Two-phase pressure drop reduction BWR assembly design

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

Dix, G.E.; Crowther, R.L.; Colby, M.J.

1991-05-21

This patent describes an improved fuel assembly for a boiling water reactor. It comprises: a fuel channel; a lower tie plate; an upper tie plate; the lower tie plate and the upper tie plate defining a two-dimensional matrix; at least one water rod the fuel rods being partial length rods.

An Examination of Upper Plate Aftershocks of the Tohoku-oki Earthquake: Are They Caused by a Long-term Change in the Dip of the Subducting Plate?

NASA Astrophysics Data System (ADS)

Oryan, B.; Buck, W. R.

2017-12-01

The Tohoku-oki earthquake was one of the strongest earthquakes ever recorded. 50-80 meters of lateral motion of the sloping seafloor resulted in a tsunami that exceeded predictions and caused one of the costliest natural disasters in history. It was also the first time extensional aftershocks were observed in the upper plate over a region as wide as 250km. Inspired by these findings, researchers found similar upper plate extensional earthquakes after reexamining seismic data from past earthquakes that had also produced large tsunamis. Such extensional aftershocks are difficult to explain in terms of standard subduction models. Most models assume that the dip of the subducting plate remains constant with time. However, geological evidence indicates that the dip angle of the subducting plate changes. We hypothesize that a reduction in the dip angle of the subducting plate can cause upper plate extensional earthquakes. This change in dip angle adds extensional bending stress to the upper plate. During an inter-seismic period, the interface is `locked' causing regional compression that prevents the release of extensional energy. Relief of compressional stresses during a megathrust event can trigger the release of the accumulated extensional energy, explaining why extensional earthquakes were observed after some megathrust events. Numerical models will be used to test our hypothesis. First, we will model long term subduction with a nearly constant dip angle. Then, we will impose a `mantle wind' to reduce the dip angle of the subducting plate. Eventually, we will model a full seismic cycle of the subduction resulting in a megathrust event. The generation of extensional earthquakes in the upper plate of our model following the megathrust event will allow us to determine whether a causal link exists between these earthquakes and a reduction in the dip angle of the subducting plate.

Omnidirectional antenna having constant phase

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

Sena, Matthew

Various technologies presented herein relate to constructing and/or operating an antenna having an omnidirectional electrical field of constant phase. The antenna comprises an upper plate made up of multiple conductive rings, a lower ground-plane plate, a plurality of grounding posts, a conical feed, and a radio frequency (RF) feed connector. The upper plate has a multi-ring configuration comprising a large outer ring and several smaller rings of equal size located within the outer ring. The large outer ring and the four smaller rings have the same cross-section. The grounding posts ground the upper plate to the lower plate while maintainingmore » a required spacing/parallelism therebetween.« less

Subducting seamounts control interplate coupling and seismic rupture in the 2014 Iquique earthquake area

PubMed Central

Geersen, Jacob; Ranero, César R.; Barckhausen, Udo; Reichert, Christian

2015-01-01

To date, the parameters that determine the rupture area of great subduction zone earthquakes remain contentious. On 1 April 2014, the Mw 8.1 Iquique earthquake ruptured a portion of the well-recognized northern Chile seismic gap but left large highly coupled areas un-ruptured. Marine seismic reflection and swath bathymetric data indicate that structural variations in the subducting Nazca Plate control regional-scale plate-coupling variations, and the limited extent of the 2014 earthquake. Several under-thrusting seamounts correlate to the southward and up-dip arrest of seismic rupture during the 2014 Iquique earthquake, thus supporting a causal link. By fracturing of the overriding plate, the subducting seamounts are likely further responsible for reduced plate-coupling in the shallow subduction zone and in a lowly coupled region around 20.5°S. Our data support that structural variations in the lower plate influence coupling and seismic rupture offshore Northern Chile, whereas the structure of the upper plate plays a minor role. PMID:26419949

Abrupt Upper-Plate Tilting Upon Slab-Transition-Zone Collision

NASA Astrophysics Data System (ADS)

Crameri, F.; Lithgow-Bertelloni, C. R.

2017-12-01

During its sinking, the remnant of a surface plate crosses and interacts with multiple boundaries in Earth's interior. The most-prominent dynamic interaction arises at the upper-mantle transition zone where the sinking plate is strongly affected by the higher-viscosity lower mantle. Within our numerical model, we unravel, for the first time, that this very collision of the sinking slab with the transition zone induces a sudden, dramatic downward tilt of the upper plate towards the subduction trench. The slab-transition zone collision sets parts of the higher-viscosity lower mantle in motion. Naturally, this then induces an overall larger return flow cell that, at its onset, tilts the upper plate abruptly by around 0.05 degrees and over around 10 Millions of years. Such a significant and abrupt variation in surface topography should be clearly visible in temporal geologic records of large-scale surface elevation and might explain continental-wide tilting as observed in Australia since the Eocene or North America during the Phanerozoic. Unravelling this crucial mantle-lithosphere interaction was possible thanks to state-of-the-art numerical modelling (powered by StagYY; Tackley 2008, PEPI) and post-processing (powered by StagLab; www.fabiocrameri.ch/software). The new model that is introduced here to study the dynamically self-consistent temporal evolution of subduction features accurate subduction-zone topography, robust single-sided plate sinking, stronger plates close to laboratory values, an upper-mantle phase transition and, crucially, simple continents at a free surface. A novel, fully-automated post-processing includes physical model diagnostics like slab geometry, mantle flow pattern, upper-plate tilt angle and trench location.

Instability of a cantilevered flexible plate in viscous channel flow

NASA Astrophysics Data System (ADS)

Balint, T. S.; Lucey, A. D.

2005-10-01

The stability of a flexible cantilevered plate in viscous channel flow is studied as a representation of the dynamics of the human upper airway. The focus is on instability mechanisms of the soft palate (flexible plate) that cause airway blockage during sleep. We solve the Navier Stokes equations for flow with Reynolds numbers up to 1500 fully coupled with the dynamics of the plate motion solved using finite-differences. The study is 2-D and based upon linearized plate mechanics. When both upper and lower airways are open, the plate is found to lose its stability through a flutter mechanism and a critical Reynolds number exists. When one airway is closed, the plate principally loses its stability through a divergence mechanism and a critical flow speed exists. However, below the divergence-onset flow speed, flutter can exist for low levels of structural damping in the flexible plate. Our results serve to extend understanding of flow-induced instability of cantilevered flexible plates and will ultimately improve the diagnosis and treatment of upper-airway disorders.

Salinity driven oceanographic upwelling

DOEpatents

Johnson, D.H.

1984-08-30

The salinity driven oceanographic upwelling is maintained in a mariculture device that includes a long main duct in the general shape of a cylinder having perforated cover plates at each end. The mariculture device is suspended vertically in the ocean such that one end of the main duct is in surface water and the other end in relatively deep water that is cold, nutrient rich and relatively fresh in comparison to the surface water which is relatively warm, relatively nutrient deficient and relatively saline. A plurality of elongated flow segregating tubes are disposed in the main duct and extend from the upper cover plate beyond the lower cover plate into a lower manifold plate. The lower manifold plate is spaced from the lower cover plate to define a deep water fluid flow path to the interior space of the main duct. Spacer tubes extend from the upper cover plate and communicate with the interior space of the main duct. The spacer tubes are received in an upper manifold plate spaced from the upper cover plate to define a surface water fluid flow path into the flow segregating tubes. A surface water-deep water counterflow is thus established with deep water flowing upwardly through the main duct interior for discharge beyond the upper manifold plate while surface water flows downwardly through the flow segregating tubes for discharge below the lower manifold plate. During such counterflow heat is transferred from the downflowing warm water to the upflowing cold water. The flow is maintained by the difference in density between the deep water and the surface water due to their differences in salinity. The upwelling of nutrient rich deep water is used for marifarming by fertilizing the nutrient deficient surface water. 1 fig.

Salinity driven oceanographic upwelling

DOEpatents

Johnson, David H.

1986-01-01

The salinity driven oceanographic upwelling is maintained in a mariculture device that includes a long main duct in the general shape of a cylinder having perforated cover plates at each end. The mariculture device is suspended vertically in the ocean such that one end of the main duct is in surface water and the other end in relatively deep water that is cold, nutrient rich and relatively fresh in comparison to the surface water which is relatively warm, relatively nutrient deficient and relatively saline. A plurality of elongated flow segregating tubes are disposed in the main duct and extend from the upper cover plate beyond the lower cover plate into a lower manifold plate. The lower manifold plate is spaced from the lower cover plate to define a deep water fluid flow path to the interior space of the main duct. Spacer tubes extend from the upper cover plate and communicate with the interior space of the main duct. The spacer tubes are received in an upper manifold plate spaced from the upper cover plate to define a surface water fluid flow path into the flow segregating tubes. A surface water-deep water counterflow is thus established with deep water flowing upwardly through the main duct interior for discharge beyond the upper manifold plate while surface water flows downwardly through the flow segregating tubes for discharge below the lower manifold plate. During such counterflow heat is transferred from the downflowing warm water to the upflowing cold water. The flow is maintained by the difference in density between the deep water and the surface water due to their differences in salinity. The upwelling of nutrient rich deep water is used for marifarming by fertilizing the nutrient deficient surface water.

A precocious adult visual center in the larva defines the unique optic lobe of the split-eyed whirligig beetle Dineutus sublineatus

PubMed Central

2013-01-01

Introduction Whirligig beetles (Coleoptera: Gyrinidae) are aquatic insects living on the water surface. They are equipped with four compound eyes, an upper pair viewing above the water surface and a lower submerged pair viewing beneath the water surface, but little is known about how their visual brain centers (optic lobes) are organized to serve such unusual eyes. We show here, for the first time, the peculiar optic lobe organization of the larval and adult whirligig beetle Dineutus sublineatus. Results The divided compound eyes of adult whirligig beetles supply optic lobes that are split into two halves, an upper half and lower half, comprising an upper and lower lamina, an upper and lower medulla and a bilobed partially split lobula. However, the lobula plate, a neuropil that in flies is known to be involved in mediating stabilized flight, exists only in conjunction with the lower lobe of the lobula. We show that, as in another group of predatory beetle larvae, in the whirligig beetle the aquatic larva precociously develops a lobula plate equipped with wide-field neurons. It is supplied by three larval laminas serving the three dorsal larval stemmata, which are adjacent to the developing upper compound eye. Conclusions In adult whirligig beetles, dual optic neuropils serve the upper aerial eyes and the lower subaquatic eyes. The exception is the lobula plate. A lobula plate develops precociously in the larva where it is supplied by inputs from three larval stemmata that have a frontal-upper field of view, in which contrasting objects such as prey items trigger a body lunge and mandibular grasp. This precocious lobula plate is lost during pupal metamorphosis, whereas another lobula plate develops normally during metamorphosis and in the adult is associated with the lower eye. The different roles of the upper and lower lobula plates in supporting, respectively, larval predation and adult optokinetic balance are discussed. Precocious development of the upper lobula plate represents convergent evolution of an ambush hunting lifestyle, as exemplified by the terrestrial larvae of tiger beetles (Cicindelinae), in which activation of neurons in their precocious lobula plates, each serving two large larval stemmata, releases reflex body extension and mandibular grasp. PMID:23421712

Revisit of Criteria and Evidence for the Tectonic Erosion vs Accretion in East Asian Margin

NASA Astrophysics Data System (ADS)

Kimura, G.; Hamahashi, M.

2015-12-01

Accretionary and erosive margins provide tectonic end-members in subduction zone and how these tectonic processes might be recorded and recognizable in ancient subduction complexes remains a challenging issue. Tectonic erosion includes sediment subduction and basal erosion along the plate boundary megathrust and drags down the crust of the upper plate into the mantle. Geologic evidence for the erosion is commonly based on lost geological tectono-stratigraphic data, i.e. gaps in the record and indirect phenomena such as subsidence of the forearc slopes. A topographically rough surface such as seamount has been suggested to work like an erosive saw carving the upper plate. Another mechanism of basal erosion has been suggested to be hydrofracturing of upper plate materials due to dehydration-induced fluid pressures, resulting in entrainment of upper plate materials into the basal décollement. Considering the interaction between the ~30 km thick crust of the upper plate and subducting oceanic plate, a subduction dip angle of ~15°, and convergent rate of ~10 cm/year, at least ~1 Ma of continuous basal erosion is necessary to induce clear subsidence of the forearc because the width of plate interface between the upper crustal and subducting plates is about 115 km (30/cos15°). In several examples of subduction zones, for example the Japan Trench and the Middle America Trench off Costa Rica, the subsidence of a few thousand metres of the forearc, combined with a lack of accretionary prism over a period of several million years, suggest that the erosive condition needs to be maintained for several to tens of million years.Such age gaps in the accretionary complex, however, do not automatically imply that tectonic erosion has taken place, as other interpretations such as no accretion, cessation of subduction, and/or later tectonic modification, are also possible. Recent drilling in the forearc of the Nankai Trough suggests that the accretion was ceased between ~12 Ma to ~8 Ma due to the transference of subduction from the Pacific Plate to the Philippine Sea Plate, as opposed to the continuous subduction of the Phillipine Sea Plate with subduction erosion.

Intraply Hybrid Composites Would Contain Control Strips

NASA Technical Reports Server (NTRS)

Chamis, Christos C.; Shiao, Chi-Yu

1996-01-01

"Smart" structural components with sensors and/or actuators distributed throughout their volumes made of intraply hybrid composite materials, according to proposal. Strips of hybrid control material interspersed with strips of ordinary (passive) composite material in some layers, providing distributed control capability. For example, near and far edges of plate bent upward by commanding bottom control strips to expand and simultaneously commanding upper control strips to contract.

Omni-directional railguns

DOEpatents

Shahinpoor, Mohsen

1995-01-01

A device for electromagnetically accelerating projectiles. The invention features two parallel conducting circular plates, a plurality of electrode connections to both upper and lower plates, a support base, and a projectile magazine. A projectile is spring-loaded into a firing position concentrically located between the parallel plates. A voltage source is applied to the plates to cause current to flow in directions defined by selectable, discrete electrode connections on both upper and lower plates. Repulsive Lorentz forces are generated to eject the projectile in a 360 degree range of fire.

Control of the Lithospheric Mantle on intracontinental Deformation: Revival of Eastern U.S. Tectonism

NASA Astrophysics Data System (ADS)

Biryol, C. B.; Wagner, L. S.; Fischer, K. M.; Hawman, R. B.

2016-12-01

The present tectonic configuration of the southeastern United States is a product of earlier episodes of arc accretion, continental collision and breakup. This region is located in the interior of the North American Plate, some 1500 km away from closest active plate margin. However, there is ongoing tectonism across the area with multiple zones of seismicity, rejuvenation of the Appalachians of North Carolina, Virginia, and Pennsylvania, and Cenozoic intraplate volcanism. The mechanisms controlling this activity and the modern-day state of stress remain enigmatic. Two factors often regarded as major contributors are plate strength and preexisting inherited structures. Recent improvements in broadband seismic data coverage in the region associated with the South Eastern Suture of the Appalachian Margin Experiment (SESAME) and EarthScope Transportable Array make it possible to obtain detailed information on the structure of the lithosphere in the region. Here we present new tomographic images of the upper mantle beneath the Southeastern United States, revealing large-scale structural variations in the upper mantle. Our results indicate fast seismic velocity patterns that can be interpreted as ongoing lithospheric foundering. We observe an agreement between the locations of these upper mantle anomalies and the location of major zones of tectonism, volcanism and seismicity, providing a viable explanation for modern-day activity in this plate interior setting long after it became a passive margin. Based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere, we propose that piecemeal delamination has occurred beneath the region throughout the Cenozoic, removing a significant amount of reworked/deformed mantle lithosphere. Ongoing lithospheric foundering beneath the eastern margin of stable North America explains significant variations in thickness of lithospheric mantle across the former Grenville deformation front.

Low-frequency band gap of locally resonant phononic crystals with a dual-base plate.

PubMed

Zuo, Shuguang; Huang, Haidong; Wu, Xudong; Zhang, Minghai; Ni, Tianxin

2018-03-01

To achieve a wider band gap and a lower cut-on frequency, a locally resonant phononic crystal (LRPC) with a dual-base plate is investigated in this paper. Compared with the LRPC with a single plate, the band structure of the LRPC with a dual-base plate is calculated using the method of plane wave expansion and verified by the finite element method. According to the analysis of the band curves of the LRPC with a dual-base plate, the mechanisms are explained. Next, the influences of the thickness of the plates, the stiffness of the springs, the mass of resonators, and the lattice constant are also investigated. The results show that the structural asymmetry between the upper and the lower plate is conducive to reducing the cut-on frequency and broadening the band gap effectively. The results indicate a different approach for the application of LRPC in vibration and noise control.

Continental lithosphere of the Arabian Plate: A geologic, petrologic, and geophysical synthesis

NASA Astrophysics Data System (ADS)

Stern, Robert J.; Johnson, Peter

2010-07-01

The Arabian Plate originated ˜ 25 Ma ago by rifting of NE Africa to form the Gulf of Aden and Red Sea. It is one of the smaller and younger of the Earth's lithospheric plates. The upper part of its crust consists of crystalline Precambrian basement, Phanerozoic sedimentary cover as much as 10 km thick, and Cenozoic flood basalt (harrat). The distribution of these rocks and variations in elevation across the Plate cause a pronounced geologic and topographic asymmetry, with extensive basement exposures (the Arabian Shield) and elevations of as much as 3000 m in the west, and a Phanerozoic succession (Arabian Platform) that thickens, and a surface that descends to sea level, eastward between the Shield and the northeastern margin of the Plate. This tilt in the Plate is partly the result of marginal uplift during rifting in the south and west, and loading during collision with, and subduction beneath, the Eurasian Plate in the northeast. But a variety of evidence suggests that the asymmetry also reflects a fundamental crustal and mantle heterogeneity in the Plate that dates from Neoproterozoic time when the crust formed. The bulk of the Plate's upper crystalline crust is Neoproterozoic in age (1000-540 Ma) reflecting, in the west, a 300-million year process of continental crustal growth between ˜ 850 and 550 Ma represented by amalgamated juvenile magmatic arcs, post-amalgamation sedimentary and volcanic basins, and granitoid intrusions that make up as much as 50% of the Shield's surface. Locally, Archean and Paleoproterozoic rocks are structurally intercalated with the juvenile Neoproterozoic rocks in the southern and eastern parts of the Shield. The geologic dataset for the age, composition, and origin of the upper crust of the Plate in the east is smaller than the database for the Shield, and conclusions made about the crust in the east are correspondingly less definitive. In the absence of exposures, furthermore, nothing is known by direct observation about the composition of the crust north of the Shield. Nonetheless, available data indicate a geologic history for eastern Arabian crust different to that in the west. The Neoproterozic crust (˜ 815-785 Ma) is somewhat older than in the bulk of the Arabian Shield, and igneous and metamorphic activity was largely finished by 750 Ma. Thereafter, the eastern part of the Plate became the site of virtually continuous sedimentation from 725 Ma on and into the Phanerozoic. This implies that a relatively strong lithosphere was in place beneath eastern Arabia by 700 Ma in contrast to a lithospheric instability that persisted to ˜ 550 Ma in the west. Lithospheric differentiation is further indicated by the Phanerozoic depositional history with steady subsidence and accumulation of a sedimentary succession 5-14 km thick in the east and a consistent high-stand and thin to no Phanerozoic accumulation over the Shield. Geophysical data likewise indicate east-west lithospheric differentiation. Overall, the crustal thickness of the Plate (depth to the Moho) is ˜ 40 km, but there is a tendency for the crust to thicken eastward by as much as 10% from 35-40 km beneath the Shield to 40-45 km beneath eastern Arabia. The crust also becomes structurally more complex with as many as 5 seismically recognized layers in the east compared to 3 layers in the west. A coincident increase in velocity is noted in the upper-crust layers. Complementary changes are evidenced in some models of the Arabian Plate continental upper mantle, indicating eastward thickening of the lithospheric mantle from ˜ 80 km beneath the Shield to ˜ 120 km beneath the Platform, which corresponds to an overall lithospheric thickening (crust and upper mantle) from ˜ 120 km to ˜ 160 km eastward. The locus of these changes coincides with a prominent magnetic anomaly (Central Arabian Magnetic Anomaly, CAMA) in the extreme eastern part of the Arabian Shield that extends north across the north-central part of the Arabian Plate. The CAMA also coincides with a major structural boundary separating a region of northerly and northwesterly basement trends in the west from a region of northerly and northeasterly trends in the northeastern part of the Plate, and with the transition from high-stand buoyant Shield to subsided Platform. Its coincidence with geophysically indicated changes in the lower crust and mantle structure suggests that a fundamental lithospheric boundary is present in the central part of the Arabian Plate. The ages and isotopic characteristics of xenoliths brought to the surface in Cenozoic basalt eruptions indicate that the lower crust and upper mantle are largely juvenile Neoproterozoic additions, meaning that the lower crust and upper mantle formed about the same time as the upper crust. This implies that the lithospheric boundary in the central part of the Arabian Plate dates from Neoproterozoic time. We conclude that lithospheric differentiation across the Arabian Plate is long lived and has controlled much of the Phanerozoic sedimentary history of the Plate.

Axially shaped channel and integral flow trippers

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

Crowther, R.L. Jr.; Johansson, E.B.; Matzner, B.

1992-02-11

This patent describes a fuel assembly. It comprises: fuel rods positioned in spaced array by upper and lower tie-plates, and open ended flow channel surrounding the array for conducting coolant upward between a lower support plate having coolant communicated thereto to an upper support grid having a steam/water outlet communicated thereto. The flow channel surrounding the array for conducting coolant about the fuel rods; the open ended channel having a polygon shaped cross section with the channel constituting a closed conduit with flat side sections connected at corners to form the enclosed conduit; means separate from the channel for connectingmore » the upper and lower tie-plates together and maintaining the fuel rods in spaced array independent of the flow channel, the improvement in the flow channel comprising tapered side walls, the tapered side walls extending from an average thick cross section adjacent the lower support plate to an average thin cross section adjacent the upper core grid whereby the channel is reduced in thickness adjacent the upper core grid to correspond with the reduced pressure adjacent the upper core grid.« less

Omni-directional railguns

DOEpatents

Shahinpoor, M.

1995-07-25

A device is disclosed for electromagnetically accelerating projectiles. The invention features two parallel conducting circular plates, a plurality of electrode connections to both upper and lower plates, a support base, and a projectile magazine. A projectile is spring-loaded into a firing position concentrically located between the parallel plates. A voltage source is applied to the plates to cause current to flow in directions defined by selectable, discrete electrode connections on both upper and lower plates. Repulsive Lorentz forces are generated to eject the projectile in a 360 degree range of fire. 4 figs.

Three-dimensional frictional plastic strain partitioning during oblique rifting

NASA Astrophysics Data System (ADS)

Duclaux, Guillaume; Huismans, Ritske S.; May, Dave

2017-04-01

Throughout the Wilson cycle the obliquity between lithospheric plate motion direction and nascent or existing plate boundaries prompts the development of intricate three-dimensional tectonic systems. Where oblique divergence dominates, as in the vast majority of continental rift and incipient oceanic domains, deformation is typically transtensional and large stretching in the brittle upper crust is primarily achieved by the accumulation of displacement on fault networks of various complexity. In continental rift depressions such faults are initially distributed over tens to hundreds of kilometer-wide regions, which can ultimately stretch and evolve into passive margins. Here, we use high-resolution 3D thermo-mechanical finite element models to investigate the relative timing and distribution of localised frictional plastic deformation in the upper crust during oblique rift development in a simplified layered lithosphere. We vary the orientation of a wide oblique heterogeneous weak zone (representing a pre-existing geologic feature like a past orogenic domain), and test the sensitivity of the shear zones orientation to a range of noise distribution. These models allow us to assess the importance of material heterogeneities for controlling the spatio-temporal shear zones distribution in the upper crust during oblique rifting, and to discuss the underlying controls governing oblique continental breakup.

Multistage Magnetic Separator of Cells and Proteins

NASA Technical Reports Server (NTRS)

Barton, Ken; Ainsworth, Mark; Daily, Bruce; Dunn, Scott; Metz, Bill; Vellinger, John; Taylor, Brock; Meador, Bruce

2005-01-01

The multistage electromagnetic separator for purifying cells and magnetic particles (MAGSEP) is a laboratory apparatus for separating and/or purifying particles (especially biological cells) on the basis of their magnetic susceptibility and magnetophoretic mobility. Whereas a typical prior apparatus based on similar principles offers only a single stage of separation, the MAGSEP, as its full name indicates, offers multiple stages of separation; this makes it possible to refine a sample population of particles to a higher level of purity or to categorize multiple portions of the sample on the basis of magnetic susceptibility and/or magnetophoretic mobility. The MAGSEP includes a processing unit and an electronic unit coupled to a personal computer. The processing unit includes upper and lower plates, a plate-rotation system, an electromagnet, an electromagnet-translation system, and a capture-magnet assembly. The plates are bolted together through a roller bearing that allows the plates to rotate with respect to each other. An interface between the plates acts as a seal for separating fluids. A lower cuvette can be aligned with as many as 15 upper cuvette stations for fraction collection during processing. A two-phase stepping motor drives the rotation system, causing the upper plate to rotate for the collection of each fraction of the sample material. The electromagnet generates a magnetic field across the lower cuvette, while the translation system translates the electromagnet upward along the lower cuvette. The current supplied to the electromagnet, and thus the magnetic flux density at the pole face of the electromagnet, can be set at a programmed value between 0 and 1,400 gauss (0.14 T). The rate of translation can be programmed between 5 and 2,000 m/s so as to align all sample particles in the same position in the cuvette. The capture magnet can be a permanent magnet. It is mounted on an arm connected to a stepping motor. The stepping motor rotates the arm to position the capture magnet above the upper cuvette into which a fraction of the sample is collected. The electronic unit includes a power switch, power-supply circuitry that accepts 110-Vac input power, an RS-232 interface, and status lights. The personal computer runs the MAGSEP software and controls the operation of the MAGSEP through the RS-232 interface. The status of the power, the translating electromagnet, the capture magnet, and the rotation of the upper plate are indicated in a graphical user interface on the computer screen.

Mechanical Evolution and Dynamics of Decollement Slip in Contractional Systems: Correlating Macro- and Micro-Scale Processes in Particle Dynamics Simulation

NASA Astrophysics Data System (ADS)

Morgan, J. K.

2014-12-01

Particle-based numerical simulations allow detailed investigations of small-scale processes and mechanisms associated with fault initiation and slip, which emerge naturally in such models. This study investigates the evolving mechanical conditions and associated micro-mechanisms during transient slip on a weak decollement propagating beneath a growing contractional wedge (e.g., accretionary prism, fold and thrust belt). The models serve as analogs of the seismic cycle, although lacking full earthquake dynamics. Nonetheless, the mechanical evolution of both decollement and upper plate can be monitored, and correlated with the particle-scale physical and contact properties, providing insights into changes that accompany such stick-slip behavior. In this study, particle assemblages consolidated under gravity and bonded to impart cohesion, are pushed at a constant velocity above a weak, unbonded decollement surface. Forward propagation of decollement slip occurs in discrete pulses, modulated by heterogeneous stress conditions (e.g., roughness, contact bridging) along the fault. Passage of decollement slip resets the stress along this horizon, producing distinct patterns: shear stress is enhanced in front of the slipped decollement due to local contact bridging and fault locking; shear stress minima occur immediately above the tip, denoting local stress release and contact reorganization following slip; more mature portions of the fault exhibit intermediate shear stress, reflecting more stable contact force distributions and magnitudes. This pattern of shear stress pre-conditions the decollement for future slip events, which must overcome the high stresses at the fault tip. Long-term slip along the basal decollement induces upper plate contraction. When upper plate stresses reach critical strength conditions, new thrust faults break through the upper plate, relieving stresses and accommodating horizontal shortening. Decollement activity retreats back to the newly formed thrust fault. The cessation of upper plate fault slip causes gradual increases in upper plate stresses, rebuilding shear stresses along the decollement and enabling renewed pulses of decollement slip. Thus, upper plate deformation occurs out of phase with decollement propagation.

3. VIEW OF MAKERS PLATE ATTACHED TO UPPER CHORD MEMBER ...

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

3. VIEW OF MAKERS PLATE ATTACHED TO UPPER CHORD MEMBER WHICH STATES 'HUSTON AND CLEVELAND CONTRACTORS, COLUMBUS, OHIO, 1904.' - Main Street Parker Pony Truss Bridge, Main Street (Route 170) spanning Yellow Creek, Poland, Mahoning County, OH

31. DETAIL VIEW OF MOVABLE SPAN, UPPER TRUSS GUSSET PLATE, ...

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

31. DETAIL VIEW OF MOVABLE SPAN, UPPER TRUSS GUSSET PLATE, CONNECTION OF VERTICAL AND HORIZONTAL MEMBERS AT BRIDGE TENDER'S MOUSE (taken in December 1983) - Sharptown Bridge, Spanning Nanticoke River, State Route 313, Sharptown, Wicomico County, MD

GOVERNOR'S COUNCIL CHAMBER; SOUTH WALL, UPPER MIDDLE. Glass plate stereopair ...

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

GOVERNOR'S COUNCIL CHAMBER; SOUTH WALL, UPPER MIDDLE. Glass plate stereopair number PA-1430-139 LC-HABS-GS05-GC-S-4 157.4836. Right (not printed) - Independence Hall Complex, Independence Hall, 500 Chestnut Street, Philadelphia, Philadelphia County, PA

Convection in three dimensions with surface plates - Generation of toroidal flow

NASA Technical Reports Server (NTRS)

Gable, Carl W.; O'Connell, Richard J.; Travis, Bryan J.

1991-01-01

This work presents numerical calculations of mantle convection that incorporate some of the basic observational constraints imposed by plate tectonics. The model is three-dimensional and includes surface plates; it allows plate velocity to change dynamically according to the forces which result from convection. It is shown that plates are an effective means of introducing a toroidal component into the flow field. After initial transients the plate motion is nearly parallel to transform faults and in the direction that tends to minimize the toroidal flow field. The toroidal field decays with depth from its value at the surface; the poloidal field is relatively constant throughout the layer but falls off slightly at the top and bottom boundaries. Layered viscosity increasing with depth causes the toroidal field to decay more rapidly, effectively confining it to the upper, low-viscosity layer. The effect of viscosity layering on the poloidal field is relatively small, which is attributed to its generation by temperature variations distributed throughout the system. The generation of toroidal flow by surface plates would seem to account for the observed nearly equal energy of toroidal and poloidal fields of plate motions on the earth. A low-viscosity region in the upper mantle will cause the toroidal flow to decay significantly before reaching the lower mantle. The resulting concentration of toroidal flow in the upper mantle may result in more thorough mixing there and account for some of the geochemical and isotopic differences proposed to exist between the upper and lower mantles.

Low thermal resistance power module assembly

DOEpatents

Hassani, Vahab; Vlahinos, Andreas; Bharathan, Desikan

2007-03-13

A power module assembly with low thermal resistance and enhanced heat dissipation to a cooling medium. The assembly includes a heat sink or spreader plate with passageways or openings for coolant that extend through the plate from a lower surface to an upper surface. A circuit substrate is provided and positioned on the spreader plate to cover the coolant passageways. The circuit substrate includes a bonding layer configured to extend about the periphery of each of the coolant passageways and is made up of a substantially nonporous material. The bonding layer may be solder material which bonds to the upper surface of the plate to provide a continuous seal around the upper edge of each opening in the plate. The assembly includes power modules mounted on the circuit substrate on a surface opposite the bonding layer. The power modules are positioned over or proximal to the coolant passageways.

Axially shaped channel and integral flow trippers

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

Crowther, R.L.; Johansson, E.B.; Matzner, B.

1988-06-07

A fuel assembly is described comprising fuel rods positioned in spaced array by upper and lower tie-plates, an open ended flow channel surrounding the array for conducting coolant upward between a lower support plate having coolant communicated thereto to an upper support grid having a steam/water outlet communicated thereto. The flow channel surrounds the array for conducting coolant about the fuel rods. The open ended channel has a polygon shaped cross section with the channel constituting a closed conduit with flat side sections connected at corners to form the enclosed conduit; means separate from the channel for connecting the uppermore » and lower tie-plates together and maintaining the fuel rods in spaced array independent of the flow channel. The improvement in the flow channel comprises tapered side walls. The tapered side walls extend from an average thick cross section adjacent the lower support plate to an average thin cross section adjacent the upper core grid whereby the channel is reduced in thickness adjacent the upper core grid to correspond with the reduced pressure adjacent the upper core grid.« less

Characterization of Upper Eyelid Tarsus and Lid Wiper Dimensions.

PubMed

Navascues-Cornago, Maria; Maldonado-Codina, Carole; Gupta, Ruchi; Morgan, Philip B

2016-09-01

To measure various dimensions of the upper tarsal plate and the area of upper lid wiper staining. The repeatability of the method of measurement was investigated. Thirty-five healthy non-contact lens wearers were enrolled. The following parameters were measured from digital images of the upper eyelid captured with a slitlamp camera: length, height, and total area of the tarsal plate and area of lid wiper staining (lissamine green). Measurements were performed in a randomized and masked fashion on two separate occasions by the same investigator using ImageJ (National Institutes of Health). Coefficients of repeatability (COR) were calculated. The dimensions (mean±SD) of the tarsal plate were 20.6±1.9 mm length, 7.9±0.8 mm height, and 103.3±18.8 mm total area. The area of lid wiper staining was 2.7±2.0 mm. No association was found between tarsal dimensions and lid wiper staining (all P>0.05). Image analysis COR values were 0.6 mm tarsal length, 0.1 mm tarsal height, 1.2 mm tarsal area, and 0.4 mm lid wiper staining. There was no significant difference between repeated measurements for any parameter (all P>0.05). Limits of agreement were narrow for all parameters, indicating good agreement between repeated measurements. This work has demonstrated that there is a wide range in the dimensions of the upper tarsal plate in an urban UK population. No association was found between the upper tarsal dimensions and lid wiper staining. ImageJ was shown to be a repeatable method to measure the dimensions of the upper tarsal plate and upper lid wiper staining.

Plumes do not Exist: Plate Circulation is Confined to Upper Mantle

NASA Astrophysics Data System (ADS)

Hamilton, W. B.

2002-12-01

Plumes from deep mantle are widely conjectured to define an absolute reference frame, inaugurate rifting, drive plates, and profoundly modify oceans and continents. Mantle properties and composition are assumed to be whatever enables plumes. Nevertheless, purported critical evidence for plume speculation is false, and all data are better interpreted without plumes. Plume fantasies are made ever more complex and ad hoc to evade contradictory data, and have no predictive value because plumes do not exist. All plume conjecture derives from Hawaii and the guess that the Emperor-Hawaii inflection records a 60-degree change in Pacific plate direction at 45 Ma. Paleomagnetic latitudes and smooth Pacific spreading patterns disprove any such change. Rationales for other fixed plumes collapse when tested, and hypotheses of jumping, splitting, and gyrating plumes are specious. Thermal and physical properties of Hawaiian lithosphere falsify plume predictions. Purported tomographic support elsewhere represents artifacts and misleading presentations. Asthenosphere is everywhere near solidus temperature, so melt needs a tensional setting for egress but not local heat. Gradational and inconsistent contrasts between MORB and OIB are as required by depth-varying melt generation and behavior in contrasted settings and do not indicate systematically unlike sources. MORB melts rise, with minimal reaction, through hot asthenosphere, whereas OIB melts react with cool lithosphere, and lose mass, by crystallizing refractories and retaining and assimilating fusibles. The unfractionated lower mantle of plume conjecture is contrary to cosmologic and thermodynamic data, for mantle below 660 km is more refractory than that above. Subduction, due to density inversion by top-down cooling that forms oceanic lithosphere, drives plate tectonics and upper-mantle circulation. It organizes plate motions and lithosphere stress, which controls plate boundaries and volcanic chains. Hinge rollback is the key to kinematics. Arcs advance and collide, fast-spreading Pacific shrinks, etc. A fore-arc basin atop an overriding plate shows that hinge and non-shortening plate front there track together: velocities of rollback and advance are equal. Convergence velocity commonly also equals rollback velocity but often is greater. Slabs sinking broadside push upper mantle back under incoming plates and force rapid Pacific spreading, whereas overriding plates flow forward with retreating hinges. Backarc basins open behind island arcs migrating with hinges. Slabs settle on uncrossable 660-km discontinuity. (Contrary tomographic claims reflect sampling and smearing artifacts, notably due to along-slab raypaths.) Plates advance over sunken slabs and mantle displaced rearward by them, and ridges spread where advancing plates pull away. Ridges migrate over asthenosphere, producing geophysical and bathymetric asymmetry, and tap fresh asthenosphere into which slab material is recycled upward. Sluggish deep-mantle circulation is decoupled from rapid upper-mantle circulation, so plate motions can be referenced to semistable lower mantle. Global plate motions make kinematic sense if Antarctica, almost ringed by departing ridges and varying little in Cenozoic paleomagnetic position, is stationary: hinges roll back, ridges migrate, and directions and velocities of plate rotations accord with subduction, including sliding and crowding of oceanic lithosphere toward free edges, as the dominant drive. (The invalid hotspot and no-net-rotation frames minimize motions of hinges and ridges, and their plate motions lack kinematic sense.) Northern Eurasia also is almost stationary, Africa rotates very slowly counterclockwise toward Aegean and Zagros, Pacific plate races toward surface-exit subduction systems, etc.

Plate Motions, Regional Deformation, and Time-Variation of Plate Motions

NASA Technical Reports Server (NTRS)

Gordon, R. G.

1998-01-01

The significant results obtained with support of this grant include the following: (1) Using VLBI data in combination with other geodetical, geophysical, and geological data to bound the present rotation of the Colorado Plateau, and to evaluate to its implications for the kinematics and seismogenic potential of the western half of the conterminous U.S. (2) Determining realistic estimates of uncertainties for VLBI data and then applying the data and uncertainties to obtain an upper bound on the integral of deformation within the "stable interior" of the North American and other plates and thus to place an upper bound on the seismogenic potential within these regions. (3) Combining VLBI data with other geodetic, geophysical, and geologic data to estimate the motion of coastal California in a frame of reference attached to the Sierra Nevada-Great Valley microplate. This analysis has provided new insights into the kinematic boundary conditions that may control or at least strongly influence the locations of asperities that rupture in great earthquakes along the San Andreas transform system. (4) Determining a global tectonic model from VLBI geodetic data that combines the estimation of plate angular velocities with individual site linear velocities where tectonically appropriate. and (5) Investigation of the some of the outstanding problems defined by the work leading to global plate motion model NUVEL-1. These problems, such as the motion between the Pacific and North American plates and between west Africa and east Africa, are focused on regions where the seismogenic potential may be greater than implied by published plate tectonic models.

SECOND FLOOR LOBBY; EAST WALL, UPPER LEFT (R). Glass plate ...

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

SECOND FLOOR LOBBY; EAST WALL, UPPER LEFT (R). Glass plate stereopair number PA-1430-139 LC-HABS-GS05-2L-E-2 (R) 157.4825. Right (not printed) - Independence Hall Complex, Independence Hall, 500 Chestnut Street, Philadelphia, Philadelphia County, PA

SECOND FLOOR LOBBY; EAST WALL, UPPER LEFT (R). Glass plate ...

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

SECOND FLOOR LOBBY; EAST WALL, UPPER LEFT (R). Glass plate stereopair number PA-1430-139 LC-HABS-GS05-2L-E-2 (R) 157.4825. Left (printed) - Independence Hall Complex, Independence Hall, 500 Chestnut Street, Philadelphia, Philadelphia County, PA

SECOND FLOOR LOBBY; EAST WALL, UPPER RIGHT (R). Glass plate ...

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

SECOND FLOOR LOBBY; EAST WALL, UPPER RIGHT (R). Glass plate stereopair number PA-1430-139 LC-HABS-GS05-2L-E-4 (R) 157.4827. Right (not printed) - Independence Hall Complex, Independence Hall, 500 Chestnut Street, Philadelphia, Philadelphia County, PA

SECOND FLOOR LOBBY; EAST WALL, UPPER RIGHT (R). Glass plate ...

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

SECOND FLOOR LOBBY; EAST WALL, UPPER RIGHT (R). Glass plate stereopair number PA-1430-139 LC-HABS-GS05-2L-E-4 (R) 157.4827. Left (printed) - Independence Hall Complex, Independence Hall, 500 Chestnut Street, Philadelphia, Philadelphia County, PA

5. DETAIL VIEW OF UPPER CHORD MEMBER, SHOWING MAKER'S PLATE ...

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

5. DETAIL VIEW OF UPPER CHORD MEMBER, SHOWING MAKER'S PLATE STATING 'KING IRON BRIDGE & MFG. CO., K & F & Z KING PATENT, CLEVELAND, O.' - Smith Road Bowstring Arch Bridge, Spanning Sycamore Creek at Smith Road (TR 62), Lykens, Crawford County, OH

REACTOR

DOEpatents

Roman, W.G.

1961-06-27

A pressurized water reactor in which automatic control is achieved by varying the average density of the liquid moderator-cooiant is patented. Density is controlled by the temperature and power level of the reactor ftself. This control can be effected by the use of either plate, pellet, or tubular fuel elements. The fuel elements are disposed between upper and lower coolant plenum chambers and are designed to permit unrestricted coolant flow. The control chamber has an inlet opening communicating with the lower coolant plenum chamber and a restricted vapor vent communicating with the upper coolant plenum chamber. Thus, a variation in temperature of the fuel elements will cause a variation in the average moderator density in the chamber which directly affects the power level of the reactor.

Constraints on mantle viscosity from convection models with plate motion history

NASA Astrophysics Data System (ADS)

Mao, W.; Zhong, S.

2017-12-01

The Earth's long-wavelength geoid and dynamic topography are mainly controlled by the mantle buoyancy and viscosity structure. Previous dynamical models for the geoid provide constraints on the 1-D mantle viscosity, using mantle buoyancy derived from seismic topography models. However, it is a challenge in these studies on how to convert seismic velocity to density anomalies and mantle buoyancy. Furthermore, these studies provide constraints only on relative viscosity variations but not on absolute magnitude of viscosity. In this study, we formulate time-dependent 3-D spherical mantle convection models with imposed plate motion history and seek constraints on mantle viscosity structure for both its radial relative variations and its absolute magnitude (i.e., Rayleigh number), using the geoid from the convection models. We found that the geoid at intermediate wavelengths of degrees 4-9 is mainly controlled by the subducted slabs in the upper mantle and the upper part of lower mantle that result from subduction from the last 50 Myr or the Cenozoic. To fit the degrees 4-9 geoid, we need viscosity contrast β defined as the ratio of the lower mantle viscosity and the asthenospheric viscosity to be larger than 2000 and Ra to be 1e8 (defined by the Earth's radius). The best fit model leads to 57% variance reduction and 76% correlation between the model and the observations. However, the long-wavelength geoid at degrees 2-3 is controlled by the lower mantle structure which requires much longer time scale to develop, as seen from our modeling. The preferred viscosity structure and Rayleigh number as constrained by the Cenozoic plate motion and the degrees 4-9 geoid no longer provide adequate fit to the geoid in models with the plate motion history for the last 450 Myr. The degrees 4-9 geoid amplitude is smaller for the models with longer plate motion history and a smaller Ra is required to fit the observation. In order to satisfy the relative amplitude between degrees 2-3 and degrees 4-9 geoid, either a gradually increase of viscosity in the upper part of lower mantle or larger thermal expansivity in the lower mantle is needed. We also consider thermo-chemical models to examine the effects of the African and Pacific thermochemical piles (i.e., LLSVPSs) on the geoid and the inferred mantle viscosity and Ra.

True Shear Parallel Plate Viscometer

NASA Technical Reports Server (NTRS)

Ethridge, Edwin; Kaukler, William

2010-01-01

This viscometer (which can also be used as a rheometer) is designed for use with liquids over a large temperature range. The device consists of horizontally disposed, similarly sized, parallel plates with a precisely known gap. The lower plate is driven laterally with a motor to apply shear to the liquid in the gap. The upper plate is freely suspended from a double-arm pendulum with a sufficiently long radius to reduce height variations during the swing to negligible levels. A sensitive load cell measures the shear force applied by the liquid to the upper plate. Viscosity is measured by taking the ratio of shear stress to shear rate.

Automatic locking orthotic knee device

NASA Technical Reports Server (NTRS)

Weddendorf, Bruce C. (Inventor)

1993-01-01

An articulated tang in clevis joint for incorporation in newly manufactured conventional strap-on orthotic knee devices or for replacing such joints in conventional strap-on orthotic knee devices is discussed. The instant tang in clevis joint allows the user the freedom to extend and bend the knee normally when no load (weight) is applied to the knee and to automatically lock the knee when the user transfers weight to the knee, thus preventing a damaged knee from bending uncontrollably when weight is applied to the knee. The tang in clevis joint of the present invention includes first and second clevis plates, a tang assembly and a spacer plate secured between the clevis plates. Each clevis plate includes a bevelled serrated upper section. A bevelled shoe is secured to the tank in close proximity to the bevelled serrated upper section of the clevis plates. A coiled spring mounted within an oblong bore of the tang normally urges the shoes secured to the tang out of engagement with the serrated upper section of each clevic plate to allow rotation of the tang relative to the clevis plate. When weight is applied to the joint, the load compresses the coiled spring, the serrations on each clevis plate dig into the bevelled shoes secured to the tang to prevent relative movement between the tang and clevis plates. A shoulder is provided on the tang and the spacer plate to prevent overextension of the joint.

Subduction and Slab Advance at Orogen Syntaxes: Predicting Exhumation Rates and Thermochronometric Ages with Numerical Modeling

NASA Astrophysics Data System (ADS)

Nettesheim, Matthias; Ehlers, Todd A.; Whipp, David M.

2017-04-01

The change in plate boundary orientation and subducting plate geometry along orogen syntaxes may have major control on the subduction and exhumation dynamics at these locations. Previous work documents that the curvature of subducting plates in 3D at orogen syntaxes forces a buckling and flexural stiffening of the downgoing plate. The geometry of this stiffened plate region, also called indenter, can be observed in various subduction zones around the world (e.g. St. Elias Range, Alaska; Cascadia, USA; Andean syntaxis, South America). The development of a subducting, flexurally stiffened indenter beneath orogen syntaxes influences deformation in the overriding plate and can lead to accelerated and focused rock uplift above its apex. Moreover, the style of deformation in the overriding plate is influenced by the amount of trench or slab advance, which is the amount of overall shortening not accommodated by underthrusting. While many subduction zones exhibit little to no slab advance, the Nazca-South America subduction and especially the early stages of the India-Eurasia collision provide end-member examples. Here, we use a transient, lithospheric-scale, thermomechanical 3D model of an orogen syntaxis to investigate the effects of subducting a flexurally stiffened plate geometry and slab advance on upper plate deformation. A visco-plastic upper-plate rheology is used, along with a buckled, rigid subducting plate. The free surface of the thermomechanical model is coupled to a landscape evolution model that accounts for erosion by fluvial and hillslope processes. The cooling histories of exhumed rocks are used to predict the evolution of low-temperature thermochronometer ages on the surface. With a constant overall shortening for all simulations, the magnitude of slab advance is varied stepwise from no advance, with all shortening accommodated by underthrusting, to full slab advance, i.e. no motion on the megathrust. We show that in models where most shortening is accommodated by subduction, the uplift is highly localized and focused in a shape resembling the geometry of the subducting plate. Strong erosion of the growing orogen can shift the center of uplift towards the orogen flanks facing the trench. In contrast, large amounts of slab advance lead to a less focused uplift with lower maximum velocities and the uplift peak located farther away from the trench. The observed thermochronometric ages follow the uplift pattern, but indicate a significantly deeper and more rapid exhumation for models with a higher underthrusting component. These variations in amount and style of upper plate deformation may help to deepen the understanding of the different types of orogeny observed at plate corners around the world.

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.

Cenozoic forearc tectonics in northeastern Japan: Relationships between outer forearc subsidence and plate boundary kinematics

NASA Astrophysics Data System (ADS)

Regalla, Christine

Here we investigate the relationships between outer forearc subsidence, the timing and kinematics of upper plate deformation and plate convergence rate in Northeast Japan to evaluate the role of plate boundary dynamics in driving forearc subsidence. The Northeastern Japan margin is one of the first non-accretionary subduction zones where regional forearc subsidence was argued to reflect tectonic erosion of large volumes of upper crustal rocks. However, we propose that a significant component of forearc subsidence could be the result of dynamic changes in plate boundary geometry. We provide new constraints on the timing and kinematics of deformation along inner forearc faults, new analyses of the evolution of outer forearc tectonic subsidence, and updated calculations of plate convergence rate. These data collectively reveal a temporal correlation between the onset of regional forearc subsidence, the initiation of upper plate extension, and an acceleration in local plate convergence rate. A similar analysis of the kinematic evolution of the Tonga, Izu-Bonin, and Mariana subduction zones indicates that the temporal correlations observed in Japan are also characteristic of these three non-accretionary margins. Comparison of these data with published geodynamic models suggests that forearc subsidence is the result of temporal variability in slab geometry due to changes in slab buoyancy and plate convergence rate. These observations suggest that a significant component of forearc subsidence at these four margins is not the product of tectonic erosion, but instead reflects changes in plate boundary dynamics driven by variable plate kinematics.

History and Evolution of Precambrian plate tectonics

NASA Astrophysics Data System (ADS)

Fischer, Ria; Gerya, Taras

2014-05-01

Plate tectonics is a global self-organising process driven by negative buoyancy at thermal boundary layers. Phanerozoic plate tectonics with its typical subduction and orogeny is relatively well understood and can be traced back in the geological records of the continents. Interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts however (e.g., Brown, 2006), suggest a different tectonic regime in the Precambrian. Due to higher radioactive heat production the Precambrian lithosphere shows lower internal strength and is strongly weakened by percolating melts. The fundamental difference between Precambrian and Phanerozoic tectonics is therefore the upper-mantle temperature, which determines the strength of the upper mantle (Brun, 2002) and the further tectonic history. 3D petrological-thermomechanical numerical modelling experiments of oceanic subduction at an active plate at different upper-mantle temperatures show these different subduction regimes. For upper-mantle temperatures < 175 K above the present day value a subduction style appears which is close to present day subduction but with more frequent slab break-off. At upper-mantle temperatures 175 - 250 K above present day values steep subduction continues but the plates are weakened enough to allow buckling and also lithospheric delamination and drip-offs. For upper-mantle temperatures > 250 K above the present day value no subduction occurs any more. The whole lithosphere is delaminating and due to strong volcanism and formation of a thicker crust subduction is inhibited. This stage of 200-250 K higher upper mantle temperature which corresponds roughly to the early Archean (Abbott, 1994) is marked by strong volcanism due to sublithospheric decompression melting which leads to an equal thickness for both oceanic and continental plates. As a consequence subduction is inhibited, but a compressional setup instead will lead to orogeny between a continental or felsic terrain and an oceanic or mafic terrain as well as internal crustal convection. Small-scale convection with plume shaped cold downwellings also in the upper mantle is of increased importance compared to the large-scale subduction cycle observed for present temperature conditions. It is also observed that lithospheric downwellings may initiate subduction by pulling at and breaking the plate. References: Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937-940. Brown, M., 2006. Duality of thermal regimes is the distinctive characteristic of plate tectonics since the neoarchean. Geology 34, 961-964. Brun, J.P., 2002. Deformation of the continental lithosphere: Insights from brittle-ductile models. Geological Society, London, Special Publications 200, 355-370.

Jacking mechanism for upper internals structure of a liquid metal nuclear reactor

DOEpatents

Gillett, James E.; Wineman, Arthur L.

1984-01-01

A jacking mechanism for raising the upper internals structure of a liquid metal nuclear reactor which jacking mechanism uses a system of gears and drive shafts to transmit force from a single motor to four mechanically synchronized ball jacks to raise and lower support columns which support the upper internals structure. The support columns have a pin structure which rides up and down in a slot in a housing fixed to the reactor head. The pin has two locking plates which can be rotated around the pin to bring bolt holes through the locking plates into alignment with a set of bolt holes in the housing, there being a set of such housing bolt holes corresponding to both a raised and a lowered position of the support column. When the locking plate is so aligned, a surface of the locking plate mates with a surface in the housing such that the support column is then supported by the locking plate and not by the ball jacks. Since the locking plates are to be installed and bolted to the housing during periods of reactor operation, the ball jacks need not be sized to react the large forces which occur or potentially could occur on the upper internals structure of the reactor during operation. The locking plates react these loads. The ball jacks, used only during refueling, can be smaller, which enable conventionally available equipment to fulfill the precision requirements for the task within available space.

Summary of IODP Expedition 344, CRISP-A2, offshore the Osa Peninsula, Costa Rica

NASA Astrophysics Data System (ADS)

Harris, R. N.; Sakaguchi, A.; Petronotis, K. E.

2013-12-01

The Costa Rica Seismogenesis Project (CRISP) is designed to elucidate the processes that control nucleation and seismic rupture of large earthquakes at erosional subduction zones. The CRISP study area is located offshore the Osa Peninsula where the incoming Cocos Ridge has lifted the seismogenic zone to within reach of scientific drilling. The incoming plate is characterized by low sediment supply, a fast convergence rate, abundant plate interface seismicity, and a change in subducting plate relief along strike. In addition to elucidating processes at erosional convergent margins, this project is complementary to other IODP deep fault drilling projects (e.g., NanTroSEIZE and J-FAST). Expedition 344 (23 October - 11 December, 2012) is the second expedition of CRISP Program A (Integrated Ocean Drilling Program Proposal 537A-Full5) that focused on the shallow lithologic, hydrologic, stress, and thermal conditions that lead to unstable slip in the seismogenic zone. With the exception of not reaching the décollement and the underthrust sediment at the toe site (U1412), Expedition 344 exceeded expectations. Material was recovered from the incoming Cocos plate (Sites U1381 and U1414), the toe of the margin (Site U1412), the mid-slope region (Site U1380), and the upper-slope region (Site U1413). Input sites U1381 and U1414 are characterized by anomalously high heat flow and the flow of fluids. These sites contained abundant ash that will be used to assess the impact of Cocos Ridge subduction on the evolution of the Central American volcanic arc. Although toe Site U1412 did not cross the décollement we did penetrate terrigenous sediments interrupted by a Miocene ooze that may reflect accretion of a frontal prism sliver. Mid-slope Site U1380 yielded a major result in that the upper plate material is not a mélange of oceanic material or the offshore extension of the Caribbean large igneous complex, but forearc basin material consisting of lithic sedimentary units. Upper-slope Site U1413 consists of a terrestrially sourced upper slope sequence consistent with high sediment accumulation rates. Preliminary biostratigraphic and paleomagnetic ages from Sites U1380 and U1413, the midslope and upper slope, respectively, yield sediment accumulation rates between ~290 and 590 m/m.y., an order of magnitude greater than estimated offshore the Nicoya Peninsula.

Imaging the deep structures of the convergent plates along the Ecuadorian subduction zone through receiver function analysis

NASA Astrophysics Data System (ADS)

Galve, A.; Charvis, P.; Regnier, M. M.; Font, Y.; Nocquet, J. M.; Segovia, M.

2017-12-01

The Ecuadorian subduction zone was affected by several large M>7.5 earthquakes. While we have low resolution on the 1942, 1958 earthquakes rupture zones extension, the 2016 Pedernales earthquake, that occurs at the same location than the 1942 earthquake, give strong constraints on the deep limit of the seismogenic zone. This downdip limit is caused by the onset of plasticity at a critical temperature (> 350-450 °C for crustal materials, or serpentinized mantle wedge, and eventually > 700 °C for dry mantle). However we still don't know exactly where is the upper plate Moho and therefore what controls the downdip limit of Ecuadorian large earthquakes seismogenic zone. For several years Géoazur and IG-EPN have maintained permanent and temporary networks (ADN and JUAN projects) along the margin to register the subduction zone seismological activity. Although Ecuador is not a good place to perform receiver function due to its position with respect to the worldwide teleseismic sources, the very long time deployment compensate this issue. We performed a frequency dependent receiver function analysis to derive (1) the thickness of the downgoing plate, (2) the interplate depth and (3) the upper plate Moho. These constraints give the frame to interpretation on the seismogenic zone of the 2016 Pedernales earthquake.

Whole-mantle convection with tectonic plates preserves long-term global patterns of upper mantle geochemistry.

PubMed

Barry, T L; Davies, J H; Wolstencroft, M; Millar, I L; Zhao, Z; Jian, P; Safonova, I; Price, M

2017-05-12

The evolution of the planetary interior during plate tectonics is controlled by slow convection within the mantle. Global-scale geochemical differences across the upper mantle are known, but how they are preserved during convection has not been adequately explained. We demonstrate that the geographic patterns of chemical variations around the Earth's mantle endure as a direct result of whole-mantle convection within largely isolated cells defined by subducting plates. New 3D spherical numerical models embedded with the latest geological paleo-tectonic reconstructions and ground-truthed with new Hf-Nd isotope data, suggest that uppermost mantle at one location (e.g. under Indian Ocean) circulates down to the core-mantle boundary (CMB), but returns within ≥100 Myrs via large-scale convection to its approximate starting location. Modelled tracers pool at the CMB but do not disperse ubiquitously around it. Similarly, mantle beneath the Pacific does not spread to surrounding regions of the planet. The models fit global patterns of isotope data and may explain features such as the DUPAL anomaly and long-standing differences between Indian and Pacific Ocean crust. Indeed, the geochemical data suggests this mode of convection could have influenced the evolution of mantle composition since 550 Ma and potentially since the onset of plate tectonics.

Bus bar electrical feedthrough for electrorefiner system

DOEpatents

Williamson, Mark; Wiedmeyer, Stanley G; Willit, James L; Barnes, Laurel A; Blaskovitz, Robert J

2013-12-03

A bus bar electrical feedthrough for an electrorefiner system may include a retaining plate, electrical isolator, and/or contact block. The retaining plate may include a central opening. The electrical isolator may include a top portion, a base portion, and a slot extending through the top and base portions. The top portion of the electrical isolator may be configured to extend through the central opening of the retaining plate. The contact block may include an upper section, a lower section, and a ridge separating the upper and lower sections. The upper section of the contact block may be configured to extend through the slot of the electrical isolator and the central opening of the retaining plate. Accordingly, relatively high electrical currents may be transferred into a glovebox or hot-cell facility at a relatively low cost and higher amperage capacity without sacrificing atmosphere integrity.

Low thermal resistance power module assembly

DOEpatents

Hassani, Vahab; Vlahinos, Andreas; Bharathan, Desikan

2010-12-28

A power module assembly (400) with low thermal resistance and enhanced heat dissipation to a cooling medium. The assembly includes a heat sink or spreader plate (410) with passageways or openings (414) for coolant that extend through the plate from a lower surface (411) to an upper surface (412). A circuit substrate (420) is provided and positioned on the spreader plate (410) to cover the coolant passageways. The circuit substrate (420) includes a bonding layer (422) configured to extend about the periphery of each of the coolant passageways and is made up of a substantially nonporous material. The bonding layer (422) may be solder material which bonds to the upper surface (412) of the plate to provide a continuous seal around the upper edge of each opening (414) in the plate. The assembly includes power modules (430) mounted on the circuit substrate (420) on a surface opposite the bonding layer (422). The power modules (430) are positioned over or proximal to the coolant passageways.

History and evolution of Subduction in the Precambrium

NASA Astrophysics Data System (ADS)

Fischer, R.; Gerya, T.

2013-12-01

Plate tectonics is a global self-organising process driven by negative buoyancy at thermal boundary layers. Phanerozoic plate tectonics with its typical subduction and orogeny is relatively well understood and can be traced back in the geological records of the continents. Interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts however (e.g. Brown, 2006), suggest a different tectonic regime in the Precambrian. Due to higher radioactive heat production the Precambrian lithosphere shows lower internal strength and is strongly weakened by percolating melts. The fundamental difference between Precambrian and Phanerozoic subduction is therefore the upper-mantle temperature, which determines the strength of the upper mantle (Brun, 2002) and the further subduction history. 3D petrological-thermomechanical numerical modelling experiments of oceanic subduction at an active plate at different upper-mantle temperatures show these different subduction regimes. For upper-mantle temperatures < 175 K above the present day value a subduction style appears which is close to present day subduction but with more frequent slab break-off. At upper-mantle temperatures 175 - 250 K above present day values steep subduction changes to shallow underplating and buckling. For upper-mantle temperatures > 250 K above the present day value no subduction occurs any more. The whole lithosphere starts to delaminate and drip-off. But the subduction style is not only a function of upper-mantle temperature but also strongly depends on the thickness of the subducting plate. If thinner present day oceanic plates are used in the Precambrian models, no shallow underplating is observed but steep subduction can be found up to an upper-mantle temperature of 200 K above present day values. Increasing oceanic plate thickness introduces a transition from steep to flat subduction at lower temperatures of around 150 K. Thicker oceanic plates in the Precambrium also agree with results from earlier studies, e.g. Abbott (1994). References: Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937-940. Brown, M., 2006. Duality of thermal regimes is the distinctive characteristic of plate tectonics since the neoarchean. Geology 34, 961-964. Brun, J.P., 2002. Deformation of the continental lithosphere: Insights from brittle-ductile models. Geological Society, London, Special Publications 200, 355-370. Subduction depends strongly on upper-mantle temperature. (a) Modern subduction with present day temperature gradients in upper-mantle and lithosphere. (b) Increase of temperature by 100 K at the lithosphere-asthenosphere boundary (LAB) leads to melting and drip-off of the of the slab-tip. (c) A temperature increase of 200 K leads to buckling of the subducting slab and Rayleigh-Taylor instabilities not only at the slab-tip but the whole LAB. At this stage subduction is no longer possible as the slab melts or breaks before it can be subducted into the mantle.

Improved upper bounds on energy dissipation rates in plane Couette flow with boundary injection and suction

NASA Astrophysics Data System (ADS)

Lee, Harry; Wen, Baole; Doering, Charles

2017-11-01

The rate of viscous energy dissipation ɛ in incompressible Newtonian planar Couette flow (a horizontal shear layer) imposed with uniform boundary injection and suction is studied numerically. Specifically, fluid is steadily injected through the top plate with a constant rate at a constant angle of injection, and the same amount of fluid is sucked out vertically through the bottom plate at the same rate. This set-up leads to two control parameters, namely the angle of injection, θ, and the Reynolds number of the horizontal shear flow, Re . We numerically implement the `background field' variational problem formulated by Constantin and Doering with a one-dimensional unidirectional background field ϕ(z) , where z aligns with the distance between the plates. Computation is carried out at various levels of Re with θ = 0 , 0 .1° ,1° and 2°, respectively. The computed upper bounds on ɛ scale like Re0 as Re > 20 , 000 for each fixed θ, this agrees with Kolmogorov's hypothesis on isotropic turbulence. The outcome provides new upper bounds to ɛ among any solution to the underlying Navier-Stokes equations, and they are sharper than the analytical bounds presented in Doering et al. (2000). This research was partially supported by the NSF Award DMS-1515161, and the University of Michigan's Rackham Graduate Student Research Grant.

Thermo-compositional and strength variability of the Australian plate: clues of intraplate deformation

NASA Astrophysics Data System (ADS)

Tesauro, M.; Kaban, M. K.; Aitken, A.

2017-12-01

The Australian plate has a long and complex tectonic history and its crust and upper mantle have been deeply investigated in the last two decades using a variety of geophysical methods. To discern temperature and compositional variations of the Australian upper mantle, we apply an iterative technique, which jointly interprets seismic tomography and gravity data. This technique consists in removing the effect of the crust from the observed gravity field and topography. In the second step, the residual mantle gravity field and residual topography are inverted to obtain a 3-D density model of the upper mantle. The inversion technique accounts for the notion that these fields are controlled by the same factors but in a different way (e.g., depending on depth and horizontal dimension of the heterogeneity.) This enables us to locate the position of principal density anomalies in the upper mantle. Afterwards, the thermal contribution to the density structure is estimated by inverting the seismic tomography model AusREM (http://rses.anu.edu.au/seismology/AuSREM/index.php). In this way, we improve the initial thermal and compositional models iteratively. The final thermal model compared to the initial one shows temperatures higher by 100-150 °C in the Archean and Proterozoic upper mantle. Furthermore, we observe larger iron depletion in the Western Australian craton than in the Proterozoic terranes. At the depths larger than 150 km, the depletion becomes negligible beneath the Proterozoic regions, while persists in the Western Australian craton also below the depth of the lithosphere. We interpret this feature as a result of the leakage of the depleted mantle, possibly caused by the erosion of the thermal boundary layer, which was thicker before than in present-days. Using the final thermo-compositional model, we estimated the strength and effective elastic distribution within the Australian lithosphere. For this purpose, we assumed a stiff rheology, on account of the mafic composition of the Australian crust. The results show large variability of the rigidity of the plate within the cratonic areas, reflecting the long tectonic history of the Australian plate. On the other hand, the younger eastern terranes are uniformly weak, due to the higher temperatures.

Upper-plate splay fault earthquakes along the Arakan subduction belt recorded by uplifted coral microatolls on northern Ramree Island, western Myanmar (Burma)

NASA Astrophysics Data System (ADS)

Shyu, J. Bruce H.; Wang, Chung-Che; Wang, Yu; Shen, Chuan-Chou; Chiang, Hong-Wei; Liu, Sze-Chieh; Min, Soe; Aung, Lin Thu; Than, Oo; Tun, Soe Thura

2018-02-01

Upper-plate structures that splay out from the megathrusts are common features along major convergent plate boundaries. However, their earthquake and tsunami hazard potentials have not yet received significant attention. In this study, we identified at least one earthquake event that may have been produced by an upper-plate splay fault offshore western Myanmar, based on U-Th ages of uplifted coral microatolls. This event is likely an earthquake that was documented historically in C.E. 1848, with an estimated magnitude between 6.8 and 7.2 based on regional structural characteristics. Such magnitude is consistent with the observed co-seismic uplift amount of ∼0.5 m. Although these events are smaller in magnitude than events produced by megathrusts, they may produce higher earthquake and tsunami hazards for local coastal communities due to their proximity. Our results also indicate that earthquake events with co-seismic uplift along the coast may not necessarily produce a flight of marine terraces. Therefore, using only records of uplifted marine terraces as megathrust earthquake proxies may overlook the importance of upper-plate splay fault ruptures, and underestimate the overall earthquake frequency for future seismic and tsunami hazards along major subduction zones of the world.

Numerical Simulation of Flow Field Within Parallel Plate Plastometer

NASA Technical Reports Server (NTRS)

Antar, Basil N.

2002-01-01

Parallel Plate Plastometer (PPP) is a device commonly used for measuring the viscosity of high polymers at low rates of shear in the range 10(exp 4) to 10(exp 9) poises. This device is being validated for use in measuring the viscosity of liquid glasses at high temperatures having similar ranges for the viscosity values. PPP instrument consists of two similar parallel plates, both in the range of 1 inch in diameter with the upper plate being movable while the lower one is kept stationary. Load is applied to the upper plate by means of a beam connected to shaft attached to the upper plate. The viscosity of the fluid is deduced from measuring the variation of the plate separation, h, as a function of time when a specified fixed load is applied on the beam. Operating plate speeds measured with the PPP is usually in the range of 10.3 cm/s or lower. The flow field within the PPP can be simulated using the equations of motion of fluid flow for this configuration. With flow speeds in the range quoted above the flow field between the two plates is certainly incompressible and laminar. Such flows can be easily simulated using numerical modeling with computational fluid dynamics (CFD) codes. We present below the mathematical model used to simulate this flow field and also the solutions obtained for the flow using a commercially available finite element CFD code.

The influence of melting on the kinematic development of the Himalayan crystalline core

NASA Astrophysics Data System (ADS)

Webb, Alexander

2016-04-01

Current hypotheses for the development and emplacement of the Himalayan crystalline core are 1) models with intense upper plate out-of-sequence activity (i.e., tunneling of channel flow, and some modes of critical taper wedge behavior) and 2) models in which the upper plate mainly records basal accretion of horses (i.e., duplexing). The two concepts can be considered end-members. A signal difference between these two models is the role of melting. The intense upper plate deformation envisioned in the first set of models has been hypothesized to be largely a product of partial melting, particularly in channel flow models. Specifically, the persistent presence of melt in the middle crust of the upper plate may dramatically lower the viscosity of these rocks, allowing distributed deformation. The second set of models - duplexing - predicts in-sequence thrusting with only minor out-of-sequence deformation. Stacking of a duplex acts like a deli cheese-slicing machine: slice after slice is cut from the intact block to a stack of slices, but neither the block (~down-going plate) nor the stack (~upper plate) features much internal deformation. In this model, partial melting produces no significant kinematic impact. The dominant preserved structural elements across the Himalayan crystalline core rocks are flattening and L-S fabrics. Structurally high portions of the crystalline core locally display complex outcrop-scale deformation associated with migmatitic rocks, and contain km-scale leucogranite bodies; both features developed in the early to middle Miocene. The flattening and L-S fabrics have been interpreted to record either (A) southwards channel tunneling across the upper plate, or (B) fabric development during metamorphism of the down-going plate, prior to accretion to the upper plate. The deformation of migmatitic rock and emplacement of leucogranite have been interpreted in support of widespread distributed deformation. Alternatively, these features may have accumulated from increments of melting and crystallization which did not produce sufficient melt during any one period to significantly alter viscosity at >100 m scales. Recent work integrating monazite and zircon geochronology with structural records shows that the Himalayan middle crust has been assembled along a series of mainly southwards-younging thrust faults throughout the early to middle Miocene. The thrust faults separate 1-5 km thick panels that experienced similar metamorphic cycles during different time periods. At this scale, out-of-sequence deformation is rare, with its apparent significance enhanced because of the high throw-to-heave ratio of out-of-sequence thrusting. These findings support the duplexing model and indicate that melting did not have a significant impact on the kinematic development of the Himalayan crystalline core.

Reactor refueling containment system

DOEpatents

Gillett, J.E.; Meuschke, R.E.

1995-05-02

A method of refueling a nuclear reactor is disclosed whereby the drive mechanism is disengaged and removed by activating a jacking mechanism that raises the closure head. The area between the barrier plate and closure head is exhausted through the closure head penetrations. The closure head, upper drive mechanism, and bellows seal are lifted away and transported to a safe area. The barrier plate acts as the primary boundary and each drive and control rod penetration has an elastomer seal preventing excessive tritium gases from escaping. The individual instrumentation plugs are disengaged allowing the corresponding fuel assembly to be sealed and replaced. 2 figs.

Reactor refueling containment system

DOEpatents

Gillett, James E.; Meuschke, Robert E.

1995-01-01

A method of refueling a nuclear reactor whereby the drive mechanism is disengaged and removed by activating a jacking mechanism that raises the closure head. The area between the barrier plate and closure head is exhausted through the closure head penetrations. The closure head, upper drive mechanism, and bellows seal are lifted away and transported to a safe area. The barrier plate acts as the primary boundary and each drive and control rod penetration has an elastomer seal preventing excessive tritium gases from escaping. The individual instrumentation plugs are disengaged allowing the corresponding fuel assembly to be sealed and replaced.

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.

Tectonic evolution of the North Patagonian Andes (41°-44° S) through recognition of syntectonic strata

NASA Astrophysics Data System (ADS)

Echaurren, A.; Folguera, A.; Gianni, G.; Orts, D.; Tassara, A.; Encinas, A.; Giménez, M.; Valencia, V.

2016-05-01

The North Patagonian fold-thrust belt (41°-44° S) is characterized by a low topography, reduced crustal thickness and a broad lateral development determined by a broken foreland system in the retroarc zone. This particular structural system has not been fully addressed in terms of the age and mechanisms that built this orogenic segment. Here, new field and seismic evidence of syntectonic strata constrain the timing of the main deformational stages, evaluating the prevailing crustal regime for the different mountain domains through time. Growth strata and progressive unconformities, controlled by extensional or compressive structures, were recognized in volcanic and sedimentary rocks from the cordilleran to the extra-Andean domain. These data were used to construct a balanced cross section, whose deep structure was investigated through a thermomechanical model that characterizes the upper plate rheology. Our results indicate two main compressive stages, interrupted by an extensional relaxation period. The first contractional stage in the mid-Cretaceous inverted Jurassic-Lower Cretaceous half graben systems, reactivating the western Cañadón Asfalto rift border ~ 500 km away from the trench, at a time of arc foreland expansion. For this stage, available thermochronological data reveal forearc cooling episodes, and global tectonic reconstructions indicate mid-ocean ridge collisions against the western edge of an upper plate with rapid trenchward displacement. Widespread synextensional volcanism is recognized throughout the Paleogene during plate reorganization; retroarc Paleocene--Eocene flare up activity is interpreted as product of a slab rollback, and fore-to-retroarc Oligocene slab/asthenospheric derived products as an expression of enhanced extension. The second stage of mountain growth occurred in Miocene time associated with Nazca Plate subduction, reaching nearly the same amplitude than the first compressive stage. Extensional weakening of the upper plate predating the described contractional stages appears as a necessary condition for abnormal lateral propagation of deformation.

P-wave Velocity Structure Across the Mariana Trench and Implications for Hydration

NASA Astrophysics Data System (ADS)

Eimer, M. O.; Wiens, D.; Lizarralde, D.; Cai, C.

2017-12-01

Estimates of the water flux at subduction zones remain uncertain, particularly the amount of water brought into the trench by the subducting plate. Normal faulting related to the bending of the incoming plate has been proposed to provide pathways for water to hydrate the crust and upper mantle. A passive and active source seismic experiment spanning both the incoming plate and forearc was conducted in 2012 in central Mariana to examine the role of hydration at subduction zones. The active-source component of the survey used the R/V M.G. Langsethairgun array and 68 short period sensors, including suspended hydrophones, deployed on 4 transects. This study at the Mariana trench offers a comparison to related studies of incoming plate hydration in Middle America, where differing thermal structures related to plate age predict different stability fields for hydrous minerals. The forearc structure is also of interest, since Mariana is characterized by large serpentine seamounts and may have a serpentinized mantle wedge. The velocity structure will also be important for the relocation of earthquakes in the incoming plate, since the seismicity can offer a constraint for the depth extent of these bending faults. We examine the P-wave velocity structure along a 400-km long wide-angle refraction transect perpendicular to the trench and spanning both the forearc and incoming plate. Preliminary results indicate a velocity reduction in the crust and uppermost mantle at the bending region of the incoming plate, relative to the plate's structure away from the trench. This reduction suggests that outer-rise faults extend into the upper mantle and may have promoted serpentinization of that material. Mantle Pn refraction phases are not observed in the forearc, consistent with the ambient noise tomography results that show upper-mantle velocities similar to that of the lower crust. The lack of contrast between the upper mantle and crustal velocities from the ambient noise has been interpreted to indicate extensive serpentinization of the shallow mantle wedge.

Seismic evidence for rotating mantle flow around subducting slab edge associated with oceanic microplate capture

NASA Astrophysics Data System (ADS)

Mosher, Stephen G.; Audet, Pascal; L'Heureux, Ivan

2014-07-01

Tectonic plate reorganization at a subduction zone edge is a fundamental process that controls oceanic plate fragmentation and capture. However, the various factors responsible for these processes remain elusive. We characterize seismic anisotropy of the upper mantle in the Explorer region at the northern limit of the Cascadia subduction zone from teleseismic shear wave splitting measurements. Our results show that the mantle flow field beneath the Explorer slab is rotating anticlockwise from the convergence-parallel motion between the Juan de Fuca and the North America plates, re-aligning itself with the transcurrent motion between the Pacific and North America plates. We propose that oceanic microplate fragmentation is driven by slab stretching, thus reorganizing the mantle flow around the slab edge and further contributing to slab weakening and increase in buoyancy, eventually leading to cessation of subduction and microplate capture.

Inverse methods-based estimation of plate coupling in a plate motion model governed by mantle flow

NASA Astrophysics Data System (ADS)

Ratnaswamy, V.; Stadler, G.; Gurnis, M.

2013-12-01

Plate motion is primarily controlled by buoyancy (slab pull) which occurs at convergent plate margins where oceanic plates undergo deformation near the seismogenic zone. Yielding within subducting plates, lateral variations in viscosity, and the strength of seismic coupling between plate margins likely have an important control on plate motion. Here, we wish to infer the inter-plate coupling for different subduction zones, and develop a method for inferring it as a PDE-constrained optimization problem, where the cost functional is the misfit in plate velocities and is constrained by the nonlinear Stokes equation. The inverse models have well resolved slabs, plates, and plate margins in addition to a power law rheology with yielding in the upper mantle. Additionally, a Newton method is used to solve the nonlinear Stokes equation with viscosity bounds. We infer plate boundary strength using an inexact Gauss-Newton method with line search for backtracking. Each inverse model is applied to two simple 2-D scenarios (each with three subduction zones), one with back-arc spreading and one without. For each case we examine the sensitivity of the inversion to the amount of surface velocity used: 1) full surface velocity data and 2) surface velocity data simplified using a single scalar average (2-D equivalent to an Euler pole) for each plate. We can recover plate boundary strength in each case, even in the presence of highly nonlinear flow with extreme variations in viscosity. Additionally, we ascribe an uncertainty in each plate's velocity and perform an uncertainty quantification (UQ) through the Hessian of the misfit in plate velocities. We find that as plate boundaries become strongly coupled, the uncertainty in the inferred plate boundary strength decreases. For very weak, uncoupled subduction zones, the uncertainty of inferred plate margin strength increases since there is little sensitivity between plate margin strength and plate velocity. This result is significant because it implies we can infer which plate boundaries are more coupled (seismically) for a realistic dynamic model of plates and mantle flow.

Cratonic roots under North America are shifted by basal drag: new evidence from gravity and geodynamic modeling

NASA Astrophysics Data System (ADS)

Kaban, M. K.; Petrunin, A.; Mooney, W. D.

2013-12-01

The impact of basal drag on the long-lived cratonic roots has been debated since the discovering of plate tectonics. Previously, evidence for a shifted mantle structure under North America was postulated from a comparison of the surface expression of the Great Meteor hotspot track versus its location at 200 km depth as inferred from seismic tomography (Eaton and Frederiksen, 2007). We present new results that are based on the integrative modeling of gravity and seismic data. The starting point is the residual gravity anomaly and residual topography, which are computed by removing of the crustal effect and of the effect of temperature variations in the upper mantle from the observed fields (Mooney and Kaban, 2010). After the temperature correction both residual fields chiefly reflect compositional density heterogeneity of the upper mantle. The residual gravity and topography are jointly inverted to determine the 3D density structure of the upper mantle. The inversion technique accounts for the fact that although these parameters are controlled by the same factors, the effect depends on depth and wavelength. Therefore, we can resolve the vertical distribution of density more reliable than by interpreting only one parameter. We found a strong negative anomaly under the North American craton, as expected for a depleted mantle. However, starting from a depth of about 200 km the depleted root is shifted west-southwest. The maximal shift reaches about 1000 km at a depth of 300 km. The direction agrees with the North American plate movement and with the anisotropy pattern in the upper mantle (e.g. Bokelmann, 2002). The results of the gravity modeling are confirmed by geodynamic modeling. The mantle flow is estimated from the density and temperature distribution derived from seismic tomography models. A 3D viscosity model is supplemented with weak boundaries based on an integrated model of plate boundary deformations. The calculated plate velocities are in a good agreement with the GPS-based models. We found a vertical gradient of the horizontal mantle flow velocity under the North American craton that relates to shear stresses deforming the cratonic root. The lateral velocity within the lowermost part of the lithosphere is about 2 mm/y faster than the overlying plate velocity. If we extrapolate this value to the past, the observed shift of the cratonic root could be achieved in about 500 Ma. Bokelmann GHR, (2002) Convection-driven motion of the North American craton: Evidence from P-wave anisotropy, Geoph. J. Int., 148, 278-287. Eaton DW and Frederiksen A, (2007) Seismic evidence for convection-driven motion of the North American plate, Nature 446, 428-431. Mooney WD, Kaban, MK., (2010). The North American Upper Mantle: Density, Composition, and Evolution, J. Geophys. Res., 115, B12424.

The Evolution of Eastern Himalayan Syntaxis of Tibetan Plateau

NASA Astrophysics Data System (ADS)

Zhang, S.; Wu, T.; Li, M.; Zhang, Y.; Hua, Y.; Zhang, B.

2017-12-01

Indian plate has been colliding with Eurasian plate since 50Ma years ago, resulting in the Tethys extinction, crust shortening and Tibetan plateau uplift. But it is still a debate how the Tibetan Plateau material escaped. This study tries to invert the distributions of dispersion phase velocity and anisotropy in Eastern Himalayan Syntaxis (EHS) based on the seismic data. We focused on the seven sub-blocks around EHS region. Sub-block "EHS" represents EHS corner with high velocity anomalies, significantly compressed in the axle and strike directions. Sub-blocks "LSD", "QTB" and "SP-GZB" are located at its northern areas with compressions also, and connected with low-velocity anomalies in both crustal and upper mantle rocks. Sub-block "ICB" is located at its southern area with low velocity anomaly, and connected with Tengchong volcano. Sub-blocks "SYDB" and "YZB" are located at its eastern areas with high velocity anomalies in both crustal and upper mantle rocks. Our results demonstrated that significant azimuthal anisotropy of crust (t£30s) and upper mantle (30s£t£60s). Crustal anisotropy indicates the orogenic belt matched well with the direction of fast propagation, and upper mantle anisotropy represents the lattic-preferred orientation (LPO) of mantle minerals (e.g. olivine and basalt), indicating the features of subducting Indian plate. Besides, Red River fault is a dextral strike fault, controlling the crustal and mantle migration. There is a narrow zone to be the channel flow of Tibetan crustal materials escaping toward Yunnan area. The evolution of EHS seems constrained by gravity isostatic mechanism. Keywords: Tibetan Plateau; Eastern Himalayan Syntaxis; Red River fault; crustal flow; surface wave; anisotropy

Intra-continental subduction and contemporaneous lateral extrusion of the upper plate: insights into Alps-Adria interactions

NASA Astrophysics Data System (ADS)

van Gelder, Inge; Willingshofer, Ernst; Sokoutis, Dimitrios; Cloetingh, Sierd

2017-04-01

A series of physical analogue experiments were performed to simulate intra-continental subduction contemporaneous with lateral extrusion of the upper plate to study the interferences between these two processes at crustal levels and in the lithospheric mantle. The lithospheric-scale models are specifically designed to represent the collision of the Adriatic microplate with the Eastern Alps, simulated by an intra-continental weak zone to initiate subduction and a weak confined margin perpendicular to the direction of convergence in order to allow for extrusion of the lithosphere. The weak confined margin is the analog for the opening of the Pannonian back-arc basin adjacent to the Eastern Alps with the direction of extension perpendicular to the strike of the orogen. The models show that intra-continental subduction and coeval lateral extrusion of the upper plate are compatible processes. The obtained deformation structures within the extruding region are similar compared to the classical setup where lateral extrusion is provoked by lithosphere-scale indentation. In the models a strong coupling across the subduction boundary allows for the transfer of abundant stresses to the upper plate, leading to laterally varying strain regimes that are characterized by crustal thickening near a confined margin and dominated by lateral displacement of material near a weak lateral confinement. During ongoing convergence the strain regimes propagate laterally, thereby creating an area of overlap characterized by transpression. In models with oblique subduction, with respect to the convergence direction, less deformation of the upper plate is observed and as a consequence the amount of lateral extrusion decreases. Additionally, strain is partitioned along the oblique plate boundary leading to less subduction in expense of right lateral displacement close to the weak lateral confinement. Both oblique and orthogonal subduction models have a strong resemblance to lateral extrusion tectonics of the Eastern Alps, where subduction of the adjacent Adriatic plate beneath the Eastern Alps is debated. Our results highlight that both indentation and subduction of Adria are valid collisional mechanisms to provoke lateral extrusion-type deformation within the Eastern Alps lithosphere, i.e. the upper plate. Moreover, the insights suggest that the Oligocene to Late Miocene structural evolution of the Eastern Alps is best described by phases of oblique and subsequent orthogonal subduction which is in line with Miocene rotations of the Adriatic plate. Furthermore, oblique subduction of the Adriatic plate provides a viable mechanism to explain the rapid decrease in slab length beneath the Eastern Alps towards the Pannonian Basin, also implying that the Adriatic slab can behave and form independently with regards to the adjacent subduction of Adria beneath the Dinarides.

The Lagrangian Multiplier Method of Finding Upper and Lower Limits to Critical Stresses of Clamped Plates

DTIC Science & Technology

1946-01-01

geometrica ~ boundary condi- tions of the problem. (2) The energy of the load-plate system is computed for this deflection surface and is then minimized...and interpolating to find the k that makes the seriw vanish. The correct value of m is that which gives the lowest value of k. For two half waves (m=2...the square plate, the present rekdively simple upper- and lower-limit calcula- tions show that his est,imatd limit of error is correct for this case

Time-Varying Upper-Plate Deformation during the Megathrust Subduction Earthquake Cycle

NASA Astrophysics Data System (ADS)

Furlong, Kevin P.; Govers, Rob; Herman, Matthew

2015-04-01

Over the past several decades of the WEGENER era, our abilities to observe and image the deformational behavior of the upper plate in megathrust subduction zones has dramatically improved. Several intriguing inferences can be made from these observations including apparent lateral variations in locking along subduction zones, which differs from interseismic to coseismic periods; the significant magnitude of post-earthquake deformation (e.g. following the 20U14 Mw Iquique, Chile earthquake, observed on-land GPS post-EQ displacements are comparable to the co-seismic displacements); and incompatibilities between rates of slip deficit accumulation and resulting earthquake co-seismic slip (e.g. pre-Tohoku, inferred rates of slip deficit accumulation on the megathrust significantly exceed slip amounts for the ~ 1000 year recurrence.) Modeling capabilities have grown from fitting simple elastic accumulation/rebound curves to sparse data to having spatially dense continuous time series that allow us to infer details of plate boundary coupling, rheology-driven transient deformation, and partitioning among inter-earthquake and co-seismic displacements. In this research we utilize a 2D numerical modeling to explore the time-varying deformational behavior of subduction zones during the earthquake cycle with an emphasis on upper-plate and plate interface behavior. We have used a simplified model configuration to isolate fundamental processes associated with the earthquake cycle, rather than attempting to fit details of specific megathrust zones. Using a simple subduction geometry, but realistic rheologic layering we are evaluating the time-varying displacement and stress response through a multi-earthquake cycle history. We use a simple model configuration - an elastic subducting slab, an elastic upper plate (shallower than 40 km), and a visco-elastic upper plate (deeper than 40 km). This configuration leads to an upper plate that acts as a deforming elastic beam at inter-earthquake loading times and rates with a viscously relaxed regime at depths greater than 40 km. Analyses of our preliminary model results lead to the following: 1. Co-seismic stress transfer from the unloading elastic layer (shallow) into an elastically loading visco-elastic layer (deeper) - extends ~ 100 km inboard of locked zone. This stress transfer affects both coseismic and post-seismic surface displacements. 2. Post-seismic response of upper plate involves seaward motion for initial 10-20 years (~ 2 Maxwell times) after EQ. This occurs in spite of there being no slip on locked plate boundary - i.e. this is not plate boundary after-slip but rather is a consequence of stress relaxation in co-seismically loaded visco-elastic layer. However standard inversions of the surface displacement field would indicate significant after-slip along the locked plate interface. 3. By approximately 80 years (8 Maxwell times) system has returned to simple linear displacement pattern - the expected behavior for a shortening elastic beam. Prior to that time, the surface (observable) displacement pattern changes substantially over time and would result in an apparent temporal variation in coupling - from near-zero coupling to fully locked over ~ 80 years post-earthquake. These preliminary results indicate that care is needed in interpreting observed surface displacement fields from GPS, InSAR, etc. during the interseismic period. temporal variations in crustal deformation observed in regions such as the recent Tohoku, Maule, and Iquique megathrust events which are ascribed to fault plane after-slip may in fact reflect processes associated with re-equilibration of the visco-elastic subduction system.

Cascadia subduction tremor muted by crustal faults

USGS Publications Warehouse

Wells, Ray; Blakely, Richard J.; Wech, Aaron G.; McCrory, Patricia A.; Michael, Andrew

2017-01-01

Deep, episodic slow slip on the Cascadia subduction megathrust of western North America is accompanied by low-frequency tremor in a zone of high fluid pressure between 30 and 40 km depth. Tremor density (tremor epicenters per square kilometer) varies along strike, and lower tremor density statistically correlates with upper plate faults that accommodate northward motion and rotation of forearc blocks. Upper plate earthquakes occur to 35 km depth beneath the faults. We suggest that the faults extend to the overpressured megathrust, where they provide fracture pathways for fluid escape into the upper plate. This locally reduces megathrust fluid pressure and tremor occurrence beneath the faults. Damping of tremor and related slow slip caused by fluid escape could affect fault properties of the megathrust, possibly influencing the behavior of great earthquakes.

Analysis of the ORNL/TSF GCFR Grid-Plate Shield Design Confirmation Experiment

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

Slater, C.O.; Cramer, S.N.; Ingersoll, D.T.

1979-08-01

The results of the analysis of the GCFR Grid-Plate Shield Design Confirmation Experiment are presented. The experiment, performed at the ORNL Tower Shielding Facility, was designed to test the adequacy of methods and data used in the analysis of the GCFR design. In particular, the experiment tested the adequacy of methods to calculate: (1) axial neutron streaming in the GCFR core and axial blanket, (2) the amount and location of the maximum fast-neutron exposure to the grid plate, and (3) the neutron source leaving the top of the grid plate and entering the upper plenum. Other objectives of the experimentmore » were to verify the grid-plate shielding effectiveness and to assess the effects of fuel-pin and subassembly spacing on radiation levels in the GCFR. The experimental mockups contained regions representing the GCFR core/blanket region, the grid-plate shield section, and the grid plate. Most core design options were covered by allowing: (1) three different spacings between fuel subassemblies, (2) two different void fractions within a subassembly by variation of the number of fuel pins, and (3) a mockup of a control-rod channel.« less

The interplay between subduction and lateral extrusion: A case study for the European Eastern Alps based on analogue models

NASA Astrophysics Data System (ADS)

van Gelder, I. E.; Willingshofer, E.; Sokoutis, D.; Cloetingh, S. A. P. L.

2017-08-01

A series of analogue experiments simulating intra-continental subduction contemporaneous with lateral extrusion of the upper plate are performed to study the interference between these two processes at crustal levels and in the lithospheric mantle. The models demonstrate that intra-continental subduction and coeval lateral extrusion of the upper plate are compatible processes leading to similar deformation structures within the extruding region as compared to the classical setup, lithosphere-scale indentation. Strong coupling across the subduction boundary allows for the transfer of stresses to the upper plate, where strain regimes are characterized by crustal thickening near a confined margin and dominated by lateral displacement of material near a weak lateral confinement. The strain regimes propagate laterally during ongoing convergence creating an area of overlap characterized by transpression. When subduction is oblique to the convergence direction, the upper plate is less deformed and as a consequence the amount of lateral extrusion decreases. In addition, strain is partitioned along the oblique plate boundary resulting in less subduction in expense of right lateral displacement close to the weak lateral confinement. Both oblique and orthogonal subduction models have a strong resemblance to lateral extrusion tectonics of the Eastern Alps (Europe), where subduction of the adjacent Adriatic plate beneath the Eastern Alps is debated. Our results imply that subduction of Adria is a valid mechanisms to induce extrusion-type deformation within the Eastern Alps lithosphere. Furthermore, our findings suggest that the Oligocene to Late Miocene structural evolution of the Eastern Alps reflects a phase of oblique subduction followed by a later stage of orthogonal subduction conform a Miocene shift in the plate motion of Adria. Oblique subduction also provides a viable mechanism to explain the rapid decrease in slab length of the Adriatic plate beneath the Eastern Alps towards the Pannonian Basin.

Why and Where do Large Shallow Slab Earthquakes Occur?

NASA Astrophysics Data System (ADS)

Seno, T.; Yoshida, M.

2001-12-01

Within a shallow portion (20-60 km depth) of subducting slabs, it has been believed that large earthquakes seldom occur because the differential stress is generally expected to be low between bending at the trench-outer rise and unbending at the intermediate-depth. However, there are several regions in which large ( M>=7.0 ) earthquakes, including three events early in this year, have occurred in this portion. Searching such events from published individual studies and Harvard University centroid moment tensor catalogue, we find nineteen events in eastern Hokkaido, Kyushu-SW Japan, Mariana, Manila, Sumatra, Vanuatu, Chile, Peru, El Salvador, Mexico, and Cascadia. Slab stresses revealed from the mechanism solutions of those large events and smaller events are tensional in a slab dip direction. However, ages of the subducting oceanic plates are generally young, which denies a possibility that the slab pull works as a cause. Except for Manila and Sumatra, the stresses in the overriding plates are characterized by the change in {σ }Hmax direction from arc-parallel in the back-arc to arc-perpendicular in the fore-arc, which implies that a horizontal stress gradient exists in the across-arc direction. Peru and Chile, where the back-arc is compressional, can be categorized into this type, because a horizontal stress gradient exists over the continent from tension in east to compression in the west. In these regions, it is expected that mantle drag forces are operating beneath the upper plates, which drive the upper plates to the trenchward overriding the subducting oceanic plates. Assuming that the mantle drag forces beneath the upper plates originate from the mantle convection currents or upwelling plumes, we infer that the upper plates driven by the convection suck the oceanic plates, making the shallow portion of the slabs in extra-tension, thus resulting in the large shallow slab earthquakes in this tectonic regime.

Segmentation of plate coupling, fate of subduction fluids, and modes of arc magmatism in Cascadia, inferred from magnetotelluric resistivity

USGS Publications Warehouse

Wannamaker, Philip E.; Evans, Rob L.; Bedrosian, Paul A.; Unsworth, Martyn J.; Maris, Virginie; McGary, R. Shane

2014-01-01

Five magnetotelluric (MT) profiles have been acquired across the Cascadia subduction system and transformed using 2-D and 3-D nonlinear inversion to yield electrical resistivity cross sections to depths of ∼200 km. Distinct changes in plate coupling, subduction fluid evolution, and modes of arc magmatism along the length of Cascadia are clearly expressed in the resistivity structure. Relatively high resistivities under the coasts of northern and southern Cascadia correlate with elevated degrees of inferred plate locking, and suggest fluid- and sediment-deficient conditions. In contrast, the north-central Oregon coastal structure is quite conductive from the plate interface to shallow depths offshore, correlating with poor plate locking and the possible presence of subducted sediments. Low-resistivity fluidized zones develop at slab depths of 35–40 km starting ∼100 km west of the arc on all profiles, and are interpreted to represent prograde metamorphic fluid release from the subducting slab. The fluids rise to forearc Moho levels, and sometimes shallower, as the arc is approached. The zones begin close to clusters of low-frequency earthquakes, suggesting fluid controls on the transition to steady sliding. Under the northern and southern Cascadia arc segments, low upper mantle resistivities are consistent with flux melting above the slab plus possible deep convective backarc upwelling toward the arc. In central Cascadia, extensional deformation is interpreted to segregate upper mantle melts leading to underplating and low resistivities at Moho to lower crustal levels below the arc and nearby backarc. The low- to high-temperature mantle wedge transition lies slightly trenchward of the arc.

A Preliminary Research into Clinical Semi-permeability Tolerance in the Field of Dental Rehabilitation

PubMed Central

Xia, H; Xiong, F

2015-01-01

ABSTRACT Objective: To study clinical semi-permeability tolerance level in the field of dental restoration. Method: Vita 95 enamel porcelain powder was adopted and 6.0% used as the control transmissivity. Discoid porcelain plates with different transmissivity, namely increasing transmissivity (0.25%, 0.5%, 1.0%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% and 4.5%) and decreasing transmissivity (-0.25%, −0.5%, −1.0%, −1.5%, −2%, −2.5%, −3% and −3.5%) were made. Forty observers judged these according to six grades: same, similar, slightly different, visibly different, recognizable and significantly different, and under the observation conditions of a neutral grey background and 45°/0° lighting. The judgment results were analysed statistically. Results: When the transmissivity of the control porcelain plates was 6.032%, and the transmissivity of test porcelain plates decreased by 1% or increased by 3%, observers could find slight differences between the test samples and the control samples. When transmissivity of test samples decreased by 2.5% or increased by 4.5%, observers thought that the two porcelain plates belonged to different orders of magnitude. Conclusions: Under the experimental conditions, the upper and lower limits of clinical semi-permeability tolerance were 3% and 1%, respectively. PMID:27400057

Initiation of the Pyrenean plate boundary fault and its effect on the near- and far-field deformation of the European plate

NASA Astrophysics Data System (ADS)

Dielforder, Armin; Frasca, Gianluca; Ford, Mary

2017-04-01

The European plate was affected by contractional deformation events in Late Cretaceous time. This is recorded by inception of thrusting and foreland basin subsidence in the Pyrenean realm, and inversion of Mesozoic rift systems in the interior of the European plate. It is widely accepted that the plate-wide deformation resulted from the onset of NE-directed convergence of Africa-Iberia relative to Europe, and a strong mechanical coupling of the plates, which allowed the transfer of stresses far into Europe. Geological data from both the Pyrenean orogen and the interior of the European plate indicate, however, that these conditions persisted only for 15-20 Myr and that Europe experienced a plate-wide stress relaxation during Paleocene time. Although a slow down in plate convergence between Africa and Europe and North Atlantic continental rifting were proposed as potential causes for the stress relaxation, the subject has remained controversial. In particular, none of the mechanisms seem to be suitable to explain the required changes in the mechanical coupling of Iberian and European plates and the associated stress transfer. Here we propose a new model for the Upper Cretaceous to Paleocene tectonic evolution of the European plate, which takes the temporal evolution of the Pyrenean plate boundary fault into account. Based on plate reconstructions, geological field-data, and restored cross-sections we argue that the plate boundary fault initiated during the Upper Cretaceous within the exhumed mantle domain situated between the rifted margins of the Iberian and European plates. At the transition from the Late Cretaceous to Paleocene, the mantle domain was closed and the rifted margins collided. This evolution was associated with a substantial change in the fault rheology leading to an overall decrease in the plate coupling force. During Paleocene time, the plate coupling force was efficiently balanced by the gravitational push of the European plate, leading to a near neutral stress state in the upper plate and the observed plate-wide stress relaxation in Europe. This study is part of the Orogen research program and conducted in close collaboration with the BRGM (Bureau de Recherches Géologiques et Minières), the CNRS (Centre National de la Recherche Scientifique), and Total.

Structure of the Sumatra wedge affected by the 26th December 2004 :Effects of the lower plate volcanic ridges.

NASA Astrophysics Data System (ADS)

Rangin, C.; Sibuet, J. C.; Lin, J. Y.; Le Pichon, X.

2009-04-01

Detailed swath-bathymetry, coupled with echo-sounder data were collected offshore the northern tip of Sumatra over the rupture area of the 26th December 2004 Mw=9.2 earthquake during the Sumatra aftershock cruise. 20 ocean bottom seismometers were also deployed in the northern Sumatra area., and more than 1000 events were identified during the 12 days recording period. We mapped recently active steeply dipping thrust fault zone within the western termination of the Sunda accreted wedge. Main N10°W trending out of sequence thrust fault zones with a discrete westward vergency and some component of dextral strike-slip motion were continuously mapped within the wedge, on the basis of bathymetry and low frequency sounder profiles. The interplate boundary does not appear to extend into the frontal part of the wedge but most probably merges in its central part along these major faults, the Lower and Upper Splay Faults. After relocation, the seismicity shows different pattern in each side of this Upper Splay Fault. East of this boundary, beneath the Aceh basin, the earthquake depths ranged from 30 to 60 km allow us to illustrate the subducted plate. In the western part, the aftershock distribution is strongly influenced by the N-S orientated oceanic fracture zones. Two clusters of earthquakes between 10 and 50 km in depth trending along N-S direction are observed in the lower wedge that we interpret to be reactive fracture zones. The lower wedge is interpreted as the northern prolongation below the wedge of the lower plate NS oceanic fracture zone ridges affected by NS trending left lateral strike-slip faults. This wedge outer ridge is in the process of being transferred to the upper plate. On the other hand the central ridge is interpreted as possible stacked volcanic ridge slivers already incorporated into the upper plate along the subduction buttress (the inner ridge of the wedge). We propose that the tectonic interaction of the volcanic Indian Ocean fracture ridges of the subducted plate with the leading edge of the upper Sunda plate subduction zone is an active tectonic transfer process of oceanic material to the upper plate. The proposed emergence of the interplate boundary into the middle part of the wedge along the Lower Splay Fault, could have favoured the formation of the giant Sumatra tsunami at moderate water depth. This docking and temporary stacking of these volcanic ridges before their subduction at depth, is favoured by the strong oblique convergence that prevails up to the Bengal basin into the north.

The role of harzburgite layers in the morphology of subducting plates and the behavior of oceanic crustal layers

NASA Astrophysics Data System (ADS)

Yoshida, Masaki

2014-05-01

Previous numerical studies of mantle convection focusing on subduction dynamics have indicated that the viscosity contrast between the subducting plate and the surrounding mantle have a primary effect on the behavior of subducting plates. The seismically observed plate stagnation at the base of the mantle transition zone (MTZ) under the Western Pacific and Eastern Eurasia is considered to mainly result from a viscosity increase at the ringwoodite to perovskite + magnesiowüstite (Rw→Pv+Mw) phase decomposition boundary, i.e., the boundary between the upper and lower mantle. The harzburgite layer, which is sandwiched between basaltic crust and depleted peridotite (lherzolite) layers, is a key component of highly viscous, cold oceanic plates. However, the possible sensitivity of the effective viscosity of harzburgite layers in the morphology of subducting plates that are flattened in the MTZ and/or penetrated in the lower mantle has not been examined systematically in previous three-dimensional (3D) numerical modeling studies that consider the viscosity increase at the boundary between the upper and lower mantle. In this study, in order to investigate the role of harzburgite layers in the morphology of subducting plates and the behavior of oceanic crustal layers, I performed a series of numerical simulations of mantle convection with semi-dynamic plate subduction in 3D regional spherical-shell geometry. The results show that a buckled crustal layer is observed under the "heel" of the stagnant slab that begins to penetrate into the lower mantle, regardless of the magnitude of the viscosity contrast between the harzburgite layer and the underlying mantle, when the factor of viscosity increase at the boundary of the upper and lower mantle is larger than 60-100. As the viscosity contrast between the harzburgite layer and the underlying mantle increases, the curvature of buckling is larger. When the viscosity increase at the boundary of the upper and lower mantle and the viscosity contrast between the harzburgite layer and the underlying mantle are larger, the volumes of crustal and harzburgite materials trapped in the mantle transition zone (MTZ) are also larger, although almost all of the materials penetrate into the lower mantle. These materials are trapped in the MTZ for over tens of millions of years. The bending of crustal layers numerically observed in the present study is consistent with seismological evidence that there is a piece of subducted oceanic crust in the uppermost lower mantle beneath the subducting slab under the Mariana trench [Niu et al., 2003, JGR]. The results of the present study suggest that when the viscosity increase at the boundary of the upper and lower mantle is larger than 60-100, a seismically observed stagnant slab is reproduced. This result is consistent with the previous independent geodynamic studies. For instance, a 2D geodynamic model with lateral viscosity variations suggested that it would need to be substantially greater than 30, say, around 100, to explain the positive geoid anomaly in the subduction zones where the subducting slab reaches the boundary between the upper and lower mantle such as that of the western Pacific [Tosi et al., 2009, GJI]. References: [1] Tajima, F. Yoshida, M. and Ohtani, E., Conjecture with water and rheological control for subducting slab in the mantle transition zone, Geoscience Frontiers, doi:10.1016/j.gsf.2013.12.005, 2014. [2] Yoshida, M. The role of harzburgite layers in the morphology of subducting plates and the behavior of oceanic crustal layers, Geophys. Res. Lett., 40(20), 5387-5392, doi:10.1002/2013GL057578, 2013. [3] Yoshida, M. and Tajima, F., On the possibility of a folded crustal layer stored in the hydrous mantle transition zone, Phys. Earth Planet. Inter., 219, 34-48, doi:10.1016/j.pepi.2013.03.004, 2013.

Heat exchanger support apparatus in a fluidized bed

DOEpatents

Lawton, Carl W.

1982-01-01

A heat exchanger is mounted in the upper portion of a fluidized combusting bed for the control of the temperature of the bed. A support, made up of tubes, is extended from the perforated plate of the fluidized bed up to the heat exchanger. The tubular support framework for the heat exchanger has liquid circulated therethrough to prevent deterioration of the support.

Lithospheric Decoupling and Rotations: Hints from Ethiopian Rift

NASA Astrophysics Data System (ADS)

Muluneh, A. A.; Cuffaro, M.; Doglioni, C.; Kidane, T.

2014-12-01

Plates move relative to the mantle because some torques are acting on them. The shear in the low-velocity zone (LVZ) at the base of the lithosphere is the expression of these torques. The decoupling is allowed by the low viscosity in the LVZ, which is likely few orders of magnitudes lower than previously estimated. The viscosity value in the LVZ controls the degree of coupling/decoupling between the lithosphere and the underlying mantle. Lateral variations in viscosity within the LVZ may explain the velocity gradient among tectonic plates as the one determining the Ethiopian Rift (ER) separating Africa from Somalia. While it remains not fully understood the mechanisms of the torques acting on the lithosphere (thermally driven mantle convection or the combination of mantle convection with astronomical forces such as the Earth's rotation and tidal drag), the stresses are transmitted across the different mechanical layers (e.g., the brittle upper crust, down to the viscous-plastic ductile lower crust and upper mantle). Differential basal shear traction at the base of the lithosphere beneath the two sides of the East African Rift System (EARS) is assumed to drive and sustain rifting. In our analysis, the differential torques acting on the lithospheric/crustal blocks drive kinematics and block rotations. Since, ER involves the whole lithosphere, we do not expect large amount of rotation. Rotation can be the result of the whole plate motion on the sphere moving along the tectonic equator, or the second order sub-rotation of a single plate. Further rotation may occur along oblique plate boundaries (e.g., left lateral transtensional setting at the ER). Small amount of vertical axis rotation of blocks in northern ER could be related to the presence of local, shallower decollement layers. Shallow brittle-ductile transition (BDT) zone and differential tilting of crustal blocks in the northern ER could hint a possibility of detachment surface between the flow in the lower crust relative to the brittle crust above. Our study suggests that kinematics of crustal blocks in the ER is controlled by Africa and Somalia plates interaction at different scale and layers.

Microstructural evidence for northeastward movement on the Chocolate Mountains fault zone, southeastern California

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

Simpson, C.

1990-01-10

Microstructural analysis of rocks from the Chocolate Mountains fault zone, Gavilan Hills area, southeastern California, show unequivocal evidence for northeast directed transport of the upper plate gneisses over lower plate Orocopia schists. Samples were taken from transects through the fault zone. Prefaulting fabrics in upper plate gneisses show a strong component of northeast directed rotational deformation under lower amphibolite facies conditions. In contrast, prefaulting lower plate Orocopia schists show strongly coaxial fabrics (minimum stretch value of 2.2) formed at greenschist grade. Mylonitic fabrics associated with the Chocolate Mountains fault are predominantly northeast directed shear bands that are unidirectional (northeastward) inmore » the gneisses but bi-directional in the schists, suggesting a significant component of nonrotational deformation occurred in the Orocopia schists during and after emplacement of the upper plate. The kinematic findings are in agreement with Dillon et al. (1989), who found that the vergence of asymmetrical folds within the fault zone indicates overthrusting to the northeast, toward the craton, in this region. The available evidence favors a single protracted northeastward movement on the Chocolate Mountains fault zone with temperatures waning as deformation proceeded.« less

Unitary plate electrode

NASA Technical Reports Server (NTRS)

Rowlette, John J. (Inventor); Clough, Thomas J. (Inventor); Josefowicz, Jack Y. (Inventor); Sibert, John W. (Inventor)

1985-01-01

The unitary electrode (10) comprises a porous sheet (12) of fiberglass the strands (14) of which contain a coating (16) of conductive tin oxide. The lower portion of the sheet contains a layer (18) of resin and the upper layer (20) contains lead dioxide forming a positive active electrode on an electrolyte-impervious layer. The strands (14) form a continuous conduction path through both layers (16, 18). Tin oxide is prevented from reduction by coating the surface of the plate facing the negative electrode with a conductive, impervious layer resistant to reduction such as a thin film (130) of lead or graphite filled resin adhered to the plate with a layer (31) of conductive adhesive. The plate (10) can be formed by casting a molten resin from kettle (60) onto a sheet of glass wool (56) overlying a sheet of lead foil and then applying positive active paste from hopper (64) into the upper layer (68). The plate can also be formed by passing an assembly of a sheet ( 80) of resin, a sheet (86) of sintered glass and a sheet (90) of lead between the nip (92) of heated rollers (93, 95) and then filling lead oxide into the pores (116) of the upper layer (118).

Forearc deformation and great subduction earthquakes: implications for cascadia offshore earthquake potential.

PubMed

McCaffrey, R; Goldfinger, C

1995-02-10

The maximum size of thrust earthquakes at the world's subduction zones appears to be limited by anelastic deformation of the overriding plate. Anelastic strain in weak forearcs and roughness of the plate interface produced by faults cutting the forearc may limit the size of thrust earthquakes by inhibiting the buildup of elastic strain energy or slip propagation or both. Recently discovered active strike-slip faults in the submarine forearc of the Cascadia subduction zone show that the upper plate there deforms rapidly in response to arc-parallel shear. Thus, Cascadia, as a result of its weak, deforming upper plate, may be the type of subduction zone at which great (moment magnitude approximately 9) thrust earthquakes do not occur.

Computer-aided design and computer-aided manufacturing cutting guides and customized titanium plates are useful in upper maxilla waferless repositioning.

PubMed

Mazzoni, Simona; Bianchi, Alberto; Schiariti, Giulio; Badiali, Giovanni; Marchetti, Claudio

2015-04-01

The purpose of the present study was to develop a computer-aided design (CAD) and computer-aided manufacturing (CAM) technique that enabled fabrication of surgical cutting guides and titanium fixation plates that would allow the upper maxilla to be repositioned correctly without a surgical splint in orthognathic patients. Ten patients were recruited. A complete CAD-CAM workflow for orthognathic surgery has 3 steps: 1) virtual planning of the surgical treatment, 2) CAD-CAM and 3-dimensional printing of customized surgical devices (surgical cutting guide and titanium fixation plates), and 3) computer-aided surgery. Upper maxilla repositioning was performed in a waferless manner using a CAD-CAM device: the surgical cutting guide was used during surgery to pilot the osteotomy line that had been planned preoperatively at the computer and the custom-made fixation titanium plates allowed desired repositioning of the maxilla. To evaluate the reproducibility of this CAD-CAM orthognathic surgical method, the virtually planned and actually achieved positions of the upper maxilla were compared. Overlap errors using a threshold value smaller than 2 mm were evaluated, and the frequency of such errors was used as a measurement of accuracy. By this definition, the accuracy was 100% in 7 patients (range in all patients, 62 to 100%; median, 92.7%). These results tend to confirm that the use of CAD-CAM cutting guides and customized titanium plates for upper maxilla repositioning represents a promising method for the accurate reproduction of preoperative virtual planning without the use of surgical splints. Copyright © 2015 American Association of Oral and Maxillofacial Surgeons. Published by Elsevier Inc. All rights reserved.

Upper-Mantel Earthquakes in the Australia-Pacific Plate Boundary Zone and the Roots of the Alpine Fault

NASA Astrophysics Data System (ADS)

Boese, C. M.; Warren-Smith, E.; Townend, J.; Stern, T. A.; Lamb, S. H.

2016-12-01

Seismicity in the upper mantle in continental collision zones is relatively rare, but observed around the world. Temporary seismometer deployments have repeatedly detected mantle earthquakes at depths of 40-100 km within the Australia-Pacific plate boundary zone beneath the South Island of New Zealand. Here, the transpressive Alpine Fault constitutes the primary plate boundary structure linking subduction zones of opposite polarity farther north and south. The Southern Alps Microearthquake Borehole Array (SAMBA) has been operating continuously since November 2008 along a 50 km-long section of the central Alpine Fault, where the rate of uplift of the Southern Alps is highest. To date it has detected more than 40 small to moderate-sized mantle events (1≤ML≤3.9). The Central Otago Seismic Array (COSA) has been in operation since late 2012 and detected 15 upper mantle events along the sub-vertical southern Alpine Fault. Various mechanisms have been proposed to explain the occurrence of upper mantle seismicity in the South Island, including intra-continental subduction (Reyners 1987, Geology); high shear-strain gradients due to depressed geotherms and viscous deformation of mantle lithosphere (Kohler and Eberhart-Phillips 2003, BSSA); high strain rates resulting from plate bending (Boese et al. 2013, EPSL), and underthrusting of the Australian plate (Lamb et al. 2015, G3). Focal mechanism analysis reveals a variety of mechanisms for the upper mantle events but predominantly strike-slip and reverse faulting. In this study, we apply spectral analysis to better constrain source parameters for these mantle events. These results are interpreted in conjunction with new information about crustal structure and low-frequency earthquakes near the Moho and in light of existing velocity, attenuation and resistivity models.

Mantle thermal history during supercontinent assembly and breakup

NASA Astrophysics Data System (ADS)

Rudolph, M. L.; Zhong, S.

2013-12-01

We use mantle convection simulations driven by plate motion boundary conditions to investigate changes in mantle temperature through time. It has been suggested that circum-Pangean subduction prevented convective thermal mixing between sub-continental and sub-oceanic regions. We performed thermo-chemical simulations of mantle convection with velocity boundary conditions based on plate motions for the past 450 Myr using Earth-like Rayleigh number and ~60% internal heating using three different plate motion models for the last 200 Myr [Lithgow-Bertelloni and Richards 1998; Gurnis et al. 2012; Seton et al. 2012; Zhang et al. 2010]. We quantified changes in upper-mantle temperature between 200-1000 km depth beneath continents (defined as the oldest 30% of Earth's surface) and beneath oceans. Sub-continental upper mantle temperature was relatively stable and high between 330 and 220 Ma, coincident with the existence of the supercontinent Pangea. The average sub-continental temperature during this period was, however, only ~10 K greater than during the preceding 100 Myr. In the ~200 Myr since the breakup of Pangea, sub-continental temperatures have decreased only ~15 K in excess of the 0.02 K/Myr secular cooling present in our models. Sub-oceanic upper mantle temperatures did not vary more than 5 K between 400 and 200 Ma and the cooling trend following Pangea breakup is less pronounced. Recent geochemical observations imply rapid upper mantle cooling of O(10^2) K during continental breakup; our models do not produce warming of this magnitude beneath Pangea or cooling of similar magnitude associated with the breakup of Pangea. Our models differ from those that produce strong sub-continental heating in that the circum-Pangean subduction curtain does not completely inhibit mixing between the sub-continental and sub-oceanic regions and we include significant internal heating, which limits the rate of temperature increase. Heat transport in our simulations is controlled to first order by plate motions. Most of the temporal variability in surface heat flow is driven by variations in seafloor spreading rate and the accompanying changes in slab velocities dominate variations in buoyancy flux at all mantle depths. Variations in plume buoyancy flux are small but are correlated with the slab buoyancy flux variations.

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.

Deciphering the 3-D distribution of fluid along the shallow Hikurangi subduction zone using P- and S-wave attenuation

NASA Astrophysics Data System (ADS)

Eberhart-Phillips, Donna; Bannister, Stephen; Reyners, Martin

2017-11-01

We use local earthquake velocity spectra to solve for the 3-D distribution of P- and S-wave attenuation in the shallow Hikurangi subduction zone in the North Island of New Zealand to gain insight into how fluids control both the distribution of slip rate deficit and slow-slip events at the shallow plate interface. Qs/Qp gives us information on the 3-D distribution of fluid saturation, which we can compare with the previously determined 3-D distribution of Vp/Vs, which gives information on pore fluid pressure. The Hikurangi margin is unusual, in that a large igneous province (the Hikurangi Plateau) is being subducted. This plateau has had two episodes of subduction-first at 105-100 Ma during north-south convergence with Gondwana, and currently during east-west convergence between the Pacific and Australian plates. We find that in the southern part of the subduction zone, where there is a large deficit in slip rate at the plate interface, the plate interface region is only moderately fluid-rich because the underlying plateau had already had an episode of dehydration during Gondwana subduction. But fluid pressure is relatively high, due to an impermeable terrane in the upper plate trapping fluids below the plate interface. The central part of the margin, where the slip rate deficit is very low, is the most fluid-rich part of the shallow subduction zone. We attribute this to an excess of fluid from the subducted plateau. Our results suggest this part of the plateau has unusually high fracture permeability, on account of it having had two episodes of bending-first at the Gondwana trench and now at the Hikurangi Trough. Qs/Qp is consistent with fluids migrating across the plate interface in this region, leaving it drained and producing high fluid pressure in the overlying plate. The northern part of the margin is a region of heterogeneous deficit in slip rate. Here the Hikurangi Plateau is subducting for the first time, so there is less fluid available from its dehydration than in the central region. Fluid pressure in the overlying plate is high, but Qs/Qp indicates that it is not uniformly fluid-rich. This heterogeneity is consistent with the rough topography of the plateau, including seamounts which entrain fluid-rich sediments. Deep slow-slip events in the southern part of the margin occur where the Moho of the overlying plate meets the plate interface, as typically seen in other deep slow-slip events worldwide. But in the central and northern parts of the margin, the locations of shallow slow-slip events appear to be controlled by a shallow brittle-viscous transition within the fluid-rich upper plate. There is also evidence that a major fault zone in the overlying plate might bleed off some of the high fluid pressure promoting slow-slip events.

Stress-Shielding Effect of Nitinol Swan-Like Memory Compressive Connector on Fracture Healing of Upper Limb

NASA Astrophysics Data System (ADS)

Fu, Q. G.; Liu, X. W.; Xu, S. G.; Li, M.; Zhang, C. C.

2009-08-01

In this article, the stress-shielding effect of a Nitinol swan-like memory compressive connector (SMC) is evaluated. Patients with fracture healing of an upper limb after SMC internal fixation or stainless steel plate fixation were randomly selected and observed comparatively. With the informed consent of the SMC group, minimal cortical bone under the swan-body and swan-neck was harvested; and in the steel plate fixation group, minimal cortical bone under the steel plate and opposite side to the steel plate was also harvested for observation. Main outcome measurements were taken such as osteocyte morphology, Harversian canal histological observation under light microscope; radiographic observation of fracture healing, and computed tomography quantitative scanning of cortical bone. As a conclusion, SMC has a lesser stress-shielding effect to fixed bone than steel plate. Finally, the mechanism of the lesser stress-shielding effect of SMC is discussed.

Reconstruction of large upper eyelid defects with a free tarsal plate graft and a myocutaneous pedicle flap plus a free skin graft.

PubMed

Toft, Peter B

2016-01-01

To review and present the results of a one-step method employing a free tarsal plate graft and a myocutaneous pedicle flap plus a free skin graft for reconstruction of large upper eyelid defects after tumour surgery. This was a retrospective case-series of 8 patients who underwent reconstruction of the upper eyelid after tumour removal. The horizontal defect involved 50-75% of the lid (3 pts.), more than 75% (3 pts.), and more than 75% plus the lateral canthus (2 pts.). The posterior lamella was reconstructed with contralateral upper eyelid tarsal plate. The anterior lamella was reconstructed with a laterally based myocutaneous pedicle flap in 7 patients, leaving a raw surface under the brow which was covered with a free skin graft. In 1 patient with little skin left under the brow, the anterior lamella was reconstructed with a bi-pedicle orbicularis muscle flap together with a free skin graft. All patients healed without necrosis, did not suffer from lagophthalmos, achieved reasonable cosmesis, and did not need lubricants. In one patient, a contact lens was necessary for three weeks because of corneal erosion. One patient still needs a contact lens 3 months after excision to avoid eye discomfort. Large upper eyelid defects can be reconstructed with a free tarsal plate graft and a laterally based myocutaneous pedicle flap in combination with a free skin graft. Two-step procedures can probably be avoided in most cases.

Fixation of osteoporotic fractures in the upper limb with a locking compression plate.

PubMed

Neuhaus, V; King, J D; Jupiter, J B

2012-01-01

Locking Compression Plate (LCP) has the advantageous feature that screws can be locked in the plate leaving an angular stable construct. There is no need to have contact between the plate and the bone to achieve stability resulting from friction of the plate-bone-construct. Therefore the plate does not need to be contoured exactly to the bone and the healing bone's periosteal blood supply is not affected. The LCP is used as a bridging plate to gain relative stability in multi-fragmentary, diaphyseal or metaphyseal fractures. Depending on the fracture, the combination hole can also allow the LCP to achieve absolute stability similar to conventional fixation techniques. Osteoporotic fractures have significant impact on morbidity and mortality. Proximal humeral and distal radius fractures are typical examples. These osteoporotic and often comminuted fractures are ideal settings/indications for LCP utilization in the upper extremity. However, the data quality is due to mostly small study populations not so powerful. Unquestionably there has been a clear and fashionable trend to choose operative treatment for these fractures, because the angular stability allows stable fixation and early functional mobilization.

Aperture-based antihydrogen gravity experiment: Parallel plate geometry

NASA Astrophysics Data System (ADS)

Rocha, J. R.; Hedlof, R. M.; Ordonez, C. A.

2013-10-01

An analytical model and a Monte Carlo simulation are presented of an experiment that could be used to determine the direction of the acceleration of antihydrogen due to gravity. The experiment would rely on methods developed by existing antihydrogen research collaborations. The configuration consists of two circular, parallel plates that have an axis of symmetry directed away from the center of the earth. The plates are separated by a small vertical distance, and include one or more pairs of circular barriers that protrude from the upper and lower plates, thereby forming an aperture between the plates. Antihydrogen annihilations that occur just beyond each barrier, within a "shadow" region, are asymmetric on the upper plate relative to the lower plate. The probability for such annihilations is determined for a point, line and spheroidal source of antihydrogen. The production of 100,000 antiatoms is predicted to be necessary for the aperture-based experiment to indicate the direction of free fall acceleration of antimatter, provided that antihydrogen is produced within a sufficiently small antiproton plasma at a temperature of 4 K.

Plate tectonics and hotspots: the third dimension.

PubMed

Anderson, D L; Tanimoto, T; Zhang, Y S

1992-06-19

High-resolution seismic tomographic models of the upper mantle provide powerful new constraints on theories of plate tectonics and hotspots. Midocean ridges have extremely low seismic velocities to a depth of 100 kilometers. These low velocities imply partial melting. At greater depths, low-velocity and high-velocity anomalies record, respectively, previous positions of migrating ridges and trenches. Extensional, rifting, and hotspot regions have deep (> 200 kilometers) low-velocity anomalies. The upper mantle is characterized by vast domains of high temperature rather than small regions surrounding hotspots; the asthenosphere is not homogeneous or isothermal. Extensive magmatism requires a combination of hot upper mantle and suitable lithospheric conditions. High-velocity regions of the upper 200 kilometers of the mantle correlate with Archean cratons.

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.

Structural control of the upper plate on the down-dip segmentation of subduction dynamics

NASA Astrophysics Data System (ADS)

Shi, Q.; Barbot, S.; Karato, S. I.; Shibazaki, B.; Matsuzawa, T.; Tapponnier, P.

2017-12-01

The geodetic and seismic discoveries of slow earthquakes in subduction zones have provided the observational evidence for the existence of the transition between megathrust earthquakes and the creeping behaviors. However, the mechanics behind slow earthquakes, and the period differential motion between the subducting slab and the overlying plate below the seismogenic zone, remain controversial. In Nankai subduction zone, the very-low-frequency earthquakes (VLFE), megathrust earthquakes, long-term slow earthquakes (duration of months or years) and the episodic tremor and slip zone (ETS) are located within the accretionary prism, the continental upper crust, the continental lower crust and the upmost mantle of the overriding plate, respectively. We use the rate-and-state friction law to simulate the periodic occurrence of VLFEs, megathrust earthquakes and the tremors in the ETS zone because of relatively high rock strength within these depth ranges. However, it is not feasible to use frictional instabilities to explain the long-term slow earthquakes in the lower crust where the ductile rock physics plays a significant role in the large-scale deformation. Here, our numerical simulations show that slow earthquakes at the depth of the lower crust may be the results of plastic instabilities in a finite volume of ductile material accompanying by the grain-size evolution. As the thickness of the fault zone increases with depth, deformation becomes distributed and the dynamic equilibrium of grain size, as a competition between thermally activated grain growth and damage-related grain size reduction, results in cycles of strain acceleration and strain deficit. In addition, we took into account the elevated pore pressure in the accretinary prism which is associated with small stress drop and low-frequency content of VLFEs and may contribute to the occurrence of tsunamigenic earthquakes. Hence, in our numerical simulations for the plate boundary system in Nankai, the down-sip segmentation of the subduction dynamic is attributed to the upper plate structure that vary with depth. The high pore pressure, grain-size evolution and alternation of the rock physics may explain the existence and the periodicity of different slow earthquakes from shallow to deep regions in the subduction zone.

Fuel cell plates with skewed process channels for uniform distribution of stack compression load

DOEpatents

Granata, Jr., Samuel J.; Woodle, Boyd M.

1989-01-01

An electrochemical fuel cell includes an anode electrode, a cathode electrode, an electrolyte matrix sandwiched between electrodes, and a pair of plates above and below the electrodes. The plate above the electrodes has a lower surface with a first group of process gas flow channels formed thereon and the plate below the electrodes has an upper surface with a second group of process gas flow channels formed thereon. The channels of each group extend generally parallel to one another. The improvement comprises the process gas flow channels on the lower surface of the plate above the anode electrode and the process gas flow channels on the upper surface of the plate below the cathode electrode being skewed in opposite directions such that contact areas of the surfaces of the plates through the electrodes are formed in crisscross arrangements. Also, the plates have at least one groove in areas of the surfaces thereof where the channels are absent for holding process gas and increasing electrochemical activity of the fuel cell. The groove in each plate surface intersects with the process channels therein. Also, the opposite surfaces of a bipolar plate for a fuel cell contain first and second arrangements of process gas flow channels in the respective surfaces which are skewed the same amount in opposite directions relative to the longitudinal centerline of the plate.

Protein Crystal Growth Apparatus for Microgravity

NASA Technical Reports Server (NTRS)

Carter, Daniel C. (Inventor); Dowling, Timothy E. (Inventor)

1997-01-01

Apparatus for growing protein crystals under microgravity environment includes a plurality of protein growth assemblies stacked one above the other within a canister. Each of the protein growth assemblies includes a tray having a number of spaced apart growth chambers recessed below an upper surface. the growth chambers each having an upstanding pedestal and an annular reservoir about the pedestal for receiving a wick and precipitating agents. A well is recessed below the top of each pedestal to define a protein crystal growth receptacle. A flexible membrane is positioned on the upper surface of each tray and a sealing plate is positioned above each membrane, each sealing plate having a number of bumpers corresponding in number and alignment to the pedestals for forcing the membrane selectively against the upper end of the respective pedestal to seal the reservoir and the receptacle when the sealing plate is forced down.

[Osteosynthesis of Weber B ankle fractures using the one-third tubular plate and refixation of the syndesmosis].

PubMed

Spering, C; Lesche, V; Dresing, K

2015-08-01

Anatomical reconstruction and recovery to complete range of function of the upper ankle joint. Therefore, the most stable but least invasive osteosynthesis is required to enable the patient early functional mobilization. Supination and pronation fracture with luxation mechanism of the upper ankle joint with or without rupture of the syndesmosis. Open fracture of the distal fibula including displaced and instable fractures. Severe peripheral arterial occlusive disease; contaminated open fractures (≥ 2nd degree); pediatric fractures with open epiphyseal plate. Supine position with ipsilateral slightly elevated hip and knee. Incision of about 8 cm length along the dorsal edge of the distal fibula. When reaching the lateral malleolus, a slight ventral angulation is necessary. Open reduction through this posterolateral approach. Secure the reposition using an interfragmentary lag screw and anatomically adjusted third tubular plate. Followed by a revision of the syndesmosis and transfixation using a tricortical position screw. Mobilization on day 1 after surgery with reduced weight-bearing when position screw is not applied; when position screw is implanted with ground contact for 6 weeks. Removal of position screw under local anesthesia after 6 weeks and pain-controlled full weight-bearing. Removal of metal after 1.5 years. Open reduction using the third tubular plate and an interfragmentary lag screw through a dorsolateral approach used in 90 % of all Weber B fractures in our clinic. Additional revision of a ruptured syndesmosis performed in 70 % and transfixation through a position screw in 40 %. Persisting instability in the upper ankle joint significantly reduced after surgical treatment compared to a conservative approach. Revisions necessary in 3.7 % of patients and pseudarthrosis diagnosed in 0.9 %. It has been shown that the preoperative x-ray and clinical examination is limited in detecting a ruptured syndesmosis.

Rheology and strength of the Eurasian continental lithosphere in the foreland of the Taiwan collision belt: Constraints from seismicity, flexure, and structural styles

NASA Astrophysics Data System (ADS)

Mouthereau, FréDéRic; Petit, Carole

2003-11-01

Deformation in western Taiwan is characterized by variable depth-frequency distribution of crustal earthquakes which are closely connected with along-strike variations of tectonic styles (thin or thick skinned) around the Peikang High, a major inherited feature of the Chinese margin. To fit the calculated high crustal geotherm and the observed distribution of the crustal seismic activity, a Qz-diorite and granulite composition for the upper and the lower crust is proposed. We then model the plate flexure, through Te estimates, using brittle-elastic-ductile plate rheology. Flexure modeling shows that the best fit combination of Te-boundary condition is for thrust loads acting at the belt front. The calculated Te vary in the range of ˜15-20 km. These values are primarily a reflection of the thermal state of the rifted Chinese margin inherited from the Oligocene spreading in the South China Sea. However, other mechanical properties such as the degree of crust/mantle coupling and the thickness of the mechanically competent crust and mantle are considered. South of the Peikang High, flexure modeling reveals lower Te associated with thinner mechanically strong layers. Variable stress/strain distribution associated with a higher degree of crust/mantle decoupling is examined to explain plate weakening. We first show that plate curvature cannot easily explain strength reduction and observed seismic activity. Additional plate-boundary forces arising from the strong coupling induced by more frontal subduction of a buoyant crustal asperity, i.e., the Peikang High, with the overriding plate are required. Favorably oriented inherited features in the adjacent Tainan basin produce acceleration of strain rates in the upper crust and hence facilitate the crust/mantle decoupling as attested by high seismic activity and thick-skinned deformation. The relative weakening of the lower crust and mantle then leads to weaken the lithosphere. By contrast, to the north, more oblique collision and the lack of inherited features keep the lithosphere stronger. This study suggests that when the Eurasian plate enters the Taiwan collision, tectonic inheritance of the continental margin exerts a strong control on the plate deformation by modifying its strength.

Shed vortex structure and phase-averaged velocity statistics in symmetric/asymmetric turbulent flat plate wakes

NASA Astrophysics Data System (ADS)

Rai, Man Mohan

2018-05-01

The near wake of a flat plate is investigated via direct numerical simulations. Many earlier experimental investigations have used thin plates with sharp trailing edges and turbulent boundary layers to create the wake. This results in large θ/DTE values (θ is the boundary layer momentum thickness toward the end of the plate and DTE is the trailing edge thickness). In the present study, the emphasis is on relatively thick plates with circular trailing edges (CTEs) resulting in θ/D values less than one (D is the plate thickness and the diameter of the CTE) and vigorous vortex shedding. The Reynolds numbers based on the plate length and D are 1.255 × 106 and 10 000, respectively. Two cases are computed: one with turbulent boundary layers on both the upper and lower surfaces of the plate (statistically the same, symmetric wake, Case TT) and the other with turbulent and laminar boundary layers on the upper and lower surfaces, respectively (asymmetric case, Case TL). The data and understanding obtained are of considerable engineering interest, particularly in turbomachinery where the pressure side of an airfoil can remain laminar or transitional because of a favorable pressure gradient and the suction side is turbulent. Shed-vortex structure and phase-averaged velocity statistics obtained in the two cases are compared here. The upper negative shed vortices in Case TL (turbulent separating boundary layer) are weaker than the lower positive ones (laminar separating boundary layer) at inception (a factor of 1.27 weaker in terms of peak phase-averaged spanwise vorticity at the first appearance of a peak). The upper vortices weaken rapidly as they travel downstream. A second feature of interest in Case TL is a considerable increase in the peak phase-averaged, streamwise normal intensity (random component) with increasing streamwise distance (x/D) that occurs near the positive vortex cores. This behavior is observed for a few diameters in the near wake. This is counter to Case TT where the peak value essentially decreases with increasing x/D. Both these effects are examined in detail, and the important contributors are identified.

Active Tectonics Around Pisagua, Northern Chile Gap: Seismological and Neotectonic Approaches

NASA Astrophysics Data System (ADS)

Comte, D.; Carrizo, D.; Peyrat, S.

2013-12-01

Northern Chile is a recognized mature seismic gap that is reaching the end of its megathrust cycle. Deformation associated with the convergence between the Nazca and the South American Plates is mainly absorbed along the interplate contact, but also partially accommodated along the upper plate. Even though distribution of the active deformation along this plate has been documented mainly in the backarc region, Late Cenozoic structures have been recognized along the forearc suggesting that some part of this deformation is also accommodated along the coastal region. Recent paleoseismological studies suggest that some of these structures are tectonically active and some could be potentially active, capable to generate shallow intraplate earthquakes (Mw˜7). However, seismological and geodetical evidences of the fault activation mechanisms are poorly documented, and the activation process remain not elucidate. Currently, Northern Chile seismic gap is monitored by regional seismic networks and partially studied by temporary local seismological experiments. Results of these studies suggest the presence of shallow seismicity along the forearc, but the relationships between upper plate faults and the seismicity has not been yet explored. We perform a detailed seismotectonic analysis of the subduction-forearc system in the central part of the Northern Chile seismic gap to establish relationships between the plate contact deformation and the upper plate faults. We present preliminary results of data recorded by a dense seismic network (three components continuous recording) deployed around Pisagua, between the coastline and the Central Depression, during several months. Pisagua region was chosen because the forearc faults exhibit an extraordinary well-preserved morphotectonic expression, and the upper part of the seismogenic interplate contact shows abundant continental intraplate seismicity that could be associated with the faults systems. The data recorded in this area allow us to better constrain the 3D geometry of faults related to plate contact using morphotectonis fault signature, well-located shallow seismicity and passive tomography. By this way, the architecture of the major forearc faults in the study area is determined for the first time using geological and geophysical approaches. Through this work, we contribute to better understand the physical relations between dynamics of the plate contact and the coastal fault activation.

Plate Margin Deformation and Active Tectonics Along the Northern Edge of the Yakutat Terrane in the Saint Elias Orogen, Alaska and Yukon, Canada

NASA Technical Reports Server (NTRS)

Bruhn, Ronald L.; Sauber, Jeanne; Cotton, Michele M.; Pavlis, Terry L.; Burgess, Evan; Ruppert, Natalia; Forster, Richard R.

2012-01-01

The northwest directed motion of the Pacific plate is accompanied by migration and collision of the Yakutat terrane into the cusp of southern Alaska. The nature and magnitude of accretion and translation on upper crustal faults and folds is poorly constrained, however, due to pervasive glaciation. In this study we used high-resolution topography, geodetic imaging, seismic, and geologic data to advance understanding of the transition from strike-slip motion on the Fairweather fault to plate margin deformation on the Bagley fault, which cuts through the upper plate of the collisional suture above the subduction megathrust. The Fairweather fault terminates by oblique-extensional splay faulting within a structural syntaxis, allowing rapid tectonic upwelling of rocks driven by thrust faulting and crustal contraction. Plate motion is partly transferred from the Fairweather to the Bagley fault, which extends 125 km farther west as a dextral shear zone that is partly reactivated by reverse faulting. The Bagley fault dips steeply through the upper plate to intersect the subduction megathrust at depth, forming a narrow fault-bounded crustal sliver in the obliquely convergent plate margin. Since . 20 Ma the Bagley fault has accommodated more than 50 km of dextral shearing and several kilometers of reverse motion along its southern flank during terrane accretion. The fault is considered capable of generating earthquakes because it is linked to faults that generated large historic earthquakes, suitably oriented for reactivation in the contemporary stress field, and locally marked by seismicity. The fault may generate earthquakes of Mw <= 7.5.

Architecture of the Distal Piedmont-Ligurian Rifted Margin in NW Italy: Hints for a Flip of the Rift System Polarity

NASA Astrophysics Data System (ADS)

Decarlis, Alessandro; Beltrando, Marco; Manatschal, Gianreto; Ferrando, Simona; Carosi, Rodolfo

2017-11-01

The Alpine Tethys rifted margins were generated by a Mesozoic polyphase magma-poor rifting leading to the opening of the Piedmont-Ligurian "Ocean." This latter developed through different phases of rifting that terminated with the exhumation of subcontinental mantle along an extensional detachment system. At the onset of simple shear detachment faulting, two margin types were generated: an upper and a lower plate corresponding to the hanging wall and footwall of the final detachment system, respectively. The two margin architectures were markedly different and characterized by a specific asymmetry. In this study the detailed analysis of the Adriatic margin, exposed in the Serie dei Laghi, Ivrea-Verbano, and Canavese Zone, enabled to recognize the diagnostic elements of an upper plate rifted margin. This thesis contrasts with the classic interpretation of the Southalpine units, previously compared with the adjacent fossil margin preserved in the Austroalpine nappes and considered as part of a lower plate. The proposed scenario suggests the segmentation and flip of the Alpine rifting system along strike and the passage from a lower to an upper plate. Following this interpretation, the European and Southern Adria margins are coevally developed upper plate margins, respectively resting NE and SW of a major transform zone that accommodates a flip in the polarity of the rift system. This new explanation has important implications for the study of the pre-Alpine rift-related structures, for the comprehension of their role during the reactivation of the margin and for the paleogeographic evolution of the Alpine orogen.

Extensional Failure of "Pre-Stressed" Lithosphere Above a Subduction Zone May Have Contributed to the Size of the Tohoku-Oki Earthquake and Tsunami

NASA Astrophysics Data System (ADS)

Buck, W. R.; Lavier, L. L.; Petersen, K. D.

2015-12-01

The Tohoku-oki earthquake was not only the costliest natural disaster in history it was the best monitored. The unprecedented data set showed that anomalously large lateral motion of the seafloor near the trench contributed to the size of the tsunami. Also, for the first time it was shown that a large subduction earthquake was followed by extensional aftershocks in a broad region of the upper plate (up to 250 km from the Japan Trench). Several observations suggest that the near-trench seafloor motion and the extensional aftershocks are linked. For example, a seismically imaged fault, just landward of the region of large seafloor motion, slipped in a normal sense during the earthquake. Also, inspired by the Tohoku data, researchers have searched for and found upper plate extensional aftershocks associated with several other subduction earthquakes that produced large tsunami. Extension of the upper plate can be driven by a reduction in the dip of a subducting slab. Such a dip change is suggested by the post-Miocene westward migration of the volcanic arc in Honshu. Numerical models show that a long-term reduction in slab dip can generate enough extensional stress to cause normal faulting over a broad region of the upper plate. The time step of the numerical model is then reduced to treat the inter-seismic time scale of 100-1000 years, when the subduction interface is locked. The interface dip continues to be reduced during the inter-seismic period, but extensional fault slip is suppressed by the relative compression of the upper plate caused by continued convergence. The relief of compressional stresses during dynamic weakening of the megathrust triggers a release of bending-related extensional strain energy. This extensional yielding can add significantly to the co-seismic radiated seismic energy and seafloor deformation. This mechanism is analogous to the breaking of a pre-stressed concrete beam supporting a bending moment when the compressional pre-stress is removed. It is plausible that similar bending is occurring at a number of subduction zones. A testable prediction of this bending model is that inter-seismic stresses can be compressional near the surface of the upper plate, but should become extensional at depths accessible to drilling.

Rheological structure of the lithosphere in plate boundary strike-slip fault zones

NASA Astrophysics Data System (ADS)

Chatzaras, Vasileios; Tikoff, Basil; Kruckenberg, Seth C.; Newman, Julie; Titus, Sarah J.; Withers, Anthony C.; Drury, Martyn R.

2016-04-01

How well constrained is the rheological structure of the lithosphere in plate boundary strike-slip fault systems? Further, how do lithospheric layers, with rheologically distinct behaviors, interact within the strike-slip fault zones? To address these questions, we present rheological observations from the mantle sections of two lithospheric-scale, strike-slip fault zones. Xenoliths from ˜40 km depth (970-1100 ° C) beneath the San Andreas fault system (SAF) provide critical constraints on the mechanical stratification of the lithosphere in this continental transform fault. Samples from the Bogota Peninsula shear zone (BPSZ, New Caledonia), which is an exhumed oceanic transform fault, provide insights on lateral variations in mantle strength and viscosity across the fault zone at a depth corresponding to deformation temperatures of ˜900 ° C. Olivine recrystallized grain size piezometry suggests that the shear stress in the SAF upper mantle is 5-9 MPa and in the BPSZ is 4-10 MPa. Thus, the mantle strength in both fault zones is comparable to the crustal strength (˜10 MPa) of seismogenic strike-slip faults in the SAF system. Across the BPSZ, shear stress increases from 4 MPa in the surrounding rocks to 10 MPa in the mylonites, which comprise the core of the shear zone. Further, the BPSZ is characterized by at least one order of magnitude difference in the viscosity between the mylonites (1018 Paṡs) and the surrounding rocks (1019 Paṡs). Mantle viscosity in both the BPSZ mylonites and the SAF (7.0ṡ1018-3.1ṡ1020 Paṡs) is relatively low. To explain our observations from these two strike-slip fault zones, we propose the "lithospheric feedback" model in which the upper crust and lithospheric mantle act together as an integrated system. Mantle flow controls displacement and the upper crust controls the stress magnitude in the system. Our stress data combined with data that are now available for the middle and lower crustal sections of other transcurrent fault systems support the prediction for constant shear strength (˜10 MPa) throughout the lithosphere; the stress magnitude is controlled by the shear strength of the upper crustal faults. Fault rupture in the upper crust induces displacement rate loading of the upper mantle, which in turn, causes strain localization in the mantle shear zone beneath the strike-slip fault. Such forced localization leads to higher stresses and strain rates in the shear zone compared to the surrounding rocks. Low mantle viscosity within the shear zone is critical for facilitating mantle flow, which induces widespread crustal deformation and displacement loading. The lithospheric feedback model suggests that strike-slip fault zones are not mechanically stratified in terms of shear stress, and that it is the time-dependent interaction of the different lithospheric layers - rather than their relative strengths - that governs the rheological behavior of the plate boundary, strike-slip fault zones.

Upper and lower plate controls on the great 2011 Tohoku-oki earthquake

PubMed Central

2018-01-01

The great 2011 Tohoku-oki earthquake [moment magnitude (Mw) 9.0)] is the best-documented megathrust earthquake in the world, but its causal mechanism is still in controversy because of the poor state of knowledge on the nature of the megathrust zone. We constrain the structure of the Tohoku forearc using seismic tomography, residual topography, and gravity data, which reveal a close relationship between structural heterogeneities in and around the megathrust zone and rupture processes of the 2011 Tohoku-oki earthquake. Its mainshock nucleated in an area with high seismic velocity, low seismic attenuation, and strong seismic coupling, probably indicating a large asperity (or a cluster of asperities) in the megathrust zone. Strong coseismic high-frequency radiations also occurred in high-velocity patches, whereas large afterslips took plate in low-velocity areas, differences that may reflect changes in fault friction and lithological variations. These structural heterogeneities in and around the Tohoku megathrust originate from both the overriding and subducting plates, which controlled the nucleation and rupture processes of the 2011 Tohoku-oki earthquake.

Axially Tapered And Bilayer Microchannels For Evaporative Cooling Devices

DOEpatents

Nilson, Robert; Griffiths, Stewart

2005-10-04

The invention consists of an evaporative cooling device comprising one or more microchannels whose cross section is axially reduced to control the maximum capillary pressure differential between liquid and vapor phases. In one embodiment, the evaporation channels have a rectangular cross section that is reduced in width along a flow path. In another embodiment, channels of fixed width are patterned with an array of microfabricated post-like features such that the feature size and spacing are gradually reduced along the flow path. Other embodiments incorporate bilayer channels consisting of an upper cover plate having a pattern of slots or holes of axially decreasing size and a lower fluid flow layer having channel widths substantially greater than the characteristic microscale dimensions of the patterned cover plate. The small dimensions of the cover plate holes afford large capillary pressure differentials while the larger dimensions of the lower region reduce viscous flow resistance.

Neogene Rift Propagation of the East African Rift System (EARS) into Central Africa and its Implications: Tectonic, Topographic and Geomorphic Impacts of the Luangwa and Luapula Rift Valleys on the Upper Congo Drainage Basin, Lake Bangweulu Wetlands and the Development of the Diffuse Southwestern Tip of the EARS.

NASA Astrophysics Data System (ADS)

Daly, M. C.; Watts, A. B.

2017-12-01

Integration of geomorphology, seismic reflection and gravity data, seismicity, DEM analysis and modelling defines a zone of NE/SW trending rifts extending into Central and SW Africa, orthogonal to the conventionally defined East African Rift System (EARS). These large-scale tectonic features have a relatively low level of seismicity and volcanism compared to the EARS, yet they generate significant topography and control the upper Congo drainage basin. They may also represent the beginning of an active but diffuse plate boundary developing to the southwest across Central Africa. The dominant feature of this broad zone is the Luangwa Rift Valley of eastern Zambia. Seismic reflection data show the Luangwa Rift developed as a thick ( 5km) Permo-Triassic basin. Inverted in the Mesozoic, it then experienced major Neogene extensional reactivation. The latter resulted in today's major border faults of varying polarity, with fault plane escarpments of up to 1000m, and associated rift flank uplifts that elevate the Central African plateau surface by 200 m. Late Miocene alluvial fans indicate a minimum age for the initiation of reactivation. Although having similar structural features to the EARS, the Luangwa Rift has a lower level of active seismicity and volcanism. 400 km northwest of the Luangwa, the north/south Luapula rift valley passes into the NE trending Mweru and Mweru Wantipa rift lakes. Pronounced border faults and fault terraces mark the NW and SE margins of these shallow lakes. Between the Luangwa and Luapula rift valleys lies the extensive upper Congo drainage basin of the Chambeshi river and the Lake Bangweulu wetlands. DEM mapping of topography from the Luangwa rift to the Luapula-Mweru Wantipa rift shows a low amplitude, large wavelength flexure of the Central African plateau surface compatible with an effective elastic thickness of 35 km. This regional warping controls the location and shape of the Chambeshi drainage basin and the Lake Bangweulu Wetlands. These results show Neogene rift valleys are active to the southwest of the EARS and are controlling the present-day continental drainage system of Central Africa. They also define a diffuse, divergent plate boundary between the Nubian Plate and an ill-defined southern African Plate that appears to exploit a zone of crustal anisotropy and thinner lithosphere.

Manual braille writer

DOEpatents

Hawk, L.S.; Turner, J.H.

1992-07-28

A manual-type braille writer is described that provides for both writing and reading in a normal left-to-right manner. In the preferred form, this braille writer has a clip board type base, and in the preferred embodiment a guide plate assembly can be moved to, and releasable fixed at, selected vertical locations along this base. The guide plate assembly is provided with a plurality of character cells uniformly spaced along rows across the guide plate assembly as well as in uniformly spaced rows. This guide plate assembly has a lower portion to be placed under a sheet of paper positioned on the clip board base and an upper portion to be positioned on top of the sheet. This upper portion is hinged with respect to the lower portion. Each character cell is typically made up of six appropriately spaced pins extending up from the lower portion that are aligned with a rosette-shaped cutout in the upper portion. A stylus member is provided that has a distal end to be fitted into the cutout of the character cell so that a recess in the end thereof presses the writing paper over the pin associated with that recess to produce a braille dot at that location. When desired, the upper portion can be lifted up so that the text already written can be read or to determine the place for initiating writing when writing has been interrupted. 10 figs.

Manual braille writer

DOEpatents

Hawk, Lawrence S.; Turner, Joe H.

1992-01-01

A manual-type braille writer that provides for both writing and reading in a normal left-to-right manner. In the preferred form, this braille writer has a clip board type base, and in the preferred embodiment a guide plate assembly can be moved to, and releasable fixed at, selected vertical locations along this base. The guide plate assembly is provided with a plurality of character cells uniformly spaced along rows across the guide plate assembly as well as in uniformly spaced rows. This guide plate assembly has a lower portion to be placed under a sheet of paper positioned on the clip board base and an upper portion to be positioned on top of the sheet. This upper portion is hinged with respect to the lower portion. Each character cell is typically made up of six appropriately spaced pins extending up from the lower portion that are aligned with a rosette-shaped cutout in the upper portion. A stylus member is provided that has a distal end to be fitted into the cutout of the character cell so that a recess in the end thereof presses the writing paper over the pin associated with that recess to produce a braille dot at that location. When desired, the upper portion can be lifted up so that the text already written can be read or to determine the place for initiating writing when writing has been interrupted.

Evolutionary aspects of the development of teeth and baleen in the bowhead whale.

PubMed

Thewissen, J G M; Hieronymus, Tobin L; George, John C; Suydam, Robert; Stimmelmayr, Raphaela; McBurney, Denise

2017-04-01

In utero, baleen whales initiate the development of several dozens of teeth in upper and lower jaws. These tooth germs reach the bell stage and are sometimes mineralized, but toward the end of prenatal life they are resorbed and no trace remains after birth. Around the time that the germs disappear, the keratinous baleen plates start to form in the upper jaw, and these form the food-collecting mechanism. Baleen whale ancestors had two generations of teeth and never developed baleen, and the prenatal teeth of modern fetuses are usually interpreted as an evolutionary leftover. We investigated the development of teeth and baleen in bowhead whale fetuses using histological and immunohistochemical evidence. We found that upper and lower dentition initially follow similar developmental pathways. As development proceeds, upper and lower tooth germs diverge developmentally. Lower tooth germs differ along the length of the jaw, reminiscent of a heterodont dentition of cetacean ancestors, and lingual processes of the dental lamina represent initiation of tooth bud formation of replacement teeth. Upper tooth germs remain homodont and there is no evidence of a secondary dentition. After these germs disappear, the oral epithelium thickens to form the baleen plates, and the protein FGF-4 displays a signaling pattern reminiscent of baleen plates. In laboratory mammals, FGF-4 is not involved in the formation of hair or palatal rugae, but it is involved in tooth development. This leads us to propose that the signaling cascade that forms teeth in most mammals has been exapted to be involved in baleen plate ontogeny in mysticetes. © 2017 Anatomical Society.

Initial Experience of US Marine Corps Forward Resuscitative Surgical System during Operation Iraqi Freedom

DTIC Science & Technology

2005-01-01

lavage, and splinting. Exter- nal fixation was used when there was concurrent vascular pro- cedures or if fractures were extremely unstable...foot open fracture Completion lower extremity amputation; completion right upper amputation; external fixation right ankle 8/Iraqi child Class 3 shock...infection Comminuted mandible fracture with loss of airway (casualty 1 in Table 2) Airway control Infection of mandibular plate at echelon 5 facility

Tectonic Structure of the Middle America Pacific Margin and Incoming Cocos Plate From Costa Rica to Guatemala

NASA Astrophysics Data System (ADS)

Ranero, C. R.; Weinrebe, W.; Grevemeyer, I.; Phipps Morgan, J.; Vannucchi, P.; von Huene, R.

2003-12-01

A new multibeam bathymetry and magnetic survey with R/V SONNE in summer 2003 has mapped the continental margin and incoming plate of NW Nicaragua, El Salvador and Guatemala, extending existing coverage from offshore Costa Rica and part of Nicaragua to a full coverage map of about 1200 km long by 100 km wide area along the plate boundary. The incoming plate along Nicaragua, El Salvador and Guatemala is of similar age and was formed at superfast spreading rates; however, its morphology changes drastically along strike. The seafloor-spreading inherited morphology is very smooth along Nicaragua, but with ridges up to 800 m high in Guatemala, with a transition across El Salvador. The development and dimensions of the dominant inherited fabric seems to be related to discontinuities at the paleospreading center. A series of troughs oblique to the main fabric may indicate the location of pseudofaults and correspond to areas where the seafloor fabric is most prominent. Bending of the oceanic plate into the trench reactivates the inherited fabric forming a well pervasive faulting system along the oceanic trench slope. The continental slope displays three morphotectonic units that roughly correspond to the upper, middle and lower slope, although the across slope width of each unit is fairly variable. Small canyons and gullies that form at the sudden dip change across the shelf break carve the upper slope. The canyons coalesce and become shallower as the dip decreases downslope. Locally some large canyons continue into the slope toe. The middle slope is a rough terrain variable in width and dip sculptured by pervasive normal faulting and locally by mass wasting processes. The lower slope is formed by en echelon terraces striking similar to the rough terrain of the incoming plate and mimicking the half graben morphology of the underthusting plate. The three morphotectonic slope domains represent differences in tectonic activity, with more stable upper slope, a middle slope dominated by tectonic extension and the thin, highly fractured upper plate of the lower slope riffling over the incoming plate topography. The trench axis is largely empty, with local turbidite ponds at the mouth of a few large canyons transecting the entire slope.

Thermal and mechanical structure of the upper mantle: A comparison between continental and oceanic models

NASA Technical Reports Server (NTRS)

Froidevaux, C.; Schubert, G.; Yuen, D. A.

1976-01-01

Temperature, velocity, and viscosity profiles for coupled thermal and mechanical models of the upper mantle beneath continental shields and old ocean basins show that under the continents, both tectonic plates and the asthenosphere, are thicker than they are beneath the oceans. The minimum value of viscosity in the continental asthenosphere is about an order of magnitude larger than in the shear zone beneath oceans. The shear stress or drag underneath continental plates is also approximately an order of magnitude larger than the drag on oceanic plates. Effects of shear heating may account for flattening of ocean floor topography and heat flux in old ocean basins.

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.

Dynamic topography in subduction zones: insights from laboratory models

NASA Astrophysics Data System (ADS)

Bajolet, Flora; Faccenna, Claudio; Funiciello, Francesca

2014-05-01

The topography in subduction zones can exhibit very complex patterns due to the variety of forces operating this setting. If we can deduce the theoretical isostatic value from density structure of the lithosphere, the effect of flexural bending and the dynamic component of topography are difficult to quantify. In this work, we attempt to measure and analyze the topography of the overriding plate during subduction compared to a pure shortening setting. We use analog models where the lithospheres are modeled by thin-sheet layers of silicone putty lying on low-viscosity syrup (asthenosphere). The model is shorten by a piston pushing an oceanic plate while a continental plate including a weak zone to localize the deformation is fixed. In one type of experiments, the oceanic plate bends and subducts underneath the continental one; in a second type the two plates are in contact without any trench, and thus simply shorten. The topography evolution is monitored with a laser-scanner. In the shortening model, the elevation increases progressively, especially in the weak zone, and is consistent with expected isostatic values. In the subduction model, the topography is characterized, from the piston to the back-wall, by a low elevation of the dense oceanic plate, a flexural bulge, the trench forming a deep depression, the highly elevated weak zone, and the continental upper plate of intermediate elevation. The topography of the upper plate is consistent with isostatic values for very early stages, but exhibits lower elevations than expected for later stages. For a same amount of shortening of the continental plate, the thickening is the same and the plate should have the same elevation in both types of models. However, comparing the topography at 20, 29 and 39% of shortening, we found that the weak zone is 0.4 to 0.6 mm lower when there is an active subduction. Theses values correspond to 2.6 to 4 km in nature. Although theses values are high, there are of the same order as dynamic topography and could represent the dynamic effect of the slab sinking into the asthenosphere and lowering the elevation of the upper plate.

Mechanical decoupling along a subduction boundary fault: the case of the Tindari-Alfeo Fault System, Calabrian Arc (central Mediterranean Sea)

NASA Astrophysics Data System (ADS)

Maesano, F. E.; Tiberti, M. M.; Basili, R.

2017-12-01

In recent years an increasing number of studies have been focused in understanding the lateral terminations of subduction zones. In the Mediterranean region, this topic is of particular interest for the presence of a "land-locked" system of subduction zones interrupted by continental collision and back-arc opening. We present a 3D reconstruction of the area surrounding the Tindari-Alfeo Fault System (TAFS) based on a dense set of deep seismic reflection profiles. This fault system represents a major NNW-SSE trending subduction-transform edge propagator (STEP) that controls the deformation zone bounding the Calabrian subduction zone (central Mediterranean Sea) to the southwest. This 3D model allowed us to characterize the mechanical and kinematic evolution of the TAFS during the Plio-Quaternary. Our study highlights the presence of a mechanical decoupling between the deformation observed in the lower plate, constituted by the Ionian oceanic crust entering the subduction zone, and the upper plate, where a thick accretionary wedge has formed. The lower plate hosts the master faults of the TAFS, whereas the upper plate is affected by secondary deformation (bending-moment faulting, localized subsidence, stepovers, and restraining/releasing bends). The analysis of the syn-tectonic sedimentary basins related to the activity of the TAFS at depth allow us to constrain the propagation rate of the deformation and of the vertical component of the slip-rate. Our findings provide a comprehensive framework of the structural setting that can be expected along a STEP boundary where contractional and transtensional features coexist at close distance from one another.

F-16XL Wing Pressure Distributions and Shock Fence Results from Mach 1.4 to Mach 2.0

NASA Technical Reports Server (NTRS)

Landers, Stephen F.; Saltzman, John A.; Bjarke, Lisa J.

1997-01-01

Chordwise pressure distributions were obtained in-flight on the upper and lower surfaces of the F-16XL ship 2 aircraft wing between Mach 1.4 and Mach 2.0. This experiment was conducted to determine the location of shock waves which could compromise or invalidate a follow-on test of a large chord laminar flow control suction panel. On the upper surface, the canopy closure shock crossed an area which would be covered by a proposed laminar flow suction panel. At the laminar flow experiment design Mach number of 1.9, 91 percent of the suction panel area would be forward of the shock. At Mach 1.4, that value reduces to 65 percent. On the lower surface, a shock from the inlet diverter would impinge on the proposed suction panel leading edge. A chordwise plate mounted vertically to deflect shock waves, called a shock fence, was installed between the inlet diverter and the leading edge. This plate was effective in reducing the pressure gradients caused by the inlet shock system.

Lateral traction of laminar flow between sliding pair with heterogeneous slip/no-slip surface

NASA Astrophysics Data System (ADS)

Wu, Zhenpeng; Zeng, Liangcai; Chen, Xiaolan; Chen, Keying; Ding, Xianzhong

2017-11-01

The problem of shaft axial motion which significantly affects the lubrication performance has been a common phenomenon in journal bearing systems. The existing work involved in the solution of shaft axial motion is also very rare. In this study, we choose to examine the flow between sliding pair in which regard we present a unique heterogeneous surface consisting of a slip zone and a no-slip zone. The results reveal the following points: 1) By appropriately arranging the slip zone to change the angle between the borderline and the moving direction of the upper plate, it is possible to control the direction of the lateral traction in which the liquid film acts on the upper plate. 2) Exponent of the power function of the borderline and aspect ratio of the computational domain are large or small are not conducive to increasing the effect of lateral traction. For the object of this study, the final results of the optimization are shown that the lateral traction can account for 20% of the resistance.

Multiple sources for late-Holocene tsunamis at Discovery Bay, Washington State, USA

USGS Publications Warehouse

Williams, H.F.L.; Hutchinson, I.; Nelson, A.R.

2005-01-01

Nine muddy sand beds interrupt a 2500-yr-old sequence of peat deposits beneath a tidal marsh at the head of Discovery Bay on the south shore of the Strait of Juan de Fuca, Washington. An inferred tsunami origin for the sand beds is assessed by means of six criteria. Although all the sand beds contain marine diatoms and almost all the beds display internal stratification, the areal extent of the oldest beds is too limited to confirm their origin as tsunami deposits. The ages of four beds overlap with known late-Holocene tsunamis generated by plate-boundary earthquakes at the Cascadia subduction zone. Diatom assemblages in peat deposits bracketing these four beds do not indicate concurrent change in elevation at Discovery Bay. Diatoms in the peat bracketing a tsunami bed deposited about 1000 cal. yr BP indicate a few decimeters of submergence, suggesting deformation on a nearby upper-plate fault. Other beds may mark tsunamis caused by more distant upper-plate earthquakes or local submarine landslides triggered by earthquake shaking. Tsunamis from both subduction zone and upper-plate sources pose a significant hazard to shoreline areas in this region.

The fate of water within Earth and super-Earths and implications for plate tectonics

PubMed Central

2017-01-01

The Earth is likely to have acquired most of its water during accretion. Internal heat of planetesimals by short-lived radioisotopes would have caused some water loss, but impacts into planetesimals were insufficiently energetic to produce further drying. Water is thought to be critical for the development of plate tectonics, because it lowers viscosities in the asthenosphere, enabling subduction. The following issue persists: if water is necessary for plate tectonics, but subduction itself hydrates the upper mantle, how is the upper mantle initially hydrated? The giant impacts of late accretion created magma lakes and oceans, which degassed during solidification to produce a heavy atmosphere. However, some water would have remained in the mantle, trapped within crystallographic defects in nominally anhydrous minerals. In this paper, we present models demonstrating that processes associated with magma ocean solidification and overturn may segregate sufficient quantities of water within the upper mantle to induce partial melting and produce a damp asthenosphere, thereby facilitating plate tectonics and, in turn, the habitability of Earth-like extrasolar planets. This article is part of the themed issue ‘The origin, history and role of water in the evolution of the inner Solar System’. PMID:28416729

The fate of water within Earth and super-Earths and implications for plate tectonics.

PubMed

Tikoo, Sonia M; Elkins-Tanton, Linda T

2017-05-28

The Earth is likely to have acquired most of its water during accretion. Internal heat of planetesimals by short-lived radioisotopes would have caused some water loss, but impacts into planetesimals were insufficiently energetic to produce further drying. Water is thought to be critical for the development of plate tectonics, because it lowers viscosities in the asthenosphere, enabling subduction. The following issue persists: if water is necessary for plate tectonics, but subduction itself hydrates the upper mantle, how is the upper mantle initially hydrated? The giant impacts of late accretion created magma lakes and oceans, which degassed during solidification to produce a heavy atmosphere. However, some water would have remained in the mantle, trapped within crystallographic defects in nominally anhydrous minerals. In this paper, we present models demonstrating that processes associated with magma ocean solidification and overturn may segregate sufficient quantities of water within the upper mantle to induce partial melting and produce a damp asthenosphere, thereby facilitating plate tectonics and, in turn, the habitability of Earth-like extrasolar planets.This article is part of the themed issue 'The origin, history and role of water in the evolution of the inner Solar System'. © 2017 The Authors.

Magma-assisted rifting in Ethiopia.

PubMed

Kendall, J-M; Stuart, G W; Ebinger, C J; Bastow, I D; Keir, D

2005-01-13

The rifting of continents and evolution of ocean basins is a fundamental component of plate tectonics, yet the process of continental break-up remains controversial. Plate driving forces have been estimated to be as much as an order of magnitude smaller than those required to rupture thick continental lithosphere. However, Buck has proposed that lithospheric heating by mantle upwelling and related magma production could promote lithospheric rupture at much lower stresses. Such models of mechanical versus magma-assisted extension can be tested, because they predict different temporal and spatial patterns of crustal and upper-mantle structure. Changes in plate deformation produce strain-enhanced crystal alignment and increased melt production within the upper mantle, both of which can cause seismic anisotropy. The Northern Ethiopian Rift is an ideal place to test break-up models because it formed in cratonic lithosphere with minor far-field plate stresses. Here we present evidence of seismic anisotropy in the upper mantle of this rift zone using observations of shear-wave splitting. Our observations, together with recent geological data, indicate a strong component of melt-induced anisotropy with only minor crustal stretching, supporting the magma-assisted rifting model in this area of initially cold, thick continental lithosphere.

The northern Lesser Antilles oblique subduction zone: new insight about the upper plate deformation, 3D slab geometry and interplate coupling.

NASA Astrophysics Data System (ADS)

Marcaillou, B.; Laurencin, M.; Graindorge, D.; Klingelhoefer, F.

2017-12-01

In subduction zones, the 3D geometry of the plate interface is thought to be a key parameter for the control of margin tectonic deformation, interplate coupling and seismogenic behavior. In the northern Caribbean subduction, precisely between the Virgin Islands and northern Lesser Antilles, these subjects remain controversial or unresolved. During the ANTITHESIS cruises (2013-2016), we recorded wide-angle seismic, multichannel reflection seismic and bathymetric data along this zone in order to constrain the nature and the geometry of the subducting and upper plate. This experiment results in the following conclusions: 1) The Anegada Passage is a 450-km long structure accross the forearc related to the extension due to the collision with the Bahamas platform. 2) More recently, the tectonic partitioning due to the plate convergence obliquity re-activated the Anegada Passage in the left-lateral strike-slip system. The partitioning also generated the left-lateral strike-slip Bunce Fault, separating the accretionary prism from the forearc. 3) Offshore of the Virgin Islands margin, the subducting plate shows normal faults parallel to the ancient spreading center that correspond to the primary fabric of the oceanic crust. In contrast, offshore of Barbuda Island, the oceanic crust fabric is unresolved (fracture zone?, exhumed mantle? ). 4) In the direction of the plate convergence vector, the slab deepening angle decreases northward. It results in a shallower slab beneath the Virgin Islands Platform compared to the St Martin-Barbuda forearc. In the past, the collision of the Bahamas platform likely changed the geodynamic settings of the northeastern corner of the Caribbean subduction zone and we present a revised geodynamic history of the region. Currently, various features are likely to control the 3D geometry of the slab: the margin convexity, the convergence obliquity, the heterogeneity of the primary fabric of the oceanic crust and the Bahamas docking. We suggest that the slab deepening angle lower beneath the Virgin Islands segment than beneath the St Martin-Barbuda segment possibly generates a northward increasing interplate coupling. As a result, it possibly favors an increase in the seismic activity and the tectonic partitioning beneath the Virgin Islands margin contrary to the St Martin-Barbuda segment.

A voice coil actuator driven active vibration isolation system with the consideration of flexible modes.

PubMed

Park, Kyihwan; Choi, Dongyoub; Ozer, Abdullah; Kim, Sangyoo; Lee, Yongkwan; Joo, Dongik

2008-06-01

We develop a four-mount active vibration isolation system (AVIS) using voice coil actuators. The flexible body modes in the upper plate of the AVIS can cause an instability problem due to control signal whose frequency is close to the resonant frequency of the flexible modes. The loop shaping technique is applied to reduce the amplitude of the control signal. We investigate the performances of the active vibration isolation system proposed in the word in the time domain and frequency domain by comparing to the passive isolation system.

Geologic map of the Hogback Mountain quadrangle, Lewis and Clark and Meagher Counties, Montana

USGS Publications Warehouse

Reynolds, Mitchell W.

2003-01-01

The geologic map of the Hogback Mountain quadrangle, scale 1:24,000, was made as part of the Montana Investigations Project to provide new information on the stratigraphy, structure, and geologic history of an area in the geologically complex southern part of the Montana disturbed belt. In the Hogback Mountain area, rocks ranging in age from Middle Proterozoic through Cretaceous are strongly folded within and under thrust plates of equivalent rocks. Continental rocks of successive thrust plates have been telescoped eastward over a buttress of the stable continent. Erosional remnants of Oligocene andesitic basalt lie on highest surfaces eroded across the strongly deformed older rocks; younger erosion has dissected the terrain deeply, producing Late Tertiary and Quaternary deposits of alluvium, colluvium, and local landslide debris in the valleys and canyons. Different stratigraphic successions are exposed at different structural levels across the quadrangle. In the northeastern part of the quadrangle at the lowest structural level, rocks of the Upper Mississippian Big Snowy Group, including the Kibbey Formation and the undivided Otter and Heath Formations, the overlying Pennsylvanian Amsden and undivided Quadrant and Phosphoria Formations, the Ellis Group, and the Kootenai Formation, are folded and broken by thrust faults. The next higher structural level, the Avalanche Butte thrust plate, exposes strongly folded and, in places, attenuated strata of Cambrian (Flathead Sandstone, Wolsey Shale, Meagher Limestone, and undivided Pilgrim Formation and Park Shale), Devonian (Maywood Formation, Jefferson Formation, and most of the Three Forks Formation), and Mississippian (uppermost part of the Three Forks Formation and Lodgepole and Mission Canyon Limestones) ages. The overlying Hogback Mountain thrust plate contains strongly folded rocks ranging in age from the Middle Proterozoic Greyson Formation to the Upper and Lower Mississippian Mission Canyon Limestone and Cretaceous diorite sills. The highest structural level, the Moors Mountain thrust plate, contains the Middle Proterozoic Greyson and Newland Formations and discontinuous Upper Proterozoic diabase sills. Rocks are complexly folded and faulted across the quadrangle. At the lowest level in the northeastern part of the quadrangle, Upper Mississippian and younger strata are folded along northwest-trending axes and broken by thrust faults that at outcrop level displace the same rocks. The central core of the quadrangle is formed by the Avalanche Butte thrust plate, which contains recumbently folded and thrust faulted Paleozoic rocks. A succession of four tight recumbent folds within the plate have axial traces that trend northwest and north-northwest, and that are both arched and downfolded along east- and northeast-trending axes. Carbonate rocks of the Mission Canyon and Lodgepole Limestones in the upper part of the Avalanche Butte thrust plate exposed in the canyon of Trout Creek are folded and attenuated in stacked east-directed recumbent folds that developed as a succession of folded duplex thrust slices. The exposed remnant of the next higher structural level, the Hogback Mountain thrust plate, contains northeast- and east-trending folds that are inverted on the upper overturned limb of a younger northwest-trending recumbent fold. The Hogback Mountain thrust fault is itself folded and, in its northernmost exposures, is overturned to dip west beneath the overlying Moors Mountain thrust plate. During post-middle Tertiary deformation, the Hogback Mountain thrust fault moved as a normal fault, down on the east. The structurally highest Moors Mountain thrust plate rests on the Avalanche Butte thrust plate in the southwestern part of the quadrangle and across both the Avalanche Butte and Hogback Mountain thrust plates along the northwest edge of the quadrangle. In the central eastern part of the map area, the edge of a large klippen of the Moors Mounta

Structural controls on the hydrogeology of the Costa Rica subduction thrust NW of the Osa Peninisula (Invited)

NASA Astrophysics Data System (ADS)

Bangs, N. L.; McIntosh, K. D.; Silver, E. A.; Kluesner, J.; Ranero, C. R.

2013-12-01

Three-dimensional seismic reflection data from the Costa Rica margin NW of the Osa peninsula have enabled us to map the subduction megathrust from the trench to ~12 km subseafloor beneath the shelf. The subduction thrust has a large, abrupt downdip transition in seismic reflection amplitude from very high to low amplitude 6 km subseafloor beneath the upper slope. This transition broadly corresponds with an increase in concentration of microseismic earthquakes potentially due to a significant increase in plate coupling (Bangs et al., 2012, AGU Fall Meeting, T13A-2587), thus linking seismic reflection amplitude to fluid content and mechanical coupling along the fault. A detailed look at the overriding plate reflectivity shows numerous high-amplitude, continuous seismic reflections through the upper plate, many of which are clearly reversed-polarity from the seafloor reflection and are thus likely active fluid conduits through the overriding margin wedge, the slope cover sediment, and the seafloor. Broadly, the structural grain of the margin wedge trends E-W and dips landward across the lower slope and onto the shelf, presumably due to stress imparted by subducting ridges. However, directly above the abrupt high-to-low plate-boundary reflection amplitude transition, structures within the overlying margin wedge reverse dip, steepen, and change strike to an ESE direction. Within this zone we interpret a set of parallel reflections with small offsets and reverse-polarity as high-angle reverse faults that act as fluid conduits leading directly into shallow fluid migration systems described by Bangs et al., 2012 (AGU Fall Meeting, T13A-2587) and Kluesner et al. [this meeting]. The coincidence between the plate-boundary reflection amplitude patterns and the change in structure implies that the fluid migration pathways that drain the plate interface are locally disrupted by overriding plate structure in two possible ways: 1) by focusing up dip fluid migration along the plate interface into a thinner but richer fluid zone along the subduction thrust, or 2) by creating a more direct, nearly vertical route along high-angle reverse faults through the overlying margin wedge to the seafloor (possibly shortened by a factor of two) and draining deeper portions of the plate-boundary more efficiently.

Mapping the influence of the deep Nazca slab on the geometry of the 660-km discontinuity beneath stable South America

NASA Astrophysics Data System (ADS)

Bianchi, M. B. D.; Assumpcao, M.; Julià, J.

2017-12-01

The fate of the deep Nazca subducted plate is poorly mapped under stable South America. Transition zone thickness and position is greatly dependent on mantle temperature and so is influenced by the colder Nazca plate position. We use a database of 35,000 LQT deconvolved receiver function traces to image the mantle transition zone and other upper mantle discontinuities under different terranes of stable South American continent. Data from the entire Brazilian Seismographic Network database, consisting of more than 80 broadband stations supplemented by 35 temporary stations deployed in west Brazil, Argentina, Paraguay, Bolivia and Uruguay were processed. Our results indicates that upper mantle velocities are faster than average under stable cratons and that most of the discontinuities are positioned with small variations in respect to nominal depths, except in places were the Nazca plate interacts with the transition zone. Under the Chaco-Pantanal basin the Nazca plate appears to be trapped in the transition zone for more than 1000 km with variations of up to 30 km in 660 km discontinuity topography under this region consistent with global tomographic models. Additional results obtained from SS precursor analysis of South Sandwich Islands teleseismic events recorded at USArray stations indicates that variations of transition zones thickness occur where the Nazca plate interacts with the upper mantle discontinuities in the northern part of Stable South American continent.

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.

Discussion Starter: The Case for Duplexing without Channel Flow During the Development and Emplacement of the Himalayan Middle Crust

NASA Astrophysics Data System (ADS)

Webb, A. G.; He, D.; Yu, H.

2015-12-01

This presentation and another presentation led by Dawn Kellett will preface a ten-minute open discussion on how the Himalayan middle crust was developed and emplaced. Current hypotheses are transitioning from a set including wedge extrusion, channel flow with focused denudation, and tectonic wedging to a revised dichotomy: models with intense upper plate out-of-sequence activity (i.e., tunneling of channel flow, and critical taper wedge behavior) versus models in which the upper plate mainly records basal accretion of horses (i.e., duplexing). Critical taper and duplexing offer a simple contrast that can be illustrated via food analogies. If a wedge is critical, it churns internally like a pile of CheeriosTM cereal pushed up an inclined plane. Stacking of a duplex acts like a deli meat-slicing machine: slice after slice is cut from the intact block to a stack of slices, but neither the block (~down-going plate) nor the stack (~upper plate) features much internal deformation. Thus critical taper and channel tunneling models predict much processing via out-of-sequence deformation, whereas duplexing predicts in-sequence thrusting. The two concepts may be considered end-members. Recent work shows that the Himalayan middle crust has been assembled along a series of mainly southwards-younging thrust faults. The thrust faults separate 1-5 km thick panels that experienced similar metamorphic cycles during different time periods. Out-of-sequence deformation is rare, with its apparent significance enhanced because of the high throw-to-heave ratio of out-of-sequence thrusting. Flattening fabrics developed prior to thrusting have been interpreted to record either (1) southwards channel tunneling across the upper plate, or (2) fabric development during metamorphism of the down-going plate. We will argue that the thrust faults dominantly represent in-sequence duplexing, and therefore conclude that the Himalaya and analogous hot orogens behave like other accretionary orogens.

Crustal and uppermost mantle structure and deformation in east-central China

NASA Astrophysics Data System (ADS)

Li, H.; Yang, X.; Ouyang, L.; Li, J.

2017-12-01

We conduct a non-linear joint inversion of receiver functions and Rayleigh wave dispersions to obtain the crustal and upper mantle velocity structure in east-central China. In the meanwhile, the lithosphere and upper mantle deformation beneath east-central China is also evaluated with teleseismic shear wave splitting measurements. The resulting velocity model reveals that to the east of the North-South Gravity Lineament, the crust and the lithosphere are significantly thinned. Furthermore, three extensive crustal/lithospheric thinning sub-regions are clearly identified within the study area. This indicates that the modification of the crust and lithosphere in central-eastern China is non-uniform due to the heterogeneity of the lithospheric strength. Extensive crustal and lithospheric thinning could occur in some weak zones such as the basin-range junction belts and large faults. The structure beneath the Dabie orogenic belt is complex due to the collision between the North and South China Blocks during the Late Paleozoic-Triassic. The Dabie orogenic belt is generally delineated by a thick crust with a mid-crust low-velocity zone and a two-directional convergence in the lithospheric scale. Obvious velocity contrast exhibits in the crust and upper mantle at both sides of the Tanlu fault, which suggests the deep penetration of this lithospheric-scale fault. Most of our splitting measurements show nearly E-W trending fast polarization direction which is slightly deviating from the direction of plate motion. The similar present-day lithosphere structure and upper mantle deformation may imply that the eastern NCC and the eastern SCB were dominated by a common dynamic process after late Mesozoic, i.e., the westward subduction of Pacific plate and the retreat of the subduction plate. The westward subduction of the Philippine plate and the long-range effects of the collision between the Indian plate and Eurasia plate during Cenozoic may have also contributed to the present velocity structure and stress environment of eastern China.

Physiologically Relevant Prosthetic Limb Movement Feedback for Upper and Lower Extremity Amputees

DTIC Science & Technology

2016-10-01

upper arm (elbow movement), Upper leg (knee movement) and lower leg ( ankle movement) to provide a physiologically relevant sense of limb movement...Additionally a BOA cable tensioning system is passed through these plates and anchored to the external surface of the socket. When tension is applied the

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.

6. BUILDER'S PLATE ON WEST TRUSS: 'MOSELEY IRON BUILDING WORKS, ...

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

6. BUILDER'S PLATE ON WEST TRUSS: 'MOSELEY IRON BUILDING WORKS, BOSTON 1888, PATENTED 1881 TO T.W.E. MOSELEY' - Upper Pacific Mills Bridge, Moved to Merrimack College, North Andover, MA, Lawrence, Essex County, MA

Crustal structure and tectonic deformation of the southern Ecuadorian margin

NASA Astrophysics Data System (ADS)

Calahorrano, Alcinoe; Collot, Jean-Yves; Sage, Françoise; Ranero, César R.

2010-05-01

Multichannel seismic lines acquired during the SISTEUR cruise (2000) provide new constraints on the structure and deformation of the subduction zone at the southern Ecuadorian margin, from the deformation front to the continental shelf of the Gulf of Guayaquil. The pre-stack depth migrated images allows to characterise the main structures of the downgoing and overriding plates and to map the margin stratigraphy in order to propose a chronology of the deformation, by means of integrating commercial well data and industry seismic lines located in the gulf area. The 100-km-long seismic lines show the oceanic Nazca plate underthrusting the South American plate, as well as the subduction channel and inter-plate contact from the deformation front to about 90 km landward and ~20 km depth. Based on seismic structure we identify four upper-plate units, consisting of basement and overlaying sedimentary sequences A, B and C. The sedimentary cover varies along the margin, being few hundreds of meters thick in the lower and middle slope, and ~2-3 km thick in the upper slope. Exceptionally, a ~10-km -thick basin, here named Banco Peru basin, is located on the upper slope at the southernmost part of the gulf. This basin seems to be the first evidence of the Gulf of Guayaquil opening resulting from the NE escaping of the North Andean Block. Below the continental shelf, thick sedimentary basins of ~6 to 8 km occupy most of the gulf area. Tectonic deformation across most of the upper-plate is dominated by extensional regime, locally disturbed by diapirism. Compression evidences are restricted to the deformation front and surrounding areas. Well data calibrating the seismic profiles indicate that an important portion of the total thickness of the sedimentary coverage of the overriding plate are Miocene or older. The data indicate the extensional deformation resulting from the NE motion of the North Andean Block and the opening of the Gulf of Guayaquil, evolves progressively in age from the southern edge of the gulf near Banco Peru, where main subsidence seems to be Miocene or older, toward the northern limit, where high subsidence rates are early Pleistocene.

Earthquake stress drops, ambient tectonic stresses and stresses that drive plate motions

USGS Publications Warehouse

Hanks, T.C.

1977-01-01

A variety of geophysical observations suggests that the upper portion of the lithosphere, herein referred to as the elastic plate, has long-term material properties and frictional strength significantly greater than the lower lithosphere. If the average frictional stress along the non-ridge margin of the elastic plate is of the order of a kilobar, as suggested by the many observations of the frictional strength of rocks at mid-crustal conditions of pressure and temperature, the only viable mechanism for driving the motion of the elastic plate is a basal shear stress of several tens of bars. Kilobars of tectonic stress are then an ambient, steady condition of the earth's crust and uppermost mantle. The approximate equality of the basal shear stress and the average crustal earthquake stress drop, the localization of strain release for major plate margin earthquakes, and the rough equivalence of plate margin slip rates and gross plate motion rates suggest that the stress drops of major plate margin earthquakes are controlled by the elastic release of the basal shear stress in the vicinity of the plate margin, despite the existence of kilobars of tectonic stress existing across vertical planes parallel to the plate margin. If the stress differences available to be released at the time of faulting are distributed in a random, white fasbion with a mean-square value determined by the average earthquake stress drop, the frequency of occurrence of constant stress drop earthquakes will be proportional to reciprocal faulting area, in accordance with empirically known frequency of occurrence statistics. ?? 1977 Birkha??user Verlag.

Petit-spot geology reveals melts in upper-most asthenosphere dragged by lithosphere

NASA Astrophysics Data System (ADS)

Machida, Shiki; Hirano, Naoto; Sumino, Hirochika; Hirata, Takafumi; Yoneda, Shigekazu; Kato, Yasuhiro

2015-09-01

Petit-spot volcanism is a phenomenon ubiquitous on Earth. It originates from melt in the upper-most mantle asthenosphere, occurring where the plate flexes and fractures before subduction. Recent geochemical and petrological studies of petit-spot volcanism lava have shown that understanding this form of volcanism can contribute to the investigation of mantle dynamics and CO2 degassing of Earth. However, geological information constraining the magma source of petit-spot remains limited. Here, we present a comprehensive dataset of geochemistry (major and trace elements, and Sr and Nd isotopic compositions) and 40Ar/39Ar ages of alkaline basaltic rocks and glasses to define the geological characteristics of petit-spot volcanoes in the northwestern Pacific. The geochemical and geochronological variations of the basalts indicate that petit-spot volcanism is characterized by a petrogenetically and temporally isolated magma system for each volcano. The basalt geochemistry further indicates that the magmas at the volcanoes were derived from the melting of a heterogeneous regional-scale source under a range of conditions. In addition, slight temporal intra-field migration of petit-spot vent fields against the plate motion was detected. These features indicate that the magma originates from isolated melt ponds at the lithosphere-asthenosphere boundary, and that the speed at which the melt ponds are dragged by the plate is only slightly slower than that of the plate motion. Our results provide detailed insight into eruption processes of asthenosphere melts induced by plate-flexure, and also suggest the complete coupling of the lithosphere to the upper-most asthenosphere in the case of large plate subduction.

Landing gear energy absorption system

NASA Technical Reports Server (NTRS)

Hansen, Christopher P. (Inventor)

1994-01-01

A landing pad system is described for absorbing horizontal and vertical impact forces upon engagement with a landing surface where circumferentially arranged landing struts respectively have a clevis which receives a slidable rod member and where the upper portion of a slidable rod member is coupled to the clevis by friction washers which are force fit onto the rod member to provide for controlled constant force energy absorption when the rod member moves relative to the clevis. The lower end of the friction rod is pivotally attached by a ball and socket to a support plate where the support plate is arranged to slide in a transverse direction relative to a housing which contains an energy absorption material for absorbing energy in a transverse direction.

Enhanced vbasis laser diode package

DOEpatents

Deri, Robert J.; Chen, Diana; Bayramian, Andy; Freitas, Barry; Kotovsky, Jack

2014-08-19

A substrate having an upper surface and a lower surface is provided. The substrate includes a plurality of v-grooves formed in the upper surface. Each v-groove includes a first side and a second side perpendicular to the first side. A laser diode bar assembly is disposed within each of the v-grooves and attached to the first side. The laser diode bar assembly includes a first adhesion layer disposed on the first side of the v-groove, a metal plate attached to the first adhesion layer, a second adhesion layer disposed over the metal plate, and a laser diode bar attached to the second adhesion layer. The laser diode bar has a coefficient of thermal expansion (CTE) substantially similar to that of the metal plate.

Ongoing niche differentiation under high gene flow in a polymorphic brackish water threespine stickleback (Gasterosteus aculeatus) population.

PubMed

Østbye, Kjartan; Taugbøl, Annette; Ravinet, Mark; Harrod, Chris; Pettersen, Ruben Alexander; Bernatchez, Louis; Vøllestad, Leif Asbjørn

2018-02-05

Marine threespine sticklebacks colonized and adapted to brackish and freshwater environments since the last Pleistocene glacial. Throughout the Holarctic, three lateral plate morphs are observed; the low, partial and completely plated morph. We test if the three plate morphs in the brackish water Lake Engervann, Norway, differ in body size, trophic morphology (gill raker number and length), niche (stable isotopes; δ 15 N, δ 13 C, and parasites (Theristina gasterostei, Trematoda spp.)), genetic structure (microsatellites) and the lateral-plate encoding Stn382 (Ectodysplasin) gene. We examine differences temporally (autumn 2006/spring 2007) and spatially (upper/lower sections of the lake - reflecting low versus high salinity). All morphs belonged to one gene pool. The complete morph was larger than the low plated, with the partial morph intermediate. The number of lateral plates ranged 8-71, with means of 64.2 for complete, 40.3 for partial, and 14.9 for low plated morph. Stickleback δ 15 N was higher in the lower lake section, while δ 13 C was higher in the upper section. Stickleback isotopic values were greater in autumn. The low plated morph had larger variances in δ 15 N and δ 13 C than the other morphs. Sticklebacks in the upper section had more T. gasterostei than in the lower section which had more Trematoda spp. Sticklebacks had less T. gasterostei, but more Trematoda spp. in autumn than spring. Sticklebacks with few and short rakers had more T. gasterostei, while sticklebacks with longer rakers had more Trematoda. spp. Stickleback with higher δ 15 N values had more T. gasterostei, while sticklebacks with higher δ 15 N and δ 13 C values had more Trematoda spp. The low plated morph had fewer Trematoda spp. than other morphs. Trait-ecology associations may imply that the three lateral plate morphs in the brackish water lagoon of Lake Engervann are experiencing ongoing divergent selection for niche and migratory life history strategies under high gene flow. As such, the brackish water zone may generally act as a generator of genomic diversity to be selected upon in the different environments where threespine sticklebacks can live.

Shed Vortex Structure and Phase-Averaged Velocity Statistics in Symmetric/Asymmetric Turbulent Flat Plate Wakes

NASA Technical Reports Server (NTRS)

Rai, Man Mohan

2017-01-01

The near wake of a flat plate is investigated via direct numerical simulations (DNS). Many earlier experimental investigations have used thin plates with sharp trailing edges and turbulent boundary layers to create the wake. This results in large theta divided by D (sub TE) values (theta is the boundary layer momentum thickness towards the end of the plate and D (sub TE) is the trailing edge thickness). In the present study the emphasis is on relatively thick plates with circular trailing edges (CTE) resulting in theta divided by D values less than one (D is the plate thickness and the diameter of the CTE), and vigorous vortex shedding. The Reynolds numbers based on the plate length and D are 1.255 x 10 (sup 6) and 10,000, respectively. Two cases are computed; one with turbulent boundary layers on both the upper and lower surfaces of the plate (statistically the same, symmetric wake, Case TT) and, a second with turbulent and laminar boundary layers on the upper and lower surfaces, respectively (asymmetric case, Case TL). The data and understanding obtained is of considerable engineering interest, particularly in turbomachinery where the pressure side of an airfoil can remain laminar or transitional because of a favorable pressure gradient and the suction side is turbulent. Shed-vortex structure and phase-averaged velocity statistics obtained in the two cases are compared here. The upper negative shed vortices in Case TL (turbulent separating boundary layer) are weaker than the lower positive ones (laminar separating boundary layer) at inception (a factor 1.27 weaker in terms of peak phase-averaged spanwise vorticity at first appearance of a peak). The upper vortices weaken rapidly as they travel downstream. A second feature of interest in Case TL is a considerable increase in the peak phase-averaged, streamwise normal intensity (random component) with increasing streamwise distance (x divided by D) that occurs nears the positive vortex cores. This behavior is observed for a few diameters in the near wake. This is counter to Case TT where the peak value essentially decreases with increasing x divided by D. Both these effects are examined in detail and the important contributors are identified.

Extreme hydrothermal conditions at an active plate-bounding fault.

PubMed

Sutherland, Rupert; Townend, John; Toy, Virginia; Upton, Phaedra; Coussens, Jamie; Allen, Michael; Baratin, Laura-May; Barth, Nicolas; Becroft, Leeza; Boese, Carolin; Boles, Austin; Boulton, Carolyn; Broderick, Neil G R; Janku-Capova, Lucie; Carpenter, Brett M; Célérier, Bernard; Chamberlain, Calum; Cooper, Alan; Coutts, Ashley; Cox, Simon; Craw, Lisa; Doan, Mai-Linh; Eccles, Jennifer; Faulkner, Dan; Grieve, Jason; Grochowski, Julia; Gulley, Anton; Hartog, Arthur; Howarth, Jamie; Jacobs, Katrina; Jeppson, Tamara; Kato, Naoki; Keys, Steven; Kirilova, Martina; Kometani, Yusuke; Langridge, Rob; Lin, Weiren; Little, Timothy; Lukacs, Adrienn; Mallyon, Deirdre; Mariani, Elisabetta; Massiot, Cécile; Mathewson, Loren; Melosh, Ben; Menzies, Catriona; Moore, Jo; Morales, Luiz; Morgan, Chance; Mori, Hiroshi; Niemeijer, Andre; Nishikawa, Osamu; Prior, David; Sauer, Katrina; Savage, Martha; Schleicher, Anja; Schmitt, Douglas R; Shigematsu, Norio; Taylor-Offord, Sam; Teagle, Damon; Tobin, Harold; Valdez, Robert; Weaver, Konrad; Wiersberg, Thomas; Williams, Jack; Woodman, Nick; Zimmer, Martin

2017-06-01

Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre. At temperatures above 300-450 degrees Celsius, usually found at depths greater than 10-15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional-mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults.

Extreme hydrothermal conditions at an active plate-bounding fault

NASA Astrophysics Data System (ADS)

Sutherland, Rupert; Townend, John; Toy, Virginia; Upton, Phaedra; Coussens, Jamie; Allen, Michael; Baratin, Laura-May; Barth, Nicolas; Becroft, Leeza; Boese, Carolin; Boles, Austin; Boulton, Carolyn; Broderick, Neil G. R.; Janku-Capova, Lucie; Carpenter, Brett M.; Célérier, Bernard; Chamberlain, Calum; Cooper, Alan; Coutts, Ashley; Cox, Simon; Craw, Lisa; Doan, Mai-Linh; Eccles, Jennifer; Faulkner, Dan; Grieve, Jason; Grochowski, Julia; Gulley, Anton; Hartog, Arthur; Howarth, Jamie; Jacobs, Katrina; Jeppson, Tamara; Kato, Naoki; Keys, Steven; Kirilova, Martina; Kometani, Yusuke; Langridge, Rob; Lin, Weiren; Little, Timothy; Lukacs, Adrienn; Mallyon, Deirdre; Mariani, Elisabetta; Massiot, Cécile; Mathewson, Loren; Melosh, Ben; Menzies, Catriona; Moore, Jo; Morales, Luiz; Morgan, Chance; Mori, Hiroshi; Niemeijer, Andre; Nishikawa, Osamu; Prior, David; Sauer, Katrina; Savage, Martha; Schleicher, Anja; Schmitt, Douglas R.; Shigematsu, Norio; Taylor-Offord, Sam; Teagle, Damon; Tobin, Harold; Valdez, Robert; Weaver, Konrad; Wiersberg, Thomas; Williams, Jack; Woodman, Nick; Zimmer, Martin

2017-06-01

Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre. At temperatures above 300-450 degrees Celsius, usually found at depths greater than 10-15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional-mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults.

Crustal structure in Tengchong Volcano-Geothermal Area, western Yunnan, China

NASA Astrophysics Data System (ADS)

Wang, Chun-Yong; Huangfu, Gang

2004-02-01

Based upon the deep seismic sounding profiles carried out in the Tengchong Volcano-Geothermal Area (TVGA), western Yunnan Province of China, a 2-D crustal P velocity structure is obtained by use of finite-difference inversion and forward travel-time fitting method. The crustal model shows that a low-velocity anomaly zone exists in the upper crust, which is related to geothermal activity. Two faults, the Longling-Ruili Fault and Tengchong Fault, on the profile extend from surface to the lower crust and the Tengchong Fault likely penetrates the Moho. Moreover, based on teleseismic receiver functions on a temporary seismic network, S-wave velocity structures beneath the geothermal field show low S-wave velocity in the upper crust. From results of geophysical survey, the crust of TVGA is characterized by low P-wave and S-wave velocities, low resistivity, high heat-flow value and low Q. The upper mantle P-wave velocity is also low. This suggests presence of magma in the crust derived from the upper mantle. The low-velocity anomaly in upper crust may be related to the magma differentiation. The Tengchong volcanic area is located on the northeast edge of the Indian-Eurasian plate collision zone, away from the eastern boundary of the Indian plate by about 450 km. Based on the results of this paper and related studies, the Tengchong volcanoes can be classified as plate boundary volcanoes.

Plate-Tectonic Circulation is Driven by Cooling From the Top and is Closed Within the Upper Mantle

NASA Astrophysics Data System (ADS)

Hamilton, W. B.

2001-12-01

Subduction drives plate tectonics and is due to cooling from the top: circulation is self-organized, and likely is closed above the discontinuity near 660 km. The contrary consensus that plate tectonics is driven by bottom heating and involves the entire mantle combines misunderstood kinematics with flawed concepts of through-the-mantle plumes and subduction. Plume conjecture came from the Emperor-Hawaii progression, the 45 Ma inflection in which was assumed to mark a 60-degree change in direction of that part of the Pacific plate over a fixed plume. Smooth spreading patterns around the east and south margin of the Pacific plate, and paleomagnetic data, disprove such a change. Speculations that plumes move, jump, etc. do not revive falsified conjecture. Geochemical distinctions between enriched island and depleted ridge basalts (which overlap) are expected products of normal upper-mantle processes, not plumes. MORB traverses solidus-T asthenosphere, whereas OIB zone-refines through subsolidus lithosphere and crust, crystallizing refractories to retain T of diminishing melt while assimilating and retaining fusibles. Tomographic inference of deep-mantle subduction is presented misleadingly and may reflect methodological and sampling artifacts (downward smearing, and concentration of recorded body waves in bundles within broad anomalies otherwise poorly sampled). Planetological and other data require hot Earth accretion, and thorough early fractionation, from material much more refractory than primitive meteorites, and are incompatible with the little-fractionated lower mantle postulated to permit whole-mantle circulation. The profound seismic discontinuity near 660 km is a thermodynamic and physical barrier to easy mass transfer in either direction. Refractory lower mantle convects slowly, perhaps in layers, and loses primarily original heat, whereas upper mantle churns rapidly, and the 660 decoupling boundary must have evolved into a compositional barrier also. Plate motions are driven by subduction, the passive falling away of oceanic lithosphere which is negatively buoyant because of top-down cooling. Slabs have top and bottom rolling hinges and sink subvertically (inclinations of slabs mark their positions, not trajectories) into the transition zone, where they are laid down on, and depress, the 660-km discontinuity. Rollback of upper hinges into subducting plates is required by plate behavior at all scales. That fronts of overriding plates advance at rollback velocity is required by common preservation atop their thin leading edges of little-deformed fore-arc basins. Convergence velocity also commonly equals rollback but is faster in some arcs. Steeply-sinking inclined slabs push sublithospheric upper mantle forward into the shrinking ocean from which they came, forcing seafloor spreading therein, and pull overriding plates behind them. Continental plates pass over sunken slabs like tanks above their basal treads, and material from, and displaced rearward by, sunken slabs is cycled into pull-apart oceans opening behind the continents, thus transferring mantle from shrinking to enlarging oceans. Hot mantle displaced above slabs enables backarc spreading. Spreading ridges, in both shrinking and enlarging oceans, are passive byproducts of subduction, and migrate because it is more energy efficient to process new asthenosphere than to get partial melt from increasingly distant sources. A plate-motion framework wherein hinges roll back, ridges migrate, Antarctica is approximately fixed, and intraplate deformation is integrated may approximate an absolute reference to sluggish lower mantle, whereas the hotspot frame is invalid, and the no-net-rotation frame minimizes trench and ridge motions.

Unsteady stokes flow of dusty fluid between two parallel plates through porous medium in the presence of magnetic field

NASA Astrophysics Data System (ADS)

Sasikala, R.; Govindarajan, A.; Gayathri, R.

2018-04-01

This paper focus on the result of dust particle between two parallel plates through porous medium in the presence of magnetic field with constant suction in the upper plate and constant injection in the lower plate. The partial differential equations governing the flow are solved by similarity transformation. The velocity of the fluid and the dust particle decreases when there is an increase in the Hartmann number.

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.

Pyroclastic Activity at Home Plate in Gusev Crater, Mars

NASA Technical Reports Server (NTRS)

Squyres, S. W.; Aharonson, O.; Clark, B. S.; Cohen, B.; Crumpler, L.; deSouza, P. A.; Farrand, W. H.; Gellert, R.; Grant, J.; Grotzinger, J. P.;

Pyroclastic activity at home plate in Gusev crater, Mars

USGS Publications Warehouse

Squyres, S. W.; Aharonson, O.; Clark, B. C.; Cohen, B. A.; Crumpler, L.; de Souza, P.A.; Farrand, W. H.; Gellert, Ralf; Grant, J.; Grotzinger, J.P.; Haldemann, A.F.C.; Johnson, J. R.; Klingelhofer, G.; Lewis, K.W.; Li, R.; McCoy, T.; McEwen, A.S.; McSween, H.Y.; Ming, D. W.; Moore, Johnnie N.; Morris, R.V.; Parker, T.J.; Rice, J. W.; Ruff, S.; Schmidt, M.; Schroder, C.; Soderblom, L.A.; Yen, A.

2007-01-01

Home Plate is a layered plateau in Gusev crater on Mars. It is composed of clastic rocks of moderately altered alkali basalt composition, enriched in some highly volatile elements. A coarse-grained lower unit lies under a finer-grained upper unit. Textural observations indicate that the lower strata were emplaced in an explosive event, and geochemical considerations favor an explosive volcanic origin over an impact origin. The lower unit likely represents accumulation of pyroclastic materials, whereas the upper unit may represent eolian reworking of the same pyroclastic materials.

Structure and Neotectonics of the Southern Chile Forearc 35°S - 40°S

NASA Astrophysics Data System (ADS)

Geersen, Jacob; Völker, David; Weinrebe, Wilhelm; Krastel-Gudegast, Sebastian; Behrmann, Jan H.

2010-05-01

The Southern Chile Forearc exhibits an extreme level of neotectonic deformation. On-land studies have documented a pronounced segmentation in the region 36°S - 41°S. However, information on the seaward continuation of the individual segments towards the Chile Trench is rare, as direct observations end at the coastline and are replaced by a less dense set of marine geophysical data. In this study we use swath bathymetric data combined with high and low-frequency reflection seismic data as well as results from heat-flow measurements to: (A) map and identify active deformation structures and investigate their spatial distribution, and (B) analyse the factors controlling segmentation along the Southern Chile Forearc. Considering the region 35°S to 40°S we found evidence for a division into four major segments; Concepcion North, Concepcion South, Nahuelbuta, and Tolten (from North to South). Within all four segments, the lower continental slope is dissected by distinct margin-parallel thrust ridges overlying active landward-dipping thrust faults, indicating the presence of an active accretionary prism. The middle and upper slope, however, shows major differences between the four segments. The Concepcion North Segment is dominated by a large margin-parallel thrust ridge. The Concepcion South Segment shows large up to 600 m high north-south aligned normal fault scarps highlighting east-west extension. The change from thrust to normal faulting domains is accompanied by a drastic decrease in surface heat-flow by a factor of up to four. Further south in the Nahuelbuta Segment, east-west trending active thrust ridges indicate north-south compression of this part of the forearc. Shortening in this segment is not only limited to the middle and upper slope, but includes the entire marine forearc and occurs perpendicular to the direction of plate convergence. In the southernmost Tolten Segment the middle and upper continental slope shows no signs of compressive or extensional deformation. For the factors controlling segmentation our data suggest that when considering the whole forearc variations in the overriding plate such as the position of continental fault zones are responsible for the large scale tectonic segmentation. The east-west oriented shortening structures in the Nahuelbuta Segment (perpendicular to the direction of plate motion) probably originate from the collision of the Chiloe Microplate with a marine buttress situated below the Concepcion South Segment. The Chiloe Microplate represents a 1000 km-sized forearc sliver, which is kinematically decoupled from stable South America along the Liquine-Ofqui and Lanalhue Fault Zones. The important transition from wholesale forearc compression to extension observed between the two Concepcion segments, however, is more likely related to plate boundary processes, i.e. different degrees of coupling and/or friction in the plate boundary itself.

Fast Gas Replacement in Plasma Process Chamber by Improving Gas Flow Pattern

NASA Astrophysics Data System (ADS)

Morishita, Sadaharu; Goto, Tetsuya; Akutsu, Isao; Ohyama, Kenji; Ito, Takashi; Ohmi, Tadahiro

2009-01-01

The precise and high-speed alteration of various gas species is important for realizing precise and well-controlled multiprocesses in a single plasma process chamber with high throughput. The gas replacement times in the replacement of N2 by Ar and that of H2 by Ar are measured in a microwave excited high-density and low electron-temperature plasma process chamber at various working pressures and gas flow rates, incorporating a new gas flow control system, which can avoid overshoot of the gas pressure in the chamber immediately after the valve operation, and a gradational lead screw booster pump, which can maintain excellent pumping capability for various gas species including lightweight gases such as H2 in a wide pressure region from 10-1 to 104 Pa. Furthermore, to control the gas flow pattern in the chamber, upper ceramic shower plates, which have thousands of very fine gas injection holes (numbers of 1200 and 2400) formed with optimized allocation on the plates, are adopted, while the conventional gas supply method in the microwave-excited plasma chamber uses many holes only opened at the sidewall of the chamber (gas ring). It has been confirmed that, in the replacement of N2 by Ar, a short replacement time of approximately 1 s in the cases of 133 and 13.3 Pa and approximately 3 s in the case of 4 Pa can be achieved when the upper shower plate has 2400 holes, while a replacement time longer than approximately 10 s is required for all pressure cases where the gas ring is used. In addition, thanks to the excellent pumping capability of the gradational lead screw booster pump for lightweight gases, it has also been confirmed that the replacement time of H2 by Ar is almost the same as that of N2 by Ar.

Isostatic models and isostatic gravity anomalies of the Arabian plate and surroundings

NASA Astrophysics Data System (ADS)

Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

2015-04-01

Isostaic anomalies represent one of the most useful "geological" reduction of the gravity field. With the isostatic correction it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. This correction is based on the fact that a major part of the near-surface load is compensated by variations of the lithosphere boundaries (chiefly the Moho and LAB) and by density variations within the crust and upper mantle. It is usually supposed that it is less important to a first order, what is the actual compensation model when reducing the effect of compensating masses, since their total weight is exactly opposite to the near-surface load. We compare several compensating models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which can not be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also the predicted "isostatic" Moho is very different from the existing observations. The second group of the isostatic models includes the Moho, which is based on existing seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). In this way we minimize regional anomalies over the Arabian plate. The residual local anomalies well correspond to tectonic structure of the plate. Still very significant anomalies are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

Influence of increasing convergence obliquity and shallow slab geometry onto tectonic deformation and seismogenic behavior along the Northern Lesser Antilles zone

NASA Astrophysics Data System (ADS)

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

2018-06-01

In subduction zones, the 3D geometry of the plate interface is one of the key parameters that controls margin tectonic deformation, interplate coupling and seismogenic behavior. The North American plate subducts beneath the convex Northern Lesser Antilles margin. This convergent plate boundary, with a northward increasing convergence obliquity, turns into a sinistral strike-slip limit at the northwestern end of the system. This geodynamic context suggests a complex slab geometry, which has never been imaged before. Moreover, the seismic activity and particularly the number of events with thrust focal mechanism compatible with subduction earthquakes, increases northward from the Barbuda-Anguilla segment to the Anguilla-Virgin Islands segment. One of the major questions in this area is thus to analyze the influence of the increasing convergence obliquity and the slab geometry onto tectonic deformation and seismogenic behavior of the subduction zone. Based on wide-angle and multichannel reflection seismic data acquired during the Antithesis cruises (2013-2016), we decipher the deep structure of this subduction zone. Velocity models derived from wide-angle data acquired across the Anegada Passage are consistent with the presence of a crust of oceanic affinity thickened by hotspot magmatism and probably affected by the Upper Cretaceous-Eocene arc magmatism forming the 'Great Arc of the Caribbean'. The slab is shallower beneath the Anguilla-Virgin Islands margin segment than beneath the Anguilla-Barbuda segment which is likely to be directly related to the convex geometry of the upper plate. This shallower slab is located under the forearc where earthquakes and partitioning deformations increase locally. Thus, the shallowing slab might result in local greater interplate coupling and basal friction favoring seismic activity and tectonic partitioning beneath the Virgin Islands platform.

Planar oscillatory stirring apparatus

NASA Technical Reports Server (NTRS)

Wolf, Martin F. (Inventor)

1987-01-01

Apparatus (11) for applying planar oscillations to a container (13). Pressurized air (99) is supplied to a moveable slide plate (27) which employs arms (19) having an air bearing vent structure (29, 31) which allows the slide plate to float and to translate. The container (13) to be oscillated is secured to the upper surface of the slide plate (27). A motor (39) driven rotating eccentric shaft (59) loosely extends into a center hole bearing (37) of the slide plate (27) to cause the oscillations.

Mechanical Properties of Spinal Ligaments for Rhesus Monkey, Baboon and Chimpanzee.

DTIC Science & Technology

1981-06-01

isolate the spine, to grossly elevate the scapulae , and to expose the dorsal aspect of the rib cage. Using a Stryker saw, the rib,: were cut at least 2...Figure 10. The upper gripping plate was attached to the actuator of the testing machine and the lower plate to the load cell. The ligament sample was held...against these plates with stainless steel bands. On the surfaces of both the plates and the bands, a waterproof abrasive mesh (silicon carbide 120

Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone

NASA Astrophysics Data System (ADS)

Canales, J. P.; Carbotte, S. M.; Nedimovic, M. R.; Carton, H. D.

2017-12-01

Water is carried by subducting slabs as a pore fluid and in structurally bound minerals, yet no comprehensive quantification of water content and how it is stored and distributed at depth within incoming plates exists for any segment of the global subduction system. Here we use controlled-source seismic data collected in 2012 as part of the Ridge-to-Trench seismic experiment to quantify the amount of pore and structurally bound water in the Juan de Fuca plate entering the Cascadia subduction zone. We use wide-angle OBS seismic data along a 400-km-long margin-parallel profile 10-15 km seaward from the Cascadia deformation front to obtain P-wave tomography models of the sediments, crust, and uppermost mantle, and effective medium theory combined with a stochastic description of crustal properties (e.g., temperature, alteration assemblages, porosity, pore aspect ratio), to analyze the pore fluid and structurally bound water reservoirs in the sediments, crust and lithospheric mantle, and their variations along the Cascadia margin. Our results demonstrate that the Juan de Fuca lower crust and mantle are much drier than at any other subducting plate, with most of the water stored in the sediments and upper crust. Previously documented, variable but limited bend faulting along the margin, which correlates with degree of plate locking, limits slab access to water, and a warm thermal structure resulting from a thick sediment cover and young plate age prevents significant serpentinization of the mantle. Our results have important implications for a number of subduction processes at Cascadia, such as: (1) the dryness of the lower crust and mantle indicates that fluids that facilitate episodic tremor and slip must be sourced from the subducted upper crust; (2) decompression rather than hydrous melting must dominate arc magmatism in northern-central Cascadia; and (3) dry subducted lower crust and mantle can explain the low levels of intermediate-depth seismicity in the Juan de Fuca slab.

Lithospheric Structure and Isostasy of Central Andes: Implication for plate Coupling

NASA Astrophysics Data System (ADS)

Mahatsente, R.; Rutledge, S.

2017-12-01

A significant section of the Peru-Chile convergent zone is building up stresses. The interseismic coupling in northern and southern Peru is significantly high indicating, elastic energy accumulation since the 1746 and 1868 earthquakes of magnitude 8.6 and 8.8 , respectively. Similar seismic patterns have also been observed in Central Chile. The plate interface beneath Central Chile is highly coupled, and the narrow zones of low coupling separate seismic gaps. The reasons for the seismic gaps and plate coupling are yet unknown, but the configuration of the slab is thought to be the main factor. Here, we assessed the locking mechanism and isostatic state of the Central Andes based on gravity models of the crust and upper mantle structure. The density models are based on satellite gravity data and are constrained by velocity models and earthquake hypocenters. The gravity models indicate a high-density batholithic structure in the fore-arc, overlying the subducting Nazca plate. This high-density body pushes downward on the slab, causing the slab to lock with the overlying continental plate. The increased compressive stress closer to the trench, due to the increased contact area between the subducting and overriding plates, may have increased the plate coupling in the Central Andes. Thus, trench parallel crustal thickness and density variations along the Central Andes and buoyancy force on the subducting Nazca plate may control plate coupling and asperity generation. The western part of the Central Andes may be undercompensated. There is a residual topography of 800 m in the western part of the Central Andes that cannot be explained by the observed crustal thicknesses. Thus, part of the observed topography in the western part of the Central Andes may be dynamically supported by mantle wedge flow below the overriding plate.

Double-null divertor configuration discharge and disruptive heat flux simulation using TSC on EAST

NASA Astrophysics Data System (ADS)

Bo, SHI; Jinhong, YANG; Cheng, YANG; Desheng, CHENG; Hui, WANG; Hui, ZHANG; Haifei, DENG; Junli, QI; Xianzu, GONG; Weihua, WANG

2018-07-01

The tokamak simulation code (TSC) is employed to simulate the complete evolution of a disruptive discharge in the experimental advanced superconducting tokamak. The multiplication factor of the anomalous transport coefficient was adjusted to model the major disruptive discharge with double-null divertor configuration based on shot 61 916. The real-time feed-back control system for the plasma displacement was employed. Modeling results of the evolution of the poloidal field coil currents, the plasma current, the major radius, the plasma configuration all show agreement with experimental measurements. Results from the simulation show that during disruption, heat flux about 8 MW m‑2 flows to the upper divertor target plate and about 6 MW m‑2 flows to the lower divertor target plate. Computations predict that different amounts of heat fluxes on the divertor target plate could result by adjusting the multiplication factor of the anomalous transport coefficient. This shows that TSC has high flexibility and predictability.

Mantle dynamics in the Mediterranean

NASA Astrophysics Data System (ADS)

Faccenna, Claudio; Becker, Thorsten W.; Auer, Ludwig; Billi, Andrea; Boschi, Lapo; Brun, Jean Pierre; Capitanio, Fabio A.; Funiciello, Francesca; Horvåth, Ferenc; Jolivet, Laurent; Piromallo, Claudia; Royden, Leigh; Rossetti, Federico; Serpelloni, Enrico

2014-09-01

The Mediterranean offers a unique opportunity to study the driving forces of tectonic deformation within a complex mobile belt. Lithospheric dynamics are affected by slab rollback and collision of two large, slowly moving plates, forcing fragments of continental and oceanic lithosphere to interact. This paper reviews the rich and growing set of constraints from geological reconstructions, geodetic data, and crustal and upper mantle heterogeneity imaged by structural seismology. We proceed to discuss a conceptual and quantitative framework for the causes of surface deformation. Exploring existing and newly developed tectonic and numerical geodynamic models, we illustrate the role of mantle convection on surface geology. A coherent picture emerges which can be outlined by two, almost symmetric, upper mantle convection cells. The downwellings are found in the center of the Mediterranean and are associated with the descent of the Tyrrhenian and the Hellenic slabs. During plate convergence, these slabs migrated backward with respect to the Eurasian upper plate, inducing a return flow of the asthenosphere from the back-arc regions toward the subduction zones. This flow can be found at large distance from the subduction zones and is at present expressed in two upwellings beneath Anatolia and eastern Iberia. This convection system provides an explanation for the general pattern of seismic anisotropy in the Mediterranean, first-order Anatolia, and Adria microplate kinematics and may contribute to the high elevation of scarcely deformed areas such as Anatolia and eastern Iberia. More generally, the Mediterranean is an illustration of how upper mantle, small-scale convection leads to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the Tethyan collision.

Discovering the Complexity of Capable Faults in Northern Chile

NASA Astrophysics Data System (ADS)

Gonzalez, G.; del Río, I. A.; Rojas Orrego, C., Sr.; Astudillo, L. A., Sr.

2017-12-01

Great crustal earthquakes (Mw >7.0) in the upper plate of subduction zones are relatively uncommon and less well documented. We hypothesize that crustal earthquakes are poorly represented in the instrumental record because they have long recurrence intervals. In northern Chile, the extreme long-term aridity permits extraordinary preservation of landforms related to fault activity, making this region a primary target to understand how upper plate faults work at subduction zones. To understand how these faults relate to crustal seismicity in the long-term, we have conducted a detailed palaeoseismological study. We performed a palaeoseismological survey integrating trench logging and photogrammetry based on UAVs. Optically stimulated luminescence (OSL) age determinations were practiced for dating deposits linked to faulting. In this contribution we present the study case of two primary faults located in the Coastal Cordillera of northern Chile between Iquique (21ºS) and Antofagasta (24ºS). We estimate the maximum moment magnitude of earthquakes generated in these upper plate faults, their recurrence interval and the fault-slip rate. We conclude that the studied upper plate faults show a complex kinematics on geological timescales. Faults seem to change their kinematics from normal (extension) to reverse (compression) or from normal to transcurrent (compression) according to the stage of subduction earthquake cycle. Normal displacement is related to coseismic stages and compression is linked to interseismic period. As result this complex interaction these faults are capable of generating Mw 7.0 earthquakes, with recurrence times on the order of thousands of years during every stage of the subduction earthquake cycle.

Lateral variations in upper-mantle seismic anisotropy in the Pacific from inversion of a surface-wave dispersion dataset

NASA Astrophysics Data System (ADS)

Eddy, C. L.; Ekstrom, G.; Nettles, M.; Gaherty, J. B.

2017-12-01

We present a three-dimensional model of the anisotropic velocity structure of the Pacific lithosphere and asthenosphere. The presence of seismic anisotropy in the oceanic upper mantle provides information about the geometry of flow in the mantle, the nature of the lithosphere-asthenosphere boundary, and the possible presence of partial melt in the asthenosphere. Our dataset consists of fundamental-mode dispersion for Rayleigh and Love waves measured between 25-250 s with paths crossing the Pacific Ocean. We invert the phase anomaly measurements directly for three-dimensional anisotropic velocity structure. Our models are radially anisotropic and include the full set of elastic parameters that describe azimuthal variations in velocity (e.g. Gc, Gs). We investigate the age dependence of seismic velocity and radial anisotropy and find that there are significant deviations from the velocities predicted by a simple oceanic plate cooling model. We observe strong radial anisotropy with vsh > vsv in the asthenosphere of the central Pacific. We investigate the radial anisotropy in the shallow lithosphere, where previous models have reported conflicting results. There is a contrast in both upper-mantle isotropic velocities and radial anisotropy between the Pacific and Nazca plates, across the East Pacific Rise. We also investigate lateral variations in azimuthal anisotropy throughout the Pacific upper mantle and find that there are large areas over which the anisotropy fast axis does not align with absolute plate motion, suggesting the presence of small-scale convection or pressure-driven flow beneath the base of the oceanic plate.

Evolution and hydration of the Juan de Fuca crust and uppermost mantle: a plate-scale seismic investigation from ridge to trench

NASA Astrophysics Data System (ADS)

Carbotte, S. M.; Canales, J.; Carton, H. D.; Nedimovic, M. R.; Han, S.; Marjanovic, M.; Gibson, J. C.; Janiszewski, H. A.; Horning, G.; Delescluse, M.; Watremez, L.; Farkas, A.; Biescas Gorriz, B.; Bornstein, G.; Childress, L. B.; Parker, B.

2012-12-01

The evolution of oceanic lithosphere involves incorporation of water into the physical and chemical structure of the crust and shallow mantle through fluid circulation, which initiates at the mid-ocean ridge and continues on the ridge flanks long after crustal formation. At subduction zones, water stored and transported with the descending plate is gradually released at depth, strongly influencing subduction zone processes. Cascadia is a young-lithosphere end member of the global subduction system where relatively little hydration of the downgoing Juan de Fuca (JdF) plate is expected due to its young age and presumed warm thermal state. However, numerous observations support the abundant presence of water within the subduction zone, suggesting that the JdF plate is significantly hydrated prior to subduction. Knowledge of the state of hydration of the JdF plate is limited, with few constraints on crustal and upper mantle structure. During the Cascadia Ridge-to-Trench experiment conducted in June-July 2012 over 4000 km of active source seismic data were acquired as part of a study of the evolution and state of hydration of the crust and shallow mantle of the JdF plate prior to subduction at the Cascadia margin. Coincident long-streamer (8 km) multi-channel seismic (MCS) and wide-angle ocean bottom seismometer (OBS) data were acquired in a two-ship program with the R/V Langseth (MGL1211), and R/V Oceanus (OC1206A). Our survey included two ridge-perpendicular transects across the full width of the JdF plate, a long trench-parallel line ~10 km seaward of the Cascadia deformation front, as well as three fan lines to study mantle anisotropy. The plate transects were chosen to provide reference sections of JdF plate evolution over the maximum range of JdF plate ages (8-9 Ma), offshore two contrasting regions of the Cascadia Subduction zone, and provide the first continuous ridge-to-trench images acquired at any oceanic plate. The trench-parallel line was designed to characterize variations in plate structure and hydration linked to JdF plate segmentation for over 450 km along the margin. Shipboard brute stacks of the MCS data reveal evidence for reactivation of abyssal hill faulting in the plate interior far from the trench. Ridgeward-dipping lower crustal reflectors are observed, similar to those observed in mature Pacific crust elsewhere, as well as conjugate reflectivity near the deformation front along the Oregon transect. Bright intracrustal reflectivity is also observed along the trench-parallel transect with marked changes in reflectivity along the Oregon and Washington margins. Initial inspection of the OBS record sections indicate good quality data with the expected oceanic crustal and upper mantle P-wave arrivals: Ps and Pg refractions through sedimentary and igneous layers, respectively, PmP wide-angle reflections from the crust-mantle transition zone, and Pn upper mantle refractions. The Pg-PmP-Pn triplication is typically observed at 40-50 km source-receiver offsets. Pn characteristics show evidence for upper mantle azimuthal anisotropic propagation: along the plate transects Pn is typically weaker and difficult to observe beyond ~80 km offsets, while along the trench-parallel transect Pn arrivals have higher amplitude and are easily observed up to source-receiver offsets of 160-180 km. An overview on the Cascadia Ridge to Trench data acquisition program and preliminary results will be presented.

Numerical Modelling of Subduction Zones: a New Beginning

NASA Astrophysics Data System (ADS)

Ficini, Eleonora; Dal Zilio, Luca; Doglioni, Carlo; Gerya, Taras V.

2016-04-01

Subduction zones are one of the most studied although still controversial geodynamic process. Is it a passive or an active mechanism in the frame of plate tectonics? How subduction initiates? What controls the differences among the slabs and related orogens and accretionary wedges? The geometry and kinematics at plate boundaries point to a "westerly" polarized flow of plates, which implies a relative opposed flow of the underlying Earth's mantle, being the decoupling located at about 100-200 km depth in the low-velocity zone or LVZ (Doglioni and Panza, 2015 and references therein). This flow is the simplest explanation for determining the asymmetric pattern of subduction zones; in fact "westerly" directed slabs are steeper and deeper with respect to the "easterly or northeasterly" directed ones, that are less steep and shallower, and two end members of orogens associated to the downgoing slabs can be distinguished in terms of topography, type of rocks, magmatism, backarc spreading or not, foredeep subsidence rate, etc.. The classic asymmetry comparing the western Pacific slabs and orogens (low topography and backarc spreading in the upper plate) and the eastern Pacific subduction zones (high topography and deep rocks involved in the upper plate) cannot be ascribed to the age of the subducting lithosphere. In fact, the same asymmetry can be recognized all over the world regardless the type and age of the subducting lithosphere, being rather controlled by the geographic polarity of the subduction. All plate boundaries move "west". Present numerical modelling set of subduction zones is based on the idea that a subducting slab is primarily controlled by its negative buoyancy. However, there are several counterarguments against this assumption, which is not able to explain the global asymmetric aforementioned signatures. Moreover, petrological reconstructions of the lithospheric and underlying mantle composition, point for a much smaller negative buoyancy than predicted, if any (e.g., Doglioni et al., 2007; Afonso et al., 2008). Therefore we attempt to generate a different model setup in which are included both a decoupling at the lithosphere base and the "westward" drift of the lithosphere that implies a relative "eastward" mantle flow. The method used for this task is an implementation of I2VIS code, a 2D thermomechanical code incorporating both a characteristics based marker-in-cell method and conservative finite-difference (FD) schemes (Gerya and Yuen, 2003). The implementation involves both the integration of the LVZ and the application of an incoming and outgoing mantle flow through the lateral boundaries of the rectangular box (that represent the basic setup of the models). This new insight in numerical modelling of subduction zones could help to have a more accurate comprehension on what is actually influencing subduction zones dynamics in order to successively explain what are the causes of this fundamental process and what are its implications on plate tectonics dynamics.

New sample cell configuration for wide-frequency dielectric spectroscopy: DC to radio frequencies.

PubMed

Nakanishi, Masahiro; Sasaki, Yasutaka; Nozaki, Ryusuke

2010-12-01

A new configuration for the sample cell to be used in broadband dielectric spectroscopy is presented. A coaxial structure with a parallel plate capacitor (outward parallel plate cell: OPPC) has made it possible to extend the frequency range significantly in comparison with the frequency range of the conventional configuration. In the proposed configuration, stray inductance is significantly decreased; consequently, the upper bound of the frequency range is improved by two orders of magnitude from the upper limit of conventional parallel plate capacitor (1 MHz). Furthermore, the value of capacitance is kept high by using a parallel plate configuration. Therefore, the precision of the capacitance measurement in the lower frequency range remains sufficiently high. Finally, OPPC can cover a wide frequency range (100 Hz-1 GHz) with an appropriate admittance measuring apparatus such as an impedance or network analyzer. The OPPC and the conventional dielectric cell are compared by examining the frequency dependence of the complex permittivity for several polar liquids and polymeric films.

Anomalous Accretionary Margin Topography Formed By Repeated Earthquakes

NASA Astrophysics Data System (ADS)

Furlong, Kevin P.

2014-05-01

It has long been recognized that accretionary margins of major subduction zones undergo substantial deformation. However even with the large amounts of shortening accommodated within the margin, for most subduction zones, there is an extended submarine portion to the accretionary, highly-deformed upper-plate between the trench and the coast. This is a vexing situation since this submarine section typically overlies the actual locked or coupled patch of the plate interface. The result of this is added difficulty in directly observing processes related to the plate interface coupling - such processes as micro-seismicity and the actual patterns of plate coupling. There are a few locations globally in which there are sub-aerially exposed terranes that lie closer to the trench and overlie the inferred coupled or seismogenic portion of the plate interface. Such regions have taken on significance in subduction zone studies as they provide locations to observe the plate interface coupling effects in the near-field. In particular the Pacific coast of Costa Rica provides such a location, and there has been substantial geologic, geophysical, and geodetic research exploiting the positions of these near-trench peninsulas (Nicoya, Osa, and Burica). These sites provide near-field access to plate-interface processes, but whether they represent typical subduction zone behavior remains an open question as the deformational processes or inherited structures that have produced this anomalous topography are not well constrained. Simply put, if the existence of these sub-aerial, near-trench terranes is a result of anomalous behavior on the plate interface (as has been suggested), then their utility in providing high-fidelity near-field insight into the plate interface properties and processes is substantially reduced. Here we propose a new mechanism that could be responsible for the formation of both the Nicoya and Osa Peninsulas in the past, and is currently producing a third peninsula - the Burica Peninsula at the intersection of the Panama fracture zone and the margin. Specifically we propose that the anomalous topography along the Pacific coast of Costa Rica has been produced by repeated, great subduction earthquakes that have ruptured across the boundary separating the Cocos and Nazca plates - the subducted continuation of the Panama fracture zone. The pattern of upper-plate shortening generated by such a process (documented in the 2007 Mw 8.1 Solomon Islands earthquake, which produced co-seismic localized uplift above the subducted transform plate boundary) convolved with the migration history of the Panama triple junction (PTJ) is proposed as the mechanism to produce substantial along-margin, long-lived accretionary margin topography. Specifically we argue that repeated great subduction earthquakes that rupture across fundamental plate boundary structures can produce substantial, long-lived upper plate deformation above the inter-seismically coupled plate interface.

Low-Stress Upper Plate Near Subduction Zones and Implications for Temporal Changes in Loading Forces

NASA Astrophysics Data System (ADS)

Wang, K.; Hu, Y.; Yoshida, K.

2016-12-01

Subduction megathrusts are weak, often with effective friction coefficients as low as 0.03. Consequently, differential stress (S1 - S3) in the nearby upper plate is low. Compression due to plate coupling and tension due to gravity are in a subtle balance that can be tipped by small perturbations. For example, the 2011 M=9 Tohoku-oki earthquake, which has a rupture-zone-average stress drop of only a few MPa, switched offshore margin-normal stress from compression to tension and affected seismicity pattern and stress directions of various parts of the land area. The low differential stress is also reflected in spatial variations of stresses, such as with changes in topography. In the Andes, crustal earthquake focal mechanisms change from thrust-faulting in low-elevation areas to normal-faulting in high-elevation areas. Given the lack of evidence for a pervasively weak crust, the low differential stress may indicate that in general the crust near subduction zones is not critically stressed. If so, crustal earthquakes do not represent pervasive failure but only local failure due to stress, material, and fluid pressure heterogeneity. If distributed permanent deformation that creates topography is not the norm, it either happens in brief episodes or took place in the past. The outer wedge may enter a compressively or extensionally critical state due to coseismic strengthening or weakening, respectively, of the shallow megathrust in largest interplate earthquakes. Temporal changes in loading forces must occur also at much larger temporal and spatial scales in response to changes in the nature of the subducting plate and other tectonic conditions. We propose that submarine wedges and high topography in the upper plate attain their geometry in geologically brief episodes of high differential stress. They normally stay in a low-stress stable state, but their geometry often reflects high-stress episodes of critical states in the past. In other words, rocks have a sustained memory for the most traumatic moments. Except for the weaker outer wedge, the upper plate does not switch from one critical state to another in megathrust earthquake cycles, such as from compressional failure to gravitational collapse.

Two-phase pressure drop reduction BWR assembly design

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

Dix, G.E.; Crowther, R.L.; Colby, M.J.

1992-05-12

This patent describes a boiling water reactor having discrete bundles of fuel rods confined within channel enclosed fuel assemblies, an improvement to a fuel bundle assembly for placement in the reactor. It comprises a fuel channel having vertically extending walls forming a continuous channel around a fuel assembly volume, the channel being open at the bottom end for engagement to a lower tie plate and open at the upper end for engagement to an upper tie plate; rods for placement within the chamber, each the rod containing fissile material for producing nuclear reaction when in the presence of sufficient moderatedmore » neutron flux; a lower tie plate for supporting the bundle of rods within the channel, the lower tie plate for supporting the bundle of rods within the channel, the lower tie plate joining the bottom of the channel to close the bottom end of the channel, the lower tie plate providing defined apertures for the inflow of water in the channel between the rods for the generating of steam during the nuclear reaction; the plurality of fuel rods extending from the lower tie plate wherein a single phase region of the water in the bundle is defined to an upward portion of the bundle wherein a two phase region of the water and steam in the bundle is defined during nuclear steam generating reaction in the fuel bundle.« less

Effect of nanostructured surface configuration on evaporation and condensation characteristics of thin film liquid argon in a nano-scale confinement

NASA Astrophysics Data System (ADS)

Kuri, Subrata Kumar; Rakibuzzaman, S. M.; Sabah, Arefiny; Ahmed, Jannat; Hasan, Mohammad Nasim

2017-12-01

Molecular dynamics simulation has been carried out to go through the evaporation and condensation characteristics of thin liquid argon film in nanoscale confinement having nanostructured boundary. Nanoscale confinement under consideration consists of hot and cold parallel platinum plates at the bottom and top end of a model cuboid inside which the fluid domain comprised of liquid argon film at the bottom plate and vapor argon in between liquid argon and upper plate of the confinement. Three different confinement configurations have been considered here: (i) Both platinum plates are flat, (ii) Upper plate consisting of transverse slots and (iii) Both plates consisting of transverse slots. The height of the slots is 1.5 nm. Considering hydrophilic nature of top and bottom plates, two different high temperatures of the hot wall was set and an observation was made. For all the structures, equilibrium molecular dynamics (EMD) was performed to reach equilibrium state at 90 K. Then the lower wall is set to two different temperatures like 110 K and 250 K for all three models to perform non-equilibrium molecular dynamics (NEMD). Various system characteristics such as atomic distribution, wall heat flux, evaporative mass flux etc. have been obtained and discussed to have a clear understanding of the effect of nanotextured surface on phase change phenomena.

Controls on continental strain partitioning above an oblique subduction zone, Northern Andes

NASA Astrophysics Data System (ADS)

Schütt, Jorina M.; Whipp, David M., Jr.

2016-04-01

Strain partitioning is a common process at obliquely convergent plate margins dividing oblique convergence into margin-normal slip on the plate-bounding fault and horizontal shearing on a strike-slip system parallel to the subduction margin. In subduction zones, strain partitioning in the upper continental plate is mainly controlled by the shear forces acting on the plate interface and the strength of the continental crust. The plate interface forces are influenced by the subducting plate dip angle and the obliquity angle between the normal to the plate margin and the convergence velocity vector, and the crustal strength of the continent is strongly affected by the presence or absence of a volcanic arc, with the presence of the volcanic arcs being common at steep subduction zones. Along the ˜7000 km western margin of South America the convergence obliquity, subduction dip angles and presence of a volcanic arc all vary, but strain partitioning is only observed along parts of it. This raises the questions, to what extent do subduction zone characteristics control strain partitioning in the overriding continental plate, and which factors have the largest influence? We address these questions using lithospheric-scale 3D numerical geodynamic experiments to investigate the influence of subduction dip angle, convergence obliquity, and weaknesses in the crust owing to the volcanic arc on strain partitioning behavior. We base the model design on the Northern Volcanic Zone of the Andes (5° N - 2° S), characterized by steep subduction (˜ 35°), a convergence obliquity between 31° -45° and extensive arc volcanism, and where strain partitioning is observed. The numerical modelling software (DOUAR) solves the Stokes flow and heat transfer equations for a viscous-plastic creeping flow to calculate velocity fields, thermal evolution, rock uplift and strain rates in a 1600 km x 1600 km box with depth 160 km. Subduction geometry and material properties are based on a simplified, generic subduction zone similar to the northern Andes. The upper surface is initially defined to resemble the Andes, but is free to deform during the experiments. We consider two main model designs, one with and one without a volcanic arc (weak continental zone). A relatively high angle of convergence obliquity is predicted to favor strain partitioning, but preliminary model results show no strain partitioning for a uniform continental crustal strength with a friction angle of Φ = 15° . However, strain partitioning does occur when including a weak zone in the continental crust resulting from arc volcanic activity with Φ = 5° . This results in margin-parallel northeastward translation of a continental sliver at 3.2 cm/year. The presence of the sliver agrees well with observations of a continental sliver identified by GPS measurements in the Northern Volcanic Zone with a translation velocity of about 1 cm/year, though the GPS-derived velocity may not be representative of the long-term rate of translation depending on whether the observation period includes one or more seismic cycles. Regardless, the observed behavior is consistent with the observed earthquake focal mechanisms and GPS measurements, suggesting significant northeastward transport of Andean crust along the margin of the northern Andes.

Subducting plate geology in three great earthquake ruptures of the western Alaska margin, Kodiak to Unimak

USGS Publications Warehouse

von Huene, Roland E.; Miller, John J.; Weinrebe, Wilhelm

2012-01-01

Three destructive earthquakes along the Alaska subduction zone sourced transoceanic tsunamis during the past 70 years. Since it is reasoned that past rupture areas might again source tsunamis in the future, we studied potential asperities and barriers in the subduction zone by examining Quaternary Gulf of Alaska plate history, geophysical data, and morphology. We relate the aftershock areas to subducting lower plate relief and dissimilar materials in the seismogenic zone in the 1964 Kodiak and adjacent 1938 Semidi Islands earthquake segments. In the 1946 Unimak earthquake segment, the exposed lower plate seafloor lacks major relief that might organize great earthquake rupture. However, the upper plate contains a deep transverse-trending basin and basement ridges associated with the Eocene continental Alaska convergent margin transition to the Aleutian island arc. These upper plate features are sufficiently large to have affected rupture propagation. In addition, massive slope failure in the Unimak area may explain the local 42-m-high 1946 tsunami runup. Although Quaternary geologic and tectonic processes included accretion to form a frontal prism, the study of seismic images, samples, and continental slope physiography shows a previous history of tectonic erosion. Implied asperities and barriers in the seismogenic zone could organize future great earthquake rupture.

Inverse models of plate coupling and mantle rheology: Towards a direct link between large-scale mantle flow and mega thrust earthquakes

NASA Astrophysics Data System (ADS)

Gurnis, M.; Ratnaswamy, V.; Stadler, G.; Rudi, J.; Liu, X.; Ghattas, O.

2017-12-01

We are developing high-resolution inverse models for plate motions and mantle flow to recover the degree of mechanical coupling between plates and the non-linear and plastic parameters governing viscous flow within the lithosphere and mantle. We have developed adjoint versions of the Stokes equations with fully non-linear viscosity with a cost function that measures the fit with plate motions and with regional constrains on effective upper mantle viscosity (from post-glacial rebound and post seismic relaxation). In our earlier work, we demonstrate that when the temperature field is known, the strength of plate boundaries, the yield stress and strain rate exponent in the upper mantle are recoverable. As the plate boundary coupling drops below a threshold, the uncertainty of the inferred parameters increases due to insensitivity of plate motion to plate coupling. Comparing the trade-offs between inferred rheological parameters found from a Gaussian approximation of the parameter distribution and from MCMC sampling, we found that the Gaussian approximation—which is significantly cheaper to compute—is often a good approximation. We have extended our earlier method such that we can recover normal and shear stresses within the zones determining the interface between subducting and over-riding plates determined through seismic constraints (using the Slab1.0 model). We find that those subduction zones with low seismic coupling correspond with low inferred values of mechanical coupling. By fitting plate motion data in the optimization scheme, we find that Tonga and the Marianas have the lowest values of mechanical coupling while Chile and Sumatra the highest, among the subduction zones we have studies. Moreover, because of the nature of the high-resolution adjoint models, the subduction zones with the lowest coupling have back-arc extension. Globally we find that the non-linear stress-strain exponent, n, is about 3.0 +/- 0.25 (in the upper mantle and lithosphere) and a pressure-independent yield stress is 150 +/- 25 MPa. The stress in the shear zones is just tens of MPa, and in preliminary models, we find that both the shear and the normal stresses are elevated in the coupled compared to the uncoupled subduction zones.

The dynamics of plate tectonics and mantle flow: from local to global scales.

PubMed

Stadler, Georg; Gurnis, Michael; Burstedde, Carsten; Wilcox, Lucas C; Alisic, Laura; Ghattas, Omar

2010-08-27

Plate tectonics is regulated by driving and resisting forces concentrated at plate boundaries, but observationally constrained high-resolution models of global mantle flow remain a computational challenge. We capitalized on advances in adaptive mesh refinement algorithms on parallel computers to simulate global mantle flow by incorporating plate motions, with individual plate margins resolved down to a scale of 1 kilometer. Back-arc extension and slab rollback are emergent consequences of slab descent in the upper mantle. Cold thermal anomalies within the lower mantle couple into oceanic plates through narrow high-viscosity slabs, altering the velocity of oceanic plates. Viscous dissipation within the bending lithosphere at trenches amounts to approximately 5 to 20% of the total dissipation through the entire lithosphere and mantle.

Analysis and flight evaluation of a small, fixed-wing aircraft equipped with hinged plate spoilers

NASA Technical Reports Server (NTRS)

Olcott, J. W.; Sackel, E.; Ellis, D. R.

1981-01-01

The results of a four phase effort to evaluate the application of hinged plate spoilers/dive brakes to a small general aviation aircraft are presented. The test vehicle was a single engine light aircraft modified with an experimental set of upper surface spoilers and lower surface dive brakes similar to the type used on sailplanes. The lift, drag, stick free stability, trim, and dynamic response characteristics of four different spoiler/dive brake configurations were determined. Tests also were conducted, under a wide range of flight conditions and with pilots of various experience levels, to determine the most favorable methods of spoiler control and to evaluate how spoilers might best be used during the approach and landing task. The effects of approach path angle, approach airspeed, and pilot technique using throttle/spoiler integrated control were investigated for day, night, VFR, and IFR approaches and landings. The test results indicated that spoilers offered significant improvements in the vehicle's performance and flying qualities for all elements of the approach and landing task, provided a suitable method of control was available.

Recent Results from the Spirit Rover at Home Plate and "Silica Valley"

NASA Astrophysics Data System (ADS)

Squyres, S. W.

2007-12-01

The Mars Exploration Rover Spirit has spent more than 500 sols exploring Home Plate in the inner basin of the Columbia Hills, and adjacent materials. Home Plate is a plateau of layered rocks 80-90 meters in diameter and ~2 meters high. The rocks are clastic and of moderately altered alkali basalt composition, enriched in some volatile elements. A coarse-grained lower unit is overlain by a finer-grained upper unit. Textural observations, including a prominent bomb sag, indicate that the lower strata were emplaced in an explosive event. Geochemical similarities to nearby volcanic rocks and the enrichment in volatile elements favor an explosive volcanic origin. Along the northern portion of Home Plate, the upper unit is very well sorted and composed of well rounded sand sized grains, pointing to textural maturity and suggesting an eolian origin. Along the southeastern portion, however, the upper unit contains some coarser granules too large to be transported by saltation. While their size is comparable to other clasts on Mars that have moved by saltation-induced creep, the observed textures clearly are consistent with emplacement as a pyroclastic surge. The upper and lower units are effectively identical in composition, so the upper unit probably represents a finer-grained fraction of pyroclastic materials that may have undergone some local reworking by wind. Rocks along the margins of Home Plate show a consistent dip toward the center of the plateau. We interpret Home Plate to be the eroded remnants of a formerly more extensive sheet of pyroclastic materials, perhaps produced in a phreatomagmatic eruption. The inward dips may have arisen when pyroclastic materials overrode and partially buried a pre-existing bowl-shaped depression such as an impact crater, draping the topography. Immediately to the east of Home Plate is a narrow valley bounded on one side by Home Plate and on the other by Mitcheltree Ridge. While operating within this valley, Spirit's inoperative right front wheel excavated a small patch of high albedo soil. Mini-TES spectra of this soil were well fit by amorphous silica, and subsequent investigation with the APXS showed a composition that was more than 90% SiO2. The deposits are also enriched in Ti. Mini-TES spectra of nearby rocks also show a strong signature of amorphous silica, and APXS spectra of these rocks also confirm a high silica content. We consider two hypotheses for the formation of these silica-rich deposits. One is that they developed via precipitation from hydrothermal fluids. Siliceous sinter deposits are common in terrestrial hydrothermal environments where fluids dissolve Si from host rocks at high temperatures and then reprecipitate silica at lower temperatures. Alternatively, the Si-rich materials may represent the remnants of formerly basaltic materials that have been extensively leached in a fumarolic environment under acid sulfate conditions. In either case, the proximity to Home Plate is consistent with formation via the interaction of basaltic volcanism with groundwater. The astrobiological implications of these Si-rich deposits may be significant. Both hydrothermal systems and fumaroles are capable of supporting microbial ecosystems on Earth, and precipitated silica deposits in both environments can preserve strong textural evidence of microbial life.

Lithospheric radial anisotropy beneath the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Chu, Risheng; Ko, Justin Yen-Ting; Wei, Shengji; Zhan, Zhongwen; Helmberger, Don

2017-05-01

The Lithosphere-Asthenosphere Boundary (LAB), where a layer of low viscosity asthenosphere decouples with the upper plate motion, plays an essential role in plate tectonics. Most dynamic modeling assumes that the shear velocity can be used as a surrogate for viscosity which provides key information about mantle flow. Here, we derive a shear velocity model for the LAB structure beneath the Gulf of Mexico allowing a detailed comparison with that beneath the Pacific (PAC) and Atlantic (ATL). Our study takes advantage of the USArray data from the March 25th, 2013 Guatemala earthquake at a depth of 200 km. Such data is unique in that we can observe a direct upward traveling lid arrival which remains the first arrival ahead of the triplications beyond 18°. This extra feature in conjunction with upper-mantle triplication sampling allows good depth control of the LAB and a new upper-mantle seismic model ATM, a modification of ATL, to be developed. ATM has a prominent low velocity zone similar to the structure beneath the western Atlantic. The model contains strong radial anisotropy in the lid where VSH is about 6% faster than VSV. This anisotropic feature ends at the bottom of the lithosphere at about the depth of 175 km in contrast to the Pacific where it extends to over 300 km. Another important feature of ATM is the weaker velocity gradient from the depth of 175 to 350 km compared to Pacific models, which may be related to differences in mantle flow.

Nuclear reactor alignment plate configuration

DOEpatents

Altman, David A; Forsyth, David R; Smith, Richard E; Singleton, Norman R

2014-01-28

An alignment plate that is attached to a core barrel of a pressurized water reactor and fits within slots within a top plate of a lower core shroud and upper core plate to maintain lateral alignment of the reactor internals. The alignment plate is connected to the core barrel through two vertically-spaced dowel pins that extend from the outside surface of the core barrel through a reinforcement pad and into corresponding holes in the alignment plate. Additionally, threaded fasteners are inserted around the perimeter of the reinforcement pad and into the alignment plate to further secure the alignment plate to the core barrel. A fillet weld also is deposited around the perimeter of the reinforcement pad. To accomodate thermal growth between the alignment plate and the core barrel, a gap is left above, below and at both sides of one of the dowel pins in the alignment plate holes through with the dowel pins pass.

Upper internals arrangement for a pressurized water reactor

DOEpatents

Singleton, Norman R; Altman, David A; Yu, Ching; Rex, James A; Forsyth, David R

2013-07-09

In a pressurized water reactor with all of the in-core instrumentation gaining access to the core through the reactor head, each fuel assembly in which the instrumentation is introduced is aligned with an upper internals instrumentation guide-way. In the elevations above the upper internals upper support assembly, the instrumentation is protected and aligned by upper mounted instrumentation columns that are part of the instrumentation guide-way and extend from the upper support assembly towards the reactor head in hue with a corresponding head penetration. The upper mounted instrumentation columns are supported laterally at one end by an upper guide tube and at the other end by the upper support plate.

Miocene tectonics of the Western Alboran domain: from mantle extensional exhumation to westward thrusting

NASA Astrophysics Data System (ADS)

Gueydan, F.; Frasca, G.; Brun, J. P.

2015-12-01

In the frame of the Africa-Europe convergence, the Mediterranean tectonic system presents a complex interaction between subduction rollback and upper-plate deformation during the Tertiary. The western Mediterranean is characterized by the exhumation of the largest subcontinental mantle massif worldwide (the Ronda Peridotite) and a narrow arcuate geometryacross the Gibraltar arc within the Betic-Rif belt (the internal part being called the Alboran domain), where the relationship between slab dynamics and surface tectonics is not well understood. New structural and geochronological data are used to argue for 1/ hyperstrechting of the continental lithosphere allowing extensional mantle exhumation to shallow depths, followed by 2/ lower miocene thrusting. Two Lower Miocene E-W-trending strike-slip corridors played a major role in the deformation pattern of the Alboran Domain, in which E-W dextral strike-slip faults, N60°-trending thrusts and N140°-trending normal faults developed simultaneously during dextral strike-slip simple shear. The inferred continuous westward translation of the Alboran Domain is accommodated by a major E-W-trending lateral ramp (strike-slip) and a N60°-trending frontal thrust. At lithosphere-scale, we interpret the observed deformation pattern as the upper-plate expression of a lateral slab tear and of its westward propagation since Lower Miocene. The crustal emplacement of the Ronda Peridotites occurred at the onset of this westward motion.The Miocene tectonics of the western Alboran is therefore marked by the inversion of a continental rift, triggered by shortening of the upper continental plate and accommodated by E-W dextral strike-slip corridors. During thrusting and westward displacement of the Alboran domain with respect to Iberia, the hot upper plate, which involved the previously exhumed sub-continental mantle, underwent fast cooling.

Impact of slab pull and incipient mantle delamination on active tectonics and crustal thickening in the Betic-Alboran-Rif system

NASA Astrophysics Data System (ADS)

Mazzotti, Stephane; Baratin, Laura-May; Chéry, Jean; Vernant, Philippe; Gueydan, Frédéric; Tahayt, Abdelilah; Mourabit, Taoufik

2017-04-01

In Western Mediterranean, the Betic-Alboran-Rif orocline accommodates the WNW-ESE convergence between the Nubia and Eurasia plates. Recent geodetic data show that present-day tectonics in northern Morocco and southernmost Spain are not compatible with this simple two-plate-convergence model: GPS observations indicate significant (2-4 mm/a) deviations from the expected plate motion, and gravity data define two major negative Bouguer anomalies beneath the Betic and south of the Rif, interpreted as a thickened crust in a state of non-isostatic equilibrium. These anomalous geodetic patterns are likely related to the recent impact of the sub-vertical Alboran slab on crustal tectonics. Using 2-D finite-element models, we study the first-order behavior of a lithosphere affected by a downward normal traction, representing the pull of a high-density body in the upper mantle (slab pull or mantle delamination). We show that a specific range of lower crust and upper mantle viscosities allow a strong coupling between the mantle and the base of the brittle crust, thus enabling (1) the efficient conversion of vertical movement (resulting from the downward traction) to horizontal movement and (2) shortening and thickening on the brittle upper crust. Our results show that incipient delamination of the Nubian continental lithosphere, linked to the Alboran slab pull, can explain the present-day abnormal tectonics and non-isostatic equilibrium in northern Morocco. Similar processes may be at play in the whole Betic-Alboran-Rif region, although the fast temporal evolution of the slab - upper plate interactions needs to be taken into account to better understand this complex system.

Trench curvature initiation: Upper plate strain pattern and volcanism Insights from the Lesser Antilles arc, St Barthélemy Island, FWI.

NASA Astrophysics Data System (ADS)

Philippon, M. M.; Legendre, L.; Münch, P.; Léticée, J. L.; Lebrun, J. F.; Maincent, G.; Mazabraud, Y.

2017-12-01

Upper plate deformation pattern reflect the mechanical behavior of subduction zones. In this study, we focus on the consequence of the entrance of a buoyant plateau within the Caribbean subduction zone during Eocene by studying the oldest cropping out rocks of the Lesser Antilles volcanic arc. Based on novel geochronological ages and available bio-stratigraphic data we show that St Barthélemy Island was built during three successive volcanic events over the Mid- Eocene to Oligo-Miocene time span. We show that magmatism is mainly Oligocene, not Eocene. Moreover, we demonstrate that tholeitic and calc-alkaline magmatism co-existed all along the arc activity. And ultimately we evidence a westward migration of the volcanism at the island scale. Furthermore, We demonstrate that during 21 Ma, the built of theses volcanoes, the stress regime evolves from pure to radial extension with a sub-horizontal σ3 showing N30° mean trend. To conclude, our novel results invalidate the chronological, geochemical and spatial evolution of the island arc magmatism formerly proposed in the early eighties. Indeed, arc magmatism in St Barthélemy was mainly related to the West-dipping Lesser Antilles subduction zone and not to the South-dipping Greater Antilles subduction and upper plate deformation evolution observed at local scale reflects large scale mechanical behavior of the Lesser Antilles subduction zone. A two steps restoration of the regional deformation shows that the switch from pure parallel to the trench extension to radial extension within the Caribbean upper plate reflects trench curvature that followed the entrance of the Bahamas bank in the Greater Antilles subduction zone and its collision.

Possible reactivation of the Vincent-Chocolate Mountains thrust in the Gavilan Hills area, southeasternmost California

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

Oyarzabal, F.R.; Jacobson, C.E.; Haxel, G.B.

The Late Cretaceous-early Tertiary Orocopia Schist (OS) of southeasternmost California consists of metamorphosed continental margin sedimentary and basaltic rocks, overlain by an upper plate of continental crust along the Vincent-Chocolate Mountains fault (VCMF). Previous analysis of late folds and shear band in OS and upper plate in the Gavilan Hills and adjacent ares indicated that the direction of transport of the upper plate was northeastward. This has been considered evidence of a SW dipping subduction zone, along which an outboard continental fragment was sutured to North America. Another view is that the VCMF was formed by underplating of the OSmore » in an Andean continental margin, and that the NE-vergent late structures formed during uplift of the OS. The authors' continuing work in the Gavilan Hills confirm the NE sense of vergence but suggests a more complex structural history. The schist is characterized by refolded folds, shear bands, and two penetrative lineations. An older lineation that ranges from N10[degree]E to N30[degree]E is widespread in the area, but is more evident at low structural levels. A second lineation ranges from N40[degree]E to N70[degree]E and is strongly developed in rocks near the VCMF. The complex folding pattern, presence of mylonitic schist, relative thinness of upper-plate mylonite, and possible retrogressive character of the shear bands suggest that the VCMF in the Gavilan Hills area may have been reactivated after original thrusting. The VCMF in the Gavilan Hills is intermediate in character between the probable subduction thrust in the San Gabriel Mountains and the reactivated faults in the Orocopia Mountains and areas surrounding the Gavilan Hills.« less

Plate-like permanent dental laminae of upper jaw dentition in adult gobiid fish, Sicyopterus japonicus.

PubMed

Moriyama, Keita; Watanabe, Shun; Iida, Midori; Sahara, Noriyuki

2010-04-01

Sicyopterus japonicus (Teleostei, Gobiidae) possesses a unique upper jaw dentition different from that known for any other teleosts. In the adults, many (up to 30) replacement teeth, from initiation to attachment, are arranged orderly in a semicircular-like strand within a capsule of connective tissue on the labial side of each premaxillary bone. We have applied histological, ultrastructural, and three-dimensional imaging from serial sections to obtain insights into the distribution and morphological features of the dental lamina in the upper jaw dentition of adult S. japonicus. The adult fish has numerous permanent dental laminae, each of which is an infolding of the oral epithelium at the labial side of the functional tooth and forms a thin plate-like structure with a wavy contour. All replacement teeth of a semicircular-like strand are connected to the plate-like dental lamina by the outer dental epithelium and form a tooth family; neighboring tooth families are completely separated from each other. The new tooth germ directly buds off from the ventro-labial margin of the dental lamina, whereas no distinct free end of the dental lamina is present, even adjacent to this region. Cell proliferation concentrated at the ventro-labial margin of the dental lamina suggests that this region is the site for repeated tooth initiation. During tooth development, the replacement tooth migrates along a semicircular-like strand and eventually erupts through the dental lamina into the oral epithelium at the labial side of the functional tooth. This unique thin plate-like permanent dental lamina and the semicircular-like strand of replacement teeth in the upper jaw dentition of adult S. japonicus probably evolved as a dental adaptation related to the rapid replacement of teeth dictated by the specialized feeding habit of this algae-scraping fish.

Pump tank divider plate for sump suction sodium pumps

DOEpatents

George, John A.; Nixon, Donald R.

1977-01-01

A circular plate extends across the diameter of "sump suction" pump, with a close clearance between the edge of the plate and the wall of the pump tank. The plate is located above the pump impeller, inlet and outlet flow nozzles but below the sodium free surface and effectively divides the pump tank into two separate chambers. On change of pump speed, the close fitting flow restriction plate limits the rate of flow into or out of the upper chamber, thereby minimizing the rate of level change in the tank and permitting time for the pump cover gas pressure to be varied to maintain an essentially constant level.

Thermal baffle for fast-breeder reacton

DOEpatents

Rylatt, John A.

1977-01-01

A liquid-metal-cooled fast-breeder reactor includes a bridge structure for separating hot outlet coolant from relatively cool inlet coolant consisting of an annular stainless steel baffle plate extending between the core barrel surrounding the core and the thermal liner associated with the reactor vessel and resting on ledges thereon, there being inner and outer circumferential webs on the lower surface of the baffle plate and radial webs extending between the circumferential webs, a stainless steel insulating plate completely covering the upper surface of the baffle plate and flex seals between the baffle plate and the ledges on which the baffle plate rests to prevent coolant from washing through the gaps therebetween. The baffle plate is keyed to the core barrel for movement therewith and floating with respect to the thermal liner and reactor vessel.

Fuel cell separator plate with bellows-type sealing flanges

DOEpatents

Louis, G.A.

1984-05-29

A fuel cell separator includes a rectangular flat plate having two unitary upper sealing flanges respectively comprising opposite marginal edges of the plate folded upwardly and back on themselves and two lower sealing flanges respectively comprising the other two marginal edges of the plate folded downwardly and back on themselves. Each of the sealing flanges includes a flat wall spaced from the plate and substantially parallel thereto and two accordion-pleated side walls, one of which interconnects the flat wall with the plate and the other of which steps just short of the plate, these side walls affording resilient compressibility to the sealing flange in a direction generally normal to the plane of the plate. Four corner members close the ends of the sealing flanges. An additional resiliently compressible reinforcing member may be inserted in the passages formed by each of the sealing flanges with the plate.

Fuel cell separator plate with bellows-type sealing flanges

DOEpatents

Louis, George A.

1986-08-05

A fuel cell separator includes a rectangular flat plate having two unitary upper sealing flanges respectively comprising opposite marginal edges of the plate folded upwardly and back on themselves and two lower sealing flanges respectively comprising the other two marginal edges of the plate folded downwardly and back on themselves. Each of the sealing flanges includes a flat wall spaced from the plate and substantially parallel thereto and two accordion-pleated side walls, one of which interconnects the flat wall with the plate and the other of which stops just short of the plate, these side walls affording resilient compressibility to the sealing flange in a directiongenerally normal to the plane of the plate. Four corner members close the ends of the sealing flanges. An additional resiliently compressible reinforcing member may be inserted in the passages formed by each of the sealing flanges with the plate.

Anatomy of the dead sea transform from lithospheric to microscopic scale

USGS Publications Warehouse

Weber, M.; Abu-Ayyash, K.; Abueladas, A.; Agnon, A.; Alasonati-Tasarova, Z.; Al-Zubi, H.; Babeyko, A.; Bartov, Y.; Bauer, K.; Becken, M.; Bedrosian, P.A.; Ben-Avraham, Z.; Bock, G.; Bohnhoff, M.; Bribach, J.; Dulski, P.; Ebbing, J.; El-Kelani, R.; Forster, A.; Forster, H.-J.; Frieslander, U.; Garfunkel, Z.; Goetze, H.J.; Haak, V.; Haberland, C.; Hassouneh, M.; Helwig, S.; Hofstetter, A.; Hoffmann-Rotrie, A.; Jackel, K.H.; Janssen, C.; Jaser, D.; Kesten, D.; Khatib, M.; Kind, R.; Koch, O.; Koulakov, I.; Laske, Gabi; Maercklin, N.; Masarweh, R.; Masri, A.; Matar, A.; Mechie, J.; Meqbel, N.; Plessen, B.; Moller, P.; Mohsen, A.; Oberhansli, R.; Oreshin, S.; Petrunin, A.; Qabbani, I.; Rabba, I.; Ritter, O.; Romer, R.L.; Rumpker, G.; Rybakov, M.; Ryberg, T.; Saul, J.; Scherbaum, F.; Schmidt, S.; Schulze, A.; Sobolev, S.V.; Stiller, M.; Stromeyer, D.; Tarawneh, K.; Trela, C.; Weckmann, U.; Wetzel, U.; Wylegalla, K.

2009-01-01

Fault zones are the locations where motion of tectonic plates, often associated with earthquakes, is accommodated. Despite a rapid increase in the understanding of faults in the last decades, our knowledge of their geometry, petrophysical properties, and controlling processes remains incomplete. The central questions addressed here in our study of the Dead Sea Transform (DST) in the Middle East are as follows: (1) What are the structure and kinematics of a large fault zone? (2) What controls its structure and kinematics? (3) How does the DST compare to other plate boundary fault zones? The DST has accommodated a total of 105 km of leftlateral transform motion between the African and Arabian plates since early Miocene (???20 Ma). The DST segment between the Dead Sea and the Red Sea, called the Arava/ Araba Fault (AF), is studied here using a multidisciplinary and multiscale approach from the ??m to the plate tectonic scale. We observe that under the DST a narrow, subvertical zone cuts through crust and lithosphere. First, from west to east the crustal thickness increases smoothly from 26 to 39 km, and a subhorizontal lower crustal reflector is detected east of the AF. Second, several faults exist in the upper crust in a 40 km wide zone centered on the AF, but none have kilometer-size zones of decreased seismic velocities or zones of high electrical conductivities in the upper crust expected for large damage zones. Third, the AF is the main branch of the DST system, even though it has accommodated only a part (up to 60 km) of the overall 105 km of sinistral plate motion. Fourth, the AF acts as a barrier to fluids to a depth of 4 km, and the lithology changes abruptly across it. Fifth, in the top few hundred meters of the AF a locally transpressional regime is observed in a 100-300 m wide zone of deformed and displaced material, bordered by subparallel faults forming a positive flower structure. Other segments of the AF have a transtensional character with small pull-aparts along them. The damage zones of the individual faults are only 5-20 m wide at this depth range. Sixth, two areas on the AF show mesoscale to microscale faulting and veining in limestone sequences with faulting depths between 2 and 5 km. Seventh, fluids in the AF are carried downward into the fault zone. Only a minor fraction of fluids is derived from ascending hydrothermal fluids. However, we found that on the kilometer scale the AF does not act as an important fluid conduit. Most of these findings are corroborated using thermomechanical modeling where shear deformation in the upper crust is localized in one or two major faults; at larger depth, shear deformation occurs in a 20-40 km wide zone with a mechanically weak decoupling zone extending subvertically through the entire lithosphere. Copyright 2009 by the American Geophysical Union.

A magneto-rheological fluid mount featuring squeeze mode: analysis and testing

NASA Astrophysics Data System (ADS)

Chen, Peng; Bai, Xian-Xu; Qian, Li-Jun; Choi, Seung-Bok

2016-05-01

This paper presents a mathematical model for a new semi-active vehicle engine mount utilizing magneto-rheological (MR) fluids in squeeze mode (MR mount in short) and validates the model by comparing analysis results with experimental tests. The proposed MR mount is mainly comprised of a frame for installation, a main rubber, a squeeze plate and a bobbin for coil winding. When the magnetic fields on, MR effect occurs in the upper gap between the squeeze plate and the bobbin, and the dynamic stiffness can be controlled by tuning the applied currents. Employing Bingham model and flow properties between parallel plates of MR fluids, a mathematical model for the squeeze type of MR mount is formulated with consideration of the fluid inertia, MR effect and hysteresis property. The field-dependent dynamic stiffness of the MR mount is then analyzed using the established mathematical model. Subsequently, in order to validate the mathematical model, an appropriate size of MR mount is fabricated and tested. The field-dependent force and dynamic stiffness of the proposed MR mount are evaluated and compared between the model and experimental tests in both time and frequency domains to verify the model efficiency. In addition, it is shown that both the damping property and the stiffness property of the proposed MR mount can be simultaneously controlled.

Nurture Versus Nature: Accounting for the Differences Between the Taiwan and Timor active arc-continent collisions

NASA Astrophysics Data System (ADS)

Harris, R. A.

2011-12-01

The active Banda arc/continent collision of the Timor region provides many important contrasts to what is observed in Taiwan, which is mostly a function of differences in the nature of the subducting plate. One of the most important differences is the thermal state of the respective continental margins: 30 Ma China passive margin versus 160 Ma NW Australian continental margin. The subduction of the cold and strong NW Australian passive margin beneath the Banda trench provides many new constraints for resolving longstanding issues about the formative stages of collision and accretion of continental crust. Some of these issues include evidence for slab rollback and subduction erosion, deep continental subduction, emplacement or demise of forearc basement, relative amounts of uplift from crustal vs. lithospheric processes, influence of inherited structure, partitioning of strain away from the thrust front, extent of mélange development, metamorphic conditions and exhumation mechanisms, continental contamination and accretion of volcanic arcs, does the slab tear, and does subduction polarity reverse? Most of these issues link to the profound control of lower plate crustal heterogeneity, thermal state and inherited structure. The thermomechanical characteristics of subducting an old continental margin allow for extensive underthrusting of lower plate cover units beneath the forearc and emplacement and uplift of extensive nappes of forearc basement. It also promotes subduction of continental crust to deep enough levels to experience high pressure metamorphism (not found in Taiwan) and extensive contamination of the volcanic arc. Seismic tomography confirms subduction of continental lithosphere beneath the Banda Arc to at least 400 km with no evidence for slab tear. Slab rollback during this process results in massive subduction erosion and extension of the upper plate. Other differences in the nature of the subducting plates in Taiwan in Timor are differences in the lateral continuity of the continental margins. The northern Australian continental margin is highly irregular with many rift basins subducting parallel to their axes. This feature gives rise to irregularities in the uplift pattern of the collision and its continental margin parallel structural grain. Another major difference between Taiwan and Timor is the mechanical stratigraphy entering the trench. The Australian continental margin bears a carbonate rich pre and post rift sequence that is separated by a 1000 m thick, over pressured mudstone unit that acts as major detachment and promotes extensive mud diapirism. The post breakup Australian Passive Margin Sequence is incorporated into the orogenic wedge by frontal accretion and forms a classic imbricate thrust stack near the front of the Banda forearc. The pre breakup Gondwana Sequence below the detachment continues at least to depth of 30 km in the subduction channel beneath the Banda forearc upper plate and stacks up into a duplex zone that forms structural culminations throughout Timor. The upper plate of both collisions is similar in nature but is deformed in different ways due to the strong influence of the lower plate. However, both have extensive subduction erosion and demise of the forearc and systematic accretion of the arc.

The Evolution of Plate and Extruded Products with High Strength and Fracture Toughness

NASA Astrophysics Data System (ADS)

Denzer, D. K.; Rioja, R. J.; Bray, G. H.; Venema, G. B.; Colvin, E. L.

From the first use of 2017-T74 on the Junkers F13, improvements have been made to plate and extruded products for applications requiring the highest attainable strength and adequate fracture toughness. One such application is the upper wing of large aircraft. The progression of these product improvements achieved through the development of alloys that include 7075-(T6 & T76), 7150-(T6 & T77) and 7055-(T77 & T79) and most recently 7255-(T77 & T79) is reviewed. The most current advancements include aluminum-copper-lithium, alloy 2055 plate and extruded products that can attain strength equivalent to that of 7055-T77 with higher modulus, similar fracture toughness and improved fatigue, fatigue crack growth and corrosion performance. The achievement of these properties is explained in terms of the several alloy design principles. The highly desired and balanced characteristics make these products ideal for upper wing applications.

Microlepidogaster arachas, a new species of hypoptopomatine catfish (Siluriformes: Loricariidae) from the upper rio Paraná basin, Brazil.

PubMed

Martins, Fernanda O; Calegari, Bárbara B; Langeani, Francisco

2013-01-22

Microlepidogaster arachas Martins, Calegari & Langeani, sp. nov., a new Hypoptopomatinae, is described from the upper rio Paraná basin. The new species is distinguished from M. longicolla and M. dimorpha by having the anterior portion of the compound supraneural plus first dorsal-fin proximal radial contacting the neural spine of the ninth vertebra. The new species differs from M. perforatus by having 18-29 dentary teeth; median series of lateral plates complete, reaching caudal-peduncle end, and continuous lateral line; and 20-24 mid-dorsal plates. Microlepidogaster arachas is further distinguished from its congeners by several other osteological features.

Thin walled channel

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

Crowther, R.L.; Johansson, E.B.

1988-06-07

A fuel assembly is described comprising fuel rods positioned in a spaced array by upper and lower tie-plates, an open ended flow channel surrounding the array for conducting coolant upward about the fuel rods, the open ended channel having a polygon shaped cross section with flat side sections connected between the corner sections; means separate from the channel connecting the upper and lower tie-plates together and maintaining the fuel rods in spaced array independent of the flow channel, improvement in the flow channel comprising: four corners having a first thickness; four sides having a second and reduced thickness from themore » corner thickness, the sides welded to the corner sections.« less

Extended plate and beam demonstration home

Treesearch

Patricia Gunderson; Vladimir Kochkin; Xiping Wang

2018-01-01

An extended plate and beam (EP&B) design was developed at Home Innovation Research Labs (Upper Marlboro, Maryland) in an effort to provide traditional light-frame wall construction details that are compatible with continuous insulating sheathing. This would encourage wide-spread adoption of high-R walls and promote greater energy efficiency in new houses. The...

Numerical study focusing on the entropy analysis of MHD squeezing flow of a nanofluid model using Cattaneo–Christov theory

NASA Astrophysics Data System (ADS)

Akmal, N.; Sagheer, M.; Hussain, S.

2018-05-01

The present study gives an account of the heat transfer characteristics of the squeezing flow of a nanofluid between two flat plates with upper plate moving vertically and the lower in the horizontal direction. Tiwari and Das nanofluid model has been utilized to give a comparative analysis of the heat transfer in the Cu-water and Al2O3-water nanofluids with entropy generation. The modeling is carried out with the consideration of Lorentz forces to observe the effect of magnetic field on the flow. The Joule heating effect is included to discuss the heat dissipation in the fluid and its effect on the entropy of the system. The nondimensional ordinary differential equations are solved using the Keller box method to assess the numerical results which are presented by the graphs and tables. An interesting observation is that the entropy is generated more near the lower plate as compared with that at the upper plate. Also, the heat transfer rate is found to be higher for the Cu nanoparticles in comparison with the Al2O3 nanoparticles.

Isostatic Model and Isostatic Gravity Anomalies of the Arabian Plate and Surroundings

NASA Astrophysics Data System (ADS)

Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

2016-04-01

The isostatic modeling represents one of the most useful "geological" reduction methods of the gravity field. With the isostatic correction, it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. Although there exist several isostatic compensation schemes, it is usually supposed that a choice of the model is not an important factor to first order, since the total weight of compensating masses remains the same. We compare two alternative models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which cannot be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also, the predicted "isostatic" Moho is very different from existing seismic observations. The second isostatic model includes the Moho, which is based on seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). According to this model, the upper mantle under the Arabian Shield is less dense than under the Platform. In the Arabian platform, the maximum density coincides with the Rub' al Khali, one of the richest oil basin in the world. This finding agrees with previous studies, showing that such basins are often underlain by dense mantle, possibly related to an eclogite layer that has caused their subsidence. The mantle density variations might be also a result of variations of the lithosphere thickness. With the combined isostatic model, it is possible to minimize regional anomalies over the Arabian plate. The residual local anomalies correspond well to tectonic structure of the plate. Still very significant anomalies, showing isostatic disturbances of the lithosphere, are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

Compressional intracontinental orogens: Ancient and modern perspectives

NASA Astrophysics Data System (ADS)

Raimondo, Tom; Hand, Martin; Collins, William J.

2014-03-01

Compressional intracontinental orogens are major zones of crustal thickening produced at large distances from active plate boundaries. Consequently, any account of their initiation and subsequent evolution must be framed outside conventional plate tectonics theory, which can only explain the proximal effects of convergent plate-margin interactions. This review considers a range of hypotheses regarding the origins and transmission of compressive stresses in intraplate settings. Both plate-boundary and intraplate stress sources are investigated as potential driving forces, and their relationship to rheological models of the lithosphere is addressed. The controls on strain localisation are then evaluated, focusing on the response of the lithosphere to the weakening effects of structural, thermal and fluid processes. With reference to the characteristic features of intracontinental orogens in central Asia (the Tien Shan) and central Australia (the Petermann and Alice Springs Orogens), it is argued that their formation is largely driven by in-plane stresses generated at plate boundaries, with the lithosphere acting as an effective stress guide. This implies a strong lithospheric mantle rheology, in order to account for far-field stress propagation through the discontinuous upper crust and to enable the support of thick uplifted crustal wedges. Alternative models of intraplate stress generation, primarily involving mantle downwelling, are rejected on the grounds that their predicted temporal and spatial scales for orogenesis are inconsistent with the observed records of deformation. Finally, inherited mechanical weaknesses, thick sedimentary blanketing over a strongly heat-producing crust, and pervasive reaction softening of deep fault networks are identified as important and interrelated controls on the ability of the lithosphere to accommodate rather than transmit stress. These effects ultimately produce orogenic zones with architectural features and evolutionary histories strongly reminiscent of typical collisional belts, suggesting that the deformational response of continental crust is remarkably similar in different tectonic settings.

The metallogenic role of east-west fracture zones in South America with regard to the motion of lithospheric plates (with an example from Brazil)

USGS Publications Warehouse

Kutina, J.; Carter, William D.; Lopez, F.X.

1978-01-01

The role of east-west fracture zones in South America is discussed with regard to global fracturing and the motion of lithospheric plates. A set of major NW-trending lineaments has been derived which show a tendency to be spaced equidistantly and may correspond to a set of east-west fractures in the "pre-drift" position of the South American plate. Statistical analysis of linears in the ERTS-mosaics shows that NW-fractures are also among the most important ones in the Andes region, suggesting that the above major lineaments extend into the basement of the Andes. Some of the old major fractures, trending east-west in the present orientation of South America, are discussed and their NE orientation in the pre-drift position of the plate is considered. An example of structural control of ore deposition in the Brazilian Shield is presented, using the maps of the RADAM Project. It is concluded that the small tin-bearing granitic bodies concentrated in the region of Sao Felix do Xingu in the state of Para represent upper parts of an unexposed granitoid massif which is controlled by the intersection of a major east-west fracture zone probably represents westward extension of the Patos Lineament of the easternmost part of Brazil, connected with the east-west fracture zone of the Para state through the basement of the Maranhao Basin (Sineclise do Maranhao-Piaui). It is expected that the proposed "Patos-Para Lineament" extends further westward and may similarly control, at intersections with fractures of other trends, some mineralization centers in the western part of the state of Para and in the state of Amazonas.

Strength and Deformation Rate of Plate Boundaries: The Rheological Effects of Grain Size Reduction, Structure, and Serpentinization.

NASA Astrophysics Data System (ADS)

Montesi, L.; Gueydan, F.

2016-12-01

Global strain rate maps reveal 1000-fold contrasts between plate interiors, oceanic or continental diffuse plate boundaries and narrow plate boundaries. Here, we show that rheological models based on the concepts of shear zone localization and the evolution of rock structure upon strain can explain these strain rate contrasts. Ductile shear zones constitute a mechanical paradox in the lithosphere. As every plastic deformation mechanism is strain-rate-hardening, ductile rocks are expected to deform at low strain rate and low stress (broad zone of deformation). Localized ductile shear zones require either a localized forcing (locally high stress) or a thermal or structural anomaly in the shear zone; either can be inherited or develop progressively as rocks deform. We previously identified the most effective process at each depth level of the lithosphere. In the upper crust and middle crust, rocks fabric controls localization. Grain size reduction is the most efficient mechanism in the uppermost mantle. This analysis can be generalized to consider a complete lithospheric section. We assume strain rate does not vary with depth and that the depth-integrated strength of the lithospheric does not change over time, as the total force is controlled by external process such as mantle convection and plate and slab buoyancy. Reducing grain size from a coarse value typical of undeformed peridotite to a value in agreement with the stress level (piezometer) while letting that stress vary from depth to depth (the integrated stress remains the same) increases the lithospheric strain rate by about a factor of 1000. This can explain the development of diffuse plate boundaries. The slightly higher strain rate of continental plate boundary may reflect development of a layered rock fabric in the middle crust. Narrow plate boundaries require additional weakening process. The high heat flux near mid-ocean ridge implies a thin lithosphere, which enhances stress (for constant integrated stress). While this can increase strain rate by another factor of 1000, another process must generate the lithospheric thickness variation in the first place. One possibility is serpentinization, which reduces the strength of the brittle crust, especially when coupled with the development of a fabric in brittle faults.

Stress Drops for Oceanic Crust and Mantle Intraplate Earthquakes in the Subduction Zone of Northeastern Japan Inferred from the Spectral Inversion Analysis

NASA Astrophysics Data System (ADS)

Si, H.; Ishikawa, K.; Arai, T.; Ibrahim, R.

2017-12-01

Understanding stress drop related to intraplate earthquakes in the subducting plate is very important for seismic hazard mitigation. In previous studies, Kita et al. (2015) analyzed stress drops for intraplate earthquakes under Hokkaido, Northern Japan, using S-coda wave spectral ratio analysis methods, and found that the stress drop for events occurring more than 10 km beneath the upper surface of the subducting plate (within the oceanic mantle) was larger than the stress drop for events occurring within 10 km of the upper surface of the subducting plate (in the oceanic crust). In this study, we focus on intraplate earthquakes that occur under Tohoku, Northeastern Japan, to determine whether similar stress drop differences may exist between earthquakes occurring within the upper 10 km of the subducting plate (within the oceanic crust) and those occurring deeper than 10 km (within the oceanic mantle), based on spectral inversion analysis of seismic waveforms recorded during the earthquakes. We selected 64 earthquakes with focal depths between 49-76 km and Mw 3.5-5.0 that occurred in the source area of the 2003 Miyagi-ken-oki earthquake (Mw 7.0) (region 1), and 82 earthquakes with focal depths between 49-67 km and Mw 3.5-5.5 in the source area of the 2011 Miyagi- ken-oki earthquake (Mw 7.1) (region 2). Records from the target earthquakes at 24 stations in region 1 and 21 stations in region 2 were used in the analysis. A 5-sec time window following S-wave onset was used for each station record. Borehole records of KiK-net station (MYGH04) was used as a reference station for both regions 1 and 2. We applied the spectral inversion analysis method of Matsunami et al. (2003) separately to regions 1 and 2. Our results show that stress drop generally increases with focal depth and that the stress drop for events occurring deeper than 10 km in the plate (within the oceanic mantle) were larger than the stress drop for events occurring within 10 km of the upper surface of the plate (within the oceanic crust). These results are consistent with previous studies.

Lithospheric strength in the active boundary between the Pacific Plate and Baja California microplate constrained from lower crustal and upper mantle xenoliths

NASA Astrophysics Data System (ADS)

Chatzaras, Vasileios; van der Werf, Thomas; Kriegsman, Leo M.; Kronenberg, Andreas; Tikoff, Basil; Drury, Martyn R.

2017-04-01

The lower crust is the most poorly understood of the lithospheric layers in terms of its rheology, particularly at active plate boundaries. We studied naturally deformed lower crustal xenoliths within an active plate boundary, in order to link their microstructures and rheological parameters to the well-defined active tectonic context. The Baja California shear zone (BCSZ), located at the western boundary of the Baja California microplate, comprises the active boundary accommodating the relative motion between the Pacific plate and Baja California microplate. The basalts of the Holocene San Quintin volcanic field carry lower crustal and upper mantle xenoliths, which sample the Baja California microplate lithosphere in the vicinity of the BCSZ. The lower crustal xenoliths range from undeformed gabbros to granoblastic two-pyroxene granulites. Two-pyroxene geothermometry shows that the granulites equilibrated at temperatures of 690-920 oC. Phase equilibria (P-T pseudosections using Perple_X) indicate that symplectites with intergrown pyroxenes, plagioclase, olivine and spinel formed at 3.6-5.4 kbar, following decompression from pressures exceeding 6 kbar. FTIR spectroscopy shows that the water content of plagioclase varies among the analyzed xenoliths; plagioclase is relatively dry in two xenoliths while one xenolith contains hydrated plagioclase grains. Microstructural observations and analysis of the crystallographic texture provide evidence for deformation of plagioclase by a combination of dislocation creep and grain boundary sliding. To constrain the strength of the lower crust and upper mantle near the BCSZ we estimated the differential stress using plagioclase and olivine grain size paleopiezomtery, respectively. Differential stress estimates for plagioclase range from 10 to 32 MPa and for olivine are 30 MPa. Thus the active microplate boundary records elevated crustal temperatures, heterogeneous levels of hydration, and low strength in both the lower crust and upper mantle. To further investigate the relative strength of the two lithospheric layers, we calculated the strain rate of plagioclase in granulites and the strain rate of olivine in lherzolites using experimental flow laws. These flow laws predict that plagioclase deforms at higher strain rates than olivine. Our data provide constraints on the viscosity structure of active transform plate boundaries and insights on how rheological processes in the lithosphere may change during plate boundary evolution.

Seismic structure and activity of the north-central Lesser Antilles subduction zone from an integrated approach: Similarities with the Tohoku forearc

NASA Astrophysics Data System (ADS)

Laigle, M.; Hirn, A.; Sapin, M.; Bécel, A.; Charvis, P.; Flueh, E.; Diaz, J.; Lebrun, J.-F.; Gesret, A.; Raffaele, R.; Galvé, A.; Evain, M.; Ruiz, M.; Kopp, H.; Bayrakci, G.; Weinzierl, W.; Hello, Y.; Lépine, J.-C.; Viodé, J.-P.; Sachpazi, M.; Gallart, J.; Kissling, E.; Nicolich, R.

2013-09-01

The 300-km-long north-central segment of the Lesser Antilles subduction zone, including Martinique and Guadeloupe islands has been the target of a specific approach to the seismic structure and activity by a cluster of active and passive offshore-onshore seismic experiments. The top of the subducting plate can be followed under the wide accretionary wedge by multichannel reflection seismics. This reveals the hidden updip limit of the contact of the upper plate crustal backstop onto the slab. Two OBS refraction seismic profiles from the volcanic arc throughout the forearc domain constrain a 26-km-large crustal thickness all along. In the common assumption that the upper plate Moho contact on the slab is a proxy of its downdip limit these new observations imply a three times larger width of the potential interplate seismogenic zone under the marine domain of the Caribbean plate with respect to a regular intra-oceanic subduction zone. Towards larger depth under the mantle corner, the top of the slab imaged from the conversions of teleseismic body-waves and the locations of earthquakes appears with kinks which increase the dip to 10-20° under the forearc domain, and then to 60° from 70 km depth. At 145 km depth under the volcanic arc just north of Martinique, the 2007 M 7.4 earthquake, largest for half a century in the region, allows to document a deep slab deformation consistent with segmentation into slab panels. In relation with this occurrence, an increased seismic activity over the whole depth range provides a new focussed image thanks to the OBS and land deployments. A double-planed dipping slab seismicity is thus now resolved, as originally discovered in Tohoku (NE Japan) and since in other subduction zones. Two other types of seismic activity uniquely observed in Tohoku, are now resolved here: "supraslab" earthquakes with normal-faulting focal mechanisms reliably located in the mantle corner and "deep flat-thrust" earthquakes at 45 km depth on the interplate fault under the Caribbean plate forearc mantle. None such types of seismicity should occur under the paradigm of a regular peridotitic mantle of the upper plate which is expected to be serpentinized by the fluids provided from the dehydrating slab beneath. This process is commonly considered as limiting the downward extent of the interplate coupling. Interpretations are not readily available either for the large crustal thickness of this shallow water marine upper plate, except when remarking its likeness to oceanic plateaus formed above hotspots. The Caribbean Oceanic Plateau of the upper plate has been formed earlier by the material advection from a mantle plume. It could then be underlain by a correspondingly modified, heterogeneous mantle, which may include pyroxenitic material among peridotites. Such heterogeneity in the mantle corner of the present subduction zone may account for the notable peculiarities in seismic structure and activity and impose regions of stick-slip behavior on the interplate among stable-gliding areas.

Formation and tectonic evolution of the Cretaceous Jurassic Muslim Bagh ophiolitic complex, Pakistan: Implications for the composite tectonic setting of ophiolites

NASA Astrophysics Data System (ADS)

Khan, Mehrab; Kerr, Andrew C.; Mahmood, Khalid

2007-10-01

The Muslim Bagh ophiolitic complex Balochistan, Pakistan is comprised of an upper and lower nappe and represents one of a number of ophiolites in this region which mark the boundary between the Indian and Eurasian plates. These ophiolites were obducted onto the Indian continental margin around the Late Cretaceous, prior to the main collision between the Indian and Eurasian plates. The upper nappe contains mantle sequence rocks with numerous isolated gabbro plutons which we show are fed by dolerite dykes. Each pluton has a transitional dunite-rich zone at its base, and new geochemical data suggest a similar mantle source region for both the plutons and dykes. In contrast, the lower nappe consists of pillow basalts, deep-marine sediments and a mélange of ophiolitic rocks. The rocks of the upper nappe have a geochemical signature consistent with formation in an island arc environment whereas the basalts of the lower nappe contain no subduction component and are most likely to have formed at a mid-ocean ridge. The basalts and sediments of the lower nappe have been intruded by oceanic alkaline igneous rocks during the northward drift of the Indian plate. The two nappes of the Muslim Bagh ophiolitic complex are thus distinctively different in terms of their age, lithology and tectonic setting. The recognition of composite ophiolites such as this has an important bearing on the identification and interpretation of ophiolites where the plate tectonic setting is less well resolved.

Numerical study on response time of a parallel plate capacitive polyimide humidity sensor based on microhole upper electrode

NASA Astrophysics Data System (ADS)

Zhou, Wenhe; He, Xuan; Wu, Jianyun; Wang, Liangbi; Wang, Liangcheng

2017-07-01

The parallel plate capacitive humidity sensor based on the grid upper electrode is considered to be a promising one in some fields which require a humidity sensor with better dynamic characteristics. To strengthen the structure and balance the electric charge of the grid upper electrode, a strip is needed. However, it is the strip that keeps the dynamic characteristics of the sensor from being further improved. The numerical method is time- and cost-saving, but the numerical study on the response time of the sensor is just of bits and pieces. The numerical models presented by these studies did not consider the porosity effect of the polymer film on the dynamic characteristics. To overcome the defect of the grid upper electrode, a new structure of the upper electrode is provided by this paper first, and then a model considering the porosity effects of the polymer film on the dynamic characteristics is presented and validated. Finally, with the help of software FLUENT, parameter effects on the response time of the humidity sensor based on the microhole upper electrode are studied by the numerical method. The numerical results show that the response time of the microhole upper electrode sensor is 86% better than that of the grid upper electrode sensor, the response time of humidity sensor can be improved by reducing the hole spacing, increasing the aperture, reducing film thickness, and reasonably enlarging the porosity of the film.

Archean upper crust transition from mafic to felsic marks the onset of plate tectonics.

PubMed

Tang, Ming; Chen, Kang; Rudnick, Roberta L

2016-01-22

The Archean Eon witnessed the production of early continental crust, the emergence of life, and fundamental changes to the atmosphere. The nature of the first continental crust, which was the interface between the surface and deep Earth, has been obscured by the weathering, erosion, and tectonism that followed its formation. We used Ni/Co and Cr/Zn ratios in Archean terrigenous sedimentary rocks and Archean igneous/metaigneous rocks to track the bulk MgO composition of the Archean upper continental crust. This crust evolved from a highly mafic bulk composition before 3.0 billion years ago to a felsic bulk composition by 2.5 billion years ago. This compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks, suggesting the onset of global plate tectonics at ~3.0 billion years ago. Copyright © 2016, American Association for the Advancement of Science.

Comparisons of Different Models on Dynamic Recrystallization of Plate during Asymmetrical Shear Rolling

PubMed Central

Zhang, Tao; Li, Lei; Lu, Shi-Hong; Gong, Hai; Wu, Yun-Xin

2018-01-01

Asymmetrical shear rolling with velocity asymmetry and geometry asymmetry is beneficial to enlarge deformation and refine grain size at the center of the thick plate compared to conventional symmetrical rolling. Dynamic recrystallization (DRX) plays a vital role in grain refinement during hot deformation. Finite element models (FEM) coupled with microstructure evolution models and cellular automata models (CA) are established to study the microstructure evolution of plate during asymmetrical shear rolling. The results show that a larger DRX fraction and a smaller average grain size can be obtained at the lower layer of the plate. The DRX fraction at the lower part increases with the ascending speed ratio, while that at upper part decreases. With the increase of the offset distance, the DRX fraction slightly decreases for the whole thickness of the plate. The differences in the DRX fraction and average grain size between the upper and lower surfaces increase with the ascending speed ratio; however, it varies little with the change of the speed ratio. Experiments are conducted and the CA models have a higher accuracy than FEM models as the grain morphology, DRX nuclei, and grain growth are taken into consideration in CA models, which are more similar to the actual DRX process during hot deformation. PMID:29342080

Comparisons of Different Models on Dynamic Recrystallization of Plate during Asymmetrical Shear Rolling.

PubMed

Zhang, Tao; Li, Lei; Lu, Shi-Hong; Gong, Hai; Wu, Yun-Xin

2018-01-17

Asymmetrical shear rolling with velocity asymmetry and geometry asymmetry is beneficial to enlarge deformation and refine grain size at the center of the thick plate compared to conventional symmetrical rolling. Dynamic recrystallization (DRX) plays a vital role in grain refinement during hot deformation. Finite element models (FEM) coupled with microstructure evolution models and cellular automata models (CA) are established to study the microstructure evolution of plate during asymmetrical shear rolling. The results show that a larger DRX fraction and a smaller average grain size can be obtained at the lower layer of the plate. The DRX fraction at the lower part increases with the ascending speed ratio, while that at upper part decreases. With the increase of the offset distance, the DRX fraction slightly decreases for the whole thickness of the plate. The differences in the DRX fraction and average grain size between the upper and lower surfaces increase with the ascending speed ratio; however, it varies little with the change of the speed ratio. Experiments are conducted and the CA models have a higher accuracy than FEM models as the grain morphology, DRX nuclei, and grain growth are taken into consideration in CA models, which are more similar to the actual DRX process during hot deformation.

Structure and Deformation of the Hikurangi-Kermadec Subduction Zone - Transitions Revealed by Seismic Wide-angle Data

NASA Astrophysics Data System (ADS)

Scherwath, M.; Kopp, H.; Flueh, E. R.; Henrys, S. A.; Sutherland, R.

2008-12-01

The Hikurangi-Kermadec subduction zone northeast of New Zealand represents an ideal target to study lateral variations of subduction zone processes. The incoming Pacific plate changes from being a large igneous province, called the Hikurangi Plateau, in the south to normal oceanic plate north of the Rapuhia Scarp. The overriding Australian plate of continental character in the south, forming the North Island of New Zealand, and changes to an island arc in the north. Further lateral variability exists in changes in volcanic and hydro-thermal activity, transitions from accretion to subduction erosion, backarc spreading and rifting, and is accompanied by northward increasing seismicity. As part of the MANGO project (Marine Geoscientific Investigations on the Input and Output of the Kermadec Subduction Zone), four marine geophysical transects of largely seismic reflection and refraction data provide constraints on the upper lithospheric structures across the Hikurangi-Kermadec Trench between 29-38 deg S. On MANGO profile 1 in the south, the initially shallow subduction of the incoming plateau coincides with crustal underplating beneath the East Cape ridge. To the west lies the 100 km wide and over 10 km deep Raukumara Basin. Seismic velocities of the upper mantle of both plates are around 8 km/s and are considered normal. In contrast, on MANGO profile 4, about 1000 km to the north around the volcanically active Raoul Island, the incoming oceanic crust appears to bend considerably steeper and thus causes a 50 km narrower forearc with a smaller forearc basin. Furthermore, the upper mantle velocities in both plates are relatively low (7.4-7.7 km/s), likely indicating strong bending related deformation of the incoming plate and thermal activity within the arc possibly due to spreading. The central two transects MANGO 2 and 3, though without data coverage of the structure of the incoming plate, are more similar to MANGO 4. The arc regions appear to be strongly affected by the activity of the arc. The arc crust of the northern MANGO 3 becomes significantly thinner in the backarc region due to extension, whereas the data from MANGO 2 likely show thermal activity from the adjacent arc volcanism.

Power training using pneumatic machines vs. plate-loaded machines to improve muscle power in older adults.

PubMed

Balachandran, Anoop T; Gandia, Kristine; Jacobs, Kevin A; Streiner, David L; Eltoukhy, Moataz; Signorile, Joseph F

2017-11-01

Power training has been shown to be more effective than conventional resistance training for improving physical function in older adults; however, most trials have used pneumatic machines during training. Considering that the general public typically has access to plate-loaded machines, the effectiveness and safety of power training using plate-loaded machines compared to pneumatic machines is an important consideration. The purpose of this investigation was to compare the effects of high-velocity training using pneumatic machines (Pn) versus standard plate-loaded machines (PL). Independently-living older adults, 60years or older were randomized into two groups: pneumatic machine (Pn, n=19) and plate-loaded machine (PL, n=17). After 12weeks of high-velocity training twice per week, groups were analyzed using an intention-to-treat approach. Primary outcomes were lower body power measured using a linear transducer and upper body power using medicine ball throw. Secondary outcomes included lower and upper body muscle muscle strength, the Physical Performance Battery (PPB), gallon jug test, the timed up-and-go test, and self-reported function using the Patient Reported Outcomes Measurement Information System (PROMIS) and an online video questionnaire. Outcome assessors were blinded to group membership. Lower body power significantly improved in both groups (Pn: 19%, PL: 31%), with no significant difference between the groups (Cohen's d=0.4, 95% CI (-1.1, 0.3)). Upper body power significantly improved only in the PL group, but showed no significant difference between the groups (Pn: 3%, PL: 6%). For balance, there was a significant difference between the groups favoring the Pn group (d=0.7, 95% CI (0.1, 1.4)); however, there were no statistically significant differences between groups for PPB, gallon jug transfer, muscle muscle strength, timed up-and-go or self-reported function. No serious adverse events were reported in either of the groups. Pneumatic and plate-loaded machines were effective in improving lower body power and physical function in older adults. The results suggest that power training can be safely and effectively performed by older adults using either pneumatic or plate-loaded machines. Copyright © 2017 Elsevier Inc. All rights reserved.

Geophysical constraints on geodynamic processes at convergent margins: A global perspective

NASA Astrophysics Data System (ADS)

Artemieva, Irina; Thybo, Hans; Shulgin, Alexey

2016-04-01

Convergent margins, being the boundaries between colliding lithospheric plates, form the most disastrous areas in the world due to intensive, strong seismicity and volcanism. We review global geophysical data in order to illustrate the effects of the plate tectonic processes at convergent margins on the crustal and upper mantle structure, seismicity, and geometry of subducting slab. We present global maps of free-air and Bouguer gravity anomalies, heat flow, seismicity, seismic Vs anomalies in the upper mantle, and plate convergence rate, as well as 20 profiles across different convergent margins. A global analysis of these data for three types of convergent margins, formed by ocean-ocean, ocean-continent, and continent-continent collisions, allows us to recognize the following patterns. (1) Plate convergence rate depends on the type of convergent margins and it is significantly larger when, at least, one of the plates is oceanic. However, the oldest oceanic plate in the Pacific ocean has the smallest convergence rate. (2) The presence of an oceanic plate is, in general, required for generation of high-magnitude (M N 8.0) earthquakes and for generating intermediate and deep seismicity along the convergent margins. When oceanic slabs subduct beneath a continent, a gap in the seismogenic zone exists at depths between ca. 250 km and 500 km. Given that the seismogenic zone terminates at ca. 200 km depth in case of continent-continent collision, we propose oceanic origin of subducting slabs beneath the Zagros, the Pamir, and the Vrancea zone. (3) Dip angle of the subducting slab in continent-ocean collision does not correlate neither with the age of subducting oceanic slab, nor with the convergence rate. For ocean-ocean subduction, clear trends are recognized: steeply dipping slabs are characteristic of young subducting plates and of oceanic plates with high convergence rate, with slab rotation towards a near-vertical dip angle at depths below ca. 500 km at very high convergence rate. (4) Local isostasy is not satisfied at the convergent margins as evidenced by strong free air gravity anomalies of positive and negative signs. However, near-isostatic equilibrium may exist in broad zones of distributed deformation such as Tibet. (5) No systematic patterns are recognized in heat flow data due to strong heterogeneity of measured values which are strongly affected by hydrothermal circulation, magmatic activity, crustal faulting, horizontal heat transfer, and also due to low number of heat flow measurements across many margins. (6) Low upper mantle Vs seismic velocities beneath the convergent margins are restricted to the upper 150 km and may be related to mantle wedge melting which is confined to shallow mantle levels. Artemieva, I.M., Thybo, H., and Shulgin, A., 2015. Geophysical constraints on geodynamic processes at convergent margins: A global perspective. Gondwana Research, http://dx.doi.org/10.1016/j.gr.2015.06.010

Baltimore Harbor and Channels Deepening Study; Chesapeake Bay Hydraulic Model Investigation.

DTIC Science & Technology

1982-02-01

neap-spring salinity vari- ability. Stations within the Patapsco River (Plates 78-90), and the Magothy River station (MA-I-1, Plate 74), immediately...to-base salinity variations are found at upper bay stations above the constriction at range CB-4. Only Magothy River sta MA-l, and sta CB-7-1 have...Across the bay at the western shore Magothy River sta MA-I-I (Plate 74) no appreciable plan-to-base salinity differences are found, although during

Project Cheesebox: a Journey into History. Volume 1

DTIC Science & Technology

1974-12-01

china and drapes . 89 In addition, the builders were also to provide "masts, spars, sails and rigging of sufficient dimensions to drive the vessel...plate iron 3/8 innh thick with a 4 inch angle iron rivetted at the top extending all round the vessel. A plate iron armour 5 feet deep, 6 inches...thick is firmly bolted to the outside of the wooden bulwark extending all round the upper vessel. This armour is composed of six thicknesses of plate

Seismology: tectonic strain in plate interiors?

PubMed

Calais, E; Mattioli, G; DeMets, C; Nocquet, J-M; Stein, S; Newman, A; Rydelek, P

2005-12-15

It is not fully understood how or why the inner areas of tectonic plates deform, leading to large, although infrequent, earthquakes. Smalley et al. offer a potential breakthrough by suggesting that surface deformation in the central United States accumulates at rates comparable to those across plate boundaries. However, we find no statistically significant deformation in three independent analyses of the data set used by Smalley et al., and conclude therefore that only the upper bounds of magnitude and repeat time for large earthquakes can be inferred at present.

16 CFR 1203.17 - Impact attenuation test.

Code of Federal Regulations, 2014 CFR

2014-01-01

... lb), the upper surface of which shall consist of a steel plate at least 12 mm (0.47 in.) thick and... aluminum plate. The geometric center of the MEP pad shall be aligned with the center vertical axis of the... orientation shall be chosen by the test personnel to provide the most severe test for the helmet. Rivets and...

16 CFR § 1203.17 - Impact attenuation test.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 135 kg (298 lb), the upper surface of which shall consist of a steel plate at least 12 mm (0.47 in... mm (1/4 in.) thick aluminum plate. The geometric center of the MEP pad shall be aligned with the... anvil sites and orientation shall be chosen by the test personnel to provide the most severe test for...

16 CFR 1203.17 - Impact attenuation test.

Code of Federal Regulations, 2012 CFR

2012-01-01

... lb), the upper surface of which shall consist of a steel plate at least 12 mm (0.47 in.) thick and... aluminum plate. The geometric center of the MEP pad shall be aligned with the center vertical axis of the... orientation shall be chosen by the test personnel to provide the most severe test for the helmet. Rivets and...

16 CFR 1203.17 - Impact attenuation test.

Code of Federal Regulations, 2011 CFR

2011-01-01

... lb), the upper surface of which shall consist of a steel plate at least 12 mm (0.47 in.) thick and... aluminum plate. The geometric center of the MEP pad shall be aligned with the center vertical axis of the... orientation shall be chosen by the test personnel to provide the most severe test for the helmet. Rivets and...

16 CFR 1203.17 - Impact attenuation test.

Code of Federal Regulations, 2010 CFR

2010-01-01

... lb), the upper surface of which shall consist of a steel plate at least 12 mm (0.47 in.) thick and... aluminum plate. The geometric center of the MEP pad shall be aligned with the center vertical axis of the... orientation shall be chosen by the test personnel to provide the most severe test for the helmet. Rivets and...

A wide-angle seismic survey of the Hecataeus Ridge, south of Cyprus: a microcontinental block from the African plate docked in a subduction zone?

NASA Astrophysics Data System (ADS)

Rahimi, Ayda; Welford, Kim; Hall, Jeremy; Hübscher, Christian; Louden, Keith; Ehrhardt, Axel

2013-04-01

Cyprus lies at the southern edge of the Aegean-Anatolian microplate, caught in the convergence of Africa and Eurasia. Subduction of the African plate below Cyprus has probably ceased and this has been attributed to the docking in the subduction zone of the Eratosthenes Seamount microcontinental fragment on the northern edge of the African plate. In early 2010, on R.V. Maria S. Merian, we conducted a wide-angle seismic survey to test the hypothesis that the Hecataeus Ridge, another possible microcontinental block lying immediately offshore SE Cyprus, might be related to an earlier docking event. The upper crust of southern Cyprus is dominated by ophiolites, with seismic velocities of up to 7 km s-1. A wide angle seismic profile along Hecataeus Ridge was populated with 15 Canadian and German ocean-bottom seismographs at 5 km intervals and these recorded shots from a 6000 cu. in. air gun array, fired approximately every 100 m. Rough topography of the seabed has made picking of phases and their modelling a demanding task. Bandpass and coherency filtering have enabled us to pick phases out to around 80 km. Tomographic inversion of short-range first arrivals provided an initial model of the shallow sub-seabed structure. Forward modelling by ray-tracing, using the code of Zelt and Smith, was then used to model crustal structure down to depths of around 20 km, with occasional evidence of reflections from deeper boundaries (Moho?). Modelling results provide good control on P-wave velocities in the top 20 km and some indications of deeper events. There is no evidence of true velocities approaching 7 km/s in the top 20 km below the Ridge that might indicate the presence of ophiolitic rocks. Regional gravity and magnetic field data tend to support this proposition. We thus conclude that Hecataeus Ridge is not composed of characteristically ophiolitic, Cyprus (upper plate) crust, and it might well be derived from the African (lower) 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.

Investigating the 3-D Subduction Initiation Processes at Transform Faults and Passive Margins

NASA Astrophysics Data System (ADS)

Peng, H.; Leng, W.

2017-12-01

Studying the processes of subduction initiation is a key for understanding the Wilson cycle and improving the theory of plate tectonics. Previous studies investigated subduction initiation with geological synthesis and geodynamic modeling methods, discovering that subduction intends to initiate at the transform faults close to oceanic arcs, and that its evolutionary processes and surface volcanic expressions are controlled by plate strength. However, these studies are mainly conducted with 2-D models, which cannot deal with lateral heterogeneities of crustal thickness and strength along the plate interfaces. Here we extend the 2-D model to a 3-D parallel subduction model with high computational efficiency. With the new model, we study the dynamic controlling factors, morphology evolutionary processes and surface expressions for subduction initiation with lateral heterogeneities of material properties along transform faults and passive margins. We find that lateral lithospheric heterogeneities control the starting point of the subduction initiation along the newly formed trenches and the propagation speed for the trench formation. New subduction tends to firstly initiate at the property changing point along the transform faults or passive margins. Such finds may be applied to explain the formation process of the Izu-Bonin-Mariana (IBM) subduction zone in the western Pacific and the Scotia subduction zone at the south end of the South America. Our results enhance our understanding for the formation of new trenches and help to provide geodynamic modeling explanations for the observed remnant slabs in the upper mantle and the surface volcanic expressions.

Constraints on the rheology of the lower crust in a strike-slip plate boundary: evidence from the San Quintín xenoliths, Baja California, Mexico

NASA Astrophysics Data System (ADS)

van der Werf, Thomas; Chatzaras, Vasileios; Marcel Kriegsman, Leo; Kronenberg, Andreas; Tikoff, Basil; Drury, Martyn R.

2017-12-01

The rheology of lower crust and its transient behavior in active strike-slip plate boundaries remain poorly understood. To address this issue, we analyzed a suite of granulite and lherzolite xenoliths from the upper Pleistocene-Holocene San Quintín volcanic field of northern Baja California, Mexico. The San Quintín volcanic field is located 20 km east of the Baja California shear zone, which accommodates the relative movement between the Pacific plate and Baja California microplate. The development of a strong foliation in both the mafic granulites and lherzolites, suggests that a lithospheric-scale shear zone exists beneath the San Quintín volcanic field. Combining microstructural observations, geothermometry, and phase equilibria modeling, we estimated that crystal-plastic deformation took place at temperatures of 750-890 °C and pressures of 400-560 MPa, corresponding to 15-22 km depth. A hot crustal geotherm of 40 ° C km-1 is required to explain the estimated deformation conditions. Infrared spectroscopy shows that plagioclase in the mafic granulites is relatively dry. Microstructures are interpreted to show that deformation in both the uppermost lower crust and upper mantle was accommodated by a combination of dislocation creep and grain-size-sensitive creep. Recrystallized grain size paleopiezometry yields low differential stresses of 12-33 and 17 MPa for plagioclase and olivine, respectively. The lower range of stresses (12-17 MPa) in the mafic granulite and lherzolite xenoliths is interpreted to be associated with transient deformation under decreasing stress conditions, following an event of stress increase. Using flow laws for dry plagioclase, we estimated a low viscosity of 1.1-1.3×1020 Pa ṡ s for the high temperature conditions (890 °C) in the lower crust. Significantly lower viscosities in the range of 1016-1019 Pa ṡ s, were estimated using flow laws for wet plagioclase. The shallow upper mantle has a low viscosity of 5.7×1019 Pa ṡ s, which indicates the lack of an upper-mantle lid beneath northern Baja California. Our data show that during post-seismic transients, the upper mantle and the lower crust in the Pacific-Baja California plate boundary are characterized by similar and low differential stress. Transient viscosity of the lower crust is similar to the viscosity of the upper mantle.

Experiment K305: Quantitative analysis of selected bone parameters. Supplement 3A: Trabecular spacing and orientation in the long bones

NASA Technical Reports Server (NTRS)

Judy, M. M.

1981-01-01

Values of mean trabecular spacing computed from optical diffraction patterns of 1:1 X-ray micrographs of tibial metaphysis and those obtained by standard image digitization techniques show excellent agreement. Upper limits on values of mean trabecular orientation deduced from diffraction patterns and the images are also in excellent agreement. Values of the ratio of mean trabecular spatial density in a region of 300 micrometers distal to the downwardly directed convexity in the cartilage growth plate to the value adjacent to the plate determined for flight animals sacrificed at recovery were significantly smaller than values for vivarium control animals. No significant differences were found in proximal regions. No significant differences in mean trabecular orientation were detected. Decreased values of trabecular spatial density and of both obsteoblastic activity and trabecular cross-sectional area noted in collateral researches suggest decreased modeling activity under weightlessness.

Evolution of Plate Tectonics on Earth since the Mid-Mesoarchean was Controlled by Sedimentary Fluxes from Continents to Oceans and Mantle Temperature

NASA Astrophysics Data System (ADS)

Sobolev, S. V.; Brown, M.

2017-12-01

Plate tectonics (PT) is the most important geological process operating on Earth, making it unique among the rocky planets in the Solar System. The question of how PT was initiated and which factors controlled its evolution over Earth's history are widely discussed, but remain controversial. It is broadly accepted that a necessary condition for initiation and stable operation of PT is maintaining low strength along plate boundaries, particularly along the subduction zone interfaces in the subduction channels. Examples from the South American Andes and other convergent margins show that unconsolidated continental sediments in trenches serve as an efficient lubricant for subduction; if these are lacking, friction in the subduction channel and strength of the plate boundary are significantly increased. We suggest that lubrication of subduction by accumulation of continental sediments in trenches played a crucial role during the evolution of PT on Earth since the mid-Mesoarchean. We posit that continental emergence and enhanced surface erosion caused an increasing flux of sediments into the oceans, which in turn lubricated subduction channels and intensified PT. Thus, peaks in orogenesis, as confirmed by several proxies, during periods of supercraton/supercontinent assembly represent periods of vigorous subduction and continental sedimentation in trenches prior to terminal collision. Conversely, a decrease in plate boundary length and a reduction in continental sediment accumulation in trenches during periods of stability after supercraton/supercontinent assembly is the likely reason for periods of lower PT vigor, including the so called `boring billion' between 1.8 and 0.8 Ga. The largest surface erosion and subduction-lubrication event occurred at the end of the `snowball' Earth epoch in the Neoproterozoic and likely accelerated the most recent episode of vigorous PT. Based on analysis of various geological observations, we suggest that the cyclic behavior of PT on Earth since the mid-Mesoarchean (the so-called `supercontinent cycle') can be interpreted in terms of the balance of power between PT, driven by slab pull and controlled by the temperature of the upper mantle, and the efficiency of lubrication in the subduction zones, controlled by accumulation of continental sediment in the trenches.

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.

Structure and lithology of the Japan Trench subduction plate boundary fault

NASA Astrophysics Data System (ADS)

Kirkpatrick, James D.; Rowe, Christie D.; Ujiie, Kohtaro; Moore, J. Casey; Regalla, Christine; Remitti, Francesca; Toy, Virginia; Wolfson-Schwehr, Monica; Kameda, Jun; Bose, Santanu; Chester, Frederick M.

2015-01-01

The 2011 Mw9.0 Tohoku-oki earthquake ruptured to the trench with maximum coseismic slip located on the shallow portion of the plate boundary fault. To investigate the conditions and physical processes that promoted slip to the trench, Integrated Ocean Drilling Program Expedition 343/343T sailed 1 year after the earthquake and drilled into the plate boundary ˜7 km landward of the trench, in the region of maximum slip. Core analyses show that the plate boundary décollement is localized onto an interval of smectite-rich, pelagic clay. Subsidiary structures are present in both the upper and lower plates, which define a fault zone ˜5-15m thick. Fault rocks recovered from within the clay-rich interval contain a pervasive scaly fabric defined by anastomosing, polished, and lineated surfaces with two predominant orientations. The scaly fabric is crosscut in several places by discrete contacts across which the scaly fabric is truncated and rotated, or different rocks are juxtaposed. These contacts are inferred to be faults. The plate boundary décollement therefore contains structures resulting from both distributed and localized deformation. We infer that the formation of both of these types of structures is controlled by the frictional properties of the clay: the distributed scaly fabric formed at low strain rates associated with velocity-strengthening frictional behavior, and the localized faults formed at high strain rates characterized by velocity-weakening behavior. The presence of multiple discrete faults resulting from seismic slip within the décollement suggests that rupture to the trench may be characteristic of this margin.

Mantle convection pattern and subcrustal stress field under South America

NASA Technical Reports Server (NTRS)

Liu, H.-S.

1980-01-01

The tectonic, igneous and metallogenic features of South America are discussed in terms of the crustal deformation associated with stresses due to mantle convection as inferred from the high degree harmonics in the geopotential field. The application of Runcorn's model for the laminar viscous flows in the upper mantle to satellite and gravity data results in a convection pattern which reveals the ascending flows between the descending Nazca plate and the overlying South American plate as well as segments of the descending Nazca plate beneath South America. The arc volcanism in South America is shown apparently to be related to the upwelling of high-temperature material induced by the subduction of the Nazca plate, with the South American basin systems associated with downwelling mantle flows. The resulting tensional stress fields are shown to be regions of structural kinship characterized by major concentrations of ore deposits and related to the cordillera, shield and igneous systems and the upward Andean movements. It is suggested that the upwelling convection flows in the upper mantle, coupled with crustal tension, have provided an uplift mechanism which has forced the hydrothermal systems in the basement rocks to the surface.

ERO modelling of tungsten erosion and re-deposition in EAST L mode discharges

NASA Astrophysics Data System (ADS)

Xie, H.; Ding, R.; Kirschner, A.; Chen, J. L.; Ding, F.; Mao, H. M.; Feng, W.; Borodin, D.; Wang, L.

2017-09-01

Tungsten erosion and re-deposition at the upper outer divertor of the Experimental Advanced Superconducting Tokamak has been modelled using the 3D Monte Carlo code ERO. The measured divertor plasma condition in attached L mode discharges with upper single null configuration has been used to build the background plasma in the simulations. The tungsten gross erosion rate is mainly determined by carbon impurity in the background plasma. Increasing carbon concentration can first increase and afterwards suppress the tungsten erosion rate. Taking into account the material mixing surface model, the influence of eroded particles returning to the surface on sputtering has been studied. Sputtering by eroded particles returning to the surface can significantly enhance the gross erosion by reduction of the carbon ratio within the surface interaction layer and by increasing the erosion rate due to sputtering by both eroded tungsten and carbon particles. Modelling indicates that carbon deposition occurs on the dome plate and part of the vertical plate close to the dome plate, whereas tungsten net erosion occurs on most of the vertical plate. The modelling results are in reasonable agreement with the experimental WI spectroscopy.

Toroidal midplane neutral beam armor and plasma limiter

DOEpatents

Kugel, H.W.; Hand, S.W. Jr.; Ksayian, H.

1985-05-31

This invention contemplates an armor shield/plasma limiter positioned upon the inner wall of a toroidal vacuum chamber within which is magnetically confined an energetic plasma in a tokamak nuclear fusion reactor. The armor shield/plasma limiter is thus of a general semi-toroidal shape and is comprised of a plurality of adjacent graphite plates positioned immediately adjacent to each other so as to form a continuous ring upon and around the toroidal chamber's inner wall and the reactor's midplane coil. Each plate has a generally semi-circular outer circumference and a recessed inner portion and is comprised of upper and lower half sections positioned immediately adjacent to one another along the midplane of the plate. With the upper and lower half sections thus joined, a channel or duct is provided within the midplane of the plate in which a magnetic flux loop is positioned. The magnetic flux loop is thus positioned immediately adjacent to the fusing toroidal plasma and serves as a diagnostic sensor with the armor shield/plasma limiter minimizing the amount of power from the energetic plasma as well as from the neutral particle beams heating the plasma incident upon the flux loop.

The seismogenic zone in the Central Costa Rican Pacific margin: high-quality hypocentres from an amphibious network

NASA Astrophysics Data System (ADS)

Arroyo, Ivonne G.; Husen, Stephan; Flueh, Ernst R.

2014-10-01

Transition from subduction of normal to thickened oceanic crust occurs in the central portion of the Costa Rican margin, where large interplate earthquakes ( M ~ 7) and abundant interseismic seismicity have been associated with subduction of bathymetric highs. We relocated ~1,300 earthquakes recorded for 6 months by a combined on- and offshore seismological network using probabilistic earthquake relocation in a 3D P-wave velocity model. Most of the seismicity originated at the seismogenic zone of the plate boundary, appearing as an 18° dipping, planar cluster from 15 to 25-30 km depth, beneath the continental shelf. Several reverse focal mechanisms were resolved within the cluster. The upper limit of this interseismic interplate seismicity seems to be controlled primarily by the overlying-plate thickness and coherency, which in turn is governed by the erosional processes and fluid release and escape at temperatures lower than ~100 to 120 °C along the plate boundary. The downdip limit of the stick-slip behaviour collocates with relative low temperatures of ~150 to 200 °C, suggesting that it is controlled by serpentinization of the mantle wedge. The distribution of the interseismic interplate seismicity is locally modified by the presence of subducted seamounts at different depths. Unlike in northern Costa Rica, rupture of large earthquakes in the last two decades seems to coincide with the area defined by the interseismic interplate seismicity.

Evidence for Sexual Dimorphism in the Plated Dinosaur Stegosaurus mjosi (Ornithischia, Stegosauria) from the Morrison Formation (Upper Jurassic) of Western USA.

PubMed

Saitta, Evan Thomas

2015-01-01

Conclusive evidence for sexual dimorphism in non-avian dinosaurs has been elusive. Here it is shown that dimorphism in the shape of the dermal plates of Stegosaurus mjosi (Upper Jurassic, western USA) does not result from non-sex-related individual, interspecific, or ontogenetic variation and is most likely a sexually dimorphic feature. One morph possessed wide, oval plates 45% larger in surface area than the tall, narrow plates of the other morph. Intermediate morphologies are lacking as principal component analysis supports marked size- and shape-based dimorphism. In contrast, many non-sex-related individual variations are expected to show intermediate morphologies. Taphonomy of a new quarry in Montana (JRDI 5ES Quarry) shows that at least five individuals were buried in a single horizon and were not brought together by water or scavenger transportation. This new site demonstrates co-existence, and possibly suggests sociality, between two morphs that only show dimorphism in their plates. Without evidence for niche partitioning, it is unlikely that the two morphs represent different species. Histology of the new specimens in combination with studies on previous specimens indicates that both morphs occur in fully-grown individuals. Therefore, the dimorphism is not a result of ontogenetic change. Furthermore, the two morphs of plates do not simply come from different positions on the back of a single individual. Plates from all positions on the body can be classified as one of the two morphs, and previously discovered, isolated specimens possess only one morph of plates. Based on the seemingly display-oriented morphology of plates, female mate choice was likely the driving evolutionary mechanism rather than male-male competition. Dinosaur ornamentation possibly served similar functions to the ornamentation of modern species. Comparisons to ornamentation involved in sexual selection of extant species, such as the horns of bovids, may be appropriate in predicting the function of some dinosaur ornamentation.

Toroidal midplane neutral beam armor and plasma limiter

DOEpatents

Kugel, Henry W.; Hand Jr, Samuel W.; Ksayian, Haig

1986-02-04

For use in a tokamak fusion reactor having a midplane magnetic coil on the inner wall of an evacuated toriodal chamber within which a neutral beam heated, fusing plasma is magnetically confined, a neutral beam armor shield and plasma limiter is provided on the inner wall of the toroidal chamber to shield the midplane coil from neutral beam shine-thru and plasma deposition. The armor shield/plasma limiter forms a semicircular enclosure around the midplane coil with the outer surface of the armor shield/plasma limiter shaped to match, as closely as practical, the inner limiting magnetic flux surface of the toroidally confined, indented, bean-shaped plasma. The armor shield/plasma limiter includes a plurality of semicircular graphite plates each having a pair of coupled upper and lower sections with each plate positioned in intimate contact with an adjacent plate on each side thereof so as to form a closed, planar structure around the entire outer periphery of the circular midplane coil. The upper and lower plate sections are adapted for coupling to heat sensing thermocouples and to a circulating water conduit system for cooling the armor shield/plasma limiter.The inner center portion of each graphite plate is adapted to receive and enclose a section of a circular diagnostic magnetic flux loop so as to minimize the power from the plasma confinement chamber incident upon the flux loop.

Toroidal midplane neutral beam armor and plasma limiter

DOEpatents

Kugel, Henry W.; Hand, Jr, Samuel W.; Ksayian, Haig

1986-01-01

For use in a tokamak fusion reactor having a midplane magnetic coil on the inner wall of an evacuated toriodal chamber within which a neutral beam heated, fusing plasma is magnetically confined, a neutral beam armor shield and plasma limiter is provided on the inner wall of the toroidal chamber to shield the midplane coil from neutral beam shine-thru and plasma deposition. The armor shield/plasma limiter forms a semicircular enclosure around the midplane coil with the outer surface of the armor shield/plasma limiter shaped to match, as closely as practical, the inner limiting magnetic flux surface of the toroidally confined, indented, bean-shaped plasma. The armor shield/plasma limiter includes a plurality of semicircular graphite plates each having a pair of coupled upper and lower sections with each plate positioned in intimate contact with an adjacent plate on each side thereof so as to form a closed, planar structure around the entire outer periphery of the circular midplane coil. The upper and lower plate sections are adapted for coupling to heat sensing thermocouples and to a circulating water conduit system for cooling the armor shield/plasma limiter.The inner center portion of each graphite plate is adapted to receive and enclose a section of a circular diagnostic magnetic flux loop so as to minimize the power from the plasma confinement chamber incident upon the flux loop.

Waveguide module comprising a first plate with a waveguide channel and a second plate with a raised portion in which a sealing layer is forced into the waveguide channel by the raised portion

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

Strassner, II, Bernd H.; Liedtke, Richard; McDonald, Jacob Jeremiah

The various technologies presented herein relate to utilizing a sealing layer of malleable material to seal gaps, etc., at a joint between edges of a waveguide channel formed in a first plate and a surface of a clamping plate. A compression pad is included in the surface of the clamping plate and is dimensioned such that the upper surface of the pad is less than the area of the waveguide channel opening on the first plate. The sealing layer is placed between the waveguide plate and the clamping plate, and during assembly of the waveguide module, the compression pad deformsmore » a portion of the sealing layer such that it ingresses into the waveguide channel opening. Deformation of the sealing layer results in the gaps, etc., to be filled, improving the operational integrity of the joint.« less

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

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.

Comparison of Subsidence Rates for Conjugate Margins of the Equatorial and Northern South Atlantic Ocean as A First-Order Constraint on Symmetry of Underlying, Early Rift Structures

NASA Astrophysics Data System (ADS)

Zavala, O.

2017-12-01

We compared subsidence histories from wells into Cretaceous-Cenozoic conjugate margins in the Equatorial and northern South Atlantic as a first-order constraint on whether rifting occurred in a symmetrical, pure shear mode, or whether rifting occurred in an asymmetrical, simple shear mode. For the pure shear mode of rifting, the prediction is for longterm subsidence on both conjugate margins to be similar and reflective of underlying, rift symmetry; for the simple shear mode of rifting, the prediction is that subsidence above the more thinned and wider, lower plate margin is greater than subsidence above the less thinned and more narrow, upper plate margin. A major caveat of this approach is that subsidence variations can be affected by other external factors that include increased sedimentation related to local deltas and structural or hotspot-related uplifts of coastal areas. In the northern Equatorial Atlantic, the longterm subsidence rate for the Guyana basin of northeastern South America of 18.52 m/Ma is less that of the Senegal area of west Africa of 54 m/Ma suggestive of an upper plate to the west and lower plate to the east. Moving southwards, the Potiguar basin of northern Brazil of 23 m/Ma is roughly the same as the Keta-Togo-Benin-Cote d'Ivoire basins of west Africa (21 m/Ma) and suggestive of an underlying rift symmetry. The Bahia Norte-Reconcavo-Sergipe-Alogoas basins of Brazil are less (28 m/Ma) than the Gabon basin (57 m/Ma) of west Africa suggesitive of an lower plate to the east and an upper plate to the west. The Bahia Sul-Espirito Santo basins of Brazil are less (20 m/Ma) than the Lower Congo basin (45 m/Ma) although the latter area includes the localized influence of the Congo delta. We compare additional evidence such as seismic reflection and refraction data and gravity modeling to the predictions of the subsidence values.

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.

Upper mantle anisotropy from teleseismic SKS splitting beneath Lützow-Holm Bay Region, East Antarctica

USGS Publications Warehouse

Usui, Y.; Kanao, M.; Kubo, A.; Hiramatsu, Y.; Negishi, H.

2007-01-01

Investigations of SKS wave splitting of teleseismic events from digital seismographs recorded at eight stations around the Lützow-Holm Bay Region have lead to understanding the evolution of the Antarctic Plate. The observed delay times of SKS splitting are up to 1.3 s, which are generally equal to the global average. A two-layer model reveals that the lower layer anisotropy is caused by the recent asthenospheric flow, as compared with the Absolute Plate Motion by the HS3-NUVEL1 model. The upper layer anisotropy corresponds well to polarization of NE–SW convergence direction between East and West Gondwana in Pan-African age. We suggest that the upper layer anisotropy was formed during Pan-African orogeny and was possibly influenced by the preexisting structure during Gondwana break-up. The origin of anisotropy is the Lattice Preferred Orientation of olivine which was caused by both paleo-tectonic events and the recent asthenospheric flow.

Nanoactuators Based on Electrostatic Forces on Dielectrics

NASA Technical Reports Server (NTRS)

Wang, Yu

2005-01-01

Nanoactuators of a proposed type would exploit the forces exerted by electric fields on dielectric materials. As used here, "nanoactuators" includes motors, manipulators, and other active mechanisms that have dimensions of the order of nanometers and/or are designed to manipulate objects that have dimensions of the order of nanometers. The underlying physical principle can be described most simply in terms of the example of a square parallel-plate capacitor in which a square dielectric plate is inserted part way into the gap between the electrode plates (see Figure Typically, the force is small from our macroscopic human perspective. The above equation shows that the force depends on the ratio between the capacitor dimensions but does not depend on the size. In other words, the force remains the same if the capacitor and the dielectric slab are shrunk to nanometer dimensions. At the same time, the masses of all components are proportional to third power of their linear dimensions. Therefore the force-to-mass ratio (and, consequently, the acceleration that can be imparted to the dielectric slab) is much larger at the nanoscale than at the macroscopic scale. The proposed actuators would exploit this effect. The upper part of Figure 2 depicts a simple linear actuator based on a parallel- plate capacitor similar to Figure 1. In this case, the upper electrode plate would be split into two parts (A and B) and the dielectric slab would be slightly longer than plate A or B. The actuator would be operated in a cycle. During the first half cycle, plate B would be grounded to the lower plate and plate A would be charged to a potential, V, with respect to the lower plate, causing the dielectric slab to be pulled under plate A. During the second half cycle, plate A would be grounded and plate B would be charged to potential V, causing the dielectric slab to be pulled under plate B. The back-and-forth motion caused by alternation of the voltages on plates A and B could be used to drive a nanopump, for example. A rotary motor, shown in the middle part of Figure 2, could include a dielectric rotor sandwiched between a top and a bottom plate containing multiple electrodes arranged symmetrically in a circle. Voltages would be applied sequentially to electrode pairs 1 and 1a, then 2 and 2a, then 3 and 3a in order to attract the dielectric rotor to sequential positions between the electrode pairs.

Molten core retention assembly

DOEpatents

Lampe, Robert F.

1976-06-22

Molten fuel produced in a core overheating accident is caught by a molten core retention assembly consisting of a horizontal baffle plate having a plurality of openings therein, heat exchange tubes having flow holes near the top thereof mounted in the openings, and a cylindrical, imperforate baffle attached to the plate and surrounding the tubes. The baffle assembly is supported from the core support plate of the reactor by a plurality of hanger rods which are welded to radial beams passing under the baffle plate and intermittently welded thereto. Preferably the upper end of the cylindrical baffle terminates in an outwardly facing lip to which are welded a plurality of bearings having slots therein adapted to accept the hanger rods.

The mantle flow field beneath western North America.

PubMed

Silver, P G; Holt, W E

2002-02-08

Although motions at the surface of tectonic plates are well determined, the accompanying horizontal mantle flow is not. We have combined observations of surface deformation and upper mantle seismic anisotropy to estimate this flow field for western North America. We find that the mantle velocity is 5.5 +/- 1.5 centimeters per year due east in a hot spot reference frame, nearly opposite to the direction of North American plate motion (west-southwest). The flow is only weakly coupled to the motion of the surface plate, producing a small drag force. This flow field is probably due to heterogeneity in mantle density associated with the former Farallon oceanic plate beneath North America.

Molecular dynamics study on evaporation and condensation characteristics of thin film liquid Argon on nanostructured surface in nano-scale confinement

NASA Astrophysics Data System (ADS)

Hasan, Mohammad Nasim; Rabbi, Kazi Fazle; Sabah, Arefiny; Ahmed, Jannat; Kuri, Subrata Kumar; Rakibuzzaman, S. M.

2017-06-01

Investigation of Molecular level phase change phenomena are becoming important in heat and mass transfer research at a very high rate, driven both by the need to understand certain fundamental phenomena as well as by a plethora of new and forthcoming applications in the areas of micro- and nanotechnologies. Molecular dynamics simulation has been carried out to go through the evaporation and condensation characteristics of thin liquid argon film in Nano-scale confinement. In the present study, a cuboid system is modeled for understanding the Nano-scale physics of simultaneous evaporation and condensation. The cuboid system consists of hot and cold parallel platinum plates at the bottom and top ends. The fluid comprised of liquid argon film at the bottom plate and vapor argon in between liquid argon and upper plate of the domain. Three different simulation domains have been created here: (i) Both platinum plates are considered flat, (ii) Upper plate consisting of transverse slots of low height and (iii) Upper plate consisting of transverse slots of bigger height. Considering hydrophilic nature of top and bottom plates, two different high temperatures of the hot wall was set and an observation was made on normal and explosive vaporizations and their impacts on thermal transport. For all the structures, equilibrium molecular dynamics (EMD) was performed to reach equilibrium state at 90 K. Then the lower wall is set to two different temperatures like 110 K and 250 K for all three models to perform non-equilibrium molecular dynamics (NEMD). For vaporization, higher temperature of the hot wall led to faster transport of the liquid argon as a cluster moving from hot wall to cold wall. But excessive temperature causes explosive boiling which seems not good for heat transportation because of less phase change. In case of condensation, an observation was made which indicates that the nanostructured transverse slots facilitate condensation. Two factors affect the rate of condensation when nanostructures are there: (i) increased surface area and (ii) the nanostructure height. The variation of temperature and evaporation number with respect to time was monitored for all cases. An estimation of heat fluxes normal to top and bottom walls also was made to focus the effectiveness of heat transfer in hydrophilic confinement.

Non-deterministic quantum CNOT gate with double encoding

NASA Astrophysics Data System (ADS)

Gueddana, Amor; Attia, Moez; Chatta, Rihab

2013-09-01

We define an Asymmetric Partially Polarizing Beam Splitter (APPBS) to be a linear optical component having different reflectivity (transmittance) coefficients, on the upper and the lower arms, for horizontally and vertically Polarized incident photons. Our CNOT model is composed by two APPBSs, one Half Wave Plate (HWP), two Polarizing Beam Splitters (PBSs), a Beam Splitter (BS) and a -phase rotator for specific wavelength. Control qubit operates with dual rail encoding while target qubit is based on polarization encoding. To perform CNOT operation in 4/27 of the cases, input and target incoming photons are injected with different wavelengths.

Magnetic force driven six degree-of-freedom active vibration isolation system using a phase compensated velocity sensor.

PubMed

Kim, Yongdae; Kim, Sangyoo; Park, Kyihwan

2009-04-01

A six-axis active vibration isolation system (AVIS) is developed using voice coil actuators. Point contact configuration is employed to have an easy assembly of eight voice coil actuators to an upper and a base plates. The velocity sensor, using an electromagnetic principle that is commonly used in the vibration control, is investigated since its phase lead characteristic causes an instability problem for a low frequency vibration. The performances of the AVIS are investigated in the frequency domain and finally validated by comparing with the passive isolation system using the atomic force microscope images.

Circularly polarized lasing in chiral modulated semiconductor microcavity with GaAs quantum wells

NASA Astrophysics Data System (ADS)

Demenev, A. A.; Kulakovskii, V. D.; Schneider, C.; Brodbeck, S.; Kamp, M.; Höfling, S.; Lobanov, S. V.; Weiss, T.; Gippius, N. A.; Tikhodeev, S. G.

2016-10-01

We report close to circularly polarized lasing at ℏ ω = 1.473 and 1.522 eV from an AlAs/AlGaAs Bragg microcavity, with 12 GaAs quantum wells in the active region and chirally etched upper distributed Bragg refractor under optical pump at room temperature. The advantage of using the chiral photonic crystal with a large contrast of dielectric permittivities is its giant optical activity, allowing to fabricate a very thin half-wave plate, with a thickness of the order of the emitted light wavelength, and to realize the monolithic control of circular polarization.

Bounds on geologically current rates of motion of groups of hot spots

NASA Astrophysics Data System (ADS)

Wang, Chengzu; Gordon, Richard G.; Zhang, Tuo

2017-06-01

It is widely believed that groups of hot spots in different regions of the world are in relative motion at rates of 10 to 30 mm a-1 or more. Here we present a new method for analyzing geologically current motion between groups of hot spots beneath different plates. In an inversion of 56 globally distributed, equally weighted trends of hot spot tracks, the dispersion is dominated by differences in trend between different plates rather than differences within plates. Nonetheless the rate of hot spot motion perpendicular to the direction of absolute plate motion, vperp, differs significantly from zero for only 3 of 10 plates and then by merely 0.3 to 1.4 mm a-1. The global mean upper bound on |vperp| is 3.2 ± 2.7 mm a-1. Therefore, hot spots move slowly and can be used to define a global reference frame for plate motions.

76 FR 9513 - Airworthiness Directives; BURKHART GROB LUFT-UND Model G 103 C Twin III SL Gliders

Federal Register 2010, 2011, 2012, 2013, 2014

2011-02-18

... plate) and tighten it, applying the torque following page 6.12 of the G 103 C TWIN III SL Maintenance...: The torque values and tolerances of the upper pulley wheel grooved nut have been standardized in the..., before further flight, readjust the torque of the upper pulley wheel grooved nut using the updated...

Umbilical mechanism

NASA Technical Reports Server (NTRS)

Barron, Daniel R. (Inventor); Jasulaitis, Vytas (Inventor); Morrill, Brion F. (Inventor)

1995-01-01

Apparatus is described for automatically mating a pair of connectors and protecting them prior to mating, which minimizes weight and uses relatively simple and reliable mechanisms. Lower and upper connectors (24, 26) are held in lower and upper parts (14, 16) of a housing, with the upper connector mounted on a carrier (32) that is motor driven to move down and mate the connectors. A pair of movable members (36, 38) serve as shields, as coarse alignment aids, and as force transmitters. The movable members are pivotally mounted at the bottom of the upper housing, and as the carrier moves down it pivots the members out of the way. The movable members have socket elements (116) that closely receive pin elements (120) on the lower housing part, to coarsely align the connectors and to react mating and unmating forces between the housings. The carrier has a pair of plate portions (60, 62) with slots (64), and the movable members have cam followers engaged with the slot walls, to move the members with precision. The carrier plate-like portions engage follower members (82) that pivot open lower shield parts (44, 46) covering the lower connector, which is mounted on four stacks of Belleville washers (142).

Active unicameral bone cysts in the upper limb are at greater risk of fracture.

PubMed

Tey, Inn Kuang; Mahadev, Arjandas; Lim, Kevin Boon Leong; Lee, Eng Hin; Nathan, Saminathan Suresh

2009-08-01

To elucidate the natural history of unicameral bone cyst (UBC) and risk factors for pathological fracture. 14 males and 8 females (mean age, 9 years) diagnosed with UBC were reviewed. Cyst location, symptoms, and whether there was any fracture or surgery were recorded. Cyst parameters were measured on radiographs, and included (1) the cyst index, (2) the ratio of the widest cyst diameter to the growth plate diameter, and (3) the adjusted distance of the cyst border from the growth plate. There were 11 upper- and 11 lower-limb cysts. 13 patients had pathological fractures and 9 did not. 20 patients were treated conservatively with limb immobilisation; 2 underwent curettage and bone grafting (one resolved and one did not). Seven cysts resolved (5 had fractures and 2 did not). The risk of fracture was higher in the upper than lower limbs (100% vs 18%, p<0.001). Fractured cysts were larger than unfractured cysts (mean cyst index, 4.5 vs. 2.2, p=0.07). Active cysts were more likely to fracture. Conservative management had a 30% resolution rate. Surgery should be considered for large active cysts in the upper limbs in order to minimise the fracture risk.

Achievement of radiative feedback control for long-pulse operation on EAST

NASA Astrophysics Data System (ADS)

Wu, K.; Yuan, Q. P.; Xiao, B. J.; Wang, L.; Duan, Y. M.; Chen, J. B.; Zheng, X. W.; Liu, X. J.; Zhang, B.; Xu, J. C.; Luo, Z. P.; Zang, Q.; Li, Y. Y.; Feng, W.; Wu, J. H.; Yang, Z. S.; Zhang, L.; Luo, G.-N.; Gong, X. Z.; Hu, L. Q.; Hu, J. S.; Li, J.

2018-05-01

The active feedback control of radiated power to prevent divertor target plates overheating during long-pulse operation has been developed and implemented on EAST. The radiation control algorithm, with impurity seeding via a supersonic molecular beam injection (SMBI) system, has shown great success in both reliability and stability. By seeding a sequence of short neon (Ne) impurity pulses with the SMBI from the outer mid-plane, the radiated power of the bulk plasma can be well controlled, and the duration of radiative control (feedforward and feedback) is 4.5 s during a discharge of 10 s. Reliable control of the total radiated power of bulk plasma has been successfully achieved in long-pulse upper single null (USN) discharges with a tungsten divertor. The achieved control range of {{f}rad} is 20%–30% in L-mode regimes and 18%–36% in H-mode regimes. The temperature of the divertor target plates was maintained at a low level during the radiative control phase. The peak particle flux on the divertor target was decreased by feedforward Ne injection in the L-mode discharges, while the Ne pulses from the SMBI had no influence on the peak particle flux because of the very small injecting volume. It is shown that although the radiated power increased, no serious reduction of plasma-stored energy or confinement was observed during the control phase. The success of the radiation control algorithm and current experiments in radiated power control represents a significant advance for steady-state divertor radiation and heat flux control on EAST for near-future long-pulse operation.

Strength of the Subduction Plate Interface beneath the Seismogenic Zone: A Microstructural Investigation of Deformation Mechanisms within a Phyllosilicate- and Amphibole-rich Shear Zone

NASA Astrophysics Data System (ADS)

Seyler, C.; Kirkpatrick, J. D.; Šilerová, D.

2017-12-01

Localization of strain at plate boundaries requires rheological weakening of the lithosphere. The rheology of the subduction plate interface is dictated by the dominant grain-scale deformation mechanisms. However, little is known about the deformation mechanisms within phases commonly found in subduction zones, such as phyllosilicates and amphiboles. We investigate the Leech River Shear Zone on Vancouver Island, British Columbia to explore deformation processes downdip of the seismogenic zone and evaluate the bulk rheology of the plate interface. This shear zone juxtaposes a metamorphosed accretionary prism against a metabasaltic oceanic plateau, representing a paleo-plate interface from the ancient Cascadia subduction zone. Preliminary geothermometry results record a prograde deformation temperature of 573.6±11.2 ˚C in the overriding accretionary wedge, and the hornblende-chlorite-epidote-plagioclase mineral assemblage suggests upper greenschist to lower amphibolite facies metamorphism of the downgoing oceanic crust. Detailed mapping of the plate interface documents a 200 m wide mylonitic shear zone developed across the lithologic contact. Asymmetric shear fabrics, isoclinal folding, boudinage, and a steeply plunging, penetrative stretching lineation are consistent with sinistral-oblique subduction. Numerous discordant quartz veins are variably sheared into sigmoidal shapes as well as isoclinally folded and boudinaged, indicating cyclical synkinematic fracture and vein formation. At the grain-scale, interconnected, anastomosing layers of muscovite, chlorite, and graphite in the accretionary prism rocks likely deformed through kinking and dislocation glide. Framework minerals such as quartz and feldspar deformed by dislocation creep. In the metabasalt, hornblende and chlorite form a continuous S—C fabric in which asymmetric hornblende porphyroclasts deformed by rigid grain rotation and dissolution-precipitation creep. The strength of the subduction plate interface beneath the seismogenic zone was therefore controlled by multiple syn-kinematic mechanisms, with overall strength dominated by the rheology of phyllosilicates and amphibole, generating very low viscosities at the plate interface and enhancing strain localization.

Rifting Process and Geomorphic Development of the Okinawa Tough, Southwest Japan

NASA Astrophysics Data System (ADS)

Sato, T.; Arai, K.; Inoue, T.; Matsumoto, D.

2012-12-01

The Ryukyu Island Arc extends from Kyushu to Taiwan, a distance of 1,200 km, along the Ryukyu Trench where the Philippine Sea Plate is subducting beneath the Eurasian Plate. The Okinawa Trough, a back arc basin has formed behind the Ryukyu Island Arc in late Pliocene to early Pleistocene. The research cruises of GH11 (from 14 July to 15 August, 2011) and GH12 (from 20 to 30 July, 2012) were carried out around the Okinawa Trough. More than 3,600 miles multi channel high-resolution seismic profiles were acquired during these cruises by the GI-gun (Generator 250 cu inch and Injector 105 cu. inch) systems with 16ch digital streamer cable. As a result, two unconformities and three depositional sequence divided by the unconformities are recognized in the trough. The lower and the midlle sequence are tilted and blocked by many normal faults, on the other hand the upper one is not tilted and shows the pattern of onlap fill. From this result, the upper sequence started to deposit after start of the rifting. Additionally, internal reflection of the upper sequence shows the cyclic activities of the rifting. The position of the rifting axis was revealed based on dip of the normal faults. As a result, rifting axis shows echelon arrangement and the displacement of the faults are varied with the segment of the arrangement. The location of the segment boundaries is correlated with geometrical boundary of the adjacent slope. Steep slope with incised valley is distributed in southwestern part where the displacement of the normal fault is large, on the other hand, gentle slope without incised valley is distributed in northeastern part where the displacement is small. This difference of the displacement strongly controls the geometry of the adjacent slope.

Mantle-circulation models with sequential data assimilation: inferring present-day mantle structure from plate-motion histories.

PubMed

Bunge, Hans-Peter; Richards, M A; Baumgardner, J R

2002-11-15

Data assimilation is an approach to studying geodynamic models consistent simultaneously with observables and the governing equations of mantle flow. Such an approach is essential in mantle circulation models, where we seek to constrain an unknown initial condition some time in the past, and thus cannot hope to use first-principles convection calculations to infer the flow history of the mantle. One of the most important observables for mantle-flow history comes from models of Mesozoic and Cenozoic plate motion that provide constraints not only on the surface velocity of the mantle but also on the evolution of internal mantle-buoyancy forces due to subducted oceanic slabs. Here we present five mantle circulation models with an assimilated plate-motion history spanning the past 120 Myr, a time period for which reliable plate-motion reconstructions are available. All models agree well with upper- and mid-mantle heterogeneity imaged by seismic tomography. A simple standard model of whole-mantle convection, including a factor 40 viscosity increase from the upper to the lower mantle and predominantly internal heat generation, reveals downwellings related to Farallon and Tethys subduction. Adding 35% bottom heating from the core has the predictable effect of producing prominent high-temperature anomalies and a strong thermal boundary layer at the base of the mantle. Significantly delaying mantle flow through the transition zone either by modelling the dynamic effects of an endothermic phase reaction or by including a steep, factor 100, viscosity rise from the upper to the lower mantle results in substantial transition-zone heterogeneity, enhanced by the effects of trench migration implicit in the assimilated plate-motion history. An expected result is the failure to account for heterogeneity structure in the deepest mantle below 1500 km, which is influenced by Jurassic plate motions and thus cannot be modelled from sequential assimilation of plate motion histories limited in age to the Cretaceous. This result implies that sequential assimilation of past plate-motion models is ineffective in studying the temporal evolution of core-mantle-boundary heterogeneity, and that a method for extrapolating present-day information backwards in time is required. For short time periods (of the order of perhaps a few tens of Myr) such a method exists in the form of crude 'backward' convection calculations. For longer time periods (of the order of a mantle overturn), a rigorous approach to extrapolating information back in time exists in the form of iterative nonlinear optimization methods that carry assimilated information into the past through the use of an adjoint mantle convection model.

Increased BMI in children-an indicator for less compliance during orthodontic treatment with removable appliances.

PubMed

von Bremen, Julia; Lorenz, Nathalie; Ludwig, Björn; Ruf, Sabine

2018-02-19

To assess whether or not childhood overweight is associated with lower levels of compliance during orthodontic therapy with removable appliances. Starting in 2011, all upper expansion plates and Sander II appliances were equipped with a Theramon® microsensor chip to assess appliance wear time objectively. According to their pre-treatment, BMI normal weight patients were matched to consecutively treated overweight or obese patients by gender, age, and appliance type. Cooperation was assessed with microelectronic wear time documentation over a period of at least 6 months. A total of 50 patients (25 overweight, 25 normal weight) with upper expansion plates and 64 patients (32 overweight, 32 normal weight) with Sander II appliances were analysed. Spearman Rho coefficients showed an indirect association between BMI and appliance wear time, indicating that the higher the BMI, the less the patients wore their appliances (P < 0.05). Furthermore, both normal- and overweight children wore upper expansion plates significantly more than Sander II appliances (P < 0.05). Although no gender-specific difference was found (P = 0.723), an age-related correlation could be verified, indicating a decrease in wear time with increasing age (P < 0.05). An increased BMI appears to be a risk factor for less appliance wear during orthodontic treatment with removable appliances. Additional factors which influenced cooperation during treatment with removable appliances were patient age and appliance type.

A model of convergent plate margins based on the recent tectonics of Shikoku, Japan

NASA Technical Reports Server (NTRS)

Bischke, R. E.

1974-01-01

A viscoelastic finite element plate tectonic model is applied to displacement data for the island of Shikoku, Japan. The flow properties and geometry of the upper portions of the earth are assumed known from geophysical evidence, and the loading characteristics are determined from the model. The nature of the forces acting on the Philippine Sea plate, particularly in the vicinity of the Nankai trough, is determined. Seismic displacement data related to the 1946 Nankaido earthquake are modeled in terms of a thick elastic plate overlying a fluidlike substratum. The sequence of preseismic and seismic displacements can be explained in terms of two independent processes operating on elastic lithospheric plates: a strain accumulation process caused by vertical downward forces acting on or within the lithosphere in the vicinity of the trench, and a strain release process caused by plate failure along a preexisting zone on weakness. This is a restatement of Reid's elastic rebound theory in terms of elastic lithospheric plates.

Bounds on geologically current rates of motion of groups of hotspots.

NASA Astrophysics Data System (ADS)

Wang, C.; Gordon, R. G.; Zhang, T.

2017-12-01

It is widely believed that groups of hotspots in different regions of the world are in relative motion at rates of 10 to 30 mm a-1 or more. Here we present a new method for analyzing geologically current motion between groups of hotspots beneath different plates. In an inversion of 56 globally distributed, equally weighted trends of hotspot tracks, the dispersion is dominated by differences in trend between different plates rather than differences within plates. Nonetheless the rate of hotspot motion perpendicular to the direction of absolute plate motion, vperp, differs significantly from zero for only three of ten plates and then by merely 0.3 to 1.4 mm a-1. The global mean upper bound on |vperp| is 3.2 ±2.7 mm a-1. Therefore, groups of hotspots move slowly and can be used to define a global reference frame for plate motions. Further implications for uncertainties in hotspot trends and current plate motion relative to hotspots will be discussed.

Syn-extensional lithogenetic sequences of the Soledad basin, central Transverse Ranges: Implications for detachment-fault models

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

Hendrix, E.D.

1993-04-01

The Soledad Basin (central Transverse Ranges, CA) contains the first recognized example of mid-Tertiary detachment-faulting west of the San Andreas fault. Displacements along the Pelona detachment fault and syn-extensional upper-plate sedimentation occurred between [approximately] 26--18 Ma, resulting in deposition of at least 4 separate lithogenetic sequences (LS) which record distinct phases of crustal response to extension. The 1st LS (lower Vasquez Fm.) predates syn-extensional volcanism and records initial basin subsidence along small, discontinuous faults. The 2nd LS (middle Vasquez Fm.) consists of both volcanic and sedimentary strata and signals simultaneous onset of magmatism and initial development of a well-defined networkmore » of high-angle, upper-plate normal faults, creating 2 separate sub-basins. Resulting alluvial fans were non-entrenched, implying that subsidence rates, and thus vertical displacement rates on high-angle faults, equaled or exceeded an estimated average sedimentation rate of 1.4 mm/yr. The 3rd LS (upper Vasquez Fm.) reflects transition to a single, well-integrated depositional basin characterized by streamflood sedimentation. This suggests an enlarged drainage basin and a decrease in subsidence rate relative to sedimentation rate, triggered possibly by uplift of the detachment lower-plate. The 4th LS (Tick Canyon Fm.) lies with angular unconformity above the 3rd LS and contains the 1st clasts eroded from the detachment lower plate. Detachment faulting in the Soledad basin appears to involve, in part, reactivation of structural zones of weakness along the Vincent thrust. Preliminary reconstructions of Soledad extension imply 25--30 km of displacement along the Pelona detachment fault system at an averaged slip rate of 3.6--4.3 mm/yr.« less

Southern Alaska as an Example of the Long-Term Consequences of Mountain Building Under the Influence of Glaciers

NASA Technical Reports Server (NTRS)

Meigs, Andrew; Sauber, Jeanne

2000-01-01

Southern Alaska is a continent-scale region of ongoing crustal deformation within the Pacific-North American plate boundary zone. Glaciers and glacial erosion have dictated patterns of denudation in the orogen over the last approx. 5 My. The orogen comprises three discrete topographic domains from south to north, respectively: (1) the Chugach/St. Elias Range; (2) the Wrangell Mountains; and (3) the eastern Alaska Range. Although present deformation is distributed across the orogen, much of the shortening and uplift are concentrated in the Chugach/St. Elias Range. A systematic increase in topographic wavelength of the range from east to west reflects east-to-west increases in the width of a shallowly-dipping segment of the plate interface, separation of major upper plate structures, and a decrease in the obliquity of plate motion relative to the plate boundary. Mean elevation decays exponentially from approx. 2500 m to approx. 1100 m from east to west, respectively. Topographic control on the present and past distribution of glaciers is indicated by close correspondence along the range between mean elevation and the modern equilibrium line altitude of glaciers (ELA) and differences in the modern ELA, mean annual precipitation and temperature across the range between the windward, southern and leeward, northern flanks. Net, range- scale erosion is the sum of: (1) primary bedrock erosion by glaciers and (2) erosion in areas of the landscape that are ice-marginal and are deglaciated at glacial minima. Oscillations between glacial and interglacial climates controls ice height and distribution, which, in turn, modulates the locus and mode of erosion in the landscape. Mean topography and the mean position of the ELA are coupled because of the competition between rock uplift, which tends to raise the ELA, and enhanced orographic precipitation accompanying mountain building, which tends to lower the ELA. Mean topography is controlled both by the 60 deg latitude and maritime setting of active deformation and by the feedback between shortening and uplift, glacial erosion, and orographic effects on climate accompanying mountain building.

The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries

NASA Technical Reports Server (NTRS)

Soloman, Sean C.

1991-01-01

The focus was in two broad areas during the most recent 6-month period: (1) the nature and dynamics of time dependent deformation and stress along major seismic zones; and (2) the nature of long-wavelength oceanic geoid anomalies in terms of lateral variations in upper mantle temperature and composition. The principle findings are described in the accompanying appendices.

Non Destructive Seal Testing Polymeric Tray

DTIC Science & Technology

2006-10-01

School of Enviromental and Biological Science Rutgers, The State University of New Jersey New Brunswick, New Jersey 08903 Principal Investigator...plate to accept new tray • Insert tray • Push “Continue” button • Lower upper compression plate and hold in position (80 psig) • Raise bottom...John J. Kingman Rd. Fort Belvoir, VA 22060-6221 Contractor: Rutgers, The State University of New Jersey THE CENTER FOR ADVANCED FOOD TECHNOLOGY

Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone

NASA Astrophysics Data System (ADS)

Canales, J. P.; Carbotte, S. M.; Nedimović, M. R.; Carton, H.

2017-11-01

Water is carried by subducting slabs as a pore fluid and in structurally bound minerals, yet no comprehensive quantification of water content and how it is stored and distributed at depth within incoming plates exists for any segment of the global subduction system. Here we use seismic data to quantify the amount of pore and structurally bound water in the Juan de Fuca plate entering the Cascadia subduction zone. Specifically, we analyse these water reservoirs in the sediments, crust and lithospheric mantle, and their variations along the central Cascadia margin. We find that the Juan de Fuca lower crust and mantle are drier than at any other subducting plate, with most of the water stored in the sediments and upper crust. Variable but limited bend faulting along the margin limits slab access to water, and a warm thermal structure resulting from a thick sediment cover and young plate age prevents significant serpentinization of the mantle. The dryness of the lower crust and mantle indicates that fluids that facilitate episodic tremor and slip must be sourced from the subducted upper crust, and that decompression rather than hydrous melting must dominate arc magmatism in central Cascadia. Additionally, dry subducted lower crust and mantle can explain the low levels of intermediate-depth seismicity in the Juan de Fuca slab.

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

Warren, Oden Lee; Asif, Syed Amanulla Syed; Oh, Yunje

A testing instrument for mechanical testing at nano or micron scale includes a transducer body, and a coupling shaft coupled with a probe tip. A transducer body houses a capacitor. The capacitor includes first and second counter electrodes and a center electrode assembly interposed therebetween. The center electrode assembly is movable with the coupling shaft relative to the first and second counter electrodes, for instance in one or more of dimensions including laterally and normally. The center electrode assembly includes a center plate coupled with the coupling shaft and one or more springs extending from the center plate. Upper andmore » lower plates are coupled with the center plate and cover the center plate and the one or more springs. A shaft support assembly includes one or more support elements coupled along the coupling shaft. The shaft support assembly provides lateral support to the coupling shaft.« less

Apparatus for adjusting and maintaining the humidity of gas at a constant value within a closed system

DOEpatents

Abernathy, Bethel R.; Walters, Ronald R.

1986-01-01

The humidity of a gas within a closed system is maintained at constant level by providing a saturated salt solution within a lower chamber in communication with an upper chamber conjointly defined by upper and lower container sections in sealing contact with each other to establish a closed container. A partition wall separates the salt solution from the test region in the upper chamber. A tube extending through the partition plate allows humidified gas to pass from the lower to the upper chamber. A glass wool plug or membranous material within the tube prevents migration of salt into the test region.

Apparatus for adjusting and maintaining the humidity of gas at a constant value within a closed system

DOEpatents

Abernathy, B.R.; Walters, R.R.

1985-08-05

The humidity of a gas within a closed system is maintained at constant level by providing a saturated salt solution within a lower chamber in communication with an upper chamber conjointly defined by upper and lower container sections in sealing contact with each other to establish a closed container. A partition wall separates the salt solution from the test region in the upper chamber. A tube extending through the partition plate allows humidified gas to pass from the lower to the upper chamber. A glass wool plug or membranous material within the tube prevents migration of salt into the test region.

Shallow depth of seismogenic coupling in southern Mexico: implications for the maximum size of earthquakes in the subduction zone

NASA Astrophysics Data System (ADS)

Suárez, Gerardo; Sánchez, Osvaldo

1996-01-01

Studies of locally recorded microearthquakes and the centroidal depths of the largest earthquakes analyzed using teleseismic data show that the maximum depth of thrust faulting along the Mexican subduction zone is anomalously shallow. This observed maximum depth of about 25 ± 5 km is about half of that observed in most subduction zones of the world. A leveling line that crosses the rupture zone of the 19 September 1985 Michoacan event was revisited after the earthquake and it shows anomalously low deformation during the earthquake. The comparison between the observed coseismic uplift and dislocation models of the seismogenic interplate contact that extend to depths ranging from 20 to 40 km shows that the maximum depth at which seismic slip took place is about 20 km. This unusually shallow and narrow zone of seismogenic coupling apparently results in the occurrence of thrust events along the Mexican subduction zone that are smaller than would be expected for a trench where a relatively young slab subducts at a rapid rate of relative motion. A comparison with the Chilean subduction zone shows that the plate interface in Mexico is half that in Chile, not only in the down-dip extent of the seismogenic zone of plate contact, but also in the distance of the trench from the coast and in the thickness of the upper continental plate. It appears that the narrow plate contact produced by this particular plate geometry in Mexico is the controlling variable defining the size of the largest characteristic earthquakes in the Mexican subduction zone.

Playing with inclined circular hydraulic jumps

NASA Astrophysics Data System (ADS)

Lebon, Luc; Saget, Beryl; Durand, Marc; Limat, Laurent; Couder, Yves; Receveur, Mathieu

2008-11-01

We have investigated the structure of the circular hydraulic jump, when the jet impacts an inclined plate. At low plate slope, quasi-circular shapes, evolving towards elliptic shapes are observed. At moderate inclinations, the upper and lower jumps become markedly different, and the lower jump is even rejected to infinity when a critical inclination is reached. Above this critical inclination, the jump is coupled to an outer dewetting contact line to give a specific object (expanding impact sheet feeding a curved rim in which the liquid is flowing tangentially). In this regime, both the position and curvature of the upper jump follows unusual scalings with the flow rate that completely differ from those observed on horizontal plates. Finally we have looked to metastable drops trapped in the circular jump at very small inclinations. As reported in a previous APS, the lowest position in the jump can become unstable and the drops oscillate around the jump perimeter. We show that this behavior requires very specific conditions of surface tension and viscosity and propose simple interpretations for the instability mechanism.

Subduction initiation and Obduction: insights from analog models

NASA Astrophysics Data System (ADS)

Agard, P.; Zuo, X.; Funiciello, F.; Bellahsen, N.; Faccenna, C.; Savva, D.

2013-12-01

Subduction initiation and obduction are two poorly constrained geodynamic processes which are interrelated in a number of natural settings. Subduction initiation can be viewed as the result of a regional-scale change in plate convergence partitioning between the set of existing subduction (and collision or obduction) zones worldwide. Intraoceanic subduction initiation may also ultimately lead to obduction of dense oceanic "ophiolites" atop light continental plates. A classic example is the short-lived Peri-Arabic obduction, which took place along thousands of km almost synchronously (within ~5-10 myr), from Turkey to Oman, while the subduction zone beneath Eurasia became temporarily jammed. We herein present analog models designed to study both processes and more specifically (1) subduction initiation through the partitioning of deformation between two convergent zones (a preexisting and a potential one) and, as a consequence, (2) the possible development of obduction, which has so far never been modeled. These models explore the mechanisms of subduction initiation and obduction and test various triggering hypotheses (i.e., plate acceleration, slab crossing the 660 km discontinuity, ridge subduction; Agard et al., 2007). The experimental setup comprises an upper mantle modelled as a low-viscosity transparent Newtonian glucose syrup filling a rigid Plexiglas tank and high-viscosity silicone plates. Convergence is simulated by pushing on a piston at one end of the model with plate tectonics like velocities (1-10 cm/yr) onto (i) a continental margin, (ii) a weakness zone with variable resistance and dip (W), (iii) an oceanic plate - with or without a spreading ridge, (iv) a subduction zone (S) dipping away from the piston and (v) an upper active continental margin, below which the oceanic plate is being subducted at the start of the experiment (as for the Oman case). Several configurations were tested over thirty-five parametric experiments. Special emphasis was placed on comparing different types of weakness zone (W) and the extent of mechanical coupling across them, particularly when plates were accelerated. Measurements of displacements and internal deformation allow for a very precise and reproducible tracking of deformation. Experiments consistently demonstrate that subduction initiation chiefly depends on how the overall shortening (or convergence) is partitionned between the weakness zone (W) and the preexisting subduction zone (S). Part of the deformation is transfered to W as soon as the increased coupling across S results in 5-10% of the convergence being transfered to the upper plate. Whether obduction develops further depends on the effective strength of W. Results (1) constrain the range of physical conditions required for subduction initiation and obduction to develop/nucleate and (2) underline the key role of acceleration for triggering obduction, rather than ridge subduction or slab resistance to penetration at the 660 km discontinuity. [Agard P., Jolivet L., Vrielynck B., Burov E. & Monié P., 2007. Plate acceleration : the obduction trigger? Earth and Planetary Science Letters, 258, 428-441.

Geologic map of the Nelson quadrangle, Lewis and Clark County, Montana

USGS Publications Warehouse

Reynolds, Mitchell W.; Hays, William H.

2003-01-01

The geologic map of the Nelson quadrangle, scale 1:24,000, was prepared as part of the Montana Investigations Project to provide new information on the stratigraphy, structure, and geologic history of an area in the geologically complex southern part of the Montana disturbed belt. In the Nelson area, rocks ranging in age from Middle Proterozoic through Cretaceous are exposed on three major thrust plates in which rocks have been telescoped eastward. Rocks within the thrust plates are folded and broken by thrust faults of smaller displacement than the major bounding thrust faults. Middle and Late Tertiary sedimentary and volcaniclastic rocks unconformably overlie the pre-Tertiary rocks. A major normal fault displaces rocks of the western half of the quadrangle down on the west with respect to strata of the eastern part. Alluvial and terrace gravels and local landslide deposits are present in valley bottoms and on canyon walls in the deeply dissected terrain. Different stratigraphic successions are exposed at different structural levels across the quadrangle. In the northeastern part, strata of the Middle Cambrian Flathead Sandstone, Wolsey Shale, and Meagher Limestone, the Middle and Upper Cambrian Pilgrim Formation and Park Shale undivided, the Devonian Maywood, Jefferson, and lower part of the Three Forks Formation, and Lower and Upper Mississippian rocks assigned to the upper part of the Three Forks Formation and the overlying Lodgepole and Mission Canyon Limestones are complexly folded and faulted. These deformed strata are overlain structurally in the east-central part of the quadrangle by a succession of strata including the Middle Proterozoic Greyson Formation and the Paleozoic succession from the Flathead Sandstone upward through the Lodgepole Limestone. In the east-central area, the Flathead Sandstone rests unconformably on the middle part of the Greyson Formation. The north edge, northwest quarter, and south half of the quadrangle are underlain by a succession of rocks that includes not only strata equivalent to those of the remainder of the quadrangle, but also the Middle Proterozoic Newland, Greyson, and Spokane Formations, Pennsylvanian and Upper Mississippian Amsden Formation and Big Snowy Group undivided, the Permian and Pennsylvanian Phosphoria and Quadrant Formations undivided, the Jurassic Ellis Group and Lower Cretaceous Kootenai Formation. Hornblende diorite sills and irregular bodies of probable Late Cretaceous age intrude Middle Proterozoic, Cambrian and Devonian strata. No equivalent intrusive rocks are present in structurally underlying successions of strata. In this main part of the quadrangle, the Flathead Sandstone cuts unconformably downward from south to north across the Spokane Formation into the upper middle part of the Greyson Formation. Tertiary (Miocene?) strata including sandstone, pebble and cobble conglomerate, and vitric crystal tuff underlie, but are poorly exposed, in the southeastern part of the quadrangle where they are overlain by late Tertiary and Quaternary gravel. The structural complexity of the quadrangle decreases from northeast to southwest across the quadrangle. At the lowest structural level (Avalanche Butte thrust plate) exposed in the canyon of Beaver Creek, lower and middle Paleozoic rocks are folded in northwest-trending east-inclined disharmonic anticlines and synclines that are overlain by recumbently folded and thrust faulted Devonian and Mississippian rocks. The Mississippian strata are imbricated adjacent to the recumbent folds. In the east-central part of the quadrangle, a structurally overlying thrust plate, likely equivalent to the Hogback Mountain thrust plate of the Hogback Mountain quadrangle adjacent to the east (Reynolds, 20xx), juxtaposes recumbently folded Middle Proterozoic and unconformably overlying lower Paleozoic rocks on the complexly folded and faulted rocks of the Avalanche Butte thrust plate. The highest structural plate, bounded below

Genèse des séquences sédimentaires du Crétacé supérieur des Aurès (Algérie). Rôle de l'eustatisme, de la tectonique, de la subsidence: une mise au pointSedimentary sequences in the Upper Cretaceous of Aures Mountains (Algerie). Eustatsy, tectonics and subsidence: a development.

NASA Astrophysics Data System (ADS)

Herkat, Missoum; Delfaud, Jean

2000-06-01

The Upper Cretaceous of Aurès has been studied using a sedimentological approach to characterize the sequential organisation and deposits distribution in the basin. The sequential chain which was observed has been correlated to eustatic cycles defined on a global scale. Palaeogeographic reconstruction shows a basin with its south margin corresponding to a proximal platform domain with essentially carbonate deposits and toward the northeast, marly sedimentation of pelagic nature. The influence of NW-SE to WNW-ESE accidents on sedimentation control has been found preponderant. Therefore a system of tilted blocks toward the south characterizes a large part of the basin. The subsidence evolution through Upper Cretaceous is marked by a recovery of a tectonic distension during some phases (Late Albian and Lower Turonian) and an essentially thermic subsidence during the other periods. Finally some precocious tectonic phases appeared as early as the Santonian-Campanian transition. The evolution of the basin was thus controlled by the drift of the African plate during the expansion of the Atlantic ocean and also the tectonic influence which began to appear in north Alpine domain.

Dynamics of upper mantle rocks decompression melting above hot spots under continental plates

NASA Astrophysics Data System (ADS)

Perepechko, Yury; Sorokin, Konstantin; Sharapov, Victor

2014-05-01

Numeric 2D simulation of the decompression melting above the hot spots (HS) was accomplished under the following conditions: initial temperature within crust mantle section was postulated; thickness of the metasomatized lithospheric mantle is determined by the mantle rheology and position of upper asthenosphere boundary; upper and lower boundaries were postulated to be not permeable and the condition for adhesion and the distribution of temperature (1400-2050°C); lateral boundaries imitated infinity of layer. Sizes and distribution of lateral points, their symmetry, and maximum temperature varied between the thermodynamic condition for existences of perovskite - majorite transition and its excess above transition temperature. Problem was solved numerically a cell-vertex finite volume method for thermo hydrodynamic problems. For increasing convergence of iterative process the method of lower relaxation with different value of relaxation parameter for each equation was used. The method of through calculation was used for the increase in the computing rate for the two-layered upper mantle - lithosphere system. Calculated region was selected as 700 x (2100-4900) km. The time step for the study of the asthenosphere dynamics composed 0.15-0.65 Ma. The following factors controlling the sizes and melting degree of the convective upper mantle, are shown: a) the initial temperature distribution along the section of upper mantleb) sizes and the symmetry of HS, c) temperature excess within the HS above the temperature on the upper and lower mantle border TB=1500-2000oC with 5-15% deviation but not exceed 2350oC. It is found, that appearance of decompression melting with HS presence initiate primitive mantle melting at TB > of 1600oC. Initial upper mantle heating influence on asthenolens dimensions with a constant HS size is controlled mainly by decompression melting degree. Thus, with lateral sizes of HS = 400 km the decompression melting appears at TB > 1600oC and HS temperature (THS) > 1900oC asthenolens size ~700 km. When THS = of 2000oC the maximum melting degree of the primitive mantle is near 40%. An increase in the TB > 1900oC the maximum degree of melting could rich 100% with the same size of decompression melting zone (700 km). We examined decompression melting above the HS having LHS = 100 km - 780 km at a TB 1850- 2100oC with the thickness of lithosphere = 100 km.It is shown that asthenolens size (Lln) does not change substantially: Lln=700 km at LHS = of 100 km; Lln= 800 km at LHS = of 780 km. In presence of asymmetry of large HS the region of advection is developed above the HS maximum with the formation of asymmetrical cell. Influence of lithospheric plate thicknesses on appearance and evolution of asthenolens above the HS were investigated for the model stepped profile for the TB ≤ of 1750oS with Lhs = 100km and maximum of THS =2350oC. With an increase of TB the Lln difference beneath lithospheric steps is leveled with retention of a certain difference to melting degrees and time of the melting appearance a top of the HS. RFBR grant 12-05-00625.

Controlling Interfacial Separation in Porous Structures by Void Patterning

NASA Astrophysics Data System (ADS)

Ghareeb, Ahmed; Elbanna, Ahmed

Manipulating interfacial response for enhanced adhesion or fracture resistance is a problem of great interest to scientists and engineers. In many natural materials and engineering applications, an interface exists between a porous structure and a substrate. A question that arises is how the void distribution in the bulk may affect the interfacial response and whether it is possible to alter the interfacial toughness without changing the surface physical chemistry. In this paper, we address this question by studying the effect of patterning voids on the interfacial-to-the overall response of an elastic plate glued to a rigid substrate by bilinear cohesive material. Different patterning categories are investigated; uniform, graded, and binary voids. Each case is subjected to upward displacement at the upper edge of the plate. We show that the peak force and maximum elongation at failure depend on the voids design and by changing the void size, alignment or gradation we may control these performance measures. We relate these changes in the measured force displacement response to energy release rate as a measure of interfacial toughness. We discuss the implications of our results on design of bulk heterogeneities for enhanced interfacial behavior.

Structure of crust and upper mantle beneath NW Himalayas, Pamir and Hindukush by multi-scale double-difference seismic tomography

NASA Astrophysics Data System (ADS)

Bhatti, Zahid Imran; Zhao, Junmeng; Khan, Nangyal Ghani; Shah, Syed Tallataf Hussain

2018-08-01

The India-Asia collision and subsequent subduction initiated the evolution of major tectonic features in the Western Syntaxis. The complex tectonic structure and shallow to deep seismicity have attracted geoscientists over the past two decades. The present research is based on a 3D tomographic inversion of P-wave arrival time data to constrain the crustal and upper mantle structure beneath the NW Himalayas and Pamir-Hindukush region using the Double-difference tomography. We utilized a very large multi-scale dataset comprising 19,080 earthquakes recorded at 397 local and regional seismic stations from 1950 to 2017. The northward dipping seismic zone coinciding with the low velocity anomaly suggests the subduction of the Indian lower crust beneath the Hindukush. The extent of the northward advancing Indian slab increases from east to west in this region. We observed no signs of northward subduction of the Indian plate under the Hindukush beyond 71°E longitude. The Indian plate overturns due south after interacting with the Asian plate beneath the southern Pamir, which correlates with the counter-clockwise rotation of the Indian plate. The Asian plate is also imaged as a southward subducting seismic zone beneath the southern Pamir. In the NW Himalayas, the northward subducting Indian plate appears as a gently dipping low velocity anomaly beneath the Karakoram Block. The stresses caused by the collision and subduction along the Shyok Suture and Indus Suture are translated to the south. The crustal scale seismicity and high velocity anomalies indicate an intense deformation in the crust, which is manifested by syntaxial bends and thrust faults to the south of the Main Mantle Thrust.

Optimal area of lateral mass mini-screws implanted in plated cervical laminoplasty: a radiography anatomy study.

PubMed

Chen, Hua; Li, Huibo; Deng, Yuxiao; Rong, Xin; Gong, Quan; Li, Tao; Song, Yueming; Liu, Hao

2017-04-01

Lateral mass mini-screws used in plated cervical laminoplasty might penetrate into facet joints. The objective is to observe this complication incidence and to identify the optimal areas for 5- and 7-mm-long mini-screws to implant on lateral mass. 47 patients who underwent plated cervical laminoplasty were included. The optimal area for mini-screws implanting was set according to pre-operative 3D CT reconstruction data. Then, each posterior-lateral mass surface was divided into three regions: 7-mm region, 5-mm region, and dangerous area. The mini-screw implanted region was recorded. Post-operative CT images were used to identify whether the mini-screws penetrated into facet joints. 235 mini-plates and 470 lateral mass mini-screws were used in the study. 117 (24.9%) mini-screws penetrated 88 (37.4%) facet joints. The 5-mm-long mini-screw optimal area occupied the upper 72, 65, 65, 64, and 65 % area of the posterior-lateral mass surface for C3-7, while the 7-mm-long mini-screw optimal area encompassed the upper 54, 39, 40, 33, and 32 %. Only 7-mm-long mini-screws were used to fix the plate to the lateral mass. 4 of 240 mini-screws in 7-mm region, 67 of the 179 mini-screws in 5-mm region, and 46 of the 51 mini-screws in dangerous region penetrated into the facet joint. The differences in the rate of facet joint penetration related to region were statistically significant (P < 0.001). The facet joint destruction by mini-screws was not a rare complication in plated cervical laminoplasty. The optimal areas we proposed may help guide the mini-screw implantation positions.

Diverse continental subduction scenarios along the Arabia-Eurasia collision zone

NASA Astrophysics Data System (ADS)

Kaban, M. K.; Petrunin, A.; El Khrepy, S.; Al-Arifi, N. S.

2017-12-01

The Arabia-Eurasia continental collision zone is one of the largest and most active on the Earth. It has been discussed already long ago that the convergence of these plates implies subduction of the lithosphere. However, scenarios of this process are still debatable. Even direction of the present-day continental subduction is not clear. Previously, principal conclusions about structure of the upper mantle in this region were chiefly based on seismic tomography results. However, seismic velocities not always provide a complete image of the deep interiors since they are chiefly affected by temperature variations and less - by composition. Here we construct a 3D model of the mantle down to 700 km, which is based on a joint inversion of seismic tomography, residual (crust free) gravity field and residual topography (Kaban et al., 2016). Several cross-sections across the collision zone demonstrate principal variations of the continental subduction scenarios from northwest to southeast. In the southeastern part we observe subduction of the Eurasian plate under the West Great Caucasus, Pontic mountains and further under the northwestern part of the Arabian plate. However, the situation is changed when we move to the East Great Caucasus and Zagros, where clear double-sided subduction is observed. The Arabian plate is subducting under the Zagros, while the Eurasian plate - under the Caucasus merging in the transition zone. This situation persists further to the southeast, where we observe the subduction of the South Caspian block under Alborz accompanied by the counteracting penetration of the Arabian plate from the south. More to the southeast, the subduction of the Arabian plate is stagnated, while the subduction of the Eurasian plate can be traced down to the bottom of the transition zone under the northeastern flank of the Arabian plate. In the southern rim of the collision zone under Makran, we don't find any evidence for the present day subduction; remnants of the formerly subducted slabs are located below 200 km. Kaban, M. K., S. El Khrepy, N. Al-Arifi, M. Tesauro, and W. Stolk (2016), Three dimensional density model of the upper mantle in the Middle East: Interaction of diverse tectonic processes, J. Geophys. Res. Solid Earth, 121.

Flat-slab subduction, whole crustal faulting, and geohazards in Alaska: Targets for Earthscope

NASA Astrophysics Data System (ADS)

Gulick, S. P.; Pavlis, T. L.; Bruhn, R. L.; Christeson, G. L.; Freymueller, J. T.; Hansen, R. A.; Koons, P. O.; Pavlis, G. L.; Roeske, S.; Reece, R.; van Avendonk, H. J.; Worthington, L. L.

2010-12-01

Crustal structure and evolution illuminated by the Continental Dynamics ST. Elias Erosion and tectonics Project (STEEP) highlights some fundamental questions about active tectonics processes in Alaska including: 1) what are the controls on far field deformation and lithospheric stabilization, 2) do strike slip faults extend through the entire crust and upper mantle and how does this influence mantle flow, and 3) how does the transition from “normal” subduction of the Pacific along the Aleutians to flat slab subduction of the Yakutat Terrane beneath southeast and central Alaska to translation of the Yakutat Terrane past North American in eastern Alaska affect geohazard assessment for the north Pacific? Active and passive seismic studies and geologic fieldwork focusing on the Yakutat Terrane show that the Terrane ranges from 15-35 km thick and is underthrusting the North American plate from the St. Elias Mountains to the Alaska Range (~500 km). Deformation of the upper plate occurs within the offshore Pamplona Zone fold and thrust belt, and onshore throughout the Robinson Mountains. Deformation patterns, structural evolution, and the sedimentary products of orogenesis are fundamentally influenced by feedbacks with glacial erosion. The Yakutat megathrust extends beneath Prince William Sound such that the 1964 Mw 9.2 great earthquake epicenter was on this plate boundary and jumped to the adjacent Aleutian megathrust coseismically; this event illuminates the potential for transitional tectonic systems to enhance geohazards. The northern, southern, and eastern limits of the Yakutat microplate are strike-slip faults that, where imaged, appear to cut the entire crustal section and may allow for crustal extrusion towards the Bering Sea. Yakutat Terrane effects on mantle flow, however, have been suggested to cross these crustal features to allow for far-field deformation in the Yukon, Brooks Range, and Amerasia Basin. From the STEEP results it is clear that the Yakutat Terrane is driving a range of tectonic and surface processes perturbing the Aleutian subduction system at its eastern extent and linking this system with Laramide style subduction and plate boundary strike-slip tectonics farther east. Targeted geodetic and seismic deployments as part of Earthscope could examine all of these features and seek to address fundamental questions about tectonic interactions.

Overview of the Kinematics of the Salton Trough and Northern Gulf of California

NASA Astrophysics Data System (ADS)

Stock, J. M.

2016-12-01

In the Salton Trough and Northern Gulf of California, transtensional rifting is leading to full continental plate breakup, as a major continental block is being transferred to an oceanic plate. Since at least 6 Ma this region has taken up most of the plate boundary slip between the Pacific and North America plates at this latitude. We review the structural history of plate separation, as constrained by many recent studies of present and past fault configurations, seismicity, and basin development as seen from geology and geophysics. Modern activity in the USA is dominated by NW-striking strike-slip faults (San Andreas, San Jacinto, Elsinore), and subsidiary NE-striking faults. There is an equally broad zone in Mexico (faults from the Mexicali Valley to the Colorado River Delta and bounding the Laguna Salada basin), including active low-angle detachment faults. In both areas, shifts in fault activity are indicated by buried faults and exhumed or buried earlier basin strata. Seismicity defines 3 basin segments in the N Gulf: Consag-Wagner, Upper Delfin, and Lower Delfin, but localization is incomplete. These basins occupy a broad zone of modern deformation, lacking single transform faults, although major strike-slip faults formed in the surrounding continental area. The off-boundary deformation on the western side of the plate boundary has changed with time, as seen by Holocene and Quaternary faults controlling modern basins in the Gulf Extensional Province of NE Baja California, and stranded Pliocene continental and marine basin strata in subaerial fault blocks. The eastern side of the plate boundary, in the shallow northeastern Gulf, contains major NW-striking faults that may have dominated the earlier (latest Miocene-early Pliocene) kinematics. The Sonoran coastal plain likely buries additional older faults and basin sequences; further studies here are needed to refine models of the earlier structural development of this sector. Despite > 250 km of plate separation, and production of new crustal area in these segments of the plate boundary, the deformation is not considered to be fully localized because some occurs outside the region of new crustal formation. Similar scenarios may need to be considered when evaluating continent-ocean transitions in other rift systems.

Current Global Absolute Plate Velocities Inferred from the Trends of Hotspot Tracks: Implications for Motion between Groups of Hotspots and Comparison and Combination with Absolute Velocities Inferred from the Orientation of Seismic Anisotropy

NASA Astrophysics Data System (ADS)

Wang, C.; Gordon, R. G.; Zheng, L.

2016-12-01

Hotspot tracks are widely used to estimate the absolute velocities of plates, i.e., relative to the lower mantle. Knowledge of current motion between hotspots is important for both plate kinematics and mantle dynamics and informs the discussion on the origin of the Hawaiian-Emperor Bend. Following Morgan & Morgan (2007), we focus only on the trends of young hotspot tracks and omit volcanic propagation rates. The dispersion of the trends can be partitioned into between-plate and within-plate dispersion. Applying the method of Gripp & Gordon (2002) to the hotspot trend data set of Morgan & Morgan (2007) constrained to the MORVEL relative plate angular velocities (DeMets et al., 2010) results in a standard deviation of the 56 hotspot trends of 22°. The largest angular misfits tend to occur on the slowest moving plates. Alternatively, estimation of best-fitting poles to hotspot tracks on the nine individual plates, results in a standard deviation of trends of only 13°, a statistically significant reduction from the introduction of 15 additional adjustable parameters. If all of the between-plate misfit is due to motion of groups of hotspots (beneath different plates), nominal velocities relative to the mean hotspot reference frame range from 1 to 4 mm/yr with the lower bounds ranging from 1 to 3 mm/yr and the greatest upper bound being 8 mm/yr. These are consistent with bounds on motion between Pacific and Indo-Atlantic hotspots over the past ≈50 Ma, which range from zero (lower bound) to 8 to 13 mm/yr (upper bounds) (Koivisto et al., 2014). We also determine HS4-MORVEL, a new global set of plate angular velocities relative to the hotspots constrained to consistency with the MORVEL relative plate angular velocities, using a two-tier analysis similar to that used by Zheng et al. (2014) to estimate the SKS-MORVEL global set of absolute plate velocities fit to the orientation of seismic anisotropy. We find that the 95% confidence limits of HS4-MORVEL and SKS-MORVEL overlap substantially and that the two sets of angular velocities differ insignificantly. Thus we combine the two sets of angular velocities to estimate ABS-MORVEL, an optimal set of global angular velocities consistent with both hotspot tracks and seismic anisotropy. ABS-MORVEL has more compact confidence limits than either SKS-MORVEL or HS4-MORVEL.

Directivity pattern of the sound radiated from axisymmetric stepped plates.

PubMed

He, Xiping; Yan, Xiuli; Li, Na

2016-08-01

For the purpose of optimal design and efficient utilization of the kind of stepped plate radiator in air, in this contribution, an approach for calculation of the directivity pattern of the sound radiated from a stepped plate in flexural vibration with a free edge is developed based on Kirchhoff-Love hypothesis and Rayleigh integral principle. Experimental tests of directivity pattern for a fabricated flat plate and two fabricated plates with one and two step radiators were carried out. It shows that the configuration of the measured directivity patterns by the proposed analytic approach is similar to those of the calculated approach. Comparison of the agreement between the calculated directivity pattern of a stepped plate and its corresponding theoretical piston show that the former radiator is equivalent to the latter, and the diffraction field generated by the unbaffled upper surface may be small. It also shows that the directivity pattern of a stepped radiator is independent of the metallic material but dependent on the thickness of base plate and resonant frequency. The thicker the thickness of base plate, the more directive the radiation is. The proposed analytic approach in this work may be adopted for any other plates with multi-steps.

Two-dimensional thermal modeling associated with subduction of the Philippine Sea plate in southern Kyushu, Japan

NASA Astrophysics Data System (ADS)

Suenaga, Nobuaki; Yoshioka, Shoichi; Matsumoto, Takumi; Ji, Yingfeng

2018-01-01

In Hyuga-nada, southern Kyushu in southwest Japan, afterslip events were found in association with the two large interplate earthquakes, which occurred on October 19 and December 3, 1996. In Kyushu, low-frequency earthquakes (LFEs) and tectonic tremors are not common, but a considerable concentration of tectonic tremors is observed beneath the Pacific coast of the Miyazaki prefecture. To investigate the generation mechanisms of these seismic events, we performed 2-D box-type time-dependent thermal modeling in southern Kyushu. As a result, the temperature range of the upper surface of the subducting Philippine Sea (PHS) plate, where the afterslip occurred, reached approximately 300 to 350 °C. The temperatures where the tectonic tremors occurred ranged from 450 to 650 °C in the mantle wedge corner. We also estimated the spatial distribution of water content within the subducting PHS plate, using phase diagrams of hydrous mid-ocean ridge basalt (MORB) and ultramafic rock. Then, we found that no characteristic phase transformations accompany the dehydration of the subducting PHS plate in the afterslip region, but phase transformation from lawsonite blueschist to lawsonite eclogite is expected within the oceanic crust of the PHS plate just below the active region of the tectonic tremors. Our estimated water content distribution is consistent with the VP/VS ratio calculated from the seismic tomography. Therefore, we conclude that the occurrence of the afterslip is controlled by the temperature condition at the plate boundary, and occurs near the down-dip limit of the seismogenic zone. On the other hand, determining the major factors leading to the occurrence of the tectonic tremors is difficult, we estimated the temperature in the mantle wedge is ranging from 450 °C to 650 °C, and dehydration of 1.0 wt% would be expected from the subducting PHS plate near the active region of the tectonic tremors.

Thermal anomalies and magmatism due to lithospheric doubling and shifting

NASA Astrophysics Data System (ADS)

Vlaar, N. J.

1983-11-01

We present some thermal and magmatic consequences of the processes of lithospheric doubling and lithospheric shifting. Lithospheric doubling concerns the obduction of a cold continental or old oceanic lithospheric plate over a young and hot oceanic lithosphere/upper mantle system, including an oceanic ridge. Lithospheric shifting concerns the translation and rotation of a lithospheric plate relative to the upper mantle. In both cases the resulting thermal state of the upper mantle below the obducting or shifting lithosphere may be perturbed relative to a "normal" continental or oceanic geothermal situation. The perturbed geothermal state gives rise to a density inversion at depth and thus induces a vertical gravitational instability which favours magmatism. We speculate about the magmatic consequences of this situation and infer that in the case of lithospheric doubling our model may account for the petrology and geochemistry of the resulting magma. The original layering and composition of the overridden young oceanic lithosphere may strongly influence magmatic processes. We dwell shortly on the genesis of kimberlites within the framework of our lithospheric doubling model and on magmatism in general. Lithospheric recycling is inherent to the mechanism of lithospheric doubling.

Effect of Shear Deformation and Continuity on Delamination Modelling with Plate Elements

NASA Technical Reports Server (NTRS)

Glaessgen, E. H.; Riddell, W. T.; Raju, I. S.

1998-01-01

The effects of several critical assumptions and parameters on the computation of strain energy release rates for delamination and debond configurations modeled with plate elements have been quantified. The method of calculation is based on the virtual crack closure technique (VCCT), and models that model the upper and lower surface of the delamination or debond with two-dimensional (2D) plate elements rather than three-dimensional (3D) solid elements. The major advantages of the plate element modeling technique are a smaller model size and simpler geometric modeling. Specific issues that are discussed include: constraint of translational degrees of freedom, rotational degrees of freedom or both in the neighborhood of the crack tip; element order and assumed shear deformation; and continuity of material properties and section stiffness in the vicinity of the debond front, Where appropriate, the plate element analyses are compared with corresponding two-dimensional plane strain analyses.

Performance of a circular cylinder piezoelectric wind energy harvester fitted with a splitter plate

NASA Astrophysics Data System (ADS)

Song, Jie; Hu, Gang; Tse, K. T.; Li, S. W.; Kwok, K. C. S.

2017-11-01

This study examines effects of the splitter plate placed in the near wake of a circular cylinder on the performance of a piezoelectric wind energy harvester through wind tunnel experiments. The kinetic energy of the harvester is gained by wind-induced vibrations of the circular cylinder. The splitter plate is attached to the leeward side of the cylinder. The ratio of the splitter plate length to the diameter of the circular cylinder (Lsp/D) ranges from 0.25 to 2.00. After attaching the splitter plate with an appropriate length, the harvester is able to sustain large amplitude vibrations beyond the wind speed range corresponding to vortex-induced vibrations. Thus, the upper bound of the wind speed range for the harvester to harness wind energy is eliminated, which significantly increases the efficiency of the harvester. Compared to the different lengths of the splitter plate, 0.65D has been found to be the optimal length for maximizing the harvested power.

Indoor test for thermal performance evaluation of Lenox-Honeywell solar collector. [conducted using Marshall Space Flight Center Solar Simulator

NASA Technical Reports Server (NTRS)

Shih, K.

1977-01-01

The test procedures used and the test results obtained from an evaluation test program conducted on a double-covered liquid solar collector under simulated conditions are presented. The test article was a flat plate solar collector using liquid as the heat transfer medium. The absorber plate was steel with the copper tubes bonded on the upper surface. The plate was coated with black chrome with an absorptivity factor of .95 and emissivity factor of .12. A time constant test and incident angle modifier test were conducted to determine the transient effect and the incident angle effect on the collector.

Obduction: Why, how and where. Clues from analog models

NASA Astrophysics Data System (ADS)

Agard, P.; Zuo, X.; Funiciello, F.; Bellahsen, N.; Faccenna, C.; Savva, D.

2014-05-01

Obduction is an odd geodynamic process characterized by the emplacement of dense oceanic “ophiolites” atop light continental plates in convergent settings. We herein present analog models specifically designed to explore the conditions (i.e., sharp increase of plate velocities - herein coined as ‘acceleration’, slab interaction with the 660 km discontinuity, ridge subduction) under which obduction may develop as a result of subduction initiation. The experimental setup comprises an upper mantle modeled as a low-viscosity transparent Newtonian glucose syrup filling a rigid Plexiglas tank and high-viscosity silicone plates. Convergence is simulated by pushing a piston with plate tectonics like velocities (1-10 cm/yr) onto a model comprising a continental margin, a weakness zone with variable resistance and dip (W), an oceanic plate (with or without a spreading ridge), a preexisting subduction zone (S) dipping away from the piston and an upper active continental margin, below which the oceanic plate is being subducted at the start of the model (as for the Neotethyan natural example). Several configurations were tested over thirty-five parametric models, with special emphasis on comparing different types of weakness zone and the degree of mechanical coupling across them. Measurements of displacements and internal deformation allow for a precise and reproducible tracking of deformation. Models consistently demonstrate that once conditions to initiate subduction are reached, obduction may develop further depending on the effective strength of W. Results (1) constrain the range of physical conditions required for obduction to develop/nucleate and (2) underline the key role of such perturbations for triggering obduction, particularly plate ‘acceleration’. They provide an explanation to the short-lived Peri-Arabic obduction, which took place along thousands of km almost synchronously (within ∼50-10 Myr), from Turkey to Oman, while the subduction zone beneath Eurasia became temporarily jammed. They also demonstrate that the emplacement of dense, oceanic material on continental lithosphere is not a mysterious process requiring extraordinary boundary conditions but results from large-scale, normal (oceanic then continental) subduction processes.

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.

Lesser Antillean Arc Initiation and Migration as a Proxy of Slab Dynamics: Geothermochronology, Thermobarometry and Structure of Saint Martin Granodiorites

NASA Astrophysics Data System (ADS)

Noury, M.; Münch, P.; Philippon, M. M.; Bernet, M.; Bruguier, O.; Balvay, M.

2017-12-01

In subduction zones, volcanic arc initiation, cessation, migration and associated upper plate deformation -i.e faulting and vertical motions- reflect large-scale slab dynamics. At the northeastern edge of the Caribbean plate, the Greater Caribbean subduction zone waned out during the Mid Eocene, following the subduction of the Bahamas bank. This arc cessation was contemporaneous with (i) a plate boundary re-organization (evolving from subduction to transform), (ii) upper plate deformation and (iii) arc initiation in the Lesser Antilles. As part of the GAARANTI project that aims at unraveling the relationships between the evolution of terrestrial Caribbean biodiversity and vertical motions resulting from the Lesser Antilles subduction zone dynamic, we study the Saint Martin granodiorites, one of the two Oligocene plutons outcropping in the Lesser Antillean forearc. We investigate the birth and evolution of the Lesser Antillean arc and its thermo-mechanical impact on the Caribbean upper plate. In order to characterize the P,T,t path of the pluton we performed several thermochronological analyses covering a wide range of temperature (U-Pb on zircon -Tc 850°C, Ar/Ar on amphibole -Tc 550°C- and biotite -Tc 325°C-, zircon and apatite fission-tracks -Tc 250 and 110°C, respectively as well as U-Th/He on apatite -Tc 60°C) coupled with in-situ thermobarometry analyses (Al in hornblendes) and structural data. Geochronology and thermobarometry reveal that the granodiorites emplaced at ca. 28 Ma, at a depth of 5 km. Based on the age difference between amphibole and biotite Ar/Ar ages, we show that the northern pluton cooled faster than the southern one. Preliminary thermochronological results show a fast cooling between 29 and 25 Ma and then a continuous and slow cooling since 25 Ma and inverse modeling points to a 10 Ma cooling event. Our investigations give insights on the thermo-mechanical evolution of the arc-forearc region of the Lesser Antilles subduction zone. Considering a mean high of 1200m for the volcanic edifice, the pluton emplaced at shallow depth (ca. 4 km) within the Caribbean plate. The pluton is bounded by N-S faults that could possibly be responsible for the 10 Ma exhumation event. This thermal event may be contemporaneous with the westward arc migration during Miocene times and may reflect slab flattening.

Fore- and Back-Arc Structures Along the Hikurangi-Kermadec Subduction Zone

NASA Astrophysics Data System (ADS)

Scherwath, M.; Kopp, H.; Flueh, E. R.; Henrys, S. A.; Sutherland, R.

2009-04-01

The Hikurangi-Kermadec subduction zone northeast of New Zealand represents an ideal target to study lateral variations of subduction zone processes. The incoming Pacific plate changes from being a large igneous province, called the Hikurangi Plateau, in the south to normal oceanic plate north of the Rapuhia Scarp. The overriding Australian plate is continental in the south, forming the North Island of New Zealand, and changes to an island arc in the north. Further lateral variability exists in changes in volcanic and hydro-thermal activity, transitions from accretion to subduction erosion, backarc spreading and rifting, and is accompanied by northward increasing seismicity. As part of the MANGO project (Marine Geoscientific Investigations on the Input and Output of the Kermadec Subduction Zone), four marine geophysical transects of largely seismic reflection and refraction data provide constraints on the upper lithospheric structures across the Hikurangi-Kermadec Trench between 29-38 degrees South. On MANGO profile 1 in the south, the initially shallow subduction of the incoming plateau coincides with crustal underplating beneath the East Cape ridge. To the west lies the 100 km wide and over 10 km deep Raukumara Basin. Seismic velocities of the upper arc mantle are around 8 km/s and are considered normal. In contrast, on MANGO profile 4, about 1000 km to the north around the volcanically active Raoul Island, the incoming oceanic crust appears to bend considerably steeper and thus causes a 50 km narrower forearc with a smaller forearc basin. Furthermore, the upper mantle velocities in both plates are relatively low (7.4-7.7 km/s), likely indicating strong bending related deformation of the incoming plate and thermal activity within the arc possibly due to spreading. Here, arc volcanism is relatively active, with many large volcanoes directly on the ridge. The central two transects MANGO 2 and 3, though without data coverage of the structure of the incoming plate, are more similar to MANGO 4. The arc regions appear to be strongly affected by the activity of the arc. The arc crust of the northern MANGO 3 becomes significantly thinner in the backarc region due to extension, and much reduced volcanism behind the ridge. The structures on MANGO 2, on the other hand, cover strong and densely spaced thermal activity from the adjacent arc volcanism, possibly linked to a recent, fluid-rich passage of the Hikurangi Plateau.

Comments on the paper of Bodin et al. (2010). Journal of African Earth Sciences, 58, pp. 489-506

NASA Astrophysics Data System (ADS)

Tlig, Saïd

2016-06-01

Bodin et al. (2010) produced an important paper in the Journal of African Earth Sciences. The main goals of this paper were: (1) the petrological and sedimentological treatment of the upper Jurassic and Cretaceous series in southern Tunisia and northern Ghadames Basin including the Hamada El Hamra area and Nafussah Mountain of Libya; (2) the reconstruction of tectonic controls on deposition and basin-fill; (3) the correlation of poorly dated lithostratigraphic columns, poor in diagnostic fauna, from northwestern Libya to southern Tunisia; and (4) the comparison between the authors' findings and assignments of global eustatic and plate tectonic events.

Fluctuating pressures in flow fields of jets

NASA Technical Reports Server (NTRS)

Schroeder, J. C.; Haviland, J. K.

1976-01-01

The powered lift configurations under present development for STOL aircraft are the externally blown flap (EBF), involving direct jet impingement on the aircraft flaps, and the upper surface blown (USB), where the jet flow is attached on the upper surface of the wing and directed downwards. Towards the goal of developing scaling laws to predict unsteady loads imposed on the structural components of these STOL aircraft from small model tests, the near field fluctuating pressure behavior for the simplified cases of a round free cold jet and the same jet impinging on a flat plate was investigated. Examples are given of coherences, phase lags (giving convection velocities), and overall fluctuating pressure levels measured. The fluctuating pressure levels measured on the flat plate are compared to surface fluctuating pressure levels measured on full-scale powered-lift configuration models.

Solar energy panel

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

Hyman, M.

1980-03-04

A light-weight, low-cost and high efficiency solar panel includes a light-weight rectangular wood frame which surrounds and houses a copper absorber plate. A pair of spaced glazings, formed from plastic film materials, are disposed above the absorber to define a pair of enclosed air spaces. The lower glazing is capable of withstanding high temperatures and the upper glazing material is capable of providing good weather resistance. The material of the upper glazing extends fully about the frame to protect the entire frame from weathering. Insulation is provided beneath the absorber plate. The frame rests on top of a bottom sheetmore » of insulative foam plastic which is wrapped in a plastic envelope. The surrounding film of the outer glazing is bonded securely to the envelope to encase the entire panel within a protective sealed envelope of weather-resistant plastic film.« less

Mantle dynamics in the Mediterranean

NASA Astrophysics Data System (ADS)

Faccenna, Claudio; Becker, Thorsten W.

2016-04-01

The Mediterranean offers a unique avenue to study the driving forces of tectonic deformation within a complex mobile belt. Lithospheric dynamics are affected by slab rollback and collision of two large, slowly moving plates, forcing fragments of continental and oceanic lithosphere to interact. Here, we review the rich and growing set of constraints from geological reconstructions, geodetic data, and crustal and upper mantle heterogeneity imaged by structural seismology. We discuss a conceptual and quantitative framework for the causes of surface deformations. Exploring existing and newly developed tectonic and numerical geodynamic models, we illustrate the role of mantle convection on surface geology. A coherent picture emerges which can be outlined by two, almost symmetric, upper mantle convection cells. The down-wellings are found in the centre of the Mediterranean, and are associated with the descent of the Tyrrhenian and the Hellenic slabs. During plate convergence, these slabs migrated, driving return flow of the asthenosphere from the backarc regions. These currents can be found at large distance from the subduction zones, and are at present expressed in two upwellings beneath Anatolia and eastern Iberia. This convection system provides an explanation for the general pattern of seismic anisotropy in the Mediterranean, the first-order Anatolia and Adria microplate kinematics, and the positive dynamic topography of Anatolia and Eastern Iberia. More generally, it is an illustration of upper mantle, small-scale convection leading to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the Tethyan collision.

Plateau subduction, intraslab seismicity and the Denali Volcanic Gap

NASA Astrophysics Data System (ADS)

Bostock, M. G.; Chuang, L. Y.; Wech, A.; Plourde, A. P.

2017-12-01

Tectonic tremors in Alaska (USA) are associated with subduction of the Yakutat plateau, but their origins are unclear due to lack of depth constraints. We have processed tremor recordings to extract low-frequency earthquakes (LFEs), and generated a set of six LFE waveform templates via iterative network matched filtering and stacking. The timing of impulsive P (compressional) wave and S (shear) wave arrivals on template waveforms places LFEs at 40-58 km depth, near the upper envelope of intraslab seismicity and immediately updip of increased levels of intraslab seismicity. S waves at near-epicentral distances display polarities consistent with shear slip on the plate boundary. We compare characteristics of LFEs, seismicity, and tectonic structures in central Alaska with those in warm subduction zones, and propose a new model for the region's unusual intraslab seismicity and the enigmatic Denali volcanic gap (i.e., an area of no volcanism where expected). We argue that fluids in the Yakutat plate are confined to its upper crust, and that shallow subduction leads to hydromechanical conditions at the slab interface in central Alaska akin to those in warm subduction zones where similar LFEs and tremor occur. These conditions lead to fluid expulsion at shallow depths, explaining strike-parallel alignment of tremor occurrence with the Denali volcanic gap. Moreover, the lack of double seismic zone and restriction of deep intraslab seismicity to a persistent low-velocity zone are simple consequences of anhydrous conditions prevailing in the lower crust and upper mantle of the Yakutat plate.

Plateau subduction, intraslab seismicity, and the Denali (Alaska) volcanic gap

USGS Publications Warehouse

Chuang, Lindsay Yuling; Bostock, Michael; Wech, Aaron; Plourde, Alexandre

2018-01-01

Tectonic tremors in Alaska (USA) are associated with subduction of the Yakutat plateau, but their origins are unclear due to lack of depth constraints. We have processed tremor recordings to extract low-frequency earthquakes (LFEs), and generated a set of six LFE waveform templates via iterative network matched filtering and stacking. The timing of impulsive P (compressional) wave and S (shear) wave arrivals on template waveforms places LFEs at 40–58 km depth, near the upper envelope of intraslab seismicity and immediately updip of increased levels of intraslab seismicity. S waves at near-epicentral distances display polarities consistent with shear slip on the plate boundary. We compare characteristics of LFEs, seismicity, and tectonic structures in central Alaska with those in warm subduction zones, and propose a new model for the region’s unusual intraslab seismicity and the enigmatic Denali volcanic gap (i.e., an area of no volcanism where expected). We argue that fluids in the Yakutat plate are confined to its upper crust, and that shallow subduction leads to hydromechanical conditions at the slab interface in central Alaska akin to those in warm subduction zones where similar LFEs and tremor occur. These conditions lead to fluid expulsion at shallow depths, explaining strike-parallel alignment of tremor occurrence with the Denali volcanic gap. Moreover, the lack of double seismic zone and restriction of deep intraslab seismicity to a persistent low-velocity zone are simple consequences of anhydrous conditions prevailing in the lower crust and upper mantle of the Yakutat plate.

Detachments of the subducted Indian continental lithosphere based on 3D finite-frequency tomographic images

NASA Astrophysics Data System (ADS)

Liang, X.; Tian, X.; Wang, M.

2017-12-01

Indian plate collided with Eurasian plate at 60 Ma and there are about 3000 km crustal shortening since the continental-continental collision. At least one third of the total amount of crustal shortening between Indian and Eurasian plates could not be accounted by thickened Tibetan crust and surface erosion. It will need a combination of possible transfer of lower crust to the mantle by eclogitization and lateral extrusion. Based on the lithosphere-asthenosphere boundary images beneath the Tibetan plateau, there is also at least the same amount deficit for lithospheric mantle subducted into upper/lower mantle or lateral extrusion with the crust. We have to recover a detailed Indian continental lithosphere image beneath the plateau in order to explain this deficit of mass budget. Combining the new teleseismic body waves recorded by SANDWICH passive seismic array with waveforms from several previous temporary seismic arrays, we carried out finite-frequency tomographic inversions to image three-dimensional velocity structures beneath southern and central Tibetan plateau to examine the possible image of subducted Indian lithosphere in the Tibetan upper mantle. We have recovered a continuous high velocity body in upper mantle and piece-wised high velocity anomalies in the mantle transition zone. Based on their geometry and relative locations, we interpreted these high velocity anomalies as the subducted and detached Indian lithosphere at different episodes of the plateau evolution. Detachments of the subducted Indian lithosphere should have a crucial impact on the volcanism activities and uplift history of the plateau.

A global geochemical model for the evolution of the mantle

NASA Technical Reports Server (NTRS)

Anderson, D. L.

1979-01-01

It is proposed that the upper mantle transition region, 220 to 670 km, is composed of eclogite which has been derived from primitive mantle by about 20 percent partial melting and that this is the source and sink of oceanic crust. The remainder of the upper mantle is garnet peridotite which is the source of continental basalts and hotspot magmas. This region is enriched in incompatible elements by hydrous and CO2 rich metasomatic fluids which have depleted the underlying layers in the L.I.L. elements and L.R.E.E. The volatiles make this a low-velocity, high attenuation, low viscosity region. The eclogite layer is internally heated and its controls the convection pattern in the upper mantle. Plate tectonics is intermittent. The continental thermal anomaly at a depth of 150-220 km triggers kimberlite and carbonatite activity, alkali and flood basalt volcanism, vertical tectonics and continental breakup. Hot spots remain active after the continents leave and build the oceanic islands. Mantle plumes rise from a depth of about 220 km. Midocean ridge basalts rise from the depleted layer below this depth. Material from this layer can also be displaced upwards by subducted oceanic lithosphere to form back-arc basins.

Crust and upper-mantle structure of Wanganui Basin and southern Hikurangi margin, North Island, New Zealand as revealed by active source seismic data

NASA Astrophysics Data System (ADS)

Tozer, B.; Stern, T. A.; Lamb, S. L.; Henrys, S. A.

2017-11-01

Wide-angle reflection and refraction data recorded during the Seismic Array HiKurangi Experiment (SAHKE) are used to constrain the crustal P-wave velocity (Vp) structure along two profiles spanning the length and width of Wanganui Basin, located landwards of the southern Hikurangi subduction margin, New Zealand. These models provide high-resolution constraints on the structure and crustal thickness of the overlying Australian and subducted Pacific plates and plate interface geometry. Wide-angle reflections are modelled to show that the subducted oceanic Pacific plate crust is anomalously thick (∼10 km) below southern North Island and is overlain by a ∼1.5-4.0 km thick, low Vp (4.8-5.4 km s-1) layer, interpreted as a channel of sedimentary material, that persists landwards at least as far as Kapiti Island. Distinct near vertical reflections from onshore shots identify a ∼4 km high mound of low-velocity sedimentary material that appears to underplate the overlying Australian plate crust and is likely to contribute to local rock uplift along the Axial ranges. The overriding Australian plate Moho beneath Wanganui Basin is imaged as deepening southwards and reaches a depth of at least 36.4 km. The Moho shape approximately mirrors the thickening of the basin sediments, suggestive of crustal downwarping. However, the observed crustal thickness variation is insufficient to explain the large negative Bouguer gravity anomaly (-160 mGal) centred over the basin. Partial serpentinization within the upper mantle with a concomitant density decrease is one possible way of reconciling this anomaly.

Large-scale trench-perpendicular mantle flow beneath northern Chile

NASA Astrophysics Data System (ADS)

Reiss, M. C.; Rumpker, G.; Woelbern, I.

2017-12-01

We investigate the anisotropic properties of the forearc region of the central Andean margin by analyzing shear-wave splitting from teleseismic and local earthquakes from the Nazca slab. The data stems from the Integrated Plate boundary Observatory Chile (IPOC) located in northern Chile, covering an approximately 120 km wide coastal strip between 17°-25° S with an average station spacing of 60 km. With partly over ten years of data, this data set is uniquely suited to address the long-standing debate about the mantle flow field at the South American margin and in particular whether the flow field beneath the slab is parallel or perpendicular to the trench. Our measurements yield two distinct anisotropic layers. The teleseismic measurements show a change of fast polarizations directions from North to South along the trench ranging from parallel to subparallel to the absolute plate motion and, given the geometry of absolute plate motion and strike of the trench, mostly perpendicular to the trench. Shear-wave splitting from local earthquakes shows fast polarizations roughly aligned trench-parallel but exhibit short-scale variations which are indicative of a relatively shallow source. Comparisons between fast polarization directions and the strike of the local fault systems yield a good agreement. We use forward modelling to test the influence of the upper layer on the teleseismic measurements. We show that the observed variations of teleseismic measurements along the trench are caused by the anisotropy in the upper layer. Accordingly, the mantle layer is best characterized by an anisotropic fast axes parallel to the absolute plate motion which is roughly trench-perpendicular. This anisotropy is likely caused by a combination of crystallographic preferred orientation of the mantle mineral olivine as fossilized anisotropy in the slab and entrained flow beneath the slab. We interpret the upper anisotropic layer to be confined to the crust of the overriding continental plate. This is explained by the shape-preferred orientation of micro-cracks in relation to local fault zones which are oriented parallel the overall strike of the Andean range. Our results do not provide any evidence for a significant contribution of trench-parallel mantle flow beneath the subducting slab to the measurements.

Plate interface rheological switches during subduction infancy: Control on slab penetration and metamorphic sole formation

NASA Astrophysics Data System (ADS)

Agard, P.; Yamato, P.; Soret, M.; Prigent, C.; Guillot, S.; Plunder, A.; Dubacq, B.; Chauvet, A.; Monié, P.

2016-10-01

Subduction infancy corresponds to the first few million years following subduction initiation, when slabs start their descent into the mantle. It coincides with the transient (yet systematic) transfer of material from the top of the slab to the upper plate, as witnessed by metamorphic soles welded beneath obducted ophiolites. Combining structure-lithology-pressure-temperature-time data from metamorphic soles with flow laws derived from experimental rock mechanics, this study highlights two main successive rheological switches across the subduction interface (mantle wedge vs. basalts, then mantle wedge vs. sediments; at ∼800 °C and ∼600 °C, respectively), during which interplate mechanical coupling is maximized by the existence of transiently similar rheologies across the plate contact. We propose that these rheological switches hinder slab penetration and are responsible for slicing the top of the slab and welding crustal pieces (high- then low-temperature metamorphic soles) to the base of the mantle wedge during subduction infancy. This mechanism has implications for the rheological properties of the crust and mantle (and for transient episodes of accretion/exhumation of HP-LT rocks in mature subduction systems) and highlights the role of fluids in enabling subduction to overcome the early resistance to slab penetration.

Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere

PubMed Central

Qi, Chao; Warren, Jessica M.

2016-01-01

Tectonic plates are a key feature of Earth’s structure, and their behavior and dynamics are fundamental drivers in a wide range of large-scale processes. The operation of plate tectonics, in general, depends intimately on the manner in which lithospheric plates couple to the convecting interior. Current debate centers on whether the transition from rigid lithosphere to flowing asthenosphere relates to increases in temperature or to changes in composition such as the presence of a small amount of melt or an increase in water content below a specified depth. Thus, the manner in which the rigid lithosphere couples to the flowing asthenosphere is currently unclear. Here we present results from laboratory-based torsion experiments on olivine aggregates with and without melt, yielding an improved database describing the crystallographic alignment of olivine grains. We combine this database with a flow model for oceanic upper mantle to predict the structure of the seismic anisotropy beneath ocean basins. Agreement between our model and seismological observations supports the view that the base of the lithosphere is thermally controlled. This model additionally supports the idea that discontinuities in velocity and anisotropy, often assumed to be the base of the lithosphere, are, instead, intralithospheric features reflecting a compositional boundary established at midocean ridges, not a rheological boundary. PMID:27606485

Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere.

PubMed

Hansen, Lars N; Qi, Chao; Warren, Jessica M

2016-09-20

Tectonic plates are a key feature of Earth's structure, and their behavior and dynamics are fundamental drivers in a wide range of large-scale processes. The operation of plate tectonics, in general, depends intimately on the manner in which lithospheric plates couple to the convecting interior. Current debate centers on whether the transition from rigid lithosphere to flowing asthenosphere relates to increases in temperature or to changes in composition such as the presence of a small amount of melt or an increase in water content below a specified depth. Thus, the manner in which the rigid lithosphere couples to the flowing asthenosphere is currently unclear. Here we present results from laboratory-based torsion experiments on olivine aggregates with and without melt, yielding an improved database describing the crystallographic alignment of olivine grains. We combine this database with a flow model for oceanic upper mantle to predict the structure of the seismic anisotropy beneath ocean basins. Agreement between our model and seismological observations supports the view that the base of the lithosphere is thermally controlled. This model additionally supports the idea that discontinuities in velocity and anisotropy, often assumed to be the base of the lithosphere, are, instead, intralithospheric features reflecting a compositional boundary established at midocean ridges, not a rheological boundary.

Thermal Aging of Oceanic Asthenosphere

NASA Astrophysics Data System (ADS)

Paulson, E.; Jordan, T. H.

2013-12-01

To investigate the depth extent of mantle thermal aging beneath ocean basins, we project 3D Voigt-averaged S-velocity variations from an ensemble of global tomographic models onto a 1x1 degree age-based regionalization and average over bins delineated by equal increments in the square-root of crustal age. From comparisons among the bin-averaged S-wave profiles, we estimate age-dependent convergence depths (minimum depths where the age variations become statistically insignificant) as well as S travel times from these depths to a shallow reference surface. Using recently published techniques (Jordan & Paulson, JGR, doi:10.1002/jgrb.50263, 2013), we account for the aleatory variability in the bin-averaged S-wave profiles using the angular correlation functions of the individual tomographic models, we correct the convergence depths for vertical-smearing bias using their radial correlation functions, and we account for epistemic uncertainties through Bayesian averaging over the tomographic model ensemble. From this probabilistic analysis, we can assert with 90% confidence that the age-correlated variations in Voigt-averaged S velocities persist to depths greater than 170 km; i.e., more than 100 km below the mean depth of the G discontinuity (~70 km). Moreover, the S travel time above the convergence depth decays almost linearly with the square-root of crustal age out to 200 Ma, consistent with a half-space cooling model. Given the strong evidence that the G discontinuity approximates the lithosphere-asthenosphere boundary (LAB) beneath ocean basins, we conclude that the upper (and probably weakest) part of the oceanic asthenosphere, like the oceanic lithosphere, participates in the cooling that forms the kinematic plates, or tectosphere. In other words, the thermal boundary layer of a mature oceanic plate appears to be more than twice the thickness of its mechanical boundary layer. We do not discount the possibility that small-scale convection creates heterogeneities in the oceanic upper mantle; however, the large-scale flow evidently advects these small-scale heterogeneities along with the plates, allowing the upper part of the asthenosphere to continue cooling with lithospheric age. The dominance of this large-scale horizontal flow may be related to the high stresses associated with its channelization in a thin (~100 km) asthenosphere, as well as the possible focusing of the subtectospheric strain in a low-viscosity channel immediately above the 410-km discontinuity. These speculations aside, the observed thermal aging of oceanic asthenosphere is inconsistent with a tenet of plate tectonics, the LAB hypothesis, which states that lithospheric plates are decoupled from deeper mantle flow by a shear zone in the upper part of the asthenosphere.

Seafloor age dependence of Rayleigh wave phase velocities in the Indian Ocean

NASA Astrophysics Data System (ADS)

Godfrey, Karen E.; Dalton, Colleen A.; Ritsema, Jeroen

2017-05-01

Variations in the phase velocity of fundamental-mode Rayleigh waves across the Indian Ocean are determined using two inversion approaches. First, variations in phase velocity as a function of seafloor age are estimated using a pure-path age-dependent inversion method. Second, a two-dimensional parameterization is used to solve for phase velocity within 1.25° × 1.25° grid cells. Rayleigh wave travel time delays have been measured between periods of 38 and 200 s. The number of measurements in the study area ranges between 4139 paths at a period of 200 s and 22,272 paths at a period of 40 s. At periods < 100 s, the phase velocity variations are strongly controlled by seafloor age and shown to be consistent with temperature variations predicted by the half-space-cooling model for a mantle potential temperature of 1400°C. The inferred thermal structure beneath the Indian Ocean is most similar to the structure of the Pacific upper mantle, where phase velocities can also be explained by a half-space-cooling model. The thermal structure is not consistent with that of the Atlantic upper mantle, which is best fit by a plate-cooling model and requires a thin plate. Removing age-dependent phase velocity from the 2-D maps of the Indian Ocean highlights anomalously high velocities at the Rodriguez Triple Junction and the Australian-Antarctic Discordance and anomalously low velocities immediately to the west of the Central Indian Ridge.

Plate boundary and major fault system in the overriding plate within the Shumagin gap at the Alaska-Aleutian subduction zone

NASA Astrophysics Data System (ADS)

Becel, A.; Shillington, D. J.; Nedimovic, M. R.; Keranen, K. M.; Li, J.; Webb, S. C.; Kuehn, H.

2013-12-01

Structure in the overriding plate is one of the parameters that may increase the tsunamigenic potential of a subduction zone but also influence the seismogenic behavior and segmentation of great earthquake rupture. The Alaska-Aleutian margin is characterized by along-strike changes in plate interface coupling over relatively small distances. Here, we present trench normal multichannel seismic (MCS) profiles acquired across the Shumagin gap that has not broken in many decades and appears to be weakly coupled. The high fold, deep penetration (636 channel, 8-km long streamer, 6600 cu.in airgun source) MCS data were acquired as part of the ALEUT project. This dataset gives us critical new constraints on the interplate boundary that can be traced over ~100 km distance beneath the forearc with high variation in its reflection response with depth. These profiles also reveal the detailed upper plate fault structure and forearc morphology. Clear reflections in the overriding plate appear to delineate one or more large faults that cross the shelf and the upper slope. These faults are observed 75 km back from the trench and seem to branch at depth and connect to the plate interface within this gap at ~11 s twtt. We compare the reflective structure of these faults to that of the plate boundary and examine where it intersects the megathrust with respect of the expected downdip limit of coupling. We also compare this major structure with the seismicity recorded in this sector. The imaged fault system is associated with a large deep basin (~6s twt) that is an inherited structure formed during the pre-Aleutian period. Basins faults appear to have accommodated primarily normal motion, although folding of sediments near the fault and complicated fault geometries in the shallow section may indicate that this fault has accommodated other types of motion during its history that may reflect the stress-state at the megathrust over time. The deformation within the youngest sediment also suggests also that this fault system might be still active. The coincident wide-angle seismic data coincident with one MCS profile allow the addition of more information about the deep P-wave velocity structure whereas the streamer tomography (Michaelson-Rotermund et al., this session) around the fault system add more detailed view into the complex structure in the shallow portions (upper 2km) of these structures showing a low velocity zone along one large fault suggesting that this fault is still active. These large-scale structures imaged in the overriding plate within the Shumagin gap are probably sufficiently profound to play a major role in the behavior of the megathrust in this area, segmentation of great earthquake rupture area, tsunami generation and may influence the frictional properties of the seismogenic zone at depth.

Control of cortical neuronal migration by glutamate and GABA

PubMed Central

Luhmann, Heiko J.; Fukuda, A.; Kilb, W.

2015-01-01

Neuronal migration in the cortex is controlled by the paracrine action of the classical neurotransmitters glutamate and GABA. Glutamate controls radial migration of pyramidal neurons by acting primarily on NMDA receptors and regulates tangential migration of inhibitory interneurons by activating non-NMDA and NMDA receptors. GABA, acting on ionotropic GABAA-rho and GABAA receptors, has a dichotomic action on radially migrating neurons by acting as a GO signal in lower layers and as a STOP signal in upper cortical plate (CP), respectively. Metabotropic GABAB receptors promote radial migration into the CP and tangential migration of interneurons. Besides GABA, the endogenous GABAergic agonist taurine is a relevant agonist controlling radial migration. To a smaller extent glycine receptor activation can also influence radial and tangential migration. Activation of glutamate and GABA receptors causes increases in intracellular Ca2+ transients, which promote neuronal migration by acting on the cytoskeleton. Pharmacological or genetic manipulation of glutamate or GABA receptors during early corticogenesis induce heterotopic cell clusters in upper layers and loss of cortical lamination, i.e., neuronal migration disorders which can be associated with neurological or neuropsychiatric diseases. The pivotal role of NMDA and ionotropic GABA receptors in cortical neuronal migration is of major clinical relevance, since a number of drugs acting on these receptors (e.g., anti-epileptics, anesthetics, alcohol) may disturb the normal migration pattern when present during early corticogenesis. PMID:25688185

The 2011 Tohoku-oki Earthquake related to a large velocity gradient within the Pacific plate

NASA Astrophysics Data System (ADS)

Matsubara, Makoto; Obara, Kazushige

2015-04-01

We conduct seismic tomography using arrival time data picked by the high sensitivity seismograph network (Hi-net) operated by National Research Institute for Earth Science and Disaster Prevention (NIED). We used earthquakes off the coast outside the seismic network around the source region of the 2011 Tohoku-oki Earthquake with the centroid depth estimated from moment tensor inversion by NIED F-net (broadband seismograph network) as well as earthquakes within the seismic network determined by Hi-net. The target region, 20-48N and 120-148E, covers the Japanese Islands from Hokkaido to Okinawa. A total of manually picked 4,622,346 P-wave and 3,062,846 S-wave arrival times for 100,733 earthquakes recorded at 1,212 stations from October 2000 to August 2009 is available for use in the tomographic method. In the final iteration, we estimate the P-wave slowness at 458,234 nodes and the S-wave slowness at 347,037 nodes. The inversion reduces the root mean square of the P-wave traveltime residual from 0.455 s to 0.187 s and that of the S-wave data from 0.692 s to 0.228 s after eight iterations (Matsubara and Obara, 2011). Centroid depths are determined using a Green's function approach (Okada et al., 2004) such as in NIED F-net. For the events distant from the seismic network, the centroid depth is more reliable than that determined by NIED Hi-net, since there are no stations above the hypocenter. We determine the upper boundary of the Pacific plate based on the velocity structure and earthquake hypocentral distribution. The upper boundary of the low-velocity (low-V) oceanic crust corresponds to the plate boundary where thrust earthquakes are expected to occur. Where we do not observe low-V oceanic crust, we determine the upper boundary of the upper layer of the double seismic zone within high-V Pacific plate. We assume the depth at the Japan Trench as 7 km. We can investigate the velocity structure within the Pacific plate such as 10 km beneath the plate boundary since the rays from the hypocenter around the coseismic region of the Tohoku-oki earthquake take off downward and pass through the Pacific plate. The landward low-V zone with a large anomaly corresponds to the western edge of the coseismic slip zone of the 2011 Tohoku-oki earthquake. The initial break point (hypocenter) is associated with the edge of a slightly low-V and low-Vp/Vs zone corresponding to the boundary of the low- and high-V zone. The trenchward low-V and low-Vp/Vs zone extending southwestward from the hypocenter may indicate the existence of a subducted seamount. The high-V zone and low-Vp/Vs zone might have accumulated the strain and resulted in the huge coseismic slip zone of the 2011 Tohoku earthquake. The low-V and low-Vp/Vs zone is a slight fluctuation within the high-V zone and might have acted as the initial break point of the 2011 Tohoku earthquake. Reference Matsubara, M. and K. Obara (2011) The 2011 Off the Pacific Coast of Tohoku earthquake related to a strong velocity gradient with the Pacific plate, Earth Planets Space, 63, 663-667. Okada, Y., K. Kasahara, S. Hori, K. Obara, S. Sekiguchi, H. Fujiwara, and A. Yamamoto (2004) Recent progress of seismic observation networks in Japan-Hi-net, F-net, K-NET and KiK-net, Research News Earth Planets Space, 56, xv-xxviii.

Flutter suppression and stability analysis for a variable-span wing via morphing technology

NASA Astrophysics Data System (ADS)

Li, Wencheng; Jin, Dongping

2018-01-01

A morphing wing can enhance aerodynamic characteristics and control authority as an alternative to using ailerons. To use morphing technology for flutter suppression, the dynamical behavior and stability of a variable-span wing subjected to the supersonic aerodynamic loads are investigated numerically in this paper. An axially moving cantilever plate is employed to model the variable-span wing, in which the governing equations of motion are established via the Kane method and piston theory. A morphing strategy based on axially moving rates is proposed to suppress the flutter that occurs beyond the critical span length, and the flutter stability is verified by Floquet theory. Furthermore, the transient stability during the morphing motion is analyzed and the upper bound of the morphing rate is obtained. The simulation results indicate that the proposed morphing law, which is varying periodically with a proper amplitude, could accomplish the flutter suppression. Further, the upper bound of the morphing speed decreases rapidly once the span length is close to its critical span length.

Early Neogene unroofing of the Sierra Nevada de Santa Marta along the Bucaramanga -Santa Marta Fault

NASA Astrophysics Data System (ADS)

Piraquive Bermúdez, Alejandro; Pinzón, Edna; Bernet, Matthias; Kammer, Andreas; Von Quadt, Albrecht; Sarmiento, Gustavo

2016-04-01

Plate interaction between Caribbean and Nazca plates with Southamerica gave rise to an intricate pattern of tectonic blocks in the Northandean realm. Among these microblocks the Sierra Nevada de Santa Marta (SNSM) represents a fault-bounded triangular massif composed of a representative crustal section of the Northandean margin, in which a Precambrian to Late Paleozoic metamorphic belt is overlain by a Triassic to Jurassic magmatic arc and collateral volcanic suites. Its western border fault belongs to the composite Bucaramanga - Santa Marta fault with a combined left lateral-normal displacement. SE of Santa Marta it exposes remnants of an Oligocene marginal basin, which attests to a first Cenoizoic activation of this crustal-scale lineament. The basin fill consists of a sequence of coarse-grained cobble-pebble conglomerates > 1000 m thick that unconformably overlay the Triassic-Jurassic magmatic arc. Its lower sequence is composed of interbedded siltstones; topwards the sequence becomes dominated by coarser fractions. These sedimentary sequences yields valuable information about exhumation and coeval sedimentation processes that affected the massif's western border since the Upper Eocene. In order to analyse uplifting processes associated with tectonics during early Neogene we performed detrital zircon U-Pb geochronology, detrital thermochronology of zircon and apatites coupled with the description of a stratigraphic section and its facies composition. We compared samples from the Aracataca basin with analog sequences found at an equivalent basin at the Oca Fault at the northern margin of the SNSM. Our results show that sediments of both basins were sourced from Precambrian gneisses, along with Mesozoic acid to intermediate plutons; sedimentation started in the Upper Eocene-Oligocene according to palynomorphs, subsequently in the Upper Oligocene a completion of Jurassic to Cretaceous sources was followed by an increase of Precambrian input that became the dominant source for sediments, this shift in provenance is related to an increase in exhumation and erosion rates. The instauration of such a highly erosive regime since the Upper Oligocene attests how the Santa Marta massif was subject to uplifting and erosion, our data shows how in the Upper Oligocene an exhaustion of Cretaceous to Permian sources was followed by an increase in Neo-Proterozoic to Meso-Proterozoic input that is related to the unroofing of the basement rocks, this accelerated exhumation is directly related to the reactivation of the Orihueca Fault as a NW verging thrust at the interior of the massif coeval with Bucaramanga-Santa Marta Fault trans-tensional tectonics in response to the fragmentation of the Farallon plate into the Nazca an Cocos Plates.

The effects of thick sediment upon continental breakup: seismic imaging and thermal modeling of the Salton Trough, southern California

NASA Astrophysics Data System (ADS)

Han, L.; Hole, J. A.; Lowell, R. P.; Stock, J. M.; Fuis, G. S.; Driscoll, N. W.; Kell, A. M.; Kent, G. M.; Harding, A. J.; Gonzalez-Fernandez, A.; Lázaro-Mancilla, O.

2015-12-01

Continental rifting ultimately creates a deep accommodation space for sediment. When a major river flows into a late-stage rift, thick deltaic sediment can change the thermal regime and alter the mechanisms of extension and continental breakup. The Salton Trough, the northernmost rift segment of the Gulf of California plate boundary, has experienced the same extension as the rest of the Gulf, but is filled to sea level by sediment from the Colorado River. Unlike the southern Gulf, seafloor spreading has not initiated. Instead, seismicity, high heat flow, and minor volcanoes attest to ongoing rifting of thin, transitional crust. Recently acquired controlled-source seismic refraction and wide-angle reflection data in the Salton Trough provide constraints upon crustal architecture and active rift processes. The crust in the central Salton Trough is only 17-18 km thick, with a strongly layered but relatively one-dimensional structure for ~100 km in the direction of plate motion. The upper crust includes 2-4 km of Colorado River sediment. Crystalline rock below the sediment is interpreted to be similar sediment metamorphosed by the high heat flow and geothermal activity. Meta-sediment extends to at least 9 km depth. A 4-5 km thick layer in the middle crust is either additional meta-sediment or stretched pre-existing continental crust. The lowermost 4-5 km of the crust is rift-related mafic magmatic intrusion or underplating from partial melting in the hot upper mantle. North American lithosphere in the Salton Trough has been almost or completely rifted apart. The gap has been filled by ~100 km of new transitional crust created by magmatism from below and sedimentation from above. These processes create strong lithologic, thermal, and rheologic layering. While heat flow in the rift is very high, rapid sedimentation cools the upper crust as compared to a linear geotherm. Brittle extension occurs within new meta-sedimentary rock. The lower crust, in comparison, is maintained hot and weak by the overlying sedimentary thermal blanket. The lower crust stretches by ductile flow and magmatism is not localized. In this passive rift driven by distant plate motions, rapid sedimentation and its thermal effects delay final breakup of the crust and the onset of seafloor spreading.

Phanerozoic growth of Asia: Geodynamic processes and evolution

NASA Astrophysics Data System (ADS)

Pubellier, Manuel; Meresse, Florian

2013-08-01

Accretion processes often obscured in mountain belts can be documented with great detail in SE Asia where these have taken place during the Tertiary. The resulting configuration showing accreted continental strips and tectonised wedges is illustrated by the Tethysides jammed between the northern Laurasian cratons (Baltica and Siberia) and Gondwanian cratons (Africa, Arabia, India and Australia). Eurasia increased progressively in size due to the amalgamation of crustal and sedimentary belts. At places where the processes are documented in the recent times, they can be included within a "collision factory" which displays the opening of basins by rifting and sea floor spreading within the upper plate, until they undergo a process of shortening, both stages being subduction-controlled. In SE Asia the early stages are illustrated in the eastern Sunda arc where the subduction of the Sunda Trench is blocked in Sumba and Timor region, and flipped into the Flores Trough in less than 2 My. The incipient shortening is at present taking place in the Pliocene Damar basins. Another stage, where half of the upper plate basin has disappeared, is documented in the Celebes Sea. The examples of deformation being transferred further inland exist in the northern Celebes Sea and the Makassar Basin. The next important stage is the complete consumption of the marginal basin where both margins collide and the accretionary wedge is thrust over the margin, as illustrated in NW Borneo and Palawan. Each of these stages is responsible for a single short-lived tectonic event, the succession of several events composes an orogen which may last for over 10 My. These events predate the arrival of the conjugate margin of the large ocean, which marks the beginning of continental subduction as observed in the Himalaya-Tibet region. These examples show that the closure is generally diachronous through time as illustrated in the Philippines. We observe that the ophiolite obducted in such context is generally of back-arc origin (upper plate) rather than the relict of the vanishing large ocean which is rarely preserved. In the Philippines, once the crust is accreted the subduction zone progressively moved southward until its present position. We propose that the lithospheric mantle of the accreted block is delaminated and rolls back in a continuous manner, whereas the crust is deformed and accreted.

High-Throughput Serum 25-Hydroxy Vitamin D Testing with Automated Sample Preparation.

PubMed

Stone, Judy

2016-01-01

Serum from bar-coded tubes, and then internal standard, are pipetted to 96-well plates with an 8-channel automated liquid handler (ALH). The first precipitation reagent (methanol:ZnSO4) is added and mixed with the 8-channel ALH. A second protein precipitating agent, 1 % formic acid in acetonitrile, is added and mixed with a 96-channel ALH. After a 4-min delay for larger precipitates to settle to the bottom of the plate, the upper 36 % of the precipitate/supernatant mix is transferred with the 96-channel ALH to a Sigma Hybrid SPE(®) plate and vacuumed through for removal of phospholipids and precipitated proteins. The filtrate is collected in a second 96-well plate (collection plate) which is foil-sealed, placed in the autosampler (ALS), and injected into a multiplexed LC-MS/MS system running AB Sciex Cliquid(®) and MPX(®) software. Two Shimadzu LC stacks, with multiplex timing controlled by MPX(®) software, inject alternately to one AB Sciex API-5000 MS/MS using positive atmospheric pressure chemical ionization (APCI) and a 1.87 min water/acetonitrile LC gradient with a 2.1 × 20 mm, 2.7 μm, C18 fused core particle column (Sigma Ascentis Express). LC-MS/MS through put is ~44 samples/h/LC-MS/MS system with dual-LC channel multiplexing. Plate maps are transferred electronically from the ALH and reformatted into LC-MS/MS sample table format using the Data Innovations LLC (DI) Instrument Manager middleware application. Before collection plates are loaded into the ALS, the plate bar code is manually scanned to download the sample table from the DI middleware to the LC-MS/MS. After acquisition-LC-MS/MS data is analyzed with AB Sciex Multiquant(®) software using customized queries, and then results are transferred electronically via a DI interface to the LIS. 2500 samples/day can be extracted by two analysts using four ALHs in 4-6 h. LC-MS/MS analysis of those samples on three dual-channel LC multiplexed LC-MS/MS systems requires 19-21 h and data analysis can be done by two analysts in 4-6 h.

Revisiting the physical characterisitics of the subduction interplate seismogenic zones

NASA Astrophysics Data System (ADS)

Heuret, Arnauld; Lallemand, Serge; Funiciello, Francesca; Piromallo, Claudia

2010-05-01

Based on the Centennial earthquake catalog, the revised 1964-2007 EHB hypocenters catalog and the 1976-2007 CMT Harvard catalog, we have extracted the hypocenters, nodal planes and seismic moments of worldwide subduction earthquakes for the 1900-2007 period. For the 1976-2007 period, we combine the focal solutions provided by Harvard and the revised hypocenters from Engdahl et al. (1998). Older events are extracted from the Centennial catalogue (Engdahl and Villasenor, 2002) and they are used to estimate the cumulated seismic moment only. The selection criteria for the subduction earthquakes are similar to those used by Mc Caffrey (1994), i.e., we test if the focal mechanisms are consistent with 1/ shallow thrust events (depth > 70 km, positive slips, and at least one nodal plane gets dip < 45°), and, 2/ the plate interface local geometry and orientation (one nodal plane is oriented toward the volcanic arc, the azimuth of this nodal plane ranges between ± 45° with respect to the trench one, its dip ranges between ± 20° with respect to the slab one and the epicentre is located seaward of the volcanic arc). Our study concerns segments of subduction zones that fit with estimated paleoruptures associated with major events (M > 8). We assume that the seismogenic zone coincides with the distribution of 5.5 < M < 7 subduction earthquakes. We provide a map of the interplate seismogenic zones for 80% of the trench systems including dip, length, downdip and updip limits, we revisit the statistical study done by Pacheco et al. (1993) and test some empirical laws obtained for example by Ruff and Kanamori (1980) in light of a more complete, detailed, accurate and uniform description of the subduction interplate seismogenic zone. Since subduction earthquakes result from stress accumulation along the interplate and stress depends on plates kinematics, subduction zone geometry, thermal state and seismic coupling, we aim to isolate some correlations between parameters. The statistical analysis reveals that: 1- vs, the subduction velocity is the first order controlling parameter of seismogenic zone variability, both in term of geometry and seismic behaviour; 2- steep dip, large vertical extent and narrow horizontal extent of the seismogenic zone are associated to fast subductions, and cold slabs, the opposite holding for slow subductions and warm slabs; the seismogenic zone usually ends in the fore-arc mantle rather than at the upper plate Moho depth; 3- seismic rate () variability is coherent with the geometry of the seismogenic zone:  increases with the dip and with the vertical extent of the seismogenic zone, and it fits with vs and with the subducting plate thermal state; 4- mega-events occurrence determines the level of seismic energy released along the subduction interface, whatever  is; 5- to some extent, the potential size of earthquakes fits with vs and with the seismogenic zone geometry, but second order controlling parameters are more difficult to detect; 6- the plate coupling, measured through Upper Plate Strain, is one possible second order parameter: mega-events are preferentially associated to neutral subductions, i.e. moderate compressive stresses along the plate interface; high plate coupling (compressive UPS) is thought to inhibit mega-events genesis by enhancing the locking of the plate interface and preventing the rupture to extend laterally. This research was supported as part of the Eurohorcs/ESF — European Young Investigators Awards Scheme (resp. F.F.), by funds from the National Research Council of Italy and other National Funding Agencies participating in the 3rd Memorandum of Understanding, as well as from the EC Sixth Framework Programme.

Reconstructing plate motion paths where plate tectonics doesn't strictly apply

NASA Astrophysics Data System (ADS)

Handy, M. R.; Ustaszewski, K.

2012-04-01

The classical approach to reconstructing plate motion invokes the assumption that plates are rigid and therefore that their motions can be described as Eulerian rotations on a spherical Earth. This essentially two-dimensional, map view of plate motion is generally valid for large-scale systems, but is not practicable for small-scale tectonic systems in which plates, or significant parts thereof, deform on time scales approaching the duration of their motion. Such "unplate-like" (non-rigid) behaviour is common in systems with a weak lithosphere, for example, in Mediterranean-type settings where (micro-)plates undergo distributed deformation several tens to hundreds of km away from their boundaries. The motion vector of such anomalous plates can be quantified by combining and comparing information from two independent sources: (1) Balanced cross sections that are arrayed across deformed zones (orogens, basins) and provide estimates of crustal shortening and/or extension. Plate motion is then derived by retrodeforming the balanced sections in a stepwise fashion from external to internal parts of mountain belts, then applying these estimates as successive retrotranslations of points on stable parts of the upper plate with respect to a chosen reference frame on the lower plate. This approach is contingent on using structural markers with tight age constraints, for example, depth-sensitive metamorphic mineral parageneses and syn-orogenic sediments with known paleogeographic provenance; (2) Geophysical images of 3D subcrustal structure, especially of the MOHO and the lithospheric mantle in the vicinity of the deformed zones. In the latter case, travel-time seismic tomography of velocity anomalies can be used to identify subducted lithospheric slabs that extend downwards from the zones of crustal shortening to the mantle transitional zone and beyond. Synthesizing information from these two sources yields plate motion paths whose validity can be tested by the degree of consistency between crustal shortening estimates and the amount of subducted lithosphere imaged at depth. This approach has several limitations: (1) shortening values in mountain belts are usually minimum estimates due to the erosion of deformational fronts and out-of-sequence thrusting that obscure or even eliminate zones of shortening. Also, subduction may occur without accretion of material to the upper plate; (2) sedimentary ages are often loosely bracketed and only high-retentivity isotopic systems yield ages near the age of mineral formation in metamorphic rocks; (3) images of seismic velocity anomalies are highly model-dependent and the anomalies themselves may have been partly lost to thermal erosion, especially in areas that have experienced heating, for example, beneath extensional basins. Thus, only a few orogens studied so far (e.g., the circum-Mediterreanean belts) have the density of geological and geophysical data needed to constrain the translation of a sufficient number of reference points to obtain a reliable plate-motion vector. Nevertheless, this approach complements established methods for determining plate motion (plate-circuits using paleomagnetic information, ocean-floor magnetic lineaments) and provides a viable alternative where such paleomagnetic information is sparse or lacking.

Shallow Moho with aseismic upper crust and deep Moho with seismic lower crust beneath the Japanese Islands obtained by seismic tomography using data from dense seismic network

NASA Astrophysics Data System (ADS)

Matsubara, Makoto; Obara, Kazushige

2015-04-01

P-wave seismic velocity is well known to be up to 7.0 km/s and over 7.5 km/s in the lower crust and in the mantle, respectively. A large velocity gradient is the definition of the Moho discontinuity between the crust and mantle. In this paper, we investigates the configuration of Moho discontinuity defined as an isovelocity plane with large velocity gradient derived from our fine-scale three-dimensional seismic velocity structure beneath Japanese Islands using data obtained by dense seismic network with the tomographic method (Matsubara and Obara, 2011). Japanese Islands are mainly on the Eurasian and North American plates. The Philippine Sea and Pacific plates are subducting beneath these continental plates. We focus on the Moho discontinuity at the continental side. We calculate the P-wave velocity gradients between the vertical grid nodes since the grid inversion as our tomographic method does not produce velocity discontinuity. The largest velocity gradient is 0.078 (km/s)/km at velocities of 7.2 and 7.3 km/s. We define the iso-velocity plane of 7.2 km/s as the Moho discontinuity. We discuss the Moho discontinuity above the upper boundary of the subducting oceanic plates with consideration of configuration of plate boundaries of prior studies (Shiomi et al., 2008; Kita et al., 2010; Hirata et al, 2012) since the Moho depth derived from the iso-velocity plane denotes the oceanic Moho at the contact zones of the overriding continental plates and the subducting oceanic plates. The Moho discontinuity shallower than 30 km depth is distributed within the tension region like northern Kyushu and coastal line of the Pacific Ocean in the northeastern Japan and the tension region at the Cretaceous as the northeastern Kanto district. These regions have low seismicity within the upper crust. Positive Bouguer anomaly beneath the northeastern Kanto district indicates the ductile material with large density in lower crust at the shallower portion and the aseismic upper crust. The Moho discontinuity deepens over 35 km in the collision zone like as Kanto Mountains, the volcanic underplating zone as the Tohoku backbone range, and non-tension region like as Chugoku Mountains. These regions associated with deep Moho are characterized by the crustal seismicity within the depth range from 20 to 30 km. The iso-depth contour of 35 km beneath the southwestern Japan is consistent with that derived from the receiver function method (Shiomi et al. 2006). There are nonvolcanic tremors and short-time slow slip events (SSE) beneath the southwestern Japan (eg. Obara, 2002). Matsubara et al. (2009) consider that the tremors and SSEs occur along the contact zone of Moho discontinuity beneath the Eurasian plate and the subducting Philippine Sea plate beneath southwestern Japan. Our Moho model is consistent with this since they exist along the southern edge of the Moho discontinuity of the continental Eurasian plate. Reference: Hirata, N., Sakai, S., Nakagawa, S., Ishikawa, M., Sato, H., Kasahara, K., Kimura, H. and Honda, R. (2012) A new tomographic image on the Philippine Sea Slab beneath Tokyo - Implication to seismic hazard in the Tokyo metropolitan region, EOS, Transactions, AGU, T11C-06. Kita, S., T. Okada, A. Hasegawa, J. Nakajima, and T. Matsuzawa (2010) Anomalous deepening of a seismic belt in the upper-plane of the double seismic zone in the Pacific slab beneath the Hokkaido corner: Possible evidence for thermal shielding caused by subducted forearc crust materials, Earth Planet. Science Lett., 290, 415-426. Matsubara, M. and K. Obara (2011) The 2011 Off the Pacific Coast of Tohoku earthquake related to a strong velocity gradient with the Pacific plate, Earth Planets Space, 63, 663-667. Matsubara, M., K. Obara, and K. Kasahara (2009) High-Vp/Vs zone accompanying non-volcanic tremors and slow-slip events beneath southwestern Japan, Tectonophysics, 472, 6-17, doi:10.1016/j.tecto.2008.06.013. Obara, K. (2002) Nonvolcanic deep tremor associated with subduction in southwest Japan. Science 296, 1679-1681. Shiomi, K., K. Obara, and H. Sato (2006) Moho depth variation beneath southwestern Japan revealed from the velocity structure based on receiver function inversion , Tectonophysics, 420, 205-221, doi:10.1016/j.tecto.2006.01.017. Shiomi, K., M. Matsubara, Y. Ito, and K. Obara (2008) Simple relationship between seismic activity along Philippine Sea slab and geometry of oceanic Moho beneath southwest Japan, Geophys. J. Int., 173, 1018-1029.

Initiation of the Andean orogeny by lower mantle subduction

NASA Astrophysics Data System (ADS)

Faccenna, Claudio; Oncken, Onno; Holt, Adam F.; Becker, Thorsten W.

2017-04-01

The Cordillera of the Andes is a double-vergent orogenic belt built up by thickening of South American plate crust. Several models provide plausible explanations for the evolution of the Andes, but the reason why shortening started at ∼50 Ma is still unclear. We explore the evolution of the subduction zone through time by restoring the position of the Nazca trench in an absolute reference frame, comparing its position with seismic tomography models and balancing the evolution of the subducting slab. Reconstructions show that the slab enters into the lower mantle at ∼ 50 ± 10 Ma, and then progressed, moving horizontally at shallow lower mantle depth while thickening and folding in the transition zone. We test this evolutionary scenario by numerical models, which illustrate that compression in the upper plate intensifies once the slab is anchored in the lower mantle. We conclude that onset of significant shortening and crustal thickening in the Andes and its sustained action over tens of million years is related to the penetration of the slab into the lower mantle, producing a slowdown of lateral slab migration, and dragging the upper plate against the subduction zone by large-scale return flow.

Initiation of the Andean orogeny by lower mantle subduction

NASA Astrophysics Data System (ADS)

Faccenna, Claudio; Oncken, Onno; Holt, Adam; Becker, Thorsten

2017-04-01

The Cordillera of the Andes is a double-vergent orogenic belt built up by thickening of South American plate crust. Several models provide plausible explanations for the evolution of the Andes, but the reason why shortening started at 50 Ma is still unclear. We explore the evolution of the subduction zone through time by restoring the position of the Nazca trench in an absolute reference frame, comparing its position with seismic tomography models and balancing the evolution of the subducting slab. Reconstructions show that the slab enters into the lower mantle at 50+10 Ma, and then progressed, moving horizontally at shallow lower mantle depth while thickening and folding in the transition zone. We test this evolutionary scenario by numerical models, which illustrate that compression in the upper plate emerges once the slab is anchored in the lower mantle. We conclude that onset of significant shortening and crustal thickening in the Andes and its sustained action over tens of million years is related to the penetration of the slab into the lower mantle, producing a slowdown of lateral slab migration, and dragging the upper plate against the subduction zone by large-scale return flow.

Initiation of the Andean orogeny by lower mantle subduction

NASA Astrophysics Data System (ADS)

Faccenna, C.; Oncken, O.; Holt, A.; Becker, T. W.

2017-12-01

The Cordillera of the Andes is a double-vergent orogenic belt built up by thickening of South American plate crust. Several models provide plausible explanations for the evolution of the Andes, but the reason why shortening started at 50 Ma is still unclear. We explore the evolution of the subduction zone through time by restoring the position of the Nazca trench in an absolute reference frame, comparing its position with seismic tomography models and balancing the evolution of the subducting slab. Reconstructions show that the slab enters into the lower mantle at 50+10 Ma, and then progressed, moving horizontally at shallow lower mantle depth while thickening and folding in the transition zone. We test this evolutionary scenario by numerical models, which illustrate that compression in the upper plate emerges once the slab is anchored in the lower mantle. We conclude that onset of significant shortening and crustal thickening in the Andes and its sustained action over tens of million years is related to the penetration of the slab into the lower mantle, producing a slowdown of lateral slab migration, and dragging the upper plate against the subduction zone by large-scale return flow.

Mapping the subducted Nazca plate in the lower mantle beneath South America

NASA Astrophysics Data System (ADS)

Contenti, S. M.; Gu, Y. J.; Okeler, A.

2009-12-01

Recent improvements in data coverage have enabled high-resolution imaging of the morphology of subduction zones and mantle plumes. In this study, we migrate the SS precursors from over 5000 seismograms to obtain a detailed map of mid- and upper-mantle reflectors beneath the northern portion of the South American subduction zone, where the oceanic Nazca plate is descending below the South American plate. In addition to an elevated 410 and depressed 660 (as expected for a subduction zone), strong mid-mantle reflectors at 800-1100 km depth are also apparent. The amplitudes of these steeply dipping reflectors are comparable to that of the 660-kilometer discontinuity. This anomaly outlines a high-velocity (therefore presumably cold) region present in recent finite-frequency based mantle velocity models, suggesting the extension of slab material into the lower mantle. The strength of the reflection is interpreted to be caused by a relatively sharp velocity change, likely due to a strong temperature gradient in combination with mineral phase transitions, the presence of water, or other chemical heterogeneities. Significant mass and heat exchange is therefore expected between the upper- and lower-mantle beneath the study region.

Rapid change of blob structure in the outer scrape-off layer (SOL)

NASA Astrophysics Data System (ADS)

Cohen, R. H.

2005-10-01

Nonlinear structures (``blobs'') driven by the magnetic field curvature and highly elongated along the field lines may exist in the tokamak SOL.footnotetextS.I. Krasheninnikov. Phys. Lett. A 283, 368 (2001) The contact of the blob end with the divertor plate significantly affects the blob structure and velocity. However, the strong shearing of the flux-tube near the X-point makes impossible direct electrical contact of the blob in the upper SOL and the divertor, so that the sheath boundary condition (BC) has to be replaced by a BC imposed near the X point.footnotetextD. Ryutov, R.H. Cohen. Contr. Pl. Phys 44, 168 (2004) We show that, at larger distances from the separatrix, in the far SOL, the connection between the upper SOL and the divertor plate is re-established, and the sheath BC becomes again relevant. During the blob's outward radial motion, this event is reflected in a sudden change of its length, from the blob extending only to the X point to the blob extending down to the plate. Likewise, a blob initially existing only in the divertor leg becomes suddenly longer, and extends to the whole SOL.

Mantle-derived peridotites in southwestern Oregon: relation to plate tectonics.

PubMed

Medaris, L G; Dott, R H

1970-09-04

A group of peridotites in southwestern Oregon contains high-pressure mineral assemblages reflecting recrystallization at high temperatures (1100 degrees to 1200 degrees C) over a range of pressure decreasing from 19 to 5 kilobars. It is proposed that the peridotites represent upper-mantle material brought from depth along the ancestral Gorda-Juan de Fuca ridge system, transported eastward by the spreading Gorda lithosphere plate, and then emplaced by thrust-faulting in the western margin of the Cordillera during late Mesozoic time.

Observations of Quasi-Love Waves in Tibet Indicates Coherent Deformation of the Crust and Upper Mantle

NASA Astrophysics Data System (ADS)

Chen, X.; Park, J. J.

2012-12-01

The high uplift of the Tibet area is caused by the continental collision between the Indian plate and the Eurasian plate. The style of deformation along with the collision is still being debated, particularly whether the deformation is vertically coherent or not, i.e., whether the upper mantle deforms coherently with the crust. In this work, we have used quasi-Love (QL) waves to constrain the anisotropy pattern around the Tibet region. The existence of anisotropy gradients has been identified with the observations of QL waves, which is a converted Rayleigh-wave motion that follows the arrival of the Love wave. Further, the locations of the anisotropy gradients have been pinned with the delay time between the Love wave and the QL wave, which is determined from cross-correlation. Our results show that the frequency content of Tibetan QL wave is centered around 10 mHz, indicating the depth range of anisotropy should be in the asthenosphere. Most of the scatterers of QL wave that we can detect lie outside the Tibet Plateau. Their distribution correlates well with the boundary of the Persia-Tibet- Burma orogeny, which has been identified from surface geologic data. This correlation, between surface geology and upper mantle anisotropy inferred from QL observations at the orogenic boundary, suggests that the crust and upper mantle of the orogeny are deforming coherently. Other scatterers that are off the Persia-Tibet-Burma orogenic boundary mostly cluster in two locations, the Tarim Basin, and the Bangong-Nujiang Suture, where there could exist contrasting anisotropy patterns in the upper mantle. The deformation in the Tibet region is complicated, yet our research suggests a vertically coherent deformation style of the upper mantle in Tibet.

Geological process of the slow earthquakes -A hypothesis from an ancient plate boundary fault rock

NASA Astrophysics Data System (ADS)

Kitamura, Y.; Kimura, G.; Kawabata, K.

2012-12-01

We present an integrated model of the deformation along the subduction plate boundary from the trench to the seismogenic zone. Over years of field based research in the Shimanto Belt accretionary complex, southwest Japan, yielded breaking-through discoveries on plate boundary processes, for example, the first finding of pseudotachylyte in the accretionary prism (Ikesawa et al., 2003). Our aim here is to unveil the geological aspects of slow earthquakes and the related plate boundary processes. Studied tectonic mélanges in the Shimanto Belt are regarded as fossils of plate boundary fault zone in subduction zone. We traced material from different depths along subduction channel using samples from on-land outcrops and ocean drilling cores. As a result, a series of progressive deformation down to the down-dip limit of the seismogenic zone was revealed. Detailed geological survey and structural analyses enabled us to separate superimposed deformation events during subduction. Material involved in the plate boundary deformation is mainly an alternation of sand and mud. As they have different competency and are suffered by simple shear stress field, sandstones break apart in flowing mudstones. We distinguished several stages of these deformations in sandstones and recognized progress in the intensity of deformation with increment of underthrusting. It is also known that the studied Mugi mélange bears pseudotachylyte in its upper bounding fault. Our conclusion illustrates that the subduction channel around the depth of the seismogenic zone forms a thick plate boundary fault zone, where there is a clear segregation in deformation style: a fast and episodic slip at the upper boundary fault and a slow and continuous deformation within the zone. The former fast deformation corresponds to the plate boundary earthquakes and the latter to the slow earthquakes. We further examined numerically whether this plate boundary fault rock is capable of releasing seismic moment enough to fit the observed slow earthquakes. The shallow very low frequent earthquakes (VLFs) are chosen to be modeled and our estimation satisfies the natural data. We emphasize that the plate boundary is not a plane but a zone. Geological setting is a clue for differentiating slow and normal earthquakes. We propose to focus on the three-dimensional fault zone comprising numbers of microfaults as the source of slow earthquakes instead of planar plate boundary. Our results also make an impact on the study of seismic energy balance because we show a possibility to give an absolute value of them from geological approach, which could not have been achieved with seismology.

Full-wave multiscale anisotropy tomography in Southern California

NASA Astrophysics Data System (ADS)

Lin, Yu-Pin; Zhao, Li; Hung, Shu-Huei

2014-12-01

Understanding the spatial variation of anisotropy in the upper mantle is important for characterizing the lithospheric deformation and mantle flow dynamics. In this study, we apply a full-wave approach to image the upper-mantle anisotropy in Southern California using 5954 SKS splitting data. Three-dimensional sensitivity kernels combined with a wavelet-based model parameterization are adopted in a multiscale inversion. Spatial resolution lengths are estimated based on a statistical resolution matrix approach, showing a finest resolution length of ~25 km in regions with densely distributed stations. The anisotropic model displays structural fabric in relation to surface geologic features such as the Salton Trough, the Transverse Ranges, and the San Andreas Fault. The depth variation of anisotropy does not suggest a lithosphere-asthenosphere decoupling. At long wavelengths, the fast directions of anisotropy are aligned with the absolute plate motion inside the Pacific and North American plates.

Bending-related faulting and mantle serpentinization at the Middle America trench.

PubMed

Ranero, C R; Morgan, J Phipps; McIntosh, K; Reichert, C

2003-09-25

The dehydration of subducting oceanic crust and upper mantle has been inferred both to promote the partial melting leading to arc magmatism and to induce intraslab intermediate-depth earthquakes, at depths of 50-300 km. Yet there is still no consensus about how slab hydration occurs or where and how much chemically bound water is stored within the crust and mantle of the incoming plate. Here we document that bending-related faulting of the incoming plate at the Middle America trench creates a pervasive tectonic fabric that cuts across the crust, penetrating deep into the mantle. Faulting is active across the entire ocean trench slope, promoting hydration of the cold crust and upper mantle surrounding these deep active faults. The along-strike length and depth of penetration of these faults are also similar to the dimensions of the rupture area of intermediate-depth earthquakes.

An analytical investigation of the performance of solar collectors as nighttime heat radiators in airconditioning cycles

NASA Technical Reports Server (NTRS)

Jones, C. B.; Smetana, F. O.

1979-01-01

It was found that if the upper and lower ends of a collector were opened, large free convention currents may be set up between the collector surface and the cover glass(es) which can result in appreciable heat rejection. If the collector is so designed that both plates surfaces are exposed to convection currents when the upper and lower ends of the collector enclosure are opened, the heat rejection rate is 300 watts sq m when the plate is 13 C above ambient. This is sufficient to permit a collector array designed to provide 100 percent of the heating needs of a home to reject the accumulated daily air conditioning load during the course of a summer night. This also permits the overall energy requirements for cooling to be reduced by at least 15 percent and shift the load on the utility entirely to the nighttime hours.

Does permanent extensional deformation in lower forearc slopes indicate shallow plate-boundary rupture?

NASA Astrophysics Data System (ADS)

Geersen, J.; Ranero, C. R.; Kopp, H.; Behrmann, J. H.; Lange, D.; Klaucke, I.; Barrientos, S.; Diaz-Naveas, J.; Barckhausen, U.; Reichert, C.

2018-05-01

Seismic rupture of the shallow plate-boundary can result in large tsunamis with tragic socio-economic consequences, as exemplified by the 2011 Tohoku-Oki earthquake. To better understand the processes involved in shallow earthquake rupture in seismic gaps (where megathrust earthquakes are expected), and investigate the tsunami hazard, it is important to assess whether the region experienced shallow earthquake rupture in the past. However, there are currently no established methods to elucidate whether a margin segment has repeatedly experienced shallow earthquake rupture, with the exception of mechanical studies on subducted fault-rocks. Here we combine new swath bathymetric data, unpublished seismic reflection images, and inter-seismic seismicity to evaluate if the pattern of permanent deformation in the marine forearc of the Northern Chile seismic gap allows inferences on past earthquake behavior. While the tectonic configuration of the middle and upper slope remains similar over hundreds of kilometers along the North Chilean margin, we document permanent extensional deformation of the lower slope localized to the region 20.8°S-22°S. Critical taper analyses, the comparison of permanent deformation to inter-seismic seismicity and plate-coupling models, as well as recent observations from other subduction-zones, including the area that ruptured during the 2011 Tohoku-Oki earthquake, suggest that the normal faults at the lower slope may have resulted from shallow, possibly near-trench breaking earthquake ruptures in the past. In the adjacent margin segments, the 1995 Antofagasta, 2007 Tocopilla, and 2014 Iquique earthquakes were limited to the middle and upper-slope and the terrestrial forearc, and so are upper-plate normal faults. Our findings suggest a seismo-tectonic segmentation of the North Chilean margin that seems to be stable over multiple earthquake cycles. If our interpretations are correct, they indicate a high tsunami hazard posed by the yet un-ruptured southern segment of the seismic gap.

Middle to Late Miocene Contractional Deformation in Costa Rica Triggered by Plate Geodynamics

NASA Astrophysics Data System (ADS)

Mescua, José Francisco; Porras, Hernán.; Durán, Patrick; Giambiagi, Laura; de Moor, Maarten; Cascante, Monserrat; Salazar, Esteban; Protti, Marino; Poblete, Fernando

2017-12-01

Contractional deformation in Costa Rica is usually attributed to the subduction of the aseismic Cocos Ridge. In this work, we review the evidences for contraction in the middle to late Miocene, prior to the arrival of the Cocos Ridge at the Middle America Trench. We find that the Miocene phase of contractional deformation is found in all of Costa Rica, probably extending to Nicaragua as well. The widespread distribution of this event requires a regional or plate geodynamic trigger. We analyze the possible mechanisms that could produce the onset of contractional deformation, using the better known case of subduction orogeny, the Andes, as an analog. We propose that a change in the direction of the Cocos plate since ˜19 Ma led to a change from oblique to orthogonal convergence, producing contractional deformation of the upper plate.

Minimum wear tube support hole design

DOEpatents

Glatthorn, Raymond H.

1986-01-01

A minimum-wear through-bore (16) is defined within a heat exchanger tube support plate (14) so as to have an hourglass configuration as determined by means of a constant radiused surface curvature (18) as defined by means of an external radius (R3), wherein the surface (18) extends between the upper surface (20) and lower surface (22) of the tube support plate (14). When a heat exchange tube (12) is disposed within the tube support plate (14) so as to pass through the through-bore (16), the heat exchange tube (12) is always in contact with a smoothly curved or radiused portion of the through-bore surface (16) whereby unacceptably excessive wear upon the heat exchange tube (12), as normally developed by means of sharp edges, lands, ridges, or the like conventionally part of the tube support plates, is eliminated or substantially reduced.

A study of the effect of a boundary layer profile on the dynamic response and acoustic radiation of flat panels. Ph.D. Thesis - Virginia Univ.

NASA Technical Reports Server (NTRS)

Mixson, J. S.

1973-01-01

The response of a thin, elastic plate to a harmonic force which drives the plate from below and a compressible air stream with a viscous boundary layer flowing parallel to the upper surface along the length was investigated. Equations governing the forced response of the coupled plate-aerodynamic system are derived along with appropriate boundary conditions. Calculations of basic solution parameters for a linear velocity profile and for a Blasius profile showed that the same system response could be obtained from each profile if appropriate values of boundary layer thickness were chosen for each profile.

Free and forced convection in Earth's upper mantle

NASA Astrophysics Data System (ADS)

Hall, Paul S.

Convective motion within Earth's upper mantle occurs as a combination of two primary modes: (1) buoyant upwelling due to the formation of gravitational instabilities at thermochemical boundary layers, and (2) passive flow associated with the divergence of lithospheric plates at mid-ocean ridges and their re-entry into the mantle at subduction zones. The first mode is driven by variations in density and is therefore classified as 'free' convection. Examples of free convection within the Earth include the diapiric flow of hydrous and/or partially molten mantle at subduction zones and mantle plumes. The second mode, while ultimately driven by density on a global scale, can be treated kinematically on the scale of the upper mantle. This type of flow is designated 'forced' convection. On the scale of individual buoyant upwellings in the upper mantle, the forced convection associated with plate tectonics acts to modify the morphology of the flow associated with free convection. Regions in which such interactions occur are typically associated with transfer of significant quantities of both mass and energy (i.e., heat) between the deep interior and the surface of the Earth and thus afford a window into the dynamics of the Earth's interior. The dynamics and the consequences of the interaction between these two modes of convection is the focus of this dissertation. I have employed both laboratory and numerical modeling techniques to investigate the interaction between free and forced convection in this study. Each of these approaches has its own inherent strengths and weaknesses. These approaches are therefore complementary, and their use in combination is particularly powerful. I have focused on two examples interaction between free and forced convection in the upper mantle in this study. Chapter I considers the interaction between ascending diapirs of hydrous and/or partially molten mantle and flow in the mantle wedge at subduction zones using laboratory models. Chapter II and Chapter III consider the interaction between an ascending mantle plume and the large scale shear flow associated with the divergence of plates at a nearby ridge axis.

3D dynamics of crustal deformation driven by oblique subduction: Northern and Central Andes

NASA Astrophysics Data System (ADS)

Schütt, Jorina M.; Whipp, David M., Jr.

2017-04-01

The geometry and relative motion of colliding plates will affect how and where they deform. In oblique subduction systems, factors such as the dip angle of the subducting plate and the convergence obliquity, as well as the presence of weak zones in the overriding plate, all influence how oblique convergence is partitioned onto various fault systems in the overriding plate. The partitioning of strain into margin-normal slip on the plate-bounding fault and horizontal shearing on a strike-slip system parallel to the margin is mainly controlled by the margin-parallel shear forces acting on the plate interface and the strength of the continental crust. While these plate interface forces are influenced by the dip angle of the subducting plate (i.e., the length of plate interface in the frictional domain) and the obliquity angle between the normal to the plate margin and the plate convergence vector, the strength of the continental crust in the upper plate is strongly affected by the presence or absence of weak zones such as regions of arc volcanism, pre-existing fault systems, or boundaries of stronger crustal blocks. In order to investigate which of these factors are most important in controlling how the overriding continental plate deforms, we compare results of lithospheric-scale 3D numerical geodynamic experiments from two regions in the north-central Andes: the Northern Volcanic Zone (NVZ; 5°N - 3°S) and adjacent Peruvian Flat Slab Segment (PFSS; 3°S -14°S). The NVZ is characterized by a 35° subduction dip angle with an obliquity angle of about 40°, extensive volcanism and significant strain partitioning in the continental crust. In contrast, the PFSS is characterized by flat subduction (the slab flattens beneath the continent at around 100 km depth for several hundred kilometers), an obliquity angle of about 20°, no volcanism and minimal strain partitioning. The plate geometry and convergence obliquity for these regions are incorporated in 3D (1600 x 1600 x 160 km) numerical experiments of oceanic subduction beneath a continent, focusing on the conditions under which strain partitioning occurs in the continental plate. In addition to different slab geometries and obliquity angles, we consider the effect of a continental crustal of uniform strength (friction angle Φ=15^°) versus one including a weak zone in the continental crust (Φ=4^°) that runs parallel to the margin. Results of our experiments show that the obliquity angle has the largest effect on initiating strain partitioning, as expected based on strain partitioning theory, but strain partitioning is clearly enhanced by the presence of a continental weakness. Margin-parallel mass transport velocities in the continental sliver are similar to the values observed in the NVZ (about 1 cm/year) in models with a continental weakness and twice as high as those without. In addition, a shallower subduction angle results in formation of a wider continental sliver. Based upon our results, the lack of strain partitioning observed in the PFSS results from both a low convergence obliquity and lack of a weak zone in the continent, even though the shallow subduction should make strain partitioning more favorable.

Upper plate contraction north of the migrating Mendocino triple junction northern California: Implications for partitioning of strain

USGS Publications Warehouse

McCrory, P.A.

2000-01-01

Geologic measurement of permanent contraction across the Cascadia subduction margin constrains one component of the tectonic deformation along the convergent plate boundary, the component critical for the seismic hazard assessment of crustal faults. A comprehensive survey of active faults in onshore subduction margin rocks at the southern end of the Cascadia subduction zone indicates that these thrust faults accommodate ??10 mm/yr of convergence oriented 020??-045??. Seismotectonic models of subduction zones typically assign this upper plate strain to the estimate of aseismic slip on the megathrust. Geodetic models include this permanent crustal strain within estimates of elastic strain accumulation on the megathrust. Both types of models underestimate the seismic hazard associated with crustal faults. Subtracting the observed contraction from the plate convergence rate (40-50 mm/yr; directed 040??-055??) leaves 30-40 mm/yr of convergence to be partitioned between slip on the megathrust, contraction within the southern Juan de Fuca plate, and crustal contraction outside the subduction complex rocks. This simple estimate of slip partitioning neglects the discrepancy between the plate convergence and contraction directions in the vicinity of the Mendocino triple junction. The San Andreas and Cascadia limbs of the Mendocino triple junction are not collinear. The eastern edge of the broad San Andreas boundary is ??85 km east of the Cascadia subduction boundary, and across this zone the Pacific plate converges directly with the North America plate. The skewed orientation of crustal structures just north of the leading edge of the Pacific plate suggests that they are deforming in a hybrid stress field resulting from both Juan de Fuca-North America motion and Pacific-North America motion. The composite convergence direction (50 mm/yr: directed 023??) is consistent with the compressive stress axis (020??) inferred from focal mechanisms of crustal earthquakes in the Humboldt region. Deformation in such a hybrid stress field implies that the crustal faults are being loaded from two major tectonic sources. The slip on crustal faults north of the Mendocino triple junction may consume 4-5 mm/yr of Pacific-Humboldt convergence. The remaining 17-18 mm/yr of convergence may be consumed as distributed shortening expressed in the high rates of uplift in the Cape Mendocino region or as northward translation of the continental margin, north of the triple junction.

Analysis of Long Bone and Vertebral Failure Patterns.

DTIC Science & Technology

1982-03-01

Roberts, B., 1976. Pathology of degenerative spondylosis in The Lumbar Spine and Back Pain (ed. M. Jayson), New York, Grune & Stratton, Inc., pp. 55-75...compressive loading failed by end plate or vertebral body fracture (Percy, 1957). The fractures were most common in the upper lumbar level, and the fracture...and upper lumbar regions which is supported Iby Perey’s findings (1957). The debris in the hematopoietic spaces appears Ito be bone fragments, but it

Actively controlling coolant-cooled cold plate configuration

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

Chainer, Timothy J.; Parida, Pritish R.

Cooling apparatuses are provided to facilitate active control of thermal and fluid dynamic performance of a coolant-cooled cold plate. The cooling apparatus includes the cold plate and a controller. The cold plate couples to one or more electronic components to be cooled, and includes an adjustable physical configuration. The controller dynamically varies the adjustable physical configuration of the cold plate based on a monitored variable associated with the cold plate or the electronic component(s) being cooled by the cold plate. By dynamically varying the physical configuration, the thermal and fluid dynamic performance of the cold plate are adjusted to, formore » example, optimally cool the electronic component(s), and at the same time, reduce cooling power consumption used in cooling the electronic component(s). The physical configuration can be adjusted by providing one or more adjustable plates within the cold plate, the positioning of which may be adjusted based on the monitored variable.« less

Importance of the Decompensative Correction of the Gravity Field for Study of the Upper Crust: Application to the Arabian Plate and Surroundings

NASA Astrophysics Data System (ADS)

Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

2017-01-01

The isostatic correction represents one of the most useful "geological" reduction methods of the gravity field. With this correction it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. However, even this reduction does not show the full gravity effect of unknown anomalies in the upper crust since their impact is substantially reduced by the isostatic compensation. We analyze a so-called decompensative correction of the isostatic anomalies, which provides a possibility to separate these effects. It was demonstrated that this correction is very significant at the mid-range wavelengths and may exceed 100 m/s2 (mGal), therefore ignoring this effect would lead to wrong conclusions about the upper crust structure. At the same time, the decompensative correction is very sensitive to the compensation depth and effective elastic thickness of the lithosphere. Therefore, these parameters should be properly determined based on other studies. Based on this technique, we estimate the decompensative correction for the Arabian plate and surrounding regions. The amplitude of the decompensative anomalies reaches ±250 m/s2 10-5 (mGal), evidencing for both, large density anomalies of the upper crust (including sediments) and strong isostatic disturbances of the lithosphere. These results improve the knowledge about the crustal structure in the Middle East.

Insight into collision zone dynamics from topography: numerical modelling results and observations

NASA Astrophysics Data System (ADS)

Bottrill, A. D.; van Hunen, J.; Allen, M. B.

2012-11-01

Dynamic models of subduction and continental collision are used to predict dynamic topography changes on the overriding plate. The modelling results show a distinct evolution of topography on the overriding plate, during subduction, continental collision and slab break-off. A prominent topographic feature is a temporary (few Myrs) basin on the overriding plate after initial collision. This "collisional mantle dynamic basin" (CMDB) is caused by slab steepening drawing, material away from the base of the overriding plate. Also, during this initial collision phase, surface uplift is predicted on the overriding plate between the suture zone and the CMDB, due to the subduction of buoyant continental material and its isostatic compensation. After slab detachment, redistribution of stresses and underplating of the overriding plate cause the uplift to spread further into the overriding plate. This topographic evolution fits the stratigraphy found on the overriding plate of the Arabia-Eurasia collision zone in Iran and south east Turkey. The sedimentary record from the overriding plate contains Upper Oligocene-Lower Miocene marine carbonates deposited between terrestrial clastic sedimentary rocks, in units such as the Qom Formation and its lateral equivalents. This stratigraphy shows that during the Late Oligocene-Early Miocene the surface of the overriding plate sank below sea level before rising back above sea level, without major compressional deformation recorded in the same area. Our modelled topography changes fit well with this observed uplift and subsidence.

The 2017/09/08 Mw 8.2 Tehuantepec, Mexico Earthquake: A Large but Compact Dip-Slip Faulting Event Severing the Slab

NASA Astrophysics Data System (ADS)

Hjorleifsdottir, V.; Iglesias, A.; Suarez, G.; Santoyo, M. A.; Villafuerte, C. D.; Ji, C.; Franco-Sánchez, S. I.; Singh, S. K.; Cruz-Atienza, V. M.; Ando, R.

2017-12-01

The Mw 8.2 September 8 earthquake occurred in the middle of the "Tehuantepec Gap", a segment of the Mexican subduction zone that has no historical mentions of a large earthquake. It was, however, not the expected subduction megathrust earthquake, but rather an intraplate, normal faulting event, in the subducting oceanic Cocos plate. The earthquake rupture initiated at a depth of 50 km and propagated NW on a near-vertical plane, breaking towards the surface. Most of the slip was concentrated in the distance range 30-100 km from the hypocenter and at depth between 15 and 50 km, with maximum slip of 15m. The earthquake seems to have broken the entire lithosphere, estimated to be 35 km thick. The strike of the fault is about 20 degrees oblique to the trench but aligned with the existing fabric on the incoming oceanic plate, suggesting a structural control by preexisting intraslab fractures and activation by the extensional stress due to the slab bending and pulling. Aftershocks occurred along the fault plane during the first day after the event, with activation of other parallel structures within the subducting plate, towards the east, as well as in upper plate, in the following days. Coulomb stress modeling suggests that the stress on the plate interface above the rupture was significantly increased where shallow thrust aftershoks took place, and reduced updip of the earthquake. There are several other examples of large intraslab normal faulting earthquakes, near the downdip edge (1931 Mw 7.8 and 1999 Mw 7.5, Oaxaca) or directly below (1997 Mw 7.1, Michoacan) the coupled plate interface, along the Mexican subduction zone. The possibility of events of similar magnitude to the 2017 earthquake occurring close to the coastline, all along this part of the subduction zone, cannot be ruled out.

Propagation of back-arc extension into the arc lithosphere in the southern New Hebrides volcanic arc

NASA Astrophysics Data System (ADS)

Patriat, M.; Collot, J.; Danyushevsky, L.; Fabre, M.; Meffre, S.; Falloon, T.; Rouillard, P.; Pelletier, B.; Roach, M.; Fournier, M.

2015-09-01

New geophysical data acquired during three expeditions of the R/V Southern Surveyor in the southern part of the North Fiji Basin allow us to characterize the deformation of the upper plate at the southern termination of the New Hebrides subduction zone, where it bends eastward along the Hunter Ridge. Unlike the northern end of the Tonga subduction zone, on the other side of the North Fiji Basin, the 90° bend does not correspond to the transition from a subduction zone to a transform fault, but it is due to the progressive retreat of the New Hebrides trench. The subduction trench retreat is accommodated in the upper plate by the migration toward the southwest of the New Hebrides arc and toward the south of the Hunter Ridge, so that the direction of convergence remains everywhere orthogonal to the trench. In the back-arc domain, the active deformation is characterized by propagation of the back-arc spreading ridge into the Hunter volcanic arc. The N-S spreading axis propagates southward and penetrates in the arc, where it connects to a sinistral strike-slip zone via an oblique rift. The collision of the Loyalty Ridge with the New Hebrides arc, less than two million years ago, likely initiated this deformation pattern and the fragmentation of the upper plate. In this particular geodynamic setting, with an oceanic lithosphere subducting beneath a highly sheared volcanic arc, a wide range of primitive subduction-related magmas has been produced including adakites, island arc tholeiites, back-arc basin basalts, and medium-K subduction-related lavas.

Ephemeral stream reaches preserve the evolutionary and distributional history of threespine stickleback in the Santa Clara and Ventura River watersheds of southern California

USGS Publications Warehouse

Richmond, Jonathan Q.; Jacobs, David K.; Backlin, Adam R.; Swift, Camm C.; Dellith, Chris; Fisher, Robert N.

2015-01-01

Much remains to be understood about the evolutionary history and contemporary landscape genetics of unarmored threespine stickleback in southern California, where populations collectively referred to as Gasterosteus aculeatus williamsoni have severely declined over the past 70+ years and are now endangered. We used mitochondrial sequence and microsatellite data to assess the population genetics and phylogeography of unarmored populations sampled immediately downstream from the type locality of G. a. williamsoni in the upper Santa Clara River, and assessed their distinctiveness with respect to low-armor populations in the downstream sections of the river and the adjacent Ventura River. We also characterized the geographic limits of different plate morphs and evaluated the congruence of those boundaries with barriers to dispersal in both river systems and to neutral genetic variation. We show substantial population structuring within the upper reach of the Santa Clara River, but little partitioning between the lower Santa Clara and Ventura Rivers—we attribute these patterns to different ancestry between spatially subdivided populations within the same drainage, a predominance of downstream gene flow, and ability for coastal dispersal between the Santa Clara and Ventura Rivers. We also show that alleles from introduced low-plate stock have infiltrated a native population in at least one upper Santa Clara River tributary, causing this formerly unarmored population to become gradually low-plated over a 30 + year time period. Measures of genetic diversity, census surveys, and severe habitat disturbance all indicate that unarmored stickleback near the type locality are currently at high risk of extinction.

Spirit Begins Drive Around Home Plate

NASA Technical Reports Server (NTRS)

2009-01-01

The hazard avoidance camera on the front of NASA's Mars Exploration Rover Spirit took this image after a drive by Spirit on the 1,829th Martian day, or sol, of Spirit's mission on the surface of Mars (Feb. 24, 2009).

On Sol 1829, Spirit drove 6.29 meters (21 feet) northwestward, away from the northern edge of the low plateau called 'Home Plate.' The track dug by the dragged right-front wheel as the rover drove backward is visible in this image, receding toward the southeast. Rock layers of the northern slope of Home Plate are visible in the upper right portion of the image.

In sols prior to 1829, the rover team had been trying to maneuver Spirit to climb onto the northern edge of Home Plate, ready to drive southward across the top of the plateau toward science destinations south of Home Plate. The Sol 1829 drive was the first move of a revised strategy to circle at least partway around Home Plate on the trek toward the sites south of the plateau.

An unrecognized major collision of the Okhotomorsk Block with East Asia during the Late Cretaceous, constraints on the plate reorganization of the Northwest Pacific

NASA Astrophysics Data System (ADS)

Yang, Yong-Tai

2013-11-01

Interactions at plate boundaries induce stresses that constitute critical controls on the structural evolution of intraplate regions. However, the traditional tectonic model for the East Asian margin during the Mesozoic, invoking successive episodes of paleo-Pacific oceanic subduction, does not provide an adequate context for important Late Cretaceous dynamics across East Asia, including: continental-scale orogenic processes, significant sinistral strike-slip faulting, and several others. The integration of numerous documented field relations requires a new tectonic model, as proposed here. The Okhotomorsk continental block, currently residing below the Okhotsk Sea in Northeast Asia, was located in the interior of the Izanagi Plate before the Late Cretaceous. It moved northwestward with the Izanagi Plate and collided with the South China Block at about 100 Ma. The indentation of the Okhotomorsk Block within East Asia resulted in the formation of a sinistral strike-slip fault system in South China, formation of a dextral strike-slip fault system in North China, and regional northwest-southeast shortening and orogenic uplift in East Asia. Northeast-striking mountain belts over 500 km wide extended from Southeast China to Southwest Japan and South Korea. The peak metamorphism at about 89 Ma of the Sanbagawa high-pressure metamorphic belt in Southwest Japan was probably related to the continental subduction of the Okhotomorsk Block beneath the East Asian margin. Subsequently, the north-northwestward change of motion direction of the Izanagi Plate led to the northward movement of the Okhotomorsk Block along the East Asian margin, forming a significant sinistral continental transform boundary similar to the San Andreas fault system in California. Sanbagawa metamorphic rocks in Southwest Japan were rapidly exhumed through the several-kilometer wide ductile shear zone at the lower crust and upper mantle level. Accretionary complexes successively accumulated along the East Asian margin during the Jurassic-Early Cretaceous were subdivided into narrow and subparallel belts by the upper crustal strike-slip fault system. The departure of the Okhotomorsk Block from the northeast-striking Asian margin resulted in the occurrence of an extensional setting and formation of a wide magmatic belt to the west of the margin. In the Campanian, the block collided with the Siberian margin, in Northeast Asia. At about 77 Ma, a new oceanic subduction occurred to the south of the Okhotomorsk Block, ending its long-distance northward motion. Based on the new tectonic model, the abundant Late Archean to Early Proterozoic detrital zircons in the Cretaceous sandstones in Kamchatka, Southwest Japan, and Taiwan are interpreted to have been sourced from the Okhotomorsk Block basement which possibly formed during the Late Archean and Early Proterozoic. The new model suggests a rapidly northward-moving Okhotomorsk Block at an average speed of 22.5 cm/yr during 89-77 Ma. It is hypothesized that the Okhotomorsk-East Asia collision during 100-89 Ma slowed down the northwestward motion of the Izanagi Plate, while slab pull forces produced from the subducting Izanagi Plate beneath the Siberian margin redirected the plate from northwestward to north-northwestward motion at about 90-89 Ma.

Double-difference Relocation of the Aftershocks of the Tecomán, Colima, Mexico Earthquake of 22 January 2003

NASA Astrophysics Data System (ADS)

Andrews, Vanessa; Stock, Joann; Ramírez Vázquez, Carlos Ariel; Reyes-Dávila, Gabriel

2011-08-01

On 22 January 2003, the M w = 7.6 Tecomán earthquake struck offshore of the state of Colima, Mexico, near the diffuse triple junction between the Cocos, Rivera, and North American plates. Three-hundred and fifty aftershocks of the Tecomán earthquake with magnitudes between 2.6 and 5.8, each recorded by at least 7 stations, are relocated using the double difference method. Initial locations are determined using P and S readings from the Red Sismológica Telemétrica del Estado de Colima (RESCO) and a 1-D velocity model. Because only eight RESCO stations were operating immediately following the Tecomán earthquake, uncertainties in the initial locations and depths are fairly large, with average uncertainties of 8.0 km in depth and 1.4 km in the north-south and east-west directions. Events occurring between 24 January and 31 January were located using not only RESCO phase readings but also additional P and S readings from 11 temporary stations. Average uncertainties decrease to 0.8 km in depth, 0.3 km in the east-west direction, and 0.7 km in the north-south direction for events occurring while the temporary stations were deployed. While some preliminary studies of the early aftershocks suggested that they were dominated by shallow events above the plate interface, our results place the majority of aftershocks along the plate interface, for a slab dipping between approximately 20° and 30°. This is consistent with the slab positions inferred from geodetic studies. We do see some upper plate aftershocks that may correspond to forearc fault zones, and faults inland in the upper plate, particularly among events occurring more than 3 months after the mainshock.

Thermal and chemical convection in planetary mantles

NASA Technical Reports Server (NTRS)

Dupeyrat, L.; Sotin, C.; Parmentier, E. M.

1995-01-01

Melting of the upper mantle and extraction of melt result in the formation of a less dense depleted mantle. This paper describes series of two-dimensional models that investigate the effects of chemical buoyancy induced by these density variations. A tracer particles method has been set up to follow as closely as possible the chemical state of the mantle and to model the chemical buoyant force at each grid point. Each series of models provides the evolution with time of magma production, crustal thickness, surface heat flux, and thermal and chemical state of the mantle. First, models that do not take into account the displacement of plates at the surface of Earth demonstrate that chemical buoyancy has an important effect on the geometry of convection. Then models include horizontal motion of plates 5000 km wide. Recycling of crust is taken into account. For a sufficiently high plate velocity which depends on the thermal Rayleigh number, the cell's size is strongly coupled with the plate's size. Plate motion forces chemically buoyant material to sink into the mantle. Then the positive chemical buoyancy yields upwelling as depleted mantle reaches the interface between the upper and the lower mantle. This process is very efficient in mixing the depleted and undepleted mantle at the scale of the grid spacing since these zones of upwelling disrupt the large convective flow. At low spreading rates, zones of upwelling develop quickly, melting occurs, and the model predicts intraplate volcanism by melting of subducted crust. At fast spreading rates, depleted mantle also favors the formation of these zones of upwelling, but they are not strong enough to yield partial melting. Their rapid displacement toward the ridge contributes to faster large-scale homogenization.

Effective strength of incoming sediments and its implications for plate boundary propagation: Nankai and Costa Rica as type examples of accreting vs. erosive convergent margins

NASA Astrophysics Data System (ADS)

Kopf, Achim

2013-11-01

The location of the seaward tip of a subduction thrust controls material transfer at convergent plate margins, and hence global mass balances. At approximately half of those margins, the material of the subducting plate is completely underthrust so that no accretion or even subduction erosion takes place. Along the remaining margins, material is scraped off the subducting plate and added to the upper plate by frontal accretion. We here examine the physical properties of subducting sediments off Costa Rica and Nankai, type examples for an erosional and an accretionary margin, to investigate which parameters control the level where the frontal thrust cuts into the incoming sediment pile. A series of rotary-shear experiments to measure the frictional strength of the various lithologies entering the two subduction zones were carried out. Results include the following findings: (1) At Costa Rica, clay-rich strata at the top of the incoming succession have the lowest strength (μres = 0.19) while underlying calcareous ooze, chalk and diatomite are strong (up to μres = 0.43; μpeak = 0.56). Hence the entire sediment package is underthrust. (2) Off Japan, clay-rich deposits within the lower Shikoku Basin inventory are weakest (μres = 0.13-0.19) and favour the frontal proto-thrust to migrate into one particular horizon between sandy, competent turbidites below and ash-bearing mud above. (3) Taking in situ data and earlier geotechnical testing into account, it is suggested that mineralogical composition rather than pore-pressure defines the position of the frontal thrust, which locates in the weakest, clay mineral-rich (up to 85 wt.%) materials. (4) Smectite, the dominant clay mineral phase at either margin, shows rate strengthening and stable sliding in the frontal 50 km of the subduction thrust (0.0001-0.1 mm/s, 0.5-25 MPa effective normal stress). (5) Progressive illitization of smectite cannot explain seismogenesis, because illite-rich samples also show velocity strengthening at the conditions tested.

[Surgical strategy for upper cervical vertebrae instability through the anterior approach].

PubMed

Huang, Wei-bing; Cai, Xian-hua; Chen, Zhuang-hong; Huang, Ji-feng; Liu, Xi-ming; Wei, Shi-jun

2013-07-01

To explore the choice and effect of internal fixation in treating upper cervical vertebrae instability through anterior approach. From March 2000 to September 2010,83 patients with upper cervical vertebrae instability were treated with internal fixation through anterior approach. There were 59 males and 24 females with a mean age of 42 years old (ranged, 20 to 68). Among these patients, 36 patients were treated with odontoid screw fixation, 16 patients with C1,2 transarticular screw fixation, 23 patients with C2,3 steel plate fixation, 5 patients with odontoid screw and transarticular screw fixation,2 patients with odontoid screw and C2.3 steel plate fixation, 1 patient with C1,2 transarticular screw and C2,3 steel plate fixation. One patient with completely cervical vertebrae cord injury died of pulmonary infection after C1,2 transarticular screw fixation. Other patients were followed up from 8 to 36 months with an average of 15 months. Upper cervical vertebrae stability were restored without vertebral artery and spinal cord injury. Thirty-six patients were treated with odontoid screw fixation and 5 patients were treated with screw combined with transarticular screw fixation obtained bone union in the dentations without bone graft. Among the 16 patients treated with C1,2 transarticular screw fixation, 13 patients obtained bone union after bone graft; 1 patient died of pulmonary infection after surgery; 1 patient with comminuted odontoid fracture of type II C and atlantoaxial anterior dislocation did not obtain bone union after bone graft,but the fibrous healing was strong enough to maintain the atlantoaixal joint stability; 1 patient with obsolete atlantoaxial anterior dislocation were re-treated with Brooks stainless steel wire fixation and bone graft through posterior approach, and finally obtained bone union. It could obtain satisfactory effects depending on the difference of cervical vertebrae instability to choose the correctly surgical method.

The crustal and mantle velocity structure in central Asia from 3D traveltime tomography

NASA Astrophysics Data System (ADS)

Sun, Y.; Martin, R. V.; Toksoz, M. N.; Pei, S.

2010-12-01

The lithospheric structure in central Asia features large blocks such as the Indian plate, the Afghan block, the Turan plate, and the Tarim block. This geologically and tectonically complicated area is also one of the most seismically active regions in the world. We developed P- and S- wave velocity structures of the central Asia in the crust using the traveltime data from Kyrgyzstan, Tajikistan, Kazakhstan, and Uzbek. We chose the events and stations between 32N65E and 45N85E and focused on the areas of Pamir and western Tianshan. In this data set, there are more than 6000 P and S arrivals received at 80 stations from about 300 events. The double difference tomography is applied to relocate events and to invert for seismic structures simultaneously. Our results provide accurate locations of earthquakes and high resolution crustal structure in this region. To extend the model deeper into the mantle through the upper mantle transition zone, ISC/EHB data for P and PP phases are combined with the ABCE data. To counteract the “smearing effect,” the crust and upper mantle velocity structure, derived from regional travel-times, is used. An adaptive grid method based on ray density is used in the inversion. A P-wave velocity model extending down to a depth of 2000 km is obtained. regional-teleseismic tomography provides a high-resolution, 3-D P-wave velocity model for the crust, upper mantle, and the transition zone. The crustal models correlate well with geologic and tectonic features. The upper mantle tomograms show the images of Tian Shan. The slab geometry is quite complex, reflecting the history of the changes in the plate motions and collision processes. Vp/Vs tomography was also determined in the study region, and an attenuation tomography was obtained as well.

Size estimates for fat inclusions in an isotropic Reissner-Mindlin plate

NASA Astrophysics Data System (ADS)

Morassi, Antonino; Rosset, Edi; Vessella, Sergio

2018-02-01

In this paper we consider the inverse problem of determining, within an elastic isotropic thick plate modelled by the Reissner-Mindlin theory, the possible presence of an inclusion made of a different elastic material. Under some a priori assumptions on the inclusion, we deduce constructive upper and lower estimates of the area of the inclusion in terms of a scalar quantity related to the work developed in deforming the plate by applying simultaneously a couple field and a transverse force field at the boundary of the plate. The approach allows us to consider plates with a boundary of Lipschitz class. The first author is supported by PRIN 2015TTJN95 ‘Identification and monitoring of complex structural systems’. The second author is supported by FRA 2016 ‘Problemi Inversi, dalla stabilità alla ricostruzione’, Università degli Studi di Trieste. The second and the third authors are supported by Progetto GNAMPA 2017 ‘Analisi di problemi inversi: stabilità e ricostruzione’, Istituto Nazionale di Alta Matematica (INdAM).

Electrically Anisotropic 35 Ma Pacific Lithosphere

NASA Astrophysics Data System (ADS)

Chesley, C. J.; Key, K.; Constable, S.; Behrens, J.; MacGregor, L.

2017-12-01

Geophysical studies of anisotropy in the oceanic lithosphere and asthenosphere can yield crucial insights into the processes of plate formation and evolution as the plate cools and thickens. While most previous studies have employed seismic methods to investigate anisotropy, here we examine the electrical conductivity anisotropy as constrained by controlled-source electromagnetic (CSEM) data collected during the Anisotropy and Physics of the Pacific Lithosphere Experiment (APPLE). Unlike passive magnetotelluric data, which are not particularly sensitive to the resistive part of the lithosphere or its anisotropy, CSEM data are highly sensitive to anisotropy in both the resistive crust and uppermost mantle. The APPLE data include a 30 km radius circular deep-tow of a Horizontal Electric Dipole (HED) transmitter around orthogonal pairs of HED receivers. The circular tow was optimized to measure azimuthal anisotropy, while radially oriented data at ranges from 14 to 70 km provided constraints on depth dependence of bulk conductivity. We inverted these data with a nonlinear anisotropic inversion that allows for laterally transverse isotropy, with the vertical plane of isotropy aligned orthogonal to the paleo-spreading direction. Our best model shows at least an order of magnitude resistivity difference between the paleo-spreading and paleo-ridge strike directions in both the crust and upper mantle. In the crust, conductivity is higher in the paleo-ridge and vertical directions. The opposite is true in the upper mantle, where conductivity is ten times higher in the paleo-spreading direction. Since the study area is centered on 35 Ma lithosphere, it is unlikely that melt plays a role in the observed anisotropy. Instead we propose that the crustal anisotropy is due to conductive clay minerals in normal faults promoted by hydration during paleo-extension close to the mid-ocean ridge. The upper mantle anisotropy potentially results from a crystal preferred orientation of olivine induced by shear deformation. These findings offer clues about the processes associated with oceanic spreading and may be of import to ophiolite studies.

Dividends from Technology Applied.

ERIC Educational Resources Information Center

Aviation/Space, 1982

1982-01-01

National Aeronautics and Space Administration's (NASA) Applications Program employs aerospace science/technology to provide direct public benefit. Topics related to this program discussed include: Landsat, earth crustal study (plate tectonics), search and rescue systems, radiation measurement, upper atmosphere research, space materials processing,…

Active and long-lived permanent forearc deformation driven by the subduction seismic cycle

NASA Astrophysics Data System (ADS)

Aron Melo, Felipe Alejandro

I have used geological, geophysical and engineering methods to explore mechanisms of upper plate, brittle deformation at active forearc regions. My dissertation particularly addresses the permanent deformation style experienced by the forearc following great subduction ruptures, such as the 2010 M w8.8 Maule, Chile and 2011 Mw9.0 Tohoku, Japan earthquakes. These events triggered large, shallow seismicity on upper plate normal faults above the rupture reaching Mw7.0. First I present new structural data from the Chilean Coastal Cordillera over the rupture zone of the Maule earthquake. The study area contains the Pichilemu normal fault, which produced the large crustal aftershocks of the megathrust event. Normal faults are the major neotectonic structural elements but reverse faults also exist. Crustal seismicity and GPS surface displacements show that the forearc experiences pulses of rapid coseismic extension, parallel to the heave of the megathrust, and slow interseismic, convergence-parallel shortening. These cycles, over geologic time, build the forearc structural grain, reactivating structures properly-oriented respect to the deformation field of each stage of the interplate cycle. Great subduction events may play a fundamental role in constructing the crustal architecture of extensional forearc regions. Static mechanical models of coseismic and interseismic upper plate deformation are used to explore for distinct features that could result from brittle fracturing over the two stages of the interplate cycle. I show that the semi-elliptical outline of the first-order normal faults along the Coastal Cordillera may define the location of a characteristic, long-lived megathrust segment. Finally, using data from the Global CMT catalog I analyzed the seismic behavior through time of forearc regions that have experienced great subduction ruptures >Mw7.7 worldwide. Between 61% and 83% of the cases where upper plate earthquakes exhibited periods of increased seismicity above background levels occurred contemporaneous to megathrust ruptures. That correlation is stronger for normal fault events than reverse or strike-slip crustal earthquakes. More importantly, for any given megathrust the summation of the Mw accounted by the forearc normal fault aftershocks appears to have a positive linear correlation with the Mw of the subduction earthquake -- the larger the megathrust the larger the energy released by forearc events.

Mid-ocean ridges produced thicker crust in the Jurassic than in Recent times

NASA Astrophysics Data System (ADS)

Van Avendonk, H. J.; Harding, J.; Davis, J. K.; Lawver, L. A.

2016-12-01

We present a compilation of published marine seismic refraction data to show that oceanic crust was 1.7 km thicker on average in the mid-Jurassic (170 Ma) than along the present-day mid-ocean ridge system. Plate reconstructions in a fixed hotspot framework show that the thickness of oceanic crust does not correlate with proximity to mantle hotspots, so it is likely that mid-plate volcanism is not the cause of this global trend. We propose that more melt was extracted from the upper mantle beneath mid-ocean ridges in the Jurassic than in recent times. Numerical studies show that temperature increase of 1 degree C in the mantle can lead to approximately 50-70 m thicker crust, so the upper mantle may have cooled 15-20 degrees C/100 Myr since 170 Ma. This average temperature decrease is larger than the secular cooling rate of the Earth's mantle, which is roughly 10 degrees C/100 Myr since the Archean. Apparently, the present-day configuration and dynamics of continental and oceanic plates removes heat more efficiently from the Earth's mantle than in its earlier history. The increase of ocean crustal thickness with plate age is also stronger in the Indian and Atlantic oceans than in the Pacific Ocean basin. This confirms that thermal insulation by the supercontinent Pangaea raised the temperature of the underlying asthenospheric mantle, which in turn led to more magmatic output at the Jurassic mid-ocean ridges of the Indian and Atlantic oceans.

Orthodontic skeletal anchorage using a palatal external plate.

PubMed

Kobayashi, Masaru; Fushima, Kenji

2014-03-01

We have developed the Anchor-Lock external plate system, which is fitted on the palate for the purpose of orthodontic skeletal anchorage. The aim of this study was to introduce the Anchor-Lock and assess its success rate. The Anchor-Lock is composed of titanium screws of 2·0-mm diameter and a titanium plate of 1·0-mm thickness. The external plate is rigidly interlocked with the heads of the screws, which are implanted trans-mucosally into palatal bone. Three types of Anchor-Lock are available. These were applied to 137 orthodontic patients (104 females and 33 males) aged 10-54 years. Two types of plate were used, a straight-shaped plate applied to the hard palate and to the anterior palate and a double-Y-shaped plate applied after tooth-borne rapid maxillary expansion. Success rate of the Anchor-Lock was 92·0% overall. No significant difference in success rate was found by age or sex of patients. Type or screw length of the Anchor-Lock did not affect success rate significantly. Success rate was significantly increased by the use of the surgical stent. The Anchor-Lock was effectively applied to distalize and/or intrude the upper molars. The Anchor-Lock system appears suitable for clinical use as an alternative to conventional screw- and plate-type orthodontic implants.

Seismic anisotropy of western Mexico and northeastern Tibet

NASA Astrophysics Data System (ADS)

Leon-Soto, Gerardo

In this dissertation, characteristics of upper mantle anisotropy, using shear wave splitting techniques, for two distinct tectonic provinces are presented. In the first part, in western Mexico, the Rivera and Cocos plates subduct beneath the North America plate constituting a young subduction setting where plate fragmentation and capture is occurring today. We characterize the upper mantle anisotropy from SKS and local S phases from the data collected by the MARS experiment (MApping the Rivera Subduction zone) and by two stations of the Mexican Servicio Sismologico National. SKS shear-wave splitting parameters indicate that the fast directions of the split SKS waves for the stations that lie on the central and southern Jalisco block are approximately trench normal. Fast polarizations of these phases also follow the convergence direction between the Rivera Plate and Jalisco block with respect to the North America plate. S-wave splitting from slab events show a small averaged delay time of about 0.2 sec for the upper 60 km of the crust and mantle. Therefore, the main source of anisotropy must reside on the entrained mantle below the young and thin Rivera Plate. Trench-oblique fast SKS split directions are observed in the western edge of the Rivera Plate and western parts of the Cocos slab. The curved pattern of fast SKS split directions in the western Jalisco block and the Rivera-Cocos gap indicate 3-D toroidal mantle flow, around the northwestern edge of the Rivera slab and Rivera- Cocos gap. This behavior profoundly affects finite strain field in the northwestern edge of the Rivera slab and the mantle wedge. The shear wave splitting results support the idea that the Rivera and Cocos plates not only moved in a down-dip direction but also have recently rolled back towards the trench and the Colima rift is intimately related to the tearing between the Rivera and Cocos plates. In the second study, the tectonic enviroment of the northeastern Tibetan plateau is considered. Shear wave splitting measurements using teleseismic SKS and SKKS phases recorded by the ASCENT (A Seismic Collaborative Experiment in Northeastern Tibet) and INDEPTH-IV (International Deep Profiling of Tibet and the Himalaya, Phase IV) experiments reveal significant anisotropy in north-eastern Tibet with a large delay time of up 2.2 sec, indicating that anisotropy exists in both the lithospheric and asthenospheric mantle. The coherence between fast polarization directions of split core phases and the left-lateral slip on eastern-striking, southeastern-striking and southern-striking faults in eastern Tibet as well as the surface velocity calculated from GPS data support the idea that left-lateral shear strain is the predominant cause of the orientation of the upper mantle petrofabrics. The left-lateral motion can be best understood as a manifestation of north-striking right-lateral simple shear exerted by the eastern edge of the underthrusting Indian plate as it penetrates into Eurasia, as well as the bending of the Eastern Himalayan Syntaxis (EHS) by the foundering Burma-Andaman-Sumatra slab. Two plausible competing models are proposed for the flow of asthenosphere. In the first, the deforming lithosphere gliding over the passive asthenosphere induces flow of the asthenosphere. In the second, the asthenosphere beneath northeastern Tibet is flowing eastward in an asthenosphere channel that lies between the Ordos plateau and Sichuan basin, and around the EHS as it is being compressed between the advancing Indian continental lithosphere and the thick Tarim and Qaidam lithospheres to the north. Delay times from stations in the EHS have a maximum of 1.3 sec suggesting that although most anisotropy is residing in the lithosphere, some may be associated with flow of the asthenosphere. The retreating Burma slab induces flow that is toroidal and located exclusively around the northern edge of the slab. The curved fast directions of split shear waves for stations in the EHS are consistent with the toroidal flow pattern as well as the rotational deformation of the overlying lithosphere. It is suggested that the foundering Burma plate may also play an important role in bending the EHS in the late Cenozoic time.

Is the Vincent fault in southern California the Laramide subduction zone megathrust?

NASA Astrophysics Data System (ADS)

Xia, H.; Platt, J. P.

2016-12-01

The Vincent fault (VF) in the San Gabriel Mountains, southern California separates a Meso-Proterozoic gneiss complex and Mesozoic granitoid rocks in the upper plate from the ocean-affiliated Late Cretaceous Pelona schist in the lower plate, and it has been widely interpreted as the original Laramide subduction megathrust. A 500 to 1000 m thick mylonite zone, consisting of a low-stress (LS) section at the bottom, a high-stress (HS) section at the top, and a weakly deformed section in between, is developed above the VF. Our kinematic, thermobarometric and geochronological analysis of the mylonite zone indicates that the VF is a normal fault. Shear sense indicators including asymmetric porphyroblasts, quartz new grain fabric, mineral fish, and quartz CPO from the HS and the LS sections exhibit a top-to-SE sense of shear on the SW-dipping mylonitic foliation, which is contrary to what one would expect for the Laramide subduction megathrust. A few samples from the LS section were overprinted by HS microstructure, implying that the LS mylonites predate the HS mylonites. TitaniQ thermometer and Si-in-muscovite barometer show that the P-T conditions are 389 ± 6 °C, 5 kbar for the LS mylonites and 329 ± 6 °C, 2.4 kbar for HS mylonites. Considering the temporal sequence of HS and LS mylonites, they are likely to be formed during exhumation. A comparison with the lower plate leads to the same conclusion. The top 80-100 m of the Pelona schist underneath the VF is folded and also mylonitized, forming the Narrows synform and S3 simultaneously. Our previous study found that S3 of the Pelona schist has a top-to-SE sense of shear and similar P-T conditions as the LS mylonite in the upper plate, so S3 of the Pelona schist is likely to be formed together with the LS mylonites in the upper plate. While mylonitization of Pelona schist (S3) overprinted both the subduction-related S1 fabric and the return-flow-related S2 fabric, it is reasonable to argue that the mylonite zone above the VF has nothing to do with subduction. The VF cuts the Narrows synform in the lower plate, indicating that the latest activity of the VF postdated mylonitization. Detrital zircon fission track ages do not show gaps in the hanging wall and no major faults in the hanging wall were discovered, so the Vincent fault and the mylonites have to be the ones that exhumed the Pelona schist.

Spiral Orbit Tribometer

NASA Technical Reports Server (NTRS)

Pepper, Stephen V.; Jones, William R., Jr.; Kingsbury, Edward; Jansen, Mark J.

2007-01-01

The spiral orbit tribometer (SOT) bridges the gap between full-scale life testing and typically unrealistic accelerated life testing of ball-bearing lubricants in conjunction with bearing ball and race materials. The SOT operates under realistic conditions and quickly produces results, thereby providing information that can guide the selection of lubricant, ball, and race materials early in a design process. The SOT is based upon a simplified, retainerless thrust bearing comprising one ball between flat races (see figure). The SOT measures lubricant consumption and degradation rates and friction coefficients in boundary lubricated rolling and pivoting contacts. The ball is pressed between the lower and upper races with a controlled force and the lower plate is rotated. The combination of load and rotation causes the ball to move in a nearly circular orbit that is, more precisely, an opening spiral. The spiral s pitch is directly related to the friction coefficient. At the end of the orbit, the ball contacts the guide plate, restoring the orbit to its original radius. The orbit is repeatable throughout the entire test. A force transducer, mounted in-line with the guide plate, measures the force between the ball and the guide plate, which directly relates to the friction coefficient. The SOT, shown in the figure, can operate in under ultra-high vacuum (10(exp -9) Torr) or in a variety of gases at atmospheric pressure. The load force can be adjusted between 45 and 450 N. By varying the load force and ball diameter, mean Hertzian stresses between 0.5 and 5.0 GPa can be obtained. The ball s orbital speed range is between 1 and 100 rpm.

Sliding mode controllers for a tempered glass furnace.

PubMed

Almutairi, Naif B; Zribi, Mohamed

2016-01-01

This paper investigates the design of two sliding mode controllers (SMCs) applied to a tempered glass furnace system. The main objective of the proposed controllers is to regulate the glass plate temperature, the upper-wall temperature and the lower-wall temperature in the furnace to a common desired temperature. The first controller is a conventional sliding mode controller. The key step in the design of this controller is the introduction of a nonlinear transformation that maps the dynamic model of the tempered glass furnace into the generalized controller canonical form; this step facilitates the design of the sliding mode controller. The second controller is based on a state-dependent coefficient (SDC) factorization of the tempered glass furnace dynamic model. Using an SDC factorization, a simplified sliding mode controller is designed. The simulation results indicate that the two proposed control schemes work very well. Moreover, the robustness of the control schemes to changes in the system's parameters as well as to disturbances is investigated. In addition, a comparison of the proposed control schemes with a fuzzy PID controller is performed; the results show that the proposed SDC-based sliding mode controller gave better results. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

14. UPPER SHOES, FIXED SHOES, ROLLER SHOES, CENTER WEB, AND ...

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

14. UPPER SHOES, FIXED SHOES, ROLLER SHOES, CENTER WEB, AND ROLLER BED PLATES. (Also includes a sheet index and a schedule of parts). American Bridge Company, Ambridge Plant No. 5, sheet no. 4, dated April 7, 1928, order no. F5073. For U.S. Steel Products Company, Pacific Coast Depot, order no. SF578. For Southern Pacific Company, order no. 8873-P-28746. various scales. - Napa River Railroad Bridge, Spanning Napa River, east of Soscol Avenue, Napa, Napa County, CA

The paleogeographic significance of Aquilapollenites occurrence in Pakistan

NASA Astrophysics Data System (ADS)

Khan, Asrar M.; Srivastava, Satish K.

2006-12-01

The occurrence of the genus Aquilapollenites in Upper Cretaceous and Neogene sediments of northwestern Pakistan is reported here. Aquilapollenites amplus, Aquilapollenites reductus, and Aquilapollenites sp. occur in the Maastrichtian palynomorph assemblage from an outcrop sample of the Mir Ali section, northern Waziristan. Aquilapollenites medeis in the Neogene Murgha Faqir Zai Formation of the Pishin Basin, Balochistan, is considered a reworked Cretaceous specimen. The Upper Cretaceous sediments of the Asian plate on the Tethys margin are considered to be the source of Aquilapollenites spp. in these samples.

Stress accumulated mechanisms on strike-slip faults

NASA Technical Reports Server (NTRS)

Turcotte, D. L.

1980-01-01

The tectonic framework causing seismicity on the San Andreas and North Anatolian faults can be understood in terms of plate tectonics. However, the mechanisms responsible for the distribution of seismicity in space and time on these faults are poorly understood. The upper part of the crust apparently behaves elastically in storing energy that is released during an earthquake. The relatively small distances from the fault in which stress is stored argue in favor of a plate with a thickness of 5-10 km. The interaction of this plate with a lower crust that is behaving as a fluid damps the seismic cycling in distances of the order of 10 km from the fault. Low measured heat flow also argues in favor of a thin plate with a low stress level on the fault. Future measurements of stress, strain, and heat flow should help to provide a better understanding of the basic mechanisms governing the behavior of strike-slip faults.

Surface wave tomography applied to the North American upper mantle

NASA Astrophysics Data System (ADS)

van der Lee, Suzan; Frederiksen, Andrew

Tomographic techniques that invert seismic surface waves for 3-D Earth structure differ in their definitions of data and the forward problem as well as in the parameterization of the tomographic model. However, all such techniques have in common that the tomographic inverse problem involves solving a large and mixed-determined set of linear equations. Consequently these inverse problems have multiple solutions and inherently undefinable accuracy. Smoother and rougher tomographic models are found with rougher (confined to great circle path) and smoother (finite-width) sensitivity kernels, respectively. A powerful, well-tested method of surface wave tomography (Partitioned Waveform Inversion) is based on inverting the waveforms of wave trains comprising regional S and surface waves from at least hundreds of seismograms for 3-D variations in S wave velocity. We apply this method to nearly 1400 seismograms recorded by digital broadband seismic stations in North America. The new 3-D S-velocity model, NA04, is consistent with previous findings that are based on separate, overlapping data sets. The merging of US and Canadian data sets, adding Canadian recordings of Mexican earthquakes, and combining fundamental-mode with higher-mode waveforms provides superior resolution, in particular in the US-Canada border region and the deep upper mantle. NA04 shows that 1) the Atlantic upper mantle is seismically faster than the Pacific upper mantle, 2) the uppermost mantle beneath Precambrian North America could be one and a half times as rigid as the upper mantle beneath Meso- and Cenozoic North America, with the upper mantle beneath Paleozoic North America being intermediate in seismic rigidity, 3) upper-mantle structure varies laterally within these geologic-age domains, and 4) the distribution of high-velocity anomalies in the deep upper mantle aligns with lower mantle images of the subducted Farallon and Kula plates and indicate that trailing fragments of these subducted oceanic plates still reside in the transition zone. The thickness of the high-velocity layer beneath Precambrian North America is estimated to be 250±70 km thick. On a smaller scale NA04 shows 1) high-velocities associated with subduction of the Pacific plate beneath the Aleutian arc, 2) the absence of expected high velocities in the upper mantle beneath the Wyoming craton, 3) a V-shaped dent below 150 km in the high-velocity cratonic lithosphere beneath New England, 4) the cratonic lithosphere beneath Precambrian North America being confined southwest of Baffin Bay, west of the Appalachians, north of the Ouachitas, east of the Rocky Mountains, and south of the Arctic Ocean, 5) the cratonic lithosphere beneath the Canadian shield having higher S-velocities than that beneath Precambrian basement that is covered with Phanerozoic sediments, 6) the lowest S velocities are concentrated beneath the Gulf of California, northern Mexico, and the Basin and Range Province.

P-wave anisotropic velocity tomography beneath the Japan islands: Large-scale images and details in the Kanto district

NASA Astrophysics Data System (ADS)

Ishise, M.; Koketsu, K.; Miyake, H.; Oda, H.

2006-12-01

The Japan islands arc is located in the convergence zone of the North American (NA), Amurian (AM), Pacific (PAC) and Philippine Sea (PHS) plates, and its parts are exposed to various tectonic settings. For example, at the Kanto district in its central part, these four plates directly interact with each, so that disastrous future earthquakes are expected along the plate boundaries and within the inland areas. In order to understand this sort of complex tectonic setting, it is necessary to know the seismological structure in various perspectives. We investigate the seismic velocity structure beneath the Japan islands in view of P-wave anisotropy. We improved a hitherto-known P-wave tomography technique so that the 3-D structure of isotropic and anisotropic velocities and earthquake hypocenter locations are determined from P-wave arrival times of local earthquakes [Ishise and Oda, 2005]. In the tomography technique, P-wave anisotropy is assumed to hold hexagonal symmetry with horizontal symmetry axis. The P-wave arrival times used in this study are complied in the Japan University Network Earthquake Catalog. The results obtained are summarized as follows; (1) the upper crust anisotropy is governed by the present-day stress field arising from the interaction between the plates surrounding the Japan islands arc, (2) the mantle anisotropy is caused by the present-day mantle flow induced by slab subduction and continental plate motion, (3) the old PAC slab keeps its original slab anisotropy which was captured when the plate was formed, while the youngest part of the PHS slab has lost the original anisotropy during its subduction and has gained new anisotropy which is controlled by the present-day stress field. We also carried out a further study on high-resolution seismic tomography for understanding the specific characteristics of the Kanto district. We mostly focused on the elucidation of the dual subduction formed by the PHS and PAC slabs using seismological data compiled by the Natural Research Institute for Earth Science and Japan Meteorological Agency. This will lead to more accurate source modeling of future plate- boundary earthquakes.

Biomechanical in vitro assessment of screw augmentation in locked plating of proximal humerus fractures.

PubMed

Röderer, Götz; Scola, Alexander; Schmölz, Werner; Gebhard, Florian; Windolf, Markus; Hofmann-Fliri, Ladina

2013-10-01

Proximal humerus fracture fixation can be difficult because of osteoporosis making it difficult to achieve stable implant anchorage in the weak bone stock even when using locking plates. This may cause implant failure requiring revision surgery. Cement augmentation has, in principle, been shown to improve stability. The aim of this study was to investigate whether augmentation of particular screws of a locking plate aimed at a region of low bone quality is effective in improving stability in a proximal humerus fracture model. Twelve paired human humerus specimens were included. Quantitative computed tomography was performed to determine bone mineral density (BMD). Local bone quality in the direction of the six proximal screws of a standard locking plate (PHILOS, Synthes) was assessed using mechanical means (DensiProbe™). A three-part fracture model with a metaphyseal defect was simulated and fixed with the plate. Within each pair of humeri the two screws aimed at the region of the lowest bone quality according to the DensiProbe™ were augmented in a randomised manner. For augmentation, 0.5 ml of bone cement was injected in a screw with multiple outlets at its tip under fluoroscopic control. A cyclic varus-bending test with increasing upper load magnitude was performed until failure of the screw-bone fixation. The augmented group withstood significantly more load cycles. The correlation of BMD with load cycles until failure and BMD with paired difference in load cycles to failure showed that augmentation could compensate for a low BMD. The results demonstrate that augmentation of screws in locked plating in a proximal humerus fracture model is effective in improving primary stability in a cyclic varus-bending test. The augmentation of two particular screws aimed at a region of low bone quality within the humeral head was almost as effective as four screws with twice the amount of bone cement. Screw augmentation combined with a knowledge of the local bone quality could be more effective in enhancing the primary stability of a proximal humerus locking plate because the effect of augmentation can be exploited more effectively limiting it to the degree required. Copyright © 2013 Elsevier Ltd. All rights reserved.

Global Models of Ridge-Push Force, Geoid, and Lithospheric Strength of Oceanic plates

NASA Astrophysics Data System (ADS)

Mahatsente, Rezene

2017-12-01

An understanding of the transmission of ridge-push related stresses in the interior of oceanic plates is important because ridge-push force is one of the principal forces driving plate motion. Here, I assess the transmission of ridge-push related stresses in oceanic plates by comparing the magnitude of the ridge-push force to the integrated strength of oceanic plates. The strength is determined based on plate cooling and rheological models. The strength analysis includes low-temperature plasticity (LTP) in the upper mantle and assumes a range of possible tectonic conditions and rheology in the plates. The ridge-push force has been derived from the thermal state of oceanic lithosphere, seafloor depth and crustal age data. The results of modeling show that the transmission of ridge-push related stresses in oceanic plates mainly depends on rheology and predominant tectonic conditions. If a lithosphere has dry rheology, the estimated strength is higher than the ridge-push force at all ages for compressional tectonics and at old ages (>75 Ma) for extension. Therefore, under such conditions, oceanic plates may not respond to ridge-push force by intraplate deformation. Instead, the plates may transmit the ridge-push related stress in their interior. For a wet rheology, however, the strength of young lithosphere (<75 Ma) is much less than the ridge-push force for both compressional and extensional tectonics. In this case, the ridge-push related stress may dissipate in the interior of oceanic plates and diffuses by intraplate deformation. The state of stress within a plate depends on the balance of far-field and intraplate forces.

A simple-shear rheometer for linear viscoelastic characterization of vocal fold tissues at phonatory frequencies.

PubMed

Chan, Roger W; Rodriguez, Maritza L

2008-08-01

Previous studies reporting the linear viscoelastic shear properties of the human vocal fold cover or mucosa have been based on torsional rheometry, with measurements limited to low audio frequencies, up to around 80 Hz. This paper describes the design and validation of a custom-built, controlled-strain, linear, simple-shear rheometer system capable of direct empirical measurements of viscoelastic shear properties at phonatory frequencies. A tissue specimen was subjected to simple shear between two parallel, rigid acrylic plates, with a linear motor creating a translational sinusoidal displacement of the specimen via the upper plate, and the lower plate transmitting the harmonic shear force resulting from the viscoelastic response of the specimen. The displacement of the specimen was measured by a linear variable differential transformer whereas the shear force was detected by a piezoelectric transducer. The frequency response characteristics of these system components were assessed by vibration experiments with accelerometers. Measurements of the viscoelastic shear moduli (G' and G") of a standard ANSI S2.21 polyurethane material and those of human vocal fold cover specimens were made, along with estimation of the system signal and noise levels. Preliminary results showed that the rheometer can provide valid and reliable rheometric data of vocal fold lamina propria specimens at frequencies of up to around 250 Hz, well into the phonatory range.

Wing download reduction using vortex trapping plates

NASA Technical Reports Server (NTRS)

Light, Jeffrey S.; Stremel, Paul M.; Bilanin, Alan J.

1994-01-01

A download reduction technique using spanwise plates on the upper and lower wing surfaces has been examined. Experimental and analytical techniques were used to determine the download reduction obtained using this technique. Simple two-dimensional wind tunnel testing confirmed the validity of the technique for reducing two-dimensional airfoil drag. Computations using a two-dimensional Navier-Stokes analysis provided insight into the mechanism causing the drag reduction. Finally, the download reduction technique was tested using a rotor and wing to determine the benefits for a semispan configuration representative of a tilt rotor aircraft.

Tomography images of the Alpine roots and surrounding upper mantle

NASA Astrophysics Data System (ADS)

Plomerova, Jaroslava; Babuska, Vladislav

2017-04-01

Teleseismic body-wave tomography represents powerful tool to study regional velocity structure of the upper mantle and to image velocity anomalies, such as subducted lithosphere plates in collisional zones. In this contribution, we recapitulate 3D models of the upper mantle beneath the Alps, which developed at a collision zone of the Eurasian and African plates. Seismic tomography studies indicate a leading role of the rigid mantle lithosphere that functioned as a major stress guide during the plate collisions. Interactions of the European lithosphere with several micro-plates in the south resulted in an arcuate shape of this mountain range on the surface and in a complicated geometry of the Alpine subductions in the mantle. Early models with one bended lithosphere root have been replaced with more advanced models showing two separate lithosphere roots beneath the Western and Eastern Alps (Babuska et al., Tectonophysics 1990; Lippitsch et al., JGR 2003). The standard isotropic velocity tomography, based on pre-AlpArray data (the currently performed passive seismic experiment in the Alps and surroundings) images the south-eastward dipping curved slab of the Eurasian lithosphere in the Western Alps. On the contrary, beneath the Eastern Alps the results indicate a very steep northward dipping root that resulted from the collision of the European plate with the Adriatic microplate. Dando et al. (2011) interpret high-velocity heterogeneities at the bottom of their regional tomographic model as a graveyard of old subducted lithospheres. High density of stations, large amount of rays and dense ray-coverage of the volume studied are not the only essential pre-requisites for reliable tomography results. A compromise between the amount of pre-processed data and the high-quality of the tomography input (travel-time residuals) is of the high importance as well. For the first time, the existence of two separate roots beneath the Alps has been revealed from carefully pre-processed, mostly the ISC-bulletin data (Babuska et al., Tectonophysics 1990). Calculated relative travel-time residuals have been assigned to source clusters and filtered relative to the residual mean of each cluster of events. We expect that future 3D studies of the mantle velocities and mantle fabrics with the use of body-wave anisotropic parameters from the AlpArray data will shed a new light on tectonic development of the complex Alpine region and its surroundings.

Microstructural and fabric characterization of brittle-ductile transitional deformation of middle crustal rocks along the Jinzhou detachment fault zone, Northeast China

NASA Astrophysics Data System (ADS)

Zhang, Juyi; Jiang, Hao; Liu, Junlai

2017-04-01

Detachment fault zones (DFZs) of metamorphic core complexes generally root into the middle crust. Exhumed DFZs therefore generally demonstrate structural, microstructural and fabric features characteristic of middle to upper crustal deformation. The Jinzhou detachment fault zone from the Liaonan metamorphic core complex is characterized by the occurrence of a sequence of fault rocks due to progressive shearing along the fault zone during exhumation of the lower plate. From the exhumed fabric zonation, cataclastic rocks formed in the upper crust occur near the Jinzhou master detachment fault, and toward the lower plate gradually changed to mylonites, mylonitic gneisses and migmatitic gneisses. Correspondingly, these fault rocks have various structural, microstructural and fabric characteristics that were formed by different deformation and recrystallization mechanisms from middle to upper crustal levels. At the meanwhile, various structural styles for strain localization were formed in the DFZ. As strain localization occurs, rapid changes in deformation mechanisms are attributed to increases in strain rates or involvement of fluid phases during the brittle-ductile shearing. Optical microscopic studies reveal that deformed quartz aggregates in the lower part of the detachment fault zone are characterized by generation of dynamically recrystallized grains via SGR and BLG recrystallization. Quartz rocks from the upper part of the DFZ have quartz porphyroclasts in a matrix of very fine recrystallized grains. The porphyroclasts have mantles of sub-grains and margins grain boundary bulges. Electron backscattered diffraction technique (EBSD) quartz c-axis fabric analysis suggests that quartz grain aggregates from different parts of the DFZ possess distinct fabric complexities. The c-axis fabrics of deformed quartz aggregates from mylonitic rocks in the lower part of the detachment fault zone preserve Y-maxima which are ascribed to intermediate temperature deformation (500-630˚ C), whereas complicated fabric patterns (e.g. asymmetric single girdles) are formed in fault rocks from the upper part of the DFZ. The increasing fabric complexity is here interpreted as the result of progressive superposition of fault rocks by shearing either at relatively shallow levels or high rate of strain, during exhumation of the lower plate and shear zone rocks. The above observations and interpretations imply that dislocation creep processes contribute to the dynamic recrystallization of quartz in the middle crustal brittle-ductile transition. Progressive shearing as a consequence of exhumation of the lower plate of the MCC contributed to the obvious structural, microstructural and fabric superpositions. Strain localization occurs as the progressive shearing proceeded. Transition of mechanisms of deformation and dynamic recrystallization during strain localization may be resulted from changes in temperature conditions, in strain rates or addition of minor amount water.

Rheology of the lithosphere and the folding caused by horizontal compression

NASA Astrophysics Data System (ADS)

Birger, B. I.

2015-05-01

The laboratory tests of rock specimens show that transient creep, at which deformations increase with time whereas strain rate decreases occurs when creep strains are sufficiently small. Since plate tectonics only permits small deformations in the lithospheric plates, the creep of the lithosphere is transient (non-steady-state). In this work, we study how the rheology of the lithosphere that possesses elasticity, brittleness (pseudo-plasticity), and creep affects the folding in the Earth's crust. Folding is caused by horizontal compression that results from the collision between the lithospheric plates. The effective viscosity characterizing the transient creep is lower than in the case of a steady-state creep and depends on the characteristic time of the considered process. The allowance for transient creep gives the distribution of the rheological properties of the horizontally compressed lithosphere in which the upper crust is brittle, whereas the lower crust and mantle lithosphere are dominated by transient creep. It is shown that the flows that arise in the lithosphere due to the instability under horizontal compression and cause folding are small-scale. These flows are concentrated in the upper brittle crust, they determine the short-wave Earth's surface topography, penetrate into the lower, creep-dominated crust to a shallow depth, and do not penetrate into the mantle. Therefore, these flows do not deform the Moho.

Characteristics of a multilayer one-touch-point ultrasonic motor for high torque

NASA Astrophysics Data System (ADS)

Jeong, Seong-Su; Park, Tae-Gone; Park, Jong-Kyu

2013-04-01

In this paper, a one-touch-point ultrasonic motor is proposed. Fabricating the stator is easy because of its simple structure and the use of a punching technique. Also, a thin stator is advantageous to use in tight spaces. A thin metal plate was used as a V-shaped stator and two to the upper and two to the lower ceramic plates were attached to the upper and the lower surfaces respectively of the metal plate. When two sinusoidal sources with a phase difference of 90 degrees were applied to the stator, an elliptical displacement was generated at contact tip of the stator. Modeling of the ultrasonic motor was done and the displacement characteristics were defined by using a finite element analysis program (ATILA). To improve the speed and the torque of the ultrasonic motor, we analyzed the effects of the leg angle and the number of ceramic layers. In addition, a model with large x-axis and y-axis displacements was fabricated, and the speed and the torque were measured under various conditions. The elliptical motion of the contact tip of the stator was consistently obtained at the resonance frequency. The maximum speed and torque were obtained by using maximum elliptical displacement model. The speed and the torque increased linearly with increasing voltage.

Detailed Image of the Subducting Plate and Upper mantle Seismic Discontinuities in the Mariana Subduction Zone

NASA Astrophysics Data System (ADS)

Tibi, R.; Wiens, D. A.; Shiobara, H.; Sugioka, H.; Yuan, X.

2006-12-01

We use P-to-S converted teleseismic phases recorded at island and ocean bottom stations in Mariana to image the subducting plate and the upper mantle seismic discontinuities in the Mariana subduction zone. The land and seafloor stations which operated from June 2003 to May 2004, were deployed within the framework of the MARGINS Subduction Factory experiment of the Mariana system. The crust in the sudducting plate is observed at about 80--90 km depth beneath the islands of Saipan, Tinian and Rota. For most of the island stations, a low velocity layer is imaged in the forearc at depth between about 20 and 60 km, with decreasing depths toward the arc. The nature of this feature is not yet clear. We found evidence for double seismic discontinuities at the base of the transition zone near the Mariana slab. A shallower discontinuity is imaged at depths of ~650--715 km, and a deeper interface lies at ~740-- 770 km depth. The amplitudes of the seismic signals suggest that the shear velocity contrasts across the two features are comparable. These characteristics support the interpretation that the discontinuities are the results of the phase transformations in olivine (ringwoodite to post-spinel) and garnet (ilminite to perovskite), respectively, for the pyrolite model of mantle composition.

Same sign dimuon search for heavy majorana mass neutrinos at the CMS experiment at CERN and design studies of a quartz plate calorimeter prototype

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

Clarida, Warren James

2012-12-01

This paper consists of two studies: the results of a search for heavy Majorana neutrinos (N) using an event signature defined by two like-sign charged muons and two jets, and the results from studies of a prototype quartz plate calorimeter. The data in the Majorana search correspond to an integrated luminosity of 5.0 fbmore » $$^{−1}$$ of pp collisions at a centre-of-mass energy of 7 TeV collected with the CMS detector at the Large Hadron Collider. No excess of events are observed beyond the expected standard model background and therefore upper limits are set on the square of the mixing element, $$|V_{\\mu N} |$$as a function of Majorana neutrino mass. These are the first direct upper limits on the heavy Majorana-neutrino mixing for m$$_N$$ > 90 GeV . The second part of this thesis is the results of performance tests of a 20-layer quartz plate calorimeter prototype. The calorimeter prototype was tested at the CERN H2 area in hadronic and electromagnetic configurations, at various en ergies of pion and electron beams. The beam test and simulation results of this prototype are reported.« less

Orifice plate for controlling solids flow, methods of use thereof and articles comprising the same

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

Jukkola, Glen D.; Teigen, Bard C.

Disclosed herein is an orifice plate comprising one or more plates having orifices disposed therein; the orifices being operative to permit the flow of solids from a moving bed heat exchanger to a solids flow control system; where the orifice plate is downstream of a tube bundle of the moving bed heat exchanger and upstream of the solids flow control system and wherein the orifice plate is operative to evenly distribute the flow of solids in the solids flow control system.

Rigidity of Major Plates and Microplates Estimated From GPS Solution GPS2006.0

NASA Astrophysics Data System (ADS)

Kogan, M. G.; Steblov, G. M.

2006-05-01

Here we analyze the rigidity of eight major lithospheric plates using our global GPS solution GPS2006.0. We included all daily observations in interval 1995.0 to 2006.0 collected at IGS stations, as well as observations at many important stations not included in IGS. Loose multiyear solution GPS2006.0 is based on daily solutions by GAMIT software, performed at SOPAC and at Columbia University; those daily solutions were combined by Kalman filter (GLOBK software) into a loose multiyear solution. The constrained solution for station positions and velocities was obtained without a conventional reference frame; instead, we applied translation and rotation in order to best fit the zero velocities of 76 stations in stable plate cores excluding the regions of postglacial rebound. Simultaneously, we estimated relative plate rotation vectors (RV) and the origin translation rate (OTR), and then corrected station velocities for it. Therefore, the velocities in GPS2006.0 are unaffected by the OTR error of ITRF2000 conventionally used to constrain a loose solution. The 1-sigma plate-residual velocity in a stable plate core is less than 1 mm/yr for the plates: Eurasia, Pacific, North and South Americas, Nubia, Australia, and Antarctica; it is 1.4 mm/yr for the Indian plate, most probably because of poorer data quality. Plate-residuals at other established plates (Arabia, Nazca, Caribbean, Philippine) were not assessed for lack of observations. From our analysis, an upper bound for the mobility of the plate inner area is 1 mm/yr. Plate- residual GPS velocities for several hypothesized microplates in east Asia, such as Okhotsk, Amuria, South China, are 3-4 times higher; corresponding strain rates for these microplates are an order of magnitude higher than for Eurasia, North America, and other large plates.

Continuous Spectrum of Crustal Structures and Spreading Processes from Volcanic Rifted Margins to Mid-Ocean Ridges

NASA Astrophysics Data System (ADS)

Karson, J. A.

2016-12-01

Structures generated by seafloor spreading in oceanic crust (and ophiolites) and thick oceanic crust of Iceland show a continuous spectrum of features that formed by similar mechanisms but at different scales. A high magma budget near the Iceland hotspot generates thick (40-25 km) mafic crust in a plate boundary zone about 50 km wide. The upper crust ( 10 km thick) is constructed by the subaxial subsidence and thickening of lavas fed by dense dike swarms over a hot, weak lower crust to produce structures analogous to seaward-dipping reflectors of volcanic rifted margins. Segmented rift zones propagate away from the hotspot creating migrating transform fault zones, microplate-like crustal blocks and rift-parallel strike-slip faults. These structures are decoupled from the underlying lower crustal gabbroic rocks that thin by along-axis flow that reduces the overall crustal thickness and smooths-out local crustal thickness variations. Spreading on mid-ocean ridges with high magma budgets have much thinner crust (10-5 km) generated at a much narrower (few km) plate boundary zone. Subaxial subsidence accommodates the thickening of the upper crust of inward-dipping lavas and outward-dipping dikes about 1-2 km thick over a hot weak lower crust. Along-axis (high-temperature ductile and magmatic) flow of lower crustal material may help account for the relatively uniform seismic thickness of oceanic crust worldwide. Spreading along even slow-spreading mid-ocean ridges near hotspots (e.g., the Reykjanes Ridge) probably have similar features that are transitional between these extremes. In all of these settings, upper crustal and lower crustal structures are decoupled near the plate boundary but eventually welded together as the crust ages and cools. Similar processes are likely to occur along volcanic rifted margins as spreading begins.

Paleostress analysis of the upper-plate rocks of Anafi Island (Cyclades, Greece)

NASA Astrophysics Data System (ADS)

Soukis, Konstantinos; Lozios, Stylianos

2017-04-01

The Attic Cycladic complex (Aegean Sea, Greece) is an area where profound extension, as a result of the Hellenic trench retreat due to slab-rollback, has exhumed mid-crustal rocks to the surface. The remnants of the upper plate are observed in the form of clippen scattered throughout the complex, occupying a very small percentage of the area. Anafi Island, located at the southeastern rim of the Attic-Cycladic complex, represents one of the few areas where a significant part of the upper plate units can be observed and studied. The complex tectonostratigraphy of Anafi Island is characterized by inverted metamorphism and includes a series of medium to high-grade metamorphic rocks that are thrusted onto a non-metamorphosed Paleogene flysch. The uppermost amphibolitic-facies thrust sheets were intruded in the late Cretaceous by intermediate to felsic magmatic rocks. The nappe pile was later destroyed in the late Miocene - Pliocene through successive stages of normal faulting that included both low- and high-angle normal faults. During that stage, supra-detachment syn-extensional sedimentation has taken place thus giving the opportunity to put some age constraints on the fault activity. Paleostress analysis with the separation and stress inversion method TRM revealed two stress tensors that can explain the fault-slip data-set of Anafi Island related to NE-SW and N-S extension, respectively. The older NE-SW trend is related to the late Miocene stress field whereas the N-S is likely related to the present day stress field. These results show that there was a gradual rotation to the trend of least principal stress axis (σ3), that could be associated with regional events such as the escape of Anatolia towards the Aegean and fastest retreat of the Hellenic subduction zone.

Seismic tomographic imaging of P- and S-waves velocity perturbations in the upper mantle beneath Iran

NASA Astrophysics Data System (ADS)

Alinaghi, Alireza; Koulakov, Ivan; Thybo, Hans

2007-06-01

The inverse tomography method has been used to study the P- and S-waves velocity structure of the crust and upper mantle underneath Iran. The method, based on the principle of source-receiver reciprocity, allows for tomographic studies of regions with sparse distribution of seismic stations if the region has sufficient seismicity. The arrival times of body waves from earthquakes in the study area as reported in the ISC catalogue (1964-1996) at all available epicentral distances are used for calculation of residual arrival times. Prior to inversion we have relocated hypocentres based on a 1-D spherical earth's model taking into account variable crustal thickness and surface topography. During the inversion seismic sources are further relocated simultaneously with the calculation of velocity perturbations. With a series of synthetic tests we demonstrate the power of the algorithm and the data to reconstruct introduced anomalies using the ray paths of the real data set and taking into account the measurement errors and outliers. The velocity anomalies show that the crust and upper mantle beneath the Iranian Plateau comprises a low velocity domain between the Arabian Plate and the Caspian Block. This is in agreement with global tomographic models, and also tectonic models, in which active Iranian plateau is trapped between the stable Turan plate in the north and the Arabian shield in the south. Our results show clear evidence of the mainly aseismic subduction of the oceanic crust of the Oman Sea underneath the Iranian Plateau. However, along the Zagros suture zone, the subduction pattern is more complex than at Makran where the collision of the two plates is highly seismic.

Extensional reactivation of the Chocolate Mountains subduction thrust in the Gavilan Hills of southeastern California

USGS Publications Warehouse

Oyarzabal, F.R.; Jacobson, C.E.; Haxel, G.B.

1997-01-01

The NE vergent Chocolate Mountains fault of south-eastern California has been interpreted as either a subduction thrust responsible for burial and prograde metamorphism of the ensimatic Orocopia Schist or as a normal fault involved in the exhumation of the schist. Our detailed structural analysis in the Gavilan Hills area provides new evidence to confirm the latter view. A zone of deformation is present at the top of the Orocopia Schist in which lineations are parallel to those in the upper plate of the Chocolate Mountains fault but oblique to ones at relatively deep levels in the schist. Both the Orocopia Schist and upper plate contain several generations of shear zones that show a transition from crystalloblastic through mylonitic to cataclastic textures. These structures formed during retrograde metamorphism and are considered to record the exhumation of the Orocopia Schist during early Tertiary time as a result of subduction return flow. The Gatuna fault, which places low-grade, supracrustal metasediments of the Winterhaven Formation above the gneisses of the upper plate, also seems to have been active at this time. Final unroofing of the Orocopia Schist occurred during early to middle Miocene regional extension and may have involved a second phase of movement on the Gatuna fault. Formation of the Chocolate Mountains fault during exhumation indicates that its top-to-the-NE sense of movement provides no constraint on the polarity of the Orocopia Schist subduction zone. This weakens the case for a previous model involving SW dipping subduction, while providing support for the view that the Orocopia Schist is a correlative of the Franciscan Complex.

Asthenosphere rheology inferred from observations of the 2012 Indian Ocean earthquake.

PubMed

Hu, Yan; Bürgmann, Roland; Banerjee, Paramesh; Feng, Lujia; Hill, Emma M; Ito, Takeo; Tabei, Takao; Wang, Kelin

2016-10-20

The concept of a weak asthenospheric layer underlying Earth's mobile tectonic plates is fundamental to our understanding of mantle convection and plate tectonics. However, little is known about the mechanical properties of the asthenosphere (the part of the upper mantle below the lithosphere) underlying the oceanic crust, which covers about 60 per cent of Earth's surface. Great earthquakes cause large coseismic crustal deformation in areas hundreds of kilometres away from and below the rupture area. Subsequent relaxation of the earthquake-induced stresses in the viscoelastic upper mantle leads to prolonged postseismic crustal deformation that may last several decades and can be recorded with geodetic methods. The observed postseismic deformation helps us to understand the rheological properties of the upper mantle, but so far such measurements have been limited to continental-plate boundary zones. Here we consider the postseismic deformation of the very large (moment magnitude 8.6) 2012 Indian Ocean earthquake to provide by far the most direct constraint on the structure of oceanic mantle rheology. In the first three years after the Indian Ocean earthquake, 37 continuous Global Navigation Satellite Systems stations in the region underwent horizontal northeastward displacements of up to 17 centimetres in a direction similar to that of the coseismic offsets. However, a few stations close to the rupture area that had experienced subsidence of up to about 4 centimetres during the earthquake rose by nearly 7 centimetres after the earthquake. Our three-dimensional viscoelastic finite-element models of the post-earthquake deformation show that a thin (30-200 kilometres), low-viscosity (having a steady-state Maxwell viscosity of (0.5-10) × 10 18 pascal seconds) asthenospheric layer beneath the elastic oceanic lithosphere is required to produce the observed postseismic uplift.

Surgical interventions for treating acute fractures or non-union of the middle third of the clavicle.

PubMed

Lenza, Mário; Faloppa, Flávio

2015-05-07

This review covers two conditions: acute clavicle fractures and non-union resulting from failed fracture healing. Clavicle (collarbone) fractures account for around 4% of all fractures. While treatment for these fractures is usually non-surgical, some types of clavicular fractures, as well as non-union of the middle third of the clavicle, are often treated surgically. This is an update of a Cochrane review first published in 2009. To evaluate the effects (benefits and harms) of different methods of surgical treatment for acute fracture or non-union of the middle third of the clavicle. We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register (27 June 2014), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2014, Issue 5), MEDLINE (1966 to June week 3 2014), EMBASE (1988 to 2014 week 25), LILACS (1982 to 27 June 2014), trial registries and reference lists of articles. We applied no language or publication restrictions. We considered randomised and quasi-randomised controlled trials evaluating any surgical intervention for treating people with fractures or non-union of the middle third of the clavicle. The primary outcomes were shoulder function or disability, pain and treatment failure (measured by the number of participants who had undergone or were being considered for a non-routine secondary surgical intervention for symptomatic non-union, malunion or other complications). Two review authors selected eligible trials, independently assessed risk of bias and cross-checked data. Where appropriate, we pooled results of comparable trials. We included seven trials in this review with 398 participants. Four trials were new in this update.The four new trials (160 participants) compared intramedullary fixation with open reduction and internal fixation with plate for treating acute middle third clavicle fractures in adults. Low quality evidence from the four trials indicated that intramedullary fixation did not result in a clinically important improvement in upper arm function (despite a statistically significant difference in its favour: standardised mean difference 0.45, 95% confidence interval (CI) 0.08 to 0.81; 120 participants, three trials) at long term follow-up of six months or more. Very low quality evidence indicated little difference between intramedullary fixation and plate fixation in pain (one trial), treatment failure resulting in non-routine surgery (2/68 with intramedullary fixation vs. 3/65 with plate fixation; risk ratio 0.69, 95% CI 0.16 to 2.97, four trials) or time to clinical fracture consolidation (three trials). There was very low quality evidence of a lower incidence of participants with adverse events (mainly infection, poor cosmetic result and symptomatic hardware) in the intramedullary fixation group (18/68 with intramedullary fixation vs. 27/65 with plate fixation; RR 0.64, 95% CI 0.39 to 1.03) but the CI of the pooled results also included the small possibility of a lower incidence in the plate fixation group. None of the four trials reported on quality of life or return to previous activities. Evidence is pending from two ongoing trials, with planned recruitment of 245 participants, testing this comparison.There was low or very low quality evidence from three small trials, each testing a different comparison. The three trials had design features that carried a high risk of bias, potentially limiting the reliability of their findings. Low-contact dynamic compression plates appeared to be associated with significantly better upper-limb function throughout the year following surgery, earlier fracture union and return to work, and a reduced incidence of implant-associated symptoms when compared with a standard dynamic compression plate in 36 adults with symptomatic non-union of the middle third of the clavicle. One quasi-randomised trial (69 participants) compared Knowles pin versus a plate for treating middle third clavicle fractures or non-union. Knowles pins appeared to be associated with lower pain levels and use of postoperative analgesics and a reduced incidence of implant-associated symptoms. One study (133 participants) found that a three-dimensional technique for fixation with a reconstruction plate was associated with a significantly lower incidence of symptomatic delayed union than a standard superior position surgical approach. Evidence is pending from two ongoing trials, with planned recruitment of 130 participants, comparing anterior versus superior plates for acute fractures. There is very limited and low quality evidence available from randomised controlled trials regarding the effectiveness of different methods of surgical fixation of fractures and non-union of the middle third of the clavicle. The evidence from four ongoing trials is likely to inform practice for the comparisons of intramedullary versus plate fixation and anterior versus superior plates for acute fractures in a future update. Further randomised trials are warranted, but in order to optimise research effort, these should be preceded by research that aims to identify priority questions.

Steel test panel helps control additives in pyrophosphate copper plating

NASA Technical Reports Server (NTRS)

Hollar, W. T.

1967-01-01

Test panel helps control maximum tolerance level for plating solution contaminants. It provides low, medium, and high-current density areas such as exist in production plating, and plating is examined for uniformity of texture and ductility.

Compact and Light-Weight Solar Spaceflight Instrument Designs Utilizing Newly Developed Miniature Free-Standing Zone Plates: EUV Radiometer and Limb-Scanning Monochromator

NASA Astrophysics Data System (ADS)

Seely, J. F.; McMullin, D. R.; Bremer, J.; Chang, C.; Sakdinawat, A.; Jones, A. R.; Vest, R.

2014-12-01

Two solar instrument designs are presented that utilize newly developed miniature free-standing zone plates having interconnected Au opaque bars and no support membrane resulting in excellent long-term stability in space. Both instruments are based on a zone plate having 4 mm outer diameter and 1 to 2 degree field of view. The zone plate collects EUV radiation and focuses a narrow bandpass through a pinhole aperture and onto a silicon photodiode detector. As a miniature radiometer, EUV irradiance is accurately determined from the zone plate efficiency and the photodiode responsivity that are calibrated at the NIST SURF synchrotron facility. The EUV radiometer is pointed to the Sun and measures the absolute solar EUV irradiance in high time cadence suitable for solar physics and space weather applications. As a limb-scanning instrument in low earth orbit, a miniature zone-plate monochromator measures the extinction of solar EUV radiation by scattering through the upper atmosphere which is a measure of the variability of the ionosphere. Both instruments are compact and light-weight and are attractive for CubeSats and other missions where resources are extremely limited.

Design and preliminary biomechanical analysis of artificial cervical joint complex.

PubMed

Jian, Yu; Lan-Tao, Liu; Zhao, Jian-ning; Jian-ning, Zhao

2013-06-01

To design an artificial cervical joint complex (ACJC) prosthesis for non-fusion reconstruction after cervical subtotal corpectomy, and to evaluate the biomechanical stability, preservation of segment movements and influence on adjacent inter-vertebral movements of this prosthesis. The prosthesis was composed of three parts: the upper/lower joint head and the middle artificial vertebrae made of Cobalt-Chromium-Molybdenum (Co-Cr-Mo) alloy and polyethylene with a ball-and-socket joint design resembling the multi-axial movement in normal inter-vertebral spaces. Biomechanical tests of intact spine (control), Orion locking plate system and ACJC prosthesis were performed on formalin-fixed cervical spine specimens from 21 healthy cadavers to compare stability, range of motion (ROM) of the surgical segment and ROM of adjacent inter-vertebral spaces. As for stability of the whole lower cervical spine, there was no significant difference of flexion, extension, lateral bending and torsion between intact spine group and ACJC prosthesis group. As for segment movements, difference in flexion, lateral bending or torsion between ACJC prosthesis group and control group was not statistically significant, while ACJC prosthesis group showed an increase in extension (P < 0.05) compared to that of the control group. In addition, ACJC prosthesis group demonstrated better flexion, extension and lateral bending compared to those of Orion plating system group (P < 0.05). Difference in adjacent inter-vertebral ROM of the ACJC prosthesis group was not statistically significant compared to that of the control group. After cervical subtotal corpectomy, reconstruction with ACJC prosthesis not only obtained instant stability, but also reserved segment motions effectively, without abnormal gain of mobility at adjacent inter-vertebral spaces.

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Towards a better classification of unclear eruptive variables: the cases of V2492 Cyg, V350 Cep, and ASASSN-15qi

NASA Astrophysics Data System (ADS)

Jurdana-Šepić, R.; Munari, U.; Antoniucci, S.; Giannini, T.; Lorenzetti, D.

2018-06-01

Context. Eruptive variables are young stars that show episodic variations of brightness: EXors/FUors variations are commonly associated with enhanced accretion outbursts occurring at intermittent cadence of months/years (EXors) and decades/centuries (FUors). Variations that can be ascribed to a variable extinction along their line of sight are instead classified as UXors. Aims: We aim at investigating the long-term photometric behaviour of three sources classified as eruptive variables. We present data from the archival plates of the Asiago Observatory relative to the fields where the targets are located. For the sake of completeness we have also analysed the Harvard plates of the same regions that cover a much longer historical period, albeit at a lower sensitivity, however we are only able to provide upper limits. Methods: A total of 273 Asiago plates were investigated, providing a total of more than 200 magnitudes for the three stars, which cover a period of about 34 yr between 1958 and 1991. We have compared our data with more recently collected literature data. Results: Our plates analysis of V2492 Cyg provides historical upper limits that seem not to be compatible with the level of the activity monitored during the last decade. Therefore, recently observed accretion phenomena could be associated with the outbursting episodes, more than repetitive obscuration. While a pure extinction does not seem the only mechanism responsible for the ASASSN-15qi fluctuations, it can account quite reasonably for the recent V350 Cep variations.

Testing Spatial Correlation of Subduction Interplate Coupling and Forearc Morpho-Tectonics

NASA Technical Reports Server (NTRS)

Goldfinger, Chris; Meigs, Andrew; Meigs, Andrew; Kaye, Grant D.; VanLaningham, Sam

2005-01-01

Subduction zones that are capable of generating great (Mw greater than 8) earthquakes appear to have a common assemblage of forearc morphologic elements. Although details vary, each have (from the trench landward), an accretionary prism, outer arc high, outer forearc basin, an inner forean: basin, and volcanic arc. This pattern is common in spite of great variation in forearc architecture. Because interseismic strain is known to be associated with a locked seismogenic plate interface, we infer that this common forearc morphology is related, in an unknown way, to the process of interseismic Strain accumulation and release in great earthquakes. To date, however, no clear relationship between the subduction process and the common elements of upper plate form has emerged. Whereas certain elements of the system, i.e. the outer arc high, are reasonably well- understood in a structural context, there is little understanding of the structural or topographic evolution of the other key elements like the inner arc and inner forearc basin, particularly with respect to the coupled zone of earthquake generation. This project developed a model of the seismologic, topographic, and uplift/denudation linkages between forearc topography and the subduction system by: 1) comparing geophysical, geodetic, and topographic data from subduction margins that generate large earthquakes; 2) using existing GPS, seismicity, and other data to model the relationship between seismic cycles involving a locked interface and upper-plate topographic development; and 3) using new GPS data and a range-scale topographic, uplift, and denudation analysis of the presently aseismic Cascadia margin to constrain topographic/plate coupling relationships at this poorly understood margin.

The lithosphere-asthenosphere boundary beneath the Korean Peninsula from S receiver functions

NASA Astrophysics Data System (ADS)

Lee, S. H.; Rhie, J.

2017-12-01

The shallow lithosphere in the Eastern Asia at the east of the North-South Gravity Lineament is well published. The reactivation of the upper asthenosphere induced by the subducting plates is regarded as a dominant source of the lithosphere thinning. Additionally, assemblage of various tectonic blocks resulted in complex variation of the lithosphere thickness in the Eastern Asia. Because, the Korean Peninsula located at the margin of the Erasian Plate in close vicinity to the trench of subducting oceanic plate, significant reactivation of the upper asthenosphere is expected. For the study of the tectonic history surrounding the Korean Peninsula, we determined the lithosphere-asthenosphere boundary (LAB) beneath the Korean Peninsula using common conversion point stacking method with S receiver functions. The depth of the LAB beneath the Korean Peninsula ranges from 60 km to 100 km and confirmed to be shallower than that expected for Cambrian blocks as previous global studies. The depth of the LAB is getting shallower to the south, 95 km at the north and 60 km at the south. And rapid change of the LAB depth is observed between 36°N and 37°N. The depth change of the LAB getting shallower to the south implies that the source of the lithosphere thinning is a hot mantle upwelling induced by the northward subduction of the oceanic plates since Mesozoic. Unfortunately, existing tectonic models can hardly explain the different LAB depth in the north and in the south as well as the rapid change of the LAB depth.

Constructing a Teleseismic Tomographic Image of Taiwan using BATS Recordings

NASA Astrophysics Data System (ADS)

Krajewski, J.; Roecker, S.

2005-12-01

Taiwan is an evolving arc-continent collision located at a complicated part of the plate boundary between the Eurasian and Philippine Sea plates. To better understand the role of the upper mantle in the dynamics of this collision, we reviewed 4 years of data from the Broadband Array in Taiwan for Seismology (BATS) in Taiwan to construct a teleseismic dataset for tomographic imaging of the subsurface of the island. From an initial selection of approximately 300 events, we used waveform correlation to generate a dataset of 4500 relative arrival times. To calculate accurate travel times in three dimensional wavespeed models over the large lateral distances in our model (~800 km), we solve the eikonal equation directly in a spherical coordinate system. We reduce the influence of smearing of crustal heterogeneity into the deeper mantle, we fix the upper 30 km to a previously determined P wavespeed model for the region. Initial resolution tests suggest a spatial limit on the order of 40 km.

Evidence for strong lateral seismic velocity variation in the lower crust and upper mantle beneath the California margin

USGS Publications Warehouse

Lai, Voon; Graves, Robert; Wei, Shengji; Helmberger, Don

2017-01-01

Regional seismograms from earthquakes in Northern California show a systematic difference in arrival times across Southern California where long period (30–50 seconds) SH waves arrive up to 15 seconds earlier at stations near the coast compared with sites towards the east at similar epicentral distances. We attribute this time difference to heterogeneity of the velocity structure at the crust-mantle interface beneath the California margin. To model these observations, we propose a fast seismic layer, with thickness growing westward from the San Andreas along with a thicker and slower continental crust to the east. Synthetics generated from such a model are able to match the observed timing of SH waveforms better than existing 3D models. The presence of a strong upper mantle buttressed against a weaker crust has a major influence in how the boundary between the Pacific plate and North American plate deforms and may explain the observed asymmetric strain rate across the boundary.

Where and why do large shallow intraslab earthquakes occur?

NASA Astrophysics Data System (ADS)

Seno, Tetsuzo; Yoshida, Masaki

2004-03-01

We try to find how often, and in what regions large earthquakes ( M≥7.0) occur within the shallow portion (20-60 km depth) of a subducting slab. Searching for events in published individual studies and the Harvard University centroid moment tensor catalogue, we find twenty such events in E. Hokkaido, Kyushu-SW, Japan, S. Mariana, Manila, Sumatra, Vanuatu, N. Chile, C. Peru, El Salvador, Mexico, N. Cascadia and Alaska. Slab stresses revealed from the mechanism solutions of these large intraslab events and nearby smaller events are almost always down-dip tensional. Except for E. Hokkaido, Manila, and Sumatra, the upper plate shows horizontal stress gradient in the arc-perpendicular direction. We infer that shear tractions are operating at the base of the upper plate in this direction to produce the observed gradient and compression in the outer fore-arc, balancing the down-dip tensional stress of the slab. This tectonic situation in the subduction zone might be realized as part of the convection system with some conditions, as shown by previous numerical simulations.

Compressive failure modes and parameter optimization of the trabecular structure of biomimetic fully integrated honeycomb plates.

PubMed

Chen, Jinxiang; Tuo, Wanyong; Zhang, Xiaoming; He, Chenglin; Xie, Juan; Liu, Chang

2016-12-01

To develop lightweight biomimetic composite structures, the compressive failure and mechanical properties of fully integrated honeycomb plates were investigated experimentally and through the finite element method. The results indicated that: fracturing of the fully integrated honeycomb plates primarily occurred in the core layer, including the sealing edge structure. The morphological failures can be classified into two types, namely dislocations and compactions, and were caused primarily by the stress concentrations at the interfaces between the core layer and the upper and lower laminations and secondarily by the disordered short-fiber distribution in the material; although the fully integrated honeycomb plates manufactured in this experiment were imperfect, their mass-specific compressive strength was superior to that of similar biomimetic samples. Therefore, the proposed bio-inspired structure possesses good overall mechanical properties, and a range of parameters, such as the diameter of the transition arc, was defined for enhancing the design of fully integrated honeycomb plates and improving their compressive mechanical properties. Copyright © 2016 Elsevier B.V. All rights reserved.

Wave propagation in magneto-electro-elastic multilayered plates with nonlocal effect

NASA Astrophysics Data System (ADS)

Chen, Jiangyi; Guo, Junhong; Pan, Ernian

2017-07-01

In this paper, analytical solutions for propagation of time-harmonic waves in three-dimensional, transversely isotropic, magnetoelectroelastic and multilayered plates with nonlocal effect are derived. We first convert the time-harmonic wave problem into a linear eigenvalue system, from which we obtain the general solutions of the extended displacements and stresses. The solutions are then employed to derive the propagator matrix which connects the field variables at the upper and lower interfaces of each layer. Making use of the continuity conditions of the physical quantities across the interface, the global propagator relation is assembled by propagating the solutions in each layer from the bottom to the top of the layered plate. From the global propagator matrix, the dispersion equation is obtained by imposing the traction-free boundary conditions on both the top and bottom surfaces of the layered plate. Dispersion curves and mode shapes in layered plates made of piezoelectric BaTiO3 and magnetostrictive CoFe2O4 materials are presented to show the influence of the nonlocal parameter, stacking sequence, as well as the orientation of incident wave on the time-harmonic field response.

Crust and Upper Mantle Structure Beneath Tibet and SW China From Seismic Tomography and Array Analysis

NASA Astrophysics Data System (ADS)

van der Hilst, R. D.; Li, C.; Yao, H.; Sun, R.; Meltzer, A. S.

2007-12-01

We will present a summary of the results of our seismological studies of crust and upper mantle heterogeneity and anisotropy beneath Tibet and SW China with data from temporary (PASSCAL) arrays as well as other regional, national, and global networks. In 2003 and 2004 MIT and CIGMR (Chengdu Institute of Geology and Mineral Resources) operated a 25 station array (3-component, broad band seismometers) in Sichuan and Yunnan provinces, SW China; during the same period Lehigh University (also in collaboration with CIGMR) operated a 75 station array in east Tibet. Data from these arrays allow delineation of mantle structure in unprecedented detail. We focus our presentation on results of two lines of seismological study. Travel time tomography (Li et al., PEPI, 2006; EPSL, 2007) with hand-picked phase arrivals from recordings at regional arrays, and combined with data from over 1,000 stations in China and with the global data base due to Engdahl et al. (BSSA, 1998), reveals substantial the structural complexity of the upper mantle beneath SE Asia. In particular, structures associated with subduction of the Indian plate beneath the Himalayas vary significantly from west Tibet (where the plate seems to have underthrusted the entire plateau) to east Tibet (where P-wave tomography provides no evidence for the presence of fast lithosphere beneath the Plateau proper). Further east, fast structures appear in the upper mantle transition zone, presumably related to stagnation of slab fragments associated with subduction of the Pacific plate. (2) Surface wave array tomography (Yao et al., GJI, 2006, 2007), using ambient noise interferometry and traditional (inter station) dispersion analysis, is used to delineate the 3-D structure of the crust and lithospheric mantle at length scales as small as 100 km beneath the MIT and Lehigh arrays. This analysis reveals a complex spatial distribution of intra-crustal low velocity zones (which may imply that crustal-scale faults influence the pattern of middle/lower crustal flow). We will also show preliminary results of surface wave inversion for azimuthal anisotropy, which - combined with previous results from shear wave splitting (Lev et al., EPSL, 2006) - give insight into the deformation of the upper mantle beneath the area under study.

Neurothekeoma palpebrae in association with multiple superficial angiomyxomas: Tegumental Angiomyxoma-Neurothekeoma syndrome (TAN syndrome).

PubMed

Kah, Tan Aik; Yong, Ku Chui; Annuar, Faridah Hanom

2011-07-01

We report a case of 10-year-old Indian girl with history of multiple superficial angiomyxoma, presented with three months history of painless right upper lid swelling. There were no visual dysfunctions. Previously, the patient had multiple superficial angiomyxoma (left pinna, left upper cheek, left upper limb, chest, right axilla, hard palate) and epidermal cyst (chin). The histopathological specimens were negative to S-100 protein antibody. Systemic review and family history was unremarkable. Excision biopsy and upper lid reconstruction were performed. Intraoperatively the tumor was multilobulated, firm, well encapsulated and did not invade the underlying tarsal plate. Histopathological features of the upperlid tumor were consistent with nerves sheath myxoma (neurothekeoma). To the best of the authors' knowledge, this is the first reported case of neurothekeoma in association with multiple superficial angiomyxoma.

Neurothekeoma palpebrae in association with multiple superficial angiomyxomas: Tegumental Angiomyxoma-Neurothekeoma syndrome (TAN syndrome)

PubMed Central

Kah, Tan Aik; Yong, Ku Chui; Annuar, Faridah Hanom

2011-01-01

We report a case of 10-year-old Indian girl with history of multiple superficial angiomyxoma, presented with three months history of painless right upper lid swelling. There were no visual dysfunctions. Previously, the patient had multiple superficial angiomyxoma (left pinna, left upper cheek, left upper limb, chest, right axilla, hard palate) and epidermal cyst (chin). The histopathological specimens were negative to S-100 protein antibody. Systemic review and family history was unremarkable. Excision biopsy and upper lid reconstruction were performed. Intraoperatively the tumor was multilobulated, firm, well encapsulated and did not invade the underlying tarsal plate. Histopathological features of the upperlid tumor were consistent with nerves sheath myxoma (neurothekeoma). To the best of the authors’ knowledge, this is the first reported case of neurothekeoma in association with multiple superficial angiomyxoma. PMID:24765328

Insight into collision zone dynamics from topography: numerical modelling results and observations

NASA Astrophysics Data System (ADS)

Bottrill, A. D.; van Hunen, J.; Allen, M. B.

2012-07-01

Dynamic models of subduction and continental collision are used to predict dynamic topography changes on the overriding plate. The modelling results show a distinct evolution of topography on the overriding plate, during subduction, continental collision and slab break-off. A prominent topographic feature is a temporary (few Myrs) deepening in the area of the back arc-basin after initial collision. This collisional mantle dynamic basin (CMDB) is caused by slab steepening drawing material away from the base of the overriding plate. Also during this initial collision phase, surface uplift is predicted on the overriding plate between the suture zone and the CMDB, due to the subduction of buoyant continental material and its isostatic compensation. After slab detachment, redistribution of stresses and underplating of the overriding plate causes the uplift to spread further into the overriding plate. This topographic evolution fits the stratigraphy found on the overriding plate of the Arabia-Eurasia collision zone in Iran and south east Turkey. The sedimentary record from the overriding plate contains Upper Oligocene-Lower Miocene marine carbonates deposited between terrestrial clastic sedimentary rocks, in units such as the Qom Formation and its lateral equivalents. This stratigraphy shows that during the Late Oligocene-Early Miocene the surface of the overriding plate sank below sea level before rising back above sea level, without major compressional deformation recorded in the same area. This uplift and subsidence pattern correlates well with our modelled topography changes.

Sensitive far uv spectrograph with a multispectral element microchannel plate detector for rocket-borne astronomy.

PubMed

Weiser, H; Vitz, R C; Moos, H W; Weinstein, A

1976-12-01

An evacuated high transmission prism spectrograph using a microchannel plate detection system with resistive strip readout was flown behind a precision pointing telescope on a sounding rocket. The construction, preparation, flight performance, and calibration stability of the system are discussed. Despite the adverse environmental conditions associated with sounding rocket flights, the microchannel detector system performed well. Far uv spectra (1160-1750 A) of stellar and planetary objects were obtained; spectral features with fluxes as low as 0.06 photons cm(-2) sec(-1) were detectable. This was achieved by operating the plates at lower than normal gains, using sensitive pulse counting electronics with both upper and lower limit discriminators, and maintaining the spectrograph and detector at a pressure of ~10(-6) Torr until reaching altitude.

Analog modelling of obduction processes

NASA Astrophysics Data System (ADS)

Agard, P.; Zuo, X.; Funiciello, F.; Bellahsen, N.; Faccenna, C.; Savva, D.

2012-04-01

Obduction corresponds to one of plate tectonics oddities, whereby dense, oceanic rocks (ophiolites) are presumably 'thrust' on top of light, continental ones, as for the short-lived, almost synchronous Peri-Arabic obduction (which took place along thousands of km from Turkey to Oman in c. 5-10 Ma). Analog modelling experiments were performed to study the mechanisms of obduction initiation and test various triggering hypotheses (i.e., plate acceleration, slab hitting the 660 km discontinuity, ridge subduction; Agard et al., 2007). The experimental setup comprises (1) an upper mantle, modelled as a low-viscosity transparent Newtonian glucose syrup filling a rigid Plexiglas tank and (2) high-viscosity silicone plates (Rhodrosil Gomme with PDMS iron fillers to reproduce densities of continental or oceanic plates), located at the centre of the tank above the syrup to simulate the subducting and the overriding plates - and avoid friction on the sides of the tank. Convergence is simulated by pushing on a piston at one end of the model with velocities comparable to those of plate tectonics (i.e., in the range 1-10 cm/yr). The reference set-up includes, from one end to the other (~60 cm): (i) the piston, (ii) a continental margin containing a transition zone to the adjacent oceanic plate, (iii) a weakness zone with variable resistance and dip (W), (iv) an oceanic plate - with or without a spreading ridge, (v) a subduction zone (S) dipping away from the piston and (vi) an upper, active continental margin, below which the oceanic plate is being subducted at the start of the experiment (as is known to have been the case in Oman). Several configurations were tested and over thirty different parametric tests were performed. Special emphasis was placed on comparing different types of weakness zone (W) and the extent of mechanical coupling across them, particularly when plates were accelerated. Displacements, together with along-strike and across-strike internal deformation in all plates were systematically measured, allowing for a very precise and reproducible tracking of deformation. Experiments demonstrate that obduction chiefly depends on how the overall shortening (or convergence) is partitionned between the weakness zone (W) and the preexisting subduction zone (S). Conditions favorable to obduction are shown to correspond to a specific range of coupling across (S) and resistance across (W). Our results thereby (1) constrain the range of physical conditions required for obduction to develop/nucleate and (2) underline the key role of acceleration for triggering obduction (rather than ridge subduction or slab resistance to penetration at the 660 km discontinuity). They also demonstrate that the emplacement of dense, oceanic material on continental lithosphere is not a mysterious process but results from some large scale, normal subduction process that do not require exotic boundary conditions. Agard P., Jolivet L., Vrielynck B., Burov E. & Monié P., 2007. Plate acceleration : the obduction trigger? Earth and Planetary Science Letters, 258, 428-441.

KSC-2010-5293

NASA Image and Video Library

2010-10-21

CAPE CANAVERAL, Fla. -- At NASA's Kennedy Space Center in Florida, testing of the Tilt-Up Umbilical Arm (TUUA) prototype's Environmental Control System Quick Disconnect takes place in the Launch Equipment Test Facility's 6,000-square-foot high bay. The prototype is used to demonstrate the safe disconnect and retraction of ground umbilical plates and associated hardware of a launch vehicle's upper stage and service module. The Environmental Control System consists of regulated air, which would be used to purge an inner tank and crew module. Since 1977, the facility has supported NASA’s Launch Services, shuttle, International Space Station, and Constellation programs, as well as commercial providers. The facility recently underwent a major upgrade to support even more programs, projects and customers. It houses a cable fabrication and molding shop, pneumatics shop, machine and weld shop and full-scale control room. Outside, the facility features a water flow test loop, vehicle motion simulator, 600-ton test fixture, launch simulation towers and a cryogenic system. Photo credit: NASA/Jack Pfaller

KSC-2010-5290

NASA Image and Video Library

2010-10-21

CAPE CANAVERAL, Fla. -- At NASA's Kennedy Space Center in Florida, testing of the Tilt-Up Umbilical Arm (TUUA) prototype's Environmental Control System Quick Disconnect takes place in the Launch Equipment Test Facility's 6,000-square-foot high bay. The prototype is used to demonstrate the safe disconnect and retraction of ground umbilical plates and associated hardware of a launch vehicle's upper stage and service module. The Environmental Control System consists of regulated air, which would be used to purge an inner tank and crew module. Since 1977, the facility has supported NASA’s Launch Services, shuttle, International Space Station, and Constellation programs, as well as commercial providers. The facility recently underwent a major upgrade to support even more programs, projects and customers. It houses a cable fabrication and molding shop, pneumatics shop, machine and weld shop and full-scale control room. Outside, the facility features a water flow test loop, vehicle motion simulator, 600-ton test fixture, launch simulation towers and a cryogenic system. Photo credit: NASA/Jack Pfaller

KSC-2010-5292

NASA Image and Video Library

2010-10-21

CAPE CANAVERAL, Fla. -- At NASA's Kennedy Space Center in Florida, testing of the Tilt-Up Umbilical Arm (TUUA) prototype's Environmental Control System Quick Disconnect takes place in the Launch Equipment Test Facility's 6,000-square-foot high bay. The prototype is used to demonstrate the safe disconnect and retraction of ground umbilical plates and associated hardware of a launch vehicle's upper stage and service module. The Environmental Control System consists of regulated air, which would be used to purge an inner tank and crew module. Since 1977, the facility has supported NASA’s Launch Services, shuttle, International Space Station, and Constellation programs, as well as commercial providers. The facility recently underwent a major upgrade to support even more programs, projects and customers. It houses a cable fabrication and molding shop, pneumatics shop, machine and weld shop and full-scale control room. Outside, the facility features a water flow test loop, vehicle motion simulator, 600-ton test fixture, launch simulation towers and a cryogenic system. Photo credit: NASA/Jack Pfaller

KSC-2010-5291

NASA Image and Video Library

2010-10-21

CAPE CANAVERAL, Fla. -- At NASA's Kennedy Space Center in Florida, testing of the Tilt-Up Umbilical Arm (TUUA) prototype's Environmental Control System Quick Disconnect takes place in the Launch Equipment Test Facility's 6,000-square-foot high bay. The prototype is used to demonstrate the safe disconnect and retraction of ground umbilical plates and associated hardware of a launch vehicle's upper stage and service module. The Environmental Control System consists of regulated air, which would be used to purge an inner tank and crew module. Since 1977, the facility has supported NASA’s Launch Services, shuttle, International Space Station, and Constellation programs, as well as commercial providers. The facility recently underwent a major upgrade to support even more programs, projects and customers. It houses a cable fabrication and molding shop, pneumatics shop, machine and weld shop and full-scale control room. Outside, the facility features a water flow test loop, vehicle motion simulator, 600-ton test fixture, launch simulation towers and a cryogenic system. Photo credit: NASA/Jack Pfaller

Tomographic Imaging of the Cascadia Subduction Zone and Juan de Fuca Plate System: Improved Methods Eliminate Artifacts and Reveal New Structures

NASA Astrophysics Data System (ADS)

Bodmer, M.; Toomey, D. R.; Hooft, E. E. E.; Bezada, M.; Schmandt, B.; Byrnes, J. S.

2017-12-01

Amphibious studies of subduction zones promise advances in understanding links between incoming plate structure, the subducting slab, and the upper mantle beneath the slab. However, joint onshore/offshore imaging is challenging due to contrasts between continental and oceanic structure. We present P-wave teleseismic tomography results for the Cascadia subduction zone (CSZ) that utilize existing western US datasets, amphibious seismic data from the Cascadia Initiative, and tomographic algorithms that permit 3D starting models, nonlinear ray tracing, and finite frequency kernels. Relative delay times show systematic onshore/offshore trends, which we attribute to structure in the upper 50 km. Shore-crossing CSZ seismic refraction models predict relative delays >1s, with equal contributions from elevation and crustal thickness. We use synthetic data to test methods of accounting for such shallow structure. Synthetic tests using only station static terms produce margin-wide, sub-slab low-velocity artifacts. Using a more realistic a priori 3D model for the upper 50 km better reproduces known input structures. To invert the observed delays, we use data-constrained starting models of the CSZ. Our preferred models utilize regional surface wave studies to construct a starting model, directly account for elevation, and use 3D nonlinear ray tracing. We image well-documented CSZ features, including the subducted slab down to 350 km, along strike slab variations below 150 km, and deep slab fragmentation. Inclusion of offshore data improves resolution of the sub-slab mantle, where we resolve localized low-velocity anomalies near the edges of the CSZ (beneath the Klamath and Olympic mountains). Our new imaging and resolution tests indicate that previously reported margin-wide, sub-slab low-velocity asthenospheric anomalies are an imaging artifact. Offshore, we observe low-velocity anomalies beneath the Gorda plate consistent with regional deformation and broad upwelling resulting from plate stagnation. At the Juan de Fuca Ridge we observe asymmetric low-velocity anomalies consistent with dynamic upwelling. Our results agree with recent offshore tomography studies using S wave data; however, differences in the recovered relative amplitudes are likely due to anisotropy, which we are exploring.

Method for controlling protein crystallization

NASA Technical Reports Server (NTRS)

Noever, David A. (Inventor)

1993-01-01

A method and apparatus for controlling the crystallization of protein by solvent evaporation including placing a drop of protein solution between and in contact with a pair of parallel plates and driving one of the plates toward and away from the other plate in a controlled manner to adjust the spacing between the plates is presented. The drop of solution forms a liquid cylinder having a height dependent upon the plate spacing thereby effecting the surface area available for solvent evaporation. When the spacing is close, evaporation is slow. Evaporation is increased by increasing the spacing between the plates until the breaking point of the liquid cylinder. One plate is mounted upon a fixed post while the other plate is carried by a receptacle movable relative to the post and driven by a belt driven screw drive. The temperature and humidity of the drop of protein solution are controlled by sealing the drop within the receptacle and mounting a heater and dessicant within the receptacle.

Method and apparatus for actively controlling a micro-scale flexural plate wave device

DOEpatents

Dohner, Jeffrey L.

2001-01-01

An actively controlled flexural plate wave device provides a micro-scale pump. A method of actively controlling a flexural plate wave device produces traveling waves in the device by coordinating the interaction of a magnetic field with actively controlled currents. An actively-controlled flexural plate wave device can be placed in a fluid channel and adapted for use as a micro-scale fluid pump to cool or drive micro-scale systems, for example, micro-chips, micro-electrical-mechanical devices, micro-fluid circuits, or micro-scale chemical analysis devices.

Design and Fabrication of Quadrupole Ion Mass Spectrometer for Upper Atmosphere.

DTIC Science & Technology

1981-09-30

34 diameter con-flat flange were T.I.G. welded to the end of each of three bowls. All bowls were then electro- polished, cleaned and sent out to have...plated surface was .0001" to .0002" thick. After gold plating, the hemispheres were mated and T.I.G. welded to form a sphere with a con-flat flange at...Valve Rotatable Conflat to fit k" Swage Lock Weld Adaptors. 5 2 3/4" Conflat Flanges machined to fit Swage Lock unions. 12 10-24 x 2 " Brass Screws necket

The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries

NASA Technical Reports Server (NTRS)

Soloman, Sean C.

1991-01-01

The focus of the research was in two broad areas: (1) the nature and dynamics of time dependent deformation and stress along major seismic zones; and (2) the nature of long wavelength oceanic geoid anomalies in terms of lateral variations in upper mantle temperature and composition. The principle findings of the research are described in the accompanying appendices. The first two and the fourth appendices are reprints of papers recently submitted for publication, and the third is the abstract of a recently completed thesis supported by this project.

Origin of dipping structures in fast-spreading oceanic lower crust offshore Alaska imaged by multichannel seismic data

NASA Astrophysics Data System (ADS)

Bécel, Anne; Shillington, Donna J.; Nedimović, Mladen R.; Webb, Spahr C.; Kuehn, Harold

2015-08-01

Multi-channel seismic (MCS) reflection profiles across the Pacific Plate south of the Alaska Peninsula reveal the internal structure of mature oceanic crust (48-56 Ma) formed at fast to intermediate spreading rates during and after a major plate re-organization. Oceanic crust formed at fast spreading rates (half spreading rate ∼ 74 mm /yr) has smoother basement topography, thinner sediment cover with less faulting, and an igneous section that is at least 1 km thicker than crust formed at intermediate spreading rates (half spreading rate ∼ 28- 34 mm /yr). MCS data across fast-spreading oceanic crust formed during plate re-organization contain abundant bright reflections, mostly confined to the lower crust above a highly reflective Moho transition zone, which has a reflection coefficient (RC) of ∼0.1. The lower crustal events dip predominantly toward the paleo-ridge axis at ∼10-30°. Reflections are also imaged in the uppermost mantle, which primarily dip away from the ridge at ∼10-25°, the opposite direction to those observed in the lower crust. Dipping events in both the lower crust and upper mantle are absent on profiles acquired across the oceanic crust formed at intermediate spreading rates emplaced after plate re-organization, where a Moho reflection is weak or absent. Our preferred interpretation is that the imaged lower crustal dipping reflections within the fast spread crust arise from shear zones that form near the spreading center in the region characterized by interstitial melt. The abundance and reflection amplitude strength of these events (RC ∼ 0.15) can be explained by a combination of solidified melt that was segregated within the shear structures, mylonitization of the shear zones, and crystal alignment, all of which can result in anisotropy and constructive signal interference. Formation of shear zones with this geometry requires differential motion between the crust and upper mantle, where the upper mantle moves away from the ridge faster than the crust. Active asthenospheric upwelling is one possible explanation for these conditions. The other possible interpretation is that lower crustal reflections are caused by magmatic (mafic/ultramafic) layering associated with accretion from a central mid-crustal magma chamber. Considering that the lower crustal dipping events have only been imaged in regions that have experienced plate re-organizations associated with ridge jumps or rift propagation, we speculate that locally enhanced mantle flow associated with these settings may lead to differential motion between the crust and the uppermost mantle, and therefore to shearing in the ductile lower crust or, alternatively, that plate reorganization could produce magmatic pulses which may lead to mafic/ultramafic banding.

Cenozoic evolution of the Yakutat-North American collision zone and structural accommodation of St. Elias syntaxis exhumation, Alaska/Yukon

NASA Astrophysics Data System (ADS)

Falkowski, Sarah; Enkelmann, Eva; Ehlers, Todd

2016-04-01

Active convergent margins potentially pose multiple natural hazards to human life and infrastructure. Tectonic strain may be further focused where convergent margins are warped into broad syntaxes. However, the processes responsible for upper plate deformation in these settings are not well understood. The St. Elias syntaxis in southeast Alaska and southwest Yukon is located at the eastern corner of the Yakutat microplate, which indents into the North American Plate and subducts at a flat angle beneath Alaska. High rates of long-term glacial erosion and exhumation (>2 mm/yr) are found on the southern, coastal flanks of the St. Elias orogen, but the deepest and most rapid exhumation is focused at the St. Elias syntaxis. In this location, transform motion transitions into subduction of the wedge-shaped, oceanic plateau of the Yakutat microplate. In order to map the spatio-temporal pattern of exhumation in the Yakutat-North American collision zone, we conducted zircon and apatite fission-track analyses of predominantly detrital, sand-sized material and five bedrock samples from 47 different glacio-fluvial catchments covering an area of ~45,000 km2 around the St. Elias syntaxis. Integration of the new thermochronologic data with prior work and other geologic and geophysical observations yielded information on past terrane accretion events at the North American margin since the late Mesozoic and the evolution of exhumation at the St. Elias syntaxis in the context of the ongoing Yakutat-North American plate collision. Our results indicate a migrating focus of the most rapid exhumation from north to south and from the upper (North American Plate) to the lower (Yakutat microplate) plate in the syntaxis area over the past ~10 Myr. This migration occurred in response to a change in plate motions, increasingly thicker crust of the subducting Yakutat microplate, and changes in surface processes after glaciation began that resulted in modification of the rheology. We propose a positive, two-sided flower structure to have accommodated the rapid, and temporarily deep (~10 km), exhumation.

The depth range of azimuthal anisotropy beneath Southern California via analyses of long-period Rayleigh-waves

NASA Astrophysics Data System (ADS)

Tsang, Stephanie Doris

The motion of the mantle beneath the tectonic plates is still unknown. Mantle shears associated with flow generate anisotropy. In order to investigate the anisotropic properties within the Earth to a range of depths within the crust and upper mantle (and perhaps beyond), long-period Rayleigh waves (periods of 51:282 ≤ T ≤ 333:33 seconds) are used in this study. One model suggests that the fast axis orientation, arising from the preferential alignment of olivine crystal grains in the upper mantle, coincides with the direction of absolute plate motion of the North-American plate. Other models suggest it is aligned with the direction of relative plate motion of the Pacific and North-American plates. A third suggests that an eastward mantle flow occurs beneath the North-American plate. There is also controversy as to the depth to which anisotropy is generated. In this thesis, the Rayleigh-wave phase velocities' dependence on a seismic event's back-azimuth angle is explored within the Southern California Seismic Network (SCSN). Because surface wave velocities vary depending on the range of depth into the Earth sampled by each period, an observed deviation of the resulting phase velocity calculations for a wide range of back-azimuth angles, (6° to 349°) with respect to a reference dispersion curve of the area, provides information on the anisotropy of the subsurface structure. Further work on the fast-axis orientation and its tectonic implications is carried out here. I find that the 2 directions 270° = 90° and 290° = 110° are possible fast-axes orientations. I also find that the amplitude of azimuthal anisotropy is insufficient to explain birefringence of S-body waves, also known as SKS splitting, suggesting that it occurs much deeper than previously thought, perhaps all the way to the transition zone. Future work might involve array analysis of Love-wave components using the beamforming approach. This approach should prove effective in yielding further insight into the heterogeneity of the subsurface structure beneath Southern California.

Development and Experimental Evaluation of Passive Fuel Cell Thermal Control

NASA Technical Reports Server (NTRS)

Colozza, Anthony J.; Jakupca, Ian J.; Castle, Charles H.; Burke, Kenneth A.

2014-01-01

To provide uniform cooling for a fuel cell stack, a cooling plate concept was evaluated. This concept utilized thin cooling plates to extract heat from the interior of a fuel cell stack and move this heat to a cooling manifold where it can be transferred to an external cooling fluid. The advantages of this cooling approach include a reduced number of ancillary components and the ability to directly utilize an external cooling fluid loop for cooling the fuel cell stack. A number of different types of cooling plates and manifolds were developed. The cooling plates consisted of two main types; a plate based on thermopyrolytic graphite (TPG) and a planar (or flat plate) heat pipe. The plates, along with solid metal control samples, were tested for both thermal and electrical conductivity. To transfer heat from the cooling plates to the cooling fluid, a number of manifold designs utilizing various materials were devised, constructed, and tested. A key aspect of the manifold was that it had to be electrically nonconductive so it would not short out the fuel cell stack during operation. Different manifold and cooling plate configurations were tested in a vacuum chamber to minimize convective heat losses. Cooling plates were placed in the grooves within the manifolds and heated with surface-mounted electric pad heaters. The plate temperature and its thermal distribution were recorded for all tested combinations of manifold cooling flow rates and heater power loads. This testing simulated the performance of the cooling plates and manifold within an operational fuel cell stack. Different types of control valves and control schemes were tested and evaluated based on their ability to maintain a constant temperature of the cooling plates. The control valves regulated the cooling fluid flow through the manifold, thereby controlling the heat flow to the cooling fluid. Through this work, a cooling plate and manifold system was developed that could maintain the cooling plates within a minimal temperature band with negligible thermal gradients over power profiles that would be experienced within an operating fuel cell stack.

Biomechanical performance of rigid compared to dynamic anterior cervical plating: analysis of adjacent upper and lower level compressive forces.

PubMed

Connor, David E; Shamieh, Khader Samer; Ogden, Alan L; Mukherjee, Debi P; Sin, Anthony; Nanda, Anil

2012-12-01

Dynamic anterior cervical plating is well established as a means of enhancing graft loading and subsequent arthrodesis. Current concerns center on the degree of adjacent-level stress induced by these systems. The aim of this study was to evaluate and compare the load transferred to adjacent levels for single-level anterior cervical discectomy and fusion utilizing rigid compared to dynamic anterior plating systems. Nine cadaveric adult human cervical spine specimens were subjected to range-of-motion testing prior to and following C5-C6 anterior cervical discectomy and fusion procedures. Interbody grafting was performed with human fibula tissue. Nondestructive biomechanical testing included flexion/extension and lateral bending loading modes. A constant displacement of 5mm was applied in each direction and the applied load was measured in newtons (N). Specimens were tested in the following order: intact, following discectomy, after rigid plating, then after dynamic plating. Adjacent level (C4-C5 [L(S)] and C6-C7 [L(I)]) compressive forces were measured using low profile load cells inserted into each disc space. The measured load values for plating systems were then normalized using values measured for the intact specimens. Mean loads transferred to L(S) and L(I) during forced flexion in specimens with rigid plating were 23.47 N and 8.76 N, respectively; while the corresponding values in specimens with dynamic plating were 18.55 N and 1.03 N, respectively. Dynamic plating yielded no significant change at L(I) and a 21.0% decrease in load at L(S) when compared with rigid plating, although the difference was not significant. The observed trend suggests that dynamic plating may diminish superior adjacent level compressive stresses. Copyright © 2012 Elsevier Ltd. All rights reserved.

The eastern Black Sea-Caucasus region during the Cretaceous: New evidence to constrain its tectonic evolution

NASA Astrophysics Data System (ADS)

Sosson, Marc; Stephenson, Randell; Sheremet, Yevgeniya; Rolland, Yann; Adamia, Shota; Melkonian, Rafael; Kangarli, Talat; Yegorova, Tamara; Avagyan, Ara; Galoyan, Ghazar; Danelian, Taniel; Hässig, Marc; Meijers, Maud; Müller, Carla; Sahakyan, Lilit; Sadradze, Nino; Alania, Victor; Enukidze, Onice; Mosar, Jon

2016-01-01

We report new observations in the eastern Black Sea-Caucasus region that allow reconstructing the evolution of the Neotethys in the Cretaceous. At that time, the Neotethys oceanic plate was subducting northward below the continental Eurasia plate. Based on the analysis of the obducted ophiolites that crop out throughout Lesser Caucasus and East Anatolides, we show that a spreading center (AESA basin) existed within the Neotethys, between Middle Jurassic and Early Cretaceous. Later, the spreading center was carried into the subduction with the Neotethys plate. We argue that the subduction of the spreading center opened a slab window that allowed asthenospheric material to move upward, in effect thermally and mechanically weakening the otherwise strong Eurasia upper plate. The local weakness zone favored the opening of the Black Sea back-arc basins. Later, in the Late Cretaceous, the AESA basin obducted onto the Taurides-Anatolides-South Armenia Microplate (TASAM), which then collided with Eurasia along a single suture zone (AESA suture).

The Nazca-South American convergence rate and the recurrence of the great 1960 Chilean earthquake

NASA Technical Reports Server (NTRS)

Stein, S.; Engeln, J. F.; Demets, C.; Gordon, R. G.; Woods, D.

1986-01-01

The seismic slip rate along the Chile Trench estimated from the slip in the great 1960 earthquake and the recurrence history of major earthquakes has been interpreted as consistent with the subduction rate of the Nazca plate beneath South America. The convergence rate, estimated from global relative plate motion models, depends significantly on closure of the Nazca - Antarctica - South America circuit. NUVEL-1, a new plate motion model which incorporates recently determined spreading rates on the Chile Rise, shows that the average convergence rate over the last three million years is slower than previously estimated. If this time-averaged convergence rate provides an appropriate upper bound for the seismic slip rate, either the characteristic Chilean subduction earthquake is smaller than the 1960 event, the average recurrence interval is greater than observed in the last 400 years, or both. These observations bear out the nonuniformity of plate motions on various time scales, the variability in characteristic subduction zone earthquake size, and the limitations of recurrence time estimates.

Can Thermal Bending Fracture Ice Shelves?

NASA Astrophysics Data System (ADS)

MacAyeal, D. R.; Sergienko, O. V.; Banwell, A. F.; Willis, I.; Macdonald, G. J.; Lin, J.

2017-12-01

Visco-elastic plates will bend if the temperature on one side is cooled. If the plate is constrained to float, as for sea ice floes, this bending will lead to tensile stresses that can fracture the ice. The hydroacoustic regime below sea ice displays increased fracture-sourced noise when air temperatures above the ice cools with the diurnal cycle. The McMurdo Ice Shelf, Antarctica, also displays a massive increase in seismicity during the cooling phase of the diurnal cycle, and this motivates the question: Can surface cooling (or other forcing with thermal consequences) drive through-thickness fracture leading to iceberg calving? Past study of this question for sea ice gives an upper limit of ice-plate thickness (order meters) for which diurnal-scale thermal bending fracture can occur; but could cooling with longer time scales induce fracture of thicker ice plates? Given the seismic evidence of thermal bending fracture on the McMurdo Ice Shelf, the authors examine this question further.

A 3-D shear velocity model of the southern North America and the Caribbean plates from ambient noise and earthquake tomography

NASA Astrophysics Data System (ADS)

Gaite, B.; Villaseñor, A.; Iglesias, A.; Herraiz, M.; Jiménez-Munt, I.

2014-10-01

We use group velocities from earthquake tomography together with group and phase velocities from ambient noise tomography (ANT) of Rayleigh-waves to invert for the 3-D shear-wave velocity structure (5-70 km) of the Caribbean (CAR) and southern North American (NAM) plates. The lithospheric model proposed offers a complete image of the crust and uppermost-mantle with imprints of the tectonic evolution. One of the most striking features inferred is the main role of the Ouachita-Marathon-Sonora orogeny front on the crustal seismic structure of NAM plate. A new imaged feature is the low crustal velocities along USA-Mexico border. The model also shows a break of the E-W mantle velocity dichotomy of the NAM and CAR plates beneath the Isthmus of Tehuantepec and Yucatan Block. High upper-mantle velocities along the Mesoamerican Subduction Zone coincide with inactive volcanic areas while the lowest velocities correspond to active volcanic arcs and thin lithospheric mantle regions.

A 3-D shear velocity model of the southern North American and Caribbean plates from ambient noise and earthquake tomography

NASA Astrophysics Data System (ADS)

Gaite, B.; Villaseñor, A.; Iglesias, A.; Herraiz, M.; Jiménez-Munt, I.

2015-02-01

We use group velocities from earthquake tomography together with group and phase velocities from ambient noise tomography (ANT) of Rayleigh waves to invert for the 3-D shear-wave velocity structure (5-70 km) of the Caribbean (CAR) and southern North American (NAM) plates. The lithospheric model proposed offers a complete image of the crust and uppermost-mantle with imprints of the tectonic evolution. One of the most striking features inferred is the main role of the Ouachita-Marathon-Sonora orogeny front on the crustal seismic structure of the NAM plate. A new imaged feature is the low crustal velocities along the USA-Mexico border. The model also shows a break of the east-west mantle velocity dichotomy of the NAM and CAR plates beneath the Isthmus of the Tehuantepec and the Yucatan Block. High upper-mantle velocities along the Mesoamerican Subduction Zone coincide with inactive volcanic areas while the lowest velocities correspond to active volcanic arcs and thin lithospheric mantle regions.

Three-dimensional couette flow of dusty fluid with heat transfer in the presence of magnetic field

NASA Astrophysics Data System (ADS)

Gayathri, R.; Govindarajan, A.; Sasikala, R.

2018-04-01

This paper is focused on the mathematical modelling of three-dimensional couette flow and heat transfer of a dusty fluid between two infinite horizontal parallel porous flat plates in the presence of an induced magnetic field. The problem is formulated using a continuum two-phase model and the resulting equations are solved analytically. The lower plate is stationary while the upper plate is undergoing uniform motion in its plane. These plates are, respectively subjected to transverse exponential injection and its corresponding removal by constant suction. Due to this type of injection velocity, the flow becomes three dimensional. The closed-form expressions for velocity and temperature fields of both the fluid and dust phase are obtained by solving the governing partial differentiation equations using the perturbation method. A selective set of graphical results is presented and discussed to show interesting features of the problem. It is found that the velocity profiles of both fluid and dust particles decrease due to the increase of (magnetic parameter) Hartmann number.

Slip analysis of squeezing flow using doubly stratified fluid

NASA Astrophysics Data System (ADS)

Ahmad, S.; Farooq, M.; Javed, M.; Anjum, Aisha

2018-06-01

The non-isothermal flow is modeled and explored for squeezed fluid. The influence of velocity, thermal and solutal slip effects on transport features of squeezed fluid are analyzed through Darcy porous channel when fluid is moving due to squeezing of upper plate towards the stretchable lower plate. Dual stratification effects are illustrated in transport equations. A similarity analysis is performed and reduced governing flow equations are solved using moderated and an efficient convergent approach i.e. Homotopic technique. The significant effects of physical emerging parameters on flow velocity, temperature and fluid concentration are reporting through various plots. Graphical explanations for drag force, Nusselt and Sherwood numbers are stated and examined. The results reveal that minimum velocity field occurs near the plate, whereas it increases far away from the plate for strong velocity slip parameter. Furthermore, temperature and fluid concentration significantly decreases with increased slip effects. The current analysis is applicable in some advanced technological processes and industrial fluid mechanics.

Constraining the velocity structure of the Juan de Fuca plate from ridge to trench with a 2D tomographic study of wide angle OBS data

NASA Astrophysics Data System (ADS)

Boulahanis, B.; Canales, J. P.; Carbotte, S. M.; Carton, H. D.; Han, S.; Nedimovic, M. R.

2016-12-01

We conduct a two-dimensional travel time tomography study of a cross-plate, 300-km long, ocean bottom seismometer (OBS) transect collected as part of the Ridge to Trench (R2T) program to investigate the structure, evolution and state of hydration of the Juan de Fuca (JdF) plate from the ridge axis to subduction at the Cascadia margin offshore Washington. Our study employs the methodology of Korenaga et al. (2000) to derive a P-wave velocity model using wide-angle data from 15 OBSs spaced on average 15 km apart, spanning from the Endeavour segment of the JdF ridge to the Cascadia accretionary prism. A top down modeling approach is employed, first assessing velocities of the sediment layer, then the crust, and finally the upper mantle; at each stage of the inversion we fix the structure of the overlaying layers. Quality of data fit is evaluated using the root mean square value of the difference between predicted and observed travel times normalized by pick uncertainty. Previous studies provide a well-resolved multi-channel seismic (MCS) reflection image of this transect (Han et al., 2016), affording good constraints of the location of basement and Moho reflectors while allowing for comparison of the relationship between velocities and crustal structure. MCS results along this transect suggest evidence of little bending faulting confined to the sediment and upper-middle crust. An initial velocity model of the sediment layer above igneous crust is constructed utilizing the MCS derived sediment velocities. A one-dimensional velocity starting model of the oceanic crust is generated using the results of Horning et al. (in press) from a quasi-parallel cross-plate transect also acquired as part of the R2T study. Seismic velocities are compared to predicted velocities for crustal and mantle lithologies at temperatures estimated from a plate-cooling model and are used to provide constraints on water contents in these layers.

Multiscale Architecture of a Subduction Complex and Insight into Large-scale Material Movement in Subduction Systems

NASA Astrophysics Data System (ADS)

Wakabayashi, J.

2014-12-01

The >1000 km by >100 km Franciscan complex of California records >100 Ma of subduction history that terminated with conversion to a transform margin. It affords an ideal natural laboratory to study the rock record of subduction-interface and related processes exhumed from 10-70 km. The Franciscan comprises coherent and block-in-matrix (mélange) units forming a nappe stack that youngs structurally downward in accretion age, indicating progressive subduction accretion. Gaps in accretion ages indicate periods of non-accretion or subduction erosion. The Franciscan comprises siliciclastic trench fill rocks, with lesser volcanic and pelagic rocks and serpentinite derived from the downgoing plate, as well as serpentinite and felsic-intermediate igneous blocks derived as detritus from the upper plate. The Franciscan records subduction, accretion, and metamorphism (including HP), spanning an extended period of subduction, rather than a single event superimposed on pre-formed stratigraphy. Melanges (serpentinite and siliciclastic matrix) with exotic blocks, that include high-grade metamorphic blocks, and felsic-intermediate igneous blocks from the upper plate, are mostly/entirely of sedimentary origin, whereas block-in-matrix rocks formed by tectonism lack exotic blocks and comprise disrupted ocean plate stratigraphy. Mélanges with exotic blocks are interbedded with coherent sandstones. Many blocks-in-melange record two HP burial events followed by surface exposure, and some record three. Paleomegathrust horizons, separating nappes accreted at different times, appear restricted to narrow fault zones of <100's of m thickness, and <50 m in best constrained cases; these zones lack exotic blocks. Large-scale displacements, whether paleomegathrust horizons, shortening within accreted nappes, or exhumation structures, are accommodated by discrete faults or narrow shear zones, rather than by significant penetrative strain. Exhumation of Franciscan HP units, both coherent and mélange, was accommodated by significant extension of the overlying plate, and possibly extension within the subduction complex, with cross-sectional extrusion, and like subduction burial, took place at different times.

Retrodeforming the Arabia-Eurasia collision zone : Age of collision and magnitude of continental subduction

NASA Astrophysics Data System (ADS)

McQuarrie, N.; van Hinsbergen, D. J. J.

2012-04-01

When did continents collide, and how is convergence partitioned after collision are first order questions that seem to defy consensus along the Alpine-Himalyan orogen. Estimates on the age of collision for Arabia and Eurasia range from late Cretaceous to Pliocene, based on a wide variety of presumed geologic responses. Both lower Miocene synorgenic strata with growth structures adjacent to the main Zagros fault and upper Oligocene to lower Miocene overlap strata over post-collisional thrusts are derived from Eurasia and require that collision was underway at least by ~25-24 Ma. However, upper plate deformation, exhumation and sedimentation are used to argue for an older, 35 Ma collision age. Africa-North America-Eurasia plate circuit rotations, combined with Red Sea rotations provides precise estimates of the relative positions between the northern Arabian margin and the southern Eurasia margin. Plate circuits indicate, from NW to SE along the collision zone 490-650 km of post-25 Ma Arabia-Eurasia convergence and 810-1070 km since 35 Ma. To assess the consequences of these collision ages for the amount of Arabian continental subduction, we compile all documented shortening within the orogen. The Zagros fold-thrust belt consists of thrusted upper crust that was offscraped from subducted Arabian continental lithosphere. Balanced cross-sections give 105-180 km of Zagros shortening (including estimates from the Zagros proper, 45-90 km, and the Zagros "crush" zone, 60-90 km). Shortening within Eurasia is estimated to be 53-75 km through the Kopet Dagh and Alborz Mountains, plus 38 km across Central Iran. These estimates suggest that the orogen has shortened 200 to 300 km since the early Miocene. Both a 25 and a 35 Ma collision estimate thus requires that a considerable portion of the Arabian plate subducted without recognized accretion of its upper crust. To balance plate circuits and documented shortening requires whole-sale subduction of ~500-800 km of continental crust since 35 Ma; for a 25 Ma collision this would be between 190-450 km. The ophiolitic fragments preserved along the suture zone allow us to test the magnitude of possible continental subduction. The Oman Ophiolite preserves the geometry and distance over which ophiolites obduced over the northern margin of Arabia in the late Cretaceous. The distance from the southwestern edge of the ophiolite to the northeastern edge of the continent is 180 km, suggesting that the Arabian continental margin plus overlying ophiolites may have extended ~200 km beyond the Main Zagros fault. Assuming that 200 km of Arabian continental margin and overlying ophiolites subducted entirely, except the few remnant ophiolite slivers remaining in the suture zone, would reconstruct ~ 400-500 km of post-collisional Arabia-Eurasia convergence, consistent with a ~25 Ma collision age. As much as 500-800 km of continental subduction required by an earlier (~35 Ma) collision age seems unlikely.

Indo-Burmese subduction of the Bengal basin controlled by 90°E ridge collison imaged from deep seismic reflection data

NASA Astrophysics Data System (ADS)

Rangin, C.; Maurin, T.

2009-12-01

As a result of the Indo Burmese active hyper-oblique subduction, part of the Bay of Bengal is presently subducting eastward below the Burmese microplate. We have conducted two deep penetration seismic reflection surveys in the north-eastern Bay of Bengal, providing the first high resolution seismic image of the Bengal basin fill and basement. On basis of these data, we are able to trace the 90°E ridge much more northward than previously thought, i.e. up to 20°N along the Indo-Burmese plate boundary. We found out that the surface deformation, the deep structure of the subduction zone and the geometry of the plate boundary could all be strongly influenced by the impact of a prominent asperity, the 90°E ridge. These effects are variable along the margin. Between 15°N and 18°N, the ridge asperity brushes the active burmese plate boundary that strikes N10°E. At this latitude, all the structures framing the Indo-Burmese wedge have a similar N10°E trend. Deformation at the plate boundary is mainly strike slip. This is confirmed by the absence of subducted slab at depth as indicated by both seismicity and tomography. The small component of shortening along this plate boundary is probably accommodated partly by the flexure of the ridge and partly within the deformed upper plate. North of 19°N, the ridge vanishes progressively. The absence of basement topography together with the large amount of sediments provided by the Brahmaputra delta facilitates the fast westward growth of the Indo-Burmese wedge. The seismicity fits a well developed subducted slab at depth,. In the narrow transition zone between 18°N and 19°N, the 90°E ridge northern tips collides with the Burmese microplate. This collision could explain the rise of a subsuface flat and ramp system offshore Ramree and Cheduba islands, and the strong uplift of the Indo-Burmese wedge in Mount Victoria area.

Integration of COCORP deep reflection and magnetic anomaly analysis in the southeastern United States: Implications for origin of the Brunswick and East Coast magnetic anomalies: Alternative interpretation and reply

USGS Publications Warehouse

Hutchinson, Deborah R.; Klitgord, Kim D.; Tréhu, Anne M.; McBride, John H.; Nelson, K. D.

1990-01-01

Integration of magnetic anomaly analysis with COCORP deep reflection data from the southeastern United States provides three new constraints on the interpretation of the Brunswick and East Coast magnetic anomalies, as well as on the reflection data. These are as follows. (1) The source of the Brunswick anomaly lies within the deep crust. This anomaly is not caused by a Mesozoic rift basin, as proposed by some workers. (2) A simple, seaward-dipping, high- susceptibility slab model can explain both the Brunswick and East Coast magnetic anomalies. The along-strike change in character of the two anomalies results largely from a change in azimuth of the source body. (3) Beneath the southeastern United States, this source body dips south, lies immediately on the south flank of the prominent southward-dipping reflective zone revealed on COCORP surveys, and was previously associated with the Alleghanian suture between North America and Africa. These results imply that a dipping, highly magnetized zone in the upper plate of the Alleghanian suture is responsible for both the Brunswick and East Coast magnetic anomalies. The high- susceptibility material responsible for these anomalies might be mafic lower continental or oceanic crust thrust upward during Alleghanian continental collision, or mafic igneous material intruded into the upper plate of the suture zone during subsequent Mesozoic rifting, or both. The latter hypothesis implies that the Alleghanian suture acted, as a zone of weakness (a repository ?) which was reactivated to control the site of ultimate Atlantic rifting and possibly initial sea-floor spreading.

46 CFR 69.65 - Calculation of volumes.

Code of Federal Regulations, 2013 CFR

2013-10-01

... accepted naval architectural practices for the spaces concerned. (b) The volume of the hull below the upper... boundary plating, in vessels constructed of metal; and (2) To the outer surface of the shell or to the... cargo space, measurements must be taken without consideration for insulation, sparring, or ceiling...

46 CFR 69.65 - Calculation of volumes.

Code of Federal Regulations, 2014 CFR

2014-10-01

... accepted naval architectural practices for the spaces concerned. (b) The volume of the hull below the upper... boundary plating, in vessels constructed of metal; and (2) To the outer surface of the shell or to the... cargo space, measurements must be taken without consideration for insulation, sparring, or ceiling...

46 CFR 69.65 - Calculation of volumes.

Code of Federal Regulations, 2012 CFR

2012-10-01

... accepted naval architectural practices for the spaces concerned. (b) The volume of the hull below the upper... boundary plating, in vessels constructed of metal; and (2) To the outer surface of the shell or to the... cargo space, measurements must be taken without consideration for insulation, sparring, or ceiling...

Decrease in oceanic crustal thickness since the breakup of Pangaea

NASA Astrophysics Data System (ADS)

van Avendonk, Harm J. A.; Davis, Joshua K.; Harding, Jennifer L.; Lawver, Lawrence A.

2017-01-01

Earth's mantle has cooled by 6-11 °C every 100 million years since the Archaean, 2.5 billion years ago. In more recent times, the surface heat loss that led to this temperature drop may have been enhanced by plate-tectonic processes, such as continental breakup, the continuous creation of oceanic lithosphere at mid-ocean ridges and subduction at deep-sea trenches. Here we use a compilation of marine seismic refraction data from ocean basins globally to analyse changes in the thickness of oceanic crust over time. We find that oceanic crust formed in the mid-Jurassic, about 170 million years ago, is 1.7 km thicker on average than crust produced along the present-day mid-ocean ridge system. If a higher mantle temperature is the cause of thicker Jurassic ocean crust, the upper mantle may have cooled by 15-20 °C per 100 million years over this time period. The difference between this and the long-term mantle cooling rate indeed suggests that modern plate tectonics coincide with greater mantle heat loss. We also find that the increase of ocean crustal thickness with plate age is stronger in the Indian and Atlantic oceans compared with the Pacific Ocean. This observation supports the idea that upper mantle temperature in the Jurassic was higher in the wake of the fragmented supercontinent Pangaea due to the effect of continental insulation.

A GPS Modeling Study of Earthquakes and Deformation in Northern Central America and along the Middle America Trench: 1999 to 2017

NASA Astrophysics Data System (ADS)

Ellis, Andria P.

Northern Central America is a tectonically complicated region prone to hazardous earthquakes due to the confluence of the Motagua-Polochic fault zone with the Middle America trench and strike-slip faults in the Central America volcanic arc. These three major fault zones converge at the western end of the Caribbean plate where the Cocos plate subducts under the North America and Caribbean plates. Literature from the 1970s and 1980s focused on whether a discrete North America-Caribbean-Cocos plate triple junction existed, and how the relative motions of the upper North America and Caribbean plates were accommodated. The discovery of a fourth major crustal block, the Central America forearc sliver, from seismic and geodetic observations made a three-plate triple junction geometrically impossible and introduced a new set of questions related to how deformation of the upper plate accommodates relative movements between the Caribbean plate, North America plate, and Central America forearc sliver where they intersect in the upper plate. My dissertation uses GPS and numerical modeling to measure and quantify earthquake transients and crustal deformation related to fault interactions in northern Central America and consists of three related chapters. The first chapter of my dissertation is a geodetic study of a M w = 7.4 subduction zone earthquake that occurred in 2012 offshore from our Guatemala GPS (Global Positioning System) network. For this study, I inverted coseismic site offsets and postseismic amplitudes to determine best-fitting coseismic and afterslip rupture distributions on the Middle America trench. I also determined the maximum likely viscoelastic deformation for the earthquake to test whether the transient postseismic deformation was dominated by fault afterslip or viscoelastic flow. This work was published in Geophysical Journal International in January 2015. The second chapter of my dissertation derives a new 200+ site GPS velocity field for northern Central America. Doing so was complicated by the occurrence of four M > 7 earthquakes since 2009, which perturbed the velocities of many of the GPS sites. To extract the interseismic velocity field from position time-series, we use TDEFNODE software to simultaneously model source parameters for coseismic rupture and transient afterslip from the 2012 El Salvador (M w = 7.3), 2012 Guatemala (Mw = 7.4), and 2009 Swan Islands (Mw = 7.3) earthquakes. The resulting, corrected best-fitting GPS site velocities are used in my third and final chapter. Finally, I address a variety of questions regarding several major faults that are the root of natural hazard studies in northern Central America. The 200+ site GPS velocity field derived in Chapter 2 far exceeds any previous velocity field for this region and represents a new standard for studying the tectonics of northern Central America. An inversion of the new velocity field using an eight-block elastic model gives the following unique or improved results with respect to previous work: 1) First evidence for a nearly rigid Chortis block south of the Motagua fault; 2) Evidence for southward transfer of slip from the western Motagua fault into the Guatemala City graben and other nearby normal faults; 3) A well-bounded estimate on partitioning of plate boundary slip on the Motagua and Polochic faults; 4) A first plate tectonic estimate of Cocos plate subduction below the Central America forearc sliver; 5) The first geodetic estimate of slip rate variations along the Central America volcanic arc, including the first slip rate estimate for the poorly-understood Jalpatagua fault in southern Guatemala; 6) The first geodetic estimate of distributed deformation in the Chiapas Tectonic Province; 7) Evidence for stronger locking offshore southern Mexico and even weaker shallow locking offshore Guatemala and El Salvador than previously estimated; 8) A refined estimate of how extension is distributed across the grabens of western Honduras and southern Guatemala; 9) Strain-rate tensors consistent with no significant deformation of the elongate Central America forearc sliver, but extension within the Gulf of Fonseca step-over in the Central America volcanic arc; 10) Evidence for slower slip along the Motagua fault than any previous estimate and a well-determined geodetic estimate for the long-term slip rate of the Polochic fault.

Seismicity near a Highly-Coupled Patch in the Central Ecuador Subduction Zone

NASA Astrophysics Data System (ADS)

Regnier, M. M.; Segovia, M.; Font, Y.; Charvis, P.; Galve, A.; Jarrin, P.; Hello, Y.; Ruiz, M. C.; Pazmino, A.

2017-12-01

The temporary onshore-offshore seismic network deployed during the 2-years period of the OSISEC project provides an unprecedented, detailed and well-focused image of the seismicity for magnitudes as low as 2.0 in the Central Ecuadorian subduction zone. Facing the southern border of the Carnegie Ridge, a shallow and discrete highly-coupled patch is correlated to the subduction of a large oceanic relief. No large earthquake is known in this area that is experiencing recurrent seismic swarms and slow slip events. The shallow and locked subduction interface shows no evidence of background seismicity that instead occurred down dip of the coupled patch where it is possibly controlled by structural features of the overriding plate. We show a clear spatial correlation between the background microseismicity, the down dip extension of the locked patch at 20 km depth and the geology of the upper plate. The dip angle of the interplate contact zone, defined by a smooth interpolation through the hypocenters of thrust events, is consistent with a progressive increase from 6° to 25° from the trench to 20 km depth. Offshore, a seismic swarm, concomitant with a slow slip event rupturing the locked area, highlights the reactivation of secondary active faults that developed within the thickened crust of the subducting Carnegie Ridge, at the leading edge of a large oceanic seamount. No seismicity was detected near the plate interface suggesting that stress still accumulates at small and isolated asperities

Experimental study on evaluation and optimization of tilt angle of parallel-plate electrodes using electrocoagulation device for oily water demulsification.

PubMed

Liu, Yang; Jiang, Wen-Ming; Yang, Jie; Li, Yu-Xing; Chen, Ming-Can; Li, Jian-Na

2017-08-01

Tilt angle of parallel-plate electrodes (APE) is very important as it improves the economy of diffusion controlled Electrocoagulation (EC) processes. This study aimed to evaluate and optimize APE of a self-made EC device including integrally rotary electrodes, at a fixed current density of 120 Am -2 . The APEs investigated in this study were selected at 0°, 30°, 45°, 60°, 90°, and a special value (α (d) ) which was defined as a special orientation of electrode when the upper end of anode and the lower end of cathode is in a line vertical to the bottom of reactor. Experiments were conducted to determine the optimum APE for demulsification process using four evaluation indexes, as: oil removal efficiency in the center between electrodes; energy consumption and Al consumption, and besides, a novel universal evaluation index named as evenness index of oil removal efficiency employed to fully reflect distribution characteristics of demulsification efficiency. At a given plate spacing of 4 cm, the optimal APE was found to be α (d) because of its potential of enhancing the mass transfer process within whole EC reactor without addition, external mechanical stirring energy, and finally the four evaluation indexed are 97.07%, 0.11 g Al g -1 oil, 2.99 kwhkg -1 oil, 99.97% and 99.97%, respectively. Copyright © 2017 Elsevier Ltd. All rights reserved.

Compact reaction cell for homogenizing and down-blending highly enriched uranium metal

DOEpatents

McLean, W. II; Miller, P.E.; Horton, J.A.

1995-05-02

The invention is a specialized reaction cell for converting uranium metal to uranium oxide. In a preferred form, the reaction cell comprises a reaction chamber with increasing diameter along its length (e.g. a cylindrical chamber having a diameter of about 2 inches in a lower portion and having a diameter of from about 4 to about 12 inches in an upper portion). Such dimensions are important to achieve the necessary conversion while at the same time affording criticality control and transportability of the cell and product. The reaction chamber further comprises an upper port and a lower port, the lower port allowing for the entry of reactant gases into the reaction chamber, the upper port allowing for the exit of gases from the reaction chamber. A diffuser plate is attached to the lower port of the reaction chamber and serves to shape the flow of gas into the reaction chamber. The reaction cell further comprises means for introducing gases into the reaction chamber and a heating means capable of heating the contents of the reaction chamber. The present invention also relates to a method for converting uranium metal to uranium oxide in the reaction cell of the present invention. The invention is useful for down-blending highly enriched uranium metal by the simultaneous conversion of highly enriched uranium metal and natural or depleted uranium metal to uranium oxide within the reaction cell. 4 figs.

Compact reaction cell for homogenizing and down-blanding highly enriched uranium metal

DOEpatents

McLean, II, William; Miller, Philip E.; Horton, James A.

1995-01-01

The invention is a specialized reaction cell for converting uranium metal to uranium oxide. In a preferred form, the reaction cell comprises a reaction chamber with increasing diameter along its length (e.g. a cylindrical chamber having a diameter of about 2 inches in a lower portion and having a diameter of from about 4 to about 12 inches in an upper portion). Such dimensions are important to achieve the necessary conversion while at the same time affording criticality control and transportability of the cell and product. The reaction chamber further comprises an upper port and a lower port, the lower port allowing for the entry of reactant gasses into the reaction chamber, the upper port allowing for the exit of gasses from the reaction chamber. A diffuser plate is attached to the lower port of the reaction chamber and serves to shape the flow of gas into the reaction chamber. The reaction cell further comprises means for introducing gasses into the reaction chamber and a heating means capable of heating the contents of the reaction chamber. The present invention also relates to a method for converting uranium metal to uranium oxide in the reaction cell of the present invention. The invention is useful for down-blending highly enriched uranium metal by the simultaneous conversion of highly enriched uranium metal and natural or depleted uranium metal to uranium oxide within the reaction cell.

Isolated intermediate-depth seismicity north of the Izu peninsula, Japan: implications for subduction of the Philippine Sea Plate

NASA Astrophysics Data System (ADS)

Nakajima, Junichi

2018-01-01

The subduction of the Philippine Sea (PHS) Plate toward the north of Izu peninsula, Japan, is of great interest because intraslab seismicity is absent where the buoyant Izu volcanic arc has been subducting over the past 15 Myr. This study analyzes 42 earthquakes in an isolated seismic cluster that occurred 100 km north of Izu peninsula at depths of 40-90 km and discusses seismogenesis in the context of plate subduction. We picked P- and S-wave arrival times of earthquakes to produce a complete hypocenter catalogue, carried out double-difference event relocations, and then determined focal mechanism solutions of 7 earthquakes from P-wave polarity data. Based on the focal mechanism solution, the largest earthquake (M3.1) is interpreted as a thrust earthquake along the upper surface of the PHS Plate. Locations of other earthquakes relative to the largest event suggest that most earthquakes occur within the subducting PHS Plate. Our results suggest that the PHS Plate north of Izu peninsula has temperatures low enough to facilitate thrust and intraslab earthquakes at depths of 60-90 km. Earthquakes are likely to occur where pore pressures are locally high, which weakens pre-existing faults. The presence of the intermediate-depth seismic cluster indicates the continuous subduction of the PHS Plate toward the north of Izu peninsula without any disruption.[Figure not available: see fulltext.

Recent Progress in Understanding the Origin of the Hawaiian-Emperor Bend

NASA Astrophysics Data System (ADS)

Gordon, R. G.; Morgan, J. P.

2016-12-01

Two main explanations have been proposed for the origin of the Hawaiian-Emperor Bend (HEB): (1) that it records a change in motion of the Pacific plate relative to a stationary Hawaiian plume [Morgan, 1971]; (2) that Pacific plate motion has been uniform but the HEB records a change from rapid (>40 mm/yr) southward motion of the Hawaiian plume, while the Emperor chain was formed, to a stationary plume while the Hawaiian chain was formed [Tarduno et al. 2003]. We summarize recent progress on this issue. Recent work invalidates prior studies that inferred significant rates of motion between hotspots since the time of the HEB. Nominal rates of motion are 2-6 mm/yr with a lower bound of zero and upper bounds of 8-13 mm/yr (95% c. l.) [Koivisto et al., 2014]. In this context, Hawaiian plume drift as great as 40 mm/yr before 50 Ma B.P. seems unlikely. Other recent work demonstrates the viability of using the orientation of seismic anisotropy in the upper mantle, combined with relative plate motions, to estimate absolute plate motions independently of hotspot tracks. Wang et al. [this meeting] show that the two reference frames agree with each other within their 95% confidence limits, thus lending credibility to both estimates. To infer motion of the Hawaiian hotspot relative to the mantle from paleomagnetic data one must ignore true polar wander (TPW), but TPW is too big to ignore and is occurring today—it is an important part of explaining the apparent polar wander of the Pacific and other plates. New evidence shows that the Hawaiian hotspot was fixed in latitude during formation of most, if not all, of the Emperor seamount chain [Seidman et al., this meeting], in contradiction to the southward motion found by Tarduno et al. [2003]. Revised timing and age-dating of the HEB (now 50 Ma; Clague [this meeting]) implies that the change in plate motion coincides with a change in Pacific-Farallon motion and other circum-Pacific tectonic events. Barkhausen et al [2013] show that the Pacific-Farallon spreading rate doubles between 50 Ma and 40 Ma coincident with the acceleration of the Pacific plate from the HEB to the Hawaiian trend and an increasing propagation rate along that trend. We conclude that current evidence still favors W. J. Morgan's original explanation for the HEB: that it records a change in Pacific plate motion relative to the deep mantle.

Passive margins getting squeezed in the mantle convection vice

NASA Astrophysics Data System (ADS)

Husson, Laurent; Yamato, Philippe; Becker, Thorsten; Pedoja, Kevin

2013-04-01

Quaternary coastal geomorphology reveals that passive margins underwent wholesale uplift at least during the glacial cycle. In addition, these not-so-passive margins often exhibit long term exhumation and tectonic inversion, which suggest that compression and tectonic shortening could be the mechanism that triggers their overall uplift. We speculate that the compression in the lithosphere gradually increased during the Cenozoic. The many mountain belts at active margins that accompany this event readily witness this increase. Less clear is how that compression increase affects passive margins. In order to address this issue, we design minimalist 2D viscous models to quantify the impact of plate collision on the stress regime. In these models, a sluggish plate is disposed on a less viscous mantle. It is driven by a "mantle conveyor belt" alternatively excited by lateral shear stresses that represent a downwelling on one side, an upwelling on the other side, or both simultaneously. The lateral edges of the plate are either free or fixed, respectively representing the cases of free convergence and collision. In practice, it dramatically changes the upper boundary condition for mantle circulation and subsequently, for the stress field. The flow pattern transiently evolves almost between two end-members, starting from a situation close to a Couette flow to a pattern that looks like a Poiseuille flow with an almost null velocity at the surface (though in the models, the horizontal velocity at the surface is not strictly null, as the lithosphere deforms). In the second case, the lithosphere is highly stressed horizontally and deforms. For an equivalent bulk driving force, compression increases drastically at passive margins if upwellings are active because they push plates towards the collision. Conversely, if only downwellings are activated, compression occurs on one half of the plate and extension on the other half, because only the downwelling is pulling the plate. Thus, active upwellings underneath oceanic plates are required to explain compression at passive margins. This conclusion is corroborated by "real-Earth" 3D spherical models, wherein the flow is alternatively driven by density anomalies inferred from seismic tomography -and therefore include both downwellings at subduction zones and upwellings above the superswells- and density anomalies that correspond to subducting slabs only. While the second scenario mostly compresses the active margins of upper plates and leave other areas at rest, the first scenario efficiently compresses passive margins where the geological record reveals their uplift, exhumation, and tectonic inversion.

Paleogeographic and paleo-oceanographic influences on carbon isotope signatures: Implications for global and regional correlation, Middle-Upper Jurassic of Saudi Arabia

NASA Astrophysics Data System (ADS)

Eltom, Hassan A.; Gonzalez, Luis A.; Hasiotis, Stephen T.; Rankey, Eugene C.; Cantrell, Dave L.

2018-02-01

Carbon isotope data (δ13C) can provide an essential means for refining paleogeographic and paleo-oceanographic reconstructions, and interpreting stratigraphic architecture within complex carbonate strata. Although the primary controls on global δ13C signatures of marine carbonates are well understood, understanding their latitudinal and regional variability is poor. To better constrain the nature and applications of δ13C stratigraphy, this study: 1) presents a new high-resolution δ13C stratigraphic curve from Middle to Upper Jurassic carbonates in the upper Tuwaiq Mountain, Hanifa, and lower Jubaila formations in central Saudi Arabia; 2) explores their latitudinal and regional variability; and 3) discusses their implications for stratigraphic correlations. Analysis of δ13C data identified six mappable units with distinct δ13C signatures (units 1-6) between up-dip and down-dip sections, and one unit (unit 7) that occurs only in the down-dip section of the study succession. δ13C data from the upper Tuwaiq Mountain Formation and the lower Hanifa Formation (units 1, 2), which represent Upper Callovian to Middle Oxfordian strata, and record two broad positive δ13C excursions. In the upper part of the Hanifa Formation (units 3-6, Early Oxfordian-Late Kimmeridgian), δ13C values decreased upward to unit 7, which showed a broad positive δ13C excursion. Isotopic data suggest similar δ13C trends between the southern margin of the Tethys Ocean (Arabian Plate; low latitude, represented by the study succession) and northern Tethys oceans (high latitude), despite variations in paleoclimatic, paleogeographic, and paleoceanographic conditions. Variations in the δ13C signal in this succession can be attributed to the burial of organic matter and marine circulation at the time of deposition. Our study uses δ13C signatures to provide independent data for chronostratigraphic constraints which help in stratigraphic correlations within heterogeneous carbonate successions.

Heat transfer optimization for air-mist cooling between a stack of parallel plates

NASA Astrophysics Data System (ADS)

Issa, Roy J.

2010-06-01

A theoretical model is developed to predict the upper limit heat transfer between a stack of parallel plates subject to multiphase cooling by air-mist flow. The model predicts the optimal separation distance between the plates based on the development of the boundary layers for small and large separation distances, and for dilute mist conditions. Simulation results show the optimal separation distance to be strongly dependent on the liquid-to-air mass flow rate loading ratio, and reach a limit for a critical loading. For these dilute spray conditions, complete evaporation of the droplets takes place. Simulation results also show the optimal separation distance decreases with the increase in the mist flow rate. The proposed theoretical model shall lead to a better understanding of the design of fins spacing in heat exchangers where multiphase spray cooling is used.

Unsteady Heat and Mass Transfer of Chemically Reacting Micropolar Fluid in a Porous Channel with Hall and Ion Slip Currents

PubMed Central

2014-01-01

This paper presents an incompressible two-dimensional heat and mass transfer of an electrically conducting micropolar fluid flow in a porous medium between two parallel plates with chemical reaction, Hall and ion slip effects. Let there be periodic injection or suction at the lower and upper plates and the nonuniform temperature and concentration at the plates are varying periodically with time. The flow field equations are reduced to nonlinear ordinary differential equations using similarity transformations and then solved numerically by quasilinearization technique. The profiles of velocity components, microrotation, temperature distribution and concentration are studied for different values of fluid and geometric parameters such as Hartmann number, Hall and ion slip parameters, inverse Darcy parameter, Prandtl number, Schmidt number, and chemical reaction rate and shown in the form of graphs. PMID:27419211

Foreshocks and aftershocks of the 2014 M8.1 Iquique, northern Chile, megathrust earthquake

NASA Astrophysics Data System (ADS)

Soto, Hugo; Sippl, Christian; Schurr, Bernd; Asch, Günter; Tilmann, Frederik; Comte, Diana; Ruiz, Sergio; Oncken, Onno

2017-04-01

The M8.1 2014 Iquique earthquake broke a central piece of the long-standing, >500 km long northern Chile seismic gap. The Iquique earthquake sequence started off with a M6.7 thrust event presumably in the upper plate seaward of the Chilean coastline. Deformation was quickly transferred onto the megathrust with three more events of M>6 until it culminated in the mainshock that broke a compact asperity with possibly up to 12 m of slip two weeks later. The mainshock was followed by vigorous aftershock sequence, including a M7.7 event just south of the main slip patch approx. two days later. The whole sequence of events was well recorded by the Integrated Plate Boundary Observatory Chile (IPOC). The IPOC network was complemented quickly after the first large foreshock by 60 additional temporary seismic stations deployed by the University of Chile and the German Research Centre for Geosciences - GFZ. Processing the continuous data with an automated multi-step process for event detection, association and phase picking, we located more than 25,000 events for one month preceding and nine months following the Iquique mainshock. Whereas the foreshocks skirt around the updip limit of the mainshock asperity, the aftershocks agglomerate in two belts, one updip and one downdip of the main asperity offshore the Chilean coast. The deepest events on the plate interface reach 65 km depth in two separated clusters under the coastal cordillera, which show a significant difference in dip, indicating strong long-wavelength slab topography or a slab tear. We will also analyze upper- and deeper intra-plate seismicity and in particular its changes following the Iquique mainshock.

The electrical conductivity during incipient melting in the oceanic low velocity zone

PubMed Central

Sifré, David; Gardés, Emmanuel; Massuyeau, Malcolm; Hashim, Leila; Hier-Majumder, Saswata; Gaillard, Fabrice

2014-01-01

A low viscosity layer in the upper mantle, the Asthenosphere, is a requirement for plate tectonics1. The seismic low velocities and the high electrical conductivities of the Asthenosphere are attributed either to sub-solidus water-related defects in olivine minerals2-4 or to a few volume percents of partial melt5-8 but these two interpretations have shortcomings: (1) The amount of H2O stored in olivine is not expected to be higher than 50 ppm due to partitioning with other mantle phases9, including pargasite amphibole at moderate temperatures10, and partial melting at high temperatures9; (2) elevated melt volume fractions are impeded by the too cold temperatures prevailing in the Asthenosphere and by the high melt mobility that can lead to gravitational segregation11,12. Here we determined the electrical conductivity of CO2-H2O-rich melts, typically produced at the onset of mantle melting. Electrical conductivity modestly increases with moderate amounts of H2O and CO2 but it dramatically increases as CO2 content exceeds 6 wt% in the melt. Incipient melts, long-expected to prevail in the asthenosphere10,13-15, can therefore trigger its high electrical conductivities. Considering depleted and enriched mantle abundances in H2O and CO2 and their effect on the petrology of incipient melting, we calculated conductivity profiles across the Asthenosphere for various plate ages. Several electrical discontinuities are predicted and match geophysical observations in a consistent petrological and geochemical framework. In moderately aged plates (>5Ma), incipient melts most likely trigger both the seismic low velocities and the high electrical conductivities in the upper part of the asthenosphere, whereas for young plates4, where seamount volcanism occurs6, higher degree of melting is expected. PMID:24784219

Body wave tomography of Iranian Plateau

NASA Astrophysics Data System (ADS)

Alinaghi, A.; Koulakov, I.; Thybo, H.

2004-12-01

The inverse teleseismic tomography approach has been adopted to study the P and S velocity structure of the crust and upper mantle across the Iranian Plateau. The method uses phase readings from earthquakes in a study area as reported by stations at teleseismic and regional distances to compute the velocity anomalies in the area. This use of source-receiver reciprocity allows tomographic studies of regions with sparse distribution of seismic stations, if only the region has sufficient seismicity. The input data for the algorithm are the arrival times of events located in Iran which were taken from the ISC catalogue (1964-1996). All the sources were located anew using a 1D spherical Earth model taking into account variable Moho depth and topography. The inversion provides relocation of events which is done simultaneously with calculation of velocity perturbations. With a series of synthetic tests we demonstrate the power of the algorithm to resolve both fancy and realistic anomalies using available earthquake sources and introducing measurement errors and outliers. The velocity anomalies show that the crust and upper mantle below the Iranian Plateau comprises a low velocity domain between the Arabian Plate and the Caspian Block, in agreement with models of the active Iranian plate trapped between the stable Turan plate in the north and the Arabian shield in the south. Our results show clear evidence of subduction at Makran in the southeastern corner of Iran where the oceanic crust of the Oman Sea subducts underneath the Iranian Plateau, a movement which is mainly aseismic. On the other hand, the subduction and collision of the two plates along the Zagros suture zone is highly seismic and in our images appear less consistent than the Makran region.

Widening of Laths in Bainite

NASA Astrophysics Data System (ADS)

Yin, Jiaqing; Hillert, Mats; Borgenstam, Annika

2017-11-01

Units of bainite in Fe-C alloys from the upper temperature range inherit their shape from Widmanstätten plates of ferrite, which are lathlike. The thickness increases by long-range diffusion of carbon and the length by short-range diffusion of carbon from the advancing edge of the tip. Both have been studied extensively and are fairly well understood. Widening growth seems to have been much neglected, but a study of some aspects of widening is now presented. The present report is the last one in a series of four morphological studies of bainite, isothermally formed in Fe-C alloys with 0.3 or 0.7 mass pct carbon, mainly in the upper temperature range. It contains a number of morphological observations made on cross sections of packets of bainite, and it elucidated a number of interesting questions about bainite and resulted in some proposals. The ferrite plates in a packet are nucleated as a group on a grain boundary, not each one separately on the side of a prior plate. Lengthening occurs by advancement of a short edge that is formed in close contact to the grain boundary. Widening of laths does not start spontaneously. It is initiated by a modification of the structure of the long edge of the lath. When it then moves, the lattice of the new ferrite is rotated relative to the ferrite formed by lengthening and the habit plane is different. In a section through the length direction, it is difficult to recognize what part of ferrite has formed by widening growth. Furthermore, it is proposed that the individual plates in a microstructure, previously used to illustrate subunits formed by repeated nucleation, were nucleated on a hidden grain boundary.

Electrical conductivity during incipient melting in the oceanic low-velocity zone.

PubMed

Sifré, David; Gardés, Emmanuel; Massuyeau, Malcolm; Hashim, Leila; Hier-Majumder, Saswata; Gaillard, Fabrice

2014-05-01

The low-viscosity layer in the upper mantle, the asthenosphere, is a requirement for plate tectonics. The seismic low velocities and the high electrical conductivities of the asthenosphere are attributed either to subsolidus, water-related defects in olivine minerals or to a few volume per cent of partial melt, but these two interpretations have two shortcomings. First, the amount of water stored in olivine is not expected to be higher than 50 parts per million owing to partitioning with other mantle phases (including pargasite amphibole at moderate temperatures) and partial melting at high temperatures. Second, elevated melt volume fractions are impeded by the temperatures prevailing in the asthenosphere, which are too low, and by the melt mobility, which is high and can lead to gravitational segregation. Here we determine the electrical conductivity of carbon-dioxide-rich and water-rich melts, typically produced at the onset of mantle melting. Electrical conductivity increases modestly with moderate amounts of water and carbon dioxide, but it increases drastically once the carbon dioxide content exceeds six weight per cent in the melt. Incipient melts, long-expected to prevail in the asthenosphere, can therefore produce high electrical conductivities there. Taking into account variable degrees of depletion of the mantle in water and carbon dioxide, and their effect on the petrology of incipient melting, we calculated conductivity profiles across the asthenosphere for various tectonic plate ages. Several electrical discontinuities are predicted and match geophysical observations in a consistent petrological and geochemical framework. In moderately aged plates (more than five million years old), incipient melts probably trigger both the seismic low velocities and the high electrical conductivities in the upper part of the asthenosphere, whereas in young plates, where seamount volcanism occurs, a higher degree of melting is expected.

Three Dimensional Forming Simulation of the Shielded Slot Plate for the MCFC Using a Ductile Fracture Criterion

NASA Astrophysics Data System (ADS)

Lee, C. H.; Yang, D. Y.; Lee, S. R.; Chang, I. G.; Lee, T. W.

2011-08-01

The shielded slot plate, which has a sheared corrugated trapezoidal pattern, is a component of the metallic bipolar plate for the molten carbonate fuel cell (MCFC). In order to increase the efficiency of the fuel cell, the unit cell of the shielded slot plate should have a relatively large upper area. Additionally, defects from the forming process should be minimized. In order to simulate the slitting process, whereby sheared corrugated patterns are formed, ductile fracture criteria based on the histories of stress and strain are employed. The user material subroutine VUMAT is employed for implementation of the material and ductile fracture criteria in the commercial FEM software ABAQUS. The variables of the ductile fracture criteria were determined by comparing the simulation results and the experimental results of the tension test and the shearing test. Parametric studies were conducted to determine the critical value of the ductile fracture criterion. Employing these ductile fracture criteria, the three dimensional forming process of the shielded slot plate was numerically simulated. The effects of the slitting process in the forming process of the shielded slot plate were analyzed through a FEM simulation and experimental studies. Finally, experiments involving microscopic and macroscopic observations were conducted to verify the numerical simulations of the 3-step forming process.

Clinico-radiological Outcome Analysis of Parallel Plating with Perpendicular Plating in Distal Humeral Intra-articular Fractures: Prospective Randomised Study

PubMed Central

Shekhawat, Vishal; Banshiwal, Ramesh Chandra; Verma, Rajender Kumar

2017-01-01

Introduction The distal humeral fractures are common fractures of upper limb and are difficult to treat. These fractures, if left untreated or inadequately treated, leads to poor outcomes. Management of distal humeral fractures are pertained to many controversies and one among them is position of plates. Aim To compare the clinical and radiological outcomes in patients with intra-articular distal humerus fractures, treated using parallel and perpendicular double plating methods. Materials and Methods A total of 38 patients with distal humerus fractures, 20 in perpendicular plating group (group A) and 18 in parallel plating group (group B), were included in this prospective randomised study. At each follow up patients were evaluated clinically and radiologically for union and the outcomes were measured in terms of Mayo Elbow Performance Score (MEPS) consisting of pain intensity, range of motion, stability and function. MEP score greater than 90 is considered as excellent; Score 75 to 89 is good; Score 60 to 74 is fair and Score less than 60 is poor. Results In our study, 15 patients (75%) in group A, and 13 patients (72.22%) in group B achieved excellent results. Two patients (10%) in group A and 4 patients (22.22%) in group B attained good results. Complications developed in 2 patients in each groups. No significant differences were found between the clinical outcomes of the two plating methods. Conclusion Neither of the plating techniques are superior to the other, as inferred from the insignificant differences in bony union, elbow function and complications between the two plating techniques. PMID:28384948

Clinico-radiological Outcome Analysis of Parallel Plating with Perpendicular Plating in Distal Humeral Intra-articular Fractures: Prospective Randomised Study.

PubMed

Govindasamy, Ramachandran; Shekhawat, Vishal; Banshiwal, Ramesh Chandra; Verma, Rajender Kumar

2017-02-01

The distal humeral fractures are common fractures of upper limb and are difficult to treat. These fractures, if left untreated or inadequately treated, leads to poor outcomes. Management of distal humeral fractures are pertained to many controversies and one among them is position of plates. To compare the clinical and radiological outcomes in patients with intra-articular distal humerus fractures, treated using parallel and perpendicular double plating methods. A total of 38 patients with distal humerus fractures, 20 in perpendicular plating group (group A) and 18 in parallel plating group (group B), were included in this prospective randomised study. At each follow up patients were evaluated clinically and radiologically for union and the outcomes were measured in terms of Mayo Elbow Performance Score (MEPS) consisting of pain intensity, range of motion, stability and function. MEP score greater than 90 is considered as excellent; Score 75 to 89 is good; Score 60 to 74 is fair and Score less than 60 is poor. In our study, 15 patients (75%) in group A, and 13 patients (72.22%) in group B achieved excellent results. Two patients (10%) in group A and 4 patients (22.22%) in group B attained good results. Complications developed in 2 patients in each groups. No significant differences were found between the clinical outcomes of the two plating methods. Neither of the plating techniques are superior to the other, as inferred from the insignificant differences in bony union, elbow function and complications between the two plating techniques.

Hybrid passive/active damping for robust multivariable acoustic control in composite plates

NASA Astrophysics Data System (ADS)

Veeramani, Sudha; Wereley, Norman M.

1996-05-01

Noise transmission through a flexible kevlar-epoxy composite trim panel into an acoustic cavity or box is studied with the intent of controlling the interior sound fields. A hybrid noise attenuation technique is proposed which uses viscoelastic damping layers in the composite plate for passive attenuation of high frequency noise transmission, and uses piezo-electric patch actuators for active control in the low frequency range. An adaptive feedforward noise control strategy is applied. The passive structural damping augmentation incorporated in the composite plates is also intended to increase stability robustness of the active noise control strategy. A condenser microphone in the interior of the enclosure functions as the error sensor. Three composite plates were experimentally evaluated: one with no damping layer, the second with a 10 mil damping layer, and the third with a 15 mil damping layer. The damping layer was cocured in the kevlar-epoxy trim panels. Damping in the plates was increased from 1.6% for the plate with no damping layer, to 5.9% for the plate with a 15 mil damping layer. In experimental studies, the improved stability robustness of the controller was demonstrated by improved adaptive feedforward control algorithm convergence. A preliminary analytical model is presented that describes the dynamic behavior of a composite panel actuated by piezoelectric actuators bonded to its surface.

Design Considerations for Gun Propellant Climatic Storage Chambers.

DTIC Science & Technology

1982-11-01

Schematic diagram of thermal element 5 4. Prototype Lhermal element 6 5. Power control circuit diagram 7 6. Power control module 7 7. Temperature...plates. Each plate is powered through a triac and temperature control circuit as shown in figure 5. Figure 6 is a photograph of an assembled power control...SHEATER PLATES Figure 5. Power control circuit diagram 4 f Figure 6. Power control module WSR.L-0295-TR -8- Figure 7. Temperature control module 9 -WSRL

Dominant controls of deep afterslip and viscous relaxation on postseismic displacements following the 2015 Mw7.8 Gorkha, Nepal earthquake

NASA Astrophysics Data System (ADS)

Zhao, B.; Burgmann, R.; Hu, Y.; Tan, K.; Wang, D.; Ghosh, A.

2016-12-01

The Mw7.8 Gorkha earthquake unzipped the lower edge of the locked east central segment of the Main Himalayan Thrust (MHT) on April 25, 2015. Addressing the potential postseismic deformation mechanisms following the earthquake is important for understanding the laterally heterogeneous rheology structure between the India plate and south Tibetan Plateau, the earthquake deformation cycle of shallowly-dipping thrust faults and for assessing seismic hazard of the surrounding un-ruptured fault zone. Here we first analyze three dimensional GPS coordinate time series both in Nepal and in south Tibetan, and calculate the initial 180-day postseismic displacements. We then investigate the contributions of kinematic afterslip, viscous relaxation in the lower crust and upper mantle, and poroelastic rebound models individually. The results show a kinematic afterslip model can explain the GPS observed three dimensional displacements very well, however it needs a very broad distribution and afterslip to depths of more than 30 km, which is unlikely according to the inferred the interseismic coupling pattern, the distribution of coseismic stress increases and evidences from seismic tomography. A viscous relaxation model can fit the far field GPS data in south Tibetan, however it fails to predict the near field GPS data in north Nepal using either homogeneous or heterogeneous rheology earth structure. The poroelastic rebound deformation model alone is also incapable to explain the observations. After removing viscous deformation derived from trial and error using stress-driven finite element model or VISCO2.5D, we obtain a reasonable kinematic afterslip model, showing narrow aseismic slip occurred to 15 to 27km depth, which is close to the average depth of aftershocks. The model inversion finds subtle afterslip in the shallow portion of the MHT and the moment release is about 2.68×1019 Nm, equivalent to a magnitude of Mw7.0. We also constrain the laterally heterogeneous rheology between the India and south Tibetan, an initial effective viscosity of 1018Pa s in Tibet's lower crust and upper mantle below 30 km, and higher viscosity of 1020Pa s in the Indian plate upper mantle.

Upper mantle seismic anisotropy beneath the West Antarctic Rift System and surrounding region from shear wave splitting analysis

NASA Astrophysics Data System (ADS)

Accardo, Natalie J.; Wiens, Douglas A.; Hernandez, Stephen; Aster, Richard C.; Nyblade, Andrew; Huerta, Audrey; Anandakrishnan, Sridhar; Wilson, Terry; Heeszel, David S.; Dalziel, Ian W. D.

2014-07-01

We constrain azimuthal anisotropy in the West Antarctic upper mantle using shear wave splitting parameters obtained from teleseismic SKS, SKKS and PKS phases recorded at 37 broad-band seismometres deployed by the POLENET/ANET project. We use an eigenvalue technique to linearize the rotated and shifted shear wave horizontal particle motions and determine the fast direction and delay time for each arrival. High-quality measurements are stacked to determine the best fitting splitting parameters for each station. Overall, fast anisotropic directions are oriented at large angles to the direction of Antarctic absolute plate motion in both hotspot and no-net-rotation frameworks, showing that the anisotropy does not result from shear due to plate motion over the mantle. Further, the West Antarctic directions are substantially different from those of East Antarctica, indicating that anisotropy across the continent reflects multiple mantle regimes. We suggest that the observed anisotropy along the central Transantarctic Mountains (TAM) and adjacent West Antarctic Rift System (WARS), one of the largest zones of extended continental crust on Earth, results from asthenospheric mantle strain associated with the final pulse of western WARS extension in the late Miocene. Strong and consistent anisotropy throughout the WARS indicate fast axes subparallel to the inferred extension direction, a result unlike reports from the East African rift system and rifts within the Basin and Range, which show much greater variation. We contend that ductile shearing rather than magmatic intrusion may have been the controlling mechanism for accumulation and retention of such coherent, widespread anisotropic fabric. Splitting beneath the Marie Byrd Land Dome (MBL) is weaker than that observed elsewhere within the WARS, but shows a consistent fast direction, possibly representative of anisotropy that has been `frozen-in' to remnant thicker lithosphere. Fast directions observed inland from the Amundsen Sea appear to be radial to the dome and may indicate radial horizontal mantle flow associated with an MBL plume head and low upper mantle velocities in this region, or alternatively to lithospheric features associated with the complex Cenozoic tectonics at the far-eastern end of the WARS.

Meteoric water circulation and rolling-hinge detachment faulting: Example of the Northern Snake Range core complex, Nevada

NASA Astrophysics Data System (ADS)

Gébelin, Aude; Teyssier, Christian; Heizler, Matthew T.; Andreas, Mulch

2014-05-01

The Northern Snake Range metamorphic core complex developed as a consequence of Oligo-Miocene extension of the Basin and Range Province and is bounded by an arched detachment that separates the cold, brittle upper crust from the ductile middle crust. On the western and eastern limbs of the arch, the detachment footwall displays continuous sections of muscovite-bearing quartzite and schist from which we report new microfabrics, δD values, and 40Ar/39Ar ages. Results indicate that the two limbs record distinct stages of the metamorphic and kinematic Cenozoic events, including Eocene collapse of previously overthickned crust in the west, and one main Oligo-Miocene extensional event in the east. Quartzite from the western part of the range preserves Eocene fabrics (~49-45 Ma) that developed during coaxial deformation in the presence of metamorphic fluids. In contrast, those from the east reveal a large component of non coaxial strain, Oligo-Miocene ages (27-21 Ma) and contain recrystallized muscovite grains indicating that meteoric fluids sourced at high elevation (low-δD) infiltrated the brittle-ductile transition zone during deformation. Percolation of meteoric fluids down to the mylonitic detachment footwall was made possible by the development of an east-dipping rolling-hinge detachment system that controlled the timing and location of active faulting in the brittle upper crust and therefore the pathway of fluids from the surface to the brittle-ductile transition. Oligo-Miocene upper crustal extension was accommodated by a fan-shaped fault pattern that generated shear and tension fractures and channelized surface fluids, while top-to-the-east ductile shearing and advection of hot material in the lower plate allowed the system to be progressively exhumed. As extension proceeded, brittle normal faults active in the wedge of the hanging wall gradually rotated and translated above the detachment fault where, became inactive and precluded the circulation of fluids from the surface to the lower plate. The Eocene section observed on the western limb represents an example of such a tilted block that was rotated and exhumed in the first stages of the rolling-hinge detachment activity.

Why did Arabia separate from Africa? Insights from 3-D laboratory experiments

NASA Astrophysics Data System (ADS)

Bellahsen, N.; Faccenna, C.; Funiciello, F.; Daniel, J. M.; Jolivet, L.

2003-11-01

We have performed 3-D scaled lithospheric experiments to investigate the role of the gravitational force exerted by a subducting slab on the deformation of the subducting plate itself. Experiments have been constructed using a dense silicone putty plate, to simulate a thin viscous lithosphere, floating in the middle of a large box filled with glucose syrup, simulating the upper mantle. We examine three different plate configurations: (i) subduction of a uniform oceanic plate, (ii) subduction of an oceanic-continental plate system and, (iii) subduction of a more complex oceanic-continental system simulating the asymmetric Africa-Eurasia system. Each model has been performed with and without the presence of a circular weak zone inside the subducting plate to test the near-surface weakening effect of a plume activity. Our results show that a subducting plate can deform in its interior only if the force distribution varies laterally along the subduction zone, i.e. by the asymmetrical entrance of continental material along the trench. In particular, extensional deformation of the plate occurs when a portion of the subduction zone is locked by the collisional process. The results of this study can be used to analyze the formation of the Arabian plate. We found that intraplate stresses, similar to those that generated the Africa-Arabia break-up, can be related to the Neogene evolution of the northern convergent margin of the African plate, where a lateral change from collision (Mediterranean and Bitlis) to active subduction (Makran) has been described. Second, intraplate stress and strain localization are favored by the presence of a weakness zone, such as the one generated by the Afar plume, producing a pattern of extensional deformation belts resembling the Red Sea-Gulf of Aden rift system.

Accretionary orogens through Earth history

USGS Publications Warehouse

Cawood, Peter A.; Kroner, A.; Collins, W.J.; Kusky, T.M.; Mooney, W.D.; Windley, B.F.

2009-01-01

Accretionary orogens form at intraoceanic and continental margin convergent plate boundaries. They include the supra-subduction zone forearc, magmatic arc and back-arc components. Accretionary orogens can be grouped into retreating and advancing types, based on their kinematic framework and resulting geological character. Retreating orogens (e.g. modern western Pacific) are undergoing long-term extension in response to the site of subduction of the lower plate retreating with respect to the overriding plate and are characterized by back-arc basins. Advancing orogens (e.g. Andes) develop in an environment in which the overriding plate is advancing towards the downgoing plate, resulting in the development of foreland fold and thrust belts and crustal thickening. Cratonization of accretionary orogens occurs during continuing plate convergence and requires transient coupling across the plate boundary with strain concentrated in zones of mechanical and thermal weakening such as the magmatic arc and back-arc region. Potential driving mechanisms for coupling include accretion of buoyant lithosphere (terrane accretion), flat-slab subduction, and rapid absolute upper plate motion overriding the downgoing plate. Accretionary orogens have been active throughout Earth history, extending back until at least 3.2 Ga, and potentially earlier, and provide an important constraint on the initiation of horizontal motion of lithospheric plates on Earth. They have been responsible for major growth of the continental lithosphere through the addition of juvenile magmatic products but are also major sites of consumption and reworking of continental crust through time, through sediment subduction and subduction erosion. It is probable that the rates of crustal growth and destruction are roughly equal, implying that net growth since the Archaean is effectively zero. ?? The Geological Society of London 2009.

Kinematics of a former oceanic plate of the Neotethys revealed by deformation in the Ulukışla basin (Turkey)

NASA Astrophysics Data System (ADS)

Gürer, Derya; van Hinsbergen, Douwe J. J.; Matenco, Liviu; Corfu, Fernando; Cascella, Antonio

2016-10-01

Kinematic reconstruction of modern ocean basins shows that since Pangea breakup a vast area in the Neotethyan realm was lost to subduction. Here we develop a first-order methodology to reconstruct the kinematic history of the lost plates of the Neotethys, using records of subducted plates accreted to (former) overriding plates, combined with the kinematic analysis of overriding plate extension and shortening. In Cretaceous-Paleogene times, most of Anatolia formed a separate tectonic plate—here termed "Anadolu Plate"—that floored part of the Neotethyan oceanic realm, separated from Eurasia and Africa by subduction zones. We study the sedimentary and structural history of the Ulukışla basin (Turkey); overlying relics of this plate to reconstruct the tectonic history of the oceanic plate and its surrounding trenches, relative to Africa and Eurasia. Our results show that Upper Cretaceous-Oligocene sediments were deposited on the newly dated suprasubduction zone ophiolites ( 92 Ma), which are underlain by mélanges, metamorphosed and nonmetamorphosed oceanic and continental rocks derived from the African Plate. The Ulukışla basin underwent latest Cretaceous-Paleocene N-S and E-W extension until 56 Ma. Following a short period of tectonic quiescence, Eo-Oligocene N-S contraction formed the folded structure of the Bolkar Mountains, as well as subordinate contractional structures within the basin. We conceptually explain the transition from extension, to quiescence, to shortening as slowdown of the Anadolu Plate relative to the northward advancing Africa-Anadolu trench resulting from collision of continental rocks accreted to Anadolu with Eurasia, until the gradual demise of the Anadolu-Eurasia subduction zone.

Seismic Attenuation of Teleseismic Body Waves in Cascadia, Measured on the Amphibious Array

NASA Astrophysics Data System (ADS)

Eilon, Z.; Abers, G. A.

2015-12-01

Fundamental questions remain about the nature of the asthenosphere, including its dynamical relationship to overlying lithosphere, melt content, and entrainment in subduction zones. We examine the evolution of this low-velocity, highly attenuating layer using data from the Cascadia Initiative's Amphibious Array, which provides unprecedented coverage of an oceanic plate from ridge crest to trench to sub-arc. Our study extends the suite of measurements achievable with OBS data, augmenting traditional travel time analysis with integrated attenuation data that are a powerful tool for imaging melt/fluids and the variation of asthenospheric character with age. Cooling models, coupled with experimentally-derived anelastic scaling relationships, indicate that thermal gradients should cause appreciable decrease in attenuation of teleseismic body waves with increasing age. This long-wavelength cooling trend may be perturbed by highly attenuating melt or volatiles concentrated at the ridge axis or beneath the Cascades arc, depending on melt fraction and pore geometry. Attenuation beyond the trench should be a strong function of the fate of asthenospheric entrainment beneath subducted plates, with implications for mass transfer to the deep mantle as well as recent models of sub-slab anisotropy. The Amphibious Array, with <70 km spacing of OBS and on-land broadband seismometers deployed between 2011 and 2015, provides a dataset of ~1 x 105 arrivals from ~700 Mw>6.0 teleseismic earthquakes. We use a spectral ratio method to compute differential attenuation (Δt*) from body wave teleseisms recorded at OBS and land stations, allowing us to estimate path-integrated quality factor in the upper mantle. Preliminary results reveal variations of ~3 s in differential travel time and >0.5 s in ΔtS* across the 0-10 Ma oceanic plate, demonstrating the strong thermal control on anelasticity. Large values of Δt* observed east of the trench may indicate entrainment of highly attenuating asthenosphere during subduction, although more work is required to categorize and remove the signal of the overriding plate. This work complements previous studies using surface waves and contributes to our developing understanding of anelastic controls on seismic parameters by probing the Earth in a different frequency range.

Evidence for High and Low Temperature Alteration across Home Plate, Gusev Crater

NASA Astrophysics Data System (ADS)

Schmidt, M. E.; Arvidson, R. E.; Des Marais, D. J.; Farrand, W. H.; Hurowitz, J. A.; Johnson, J. R.; McCoy, T. J.; Ming, D. W.; Ruff, S. W.; Schröder, C.

2008-12-01

Over the last ~2 years in Gusev Crater, the Mars Exploration Rover Spirit has observed coherent variations in mineralogy and geochemistry along an almost circular traverse of Home Plate, an 80 m-diameter outcrop of layered, basaltic tephra. Observations of Home Plate from orbit by the High Resolution Imaging Science Experiment (HiRISE) camera (0.3 m per pixel) and from the summit of Husband Hill (0.7 km to the north) by the Panoramic Camera (Pancam) onboard Spirit show clear longitudinal differences in visible/near- infrared (VNIR) colors, where its eastern region is more blue and western region is more red. Up close, Pancam spectra of rock targets brushed by the Rock Abrasion Tool (RAT) revealed similar variations and confirm that color contrasts observed at greater distances reflect meaningful differences in outcrop mineralogy. Mineralogical observations by the Spirit Mössbauer Spectrometer and Miniature Thermal Emission Spectrometer (Mini-TES) are consistent with the VNIR data, indicating that pyroxene and magnetite dominate the Fe-bearing assemblage at the east side, while olivine, nanophase ferric oxide (npOx), and glass are more abundant at the west. Alpha Particle X-Ray Spectrometer (APXS) observations indicate that eastern Home Plate has higher concentrations of Si, Al, Zn, Ni, and K, while Cl and Br are higher in the west. Compositional similarities in major elements between the two sides of Home Plate, as well as geologic observations indicate that upper, cross-bedded materials that span Home Plate belong to the same stratigraphic unit. However the compositions of more fluid-soluble elements and Fe-bearing minerals in the upper unit vary independently of stratigraphy. We propose that these variations are the result of two distinct alteration regimes: one that produced npOx at the west and another that recrystallized olivine to form pyroxene by Si addition at the east. Abundant npOx at the west is the likely product of breakdown and oxidation of glass or other igneous phases by either low temperature hydrothermal alteration or chemical weathering. Some mass transport during the recrystallization event is implied by small but systematic changes in composition across Home Plate (e.g., decreasing SiO2 and Zn from east to west). Under hydrothermal conditions, SiO2 solubility is increased and Zn and Ni can form temperature-dependent complexes with Cl. The higher concentrations of SiO2, Zn, and Ni in eastern Home Plate rocks indicate that higher temperatures were likely attained there (likely ~300° C to subsolidus temperatures). The localized nature of the high temperature alteration indicates perhaps that the event was relatively short-lived, temperature gradients were steep, and lateral advection was minor across Home Plate.

Spatial distribution of exhumation at the Yakutat plate corner and the role of glacial erosion, southeast Alaska/southwest Yukon

NASA Astrophysics Data System (ADS)

Falkowski, S.; Enkelmann, E.; Ehlers, T. A.

2013-12-01

Our study investigates the spatial and temporal patterns of exhumation along the northernmost part of the transpressive Fairweather Fault in the St. Elias Mountains, southeast Alaska/southwest Yukon. The dextral Fairweather transform fault forms the eastern boundary between the obliquely colliding Yakutat Terrane and the North American Plate. The subduction-collision of the Yakutat Terrane created the St. Elias orogen, which became a prime example to study climate-tectonics interactions. For the past 5-6 myr glacial erosion and mountain building processes coevolved and seem to have become interdependent. We focus on the plate corner region, where the Fairweather Fault bends and tectonics transitions into convergence style. The plate corner is the region of the highest topography (up to 5959 m), extreme relief (up to 5000 m), high seismicity (M>7), and thick, extensive glacial systems (Seward/Bagley and Hubbard glaciers) that erode and transport sediment into the Pacific Ocean. A shortcoming of previous thermochronologic exhumation studies has been that bedrock sampling is restricted to high elevations due to the ice coverage. Using a detrital sampling approach discovered an area of recent, deep exhumation beneath the Seward Glacier by means of detrital zircon fission-track analyses (~3-2 Ma age populations, closure temperature of 250×40 °C). Throughout the rest of the mountains exhumation has been found to be rapid, too, but shallow, resulting in much older zircon cooling ages. To complement previous detrital studies, we collected 26 samples from modern glacio-fluvial sand deposits to gain a better spatial coverage for the cooling signals of the glaciated region of the northernmost Fairweather Fault and the plate corner region. To investigate the long-term exhumation history we conducted zircon fission-track analyses, which yielded 2718 new single grain ages that range between 0.2 Ma and 293 Ma. Each detrital sample contains three to five age populations with peak ages between 1.2×0.7 Ma and 267×64 Ma (1σ). The age distributions show distinctly different exhumation signals for the upper (North American Plate) and lower (Yakutat Terrane) plate of the subduction-collision zone with dominantly Eocene and older cooling on the lower plate and Miocene and younger cooling on the upper plate. The regional distributions of the cooling ages reveal that the area of rapid, deep exhumation extends farther east than previously expected. Furthermore, we propose a large-scale flower-structure that developed since the earliest Pliocene around the northern Fairweather Fault to accommodate strain partitioning within the syntaxis. This development coincides with the onset of glaciation of the orogen and glaciers most likely play an important role in facilitating rock exhumation and uplift by efficiently evacuating material.

Uneven Meibomian Gland Dropout Over the Tarsal Plate and its Correlation With Meibomian Gland Dysfunction.

PubMed

Yin, Yue; Gong, Lan

2015-10-01

To evaluate the distribution of meibomian gland dropout and analyze the correlation between dropout and meibomian gland dysfunction (MGD). A total of 161 eyes of 85 patients with MGD were recruited as the MGD group; 88 eyes of 46 health volunteers were enrolled as the control group (2:1 matched for age and sex). Examinations included the Schirmer I test, breakup time, symptom questionnaire, corneal fluorescein staining, meibum quality, meibomian gland expressibility, and meibomian gland dropout. (1) The incidences of chalazion and eyelid surgery were significantly higher in patients with MGD. (2) All clinical indexes were better in healthy volunteers (all P < 0.05). (3) The dropout in the upper eyelid was statistically lower (P < 0.01) in both groups. The nasal and/or temporal part had higher dropout than did the middle part, except in the lower eyelid of the control group. (4) The entire or partial dropout was positively related to MGD occurrence. Both additive dropout of the entire 2 eyelids and that of the 2 nasal parts had the strongest correlation (r = 0.792, P < 0.01). (5) In the MGD group, breakup time was most negatively related to upper nasal dropout (r = -0.229, P < 0.05). The corneal staining score was positively related only to the dropout of additive (r = 0.185, P < 0.05) and lower (r = 0.258, P < 0.05) middle parts. (1) Uneven dropouts exist in different or single eyelids. (2) Dropout evaluation is better when covering the entire area of both upper and lower meibomians. (3) Nasal part dropout plays a more essential role than the other dropouts in MGD occurrence.

Fractional-order positive position feedback compensator for active vibration control of a smart composite plate

NASA Astrophysics Data System (ADS)

Marinangeli, L.; Alijani, F.; HosseinNia, S. Hassan

2018-01-01

In this paper, Active Vibration Control (AVC) of a rectangular carbon fibre composite plate with free edges is presented. The plate is subjected to out-of-plane excitation by a modal vibration exciter and controlled by Macro Fibre Composite (MFC) transducers. Vibration measurements are performed by using a Laser Doppler Vibrometer (LDV) system. A fractional-order Positive Position Feedback (PPF) compensator is proposed, implemented and compared to the standard integer-order PPF. MFC actuator and sensor are positioned on the plate based on maximal modal strain criterion, so as to control the second natural mode of the plate. Both integer and fractional-order PPF allowed for the effective control of the second mode of vibration. However, the newly proposed fractional-order controller is found to be more efficient in achieving the same performance with less actuation voltage. Moreover, it shows promising performance in reducing spillover effect due to uncontrolled modes.

Crustal structure of the Sunda-Banda arc transition: results from marine geophysical investigations offshore eastern Indonesia

NASA Astrophysics Data System (ADS)

Planert, L.; Shulgin, A.; Kopp, H.; Lueschen, E.; Mueller, C.; Flueh, E.; Djajadihardja, Y.; Engels, M.

2009-04-01

The Sunda-Banda arc transition, the easternmost portion of the Indonesian convergent margin, presents a probably unique natural laboratory to study lower plate variability and related upper plate deformation in the so-called ‘subduction factory' for a deeper understanding of forearc evolution. In neighboring margin segments, we can observe strong changes of the incoming plate (transition from an oceanic to a continental lower plate, increasing plate age to the East, presence/absence of an oceanic plateau, variability in plate roughness) as well as a wide range of corresponding forearc structures, including large sedimentary basins and an accretionary prism/outer arc high of variable size and shape. During RV Sonne cruise SO190 in 2006 (SINDBAD: Seismic and Geoacoustic Investigations along the Sunda-Banda Arc Transition), we acquired a combination of seismic wide-angle OBH/OBS refraction, multichannel streamer and gravity data in order to study the seismic velocity structure of the subducting crust and the overriding island arc along a number of trench normal corridors located between 113°E and 121°E. Additionally, a number of trench parallel profiles were conducted which mainly focus on the internal structure of the large sedimentary basins and which were also intended for further clarifying the type of underlying forearc crust and mantle respectively. We used a tomographic approach for refracted and reflected phases to obtain seismic velocity models which again were used for prestack depth-migration of the MCS data. In turn, we incorporated the highly resolved sedimentary portions as a priori structure in our tomography. The results show the seismic velocity structure of the incoming plate, starting 100 km seaward of the trench, and the adjoining forearc down to depths of 20-28 km, i.e. well into the upper mantle, and at the same time fit the gravity data very well, using simple velocity-density relations. In the Argo abyssal plain, the models show 8.0-8.5 km thick oceanic crust. The velocities in the crust and uppermost mantle are reduced within distances of ~50 km seaward of the trench, which coincides with the onset of normal faulting on the incoming oceanic plate. Anomalously low mantle velocities of 7.5 km/s directly beneath the Moho are possibly due to the intrusion of seawater and subsequent serpentinisation of mantle peridotite. Landward of the trench in the outer arc high, velocities do not exceed 5.5 km/s down to the top of the subducting slab, which can be traced over ~70 km length beneath the forearc down to ~13 km depth. The plate boundary is of irregular shape, obviously imprinted by the complex deformation of the oceanic basement prior to subduction, which is further amplified as response to thrusting/downbending of the dissected oceanic blocks. Offshore Lombok island, our models reveal the geometry of the Lombok basin as well as the forearc Moho in ~16 km depth. Reduced upper mantle velocities suggest a hydrated shallow mantle wedge for this corridor. Further east offshore Sumba island, where the Java trench terminates and the transition to the collisional regime further east occurs, our models show a subducting oceanic plate of similar thickness and structure. But different to the situation offshore Lombok, we find no evidence for a shallow mantle wedge beneath the forearc; crustal-type velocities are found down to depths of ~20 km. The different forearc regime is most likely related to the collision with the Sumba block. Our results give a detailed view into the complex structure in both the deeper and shallower portions of this convergent margin.

Systems and Methods for the Electrodeposition of a Nickel-cobalt Alloy

NASA Technical Reports Server (NTRS)

Ogozalek, Nance Jo (Inventor); Wistrand, Richard E. (Inventor)

2013-01-01

Systems and methods for electrodepositing a nickel-cobalt alloy using a rotating cylinder electrode assembly with a plating surface and an electrical contact. The assembly is placed within a plating bath and rotated while running a plating cycle. Nickel-cobalt alloy deposition is selectively controlled by controlling current density distribution and/or cobalt content in the plating bath while running the plating cycle to deposit an alloy of a desired yield strength onto the plating surface in a single plating cycle. In various embodiments, the rotating cylinder may be used as an insitu monitoring method to assist in obtaining the properties desired.

Microgravity Spray Cooling Research for High Powered Laser Applications

NASA Technical Reports Server (NTRS)

Zivich, Chad P.

2004-01-01

An extremely powerful laser is being developed at Goddard Space Flight Center for use on a satellite. This laser has several potential applications. One application is to use it for upper atmosphere weather research. In this case, the laser would reflect off aerosols in the upper atmosphere and bounce back to the satellite, where the aerosol velocities could be calculated and thus the upper atmosphere weather patterns could be monitored. A second application would be for the US. Air Force, which wants to use the laser strategically as a weapon for satellite defense. The Air Force fears that in the coming years as more and more nations gain limited space capabilities that American satellites may become targets, and the laser could protect the satellites. Regardless of the ultimate application, however, a critical step along the way to putting the laser in space is finding a way to efficiently cool it. While operating the laser becomes very hot and must be cooled to prevent overheating. On earth, this is accomplished by simply running cool tap water over the laser to keep it cool. But on a satellite, this is too inefficient. This would require too much water mass to be practical. Instead, we are investigating spray cooling as a means to cool the laser in microgravity. Spray cooling requires much less volume of fluid, and thus could be suitable for use on a satellite. We have inherited a 2.2 second Drop Tower rig to conduct our research with. In our experiments, water is pressurized with a compressed air tank and sprayed through a nozzle onto our test plate. We can vary the pressure applied to the water and the temperature of the plate before an experiment trial. The whole process takes place in simulated microgravity in the 2.2 second Drop Tower, and a high speed video camera records the spray as it hits the plate. We have made much progress in the past few weeks on these experiments. The rig originally did not have the capability to heat the test plate, but I did some heat transfer calculations and picked out a heater to order for the rig. I learned QBasic programming language to change the operating code for our drops, allowing us to rapidly cycle the spray nozzle open and closed to study the effects. We have derived an equation for flow rate vs. pressure for our experiment. We have recorded several videos of drops at different pressures, some with heated test plate and some without, and have noticed substantial differences in the liquid behavior. I have also changed the computer program to write a file with temperature vs. time profiles for the test plate, and once the necessary thermocouple comes in (it was ordered last week), we will have temperature profiles to accompany the videos. Once we have these temperature profiles to go with the videos, we will be able to see how the temperature is affected by the spray at different pressures, and how the spray changes its behavior once as the plate changes from hot to cool. With quantitative temperature data, we can then mathematically model the heat transfer from the plate to the cooling spray. Finally, we can look at the differences between trials in microgravity and those in normal earth gravity.

Strike-slip earthquakes in the oceanic lithosphere: Observations of exceptionally high apparent stress

USGS Publications Warehouse

Choy, George; McGarr, A.

2002-01-01

The radiated energies, ES, and seismic moments, M0, for 942 globally distributed earthquakes that occurred between 1987 to 1998 are examined to find the earthquakes with the highest apparent stresses (τa=μES/M0, where μ is the modulus of rigidity). The globally averaged τa for shallow earthquakes in all tectonic environments and seismic regions is 0.3 MPa. However, the subset of 49 earthquakes with the highest apparent stresses (τa greater than about 5.0 MPa) is dominated almost exclusively by strike-slip earthquakes that occur in oceanic environments. These earthquakes are all located in the depth range 7–29 km in the upper mantle of the young oceanic lithosphere. Many of these events occur near plate-boundary triple junctions where there appear to be high rates of intraplate deformation. Indeed, the small rapidly deforming Gorda Plate accounts for 10 of the 49 high-τa events. The depth distribution of τa, which shows peak values somewhat greater than 25 MPa in the depth range 20–25 km, suggests that upper bounds on this parameter are a result of the strength of the oceanic lithosphere. A recently proposed envelope for apparent stress, derived by taking 6 per cent of the strength inferred from laboratory experiments for young (less than 30 Ma) deforming oceanic lithosphere, agrees well with the upper-bound envelope of apparent stresses over the depth range 5–30 km. The corresponding depth-dependent shear strength for young oceanic lithosphere attains a peak value of about 575 MPa at a depth of 21 km and then diminishes rapidly as the depth increases. In addition to their high apparent stresses, which suggest that the strength of the young oceanic lithosphere is highest in the depth range 10–30 km, our set of high-τa earthquakes show other features that constrain the nature of the forces that cause interplate motion. First, our set of events is divided roughly equally between intraplate and transform faulting with similar depth distributions of τa for the two types. Secondly, many of the intraplate events have focal mechanisms with the T-axes that are normal to the nearest ridge crest or subduction zone and P-axes that are normal to the proximate transform fault. These observations suggest that forces associated with the reorganization of plate boundaries play an important role in causing high-τa earthquakes inside oceanic plates. Extant transform boundaries may be misaligned with current plate motion. To accommodate current plate motion, the pre-existing plate boundaries would have to be subjected to large horizontal transform push forces. A notable example of this is the triple junction near which the second large aftershock of the 1992 April Cape Mendocino, California, sequence occurred. Alternatively, subduction zone resistance may be enhanced by the collision of a buoyant lithosphere, a process that also markedly increases the horizontal stress. A notable example of this is the Aleutian Trench near which large events occurred in the Gulf of Alaska in late 1987 and the 1998 March Balleny Sea M= 8.2 earthquake within the Antarctic Plate.

Seismic Migration Imaging of the Crust and Upper Mantle Discontinuity Structure beneath Southern Taiwan

NASA Astrophysics Data System (ADS)

Liu, Y.-S.; Kuo, B.-Y.

2009-04-01

Taiwan is located in the convergent plate boundary zone where the Philippine Sea plate has obliquely collided on the Asian continental margin, initiating the arc-continent collision and subsequent mountain-building in Taiwan. Receiver function has been a powerful tool to image seismic velocity discontinuity structure in the crust and upper mantle which can help illuminate the deep dynamic process of active Taiwan orogeny. In this study, we adopt backprojection migration processing of teleseismic receiver functions to investigate the crust and upper mantle discontinuities beneath southern Taiwan, using the data from Southern Taiwan Transect Seismic Array (STTA), broadband stations of Central Weather Bureau (CWB), Broadband Array in Taiwan for Seismology (BATS), and Taiwan Integrated Geodynamics Research (TAIGER). This composite east-west trending linear array has the aperture of about 150 km with the station spacing of ~5-10 km. Superior to the common midpoint (CMP) stack approach, the migration can properly image the dipping, curved, or laterally-varying topography of discontinuous interfaces which very likely exist under the complicated tectonic setting of Taiwan. We first conduct synthetic experiments to test the depth and lateral resolution of migration images based on the WKBJ synthetic waveforms calculated from available source and receiver distributions. We will next construct the 2-D migration image under the array to reveal the topographic variation of the Moho and lithosphere discontinuities beneath southern Taiwan.

Contrasting upper-mantle shear wave anisotropy across the transpressive Queen Charlotte margin

NASA Astrophysics Data System (ADS)

Cao, Lingmin; Kao, Honn; Wang, Kelin

2017-10-01

In order to investigate upper mantle and crustal anisotropy along the transpressive Queen Charlotte margin between the Pacific (PA) and North America (NA) plates, we conducted shear wave splitting analyses using 17 seismic stations in and around the island of Haida Gwaii, Canada. Despite the limited station coverage at present, our reconnaissance study does reveal a systematic pattern of mantle anisotropy in this region. Fast directions derived from teleseismic SKS-phase splitting are mostly margin-parallel (NNW-SSE) near the plate boundary but transition to predominantly E-W-trending farther away. We propose that the former is associated with the absolute motion of PA, and the latter reflects a transition from this direction to that of the absolute motion of NA. The broad width of the zone of transition from the PA to NA direction is probably caused by the very obliquely subducting PA slab that travels primarily in the margin-parallel direction. Anisotropy of Haida Gwaii based on local earthquakes features a fast direction that cannot be explained with regional stresses and is probably associated with local structural fabric within the overriding crust. Our preliminary shear wave splitting measurements and working hypotheses based on them will serve to guide more refined future studies to unravel details of the geometry and kinematics of the subducted PA slab, as well as the viscous coupling between the slab and upper mantle in other transpressive margins.

Constraints on Slow Slip from Landsliding and Faulting

NASA Astrophysics Data System (ADS)

Delbridge, Brent Gregory

The discovery of slow-slip has radically changed the way we understand the relative movement of Earth's tectonic plates and the accumulation of stress in fault zones that fail in large earthquakes. Prior to the discovery of slow-slip, faults were thought to relieve stress either through continuous aseismic sliding, as is the case for continental creeping faults, or in near instantaneous failure. Aseismic deformation reflects fault slip that is slow enough that both inertial forces and seismic radiation are negligible. The durations of observed aseismic slip events range from days to years, with displacements of up to tens of centimeters. These events are not unique to a specific depth range and occur on faults in a variety of tectonic settings. This aseismic slip can sometimes also trigger more rapid slip somewhere else on the fault, such as small embedded asperities. This is thought to be the mechanism generating observed Low Frequency Earthquakes (LFEs) and small repeating earthquakes. I have preformed a series of studies to better understanding the nature of tectonic faulting which are compiled here. The first is entitled "3D surface deformation derived from airborne interferometric UAVSAR: Application to the Slumgullion Landslide", and was originally published in the Journal of Geophysical Research in 2016. In order to understand how landslides respond to environmental forcing, we quantify how the hydro-mechanical forces controlling the Slumgullion Landslide express themselves kinematically in response to the infiltration of seasonal snowmelt. The well-studied Slumgullion Landslide, which is 3.9 km long and moves persistently at rates up to 2 cm/day is an ideal natural laboratory due to its large spatial extent and rapid deformation rates. The lateral boundaries of the landslide consist of strike-slip fault features, which over time have built up large flank ridges. The second study compiled here is entitled "Temporal variation of intermediate-depth earthquakes around the time of the M9.0 Tohoku-oki earthquake" and was originally published in Geophysical Research Letters in 2017. The temporal evolution of intermediate depth seismicity before and after the 2011 M 9.0 Tohoku-oki earthquake reveals interactions between plate interface slip and deformation in the subducting slab. I investigate seismicity rate changes in the upper and lower planes of the double seismic zone beneath northeast Japan. The average ratio of upper plane to lower plane activity and the mean deep aseismic slip rate both increased by factor of two. An increase of down-dip compression in the slab resulting from coseismic and postseismic deformation enhanced seismicity in the upper plane, which is dominated by events accommodating down-dip shortening from plate unbending. In the third and final study included here I use geodetic measurements to place a quantitative upper bound on the size of the slow slip accompanying large bursts of quasi-periodic tremors and LFEs on the Parkfield section of the SAF. We use a host of analysis methods to try to isolate the small signal due to the slow slip and characterize noise properties. We find that in addition to subduction zones, transform faults are also capable of producing ETSs. However, given the upper-bounds from our analysis, surface geodetic measurements of this slow slip is likely to remain highly challenging.

Flexible thermal apparatus for mounting of thermoelectric cooler

NASA Technical Reports Server (NTRS)

Jones, Jack A. (Inventor); Petrick, S. Walter (Inventor); Bard, Steven (Inventor)

1991-01-01

A flexible heat transfer apparatus used to flexibly connect and thermally couple a thermoelectric cooler to an object to be cooled is disclosed. The flexible heat transfer apparatus consists of a pair of flexible corrugated sheets made from high thermal conductivity materials such as copper, aluminum, gold, or silver. The ridges of the corrugated sheets are oriented perpendicular to one another and bonded sandwich-fashion between three plates to define an upper section and a lower section. The upper section provides X flexure, the lower section provides Y flexure, and both sections together provide Z flexure.

Study on numerical simulation of asymmetric structure aluminum profile extrusion based on ALE method

NASA Astrophysics Data System (ADS)

Chen, Kun; Qu, Yuan; Ding, Siyi; Liu, Changhui; Yang, Fuyong

2018-05-01

Using the HyperXtrude module based on the Arbitrary Lagrangian-Eulerian (ALE) finite element method, the paper simulates the steady extrusion process of the asymmetric structure aluminum die successfully. A verification experiment is carried out to verify the simulation results. Having obtained and analyzed the stress-strain field, temperature field and extruded velocity of the metal, it confirms that the simulation prediction results and the experimental schemes are consistent. The scheme of the die correction and optimization are discussed at last. By adjusting the bearing length and core thickness, adopting the structure of feeder plate protection, short shunt bridge in the upper die and three-level bonding container in the lower die to control the metal flowing, the qualified aluminum profile can be obtained.

Clinical comparison of two different plating methods in minimally invasive plate osteosynthesis for clavicular midshaft fractures: A randomized controlled trial.

PubMed

Sohn, Hoon-Sang; Shon, Min Soo; Lee, Kyung-Hag; Song, Si-Jung

2015-11-01

The aim of this study was to compare the clinical and radiographic outcomes between two different plating methods (superior vs. anteroinferior) in minimally invasive plate osteosynthesis (MIPO) for acute displaced clavicular shaft fractures. A prospective, randomized controlled trial was performed in a single centre. Nineteen patients were treated with superior plating and 18 with anteroinferior plating using the MIPO technique. A 3.5-mm locking reconstruction plate was bent preoperatively and applied to either the anteroinferior or superior aspect of the clavicle through two separate incisions. The operating time, time to union, the proportional length difference, complications, and functional outcome of the shoulder joint were evaluated using the Constant score and the University of California Los Angeles (UCLA) score. There was no statistically significant difference in the Constant score and UCLA score. The mean time to union was 16.8 weeks for superior plating and 17.1 weeks for anteroinferior plating (p=0.866). The average operation time was 77.2min in superior plating and 79.4min in anteroinferior plating (p=0.491). One patient in the superior plating group showed plate failure. Despite no significant difference, one patient had nonunion in the superior plating group (p>0.999). From a clinical perspective, although MIPO with anteroinferior plating provides better outcomes especially in complications without statistically significant difference, both plating methods provided satisfactory clinical and radiographic outcomes. Level I, a single-centre, prospective, randomized controlled trial. Copyright © 2015 Elsevier Ltd. All rights reserved.

The New Britain trench and 149° embayment, Western Solomon Sea

NASA Astrophysics Data System (ADS)

Tiffin, D. L.; Davies, H. L.; Honza, E.; Lock, J.; Okuda, Y.

1987-09-01

The western New Britain Trench contains relatively thin sediment fill in the east, compared to the west where a sequence of thick turbidites is ponded behind a basement high in the trench axis, The trench trends toward Huon Gulf, but intersects the Trobriand Trench at an acute angle at the 149° Embayment, where both trenches end. Seismic structure west of the trench is incoherent, related to incipient collision of the Indian-Australia Plate and the South Bismarck Plate. The collision suture is marked by the Markham Canyon, continuous in its upper reaches with the Ramu-Markham Fault Zone on shore.

Posttraumatic tibia valga: a case demonstrating asymmetric activity at the proximal growth plate on technetium bone scan

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

Zionts, L.E.; Harcke, H.T.; Brooks, K.M.

1987-07-01

Posttraumatic tibia valga is a well-recognized complication following fracture of the upper tibial metaphysis in young children. We present a case of a child who developed a valgus deformity following fracture of the proximal tibia and fibula in which quantitative bone scintigraphy at 5 months after injury demonstrated increased uptake at the proximal tibial growth plate with proportionally greater uptake on the medial side. This finding suggests that the valgus deformity in this patient was due to a relative increase in vascularity and consequent overgrowth of the medial portion of the proximal tibial physis.

Control of boundary layer transition location and plate vibration in the presence of an external acoustic field

NASA Technical Reports Server (NTRS)

Maestrello, L.; Grosveld, F. W.

1991-01-01

The experiment is aimed at controlling the boundary layer transition location and the plate vibration when excited by a flow and an upstream sound source. Sound has been found to affect the flow at the leading edge and the response of a flexible plate in a boundary layer. Because the sound induces early transition, the panel vibration is acoustically coupled to the turbulent boundary layer by the upstream radiation. Localized surface heating at the leading edge delays the transition location downstream of the flexible plate. The response of the plate excited by a turbulent boundary layer (without sound) shows that the plate is forced to vibrate at different frequencies and with different amplitudes as the flow velocity changes indicating that the plate is driven by the convective waves of the boundary layer. The acoustic disturbances induced by the upstream sound dominate the response of the plate when the boundary layer is either turbulent or laminar. Active vibration control was used to reduce the sound induced displacement amplitude of the plate.

Lateral heterogeneity and azimuthal anistropy of the upper mantle: Love and Rayleigh waves 100-250 sec

NASA Technical Reports Server (NTRS)

Tanimoto, T.; Anderson, D. L.

1983-01-01

The lateral heterogeneity and apparent anisotropy of the upper mantle are studied by measuring Rayleigh and Love wave phase velocities in the period range 100-250 sec. Spherical harmonic descriptions of the lateral heterogeneity are obtained for order and degree up to 1=m=10. Slow regions are evident at the East Pacific rise, northeast Africa, Tibet, Tasman sea, southwestern North America and triple junctions in the Northern Atlantic and Indian oceans. Fast regions occur in Australia, western Pacific and the eastern Atlantic. Details which are not evident in previous studies include two fast regions in the central Pacific and the subduction zone in the Scotia Arc region. Inversion for azimuthal dependence showed (1) little correlation between the fast phase velocity directions and the plate motion vector in plate interiors, but (2) correlation of the fast direction with the perpendicular direction to trenches and ridges. Phase velocity is high when waves propagate perpendicular to these structures. Severe tradeoffs exist between heterogeneity and azimuthal dependence because of the yet unsatisfactory path coverage.

Lateral heterogeneity and azimuthal anisotropy of the upper mantle - Love and Rayleigh waves 100-250 sec

NASA Technical Reports Server (NTRS)

Tanimoto, T.; Anderson, D. L.

1985-01-01

The lateral heterogeneity and apparent anisotropy of the upper mantle are studied by measuring Rayleigh and Love wave phase velocities in the period range 100-250 sec. Spherical harmonic descriptions of the lateral heterogeneity are obtained for order and degree up to 1=m=10. Slow regions are evident at the East Pacific rise, northeast Africa, Tibet, Tasman sea, southwestern North America and triple junctions in the Northern Atlantic and Indian oceans. Fast regions occur in Australia, western Pacific and the eastern Atlantic. Details which are not evident in previous studies include two fast regions in the central Pacific and the subduction zone in the Scotia Arc region. Inversion for azimuthal dependence showed (1) little correlation between the fast phase velocity directions and the plate motion vector in plate interiors, but (2) correlation of the fast direction with the perpendicular direction to trenches and ridges. Phase velocity is high when waves propagate perpendicular to these structures. Severe tradeoffs exist between heterogeneity and azimuthal dependence because of the yet unsatisfactory path coverage.

Separator

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

Ashbrook, C.L.

1970-09-22

A separator consists of a housing having an upper fluid inlet and a lower fluid outlet in the sides of the housing. An inverted conical tube is disposed internally of the housing and is in fluid communication with the fluid inlet. The upper fluid inlet tangentially intersects the inverted conical tube so as to create a rotating vortex upon introduction of the mixture. Axially disposed within the vortex tube at the upper end is a withdrawal tube for removing lighter mixture components that are drawn toward the center of the tube. At the lower end of the vortex tube ismore » an adjustable impact plate for transmitting a concussion wave through the vortexed body, so as to cause cavitation. Heavier mixture components gravitate toward the lower fluid outlet and are withdrawn through it. (7 claims)« less

Precise hypocenter distribution and earthquake generating and stress in and around the upper-plane seismic belt in the subducting Pacific slab beneath NE Japan

NASA Astrophysics Data System (ADS)

Kita, S.; Okada, T.; Nakajima, J.; Matsuzawa, T.; Uchida, N.; Hasegawa, A.

2007-12-01

1. Introduction We found an intraslab seismic belt (upper-plane seismic belt) in the upper plane of the double seismic zone within the Pacific slab, running interface at depths of 70-100km beneath the forearc area. The location of the deeper limits of this belt appears to correspond to one of the facies boundaries (from jadeite lawsonite blueschist to lawsonite amphibole eclogite) in the oceanic crust [Kita et al., 2006, GRL]. In this study, we precisely relocated intraslab earthquakes by using travel time differences calculated by the waveform cross-spectrum analysis to obtain more detailed distribution of the upper plane-seismic belt within the Pacific slab beneath NE Japan. We also discuss the stress field in the slab by examining focal mechanisms of the earthquakes. 2. Data and Method We relocated events at depths of 50-00 km for the period from March 2003 to November 2006 from the JMA earthquake catalog. We applied the double-difference hypocenter location method (DDLM) by Waldhauser and Ellsworth (2000) to the arrival time data of the events. We use relative earthquake arrival times determined both by the waveform cross-spectrum analysis and by the catalog-picking data. We also determine focal mechanisms using the P wave polarity. 3. Spatial distribution of relocated hypocenters In the upper portion of the slab crust, seismicity is very active and distributed relatively homogeneously at depths of about 70-100km parallel to the volcanic front, where the upper-plane seismic belt has been found. In the lower portion of slab crust and/or the uppermost portion of the slab mantle, seismicity is spatially very limited to some small areas (each size is about 20 x 20km) at depths around 65km. Two of them correspond to the aftershock area of the 2003 Miyagi (M7.1) intraslab earthquake and that of the 1987 Iwaizumi (M6.6) intraslab earthquake, respectively. Based on the dehydration embrittelment hypothesis, the difference of the spatial distribution of the seismicity in the slab should correspond to the difference of the spatial distribution of the hydrated minerals and their dehydration reactions. In the upper slab crust, the upper-plane seismic belt is found because the hydrated minerals could be distributed homogeneously and the dehydration reaction (from jadeite lawsonite blueschist to lawsonite amphibole eclogite [Hacker et al., 2003b]) occurs perhaps largely at depth of 70-100km. Our result also suggests that in the lower portion of the slab crust and/or the uppermost portion of the slab mantle, the hydrated minerals could be inhomogeneously distributed and the seismicity occurs at depths around 65km, where another dehydration reaction may exist. 4. Characteristics of the focal mechanisms We examined the stress distribution within the slab by using focal mechanisms of the upper plane, interplane and lower plane events. From the plate interface to about 20 km below it, downdip-compressional (DC) type events are dominant. Below 20km from the plate interface, downdip-tensional (DT) type events are dominant. Many of interplane events have DC type focal mechanisms because of their locations in the uppermost portions of the slab mantle. These results indicate that the stress neutral plane from the DC type to DT type could be located at depth of about 20km from the plate interface.

Non-linear feedbacks drive strain partitioning within an active orogen, southern Alaska

NASA Astrophysics Data System (ADS)

Hooks, B.; Koons, P. O.; Upton, P.

2011-12-01

Temperature plays a very important role in the partitioning of deformation within an active orogen. Local variations in the thermal structure of actively uplifting areas can reinforce focused partitioning of strain locally, whereas regional variations can alter deformation patterns on a much broader scale resulting in the re-organization of an entire orogen. Within southern Alaska, the Yakutat micro-terrane has been subducting beneath North America over the previous ~10 Ma. Early deformation related to this event drove uplift of the Alaska Range, as evidenced by stratigraphic and thermochronologic datasets. This was followed by a southerly discontinuous spatial jump in the deformation front to the coastal St. Elias Range. Here we present 3D numerical models that simulate deformation of Earth materials given assigned applied velocity boundary conditions and mechanical and thermal constitutive relationships on a macro- (plate boundary) and meso-scale (<50-km). The goal is to reproduce first-order strain and uplift patterns within this evolving orogen. The macro-scale model undergoes a spatial and temporal reorganization of deformation as strain is progressively shifted to a trench-ward orogenic wedge, the inlet orogen. Subduction related cooling of the fore-arc (i.e. tectonic refrigeration) provides control on the location of the inlet orogen. This control is based upon the creation of a thin sliver of cold, strong material along the mega-thrust interface. The stronger mega-thrust facilitates more efficient transfer of strain, driving the formation of the inlet orogen and determining the location of its frontal toe. This toe is further stabilized by upward displacement of the upper crust over the refrigerated section. This upward motion causes thermal weakening of the upper crust as a tectonic aneurysm with the location controlled by the thermally strengthened lower crust. The net result is an ever weakening upper crust that focuses strain creating dramatic topography, extreme rates of erosion and uplift, and fast exhumation.

Active constrained layer damping of geometrically nonlinear vibrations of functionally graded plates using piezoelectric fiber-reinforced composites

NASA Astrophysics Data System (ADS)

Panda, Satyajit; Ray, M. C.

2008-04-01

In this paper, a geometrically nonlinear dynamic analysis has been presented for functionally graded (FG) plates integrated with a patch of active constrained layer damping (ACLD) treatment and subjected to a temperature field. The constraining layer of the ACLD treatment is considered to be made of the piezoelectric fiber-reinforced composite (PFRC) material. The temperature field is assumed to be spatially uniform over the substrate plate surfaces and varied through the thickness of the host FG plates. The temperature-dependent material properties of the FG substrate plates are assumed to be graded in the thickness direction of the plates according to a power-law distribution while the Poisson's ratio is assumed to be a constant over the domain of the plate. The constrained viscoelastic layer of the ACLD treatment is modeled using the Golla-Hughes-McTavish (GHM) method. Based on the first-order shear deformation theory, a three-dimensional finite element model has been developed to model the open-loop and closed-loop nonlinear dynamics of the overall FG substrate plates under the thermal environment. The analysis suggests the potential use of the ACLD treatment with its constraining layer made of the PFRC material for active control of geometrically nonlinear vibrations of FG plates in the absence or the presence of the temperature gradient across the thickness of the plates. It is found that the ACLD treatment is more effective in controlling the geometrically nonlinear vibrations of FG plates than in controlling their linear vibrations. The analysis also reveals that the ACLD patch is more effective for controlling the nonlinear vibrations of FG plates when it is attached to the softest surface of the FG plates than when it is bonded to the stiffest surface of the plates. The effect of piezoelectric fiber orientation in the active constraining PFRC layer on the damping characteristics of the overall FG plates is also discussed.

Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust

USGS Publications Warehouse

von Huene, Roland E.; Scholl, D. W.

1991-01-01

At ocean margins where two plates converge, the oceanic plate sinks or is subducted beneath an upper one topped by a layer of terrestrial crust. This crust is constructed of continental or island arc material. The subduction process either builds juvenile masses of terrestrial crust through arc volcanism or new areas of crust through the piling up of accretionary masses (prisms) of sedimentary deposits and fragments of thicker crustal bodies scraped off the subducting lower plate. At convergent margins, terrestrial material can also bypass the accretionary prism as a result of sediment subduction, and terrestrial matter can be removed from the upper plate by processes of subduction erosion. Sediment subduction occurs where sediment remains attached to the subducting oceanic plate and underthrusts the seaward position of the upper plate's resistive buttress (backstop) of consolidated sediment and rock. Sediment subduction occurs at two types of convergent margins: type 1 margins where accretionary prisms form and type 2 margins where little net accretion takes place. At type 2 margins (???19,000 km in global length), effectively all incoming sediment is subducted beneath the massif of basement or framework rocks forming the landward trench slope. At accreting or type 1 margins, sediment subduction begins at the seaward position of an active buttress of consolidated accretionary material that accumulated in front of a starting or core buttress of framework rocks. Where small-to-mediumsized prisms have formed (???16,300 km), approximately 20% of the incoming sediment is skimmed off a detachment surface or decollement and frontally accreted to the active buttress. The remaining 80% subducts beneath the buttress and may either underplate older parts of the frontal body or bypass the prism entirely and underthrust the leading edge of the margin's rock framework. At margins bordered by large prisms (???8,200 km), roughly 70% of the incoming trench floor section is subducted beneath the frontal accretionary body and its active buttress. In rounded figures the contemporary rate of solid-volume sediment subduction at convergent ocean margins (???43,500 km) is calculated to be 1.5 km3/yr. Correcting type 1 margins for high rates of terrigenous seafloor sedimentation during the past 30 m.y. or so sets the long-term rate of sediment subduction at 1.0 km3/yr. The bulk of the subducted material is derived directly or indirectly from continental denudation. Interstitial water currently expulsed from accreted and deeply subducted sediment and recycled to the ocean basins is estimated at 0.9 km3/yr. The thinning and truncation caused by subduction erosion of the margin's framework rock and overlying sedimentary deposits have been demonstrated at many convergent margins but only off northern Japan, central Peru, and northern Chile has sufficient information been collected to determine average or long-term rates, which range from 25 to 50 km3/m.y. per kilometer of margin. A conservative long-term rate applicable to many sectors of convergent margins is 30 km3/km/m.y. If applied to the length of type 2 margins, subduction erosion removes and transports approximately 0.6 km3/yr of upper plate material to greater depths. At various places, subduction erosion also affects sectors of type 1 margins bordered by small- to medium-sized accretionary prisms (for example, Japan and Peru), thus increasing the global rate by possibly 0.5 km3/yr to a total of 1.1 km3/yr. Little information is available to assess subduction erosion at margins bordered by large accretionary prisms. Mass balance calculations allow assessments to be made of the amount of subducted sediment that bypasses the prism and underthrusts the margin's rock framework. This subcrustally subducted sediment is estimated at 0.7 km3/yr. Combined with the range of terrestrial matter removed from the margin's rock framework by subduction erosion, the global volume of subcrustally subducted materia

Lithospheric velocity structure of the Anatolian plateau-Caucasus-Caspian region

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

Gök, R.; Mellors, R. J.; Sandvol, E.

The Anatolian plateau-Caucasus-Caspian region is an area of complex lithospheric structure accompanied by large variations in seismic wave velocities. Despite the complexity of the region, little is known about the detailed lithospheric structure. Using data from 31 new, permanent broadband seismic stations along with results from a previous 29 temporary seismic stations and 3 existing global seismic stations in the region, a 3-D velocity model is developed using joint inversion of teleseismic receiver functions and surface waves. Both group and phase dispersion curves (Love and Rayleigh) were derived from regional and teleseismic events. Additional Rayleigh wave group dispersion curves weremore » determined using ambient noise correlation. Receiver functions were calculated using P arrivals from 789 teleseismic (30°–90°) earthquakes. The stacked receiver functions and surface wave dispersion curves were jointly inverted to yield the absolute shear wave velocity to a depth of 100 km at each station. The depths of major discontinuities (sediment-basement, crust-mantle, and lithosphere-asthenosphere) were inferred from the velocity-depth profiles at the location of each station. Distinct spatial variations in crustal and upper mantle shear velocities were observed. The Kura basin showed slow (~2.7–2.9 km/s) upper crustal (0–11 km) velocities but elevated (~3.8–3.9 km/s) velocities in the lower crust. The Anatolian plateau varied from ~3.1–3.2 in the upper crust to ~3.5–3.7 in the lower crust, while velocities in the Arabian plate (south of the Bitlis suture) were slightly faster (upper crust between 3.3 and 3.4 km/s and lower crust between 3.8 and 3.9 km/s). The depth of the Moho, which was estimated from the shear velocity profiles, was 35 km in the Arabian plate and increased northward to 54 km at the southern edge of the Greater Caucasus. Moho depths in the Kura and at the edge of the Caspian showed more spatial variability but ranged between 35 and 45 km. Upper mantle velocities were slow under the Anatolian plateau but increased to the south under the Arabian plate and to the east (4.3–4.4 km/s) under the Kura basin and Greater Caucasus. The areas of slow mantle coincided with the locations of Holocene volcanoes. Differences between Rayleigh and Love dispersions at long wavelengths reveal a pronounced variation in anisotropy between the Anatolian plateau and the Kura basin.« less

Lithospheric velocity structure of the Anatolian plateau-Caucasus-Caspian region

DOE PAGES

Gök, R.; Mellors, R. J.; Sandvol, E.; ...

2011-05-07

The Anatolian plateau-Caucasus-Caspian region is an area of complex lithospheric structure accompanied by large variations in seismic wave velocities. Despite the complexity of the region, little is known about the detailed lithospheric structure. Using data from 31 new, permanent broadband seismic stations along with results from a previous 29 temporary seismic stations and 3 existing global seismic stations in the region, a 3-D velocity model is developed using joint inversion of teleseismic receiver functions and surface waves. Both group and phase dispersion curves (Love and Rayleigh) were derived from regional and teleseismic events. Additional Rayleigh wave group dispersion curves weremore » determined using ambient noise correlation. Receiver functions were calculated using P arrivals from 789 teleseismic (30°–90°) earthquakes. The stacked receiver functions and surface wave dispersion curves were jointly inverted to yield the absolute shear wave velocity to a depth of 100 km at each station. The depths of major discontinuities (sediment-basement, crust-mantle, and lithosphere-asthenosphere) were inferred from the velocity-depth profiles at the location of each station. Distinct spatial variations in crustal and upper mantle shear velocities were observed. The Kura basin showed slow (~2.7–2.9 km/s) upper crustal (0–11 km) velocities but elevated (~3.8–3.9 km/s) velocities in the lower crust. The Anatolian plateau varied from ~3.1–3.2 in the upper crust to ~3.5–3.7 in the lower crust, while velocities in the Arabian plate (south of the Bitlis suture) were slightly faster (upper crust between 3.3 and 3.4 km/s and lower crust between 3.8 and 3.9 km/s). The depth of the Moho, which was estimated from the shear velocity profiles, was 35 km in the Arabian plate and increased northward to 54 km at the southern edge of the Greater Caucasus. Moho depths in the Kura and at the edge of the Caspian showed more spatial variability but ranged between 35 and 45 km. Upper mantle velocities were slow under the Anatolian plateau but increased to the south under the Arabian plate and to the east (4.3–4.4 km/s) under the Kura basin and Greater Caucasus. The areas of slow mantle coincided with the locations of Holocene volcanoes. Differences between Rayleigh and Love dispersions at long wavelengths reveal a pronounced variation in anisotropy between the Anatolian plateau and the Kura basin.« less

A reevaluation of the age of the Vincent-Chocolate Mountains thrust system, southern California

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

Jacobsen, C.E.; Barth, A.P.

1993-04-01

The Vincent-Chocolate Mountains (VCM) thrust superposes Mesozoic arc plutons and associated Precambrian country rock above subduction-related Pelona-Orocopia schist. The thrust is disrupted in many areas by postmetamorphic deformation, but appears to be intact in the San Gabriel Mountains. Two Rb-Sr mineral-isochron ages from Pelona Schist and mylonite in the San Gabriel Mountains led Ehlig (1981) to conclude that the original thrusting event occurred at c. 60 Ma. However, biotite K-Ar ages determined by Miller and Morton (1980) for upper plate in the same area caused Dillon (1986) to reach a different conclusion. The biotite ages range mainly from 74--60 Mamore » and increase structurally upward from the VCM thrust. Dillon (1986) inferred that the age gradient was due to uplift and cooling of the upper plate during underthrusting of Pelona Schist. This would indicate that the VCM thrust was at least 74 Ma in age. An alternative to the interpretation of Dillon (1986) is that the biotite age gradient largely predates the VCM thrust. Upward heat flow, leading to older ages at higher structural levels, could have resulted from either static cooling of Cretaceous plutons or uplift and erosion induced by crustal thickening during possible west-directed intra-arc thrusting at c. 88--78 Ma (May and Walker, 1989). Subsequent underthrusting of Pelona Schist would establish a cold lower boundary to the crust and cause the closure of isotopic systems in the base of the upper plate. A 60 Ma time of thrusting is also suggested by two amphibole [sup 40]Ar/[sup 39]Ar ages from the Pelona Schist of the San Gabriel Mountains. Peak metamorphic temperature in this area was below 480 C and amphibole ages should thus indicate time of crystallization rather than subsequent cooling. Four phengite [sup 40]Ar/[sup 39]Ar ages of 55--61 Ma from Pelona Schist and mylonite indicate rapid cooling from peak metamorphic temperatures, consistent with subduction refrigeration.« less