 1,064-nm narrowband (<0.02 nm) diode laser that is discretely driven in a new short-pulsed mode, enabling continuously tunable seed pulse widths in the 0.2-to-0.4-ns range. The amplifier gain unit consists of a pair of Brewster-cut 6-bounce zigzag Nd:YAG laser slabs, oriented 90deg relative to each other in the amplifier head. This arrangement creates a net-symmetrical thermal lens effect (an opposing singleaxis effect in each slab), and makes thermo-optical corrections simple by optimizing the curvature of the nearest cavity mirror. Each slab is pumped by a single 120-W, pulsed 808-nm laser diode array. In this configuration, the average pump beam distribution in the slabs had a 1-D Gaussian shape, which matches the estimated cavity mode size. A half-wave plate between the slabs reduces losses from Fresnel reflections due to the orthogonal slabs Brewster-cut end faces. Successful "temporal" seeding of the regenerative amplifier cavity results in a cavity Q-switch pulse envelope segmenting into shorter pulses, each having the width of the input seed, and having a uniform temporal separation corresponding to the cavity round-trip time of approx. =10 ns. The pulse energy is allowed to build on successive passes in the regenerative amplifier cavity until a maximum is reached, (when cavity gains and losses are equal), after which the pulse is electro- optically switched out on the next round trip The overall gain of the amplifier is approx. =82 dB (or a factor of 1.26 million). After directing the amplified output through a LBO frequency doubling crystal, approx. = 2.1 W of 532-nm output (>1 mJ) was measured. This corresponds to a nonlinear conversion efficiency of >60%. Furthermore, by pulse pumping this system, a single pulse per laser shot can be created for the SLR (satellite laser ranging) measurement, and this can be ejected into the instrument. This is operated at the precise frequency needed by the measurement, as opposed to commercial short-pulsed, mode-locked systems that need to operate in a continuous fashion, or CW (continuous wave), and create pulses at many MHz. Therefore, this design does not need to throw away or dump 99% of the laser energy to produce what is required; this system can be far smaller, more efficient, cheaper, and readily deployed in the field when packaged efficiently. Finally, by producing custom diode seed pulses electronically, two major advantages over commercial systems are realized: First, this pulse shape is customizable and not affected by the cavity length or gain of the amplifier cavity, and second, it can produce adjustable (selectable) pulse widths by simply adding multiple seed diodes and coupling each into commercial, low-cost fiber-optic combiners.

Influence of Initial Geometry and Boundary Conditions on Flat Subduction Models and Resulting Topography

NASA Astrophysics Data System (ADS)

Nelson, P.; Moucha, R.

2014-12-01

Numerical investigations of surface deformation in response to flat slab subduction began with seminal papers by Bird (1988) and Mitrovica et al. (1989). Recently, a number of numerical studies have begun to explore the complexity in the dynamics of flat-slab subduction initiation and continuation, but did not address the corresponding surface deformation (English et al., 2003; Pérez-Campos et al., 2008; Liu et al., 2010; Jones et al., 2011; Arrial and Billen, 2013; Vogt and Gerya, 2014). Herein, we explore the conditions that lead to flat-slab subduction and characterize the resulting surface deformation using a 2D finite-difference marker-in-cell method. We specifically explore how initial model geometry and boundary conditions affect the evolution of the angle at which a slab subducts in the presence/absence of a buoyant oceanic plateau and the resulting surface topography. In our simulations, the surface is tracked through time as an internal erosion/sedimentation surface. The top boundary of the crust is overlaid by a "sticky" (viscous 10^17 Pa.s) water/air layer with correspondingly stratified densities. We apply a coupled surface processes model that solves the sediment transport/diffusion erosion equation at each time step to account for the corresponding crustal mass flux and its effect on crustal deformation. Model results show the initial angle of subduction has a substantial impact on the subduction angle of the slab and hence the evolution of topography. The results also indicate plate velocity and the presence of an oceanic plateau in a forced subduction only have a moderate effect on the angle of subduction.

The Viability and Style of the Modern Plate-Tectonic Subduction Process in a Hotter Earth

NASA Astrophysics Data System (ADS)

van Hunen, J.; van den Berg, A.; Vlaar, N. J.

2001-12-01

The Earth was probably warmer during the Archean and Proterozoic, and a 50 to 300 K mantle temperature increase has been suggested. This resulted in a thicker basaltic oceanic crust and underlying harzburgitic layer, and increased buoyancy of the lithosphere. This phenomenon has raised questions about the style or even the existence of plate tectonics in a younger Earth. Buoyant, low-angle subduction (e.g. below overriding plates) could have been more important, but also alternative tectonic styles, such as small-scale layered convection within the thickened crust have been proposed. We conducted 2-D Cartesian numerical model calculations to quantify the viability of the subduction process for an Earth with a higher potential temperature.As the basalt-to-eclogite transition in the crust plays an important role in the buoyancy of the oceanic plate and slab, and therefore also in its propensity to subduct, the kinetics of this phase transition is included in the numerical model. One set of model results suggest that flat subduction below a continuously overriding lithosphere, or lithospheric doubling, can give rise to flat subduction up to a mantle temperature, which is not much higher (38 to 75 K) than today. An even hotter mantle is too weak to support the flat slab, so that fast, steep Benioff subduction develops. We performed another set of model calculations to examine the possibility of modern-style subduction in a hotter Earth, without extra driving forces such as lithospheric doubling. We use again the mechanism of lithospheric doubling, but only to trigger the subduction process, and switch it off after a few million years, when `active' subduction developes. For a mantle temperature increase up to 150 K, we find subduction to be essentially the same as today, but subduction rates increase with increasing mantle temperature and increasing eclogitisation rates. For a 225 K mantle temperature increase, considerable amounts of the dense eclogitic crust delaminate from its mantle lithosphere, and sink rapidly into the mantle, which leaves the remainder of the slab too buoyant to continue the subduction process. For a 300 K hotter mantle, the mechanical coherence of the descending slab is reduced to such extent that frequent detachment of small pieces of the slab occur. These results indicate that the eventual viability and `mode' of the plate tectonic mechanism in a hotter Earth is determined by a complicated interaction between crustal thickness, eclogitisation rate, slab age, and the rheology of both crust and mantle.

Laboratory experiments on subduction-induced circulation in the wedge and the evolution of mantle diapirs

NASA Astrophysics Data System (ADS)

Sylvia, R. T.; Kincaid, C. R.; Behn, M. D.; Zhang, N.

2014-12-01

Circulation in subduction zones involves large-scale, forced-convection by the motion of the down-going slab and small scale, buoyant diapirs of hydrated mantle or subducted sediments. Models of subduction-diapir interaction often neglect large-scale flow patterns induced by rollback, back-arc extension and slab morphology. We present results from laboratory experiments relating these parameters to styles of 4-D wedge circulation and diapir ascent. A glucose fluid is used to represent the mantle. Subducting lithosphere is modeled with continuous rubber belts moving with prescribed velocities, capable of reproducing a large range in downdip relative rollback plate rates. Differential steepening of distinct plate segments simulates the evolution of slab gaps. Back-arc extension is produced using Mylar sheeting in contact with fluid beneath the overriding plate that moves relative to the slab rollback rate. Diapirs are introduced at the slab-wedge interface in two modes: 1) distributions of low density rigid spheres and 2) injection of low viscosity, low density fluid to the base of the wedge. Results from 30 experiments with imposed along-trench (y) distributions of buoyancy, show near-vertical ascent paths only in cases with simple downdip subduction and ratios (W*) of diapir rise velocity to downdip plate rate of W*>1. For W* = 0.2-1, diapir ascent paths are complex, with large (400 km) lateral offsets between source and surfacing locations. Rollback and back-arc extension enhance these offsets, occasionally aligning diapirs from different along-trench locations into trench-normal, age-progressive linear chains beneath the overriding plate. Diapirs from different y-locations may surface beneath the same volcanic center, despite following ascent paths of very different lengths and transit times. In cases with slab gaps, diapirs from the outside edge of the steep plate move 1000 km parallel to the trench before surfacing above the shallow dipping plate. "Dead zones" resulting from lateral and vertical shear in the wedge above the slab gap, produce slow transit times. These 4-D ascent pathways are being incorporated into numerical models on the thermal and melting evolution of diapirs. Models show subduction-induced circulation significantly alters diapir ascent beneath arcs.

Seismic tomographic constraints on plate-tectonic reconstructions of Nazca subduction under South America since late Cretaceous (˜80 Ma)

NASA Astrophysics Data System (ADS)

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

2017-12-01

Global seismic tomography has provided new and increasingly higher resolution constraints on subducted lithospheric remnants in terms of their position, depth, and volumes. In this study we aim to link tomographic slab anomalies in the mantle under South America to Andean geology using methods to unfold (i.e. structurally restore) slabs back to earth surface and input them to globally consistent plate reconstructions (Wu et al., 2016). The Andean margin of South America has long been interpreted as a classic example of a continuous subduction system since early Jurassic or later. However, significant gaps in Andean plate tectonic reconstructions exist due to missing or incomplete geology from extensive Nazca-South America plate convergence (i.e. >5000 km since 80 Ma). We mapped and unfolded the Nazca slab from global seismic tomography to produce a quantitative plate reconstruction of the Andes back to the late Cretaceous 80 Ma. Our plate model predicts the latest phase of Nazca subduction began in the late Cretaceous subduction after a 100 to 80 Ma plate reorganization, which is supported by Andean geology that indicates a margin-wide compressional event at the mid-late Cretaceous (Tunik et al., 2010). Our Andean plate tectonic reconstructions predict the Andean margin experienced periods of strike-slip/transtensional and even divergent plate tectonics between 80 to 55 Ma. This prediction is roughly consistent with the arc magmatism from northern Chile between 20 to 36°S that resumed at 80 Ma after a magmatic gap. Our model indicates the Andean margin only became fully convergent after 55 Ma. We provide additional constraints on pre-subduction Nazca plate paleogeography by extracting P-wave velocity perturbations within our mapped slab surfaces following Wu et al. (2016). We identified localized slow anomalies within our mapped Nazca slab that apparently show the size and position of the subducted Nazca ridge, Carnegie ridge and the hypothesized Inca plateau within the Nazca slab. These intra-slab velocity anomalies provide the most complete tomographic evidence to date in support the classic, but still controversial hypothesis of subducted, relatively buoyant oceanic lithosphere features along the Andean margin.

Variations in Melt Generation and Migration along the Aleutian Arc (Invited)

NASA Astrophysics Data System (ADS)

Plank, T. A.; Van Keken, P. E.

2013-12-01

The generation and ascent of mantle melt beneath volcanic arcs sets the course for how magmas differentiate to form the continental crust and erupt explosively from volcanoes. Although the basic framework of melting at subduction zones is understood to involve the convective influx of hot mantle (Tp ≥ 1300°C) and advective transport of water-rich fluids from the subducting slab, the P-T paths that melts follow during melt generation and migration are still not well known. The Aleutian Arc provides an opportunity to explore the conditions of mantle melting in the context of volcanoes that span an unusually large range in the depth to the slab, from Seguam island, with among the shallowest depths to the slab worldwide (~65 km, [1]) to Bogoslof island, behind the main volcanic front and twice the depth to the slab (~130 km). Here we combine thermal models tuned to Aleutian subduction parameters [after 2] with petrological estimates of the T and P of mantle-melt equilibration, using a major element geothermometer [3] and estimates of H2O and fO2 from olivine-hosted melt inclusion measurements [4] for basaltic magmas from 6 volcanoes in the central Aleutians (Korovin, Seguam, Bogoslof, Pakushin, Akutan, Shishaldin). We find mantle-melt equilibration conditions to vary systematically as a function of the depth to the slab, from 30 km and 1220°C (for Seguam) to 60 km and 1300°C (for Bogoslof). Such shallow depths, which extend up to the Moho, define a region perched well above the hot core of the mantle wedge predicted from thermal models, even considering the shallow depths of slab-mantle coupling (< 60 km) required to supply hot mantle beneath Seguam. Thus, even though the greatest melt production will occur in the hot core of the wedge (50-100 km depth), melts apparently ascend and re-equilibrate in the shallowest mantle. Volcanoes that overlie the greatest depth to the slab, and lie furthest from the wedge corner, stall at greater depths (~60 km), at the base of the conductive upper plate (i.e., lithosphere). The conductive lid and isotherms shallow toward the wedge corner. This leads to shallower depths of melt equilibration at shallower depths to the slab. A second effect is infiltration of melt into the thinning lithosphere, likely due to the increase in strain-rate toward the wedge corner, which favors melt segregation, migration, and shallow equilibration [5]. Such a process is developed most beneath Seguam, where melts collect at the Moho (~ 30km), but are still > 1200°C. Such equilibration depths in the uppermost mantle (30-60 km) and temperatures typical of the base of the conductive lid appear to characterize most modeled primary arc magmas [6], and point to a final re-setting point in the mantle that controls the composition of bulk arc crust. [1] Syracuse & Abers, 2006, G3. [2] Syracuse, van Keken, Abers, (2010) PEPI. [3] Lee, Luffi, Plank, Dalton, Leeman (2009) EPSL. [4] Zimmer et al. (2010) J.Pet. [5] Holzman & Kendall (2010). [6] Ruscitto et al. (2012) G3.

Thin lead sheets in the decorative features in Pavia Charterhouse.

PubMed

Colombo, Chiara; Realini, Marco; Sansonetti, Antonio; Rampazzi, Laura; Casadio, Francesca

2006-01-01

The facade of the church of the Pavia Charterhouse, built at the end of the 15th century, shows outstanding decorative features made of different stone materials, such as marbles, breccias and sandstones. Magnificent ornamental elements are made of thin lead sheets, and some marble slabs are inlaid with them. Metal elements are shaped in complex geometric and phytomorphic design, to form a Greek fret in black contrasting with the white Carrara marble. Lead pins were fixed to the back of the thin lead sheets with the aim of attaching the metal elements to the marble; in so doing the pins and the lead sheets constitute a single piece of metal. In some areas, lead elements have been lost, and they have been substituted with a black plaster, matching the colour of the metal. To the authors' knowledge, this kind of decorative technique is rare, and confirms the refinement of Renaissance Lombard architecture. This work reports on the results of an extensive survey of the white, orange and yellowish layers, which are present on the external surface of the lead. The thin lead sheets have been characterized and their state of conservation has been studied with the aid of Optical Microscopy, SEM-EDS, FTIR and Raman analyses. Lead sulphate, lead carbonates and oxides have been identified as decay products.

46 CFR 164.013-5 - Acceptance tests.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 6 2010-10-01 2010-10-01 false Acceptance tests. 164.013-5 Section 164.013-5 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL MATERIALS Foam, Unicellular Polyethylene (Buoyant, Slab, Slitted Trigonal Pattern...

46 CFR 164.013-5 - Acceptance tests.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 6 2011-10-01 2011-10-01 false Acceptance tests. 164.013-5 Section 164.013-5 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL MATERIALS Foam, Unicellular Polyethylene (Buoyant, Slab, Slitted Trigonal Pattern...

Stainless steel prestressing strands and bars for use in prestressed concrete girders and slabs.

DOT National Transportation Integrated Search

2015-08-01

Corrosion decay on structures has continued to be a challenge in the scientific and engineering : communities, where significant federal and state funds have been spent towards replacement or rehabilitation : of bridges that were damaged by corrosion...

Nonreciprocal reflection-beam isolators for far-infrared use

NASA Technical Reports Server (NTRS)

Kanda, M.; May, W. G.

1973-01-01

Magnetoplasma reflection-beam isolators for submillimeter-wave use are discussed in theory and experiment. The basic device uses the Kerr transverse magnetooptic effect (plane of polarization of the EM wave in the plane of incidence, which is perpendicular to a dc magnetic field) in InSb near room temperature. When the semiconductor slab is covered with a thin dielectric layer acting as a matching transformer, improved performance is predicted and observed at 337 microns, and very efficient isolator performance is predicted for 118 microns. Physical arguments are presented to explain the nonreciprocal phenomenon and lead to better device design.

HiLASE: development of fully diode pumped disk lasers with high average power

NASA Astrophysics Data System (ADS)

Divoky, M.; Smrz, M.; Chyla, M.; Sikocinski, P.; Severova, P.; Novák, O.; Huynh, J.; Nagisetty, S. S.; Miura, T.; Liberatore, C.; Pilař, J.; Slezak, O.; Sawicka, M.; Jambunathan, V.; Gemini, L.; Vanda, J.; Svabek, R.; Endo, A.; Lucianetti, A.; Rostohar, D.; Mason, P. D.; Phillips, P. J.; Ertel, K.; Banerjee, S.; Hernandez-Gomez, C.; Collier, J. L.; Mocek, T.

2015-02-01

An overview of Czech national R&D project HiLASE (High average power pulsed LASEr) is presented. The HiLASE project aims at development of pulsed DPSSL for hi-tech industrial applications. HiLASE will be a user oriented facility with several laser systems with output parameters ranging from a few picosecond pulses with energy of 5 mJ to 0.5 J and repetition rate of 1-100 kHz (based on thin disk technology) to systems with 100 J output energy in nanosecond pulses with repetition rate of 10 Hz (based on multi-slab technology).

Active and fossil mantle flows in the western Alpine region unravelled by seismic anisotropy analysis and high-resolution P wave tomography

NASA Astrophysics Data System (ADS)

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

2018-04-01

The anisotropy of seismic velocities in the mantle, when integrated with high-resolution tomographic models and geologic information, can be used to detect active mantle flows in complex plate boundary areas, providing new insights on the impact of mantle processes on the topography of mountain belts. Here we use a densely spaced array of temporary broadband seismic stations to analyze the seismic anisotropy pattern of the western Alpine region, at the boundary between the Alpine and Apenninic slabs. Our results are supportive of a polyphase development of anisotropic mantle fabrics, possibly starting from the Jurassic to present. Geophysical data presented in this work, and geologic evidence taken from the literature, indicate that: (i) fossil fabrics formed during Tethyan rifting may be still preserved within the Alpine and Apenninic slabs; (ii) mantle deformation during Apenninic slab rollback is not compensated by a complete toroidal flow around the northern tip of the retreating slab; (iii) the previously observed continuous trend of anisotropy fast axes near-parallel to the western Alpine arc is confirmed. We observe that this arc-parallel trend of fast axes is located in correspondence to a low velocity anomaly in the European upper mantle, beneath regions of the Western and Ligurian Alps showing the highest uplift rates. We propose that the progressive rollback of the Apenninic slab, in the absence of a counterclockwise toroidal flow at its northern tip, induced a suction effect at the scale of the supraslab mantle. The resulting mantle flow pattern was characterized by an asthenospheric counterflow at the rear of the unbroken Western Alps slab and around its southern tip, and by an asthenospheric upwelling, mirrored by low P wave velocities, that would have favored the topographic uplift of the Alpine belt from the Mont Blanc to the Mediterranean sea.

Effect of 3-D heterogeneous-earth on rheology inference of postseismic model following the 2012 Indian Ocean earthquake

NASA Astrophysics Data System (ADS)

Pratama, C.; Ito, T.; Sasajima, R.; Tabei, T.; Kimata, F.; Gunawan, E.; Ohta, Y.; Yamashina, T.; Ismail, N.; Muksin, U.; Maulida, P.; Meilano, I.; Nurdin, I.; Sugiyanto, D.; Efendi, J.

2017-12-01

Postseismic deformation following the 2012 Indian Ocean earthquake has been modeled by several studies (Han et al. 2015, Hu et al. 2016, Masuti et al. 2016). Although each study used different method and dataset, the previous studies constructed a significant difference of earth structure. Han et al. (2015) ignored subducting slab beneath Sumatra while Masuti et al. (2016) neglect sphericity of the earth. Hu et al. (2016) incorporated elastic slab and spherical earth but used uniform rigidity in each layer of the model. As a result, Han et al. (2015) model estimated one order higher Maxwell viscosity than the Hu et al. (2016) and half order lower Kelvin viscosity than the Masuti et al. (2016) model predicted. In the present study, we conduct a quantitative analysis of each heterogeneous geometry and parameter effect on rheology inference. We develop heterogeneous three-dimensional spherical-earth finite element models. We investigate the effect of subducting slab, spherical earth, and three-dimensional earth rigidity on estimated lithosphere-asthenosphere rheology beneath the Indian Ocean. A wide range of viscosity structure from time constant rheology to time dependent rheology was chosen as previous studies have been modeled. In order to evaluate actual displacement, we compared the model to the Global Navigation Satellite System (GNSS) observation. We incorporate the GNSS data from previous studies and introduce new GNSS site as a part of the Indonesian Continuously Operating Reference Stations (InaCORS) located in Sumatra that has not been used in the last analysis. As a preliminary result, we obtained the effect of the spherical earth and elastic slab when we assumed burgers rheology. The model that incorporates the sphericity of the earth needs a one third order lower viscosity than the model that neglects earth curvature. The model that includes elastic slab needs half order lower viscosity than the model that excluding the elastic slab.

Interplay between deformation, fluid release and migration across a nascent subduction interface: evidence from Oman-UAE and implications for warm subduction zones

NASA Astrophysics Data System (ADS)

Agard, Philippe; Prigent, Cécile; Soret, Mathieu; Guillot, Stéphane; Dubacq, Benoît

2017-04-01

Frozen-in subduction plate interfaces preserving the first 1-2 My of the subduction history are found beneath ophiolites. These contacts are a key target to study the inception of mantle wedge metasomatism and the mechanical coupling between the upper plate and the top part of the sinking slab shortly after subduction initiation. Combining structural field and EBSD data, detailed petrology, thermodynamic modelling and geochemistry on both sides, i.e. the base of the mantle wedge (Oman-UAE basal peridotites) and the underlying accreted crustal fragments from the subducting slab (metamorphic soles), this study documents the continuous evolution of the plate contact from 1 GPa 900-750°C to 0.6 GPa 750-600°C, with emphasis on strain localization and feedbacks between deformation and fluid migration. In the mantle wedge, the (de)formation of proto-ultramylonitic peridotites is coeval with mantle metasomatism by focused hydrous fluid migration. Peridotite metasomatism results in the precipitation of new minerals (clinopyroxene, amphibole and spinel ± olivine and orthopyroxene) and their enrichment in FMEs (particularly B, Li and Cs, with concentrations up to 40 times that of the PM). Boron concentrations and isotopes (δ11B of metasomatized peridotites up to +25‰) suggest that these fluids with a "subduction signature" are probably sourced from the dehydrating amphibolitic metamorphic sole. Concomitantly, deformation in the lower plate results in the stepwise formation, detachment and accretion to the mylonitic s.l. mantle of successive slices of HT metabasalts from the downgoing slab, equilibrated at amphibolite/granulite conditions (900-750°C). Two major stages may be outlined: - between 900 and 750°C, the garnet-clinopyroxene-amphibole bearing sinking crust (with melting < 6 vol%) gets juxtaposed and mechanically coupled to the mantle, leading to the transfer of subduction fluids and metasomatism (possibly into the arc zone ultimately). Deformation is distributed on the km scale, typically 200-500 m thick in the mantle and 100-200 m thick in the slab crust. Dislocation creep is the dominant mechanism in the mantle wedge while, in the lower plate crust, deformation is accomodated by cataclasis and reorientation of amphibole grains and dislocation creep of clinopyroxene. Amphibole LPO suggests that granulite to amphibolite deformation was accommodated by thinning of the crustal fragments accreted to the upper plate (by up to a factor of 5-10). - between 750-600°C, the plate contact is further deformed (and partially exhumed) with considerable increase in strain localization on both sides, and fluid channelization in the mantle through (milli)metric ultramylonitic shear bands. Strain is accommodated by a change from olivine dislocation to grain size sensitive creep in mantle ultramylonites, and in the footwall by dislocation creep of amphibole and plagioclase (with progressive increase of rigid body rotation). This example sheds light on the behaviour of warm subductions (e.g., Cascadia, Nankai) where slab material gets amphibolitized at depths of 40 km, on how fluids are fluxed into the mantle wedge and how mechanical coupling resumes at depth (i.e., beyond those where serpentine is stable). Documented deformation patterns also suggest that, where serpentine is stable in the mantle wedge, deformation should be very localized.

Thickness of the Descending Philippine Sea Plate Estimated from Tomographic Images beneath the Kumano Basin, along the Nankai Trough, Southwestern Japan

NASA Astrophysics Data System (ADS)

Kamiya, S.; Suzuki, K.; Takahashi, N.

2015-12-01

The Philippine Sea plate subducts northwestward beneath the Japanese islands from the south. The average thickness of the overall Philippine Sea plate has been investigated in the oceanic area using surface wave analyses [e.g. Abe and Kanamori, 1970], suggesting a thin (30-40 km thick) plate. On the other hand, several studies have indicated a thicker Philippine Sea plate based on source mechanisms and seismicity in the eastern rim of the plate [Seno, 1987; Moriyama et al., 1989]. From tomographic images, Kamiya and Kobayashi [2007] pointed out that the subducting Philippine Sea slab has thickness variation with a stepwise offset east of Izu Peninsula. The eastern (the Kanto district) and western (north of Izu Peninsula and the Tokai district) regions have respective thicknesses of 60 and 25 km. In the Kumano basin, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) developed the Dense Oceanfloor Network System for Earthquakes and Tsunami (DONET) in order to monitor seismic activity [Kaneda et al., 2009; Kawaguchi et al., 2010]. DONET ocean-bottom stations are connected with an optical fiber cable, and data are transferred in real time to our laboratory at JAMSTEC. The present study obtains three-dimensional P-wave and S-wave seismic velocity models beneath the Kumano basin by employing an travel time tomography technique. We pick arrival times of P and S waves from the waveform data recorded by the DONET system during the period from January 2011 to December 2014. In order to improve the resolution in the deeper regions than the seismic area inside of the descending slab, we also pick arrival times from the seismic events occurred outside of this district. We use these picked arrival times adding to the JMA catalogue data in seismic tomography. From the obtained tomographic images, we find high velocity anomalies corresponding to the descending Philippine Sea slab. We also find low velocity anomalies under the high velocity slab clearly. There seems to be a sharp velocity contrast between the anomalies. We can estimate the thickness of the descending slab at about 30 km, which is almost consistent with the thickness beneath the Tokai district estimated by Kamiya and Kobayashi [2007] and comparable to the effective elastic thickness beneath the eastern part of the Shikoku basin estimated by Yoshioka and Ito [2001].

46 CFR 164.013-2 - Incorporation by reference.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 6 2011-10-01 2011-10-01 false Incorporation by reference. 164.013-2 Section 164.013-2 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL MATERIALS Foam, Unicellular Polyethylene (Buoyant, Slab, Slitted Trigonal Pattern...

46 CFR 164.013-2 - Incorporation by reference.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 6 2010-10-01 2010-10-01 false Incorporation by reference. 164.013-2 Section 164.013-2 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL MATERIALS Foam, Unicellular Polyethylene (Buoyant, Slab, Slitted Trigonal Pattern...

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

DOT National Transportation Integrated Search

2014-10-01

This report presents the findings associated with an effort to develop a complementary pavement : roughness indexing system that utilizes the 25 ft. Moving Baselength Roughness Index (IRI25-ft) : alongside the posted speed localized roughness index (...

Stainless steel prestressing strands and bars for use in prestressed concrete girders and slabs : [research summary].

DOT National Transportation Integrated Search

2015-08-01

Corrosion decay on structures has continued to be a challenge in the scientific : and engineering communities, where significant federal and state funds have : been spent towards replacement or rehabilitation of bridges that were damaged : by corrosi...

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.

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.

Boron desorption and fractionation in Subduction Zone Fore Arcs: Implications for the sources and transport of deep fluids

NASA Astrophysics Data System (ADS)

Saffer, Demian M.; Kopf, Achim J.

2016-12-01

At many subduction zones, pore water geochemical anomalies at seafloor seeps and in shallow boreholes indicate fluid flow and chemical transport from depths of several kilometers. Identifying the source regions for these fluids is essential toward quantifying flow pathways and volatile fluxes through fore arcs, and in understanding their connection to the loci of excess pore pressure at depth. Here we develop a model to track the coupled effects of boron desorption, smectite dehydration, and progressive consolidation within sediment at the top of the subducting slab, where such deep fluid signals likely originate. Our analysis demonstrates that the relative timing of heating and consolidation is a dominant control on pore water composition. For cold slabs, pore water freshening is maximized because dehydration releases bound water into low porosity sediment, whereas boron concentrations and isotopic signatures are modest because desorption is strongly sensitive to temperature and is only partially complete. For warmer slabs, freshening is smaller, because dehydration occurs earlier and into larger porosities, but the boron signatures are larger. The former scenario is typical of nonaccretionary margins where insulating sediment on the subducting plate is commonly thin. This result provides a quantitative explanation for the global observation that signatures of deeply sourced fluids are generally strongest at nonaccretionary margins. Application of our multitracer approach to the Costa Rica, N. Japan, N. Barbados, and Mediterranean Ridge subduction zones illustrates that desorption and dehydration are viable explanations for observed geochemical signals, and suggest updip fluid migration from these source regions over tens of km.

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.

Defect detection in slab surface: a novel dual Charge-coupled Device imaging-based fuzzy connectedness strategy.

PubMed

Zhao, Liming; Ouyang, Qi; Chen, Dengfu; Udupa, Jayaram K; Wang, Huiqian; Zeng, Yuebin

2014-11-01

To provide an accurate surface defects inspection system and make the automation of robust image segmentation method a reality in routine production line, a general approach is presented for continuous casting slab (CC-slab) surface defects extraction and delineation. The applicability of the system is not tied to CC-slab exclusively. We combined the line array CCD (Charge-coupled Device) traditional scanning imaging (LS-imaging) and area array CCD laser three-dimensional (3D) scanning imaging (AL-imaging) strategies in designing the system. Its aim is to suppress the respective imaging system's limitations. In the system, the images acquired from the two CCD sensors are carefully aligned in space and in time by maximum mutual information-based full-fledged registration schema. Subsequently, the image information is fused from these two subsystems such as the unbroken 2D information in LS-imaging and 3D depressed information in AL-imaging. Finally, on the basis of the established dual scanning imaging system the region of interest (ROI) localization by seed specification was designed, and the delineation for ROI by iterative relative fuzzy connectedness (IRFC) algorithm was utilized to get a precise inspection result. Our method takes into account the complementary advantages in the two common machine vision (MV) systems and it performs competitively with the state-of-the-art as seen from the comparison of experimental results. For the first time, a joint imaging scanning strategy is proposed for CC-slab surface defect inspection that allows a feasible way of powerful ROI delineation strategies to be applied to the MV inspection field. Multi-ROI delineation by using IRFC in this research field may further improve the results.

Dynamic Modeling of Back-arc Extension in the Aegean Sea and Western Anatolia

NASA Astrophysics Data System (ADS)

Mazlum, Ziya; Göğüş, Oğuz H.; Sözbilir, Hasan; Karabulut, Hayrullah; Pysklywec, Russell N.

2015-04-01

Western Anatolian-Aegean regions are characterized by large-scale lithospheric thinning and extensional deformation. While many geological observations suggest the formation of rift basins, normal faulting, exhumation of metamorphic rocks, and back-arc volcanism, the primary cause and the geodynamic driving mechanisms for the lithospheric thinning and extension are not well understood. Previous studies suggest three primary geodynamic hypotheses to address the extension in the Aegean-west Anatolia: 1) Slab retreat/roll-back model, inferred by the southward younging magmatism and metamorphic exhumations; 2) Gravitational collapse of the overthickened (post orogenic) lithosphere, interpreted by the structural studies that suggests tectonic mode switching from contraction to extension; 3) Lateral extrusion (escape tectonics) associated with the continental collision in East Anatolia. We use 2-D thermo-mechanical numerical subduction experiments to investigate how subduction retreat and related back-arc basin opening are controlled by a) changing length and thickness of the subducting plate, b) the dip angle of the subducting slab and c) various thickness and thermal properties of the back-arc lithosphere. Subsequently, we explore the surface response to the subduction retreat model in conjunction with the gravitational (orogenic) collapse in the presumed back-arc region. Quantitative model predictions (e.g., crustal thickness, extension rate) are tested against a wide range of available geological and geophysical observations from the Aegean and west Anatolia regions and these results are reconciled with regional tectonic observations. Our model results are interpreted in the context of different surface response in the extensional regime (back-arc) for the Aegean and western Anatolia, where these two regions have been presumably segmented by the right lateral transfer fault system (Izmir-Balıkesir transfer zone).

Sequence stratigraphic principles applied to the Miocene Hawthorn Group, west-central Florida

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

Norton, V.L.; Randazzo, A.F.

1993-03-01

Sequence boundaries for the Miocene Hawthorn Group in the ROMP 20 drill core from Osprey, Sarasota County, FL were generally delineated by lithologic variations recognized from core slabs, thin section analysis, and geophysical logs. At least six depositional sequences representing third order sea level fluctuations were identified. Depositional environments were determined on the basis of the characteristic lithologic constituents including rip-up clasts, pellets, fossils, laminations, burrow, degree of induration, and grain sorting. The sequence boundaries appear to have formed when the rate of the eustatic fall exceeded basin subsidence rates producing a relative sea level fall at a depositional shorelinemore » break. As a result of the basinward facies shift associated with this sequence type, peritidal facies may directly overlie deeper water facies. Subaerial exposure and erosion can be expected. The sequence of facies representing progressively deeper water depositional environments, followed by a progressive shallowing, were present between bounding surfaces. Among the six sequences recognized, four were clearly delineated as representative of regression, subaerial exposure, and subsequent transgression. Two sequences were less clearly defined and probably represent transitional facies which had exposure surfaces developed. Comparison of the petrologically established sequence stratigraphy with published sea level curves resulted in a strong correlation between the number of sequences recognized and the number of coastal on-lap/off-lap cycles depicted for the early to middle Miocene. This correlation suggests that petrologic examination of core slabs, with supplemental thin section data, can provide useful information regarding the recognition of stratigraphic sequences and relative sea level fluctuations, particularly, in situations where seismic data may not be available.« less

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.

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.

Oppositely directed pairs of propagating rifts in back-arc basins: Double saloon door seafloor spreading during subduction rollback

NASA Astrophysics Data System (ADS)

Martin, A. K.

2006-06-01

When a continent breaks up into two plates, which then separate from each other about a rotation pole, it can be shown that if initial movement is taken up by lithospheric extension, asthenospheric breakthrough and oceanic accretion propagate toward the pole of rotation. Such a propagating rift model is then applied to an embryonic centrally located rift which evolves into two rifts propagating in opposite directions. The resultant rhombic shape of the modeled basin, initially underlain entirely by thinned continental crust, is very similar to the Oligocene to Burdigalian back-arc evolution of the Valencia Trough and the Liguro-Provencal Basin in the western Mediterranean. Existing well and seismic stratigraphic data confirm that a rift did initiate in the Gulf of Lion and propagated southwest into the Valencia Trough. Similarly, seismic refraction, gravity, and heat flow data demonstrate that maximum extension within the Valencia Trough/Liguro-Provencal Basin occurred in an axial position close to the North Balearic Fracture Zone. The same model of oppositely propagating rifts, when applied to the Burdigalian/Langhian episode of back-arc oceanic accretion within the Liguro-Provencal and Algerian basins, predicts a number of features which are borne out by existing geological and geophysical, particularly magnetic data. These include the orientation of subparallel magnetic anomalies, presumed to be seafloor spreading isochrons, in both basins; concave-to-the-west fracture zones southwest of the North Balearic Fracture Zone, and concave-to-the-east fracture zones to its northeast; a spherical triangular area of NW oriented seafloor spreading isochrons southwest of Sardinia; the greater NW extension of the central (youngest?) magnetic anomaly within this triangular area, in agreement with the model-predicted northwestward propagation of a rift in this zone; successively more central (younger) magnetic anomalies abutting thinned continental crust nearer to the pole of rotation in the Liguro-Provencal Basin. The latter feature demonstrates that a rift also propagated northeast in the Liguro-Provencal Basin, at least in its oceanic accretion phase of development. An adaptation of an existing model for subduction slab detachment occurring along the North African margin in the late Burdigalian/Langhian, proposes propagation in opposite directions of the slab tear. The resultant rhombic slab detachment is closely associated in space and time with the rhombic form of the Algerian/Liguro-Provencal basins, suggesting a cause and effect relationship.

Fundamental phenomena on fuel decomposition and boundary-layer combustion processes with applications to hybrid rocket motors

NASA Technical Reports Server (NTRS)

Kuo, Kenneth K.; Lu, Yeu-Cherng; Chiaverini, Martin J.; Harting, George C.; Johnson, David K.; Serin, Nadir

1995-01-01

The experimental study on the fundamental processes involved in fuel decomposition and boundary-layer combustion in hybrid rocket motors is continuously being conducted at the High Pressure Combustion Laboratory of The Pennsylvania State University. This research will provide a useful engineering technology base in the development of hybrid rocket motors as well as a fundamental understanding of the complex processes involved in hybrid propulsion. A high-pressure, 2-D slab motor has been designed, manufactured, and utilized for conducting seven test firings using HTPB fuel processed at PSU. A total of 20 fuel slabs have been received from the Mcdonnell Douglas Aerospace Corporation. Ten of these fuel slabs contain an array of fine-wire thermocouples for measuring solid fuel surface and subsurface temperatures. Diagnostic instrumentation used in the test include high-frequency pressure transducers for measuring static and dynamic motor pressures and fine-wire thermocouples for measuring solid fuel surface and subsurface temperatures. The ultrasonic pulse-echo technique as well as a real-time x-ray radiography system have been used to obtain independent measurements of instantaneous solid fuel regression rates.

Fundamental phenomena on fuel decomposition and boundary-layer combustion processes with applications to hybrid rocket motors

NASA Astrophysics Data System (ADS)

Kuo, Kenneth K.; Lu, Yeu-Cherng; Chiaverini, Martin J.; Harting, George C.; Johnson, David K.; Serin, Nadir

The experimental study on the fundamental processes involved in fuel decomposition and boundary-layer combustion in hybrid rocket motors is continuously being conducted at the High Pressure Combustion Laboratory of The Pennsylvania State University. This research will provide a useful engineering technology base in the development of hybrid rocket motors as well as a fundamental understanding of the complex processes involved in hybrid propulsion. A high-pressure, 2-D slab motor has been designed, manufactured, and utilized for conducting seven test firings using HTPB fuel processed at PSU. A total of 20 fuel slabs have been received from the Mcdonnell Douglas Aerospace Corporation. Ten of these fuel slabs contain an array of fine-wire thermocouples for measuring solid fuel surface and subsurface temperatures. Diagnostic instrumentation used in the test include high-frequency pressure transducers for measuring static and dynamic motor pressures and fine-wire thermocouples for measuring solid fuel surface and subsurface temperatures. The ultrasonic pulse-echo technique as well as a real-time x-ray radiography system have been used to obtain independent measurements of instantaneous solid fuel regression rates.

Assessment of Continuous Resistivity Profiling for the Characterization of Paved Roads

NASA Astrophysics Data System (ADS)

Chouteau, M.; Vallieres, S.; Miralles, M.

2004-05-01

We have assessed the continuous resistivity profiling method using towed arrays as a diagnostic NDT method for the evaluation of pavements. Whether the pavement consists of a sequence of asphalt, concrete slab and subgrade layer (rigid pavement) or a layer of asphalt overlying a subgrade and grade base layers (flexible pavement) defects within those different layers can cause pavement deterioration that must be identified. We first examine the response of the method to the various problems using numerical modeling. It is shown that with an optimally designed system the method allows the determination of the thickness and the location of cracks in the asphalt cover. It is also sensitive to the presence of cracks, internal defects and chloride ions (de-icing salt) within the concrete slab below. For reinforced concrete it is possible to estimate the concrete resistivity related directly to its composition (quality) and the thickness of the top coating over the level of rebars. A low resistivity of concrete will usually be diagnostic of advanced stage of rebar corrosion and delamination could occur. However it is shown that the rebars cause current channeling and the depth of investigation is limited then to the depth of the first row of rebars. Finally heterogeneities within the foundation reflecting subsidence, bad drainage, frost-defrost cycles or cavities can be mapped. The optimal design is based on a system with 10 to 20 receiver dipoles and one transmitter dipole (first or last of the array) with a dipole length typically of 10 cm that can be used in equatorial or in-line mode. Static resistivity measurements have been carried out at the laboratory scale over concrete slabs built to verify results obtained from the numerical modeling. Observed data fit very well the modeled data and validate the overall conclusions. Tests have been performed in December 2003 in some selected streets (6 visited, 3 re-visited) of Montreal using a CORIM system (Iris Instruments, France), a capacitively-coupled resistivity towed equatorial array that continuously record data collected with six receiver dipoles and one transmitter dipole. Typical acquisition sampling and velocity were 0,20-0,50 m and 1 to 2 km/h respectively. Although the system is not optimally designed for the applications described above it provides useful diagnostic information about the state of deterioration of pavement. Data have been imaged using 2D resistivity inversion. In general it shows a high resistivity for the shallow depth related to the asphalt layer and a decreasing resistivity with depth related to the concrete slab first and the granular foundation below. Lateral variations appear to be correlated with degradation of the concrete slab.

Orogenic delamination - dynamics, effects, and geological expression

NASA Astrophysics Data System (ADS)

Ueda, Kosuke; Gerya, Taras

2010-05-01

Unbundling of continental lithosphere and removal of its mantle portion have been described by two mutually rather exclusive models, convective thinning and integral delamination. Either disburdens the remaining lithosphere, weakens the remainder, and causes uplift and extension. Increased heat flux is likely to promote high-degree crustal melting, and has been viewed as a source for voluminous granitic intrusions in late or collapsing orogenic settings. Collapse may be driven by any of gravitational potential differences from orogen to foreland, by stress inversion in the unburdened domain, or by suction of a retreating trench. In this study, we investigate prerequisites, mechanism, and development paths for orogeny-related mantle lithosphere removal. Our experiments numerically reproduce delamination which self-consistently results from the dynamics of a decoupling collision zone. In particular, it succeeds without a seed facilitating initial separation of layers. External shortening of a continent - ocean - continent assembly, such as to initiate oceanic subduction, is lifted before the whole oceanic part is consumed, leaving slab pull to govern further convergence. Once buoyant continental crust enters, the collision zone locks, and convergence diminishes. Under favourable conditions, delamination then initiates close to the edge of the mantle wedge and at deep crustal levels. While it initially separates upper crust from lower crust according to the weakness minimum in the lithospheric strength profile, the lower crust is eventually also delaminated from the subducting lithospheric mantle, owing to buoyancy differences. The level of delamination within the lithosphere seems thus first rheology-controlled, then density-controlled. Subduction-coupled delamination is contingent on retreat and decoupling of the subducting slab, which in turn is dependent on effective rheological weakening of the plate contact. Weakening is a function of shear-heating and hereby of collision rate, melting and hydration, the latter two incorporating the effects of sediment subduction and phase changes. The drag available for slab retreat scales with the age of the descending oceanic lithosphere; integrated strength of the lithosphere and activation volume for mantle creep additionally control angle and depth of the descent. Fully developed delamination is observed from between 10 to 15 Ma after collision ceases, with following trenchward migration of the delamination front. Consequently, the main maximum extension migrates, while local, partly intermittent compression can be observed on smaller scale. Across the orogen, extension thus has a strongly diachronous main component. We track common surface observables such as heat flow, partially melted rocks (domal migmatites), and predicted geo-/thermochronological ages over the evolving plate boundary. Geochemical projections of our observations confirm potential contamination of reservoirs - although the net delamination level follows the Moho, some crustal remnants along the old slab still sink through the 660-discontinuity. On the other hand, the base of the delaminated domain is not as plain a contact as in concept. Where the contact of asthenosphere with delaminated crust is the location of high-degree melting, also traces of original lithospheric mantle can be entangled. Our results do not fully support the conceptual distinction between convective thinning and blockwise delamination. While the foundering portion initially retains a fairly coherent, slab-like perimeter, the actual separation of layers in a limited process-zone occurs in smaller -scale eddies. Also, convection of the whole uprising asthenosphere wedge is dynamically not discernible from the latter and crucial for the removal of lithospheric mantle. The removed lithosphere does initially not convect, but subsequently shows an increasing tendency to drip down. In the presented case, extension in the axial zone of the orogen is not (only) caused by unsupported gravitational potential of the core domain itself, but actively driven by slab retreat with a shallow mantle dynamic contribution.

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.

Subduction Drive of Plate Tectonics

NASA Astrophysics Data System (ADS)

Hamilton, W. B.

2003-12-01

Don Anderson emphasizes that plate tectonics is self-organizing and is driven by subduction, which rights the density inversion generated as oceanic lithosphere forms by cooling of asthenosphere from the top. The following synthesis owes much to many discussions with him. Hinge rollback is the key to kinematics, and, like the rest of actual plate behavior, is incompatible with bottom-up convection drive. Subduction hinges (which are under, not in front of, thin leading parts of arcs and overriding plates) roll back into subducting plates. The Pacific shrinks because bounding hinges roll back into it. Colliding arcs, increasing arc curvatures, back-arc spreading, and advance of small arcs into large plates also require rollback. Forearcs of overriding plates commonly bear basins which preclude shortening of thin plate fronts throughout periods recorded by basin strata (100 Ma for Cretaceous and Paleogene California). This requires subequal rates of advance and rollback, and control of both by subduction. Convergence rate is equal to rates of rollback and advance in many systems but is greater in others. Plate-related circulation probably is closed above 650 km. Despite the popularity of concepts of plumes from, and subduction into, lower mantle, there is no convincing evidence for, and much evidence against, penetration of the 650 in either direction. That barrier not only has a crossing-inhibiting negative Clapeyron slope but also is a compositional boundary between fractionated (not "primitive"), sluggish lower mantle and fertile, mobile upper mantle. Slabs sink more steeply than they dip. Slabs older than about 60 Ma when their subduction began sink to, and lie down on and depress, the 650-km discontinuity, and are overpassed, whereas younger slabs become neutrally buoyant in mid-upper mantle, into which they are mixed as they too are overpassed. Broadside-sinking old slabs push all upper mantle, from base of oceanic lithosphere down to the 650, back under shrinking oceans, forcing rapid Pacific spreading. Slabs suck forward overriding arcs and continental lithosphere, plus most subjacent mantle above the transition zone. Changes in sizes of oceans result primarily from transfer of oceanic lithosphere, so backarcs and expanding oceans spread only slowly. Lithosphere parked in, or displaced from, the transition zone, or mixed into mid-upper mantle, is ultimately recycled, and regional variations in age of that submerged lithosphere may account for some regional contrasts in MORB. Plate motions make no kinematic sense in either the "hotspot" reference frame (HS; the notion of fixed plumes is easily disproved) or the no-net-rotation frame (NNR) In both, for example, many hinges roll forward, impossible with gravity drive. Subduction-drive predictions are fulfilled, and paleomagnetic data are satisfied (as they are not in HS and NNR), in the alternative framework of propulsionless Antarctica fixed relative to sluggish lower mantle. Passive ridges migrate away from Antarctica on all sides, and migration of these and other ridges permits tapping fresh asthenosphere. (HS and NNR tend to fix ridges). Ridge migration and spreading rates accord with subduction drive. All trenches roll back when allowance is made for back-arc spreading and intracontinental deformation. Africa rotates slowly toward subduction systems in the NE, instead of moving rapidly E as in HS and NNR. Stable NW Eurasia is nearly stationary, instead of also moving rapidly, and S and E Eurasian deformation relates to subduction and rollback. The Americas move Pacificward at almost the full spreading rates of passive ridges behind them. Lithosphere has a slow net westward drift. Reference: W.B. Hamilton, An alternative Earth, GSA Today, in press.

Real-time measurement of flow rate in microfluidic devices using a cantilever-based optofluidic sensor.

PubMed

Cheri, Mohammad Sadegh; Latifi, Hamid; Sadeghi, Jalal; Moghaddam, Mohammadreza Salehi; Shahraki, Hamidreza; Hajghassem, Hasan

2014-01-21

Real-time and accurate measurement of flow rate is an important reqirement in lab on a chip (LOC) and micro total analysis system (μTAS) applications. In this paper, we present an experimental and numerical investigation of a cantilever-based optofluidic flow sensor for this purpose. Two sensors with thin and thick cantilevers were fabricated by engraving a 2D pattern of cantilever/base on two polymethylmethacrylate (PMMA) slabs using a CO2 laser system and then casting a 2D pattern with polydimethylsiloxane (PDMS). The basic working principle of the sensor is the fringe shift of the Fabry-Pérot (FP) spectrum due to a changing flow rate. A Finite Element Method (FEM) is used to solve the three dimensional (3D) Navier-Stokes and structural deformation equations to simulate the pressure distribution, velocity and cantilever deflection results of the flow in the channel. The experimental results show that the thin and thick cantilevers have a minimum detectable flow change of 1.3 and 4 (μL min(-1)) respectively. In addition, a comparison of the numerical and experimental deflection of the cantilever has been done to obtain the effective Young's modulus of the thin and thick PDMS cantilevers.

On the possibility of an alpha-sq omega-type dynamo in a thin layer inside the sun

NASA Technical Reports Server (NTRS)

Choudhuri, Arnab Rai

1990-01-01

If the solar dynamo operates in a thin layer of 10,000-km thickness at the interface between the convection zone and the radiative core, using the facts that the dynamo should have a period of 22 years and a half-wavelength of 40 deg in the theta-direction, it is possible to impose restrictions on the values which various dynamo parameters are allowed to have. It is pointed out that the dynamo should be of alpha-sq omega nature, and kinematical calculations are presented for free dynamo waves and for dynamos in thin rectangular slabs with appropriate boundary conditions. An alpha-sq omega dynamo is expected to produce a significant poloidal field which does not leak to the solar surface. It is found that the turbulent diffusity eta and alpha-coefficient are restricted to values within about a factor of 10, the median values being eta of about 10 to the 10th sq cm/sec and alpha of about 10 cm/sec. On the basis of mixing length theory, it is pointed out that such values imply a reasonable turbulent velocity of the order 30 m/s, but rather small turbulent length scales like 300 km.

Scars of the Farallon Plate in the High Plains Revealed by 3D Wavefield Imaging with the Earthscope Transportable Array

NASA Astrophysics Data System (ADS)

Pavlis, G. L.; Yang, X.

2012-12-01

We used P to S conversion data from the Earthscope Automated Receiver function Survey (EARS) to image the upper mantle from the west coast to the Mississippi River. We used 178,300 radial and transverse receiver function estimates that survived automated editing procedures defined by EARS. Processing delays by EARS limited the data to the period through April 5, 2012. We processed these data with a three-component, fully three-dimensional, prestack, wavefield imaging procedure that we have referred to previously as plane-wave migration. Previous results with earlier generations of the EARS data and the same technique revealed the presence of a continuous, east-dipping horizon throughout the entire Cordillera between a depth of approximately 200-450 km with hints of penetration of this horizon through the 410 km discontinuity. This surface was interpreted as a marker on the top of the actively subducting Juan de Fuca/Farallon slab through cross-validation with all published body wave tomography models derived from USArray data. The new results reveal a surprisingly similar feature under the high plains. We observe a high-amplitude, east-dipping horizon that begins near the Rocky Mountain front and intersects the 410 km discontinuity at approximately the longitude of the Kansas-Missouri border. The lateral extent of this feature, however, is more limited. It disappears to the north around the Kansas-Nebraska border and to the south within central Texas. This region corresponds closely with the "big break" defined in tomography models of Sigloch (2011. She interpreted this feature as a residual signature of a westward jump of the Farallon slab at the close of the Laramide orogeny that is commonly viewed as a period of flat-slab subduction. We suggest the feature we image is equivalent to the east-dipping feature presently seen under the Cordillera. The feature imaged in the Cordillera can be directly linked to active processes. If a comparable process maintains what we see in the high plains it may mark a boundary where the cratonic keel is overriding the mantle above the transition zone along a zone of deformation originally created in the Laramide. This may be an explanation of the elevated topography of the high plains. An alternative explanation is we are seeing a residual scar from the Laramide, but that would require this region of the mantle to have been static for the order of 70 Myr and that the craton moves over the mantle along a thin deformation zone.

Crustal Structure of the Yakutat Microplate: New Parameters for Understanding the Evolution of the Chugach-St.Elias Orogeny

NASA Astrophysics Data System (ADS)

Worthington, L. L.; Christeson, G. L.; van Avendonk, H. J.; Gulick, S. P.

2009-12-01

We present results of a 2008 marine seismic reflection/refraction survey acquired as part of the St. Elias Erosion and Tectonics Project (STEEP), a multi-disciplinary NSF-Continental Dynamics project aimed at tectonic-climate interaction, structural evolution and geodynamics in the Chugach-St. Elias orogen. The Chugach-St.Elias orogen is the result of flat-slab subduction and collision of the Yakutat (YAK) microplate with North Amercian (NA) on the southern Alaska margin during the last ~10Ma. A fundamental goal of STEEP is to address controversy related to the deep crustal structure of the YAK block itself, describe its offshore structural relationships and constrain its buoyancy in order to understand the orogenic driver. Marine seismic reflection profiles acquired across the offshore YAK microplate provide the first regional images of the top of the subducting YAK basement. The basement reflector is observed near the seafloor at the Dangerous River Zone (DRZ) and is overlain by up to 12 km of sediments near Kayak Island, resulting in a basement dip of ~3° in the direction of subduction. The basement reflector also shallows near the shelf-edge adjacent to the Transition Fault, the YAK-Pacific boundary. These observations are indicative of an overall regional basement tilt towards the NA continent. Two coincident wide-angle refraction profiles constrain YAK crustal thickness between 30-35km, >20km thicker than normal oceanic crust, and lower crustal velocities potentially >7km/s. Crustal velocity and thickness are comparable to the Kerguelen oceanic plateau and the Siletz terrane. These results are the first direct observations in support of the oceanic plateau theory for the origin of the YAK microplate. Crustal velocity and structure are continuous across the DRZ on the YAK shelf, which is historically described as a vertical boundary between continental crust on the east and oceanic basement on the west. Instead, we observe a gradual shallowing of elevated crustal velocities associated with the aforementioned basement high near DRZ. Interestingly, observed Moho arrivals across the profile do not mimic the dipping trajectory of the basement reflector, indicating that the YAK slab may be slightly wedge-shaped, thinning in the direction of subduction. If true, the following implications for the YAK-NA collision must be considered: first, that uplift and deformation have intensified through time as thicker, more buoyant YAK crust attempts to subduct; second, migration of intense uplift from west to east across the orogen is partly controlled by underlying slab structure at depth.

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.

Seismic structure of southern margin of the 2011 Tohoku-Oki Earthquake aftershocks area: slab-slab contact zone beneath northeastern Kanto, central Japan

NASA Astrophysics Data System (ADS)

Kurashimo, E.; Sato, H.; Abe, S.; Mizohata, S.; Hirata, N.

2011-12-01

The 2011 Tohoku-Oki Earthquake (Mw9.0) occurred on the Japan Trench off the eastern shore of northern Honshu, Japan. The southward expansion of the afterslip area has reached the Kanto region, central Japan (Ozawa et al., 2011). The Philippine Sea Plate (PHS) subducts beneath the Kanto region. The bottom of the PHS is in contact with the upper surface of the Pacific Plate (PAC) beneath northeastern Kanto. Detailed structure of the PHS-PAC contact zone is important to constrain the southward rupture process of the Tohoku-Oki Earthquake and provide new insight into the process of future earthquake occurrence beneath the Kanto region. Active and passive seismic experiments were conducted to obtain a structural image beneath northeastern Kanto in 2010 (Sato et al., 2010). The geometry of upper surface of the PHS has been revealed by seismic reflection profiling (Sato et al., 2010). Passive seismic data set is useful to obtain a deep structural image. Two passive seismic array observations were conducted to obtain a detailed structure image of the PHS-PAC contact zone beneath northeastern Kanto. One was carried out along a 50-km-long seismic line trending NE-SW (KT-line) and the other was carried out along a 65-km-long seismic line trending NW-SE (TM-line). Sixty-five 3-component portable seismographs were deployed on KT-line with 500 to 700 m interval and waveforms were continuously recorded during a four-month period from June, 2010. Forty-five 3-component portable seismographs were deployed on TM-line with about 1-2 km spacing and waveforms were continuously recorded during the seven-month period from June, 2010. Arrival times of earthquakes were used in a joint inversion for earthquake locations and velocity structure, using the iterative damped least-squares algorithm, simul2000 (Thurber and Eberhart-Phillips, 1999). The relocated hypocenter distribution shows that the seismicity along the upper surface of the PAC is located at depths of 45-75 km beneath northeastern Kanto. The seismicity associated with the northwestward subducting PHS can be traced to a depth of 60 km. The depth section of Vp/Vs structure shows the lateral variation of the Vp/Vs values along the top of the PHS. Clustered earthquakes are located in and around the high Vp/Vs zone. High Vp/Vs ratio and low Vp zone with low seismicity is observed in the slab-slab contact zone beneath northeastern Kanto. The heterogeneity of the slab-slab contact zone beneath northeastern Kanto may affect the southward expansion of the afterslip of the Tohoku-Oki Earthquake. Acknowledgments: This study was supported by the Earthquake Research Institute cooperative research program.

Structural load testing and flexure analysis of the Route 701 Bridge in Louisa County, Virginia : supplemental report.

DOT National Transportation Integrated Search

2006-01-01

A continuous slab bridge in Louisa County, Virginia, on Route 701 developed a planar horizontal crack along the length of all three spans. This project was designed to determine if the current 12-ton posted load restriction of the bridge (instituted ...

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 : ...

Structural load testing and flexure analysis of the Route 701 Bridge in Louisa County, Virginia.

DOT National Transportation Integrated Search

2004-01-01

A continuous slab bridge in Louisa County, Virginia, on Route 701 developed a planar horizontal crack along the length of all three spans. This project was designed to determine if the current load rating of the bridge could be raised and to document...

The Role of the Indian Slab on the Rotational Deformation around the Eastern Himalayan Syntaxis and Intraplate Volcanism in the Southwest China

NASA Astrophysics Data System (ADS)

Sandvol, E. A.

2016-12-01

Studies of the evolution of the India-Eurasia collision have shown that the geodynamic processes associated with trench/slab rollback in the western Pacific and Indonesia have played a significant role in the large-scale rotational deformational patterns and influenced the building of the Tibetan Plateau. Prior measurements of the surface crustal velocities across the Southeastern Tibetan Plateau, western Sichuan, Yunnan and Myanmar are characterized by clockwise rotation around the Eastern Himalayan Syntaxis (up to 1.7° per million years). Relative to South China, there is no eastward extrusion of crustal material beyond the eastern margin of the Tibetan Plateau. The crustal clockwise rotational deformation appears continues into northern Myanmar, accommodated by a series of East Northeast - West Southwest left-lateral strike-slip faults bounded between the Sagaing Fault and the Red River Fault. The relative contribution of crustal and mantle processes to surface clockwise rotational deformation remains to be determined. GPS, earthquake source and fault slip data indicate that crustal rotational deformation extends at least to the Sagaing Fault, the western boundary of the Burma microplate, however, mantle deformation inferred from SKS and SKKS shear wave splitting data deviates greatly from crustal deformation in regions south of 27°N. Whether this lack of coherence in crustal in mantle deformation extends west of the Saigaing Fault and across the Burma microplate remains unclear. The concave eastward curvature of the northern section of the Sagaing Fault may be related to the rotational push from the east. An additional factor that is important is the segmentation and geometry of the subducting Indian slab along the Indo-Burman Arc. There is some evidence from seismicity and focal mechanisms that the slab is broken into pieces. Furthermore, if the Indian slab is broken from slabs resting in the transition zone then the below-slab flow may be responsible for the intraplate volcanoes and N-S trending rifts in the Tengchong volcanic field, Yunnan Province, China. In order to better understand the interaction between the deformation of the crust along the boundaries of the Burma microplate we are hoping to use data from a planned 70-station broadband seismic array in the northern and central parts of Myanmar.

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.

Three-Dimensional Variation of the Slab Geometry Along Strike and Along Dip in the Cascadia Subduction

NASA Astrophysics Data System (ADS)

Gao, H.

2017-12-01

The crust and upper mantle seismic structure, spanning from the Juan de Fuca and Gorda spreading centers to the Cascade arc, is imaged with full-wave propagation simulation and ambient noise tomography. To retrieve Rayleigh-wave Empirical Green's Functions between station pairs, we process the vertical component of continuous seismic data recorded between 2004 and 2015 by about 800 stations, including three offshore seismic networks (the Cascadia Initiative Amphibious Array, the Blanco Transform OBS experiment, and the Gorda Deformation Zone OBS experiment) and all available broadband inland stations. The spreading centers have anomalously low shear-wave velocity beneath the oceanic lithosphere. Around the Cobb axial seamount, we observe a low velocity anomaly underlying a relatively thin oceanic lithosphere, indicating its influence on the Juan de Fuca ridge. The tomographic imaging reveals great details of the seismic feature of the oceanic lithosphere prior to and after subduction, which varies significantly along strike and along dip. On average, the thickness of the oceanic lithosphere is about 30-45 km. The Juan de Fuca lithosphere appears to be relatively thin around the ridge, especially beneath the Cobb axial seamount, and then gradually thickens with increasing distance from the ridge. The thickness of the Gorda plate appears to be constant, which is probably due to the small size of the subduction system from formation to subduction. It is noteworthy that the oceanic plate is imaged relatively weaker beneath the trench compared to other parts of the plate. We suggest that in addition to the possible hydration of the oceanic mantle lithosphere, other mechanisms must be considered to explain the observed seismic feature around the trench. Further landward, very low velocity anomalies are observed above the plate interface along the Cascade forearc, indicative of subducted sediments.

Lithospheric Contributions to Arc Magmatism: Isotope Variations Along Strike in Volcanoes of Honshu, Japan

PubMed

Kersting; Arculus; Gust

1996-06-07

Major chemical exchange between the crust and mantle occurs in subduction zone environments, profoundly affecting the chemical evolution of Earth. The relative contributions of the subducting slab, mantle wedge, and arc lithosphere to the generation of island arc magmas, and ultimately new continental crust, are controversial. Isotopic data for lavas from a transect of volcanoes in a single arc segment of northern Honshu, Japan, have distinct variations coincident with changes in crustal lithology. These data imply that the relatively thin crustal lithosphere is an active geochemical filter for all traversing magmas and is responsible for significant modification of primary mantle melts.

Design and simulation of a planar micro-optic free-space receiver

NASA Astrophysics Data System (ADS)

Nadler, Brett R.; Hallas, Justin M.; Karp, Jason H.; Ford, Joseph E.

2017-11-01

We propose a compact directional optical receiver for free-space communications, where a microlens array and micro-optic structures selectively couple light from a narrow incidence angle into a thin slab waveguide and then to an edge-mounted detector. A small lateral translation of the lenslet array controls the coupled input angle, enabling the receiver to select the transmitter source direction. We present the optical design and simulation of a 10mm x 10mm aperture receiver using a 30μm thick silicon waveguide able to couple up to 2.5Gbps modulated input to a 10mm x 30μm wide detector.

Omnidirectional and broadband absorption enhancement from trapezoidal Mie resonators in semiconductor metasurfaces

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

Pala, Ragip A.; Butun, Serkan; Aydin, Koray

2016-09-19

Light trapping in planar ultrathin-film solar cells is limited due to a small number of optical modes available in the thin-film slab. A nanostructured thin-film design could surpass this limit by providing broadband increase in the local density of states in a subwavelength volume and maintaining efficient coupling of light. Here we report a broadband metasurface design, enabling efficient and broadband absorption enhancement by direct coupling of incoming light to resonant modes of subwavelength scale Mie nanoresonators defined in the thin-film active layer. Absorption was investigated both theoretically and experimentally in prototypes consisting of lithographically patterned, two-dimensional periodic arrays ofmore » silicon nanoresonators on silica substrates. A crossed trapezoid resonator shape of rectangular cross section is used to excite broadband Mie resonances across visible and near-IR spectra. Our numerical simulations, optical absorption measurements and photocurrent spectral response measurements demonstrate that crossed trapezoidal Mie resonant structures enable angle-insensitive, broadband absorption. A short circuit current density of 12.0 mA/cm 2 is achieved in 210 nm thick patterned Si films, yielding a 4-fold increase compared to planar films of the same thickness. As a result, it is suggested that silicon metasurfaces with Mie resonator arrays can provide useful insights to guide future ultrathin-film solar cell designs incorporating nanostructured thin active layers.« less

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.

Tectonic evolution and mantle structure of the Caribbean

NASA Astrophysics Data System (ADS)

van Benthem, Steven; Govers, Rob; Spakman, Wim; Wortel, Rinus

2013-06-01

investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic P wave velocity structure under the Caribbean region. In the upper mantle, positive seismic anomalies are imaged under the Lesser Antilles and Puerto Rico. These anomalies are interpreted as remnants of Atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the Lesser Antilles island arc during the past 45 Myr. The imaged Lesser Antilles slab consists of a northern and southern anomaly, separated by a low-velocity anomaly across most of the upper mantle, which we interpret as the subducted North America-South America plate boundary. The southern edge of the imaged Lesser Antilles slab agrees with vertical tearing of South America lithosphere. The northern Lesser Antilles slab is continuous with the Puerto Rico slab along the northeastern plate boundary. This results in an amphitheater-shaped slab, and it is interpreted as westward subducting North America lithosphere that remained attached to the surface along the northeastern boundary of the Caribbean plate. At the Muertos Trough, however, material is imaged until a depth of only 100 km, suggesting a small amount of subduction. The location and length of the imaged South Caribbean slab agrees with proposed subduction of Caribbean lithosphere under the northern South America plate. An anomaly related to proposed Oligocene subduction at the Nicaragua rise is absent in the tomographic model. Beneath Panama, a subduction window exists across the upper mantle, which is related to the cessation of subduction of the Nazca plate under Panama since 9.5 Ma and possibly the preceding subduction of the extinct Cocos-Nazca spreading center. In the lower mantle, two large anomaly patterns are imaged. The westernmost anomaly agrees with the subduction of Farallon lithosphere. The second lower mantle anomaly is found east of the Farallon anomaly and is interpreted as a remnant of the late Mesozoic subduction of North and South America oceanic lithosphere at the Greater Antilles, Aves ridge, and Leeward Antilles. The imaged mantle structure does not allow us to discriminate between an "Intra-Americas origin" and a "Pacific origin" of the Caribbean plate.

Tectonic evolution and mantle structure of the Caribbean

NASA Astrophysics Data System (ADS)

Benthem, Steven; Govers, Rob; Spakman, Wim; Wortel, Rinus

2013-06-01

investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic P wave velocity structure under the Caribbean region. In the upper mantle, positive seismic anomalies are imaged under the Lesser Antilles and Puerto Rico. These anomalies are interpreted as remnants of Atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the Lesser Antilles island arc during the past ~45 Myr. The imaged Lesser Antilles slab consists of a northern and southern anomaly, separated by a low-velocity anomaly across most of the upper mantle, which we interpret as the subducted North America-South America plate boundary. The southern edge of the imaged Lesser Antilles slab agrees with vertical tearing of South America lithosphere. The northern Lesser Antilles slab is continuous with the Puerto Rico slab along the northeastern plate boundary. This results in an amphitheater-shaped slab, and it is interpreted as westward subducting North America lithosphere that remained attached to the surface along the northeastern boundary of the Caribbean plate. At the Muertos Trough, however, material is imaged until a depth of only 100 km, suggesting a small amount of subduction. The location and length of the imaged South Caribbean slab agrees with proposed subduction of Caribbean lithosphere under the northern South America plate. An anomaly related to proposed Oligocene subduction at the Nicaragua rise is absent in the tomographic model. Beneath Panama, a subduction window exists across the upper mantle, which is related to the cessation of subduction of the Nazca plate under Panama since 9.5 Ma and possibly the preceding subduction of the extinct Cocos-Nazca spreading center. In the lower mantle, two large anomaly patterns are imaged. The westernmost anomaly agrees with the subduction of Farallon lithosphere. The second lower mantle anomaly is found east of the Farallon anomaly and is interpreted as a remnant of the late Mesozoic subduction of North and South America oceanic lithosphere at the Greater Antilles, Aves ridge, and Leeward Antilles. The imaged mantle structure does not allow us to discriminate between an "Intra-Americas origin" and a "Pacific origin" of the Caribbean plate.

Seismological observations at the Northern Andean region of Colombia: Evidence for a shallowly subducting Caribbean Slab and an extensional regime in the upper plate

NASA Astrophysics Data System (ADS)

Monsalve, G.; Cardona, A.; Yarce, J.; Alvira, D.; Poveda, E.

2013-05-01

A number of seismological observations, among which we can mention teleseismic travel time residuals, P to S receiver functions and Pn velocity quantification, suggest a clear distinction between the seismic structure of the crust and uppermost mantle between the plains on the Caribbean coast of Colombia and the mountains at the Northern Andean region. Absolute and relative travel time residuals indicate the presence of a seismically fast material in the upper mantle beneath northern Colombia; preliminary results of Pn studies show a region of relatively slow Pn velocities (between 7.8 and 7.9 km/s) underneath the Caribbean coast, contrasting with values greater than 8 km/s beneath the Central and Western cordilleras of Colombia, and the Pacific coast; receiver functions suggest a significantly thinner crust beneath the Caribbean coast, with a crustal thickness between 25 and 30 km, than beneath the Northern Andean zone at the cordilleras of Colombia, where it exceeds 40 km and reaches about 57 km at the location of Bogota. Besides the obviuos discrepancies that appear in response to different topography, we think that the seismological observations are a consequence of the presence of two very distinct slab segments beneath Colombia and contrasting behaviors of the upper plate, which correspond to Caribbean and Nazca subductions. Our seismic observations can be explained by a shallowly subducting Caribbean Plate, in the absence of an asthenospheric wedge, that steepens at about the location of the Bucaramanga nest, and a thinned continental crust that reflects an extensional component linked to oblique convergence of the Caribbean, which contrasts with the crustal thickening in the Andean Cordillera linked to crustal shortening and Nazca plate subuction. These new data are consistent with the idea of of a relatively warm Nazca slab of Neogene age which seems to have a relatively frontal convergence, and a colder, more buoyant Caribbean slab which represents an oceanic plateau of Cretaceous age that is characterized by an oblique convergence relation that has promoted extensional tectonics in the upper plate.

The Role of a Weak Layer at the Base of an Oceanic Plate on Subduction Dynamics

NASA Astrophysics Data System (ADS)

Carluccio, R.; Moresi, L. N.; Kaus, B. J. P.

2017-12-01

Plate tectonics relies on the concept of an effectively rigid lithospheric lid moving over a weaker asthenosphere. In this model, the lithosphere asthenosphere boundary (LAB) is a first-order discontinuity that accommodates differential motion between tectonic plates and the underlying mantle. Recent seismic studies have revealed the existence of a low velocity and high electrical conductivity layer at the base of subducting tectonic plates. This thin layer has been interpreted as being weak and slightly buoyant and it has the potential to influence the dynamics of subducting plates. However, geodynamically, the role of a weak layer at the base of the lithosphere remains poorly studied, especially at subduction zones. Here, we use numerical models to investigate the first-order effects of a weak buoyant layer at the LAB on subduction dynamics. We employ both 2-D and 3-D models in which the slab and the mantle are either linear viscous or have a more realistic temperature-dependent, visco-elastic-plastic rheology and we vary the properties of the layer at the base of the oceanic lithosphere. Our results show that the presence of a weak layer affects the dynamics of plates, primarily by increasing the subduction speed and also influences the morphology of subducting slab. For moderate viscosity contrasts (<100) and a layer thickness of ˜30 km, it increases the plate velocity but not the overall shape of the slab. However, for larger viscosity contrasts (>1000), it can also change the morphology of the subduction itself and for thinner and more buoyant layers, the overall effect is reduced. The overall impact of this effects may depend on the effective contrast between the properties of the slab and the weak layer + mantle systems, and so, by the layer characteristics modelled such as its viscosity, density, thickness and rheology. In this study, we show and summarise this impact consistently with the recent seismological constraints and observations, for example, a pile-up of weak material in the bending zone of the subducting plate.

Transition from slab to slabless: Results from the 1993 Mendocino triple junction seismic experiment

USGS Publications Warehouse

Beaudoin, B.C.; Godfrey, N.J.; Klemperer, S.L.; Lendl, C.; Trehu, A.M.; Henstock, T.J.; Levander, A.; Holl, J.E.; Meltzer, A.S.; Luetgert, J.H.; Mooney, W.D.

1996-01-01

Three seismic refraction-reflection profiles, part of the Mendocino triple junction seismic experiment, allow us to compare and contrast crust and upper mantle of the North American margin before and after it is modified by passage of the Mendocino triple junction. Upper crustal velocity models reveal an asymmetric Great Valley basin overlying Sierran or ophiolitic rocks at the latitude of Fort Bragg, California, and overlying Sierran or Klamath rocks near Redding, California. In addition, the upper crustal velocity structure indicates that Franciscan rocks underlie the Klamath terrane east of Eureka, California. The Franciscan complex is, on average, laterally homogeneous and is thickest in the triple junction region. North of the triple junction, the Gorda slab can be traced 150 km inboard from the Cascadia subduction zone. South of the triple junction, strong precritical reflections indicate partial melt and/or metamorphic fluids at the base of the crust or in the upper mantle. Breaks in these reflections are correlated with the Maacama and Bartlett Springs faults, suggesting that these faults extend at least to the mantle. We interpret our data to indicate tectonic thickening of the Franciscan complex in response to passage of the Mendocino triple junction and an associated thinning of these rocks south of the triple junction due to assimilation into melt triggered by upwelling asthenosphere. The region of thickened Franciscan complex overlies a zone of increased scattering, intrinsic attenuation, or both, resulting from mechanical mixing of lithologies and/or partial melt beneath the onshore projection of the Mendocino fracture zone. Our data reveal that we have crossed the southern edge of the Gorda slab and that this edge and/or the overlying North American crust may have fragmented because of the change in stress presented by the edge.

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.

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).

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.

Development of a Cost-Effective Modular Pixelated NaI(Tl) Detector for Clinical SPECT Applications

PubMed Central

Rozler, Mike; Liang, Haoning; Chang, Wei

2013-01-01

A new pixelated detector for high-resolution clinical SPECT applications was designed and tested. The modular detector is based on a scintillator block comprised of 2.75×2.75×10 mm3 NaI(Tl) pixels and decoded by an array of 51 mm diameter single-anode PMTs. Several configurations, utilizing two types of PMTs, were evaluated using a collimated beam source to measure positioning accuracy directly. Good pixel separation was observed, with correct pixel identification ranging from 60 to 72% averaged over the entire area of the modules, depending on the PMT type and configuration. This translates to a significant improvement in positioning accuracy compared to continuous slab detectors of the same thickness, along with effective reduction of “dead” space at the edges. The observed 10% average energy resolution compares well to continuous slab detectors. The combined performance demonstrates the suitability of pixelated detectors decoded with a relatively small number of medium-sized PMTs as a cost-effective approach for high resolution clinical SPECT applications, in particular those involving curved detector geometries. PMID:24146436

Electrically tunable robust edge states in graphene-based topological photonic crystal slabs

NASA Astrophysics Data System (ADS)

Song, Zidong; Liu, HongJun; Huang, Nan; Wang, ZhaoLu

2018-03-01

Topological photonic crystals are optical structures supporting topologically protected unidirectional edge states that exhibit robustness against defects. Here, we propose a graphene-based all-dielectric photonic crystal slab structure that supports two-dimensionally confined topological edge states. These topological edge states can be confined in the out-of-plane direction by two parallel graphene sheets. In the structure, the excitation frequency range of topological edge states can be dynamically and continuously tuned by varying bias voltage across the two parallel graphene sheets. Utilizing this kind of architecture, we construct Z-shaped channels to realize topological edge transmission with diffrerent frequencies. The proposal provides a new degree of freedom to dynamically control topological edge states and potential applications for robust integrated photonic devices and optical communication systems.

Slotted rectangular waveguide with dielectric sandwich structure inside

NASA Astrophysics Data System (ADS)

Abdullin, R. R.; Sokolov, R. I.

2018-03-01

This paper continues the series of works devoted to the investigation of leaky-wave antenna based on layered rectangular waveguide with periodic transverse slots in broad face. Previously developed wavenumber calculation technique has been adapted for analysis of slotted sandwich waveguide with three layers at least. The paper provides the numerical results of velocity factor dependencies for partially filled slotted rectangular waveguide containing a dielectric slab in the middle position inside or an air gap between two dielectric slabs. Additionally, dispersion properties are also considered for multilayer waveguide with linear laws combinations of thickness and permittivity. This allows recognizing the trends to develop new prospective antennas with complex patterns of tilt angle change. All numerical results obtained are confirmed with the in-situ measurements of transmission coefficient phase.

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...

Lateral evolution of the deep crustal structure of the Lesser Antilles Island arc from wide-angle seismic modelling.

NASA Astrophysics Data System (ADS)

Klingelhoefer, F.; Laurencin, M.; Marcaillou, B.; Graindorge, D.; Evain, M.; Lebrun, J. F.

2016-12-01

One of the goals of the Antithesis cruises (2013 and 2016) was investigating the deep structure of the Lesser Antilles subduction zone in order to: 1) constrain the possible along-strike variations of deep margin structures and slab geometry, 2) assess the nature of the crust and 3) discuss the potential impact of these structures on seismic hazard. Four combined wide-angle and multichannel seismic profiles were acquired between Barbuda and the Virgin Islands using 66 ocean bottom seismometers, a 4.5 km digital streamer and a 7200 cu inch seismic source. Along every line, we performed forward modelling of the wide-angle seismic data, gravity models and synthetic data calculations. The 5-7-km-thick subducting Atlantic oceanic plate is modelled with a single layer along every profile. The sedimentary prism fill is globally thin with maximal 5 km thick and 20-30 km wide. The 18-km-thick Caribbean crust is subdivided in 2 or 3 layers interpreted, from top to bottom, as following. A 2 to 4 km thick upper layer with velocity ranging from 2.5 to 3.5 km/s possibly consists of consolidate sediments or a carbonate platform. The underlying 4 to 6 km thick layer, with velocity ranging from 4.7 to 6.15 km/s might correspond to volcanic products. The lower 15 km thick lower crustal layer shows velocity up to 7.4 km/s, typical of basal velocities in oceanic crust. The structure and velocity model is thus closely consistent with a possibly overthickened oceanic crust. Our southernmost model, offshore of Barbuda, reveal a general crust structure and slab geometry which appear very to those described South of Guadeloupe along a line proposed by Kopp et al. (2011). It suggests an overall homogeneity for these structural features within the central segment of the Lesser Antilles (Martinique - Antigua). When the overall structure of the Caribbean plate is stable, the deep structure of the frontal margin and slab geometry is evolving from south to north. The wideness and thickness of the prism decrease toward the north as a consequence of the presence of blocking ridges and less sediment inputs. Frontal bending of the slab is also decreasing toward the north leading to a less steep slab within the first 30 kilometers as a consequence of increasing obliquity of subduction in the northern Antilles. This phenomena may increase the wideness of a seismogenic zone?

Heterogeneous source components of intraplate basalts from NE China induced by the ongoing Pacific slab subduction

NASA Astrophysics Data System (ADS)

Chen, Huan; Xia, Qun-Ke; Ingrin, Jannick; Deloule, Etienne; Bi, Yao

2017-02-01

The subduction of oceanic slabs is widely accepted to be a main reason for chemical heterogeneities in the mantle. However, determining the contributions of slabs in areas that have experienced multiple subduction events is often difficult due to possible overlapping imprints. Understanding the temporal and spatial variations of source components for widespread intraplate small volume basalts in eastern China may be a basis for investigating the influence of the subducted Pacific slab, which has long been postulated but never confirmed. For this purpose, we investigated the Chaihe-aershan volcanic field (including more than 35 small-volume Quaternary basaltic volcanoes) in NE China and measured the oxygen isotopes and water content of clinopyroxene (cpx) phenocrysts using secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR), respectively. The water content of magma was then estimated based on the partition coefficient of H2O between cpx and the basaltic melt. The δ18O of cpx phenocrysts (4.28‰ to 8.57‰) and H2O content of magmas (0.19 wt.%-2.70 wt.%) show large variations, reflecting the compositional heterogeneity of the mantle source. The δ18O values and H2O content within individual samples also display considerable variation, suggesting the mixing of magmas and that the magma mixing occurred shortly before the eruption. The relation between the δ18O values of cpx phenocrysts and the H2O/Ce ratio, Ba/Th ratio and Eu anomaly of whole rocks demonstrates the contributions of three components to the mantle source (hydrothermally altered upper oceanic crust and marine sediments, altered lower gabbroic oceanic crust, and ambient mantle). The proportions of these three components have varied widely over time (∼1.37 Ma to ∼0.25 Ma). The Pacific slab is constantly subducted under eastern Asia and continuously transports recycled materials to the deep mantle. The temporal heterogeneity of the source components may be caused by ongoing Pacific slab subduction. Combined with other basalt localities in eastern China (Shuangliao basalts, Taihang basalts and Shangdong basalts), the contributions of recycled oceanic components in their mantle source are heterogeneous. This spatial heterogeneity of mantle sources may be induced by variable alterations and dehydration during the recycling process of the Pacific slab. Our results show that the source components of Cenozoic intraplate small-volume basalts in eastern China are temporally and spatially heterogeneous, which is likely induced by the ongoing subduction of the Pacific slab. This demonstrates that integrating the temporal variations in geochemical characteristics and tectonic history of a study region can identify the subducted oceanic plate that induced enriched components in the mantle source of intraplate basalts.

Prevalence of African swine fever virus and classical swine fever virus antibodies in pigs in Benue State, Nigeria.

PubMed

Asambe, A; Sackey, A K B; Tekdek, L B

2018-03-01

This study investigated the prevalence of African swine fever virus (ASFV) and classical swine fever virus (CSFV) antibodies in pigs in Benue State, Nigeria. Serum samples were collected from a total of 460 pigs, including 416 from 74 piggeries and 44 from Makurdi slaughter slab. The samples were analysed using indirect enzyme-linked immunosorbent assay (ELISA) test kit to detect the presence of ASFV antibodies, while competitive ELISA test kit was used to detect antibodies to CSFV. Our findings showed a total ASF prevalence of 13 (2.8%), while prevalences of 7 (1.7%) and 6 (13.6%) were observed in piggeries and in Makurdi slaughter slab, respectively. However, no CSFV antibody sera were detected in this study. Relatively higher ASFV antibody-positive pigs were detected in the slaughter slab than in piggeries. The difference in prevalence of ASF between the two locations was significantly associated (p = 0.017). These findings suggest the presence of ASFV antibody-positive pig in Benue State, Nigeria. Continuous surveillance and monitoring of these diseases among pigs in Nigeria to prevent any fulminating outbreak are recommended.

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.

Instrumentation by accelerometers and distributed optical fiber sensors of a real ballastless track structure

NASA Astrophysics Data System (ADS)

Chapeleau, Xavier; Cottineau, Louis-Marie; Sedran, Thierry; Cailliau, Joël; Gueguen, Ivan; Dumoulin, Jean

2015-04-01

While relatively expensive to build, ballastless track structures are presently seen as an attractive alternative to conventional ballast. Firstly, they are built quickly since the slabs can be cast in place in an automated fashion by a slipform paver. Secondly, with its service life of at least 60 years, they requires little maintenance and hence they offers great availability. Other reasons for using ballastless tracks instead of ballasted tracks are the lack of suitable ballast material and the need of less noise and vibration for high-speed, in particularly. In the framework of a FUI project (n° 072906053), a new ballastless track structure based on concrete slabs was designed and its thermal-mechanical behavior in fatigue under selected mechanical and thermal conditions was tested on a real scale mockup in our laboratory [1,2]. By applying to the slabs both together mechanical stresses and thermal gradients, finite elements simulation and experimental results show that the weather conditions influence significantly the concrete slabs curvatures and by the way, the contact conditions with the underlaying layers. So it is absolutely necessary to take into account this effect in the design of the ballastless track structures in order to guarantee a long target life of at least of 50 years. After design and experimental tests in laboratory, a real ballastless track structure of 1km was built in France at the beginning of year 2013. This structure has 2 tracks on which several trains circulate every day since the beginning of year 2014. Before the construction, it was decided to monitor this structure to verify that the mechanical behavior is conform to the simulations. One part of the instrumentation is dedicated to monitor quasi-continuously the evolution of the curvature of a concrete slab. For this, 2 accelerometers were fixed on the slab under the track. One was placed on the edge and the other in the middle of the slab. The acquisition of the signals by a nano computer (called Pegase and developed at Ifsttar for data acquisition [3]) were performed automatically every time that a threshold is exceeded due to the passage of a train. These data are then send to a web server via a 3G Wireless Network. Many data was thus stored daily for several months. Moreover, several thermocouples were embedded at different depths in order to measure thermal gradients into the track slab. From the accelerometers signals, the deflection of the track slab are then obtained and compared to the measurements of thermal gradients. This comparison show clearly the daily evolution of the curvature with the thermal gradient changes as estimated by the simulation. This result was confirmed indirectly by strain profile measurements obtained by the Rayleigh fiber optic sensing technique. Two fiber optics embedded in the upper and lower part of the foundation slab show that contact conditions between the foundation slab and the track slab change with thermal gradient. 1 - X. Chapeleau, T. Sedran, L.-M. Cottineau, J. Cailliau, F. Taillade, I. Gueguen, J.-M. Henault. Study of ballastless track structure monitoring by distributed optical fiber sensors on a real-scale mockup in laboratory. Engineering Structures, 2013, 56, pp. 1751-1757. 2 - X. Chapeleau, L.-M. Cottineau, T. Sedran, J. Cailliau, I. Gueguen. Instrumentation by distributed optical fiber sensors of a new ballastless track structure. EGU General Assembly 2013, held 7-12 April, 2013 in Vienna, Austria, id. EGU2013-8946 3 - V. Le Cam, L. Lemarchand, L-M. Cottineau and F. Bourquin. Design of a generic smart and wireless sensors network - benefits of emerging technologies. Structural Health Monitoring 2008, 1(1), pp. 598-605.

Plate tectonics. Seismological detection of slab metamorphism.

PubMed

Julian, Bruce

2002-05-31

The occurrence of more or less continuous ground vibrations ("volcanic tremor") is an important indicator of volcanic activity. But results from the "Hi-net" seismic network in Japan reported by Obara show that continuous ground vibrations can occur far away from any volcanic activity. In his Perspective, Julian discusses the idea that this tremor is excited by flow of metamorphic fluids. He also identifies other possible locations where such a tremor may be detected and explains what may be learnt from measuring it.

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.

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.

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...

Receiver Functions Imaging of the Moho and LAB in the Southern Caribbean plate boundary and Venezuela

NASA Astrophysics Data System (ADS)

Masy, J.; Levander, A.; Niu, F.

2011-12-01

We have made teleseismic Ps and Sp receiver functions from data recorded from 2003 to 2009 by the permanent national seismic network of Venezuela, the BOLIVAR (Broadband Onshore-offshore Lithospheric Investigation of Venezuela and the Antilles arc Region) and WAVE (Western Array for Venezuela) experiments. The receiver functions show rapid variations in Moho and lithosphere-asthenosphere boundary (LAB) depths both across and along the southern Caribbean plate boundary region. We used a total of 69 events with Mw > 6 occurring at epicentral distances from 30° to 90° for the Ps receiver functions, and 43 events with Mw > 5.7 from 55° to 85° to make Sp receiver functions. For CCP stacking we constructed a 3D velocity model from numerous active source profiles (Schmitz et al., 2001; Bezada et al., 2007; Clark et al., 2008; Guedez, 2008; Magnani et al., 2009), from finite-frequency P wave upper mantle tomography model of Bezada et al., (2010) and the Rayleigh wave tomography model of Miller et al., (2009). The Moho ranges in depth from ~25 km beneath the Caribbean Large Igneous Provinces to ~55 km beneath the Mérida Andes in western Venezuela. These results are consistent with previous receiver functions studies (Niu et al., 2007) and the available active source profiles. Beneath the Maracaibo Block in northwestern Venezuela, we observe a strong positive signal at 40 to 60 km depth dipping ~6° towards the continent. We interpret this as the Moho of the Caribbean slab subducting beneath northernmost South America from the west. Beneath northern Colombia and northwestern Venezuela the top of this slab has been previously inferred from intermediate depth seismicity (Malavé and Suarez, 1995), which indicates a slab dipping between 20° - 30° beneath Lake Maracaibo. Our results could indicate that the slab is tearing beneath Lake Maracaibo as suggested previously by Masy et al. (2011). The deeper (> 100 km depth) part of the slab has been imaged using P-wave tomography (Bezada et al, 2010). Like others we attribute the uplift of the Mérida Andes to flat Caribbean slab subduction (for example Kellogg and Bonini, 1982). In central Venezuela beneath the Cordillera de la Costa we observe a positive signal shallower than the Moho at <30 km depth beneath the entire range. We interpret this as a detachment surface beneath Caribbean & arc terranes thrust onto the SA margin (Bezada et al., 2010). The lithosphere-asthenosphere boundary (LAB) beneath the Mérida Andes is shallow, ~65km depth, and parallels the range. In the plate boundary region under the Cordillera de la Costa the lithosphere is also thin, ~65km, beneath the Cariaco basin the lithosphere thickens to 85 km. In the far east under Serranía del Interior the lithosphere is ~75 km. Cratonic lithosphere thickness varies from 85 to 100 km.

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.

Lithospheric Structure and Shape of Subducting Nazca Plate in the Pampean Flat Slab Region of Argentina

NASA Astrophysics Data System (ADS)

Linkimer, L.; Beck, S. L.; Zandt, G.; Alvarado, P. M.; Anderson, M. L.; Gilbert, H. J.; Zhang, H.

2011-12-01

We obtain earthquake locations and a detailed three-dimensional model of the subduction zone velocity structure in west-central Argentina by applying a regional-scale double-difference tomography algorithm to earthquake data recorded by the SIEMBRA (2007-2009) and ESP (2008-2010) broadband seismic networks. In this region, the flat subduction of the Nazca Plate including the Juan Fernandez Ridge is spatially correlated in the overriding South America Plate with a gap in the arc volcanism and the thick-skinned, basement-cored uplifts of the Sierras Pampeanas. Our model shows the subducting Nazca Plate as a mostly continuous band of increased (2-6%) P- and S- wave velocities (Vp and Vs). The lithospheric mantle of the South America Plate appears to be heterogeneous but mostly characterized by Vp of 8.0-8.2 km/s, Vs of 4.5-4.7 km/s, and Vp/Vs ratio of 1.75-1.78, which is consistent with either a depleted lherzolite or harzburgite. We observe a region of higher Vp/Vs ratio (1.78-1.80) that we correlated with up to 10% hydration of mantle peridotites above the flat slab. In addition, we observe localized regions of lower Vp/Vs ratio (1.71-1.73) in the mantle above the westernmost part of the flat slab, suggesting orthopyroxene enrichment. Our velocity observations are consistent with the presence of Paleozoic carbonate rocks in the Precordillera and the differences in composition for the Sierras Pampeanas basement: a more mafic composition for Cuyania Terrane in the west and a more felsic composition for the Pampia Terrane in the east. Additionally, we present new contours for the Wadati-Benioff Zone (WBZ). The top of the WBZ of the Nazca Plate is nearly flat at ~100 km depth approximately within the region of latitude 28-32°S and longitude 70-68.5°W. We determined that WBZ is a single layer of seismicity with thickness of 10-15 km, which may correspond to the dehydration of the subducting oceanic mantle. We found that the flat slab region is wider (~240 km) than the Juan Fernandez Ridge offshore (~100 km), and together with the shape of the slab contours may reflect the response of the geometry of the slab to the southward migration of the buoyant ridge. The non-uniform spatial distribution of the slab seismicity may reflect the variability in the hydration state of the subducting Nazca Plate with greater release of water from the subducted ridge region.

Shape of Subducting Nazca Plate and Lithospheric Structure in the Pampean Flat Slab Region of Argentina

NASA Astrophysics Data System (ADS)

Linkimer, L.; Beck, S. L.; Zandt, G.; Alvarado, P. M.; Anderson, M. L.; Gilbert, H. J.; Zhang, H.

2013-05-01

We obtain earthquake locations and a detailed three-dimensional model of the subduction zone velocity structure in west-central Argentina by applying a regional-scale double-difference tomography algorithm to earthquake data recorded by the SIEMBRA (2007-2009) and ESP (2008-2010) broadband seismic networks. In this region, the flat subduction of the Nazca Plate including the Juan Fernandez Ridge is spatially correlated in the overriding South America Plate with a gap in the arc volcanism and the thick-skinned, basement-cored uplifts of the Sierras Pampeanas. Our model shows the subducting Nazca Plate as a mostly continuous band of increased (2-6%) P- and S- wave velocities (Vp and Vs). The lithospheric mantle of the South America Plate appears to be heterogeneous but mostly characterized by Vp of 8.0-8.2 km/s, Vs of 4.5-4.7 km/s, and Vp/Vs ratio of 1.75-1.78, which is consistent with either a depleted lherzolite or harzburgite. We observe a region of higher Vp/Vs ratio (1.78-1.80) that we correlated with up to 10% hydration of mantle peridotites above the flat slab. In addition, we observe localized regions of lower Vp/Vs ratio (1.71-1.73) in the mantle above the westernmost part of the flat slab, suggesting orthopyroxene enrichment. Our velocity observations are consistent with the presence of Paleozoic carbonate rocks in the Precordillera and the differences in composition for the Sierras Pampeanas basement: a more mafic composition for Cuyania Terrane in the west and a more felsic composition for the Pampia Terrane in the east. Additionally, we present new contours for the Wadati-Benioff Zone (WBZ). The top of the WBZ of the Nazca Plate is nearly flat at ~100 km depth approximately within the region of latitude 28-32°S and longitude 70-68.5°W. We determined that WBZ is a single layer of seismicity with thickness of 10-15 km, which may correspond to the dehydration of the subducting oceanic mantle. We found that the flat slab region is wider (~240 km) than the Juan Fernandez Ridge offshore (~100 km), and together with the shape of the slab contours may reflect the response of the geometry of the slab to the southward migration of the buoyant ridge. The non-uniform spatial distribution of the slab seismicity may reflect the variability in the hydration state of the subducting Nazca Plate with greater release of water from the subducted ridge region.

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.

Picosecond time scale dynamics of short pulse laser-driven shocks in tin

NASA Astrophysics Data System (ADS)

Grigsby, W.; Bowes, B. T.; Dalton, D. A.; Bernstein, A. C.; Bless, S.; Downer, M. C.; Taleff, E.; Colvin, J.; Ditmire, T.

2009-05-01

The dynamics of high strain rate shock waves driven by a subnanosecond laser pulse in thin tin slabs have been investigated. These shocks, with pressure up to 1 Mbar, have been diagnosed with an 800 nm wavelength ultrafast laser pulse in a pump-probe configuration, which measured reflectivity and two-dimensional interferometry of the expanding rear surface. Time-resolved rear surface expansion data suggest that we reached pressures necessary to shock melt tin upon compression. Reflectivity measurements, however, show an anomalously high drop in the tin reflectivity for free standing foils, which can be attributed to microparticle formation at the back surface when the laser-driven shock releases.

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...

Mantle Flow and Melting Processes Beneath Back-Arc Basins

NASA Astrophysics Data System (ADS)

Hall, P. S.

2007-12-01

The chemical systematics of back-arc basin basalts suggest that multiple mechanisms of melt generation and transport operate simultaneously beneath the back-arc, resulting in a continuum of melts ranging from a relatively dry, MORB-like end-member to a wet, slab-influenced end-member [e.g., Kelley et al., 2006; Langmuir et al., 2006]. Potential melting processes at work include adiabatic decompression melting akin to that at mid-ocean ridges, diapiric upwelling of hydrous and/or partially molten mantle from above the subducting lithospheric slab [e.g., Marsh, 1979; Hall and Kincaid, 2001; Gerya and Yuen, 2003], and melting of back-arc mantle due to a continuous flux of slab-derived hydrous fluid [Kelley et al., 2006]. In this study, we examine the potential for each of these melting mechanisms to contribute to the observed distribution of melts in back-arc basins within the context of upper mantle flow (driven by plate motions) beneath back-arcs, which ultimately controls temperatures within the melting region. Mantle velocities and temperatures are derived from numerical geodynamic models of subduction with back-arc spreading that explicitly include adiabatic decompression melting through a Lagrangian particle scheme and a parameterization of hydrous melting. Dynamical feedback from the melting process occurs through latent heating and viscosity increases related to dehydration. A range of parameters, including subduction rate and trench-back-arc separation distances, is explored. The thermal evolution of individual diapirs is modeled numerically as they traverse the mantle, from nucleation above the subducting slab to melting beneath the back-arc spreading center, and a range of diapir sizes and densities and considered.

Absolute Plate Motion Control Since the Triassic from the Cocos Slab and its Associated Subduction Record in Mexico

NASA Astrophysics Data System (ADS)

Boschman, L.; Van Hinsbergen, D. J. J.; Langereis, C. G.; Molina-Garza, R. S.; Kimbrough, D. L.; Spakman, W.

2017-12-01

A positive wave speed anomaly interpreted as the Cocos slab stretches from the uppermost mantle at the Middle America trench in the west, to the lowermost mantle below the Atlantic in the east. The length and continuity of this slab indicates long-lived, uninterrupted eastward subduction of the attached Cocos Plate and its predecessor, the Farallon Plate. The geological record of Mexico contains Triassic to present day evidence of subduction, of which the post-Late Cretaceous phase is of continental margin-style. Interpretations of the pre-Upper Cretaceous subduction-related rock assemblages are under debate, and vary from far-travelled exotic intra-oceanic island arc character to in-situ extended continental margin origin. We present new paleomagnetic data that show that Triassic, Jurassic and Cretaceous subduction-related rocks from the Vizcaíno Peninsula and the Guerrero terrane have a paleolatitudinal plate motion history that is equal to that of the North American continent. This suggests that these rock assemblages were part of the overriding plate and were perhaps only separated from the North American continent by temporal fore- or back-arc spreading. The entire Triassic-present day subduction record, and hence, reconstructed trench location, can therefore be linked to the Cocos slab, which provides control on longitudinal plate motion of North America since the time of Pangea. Compared to the latest state of the art mantle frames, in which longitudes are essentially unconstrained for pre-Cretaceous times, our reconstructed absolute position of North America requires a significant westward longitudinal shift for Mesozoic times.

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.

Photonic slab heterostructures based on opals

NASA Astrophysics Data System (ADS)

Palacios-Lidon, Elisa; Galisteo-Lopez, Juan F.; Juarez, Beatriz H.; Lopez, Cefe

2004-09-01

In this paper the fabrication of photonic slab heterostructures based on artificial opals is presented. The innovated method combines high-quality thin-films growing of opals and silica infiltration by Chemical Vapor Deposition through a multi-step process. By varying structure parameters, such as lattice constant, sample thickness or refractive index, different heterostructures have been obtained. The optical study of these systems, carried out by reflectance and transmittance measurements, shows that the prepared samples are of high quality further confirmed by Scanning Electron Microscopy micrographs. The proposed novel method for sample preparation allows a high control of the involved structure parameters, giving the possibility of tunning their photonic behavior. Special attention in the optical response of these materials has been addressed to the study of planar defects embedded in opals, due to their importance in different photonic fields and future technological applications. Reflectance and transmission measurements show a sharp resonance due to localized states associated with the presence of planar defects. A detailed study of the defect mode position and its dependance on defect thickness and on the surrounding photonic crystal is presented as well as evidence showing the scalability of the problem. Finally, it is also concluded that the proposed method is cheap and versatile allowing the preparation of opal-based complex structures.

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.

Constraining the hydration of the subducting Nazca plate beneath Northern Chile using subduction zone guided waves

NASA Astrophysics Data System (ADS)

Garth, Tom; Rietbrock, Andreas

2017-09-01

Guided wave dispersion is observed from earthquakes at 180-280 km depth recorded at stations in the fore-arc of Northern Chile, where the 44 Ma Nazca plate subducts beneath South America. Characteristic P-wave dispersion is observed at several stations in the Chilean fore-arc with high frequency energy (>5 Hz) arriving up to 3 s after low frequency (<2 Hz) arrivals. This dispersion has been attributed to low velocity structure within the subducting Nazca plate which acts as a waveguide, retaining and delaying high frequency energy. Full waveform modelling shows that the single LVL proposed by previous studies does not produce the first motion dispersion observed at multiple stations, or the extended P-wave coda observed in arrivals from intermediate depth events within the Nazca plate. These signals can however be accurately accounted for if dipping low velocity fault zones are included within the subducting lithospheric mantle. A grid search over possible LVL and faults zone parameters (width, velocity contrast and separation distance) was carried out to constrain the best fitting model parameters. Our results imply that fault zone structures of 0.5-1.0 km thickness, and 5-10 km spacing, consistent with observations at the outer rise are present within the subducted slab at intermediate depths. We propose that these low velocity fault zone structures represent the hydrated structure within the lithospheric mantle. They may be formed initially by normal faults at the outer rise, which act as a pathway for fluids to penetrate the deeper slab due to the bending and unbending stresses within the subducting plate. Our observations suggest that the lithospheric mantle is 5-15% serpentinised, and therefore may transport approximately 13-42 Tg/Myr of water per meter of arc. The guided wave observations also suggest that a thin LVL (∼1 km thick) interpreted as un-eclogitised subducted oceanic crust persists to depths of at least 220 km. Comparison of the inferred seismic velocities with those predicted for various MORB assemblages suggest that this thin LVL may be accounted for by low velocity lawsonite-bearing assemblages, suggesting that some mineral-bound water within the oceanic crust may be transported well beyond the volcanic arc. While older subducting slabs may carry more water per metre of arc, approximately one third of the oceanic material subducted globally is of a similar age to the Nazca plate. This suggests that subducting oceanic lithosphere of this age has a significant role to play in the global water cycle.

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.

Constraining the age of Aboriginal rock art using cosmogenic Be-10 and Al-26 dating of rock shelter collapse in the Kimberley region, Australia.

NASA Astrophysics Data System (ADS)

Cazes, Gaël; Fink, David; Fülöp, Réka-Hajnalka; Codilean, Alexandru T.

2017-04-01

The Kimberley region, northwest Australia, possesses an extensive and diverse collection of aboriginal rock art that potentially dates to more than 40,000 years ago. However, dating of such art using conventional techniques remains problematic. Here, we develop a new approach which makes use of the difference in production rates of in-situ 10Be and 26Al between intact rock walls and exposed surfaces of detached slabs from rock art shelters to constrain the age of Aboriginal rock-art. In the prevailing sandstone lithology of the Kimberley region, open cave-like rock shelters with cantilevered overhangs evolve by the collapse of unstable, partially rectangular, blocks weakened typically along joint-lines and fractures. On release, those slabs which extend outside the rock face perimeter will experience a higher production rate of cosmogenic 10Be and 26Al than the adjacent rock which remains intact within the shelter. The dating of these freshly exposed slabs can help reconstruct rock-shelter formation and provide either maximum or minimum ages for the rock art within the shelter. At each site, both the upper-face of the newly exposed fallen slab and the counterpart intact rock surface on the ceiling need to be sampled at their exact matching-point to ensure that the initial pre-release cosmogenic nuclide concentration on slab and ceiling are identical. The calculation of the timing of the event of slab release is strongly dependent on the local production rate, the new shielding of the slab surface and the post-production that continues on the ceiling sample at the matching point. The horizon, ceiling and slab shielding are estimated by modelling the distribution of neutron and muon trajectories in the irregular shaped rock-shelter and slab using 3D photogrammetric reconstruction from drone flights and a MATLAB code (modified from G. Balco, 2014) to estimate attenuation distances and model the production rate at each sample. Five rock-art sites have been dated and results range from 9.8 ± 1.9 kyr to 180.8 ± 22.3 kyr, While the date obtained for the youngest site can be interpreted as both a maximum and minimum age for the art due to its positioning over different walls of this specific shelter, all the other sites give maximum art ages which are significantly older than presumed human occupation in Australia. However, within the context of regional landscape geomorphology, these relatively young ages give new insights into the contrasting modes of landscape evolution in the Kimberley, and the importance of episodic escarpment retreat overprinted by passive basin-wide denudation which from numerous previous measurements are as low as 1-5 mm/ka (i.e. averaging timescales of ˜400 kyr). A large number of similar sites in the region have been mapped and are potential candidates for this new approach which can constrain the controversial relative chronology of the various aboriginal rock art styles.

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.

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.

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.

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.

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...

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.

Subduction zone decoupling/retreat modeling explains south Tibet (Xigaze) and other supra-subduction zone ophiolites and their UHP mineral phases

NASA Astrophysics Data System (ADS)

Butler, Jared P.; Beaumont, Christopher

2017-04-01

The plate tectonic setting in which proto-ophiolite 'oceanic' lithosphere is created remains controversial with a number of environments suggested. Recent opinions tend to coalesce around supra-subduction zone (SSZ) forearc extension, with a popular conceptual model in which the proto-ophiolite forms during foundering of oceanic lithosphere at the time of spontaneous or induced onset of subduction. This mechanism is favored in intra-oceanic settings where the subducting lithosphere is old and the upper plate is young and thin. We investigate an alternative mechanism; namely, decoupling of the subducting oceanic lithosphere in the forearc of an active continental margin, followed by subduction zone (trench) retreat and creation of a forearc oceanic rift basin, containing proto-ophiolite lithosphere, between the continental margin and the retreating subduction zone. A template of 2D numerical model experiments examines the trade-off between strength of viscous coupling in the lithospheric subduction channel and net slab pull of the subducting lithosphere. Three tectonic styles are observed: 1) C, continuous subduction without forearc decoupling; 2) R, forearc decoupling followed by rapid subduction zone retreat; 3) B, breakoff of subducting lithosphere followed by re-initiation of subduction and in some cases, forearc decoupling (B-R). In one case (BA-B-R; where BA denotes backarc) subduction zone retreat follows backarc rifting. Subduction zone decoupling is analyzed using frictional-plastic yield theory and the Stefan solution for the separation of plates containing a viscous fluid. The numerical model results are used to explain the formation of Xigaze group ophiolites, southern Tibet, which formed in the Lhasa terrane forearc, likely following earlier subduction and not necessarily during subduction initiation. Either there was normal coupled subduction before subduction zone decoupling, or precursor slab breakoff, subduction re-initiation and then decoupling. Rapid deep upper-mantle circulation in the models during subduction zone retreat can exhume and emplace material in the forearc proto-ophiolite from as deep as the mantle transition zone, thereby explaining diamonds and other 10-15 GPa UHP phases in Tibetan ophiolites.

Nature of the basement of the East Anatolian plateau: Implications for the lithospheric foundering processes

NASA Astrophysics Data System (ADS)

Topuz, G.; Candan, O.; Zack, T.; Yılmaz, A.

2017-12-01

The East Anatolian Plateau (Turkey) is characterized by (1) an extensive volcanic-sedimentary cover of Neogene to Quaternary age, (2) crustal thicknesses of 42-50 km, and (3) an extremely thinned lithospheric mantle. Its basement beneath the young cover is thought to consist of oceanic accretionary complexes of Late Cretaceous to Oligocene age. The attenuated state of the lithospheric mantle and the causes of the young volcanism are accounted for by slab steepening and subsequent break-off. We present field geological, petrological and geochronological data on three basement inliers (Taşlıçay, Akdağ and Ilıca) in the region. These areas are made up of amphibolite- to granulite-facies rocks, comprising marble, amphibolite, metapelite, quartzite and metagranite. The granulite-facies domain is equilibrated at 0.7 GPa and 800 ˚C at 83 ± 2 Ma (2σ). The metamorphic rocks are intruded by subduction-related coeval gabbroic, quartz monzonitic to tonalitic rocks. Both the metamorphic rocks and the intrusions are tectonically overlain by ophiolitic rocks. All these crystalline rocks are unconformably overlain by lower Maastrichtien clastic rocks and reefal limestone, suggesting that the exhumation at the earth's surface and juxtaposition with ophiolitic rocks occurred by early Maastrichtien. U-Pb dating on igneous zircon from metagranite yielded a protolith age of 445 ± 10 Ma (2σ). The detrital zircons from a metaquartzite point to Neoproterozoic to Early Paleozoic provenance. All these data favor a more or less continuous continental substrate to the allochthonous ophiolitic rocks beneath the young volcanic-sedimentary cover. The metamorphism and coeval magmatism can be regarded as the middle- to lower-crustal root of the Late Cretaceous magmatic arc that developed due to northward subduction along the Bitlis-Zagros suture. The presence of a continental basement beneath the young cover requires that the loss of the lithospheric mantle from beneath the East Anatolian plateau have resulted from other processes of lithospheric foundering, rather than just slab steepening and break-off. This research is funded by a research grant (#114Y228) from TÜBİTAK.

How the interior viscosity structure of a terrestrial planet controls plate driving forces and plate tectonics

NASA Astrophysics Data System (ADS)

Hoeink, T.; Lenardic, A.; Jellinek, M.; Richards, M. A.

2011-12-01

One of the fundamental unresolved problems in Earth and planetary science is the generation of plate tectonics from mantle convection. Important achievements can be made when considering rheological properties in the context of mantle convection dynamics. Among these milestones are (1) a deeper understanding of the balance of forces that drive and resist plate motion and (2) the dynamic generation of narrow plate boundaries (that lead to a piecewise continuous surface velocity distribution). Extending classic plate-tectonic theory we predict a plate driving force due to viscous coupling at the base of the plate from fast flow in the asthenosphere. Flow in the asthenosphere is due to shear-driven contributions from an overriding plate and due to additional pressure-driven contributions. We use scaling analysis to show that the extent to which this additional plate-driving force contributes to plate motions depends on the lateral dimension of plates and on the relative viscosities and thicknesses of lithosphere and asthenosphere. Whereas slab-pull forces always govern the motions of plates with a lateral extent greater than the mantle depth, asthenosphere-drive forces can be relatively more important for smaller (shorter wavelength) plates, large relative asthenosphere viscosities or large asthenosphere thicknesses. Published plate velocities, tomographic images and age-binned mean shear wave velocity anomaly data allow us to estimate the relative contributions of slab-pull and asthenosphere-drive forces driving the motions of the Atlantic and Pacific plates. At the global scale of terrestrial planets, we use 3D spherical shell simulations of mantle convection with temperature-, depth- and stress dependent rheology to demonstrate that a thin low-viscosity layer (asthenosphere) governs convective stresses imparted to the lithosphere. We find, consistent with theoretical predictions, that convective stresses increase for thinner asthenospheres. This result might eliminate the need for special weakening mechanisms to generate plate tectonics from mantle convection. Our results elucidate the role of the asthenosphere for plate tectonics on Earth, and also provide insights into the differences in tectonic styles between Earth and Venus.

Tectonic evolution and mantle structure of the Caribbean

NASA Astrophysics Data System (ADS)

van Benthem, Steven; Govers, Rob; Spakman, Wim; Wortel, Rinus

2013-04-01

In the broad context of investigating the relationship between deep structure & processes and surface expressions, we study the Caribbean plate and underlying mantle. We investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic P-wave velocity structure under the Caribbean region. In the upper mantle, positive seismic anomalies are imaged under the Lesser Antilles and Puerto Rico. These anomalies are interpreted as remnants of Atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the Lesser Antilles island arc during the past ~45 Myr. The imaged Lesser-Antilles slab consists of a northern and southern anomaly, separated by a low velocity anomaly across most of the upper mantle, which we interpret as the subducted North-South America plate boundary. The southern edge of the imaged Lesser Antilles slab agrees with vertical tearing of South America lithosphere. The northern Lesser Antilles slab is continuous with the Puerto Rico slab along the northeastern plate boundary. This results in an amphitheater-shaped slab and it is interpreted as westward subducting North America lithosphere that remained attached to the surface along the northern boundary. At the Muertos Trough, however, material is imaged until a depth of only 100 km, suggesting a small amount of subduction. The location and length of the imaged South Caribbean slab agrees with proposed subduction of Caribbean lithosphere under the northern South America plate. An anomaly related to proposed Oligocene subduction at the Nicaragua rise is absent in the tomographic model. Beneath Panama, a subduction window exists across the upper mantle, which is related to the cessation of subduction of the Nazca plate under Panama since 9.5 Ma and possibly the preceding subduction of the extinct Cocos-Nazca spreading center. In the lower mantle two large anomaly patterns are imaged. The westernmost anomaly agrees with the subduction of Farallon lithosphere. The second lower mantle anomaly is found east of the Farallon anomaly and is interpreted as a remnant of the late Mesozoic subduction of North and South America oceanic lithosphere at the Greater Antilles, Aves ridge and Leeward Antilles. The imaged mantle structure does not allow us to discriminate between an 'Intra-Americas' origin and a 'Pacific origin' of the Caribbean plate.

Effects of subduction and slab gaps on mantle flow beneath the Lesser Antilles based on observations of seismic anisotropy

NASA Astrophysics Data System (ADS)

Schlaphorst, David; Kendall, J.-Michael; Baptie, Brian; Latchman, Joan L.; Bouin, Marie-Paule

2016-04-01

Subduction is a key process in the formation of continental crust. However, the interaction of the mantle with the subducting slab is not fully understood and varies between subduction zones. The flow geometry and stress patterns influence seismic anisotropy; since anisotropic layers lead to variations in the speed of seismic waves as a function of the direction of wave propagation, mantle flow can be constrained by investigating the structure of these anisotropic layers. In this study we investigate seismic anisotropy in the eastern Greater and the Lesser Antilles along a subduction environment, including the crust and the upper mantle as regions of interest. We use a combination of teleseismic and local events recorded at three-component broadband seismic stations on every major island in the area to observe and distinguish between anisotropy in the crust, the mantle wedge and the sub-slab mantle. Local event delay times (0.21±0.12s) do not increase with depth, indicating a crustal origin and an isotropic mantle wedge. Teleseismic delay times are larger (1.34±0.47s), indicating sub-slab anisotropy. The results suggest trench-parallel mantle flow, with the exception of trench-perpendicular alignment in narrow regions east of Puerto Rico and south of Martinique, suggesting mantle flow through gaps in the slab. This agrees with the continuous northward mantle flow that is caused by the subducting slab proposed by previous studies of that region. We were able to identify a pattern previously unseen by other studies; on St. Lucia a trench-perpendicular trend also indicated by the stations around can be observed. This pattern can be explained by a mantle flow through a gap induced by the subduction of the boundary zone between the North and South American plates. This feature has been proposed for that area using tomographic modelling (van Benthem et al., 2013). It is based on previous results by Wadge & Shepherd (1984), who observed a vertical gap in the Wadati-Benioff zone at that location using a seismicity catalogue from local seismic networks. This work strengthens the argument for that location to be the plate boundary between the North and South American plates.

Dynamics of subduction, accretion, exhumation and slab roll-back: Mediterranean scenarios

NASA Astrophysics Data System (ADS)

Tirel, C.; Brun, J.; Burov, E. B.; Wortel, M. J.; Lebedev, S.

2010-12-01

A dynamic orogen reveals various tectonic processes brought about by subduction: accretion of oceanic and continental crust, exhumation of UHP-HP rocks, and often, back-arc extension. In the Mediterranean, orogeny is strongly affected by slab retreat, as in the Aegean and Tyrrhenian Seas. In order to examine the different dynamic processes in a self-consistent manner, we perform a parametric study using the fully coupled thermo-mechanical numerical code PARAFLAM. The experiments reproduce a subduction zone in a slab pull mode, with accretion of one (the Tyrrhenian case) and two continental blocks (the Aegean case) that undergo, in sequence, thrusting, burial and exhumation. The modeling shows that despite differences in structure between the two cases, the deformation mechanisms are fundamentally similar and can be described as follows. The accretion of a continental block at the trench beneath the suture zone begins with its burial to UHP-HP conditions and thrusting. Then the continental block is delaminated from its subducting lithosphere. During the subduction-accretion process, the angle of the subducting slab increases due to the buoyancy of the continental block. When the oceanic subduction resumes, the angle of the slab decreases to reach a steady-state position. The Aegean and Tyrrhenian scenarios diverge at this stage, due naturally to the differences of their accretion history. When continental accretion is followed by oceanic subduction only, the continental block that has been accreted and detached stays at close to the trench and does not undergo further deformation, despite the continuing rollback. The extensional deformation is located further within the overriding plate, resulting in continental breakup and the development of an oceanic basin, as in the Tyrrhenian domain. When the continental accretion is followed first by oceanic subduction and then by accretion of another continental block, however, the evolution of the subduction zone is different. The angle of the subducting slab increases again, following the arrival of the second continental block. The first continental block is now disconnected from the trench and is strongly heated by the asthenosphere that rises to just below the Moho. The locus of extension, originally in the overriding plate, moves to the first continental block, resulting in the development of metamorphic core complexes, as in the Aegean domain. Simultaneously, the second continent undergoes burial to UHP-HP conditions, thrusting and exhumation.

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.

Bowers Swell: Evidence for a zone of compressive deformation concentric with Bowers Ridge, Bering Sea

USGS Publications Warehouse

Marlow, M. S.; Cooper, A. K.; Dadisman, S.V.; Geist, E.L.; Carlson, P.R.

1990-01-01

Bowers Swell is a newly discovered bathymetric feature which is up to 90 m high, between 12 and 20 km wide, and which extends arcuately about 400 km along the northern and eastern sides of Bowers Ridge. The swell was first revealed on GLORIA sonographs and subsequently mapped on seismic reflection and 3.5 kHz bathymetric profiles. These geophysical data show that the swell caps an arcuate anticlinal ridge, which is composed of deformed strata in an ancient trench on the northern and eastern sides of Bowers Ridge. The trench fill beneath the swell is actively deforming, as shown by faulting of the sea floor and by thinning of the strata across the crest of the swell. Thinning and faulting of the trench strata preclude an origin for the swell by simple sediment draping over an older basement high. We considered several models for the origin of Bowers Swell, including folding and uplift of the underlying trench sediment during the interaction between the Pacific plate beneath the Aleutian Ridge and a remnant oceanic slab beneath Bowers Ridge. However, such plate motions should generate extensive seismicity beneath Bowers Ridge, which is aseismic, and refraction data do not show any remnant slab beneath Bowers Ridge. Another origin considered for Bowers Swell invokes sediment deformation resulting from differential loading and diapirism in the trench fill. However, diapirism is not evident on seismic reflection profiles across the swell. We favour a model in which sediment deformation and swell formation resulted from a few tens of kilometers of low seismicity motion by intraplate crustal blocks beneath the Aleutian Basin. This motion may result from the translation of blocks in western Alaska to the south-west, forcing the movement of the Bering Sea margin west of Alaska into the abyssal Aleutian Basin. ?? 1990.

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.

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.

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.

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.

Nonlinear dynamics in low permittivity media: the impact of losses.

PubMed

Vincenti, M A; de Ceglia, D; Scalora, M

2013-12-02

Slabs of materials with near-zero permittivity display enhanced nonlinear processes. We show that field enhancement due to the continuity of the longitudinal component of the displacement field drastically enhances harmonic generation. We investigate the impact of losses with and without bulk nonlinearities and demonstrate that in the latter scenario surface, magnetic and quadrupolar nonlinear sources cannot always be ignored.

Comparative study of high power Tm:YLF and Tm:LLF slab lasers in continuous wave regime.

PubMed

Berrou, Antoine; Collett, Oliver J P; Morris, Daniel; Esser, M J Daniel

2018-04-16

We report on Tm:YLF and Tm:LLF slab lasers (1.5 x 11 x 20 mm 3 ) end pumped from one end with a high-brightness 792 nm laser diode stack. These two lasers are compared under identical pump conditions in continuous-wave regime. A stronger negative thermal lens in Tm:LLF than in Tm:YLF is highlighted, making it more difficult to operate the Tm:LLF laser under stable lasing conditions. In a configuration where the high reflectivity cavity mirror has a radius of curvature of r = 150 mm, the Tm:YLF (Tm:LLF) laser produces a maximum output power of 150 W (143 W) for 428 W of incident pump power (respectively). For a second cavity configuration where the high reflectivity cavity mirror has a radius of curvature of r = 500 mm, the Tm:YLF laser produces a maximum output power of 164 W for 412 W of incident pump power and a 57% slope efficiency with respect to the absorbed pump power. The emitted wavelength of these two lasers are measured as a function of the output coupler reflectivity and it shows that Tm:LLF laser emits at a longer wavelength than Tm:YLF.

Limits on the critical length of damage in weak snowpack layers from en-echelon slab fracture spacing observed during avalanche release

NASA Astrophysics Data System (ADS)

Gauthier, D.; Hutchinson, D. J.

2012-04-01

We present simple estimates of the maximum possible critical length of damage or fracture in a weak snowpack layer required to maintain the propagation that leads to avalanche release, based on observations of 'en-echelon' slab fractures during avalanche release. These slab fractures may be preserved in situ if the slab does not slide down slope. The en-echelon fractures are spaced evenly, normally with one every one to ten metres or more. We consider a simple two-dimensional model of a slab and weak layer, with upslope fracture propagating the weak layer, and examine the relationship between the weak layer and en-echelon slab fractures. We assume that the slab fracture occurs in tension, and initiates at either the base or surface of the slab in the area of peak tensile stress at the tip of the weak layer fracture. We also assume that if at the time the slab is completely bisected by fracture the propagation in the weak layer will arrest spontaneously if it has not advanced beyond the critical length. In this scenario, en-echelon slab fractures may only form when the weak layer fracture repeatedly exceeds the critical length; otherwise, there could be only a single slab fracture. We estimate the position of the weak layer fracture at the time of slab bisection using the slab thickness and ratio between the fracture speeds in the weak layer and slab. We show that in the simple model en-echelon fractures only form if the slab thickness multiplied by the velocity ratio is greater than the critical length. Of course, the critical length must also be less than the en-echelon spacing. It follows that the first relationship must be valid independent of the occurrence of en-echelon fractures, although the speed ratio may be process-dependent and difficult to estimate. We use this method to calculate maximum critical lengths for propagation in actual avalanches with and without en echelon fractures, and discuss the implications for comparing competing propagation models. Furthermore, we discuss the possible applications to other cases of progressive basal failure and en-echelon fracturing, e.g. the ribbed flow bowls or so-called 'thumbprint' morphology which sometimes develops during landsliding in sensitive clay soils.

Nanolevitation Phenomena in Real Plane-Parallel Systems Due to the Balance between Casimir and Gravity Forces

PubMed Central

2015-01-01

We report on the theoretical analysis of equilibrium distances in real plane-parallel systems under the influence of Casimir and gravity forces at thermal equilibrium. Due to the balance between these forces, thin films of Teflon, silica, or polystyrene in a single-layer configuration and immersed in glycerol stand over a silicon substrate at certain stable or unstable positions depending on the material and the slab thickness. Hybrid systems containing silica and polystyrene, materials which display Casimir forces and equilibrium distances of opposite nature when considered individually, are analyzed in either bilayer arrangements or as composite systems made of a homogeneous matrix with small inclusions inside. For each configuration, equilibrium distances and their stability can be adjusted by fine-tuning of the volume occupied by each material. We find the specific conditions under which nanolevitation of realistic films should be observed. Our results indicate that thin films of real materials in plane-parallel configurations can be used to control suspension or stiction phenomena at the nanoscale. PMID:26405466

Fabrication of seamless calandria tubes by cold pilgering route using 3-pass and 2-pass schedules

NASA Astrophysics Data System (ADS)

Saibaba, N.

2008-12-01

Calandria tube is a large diameter, extremely thin walled zirconium alloy tube which has diameter to wall thickness ratio as high as 90-95. Such tubes are conventionally produced by the 'welded route', which involves extrusion of slabs followed by a series of hot and cold rolling passes, intermediate anneals, press forming of sheets into circular shape and closing the gap by TIG welding. Though pilgering is a well established process for the fabrication of seamless tubes, production of extremely thin walled tubes offers several challenges during pilgering. Nuclear fuel complex (NFC), Hyderabad, has successfully developed a process for the production of Zircaloy-4 calandria tubes by adopting the 'seamless route' which involves hot extrusion of mother blanks followed by three-pass pilgering or two-pass pilgering schedules. This paper deals with standardization of the seamless route processes for fabrication of calandria tubes, comparison between the tubes produced by 2-pass and 3-pass pilgering schedules, role of ultrasonic test charts for control of process parameters, development of new testing methods for burst testing and other properties.

Migrating pattern of deformation prior to the Tohoku-Oki earthquake revealed by GRACE data

NASA Astrophysics Data System (ADS)

Panet, Isabelle; Bonvalot, Sylvain; Narteau, Clément; Remy, Dominique; Lemoine, Jean-Michel

2018-05-01

Understanding how and when far-field continuous motions lead to giant subduction earthquakes remains a challenge. An important limitation comes from an incomplete description of aseismic mass fluxes at depth along plate boundaries. Here we analyse Earth's gravity field variations derived from GRACE satellite data in a wide space-time domain surrounding the Mw 9.0 2011 Tohoku-Oki earthquake. We show that this earthquake is the extreme expression of initially silent deformation migrating from depth to the surface across the entire subduction system. Our analysis indeed reveals large-scale gravity and mass changes throughout three tectonic plates and connected slabs, starting a few months before March 2011. Before the Tohoku-Oki earthquake rupture, the gravity variations can be explained by aseismic extension of the Pacific plate slab at mid-upper mantle depth, concomitant with increasing seismicity in the shallower slab. For more than two years after the rupture, the deformation propagated far into the Pacific and Philippine Sea plate interiors, suggesting that subduction accelerated along 2,000 km of the plate boundaries in March 2011. This gravitational image of the earthquake's long-term dynamics provides unique information on deep and crustal processes over intermediate timescales, which could be used in seismic hazard assessment.

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.

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.

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.

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...

Imaging label-free biosensor with microfluidic system

NASA Astrophysics Data System (ADS)

Jahns, S.; Glorius, P.; Hansen, M.; Nazirizadeh, Y.; Gerken, M.

2015-06-01

We present a microfluidic system suitable for parallel label-free detection of several biomarkers utilizing a compact imaging measurement system. The microfluidic system contains a filter unit to separate the plasma from human blood and a functionalized, photonic crystal slab sensor chip. The nanostructure of the photonic crystal slab sensor chip is fabricated by nanoimprint lithography of a period grating surface into a photoresist and subsequent deposition of a TiO2 layer. Photonic crystal slabs are slab waveguides supporting quasi-guided modes coupling to far-field radiation, which are sensitive to refractive index changes due to biomarker binding on the functionalized surface. In our imaging read-out system the resulting resonance shift of the quasi-guided mode in the transmission spectrum is converted into an intensity change detectable with a simple camera. By continuously taking photographs of the sensor surface local intensity changes are observed revealing the binding kinetics of the biomarker to its specific target. Data from two distinct measurement fields are used for evaluation. For testing the sensor chip, 1 μM biotin as well as 1 μM recombinant human CD40 ligand were immobilized in spotsvia amin coupling to the sensor surface. Each binding experiment was performed with 250 nM streptavidin and 90 nM CD40 ligand antibody dissolved in phosphate buffered saline. In the next test series, a functionalized sensor chip was bonded onto a 15 mm x 15 mm opening of the 75 mm x 25 mm x 2 mm microfluidic system. We demonstrate the functionality of the microfluidic system for filtering human blood such that only blood plasma was transported to the sensor chip. The results of first binding experiments in buffer with this test chip will be presented.

Deformation of the Pacific/North America plate boundary at Queen Charlotte Fault: The possible role of rheology

USGS Publications Warehouse

ten Brink, Uri S.; Miller, Nathaniel; Andrews, Brian; Brothers, Daniel; Haeussler, Peter J.

2018-01-01

The Pacific/North America (PA/NA) plate boundary between Vancouver Island and Alaska is similar to the PA/NA boundary in California in its kinematic history and the rate and azimuth of current relative motion, yet their deformation styles are distinct. The California plate boundary shows a broad zone of parallel strike slip and thrust faults and folds, whereas the 49‐mm/yr PA/NA relative plate motion in Canada and Alaska is centered on a single, narrow, continuous ~900‐km‐long fault, the Queen Charlotte Fault (QCF). Using gravity analysis, we propose that this plate boundary is centered on the continent/ocean boundary (COB), an unusual location for continental transform faults because plate boundaries typically localize within the continental lithosphere, which is weaker. Because the COB is a boundary between materials of contrasting elastic properties, once a fault is established there, it will probably remain stable. We propose that deformation progressively shifted to the COB in the wake of Yakutat terrane's northward motion along the margin. Minor convergence across the plate boundary is probably accommodated by fault reactivation on Pacific crust and by an eastward dipping QCF. Underthrusting of Pacific slab under Haida Gwaii occurs at convergence angles >14°–15° and may have been responsible for the emergence of the archipelago. The calculated slab entry dip (5°–8°) suggests that the slab probably does not extend into the asthenosphere. The PA/NA plate boundary at the QCF can serve as a structurally simple site to investigate the impact of rheology and composition on crustal deformation and the initiation of slab underthrusting.

The effects of subduction termination on the continental lithosphere: Linking volcanism, deformation, surface uplift, and slab tearing in central Anatolia

NASA Astrophysics Data System (ADS)

Delph, Jonathan R.; Abgarmi, Bijan; Ward, Kevin M.; Beck, Susan L.; Arda Ozacar, A.; Zandt, George; Sandvol, Eric; Turkelli, Niyazi; Kalafat, Dogan

2017-04-01

The lithospheric evolution of Anatolia is largely defined by processes associated with the terminal stages of subduction along its southern margin. Central Anatolia represents the transition from the subduction of oceanic lithosphere at the Aegean trench in the west to the Arabian - Eurasian continental collision in the east. In the overriding plate, this complicated transition is contemporaneous with uplift along the southern margin of central Anatolia (2 km in 6 Myr), voluminous felsic-intermediate ignimbrite eruptions (>1000 km3), extension, and tectonic deformation reflected by abundant low-magnitude seismic activity. The addition of 72 seismic stations as part of the Continental Dynamics - Central Anatolian Tectonics project, along with development of a new approach to the joint inversion of receiver functions and dispersion data, enables us obtain a high-resolution 3D shear wave velocity model of central Anatolia down to 150 km. This new velocity model has important implications for the complex interactions between the downgoing, segmenting African lithosphere and the overriding Anatolian Plate. These results reveal that the lithosphere of central Anatolia and the northern Arabian Plate is thin (<50 to 80 km). The Central Taurus Mountains, which have experienced 2 km of uplift in the past 6 Ma, are underlain by the fastest shear velocities in the region (>4.5 km/s), indicating the presence of the Cyprean slab beneath central Anatolia. Thus, uplift of the Central Taurus Mountains may be due to slab rebound after the detachment of the oceanic portion of the Cyprean slab beneath Anatolia rather than the presence of shallow asthenospheric material. These fast velocities extend to the northern margin of the Central Taurus Mountains, giving way to a NE-SW trend of very slow upper mantle shear wave velocities (<4.2 km/s) beneath the Central Anatolian Volcanic Province. These slow velocities are interpreted to be shallow, warm asthenosphere in which melt is present. The combination of a shallow asthenosphere and lithospheric-scale weaknesses associated with relict tectonic structures formed during the assembly of Anatolia are responsible for the spatial distribution of volcanism in the Central Anatolian Volcanic Province. Finally, we present a model for the evolution of central Anatolia that brings together the volcanism, extension in the Kirsehir Block, uplift of the southern margin of central Anatolia, and our seismic images.

Imaging megathrust zone and Yakutat/Pacific plate interface in Alaska subduction zone

NASA Astrophysics Data System (ADS)

Kim, Y.; Abers, G. A.; Li, J.; Christensen, D. H.; Calkins, J. A.

2013-05-01

We image the subducted slab underneath a 450 km long transect of the Alaska subduction zone. Dense stations in southern Alaska are set up to investigate (1) the geometry and velocity structure of the downgoing plate and their relation to slab seismicity, and (2) the interplate coupled zone where the great 1964 (magnitude 9.3) had greatest rupture. The joint teleseismic migration of two array datasets (MOOS, Multidisciplinary Observations of Onshore Subduction, and BEAAR, Broadband Experiment Across the Alaska Range) based on teleseismic receiver functions (RFs) using the MOOS data reveal a shallow-dipping prominent low-velocity layer at ~25-30 km depth in southern Alaska. Modeling of these RF amplitudes shows a thin (<6.5 km) low-velocity layer (shear wave velocity of ~3 km/s), which is ~20-30% slower than normal oceanic crustal velocities, between the subducted slab and the overriding North American plate. The observed low-velocity megathrust layer (with P-to-S velocity ratio (Vp/Vs) exceeding 2.0) may be due to a thick sediment input from the trench in combination of elevated pore fluid pressure in the channel. The subducted crust below the low-velocity channel has gabbroic velocities with a thickness of 11-12 km. Both velocities and thickness of the low-velocity channel abruptly increase as the slab bends in central Alaska, which agrees with previously published RF results. Our image also includes an unusually thick low-velocity crust subducting with a ~20 degree dip down to 130 km depth at approximately 200 km inland beneath central Alaska. The unusual nature of this subducted segment has been suggested to be due to the subduction of the Yakutat terrane. We also show a clear image of the Yakutat and Pacific plate subduction beneath the Kenai Peninsula, and the along-strike boundary between them at megathrust depths. Our imaged western edge of the Yakutat terrane, at 25-30 km depth in the central Kenai along the megathrust, aligns with the western end of the geodetically locked patch with high slip deficit, and coincides with the boundary of aftershock events from the 1964 earthquake. It seems plausible that this sharp change in the nature of the downgoing plate controls the slip distribution of great earthquakes on this plate interface.

Imaging megathrust zone and Yakutat/Pacific plate interface in Alaska subduction zone

NASA Astrophysics Data System (ADS)

Kim, Y.; Abers, G. A.; Li, J.; Christensen, D. H.; Calkins, J. A.

2012-12-01

We image the subducted slab underneath a 450 km long transect of the Alaska subduction zone. Dense stations in southern Alaska are set up to investigate (1) the geometry and velocity structure of the downgoing plate and their relation to slab seismicity, and (2) the interplate coupled zone where the great 1964 (magnitude 9.3) had greatest rupture. The joint teleseismic migration of two array datasets (MOOS, Multidisciplinary Observations of Onshore Subduction, and BEAAR, Broadband Experiment Across the Alaska Range) based on teleseismic receiver functions (RFs) using the MOOS data reveal a shallow-dipping prominent low-velocity layer at ~25-30 km depth in southern Alaska. Modeling of these RF amplitudes shows a thin (3-6.5 km) low-velocity layer (shear wave velocity less than 3 km/s), which is ~20-30% slower than normal oceanic crustal velocities, between the subducted slab and the overriding North America plate. The observed low-velocity megathrust layer (with Vp/Vs ratio exceeding 2.0) may be due to a thick sediment input from the trench in combination of elevated pore fluid pressure in the channel. The subducted crust below the low-velocity channel has gabbroic velocities with a thickness of 11-15 km. Both velocities and thickness of the low-velocity channel abruptly increase as the slab bends in central Alaska, which agrees with previously published RF results. Our image also includes an unusually thick low-velocity crust subducting with a ~20 degree dip down to 130 km depth at approximately 200 km inland beneath central Alaska. The unusual nature of this subducted segment has been suggested to be due to the subduction of the Yakutat terrane. Subduction of this buoyant crust could explain the shallow dip of the thrust zone beneath southern Alaska. We also show a clear image of the Yakutat and Pacific plate subduction beneath the Kenai Peninsula, and the along-strike boundary between them at megathrust depths. Our imaged western edge of the Yakutat terrane, at ~30-42 km depth in the central Kenai along the megathrust, aligns with the western end of the geodetically locked patch with high slip deficit, and coincides with the boundary of aftershock events from the 1964 earthquake. It seems plausible that this sharp change in the nature of the downgoing plate controls the slip distribution of great earthquakes on this plate interface.

Experimental study on beam for composite CES structural system

NASA Astrophysics Data System (ADS)

Matsui, Tomoya

2017-10-01

Development study on Concrete Encase Steel (CES) composite structure system has been continuously conducted toward the practical use. CES structure is composed of steel and fiber reinforced concrete. In previous study, it was found that CES structure has good seismic performance from experimental study of columns, beam - column joints, shear walls and a two story two span frame. However, as fundamental study on CES beam could be lacking, it is necessary to understand the structural performance of CES beam. In this study, static loading tests of CES beams were conducted with experimental valuable of steel size, the presence or absence of slab and thickness of slab. And restoring characteristics, failure behavior, deformation behavior, and strength evaluation method of CES beam were investigated. As the results, it was found that CES beam showed stable hysteresis behavior. Furthermore it was found that the flexural strength of the CES beam could be evaluated by superposition strength theory.

Photon migration through a turbid slab described by a model based on diffusion approximation. I. Theory.

PubMed

Contini, D; Martelli, F; Zaccanti, G

1997-07-01

The diffusion approximation of the radiative transfer equation is a model used widely to describe photon migration in highly diffusing media and is an important matter in biological tissue optics. An analysis of the time-dependent diffusion equation together with its solutions for the slab geometry and for a semi-infinite diffusing medium are reported. These solutions, presented for both the time-dependent and the continuous wave source, account for the refractive index mismatch between the turbid medium and the surrounding medium. The results have been compared with those obtained when different boundary conditions were assumed. The comparison has shown that the effect of the refractive index mismatch cannot be disregarded. This effect is particularly important for the transmittance. The discussion of results also provides an analysis of the role of the absorption coefficient in the expression of the diffusion coefficient.

Interaction between the Dauki and the Indo-Burman convergence boundaries from teleseismic and locally recorded earthquake data

NASA Astrophysics Data System (ADS)

Howe, M.; Moulik, P.; Seeber, L.; Kim, W.; Steckler, M. S.

2012-12-01

The Himalayan and the Burma Arcs converge onto the Indian plate from opposite sides near their syntaxial juncture and have reduced it to a sliver. Both geology and seismicity point to recent internal deformation and high seismogenic potential within this sliver. Large historical earthquakes, including the Great Indian earthquake of 1897 (Mw ~8.1), along with the recent seismicity, suggest that the cratonic blocks in the region are bounded by active faults. The most prominent is the E-W trending Dauki Fault, a deeply-rooted, north-dipping thrust fault, situated between the Shillong massif to the north and the Sylhet Basin to the south. Along the Burma Arc, the subducted seismogenic slab of the Indian plate is continuous north to the syntaxis. Yet the Naga and Tripura segments of the accretionary fold belt, respectively north and south of the easterly extrapolation of the Dauki fault, are distinct. Accretion has advanced far westward into the foredeep of the Dauki structure along the front of the Tripura segment, while it has remained stunted facing the uplifted Shillong massif along the Naga segment. Moreover, the Dauki topographic front can be traced eastwards across the Burma Arc separating the two segments. Recent earthquakes support the hypothesis that the Dauki convergence structure continues below the Burma accretionary belt. Using teleseismic and regional data from the deployment of a local network, we explore the interaction of the Dauki thrust fault with the Burma Arc subduction zone. Preliminary observations include: While seismicity is concentrated in the slab at the eastward extrapolation of the Dauki fault, shallow seismicity is diffuse and does not illuminate the Dauki fault itself. P-axes in moment-tensor solutions of earthquakes within the Indian plate tend to be directed N-S and are locally parallel to the India-Burma boundary, particularly in the slab. T-axes tend to be oriented E-W with a strong tendency to follow the slab down dip. This pattern is remarkably consistent, despite the scattered seismicity, and suggests that the stress in the Indian plate, including the subducted oceanic portion of the plate, is still primarily controlled by the Himalayan collision to the north and down-dip pull by the Burma slab. Moment tensor solutions for some of the shallow earthquakes along the fold belt are consistent with geodetic results, showing partitioning of the oblique India-Burma convergence between belt-parallel dextral faults and belt-normal shortening by thrust faults. Relocations of the events using the double-difference algorithm may provide additional constraints on the geometry of the slab. In addition to the analysis of teleseismic data, a network of six seismic stations was also installed in Bangladesh in the region surrounding Sylhet, south of the Shillong Plateau during 2007-2008. Over 200 regional and local events are detected and located by the Sylhet array. About a dozen events are large enough allowing us to determine focal depths and mechanisms that will augment the catalog of the teleseismic events, providing additional insights into the tectonics in the region.

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).

U-TH-PA-RA study of the Kamchatka arc: new constraints on the genesis of arc lavas

NASA Astrophysics Data System (ADS)

Dosseto, Anthony; Bourdon, Bernard; Joron, Jean-Louis; Dupré, Bernard

2003-08-01

The 238U- 230Th- 226Ra and 235U- 231Pa disequilibria have been measured by mass spectrometry in historic lavas from the Kamchatka arc. The samples come from three closely located volcanoes in the Central Kamchatka Depression (CKD), the most active region of subducted-related volcanism in the world. The large excesses of 226Ra over 230Th found in the CKD lavas are believed to be linked to slab dehydration. Moreover, the samples show the uncommon feature of ( 230Th/ 238U) activity ratios both lower and higher than 1. The U-series disequilibria are characterized by binary trends between activity ratios, with ( 231Pa/ 235U) ratios all >1. It is shown that these correlations cannot be explained by a simple process involving a combination of slab dehydration and melting. We suggest that they are more likely to reflect mixing between two end-members: a high-magnesia basalt (HMB) end-member with a clear slab fluid signature and a high-alumina andesite (HAA) end-member reflecting the contribution of a slab-derived melt. The U-Th-Ra characteristics of the HMB end-member can be explained either by a two-step fluid addition with a time lag of 150 ka between each event or by continuous dehydration. The inferred composition for the dehydrating slab is a phengite-bearing eclogite. Equilibrium transport or dynamic melting can both account for 231Pa excess over 235U in HMB end-member. Nevertheless, dynamic melting is preferred as equilibrium transport melting requires unrealistically high upwelling velocities to preserve fluid-derived 226Ra/ 230Th. A continuous flux melting model is also tested. In this model, 231Pa- 235U is quickly dominated by fluid addition and, for realistic extents of melting, this process cannot account for ( 231Pa/ 235U) ratios as high as 1.6, as observed in the HMB end-member. The involvement of a melt derived from the subducted oceanic crust is more likely for explaining the HAA end-member compositions than crustal assimilation. Melting of the oceanic crust is believed to occur in presence of residual phengite and rutile, resulting in no 226Ra- 230Th disequilibrium and low 231Pa excess over 235U in the high-alumina andesites. Consequently, it appears that high-alumina andesites and high-magnesia basalts have distinct origins: the former being derived from melting of the subducted oceanic crust and the latter from hydrated mantle. It seems that there is no genetic link between these two magma types, in contrast with what was previously believed.

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..

Optical spectrophotometry of oscillations and flickering in AE Aquarii

NASA Technical Reports Server (NTRS)

Welsh, William F.; Horne, Keith; Oke, J. B.

1993-01-01

We observed rapid variations in the nova-like cataclysmic variable AE Aquarii for 1.7 hr with 4.3 s time resolution using the 30-channel (3227-10494 A) spectrophotometer on the Hale 5 m telescope. The 16.5 and 33.0 s oscillations show a featureless blue spectrum that can be represented by a blackbody with temperature and area much smaller than the accretion disk. Models consisting of the sum of a K star spectrum and a hydrogen slab in LTE at T = 6000-10,000 K can fit the spectrum of AE Aquarii reasonably well. The spectrum of a flare indicates optically thin gas with T = 8000-12,000 K. The energy released by the flare is large compared to typical stellar flares.

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.

The Western Edge of Cratonic North America and Topography of the Northern U.S. Rocky Mountains

NASA Astrophysics Data System (ADS)

Foster, D. A.; Russo, R. M.; van der Lee, S.; Mueller, P. A.

2009-12-01

We used seismic structure of the upper mantle determined via waveform inversions of surface and regional shear waves (Beadle and van der Lee, 2007) to examine the 3-D geometry of the base of North American lithosphere at the junction between thick, stable cratonic eastern North America and the thinner, recently tectonized western part of the continent. This boundary has been affected by long-term subduction beneath North America. Variability in convergence rates and directions, and especially in slab dip, have been postulated as important controls on the configuration of the transition from thick to thin lithosphere, and on the distribution and degree of crustal deformation and volcanism in the western U.S. We show that the lithospheric thickness transition at depths of 70-130 km - defined as contours of zero shear velocity anomaly - correlates strongly with the high topography of Laramide uplifts in the northern Rockies, which lie west of this seismically defined craton edge. The transition from thick to thin lithosphere also includes an embayment symmetrically centered on the Yellowstone hotspot, offset cratonward from the surface position of the hotspot by ca. 140-180 km at depths of 130-150 km. We interpret this structure as a reduction of cratonic seismic velocities reflecting the thermal halo around the hotspot, and perhaps associated with the separation of the lower lithosphere. The steep velocity gradient (boundary) east of the hotspot occurs along the Big Horn Mountains, and distributed mountain ranges of southwestern Montana. The steep transition between thin and thick lithosphere turns sharply west along the northern margin of the Helena thrust salient-Lewis and Clark fault zone, where it may reflect the edge of the Archean Medicine Hat Block and/or the northern termination of the influence shallow Farallon slab subduction the during Laramide time. Laramide-style basement uplifts are absent north of this zone and the eastern front ranges of the Rockies in northern Montana and Alberta are located further west. South of the Yellowstone lithospheric embayment, a westward salient of high seismic velocities at 70-130 km depths coincides with near surface structures along the Cheyenne Belt, possibly representing an accreted relict subduction margin. Relationships between anomalously hot asthenosphere and thin lithosphere are widely supported for the Basin and Range Province. East of this region, the location of the western edge of thick cratonic North American lithosphere and associated transitions from high to lower topography suggests a strong relationship that dates back to Laramide subduction erosion, and subsequent influence on the thermal/chemical modifications to the lithosphere during Cenozoic and Recent times.

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.

Slab-controlled Tectonomagmatism of the Pacific Northwest: A Holistic view of Columbia River, High Lava Plains, and Snake River Plain/Yellowstone Volcanism

NASA Astrophysics Data System (ADS)

James, D. E.; Fouch, M. J.; Long, M. D.; Druken, K. A.; Wagner, L. S.; Chen, C.; Carlson, R. W.

2012-12-01

We interpret post-20 Ma tectonomagmatism across the U.S. Pacific Northwest in the context of subduction related processes. While mantle plume models have long enjoyed favor as an explanation for the post 20-Ma magmatism in the region, conceptually their support has hinged almost entirely on two major features: (1) Steens/Columbia River flood basalt volcanism (plume head); and (2) The Snake River Plain/Yellowstone hotspot track (plume tail). Recent work, synthesized in this presentation, suggests that these features are more plausibly the result of mantle dynamical processes driven by southerly truncation of the Farallon/Juan de Fuca subduction zone and slab detachment along the evolving margin of western North America (Long et al., 2012; James et al., 2011). Plate reconstructions indicate that shortening of the subduction zone by the northward migration of the Mendocino triple junction resulted in a significant increase in the rate of trench retreat and slab rollback ca 20 Ma. Both numerical modeling and physical tank experiments in turn predict large-scale mantle upwelling and flow around the southern edge of the rapidly retreating slab, consistent both with the observed Steens/Columbia River flood volcanism and with the strong E-W mantle fabric observed beneath the region of the High Lava Plains of central and eastern Oregon. The High Lava Plains and Snake River Plain time-progressive volcanism began concurrently about 12 Ma, but along highly divergent tracks and characterized by strikingly different upper mantle structure. Crustal and upper mantle structure beneath the High Lava Plains exhibits evidence typical of regional extension; i.e. thin crust, flat and sharp Moho, and an uppermost mantle with low velocities but otherwise largely devoid of significant vertical structure. In contrast, the Snake River Plain exhibits ultra-low mantle velocities to depths of about 180 km along the length of the hotspot track. Seismic images of the upper mantle in the depth range 300-600 km show that a northern segment of the orphaned Farallon plate lies sub-horizontally in the mantle transition zone parallel to and along the length of the SRP. The images also provide evidence for present-day upwelling from the deep upper mantle around the northern edge of the remnant slab beneath SRP as well as around its leading tip beneath Yellowstone. These results, coupled with petrologic and geochemical constraints, provide compelling support for a subduction model that accounts for virtually all post-20 Ma Cenozoic volcanism and structural deformation in the Cascadian back arc. James, D.E., Fouch, M.J., Carlson, R.W., Roth, J.B., 2011. Slab fragmentation, edge flow, and the origin of the Yellowstone hotspot track. Earth and Planetary Science Letters 311, 124-135. Long, M.D., Till, C.B., Druken, K.A., Carlson, R.W., Wagner, L.S., Fouch, M.J., James, D.E., Grove, T.L., Schmerr, N., Kincaid, C., 2012. Mantle dynamics beneath the Pacific Northwest and generation of voluminous back-arc volcanism. G-cubed in press.

Near-surface elastic changes in the Ross Ice Shelf arising from transient storm and melt forcing observed with high-frequency ambient seismic noise

NASA Astrophysics Data System (ADS)

Chaput, J.; Aster, R. C.; Baker, M. G.; Gerstoft, P.; Bromirski, P. D.; Nyblade, A.; Stephen, R. A.; Wiens, D.

2017-12-01

Ice shelf collapse can herald subsequent grounded ice instability. However, robust understanding of external mechanisms capable of triggering rapid changes remains elusive. Improved understanding therefore requires improved remote and in-situ measurements of ice shelf properties. Using nearly three years of continuous data from a recently deployed 34-station broadband seismic array on the Ross Ice Shelf, we analyze persistent temporally varying, anisotropic near-surface resonant wave modes at frequencies above 1 Hz that are highly sensitive to small changes in elastic shelf properties to depths of tens of m. We further find that these modes exhibit both progressive (on the scale of months) and rapid (on the scale of hours) changes in frequency content. The largest and most rapid excursions are associated with forcing from local storms, and with a large regional ice shelf melt event in January 2016. We hypothesize that temporally variable behavior of the resonance features arises from wind slab formation during storms and/or to porosity changes, and to the formation of percolation-related refrozen layers and thinning in the case of surface melting. These resonance variations can be reproduced and inverted for structural changes using numerical wave propagation models, and thus present an opportunity for 4-D structural monitoring of shallow ice shelf elasticity and structure using long-duration seismic recordings.

Feature tracking for automated volume of interest stabilization on 4D-OCT images

NASA Astrophysics Data System (ADS)

Laves, Max-Heinrich; Schoob, Andreas; Kahrs, Lüder A.; Pfeiffer, Tom; Huber, Robert; Ortmaier, Tobias

2017-03-01

A common representation of volumetric medical image data is the triplanar view (TV), in which the surgeon manually selects slices showing the anatomical structure of interest. In addition to common medical imaging such as MRI or computed tomography, recent advances in the field of optical coherence tomography (OCT) have enabled live processing and volumetric rendering of four-dimensional images of the human body. Due to the region of interest undergoing motion, it is challenging for the surgeon to simultaneously keep track of an object by continuously adjusting the TV to desired slices. To select these slices in subsequent frames automatically, it is necessary to track movements of the volume of interest (VOI). This has not been addressed with respect to 4DOCT images yet. Therefore, this paper evaluates motion tracking by applying state-of-the-art tracking schemes on maximum intensity projections (MIP) of 4D-OCT images. Estimated VOI location is used to conveniently show corresponding slices and to improve the MIPs by calculating thin-slab MIPs. Tracking performances are evaluated on an in-vivo sequence of human skin, captured at 26 volumes per second. Among investigated tracking schemes, our recently presented tracking scheme for soft tissue motion provides highest accuracy with an error of under 2.2 voxels for the first 80 volumes. Object tracking on 4D-OCT images enables its use for sub-epithelial tracking of microvessels for image-guidance.

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.

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.

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.

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.

Ultrashort soliton switching based on coherent energy hiding.

PubMed

Romagnoli, M; Wabnitz, S; Zoccolotti, L

1991-08-15

Coherent coupling between light and atoms may be exploited for conceiving a novel class of all-optical signalprocessing devices without a direct counterpart in the continuous-wave regime. We show that the self-switching of ultrashort soliton pulses on resonance with a transition of doping centers in a slab waveguide directional coupler is based on nonlinear group-velocity (instead of the usual phase-velocity) changes.

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.

Method for measurement of radon diffusion and solubility in solid materials

NASA Astrophysics Data System (ADS)

Maier, Andreas; Weber, Uli; Dickmann, Jannis; Breckow, Joachim; van Beek, Patrick; Schardt, Dieter; Kraft, Gerhard; Fournier, Claudia

2018-02-01

In order to study the permeation i.e. the diffusion and solubility of radon gas in biological material, a new setup was constructed and a novel analysis was applied to obtain diffusion and solubility coefficients. Thin slabs of solid materials were installed between detector housing and the surrounding radon exposure chamber of 50 Ls volume. In this setup radon can diffuse through thin test samples into a cylindrical volume of 5 mm height and 20 mm diameter and reach an α-particle detector. There the 5.49 MeV α-decay of the penetrating radon atoms is measured by a silicon surface barrier detector. The time dependent activities inside the small detector volume are recorded after injection of a known radon activity concentration into the outer chamber. Analyzing the time behavior of the integral α-activity from radon in the small vessel, both, the diffusion coefficient and solubility of the test material can be determined, based on a new mathematical model of the diffusion process concerning the special boundary conditions given by the experimental setup. These first measurements were intended as proof of concept for the detection system and the data analysis. Thin polyethylene foils (LDPE) were selected as material for the diffusion measurements and the results were in agreement with data from literature. In further measurements, we will concentrate on biological material like bone, fat and other tissues.

Sol-gel nano-porous silica-titania thin films with liquid fill for optical interferometric sensors

NASA Astrophysics Data System (ADS)

Martin, Andrew J.; Green, Mino

1990-11-01

The production of thin films whose refractive index is measurand specific, for use in an interferometric fiber optic chemical sensor, is discussed. The problem of making such coatings has been tackled by a system we have termed the "guest-host" approach, in which an active liquid whose index varies with measurand, is contained within a porous glass host of fixed index. Suitable porous silica-titania glass films have been produced via the sol-gel process. The use of this system enables the index of the glass to be varied, so that the composite index of the liquid filled film can be tailored to that required by the optical system. The sol-gel method developed is based upon the hydrolysis and polymerisation of metal alkoxides, in an acidic aqueous/alcoholic solution. Thin film slab waveguides were deposited in order to measure the light scattering losses, which were found to be typically ''1dB/cm. The porosity of films was studied using a new technique developed in which water adsorption isotherms are plotted using ellipsometry. The pore size was found to be very small of pore diameter in the nanometer range, and the total porosity -1O%. Both of these factors were increased by the removal of residual organic material, using hydrogen peroxide. Finally the use of pH indicator dyes as a liquid fill is discussed, to produce a pH sensor.

Tomotectonic constraints on the assembly of Jura-cretaceous western North America, and a southwest Pacific analogue

NASA Astrophysics Data System (ADS)

Mihalynuk, M. G.; Sigloch, K.

2017-12-01

We integrate the topology of subducted slabs imaged beneath North America by seismic tomography, with surviving Atlantic and Pacific seafloor isochrons, to reveal evolving arc, trench, and plate geometries back to the breakup of Pangea. Land geological evidence is used to independently validate or reject the inferred paleogeographies. Such tomotectonic analysis offers a methodology for resolving fundamental questions about the assembly of North America. For example: When, where and how did superterranes collide with North America? Did an Andean-type margin exist along western North America for all times between Cenozoic Cascade arc formation and the Jurassic, when an arc was rooted in continental crust of southwest USA? Deep mantle and seafloor isochron evidence show that TWO massive arc complexes originated in the seas west of Pangea as it started to fragment ( 190-170 Ma), a time when eastward subduction beneath the continental margin arc was shutting down. Most recognizable, and 2000-4000 km off the west coast of Pangea, is a >10,000 km long, east-pointing chevron of slab walls in the lower mantle, with its apex near present-day Nova Scotia. Formerly considered Farallon slab, its location and geometry are not consistent with continent-hugging, Jurassic to Recent Farallon subduction. Instead, a second massive and more westerly slab wall, 4000 - 6000 km west of Pangea, must have intercepted and consumed all northern Farallon lithosphere, and continues to do so beneath the Cascades. Both slabs initiated intraoceanic. Their arcs did not contribute to an Andean-style margin until they were diachronously overridden by North America, beginning 155 Ma. Implied is a continent-spanning suture between these two arc complexes and North America. Land geological evidence of this suture is an Alaska to Mexico track of at least 12 Jura-Cretaceous basins that collapsed between the Insular and Intermontane microcontinents, over half of which contain relicts of mantle. A conceptual framework for the Early Cretaceous North American suturing is found in the southwest Pacific. An analogous arrangement of plates and diachronous suture is forming today as Australia overrides arcs to its north.

DAPHNE silicon photonics technological platform for research and development on WDM applications

NASA Astrophysics Data System (ADS)

Baudot, Charles; Fincato, Antonio; Fowler, Daivid; Perez-Galacho, Diego; Souhaité, Aurélie; Messaoudène, Sonia; Blanc, Romuald; Richard, Claire; Planchot, Jonathan; De-Buttet, Come; Orlando, Bastien; Gays, Fabien; Mezzomo, Cécilia; Bernard, Emilie; Marris-Morini, Delphine; Vivien, Laurent; Kopp, Christophe; Boeuf, Frédéric

2016-05-01

A new technological platform aimed at making prototypes and feasibility studies has been setup at STMicroelectronics using 300mm wafer foundry facilities. The technology, called DAPHNE (Datacom Advanced PHotonic Nanoscale Environment), is devoted at developing and evaluating new devices and sub-systems in particular for wavelength division multiplexing (WDM) applications and ring resonator based applications. Developed in the course of PLAT4MFP7 European project, DAPHNE is a flexible platform that fits perfectly R&D needs. The fabrication flow enables the processing of photonic integrated circuits using a silicon-on-insulator (SOI) of 300nm, partial etches of 150nm and 50nm and a total silicon etching. Consequently, two varieties of rib waveguides and one strip waveguide can be fabricated simultaneously with auto-alignment properties. The process variability on the 150nm partially etched silicon and the thin 50nm slab region are both less than 6 nm. Using a variety of different implantation configurations and a back-end of line of 5 metal layers, active devices are fabricated both in germanium and silicon. An available far back-end of line process consists of making 20 μm diameter copper posts on top of the electrical pads so that an electronic integrated circuit can be bonded on top the photonic die by 3D integration. Besides having those fabrication process options, DAPHNE is equipped with a library of standard cells for optical routing and multiplexing. Moreover, typical Mach-Zehnder modulators based on silicon pn junctions are also available for optical signal modulation. To achieve signal detection, germanium photodetectors also exist as standard cells. The measured single-mode propagation losses are 3.5 dB/cm for strip, 3.7 dB/cm for deep-rib (50nm slab) and 1.4 dB/cm for standard rib (150nm slab) waveguides. Transition tapers between different waveguide structures are as low as 0.006 dB.

Constraints on upper mantle Vp/Vs ratio variations beneath eastern North China from receiver function tomography

NASA Astrophysics Data System (ADS)

Si, Shaokun; Tian, Xiaobo; Gao, Rui

2017-05-01

To detect the thinning, modification, and replacement of the basement of the lithosphere is a key step in understanding the destruction mechanism of the North China lithosphere. The difference of the basement of the lithosphere is mainly displayed by the variation of the peridotite composition and its physical state. Vp/Vs ratio (hereafter referred to as velocity ratio) is more sensitive to this change than Vp or Vs alone. By means of the strong dependence of the travel-time of the wave converted at the 410-km discontinuity (P410s) observed in the receiver function (RF) on the velocity ratio in the upper mantle, we developed a new mapping method to constrain the velocity ratio between the Moho and 410-km discontinuity. Using the RFs extracted from 246 broadband stations beneath the North China Craton (NCC), we obtained a high-resolution velocity ratio image of the upper mantle. The abnormal velocity ratio indicates a strong lateral variation of the mineral composition in the upper mantle beneath North China. Two low-velocity-ratio patches are imaged at the top of the upper mantle and the 410 km depth, respectively. The former may be related to the orthopyroxene enrichment in the lithospheric mantle, and the latter may reflect the stagnant Pacific slab in the mantle transition zone (MTZ). A prominent high-velocity-ratio anomaly is also imaged in the upper mantle beneath the Shaanxi-Shanxi rift system in the central NCC, with the highest anomaly reaching 10%. We speculate that the high velocity ratio of upper mantle is related to convective flow due to slab dehydration in the MTZ. The dehydration of the retained slab in the MTZ results in partial melting and upwelling of upper mantle materials. Such convective flow and their melting are closely related to the Cenozoic basalt eruption in the northern section of the Shaanxi-Shanxi rift system.

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.

Transforming guided waves with metamaterial waveguide cores

NASA Astrophysics Data System (ADS)

Viaene, S.; Ginis, V.; Danckaert, J.; Tassin, P.

2016-04-01

Metamaterials make use of subwavelength building blocks to enhance our control on the propagation of light. To determine the required material properties for a given functionality, i.e., a set of desired light flows inside a metamaterial device, metamaterial designs often rely on a geometrical design tool known as transformation optics. In recent years, applications in integrated photonics motivated several research groups to develop two-dimensional versions of transformation optics capable of routing surface waves along graphene-dielectric and metal-dielectric interfaces. Although guided electromagnetic waves are highly relevant to applications in integrated optics, no consistent transformation-optical framework has so far been developed for slab waveguides. Indeed, the conventional application of transformation optics to dielectric slab waveguides leads to bulky three-dimensional devices with metamaterial implementations both inside and outside of the waveguide's core. In this contribution, we develop a transformationoptical framework that still results in thin metamaterial waveguide devices consisting of a nonmagnetic metamaterial core of varying thickness [Phys. Rev. B 93.8, 085429 (2016)]. We numerically demonstrate the effectiveness and versatility of our equivalence relations with three crucial functionalities: a beam bender, a beam splitter and a conformal lens. Our devices perform well on a qualitative (comparison of fields) and quantitative (comparison of transmitted power) level compared to their bulky counterparts. As a result, the geometrical toolbox of transformation optics may lead to a plethora of integrated metamaterial devices to route guided waves along optical chips.

Noncontingent reinforcement without extinction plus differential reinforcement of alternative behavior during treatment of problem behavior.

PubMed

Fritz, Jennifer N; Jackson, Lynsey M; Stiefler, Nicole A; Wimberly, Barbara S; Richardson, Amy R

2017-07-01

The effects of noncontingent reinforcement (NCR) without extinction during treatment of problem behavior maintained by social positive reinforcement were evaluated for five individuals diagnosed with autism spectrum disorder. A continuous NCR schedule was gradually thinned to a fixed-time 5-min schedule. If problem behavior increased during NCR schedule thinning, a continuous NCR schedule was reinstated and NCR schedule thinning was repeated with differential reinforcement of alternative behavior (DRA) included. Results showed an immediate decrease in all participants' problem behavior during continuous NCR, and problem behavior maintained at low levels during NCR schedule thinning for three participants. Problem behavior increased and maintained at higher rates during NCR schedule thinning for two other participants; however, the addition of DRA to the intervention resulted in decreased problem behavior and increased mands. © 2017 Society for the Experimental Analysis of Behavior.

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.

The FLAME-slab method for electromagnetic wave scattering in aperiodic slabs

NASA Astrophysics Data System (ADS)

Mansha, Shampy; Tsukerman, Igor; Chong, Y. D.

2017-12-01

The proposed numerical method, "FLAME-slab," solves electromagnetic wave scattering problems for aperiodic slab structures by exploiting short-range regularities in these structures. The computational procedure involves special difference schemes with high accuracy even on coarse grids. These schemes are based on Trefftz approximations, utilizing functions that locally satisfy the governing differential equations, as is done in the Flexible Local Approximation Method (FLAME). Radiation boundary conditions are implemented via Fourier expansions in the air surrounding the slab. When applied to ensembles of slab structures with identical short-range features, such as amorphous or quasicrystalline lattices, the method is significantly more efficient, both in runtime and in memory consumption, than traditional approaches. This efficiency is due to the fact that the Trefftz functions need to be computed only once for the whole ensemble.

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.

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.

Nuclear reactor containment structure with continuous ring tunnel at grade

DOEpatents

Seidensticker, Ralph W.; Knawa, Robert L.; Cerutti, Bernard C.; Snyder, Charles R.; Husen, William C.; Coyer, Robert G.

1977-01-01

A nuclear reactor containment structure which includes a reinforced concrete shell, a hemispherical top dome, a steel liner, and a reinforced-concrete base slab supporting the concrete shell is constructed with a substantial proportion thereof below grade in an excavation made in solid rock with the concrete poured in contact with the rock and also includes a continuous, hollow, reinforced-concrete ring tunnel surrounding the concrete shell with its top at grade level, with one wall integral with the reinforced concrete shell, and with at least the base of the ring tunnel poured in contact with the rock.

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.

Constraints on the Geometry of the Farallon Slab from the Joint Interpretation of All Available Imaging Results from the Earthscope USArray Deployment in the Lower 48 States

NASA Astrophysics Data System (ADS)

Esker, A.; Pavlis, G. L.

2017-12-01

We assembled all available seismic tomography models distributed through the IRIS DMC and other sources. We combined these images with our own results using 3D plane wave migration of P to S conversion data derived from the USArray data set and other broadband seismic stations in the lower 48 states. All the tomography models were converted into SEGY format and interpolated onto a regular grid in a UTM reference frame. That innovation makes joint interpretation feasible using a seismic interpretation software (Petrel) because we treat both the tomography models and scattered wave image results as if they were 3D seismic reflection data. The careful designed interface of a modern exploration package makes exploring a range of interpretation packages much faster and allowed us to produce a more comprehensive interpretation of all available data. The tomography models are nearly an order of magnitude smoother than the scattered wave images, so we use the tomography models as a cross-validation in interpretation unless the scattered wave images are ambiguous. The focus of this study is testing a conjecture in an earlier paper (Pavlis, 2011) for the presence of a single continuous horizon interpreted as the top of the Farallon Slab. As in the previous paper we constrained the western edge of this surface with the location of Cascadia trench as well as a virtual edge from a back projection of the Mendocino triple junction using Pacific-North America motion over the past 30 Ma. We also simulated crustal multiple effects on the plane wave migration results using crustal geometry estimates produced by the Earthscope Automated Receiver Survey (EARS). This confirmed the scattered wave images were not reliable in the upper mantle at depths shallower than 200 km due to contamination by crustal multiples. Most tomography models show a steep dip in the slab immediately east of the volcanic arc and our surface follows the average geometry defined by a visual comparison of all the models. In eastern Oregon and northern Nevada the tomography models consistently show a general flattening of the slab over the 410 km discontinuity. A consistent horizon is observed in the most recent plane wave imaging and at we use that horizon to define the top of slab there. Our interpretations also confirmed a sharp increase in dip of the slab in eastern Wyoming and Montana.

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.

Tectonic mode switches and the nature of orogenesis

NASA Astrophysics Data System (ADS)

Lister, Gordon; Forster, Marnie

2009-12-01

The birth and death of many mountain belts occurs in lithosphere that over-rides major subduction zones. Here the tectonic mode (shortening versus extension) can abruptly switch, even during continuous and otherwise smooth convergence. If the hinge line of the foundering slab rapidly retreats (i.e. rolls back), the foundering slab creates a gravitational potential well into which the orogen collapses. This motion, coupled with stress guides, can "pull" the orogen apart. A slowing of roll-back (or of hinge retreat) means that the subduction flexure may subsequently begin to be "pushed back" or be "pushed over" by the advancing orogen. The consequence of such changes in relative motion is that orogenic belts are affected by abrupt tectonic mode switches. The change from "push" to "pull" leads to a sudden change from horizontal extension to horizontal shortening, potentially throughout the entire mass of the orogenic lithosphere that over-rides the subducting slab. The sequencing of these tectonic mode switches affects the thermal evolution of the orogen, and thus fundamentally determines the nature of orogenesis. This insight led to us to our quite different views as to how orogens work. It is evident that orogens affected by abrupt "push-pull" mode switches are characterized by high-pressure metamorphism, whereas orogens affected by abrupt "pull-push" mode switches are characterized by high-temperature metamorphism, magmatism and anatexis.

Measurement and calculation of neutron leakage spectra from slab samples of beryllium, gallium and tungsten irradiated with 14.8 MeV neutrons

NASA Astrophysics Data System (ADS)

Nie, Y. B.; Ruan, X. C.; Ren, J.; Zhang, S.; Han, R.; Bao, J.; Huang, H. X.; Ding, Y. Y.; Wu, H. C.; Liu, P.; Zhou, Z. Y.

2017-09-01

In order to make benchmark validation of the nuclear data for gallium (Ga), tungsten (W) and beryllium (Be) in existing modern evaluated nuclear data files, neutron leakage spectra in the range from 0.8 to 15 MeV from slab samples were measured by time-of-flight technique with a BC501 scintillation detector. The measurements were performed at China Institute of Atomic Energy (CIAE) using a D-T neutron source. The thicknesses of the slabs were 0.5 to 2.5 mean free path for 14.8 MeV neutrons, and the measured angles were chosen to be 60∘ and 120∘. The measured spectra were compared with those calculated by the continuous energy Monte-Carlo transport code MCNP, using the data from the CENDL-3.1, ENDF/B-VII.1 and JENDL-4.0 nuclear data files, the comparison between the experimental and calculated results show that: The results from all three libraries significantly underestimate the cross section in energy range of 10-13 MeV for Ga; For W, the calculated spectra using data from CENDL-3.1 and JENDL-4.0 libraries show larger discrepancies with the measured ones, especially around 8.5-13.5 MeV; and for Be, all the libraries led to underestimation below 3 MeV at 120∘.

Supercritical fluid in the mantle transition zone deduced from H-D interdiffusion of wadsleyite

NASA Astrophysics Data System (ADS)

Sun, Wei; Yoshino, Takashi; Sakamoto, Naoya; Yurimoto, Hisayoshi

2018-02-01

Knowledge of the distribution of water in the Earth's mantle is key to understanding the mantle convection and geochemical evolution of the Earth. As wadsleyite and ringwoodite can incorporate large amounts of water in their crystal structures, proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge, where descending slab stagnates at the transition zone. However, there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies, because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite. Here we report the hydrogen self-diffusion coefficient obtained from H-D interdiffusion experiments in wadsleyite single-crystal couples. Our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone. In contrast, the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle, probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales. This phenomenon provides an alternative explanation for both the high-conductivity and seismic-velocity anomalies observed in the mantle wedge at the transition-zone depth.

A role for subducted super-hydrated kaolinite in Earth's deep water cycle

NASA Astrophysics Data System (ADS)

Hwang, Huijeong; Seoung, Donghoon; Lee, Yongjae; Liu, Zhenxian; Liermann, Hanns-Peter; Cynn, Hyunchae; Vogt, Thomas; Kao, Chi-Chang; Mao, Ho-Kwang

2017-12-01

Water is the most abundant volatile component in the Earth. It continuously enters the mantle through subduction zones, where it reduces the melting temperature of rocks to generate magmas. The dehydration process in subduction zones, which determines whether water is released from the slab or transported into the deeper mantle, is an essential component of the deep water cycle. Here we use in situ and time-resolved high-pressure/high-temperature synchrotron X-ray diffraction and infrared spectra to characterize the structural and chemical changes of the clay mineral kaolinite. At conditions corresponding to a depth of about 75 km in a cold subducting slab (2.7 GPa and 200 °C), and in the presence of water, we observe the pressure-induced insertion of water into kaolinite. This super-hydrated phase has a unit cell volume that is about 31% larger, a density that is about 8.4% lower than the original kaolinite and, with 29 wt% H2O, the highest water content of any known aluminosilicate mineral in the Earth. As pressure and temperature approach 19 GPa and about 800 °C, we observe the sequential breakdown of super-hydrated kaolinite. The formation and subsequent breakdown of super-hydrated kaolinite in cold slabs subducted below 200 km leads to the release of water that may affect seismicity and help fuel arc volcanism at the surface.

Seismic attenuation structure beneath Nazca Plate subduction zone in southern Peru

NASA Astrophysics Data System (ADS)

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

2017-12-01

We estimate seismic attenuation in terms of quality factors, QP and QS using P and S phases, respectively, beneath Nazca Plate subduction zone between 10°S and 18.5°S latitude in southern Peru. We first relocate 298 earthquakes with magnitude ranges of 4.0-6.5 and depth ranges of 20-280 km. We measure t*, which is an integrated attenuation through the seismic raypath between the regional earthquakes and stations. The measured t* are inverted to construct three-dimensional attenuation structures of southern Peru. Checkerboard test results for both QP and QS structures ensure good resolution in the slab-dip transition zone between flat and normal slab subduction down to a depth of 200 km. Both QP and QS results show higher attenuation continued down to a depth of 50 km beneath volcanic arc and also beneath the Quimsachata volcano, the northernmost young volcano, located far east of the main volcanic front. We also observe high attenuation in mantle wedge especially beneath the normal subduction region in both QP and QS (100-130 in QP and 100-125 in QS) and slightly higher QP and QS beneath the flat-subduction and slab-dip transition regions. We plan to relate measured attenuation in the mantle wedge to material properties such as viscosity to understand the subduction zone dynamics.

Evidence of lower-mantle slab penetration phases in plate motions.

PubMed

Goes, Saskia; Capitanio, Fabio A; Morra, Gabriele

2008-02-21

It is well accepted that subduction of the cold lithosphere is a crucial component of the Earth's plate tectonic style of mantle convection. But whether and how subducting plates penetrate into the lower mantle is the subject of continuing debate, which has substantial implications for the chemical and thermal evolution of the mantle. Here we identify lower-mantle slab penetration events by comparing Cenozoic plate motions at the Earth's main subduction zones with motions predicted by fully dynamic models of the upper-mantle phase of subduction, driven solely by downgoing plate density. Whereas subduction of older, intrinsically denser, lithosphere occurs at rates consistent with the model, younger lithosphere (of ages less than about 60 Myr) often subducts up to two times faster, while trench motions are very low. We conclude that the most likely explanation is that older lithosphere, subducting under significant trench retreat, tends to lie down flat above the transition to the high-viscosity lower mantle, whereas younger lithosphere, which is less able to drive trench retreat and deforms more readily, buckles and thickens. Slab thickening enhances buoyancy (volume times density) and thereby Stokes sinking velocity, thus facilitating fast lower-mantle penetration. Such an interpretation is consistent with seismic images of the distribution of subducted material in upper and lower mantle. Thus we identify a direct expression of time-dependent flow between the upper and lower mantle.

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.

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.

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.

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.

Effect of scanning speed on continuous wave laser scribing of metal thin films: theory and experiment

NASA Astrophysics Data System (ADS)

Shahbazi, AmirHossein; Koohian, Ata; Madanipour, Khosro

2017-01-01

In this paper continuous wave laser scribing of the metal thin films have been investigated theoretically and experimentally. A formulation is presented based on parameters like beam power, spot size, scanning speed and fluence thresholds. The role of speed on the transient temperature and tracks width is studied numerically. By using two frameworks of pulsed laser ablation of thin films and laser printing on paper, the relation between ablation width and scanning speed has been derived. Furthermore, various speeds of the focused 450 nm continuous laser diode with an elliptical beam spot applied to a 290 nm copper thin film coated on glass, experimentally. The beam power was 150 mW after spatial filtering. By fitting the theoretical formulation to the experimental data, the threshold fluence and energy were obtained to be 13.2 J mm-2 and 414~μ J respectively. An anticipated theoretical parameter named equilibrium~border was verified experimentally. It shows that in the scribing of the 290 nm copper thin film, at a distance where the intensity reaches about 1/e of its maximum value, the absorbed fluence on the surface is equal to zero. Therefore the application of continuous laser in metal thin film ablation has different mechanism from pulsed laser drilling and beam scanning in printers.

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

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.

Tunable Optical Sources.

DTIC Science & Technology

1980-11-01

finite aperture size 5. A. E. Siegman , "Unstable optical resonators for laser of the YAG rod, applications," Proc. IEEE 53, 217-287 (1965); "Unstable...Pumped LiNbO3 Tunable Source Radial Birefringent Element Computer Controlled Laser Attenuator Slab Configuration Laser Source 20. ABSTRACT (Continue on...have invented and demonstrated a computer controlled laser attenu- ator. .... Cont inued DD Il 7 1473 EDITION OF I NOV 01 IS OBSOLETE UNCLASSIFIEDAN

Agarose electrophoresis of DNA in discontinuous buffers, using a horizontal slab apparatus and a buffer system with improved properties.

PubMed

Zsolnai, A; Orbán, L; Chrambach, A

1993-03-01

Using a horizontal slab apparatus with a buffer in the reservoirs at the level of the gel ("sea-level electrophoresis"), the retrograde discontinuous buffer system reported by Wiltfang et al. for sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of proteins was applied to DNA electrophoresis. This application yielded the advantages of an increased displacement rate of the moving boundary front and a decrease in the concentration of the counterion base in the resolving phase, which yielded reduced relative mobility values at equivalent gel concentrations and practicable low buffer concentrations. The change of relative mobilities (Rf) with a variation of field strength is decreased compared to that of the migration rate in the continuous Tris-boric-acid-EDTA (TBE) buffer and thus the robustness of the system is improved, as well as the efficiency of separation. The system of Wiltfang et al. has in common with previously described discontinuous DNA system, that it is able to stack DNA from dilute samples and is insensitive to sample components with lower net mobilities than DNA, such as acetate. However, the variance of Rf at constant current density in the discontinuous buffer system is not improved over that of the migration rate at constant field strength in the continuous TBE buffer.

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.

X-ray computed tomography datasets for forensic analysis of vertebrate fossils.

PubMed

Rowe, Timothy B; Luo, Zhe-Xi; Ketcham, Richard A; Maisano, Jessica A; Colbert, Matthew W

2016-06-07

We describe X-ray computed tomography (CT) datasets from three specimens recovered from Early Cretaceous lakebeds of China that illustrate the forensic interpretation of CT imagery for paleontology. Fossil vertebrates from thinly bedded sediments often shatter upon discovery and are commonly repaired as amalgamated mosaics grouted to a solid backing slab of rock or plaster. Such methods are prone to inadvertent error and willful forgery, and once required potentially destructive methods to identify mistakes in reconstruction. CT is an efficient, nondestructive alternative that can disclose many clues about how a specimen was handled and repaired. These annotated datasets illustrate the power of CT in documenting specimen integrity and are intended as a reference in applying CT more broadly to evaluating the authenticity of comparable fossils.

Exact Dispersion Study of an Asymmetric Thin Planar Slab Dielectric Waveguide without Computing {d^2}β/{d{k^2}} Numerically

NASA Astrophysics Data System (ADS)

Raghuwanshi, Sanjeev Kumar; Palodiya, Vikram

2017-08-01

Waveguide dispersion can be tailored but not the material dispersion. Hence, the total dispersion can be shifted at any desired band by adjusting the waveguide dispersion. Waveguide dispersion is proportional to {d^2}β/d{k^2} and need to be computed numerically. In this paper, we have tried to compute analytical expression for {d^2}β/d{k^2} in terms of {d^2}β/d{k^2} accurately with numerical technique, ≈ 10^{-5} decimal point. This constraint sometimes generates the error in calculation of waveguide dispersion. To formulate the problem we will use the graphical method. Our study reveals that we can compute the waveguide dispersion enough accurately for various modes by knowing - β only.

Computationally efficient method for optical simulation of solar cells and their applications

NASA Astrophysics Data System (ADS)

Semenikhin, I.; Zanuccoli, M.; Fiegna, C.; Vyurkov, V.; Sangiorgi, E.

2013-01-01

This paper presents two novel implementations of the Differential method to solve the Maxwell equations in nanostructured optoelectronic solid state devices. The first proposed implementation is based on an improved and computationally efficient T-matrix formulation that adopts multiple-precision arithmetic to tackle the numerical instability problem which arises due to evanescent modes. The second implementation adopts the iterative approach that allows to achieve low computational complexity O(N logN) or better. The proposed algorithms may work with structures with arbitrary spatial variation of the permittivity. The developed two-dimensional numerical simulator is applied to analyze the dependence of the absorption characteristics of a thin silicon slab on the morphology of the front interface and on the angle of incidence of the radiation with respect to the device surface.

Efficiency of Launching Highly Confined Polaritons by Infrared Light Incident on a Hyperbolic Material.

PubMed

Dai, Siyuan; Ma, Qiong; Yang, Yafang; Rosenfeld, Jeremy; Goldflam, Michael D; McLeod, Alex; Sun, Zhiyuan; Andersen, Trond I; Fei, Zhe; Liu, Mengkun; Shao, Yinming; Watanabe, Kenji; Taniguchi, Takashi; Thiemens, Mark; Keilmann, Fritz; Jarillo-Herrero, Pablo; Fogler, Michael M; Basov, D N

2017-09-13

We investigated phonon-polaritons in hexagonal boron nitride-a naturally hyperbolic van der Waals material-by means of the scattering-type scanning near-field optical microscopy. Real-space nanoimages we have obtained detail how the polaritons are launched when the light incident on a thin hexagonal boron nitride slab is scattered by various intrinsic and extrinsic inhomogeneities, including sample edges, metallic nanodisks deposited on its top surface, random defects, and surface impurities. The scanned tip of the near-field microscope is itself a polariton launcher whose efficiency proves to be superior to all the other types of polariton launchers we studied. Our work may inform future development of polaritonic nanodevices as well as fundamental studies of collective modes in van der Waals materials.

X-ray computed tomography datasets for forensic analysis of vertebrate fossils

PubMed Central

Rowe, Timothy B.; Luo, Zhe-Xi; Ketcham, Richard A.; Maisano, Jessica A.; Colbert, Matthew W.

2016-01-01

We describe X-ray computed tomography (CT) datasets from three specimens recovered from Early Cretaceous lakebeds of China that illustrate the forensic interpretation of CT imagery for paleontology. Fossil vertebrates from thinly bedded sediments often shatter upon discovery and are commonly repaired as amalgamated mosaics grouted to a solid backing slab of rock or plaster. Such methods are prone to inadvertent error and willful forgery, and once required potentially destructive methods to identify mistakes in reconstruction. CT is an efficient, nondestructive alternative that can disclose many clues about how a specimen was handled and repaired. These annotated datasets illustrate the power of CT in documenting specimen integrity and are intended as a reference in applying CT more broadly to evaluating the authenticity of comparable fossils. PMID:27272251

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.

Three Dimensional Viscoelastic Postseismic Deformation of the 2013 Mw8.3 Okhotsk Deep-Focus Earthquake

NASA Astrophysics Data System (ADS)

Hu, Y.; Burgmann, R.; Shestakov, N.; Titkov, N. N.; Serovetnikov, S.; Prytkov, A.; Vasilenko, N. F.; Wang, K.

2016-12-01

The upper mantle rheology at depths within a few hundred kilometers has been well studied through shallow great megathrust earthquakes. However, understanding of the mantle rheology at greater depths, such as in the vicinity of the transition zone, has been limited by the lack of direct or indirect measurements. The largest well-recorded deep earthquake with magnitude Mw 8.3 occurred within the subducting Pacific plate at 600 km depth beneath the Okhotsk Sea on May 24, 2013. Twenty-seven continuous GPS stations in this region recorded coseismic displacements of up to 15 mm in the horizontal direction and up to 20 mm in the vertical direction. Within three years after the earthquake seventeen continuous GPS stations underwent transient westward motion of up to 8 mm/yr and vertical motion of up to 10 mm/yr. The geodetically delineated postseismic crustal deformation thus provides a unique opportunity to study the three dimensional heterogeneity of the mantle rheology and properties of the subducting slab at great depths. We have developed three-dimensional viscoelastic finite element models of the 2013 Okhotsk earthquake to explore these questions. Our initial model includes an elastic lithosphere including the subducting slab, a viscoelastic continental upper mantle and a viscoelastic oceanic upper mantle. We assume that the upper mantle is characterized by a bi-viscous Burgers rheology. For simplicity, we assume that the transient Kelvin viscosity is one order of magnitude lower than that of the steady-state Maxwell viscosity. Our preliminary models indicate that the viscosity of the upper mantle beneath the transition zone has to be at least one order of magnitude lower than that of the upper mantle at shallower depths. A viscoelastic subducting slab at depths >400 km with viscosities of 2-3 orders of magnitude higher than that of the mantle wedge provides a better fit to the observed surface velocities.

From underplating to delamination-retreat in the northern Apennines

NASA Astrophysics Data System (ADS)

Chiarabba, C.; Giacomuzzi, G.; Bianchi, I.; Agostinetti, N. P.; Park, J.

2014-10-01

Recordings of teleseismic earthquakes from a dense set of temporary and permanent broadband seismic stations reveal the lithospheric structure of the northern Apennines and support the scenario of a retreating detachment within the mid-crust. Lithospheric delamination appears crucial to the formation and evolution of the Apennines orogen. Receiver-function (RF) stacks outline a continuous west-dipping Ps converted phase from a positive velocity jump that we interpret as the top of the lower crust and mantle of the Adria continental lithosphere, which is descending into the shallow mantle. The correlation of seismicity with two RF profiles across the northern Apennines suggests distinct stages of lithospheric delamination. Active penetration of the detachment into the Adria lithosphere seems evident in the south/east, with induced shallow-mantle flow facilitated by slab dehydration. Penetration of the detachment in the north/west seems to have arrested, and is possibly marked by crustal underplating. This layer atop the Apennines slab is visible only down to 80 km depth and suspends above an oppositely-dipping paired positive/negative Ps converted phase in stacked receiver functions. The break in the west-dipping Adria lithosphere conflicts with a westward-subduction scenario continuous from the Oligocene. Lateral changes of deep structure and seismicity along the northern Apennines suggest that underplating of crustal material and delamination-retreat are distinct mechanisms active today in the western and eastern sectors, respectively, of the northern Apennines. Negative Ps-pulses at 100-120 km depth help to define a seismic lithosphere-asthenosphere boundary (LAB), but cross-cut a volume of high-velocity mantle rock, as inferred from tomographic models. We hypothesize that this seismic LAB is a rheological discontinuity that affects the frequency band of seismic body waves, but not the long-term viscous response that governs the evolution and eventual detachment of the continental slab.

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.

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.

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.