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.

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.

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

Nuclear reactor internals alignment configuration

DOEpatents

Gilmore, Charles B [Greensburg, PA; Singleton, Norman R [Murrysville, PA

2009-11-10

An alignment system that employs jacking block assemblies and alignment posts around the periphery of the top plate of a nuclear reactor lower internals core shroud to align an upper core plate with the lower internals and the core shroud with the core barrel. The distal ends of the alignment posts are chamfered and are closely received within notches machined in the upper core plate at spaced locations around the outer circumference of the upper core plate. The jacking block assemblies are used to center the core shroud in the core barrel and the alignment posts assure the proper orientation of the upper core plate. The alignment posts may alternately be formed in the upper core plate and the notches may be formed in top plate.

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.

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.

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.

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

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.

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.

Divergent plate motion drives rapid exhumation of (ultra)high pressure rocks

NASA Astrophysics Data System (ADS)

Liao, Jie; Malusà, Marco G.; Zhao, Liang; Baldwin, Suzanne L.; Fitzgerald, Paul G.; Gerya, Taras

2018-06-01

Exhumation of (ultra)high pressure [(U)HP] rocks by upper-plate divergent motion above an unbroken slab, first proposed in the Western Alps, has never been tested by numerical methods. We present 2D thermo-mechanical models incorporating subduction of a thinned continental margin beneath either a continental or oceanic upper plate, followed by upper-plate divergent motion away from the lower plate. Results demonstrate how divergent plate motion may trigger rapid exhumation of large volumes of (U)HP rocks directly to the Earth's surface, without the need for significant overburden removal by erosion. Model exhumation paths are fully consistent with natural examples for a wide range of upper-plate divergence rates. Exhumation rates are systematically higher than the divergent rate imposed to the upper plate, and the modeled size of exhumed (U)HP domes is invariant for different rates of upper-plate divergence. Major variations are instead predicted at depth for differing model scenarios, as larger amounts of divergent motion may allow mantle-wedge exhumation to shallow depth under the exhuming domes. The transient temperature increase, due to ascent of mantle-wedge material in the subduction channel, has a limited effect on exhumed continental (U)HP rocks already at the surface. We test two examples, the Cenozoic (U)HP terranes of the Western Alps (continental upper plate) and eastern Papua New Guinea (oceanic upper plate). The good fit between model predictions and the geologic record in these terranes encourages the application of these models globally to pre-Cenozoic (U)HP terranes where the geologic record of exhumation is only partly preserved.

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.

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.

Multicolor printing plate joining

NASA Technical Reports Server (NTRS)

Waters, W. J. (Inventor)

1984-01-01

An upper plate having ink flow channels and a lower plate having a multicolored pattern are joined. The joining is accomplished without clogging any ink flow paths. A pattern having different colored parts and apertures is formed in a lower plate. Ink flow channels each having respective ink input ports are formed in an upper plate. The ink flow channels are coated with solder mask and the bottom of the upper plate is then coated with solder. The upper and lower plates are pressed together at from 2 to 5 psi and heated to a temperature of from 295 F to 750 F or enough to melt the solder. After the plates have cooled and the pressure is released, the solder mask is removed from the interior passageways by means of a liquid solvent.

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.

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.

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.

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.

PWR integral tie plate and locking mechanism

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

Flora, B.S.; Osborne, J.L.

1980-08-26

A locking mechanism for securing an upper tie plate to the tie rods of a nuclear fuel bundle is described. The mechanism includes an upper tie plate assembly and locking sleeves fixed to the ends of the tie rods. The tie plate is part of the upper tie plate assembly and is secured to the fuel bundle by securing the entire upper tie plate assembly to the locking sleeves fixed to the tie rods. The assembly includes, in addition to the tie plate, locking nuts for engaging the locking sleeves, retaining sleeves to operably connect the locking nuts to themore » assembly, a spring biased reaction plate to restrain the locking nuts in the locked position and a means to facilitate the removal of the entire assembly as a unit from the fuel bundle.« less

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.

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.

Analog Modeling of the Interplay between Subduction and Lateral Extrusion in the European Alps

NASA Astrophysics Data System (ADS)

van Gelder, I. E.; Willingshofer, E.; Sokoutis, D.

2014-12-01

In the European Alps lateral extrusion is traditionally viewed as a lithospheric scale process that is related to northward indentation of a weak orogenic wedge (the eastern Alps) by a rigid indenter in upper plate position (the Adriatic plate). Critical for the efficiency of the extrusion process is the presence of a 'free boundary' at high angle to the indentation direction. The 'free boundary' in the eastern Alps is the result of the eastward extending Pannonian realm synchronous to indentation. However, indentation has become debatable as recent high-resolution tomography suggests that the Adriatic mantle lithosphere subducted under the extruding Alps. These findings raise first order questions related to: (a) the partitioning of deformation between lateral extrusion of the upper plate and coeval subduction of Adria, (b) the rheology of the lower and upper plates, and (c) the rheology of the plate contact controlling the amount of extrusion on the upper plate vs. accretion on the lower plate.In this analog modeling study, we couple for the first time lateral extrusion tectonics to subduction of the lower plate; thus, extrusion taking place in the upper plate. Within the lithospheric scale models, the lithospheres of the two plates are weakly coupled along an inclined boundary and have contrasting mantle lithosphere strength (stronger in the subducting plate). The interplay of extrusion vs subduction is inferred by varying the mechanical boundary conditions, e.g. the degree of resistance at the 'unconstrained' margin, the strength contrast between the upper and the lower plates and the width of the indented region.The experimental results emphasize that extrusion in the eastern Alps is compatible with coeval subduction of the Adriatic plate. The first experimental series suggests that the following mechanical conditions play a key role in the interplay between extrusion and subduction: (a) the extruding plate is weaker than the subducting plate, (b) the plate contact is weak in order to trigger the subduction of the lower plate, and (c) the eastern boundary is weak and thus allows for accommodating the extruding upper plate.

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.

Piezoelectric film load cell robot collision detector

DOEpatents

Lembke, J.R.

1988-03-15

A piezoelectric load cell which can be utilized for detecting collisions and obstruction of a robot arm end effector includes a force sensing element of metallized polyvinylidene fluoride (PVDF) film. The piezoelectric film sensing element and a resilient support pad are clamped in compression between upper and lower plates. The lower plate has a central recess in its upper face for supporting the support pad and sensing element, while the upper plate has a corresponding central projection formed on its lower face for bearing on the sensing element and support pad. The upper and lower plates are dowelled together for concentric alignment and screwed together. The upper and lower plates are also adapted for mounting between the robot arm wrist and end effector. 3 figs.

Piezoelectric film load cell robot collision detector

DOEpatents

Lembke, John R.

1989-04-18

A piezoelectric load cell which can be utilized for detecting collisions and obstruction of a robot arm end effector includes a force sensing element of metallized polyvinylidene fluoride (PVDF) film. The piezoelectric film sensing element and a resilient support pad are clamped in compression between upper and lower plates. The lower plate has a central recess in its upper face for supporting the support pad and sensing element, while the upper plate has a corresponding central projection formed on its lower face for bearing on the sensing element and support pad. The upper and lower plates are dowelled together for concentric alignment and screwed together. The upper and lower plates are also adapted for mounting between the robot arm wrist and end effector.

Piezoelectric film load cell robot collision detector

DOEpatents

Lembke, J.R.

1989-04-18

A piezoelectric load cell which can be utilized for detecting collisions and obstruction of a robot arm end effector includes a force sensing element of metallized polyvinylidene fluoride (PVDF) film. The piezoelectric film sensing element and a resilient support pad are clamped in compression between upper and lower plates. The lower plate has a central recess in its upper face for supporting the support pad and sensing element, while the upper plate has a corresponding central projection formed on its lower face for bearing on the sensing element and support pad. The upper and lower plates are doweled together for concentric alignment and screwed together. The upper and lower plates are also adapted for mounting between the robot arm wrist and end effector. 3 figs.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Origin of the Indian Ocean-type isotopic signature in basalts from Philippine Sea plate spreading centers: An assessment of local versus large-scale processes

NASA Astrophysics Data System (ADS)

Hickey-Vargas, Rosemary

1998-09-01

Basalts erupted from spreading centers on the Philippine Sea plate between 50 Ma and the present have the distinctive isotopic characteristics of Indian Ocean mid-ocean ridge basalt (MORB), such as high 208Pb/204Pb and low 143Nd/144Nd for a given 206Pb/204Pb compared with Pacific and Atlantic Ocean MORB. This feature may indicate that the upper mantle of the Philippine Sea plate originated as part of the existing Indian Ocean upper mantle domain, or, alternatively, that local processes duplicated these isotopic characteristics within the sub-Philippine Sea plate upper mantle. Synthesis of new and published isotopic data for Philippine Sea plate basin basalts and island arc volcanic rocks, radiometric ages, and tectonic reconstructions of the plate indicates that local processes, such as contamination of the upper mantle by subducted materials or by western Pacific mantle plumes, did not produce the Indian Ocean-type signature in Philippine Sea plate MORB. It is more likely that the plate originated over a rapidly growing Indian Ocean upper mantle domain that had spread into the area between Australia/New Guinea and southeast Asia before 50 Ma.

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.

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.

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.

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.

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.

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.

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

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.

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.

High-Powered, Ultrasonically Assisted Thermal Stir Welding

NASA Technical Reports Server (NTRS)

Ding, Robert

2013-01-01

This method is a solid-state weld process capable of joining metallic alloys without melting. The weld workpieces to be joined by thermal stir welding (TSW) are drawn, by heavy forces, between containment plates past the TSW stir tool that then causes joining of the weld workpiece. TSW is similar to friction stir welding (FSW) in that material is heated into a plastic state (not melted) and stirred using a stir rod. The FSW pin tool is an integrated geometrical structure consisting of a large-diameter shoulder, and a smaller-diameter stir pin protruding from the shoulder. When the pin is plunged into a weld workpiece, the shoulder spins on the surface of the weld workpiece, thus inducing frictional heat into the part. The pin stirs the fraying surfaces of the weld joint, thus joining the weld workpiece into one structure. The shoulder and stir pin of the FSW pin tool must rotate together at a desired rotational speed. The induced frictional energy control and stir pin control of the pin tool cannot be de-coupled. The two work as one integrated unit. TSW, on the other hand, de-couples the heating and stirring of FSW, and allows for independent control of each process element. A uniquely designed induction coil heats the weld workpiece to a desired temperature, and once heated, the part moves into a stir rod whose RPM is also independently controlled. As the weld workpiece moves into the stir rod, the piece is positioned, or sandwiched, between upper and lower containment plates. The plate squeezes together, thus compressing the upper and lower surfaces of the weld workpiece. This compressive force, also called consolidation force, consolidates the plastic material within the weld nugget material as it is being stirred by the stir rod. The stir rod is positioned through the center of the top containment plate and protrudes midway through the opposite lower containment plate where it is mechanically captured. The upper and lower containment plates are separated by a distance equal to the thickness of the material being welded. The TSW process can be significantly improved by reducing the draw forces. This can be achieved by reducing the friction forces between the weld workpieces and the containment plates. High-power ultrasonic (HPU) vibrations of the containment plates achieve friction reduction in the TSW process. Furthermore, integration of the HPU energy into the TSW stir rod can increase tool life of the stir rod, and can reduce shear forces to which the stir rod is subjected during the welding process. TSW has been used to successfully join 0.500-in (˜13-mm) thick commercially pure (CP) titanium, titanium 6AL- 4V, and titanium 6AL-4V ELI in weld joint lengths up to 9 ft (˜2.75-m) long. In addition, the TSW process was used to fabricate a sub-scale hexagonally shaped gun turret component for the U.S. Navy. The turret is comprised of six 0.5000-in (˜13-mm) thick angled welds. Each angled weld joint was prepared by machining the mating surfaces to 120deg. The angled weld joint was then fixtured using an upper and lower containment plate of the same geometry of the angled weld joint. The weld joint was then stirred by the stir rod as it and the upper and lower containment plates traverse through the angled joint prep.

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.

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.

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.

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.

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.

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.

MEMS closed-loop control incorporating a memristor as feedback sensing element

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

Garcia, Ernest J.; Almeida, Sergio F.; Mireles, Jr., Jose

In this work the integration of a memristor with a MEMS parallel plate capacitor coupled by an amplification stage is simulated. It is shown that the MEMS upper plate position can be controlled up to 95% of the total gap. Due to its common operation principle, the change in the MEMS plate position can be interpreted by the change in the memristor resistance, or memristance. A memristance modulation of ~1 KΩ was observed. A polynomial expression representing the MEMS upper plate displacement as a function of the memristance is presented. Thereafter a simple design for a voltage closed-loop control ismore » presented showing that the MEMS upper plate can be stabilized up to 95% of the total gap using the memristor as a feedback sensing element. As a result, the memristor can play important dual roles in overcoming the limited operation range of MEMS parallel plate capacitors and in simplifying read-out circuits of those devices by representing the motion of the upper plate in the form of resistance change instead of capacitance change.« less

MEMS closed-loop control incorporating a memristor as feedback sensing element

DOE PAGES

Garcia, Ernest J.; Almeida, Sergio F.; Mireles, Jr., Jose; ...

2015-12-01

In this work the integration of a memristor with a MEMS parallel plate capacitor coupled by an amplification stage is simulated. It is shown that the MEMS upper plate position can be controlled up to 95% of the total gap. Due to its common operation principle, the change in the MEMS plate position can be interpreted by the change in the memristor resistance, or memristance. A memristance modulation of ~1 KΩ was observed. A polynomial expression representing the MEMS upper plate displacement as a function of the memristance is presented. Thereafter a simple design for a voltage closed-loop control ismore » presented showing that the MEMS upper plate can be stabilized up to 95% of the total gap using the memristor as a feedback sensing element. As a result, the memristor can play important dual roles in overcoming the limited operation range of MEMS parallel plate capacitors and in simplifying read-out circuits of those devices by representing the motion of the upper plate in the form of resistance change instead of capacitance change.« less

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.

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.

Sandbox Simulations of the Evolution of a Subduction Wedge following Subduction Initiation

NASA Astrophysics Data System (ADS)

Brandon, M. T.; Ma, K. F.; DeWolf, W.

2012-12-01

Subduction wedges at accreting subduction zones are bounded by a landward dipping pro-shear zone (= subduction thrust) and a seaward-dipping retro-shear zone in the overriding plate. For the Cascadia subduction zone, the surface trace of the retro-shear zone corresponds to the east side of the Coast Ranges of Oregon and Washington and the Insular Mountains of Vancouver Island. This coastal high or forearc high shows clear evidence of long-term uplift and erosion along its entire length, indicating that it is an active part of the Cascadia subduction wedge. The question addressed here is what controls the location of the retro-shear zone? In the popular double-sided wedge model of Willet et al (Geology 1993), the retro-shear zone remains pinned to the S point, which is interpreted to represent where the upper-plate Moho intersects the subduction zone. For this interpretation, the relatively strong mantle is considered to operate as a flat backstop. That model, however. is somewhat artificial in that the two plates collide in a symmetric fashion with equal crustal thicknesses on both sides. Using sandbox experiments, we explore a more realistic configuration where the upper and lower plate are separated by a gentle dipping (10 degree) pro-shear zone, to simulate the initial asymmetric geometry of the subduction thrust immediately after initiation of subduction. The entire lithosphere must fail along some plane for subduction to begin and this failure plane must dip in the direction of subduction. Thus, the initial geometry of the overriding plate is better approximated as a tapered wedge than as a layer of uniform thickness, as represented in the Willett et al models. We demonstrate this model using time-lapse movies of a sand wedge above a mylar subducting plate. We use particle image velocimetry (PIV) to show the evolution of strain and structure within the overriding plate. Material accreted to the tapered end of the overriding plate drives deformation and causes the retro-shear zone to propagate rearward with time. The main conclusion is that the rearward propagation will cease only when 1) the retro shear zone reaches the S point (i.e. the mantle cutoff in the upper plate) or 2) the erosion outflux from the subduction wedge matches the accretionary influx. Given the location of the upper plate Moho at Cascadia, it seems that erosion is the control factor in pinning the retro shear zone there.

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.

Deep Structure of Northern Apennines Subduction Orogen (Italy) as Revealed by a Joint Interpretation of Passive and Active Seismic Data

NASA Astrophysics Data System (ADS)

Piana Agostinetti, Nicola; Faccenna, Claudio

2018-05-01

The Apennines is a well-studied orogeny formed by the accretion of continental slivers during the subduction of the Adriatic plate, but its deep structure is still a topic of controversy. Here we illuminated the deep structure of the Northern Apennines belt by combining results from the analysis of active seismic (CROP03) and receiver function data. The result from combining these two approaches provides a new robust view of the structure of the deep crust/upper mantle, from the back-arc region to the Adriatic subduction zone. Our analysis confirms the shallow Moho depth beneath the back-arc region and defines the top of the downgoing plate, showing that the two plates separate at depth about 40 km closer to the trench than reported in previous reconstructions. This spatial relationship has profound implications for the geometry of the shallow subduction zone and of the mantle wedge, by the amount of crustal material consumed at trench.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Research of hail impact on aircraft wheel door with lattice hybrid structure

NASA Astrophysics Data System (ADS)

Li, Shengze; Jin, Feng; Zhang, Weihua; Meng, Xuanzhu

2016-09-01

Aimed at a long lasting issue of hail impact on aircraft structures and aviation safety due to its high speed, the resistance performance of hail impact on the wheel door of aircraft with lattice hybrid structure is investigated. The proper anti-hail structure can be designed both efficiency and precision based on this work. The dynamic responses of 8 different sandwich plates in diverse impact speed are measured. Smoothed Particle Hydrodynamic (SPH) method is introduced to mimic the speciality of solid-liquid mixture trait of hailstone during the impact process. The deformation and damage degree of upper and lower panel of sandwich plate are analysed. The application range and failure mode for the relevant structure, as well as the energy absorbing ratio between lattice structure and aluminium foam are summarized. Results show that the tetrahedral sandwich plate with aluminium foam core is confirmed the best for absorbing energy. Furthermore, the high absorption characteristics of foam material enhance the capability of the impact resistance for the composition with lattice structure without increasing the structure surface density. The results of study are of worth to provide a reliable basis for reduced weight aircraft wheel door.

Adjoint tomography of Europe

NASA Astrophysics Data System (ADS)

Zhu, H.; Bozdag, E.; Peter, D. B.; Tromp, J.

2010-12-01

We use spectral-element and adjoint methods to image crustal and upper mantle heterogeneity in Europe. The study area involves the convergent boundaries of the Eurasian, African and Arabian plates and the divergent boundary between the Eurasian and North American plates, making the tectonic structure of this region complex. Our goal is to iteratively fit observed seismograms and improve crustal and upper mantle images by taking advantage of 3D forward and inverse modeling techniques. We use data from 200 earthquakes with magnitudes between 5 and 6 recorded by 262 stations provided by ORFEUS. Crustal model Crust2.0 combined with mantle model S362ANI comprise the initial 3D model. Before the iterative adjoint inversion, we determine earthquake source parameters in the initial 3D model by using 3D Green functions and their Fréchet derivatives with respect to the source parameters (i.e., centroid moment tensor and location). The updated catalog is used in the subsequent structural inversion. Since we concentrate on upper mantle structures which involve anisotropy, transversely isotropic (frequency-dependent) traveltime sensitivity kernels are used in the iterative inversion. Taking advantage of the adjoint method, we use as many measurements as can obtain based on comparisons between observed and synthetic seismograms. FLEXWIN (Maggi et al., 2009) is used to automatically select measurement windows which are analyzed based on a multitaper technique. The bandpass ranges from 15 second to 150 second. Long-period surface waves and short-period body waves are combined in source relocations and structural inversions. A statistical assessments of traveltime anomalies and logarithmic waveform differences is used to characterize the inverted sources and structure.

Three-dimensional velocity structure of crust and upper mantle in southwestern China and its tectonic implications

USGS Publications Warehouse

Wang, Chun-Yong; Chan, W.W.; Mooney, W.D.

2003-01-01

Using P and S arrival times from 4625 local and regional earthquakes recorded at 174 seismic stations and associated geophysical investigations, this paper presents a three-dimensional crustal and upper mantle velocity structure of southwestern China (21??-34??N, 97??-105??E). Southwestern China lies in the transition zone between the uplifted Tibetan plateau to the west and the Yangtze continental platform to the east. In the upper crust a positive velocity anomaly exists in the Sichuan Basin, whereas a large-scale negative velocity anomaly exists in the western Sichuan Plateau, consistent with the upper crustal structure under the southern Tibetan plateau. The boundary between these two anomaly zones is the Longmen Shan Fault. The negative velocity anomalies at 50-km depth in the Tengchong volcanic area and the Panxi tectonic zone appear to be associated with temperature and composition variations in the upper mantle. The Red River Fault is the boundary between the positive and negative velocity anomalies at 50-km depth. The overall features of the crustal and the upper mantle structures in southwestern China are a low average velocity, large crustal thickness variations, the existence of a high-conductivity layer in the crust or/and upper mantle, and a high heat flow value. All these features are closely related to the collision between the Indian and the Asian plates.

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.

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.

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.

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.

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.

Reconstructing mantle heterogeneity with data assimilation based on the back-and-forth nudging method: Implications for mantle-dynamic fitting of past plate motions

NASA Astrophysics Data System (ADS)

Glišović, Petar; Forte, Alessandro

2016-04-01

The paleo-distribution of density variations throughout the mantle is unknown. To address this question, we reconstruct 3-D mantle structure over the Cenozoic era using a data assimilation method that implements a new back-and-forth nudging algorithm. For this purpose, we employ convection models for a compressible and self-gravitating mantle that employ 3-D mantle structure derived from joint seismic-geodynamic tomography as a starting condition. These convection models are then integrated backwards in time and are required to match geologic estimates of past plate motions derived from marine magnetic data. Our implementation of the nudging algorithm limits the difference between a reconstruction (backward-in-time solution) and a prediction (forward-in-time solution) on over a sequence of 5-million-year time windows that span the Cenozoic. We find that forward integration of reconstructed mantle heterogeneity that is constrained to match past plate motions delivers relatively poor fits to the seismic-tomographic inference of present-day mantle heterogeneity in the upper mantle. We suggest that uncertainties in the past plate motions, related for example to plate reorganization episodes, could partly contribute to the poor match between predicted and observed present-day heterogeneity. We propose that convection models that allow tectonic plates to evolve freely in accord with the buoyancy forces and rheological structure in the mantle could provide additional constraints on geologic estimates of paleo-configurations of the major tectonic plates.

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.

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.

The African and Pacific Superplume Structures Constrained by Assembly and Breakup of Pangea

NASA Astrophysics Data System (ADS)

Zhang, N.; Zhong, S.; Leng, W.; Li, Z.

2009-12-01

Seismic tomography studies indicate that the Earth’s mantle structure is characterized by African and Pacific seismically slow velocity anomalies (i.e., superplumes) and circum-Pacific seismically fast anomalies (i.e., a globally spherical harmonic degree-2 structure). McNamara and Zhong (2005) have demonstrated that the African and Pacific superplume structures result from dynamic interaction between mantle convection and surface plate motion history in the last 120 Ma. However, their models produce slightly stronger degree 3 structure than degree 2 near the CMB. Here, we construct a proxy model of plate motions for the African hemisphere for the last 450 Ma since the Early Paleozoic using the paleogeographic reconstruction of continents constrained by paleomagnetic and geological observations. Using this proxy model for plate motion history as the time-dependent surface boundary conditions for a 3-dimensional spherical model of thermochemical mantle convection, we calculate the present-day mantle structure and explore the evolution of mantle structures since the Early Paleozoic. Our model calculations reproduce well the present-day mantle structure including the African and Pacific superplumes. The power spectra of our calculated present-day temperature field shows that the strongest power occurs at degree 2 in the lower mantle while in the upper mantle the strongest power is at degree 3. The degree correlation between tomography model S20RTS and our calculated temperature field shows a high correlation at the degree 1 and degree 2 in the lower mantle while the upper mantle and the short wavelength structures do not correlate well. The summed degree correlation for the lower mantle shows a relatively good correlation for the bottom 300 km of the mantle but the correlation is significantly reduced at depth 600 km above the CMB. For the evolution of mantle structures, we focus on the evolution of the African superplume. Our results suggest that the mantle in the African hemisphere before the assembly of Pangea is predominated by the cold downwelling structure resulting from plate convergence between Gondwana and Laurussia and the cold Africa hemisphere changes to hot due to the return flows from the circum-Pangea subduction after Pangea formation. Based on our results, we suggest that the African superplume structure may be formed no earlier than ~230 Ma ago (i.e., ~100 Ma after the assembly of Pangea).

Geologic Map of the Sulphur Mountain Quadrangle, Park County, Colorado

USGS Publications Warehouse

Bohannon, Robert G.; Ruleman, Chester A.

2009-01-01

The main structural element in the Sulphur Mountain quadrangle is the Elkhorn thrust. This northwest-trending fault is the southernmost structure that bounds the west side of the Late Cretaceous and early Tertiary Front Range basement-rock uplift. The Elkhorn thrust and the Williams Range thrust that occurs in the Dillon area north of the quadrangle bound the west flank of the Williams Range and the Front Range uplift in the South Park area. Kellogg (2004) described widespread, intense fracturing, landsliding, and deep-rooted scarps in the crystalline rocks that comprise the upper plate of the Williams Range thrust. The latter thrust is also demonstrably a low-angle structure upon which the fractured bedrock of the upper plate was translated west above Cretaceous shales. Westward thrusting along the border of the Front Range uplift is probably best developed in that area. By contrast, the Elkhorn in the Sulphur Mountain quadrangle is poorly exposed and occurs in an area of relatively low relief. The thrust also apparently ends in the central part of the quadrangle, dying out into a broad area of open, upright folds with northwest axes in the Sulphur Mountain area.

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.

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.

Models of earth structure inferred from neodymium and strontium isotopic abundances

PubMed Central

Wasserburg, G. J.; DePaolo, D. J.

1979-01-01

A simplified model of earth structure based on the Nd and Sr isotopic characteristics of oceanic and continental tholeiitic flood basalts is presented, taking into account the motion of crustal plates and a chemical balance for trace elements. The resulting structure that is inferred consists of a lower mantle that is still essentially undifferentiated, overlain by an upper mantle that is the residue of the original source from which the continents were derived. PMID:16592688

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.

Trench-parallel variations in Pacific and Indo-Australian crustal velocity structure due to Louisville Ridge seamount subduction

NASA Astrophysics Data System (ADS)

Stratford, W. R.; Knight, T. P.; Peirce, C.; Watts, A. B.; Grevemeyer, I.; Paulatto, M.; Bassett, D.; Hunter, J.; Kalnins, L. M.

2012-12-01

Variations in trench and forearc morphology, and lithospheric velocity structure are observed where the Louisville Ridge seamount chain subducts at the Tonga-Kermadec Trench. Subduction of these seamounts has affected arc and back-arc processes along the trench for the last 5 Myr. High subduction rates (80 mm/yr in the north, 55 mm/yr in the south), a fast southwards migrating collision zone (~180 km/myr), and the obliquity of the subducting plate and the seamount chain to the trench, make this an ideal location to study the effects of seamount subduction on lithospheric structure. The "before and after" subduction regions have been targeted by several large-scale geophysical projects in recent years; the most recent being the R/V Sonne cruise SO215 in 2011. The crust and upper mantle velocity structure observed in profiles along strike of the seamount chain and perpendicular to the trench from this study, are compared to a similar profile from SO195, recorded ~100 km to the north. The affects of the passage of the seamounts through the subduction system are indicated by velocity anomalies in the crust and mantle of the overriding plate. Preliminary results indicate that in the present collision zone, mantle velocities (Pn) are reduced by ~5%. Around 100 km to the north, where seamounts are inferred to have subducted ~1 Myr ago, a reduction of 7% in mantle P-wave velocity is observed. The width of the trench slope and elevation of the forearc also vary along strike. At the collision zone a >100 km wide collapse region of kilometre-scale block faults comprise the trench slope, while the forearc is elevated. The elevated forearc has a 5 km think upper crust with a Vp of 2.5-5.5 km/s and the collapse zone also has upper crustal velocities as low as 2.5 km/s. To the east in the Pacific Plate, lower P-wave velocities are also observed and attributed to serpentinization due to deep fracturing in the outer trench high. Large bending faults permeate the crust and the Osbourn Seamount, currently on the verge of subduction, is fractured stepwise down into the trench. Pn velocities in the hinge zone of the Pacific Plate are as low as 7.3 km/s indicating that fracturing and serpentinization may also extend to sub-crustal depths. Finally, trench-parallel variations in subduction zone velocity structure are used to infer the degree to which seamount subduction has altered the physical state of the Pacific and Indo-Australian plates both pre- and post subduction.

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

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.

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.

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.

Three-dimensional shear wave velocity structure in the Atlantic upper mantle

NASA Astrophysics Data System (ADS)

James, Esther Kezia Candace

Oceanic lithosphere constitutes the upper boundary layer of the Earth's convecting mantle. Its structure and evolution provide a vital window on the dynamics of the mantle and important clues to how the motions of Earth's surface plates are coupled to convection in the mantle below. The three-dimensional shear-velocity structure of the upper mantle beneath the Atlantic Ocean is investigated to gain insight into processes that drive formation of oceanic lithosphere. Travel times are measured for approximately 10,000 fundamental-mode Rayleigh waves, in the period range 30-130 seconds, traversing the Atlantic basin. Paths with >30% of their length through continental upper mantle are excluded to maximize sensitivity to the oceanic upper mantle. The lateral distribution of Rayleigh wave phase velocity in the Atlantic upper mantle is explored with two approaches. One, phase velocity is allowed to vary only as a function of seafloor age. Two, a general two-dimensional parameterization is utilized in order to capture perturbations to age-dependent structure. Phase velocity shows a strong dependence on seafloor age, and removing age-dependent velocity from the 2-D maps highlights areas of anomalously low velocity, almost all of which are proximal to locations of hotspot volcanism. Depth-dependent variations in vertically-polarized shear velocity (Vsv) are determined with two sets of 3-D models: a layered model that requires constant VSV in each depth layer, and a splined model that allows VSV to vary continuously with depth. At shallow depths (˜75 km) the seismic structure shows the expected dependence on seafloor age. At greater depths (˜200 km) high-velocity lithosphere is found only beneath the oldest seafloor; velocity variations beneath younger seafloor may result from temperature or compositional variations within the asthenosphere. The age-dependent phase velocities are used to constrain temperature in the mantle and show that, in contrast to previous results for the Pacific, phase velocities for the Atlantic are not consistent with a half-space cooling model but are best explained by a plate-cooling model with thickness of 75 km and mantle temperature of 1400°C. Comparison with data such as basalt chemistry and seafloor elevation helps to separate thermal and compositional effects on shear velocity.

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.

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.

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.

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.

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

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.

Satellite tidal magnetic signals constrain oceanic lithosphere-asthenosphere boundary.

PubMed

Grayver, Alexander V; Schnepf, Neesha R; Kuvshinov, Alexey V; Sabaka, Terence J; Manoj, Chandrasekharan; Olsen, Nils

2016-09-01

The tidal flow of electrically conductive oceans through the geomagnetic field results in the generation of secondary magnetic signals, which provide information on the subsurface structure. Data from the new generation of satellites were shown to contain magnetic signals due to tidal flow; however, there are no reports that these signals have been used to infer subsurface structure. We use satellite-detected tidal magnetic fields to image the global electrical structure of the oceanic lithosphere and upper mantle down to a depth of about 250 km. The model derived from more than 12 years of satellite data reveals a ≈72-km-thick upper resistive layer followed by a sharp increase in electrical conductivity likely associated with the lithosphere-asthenosphere boundary, which separates colder rigid oceanic plates from the ductile and hotter asthenosphere.

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.

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.

Silver Peak Innovative Exploration Project (Ram Power Inc.)

DOE Data Explorer

Miller, Clay

2010-01-01

Data generated from the Silver Peak Innovative Exploration Project, in Esmeralda County, Nevada, encompasses a “deep-circulation (amagmatic)” meteoric-geothermal system circulating beneath basin-fill sediments locally blanketed with travertine in western Clayton Valley (lithium-rich brines from which have been mined for several decades). Spring- and shallow-borehole thermal-water geochemistry and geothermometry suggest that a Silver Peak geothermal reservoir is very likely to attain the temperature range 260- 300oF (~125-150oC), and may reach 300-340oF (~150-170oC) or higher (GeothermEx, Inc., 2006). Results of detailed geologic mapping, structural analysis, and conceptual modeling of the prospect (1) support the GeothermEx (op. cit.) assertion that the Silver Peak prospect has good potential for geothermal-power production; and (2) provide a theoretical geologic framework for further exploration and development of the resource. The Silver Peak prospect is situated in the transtensional (regional shearing coupled with extension) Walker Lane structural belt, and squarely within the late Miocene to Pliocene (11 Ma to ~5 Ma) Silver Peak-Lone Mountain metamorphic core complex (SPCC), a feature that accommodated initial displacement transfer between major right-lateral strike- slip fault zones on opposite sides of the Walker Lane. The SPCC consists essentially of a ductiley-deformed lower plate, or “core,” of Proterozoic metamorphic tectonites and tectonized Mesozoic granitoids separated by a regionally extensive, low-angle detachment fault from an upper plate of severely stretched and fractured structural slices of brittle, Proterozoic to Miocene-age lithologies. From a geothermal perspective, the detachment fault itself and some of the upper-plate structural sheets could function as important, if secondary, subhorizontal thermal-fluid aquifers in a Silver Peak hydrothermal system.

Subduction-Related Structure in the Mw 9.2, 1964 Megathrust Rupture Area Offshore Kodiak Island, Alaska

NASA Astrophysics Data System (ADS)

Krabbenhoeft, A.; von Huene, R.; Klaeschen, D.; Miller, J. J.

2016-12-01

Some of the largest earthquakes worldwide, including the 1964 9.2 Mw megathrust earthquake, occurred in Alaskan subduction zones. To better understand rupture processes and their mechanisms, we relate seafloor morphology from multibeam and regional bathymetric compilations with sub-seafloor images and seismic P-wave velocity structures. We re-processed legacy multichannel seismic (MCS) data including shot- and intra-shotgather interpolation, multiple removal and Kirchhoff depth migration. These images even reveal the shallow structure of the subducting oceanic crust. Traveltime tomography of a coincident vintage (1994) wide angle dataset reveals the P-wave velocity distribution as well as the deep structure of the subducting plate to the ocean crust Moho. The subducting oceanic crust morphology is rough and partly hidden by a thick sediment cover that reaches 3 km depth at the trench axis. Bathymetry shows two major contrasting upper plate morphologies: the shallow dipping lower slope consists of trench-parallel ridges that form the accreted prism whereas the steep rough middle and upper slopes are composed of competent older rock.Thrust faults are distributed across the entire slope, some of which connect with the subducted plate interface. A subtle change in seafloor gradient from the lower to the middle slope coincides with a thrust fault zone marking the boundary between the margin framework and the frontal prism. It corresponds to the most prominent lateral increase in seismic P-wave velocities, 25 km landward of the trench axis.Major thrusts in several MCS-lines are correlated with bathymetric data, showing their > 100 km lateral extent, which might also be tsunamigenic paths of earthquake rupture from the seismogenic zone to the seafloor.

STS-117 Rotating Service Structure move

NASA Image and Video Library

2007-01-30

The rotating service structure on Launch Pad 39A has moved for the first time in more than a year due to maintenance and upgrades on the pad. Some of the work included sandblasting the structure to remove rust and repainting. In addition, the RSS was jacked up and a new upper-bearing race assembly installed where the RSS pivots against the fixed service structure and a half-inch steel plate added. Pad 39A is being made ready for its first launch in four years, the upcoming STS-117 on March 15.

STS-117 Rotating Service Structure move

NASA Image and Video Library

2007-01-30

The rotating service structure on Launch Pad 39A is being moved for the first time in more than a year due to maintenance and upgrades on the pad. Some of the work included sandblasting the structure to remove rust and repainting. In addition, the RSS was jacked up and a new upper-bearing race assembly installed where the RSS pivots against the fixed service structure and a half-inch steel plate added. Pad 39A is being made ready for its first launch in four years, the upcoming STS-117 on March 15.

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.

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.

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.

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.

Crustal and Upper Mantle Structure of the Taupo Volcanic Zone, North Island, New Zealand.

NASA Astrophysics Data System (ADS)

Harrison, A. J.; White, R. S.

2003-12-01

The Taupo Volcanic Zone (TVZ) is a major Pliocene-Quaternary NNE-SSW orientated,volcano-tectonic complex, about 250 km long and up to 60 km wide in the central North Island of New Zealand. The TVZ is one of the largest and most frequently active rhyolitic magmatic systems on Earth, characterised by intense shallow seismic activity, high natural heat flow (some 12-20 times the continental norm) and active NW-SE extension. To the north of the TVZ, subduction of the Pacific Plate beneath the oceanic lithosphere of the Australian Plate is accompanied by a region of back-arc extension (the Havre Trough). The TVZ marks the southern continuation of this back-arc extension into continental lithosphere.The TVZ therefore represents an ideal opportunity to study the onset of back-arc spreading onshore. Here we present forward and inverse models of the crustal structure beneath the TVZ. These models incorporate both active and passive source data acquired from the NIGHT (North Island GeopHysical Transect) project. Common to both models is a 2-3km deep basin of low velocity sediments which we interpret to be ignimbrite deposits. Typical basement velocities of ˜6km/s are observed beneath and to either side of the TVZ, where they correlate well with mapped outcrops of basement rocks. Velocities of around 7.3 km/s are observed at depths greater than 16 km beneath the TVZ. Such velocities may be interpreted as anomalously low velocity upper manlte or heavly intruded lower crust. Having constrained the crustal structure we then use earthquake events from the subducting Pacific Plate to yield information on the velocity structure of the upper mantle beneath the TVZ. NIGHT Working Group A. Harrison, J. Haines, R. White (University of Cambridge,United Kingdom); S. Henrys, S. Bannister, I. Pecher, F. Davey (Inst. Geological and Nuclear Sciences, Lower Hutt, New Zealand); T. Stern, W. Stratford (Victoria University of Wellington, New Zealand); H. Shimamura, Y. Nishimura, and A. Yamada (Hokkaido University, Sapporo, Japan).

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.

Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean: Ancient Slab Beneath the Indian Ocean

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

Simmons, N. A.; Myers, S. C.; Johannesson, G.

In this study, ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along anmore » extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.« less

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.

Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean: Ancient Slab Beneath the Indian Ocean

DOE PAGES

Simmons, N. A.; Myers, S. C.; Johannesson, G.; ...

2015-11-14

In this study, ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along anmore » extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.« less

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.

Isostatic and Decompensative Gravity Anomalies of the Arabian Plate and Surrounding Regions: a Key for the Crustal Structure

NASA Astrophysics Data System (ADS)

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

2016-12-01

The isostatic anomalies are often considered as one of the most useful correction of the gravity field for investigation of the upper crust structure in many practical applications. By applying this correction, a substantial part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomaly, can be removed. With this approach, it is not even necessary to know the deep density structure of the crust and upper mantle in details; it is sufficient to prescribe some type of compensation (regional vs. local) and a compensation depth. However, even when all the parameters are chosen correctly, this reduction of the gravity field does not show the full gravity effect of unknown anomalies in the crust. The last ones should be also compensated to some extent; therefore their impact is substantially reduced by the isostatic compensation. Long ago (Cordell et al., 1991), it was suggested a so-called decompensative correction of the isostatic anomalies, which provides a possibility to separate these effects. However, the decompensative correction is very sensitive to the parameters of the compensation scheme. In the present study we analyse the ways to choose these parameters and extend this approach by assuming a possibility for the regional compensation via elastic deformations of the lithosphere. Based on this technique, we estimate the isostatic and decompensative anomalies for the Arabian plate and surrounding regions. The parameters of the isostatic model are chosen based on previous studies. It was demonstrated that the decompensative correction is very significant at the mid-range wavelengths and may exceed 100 mGal, therefore ignoring this effect would lead to wrong conclusions about the upper crust structure. The total amplitude of the decompensative anomalies reaches ±250 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. Cordell, L., Zorin, Y. A., & Keller, G. R. (1991). The decompensative gravity anomaly and deep structure of the region of the Rio Grande rift. Journal of Geophysical Research: Solid Earth (1978-2012), 96(B4), 6557-6568.

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).

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

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.

Ground Truth, Magnitude Calibration and Regional Phase Propagation and Detection in the Middle East and Horn of Africa

DTIC Science & Technology

2007-09-01

consists of late Proterozoic crystalline basement overlain by Tertiary and Quaternary volcanic rocks in some places. The breakup of the Arabian Plate from...with structure directly below the crust. To investigate upper mantle structure under the Arabian Shield, measured and inverted relative travel times...Plateau, Zagros Mountains, Arabian Peninsula, Turkish Plateau, Gulf of Aqaba, Dead Sea Rift) and the Horn of Africa (including the northern part of

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.

P-wave tomography of the Chile Triple Junction region

NASA Astrophysics Data System (ADS)

Miller, M. R.; Priestley, K. F.; Tilmann, F. J.; Iwamori, H.; Bataille, K.

2010-12-01

We investigate the crustal and upper mantle structure of the Aysén region of Chile. This region is situated from 44 to 49oS, a place where the diverging oceanic Nazca and Antarctic plates subduct beneath the South American continent. The Seismic Experiment in the Aysén Region of CHile (SEARCH) project operated a network of up to 60 land-based seismometers in this region between 2004 and 2006, centred over a 6 Ma subducted spreading centre between the oceanic plates. The data is used to examine the P-wave velocity structure beneath the region using relative-arrival teleseismic travel time tomography, using 2534 P-wave residuals from 173 teleseismic earthquakes. It is possible to image the velocity structure beneath the seismic network down to ˜300 km depth. The velocity structure has a maximum resolution of ˜60 km and shows a large difference between the northern and southern parts of the region. To the north, a ˜100 km thick fast anomaly exists which dips away from the subduction trench; this is likely to be related to the subducting Nazca plate. Going to the south, as the age of this plate at the subduction trench decreases, the fast anomaly migrates further from the trench suggesting that the Nazca plate subducts at a low angle over a larger distance before the subduction angle steepens and hence slab tears exist across the fracture zones between parts of the slab of different age. Where the 6 Ma subducted ridge segment is predicted to lie there is a region of lower velocities between ˜200 and ˜100 km depth, and no fast region associated with a subducting slab is present. Instead, the lower velocities indicate the presence of an asthenospheric window between the subducted Nazca and Antarctic plate.

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.

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.

The Cascadia Subduction Zone: two contrasting models of lithospheric structure

USGS Publications Warehouse

Romanyuk, T.V.; Blakely, R.; Mooney, W.D.

1998-01-01

The Pacific margin of North America is one of the most complicated regions in the world in terms of its structure and present day geodynamic regime. The aim of this work is to develop a better understanding of lithospheric structure of the Pacific Northwest, in particular the Cascadia subduction zone of Southwest Canada and Northwest USA. The goal is to compare and contrast the lithospheric density structure along two profiles across the subduction zone and to interpet the differences in terms of active processes. The subduction of the Juan de Fuca plate beneath North America changes markedly along the length of the subduction zone, notably in the angle of subduction, distribution of earthquakes and volcanism, goelogic and seismic structure of the upper plate, and regional horizontal stress. To investigate these characteristics, we conducted detailed density modeling of the crust and mantle along two transects across the Cascadia subduction zone. One crosses Vancouver Island and the Canadian margin, the other crosses the margin of central Oregon.

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

Satellite Tidal Magnetic Signals Constrain Oceanic Lithosphere-Asthenosphere Boundary Earth Tomography with Tidal Magnetic Signals

NASA Technical Reports Server (NTRS)

Grayver, Alexander V.; Schnepf, Neesha R.; Kuvshinov, Alexey V.; Sabaka, Terence J.; Chandrasekharan, Manoj; Olsen, Niles

2016-01-01

The tidal flow of electrically conductive oceans through the geomagnetic field results in the generation of secondary magnetic signals, which provide information on the subsurface structure. Data from the new generation of satellites were shown to contain magnetic signals due to tidal flow; however, there are no reports that these signals have been used to infer subsurface structure. Here we use satellite-detected tidal magnetic fields to image the global electrical structure of the oceanic lithosphere and upper mantle down to a depth of about 250 km. The model derived from more than 12 years of satellite data reveals an Approximately 72 km thick upper resistive layer followed by a sharp increase in electrical conductivity likely associated with the lithosphere-asthenosphere boundary, which separates colder rigid oceanic plates from the ductile and hotter asthenosphere.

Satellite tidal magnetic signals constrain oceanic lithosphere-asthenosphere boundary

PubMed Central

Grayver, Alexander V.; Schnepf, Neesha R.; Kuvshinov, Alexey V.; Sabaka, Terence J.; Manoj, Chandrasekharan; Olsen, Nils

2016-01-01

The tidal flow of electrically conductive oceans through the geomagnetic field results in the generation of secondary magnetic signals, which provide information on the subsurface structure. Data from the new generation of satellites were shown to contain magnetic signals due to tidal flow; however, there are no reports that these signals have been used to infer subsurface structure. We use satellite-detected tidal magnetic fields to image the global electrical structure of the oceanic lithosphere and upper mantle down to a depth of about 250 km. The model derived from more than 12 years of satellite data reveals a ≈72-km-thick upper resistive layer followed by a sharp increase in electrical conductivity likely associated with the lithosphere-asthenosphere boundary, which separates colder rigid oceanic plates from the ductile and hotter asthenosphere. PMID:27704045

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.

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.

Gyroscope and Micromirror Design Using Vertical-Axis CMOS-MEMS Actuation and Sensing

DTIC Science & Technology

2002-01-01

Interference pattern around the upper anchor (each fringe occurs at 310 nm vertical displacement...described above require extra lithography step(s) other than standard CMOS lithography steps and/or deposition of structural and sacrificial materials...Instruments’ dig- ital mirror device ( DMD ) [43]. The aluminum thin-film technology with vertical parallel- plate actuation has difficulty in achieving

Garnet Signatures in Geophysical and Geochemical Observations: Insights into the Thermo-Petrological Structure of Oceanic Upper Mantle

NASA Astrophysics Data System (ADS)

Grose, C. J.; Afonso, J. C.

2013-12-01

We have developed new physically comprehensive thermal plate models of the oceanic lithosphere which incorporate temperature- and pressure-dependent heat transport properties and thermal expansivity, melting beneath ridges, hydrothermal circulation near ridge axes, and insulating oceanic crust. These models provide good fits to global databases of seafloor topography and heat flow, and seismic evidence of thermal structure near ridge axes. We couple these thermal plate models with thermodynamic models to predict the petrology of oceanic lithosphere. Geoid height predictions from our models suggest that there is a strong anomaly in geoid slope (over age) above ~25 Ma lithosphere due to the topography of garnet-field mantle. A similar anomaly is also present in geoid data over fracture zones. In addition, we show that a new assessment of a large database of ocean island basalt Sm/Yb systematics indicates that there is an unmistakable step-like increase in Sm/Yb values around 15-20 Ma, indicating the presence of garnet. To explain this feature, we have attempted to couple our thermo-petrological models of oceanic upper mantle with an open system, non-modal, dynamic melting model with diffusion kinetics to investigate trace element partitioning in an ascending mantle column.

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

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.

STS-117 Rotating Service Structure move

NASA Image and Video Library

2007-01-30

The rotating service structure on Launch Pad 39A has been fully opened for the first time in more than a year due to maintenance and upgrades on the pad. Some of the work included sandblasting the structure to remove rust and repainting. In addition, the RSS was jacked up and a new upper-bearing race assembly installed where the RSS pivots against the fixed service structure and a half-inch steel plate added. Pad 39A is being made ready for its first launch in four years, the upcoming STS-117 on March 15. Photo credit: NASA/George Shelton

STS-117 Rotating Service Structure move

NASA Image and Video Library

2007-01-30

Workers on Launch Pad 39A get ready to begin the movement of the rotating service structure above them. The RSS has not been rotated for more than a year during the maintenance and upgrades on the pad. Some of the work included sandblasting the structure to remove rust and repainting. In addition, the RSS was jacked up and a new upper-bearing race assembly installed where the RSS pivots against the fixed service structure and a half-inch steel plate added. Pad 39A is being made ready for its first launch in four years, the upcoming STS-117 on March 15.

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.

A Broadband High-Gain Bi-Layer Log-Periodic Dipole Array (LPDA) for Ultra High Frequency (UHF) Conformal Load Bearing Antenna Structures (CLAS) Applications

DTIC Science & Technology

2014-08-01

AFRL-RQ-WP-TR-2014-0212 University of South Carolina Department of Electrical Engineering Columbia, SC 29208 Structures Technology Branch...S2603-04-C01. Cleared for Public Release - Case Number: . Nicholas Bishop and M. Ali are with the Department of Electrical Engineering, University of...Lower substrate Upper substrate Foam core Coax Feed tube LPDA traces Coax inner conductor Feed tube Copper plate Input 88ABW-2014-3668, 8

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.

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.

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.

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.

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.

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.

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.

Crust and upper mantle shear wave structure of Northeast Algeria from Rayleigh wave dispersion analysis

NASA Astrophysics Data System (ADS)

Radi, Zohir; Yelles-Chaouche, Abdelkrim; Corchete, Victor; Guettouche, Salim

2017-09-01

We resolve the crust and upper mantle structure beneath Northeast Algeria at depths of 0-400 km, using inversion of fundamental mode Rayleigh wave. Our data set consists of 490 earthquakes recorded between 2007 and 2014 by five permanent broadband seismic stations in the study area. Applying a combination of different filtering technics and inversion method shear wave velocities structure were determined as functions of depth. The resolved changes in Vs at 50 km depth are in perfect agreement with crustal thickness estimates, which reflect the study area's orogenic setting, partly overlying the collision zone between the African and Eurasian plates. The inferred Moho discontinuity depths are close to those estimated for other convergent areas. In addition, there is good agreement between our results and variations in orientations of regional seismic anisotropy. At depths of 80-180 km, negative Vs anomalies at station CBBR suggest the existence of a failed subduction slab.

Evaluating the Effect of Minimizing Screws on Stabilization of Symphysis Mandibular Fracture by 3D Finite Element Analysis.

PubMed

Kharmanda, Ghias; Kharma, Mohamed-Yaser

2017-06-01

The objective of this work is to integrate structural optimization and reliability concepts into mini-plate fixation strategy used in symphysis mandibular fractures. The structural reliability levels are next estimated when considering a single failure mode and multiple failure modes. A 3-dimensional finite element model is developed in order to evaluate the ability of reducing the negative effect due to the stabilization of the fracture. Topology optimization process is considered in the conceptual design stage to predict possible fixation layouts. In the detailed design stage, suitable mini-plates are selected taking into account the resulting topology and different anatomical considerations. Several muscle forces are considered in order to obtain realistic predictions. Since some muscles can be cut or harmed during the surgery and cannot operate at its maximum capacity, there is a strong motivation to introduce the loading uncertainties in order to obtain reliable designs. The structural reliability is carried out for a single failure mode and multiple failure modes. The different results are validated with a clinical case of a male patient with symphysis fracture. In this case while use of the upper plate fixation with four holes, only two screws were applied to protect adjacent vital structure. This behavior does not affect the stability of the fracture. The proposed strategy to optimize bone plates leads to fewer complications and second surgeries, less patient discomfort, and shorter time of healing.

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

Regional P wave velocity structure of the Northern Cascadia Subduction Zone

USGS Publications Warehouse

Ramachandran, K.; Hyndman, R.D.; Brocher, T.M.

2006-01-01

This paper presents the first regional three-dimensional, P wave velocity model for the Northern Cascadia Subduction. Zone (SW British Columbia and NW Washington State) constructed through tomographic inversion of first-arrival traveltime data from active source experiments together with earthquake traveltime data recorded at permanent stations. The velocity model images the structure of the subducting Juan de Fuca plate, megathrust, and the fore-arc crust and upper mantle. Beneath southern Vancouver Island the megathrust above the Juan de Fuca plate is characterized by a broad zone (25-35 km depth) having relatively low velocities of 6.4-6.6 km/s. This relative low velocity zone coincides with the location of most of the episodic tremors recently mapped beneath Vancouver Island, and its low velocity may also partially reflect the presence of trapped fluids and sheared lower crustal rocks. The rocks of the Olympic Subduction Complex are inferred to deform aseismically as evidenced by the lack of earthquakes withi the low-velocity rocks. The fore-arc upper mantle beneath the Strait of Georgia and Puget Sound is characterized by velocities of 7.2-7.6 km/s. Such low velocities represent regional serpentinization of the upper fore-arc mantle and provide evidence for slab dewatering and densification. Tertiary sedimentary basins in the Strait of Georgia and Puget Lowland imaged by the velocity model lie above the inferred region of slab dewatering and densification and may therefore partly result from a higher rate of slab sinking. In contrast, sedimentary basins in the Strait of Juan de Fuca lie in a synclinal depression in the Crescent Terrane. The correlation of in-slab earthquake hypocenters M>4 with P wave velocities greater than 7.8 km/s at the hypocenters suggests that they originate near the oceanic Moho of the subducting Juan de Fuca plate. Copyright 2006 by the American Geophysical Union.

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

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.

Deep seismic structure and tectonics of northern Alaska: Crustal-scale duplexing with deformation extending into the upper mantle

USGS Publications Warehouse

Fuis, G.S.; Murphy, J.M.; Lutter, W.J.; Moore, Thomas E.; Bird, K.J.; Christensen, N.I.

1997-01-01

Seismic reflection and refraction and laboratory velocity data collected along a transect of northern Alaska (including the east edge of the Koyukuk basin, the Brooks Range, and the North Slope) yield a composite picture of the crustal and upper mantle structure of this Mesozoic and Cenozoic compressional orogen. The following observations are made: (1) Northern Alaska is underlain by nested tectonic wedges, most with northward vergence (i.e., with their tips pointed north). (2) High reflectivity throughout the crust above a basal decollement, which deepens southward from about 10 km depth beneath the northern front of the Brooks Range to about 30 km depth beneath the southern Brooks Range, is interpreted as structural complexity due to the presence of these tectonic wedges, or duplexes. (3) Low reflectivity throughout the crust below the decollement is interpreted as minimal deformation, which appears to involve chiefly bending of a relatively rigid plate consisting of the parautochthonous North Slope crust and a 10- to 15-km-thick section of mantle material. (4) This plate is interpreted as a southward verging tectonic wedge, with its tip in the lower crust or at the Moho beneath the southern Brooks Range. In this interpretation the middle and upper crust, or all of the crust, is detached in the southern Brooks Range by the tectonic wedge, or indentor: as a result, crust is uplifted and deformed above the wedge, and mantle is depressed and underthrust beneath this wedge. (5) Underthrusting has juxtaposed mantle of two different origins (and seismic velocities), giving rise to a prominent sub-Moho reflector. Copyright 1997 by the American Geophysical Union.

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.

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.

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.

KSC-07pd0202

NASA Image and Video Library

2007-01-30

KENNEDY SPACE CENTER, FLA. -- The rotating service structure on Launch Pad 39A is being moved for the first time in more than a year due to maintenance and upgrades on the pad. Some of the work included sandblasting the structure to remove rust and repainting. In addition, the RSS was jacked up and a new upper-bearing race assembly installed where the RSS pivots against the fixed service structure and a half-inch steel plate added. Pad 39A is being made ready for its first launch in four years, the upcoming STS-117 on March 15. Photo credit: NASA/George Shelton

KSC-07pd0204

NASA Image and Video Library

2007-01-30

KENNEDY SPACE CENTER, FLA. -- The rotating service structure on Launch Pad 39A has been fully opened for the first time in more than a year due to maintenance and upgrades on the pad. Some of the work included sandblasting the structure to remove rust and repainting. In addition, the RSS was jacked up and a new upper-bearing race assembly installed where the RSS pivots against the fixed service structure and a half-inch steel plate added. Pad 39A is being made ready for its first launch in four years, the upcoming STS-117 on March 15. Photo credit: NASA/George Shelton

KSC-07pd0203

NASA Image and Video Library

2007-01-30

KENNEDY SPACE CENTER, FLA. -- The rotating service structure on Launch Pad 39A has moved for the first time in more than a year due to maintenance and upgrades on the pad. Some of the work included sandblasting the structure to remove rust and repainting. In addition, the RSS was jacked up and a new upper-bearing race assembly installed where the RSS pivots against the fixed service structure and a half-inch steel plate added. Pad 39A is being made ready for its first launch in four years, the upcoming STS-117 on March 15. Photo credit: NASA/George Shelton

KSC-07pd0201

NASA Image and Video Library

2007-01-30

KENNEDY SPACE CENTER, FLA. -- The rotating service structure on Launch Pad 39A is being moved for the first time in more than a year due to maintenance and upgrades on the pad. Some of the work included sandblasting the structure to remove rust and repainting. In addition, the RSS was jacked up and a new upper-bearing race assembly installed where the RSS pivots against the fixed service structure and a half-inch steel plate added. Pad 39A is being made ready for its first launch in four years, the upcoming STS-117 on March 15. Photo credit: NASA/George Shelton

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.

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.

Structure of the Lithosphere and Upper Mantle Across the Arabian Peninsula

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

Al-Amri, A; Rodgers, A

2007-01-05

Analysis of modern broadband (BB) waveform data allows for the inference of seismic velocity structure of the crust and upper mantle using a variety of techniques. This presentation will report inferences of seismic structure of the Arabian Plate using BB data from various networks. Most data were recorded by the Saudi Arabian National Digital Seismic Network (SANDSN) which consists of 38 (26 BB, 11 SP) stations, mostly located on the Arabian Shield. Additional data were taken from the 1995-7 Saudi Arabian IRIS-PASSCAL Deployment (9 BB stations) and other stations across the Peninsula. Crustal structure, inferred from teleseismic P-wave receiver functions,more » reveals thicker crust in the Arabian Platform (40-45 km) and the interior of the Arabian Shield (35-40 km) and thinner crust along the Red Sea coast. Lithospheric thickness inferred from teleseismic S-wave receiver functions reveals very thin lithosphere (40-80 km) along the Red Sea coast which thickens rapidly toward the interior of the Arabian Shield (100-120 km). We also observe a step of 20-40 km in lithospheric thickness across the Shield-Platform boundary. Seismic velocity structure of the upper mantle inferred from teleseismic P- and S-wave travel time tomography reveals large differences between the Shield and Platform, with the Shield being underlain by slower velocities, {+-}3% for P-waves and {+-}6% for S-waves. Seismic anisotropy was inferred from shear-wave splitting, using teleseismic SKS waveforms. Results reveal a splitting time of approximately 1.4 seconds, with the fast axis slightly east of north. The shear-wave splitting results are consistent across the Peninsula, with a slight clockwise rotation parallel for stations near the Gulf of Aqaba. In summary, these results allow us to make several conclusions about the tectonic evolution and current state of the Arabian Plate. Lithospheric thickness implies that thinning near the Red Sea has accompanied the rupturing of the Arabian-Nubian continental lithosphere. The step in the lithospheric thickness across the Shield-Platform boundary likely reveals a pre-existing difference in the lithospheric structure prior to accretion of the terranes composing the eastern Arabian Shield. Tomographic imaging of upper mantle velocities implies a single large-scale thermal anomaly underlies the Arabian Shield and is associated with Cenozoic uplift and volcanism.« less

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.

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.

Shear wave reflectivity imaging of the Nazca-South America subduction zone: Stagnant slab in the mantle transition zone?

NASA Astrophysics Data System (ADS)

Contenti, Sean; Gu, Yu Jeffrey; Ökeler, Ahmet; Sacchi, Mauricio D.

2012-01-01

In this study we utilize over 5000 SS waveforms to investigate the high-resolution mantle reflectivity structure down to 1200 km beneath the South American convergent margin. Our results indicate that the dynamics of the Nazca subduction are more complex than previously suggested. The 410- and 660-km seismic discontinuities beneath the Pacific Ocean and Amazonian Shield exhibit limited lateral depth variations, but their depths vary substantially in the vicinity of the subducting Nazca plate. The reflection amplitude of the 410-km discontinuity is greatly diminished in a ˜1300-km wide region in the back-arc of the subducting plate, which is likely associated with a compositional heterogeneity on top of the upper mantle transition zone. The underlying 660-km discontinuity is strongly depressed, showing localized depth and amplitude variations both within and to the east of the Wadati-Benioff zone. The width of this anomalous zone (˜1000 km) far exceeds that of the high-velocity slab structure and suggesting significant slab deformation within the transition zone. The shape of the 660-km discontinuity and the presence of lower mantle reflectivity imply both stagnation and penetration are possible as the descending Nazca slab impinges upon the base of the upper mantle.

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

bedle, H; Matzel, E; Flanagan, M

This report summarizes the data analysis achieved during Heather Bedle's eleven-week Technical Scholar internship at Lawrence Livermore National Labs during the early summer 2006. The work completed during this internship resulted in constraints on the crustal and upper mantle S-velocity structure in Northern Africa, the Mediterranean, the Middle East, and Europe, through the fitting of regional waveform data. This data extends current raypath coverage and will be included in a joint inversion along with data from surface wave group velocity measurements, S and P teleseismic arrival time data, and receiver function data to create an improved velocity model of themore » upper mantle in this region. The tectonic structure of the North African/Mediterranean/Europe/Middle Eastern study region is extremely heterogeneous. This region consists of, among others, stable cratons and platforms such as the West Africa Craton, and Baltica in Northern Europe; oceanic subduction zones throughout the Mediterranean Sea where the African and Eurasian plate collide; regions of continental collision as the Arabian Plate moves northward into the Turkish Plate; and rifting in the Red Sea, separating the Arabian and Nubian shields. With such diverse tectonic structures, many of the waveforms were difficult to fit. This is not unexpected as the waveforms are fit using an averaged structure. In many cases the raypaths encounter several tectonic features, complicating the waveform, and making it hard for the software to converge on a 1D average structure. Overall, the quality of the waveform data was average, with roughly 30% of the waveforms being discarded due to excessive noise that interfered with the frequency ranges of interest. An inversion for the 3D S-velocity structure of this region was also performed following the methodology of Partitioned Waveform Inversion (Nolet, 1990; Van der Lee and Nolet, 1997). The addition of the newly fit waveforms drastically extends the range of the model. The model now extends as far east in Africa to cover Chad and Niger, and reaches south to cover Zambia. The model is also stretched eastward to cover the eastern half of India, and northward to cover the southern portion of Scandinavia.« less

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.

Immediate effects of EVA midsole resilience and upper shoe structure on running biomechanics: a machine learning approach

PubMed Central

Gavião Neto, Wilson P.; Roveri, Maria Isabel; Oliveira, Wagner R.

2017-01-01

Background Resilience of midsole material and the upper structure of the shoe are conceptual characteristics that can interfere in running biomechanics patterns. Artificial intelligence techniques can capture features from the entire waveform, adding new perspective for biomechanical analysis. This study tested the influence of shoe midsole resilience and upper structure on running kinematics and kinetics of non-professional runners by using feature selection, information gain, and artificial neural network analysis. Methods Twenty-seven experienced male runners (63 ± 44 km/week run) ran in four-shoe design that combined two resilience-cushioning materials (low and high) and two uppers (minimalist and structured). Kinematic data was acquired by six infrared cameras at 300 Hz, and ground reaction forces were acquired by two force plates at 1,200 Hz. We conducted a Machine Learning analysis to identify features from the complete kinematic and kinetic time series and from 42 discrete variables that had better discriminate the four shoes studied. For that analysis, we built an input data matrix of dimensions 1,080 (10 trials × 4 shoes × 27 subjects) × 1,254 (3 joints × 3 planes of movement × 101 data points + 3 vectors forces × 101 data points + 42 discrete calculated kinetic and kinematic features). Results The applied feature selection by information gain and artificial neural networks successfully differentiated the two resilience materials using 200(16%) biomechanical variables with an accuracy of 84.8% by detecting alterations of running biomechanics, and the two upper structures with an accuracy of 93.9%. Discussion The discrimination of midsole resilience resulted in lower accuracy levels than did the discrimination of the shoe uppers. In both cases, the ground reaction forces were among the 25 most relevant features. The resilience of the cushioning material caused significant effects on initial heel impact, while the effects of different uppers were distributed along the stance phase of running. Biomechanical changes due to shoe midsole resilience seemed to be subject-dependent, while those due to upper structure seemed to be subject-independent. PMID:28265506

Immediate effects of EVA midsole resilience and upper shoe structure on running biomechanics: a machine learning approach.

PubMed

Onodera, Andrea N; Gavião Neto, Wilson P; Roveri, Maria Isabel; Oliveira, Wagner R; Sacco, Isabel Cn

2017-01-01

Resilience of midsole material and the upper structure of the shoe are conceptual characteristics that can interfere in running biomechanics patterns. Artificial intelligence techniques can capture features from the entire waveform, adding new perspective for biomechanical analysis. This study tested the influence of shoe midsole resilience and upper structure on running kinematics and kinetics of non-professional runners by using feature selection, information gain, and artificial neural network analysis. Twenty-seven experienced male runners (63 ± 44 km/week run) ran in four-shoe design that combined two resilience-cushioning materials (low and high) and two uppers (minimalist and structured). Kinematic data was acquired by six infrared cameras at 300 Hz, and ground reaction forces were acquired by two force plates at 1,200 Hz. We conducted a Machine Learning analysis to identify features from the complete kinematic and kinetic time series and from 42 discrete variables that had better discriminate the four shoes studied. For that analysis, we built an input data matrix of dimensions 1,080 (10 trials × 4 shoes × 27 subjects) × 1,254 (3 joints × 3 planes of movement × 101 data points + 3 vectors forces × 101 data points + 42 discrete calculated kinetic and kinematic features). The applied feature selection by information gain and artificial neural networks successfully differentiated the two resilience materials using 200(16%) biomechanical variables with an accuracy of 84.8% by detecting alterations of running biomechanics, and the two upper structures with an accuracy of 93.9%. The discrimination of midsole resilience resulted in lower accuracy levels than did the discrimination of the shoe uppers. In both cases, the ground reaction forces were among the 25 most relevant features. The resilience of the cushioning material caused significant effects on initial heel impact, while the effects of different uppers were distributed along the stance phase of running. Biomechanical changes due to shoe midsole resilience seemed to be subject-dependent, while those due to upper structure seemed to be subject-independent.

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.

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.

Sunda-Banda Arc Transition: Marine Wide-Angle Seismic Modeling

NASA Astrophysics Data System (ADS)

Shulgin, A.; Planert, L.; Kopp, H.; Mueller, C.; Lueschen, E.; Engels, M.; Flueh, E.; Djajadihardja, Y.; Sindbad Working Group, T

2008-12-01

The Sunda-Banda Arc transition is the region of active convergence and collision of the Indo-Australian and Eurasian Plates. The style of subduction changes from an oceanic-island arc subduction to a continental- island arc collision. The character of the incoming plate varies from the rough topography of the Roo Rise, to the smooth seafloor of the Abyssal Plain off Bali, Sumbawa. Forearc structures include well-developed forearc basins and an accretionary prism/outer forearc high of variable size and shape. To quantify the variability of structure of the lower plate and the effects on the upper plate a refraction seismic survey was carried during cruise SO190-2. A total of 245 ocean bottom seismometers were deployed along 1020 nm of wide-angle seismic profiles in four major north-south oriented corridors. To assess the velocity structure we used a tomographic method which jointly inverts for refracted and reflected phases. The sedimentary layers of the models, obtained by the analysis of high-resolution MCS data (see Lueschen et al), were incorporated into the starting model. The obtained models exhibit strong changes of the incoming oceanic crust for the different portions of the margin: The westernmost profile off eastern Java shows a crustal thickness of more than 15 km, most likely related to the presence of an oceanic plateau. Profiles off Lombok reveal an oceanic crust of 8-9 km average thickness in the Argo Abyssal Plain. Crustal and upper mantle velocities are slightly decreased within an area of about 50-60 km seaward of the trench, indicating fracturing and related serpentinization due to bending of the oceanic crust and associated normal faulting. The outer forearc high is characterized by velocities of 2.5-5.5 km/s. For the Lombok Basin, the profiles show a sedimentary infill of up to 3.5 km thick and typical sediment velocities of 1.75-3.0 km/s. A reflector at 16 km depth and velocity values of 7.4-7.8 km/s beneath it suggest the presence of a shallow forearc mantle and a hydrated mantle wedge in this part of the margin. See in this session Planert et al.

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.

High-Resolution P'P' Precursor Imaging of Nazca-South America Plate Boundary Zones and Inferences for Transition Zone Temperature and Composition

NASA Astrophysics Data System (ADS)

Gu, Y. J.; Schultz, R.

2013-12-01

Knowledge of upper mantle transition zone stratification and composition is highly dependent on our ability to efficiently extract and properly interpret small seismic arrivals. A promising high-frequency seismic phase group particularly suitable for a global analysis is P'P' precursors, which are capable of resolving mantle structures at vertical and lateral resolution of approximately 5 and 200 km, respectively, owing to their shallow incidence angle and small, quasi-symmetric Fresnel zones. This study presents a simultaneous analysis of SS and P'P' precursors based on deconvolution, Radon transform and depth migration. Our multi-resolution survey of the mantle near Nazca-South America subduction zone reveals both olivine and garnet related transitions at depth below 400 km. We attribute a depressed 660 to thermal variations, whereas compositional variations atop the upper-mantle transition zone are needed to explain the diminished or highly complex reflected/scattered signals from the 410 km discontinuity. We also observe prominent P'P' reflections within the transition zone, especially near the plate boundary zone where anomalously high reflection amplitudes result from a sharp (~10 km thick) mineral phase change resonant with the dominant frequency of the P'P' precursors. Near the base of the upper mantle, the migration of SS precursors shows no evidence of split reflections near the 660-km discontinuity, but potential majorite-ilmenite (590-640 km) and ilmenite-perovskite transitions (740-750 km) are identified based on similarly processed high-frequency P'P' precursors. At nominal mantle temperatures these two phase changes may be seismically indistinguishable, but colder mantle conditions from the descending Nazca plate, the presence of water and variable Fe contents may cause sufficient separation for a reliable analysis. In addition, our preliminary results provide compelling evidence for multiple shallow lower-mantle reflections (at ~800 km) along the elongated plate boundary zones of South America. Slab stagnation at the base of the transition zone could play a key role, though a proper interpretation of this finding would likely entail compositional (rather than strictly thermal) variations in the vicinity of the descending oceanic crust and lithosphere. Overall, the resolution and sensitivity differences between low/intermediate- S and high-frequency P wave reflections are key considerations toward reconciling seismic and mineralogical models of transition zone structure, both at the study location and worldwide.

The Importance of Lower Mantle Structure to Plate Stresses and Plate Motions

NASA Astrophysics Data System (ADS)

Holt, W. E.; Wang, X.; Ghosh, A.

2016-12-01

Plate motions and plate stresses are widely assumed as the surface expression of mantle convection. The generation of plate tectonics from mantle convection has been studied for many years. Lithospheric thickening (or ridge push) and slab pull forces are commonly accepted as the major driving forces for the plate motions. However, the importance of the lower mantle to plate stresses and plate motions remains less clear. Here, we use the joint modeling of lithosphere and mantle dynamics approach of Wang et al. (2015) to compute the tractions originating from deeper mantle convection and follow the method of Ghosh et al. (2013) to calculate gravitational potential energy per unit area (GPE) based on Crust 1.0 (Laske et al., 2013). Absolute values of deviatoric stresses are determined by the body force distributions (GPE gradients and traction magnitudes applied at the base of the lithosphere). We use the same relative viscosity model that Ghosh et al. (2013) used, and we solve for one single adjustable scaling factor that multiplies the entire relative viscosity field to provide absolute values of viscosity throughout the lithosphere. This distribution of absolute values of lithosphere viscosities defines the magnitudes of surface motions. In this procedure, the dynamic model first satisfies the internal constraint of no-net-rotation of motions. The model viscosity field is then scaled by the single factor until we achieve a root mean square (RMS) minimum between computed surface motions and the kinematic no-net-rotation (NNR) model of Kreemer et al. (2006). We compute plate stresses and plate motions from recently published global tomography models (over 70 based on Wang et al., 2015). We find that RMS misfits are significantly reduced when details of lower mantle structure from the latest tomography models are added to models that contain only upper and mid-mantle density distributions. One of the key reasons is that active upwelling from the Large Low Shear Velocity Provinces (LLSVPs) in the lower mantle in Pacific (Frost and Rost, 2014) provides important components of mantle flow affecting plate stresses and motions. We demonstrate in this paper how lower mantle density heterogeneity has a marked influence on plate stresses and plate motions.

Nuclear reactor I

DOEpatents

Ference, Edward W.; Houtman, John L.; Waldby, Robert N.

1977-01-01

A nuclear reactor, particularly a liquid-metal breeder reactor whose upper internals include provision for channeling the liquid metal flowing from the core-component assemblies to the outlet plenum in vertical paths in direction generally along the direction of the respective assemblies. The metal is channeled by chimneys, each secured to, and extending from, a grid through whose openings the metal emitted by a plurality of core-component assemblies encompassed by the grid flows. To reduce the stresses resulting from structural interaction, or the transmissive of thermal strains due to large temperature differences in the liquid metal emitted from neighboring core-component assemblies, throughout the chimneys and the other components of the upper internals, the grids and the chimneys are supported from the heat plate and the core barrel by support columns (double portal support) which are secured to the head plate at the top and to a member, which supports the grids and is keyed to the core barrel, at the bottom. In addition to being restrained from lateral flow by the chimneys, the liquid metal is also restrained from flowing laterally by a peripheral seal around the top of the core. This seal limits the flow rate of liquid metal, which may be sharply cooled during a scram, to the outlet nozzles. The chimneys and the grids are formed of a highly-refractory, high corrosion-resistant nickel-chromium-iron alloy which can withstand the stresses produced by temperature differences in the liquid metal. The chimneys are supported by pairs of plates, each pair held together by hollow stubs coaxial with, and encircling, the chimneys. The plates and stubs are a welded structure but, in the interest of economy, are composed of stainless steel which is not weld compatible with the refractory metal. The chimneys and stubs are secured together by shells of another nickel-chromium-iron alloy which is weld compatible with, and is welded to, the stubs and has about the same coefficient of expansion as the highly-refractory, high corrosion-resistant alloy.

Svecofennian orogeny in an evolving convergent margin setting

NASA Astrophysics Data System (ADS)

Korja, Annakaisa

2015-04-01

The dominant tectonic mode changes from extension to convergence at around 1.9 Ga in Fennoscandian. The lithological record suggests short lived subduction-related magmatic events followed by deformation and low-pressure high temperature metamorphism. At around 1.8 Ga the subduction systems seem to have stabilized implying continuous supply of oceanic lithosphere. The evolution of the convergent margin is recorded in the rock record and crustal architecture of the long lived Svecofennian orogeny (1.9-1.7 Ga). A closer look at the internal structure of the Svecofennian orogen reveals distinct regional differences. The northern and central parts of the Svecofennian orogen that have been formed during the initial accretionary phase - or compilation of the nucleus - have a thick three-layer crust and with thick mafic lower crust (10-30 km) and block-like internal architecture. Reflection profiles (FIRE1-3) image listric structures flattening on crustal scale décollement zones at the upper-middle crust and middle-upper crust boundaries. The crustal architecture together with large volumes of exposed granitoid rocks suggests spreading of the orogen and the development of an orogenic plateau west of the continental convergence boundary. The architecture is reminiscent of a large hot orogen. Within the western and southwestern part of the Svecofennian orogen (BABEL B, 1, 2, 3&4), which have been envisioned to have formed during continuous subduction phase, the crust is thinner (45-50 km) and it is hosting crustal blocks having one to two crustal layers. Layering is poorly developed in crustal blocks that are found S-SW of NE-dipping mantle reflections previously interpreted as paleo-subduction zones. Within these blocks, the crustal scale reflective structures dip NE (prowedge) or form pop-up wedges (uplifted plug) above the paleo-subduction zones. Crustal blocks with well-developed two-layer crust are located NE of the paleo-subduction zone. The architecture can be interpreted to image a series of abandoned accretion zones where the orogenic structure has developed from a young and cold orogen (BABEL 2,3&4) to a transitional (BABEL 1,6,B) one as the plate boundary is retreating during SW wards. The fast retreating rate of the subduction zone may not only have formed continental back-arc environment but may have restricted the thickening of the upper plate and the growth rate of the orogen. Altogether the architecture suggests a long-lived southwesterly retreating subduction system, with continental back-arc formation in its rear parts and well developed system of prowedge-retrowedge-uplifted plug close to a subduction conduit. Changes in the relative velocities of the upper and lower plate may have resulted in repetitive extensional and compressional phases of the orogeny as has been previously suggested for the southern part of the Svecofennian orogen.

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.

Structure of the Cascadia Subduction Zone Imaged Using Surface Wave Tomography

NASA Astrophysics Data System (ADS)

Schaeffer, A. J.; Audet, P.

2017-12-01

Studies of the complete structure of the Cascadia subduction zone from the ridge to the arc have historically been limited by the lack of offshore ocean bottom seismograph (OBS) infrastructure. On land, numerous dense seismic deployments have illuminated detailed structures and dynamics associated with the interaction between the subducting oceanic plate and the overriding continental plate, including cycling of fluids, serpentinization of the overlying forearc mantle wedge, and the location of the upper surface of the Juan de Fuca plate as it subducts beneath the Pacific Northwest. In the last half-decade, the Cascadia Initiative (CI), along with Neptune (ONC) and several other OBS initiatives, have instrumented both the continental shelf and abyssal plains off shore of the Cascadia subduction zone, facilitating the construction of a complete picture of the subduction zone from ridge to trench and volcanic arc. In this study, we present a preliminary azimuthally anisotropic surface-wave phase-velocity based model of the complete system, capturing both the young, unaltered Juan de Fuca plate from the ridge, to its alteration as it enters the subduction zone, in addition to the overlying continent. This model is constructed from a combination of ambient noise cross-correlations and teleseismic two station interferometry, and combines together concurrently running offshore OBS and onshore stations. We furthermore perform a number of representative 1D depth inversions for shear velocity to categorize the pristine oceanic, subducted oceanic, and continental crust and lithospheric structure. In the future the dispersion dataset will be jointly inverted with receiver functions to constrain a 3D shear-velocity model of the complete region.

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.

SH wave structure of the crust and upper mantle in southeastern margin of the Tibetan Plateau from teleseismic Love wave tomography

NASA Astrophysics Data System (ADS)

Fu, Yuanyuan V.; Jia, Ruizhi; Han, Fengqin; Chen, Anguo

2018-06-01

The deep structure of southeastern Tibet is important for determining lateral plateau expansion mechanisms, such as movement of rigid crustal blocks along large strike-slip faults, continuous deformation or the eastward crustal channel flow. We invert for 3-D isotropic SH wave velocity model of the crust and upper mantle to the depth of 110 km from Love wave phase velocity data using a best fitting average model as the starting model. The 3-D SH velocity model presented here is the first SH wave velocity structure in the study area. In the model, the Tibetan Plateau is characterized by prominent slow SH wave velocity with channel-like geometry along strike-slip faults in the upper crust and as broad zones in the lower crust, indicating block-like and distributed deformation at different depth. Positive radial anisotropy (VSH > VSV) is suggested by a high SH wave and low SV wave anomaly at the depths of 70-110 km beneath the northern Indochina block. This positive radial anisotropy could result from the horizontal alignment of anisotropic minerals caused by lithospheric extensional deformation due to the slab rollback of the Australian plate beneath the Sumatra trench.

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.

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 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.

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.

Structure of the European upper mantle revealed by adjoint tomography

NASA Astrophysics Data System (ADS)

Zhu, Hejun; Bozdağ, Ebru; Peter, Daniel; Tromp, Jeroen

2012-07-01

Images of the European crust and upper mantle, created using seismic tomography, identify the Cenozoic Rift System and related volcanism in central and western Europe. They also reveal subduction and slab roll back in the Mediterranean-Carpathian region. However, existing tomographic models are either high in resolution, but cover only a limited area, or low in resolution, and thus miss the finer-scale details of mantle structure. Here we simultaneously fit frequency-dependent phase anomalies of body and surface waveforms in complete three-component seismograms with an iterative inversion strategy involving adjoint methods, to create a tomographic model of the European upper mantle. We find that many of the smaller-scale structures such as slabs, upwellings and delaminations that emerge naturally in our model are consistent with existing images. However, we also derive some hitherto unidentified structures. Specifically, we interpret fast seismic-wave speeds beneath the Dinarides Mountains, southern Europe, as a signature of northeastward subduction of the Adria plate; slow seismic-wave speeds beneath the northern part of the Rhine Graben as a reservoir connected to the Eifel hotspot; and fast wave-speed anomalies beneath Scandinavia as a lithospheric drip, where the lithosphere is delaminating and breaking away. Our model sheds new light on the enigmatic palaeotectonic history of Europe.

Structural variability of the Tonga-Kermadec forearc characterized using robustly constrained geophysical data

NASA Astrophysics Data System (ADS)

Funnell, M. J.; Peirce, C.; Robinson, A. H.

2017-09-01

Subducting bathymetric anomalies enhance erosion of the overriding forearc crust. The deformation associated with this process is superimposed on pre-existing variable crustal and sedimentary structures developed as a subduction system evolves. Recent attempts to determine the effect and timescale of Louisville Ridge seamount subduction on the Tonga-Kermadec forearc have been limited by simplistic models of inherited overriding crustal structure that neglect along-strike variability. Synthesis of new robustly tested seismic velocity and density models with existing data sets from the region, highlight along-strike variations in the structure of the Tonga-Kermadec subducting and overriding plates. As the subducting plate undergoes bend-faulting and hydration throughout the trench-outer rise region, observed oceanic upper- and mid-crustal velocities are reduced by ∼1.0 km s-1 and upper mantle velocities by ∼0.5 km s-1. In the vicinity of the Louisville Ridge Seamount Chain (LRSC), the trench shallows by 4 km and normal fault throw is reduced by >1 km, suggesting that the subduction of seamounts reduces plate deformation. We find that the extinct Eocene frontal arc, defined by a high velocity (7.0-7.4 km s-1) and density (3.2 g cm-3) lower-crustal anomaly, increases in thickness by ∼6 km, from 12 to >18 km, over 300 km laterally along the Tonga-Kermadec forearc. Coincident variations in bathymetry and free-air gravity anomaly indicate a regional trend of northward-increasing crustal thickness that predates LRSC subduction, and highlight the present-day extent of the Eocene arc between 32°S and ∼18°S. Within this framework of existing forearc crustal structure, the subduction of seamounts of the LRSC promotes erosion of the overriding crust, forming steep, gravitationally unstable, lower-trench slopes. Trench-slope stability is most likely re-established by the collapse of the mid-trench slope and the trenchward side of the extinct Eocene arc, which, within the framework of forearc characterization, implies seamount subduction commenced at ∼22°S.

Structure of the Sumatra-Andaman subduction zone

NASA Astrophysics Data System (ADS)

Pesicek, Jeremy Dale

We have conducted studies of the Sumatra-Andaman subduction zone using newly available teleseismic data resulting from the aftershock sequences of the 2004, 2005, and 2007 great earthquakes that occurred offshore of the island of Sumatra. In order to better exploit the new data, existing methodologies have been adapted and advanced in several ways to obtain results at a level of precision not previously possible from teleseismic data. Seismic tomography studies of the mantle were conducted using an improved iterative technique that accounts for fine-scale three-dimensional (3-D) velocity variations inside the study region and coarser global velocity variations outside the region. More precise earthquake locations were determined using a double-difference technique that has been extended to teleseismic distances using spherical ray tracing through the nested 3-D regional-global velocity models. Earthquake relocation was included in the iterative tomography scheme and was found to significantly enhance the recovery of slab velocity anomalies. Finally, because crustal structure is poorly constrained by the teleseismic data, 3-D density modeling of the crust was conducted using newly available satellite gravity data and a spherical prism gravity algorithm. The results of these studies better constrain the structure of the Sumatra-Andaman subduction zone, including the geometry of the mantle slab, position of the megathrust, and structural features of the downgoing plate. Tomography results reveal continuous upper mantle slab anomalies with significant variations in dip throughout the region. Broad curvature of the fast anomalies beneath northern Sumatra, similar to curvature of the trench and volcanic arc at the surface, is interpreted as folding of the upper mantle slab. Earthquake relocations show systematic shifts of the hypocenters to the northeast and to shallower depths, each with average changes of 5 km. Reduced scatter in the relocations better constrain the megathrust plate boundary and the regions of coseismic slip during the 2004 and 2005 great earthquakes. In addition, the relocations reveal discrete seismic features on the downgoing plate not previously visible in teleseismic catalogs. The new velocity model and earthquake locations provide the most comprehensive view of the deep structure of the Sumatra-Andaman subduction zone yet available.

KSC-07pd0200

NASA Image and Video Library

2007-01-30

KENNEDY SPACE CENTER, FLA. -- Workers on Launch Pad 39A get ready to begin the movement of the rotating service structure above them. The RSS has not been rotated for more than a year during the maintenance and upgrades on the pad. Some of the work included sandblasting the structure to remove rust and repainting. In addition, the RSS was jacked up and a new upper-bearing race assembly installed where the RSS pivots against the fixed service structure and a half-inch steel plate added. Pad 39A is being made ready for its first launch in four years, the upcoming STS-117 on March 15. Photo credit: NASA/George Shelton

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.

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.

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.

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 PILOT SEARCH FOR EVIDENCE OF EXTRASOLAR EARTH-ANALOG PLATE TECTONICS

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

Jura, M.; Klein, B.; Xu, S.

Relative to calcium, both strontium and barium are markedly enriched in Earth's continental crust compared to the basaltic crusts of other differentiated rocky bodies within the solar system. Here, we both re-examine available archived Keck spectra to place upper bounds on n(Ba)/n(Ca) and revisit published results for n(Sr)/n(Ca) in two white dwarfs that have accreted rocky planetesimals. We find that at most only a small fraction of the pollution is from crustal material that has experienced the distinctive elemental enhancements induced by Earth-analog plate tectonics. In view of the intense theoretical interest in the physical structure of extrasolar rocky planets,more » this search should be extended to additional targets.« less

Radial anisotropy of Northeast Asia inferred from Bayesian inversions of ambient noise data

NASA Astrophysics Data System (ADS)

Lee, S. J.; Kim, S.; Rhie, J.

2017-12-01

The eastern margin of the Eurasia plate exhibits complex tectonic settings due to interactions with the subducting Pacific and Philippine Sea plates and the colliding India plate. Distributed extensional basins and intraplate volcanoes, and their heterogeneous features in the region are not easily explained with a simple mechanism. Observations of radial anisotropy in the entire lithosphere and the part of the asthenosphere provide the most effective evidence for the deformation of the lithosphere and the associated variation of the lithosphere-asthenosphere boundary (LAB). To infer anisotropic structures of crustal and upper-mantle in this region, radial anisotropy is measured using ambient noise data. In a continuation of previous Rayleigh wave tomography study in Northeast Asia, we conduct Love wave tomography to determine radial anisotropy using the Bayesian inversion techniques. Continuous seismic noise recordings of 237 broad-band seismic stations are used and more than 55,000 group and phase velocities of fundamental mode are measured for periods of 5-60 s. Total 8 different types of dispersion maps of Love wave from this study (period 10-60 s), Rayleigh wave from previous tomographic study (Kim et al., 2016; period 8-70 s) and longer period data (period 70-200 s) from a global model (Ekstrom, 2011) are jointly inverted using a hierarchical and transdimensional Bayesian technique. For each grid-node, boundary depths, velocities and anisotropy parameters of layers are sampled simultaneously on the assumption of the layered half-space model. The constructed 3-D radial anisotropy model provides much more details about the crust and upper mantle anisotropic structures, and about the complex undulation of the LAB.

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.

Coupled anisotropic and isotropic tomography of the upper mantle beneath northern Fennoscandia - Application of a novel code AniTomo

NASA Astrophysics Data System (ADS)

Munzarova, Helena; Plomerova, Jaroslava; Kissling, Edi; Vecsey, Ludek; Babuska, Vladislav

2017-04-01

Seismological investigations of the continental mantle lithosphere, particularly its anisotropic structure, advance our understanding of plate tectonics and formation of continents. Orientation of the anisotropic fabrics reflects stress fields during the lithosphere origin and its later deformations. To contribute to studies of the large-scale upper-mantle anisotropy, we have developed code AniTomo for regional anisotropic tomography. AniTomo allows a simultaneous inversion of relative travel time residuals of teleseismic P waves for 3D distribution of isotropic-velocity perturbations and anisotropy in the upper mantle. Weak hexagonal anisotropy with symmetry axis oriented generally in 3D is assumed. The code was successfully tested on a large series of synthetic datasets and synthetic structures. In this contribution we present results of the first application of novel code AniTomo to real data, i.e., relative travel-time residuals of teleseismic P waves recorded during passive seismic experiment LAPNET in the northern Fennoscandia between 2007 and 2009. The region of Fennoscandia is a suitable choice for the first application of the new code. This Precambrian region is tectonically stable and has a thick anisotropic mantle lithosphere (Plomerova and Babuska, Lithos 2010) without significant thermal heterogeneities. In the resulting anisotropic model of the upper mantle beneath the northern Fennoscandia, the strongest anisotropy and the largest velocity perturbations concentrate in the mantle lithosphere. We delimit regions of laterally and vertically consistent anisotropy in the mantle-lithospheric part of the model. In general, the identified anisotropic regions correspond to domains detected by joint interpretation of lateral variations of the P- and SKS-wave anisotropic parameters (Plomerova et al., Solid Earth 2011). Particularly, the mantle lithosphere in the western part of the volume studied exhibits a distinct and uniform fabric that is sharply separated from the surrounding regions. The eastern boundary of this region gradually shifts westward with increasing depth in the tomographic model. We connect the retrieved domain-like anisotropic structure of the mantle lithosphere in the northern Fennoscandia with preserved fossil fabrics of the Archean micro-plates, accreted during the Precambrian orogenic processes.

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.

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.

Lithospheric electrical structure of the middle Lhasa terrane in the south Tibetan plateau

NASA Astrophysics Data System (ADS)

Liang, Hongda; Jin, Sheng; Wei, Wenbo; Gao, Rui; Ye, Gaofeng; Zhang, Letian; Yin, Yaotian; Lu, Zhanwu

2018-04-01

The Lhasa terrane in southern Tibetan plateau is a huge tectono-magmatic belt and an important metallogenic belt. Its formation evolution process and mineralization are affected by the subduction of oceanic plate and subsequent continental collision. However, the evolution of Lhasa terrane has been a subject of much debate for a long time. The Lithospheric structure records the deep processes of the subduction of oceanic plate and continental collision. The magnetotelluric (MT) method can probe the sub-surface electrical conductivity, newly dense broadband and long period magnetotelluric data were collected along a south-north trending profile that across the Lhasa terrane at 88°-89°E. Dimensionality analyses demonstrated that the MT data can be interpreted using two-dimensional approaches, and the regional strike direction was determined as N110°E.Based on data analysis results, a two-dimensional (2-D) resistivity model of crust and upper mantle was derived from inversion of the transverse electric mode, transverse magnetic mode and vertical magnetic field data. Inversion model shows a large north-dipping resistor that extended from the upper crust to upper mantle beneath the Himalaya and the south of Lhasa Terrane, which may represent the subducting Indian continental lithosphere. The 31°N may be an important boundary in the Lhasa Terrane, the south performs a prominent high-conductivity anomaly from the lower crust to upper mantle which indicates the existence of asthenosphere upwelling, while the north performs a higher resistivity and may have a reworking ancient basement. The formation of the ore deposits in the study area may be related to the upwelling of the mantle material triggered by slab tearing and/or breaking off of the Indian lithosphere, and the mantle material input also contributed the total thickness of the present-day Tibetan crust. The results provide helpful constrains to understand the mechanism of the continent-continent collision and the regional exploratory prospect of the deep resources.

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.

Geophysical study of the structure and processes of the continental convergence zones: Alpine-Himalayan Belt

NASA Technical Reports Server (NTRS)

Toksoez, M. N.

1981-01-01

The seismic wave velocity structure in the crust and upper mantle region beneath the Tibetan plateau was studied in detail. Also, a preliminary study of the uppermost mantle P wave velocity beneath Iran and Turkey was carried out, and the results are compared with those for the Tibetan plateau. These two studies compose the bulk of the efforts on the observational aspects of continental collision zones in addition to satellite derived data. On the theoretical aspects the thermal evolution of converging plate boundaries was explored using a finite difference scheme.

Evolution of the Alpine Tethys (Sava) suture zone in Fruška Gora Mountains (N Serbia): from orogenic building to tectonic omissions

NASA Astrophysics Data System (ADS)

Toljić, Marinko; Matenco, Liviu; ĐErić, Nevenka; Milivojević, Jelena; Gerzina, Nataša.; Stojadinović, Uros

2010-05-01

The Fru\\vska Gora Mountains in northern Serbia offers an unique opportunity to study the Cretaceous-Eocene evolution of the NE part of the Dinarides, which is largely covered elsewhere beneath the thick Miocene sediments of the Pannonian basin, deposited during the back-arc collapse associated with the subduction and roll-back recorded in the external Carpathians. The structural grain of the Fru\\vska Gora Mountains is the one of a large scale antiform, exposing a complex puzzle of highly deformed metamorphic rocks in its centre and Triassic-Miocene sequence of non-metamorphosed sediments, ophiolites and volcanics along its flanks. The metamorphic rocks were the target of structural investigations coupled with paleontological dating (conodonts, palynomorphs and radiolarians) in an effort to unravel the geodynamic evolution of an area thought to be located near the suture zone between the Tisza upper plate and the Adriatic lower plate, i.e. the Sava subduction zone of the Dinarides (e.g., Pamic, 2002; Schmid et al., 2008). The existence of this subduction zone was previously inferred here by local observations, such as metamorphosed Mesozoic sediments containing Middle Triassic conodonts (Đurđanović, 1971) or Early Cretaceous blue schists metamorphism (123±5 Ma, Milovanović et al., 1995). The metamorphic sequence is characterized by a Paleozoic age meta-sedimentary basement which contains palynomorphs of Upper Paleozoic - Carboniferous age and a meta-sedimentary and meta-volcanic sequence which contain a succession of contrasting metamorphosed lithologies such sandstones, black limestones, shallow water white limestones, basic volcanic sequences, deep nodular limestiones, radiolarites, meta-ophiolites and turbiditic sequences. The lower part of the sequence is contrastingly similar with the Triassic cover of the Drina-Ivanijca thrust sheet and its metamorphosed equivalent observed in the Kopaonik and Studenica series (Schefer et al., in press). This observation is supported by the newly found micro-fauna of Upper Triassic in age in the meta-sandstones associated with meta-volcanics on the SW slopes of the mountain. The upper part of the sequence display metamorphosed "flysh"-type of sequences and meta-basalts. In these deposits, slightly metamorphosed siliciclastics (lithic sandstones with volcanic-derived clasts) previously interpreted as Upper Jurassic mélange have proved to contain Upper Cretaceous palynomorphs. Among the rocks exposed in the metamorphic core of the mountains, the SW slope of Fru\\vska Gora offers the optimal locality for the study of the kinematic evolution. Here, four phases of folding have been mapped, being associated mainly with large-scale regional contraction. The first phase is characterized by isoclinal folding, with reconstructed SW vergence. The second generation of E-W oriented and coaxial folds is asymmetric and is up to metres in size, displaying a south vergence and has largely refolded the previous generation. The third event was responsible for the formation of upright folds, yet again E-W oriented, re-folding earlier structures. The first two phases of folding are associated with metamorphic conditions, while the third was apparently near the transition with the brittle domain. The relationship with a fourth folding event observed also in the non-metamorphosed clastic-carbonate rocks is rather uncertain, but is apparently associated with the present day antiformal structure of the Fuska Gora Mountains. Interestingly, the metamorphosed Triassic and Upper Cretaceous carbonatic-clastic sequence in the core of the antiform is in structural contact along the antiformal flanks with Lower-Middle Triassic and Upper Cretaceous-Paleogene sediments which display the same facies, but these are not metamorphosed. This demonstrates a large scale tectonic omission along the flanks of the Fru\\vska Gora antiform, 9-10km of rocks being removed by what we speculatively define as an extensional detachment exhuming the metamorphic core. This detachment has been subsequently folded into the present-day antiformal geometry of the Fru\\vska Gora Mountains. These findings demonstrate that the metamorphic and non-metamorphic Upper Cretaceous - Paleogene clastic-carbonate sediments belongs to the main Alpine Tethys (Sava) subduction zone of the Dinarides. The Paleozoic-Triassic metamorphic and non-metamorphic rocks belong to the distal Adriatic lower plate, or more precisely to the Jadar-Kopaonik composite thrust sheet (Schmid et al., 2008), while the layer of serpentinized peridotite found at their contact most probably belongs to the Western Vardar ophiolites obducted over the Adriatic plate during Late Jurassic - Earliest Cretaceous. The distal Jadar-Kopaonik composite unit was partly affected by strong contractional deformation and a Late Eocene greenschist facies metamorphism during the main phase of subduction and collision, similarly to what has been observed elsewhere in the Dinarides (Pamić, 2002; Schefer et al., in press). A Miocene phase of core-complex formation was responsible for the large tectonic omission observed, being probably followed by the formation of a wide open antiformal structure during the Pliocene-Quaternary inversion of the Pannonian basin.

Study of interface influence on bending performance of CFRP with embedded optical fibers

NASA Astrophysics Data System (ADS)

Liu, Rong-mei; Liang, Da-kai

2008-11-01

Studies showed that the bending strength of composite would be affected by embedded optical fibers. Interface strength between the embedded optical fiber and the matrix was studied in this paper. Based on the single fiber pull out tests, the interfacial shear strength between the coating and the clad is the weakest. The shear strength of the optical fiber used in this study is near to 0.8MPa. In order to study the interfacial effect on bending property of generic smart structure, a quasi-isotropic composite laminates were produced from Toray T300C/ epoxy prepreg. Optical fibers were embedded within different orientation plies of the plates, with the optical fibers embedded in the same direction. Accordingly, five different types of plates were produced. Impact tests were carried out on the 5 different plate types. It is shown that when the fiber was embedded at the upper layer, the bending strength drops mostly. The bending normal stress on material arrives at the maximum. So does the normal stress applied on the optical fiber at the surface. Therefore, destructions could originate at the interface between the coating and the clad foremost. The ultimate strength of the smart structure will be affected furthest.

Soft-sediment deformation structures in the late Miocene Şelmo Formation around Adıyaman area, Southeastern Turkey

NASA Astrophysics Data System (ADS)

Koç Taşgın, Calibe; Orhan, Hükmü; Türkmen, İbrahim; Aksoy, Ercan

2011-04-01

The Şelmo Formation was deposited in the basins associated with the Southeastern Anatolian Thrust Belt and East Anatolian Fault Zone in SE Turkey. These structures developed as a result of compressional stresses created by the movement of the Arabian plate to the north and the Eurasian plate to the west from early Miocene to late Pliocene. The outcrops of the Şelmo Formation in the Adýyaman area (SE Turkey) comprise braided river deposits (lower alluvial unit) at the base, lacustrine and deltaic deposits in the middle (lacustrine unit) and low sinuousity river and alluvial deposits at the top (upper alluvial unit). Soft-sediment deformation structures were developed in sandstone, siltstone and marl of the deltaic and lacustrine unit of the Şelmo Formation. These are slumps, recumbent folds, load casts, ball-and-pillow structures, flame structures, neptunian dykes, chaotically associated structures and synsedimentary faults. The tectonic setting of the basin, the lateral extent of the soft-sediment deformation structures over tens of kilometers, their similarities to deformation structures interpreted as being induced seismically in other regions worldwide or in a laboratory setting, and being confined by undeformed layers suggest that the main trigger system was related to seismic activity in the area.

Seismic reflection imaging of two megathrust shear zones in the northern Cascadia subduction zone.

PubMed

Calvert, Andrew J

2004-03-11

At convergent continental margins, the relative motion between the subducting oceanic plate and the overriding continent is usually accommodated by movement along a single, thin interface known as a megathrust. Great thrust earthquakes occur on the shallow part of this interface where the two plates are locked together. Earthquakes of lower magnitude occur within the underlying oceanic plate, and have been linked to geochemical dehydration reactions caused by the plate's descent. Here I present deep seismic reflection data from the northern Cascadia subduction zone that show that the inter-plate boundary is up to 16 km thick and comprises two megathrust shear zones that bound a >5-km-thick, approximately 110-km-wide region of imbricated crustal rocks. Earthquakes within the subducting plate occur predominantly in two geographic bands where the dip of the plate is inferred to increase as it is forced around the edges of the imbricated inter-plate boundary zone. This implies that seismicity in the subducting slab is controlled primarily by deformation in the upper part of the plate. Slip on the shallower megathrust shear zone, which may occur by aseismic slow slip, will transport crustal rocks into the upper mantle above the subducting oceanic plate and may, in part, provide an explanation for the unusually low seismic wave speeds that are observed there.

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.

Using cross correlations of turbulent flow-induced ambient vibrations to estimate the structural impulse response. Application to structural health monitoring.

PubMed

Sabra, Karim G; Winkel, Eric S; Bourgoyne, Dwayne A; Elbing, Brian R; Ceccio, Steve L; Perlin, Marc; Dowling, David R

2007-04-01

It has been demonstrated theoretically and experimentally that an estimate of the impulse response (or Green's function) between two receivers can be obtained from the cross correlation of diffuse wave fields at these two receivers in various environments and frequency ranges: ultrasonics, civil engineering, underwater acoustics, and seismology. This result provides a means for structural monitoring using ambient structure-borne noise only, without the use of active sources. This paper presents experimental results obtained from flow-induced random vibration data recorded by pairs of accelerometers mounted within a flat plate or hydrofoil in the test section of the U.S. Navy's William B. Morgan Large Cavitation Channel. The experiments were conducted at high Reynolds number (Re > 50 million) with the primary excitation source being turbulent boundary layer pressure fluctuations on the upper and lower surfaces of the plate or foil. Identical deterministic time signatures emerge from the noise cross-correlation function computed via robust and simple processing of noise measured on different days by a pair of passive sensors. These time signatures are used to determine and/or monitor the structural response of the test models from a few hundred to a few thousand Hertz.

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.

Implementation of Structural Health Monitoring for the USMC CH-53E

DTIC Science & Technology

2010-01-01

assembly, main rotor hub upper plate assembly, main rotor blade extender, main gear box housing, main gearbox shaft , and the main rotor spindle ...spectrum. The objective is to determine if an aircraft is flown more or less severely than designed , and to provide benefit in the form of either...aircraft is flown more or less severely than designed , and to provide benefit in the form of either safety or economy. Although most of the beneficiaries

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.

Structural record of Lower Miocene westward motion of the Alboran Domain in the Western Betics, Spain

NASA Astrophysics Data System (ADS)

Frasca, Gianluca; Gueydan, Frédéric; Brun, Jean-Pierre

2015-08-01

In the framework of the Africa-Europe convergence, the Mediterranean system presents a complex interaction between subduction rollback and upper-plate deformation during the Tertiary. The western end of the system shows a narrow arcuate geometry across the Gibraltar arc, the Betic-Rif belt, in which the relationship between slab dynamics and surface tectonics is not well understood. The present study focuses on the Western Betics, which is characterized by two major thrusts: 1) the Internal/External Zone Boundary limits the metamorphic domain (Alboran Domain) from the fold-and-thrust belts in the External Zone; 2) the Ronda Peridotites Thrust allows the juxtaposition of a strongly attenuated lithosphere section with large bodies of sub-continental mantle rocks on top of upper crustal rocks. New structural data show that two major E-W strike-slip corridors played a major role in the deformation pattern of the Alboran Domain, in which E-W dextral strike-slip faults, N60° thrusts and N140° normal faults developed simultaneously during dextral strike-slip simple shear. Olistostromic sediments of Lower Miocene age were deposited and deformed in this tectonic context and hence provide an age estimate for the inferred continuous westward translation of the Alboran Domain that is accommodated by an E-W lateral (strike-slip) ramp and a N60° frontal thrust. The crustal emplacement of large bodies of sub-continental mantle may occur at the onset of this westward thrusting in the Western Alboran domain. At lithosphere-scale, we interpret the observed deformation pattern as the subduction upper-plate expression of a lateral slab tear and its westward propagation since the Lower Miocene.

Correlations between Crustal Structure and Slip on the Cascadia Megathrust (Invited)

NASA Astrophysics Data System (ADS)

Trehu, A. M.

2013-12-01

A number of active-source seismic imaging experiments of the Cascadia forearc margin have been conducted over the past three decades. Seismic P-wave velocity models derived from these experiments, when combined with geodetic, potential field, morphological and other data, reveal structures in both the upper and lower plate that can be correlated with current microseismic activity, geodetic signals indicating interplate locking, and apparent segmentation of past large plate boundary earthquakes as determined from onshore and offshore paleoseismic data. These data are being interpreted to construct maps of the apparent seismic velocity structure averaged over several km above and below the expected plate boundary and extending from the region characterized by episodic tremor and slip up dip to the deformation front. Preliminary results for the recent CIET, COAST and Ridge-to-Trench experiments that support, challenge or extend an evolving working model for structural constraints on plate boundary deformation in Cascadia will also be discussed. Other co-PIs who have planned and executed the CIET, COAST and Ridge-to-Trench experiments are listed below with the lead PI for each group listed first. CIET (Cascadia Initiative Science Team): Doug Toomey, Emilie Hooft (both at Un. of Oregon); Bob Dziak (Oregon State Un. NOAA); William Wilcock (Un. Washington); Susan Schwartz (UC Santa Cruz); John Collins, Jeff McGuire (WHOI); Maya Tolstoy (LDEO); Richard Allen (UC Berkeley) COAST (Cascadia Open-Access Seismic Transects): Steve Holbrook (Un. Wyoming); Graham Kent (Un. Nevada Reno); Katie Keranen (Un. Oklahoma); Paul Johnson (Un. Washington); Jackie Caplan-Auerbach (Western Washington Un.); Harold Tobin (Un. Wisconson) Ridge-to-Trench: Suzanne Carbotte, Helene Carton, Geoff Abers (all at LDEO); Pablo Canales (WHOI); Mladen Nedimovic (Dalhousie Un.)

The Electrical Resistivity Structure of the Eastern Anatolian Collision Zone, Northeastern Anatolia

NASA Astrophysics Data System (ADS)

Cengiz, Özlem; Tuǧrul Başokur, Ahmet; Tolak Çiftçi, Elif

2016-04-01

The Northeastern Anatolia is located at the intensely deformed Eastern Anatolian Collision Zone (EACZ), and its tectonic framework is characterized by the collision of the Arabian plate with Eurasian. Although extensive attention is given to understand the crustal and upper mantle processes at this convergent boundary, there is still an ongoing debate over the geodynamic processes of the region. In this study, we were specifically interested in the geoelectric properties and thus geodynamics of the crust beneath the EACZ. Magnetotelluric (MT) measurements were made on two profiles across the north of the EACZ in 1998 as part of a national project undertaken by the Turkish Petroleum Corporation (TPAO). MT data in the frequency range of 300-0.001 Hz were collected from 168 stations located along 78 km north to south and 47 km west to east profiles where direct convergence occurs between Arabian and Eurasian plates. Two and three-dimensional inversion algorithms were used to obtain resistivity models of the study area. According to these models, the upper crust consists of low resistivity sedimentary rocks (<30 Ωm) that are underlain by highly resistive (~500-1000 Ωm) crystalline basement rocks of the Eastern Anatolian Accretionary Complex and Pontides. While the upper and lower crustal resistivity at the northern part of the study area shows a layered structure, significant horizontal and vertical variations for the rest of the EACZ exists on resistivity models. The broad low resistivity zones (<50 Ωm) observed at mid and lower crustal levels throughout the EACZ. These fluid-rich regions along with high temperatures could indicate weak zones representing the locations of active deformation induced by continent-continent collision and correlate with volcanic centers in the region. The variation in the resistivity structure supports the southward subduction model with the resistive continental block and the deep conductive zones presumably corresponding to the oceanic crust.

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.

Heat flow evidence for hydrothermal circulation in the volcanic basement of subducting plates

NASA Astrophysics Data System (ADS)

Harris, R. N.; Spinelli, G. A.; Fisher, A. T.

2017-12-01

We summarize and interpret evidence for hydrothermal circulation in subducting oceanic basement from the Nankai, Costa Rica, south central Chile, Haida Gwaii, and Cascadia margins and explore the influence of hydrothermal circulation on plate boundary temperatures in these settings. Heat flow evidence for hydrothermal circulation in the volcanic basement of incoming plates includes: (a) values that are well below conductive (lithospheric) predictions due to advective heat loss, and (b) variability about conductive predictions that cannot be explained by variations in seafloor relief or thermal conductivity. We construct thermal models of these systems that include an aquifer in the upper oceanic crust that enhances heat transport via a high Nusselt number proxy for hydrothermal circulation. At the subduction zones examined, patterns of seafloor heat flow are not well fit by purely conductive simulations, and are better explained by simulations that include the influence of hydrothermal circulation. This result is consistent with the young basement ages (8-35 Ma) of the incoming igneous crust at these sites as well as results from global heat flow analyses showing a significant conductive heat flow deficit for crustal ages less than 65 Ma. Hydrothermal circulation within subducting oceanic basement can have a profound influence on temperatures close to the plate boundary and, in general, leads to plate boundary temperatures that are cooler than those where fluid flow does not occur. The magnitude of cooling depends on the permeability structure of the incoming plate and the evolution of permeability with depth and time. Resolving complex relationships between subduction processes, the permeability structure in the ocean crust, and the dynamics of hydrothermal circulation remains an interdisciplinary frontier.

An Integrated View of Tectonics in the North Pacific Derived from GPS

NASA Astrophysics Data System (ADS)

Elliott, J.; Freymueller, J.; Marechal, A.; Larsen, C.; Perea Barreto, M. A.

2015-12-01

Textbooks show a simple picture of the tectonics of the North Pacific, with discrete deformation along the boundary between the Pacific and North American plates along the Aleutian megathrust and Fairweather/Queen Charlotte fault system. Reality is much more complex, with a pattern of broadly distributed deformation. This is in part due to a number of studies and initiatives (such as PBO) in recent years that have greatly expanded the density of GPS data throughout the region. We present an overview of the GPS data acquired and various tectonic interpretations developed over the past decade and discuss a current effort to integrate the available data into a regional tectonic model for Alaska and northwestern Canada. Rather than discrete plate boundaries, we observe zones of concentrated deformation where the majority of the relative plate motion is accommodated. Within these zones, there are major fault systems, such as the Fairweather-Queen Charlotte transform and the Aleutian megathrust, where most of the deformation occurs along a main structure, but often motion is instead partitioned across multiple faults, such as the fold-and-thrust belt of the eastern St. Elias orogen. In zones of particular complexity, such as the eastern syntaxis of the St. Elias orogen, the deformation is better described by continuum deformation than localized strain along crustal structures. Strain is transferred far inboard, either by diffuse deformation or along fault system such as the Denali fault, and outboard of the main zones of deformation. The upper plate, if it can be called such, consists of a number of blocks and deforming zones while the lower plate is segmented between the Yakutat block and Pacific plate and is also likely undergoing internal deformation.

Study on 3-D velocity structure of crust and upper mantle in Sichuan-yunnan region, China

USGS Publications Warehouse

Wang, C.; Mooney, W.D.; Wang, X.; Wu, J.; Lou, H.; Wang, F.

2002-01-01

Based on the first arrival P and S data of 4 625 regional earthquakes recorded at 174 stations dispersed in the Yunnan and Sichuan Provinces, the 3-D velocity structure of crust and upper mantle in the region is determined, incorporating with previous deep geophysical data. In the upper crust, a positive anomaly velocity zone exists in the Sichuan basin, whereas a negative anomaly velocity zone exists in the western Sichuan plateau. The boundary between the positive and negative anomaly zones is the Longmenshan fault zone. The images of lower crust and upper mantle in the Longmenshan fault, Xianshuihe fault, Honghe fault and others appear the characteristic of tectonic boundary, indicating that the faults litely penetrate the Moho discontinuity. The negative velocity anomalies at the depth of 50 km in the Tengchong volcanic area and the Panxi tectonic zone appear to be associated with the temperature and composition variations in the upper mantle. The overall features of the crustal and the upper mantle structures in the Sichuan-Yunnan region are the lower average velocity in both crust and uppermost mantle, the large crustal thickness variations, and the existence of high conductivity layer in the crust or/and upper mantle, and higher geothermal value. All these features are closely related to the collision between the Indian and the Asian plates. The crustal velocity in the Sichuan-Yunnan rhombic block generally shows normal.value or positive anomaly, while the negative anomaly exists in the area along the large strike-slip faults as the block boundary. It is conducive to the crustal block side-pressing out along the faults. In the major seismic zones, the seismicity is relative to the negative anomaly velocity. Most strong earthquakes occurred in the upper-mid crust with positive anomaly or normal velocity, where the negative anomaly zone generally exists below.

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

Negus-De Wys, J.; Dixon, J. M.; Evans, M. A.

This document consists of the following papers: inorganic geochemistry studies of the Eastern Kentucky Gas Field; lithology studies of upper Devonian well cuttings in the Eastern Kentucky Gas Field; possible effects of plate tectonics on the Appalachian Devonian black shale production in eastern Kentucky; preliminary depositional model for upper Devonian Huron age organic black shale in the Eastern Kentucky Gas Field; the anatomy of a large Devonian black shale gas field; the Cottageville (Mount Alto) Gas Field, Jackson County, West Virginia: a case study of Devonian shale gas production; the Eastern Kentucky Gas Field: a geological study of the relationshipsmore » of Ohio Shale gas occurrences to structure, stratigraphy, lithology, and inorganic geochemical parameters; and a statistical analysis of geochemical data for the Eastern Kentucky Gas Field.« less

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.

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.

The Effects of Rapid Sedimentation upon Continental Breakup: Kinematic and Thermal Modeling of the Salton Trough, Southern California, Based upon Recent Seismic Images

NASA Astrophysics Data System (ADS)

Han, L.; Hole, J. A.; Lowell, R. P.; Stock, J. M.; Fuis, G. S.

2016-12-01

The Salton Seismic Imaging Project (SSIP) illuminated crustal and upper mantle structure of the Salton Trough, the northern-most rift segment of the Gulf of California plate boundary. The crust is 17-18 km thick and homogeneous for 100 km in the plate motion direction. New crust is being created by distributed rift magmatism, Colorado River sedimentation, and metamorphism of the sediment. A 5 km thick pre-existing crustal layer may still exist. The crust has not broken apart to enable initiation of seafloor spreading. A one-dimensional time-dependent kinematic and thermal model was developed to simulate these observations. We assume that all crustal layers are stretched uniformly during extension. Distributed mafic magmatism and sedimentation are added simultaneously to compensate for the crustal thinning. The ratio of magmatism to sedimentation is constrained by the seismic observations. Heat is transported by thermal conduction and by advection due to stretching of the crust. A constant temperature boundary at the Moho is used to represent partial melting in the upper mantle. Assuming a constant plate motion rate, the zone of active rifting extends linearly with time. The crustal thickness and internal structure also evolve with time. The model constraints are the observed seismic structure and heat flow. The model rapidly reaches quasi-steady state, and could continue for many millions of years. The observed seismic structure and heat flow are reproduced after 3 Myr. The yield strength profile calculated from lithology and model temperature indicates that ductile deformation in the middle and lower crust dominates the crustal rheology. Rapid sedimentation delays crustal breakup and the initiation of seafloor spreading by maintaining the thickness of the crust and keeping it predominantly ductile. This process probably occurs wherever a large river flows into an active rift driven by far-field extension. It may have built passive margins in many locations globally, such as the Gulf of Mexico. This type of passive margin consists of mostly new crust created by magmatism and metamorphism of sediment. Along such margins, metamorphosed sediment could be misinterpreted as stretched pre-existing continental crust.

Mapping the evolving strain field during continental breakup from crustal anisotropy in the Afar Depression

PubMed Central

Keir, Derek; Belachew, M.; Ebinger, C.J.; Kendall, J.-M.; Hammond, J.O.S.; Stuart, G.W.; Ayele, A.; Rowland, J.V.

2011-01-01

Rifting of the continents leading to plate rupture occurs by a combination of mechanical deformation and magma intrusion, yet the spatial and temporal scales over which these alternate mechanisms localize extensional strain remain controversial. Here we quantify anisotropy of the upper crust across the volcanically active Afar Triple Junction using shear-wave splitting from local earthquakes to evaluate the distribution and orientation of strain in a region of continental breakup. The pattern of S-wave splitting in Afar is best explained by anisotropy from deformation-related structures, with the dramatic change in splitting parameters into the rift axis from the increased density of dyke-induced faulting combined with a contribution from oriented melt pockets near volcanic centres. The lack of rift-perpendicular anisotropy in the lithosphere, and corroborating geoscientific evidence of extension dominated by dyking, provide strong evidence that magma intrusion achieves the majority of plate opening in this zone of incipient plate rupture. PMID:21505441

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.

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.

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.

A Review of Geophysical Constraints on the Deep Structure of the Tibetan Plateau, the Himalaya and the Karakoram, and their Tectonic Implications

NASA Astrophysics Data System (ADS)

Molnar, P.

1988-09-01

The Tibetan Plateau, the Himalaya and the Karakoram are the most spectacular consequences of the collision of the Indian subcontinent with the rest of Eurasia in Cainozoic time. Accordingly, the deep structures beneath them provide constraints on both the tectonic history of the region and on the dynamic processes that have created these structures. The dispersion of seismic surface waves requires that the crust beneath Tibet be thick: nowhere less than 50 km, at least 65 km, in most areas, but less than 80 km in all areas that have been studied. Wide-angle reflections of P-waves from explosive sources in southern Tibet corroborate the existence of a thick crust but also imply the existence of marked lateral variations in that thickness, or in the velocity structure of the crust. Thus isostatic compensation occurs largely by an Airy-type mechanism, unlike that, for instance, of the Basin and Range Province of western North America where a hot upper mantle buoys up a thin crust. The P-wave and S-wave velocities in the uppermost mantle of most of Tibet are relatively high and typical of those of Precambrian shields and stable platforms: Vp = 8.1 km s-1 or higher, and Vs≈ 4.7 km s-1. Travel times and waveforms of S-waves passing through the uppermost mantle of much of Tibet, however, require a much lower average velocity in the uppermost mantle than that of the Indian, or other, shields. They indicate a thick low-velocity zone in the upper mantle beneath Tibet, reminiscent of tectonically active regions. These data rule out a shield structure beneath northern Tibet and suggest that if such a structure does underlie part of the plateau, it does so only beneath the southern part. Lateral variations in the upper-mantle structure of Tibet are apparent from differences in travel times of S-waves from earthquakes in different parts of Tibet, in the attenuation of short-period phases, Pn and Sn, that propagate through the uppermost mantle of Tibet, and in surface-wave dispersion for different paths. The notably lower velocities and the greater attenuation in the mantle of north--central Tibet than elsewhere imply higher temperatures there and are consistent with the occurrence of active and young volcanism in roughly the same area. Surface-wave dispersion across north--central Tibet also requires a thinner crust in that area than in most of the plateau. Consequently the relatively uniform height of the plateau implies that isostatic compensation in the north--central part of Tibet occurs partly because the density of the relatively hot material in the upper mantle is lower than that elsewhere beneath Tibet, the mechanism envisioned by Pratt. Several seismological studies provide evidence consistent with a continuity of the Indian Shield, and its cold thick lithosphere, beneath the Himalaya. Fault-plane solutions and focal depths of the majority of moderate earthquakes in the Himalaya are consistent with their occurring on the top surface of the gently flexed, intact Indian plate that has underthrust the Lesser Himalaya roughly 80-100 km or more. P-waves from explosions in southern Tibet and recorded in Nepal can be interpreted as wide-angle reflections from this fault zone. P-wave delays across the Tarbela network in Pakistan from distant earthquakes indicate a gentle dip of the Moho beneath the array without pronounced later variations in upper-mantle structure. High Pn and Sn velocities beneath the Himalaya and normal to early S-wave arrival times from Himalayan earthquakes recorded at teleseismic distances are consistent with Himalaya being underlain by the same structure that underlies India. Results from explosion seismology indicate an increase in crustal thickness from the Indo--Gangetic Plain across the Himalaya to southern Tibet, but Hirn, Lepine, Sapin and their co-workers inferred that the depth of the Moho does not increase smoothly northward, as it would if the Indian Shield had been underthrust coherently beneath the Himalaya. They interpreted wide-angle reflections as evidence for steps in the Moho displaced from one another on southward-dipping faults. Although I cannot disprove this interpretation, I think that one can recognize a sequence of signals on their wide-angle reflection profiles that could be wide-angle reflections from a northward-dipping Moho. Gravity anomalies across the Himalaya show that both the Indo--Gangetic Plain and the Himalaya are not in local isostatic equilibrium. A mass deficit beneath the plain is apparently caused by the flexure of the Indian Shield and by the low density of the sedimentary rock in the basin formed by the flexure. The mass excess in the Himalaya seems to be partly supported by the strength of the Indian plate, for which the flexural rigidity is particularly large. An increase in the Bouguer gravity gradient from about 1 mGal km-1 (1 mGal = 10-3 cm s-2) over the Indo--Gangetic Plain to 2 mGal km-1 over the Himalaya implies a marked steepening of the Moho, and therefore a greater flexure of the Indian plate, beneath the Himalaya. This implies a northward decrease in the flexural rigidity of the part of the Indian plate underlying the range. Nevertheless, calculations of deflections of elastic plates with different flexural rigidities and flexed by the weight of the Himalaya show larger deflections and yield more negative gravity anomalies than are observed. Thus, some other force, besides the flexural strength of the plate, must contribute to the support of the range. A bending moment applied to the end of the Indian plate could flex the plate up beneath the range and provide the needed support. The source of this moment might be gravity acting on the mantle portion of the subducting Indian continental lithosphere with much or all of the crust detached from it. Seismological studies of the Karakoram are consistent with its being underlain by particularly cold material in the upper mantle. Intermediate-depth earthquakes occur between depths of 70 and 100 km but apparently do not define a zone of subducted oceanic lithosphere. Rayleigh-wave phase velocities are particularly high for paths across this area and imply high shear wave velocities in the upper mantle. Isostatic gravity anomalies indicate a marked low of 70 mGal over the Karakoram, which could result from a slightly thickened crust pulled down by the sinking of cold material beneath it. Geophysical constraints on the structure of Tibet, the Himalaya and the Karakoram are consistent with a dynamic uppermost mantle that includes first, the plunging of cold material into the asthenosphere beneath southern Tibet and the Karakoram, as the Indian plate slides beneath the Himalaya, and second, an upwelling of hot material beneath north--central Tibet. The structure is too poorly resolved to require such dynamic flow, but the existence for both a hot uppermost mantle beneath north--central Tibet and a relatively cold uppermost mantle beneath southern Tibet and the Karakoram seem to be required. Both group and phase velocities of Rayleigh waves and Love waves are delayed along paths crossing Tibet. The low velocities require a crustal thickness in excess of 50 km, and for most regions in excess of 60 km. Crustal thicknesses in excess of 80 km can be ruled out for all paths studied, and for most of Tibet, a crustal thickness of 65-70 km seems required. Clear evidence for lateral heterogeneity beneath Tibet is provided not only by body waves (discussed below) but also by surface waves (Brandon & Romanowicz 1986), which show an area of lower uppermost shear-wave velocity and thinner crust in north--central Tibet than elsewhere in the plateau. These variations might explain the differences in group velocities measured by different workers, and the different structures that they deduced, but if so, they also render the regionalization of surface-wave dispersion into arbitrary tectonic provinces risky. Although Rayleigh-wave phase velocities can resolve large differences in upper-mantle velocities for regions the size of Tibet, constraints on these velocities are best derived from body waves. Thus, with the exceptions of Brandon & Romanowicz's (1986) detailed investigation of north--central Tibet, the study of southernmost Tibet by Jobert et al. (1985) and that of Romanowicz (1982) for the northeasternmost part of the plateau, I do not think that surface waves have placed an important bound on the velocity in the upper mantle beneath Tibet. The seismic data are broadly consistent with partial melting of the uppermost mantle of north--central Tibet, where recent volcanism has been observed. Correspondingly, there is no suggestion of such low velocities, and such high temperatures, in the mantle elsewhere beneath Tibet, for which late-Cainozoic volcanism has not been reported. The results are also consistent with a slightly thinner crust in north--central Tibet than farther south, suggesting that both Airy and Pratt isostasy share compensation for north--central Tibet's great height. Finally, the average shear-wave velocity in the upper mantle of southern Tibet seems to be higher than that in northern Tibet, but neither is the degree of difference well determined, nor is the location of the transition from one to the other well mapped.

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

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

Ridge asymmetry and deep aqueous alteration at the trench observed from Rayleigh wave tomography of the Juan de Fuca plate

NASA Astrophysics Data System (ADS)

Bell, Samuel; Ruan, Youyi; Forsyth, Donald W.

2016-10-01

Using Rayleigh wave tomography of noise-removed ocean bottom seismometer data from the Cascadia Initiative, we illuminate the structure of the upper mantle beneath the Juan de Fuca plate. Beneath the Juan de Fuca ridge, there is strong asymmetry, with a pronounced low-velocity zone in the 25-65 km depth range. Extending to the west from the spreading axis, this anomaly has velocities low enough to indicate the presence of melt. The asymmetry in velocity structure and the much greater abundance of seamounts on the west flank of the ridge suggest that dynamic, buoyant upwelling is important, perhaps triggered by thermal or compositional anomalies beneath Axial Seamount. In contrast, there is no evidence for asymmetry in the axial zone or lower than expected velocities beneath the Gorda ridge. On the eastern flank of the Juan de Fuca ridge, the shear velocity in the 25-65 depth range is higher than expected; the lithosphere appears to be colder and thicker than predicted by standard plate cooling models, perhaps caused by the downwelling counterpart of the upwelling on the west side of the ridge. Close to the trench, there is a sharp decrease in shear velocity. We interpret this as aqueous alteration caused by hydrothermal circulation through deep normal faults associated with bending of the plate. Beneath the Astoria and Nitinat fans, where abyssal plain sediment is thickest, the velocity decrease is much smaller, which is consistent with a thick sediment cap that prevents hydrothermal alteration of the plate.

Deep electrical resistivity structure of northwestern Costa Rica

NASA Astrophysics Data System (ADS)

Brasse, H.; Kapinos, G.; Mütschard, L.; Alvarado, G. E.; Worzewski, T.; Jegen, M.

2009-01-01

First long-period magnetotelluric investigations were conducted in early 2008 in northwestern Costa Rica, along a profile that extends from the coast of the Pacific Ocean, traverses the volcanic arc and ends currently at the Nicaraguan border. The aim of this study is to gain insight into the electrical resistivity structure and thus fluid distribution at the continental margin where the Cocos plate subducts beneath the Caribbean plate. Preliminary two-dimensional models map the only moderately resistive mafic/ultramafic complexes of the Nicoya Peninsula (resistivity of a few hundred Ωm), the conductive forearc and the backarc basins (several Ωm). Beneath the backarc basin the data image a poor conductor in the basement with a clear termination in the south, which may tentatively be interpreted as the Santa Elena Suture. The volcanic arc shows no pronounced anomaly at depth, but a moderate conductor underlies the backarc with a possible connection to the upper mantle. A conductor at deep-crustal levels in the forearc may reflect fluid release from the downgoing slab.

Full-waveform Inversion for Localized 3-D S-velocity Structure in D" Beneath the Caribbean using US-Array Data

NASA Astrophysics Data System (ADS)

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

2015-12-01

The region beneath Central America is known to have significant lateral velocity heterogeneities from the upper mantle down to the lowermost mantle. It is also known for its long history of subducting oceanic plates and fragmented plate remnants that sunk to the lowermost mantle (e.g., Ren et al., 2007). In this study, we use localized full-waveform inversion to invert for the 3-D S-velocity beneath the Caribbean. We use the DSM (Kawai et al., 2006) to compute 1-D synthetic seismograms and the first-order Born approximation to compute the partial derivatives for 3-D structure. We use a larger dataset with better coverage than Kawai et al. (2014), consisting of S and ScS phases from US-Array data for events in South America. The resulting 3-D model can contribute to understanding whether the cause of the velocity anomalies is thermal, chemical, or due to phase transitions.

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.

Imaging the Subduction Plate Interface Using Low-Frequency Earthquakes

NASA Astrophysics Data System (ADS)

Plourde, A. P.; Bostock, M. G.

2015-12-01

Low-frequency Earthquakes (LFEs) in subduction zones are commonly thought to represent slip on the plate interface. They have also been observed to lie near or within a zone of low shear-wave velocity, which is modelled as fluid-rich upper oceanic crust. Due to relatively large depth uncertainties in absolute hypocenters of most LFE families, their location relative to an independently imaged subucting plate and, consequently, the nature of the plate boundary at depths between 30-45 km have not been precisely determined. For a selection of LFE families in northern Washington, we measure variations in arrival time of individual LFE detections using multi-channel cross-correlation incorporating both arrivals at the same station and different events (cross-detection data), and the same event but different stations (cross-station data). Employing HypoDD, these times are used to generate relative locations for individual LFE detections. After creating templates from spatial subgroups of detections, network cross-correlation techniques will be used to search for new detections in neighbouring areas, thereby expanding the local catalogue and enabling further subdivision. By combining the source ``arrays'' and the receiver arrays from the Array of Arrays experiment we plan to interrogate plate boundary structure using migration of scattered waves from the subduction complex as previously documented beneath southern Vancouver Island.

Blended-Wing-Body Structural Technology Study

NASA Technical Reports Server (NTRS)

Starnes, James H.

1998-01-01

In most studies of stability of plates, the axial stress has been taken as uniform compression throughout flat rectangular plates. Buckling of isotropic plates under a compressive stress that varies linearly from one loaded edge to the other has been studied by Libove et al. Cases of practical interest exist, however, in which the axial stress is not uniform but varies from tension at both loaded edges to compression in the middle. An example is the stability of the crown of the hat stiffened panel, a candidate configuration of the upper and lower skin of the Blended Wing Body (BWB) Aircraft. The BWB Aircraft is an advanced long-range ultra-high-capacity airliner with the principal feature being the pressurized wide double-deck body which is blended into the wing. In the present research, analytical methods are used to investigate the local stability of the crown in order to minimize its weight while optimizing its buckling strength. The crown is modeled as a rectangular laminated composite plate subjected to a second degree parabolic variation of axial stresses in the longitudinal direction. A varying tension-compression- tension axial stresses are induced in the crown of the stiffeners due to bending. The change in axial stresses is equilibrated by nonuniform shear stresses along the plate edges and transverse normal stresses.

Evolution of Meso-Cenozoic lithospheric thermal-rheological structure in the Jiyang sub-basin, Bohai Bay Basin, eastern North China Craton

NASA Astrophysics Data System (ADS)

Xu, Wei; Qiu, Nansheng; Wang, Ye; Chang, Jian

2018-01-01

The Meso-Cenozoic lithospheric thermal-rheological structure and lithospheric strength evolution of the Jiyang sub-basin were modeled using thermal history, crustal structure, and rheological parameter data. Results indicate that the thermal-rheological structure of the Jiyang sub-basin has exhibited obvious rheological stratification and changes over time. During the Early Mesozoic, the uppermost portion of the upper crust, middle crust, and the top part of the upper mantle had a thick brittle layer. During the early Early Cretaceous, the top of the middle crust's brittle layer thinned because of lithosphere thinning and temperature increase, and the uppermost portion of the upper mantle was almost occupied by a ductile layer. During the late Early Cretaceous, the brittle layer of the middle crust and the upper mantle changed to a ductile one. Then, the uppermost portion of the middle crust changed to a thin brittle layer in the late Cretaceous. During the early Paleogene, the thin brittle layer of the middle crust became even thinner and shallower under the condition of crustal extension. Currently, with the decrease in lithospheric temperature, the top of the upper crust, middle crust, and the uppermost portion of the upper mantle are of a brittle layer. The total lithospheric strength and the effective elastic thickness ( T e) in Meso-Cenozoic indicate that the Jiyang sub-basin experienced two weakened stages: during the late Early Cretaceous and the early Paleogene. The total lithospheric strength (approximately 4-5 × 1013 N m-1) and T e (approximately 50-60 km) during the Early Mesozoic was larger than that after the Late Jurassic (2-7 × 1012 N m-1 and 19-39 km, respectively). The results also reflect the subduction, and rollback of Pacific plate is the geodynamic mechanism of the destruction of the eastern North China Craton.

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.

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.

Crustal anisotropy along the North Anatolian Fault Zone from receiver functions

NASA Astrophysics Data System (ADS)

Licciardi, Andrea; Eken, Tuna; Taymaz, Tuncay; Piana Agostinetti, Nicola; Yolsal-Çevikbilen, Seda; Tilmann, Frederik

2016-04-01

The North Anatolian Fault Zone (NAFZ) that is considered to be one of the largest plate-bounding transform faults separates the Anatolian Plate to the south from the Eurasian Plate to the north. A proper estimation of the crustal anisotropy in the area is a key point to understand the present and past tectonic processes associated with the plate boundary as well as for assessing its strength and stability. In this work we used data from the North Anatolian Fault (NAF) passive seismic experiment in order to retrieve the anisotropic properties of the crust by means of the receiver function (RF) method. This approach provides robust constraints on the location at depth of anisotropic bodies compared to other seismological tools like S-waves splitting observations where anisotropic parameters are obtained through a path-integrated measurement process over depth. We computed RFs from teleseismic events, for 39 stations with a recording period of nearly 2 years, providing an excellent azimuthal coverage. The observed azimuthal variations in amplitudes and delay times on the Radial and Transverse RF indicate the presence of anisotropy in the crust. Isotropic and anisotropic effects on the RFs are analyzed separately after harmonic decomposition of the RF dataset (Bianchi et al. 2010). Pseudo 2D profiles are built to observe both the seismic isotropic structure and the depth-dependent lateral variations of crustal anisotropy in the area, including orientation of the symmetry axis. Preliminary results show that the isotropic structure is characterized by a complex crustal setting above a nearly flat Moho at a depth of ~40 km in the central portion of the studied area. Strong anisotropy is present in the upper crust along some portions of the NAFZ and the Ezinepazari-Sungurlu Fault (ESF), with a strong correlation between the orientation of the symmetry axis of anisotropy and the strike of the main geological structures. More complex patterns of anisotropy are present in the middle and lower crust as well as in the upper mantle. Bianchi, I., J. Park, N. Piana Agostinetti, and V. Levin (2010), Mapping seismic anisotropy using harmonic decomposition of receiver functions: An application to Northern Apennines, Italy, J. Geophys. Res., 115, B12317, doi:10.1029/2009JB007061.

Detecting slab structure beneath the Banda Arc from waveform analysis of deep focus earthquakes

NASA Astrophysics Data System (ADS)

Miller, M. S.; Sun, D.; Holt, A. F.

2017-12-01

We investigate the structure of the subducting Australian slab by utilizing 30 recently installed, temporary broadband seismometers (YS network) in the Banda Arc region of the Indonesia archipelago. This region is of particular tectonic interest as it is the archetypal example of a young arc-continent collision along with known varied lithospheric structure of the incoming Australian plate. Previous (e.g. Widiyantoro et al. 2011) and preliminary body wave tomography (Harris et al., this session) indicate complex subducted slab structures, where gaps in fast velocity anomalies in the upper mantle are interpreted as slab tears and are linked to the variation in the incoming plate structures. The detailed shape and location of these tears are important for kinematic reconstructions and for understanding the evolution of the entire subduction system. However, tomographic images are inherently smooth due to being produced with damped inversions and therefore underestimate the sharpness of these structures. We investigate possible sharp-sided structures within and at the edges of the subducted plate from deep focus earthquakes beneath the Banda Arc that occur beneath the seismic stations. Preliminary results show that the energy associated with the P-wave first arrival exhibits large variability between waveforms recorded at different stations along the arc, both in terms of frequency content and maximum amplitudes. Three main observations are shown with these initial results: (i) Variation in frequency content along strike from the deep events; (ii) There are two "regions" that have low frequency signals which possibly correspond to subducted continental lithosphere; (iii) There are two "regions" that have high frequency signals which possibly correspond to subducted oceanic lithosphere.

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.

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-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.

Lithosphere Structure of the Rivera Plate - Jalisco Block Contact Zone: Septentrional Region of the Islas Marías (Mexico)

NASA Astrophysics Data System (ADS)

Madrigal-Ávalos, L. A.; Nunez, D.; Escalona-Alcazar, F. D. J.; Nuñez-Cornu, F. J.; Barba, D. C., Sr.; Danobeitia, J.

2017-12-01

The western margin of Mexico is a tectonic complex region where large earthquakes occurred with very destructive consequences, including the generation of big tsunamis. This fact is mainly the result of the Rivera plate subduction beneath the North American plate and the Jalisco Block implying a high potential seismic risk. In the north, between the Tamayo Fracture Zone and the Mesoamerican Trench, the Islas Marías region is a complex tectonic limit within the interaction of the Rivera plate oceanic crust and the Jalisco Block continental crust. In order to know the shallow and deep structure of the Rivera plate - Jalisco Block contact zone and to be able to determine these potential seismic sources, the TSUJAL geophysical experiment was carried out from 2012 to 2016. As part of this project, we present the results of the processed and analyzed MCS and WAS data along the TS09 and RTSIM01 seismic transects, respectively, across the septentrional region of Islas Marías. These marine seismic lines are coincident with 110 km length for MCS and 240 km for WAS, and perpendicular to the coastline with SW-NE orientation. The seismic sources used in this work aboard RRS James Cook consisted of 12 guns with a total capacity for WAS data of 5800 in3 every 120 s and 3540 in3 every 50 m for MCS data. The MCS data were acquired with a 5.85 km length streamer with a 468 active channels, while the WAS data were recorded by a network of 4 OBS and 27 land seismic stations. After data processing and joint interpretation, it was possible to determine that shallow structure is mainly constituted by normal faults associated to graben structures forming sedimentary basins with non-deformed sediments in the basement. While the deep structure is characterized by depths from 9 to 12 km in the oceanic crust and 18 to 21 km in the continental crust. The deepest layers of the upper mantle were determined up to 35 km depth. In this study, it was possible to calculate a dip angle between 6° and 8°.

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.

Crustal and Upper Mantle Velocity Structure beneath Northwestern South America revealed by the CARMArray

NASA Astrophysics Data System (ADS)

Miao, W.; Cornthwaite, J.; Levander, A.; Niu, F.; Schmitz, M.; Dionicio, V.; Nader-Nieto, M. F.

2017-12-01

The Caribbean plate (CAR) is a fragment of the Farallon plate heavily modified by igneous processes that created the Caribbean large igneous province (CLIP) between 110 and 80 Ma.The CAR collided with and initiated subduction beneath northwestern South America plate (SA) at about 60-55 Ma as a narrow flat-slab subduction zone with an accretionary prism offshore, but no volcanic arc. Large scale regional tomography suggests that 1000 km of the CAR has been subducted (Van Benthem et al., 2013, JGR). The flat slab has caused Laramide-style basement uplifts of the Merida Andes, Sierra de la Perija, and Santa Marta ranges with elevations >5 km. The details of subduction geometry of the CAR plate beneath northeastern Colombia and northwestern Venezuela are complicated and remain unclear. The region of slab steepening lies below the triangular Maracaibo block (Bezada et al, 2010, JGR), bounded by major strike slip faults and currently escaping to the north over the CAR. Geodetic data suggests the this region has the potential for a magnitude 8+ earthquake (Bilham and Mencin, 2013, AGU Abstract). To better understand the subduction geometry, we deployed 65 broadband (BB) stations across northeastern Colombia and northwestern Venezuela in April of 2016. The 65 stations interweave with the 32 existing Colombian and Venezuelan BB stations, forming a 2-D array (hereafter referred to as CARMArray) with a station spacing of 35-100 km that covers an area of 600 km by 400 km extending from the Caribbean coast in Colombia to the interior plains of Venezuela. With data from the first year of operation, we have measured the Rayleigh wave phase velocities and Z/H ratios in the period range of 8-40 s using both ambient noise and earthquake data recorded by the CARMArray. We also generated Ps receiver functions from waveform data of teleseismic events recorded by the array. We then jointly inverted the three datasets to construct a 3-D S-wave velocity model beneath the array. We will report the initial results of the inversion and discuss the lateral variations of crustal and upper mantle structure and their potential links with surface geology and regional tectonics.

Reconnaissance geology of the Central Mastuj Valley, Chitral State, Pakistan

USGS Publications Warehouse

Stauffer, Karl W.

1975-01-01

The Mastuj Valley in Chitral State is a part of the Hindu Kush Range, and is one of the structurally most complicated areas in northern Pakistan. Sedimentary rocks ranging from at least Middle Devonian to Cretaceous, and perhaps Early Tertiary age lie between ridge-forming granodiorite intrusions and are cut by thrust faults. The thrust planes dip 10? to 40? to the north- west. Movement of the upper thrust plates has been toward the southeast relative to the lower blocks. If this area is structurally typical of the Hindu-Kush and Karakoram Ranges, then these mountains are much more tectonically disturbed than previously recorded, and suggest compression on a scale compatible with the hypothesis that the Himalayan, Karakoram, and Hindu Kush Ranges form part of a continental collision zone. The thrust faults outline two plates consisting of distinctive sedimentary rocks. The lower thrust plate is about 3,000 feet thick and consists of the isoclinally folded Upper Cretaceous to perhaps lower Tertiary Reshun Formation. It has overridden the Paleozoic metasedimentary rocks of the Chitral Slate unit. This thrust plate is, in turn, overridden by an 8,000-foot thick sequence consisting largely of Devonian to Carboniferous limestones and quartzites. A key factor in the tectonic processes has been the relatively soft and plastic lithology of the siltstone layers in the Reshun Formation which have acted as lubricants along the principal thrust faults, where they are commonly found today as fault slices and smears. The stratigraphic sequence, in the central Mastuj Valley was tentatively divided into 9 mapped units. The fossiliferous shales and carbonates of the recently defined Shogram Formation and the clastlcs of the Reshun Formation have been fitted into a sequence of sedimentary rocks that has a total thick- ness of at least 13,000 feet and ranges in age from Devonian to Neogene. Minerals of potential economic significance include antimony sulfides which have been mined elsewhere in Chitral, the tungstate, scheelite, which occurs in relatively high concentrations in heavy-mineral fractions of stream sands, and an iron-rich lateritic rock.

Magnetotelluric imaging of the subducting slab in Cascadia with constraints from seismology

NASA Astrophysics Data System (ADS)

Yang, B.; Egbert, G. D.; Kelbert, A.; Humphreys, E.

2015-12-01

We present results from three-dimensional (3D) inversion of long-period magnetotelluric (MT) data from Cascadia, using seismological constraints on plate geometry and back-arc structure, to refine 3D images of electrical resistivity across this subduction zone. For this study we employed the impedances and vertical transfer functions from 144 sites from the EarthScope Transportable Array, along with data from previous higher density MT profiles from Cascadia (EMSLAB, CAFE-MT etc.). Morphological parameters for the subducting Juan de Fuca and Gorda plates (e.g. upper boundary and thickness) were extracted from McCrory et al (2012) and Schmandt and Humphreys (2010) seismological models and used to define a resistive subducting slab structure in 3D. This was then either used as a prior model, or fixed (both resistivity and geometry) during the MT inversion. By imposing constraints on the geometry of the slab (which is otherwise imaged as an amorphous broad resistive zone) we improve recovery and resolution of subduction related conductivity features. The constrained inversions also allowed us to test sensitivity of the MT data to variants on slab geometry, such as the proposed slab "tear" near the Oregon-Washington border suggested by some seismic tomography models, and to explore consistency of the MT data with seismic models, which suggest segmentation of back-arc upwelling. Three zones of substantially reduced resistivity were found, all exhibiting significant along-strike variability. In the forearc, an N-S stripe of high conductivity (10 ohm-m or less) was found just above the plate interface, near the tip of the mantle wedge. This conductive feature is spatially coincident with mapped locations of episodic tremor and slip, and likely represents aqueous fluids associated with slab dehydration. To the east, a second, clearly separated, N-S elongate zone of similarly high conductivity occurs in the mid-lower crust and upper mantle beneath the modern arc, again likely representing fluids, and in some cases melt. Finally, in the back-arc a broader, and generally more subdued (20-30 ohm-m), zone of reduced resistivity occurs in the North American mantle above the plate interface.

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.

Crustal structure and evolution of the Pyrenean-Cantabrian belt: A review and new interpretations from recent concepts and data

NASA Astrophysics Data System (ADS)

Teixell, A.; Labaume, P.; Ayarza, P.; Espurt, N.; de Saint Blanquat, M.; Lagabrielle, Y.

2018-01-01

This paper provides a synthesis of current data and interpretations on the crustal structure of the Pyrenean-Cantabrian orogenic belt, and presents new tectonic models for representative transects. The Pyrenean orogeny lasted from Santonian ( 84 Ma) to early Miocene times ( 20 Ma), and consisted of a spatial and temporal succession of oceanic crust/exhumed mantle subduction, rift inversion and continental collision processes at the Iberia-Eurasia plate boundary. A good coverage by active-source (vertical-incidence and wide-angle reflection) and passive-source (receiver functions) seismic studies, coupled with surface data have led to a reasonable knowledge of the present-day crustal architecture of the Pyrenean-Cantabrian belt, although questions remain. Seismic imaging reveals a persistent structure, from the central Pyrenees to the central Cantabrian Mountains, consisting of a wedge of Eurasian lithosphere indented into the thicker Iberian plate, whose lower crust is detached and plunges northwards into the mantle. For the Pyrenees, a new scheme of relationships between the southern upper crustal thrust sheets and the Axial Zone is here proposed. For the Cantabrian belt, the depth reached by the N-dipping Iberian crust and the structure of the margin are also revised. The common occurrence of lherzolite bodies in the northern Pyrenees and the seismic velocity and potential field record of the Bay of Biscay indicate that the precursor of the Pyrenees was a hyperextended and strongly segmented rift system, where narrow domains of exhumed mantle separated the thinned Iberian and Eurasian continental margins since the Albian-Cenomanian. The exhumed mantle in the Pyrenean rift was largely covered by a Mesozoic sedimentary lid that had locally glided along detachments in Triassic evaporites. Continental margin collision in the Pyrenees was preceded by subduction of the exhumed mantle, accompanied by the pop-up thrust expulsion of the off-scraped sedimentary lid above. To the west, oceanic subduction of the Bay of Biscay under the North Iberian margin is supported by an upper plate thrust wedge, gravity and magnetic anomalies, and 3D inclined sub-crustal reflections. However, discrepancies remain for the location of continent-ocean transitions in the Bay of Biscay and for the extent of oceanic subduction. The plate-kinematic evolution during the Mesozoic, which involves issues as the timing and total amount of opening, as well as the role of strike-slip drift, is also under debate, discrepancies arising from first-order interpretations of the adjacent oceanic magnetic anomaly record.

The bright spot in the West Carpathian upper mantle: a trace of the Tertiary plate collision-and a caveat for a seismologist

NASA Astrophysics Data System (ADS)

Środa, Piotr

2010-07-01

The 2-D full waveform modelling of the mantle arrivals from the CELEBRATION 2000 profiles crossing the Carpathian orogen suggests two possible tectonic models for the collision of ALCAPA (Alpine-Carpathian-Pannonian) and the European Plate in the West Carpathians in southern Poland and Slovakia. Due to an oblique (NE-SW) convergence of plates, the character of the collision may change along the zone of contact of the plates: in the western part of the area an earlier collision might have caused substantial crustal shortening and formation of a crocodile-type structure, with the delaminated lower crust of ~100km length acting as a north-dipping reflecting discontinuity in the uppermost mantle. In the eastern part, a less advanced collision only involved the verticalization of the subducted slab remnant after a slab break-off. The lower crustal remnant of ~10km size in the uppermost mantle acts as a pseudo-diffractor generating observable mantle arrivals. Due to the similarity of synthetic data generated by both models, the question of the non-uniqueness of seismic data interpretation, that may lead to disparate tectonic inferences, is also discussed.

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.

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.

Density structure of the lithosphere in the southwestern United States and its tectonic significance

USGS Publications Warehouse

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

2001-01-01

We calculate a density model of the lithosphere of the southwestern United States through an integrated analysis of gravity, seismic refraction, drill hole, and geological data. Deviations from the average upper mantle density are as much as ?? 3%. A comparison with tomographic images of seismic velocities indicates that a substantial part (>50%) of these density variations is due to changes in composition rather than temperature. Pronounced mass deficits are found in the upper mantle under the Basin and Range Province and the northern part of the California Coast Ranges and adjacent ocean. The density structure of the northern and central/southern Sierra Nevada is remarkably different. The central/southern part is anomalous and is characterized by a relatively light crust underlain by a higher-density upper mantle that may be associated with a cold, stalled subducted plate. High densities are also determined within the uppermost mantle beneath the central Transverse Ranges and adjoining continental slope. The average density of the crystalline crust under the Great Valley and western Sierra Nevada is estimated to be up to 200 kg m~3 higher than the regional average, consistent with tectonic models for the obduction of oceanic crust and uppermost mantle in this region.

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.

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.

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

Tectonic framework of northeast Egypt and its bearing on hydrocarbon exploration

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

Khalil, M.; Moustafa, A.R.

1995-08-01

Detailed structural study of northern and central Sinai, the northern Eastern Desert, and the northern Gulf of Suez clarified the tectonic framework of northeast Egypt. This framework is related to the movements between the African Plate and the Eurasian and Arabian Plates. Late Cretaceous folding and thrusting in response to oblique convergence between the African and Eurasian Plates formed NE-ENE oriented, doubly plunging, en echelon folds of the northern Egypt fold belt. This fold belt is well exposed in northern Sinai and a few other places but is concealed under younger sediments in the other parts of northern Egypt. Youngermore » folding of local importance is related to dextral slip on the Themed Fault (Central Sinai) in post Middle Eocene-pre Miocene time. Early Miocene rifting of the Afro-Arabian Plate led to the opening of the Suez rift and deposition of significant syn-rift facies. Half grabens and tilted fault blocks dominate the rift. Slightly tilted fault blocks characterize the competent Middle Eocene limestones of the Eastern Desert south of the Cairo-Suez road but north of this road, Middle Eocene rocks are locally dragged on nearby E-W and NW-SE oriented faults forming fault-drag folds. Ductile Upper Eocene and Miocene rocks are also folded about gentle NW-SE oriented doubly plunging folds. The different stages of tectonic activity in northern Egypt contributed to the development of different types of structural traps as well as different source, reservoir, and cap rocks. The sedimentary history of the region indicates well developed marine sediments of Jurassic, Cretaceous, Eocene, and Miocene ages. Basin development in structurally low areas provided good sites for hydrocarbon generation and maturation.« less

[Anatomy and imaging study of a new upper-agger nasi pathway of frontal sinus surgery].

PubMed

Liu, Zhixian; Li, Xiaohui; Wang, Peng; Yang, Gui; Li, Xingwei; Zhao, Peng

2014-10-01

To investigate the new surgical pathway of endoscopic frontal sinus surgery for frontal sinus lesions through the upper-agger nasi approach. The computed tomography (CT) scans from 32 patients were collected and subjected to three-dimensional reconstruction by Mimics. The distance in sagittal planes from anterior ethmoid artery to midpoint of axilla and to skull base attachment at anterior middle turbinate was measured. The distance in coronal planes between the perpendicular plate of middle turbinate and the orbital lamina was also detected as well as the height of agger nasi. Three-dimensional structures of the frontal sinus and its surrounding cells was reconstructed by Sinuses Trachea I software. We integrated the CT scans and the above data for simulating surgical operation on cadaveric heads. (1) Skull base attachment at anterior middle turbinate located at the anterior or posterior of aperture of frontal sinus. (2) The mean distance between anterior ethmoid artery and midpoint of axilla was (22.23 ± 2.78) mm on the left side and (22.30 ± 2.80) mm on right. The mean distance between anterior ethmoid artery and skull base attachment at anterior middle turbinate was (15.31 ± 2.82) mm on left and (15.39 ± 3.53) mm on right. The distance between perpendicular plate of middle turbinate and orbital lamina was (7.61 ± 1.34) mm on left and (7.80 ± 1.40) mm on right side. The height of the agger nasi was (8.33 ± 2.14) mm on left and (8.00 ± 2.57) mm on right. There was no statistical difference in the above data between left and right side (P > 0.05). (3) The visible three-dimensional structure showed that skull base attachment at the anterior middle turbinate was closely adjoined the aperture of frontal sinus, the space between sub-outer side of the attachment and orbital lamina, above the agger nasi cell or the upper area of the agger nasi cell was solely cell structures. Endoscopic frontal sinus surgery for frontal sinus lesions through the upper-agger nasi approach was practicable to solitary frontal sinus lesions and to solve the complex frontal sinus or frontal recess lesions by flexible operation according to the feature of the lesions.

Tectono-sedimentary evolution of the eastern Gulf of Aden conjugate passive margins: Narrowness and asymmetry in oblique rifting context

NASA Astrophysics Data System (ADS)

Nonn, Chloé; Leroy, Sylvie; Khanbari, Khaled; Ahmed, Abdulhakim

2017-11-01

Here, we focus on the yet unexplored eastern Gulf of Aden, on Socotra Island (Yemen), Southeastern Oman and offshore conjugate passive margins between the Socotra-Hadbeen (SHFZ) and the eastern Gulf of Aden fracture zones. Our interpretation leads to onshore-offshore stratigraphic correlation between the passive margins. We present a new map reflecting the boundaries between the crustal domains (proximal, necking, hyper-extended, exhumed mantle, proto-oceanic and oceanic domains) and structures using bathymetry, magnetic surveys and seismic reflection data. The most striking result is that the magma-poor conjugate margins exhibit asymmetrical architecture since the thinning phase (Upper Rupelian-Burdigalian). Their necking domains are sharp ( 40-10 km wide) and their hyper-extended domains are narrow and asymmetric ( 10-40 km wide on the Socotra margin and 50-80 km wide on the Omani margin). We suggest that this asymmetry is related to the migration of the rift center producing significant lower crustal flow and sequential faulting in the hyper-extended domain. Throughout the Oligo-Miocene rifting, far-field forces dominate and the deformation is accommodated along EW to N110°E northward-dipping low angle normal faults. Convection in the mantle near the SHFZ may be responsible of change in fault dip polarity in the Omani hyper-extended domain. We show the existence of a northward-dipping detachment fault formed at the beginning of the exhumation phase (Burdigalien). It separates the northern upper plate (Oman) from southern lower plate (Socotra Island) and may have generated rift-induced decompression melting and volcanism affecting the upper plate. We highlight multiple generations of detachment faults exhuming serpentinized subcontinental mantle in the ocean-continent transition. Associated to significant decompression melting, final detachment fault may have triggered the formation of a proto-oceanic crust at 17.6 Ma and induced late volcanism up to 10 Ma. Finally, the setting up of a steady-state oceanic spreading center occurs at 17 Ma.

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.

From an active continental plate margin to continental collision: New constraints from the petrological, structural and geochronological record of the (ultra) high-P metamorphic Rhodope domain (N-Greece)

NASA Astrophysics Data System (ADS)

Mposkos, E.; Krohe, A.; Wawrzenitz, N.; Romer, R. L.

2012-04-01

The Rhodope domain occupies a key area along the suture between the European and the Apulian/Adriatic plate (Schmid et al., 2008), which collided in the early Tertiary (closure of the Vardar/Axios ocean, cf. Mposkos & Krohe, 2006). An integrated study of the geochronological, tectonic and petrological data of the Rhodope domain provides the unique opportunity resolving a 160 my lasting metamorphic evolution (Jurassic to Miocene) of an active plate margin to a high degree. The Greek Rhodope consists of several composite metamorphic complexes bounded by the Nestos thrust and several normal detachment systems. The PT- and structural records of the complexes constrain metamorphic, magmatic and tectonic processes, associated with subduction along a convergent plate margin including UHP metamorphism, MP to HP metamorphism associated with continental collision, and core complex formation linked to Aegean back arc extension. We focus on the Sidironero Complex that shows a polymetamorphic history. This is documented by SHRIMP and LA-ICP-MS U-Pb zircon ages of ca. 150 Ma from garnet-kyanite gneisses that are interpreted to record the HP/UHP metamorphism (Liati, 2005; Krenn et al., 2010). SHRIMP zircon ages of ca. 51 Ma from an amphibolitized eclogite is interpreted by Liati (2005) to record a second Eocene HP metamorphic event. We present new data from an integrated petrological, geochronological and tectonic study. Granulite facies and upper amphibolite facies metamorphic conditions are recorded by the mineral assemblage Grt-Ky-Bt-Pl-Kfs-Qtz-Rt and Grt-Ky-Bt-Ms-Pl-Qtz-Rt, respectively, in deformed migmatitic metapelites. Deformation occurred under granulite facies conditions. Monazites from the matrix, that formed during the granulite facies deformation, lack core/rim structures and are only locally patchy zoned. Monazite chemical compositions are related to varying reaction partners. Single grains and fractions of few grains yield ID-TIMS U-Pb ages that plot along the concordia between 64 to 60 Ma. One date of 55 Ma might represent Pb-loss during later fluid-induced dissolution-reprecipitation. We discuss the following questions: What is the history of the high-P metamorphic rocks in the Sidironero Complex? Were high-P rocks that have been already exhumed again dragged into the subduction channel? Which rocks from the upper plate are affected by high-P metamorphism evincing that subduction erosion is an important mechanism? We reconsider the significance of the P-T-t evolution in the light of the tectonic processes that took place along the depth extension of a convergent plate interface and during subsequent continental collision along the European/Apulian Suture zone. Krenn et al., 2010. Tectonics 29, TC4001. Liati, A., 2005. Contribution to Mineralogy and Petrology 150, 608-630. Mposkos, E. & Krohe, A. 2006. Canadian Journal of Earth Sciences 43, 1755-1776. Schmid S.M., et al. 2008. Swiss Journal of Geoscience 101, 139-183.

Geometry of the Arabia-Somalia Plate Boundary into Afar: Preliminary Results from the Seismic Profile Across the Asal Rift (Djibouti)

NASA Astrophysics Data System (ADS)

Vergne, J.; Doubre, C.; Mohamed, K.; Tiberi, C.; Leroy, S.; Maggi, A.

2010-12-01

In the Afar Depression, the Asal-Ghoubbet Rift in Djibouti is a young segment on land at the propagating tip of the Aden Ridge. This segment represents an ideal laboratory to observe the mechanisms of extension and the structural evolutions involved, from the continental break-up to the first stage of oceanic spreading. However, we lack first order information about the crustal and upper mantle structure in this region, which for example prevent detailed numerical modeling of the deformations observed at the surface from GPS or InSAR. Moreover the current permanent network is not well suited to precisely constrain the ratio of seismic/aseismic deformation and to characterize the active deformation and the rifting dynamics. Since November 2009 we have maintained a temporary network of 25 seismic stations deployed along a 150 km-long profile. Because we expect rapid variations of the lithospheric structure across the 10 km-wide central part of the rift, we gradually decreased the inter-stations spacing to less than 1 km in the middle section of the profile. In order to obtain a continuous image of the plate boundary, from the topographic surface to the upper mantle, several techniques and methods will be applied: P and S wave receiver functions, tomographies based on body waves, surface waves and seismic noise correlation, anisotropy, and finally a gravity-seismic joint inversion. We present some preliminary results deduced from the receiver functions applied to the data acquired during the first months of the experiment. We migrate several sets of receiver functions computed in various frequency bands to resolve both mantle interfaces and fine scale structures within the thin crust in the center of the rift. These first images confirm a rapid variation of the Moho depth on both sides of the rift and a very complex lithospheric structure in the central section with several low velocity zones within the top 50km that might correspond to magma lenses.

P-wave velocity structure offshore central Sumatra: implications for compressional and strike-slip faulting

NASA Astrophysics Data System (ADS)

Karplus, M.; Henstock, T.; McNeill, L. C.; Vermeesch, P. M. T.; Barton, P. J.

2014-12-01

The Sunda subduction zone features significant along-strike structural variability including changes in accretionary prism and forearc morphology. Some of these changes have been linked to changes in megathrust faulting styles, and some have been linked to other thrust and strike-slip fault systems across this obliquely convergent margin (~54-58 mm/yr convergence rate, 40-45 mm/yr subduction rate). We examine these structural changes in detail across central Sumatra, from Siberut to Nias Island, offshore Indonesia. In this area the Investigator Fracture Zone and the Wharton Fossil Ridge, features with significant topography, are being subducted, which may affect sediment thickness variation and margin morphology. We present new seismic refraction P-wave velocity models using marine seismic data collected during Sonne cruise SO198 in 2008. The experiment geometry consisted of 57 ocean bottom seismometers, 23 land seismometers, and over 10,000 air gun shots recorded along ~1750 km of profiles. About 130,000 P-wave first arrival refractions were picked, and the picks were inverted using FAST (First Arrivals Refraction Tomography) 3-D to give a velocity model, best-resolved in the top 25 km. Moho depths, crustal composition, prism geometry, slab dip, and upper and lower plate structures provide insight into the past and present tectonic processes at this plate boundary. We specifically examine the relationships between velocity structure and faulting locations/ styles. These observations have implications for strain-partitioning along the boundary. The Mentawai Fault, located west of the forearc basin in parts of Central Sumatra, has been interpreted variably as a backthrust, strike-slip, and normal fault. We integrate existing data to evaluate these hypotheses. Regional megathrust earthquake ruptures indicate plate boundary segmentation in our study area. The offshore forearc west of Siberut is almost aseismic, reflecting the locked state of the plate interface, which last ruptured in 1797. The weakly-coupled Batu segment experiences sporadic clusters of events near the forearc slope break. The Nias segment in the north ruptured in the 2005 M8.7 earthquake. We compare P-wave velocity structure to the earthquake data to examine potential links between lithospheric structure and seismogenesis.

The sup 40 Ar/ sup 39 Ar geochronology of the Pelona schist and related rocks, southern California

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

Jacobson, C.E.

1990-01-10

Seventeen {sup 40}Ar/{sup 39}Ar ages for hornblende, celadonitic muscovite, and biotite from the Pelona, Orocopia, Rand, and Portal Ridge (POR) schists range from 39 to 85 Ma. Two muscovites and one hornblende from the Rand Schist have ages of 72 to 74 Ma, indistinguishable from the K-Ar age of 74 Ma for hornblende from a posttectonic granodiorite that intrudes the schist, but younger than the 70 Ma U-Pb age of the intrusion. Four muscovite and two hornblende ages for schist and mylonite from the East Fork area of the San Gabriel Mountains range from 55 to 61 Ma. Concordance ofmore » schist and upper plate ages confirms structural and metamorphic evidence that the Vincent thrust in the San Gabriel Mountains has not undergone significant postmetamorphic disruption. Ages from the Orocopia Mountains are 75 Ma for hornblende from nonmylonitic upper plate, 52 Ma for muscovite from structurally high Orocopia Schist that is mylonitic, and 41 Ma for muscovite from nonmylonitic Orocopia Schist. These are consistent with field evidence that the Orocopia thrust is a postmetamorphic normal fault. Muscovite and hornblende from the Gavilan Hills have ages of 48 to 50 Ma, younger than ages from the San Gabriel Mountains but similar to schist ages from the Orocopia Mountains. The geochronologic and structural complexities of the Vincent, Chocolate Mountains, Orocopia, and Rand thrusts imply that previously cited northeastward vergence may not relate to prograde metamorphism (subduction) of the POR schists. The data indicate substantial uplift of the POR schists prior to middle Tertiary detachment faulting, which confirms other geochronologic evidence of uplift in southern California and southern Arizona during the Late Cretaceous-early Tertiary.« less

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

Lithospheric Structure across the Alaskan Cordillera from Surface Waves and Receiver Functions

NASA Astrophysics Data System (ADS)

Ward, K. M.; Lin, F. C.

2017-12-01

The long awaited Transportable Array (TA) deployment in Alaska and western Canada is nearing its final deployment stage. With only one more deployment season, most of the TA station locations have been occupied and begun providing data. These TA stations combined with upgraded existing locations have provided enough high-quality data to begin investigating the crustal and upper mantle structure across the entire Alaskan Cordillera. From a tectonic standpoint, many interesting questions remain unanswered. For example, how does the transition from oceanic-oceanic subduction to continental-oceanic normal subduction to continental-oceanic "flat-slab" subduction to strike-slip conservative plate motion affect the deformation/uplift of the overriding plate and mantle geodynamic characteristics? How does the long and completed terrene accretion process partition stress/strain in the crust? On more local scales, are there any significant mid-crustal magmatic systems as observed in other sections of the American Cordillera, and if so, what is there role in uplift and crustal deformation? Our approach to investigating these questions is though surface wave imaging from ambient noise and earthquake generated sources along with Rayleigh wave ellipticity paired with Ps receiver functions. Our preliminary tomography results agree with previous studies but expand the spatial coverage showing additional detail. Our ellipticity results show a heterogeneous but spatially consistent anisotropic shallow crust. Although the complete TA data set has not yet been collected, we have jointly inverted surface waves with receiver functions for a 3-D shear-wave velocity model across the entire Alaskan Cordillera. Key features of our velocity model include a high-velocity feature in the upper mantle associated with the subducting Pacific plate that extends north of the seismicity used to contour the geometry of the slab and mid-crustal low-velocity zones associated with the active volcanics in the Wrangell mountains and along the Aleutian arc.

Seismic anisotropy in central North Anatolian Fault Zone and its implications on crustal deformation

NASA Astrophysics Data System (ADS)

Licciardi, A.; Eken, T.; Taymaz, T.; Piana Agostinetti, N.; Yolsal-Çevikbilen, S.

2018-04-01

We investigate the crustal seismic structure and anisotropy around the central portion of the North Anatolian Fault Zone, a major plate boundary, using receiver function analysis. The characterization of crustal seismic anisotropy plays a key role in our understanding of present and past deformation processes at plate boundaries. The development of seismic anisotropy in the crust arises from the response of the rocks to complicated deformation regimes induced by plate interaction. Through the analysis of azimuthally-varying signals of teleseismic receiver functions, we map the anisotropic properties of the crust as a function of depth, by employing the harmonic decomposition technique. Although the Moho is located at a depth of about 40 km, with no major offset across the area, our results show a clear asymmetric distribution of crustal properties between the northern and southern blocks, divided by the North Anatolian Fault Zone. Heterogeneous and strongly anisotropic crust is present in the southern block, where complex intra-crustal signals are the results of strong deformation. In the north, a simpler and weakly anisotropic crust is typically observed. The strongest anisotropic signal is located in the first 15 km of the crust and is widespread in the southern block. Stations located on top of the main active faults in the area indicate the highest amplitudes, together with fault-parallel strikes of the fast plane of anisotropy. We interpret the origin of this signal as due to structure-induced anisotropy, and roughly determine its depth extent up to 15-20 km for these stations. Away from the faults, we suggest the contribution of previously documented uplifted basement blocks to explain the observed anisotropy at upper and middle crustal depths. Finally, we interpret coherent NE-SW orientations below the Moho as a result of frozen-in anisotropy in the upper mantle, as suggested by previous studies.

Quasi-quantitative analysis of the lithospheric rheology across an incipient continental rift based on 3-D magnetotelluric imaging of Linfen Basin within the North China Craton

NASA Astrophysics Data System (ADS)

Yin, Y.; Jin, S.; Wei, W.; Ye, G.; Dong, H.; Zhang, L.

2017-12-01

The Shanxi Rift being located within the interior of the North China Craton and far from any plate boundaries has undergone dramatic deformation and seismicity during the Cenozoic. In this study, we build 3-D lithospheric resistivity model by MT array data, across the Linfen Basin which is the most active segment of this intraplate rift. Accordingly, combined with previous rock physics experimental results, we estimate the fluid contents of lower crustal granulites and upper mantle peridotites and thereby the rough distribution of lithospheric rheological strength. On the two sides of Linfen Basin, lithosphere beneath the Precambrian terranes are of high strength. By contrast, a high-conductivity nearly upright lithosphere weak zone occurs beneath the eastern margin of the Linfen Basin and appears to be connected to the high-conductivity and therefore weak lower crust just beneath the basin, probably indicating a structure of asthenospheric upwelling causing the lower crustal decoupling through lateral drag forces. The distribution of lithospheric weak zones, brittle faults, ductile shear zones and detachment structures determined from our resistivity model is in good agreement with the 8-My stage model of a previous numerical geodynamic simulation for continental rift evolution by reconstruction of the South Atlantic plate. Accordingly, we suggest that the lithospheric weak zone could be a preexisting Precambrian shear zone and has reactivated as an asthenospheric upwelling conduit under the far-field effects of Indo- Asian collision or Pacific Plate subduction since the late Mesozoic. This process could have caused the upper crustal extension and rifting through the stress regulation by the plastic lower crust, which could be the mechanism of rift formation. In summary, we suggest the Linfen segment of the Shanxi Rift, is a simple shear mode rift in the incipient stage of rift evolution, rather than a mature pure shear mode one as determined by precious seismic imaging.

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.

Wear of carbide inserts with complex surface treatment when milling nickel alloy

NASA Astrophysics Data System (ADS)

Fedorov, Sergey; Swe, Min Htet; Kapitanov, Alexey; Egorov, Sergey

2018-03-01

One of the effective ways of strengthening hard alloys is the creating structure layers on their surface with the gradient distribution of physical and mechanical properties between the wear-resistant coating and the base material. The article discusses the influence of the near-surface layer which is modified by low-energy high-current electron-beam alloying and the upper anti-friction layer in a multi-component coating on the wear mechanism of the replaceable multifaceted plates in the dry milling of the difficult to machine nickel alloys.

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.

P wave anisotropic tomography of the Alps

NASA Astrophysics Data System (ADS)

Hua, Yuanyuan; Zhao, Dapeng; Xu, Yixian

2017-06-01

The first tomographic images of P wave azimuthal and radial anisotropies in the crust and upper mantle beneath the Alps are determined by joint inversions of arrival time data of local earthquakes and teleseismic events. Our results show the south dipping European plate with a high-velocity (high-V) anomaly beneath the western central Alps and the north dipping Adriatic plate with a high-V anomaly beneath the Eastern Alps, indicating that the subduction polarity changes along the strike of the Alps. The P wave azimuthal anisotropy is characterized by mountain chain-parallel fast-velocity directions (FVDs) in the western central Alps and NE-SW FVDs in the Eastern Alps, which may be caused by mantle flow induced by the slab subductions. Our results reveal a negative radial anisotropy (i.e., Vph < Vpv) within the subducting slabs and a positive radial anisotropy (i.e., Vph > Vpv) in the low-velocity mantle wedge, which may reflect the subvertical plate subduction and its induced mantle flow. The results of anisotropic tomography provide important new information on the complex mantle structure and dynamics of the Alps and adjacent regions.

Formation of hydrothermal pits and the role of seamounts in the Guatemala Basin (Equatorial East Pacific) from heat flow, seismic, and core studies

NASA Astrophysics Data System (ADS)

Villinger, H. W.; Pichler, T.; Kaul, N.; Stephan, S.; Pälike, H.; Stephan, F.

2017-01-01

We acquired seismic and heat flow data and collected sediment cores in three areas in the Guatemala Basin (Cocos Plate, Eastern Pacific) to investigate the process by which depressions (pits) in the sedimentary cover on young oceanic crust were formed. Median heat flow of 55 mW/m2 for the three areas is about half of the expected conductive cooling value. The heat deficit is caused by massive recharge of cold seawater into the upper crust through seamounts which is inferred from depressed heat flow in the vicinity of seamounts. Heat flow inside of pits is always elevated, in some cases up to three times (max. 300 mW/m2) relative to background. None of the geochemical pore water profiles from cores inside and outside of the pits show any evidence of active fluid flow inside the pits. All three areas originated within the high productivity equatorial zone and moved northwest over the past 15 to 18 Ma. Pits found in the working areas are likely relict dissolution structures formed by diffuse hydrothermal venting in a zone of high biogenic carbonate production which were sealed when they moved north. It is likely that these pits were discharge sites of "hydrothermal siphons" where recharging seamounts could feed cold seawater via the upper crust to several discharging pits. Probably pit density on the whole Cocos Plate is similar to the three working areas and which may explain the huge heat deficit of the Cocos Plate.

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.

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.

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.

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.

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.

Tectonic analysis and paleo-stress determination of the upper lava section at ODP/IODP site 1256 (East Pacific Ocean)

NASA Astrophysics Data System (ADS)

Fontana, Emanuele

2015-09-01

Research on the deep sea is of great importance for a better understanding of the mechanism of magma emplacement and the tectonic evolution of oceanic crust. However, details of the internal structure in the upper levels of the oceanic crust are much less complete than that of the more fully studied sub-aerial areas. For the first time, this study proposes a dynamic analysis using the inversion method on core data derived from the drilled basement of the present-day intact oceanic crust at ODP/IODP Site 1256 in the Cocos plate. The research is based on an innovative core reorientation process and combines different stress hypothesis approaches for the analysis of heterogeneous failure-slip data via exploitation of two distinct techniques. From the analysis of the failure-slip data, both techniques produce 5 distinct subsystem datasets. All calculated subsystems are mechanically and geometrically admissible. Interpretation of the results allows the researchers to note a complex local and regional tectonic evolution deriving from the interplay of (1) the ridge push and rotation of both the East Pacific Rise and the Cocos-Nazca Spreading Center, (2) the effect of the slab pull of the Middle America Trench, (3) the influence of lava emplacement mechanisms, and (4) intra-plate deformation.

Mountain Building in Central and Western Tien Shan Orogen: Insight from Joint Inversion of Surface Wave Phase Velocities and Body Wave Travel Times

NASA Astrophysics Data System (ADS)

Wu, S.; Yang, Y.; Wang, K.

2017-12-01

The Tien Shan orogeny, situated in central Asia about 2000 km away from the collision boundary between Indian plate and Eurasian plate, is one of the highest, youngest, and most active intracontinental mountain belts on the earth. It first formed during the Paleozoic times and became reactivated at about 20Ma. Although many studies on the dynamic processes of the Tien Shan orogeny have been carried out before, its tectonic rejuvenation and uplift mechanism are still being debated. A high-resolution model of crust and mantle beneath Tien Shan is critical to discern among competing models for the mountain building. In this study, we collect and process seismic data recorded by several seismic arrays in the central and western Tien Shan region to generate surface wave dispersion curves at 6-140 s period using ambient noise tomography (ANT) and two-plane surface wave tomography (TPWT) methods. Using these dispersion curves, we construct a high-resolution 3-D image of shear wave velocity (Vs) in the crust and upper mantle up to 300 km depth. Our current model constrained only by surface waves shows that, under the Tien Shan orogenic belt, a strong low S-wave velocity anomaly exists in the uppermost mantle down to the depth of 200km, supporting the model that the hot upper mantle is upwelling under the Tien Shan orogenic belt, which may be responsible for the mountain building. To the west of central Tien Shan across the Talas-Fergana fault, low S-wave velocity anomalies in the upper mantle become much weaker and finally disappear beneath the Fergana basin. Because surface waves are insensitive to the structures below 300 km, body wave arrival times will be included for a joint inversion with surface waves to generate S-wave velocity structure from the surface down to the mantle transition zone. The joint inversion of both body and surface waves provide complementary constraints on structures at different depths and helps to achieve a more realistic model compared with body wave or surface wave tomography alone. The joint inversion model will be presented.

Generation of fractional acoustic vortex with a discrete Archimedean spiral structure plate

NASA Astrophysics Data System (ADS)

Jia, Yu-Rou; Wei, Qi; Wu, Da-Jian; Xu, Zheng; Liu, Xiao-Jun

2018-04-01

Artificial structure plates engraved with discrete Archimedean spiral slits have been well designed to achieve fractional acoustic vortices (FAVs). The phase and pressure field distributions of FAVs are investigated theoretically and demonstrated numerically. It is found that the phase singularities relating to the integer and fractional parts of the topological charge (TC) result in dark spots in the upper half of the pressure field profile and a low-intensity stripe in the lower half of the pressure field profile, respectively. The dynamic progress of the FAV is also discussed in detail as TC increases from 1 to 2. With increasing TC from 1 to 1.5, the splitting of the phase singularity leads to the deviation of the phase of the FAV from the integer case and hence a new phase singularity occurs. As TC m increases from 1.5 to 2, two phase singularities of the FAV approach together and finally merge as a new central phase singularity. We further perform an experiment based on the Schlieren method to demonstrate the generation of the FAV.

3D receiver function Kirchhoff depth migration image of Cascadia subduction slab weak zone

NASA Astrophysics Data System (ADS)

Cheng, C.; Allen, R. M.; Bodin, T.; Tauzin, B.

2016-12-01

We have developed a highly computational efficient algorithm of applying 3D Kirchhoff depth migration to telesismic receiver function data. Combine primary PS arrival with later multiple arrivals we are able to reveal a better knowledge about the earth discontinuity structure (transmission and reflection). This method is highly useful compare with traditional CCP method when dipping structure is met during the imaging process, such as subduction slab. We apply our method to the reginal Cascadia subduction zone receiver function data and get a high resolution 3D migration image, for both primary and multiples. The image showed us a clear slab weak zone (slab hole) in the upper plate boundary under Northern California and the whole Oregon. Compare with previous 2D receiver function image from 2D array(CAFE and CASC93), the position of the weak zone shows interesting conherency. This weak zone is also conherent with local seismicity missing and heat rising, which lead us to think about and compare with the ocean plate stucture and the hydralic fluid process during the formation and migration of the subduction slab.

Analogue modeling of rotational orogenic wedges: implications for the Neogene structural evolution of the Southern Central Andes (33°-35°S)

NASA Astrophysics Data System (ADS)

Herrera, S. S.; Farías, M.; Pinto, L.; Yagupsky, D. L.; Guzman, C.; Charrier, R.

2017-12-01

Structural evolution of the southernmost Central Andes is a major subject of debate. Overall vergence within the range and how intra-continental subduction prompts Andean orogeny are controversial topics. Between 33°-35° S, strike of the western slope main structures shifts southwards, from N-S to NNE-SSW, defining the Maipo Orocline. Likely, width of the Principal Cordillera increases southwards. Despite, a progressive southward decrease in orogenic volume has been determined for the segment. To understand such latitudinal variations, and to provide explanations for overall vergence, we carry out analogue models of contractional wedges to explore upper-crustal thrust system development with a progressive variation of the convergence vector. The model setup consisted of a fixed plate on which a mobile plate generated a velocity discontinuity. The upper-crust was simulated using low-cohesive quartz sand. The mobile plate was fixed at its northern end to a pivot, thus progressively incrementing shortening and the obliquity of convergence southwards. PIV photogrammetry recorded wedge evolution. A classical doubly-vergent wedge was formed, consisting of a steep 35° dipping, static thrust on the retro-side, an uplifted core, and an incipient forward-breaking, 25° critically tapered imbricated thrust fan on the pro-side, wider (in plan-view) where the imposed shortening reached the maximum. The resulting wedge is reminiscent of: the steep western Andean slope, in which the bordering thrust has maintained its present position during the Neogene; and the east-vergent fold-and-thrust belt of the eastern slope. The asymmetrical doubly vergence of the model suggests west-directed subduction of the South American continent beneath the orogen. The southward width increase is geometrically comparable to the natural analogue, yet we observe a flat contrast with orogenic shortening and volume estimates for the region. This can be attributed to the fact that uplift and erosion interplay, and the role of pre-Andean structures are not addressed in this approach. Rotation within the model wedge is consistent with paleomagnetic data for the 33°-35°S segment. Nevertheless, our model fails to explain curvature of the Maipo Orocline, suggesting that other lithospheric processes might control bending of the range.

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.

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.

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.

Crustal deformation: Earth vs Venus

NASA Technical Reports Server (NTRS)

Turcotte, D. L.

1989-01-01

It is timely to consider the possible tectonic regimes on Venus both in terms of what is known about Venus and in terms of deformation mechanisms operative on the earth. Plate tectonic phenomena dominate tectonics on the earth. Horizontal displacements are associated with the creation of new crust at ridges and destruction of crust at trenches. The presence of plate tectonics on Venus is debated, but there is certainly no evidence for the trenches associated with subduction on the earth. An essential question is what kind of tectonics can be expected if there is no plate tectonics on Venus. Mars and the Moon are reference examples. Volcanic constructs appear to play a dominant role on Mars but their role on Venus is not clear. On single plate planets and satellites, tectonic structures are often associated with thermal stresses. Cooling of a planet leads to thermal contraction and surface compressive features. Delamination has been propsed for Venus by several authors. Delamination is associated with the subduction of the mantle lithosphere and possibly the lower crust but not the upper crust. The surface manifestations of delamination are unclear. There is some evidence that delamination is occurring beneath the Transverse Ranges in California. Delamination will certainly lead to lithospheric thinning and is likely to lead to uplift and crustal thinning.

Dislocation of the incus into the external auditory canal after mountain-biking accident.

PubMed

Saito, T; Kono, Y; Fukuoka, Y; Yamamoto, H; Saito, H

2001-01-01

We report a rare case of incus dislocation to the external auditory canal after a mountain-biking accident. Otoscopy showed ossicular protrusion in the upper part of the left external auditory canal. CT indicated the disappearance of the incus, and an incus-like bone was found in the left external auditory canal. There was another bony and board-like structure in the attic. During the surgery, a square-shaped bony plate (1 x 1 cm) was found in the attic. It was determined that the bony plate had fallen from the tegmen of the attic. The fracture line in the posterosuperior auditory canal extending to the fossa incudis was identified. According to these findings, it was considered that the incus was pushed into the external auditory canal by the impact of skull injury through the fractured posterosuperior auditory canal, which opened widely enough for incus dislocation. Copyright 2001 S. Karger AG, Basel

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.

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.

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.

A Long-term Slip Model for the San Ramón Fault, Santiago de Chile, from Tectonically Reconcilable Boundary Conditions

NASA Astrophysics Data System (ADS)

Aron, F.; Estay, N.; Cembrano, J. M.; Yanez, G. A.

2016-12-01

We constructed a 3D Boundary Elements model simulating subduction of the Nazca plate underneath South America, from 29° to 38° S, to compute long-term surface deformation and slip rates on crustal faults imbedded in the upper-plate wedge of the Andean orogen. We tested our model on the San Ramón Fault (SRF), a major E-dipping, thrust structure limiting the western front of the Main Cordillera with surface expression along the entire, 40 km long, extension of the Santiago de Chile basin. Long-lived thrusting has produced more than 2 km of differential uplift of the mountains. Given its proximity to the country's largest city, this potentially seismogenic fault —dormant during historic times— has drawn increasing public attention. We used earthquake hypocenters captured over a one-year seismic deployment, 2D resistivity profiles, and published geologic cross-sections to determine the geometry of the SRF. The base of the lithosphere and plate interface surfaces were defined based on average Andean values and the Slab1.0 model. The simulation reproduces plate convergence and mechanic decoupling of the lithospheric plates across the subduction seismic cycle using mixed boundary conditions. Relative plate motion is achieved prescribing uniform, far-field horizontal displacement over the depth extension of both the oceanic and continental lithospheric plates. Long-term deformation is carried out in two steps. First, the modeled surfaces are allowed to slip freely emulating continuous slip on the subduction megathrust; subsequently, zero displacement is prescribed on the locking zone of the megathrust down to 40 km depth, while keeping the rest of the surfaces traction free, mimicking interseismic conditions. Long-term slip rate fields obtained for the SRF range between 0.1 and 1% the plate convergence rate, with maximum values near the surface. Interestingly, at an estimated 76-77 mm/yr relative plate motion velocity, those rates agree well with what has been reported on studies at one paleoseismic trench site across the fault. These results might contribute to determining possible seismic scenarios for Santiago but perhaps more importantly, our approach could be use in estimations of long-term slip rates and surface deformation due to other crustal structures with unknown displacement history.

Crustal Structure across Southern Islas Marías (Nayarit, Mexico) from Wide-Angle Data (TSUJAL Project)

NASA Astrophysics Data System (ADS)

Nunez, D.; Barba, D. C., Sr.; Nuñez-Cornu, F. J.; Danobeitia, J.; Garcia Millan, N.

2015-12-01

The Mexican Pacific Margin is an interesting geological and tectonic study region due to the subduction processes that involve Rivera plate, North American plates and Jalisco Block. This region has been recently studied by the TSUJAL geophysical experiment during 2014. The main goal of this project is to achieve a better knowledge about this active margin and the seismic and tsunamigenic potential structural sources. To carry out this objective a set of multibeam bathymetric, potential fields, high resolution seismic, MCS and WAS data were obtained. In the frame of this study, we present the most significant results of wide angle seismic profile RTSIM04 carried out across the southern region of Islas Marías perpendicular to the coast towards Tepic in Nayarit with 220 km of length and SW-NE orientated. This profile is made of by a network of 4 OBS and 30 land seismic stations, deployed specially for this project, which registered the air gun shots provided by RRS James Cook every 120 s. Data obtained after processing and interpretation characterize seismically the contact zone between Rivera and North American plates from 30 to 60 km of model distance. Moreover, a cortical thickening from 9 to 20 km is observed towards to the coast. In the upper mantle, P-wave velocities of 7.9-8.4 km/s up to maximum depth of 50 km have been determined.

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.

High-resolution reconstructions of Pacific-North America plate motion: 20 Ma to present

NASA Astrophysics Data System (ADS)

DeMets, C.; Merkouriev, S.

2016-11-01

We present new rotations that describe the relative positions and velocities of the Pacific and North America plates at 22 times during the past 19.7 Myr, offering ≈1-Myr temporal resolution for studies of the geotectonic evolution of western North America and other plate boundary locations. Derived from ≈18 000 magnetic reversal, fracture zone and transform fault identifications from the Pacific-Antarctic-Nubia-North America plate circuit and the velocities of 935 GPS sites on the Pacific and North America plates, the new rotations and GPS-derived angular velocity indicate that the rate of motion between the two plates increased by ≈70 per cent from 19.7 to 9±1 Ma, but changed by less than 2 per cent since 8 Ma and even less since 4.2 Ma. The rotations further suggest that the relative plate direction has rotated clockwise for most of the past 20 Myr, with a possible hiatus from 9 to 5 Ma. This conflicts with previously reported evidence for a significant clockwise change in the plate direction at ≈8-6 Ma. Our new rotations indicate that Pacific plate motion became obliquely convergent with respect to the San Andreas Fault of central California at 5.2-4.2 Ma, in agreement with geological evidence for a Pliocene onset of folding and faulting in central California. Our reconstruction of the northern Gulf of California at 6.3 Ma differs by only 15-30 km from structurally derived reconstructions after including 3-4 km Myr-1 of geodetically measured slip between the Baja California Peninsula and Pacific plate. This implies an approximate 15-30 km upper bound for plate non-rigidity integrated around the global circuit at 6.3 Ma. A much larger 200±54 km discrepancy between our reconstruction of the northern Gulf of California at 12 Ma and that estimated from structural and marine geophysical observations suggests that faults in northwestern Mexico or possibly west of the Baja California Peninsula accommodated large amounts of obliquely divergent dextral shear from 12-6.3 Ma. Pacific-North America plate motion since 16 Myr estimated with our new rotations agrees well with structurally summed deformation along two transects of western North America between the Colorado Plateau and western California, with a difference as small as 40 km out of 760 km of margin-parallel motion. A strong resemblance between a 20-Myr-to-present flow line reconstructed with our new rotations and the traces of the 700-km-long Queen Charlotte Fault and continental slope west of Canada suggests that the plate margin geometry was influenced by the passage of the Pacific plate and Yakutat block. The new rotations also suggest that (1) oblique convergence west of Canada initiated at 12-11 Ma, 5-8 Myr earlier than previously estimated, (2) no significant margin-normal shortening has occurred in areas of Canada located east of the Haida Gwaii archipelago since 20 Ma and (3) Pacific plate underthrusting of Haida Gwaii has accommodated the margin-normal component of plate motion since 12-11 Ma. Our rotations suggest an ≈70 per cent increase in the rate that the Pacific plate has been consumed by subduction beneath the Aleutian arc since 19.7 Ma, with still-unknown consequences for the rate of arc magmatism.

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.

Locking, mass flux and topographic response at convergent plate boundaries - the Chilean case

NASA Astrophysics Data System (ADS)

Oncken, Onno

2016-04-01

On the long term, convergent plate boundaries have been shown to be controlled by either accretion/underplating or by subduction erosion. Vertical surface motion is coupled to convergence rate - typically with an uplift rate of the coastal area ranging from 0 to +50% of convergence rate in accretive systems, and -20 to +30% in erosive systems. Vertical kinematics, however, are not necessarily linked to horizontal strain mode, i.e. upper plate shortening or extension, in a simple way. This range of kinematic behaviors - as well as their acceleration where forearcs collide with oceanic ridges/plateau - is well expressed along the Chilean plate margin. Towards the short end of the time scale, deformation appears to exhibit a close correlation with the frictional properties and geodetic locking at the plate interface. Corroborating analogue experiments of strain accumulation during multiple earthquake cycles, forearc deformation and uplift focus above the downdip and updip end of seismic coupling and slip and are each related to a particular stage of the seismic cycle, but with opposite trends for both domains. Similarly, barriers separating locked domains along strike appear to accumulate most upper plate faulting interseismically. Hence, locking patters are reflected in topography. From the long-term memory contained in the forearc topography the relief of the Chilean forearc seems to reflect long term stability of the observed heterogeneity of locking at the plate interface. This has fundamental implications for spatial and temporal distribution of seismic hazard. Finally, the nature of locking at the plate interface controlling the above kinematic behavior appears to be strongly controlled by the degree of fluid overpressuring at the plate interface suggesting that the hydraulic system at the interface takes a key role for the forearc response.

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.

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

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.

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.

Effects of boundary-layer separation controllers on a desktop fume hood.

PubMed

Huang, Rong Fung; Chen, Jia-Kun; Hsu, Ching Min; Hung, Shuo-Fu

2016-10-02

A desktop fume hood installed with an innovative design of flow boundary-layer separation controllers on the leading edges of the side plates, work surface, and corners was developed and characterized for its flow and containment leakage characteristics. The geometric features of the developed desktop fume hood included a rearward offset suction slot, two side plates, two side-plate boundary-layer separation controllers on the leading edges of the side plates, a slanted surface on the leading edge of the work surface, and two small triangular plates on the upper left and right corners of the hood face. The flow characteristics were examined using the laser-assisted smoke flow visualization technique. The containment leakages were measured by the tracer gas (sulphur hexafluoride) detection method on the hood face plane with a mannequin installed in front of the hood. The results of flow visualization showed that the smoke dispersions induced by the boundary-layer separations on the leading edges of the side plates and work surface, as well as the three-dimensional complex flows on the upper-left and -right corners of the hood face, were effectively alleviated by the boundary-layer separation controllers. The results of the tracer gas detection method with a mannequin standing in front of the hood showed that the leakage levels were negligibly small (≤0.003 ppm) at low face velocities (≥0.19 m/s).

Revisiting the structure, age, and evolution of the Wharton Basin to better understand subduction under Indonesia

NASA Astrophysics Data System (ADS)

Jacob, Jensen; Dyment, Jérôme; Yatheesh, V.

2014-01-01

the subduction processes along the Sunda Trench requires detailed constraints on the subducting lithosphere. We build a detailed tectonic map of the Wharton Basin based on reinterpretation of satellite-derived gravity anomalies and marine magnetic anomalies. The Wharton Basin is characterized by a fossil ridge, dated 36.5 Ma, offset by N-S fracture zones. Magnetic anomalies 18 to 34 (38-84 Ma) are identified on both flanks, although a large part of the basin has been subducted. We analyze the past plate kinematic evolution of the Wharton Basin by two-plate (India-Australia) and three-plate (India-Australia-Antarctica) reconstructions. Despite the diffuse plate boundaries within the Indo-Australian plate for the last 20 Ma, we obtain finite rotation parameters that we apply to reconstruct the subducted Wharton Basin and constrain the thickness, buoyancy, and rheology of the subducting plate. The lower subductability of younger lithosphere off Sumatra has important consequences on the morphology, with a shallower trench, forearc islands, and a significant inward deviation of the subduction system. This deviation decreases in the youngest area, where the Wharton fossil spreading center enters subduction: The discontinuous magmatic crust and serpentinized upper mantle, consequences of the slow spreading rates at which this area was formed, weaken the mechanical resistance to subduction and facilitate the restoration of the accretionary prism. Deeper effects include the possible creation of asthenospheric windows beneath the Andaman Sea, in relation to the long-offset fracture zones, and east of 105°E, as a result of subduction of the spreading center.

From a collage of microplates to stable continental crust - an example from Precambrian Europe

NASA Astrophysics Data System (ADS)

Korja, Annakaisa

2013-04-01

Svecofennian orogen (2.0-1.7 Ga) comprises the oldest undispersed orogenic belt on Baltica and Eurasian plate. Svecofennian orogenic belt evolved from a series of short-lived terrane accretions around Baltica's Archean nucleus during the formation of the Precambrian Nuna supercontinent. Geological and geophysical datasets indicate W-SW growth of Baltica with NE-ward dipping subduction zones. The data suggest a long-lived retreating subduction system in the southwestern parts whereas in the northern and central parts the northeasterly transport of continental fragments or microplates towards the continental nucleus is also documented. The geotectonic environment resembles that of the early stages of the Alpine-Himalayan or Indonesian orogenic system, in which dispersed continental fragments, arcs and microplates have been attached to the Eurasian plate margin. Thus the Svecofennian orogeny can be viewed as proxy for the initial stages of an internal orogenic system. Svecofennian orogeny is a Paleoproterozoic analogue of an evolved orogenic system where terrane accretion is followed by lateral spreading or collapse induced by change in the plate architecture. The exposed parts are composed of granitoid intrusions as well as highly deformed supracrustal units. Supracrustal rocks have been metamorphosed in LP-HT conditions in either paleo-lower-upper crust or paleo-upper-middle crust. Large scale seismic reflection profiles (BABEL and FIRE) across Baltica image the crust as a collage of terranes suggesting that the bedrock has been formed and thickened in sequential accretions. The profiles also image three fold layering of the thickened crust (>55 km) to transect old terrane boundaries, suggesting that the over-thickened bedrock structures have been rearranged in post-collisional spreading and/or collapse processes. The middle crust displays typical large scale flow structures: herringbone and anticlinal ramps, rooted onto large scale listric surfaces also suggestive of spreading. Close to the original ocean-continent plate boundary, in the core of the Svecofennian orogen, the thickened accretionary crust carries pervasive stretching lineations at surface and seismic vp-velocity anisotropy in the crust. The direction of spreading and crustal flow seems to be diverted by shapes of the pre-existing boundaries. It is concluded that lateral spreading and midcrustal flow not only rearrange the bedrock architecture but also stabilize the young accreted continental crust in emerging internal orogenic systems. Pre-existing microplate/terrane boundaries will affect the final architecture of the orogenic belt.

Shoreline-crossing shear-velocity structure of the Juan de Fuca plate and Cascadia subduction zone from surface waves and receiver functions

NASA Astrophysics Data System (ADS)

Janiszewski, Helen; Gaherty, James; Abers, Geoffrey; Gao, Haiying

2017-04-01

The Cascadia subduction zone (CSZ) is the site of the onshore-offshore Cascadia Initiative, which deployed seismometers extending from the Juan de Fuca ridge to the subduction zone and onshore beyond the volcanic arc. This array allows the unique opportunity to seismically image the evolution and along-strike variation of the crust and mantle of the entire CSZ. We compare teleseismic receiver functions, ambient-noise Rayleigh-wave phase velocities in the 10-20 s period band, and earthquake-source Rayleigh-wave phase velocities from 20-100 s, to determine shear-velocity structure in the upper 200 km. Receiver functions from both onshore and shallow-water offshore sites provide constraints on crustal and plate interface structure. Spectral-domain fitting of ambient-noise empirical Green's functions constrains shear velocity of the crust and shallow mantle. An automated multi-channel cross-correlation analysis of teleseismic Rayleigh waves provides deeper lithosphere and asthenosphere constraints. The amphibious nature of the array means it is essential to examine the effect of noise variability on data quality. Ocean bottom seismometers (OBS) are affected by tilt and compliance noise. Removal of this noise from the vertical components of the OBS is essential for the teleseismic Rayleigh waves; this stabilizes the output phase velocity maps particularly along the coastline where observations are predominately from shallow water OBS. Our noise-corrected phase velocity maps reflect major structures and tectonic transitions including the transition from high-velocity oceanic lithosphere to low-velocity continental lithosphere, high velocities associated with the subducting slab, and low velocities beneath the ridge and arc. We interpret the resulting shear-velocity model in the context of temperature and compositional variation in the incoming plate and along the strike of the CSZ.

Shoreline-Crossing Shear-Velocity Structure of the Juan de Fuca Plate and Cascadia Subduction Zone from Surface Waves and Receiver Functions

NASA Astrophysics Data System (ADS)

Janiszewski, H. A.; Gaherty, J. B.; Abers, G. A.; Gao, H.

2016-12-01

The Cascadia subduction zone (CSZ) is the site of the onshore-offshore Cascadia Initiative, which deployed seismometers extending from the Juan de Fuca ridge to the subduction zone and onshore beyond the volcanic arc. This array allows the unique opportunity to seismically image the evolution and along-strike variation of the crust and mantle of the entire CSZ. We compare teleseismic receiver functions, ambient-noise Rayleigh-wave phase velocities in the 10-20 s period band, and earthquake-source Rayleigh-wave phase velocities from 20-100 s, to determine shear-velocity structure in the upper 200 km. Receiver functions from both onshore and shallow-water offshore sites provide constraints on crustal and plate interface structure. Spectral-domain fitting of ambient-noise empirical Green's functions constrains shear velocity of the crust and shallow mantle. An automated multi-channel cross-correlation analysis of teleseismic Rayleigh waves provides deeper lithosphere and asthenosphere constraints. The amphibious nature of the array means it is essential to examine the effect of noise variability on data quality. Ocean bottom seismometers (OBS) are affected by tilt and compliance noise. Removal of this noise from the vertical components of the OBS is essential for the teleseismic Rayleigh waves; this stabilizes the output phase velocity maps particularly along the coastline where observations are predominately from shallow water OBS. Our noise-corrected phase velocity maps reflect major structures and tectonic transitions including the transition from high-velocity oceanic lithosphere to low-velocity continental lithosphere, high velocities associated with the subducting slab, and low velocities beneath the ridge and arc. We interpret the resulting shear-velocity model in the context of temperature and compositional variation in the incoming plate and along the strike of the CSZ.

Structure and kinematics of segment-scale crustal accretion processes in Iceland and implications for analogous mid-ocean ridge systems

NASA Astrophysics Data System (ADS)

Siler, Drew Lorenz

2011-12-01

The sub-surface geologic structure of the crust is controlled by the magmatic and tectonic processes that construct the crust during plate spreading. As a result, geologic structure provides constraints on the processes that occur during plate spreading. The crust of the Skagi region of northern Iceland, where this study was focused, was accreted by magmatic construction to Iceland ˜7-10 Ma and subsequently glacially eroded, exhuming ˜1-3 km of structural relief. Continuous spreading-parallel and spreading-orthogonal mountain ranges expose the crust accreted at discrete spreading segments, the fundamental intervals upon which plate spreading and crustal accretion occur. As a result, Skagi is an ideal location to employ geologic structure analysis to study magmatic rifting processes. Within spreading segments structural patterns vary significantly between segment centers and distal fissure swarms. While segment centers are characterized by focused magmatic construction and km-scale sub-volcanic subsidence, fissure swarms are characterized by limited magmatic construction, minor sub-axial subsidence and lateral dike injection. Such along-strike variation indicates that both magma in the upper crust and gabbroic material in the lower crust must be redistributed along-strike within spreading segments during plate spreading. Material flow is directed from beneath segment centers towards distal fissure swarms. At the regional scale, each spreading segment is a structurally discrete interval of Iceland's Neovolcanic Zone. As a result of west-northwestward movement of Iceland relative to the Iceland hotspot, the rift zone axis has progressively relocated to the east-southeast with time, leaving a series of abandoned rift zones throughout western Iceland. A compilation of published K/Ar and 40Ar/39Ar age data and geologic data from across northern Iceland shows that rift relocation occurs via frequent (2-3 Ma), small-scale (˜20 km) rift propagations rather than rare, 100s of km 'rift jumps' as is conventional models suggest. The structure relationships we define in the Icelandic crust are similar to that of other magmatic rift systems including Mid-Ocean Ridges, continental rifts and ancient volcanic rift margins. As such, we suggest that many of the crustal accretion processes we have inferred from Icelandic data may be important in these analogous environments as well.

The Transantarctic Mountains of southern Victoria Land: The application of Apatite fission track analysis to a rift shoulder uplift

NASA Astrophysics Data System (ADS)

Fitzgerald, Paul G.

1992-06-01

A fission track study of the Transantarctic Mountains (TAM) in the Granite Harbour and Wilson Piedmont Glacier areas of southern Victoria Land reveals information on the timing of uplift, the amount of uplift and erosion, and the structure of the mountains, especially the onshore Transantarctic Mountain Front (TAM Front), which represents the boundary between East and West Antarctica. Apatite ages are < 175 Ma and represent a thermal regime established after heating accompanying Jurassic magmatism. An apatite age profile from Mount England records a break in slope indicating uplift began at ˜55 Ma. Horizontal sampling traverses, plus fieldwork, delineate the structure of the TAM Front as a zone of north-south striking, steeply dipping normal faults, with displacements, dominantly down to the east, of 40-1000 m. The overall structure of the mountains in the area studied can be envisaged as a large tilt block or flexure. Its westerly limb dips gently under the ice cap, compared to its faulted eastern edge, the TAM Front. The bounding structure to the south is the Ferrar fault and to the north is a graben through which the Mackay Glacier drains the polar plateau. The edge of the flexure, or axis of maximum uplift, lies at Mount Termination, ˜30 km west of the McMurdo Sound coast. There has been ˜6 km of uplift since the early Cenozoic and 4.5-5 km of erosion along this axis. The amount of uplift decreases to the west at the same rate as the decrease in dip of the Kukri Peneplain, but the amount of erosion decreases more quickly as indicated by the increasing height of the mountains to the west. The axis of maximum uplift is traced north to Granite Harbour. The axis does not parallel the coast but has a more northerly trend. North-south striking longitudinal faults that delineate the structure of the TAM Front lie at an acute angle to the axis, indicating a dextral component to the dominantly east-west extension in the Ross Embayment. Architecture of the TAM typifies the features of an upper plate passive mountain range, whereas the Ross Embayment has the characteristics of a lower plate. The TAM Front represents an upper plate breakaway zone. Transfer faults may exist up major outlet glaciers that cut the TAM. The inflection point in the coastline at the southern end of McMurdo Sound may be due to the presence of a major transfer fault up or near the Skelton Glacier.

The structure, isostasy and gravity field of the Levant continental margin and the southeast Mediterranean area

NASA Astrophysics Data System (ADS)

Segev, Amit; Rybakov, Michael; Lyakhovsky, Vladimir; Hofstetter, Avraham; Tibor, Gidon; Goldshmidt, Vladimir; Ben Avraham, Zvi

2006-10-01

A 3-D layered structure of the Levant and the southeastern Mediterranean lithospheric plates was constructed using interpretations of seismic measurements and borehole data. Structural maps of three principal interfaces, elevation, top basement and the Moho, were constructed for the area studied. This area includes the African, Sinai and Arabian plates, the Herodotus and the Levant marine basins and the Nile sedimentary cone. In addition, an isopach map of the Pliocene sediments, as well as the contemporaneous amount of denuded rock units, was prepared to enable setting up the structural map of the base Pliocene sediment. Variable density distributions are suggested for the sedimentary succession in accord with its composition and compaction. The spatial density distribution in the crystalline crust was calculated by weighting the thicknesses of the lower mafic and the upper felsic crustal layers, with densities of 2.9 g/cm 3 and 2.77 g/cm 3, respectively. Results of the local (Airy) isostatic modeling with compensation on the Moho interface show significant deviations from the local isostasy and require variable density distribution in the upper mantle. Moving the compensation level to the base of the lithosphere (˜ 100 km depth) and adopting density variations in the mantle lithosphere yielded isostatic compensation (± 200 m) over most of the area studied. The spatial pattern obtained of a density distribution with a range of ± 0.05 g/cm 3 is supported by a regional heat flux. Simulations of the flexure (Vening Meinesz) isostasy related to the Pliocene to Recent sedimentary loading and unloading revealed concentric oscillatory negative and positive anomalies mostly related to the Nile sedimentary cone. Such anomalies may explain the rapid subsidence in the Levant Basin and the arching in central Israel, northern Sinai and Egypt during Pliocene-Recent times. Comparison between the observed (Bouguer) gravity and the calculated gravity for the constructed 3-D lithospheric structure, which has variable density distributions, provided a good match and an independent constraint for the large-scale structure suggested and confirmed an oceanic nature for the Levant Basin lithosphere.

Structural deformation and detailed architecture of accretionary wedge in the northern Manila subduction zone

NASA Astrophysics Data System (ADS)

Gao, J.; Wu, S.; Yao, Y.; Chen, C.

2017-12-01

The South China Sea (SCS) which located at the southeast edge of the Eurasian plate, is heavily influenced by the Philippine Sea plate and the Indo-Australian plate. As eastern boundary of the SCS, Manila subduction zone was created by the northwestern movement of the Philippine Sea plate, recorded the key information on formation and evolution of the SCS and often triggered off earthquakes and tsunami in the East and South Asia. Using high resolution multi-channel seismic data across the northern Manila subduction zone, this study analyzed sedimentary characteristics of oceanic basin and trench, and fine described features of structural deformation and architecture of accretionary wedge and magmatism to discuss the time of subduction inception, thrust motion and influence of seamount subduction on the geometry of the Manila trench. Results show that lower slope of accretionary wedge mainly consist of imbricated thrusts with blind thrust as the frontal fault and structural wedge whereas upper slope was obscure for intensely structural deformation and magmatism. All the thrust faults merged into a detachment fault/surface which may root in Lower Miocene or even older strata, cut off the Miocene near buried seamount and extended the Pliocene upward, suggesting that this detachment fault was obviously influenced by buried seamount and basement high below the accretionary wedge. Magmatism began to be active from late Miocene and continued to be intense during Pliocene and Quaternary in the oceanic basin, trench and accretionary wedge. Based on characteristics of sedimentary and structural deformation, this study proposed that accretionary wedge of the northern Manila subduction zone formed before 16.5 Ma and propagated to the SCS through piggyback propagation thrusting when seafloor spreading of the SCS was still ongoing before 15 Ma. Subduction of extended continental crust in the northeastern SCS created a significantly concaving eastward to geometric shape of the northern Manila trench. With the subducting of fossil ridge of the SCS to the Manila trench and ridge/trench collision happening in the future, the convexly westward arc feature of Manila trench was changed to flat and will be even concave eastward.

Rheological properties of the lower crust and upper mantle beneath Baja California: a microstructural study of xenoliths from San Quintin

NASA Astrophysics Data System (ADS)

Van der Werf, Thomas F.; Chatzaras, Vasileios; Tikoff, Basil; Drury, Martyn R.

2016-04-01

Baja California is an active transtensional rift zone, which links the San Andreas Fault with the East Pacific Rise. The erupted basalts of the Holocene San Quintin volcanic field contain xenoliths, which sample the lower crust and upper mantle beneath Baja California. The aim of this research is to gain insight in the rheology of the lower crust and the upper mantle by investigating the xenolith microstructure. Microstructural observations have been used to determine the dominant deformation mechanisms. Differential stresses were estimated from recrystallized grain size piezometry of plagioclase and clinopyroxene for the lower crust and olivine for the upper mantle. The degree of deformation can be inferred from macroscopic foliations and the deformation microstructures. Preliminary results show that both the lower crust and the upper mantle have been affected by multiple stages of deformation and recrystallization. In addition the dominant deformation mechanism in both the lower crust and the upper mantle is dislocation creep based on the existence of strong crystallographic preferred orientations. The differential stress estimates for the lower crust are 10-29 MPa using plagioclase piezometry and 12-35 MPa using clinopyroxene piezometry. For the upper mantle, differential stress estimates are 10-20 MPa. These results indicate that the strength of the lower crust and the upper mantle are very similar. Our data do not fit with the general models of lithospheric strength and may have important implications for the rheological structure of the lithosphere in transtensional plate margins and for geodynamic models of the region.

Tectonic plates, D (double prime) thermal structure, and the nature of mantle plumes

NASA Technical Reports Server (NTRS)

Lenardic, A.; Kaula, W. M.

1994-01-01

It is proposed that subducting tectonic plates can affect the nature of thermal mantle plumes by determining the temperature drop across a plume source layer. The temperature drop affects source layer stability and the morphology of plumes emitted from it. Numerical models are presented to demonstrate how introduction of platelike behavior in a convecting temperature dependent medium, driven by a combination of internal and basal heating, can increase the temperature drop across the lower boundary layer. The temperature drop increases dramatically following introduction of platelike behavior due to formation of a cold temperature inversion above the lower boundary layer. This thermal inversion, induced by deposition of upper boundary layer material to the system base, decays in time, but the temperature drop across the lower boundary layer always remains considerably higher than in models lacking platelike behavior. On the basis of model-inferred boundary layer temperature drops and previous studies of plume dynamics, we argue that generally accepted notions as to the nature of mantle plumes on Earth may hinge on the presence of plates. The implication for Mars and Venus, planets apparently lacking plate tectonics, is that mantle plumes of these planets may differ morphologically from those of Earth. A corollary model-based argument is that as a result of slab-induced thermal inversions above the core mantle boundary the lower most mantle may be subadiabatic, on average (in space and time), if major plate reorganization timescales are less than those acquired to diffuse newly deposited slab material.

Three-dimensional tomographic mapping related to primary stability and structural miniscrew characteristics.

PubMed

Silvestrini Biavati, A; Tecco, S; Migliorati, M; Festa, F; Panza, G; Marzo, G; Gherlone, E; Tetè, S

2011-05-01

To evaluate the maxilla, mandible, and cortical plates on computerized tomographic (CT) scans to achieve accurate three-dimensional bone thickness measurements. We selected the CT scans of 25 subjects (among 102), aged 18-58 years (10 men, 15 women), with nearly complete dentition. We performed interradicular and bucco-lingual (including cortical plate thickness) measurements in dental areas distal to the canines in both alveolar arches, at three levels (5, 8, and 11 mm) from the alveolar ridge. The mean thicknesses of the cortical plates in the maxilla were 1.10 mm buccally and 1.27 mm on the palatal side (p < 0.05). In the mandible, cortical plates were 2.23 mm buccally and 2.02 mm lingually. Mandibular buccal and lingual cortical plates became thicker distally in the second and third molar areas. There was considerable variation in cortical thickness (from 0.25 to 5.50 mm). Based on interradicular distances, only 13% of measured sites in the maxilla were suitable for miniscrew insertion (≥3.3 mm), but 63% of sites were suitable in the mandible. This study showed considerable individual variation in bone thickness. Our data suggested that the palatal/lingual side may provide greater primary stability for miniscrews. The palatal area, between the second upper bicuspid and the first molar, appeared to be the most suitable area for tapered 7- to 9-mm miniscrews, starting at 1.5-2 mm from the alveolar crest. © 2011 John Wiley & Sons A/S.

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.

Shear wave velocity structure of the Anatolian Plate and surrounding regions using Ambient Noise Tomography

NASA Astrophysics Data System (ADS)

Delph, J. R.; Beck, S. L.; Zandt, G.; Biryol, C. B.; Ward, K. M.

2013-12-01

The Anatolian Plate consists of various lithospheric terranes amalgamated during the closure of the Tethys Ocean, and is currently extruding to the west in response to a combination of the collision of the Arabian plate in the east and the roll back of the Aegean subduction zone in the west. We used Ambient Noise Tomography (ANT) at periods <= 40s to investigate the crust and uppermost mantle structure of the Anatolian Plate. We computed a total of 13,779 unique cross-correlations using one sample-per-second vertical component broadband seismic data from 215 stations from 8 different networks over a period of 7 years to compute fundamental-mode Rayleigh wave dispersion curves following the method of Benson et al. (2007). We then inverted the dispersion data to calculate phase velocity maps for 11 periods from 8 s - 40 s throughout Anatolia and the Aegean regions (Barmin et al. 2001). Using smoothed Moho values derived from Vanacore et al. (2013) in our starting models, we inverted our dispersion curves using a linear least-squares iterative inversion scheme (Herrmann & Ammon 2004) to produce a 3-D shear-wave velocity model of the crust and uppermost mantle throughout Anatolia and the Aegean. We find a good correlation between our seismic shear wave velocities and paleostructures (suture zones) and modern deformation (basin formation and fault deformation). The most prominent crustal velocity contrasts occur across intercontinental sutures zones, resulting from the juxtaposition of the compositionally different basements of the amalgamated terranes. At shallow depths, seismic velocity contrasts correspond closely with surficial features. The Thrace, Cankiri and Tuz Golu basins, and accretionary complexes related to the closure of the Neotethys are characterized by slow shear wave velocities, while the Menderes and Kirsehir Massifs, Pontides, and Istanbul Zone are characterized by fast velocities. We find that the East Anatolia Plateau has slow shear-wave velocities, as expected due to high heat flow and active volcanism. The Tuz Golu fault has a visible seismic signal down to ~15 km below sea level, and the eastern Inner-Tauride Suture corresponding to the Central Anatolian Fault Zone may extend into the mantle. The Isparta Angle separates the actively extending portion of western Anatolia from the plateau regions in the east, and the largest anomaly (slow velocities) extending into the upper mantle is observed under the western flank of the Isparta Angle, corresponding to the Fethiye-Burdur fault zone. We attribute these slow shear-wave velocities to the effects of complex deformations within the crust as a result of the interactions of the African and Anatolian Plates. In the upper mantle, slow shear-wave velocities are consistent with a slab tear along a STEP fault corresponding to the extensions of the Pliny and Strabo Transform faults, allowing asthenosphere to rise to very shallow depths. The upper mantle beneath the Taurides exhibits very slow shear-wave velocities, in agreement with possible delamination or slab-breakoff (Cosentino et al. 2012) causing rapid uplift in the last 8 million years.

Seismic structure of the lithosphere and upper mantle beneath the ocean islands near mid-oceanic ridges

NASA Astrophysics Data System (ADS)

Haldar, C.; Kumar, P.; Kumar, M. Ravi

2014-05-01

Deciphering the seismic character of the young lithosphere near mid-oceanic ridges (MORs) is a challenging endeavor. In this study, we determine the seismic structure of the oceanic plate near the MORs using the P-to-S conversions isolated from quality data recorded at five broadband seismological stations situated on ocean islands in their vicinity. Estimates of the crustal and lithospheric thickness values from waveform inversion of the P-receiver function stacks at individual stations reveal that the Moho depth varies between ~ 10 ± 1 km and ~ 20 ± 1 km with the depths of the lithosphere-asthenosphere boundary (LAB) varying between ~ 40 ± 4 and ~ 65 ± 7 km. We found evidence for an additional low-velocity layer below the expected LAB depths at stations on Ascension, São Jorge and Easter islands. The layer probably relates to the presence of a hot spot corresponding to a magma chamber. Further, thinning of the upper mantle transition zone suggests a hotter mantle transition zone due to the possible presence of plumes in the mantle beneath the stations.

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.

Seismic structure of the European crust and upper mantle based on adjoint tomography

NASA Astrophysics Data System (ADS)

Zhu, H.; Bozdag, E.; Peter, D.; Tromp, J.

2013-12-01

We present a new crustal and upper mantle model for the European continent and the North Atlantic Ocean, named EU60. It is constructed based on adjoint tomography and involves 3D variations in elastic wavespeeds, anelastic attenuation, and radial/azimuthal anisotropy. Long-wavelength elastic wavespeed structure of EU60 agree with previous body- and surface-wave tomographic models. Some hitherto unidentified features, such as the Adria microplate, naturally emerge from smoothed starting model. Subducting slabs, slab detachment, ancient suture zones, continental rifts and back-arc basins are well resolved in EU60. For anelastic structure, we find an anti-correlation between shear wavespeeds and anelastic attenuation at shallow depths. At greater depths, this anti-correlation becomes relatively weak, in agreement with previous attenuation studies at global scales. Consistent with radial anisotropy in 1D reference models, the European continent is dominated by features with radially anisotropic parameter xi>1, indicating the presence of horizontal flow within the upper mantle. In addition, subduction zones, such as the Apennines and Hellenic arcs, are characterized as vertical flow with xi<1 at depths greater than 150~km. For azimuthal anisotropy, we find that the direction of fast anisotropic axis is well correlated with complicated tectonic evolution in this region, such as extension along the North Atlantic Ridge, trench retreat in the Mediterranean and counter-clockwise rotation of the Anatolian Plate. The ``point spread function'' is used to assess image quality and analyze tradeoff between different model parameters.

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.

A New Comprehensive Model for Crustal and Upper Mantle Structure of the European Plate

NASA Astrophysics Data System (ADS)

Morelli, A.; Danecek, P.; Molinari, I.; Postpischl, L.; Schivardi, R.; Serretti, P.; Tondi, M. R.

2009-12-01

We present a new comprehensive model of crustal and upper mantle structure of the whole European Plate — from the North Atlantic ridge to Urals, and from North Africa to the North Pole — describing seismic speeds (P and S) and density. Our description of crustal structure merges information from previous studies: large-scale compilations, seismic prospection, receiver functions, inversion of surface wave dispersion measurements and Green functions from noise correlation. We use a simple description of crustal structure, with laterally-varying sediment and cristalline layers thickness and seismic parameters. Most original information refers to P-wave speed, from which we derive S speed and density from scaling relations. This a priori crustal model by itself improves the overall fit to observed Bouguer anomaly maps, as derived from GRACE satellite data, over CRUST2.0. The new crustal model is then used as a constraint in the inversion for mantle shear wave speed, based on fitting Love and Rayleigh surface wave dispersion. In the inversion for transversely isotropic mantle structure, we use group speed measurements made on European event-to-station paths, and use a global a priori model (S20RTS) to ensure fair rendition of earth structure at depth and in border areas with little coverage from our data. The new mantle model sensibly improves over global S models in the imaging of shallow asthenospheric (slow) anomalies beneath the Alpine mobile belt, and fast lithospheric signatures under the two main Mediterranean subduction systems (Aegean and Tyrrhenian). We map compressional wave speed inverting ISC travel times (reprocessed by Engdahl et al.) with a non linear inversion scheme making use of finite-difference travel time calculation. The inversion is based on an a priori model obtained by scaling the 3D mantle S-wave speed to P. The new model substantially confirms images of descending lithospheric slabs and back-arc shallow asthenospheric regions, shown in other more local high-resolution tomographic studies, but covers the whole range of the European Plate. We also obtain three-dimensional mantle density structure by inversion of GRACE Bouguer anomalies locally adjusting density and the scaling relation between seismic wave speeds and density. We validate the new comprehensive model through comparison of recorded seismograms with numerical simulations based on SPECFEM3D. This work is a contribution towards the definition of a reference earth model for Europe. To this extent, in order to improve model dissemination and comparison, we propose the adoption of a common exchange format for tomographic earth models based on JSON, a lightweight data-interchange format supported by most high-level programming languages. We provide tools for manipulating and visualising models, described in this standard format, in Google Earth and GEON IDV.

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.

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.

Aeroelastic Tailoring via Tow Steered Composites

NASA Technical Reports Server (NTRS)

Stanford, Bret K.; Jutte, Christine V.

2014-01-01

The use of tow steered composites, where fibers follow prescribed curvilinear paths within a laminate, can improve upon existing capabilities related to aeroelastic tailoring of wing structures, though this tailoring method has received relatively little attention in the literature. This paper demonstrates the technique for both a simple cantilevered plate in low-speed flow, as well as the wing box of a full-scale high aspect ratio transport configuration. Static aeroelastic stresses and dynamic flutter boundaries are obtained for both cases. The impact of various tailoring choices upon the aeroelastic performance is quantified: curvilinear fiber steering versus straight fiber steering, certifiable versus noncertifiable stacking sequences, a single uniform laminate per wing skin versus multiple laminates, and identical upper and lower wing skins structures versus individual tailoring.

The North Sakhalin Neogene total petroleum system of eastern Russia

USGS Publications Warehouse

Lindquist, S.J.

2000-01-01

The North Sakhalin Basin Province of eastern Russia contains one Total Petroleum System (TPS) ? North Sakhalin Neogene ? with more than 6 BBOE known, ultimately recoverable petroleum (61% gas, 36% oil, 3% condensate). Tertiary rocks in the basin were deposited by the prograding paleo-Amur River system. Marine to continental, Middle to Upper Miocene shale to coaly shale source rocks charged marine to continental Middle Miocene to Pliocene sandstone reservoir rocks in Late Miocene to Pliocene time. Fractured, self-sourced, Upper Oligocene to Lower Miocene siliceous shales also produce hydrocarbons. Geologic history is that of a Mesozoic Asian passive continental margin that was transformed into an active accretionary Tertiary margin and Cenozoic fold belt by the collision of India with Eurasia and by the subduction of Pacific Ocean crustal plates under the Asian continent. The area is characterized by extensional, compressional and wrench structural features that comprise most known traps.

Constraints on the tectonics of the Mule Mountains thrust system, southeast California and southwest Arizona

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

Tosdal, R.M.

1990-11-10

The Mule Mountains thrust system crops out discontinuously over a 100-km-strike length in the Blythe-Quartzsite region of southeast California and southwest Arizona. Along the thrust system, middle and upper crustal metamorphic and plutonic rocks of Proterozoic and Mesozoic age are thrust north-northeastward (015{degree} to 035{degree}) over a lower plate metamorphic terrane that formed part of the Proterozoic North American craton, its Paleozoic sedimentary rock cover, overlying Mesozoic volcanic and sedimentary rocks, and the intruding Jurassic and Cretaceous granitic rocks. Stratigraphic, petrologic, and Pb isotopic ties for Jurassic granitoids and for Jurassic( ) and Cretaceous sedimentary rocks across the various partsmore » of the thrust system indicate that related crustal blocks are superposed and preclude it from having large displacements. The thick-skinned thrust system is structurally symmetrical along its length with a central domain of synmetamorphic thrust faults that are flanked by western and eastern domains where lower plate domains where lower plate synclines underlie the thrusts. Deformation occurred under low greenschist facies metamorphic conditions in the upper crust. Movement along the thrust system was probably limited to no more than a few tens of kilometers and occurred between 79{plus minus}2 Ma and 70{plus minus}4 Ma. The superposition of related rocks and the geometry of the thrust system preclude it from being a major tectonic boundary of post-Middle Jurassic age, as has been previously proposed. Rather, the thrust system forms the southern boundary of the narrow zone of Cretaceous intracratonic deformation, and it is one of the last tectonic events in the zone prior to regional cooling.« less

An upper bound on the electrical conductivity of hydrated oceanic mantle at the onset of dehydration melting

NASA Astrophysics Data System (ADS)

Naif, Samer

2018-01-01

Electrical conductivity soundings provide important constraints on the thermal and hydration state of the mantle. Recent seafloor magnetotelluric surveys have imaged the electrical conductivity structure of the oceanic upper mantle over a variety of plate ages. All regions show high conductivity (0.02 to 0.2 S/m) at 50 to 150 km depths that cannot be explained with a sub-solidus dry mantle regime without unrealistic temperature gradients. Instead, the conductivity observations require either a small amount of water stored in nominally anhydrous minerals or the presence of interconnected partial melts. This ambiguity leads to dramatically different interpretations on the origin of the asthenosphere. Here, I apply the damp peridotite solidus together with plate cooling models to determine the amount of H2O needed to induce dehydration melting as a function of depth and plate age. Then, I use the temperature and water content estimates to calculate the electrical conductivity of the oceanic mantle with a two-phase mixture of olivine and pyroxene from several competing empirical conductivity models. This represents the maximum potential conductivity of sub-solidus oceanic mantle at the limit of hydration. The results show that partial melt is required to explain the subset of the high conductivity observations beneath young seafloor, irrespective of which empirical model is applied. In contrast, the end-member empirical models predict either nearly dry (<20 wt ppm H2O) or slightly damp (<200 wt ppm H2O) asthenosphere for observations of mature seafloor. Since the former estimate is too dry compared with geochemical constraints from mid-ocean ridge basalts, this suggests the effect of water on mantle conductivity is less pronounced than currently predicted by the conductive end-member empirical model.

Brittle deformation during Alpine basal accretion and the origin of seismicity nests above the subduction interface

NASA Astrophysics Data System (ADS)

Menant, Armel; Angiboust, Samuel; Monié, Patrick; Oncken, Onno; Guigner, Jean-Michel

2018-04-01

Geophysical observations on active subduction zones have evidenced high seismicity clusters at 20-40 km depth in the fore-arc region whose origin remains controversial. We report here field observations of pervasive pseudotachylyte networks (interpreted as evidence for paleo-seismicity) in the now-exhumed Valpelline continental unit (Dent Blanche complex, NW. Alps, Italy), a tectonic sliver accreted to the upper plate at c. 30 km depth during the Paleocene Alpine subduction. Pre-alpine granulite-facies paragneiss from the core of the Valpelline unit are crosscut by widespread, mm to cm-thick pseudotachylyte veins. Co-seismic heating and subsequent cooling led to the formation of Ti-rich garnet rims, ilmenite needles, Ca-rich plagioclase, biotite microliths and hercynite micro-crystals. 39Ar-40Ar dating yields a 51-54 Ma age range for these veins, thus suggesting that frictional melting events occurred near peak burial conditions while the Valpelline unit was already inserted inside the duplex structure. In contrast, the base of the Valpelline unit underwent synchronous ductile and brittle, seismic deformation under water-bearing conditions followed by a re-equilibration at c. 40 Ma (39Ar-40Ar on retrograded pseudotachylyte veins) during exhumation-related deformation. Calculated rheological profiles suggest that pseudotachylyte veins from the dry core of the granulite unit record upper plate micro-seismicity (Mw 2-3) formed under very high differential stresses (>500 MPa) while the sheared base of the unit underwent repeated brittle-ductile deformation at much lower differential stresses (<40 MPa) in a fluid-saturated environment. These results demonstrate that some of the seismicity clusters nested along and above the plate interface may reflect the presence of stiff tectonic slivers rheologically analogous to the Valpelline unit acting as repeatedly breaking asperities in the basal accretion region of active subduction zones.

Dissonance and harmony between global and regional-scale seismic anisotropy and mantle dynamics

NASA Astrophysics Data System (ADS)

Becker, T. W.

2017-12-01

Huge numbers of SKS splitting observations and improved surface-wave based models of azimuthal anisotropy have advanced our understanding of how convection is recorded in mantle fabrics in the upper mantle. However, we are still debating the relative importance of frozen to actively forming olivine fabrics, subduction zone anisotropy lacks a clear reference model, and regional marine studies yield conflicting evidence as to what exactly is going on at the base of the plates and below. Here, I review the degree of agreement between regional and global observations of seismic anisotropy and how well those may be matched by first-order mantle convection models. Updated bean counting can help contextualize the spatial scales of alignment, and I discuss several examples of the relative roles of plate shear to mantle density anomalies and frozen-in structure for oceanic and continental plates. Resolution of seismological models is globally uneven, but there are some locales where such exercises may yield information on the relative strength of asthenosphere and mantle. Another long-standing question is how olivine fabrics record flow under different stress and volatile conditions. I illustrate how different petrological assumptions might be used to reconcile observations of azimuthal dependency of wave speeds for both Love and Rayleigh waves, and how this could improve our models of the upper mantle, much in the spirit of Montagner's vectorial tomography. This is but one approach to improve the regional realism of global geodynamic background models to understand where in space and time dissonance arises, and if a harmonious model may yet be constructed given our assumptions about the workings of the mantle.

Forearc structure beneath southwestern British Columbia: A three-dimensional tomographic velocity model

USGS Publications Warehouse

Ramachandran, K.; Dosso, S.E.; Spence, G.D.; Hyndman, R.D.; Brocher, T.M.

2005-01-01

This paper presents a three-dimensional compressional wave velocity model of the forearc crust and upper mantle and the subducting Juan de Fuca plate beneath southwestern British Columbia and the adjoining straits of Georgia and Juan de Fuca. The velocity model was constructed through joint tomographic inversion of 50,000 first-arrival times from earthquakes and active seismic sources. Wrangellia rocks of the accreted Paleozoic and Mesozoic island arc assemblage underlying southern Vancouver Island in the Cascadia forearc are imaged at some locations with higher than average lower crustal velocities of 6.5-7.2 km/s, similar to observations at other island arc terranes. The mafic Eocene Crescent terrane, thrust landward beneath southern Vancouver Island, exhibits crustal velocities in the range of 6.0-6.7 km/s and is inferred to extend to a depth of more than 20 km. The Cenozoic Olympic Subduction Complex, an accretionary prism thrust beneath the Crescent terrane in the Olympic Peninsula, is imaged as a low-velocity wedge to depths of at least 20 km. Three zones with velocities of 7.0-7.5 km/s, inferred to be mafic and/or ultramafic units, lie above the subducting Juan de Fuca plate at depths of 25-35 km. The forearc upper mantle wedge beneath southeastern Vancouver Island and the Strait of Georgia exhibits low velocities of 7.2-7.5 km/s, inferred to correspond to ???20% serpentinization of mantle peridotites, and consistent with similar observations in other warm subduction zones. Estimated dip of the Juan de Fuca plate beneath southern Vancouver Island is ???11??, 16??, and 27?? at depths of 30, 40, and 50 km, respectively. Copyright 2005 by the American Geophysical Union.

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 lost generation of impact structures: Imaging the Arctic and Antarctic in magnetics and gravity

NASA Astrophysics Data System (ADS)

Purucker, M. E.

2017-12-01

The process of convection that drives plate tectonics has fragmented the early record on the continents, and subducted it in the oceans. Erosion blurs the upper surfaces of impact structures exposed to the atmosphere beyond recognition after a few million years. The largest confirmed impact structures on the Earth are Vredefort, Chicxulub, and Sudbury, with crater diameters averaging 150 km, and maximum ages of about 2 Ga. Contrast this with the situation at Mars or the Moon, where the largest confirmed impact structures have diameters of 2000 km, and ages of 4 Ga. The giant impact basins that form the most ancient, and most prominent, visible structures on the other terrestrial planets and moons have vanished on the Earth. Only with the use of techniques like magnetics and gravity is it possible to see deeper within the crust. We identify possible impact structure(s) in the Arctic and Antarctic in this way, and discuss techniques that can be used to confirm or refute these identifications.

Neural network analysis for geological interpretation of tomographic images beneath the Japan Islands

NASA Astrophysics Data System (ADS)

Kuwatani, T.; Toriumi, M.

2009-12-01

Recent advances in methodologies of geophysical observations, such as seismic tomography, seismic reflection method and geomagnetic method, provide us a large amount and a wide variety of data for physical properties of a crust and upper mantle (e.g. Matsubara et al. (2008)). However, it has still been difficult to specify a rock type and its physical conditions, mainly because (1) available data usually have a lot of error and uncertainty, and (2) physical properties of rocks are greatly affected by fluid and microstructures. The objective interpretation and quantitative evaluation for lithology and fluid-related structure require the statistical analyses of integrated geophysical and geological data. Self-Organizing Maps (SOMs) are unsupervised artificial neural networks that map the input space into clusters in a topological form whose organization is related to trends in the input data (Kohonen 2001). SOMs are powerful neural network techniques to classify and interpret multiattribute data sets. Results of SOM classifications can be represented as 2D images, called feature maps which illustrate the complexity and interrelationships among input data sets. Recently, some works have used SOM in order to interpret multidimensional, non-linear, and highly noised geophysical data for purposes of geological prediction (e.g. Klose 2006; Tselentis et al. 2007; Bauer et al. 2008). This paper describes the application of SOM to the 3D velocity structure beneath the whole Japan islands (e.g. Matsubara et al. 2008). From the obtained feature maps, we can specify the lithology and qualitatively evaluate the effect of fluid-related structures. Moreover, re-projection of feature maps onto the 3D velocity structures resulted in detailed images of the structures within the plates. The Pacific plate and the Philippine Sea plate subducting beneath the Eurasian plate can be imaged more clearly than the original P- and S-wave velocity structures. In order to understand more precise prediction of lithology and its structure, we will use the additional input data sets, such as tomographic images of random velocity fluctuation (Takahashi et al. 2009) and b-value mapping data. Additionally, different kinds of data sets, including the experimental and petrological results (e.g. Christensen 1991; Hacker et al. 2003) can be applied to our analyses.

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.

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.

Rotation Capacity of Bolted Flush End-Plate Stiffened Beam-to-Column Connection

NASA Astrophysics Data System (ADS)

Ostrowski, Krzysztof; Kozłowski, Aleksander

2017-06-01

One of the flexibility parameters of semi-rigid joints is rotation capacity. Plastic rotation capacity is especially important in plastic design of framed structures. Current design codes, including Eurocode 3, do not posses procedures enabling designers to obtain value of rotation capacity. In the paper the calculation procedure of the rotation capacity for stiffened bolted flush end-plate beam-to-column connections has been proposed. Theory of experiment design was applied with the use of Hartley's PS/DS-P:Ha3 plan. The analysis was performed with the use of finite element method (ANSYS), based on the numerical experiment plan. The determination of maximal rotation angle was carried out with the use of regression analysis. The main variables analyzed in parametric study were: pitch of the bolt "w" (120-180 mm), the distance between the bolt axis and the beam upper edge cg1 (50-90 mm) and the thickness of the end-plate tp (10-20 mm). Power function was proposed to describe available rotation capacity of the joint. Influence of the particular components on the rotation capacity was also investigated. In the paper a general procedure for determination of rotation capacity was proposed.

Mechanisms for creating accommodation space during early Tertiary sedimentation in Tibet.

NASA Astrophysics Data System (ADS)

Studnicki-Gizbert, C.; Burchfiel, B. C.

2003-12-01

The Tibetan plateau is for the most part underlain by rocks of pre-Cenozoic age, a fact that has hindered the identification of Cenozoic shortening structures that can be unequivocally related to the effects of India-Asia collision. Notably, however, the Qiangtang block contains a number of small, short wavelength basins filled with terrestrial sediments of early Tertiary age. Where these basins have been well studied, sedimentation is recognized as having occurred coevally with compressional deformation. The classic treatment of compressional basins appeals to accommodation space created by the flexure of an elastic plate in response to loads created by adjacent thrust fault bound ranges. It is unlikely that the Tertiary basins of the Qiangtang block formed in this manner. The wavelength of a classically modelled flexural basin is a basically a function of the thickness of the elastic plate and the density difference between sedimentary fill and ductile material underlying the plate. Assuming a model of elastic flexure, the very small wavelengths (5 - 30km) characteristic of Qiangtang basins would then imply extremely thin (~ 1-5 km) effective elastic plate thicknesses. These very low values are difficult to reconcile with any reasonable characterization of crustal rheology. Instead, these relatively small basins likely record the creation of accommodation space created by differential uplift across the strike of folds and faults. Stratal geometries and sedimentation rates reflect the kinematics and geometries of local compressional structures and the mechanical basis for the creation of accommodation space remains uncertain. Finally, the origin of these basins makes it unlikely that early Tertiary sedimentation represents a significant fraction of the upper crust of Tibetan plateau.

Marine forearc extension in the Hikurangi Margin: New insights from high-resolution 3D seismic data

NASA Astrophysics Data System (ADS)

Böttner, Christoph; Gross, Felix; Geersen, Jacob; Mountjoy, Joshu; Crutchley, Gareth; Krastel, Sebastian

2017-04-01

In subduction zones upper-plate normal faults have long been considered a tectonic feature primarily associated with erosive margins. However, increasing data coverage has proven that similar features also occur in accretionary margins, such as Cascadia, Makran, Nankai or Central Chile, where kinematics are dominated by compression. Considering their wide distribution there is, without doubt, a significant lack of qualitative and quantitative knowledge regarding the role and importance of normal faults and zones of extension for the seismotectonic evolution of accretionary margins. We use a high-resolution 3D P-Cable seismic volume from the Hikurangi Margin acquired in 2014 to analyze the spatial distribution and mechanisms of upper-plate normal faulting. The study area is located at the upper continental slope in the area of the Tuaheni landslide complex. In detail we aim to (1) map the spatial distribution of normal faults and characterize their vertical throws, strike directions, and dip angles; (2) investigate their possible influence on fluid migration in an area, where gas hydrates are present; (3) discuss the mechanisms that may cause extension of the upper-slope in the study area. Beneath the Tuaheni Landslide Complex we mapped about 200 normal faults. All faults have low displacements (<15 m) and dip at high (> 65°) angles. About 71% of the faults dip landward. We found two main strike directions, with the majority of faults striking 350-10°, parallel to the deformation front. A second group of faults strikes 40-60°. The faults crosscut the BSR, which indicates the base of the gas hydrate zone. In combination with seismically imaged bright-spots and pull-up structures, this indicates that the normal faults effectively transport fluids vertically across the base of the gas hydrate zone. Localized uplift, as indicated by the presence of the Tuaheni Ridge, might support normal faulting in the study area. In addition, different subduction rates across the margin may also favor extension between the segments. Future work will help to further untangle the mechanisms that cause extension of the upper continental slope.

Geological and geodynamic investigations of Alaskan tectonics: Responses in the ancient and modern geologic records to oblique plate convergence

NASA Astrophysics Data System (ADS)

Kalbas, James L.

Stratigraphic, structural, and geophysical modeling studies focusing on both the Mesozoic and modern development of southern Alaska aid in understanding the nature of tectonic responses to oblique plate convergence. Analyses of the Lower to Upper (?) Cretaceous Kahiltna assemblage of the western Alaska Range and the Upper Cretaceous Kuskokwim Group of the northern Kuskokwim Mountains provide a stratigraphic record of orogenic growth in southwestern Alaska. The Kahiltna assemblage records dominantly west-directed gravity-flow transport of sediment to the axis of an obliquely closing basin that made up the suture zone between the allochthonous Wrangellia composite terrane and the North American pericratonic margin. Stratigraphic, compositional, and geochronologic analyses suggest that submarine-fan systems of the Kahiltna basin were fed from the subearial suture zone and contain detrital grains derived from both allochthonous and pericratonic sources, thereby implying a relatively close proximity of the island-arc terrane to the North American margin by late Early Cretaceous time. In contrast, Upper Cretaceous strata exposed immediately west of the Kahiltna assemblage record marine deposition during a period of transition from island arc accretion to strike-slip tectonics. The new stratigraphic model presented here recognizes diverse bathyal- to shelfal-marine depositional systems within the Kuskokwim Group that represent distinctive regional sediment entry points to the basin. Collectively, these strata suggest that the Kuskokwim Group represents the waning stages of marine deposition in a long-lived intra-oceanic and continental margin basin. Geodynamic studies focus on the mechanics of contemporary fault systems in southern Alaska inboard of the collisional Yakutat microplate. Finite-element analyses predict that a poorly understood Holocene strike-slip fault in the St. Elias Mountains transfers shear from the Queen Charlotte fault northward to the Denali fault, thereby forming a continuous transform system that accommodates right-lateral motion of the Pacific plate and Yakutat microplate relative to the stable North American craton. Although the best-fit model implies some component of anelastic deformation in the vicinity of the St. Elias Mountains and the western Alaska Range, results imply overall block-like behavior throughout the area of interest.

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

NASA Astrophysics Data System (ADS)

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

2011-12-01

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

Seismicity and structure of Nazca Plate subduction zone in southern Peru

NASA Astrophysics Data System (ADS)

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

2016-12-01

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

Upper mantle seismic structure beneath southwest Africa from finite-frequency P- and S-wave tomography

NASA Astrophysics Data System (ADS)

Youssof, Mohammad; Yuan, Xiaohui; Tilmann, Frederik; Heit, Benjamin; Weber, Michael; Jokat, Wilfried; Geissler, Wolfram; Laske, Gabi; Eken, Tuna; Lushetile, Bufelo

2015-04-01

We present a 3D high-resolution seismic model of the southwestern Africa region from teleseismic tomographic inversion of the P- and S- wave data recorded by the amphibious WALPASS network. We used 40 temporary stations in southwestern Africa with records for a period of 2 years (the OBS operated for 1 year), between November 2010 and November 2012. The array covers a surface area of approximately 600 by 1200 km and is located at the intersection of the Walvis Ridge, the continental margin of northern Namibia, and extends into the Congo craton. Major questions that need to be understood are related to the impact of asthenosphere-lithosphere interaction, (plume-related features), on the continental areas and the evolution of the continent-ocean transition that followed the break-up of Gondwana. This process is supposed to leave its imprint as distinct seismic signature in the upper mantle. Utilizing 3D sensitivity kernels, we invert traveltime residuals to image velocity perturbations in the upper mantle down to 1000 km depth. To test the robustness of our tomographic image we employed various resolution tests which allow us to evaluate the extent of smearing effects and help defining the optimum inversion parameters (i.e., damping and smoothness) used during the regularization of inversion process. Resolution assessment procedure includes also a detailed investigation of the effect of the crustal corrections on the final images, which strongly influenced the resolution for the mantle structures. We present detailed tomographic images of the oceanic and continental lithosphere beneath the study area. The fast lithospheric keel of the Congo Craton reaches a depth of ~250 km. Relatively low velocity perturbations have been imaged within the orogenic Damara Belt down to a depth of ~150 km, probably related to surficial suture zones and the presence of fertile material. A shallower depth extent of the lithospheric plate of ~100 km was observed beneath the ocean, consistent with plate-cooling models. In addition to tomographic images, the seismic anisotropy measurements within the upper mantle inferred from teleseismic shear waves indicate a predominant NE-SW orientation for most of the land stations. Current results indicate no evidence for a consistent signature of fossil plume.

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.

Semiconductor acceleration sensor

NASA Astrophysics Data System (ADS)

Ueyanagi, Katsumichi; Kobayashi, Mitsuo; Goto, Tomoaki

1996-09-01

This paper reports a practical semiconductor acceleration sensor especially suited for automotive air bag systems. The acceleration sensor includes four beams arranged in a swastika structure. Two piezoresistors are formed on each beam. These eight piezoresistors constitute a Wheatstone bridge. The swastika structure of the sensing elements, an upper glass plate and a lower glass plate exhibit the squeeze film effect which enhances air dumping, by which the constituent silicon is prevented from breakdown. The present acceleration sensor has the following features. The acceleration force component perpendicular to the sensing direction can be cancelled. The cross-axis sensitivity is less than 3 percent. And, the erroneous offset caused by the differences between the thermal expansion coefficients of the constituent materials can be canceled. The high aspect ratio configuration realized by plasma etching facilitates reducing the dimensions and improving the sensitivity of the acceleration sensor. The present acceleration sensor is 3.9 mm by 3.9 mm in area and 1.2 mm in thickness. The present acceleration sensor can measure from -50 to +50 G with sensitivity of 0.275 mV/G and with non-linearity of less than 1 percent. The acceleration sensor withstands shock of 3000 G.

Profiling the robustness, efficiency and limits of the forward-adjoint method for 3-D mantle convection modelling

NASA Astrophysics Data System (ADS)

Price, M. G.; Davies, J. H.

2018-02-01

Knowledge of Earth's past mantle structure is inherently unknown. This lack of knowledge presents problems in many areas of Earth science, including in mantle circulation modelling (MCM). As a mathematical model of mantle convection, MCMs require boundary and initial conditions. While boundary conditions are readily available from sources such as plate reconstructions for the upper surface, and as free slip at the core-mantle boundary, the initial condition is not known. MCMs have historically `created' an initial condition using long `spin up' processes using the oldest available plate reconstruction period available. While these do yield good results when models are run to present day, it is difficult to infer with confidence results from early in a model's history. Techniques to overcome this problem are now being studied in geodynamics, such as by assimilating the known internal structure (e.g. from seismic tomography) of Earth at present day backwards in time. One such method is to use an iterative process known as the forward-adjoint method. While this is an efficient means of solving this inverse problem, it still strains all but the most cutting edge computational systems. In this study we endeavour to profile the effectiveness of this method using synthetic test cases as our known data source. We conclude that savings in terms of computational expense for forward-adjoint models can be achieved by streamlining the time-stepping of the calculation, as well as determining the most efficient method of updating initial conditions in the iterative scheme. Furthermore, we observe that in the models presented, there exists an upper limit on the time interval over which solutions will practically converge, although this limit is likely to be linked to Rayleigh number.

Combined constraints on the structure and physical properties of the East Antarctic lithosphere from geology and geophysics.

NASA Astrophysics Data System (ADS)

Reading, A. M.; Staal, T.; Halpin, J.; Whittaker, J. M.; Morse, P. E.

2017-12-01

The lithosphere of East Antarctica is one of the least explored regions of the planet, yet it is gaining in importance in global scientific research. Continental heat flux density and 3D glacial isostatic adjustment studies, for example, rely on a good knowledge of the deep structure in constraining model inputs.In this contribution, we use a multidisciplinary approach to constrain lithospheric domains. To seismic tomography models, we add constraints from magnetic studies and also new geological constraints. Geological knowledge exists around the periphery of East Antarctica and is reinforced in the knowledge of plate tectonic reconstructions. The subglacial geology of the Antarctic hinterland is largely unknown but the plate reconstructions allow the well-posed extrapolation of major terranes into the interior of the continent, guided by the seismic tomography and magnetic images. We find that the northern boundary of the lithospheric domain centred on the Gamburtsev Subglacial Mountains has a possible trend that runs south of the Lambert Glacier region, turning coastward through Wilkes Land. Other periphery-to-interior connections are less well constrained and the possibility of lithospheric domains that are entirely sub-glacial is high. We develop this framework to include a probabilistic method of handling alternate models and quantifiable uncertainties. We also show first results in using a Bayesian approach to predicting lithospheric boundaries from multivariate data.Within the newly constrained domains, we constrain heat flux (density) as the sum of basal heat flux and upper crustal heat flux. The basal heat flux is constrained by geophysical methods while the upper crustal heat flux is constrained by geology or predicted geology. In addition to heat flux constraints, we also consider the variations in friction experienced by moving ice sheets due to varying geology.

The plume head-continental lithosphere interaction using a tectonically realistic formulation for the lithosphere

NASA Astrophysics Data System (ADS)

Burov, E.; Guillou-Frottier, L.

2005-05-01

Current debates on the existence of mantle plumes largely originate from interpretations of supposed signatures of plume-induced surface topography that are compared with predictions of geodynamic models of plume-lithosphere interactions. These models often inaccurately predict surface evolution: in general, they assume a fixed upper surface and consider the lithosphere as a single viscous layer. In nature, the surface evolution is affected by the elastic-brittle-ductile deformation, by a free upper surface and by the layered structure of the lithosphere. We make a step towards reconciling mantle- and tectonic-scale studies by introducing a tectonically realistic continental plate model in large-scale plume-lithosphere interaction. This model includes (i) a natural free surface boundary condition, (ii) an explicit elastic-viscous(ductile)-plastic(brittle) rheology and (iii) a stratified structure of continental lithosphere. The numerical experiments demonstrate a number of important differences from predictions of conventional models. In particular, this relates to plate bending, mechanical decoupling of crustal and mantle layers and tension-compression instabilities, which produce transient topographic signatures such as uplift and subsidence at large (>500 km) and small scale (300-400, 200-300 and 50-100 km). The mantle plumes do not necessarily produce detectable large-scale topographic highs but often generate only alternating small-scale surface features that could otherwise be attributed to regional tectonics. A single large-wavelength deformation, predicted by conventional models, develops only for a very cold and thick lithosphere. Distinct topographic wavelengths or temporarily spaced events observed in the East African rift system, as well as over French Massif Central, can be explained by a single plume impinging at the base of the continental lithosphere, without evoking complex asthenospheric upwelling.

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 Mesozoic-Cenozoic igneous intrusions and related sediment-dominated hydrothermal activities in the South Yellow Sea Basin, the Western Pacific continental margin

NASA Astrophysics Data System (ADS)

Yumao, Pang; Xunhua, Zhang; Guolin, Xiao; Luning, Shang; Xingwei, Guo; Zhenhe, Wen

2018-04-01

Various igneous complexes were identified in multi-channel seismic reflection profiles from the South Yellow Sea Basin. It is not rare that magmatic intrusions in sedimentary basins cause strong thermal perturbations and hydrothermal activities. Some intrusion-related hydrothermal vent complexes have been identified and they are considered to originate from the deep sedimentary contact aureole around igneous intrusions and terminate in upper vents structures, and are linked by a vertical conduit system. The upper vent complexes are usually eye-shaped, dome-shaped, fault-related, crater-shaped or pock-shaped in seismic profiles. A schematic model was proposed to illustrate the structures of different types of hydrothermal vent complexes. A conceptual conduit model composed of an upper pipe-like part and a lower branching part was also derived. Hydrothermal vent complexes mainly developed during the Middle-Late Cretaceous, which is coeval with, or shortly after the intrusion. The back-arc basin evolution of the area which is related to the subduction of the Paleo-Pacific plate during the Mesozoic-Cenozoic may be the principal factor for voluminous igneous complexes and vent complexes in this area. It is significant to study the characteristics of igneous complexes and related hydrothermal vent complexes, which will have implications for the future study of this area.

Formation of cratonic lithosphere during the initiation of plate tectonics

NASA Astrophysics Data System (ADS)

Moresi, L. N.; Beall, A.; Cooper, C. M.

2017-12-01

The Earth's oldest near-surface material, the cratonic crust, is typically underlain by unusually thick Archean lithosphere (<300 km). This cratonic lithosphere likely thickened in a high compressional stress environment. Mantle convection in the hotter Archean Earth would have imparted relatively low stresses on the lithosphere, whether or not tectonics was operating, so a high stress signal from the early Earth is paradoxical. We propose that a rapid transition, from a stagnant lid Earth to the onset of plate tectonics, generated the high stresses required to thicken the cratonic lithosphere. Numerical calculations are used to demonstrate that an existing buoyant and strong layer, representing harzburgite and felsic crust, can thicken and stabilize during the lid-breaking event. The peak compressional stress experienced by lithosphere is 3-4 higher than for the stagnant lid or mobile lid regimes immediately before and after. It is plausible that the cratonic lithosphere has still not returned to this high stress-state, explaining its stability. The lid-breaking thickening event reproduces craton features previously attributed to subduction: thrust structures, assembled crustal fragments and transport of basaltic upper crust to depths required to generate felsic melt. Palaeoarchean `pre-tectonic' structures can also survive the lid-breaking event, acting as strong crustal rafts. Together, the results indicate that the signature of a catastrophic switch, from a stagnant lid Earth to the initiation of plate tectonics, has been captured and preserved in the unusual characteristics of cratonic crust and lithosphere.

The evolution of shallow crustal structures in early rift-transform interaction: a case study in the northern Gulf of California.

NASA Astrophysics Data System (ADS)

Farangitakis, Georgios-Pavlos; van Hunen, Jeroen; Kalnins, Lara M.; Persaud, Patricia; McCaffrey, Kenneth J. W.

2017-04-01

The Gulf of California represents a young oblique rift/transtensional plate boundary in which all of the transform faults are actively shearing the crust, separated by active rift segments. Previous workers have shown that in the northern Gulf of California, the relative plate motion between the Pacific and North American plates is distributed between: a) the Cerro Prieto Fault (CPF) in the NE b) the Ballenas Transform Fault (BTF) in the SW and c) a pull-apart structure located between these two faults consisting of a number of extensional basins (the Wagner, Consag, and Upper and Lower Delfin basins). A plate boundary relocation at approximately 2 Ma, continued to separate Isla Angel de la Guarda from the Baja California peninsula and created the 200x70 km2 NE-SW pull-apart structure located northeast of the BTF. Here we use seismic stratigraphy analysis of the UL9905 high resolution reflection seismic dataset acquired by the Lamont-Doherty Earth Observatory, Caltech, and the Centro de Investigación Científica y de Educación Superior de Ensenada to build on previous structural interpretations and seek to further understand the processes that formed the structural and sedimentary architecture of the pull-apart basin in the northern Gulf of California. We examine the formation of depositional and deformation structures in relation to the regional tectonics to provide insight into the development of structural patterns and related seismic-stratigraphic features in young rift-transform interactions. Using bathymetric data, characteristic seismic-stratigraphic packages, and seismic evidence of faulting, we confirm the existence of three major structural domains in the northern Gulf of California and examine the interaction of the seismic stratigraphy and tectonic processes in each zone. The first and most distinctive is an abrupt NE-SW 28x5 km2 depression on the seabed of the Lower Delfin Basin. This is aligned orthogonally to the BTF, is situated at its northern end, and is an active rift. The second structural domain is a large, NE-SW-trending anticlinorium 60 km wide to the southeast of the rift zone, towards the Tiburon basin. One possibility is that it represents a positive flower structure and thus indicates a transpressional domain. However, individual structures within the broader zone are normal faults and negative flower structures, suggesting transtensional deformation, and the overall structure may be a roll-over antiform formed on a deep detachment structure. Finally, a strike-slip-dominated zone occurs along the northward continuation of the Ballenas Transform Fault. This is accompanied by the formation of submarine volcanic knolls. These patterns can be compared with seismic stratigraphy facies and structural patterns in mature transform margins and potentially give insight into their early history.

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.

Interseismic deformation at the leading edge of obliquely converging Burmese plate in densely populated Bangladesh.

NASA Astrophysics Data System (ADS)

Akhter, S. H.; Steckler, M. S.; Seeber, L.; Mondal, D. R.; Goodbred, S. L., Jr.

2016-12-01

Densely populated Bangladesh sits at the juncture of 3-tectonic plates, India to the west and southwest, Eurasia to the north and non-rigid Burma platelet to the east. Moreover, the plate boundary between India and Burma passes through Bangladesh - the eastern part belongs to Burma plate while the western part belongs to Indian plate. Eastern Bangladesh, northeastern India and western Myanmar is characterized by the up to 250 km wide and 1400 km long Indo-Burma fold and thrust belt resulting from the oblique convergence of India-Burma plates. The northern extension of the Sumatra-Andaman subduction zone evolved from typical oceanic subduction in the Paleogene to the present subaerial subduction of the Ganges-Brahmaputra Delta. Subduction of the thick sedimentary pile has created the broad accretionary prism that prograding westward in Bangladesh. The deformation front runs near the low elevation Meghna estuary to the south and Sylhet marshes to the north. It is further demarcated by the westernmost buried anticlines of the fold and thrust belt, the Shahbazpur, Muladi, Kamta structures west of the Meghna River and Chatak structure in Sylhet. This position is reinforced by variations in the depth of the Holocene/Pleistocene boundary from shallow drilling. Recent GPS analysis demonstrates that the Indo-Burman subduction in deltaic Bangladesh is still active with convergence of 13 to 17 mm/y and that the décollement beneath the fold-thrust belt is locked (Steckler et. al., 2016). A megathrust earthquake occurred along Chittagong-Arakan coast in 1762 and a great earthquake in Upper Assam in 1548 brought remarkable changes in topography of these regions. A seismic gap exists between these two regions, i.e., in the Chittagong-Sylhet segment. The amount of elastic energy that has been stored in this seismic gap for at least 400 years is likely to slip >6m of the megathrust with a potential earthquake of Mw 8.2+ although it is unknown if the megathrust is seismogenic up to the deformation front.

Megathrust Earthquakes and Sediment Input to the Subduction Channel

NASA Astrophysics Data System (ADS)

Scholl, David W.; Keranen, Katie; von Huene, Roland; Wells, Ray; Ryan, Holly; Kirby, Stephen

2010-05-01

HABITATS OF GREAT MEGATHRUST EARTHQUAKES: Great megathrust earthquakes (Mw8.5 or higher) most commonly (~65%) nucleate along subduction zones (SZ) bordered by laterally continuous (more than 500 km), sediment-flooded trenches. Examples include: south-central Chile (1922, Mw8.5; 1960, Mw9.5), eastern Alaska (1964, Mw9.2), Sumatra (2004, Mw9.1), Cascadia (1700, Mw9.0), Colombia (1906, Mw8.8), Sumatra (1883, Mw8.8), west-central Aleutian (1965, Mw8.7), central Aleutian (1986, Mw8.7), Sumatra (2005, Mw8.6), and Nankai (1707, Mw8.5). All known megathrust events greater than Mw9 ruptured at sediment-charged SZs (Alaska, S.C. Chile, Sumatra). Sediment entering high-seismicity SZs is typically a 1-3-km-thick wedge of trench-axis turbidite beds overlying a 0.3-2-km-thick sequence of hemipelagic or abyssal turbiditic deposits that accrued seaward of the trench. Most commonly, laterally-continuous turbidite wedges are built by down-axis flowing turbidity currents sourced from mountainous and/or glaciated drainages (e.g., SE Alaska, Cascadia, Southern Andes, Himalaya). Great rupture events also occur at SZs receiving little sediment, for example Kamchatka (1952, Mw9.0), Kuril Islands (1963, Mw8.5) and north Chile SZs (1868, Mw9.0). These SZs exhibit evidence of upper plate thinning, subsidence, and truncation effected by frontal and basal subduction erosion. They also have a SC filled with ~1 km or more of debris in transport toward the mantle. WORKINGS OF THE SUBDUCTION CHANNEL (SC): Beneath the submerged forearc, the SC functions to transport subducted ocean floor sediment and tectonically eroded forearc debris toward and ultimately into the mantle. The SC is the lowest structural unit containing upper plate crustal material and the seismogenic zone runs along the SC's upper boundary. It has long been conjectured (e.g., Ruff, 1989; PAGEOPH, v. 129. Nos 1/2) that a laterally uninterrupted, sediment- or debris-charged SC serves to smooth the surface of interplate slip to set up conditions for lengthy, high moment-release ruptures. Maximum slip is commonly concentrated beneath a locally thinned, upper plate crust underlying prominent forearc basins. These structures, in positive feed back, are likely deepened co-seismically by enhance basal subduction erosion. The removed material presumably lowers the effective stress on the decollement and sets up conditions for follow-on events of high, co-seismic slip. The SC also works tectonically to underplate the base of the inner submerged forearc and induce co-seismic uplift at high-angle reverse faults. SEISMIC CONSEQUENCES OF SUBDUCTION ZONE FEEDING: Observations imply that subducted bathymetric ridges and seamounts act to both nucleate seismic rupture and also arrest lateral rupturing. Thick sections of sedimentary and erosional debris entering the subduction channel appear to act differently and favor (1) continuation of rupture, (2) large slip beneath forearc basins, and (3) propogation of slip upward at outer-forearc splay faults and nearshore reverse faults to generate both local and trans-oceanic tsunamis. The potential for nucleation of great megathrust earthquakes along thickly sediment SZs, no matter the rate or lower plate underthrusting, obliquity of convergence, or crustal age, must be set high. Similarly, seismogenic risk for highly erosional SZs little perturbed by subducting relief must also be set high.

Geodetic Imaging of Glacio-Seismotectonic Processes in Southern Alaska

NASA Astrophysics Data System (ADS)

Sauber, J.; Bruhn, R.; Forster, R.; Hofton, M.

2008-12-01

Across southern Alaska the northwest directed motion of the Pacific plate is accompanied by migration and collision of the Yakutat terrane. The Yakutat terrane is a fragment of the North American plate margin that is partly subducted beneath and partly accreted to the continental margin. Over the last couple of decades the rate of ongoing deformation associated with subduction and a locked main thrust zone has been estimated by geodetic measurements. In the last five years more extensive geodetic measurements, structural and tectonic field studies, thermochronolgy, and high-resolution lidar have been acquired and analyzed as part of the STEEP project [Pavlis et al., 2006]. The nature and magnitude of accretion and translation on upper crustal faults and folds remains uncertain, however, due to complex variations in the style of tectonic deformation, pervasive and changing glaciation, and the logistical challenges of conducting field studies in formidable topography. In this study, we analyze new high-resolution lidar data to extract locations, geometry, and heights of seismogenic faults and zones of active folding across the Malaspina-Seward-Bagley region of the southern Alaska plate boundary that is hypothesized to accommodate upper crustal shortening and right-lateral slip. Airborne Topographic Mapper (ATM) lidar swath data acquired by Krabill et al. in the summer of 2005 and ICESat data (1993-present) cross a number of proposed faults and folds partially masked by glaciation, including the Malaspina thrust, Esker Creek, Chugach-St.Elias thrust, and Contact. Focal mechanisms from this region indicate mostly shallow (0-30 km) thrust and oblique strike-slip faulting. Similarly, rupture in the 1979 St. Elias earthquake (M=7.4) started as a shallow, north-dipping thrust that later changed to more steeply NE dipping with a large right-lateral strike-slip component. Additionally, we are using the morphology and dynamics of glaciers derived from L-Band SAR ice velocities and SAR images to infer the large scale sub-ice structures that form the structural framework of the Seward-Bagley Basins. The new lidar, InSAR, and STEEP results provide constraints that enable us to critically re-evaluate alternate models of the nature of tectonics and structures hidden beneath the ice originally proposed by Ford et al [2003] . Ford, A.L., R.R. Forster, and R.L. Bruhn, 2003, Ice surface velocity patterns on Seward Glacier, Alaska/Yukon, and their implications for regional tectonics in the Saint Elias Mountains, Annals of Glaciology, 36, 21-28.

Spatial distribution of reflection intensity of the upper surface of the Philippine Sea plate, near the main slip area of the Boso Slow Slip Events

NASA Astrophysics Data System (ADS)

Kono, A.; Sato, T.; Shinohara, M.; Mochizuki, K.; Yamada, T.; Uehira, K.; Shimbo, T.; Machida, Y.; Hino, R.; Azuma, R.

2017-12-01

Off the Boso Peninsula, Japan, the Pacific plate (PAC) is subducting westward beneath the Honshu Island Arc (HIA) and the Philippine Sea plate (PHS), while the PHS is subducting northwestward under the HIA. Such tectonic interactions have caused various seismic events such as the Boso Slow Slip Events (SSEs). To better understand these seismic events, it is important to determine the structure under this region. In May 2017, we published 2D P-wave velocity structure under the survey area, and showed geometry of the upper surface of PHS (UPHS) and reflection intensity variation along it. From our result and previous studies, relatively strong reflection from the UPHS can be observed near the main slip area of Boso SSEs, and such reflective area may relate with the Boso SSEs. However, it is still insufficient to link both only from the 2D models and further work is needed to reveal spatial distribution of the strong reflection area. From July to August 2009, we conducted a marine seismic experiment using airgun as source off the east coast of the Boso Peninsula. Airgun was shot along the 4 survey lines, and 27 Ocean Bottom Seismometers (OBSs) were deployed in the survey area. In our presentation, we used 18 OBSs to determine 3D P-wave velocity structure. We estimated 3D velocity structure from airgun data recorded in the OBSs by using the FAST (Zelt and Barton, 1998). Next, we picked the reflection traveltimes likely reflected from the UPHS and applied them to the Traveltime mapping method (Fujie et al. 2006) to estimate spatial locations of the reflectors. As a result, reflections from the UPHS seem to concentrate near the main slip area of the Boso SSEs and an area where the serpentine seamount chain of the Izu-Bonin subduction zone is subducting. Acknowledgement The marine seismic experiment was conducted by R/V Hakuhou-maru of Japan Agency for Marine-Earth Science and Technology, and the OBSs were retrieved by Shincho-maru of Shin-Nihon-Kaiji co. Ltd. (Present, Fukada salvage co. Ltd.). We would like to thank captains and the crew of Hakuho-maru and Shincho-maru. This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of japan, under its Observation and Research Program for Prediction of Earthquakes and Volcanic Eruptions, and from the Grants in Aid for Scientific Research (25287109).

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.

Understanding Extension in the Southern Marianas and the Challenger Deep: a 21ST Century Geoscientific Challenge

NASA Astrophysics Data System (ADS)

Stern, R. J.; Ribeiro, J. M.; Martinez, F.; Ohara, Y.

2017-12-01

The Challenger Deep (CD) is the deepest spot on Earth's solid surface and the reasons for its great depth are controversial. In general, trench depths (without sediments) are thought to reflect slab age; old oceanic lithosphere arrives at the trench deeper so similar downbending makes deeper trenches than young oceanic lithosphere. Slab tears and edges and short slabs also may help trenches deepen by making it easier to roll back. In the case of the CD, we are unsure of subducted oceanic lithosphere age because this lies near the juncture of Jurassic and Oligocene crusts. A slab edge to the west and a slab tear to the east may also help the Pacific plate roll back and contribute to its depth. A possible unexamined reason for CD's great depth may be strong extension of the overlying plate associated with opening of the Mariana Trough backarc basin (MT-BAB). GPS on islands indicate southward-increasing extension rates of at least 45mm/yr at the latitude of Guam (Kato et al. 2003 GRL; see Martinez et al. T037 for more info); extension rates are likely to be greater in the MT-BAB north of CD. There are few convergent margins where strong extension affects the overriding plate. Overriding plate extension may help deepen trenches by narrowing the plate coupling zone (Gvirtzman and Stern 2003 Tectonics). Asthenosphere outflow from the shrinking Philippine Sea plate could also push against the slab to depress it. The region around the CD is very deep water, presenting major challenges for future study. The combined deepwater assets and brainpower of the US, Japan, and China are needed to do this work. Both subducting and overriding plates need study. For the downgoing plate, we need IODP drilling and refraction studies to determine its age and crustal and lithospheric structure; electromagnetic sounding would also help reveal upper plate structure. We need passive OBS studies to map slab tears and edges. We need to better understand the tectonic evolution of the MT-BAB-CD region over the last few Ma. To do this, we need better sampling of seafloor basalts to determine their composition and age. Further exploration is needed to find more forearc seeps such as Shinkai Seep Field (Okumura et al. 2016, G3). Understanding the CD and surrounding region provides a natural focus for joint US-Japan-China marine geoscientific research in the 21st Century.

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

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.

The petrology, structure and geochemistry of an Archean terrane in the North Snowy Block, Beartooth Mountains, Montana

NASA Astrophysics Data System (ADS)

Mogk, D. W.

1984-12-01

Six major rock units in the North Snowy Block in an Archean mobile belt are recognized between all units representing discontinuities in metamorphic grade, structural style, geochemistry, and isotopic ages. Four of the units occur in NE trending linear belts; the Basement Gneiss; the phyllitic Davis Creek Schist; the mount cowen augen gneis; the Paragneiss unit. Overlying the linear units is the 3.2 Ga old Pine Creek Nappe Complex, an isoclinally folded, middle to upper amphibolite facies, thrust nappe consisting of the Barney Creek Amphibolite, George Lake Marble and Jewel Quartzite. The highest structural units, including a thick sequence of upper amphibolite grade supracrustal rocks and a lower section of injected 3.4 Ga old granitic to tonalitic migmatitic rocks were emplaced on the Columbine Thrust. It is shown that there was secular variation in tectonic style in the Archean of southwest Montana. Three stages are recognized: (1) melting of ancient matic crust produced trondhjemitic continental nuclei; (2) numerous ensialic basins were created and destroyed, resulting in high grade metamorphism and mignatization of supracrustal rocks; and (3) contemporary style plate tectonics resulted in generation of large volumes of andesities and calc-alkaline granitic rocks, transcurrent faulting, and thrust faulting.

Anatomy of a metamorphic core complex: seismic refraction/wide-angle reflection profiling in southeastern California and western Arizona

USGS Publications Warehouse

McCarthy, J.; Larkin, S.P.; Fuis, G.S.; Simpson, R.W.; Howard, K.A.

1991-01-01

The metamorphic core complex belt in southeastern California and western Arizona is a NW-SE trending zone of unusually large Tertiary extension and uplift. Midcrustal rocks exposed in this belt raise questions about the crustal thickness, crustal structure, and the tectonic evolution of the region. Three seismic refraction/wide-angle reflection profiles were collected to address these issues. The results presented here, which focus on the Whipple and Buckskin-Rawhide mountains, yield a consistent three-dimensiional image of this part of the metamorphic core complex belt. The final model consists of a thin veneer (<2 km) of upper plate and fractured lower plate rocks (1.5-5.5 km s-1) overlying a fairly homogeneous basement (~6.0 km s-1) and a localized high-velocity (6.4 km s -1) body situated beneath the western Whipple Mountains. A prominent midcrustal reflection is identified beneath the Whipple and Buckskin Rawhide mountains between 10 and 20km depth. -from Authors

Lithosphere-asthenosphere interaction beneath Ireland from joint inversion of teleseismic P-wave delay times and GRACE gravity

NASA Astrophysics Data System (ADS)

O'Donnell, J. P.; Daly, E.; Tiberi, C.; Bastow, I. D.; O'Reilly, B. M.; Readman, P. W.; Hauser, F.

2011-03-01

The nature and extent of the regional lithosphere-asthenosphere interaction beneath Ireland and Britain remains unclear. Although it has been established that ancient Caledonian signatures pervade the lithosphere, tertiary structure related to the Iceland plume has been inferred to dominate the asthenosphere. To address this apparent contradiction in the literature, we image the 3-D lithospheric and deeper upper-mantle structure beneath Ireland via non-linear, iterative joint teleseismic-gravity inversion using data from the ISLE (Irish Seismic Lithospheric Experiment), ISUME (Irish Seismic Upper Mantle Experiment) and GRACE (Gravity Recovery and Climate Experiment) experiments. The inversion combines teleseismic relative arrival time residuals with the GRACE long wavelength satellite derived gravity anomaly by assuming a depth-dependent quasilinear velocity-density relationship. We argue that anomalies imaged at lithospheric depths probably reflect compositional contrasts, either due to terrane accretion associated with Iapetus Ocean closure, frozen decompressional melt that was generated by plate stretching during the opening of the north Atlantic Ocean, frozen Iceland plume related magmatic intrusions, or a combination thereof. The continuation of the anomalous structure across the lithosphere-asthenosphere boundary is interpreted as possibly reflecting sub-lithospheric small-scale convection initiated by the lithospheric compositional contrasts. Our hypothesis thus reconciles the disparity which exists between lithospheric and asthenospheric structure beneath this region of the north Atlantic rifted margin.

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.

Protracted tectono-metamorphic history of the SE Superior Province : contribution of 40Ar/39Ar thermochronology in the Abitibi-Opatica contact zone, Québec, Canada

NASA Astrophysics Data System (ADS)

Daoudene, Yannick; Tremblay, Alain; Ruffet, Gilles; Leclerc, François; Goutier, Jean

2015-04-01

Archean orogens mainly consist of greenstone belts juxtaposing deeper crustal domains of TTG-type plutonic rocks. The greenstone belts show regional folds, penetrative steeply-dipping fabrics, and localised shear zones, whereas the plutonic belts predominantly display dome structures. Concurrently, rocks in Archean orogens undergone MT/HT-LP/MP metamorphic conditions that vary, from upper to lower crustal domains, between greenschist- and granulite-facies, respectively. These structural and metamorphic variations are well-documented, but modes of deformation related to such orogens is still debated. Some studies suggest that the Archean tectonic processes were comparable to present-day plate tectonics and the Archean greenstone belts were interpreted as tectonic collages commonly documented in Phanerozoic subduction/collision zones. Alternative models propose that the Archean tectonics were different from those predicted by the plate tectonics paradigm, mainly due to the existence of a hotter mantle and a mechanically weak crust. In such models, the burying and exhumation of crustal rocks are attributed to the vertical transfer of material, resulting in the development of pop-down and domes structures. As a contribution of the study of mechanisms that might have operated during the Archean, we present a structural and metamorphic study of the contact zone between the Abitibi subprovince (ASP), which contains greenstone belts, and the Opatica subprovince (OSP), which is dominated by plutonic rocks, of the Superior Province. The 40Ar/39Ar dating of amphiboles and micas is used to constrain the age and duration of regional metamorphism and associated deformations. On the basis of seismic profiling, showing a north-dipping lithospheric-scale reflector, the ASP-OSP contact has been interpreted as the surficial trace of an Archean subduction zone. However, our structural analysis suggest that the ASP overlies the OSP and that the ASP-OSP contact does not show evidences of an important sub-vertical shearing deformation as expected if it was a major upper plate-lower plate boundary. Furthermore, the contact does not present significant metamorphic break between the two domains, but a progressive increasing of metamorphism toward the OSP, from greenschist- to amphibolite-facies conditions. Based on these structural and metamorphic characteristics, we suggest that the OSP exposes the deepest rocks at outcrop of an ASP-OSP crust in the study area. Regionally, the 40Ar/39Ar ages acquired during this study indicate that the ASP-OSP contact records a protracted metamorphic history that started around 2685 Ma. The structural and isotopic age data suggest that, from ~2685 Ma to ~2632 Ma, the deepest level of the ASP and the underlying OSP reached amphibolite-facies metamorphic conditions and that regional deformation was accommodated by an overall horizontal shortening and sub-vertical transfers of crustal material. Subsequently, the cooling of these crustal rocks was accompanied by strain localisation, which led to the development of oblique strike-slip shear zones from ~2600 Ma, when the lateral flowing of crustal material became predominant. Our 40Ar/39Ar data compared with metamorphic ages documented in adjacent areas of the Superior Province suggests that the peak and duration of regional metamorphism might have been coeval over a large region. This rather favours a mode of pervasive deformation as expected in vertical tectonics.

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.

Velocity model calibration as a tool to improve regional wave moment tensors: Application to the Basin and Range Province

NASA Astrophysics Data System (ADS)

Ichinose, G. A.

2006-12-01

Many scientific issues for the Basin and Range Province (BRP) remain unsettled including structural evolution, strain rates, slip partitioning and earthquake source physics. A catalog of earthquake source parameters including locations and moment tensors is the basis for tectonic and geophysical study. New instrumentation from the Advance National Seismic System, EarthScope Plate Boundary Observatory, Bigfoot and US-Array brings the opportunity for high quality research; therefore, a catalog is an underlying foundation for examining the BRP. We are continuing to generate a moment tensor catalog for the BRP (Mw<3.5) using long-period regional waves spanning back to 1990. Iterative waveform inversion method (e.g., Nolet et al., 1986, Randell, 1994) is used to calibrate the BRP velocity and density structure using two northern and southern BRP earthquakes. The calibrated models generate realistic synthetics for (f<0.5Hz) with ~50-80% variance reduction. We averaged all path specific models to construct a 1-D BRP community background model. The crust is relatively simple between 5-20km (~6.12km/s) and there is a strong velocity gradient in the upper 5- km. There are lower velocities in the upper crust but higher velocities in the mid-crust for the Sierra Nevada paths relative to BRP. There is also a lower crust high-velocity anomaly near Battle Mountain and Elko that is faster by ~5% and may indicate a wider area of under-plating by basaltic magmas. There are significant low velocity zones in the upper and mid crust mainly across the Walker Lane Belt that may indicate the presence of fluids. We are continuing to work on assessing the performance of these newly calibrated models in improving the estimation of moment tensors down to lower magnitudes and mapping out holes in the seismic network which can be filled to improve moment tensor catalog. We also are looking at how these models work at locating earthquakes and comparing synthetics with those computed from models constrained from different data including refraction, surface wave dispersion, and travel-time tomography.

Travel-time Tomography of the Upper Mantle using Amphibious Array Seismic Data from the Cascadia Initiative and EarthScope

NASA Astrophysics Data System (ADS)

Cafferky, S.; Schmandt, B.

2013-12-01

Offshore and onshore broadband seismic data from the Cascadia Initiative and EarthScope provide a unique opportunity to image 3-D mantle structure continuously from a spreading ridge across a subduction zone and into continental back-arc provinces. Year one data from the Cascadia Initiative primarily covers the northern half of the Juan de Fuca plate and the Cascadia forearc and arc provinces. These new data are used in concert with previously collected onshore data for a travel-time tomography investigation of mantle structure. Measurement of relative teleseismic P travel times for land-based and ocean-bottom stations operating during year one was completed for 16 events using waveform cross-correlation, after bandpass filtering the data from 0.05 - 0.1 Hz with a second order Butterworth filter. Maps of travel-time delays show changing patterns with event azimuth suggesting that structural variations exist beneath the oceanic plate. The data from year one and prior onshore travel time measurements were used in a tomographic inversion for 3-D mantle P-velocity structure. Inversions conducted to date use ray paths determined by a 1-D velocity model. By meeting time we plan to present models using ray paths that are iteratively updated to account for 3-D structure. Additionally, we are testing the importance of corrections for sediment and crust thickness on imaging of mantle structure near the subduction zone. Low-velocities beneath the Juan de Fuca slab that were previously suggested by onshore data are further supported by our preliminary tomographic inversions using the amphibious array data.

[Study on shape and structure of calcified cartilage zone in normal human knee joint].

PubMed

Wang, Fuyou; Yang, Liu; Duan, Xiaojun; Tan, Hongbo; Dai, Gang

2008-05-01

To explore the shape and structure of calcified cartilage zone and its interface between the non-calcified articular cartilage and subchondral bone plate. The normal human condyles of femur (n=20) were obtained from the tissue bank donated by the residents, 10 males and 10 females, aged 17-45 years. The longitudinal and transverse paraffin sections were prepared by the routine method. The shape and structure of calcified cartilage zone were observed with the Safranin O/fast green and von kossa stain method. The interface conjunction among zones of cartilage was researched by SEM and the 3D structural model was established by serial sections and modeling technique. Articular bone-cartilage safranin O/fast green staining showed that cartilage was stained red and subchondral bone was stained blue. The calcified cartilage zone was located between the tidemark and cement line. Von kossa staining showed that calcified cartilage zone was stained black and sharpness of structure border. Upper interface gomphosised tightly with the non-calcified cartilage by the wave shaped tidemark and lower interface anchored tightly with the subchondral bone by the uneven comb shaped cement line. The non-calcified cartilage zone was interlocked tightly in the manner of "ravine-engomphosis" by the calcified cartilage zone as observed under SEM, and the subchondral bone was anchored tightly in the manner of"comb-anchor" by the in the calcified cartilage zone 3D reconstruction model. The calcified cartilage zone is an important structure in the articular cartilage. The articular cartilage is fixed firmly into subchondral bone plate by the distinctive conjunct interfaces of calcified cartilage zone.

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.

Net Rotation of the Lithosphere in Mantle Convection Models with Self-consistent Plate Generation

NASA Astrophysics Data System (ADS)

Gerault, M.; Coltice, N.

2017-12-01

Lateral variations in the viscosity structure of the lithosphere and the mantle give rise to a discordant motion between the two. In a deep mantle reference frame, this motion is called the net rotation of the lithosphere. Plate motion reconstructions, mantle flow computations, and inferences from seismic anisotropy all indicate some amount of net rotation using different mantle reference frames. While the direction of rotation is somewhat consistent across studies, the predicted amplitudes range from 0.1 deg/Myr to 0.3 deg/Myr at the present-day. How net rotation rates could have differed in the past is also a subject of debate and strong geodynamic arguments are missing from the discussion. This study provides the first net rotation calculations in 3-D spherical mantle convection models with self-consistent plate generation. We run the computations for billions of years of numerical integration. We look into how sensitive the net rotation is to major tectonic events, such as subduction initiation, continental breakup and plate reorganisations, and whether some governing principles from the models could guide plate motion reconstructions. The mantle convection problem is solved with the finite volume code StagYY using a visco-pseudo-plastic rheology. Mantle flow velocities are solely driven by buoyancy forces internal to the system, with free slip upper and lower boundary conditions. We investigate how the yield stress, the mantle viscosity structure and the properties of continents affect the net rotation over time. Models with large lateral viscosity variations from continents predict net rotations that are at least threefold faster than those without continents. Models where continents cover a third of the surface produce net rotation rates that vary from nearly zero to over 0.3 deg/Myr with rapide increase during continental breakup. The pole of rotation appears to migrate along no particular path. For all models, regardless of the yield stress and the presence of continental material, the most substantial variations in amplitude and direction of rotation occur over a few tenth of millions of years. It suggests that, to first order, the net rotation is closely related to the tectonic make-up of the surface, evolving with the nature of plate boundaries and the physical arrangement of the plates.

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.

Material orientation design of planar structures with prescribed anisotropy classes. Study of rhombic systems

NASA Astrophysics Data System (ADS)

Czubacki, Radosław

2018-01-01

The paper deals with the minimum compliance problem of 2D structures made of a non-homogeneous elastic material. In the first part of the paper a comparison between solutions of Free Material Design (FMD), Cubic Material Design (CMD) and Isotropic Material Design (IMD) is shown for a simply supported plate in a shape of a deep beam, subjected to a concentrated in-plane force at its upper face. The isoperimetric condition fixes the value of the cost of the design expressed as the integral of the trace of the Hooke tensor. In the second part of the paper the material design approaches are extended to rhombic system in 2D. For the rhombic system the material properties of the structures are set, the design variables being the trajectories of anisotropy directions which in 2D are described by one parameter. In the Orthotropic Orientation Design (OOD) no isoperimetric condition is used.

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.

Seismic structure of subducted Philippine Sea plate beneath the southern Ryukyu arc by receiver function and local earthquakes tomography

NASA Astrophysics Data System (ADS)

Nakamura, M.

2012-12-01

Seismic coupling of the Ryukyu subduction zone is assumed to be weak from the lack of historical interplate large earthquakes. However, recent investigation of repeating slow slip events (Heki & Kataoka, 2008), shallow low frequency earthquakes (Ando et al., 2012), and source of 1771 Yaeyama mega-tsunami (Nakamura, 2009), showed that the interplate coupling is not weak in the south of Ryukyu Trench. The biannually repeating SSEs (Mw=6.5) occur at the depth of 20-40 km on the upper interface of the subducted Philippine Sea plate beneath Yaeyama region, where earthquake swarm occurred on 1991 and 1992. To reveal the relation among the crustal structure, earthquake swarms, and occurrence of slow slip events (SSE), local earthquake tomography and receiver function (RF) analysis was computed in the southwestern Ryukyu arc. A tomographic inversion was used to determine P and S wave structures beneath Iriomote Island in the southwestern Ryukyu region for comparison with the locations of the SSE. The seismic tomography (Thurber & Eberhart-Phillips, 1999) was employed. The P- and S- wave arrival time data picked manually by Japan Meteorological Agency (JMA) are used. The 6750 earthquakes from January 2000 to July 2012 were used. For the calculation of the receiver function, the 212 earthquakes whose magnitudes are over 6.0 and epicentral distances are between 30 and 90 degrees were selected. The teleseicmic waveforms observed at two short-period seismometers of the JMA, and one broadband seismometer of F-net of National Research Institute for Earth Science and Disaster Prevention were used. The water level method (the water level is 0.01) is applied to original waveforms. Assuming that each later phase in a RF is the wave converted from P to S at a depth, I transformed the time domain RF into the depth domain one along each ray path in a reference velocity model. The JMA2001 velocity model is used in this study. The results of tomography show that the low Vp and high Vp/Vs anomalies are distributed along the hypocenters in the subducted slab. The plate interface is about 10 km above the slab earthquakes from the trace of negative RF amplitude. The slab earthquakes are distributed along the trace of positive RF amplitude. Therefore the slab earthquakes occur near the oceanic Moho of the PHS. The fault depth of the SSEs corresponds to the plate interface within 5 km. The fault-planes of the SSE are located above the low Vp and high Vp/Vs zone. Assuming that the difference between high Vp/Vs and low Vp/Vs originates to the fluid contents, this would be interpreted that the fluids from the subducted oceanic crust cannot be transported upward and is trapped at the plate interface. The observed strong S-wave reflector (Nakamura, 2001) in the upper interface of the subducted plate also supports the idea. The top of the faults of the SSEs connects to the cluster of earthquake swarms in the lower crust. This suggests that the trapped fluids are transported upward along the faults, accumulates in the lower crust, and induce the swarm of micro-earthquakes in the lower crust.

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.

An Intracratonic Record of North American Tectonics

NASA Astrophysics Data System (ADS)

Lovell, Thomas Rudolph

Investigating how continents change throughout geologic time provides insight into the underlying plate tectonic process that shapes our world. Researchers aiming to understand plate tectonics typically investigate records exposed at plate margins, as these areas contain direct structural and stratigraphic information relating to tectonic plate interaction. However, these margins are also susceptible to destruction, as orogenic processes tend to punctuate records of plate tectonics. In contrast, intracratonic basins are long-lived depressions located inside cratons, shielded from the destructive forces associated with the plate tectonic process. The ability of cratonic basins to preserve sedimentological records for extended periods of geologic time makes them candidates for recording long term changes in continents driven by tectonics and eustacy. This research utilizes an intracratonic basin to better understand how the North American continent has changed throughout Phanerozoic time. This research resolves geochronologic, thermochronologic, and sedimentologic changes throughout Phanerozoic time (>500 Ma) within the intracratonic Illinois Basin detrital record. Core and outcrop sampling provide the bulk of material upon which detrital zircon geochronologic, detrital apatite thermochronologic, and thin section petrographic analyses were performed. Geochronologic evidence presented in Chapters 2 and 3 reveal the Precambrian - Cretaceous strata of the intracratonic Illinois Basin yield three detrital zircon U-Pb age assemblages. Lower Paleozoic strata yield ages corresponding to predominantly cratonic sources (Archean - Mesoproterozoic). In contrast, Middle - Upper Paleozoic strata have a dominant Appalachian orogen (Neoproterozoic - Paleozoic) signal. Cretaceous strata yield similar ages to underlying Upper Paleozoic strata. We conclude that changes in the provenance of Illinois Basin strata result from eustatic events and tectonic forcings. This evidence demonstrates that changes in the detrital record of the Illinois Basin coincide with well-documented, major tectonic and eustatic events that altered and shaped North American plate margins. Chapter 4 presents 24 apatite (U-Th)/He (AHe) ages (3 - 423 Ma) taken from subsurface Cambrian and Pennsylvanian sandstones in the Illinois Basin. Time-temperature simulations used to reproduce these ages predict a basin thermal history with a maximum temperature of 170°C in post-Pennsylvanian time followed by Mesozoic cooling at 0.3°C/Myr. These thermal simulations suggest 3 km of additional post-Pennsylvanian burial (assuming 30°C/km geotherm) followed by subsequent Mesozoic - Cenozoic removal. This burial-exhumation history is concurrent with Late Mesozoic tectoniceustatic fluctuations, including Atlantic and Gulf of Mexico opening, rejuvenation of the Appalachian region, and Gulf of Mexico sediment influx, and the Cretaceous high sea level stand. The Geochronologic and thermochronologic evidence presented in the following chapters suggests the Illinois Basin potentially contains a more robust record of North American tectonics than previously thought. These observations provide a new perspective on the utility of intracratonic basins in understanding long term changes to continental bodies.

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.

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.

Three-dimensional inversion of regional P and S arrival times in the East Aleutians and sources of subduction zone gravity highs

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

Abers, G.A.

1994-03-10

Free-air gravity highs over forearcs represent a large fraction of the power in the Earth`s anomalous field, yet their origin remains uncertain. Seismic velocities, as indicators of density, are estimated here as a means to compare the relative importance of upper plate sources for the gravity high with sources in the downgoing plate. P and S arrival times for local earthquakes, recorded by a seismic network in the eastern Aleutians, are inverted for three-dimensional velocity structure between the volcanic arc and the downgoing plate. A three-dimensional ray tracing scheme is used to invert the 7974 P and 6764 S arrivalsmore » for seismic velocities and hypocenters of 635 events. One-dimensional inversions show that station P residuals are systematically 0.25 - 0.5 s positive at stations 0-30 km north of the Aleutian volcanic arc, indicating slow material, while residuals at stations 10-30 km south of the arc are 0.1-0.25 s negative. Both features are explained in three-dimensional inversions by velocity variations at depths less than 25-35 km. Tests using a one-dimensional or a two-dimensional slab starting model show that below 100 km depth, velocities are poorly determined and trade off almost completely with hypocenters for earthquakes at these depths. The locations of forearc velocity highs, in the crust of the upper plate, correspond to the location of the gravity high between the trench and volcanic arc. Free-air anomalies, calculated from the three-dimensional velocity inversion result, match observed gravity for a linear density-velocity relationship between 0.1 and 0.3 (Mg m{sup {minus}3})/(km s{sup {minus}1}), when a 50-km-thick slab is included with a density of 0.055{+-}0.005 Mg m{sup {minus}3}. Values outside these ranges do not match the observed gravity. The slab alone contributes one third to one half of the total 75-150 mGal amplitude of the gravity high but predicts a high that is much broader than is observed.« less

Tectonic predictions with mantle convection models

NASA Astrophysics Data System (ADS)

Coltice, Nicolas; Shephard, Grace E.

2018-04-01

Over the past 15 yr, numerical models of convection in Earth's mantle have made a leap forward: they can now produce self-consistent plate-like behaviour at the surface together with deep mantle circulation. These digital tools provide a new window into the intimate connections between plate tectonics and mantle dynamics, and can therefore be used for tectonic predictions, in principle. This contribution explores this assumption. First, initial conditions at 30, 20, 10 and 0 Ma are generated by driving a convective flow with imposed plate velocities at the surface. We then compute instantaneous mantle flows in response to the guessed temperature fields without imposing any boundary conditions. Plate boundaries self-consistently emerge at correct locations with respect to reconstructions, except for small plates close to subduction zones. As already observed for other types of instantaneous flow calculations, the structure of the top boundary layer and upper-mantle slab is the dominant character that leads to accurate predictions of surface velocities. Perturbations of the rheological parameters have little impact on the resulting surface velocities. We then compute fully dynamic model evolution from 30 and 10 to 0 Ma, without imposing plate boundaries or plate velocities. Contrary to instantaneous calculations, errors in kinematic predictions are substantial, although the plate layout and kinematics in several areas remain consistent with the expectations for the Earth. For these calculations, varying the rheological parameters makes a difference for plate boundary evolution. Also, identified errors in initial conditions contribute to first-order kinematic errors. This experiment shows that the tectonic predictions of dynamic models over 10 My are highly sensitive to uncertainties of rheological parameters and initial temperature field in comparison to instantaneous flow calculations. Indeed, the initial conditions and the rheological parameters can be good enough for an accurate prediction of instantaneous flow, but not for a prediction after 10 My of evolution. Therefore, inverse methods (sequential or data assimilation methods) using short-term fully dynamic evolution that predict surface kinematics are promising tools for a better understanding of the state of the Earth's mantle.

New Constraints on Extensional Environments through Analysis of Teleseisms

NASA Astrophysics Data System (ADS)

Eilon, Zachary Cohen

We apply a variety of teleseismic methodologies to investigate the upper mantle structure in extensional environments. Using a body wave dataset collected from a regional deployment in the Woodlark Rift, Papua New Guinea, we image anisotropic velocity structure of a rapidly extending rift on the cusp of continental breakup. In the process, we develop a technique for azimuthal anisotropy tomography that is generally applicable to regions of relatively simple anisotropic structure. The Cascadia Initiative ocean bottom seismometer (OBS) deployment provides coverage of an entire oceanic plate in unprecedented detail; we measure attenuation and velocities of teleseisms to characterize the temperature and melt structure from ridge to trench. Our study of shear wave splitting reveals strong azimuthal anisotropy within the Woodlark Rift with fairly uniform fast directions parallel to extension. This observation differs markedly from other continental rifts and resembles the pattern seen at mid-ocean ridges. This phenomenon is best explained by extension-related strain causing preferential alignment of mantle olivine. We develop a simple relationship that links total extension to predicted splitting, and show that it explains the apparent dichotomy in rifts' anisotropy. Finite frequency tomography using a dataset of teleseismic P- and S-wave differential travel times reveals the upper mantle velocity structure of the Woodlark Rift. A well developed slow rift axis extending >250 km along strike from the adjacent seafloor spreading centers demonstrates the removal of mantle lithosphere prior to complete crustal breakup. We argue that the majority of this rift is melt-poor, in agreement with geochemical results. A large temperature gradient arises from the juxtaposition of upwelled axial asthenosphere with a previously unidentified cold structure north of the rift that hosts well located intermediate depth earthquakes. Localization of upper mantle extension is apparent from the velocity structure of the rift axis and may result from the presence of water following recent subduction. In order to resolve potential tradeoffs between anisotropy and velocity gradients, we develop a novel technique for the joint inversion of Delta VS and strength of azimuthal anisotropy using teleseismic direct S-waves. This approach exploits the natural geometry of the regional tectonics and the relative consistency of observed splits; the imposed orthogonality of anisotropic structure takes care of the non-commutative nature of multi-layer splitting. Our tomographic models reveal the breakup of continental lithosphere in the anisotropy signal, as pre-existing fabric breaks apart and is replaced by upwelling asthenosphere that simultaneously advects and accrues an extension-related fabric. Accounting for anisotropy removes apparent noise in isotropic travel times and clarifies the velocity model. Taken together, our results paint a detailed and consistent picture of a highly extended continental rift. Finally, we collect a dataset of differential travel time (delta T) and attenuation (Deltat*) measurements of P- and S-waves recorded on OBS stations that span the Juan de Fuca and Gorda plates. We observe large gradients in Delta t*, with values as high as 2.0 s for S-waves at the ridge axes. Such high values of differential attenuation are not compatible with a purely thermal control, nor are they consistent with focusing effects. We assert that melt, grainsize, and water enhance anelastic effects beneath the ridge. The combination of attenuation and velocity measurements enables us to place quantitative constraints on the properties of the upper mantle in the vicinity of the spreading axis.

Geodynamic models of the deep structure of the natural disaster regions of the Earth

NASA Astrophysics Data System (ADS)

Rodnikov, A. G.; Sergeyeva, N. A.; Zabarinskaya, L. P.

2012-04-01

Investigation of the deep structure and creation of geodynamic models of natural disaster regions are important for understanding of the nature of such phenomena as earthquakes, eruptions of volcanoes, tsunami and others. Carrying out of such researches is necessary for definition of areas of potential risk, forecasting and the prevention of negative consequences of acts of nature. Research region is active continental margins of the Sea of Okhotsk, and especially the area of Neftegorsk earthquake which has occurred on May, 28th 1995 in the North Sakhalin and caused many victims and destructions. The geodynamic model of the lithosphere in the region of Neftegorsk earthquake has been constructed along the profile crossing the North Sakhalin Basin, Deryugin Basin and ophiolite complex between them. The Deryugin Basin was formed at the site of an ancient deep trench after the subduction of the Okhotsk Sea Plate under Sakhalin. The basin is located above a hot plume in the mantle at a depth of 25 km. The ophiolite belt of ultramafic magmatic rocks is an ancient (K2-Pg) paleosubduction zone separating the Deryugin basin from the North Sakhalin Basin. The thickness of the ancient seismic focal zone is 80 km. It is probably that the structures of the North Sakhalin have been formed in the following way. In the Late Cretaceous the oceanic Okhotsk Sea Plate subducted under Sakhalin, the eastern part of which was an andesite island arc. Approximately in Miocene the subduction of the plate apparently ceased. In that time the Tatar Rift Strait was formed. Ophiolite rocks of the subduction zones as a result of compression have been squeezed out on a surface. The ophiolite complex combined by the ultrabasic rocks, fixes position of ancient subduction zone. It is probable that the manifestation of the Neftegorsk earthquake was a result of activization of this ancient subduction zone. On a surface the subduction zone manifests itself as deep faults running along Sakhalin. The center of the Neftegorsk earthquake was directly formed by burst of activity of this ancient subduction zone. From a position of the ancient subduction zone under Sakhalin, which is a cause of strong earthquakes here, it follows that the region is one of seismic dangerous in Russia. Constructed on the basis of complex interpretation of the geologic-geophysical data the geodynamic models of natural disaster regions give the chance: to study a deep structure under seismic dangerous zones; to investigate a role of deep processes in the upper mantle in formation of structures of earth crust; to relate the geological features, tectonomagmatic, hydrothermal activity with the processes in the upper mantle; to plot maps in detail with zones of increasing risks to prevent active building or other economic activities in such dangerous regions.

3D Rheological Modeling of NW Intraplate Europe, Deciphering Spatial Integrated strength patterns, Mechanical Strong Layering and EET

NASA Astrophysics Data System (ADS)

Beekman, F.; Hardebol, N.; Cloetingh, S.; Tesauro, M.

2006-12-01

Better understanding of 3D rheological heterogeneity of the European Lithosphere provide the key to tie the recorded intraplate deformation pattern to stress fields transmitted into plate interior from plate boundary forces. The first order strain patterns result from stresses transmitted through the European lithosphere that is marked by a patchwork of high strength variability from inherited structural and compositional heterogeneities and upper mantle thermal perturbations. As the lithospheric rheology depends primarily on its spatial structure, composition and thermal estate, the 3D strength model for the European lithosphere relies on a 3D compositional model that yields the compositional heterogeneities and an iteratively calculated thermal cube using Fouriers law for heat conduction. The accurate appraisal of spatial strength variability results from proper mapping and integration of the geophysical compositional and thermal input parameters. Therefore, much attention has been paid to a proper description of first order structural and tectonic features that facilitate compilation of the compositional and thermal input models. As such, the 3D strength model reflects the thermo-mechanical structure inherited from the Europeans polyphase deformation history. Major 3D spatial mechanical strength variability has been revealed. The East-European and Fennoscandian Craton to the NE exhibit high strength (30-50 1012 N/m) from low mantle temperatures and surface heatflow of 35-60 mW/m2 while central and western Europe reflect a polyphase Phanerozoic thermo- tectonic history. Here, regions with high rigidity are formed primarily by patches of thermally stabilized Variscan Massifs (e.g. Rhenish, Armorican, Bohemian, and Iberian Massif) with low heatflow and lithospheric thickness values (50-65 mW/m2; 110-150 km) yielding strengths of ~15-25 1012 N/m. In contrast, major axis of weakened lithosphere coincides with Cenozoic Rift System (e.g. Upper and Lower Rhine Grabens, Pannonian Basin and Massif Central) attributed to the presence of tomographically imaged plumes. This study has elucidated the memory of the present-days Europeans lithosphere induced by compositional and thermal heterogeneities. The resulting lateral strength variations has a clear signature of the pst lithospheres polyphase deformation and also entails active tectonics, tectonically induced topography and surface processes.

An oceanic plateau subduction offshore Eastern Java

NASA Astrophysics Data System (ADS)

Shulgin, A.; Kopp, H.; Mueller, C.; Planert, L.; Lueschen, E.; Flueh, E. R.; Djajadihardja, Y.

2010-12-01

The area offshore Java represents one of a few places globally where the early stage of subduction of an oceanic plateau is observed. We study the little investigated Roo Rise oceanic plateau on the Indian plate, subducting beneath Eurasia.Our study area is located south of eastern Java and covers the edge of the Roo Rise plateau, the Java trench and the entire forearc section. For the first time the detailed deep structure of the Roo Rise is studied, subduction of which has a significant effect on the forearc dynamics and evolution and the increase of the geohazards risks. The tsunamogenic earthquakes of 1994 and 2006 are associated with the oceanic plateau edge been subducted. We present integrated results of a refraction/wide-angle reflection tomography, gravity modeling, and multichannel reflection seismic imaging using data acquired in 2006 along a corridor centered around 113°E and composed of a 340 km long N-S profile and a 130 km long E-W oriented profile. The composite structural models reveal the previously unresolved deep geometry of the collision zone and the structure of the oceanic plateau. The crustal thickness of the Roo Rise plateau is ranging from 18 to 12 km. The structure of the upper crust of the incoming oceanic plate shows the extreme degree of fracturing in its top section, and is associated with a plate bending. The forearc Moho has a depth range from 16 to 20 km. The gravity modeling requires a sharp crustal thickness increase below Java. Within our profiles we do not recover any direct evidence for the presence of the bathymetric features on the oceanic plate currently present below the accretionary prism, responsible for the tsunamogenic earthquake triggering. However vertical variations of the forearc basement edge are observed on the trench-parallel profile, which opens a discussion on the origin of such basement undulations, together with a localized patchy uplift character of the forearc high.The complex geometry of the backstop suggests two models for the structural formation within this segment of the margin. The subducting plateau is affecting the stress field within the accretionary complex and the backstop edge, which favors the initiation of large, potentially tsunamogenic earthquakes such as the 1994 Mw=7.8 tsunamogenic event.

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.

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.

Characterization of dermal plates from armored catfish Pterygoplichthys pardalis reveals sandwich-like nanocomposite structure.

PubMed

Ebenstein, Donna; Calderon, Carlos; Troncoso, Omar P; Torres, Fernando G

2015-05-01

Dermal plates from armored catfish are bony structures that cover their body. In this paper we characterized structural, chemical, and nanomechanical properties of the dermal plates from the Amazonian fish Pterygoplichthys pardalis. Analysis of the morphology of the plates using scanning electron microscopy (SEM) revealed that the dermal plates have a sandwich-like structure composed of an inner porous matrix surrounded by two external dense layers. This is different from the plywood-like laminated structure of elasmoid fish scales but similar to the structure of osteoderms found in the dermal armour of some reptiles and mammals. Chemical analysis performed using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) results revealed similarities between the composition of P. pardalis plates and the elasmoid fish scales of Arapaima gigas. Reduced moduli of P. pardalis plates measured using nanoindentation were also consistent with reported values for A. gigas scales, but further revealed that the dermal plate is an anisotropic and heterogeneous material, similar to many other fish scales and osteoderms. It is postulated that the sandwich-like structure of the dermal plates provides a lightweight and tough protective layer. Copyright © 2015 Elsevier Ltd. All rights reserved.

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

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.

Bussing Structure In An Electrochemical Cell

DOEpatents

Romero, Antonio L.

2001-06-12

A bussing structure for bussing current within an electrochemical cell. The bussing structure includes a first plate and a second plate, each having a central aperture therein. Current collection tabs, extending from an electrode stack in the electrochemical cell, extend through the central aperture in the first plate, and are then sandwiched between the first plate and second plate. The second plate is then connected to a terminal on the outside of the case of the electrochemical cell. Each of the first and second plates includes a second aperture which is positioned beneath a safety vent in the case of the electrochemical cell to promote turbulent flow of gasses through the vent upon its opening. The second plate also includes protrusions for spacing the bussing structure from the case, as well as plateaus for connecting the bussing structure to the terminal on the case of the electrochemical cell.

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.

The vibroacoustic response and sound absorption performance of multilayer, microperforated rib-stiffened plates

NASA Astrophysics Data System (ADS)

Zhou, Haian; Wang, Xiaoming; Wu, Huayong; Meng, Jianbing

2017-10-01

The vibroacoustic response and sound absorption performance of a structure composed of multilayer plates and one rigid back wall are theoretically analyzed. In this structure, all plates are two-dimensional, microperforated, and periodically rib-stiffened. To investigate such a structural system, semianalytical models of one-layer and multilayer plate structures considering the vibration effects are first developed. Then approaches of the space harmonic method and Fourier transforms are applied to a one-layer plate, and finally the cascade connection method is utilized for a multilayer plate structure. Based on fundamental acoustic formulas, the vibroacoustic responses of microperforated stiffened plates are expressed as functions of a series of harmonic amplitudes of plate displacement, which are then solved by employing the numerical truncation method. Applying the inverse Fourier transform, wave propagation, and linear addition properties, the equations of the sound pressures and absorption coefficients for the one-layer and multilayer stiffened plates in physical space are finally derived. Using numerical examples, the effects of the most important physical parameters—for example, the perforation ratio of the plate, sound incident angles, and periodical rib spacing—on sound absorption performance are examined. Numerical results indicate that the sound absorption performance of the studied structure is effectively enhanced by the flexural vibration of the plate in water. Finally, the proposed approaches are validated by comparing the results of stiffened plates of the present work with solutions from previous studies.

Mobility power flow analysis of coupled plate structure subjected to mechanical and acoustic excitation

NASA Technical Reports Server (NTRS)

Cuschieri, J. M.

1992-01-01

The mobility power flow approach that was previously applied in the derivation of expressions for the vibrational power flow between coupled plate substructures forming an L configuration and subjected to mechanical loading is generalized. Using the generalized expressions, both point and distributed mechanical loads on one or both of the plates can be considered. The generalized approach is extended to deal with acoustic excitation of one of the plate substructures. In this case, the forces (acoustic pressures) acting on the structure are dependent on the response of the structure because of the scattered pressure component. The interaction between the plate structure and the acoustic fluid leads to the derivation of a corrected mode shape for the plates' normal surface velocity and also for the structure mobility functions. The determination of the scattered pressure components in the expressions for the power flow represents an additional component in the power flow balance for the source plate and the receiver plate. This component represents the radiated acoustical power from the plate structure. For a number of coupled plate substrates, the acoustic pressure generated by one substructure will interact with the motion of another substructure. That is, in the case of the L-shaped plate, acoustic interaction exists between the two plate substructures due to the generation of the acoustic waves by each of the substructures. An approach to deal with this phenomena is described.

Separator plate for a fuel cell

DOEpatents

Petri, R.J.; Meek, J.; Bachta, R.P.; Marianowski, L.G.

1996-04-02

A separator plate is described for a fuel cell comprising an anode current collector, a cathode current collector and a main plate, the main plate disposed between the anode current collector and the cathode current collector. The anode current collector forms a flattened peripheral wet seal structure and manifold wet seal structure on the anode side of the separator plate and the cathode current collector forms a flattened peripheral wet seal structure and manifold wet seal structure on the cathode side of the separator plate. In this manner, the number of components required to manufacture and assemble a fuel cell stack is reduced. 9 figs.

Separator plate for a fuel cell

DOEpatents

Petri, Randy J.; Meek, John; Bachta, Robert P.; Marianowski, Leonard G.

1996-01-01

A separator plate for a fuel cell comprising an anode current collector, a cathode current collector and a main plate, the main plate disposed between the anode current collector and the cathode current collector. The anode current collector forms a flattened peripheral wet seal structure and manifold wet seal structure on the anode side of the separator plate and the cathode current collector forms a flattened peripheral wet seal structure and manifold wet seal structure on the cathode side of the separator plate. In this manner, the number of components required to manufacture and assemble a fuel cell stack is reduced.

Geology of Raymond Canyon, Sublette Range, western Wyoming

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

Shoemaker, W.A.

1984-07-01

Raymond Canyon is located on the west side of the Sublette Range, Lincoln County, Wyoming. The study area is just east of the Idaho border and 10 mi (16 km) southeast of Geneva, Idaho. Formations exposed range in age from Late Pennsylvanian to Tertiary (Pliocene) and include: the lower part of the Wells Formation (Pennsylvanian, total thickness 720 ft or 219 m); the upper part of the Wells Formation and the Phosphoria Formation (both Permian, 153-210 ft or 47-64 m); the Dinwoody Formation (185 ft or 56 m); Woodside Shale (540 ft or 165 m); Thaynes Limestone (2345 ft ormore » 715 m); and Ankareh Formation (930 ft or 283 m), all of Triassic age; the Nugget Sandstone (1610 ft or 491 m), Twin Creek Limestone, Preuss Sandstone, and Stump Formation, all of Jurassic age; and the Salt Lake formation and the Sublette conglomerate, both Pliocene postorogenic continental deposits. Generally these formations are thinner than in nearby areas to the west and northwest. Raymond Canyon lies on the upper plate of the Tunp thrust and the lower plate of the Crawford thrust of the Idaho-Wyoming thrust belt. Thus, it lies near the middle of the imbricate stack of shallowly dipping thrust faults that formed in the late Mesozoic. Study of the stratigraphy, structure, petrography, and inferred depositional environments exposed in Raymond Canyon may be helpful to those engaged in energy development in the Idaho-Wyoming thrust belt.« less

New Insight Into The Crustal Structure of The Continental Margin Off NW Sabah/borneo

NASA Astrophysics Data System (ADS)

Barckhausen, U.; Franke, D.; Behain, D.; Meyer, H.

The continental margin offshore NW Sabah/Borneo (Malaysia) has been investigated with reflection and refraction seismics, magnetics, and gravity during the recent cruise BGR01-POPSCOMS. A total of 4000 km of geophysical profiles has been acquired, thereof 2900 km with reflection seismics. Like in major parts of the South China Sea, the area seaward of the Sabah Trough consists of extended continental lithosphere. We found evidence that the continental crust also underlies the continental slope land- ward of the Trough, a fact that raises many questions about the tectonic history and development of this margin. The characteristic pattern of rotated fault blocks and half grabens and the carbon- ates which are observed all over the Dangerous Grounds can be traced a long way landward of the Sabah Trough beneath the sedimentary succession of the upper plate. The magnetic anomalies which are dominated by the magnetic signatures of relatively young volcanic features also continue under the continental slope. The sedimentary rocks of the upper plate, in contrast, seem to generate hardly any magnetic anoma- lies. We suspect that the volcanic activity coincided with the collision of Borneo and the Dangerous Grounds in middle or late Miocene time. The emplacement of an al- lochtonous terrane on top of the extended continental lithosphere could be explained by overthrusting as a result of the collision or it could be related to gravity sliding following a broad uplift of NW Borneo at the same time.

An oceanic plateau subduction: A case study offshore Eastern Java.

NASA Astrophysics Data System (ADS)

Shulgin, Alexey; Kopp, Heidrun; Mueller, Christian; Planert, Lars; Lueschen, Ewald; Flueh, Ernst; Djajadihardja, Yusuf

2010-05-01

The area offshore Java represents one of a few places globally where the early stage of subduction of an oceanic plateau is observed. Our study area is located south of eastern Java and covers the edge of the Roo Rise plateau, the Java trench and the entire forearc section. For the first time the detailed deep structure of the Roo Rise is studied, subduction of which has a significant effect on the forearc dynamics and evolution and the increase of the geohazards risks. The tsunamogenic earthquakes of 1994 and 2006 are associated with the oceanic plateau edge been subducted. We present integrated results of a refraction/wide-angle reflection tomography, gravity modeling, and multichannel reflection seismic imaging using data acquired in 2006 along a corridor centered around 113°E and composed of a 340 km long N-S profile and a 130 km long E-W oriented profile. The composite structural models reveal the previously unresolved deep geometry of the collision zone and the structure of the oceanic plateau. The crustal thickness of the Roo Rise plateau is ranging from 18 to 12 km. The structure of the upper crust of the incoming oceanic plate shows the extreme degree of fracturing in its top section, and is associated with a plate bending. The forearc Moho has a depth range from 16 to 20 km. The gravity modeling requires a sharp crustal thickness increase below Java. Within our profiles we do not recover any direct evidence for the presence of the bathymetric features on the oceanic plate currently present below the accretionary prism, responsible for the tsunamogenic earthquake triggering. However vertical variations of the forearc basement edge are observed on the trench-parallel profile, which opens a discussion on the origin of such basement undulations, together with a localized patchy uplift character of the forearc high.

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

Rotation, narrowing and preferential reactivation of brittle structures during oblique rifting

NASA Astrophysics Data System (ADS)

Huismans, R. S.; Duclaux, G.; May, D.

2017-12-01

Occurrence of multiple faults populations with contrasting orientations in oblique continental rifts and passive margins has long sparked debate about relative timing of deformation events and tectonic interpretations. Here, we use high-resolution three-dimensional thermo-mechanical numerical modeling to characterize the evolution of the structural style associated with moderately oblique rifting in the continental lithosphere. Automatic analysis of the distribution of active extensional shears at the surface of the model demonstrates a characteristic deformation sequence. We show that upon localization, Phase 1 wide oblique en-échelon grabens develop, limited by extensional shears oriented orthogonal to σ3. Subsequent widening of the grabens is accompanied by a progressive rotation of the Phase 1 extensional shears that become sub-orthogonal the plate motion direction. Phase 2 is marked by narrowing of active deformation resulting from thinning of the continental lithosphere and development of a second-generation of extensional shears. During Phase 2 deformation localizes both on plate motion direction-orthogonal structures that reactivate rotated Phase 1 shears, and on new oblique structures orthogonal to σ3. Finally, Phase 3 consists in the oblique rupture of the continental lithosphere and produces an oceanic domain where oblique ridge segments are linked with highly oblique accommodation zones. We conclude that while new structures form normal to σ3 in an oblique rift, progressive rotation and long-term reactivation of Phase 1 structures promotes orthorhombic fault systems, critical to accommodate upper crustal extension and control oblique passive margin architecture. The distribution, orientation, and evolution of frictional-plastic structures observed in our models is remarkably similar to documented fault populations in the Gulf of Aden conjugate passive margins, which developed in moderately oblique extensional settings.

Topography of the Central Alps in the light of Tertiary collisional tectonics

NASA Astrophysics Data System (ADS)

Rosenberg, Claudio; Garcia, Sebastian

2013-04-01

Collisional shortening in the Central Alps is partitioned very differently between the upper and lower plates along the strike of the orogen. North of the Insubric Line, the amount of post-nappe shortening accommodated in the wedge of accreted lower crustal material, increases westwards, whereas south of the Insubric Line, post-nappe shortening accommodated in the upper plate increases eastward (Rosenberg and Kissling, 2013). Taking the Bergell pluton as a time marker, the age of these deformations is inferred to be post 30 Ma. We investigate the present-day topography of the Central Alps, in order to test whether the systematic, along-strike changes, in the amounts of post-nappe shortening are associated to a systematic change in the topographic signature. In order to do so, the maximum and minimum elevations, and the local relief along a series of N-S sections are analysed and compared. The analysis of these topographic sections shows that the local relief varies following two along-strike trends: 1. North of the Insubric Line, i.e. in the wedge of accreted lower crust, the relief decreases from west to east, showing the transition from a highly incised topography in the west to a plateau-like topography in the East. 2. South of the Insubric Line, i.e. in the lower plate, the relief increases from East to West. These trends point to a positive correlation between the amount of shortening and the intensity of local relief. Linear correlations between local relief and uplift rate (e.g. Hurtez et al., 1999), and between local relief and shortening rates (Champagnac et al., 2012) have been inferred for different, tectonically active areas. Areas of larger finite shortening in the Central Alps, characterized by higher local relief, probably correspond to areas of higher shortening (and uplift) rates during Alpine collision. Considering the very slow, present-day, convergent movements across the Central Alps (Noquet and Calais, 2004) it is not clear whether the observed correlation between shortening and relief is the result of past, but still active tectonics or a well preserved relict of Miocene teconic activity. References: Champagnac, J.-D., P. Molnar, C. Sue, and F. Herman (2012), Tectonics, climate, and mountain topography, J. Geophys. Res., 117, B02403, doi:10.1029/2011JB008348. Hurtez, J._E., Lucazeau, F., Lavé, J., and Avouac, J.-P. (1999), Investigation of the relationships between basin morphology, tectonic uplift, and denudation from the study of an active fold belt in the Siwalik Hills, central Nepal. J. Geophys. Res., 104, NO. B6, PAGES 12,779-12,796 Nocquet, J.-M. and Calais, E. (2004), Geodetic measurements of crustal deformation in the Western Mediterranean and Europe. Pure and Applied Geophysics, 161, 661-681, doi:10.1007/s00024-003-2468-z Rosenberg, C.L. and Kissling, E. (2013), 3D Structure of collision in the Central Alps: lower-plate or upper-plate indentation? EGU Abstract volume, EGU2013-ASC-2013-7946.

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.

Quasi-discrete particle motion in an externally imposed, ordered structure in a dusty plasma at high magnetic field

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

Thomas, Edward, E-mail: etjr@auburn.edu; Konopka, Uwe; Lynch, Brian

Dusty plasmas have been studied in argon, radio frequency (rf) glow discharge plasmas at magnetic fields up to 2.5 T where the electrons and ions are strongly magnetized. Plasmas are generated between two parallel plate electrodes where the lower, powered electrode is solid and the upper electrode supports a dual mesh consisting of #24 brass and #30 aluminum wire cloth. In this experiment, we study the formation of imposed ordered structures and particle dynamics as a function of magnetic field. Through observations of trapped particles and the quasi-discrete (i.e., “hopping”) motion of particles between the trapping locations, it is possible tomore » make a preliminary estimate of the potential structure that confines the particles to a grid structure in the plasma. This information is used to gain insight into the formation of the imposed grid pattern of the dust particles in the plasma.« less

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

Crustal anisotropy across northern Japan from receiver functions.

PubMed

Bianchi, I; Bokelmann, G; Shiomi, K

2015-07-01

Northern Japan is a tectonically active area, with the presence of several volcanoes, and with frequent earthquakes among which the destructive M w  = 8.9-9.0 Tohoku-oki occurred on 11 March 2011. Tectonic activity leaves an imprint on the crustal structures, on both the upper and the lower layers. To investigate the crust in northern Japan, we construct a receiver function data set using teleseismic events recorded at 58 seismic stations belonging to the Japanese National (Hi-net) network. We isolate the signals, in the receiver function wavelet, that witness the presence of anisotropic structures at depth, with the aim of mapping the variation of anisotropy across the northern part of the island. This study focuses on the relation among anisotropy detected in the crust, stresses induced by plate convergence across the subduction zone, and the intrinsic characteristics of the rocks. Our results show how a simple velocity model with two anisotropic layers reproduces the observed data at the stations. We observe a negligible or small amount of signal related to anisotropy in the eastern part of the study area (i.e., the outer arc) for both upper and lower crust. Distinct anisotropic features are observed at the stations on the western part of the study area (i.e., the inner arc) for both upper and lower crust. The symmetry axes are mostly E-W oriented. Deviation from the E-W orientation is observed close to the volcanic areas, where the higher geothermal gradient might influence the deformation processes.

Evidence for Moho-lower crustal transition depth diking and rifting of the Sierra Nevada microplate

NASA Astrophysics Data System (ADS)

Smith, Kenneth D.; Kent, Graham M.; Seggern, David P.; Driscoll, Neal W.; Eisses, Amy

2016-10-01

Lithospheric rifting most often initiates in continental extensional settings where "breaking of a plate" may or may not progress to sea floor spreading. Generally, the strength of the lithosphere is greater than the tectonic forces required for rupture (i.e., the "tectonic force paradox"), and it has been proposed that rifting requires basaltic magmatism (e.g., dike emplacement) to reduce the strength and cause failure, except for the case of a thin lithosphere (<30 km thick). Here we isolate two very similar and unprecedented observations of Moho-lower crustal transition dike or fluid injection earthquake swarms under southern Sierra Valley (SV: 2011-2012) and North Lake Tahoe (LT: 2003-2004), California. These planar distributions of seismicity can be interpreted to define the end points, and cover 25% of the length, of an implied 56 km long structure, each striking N45°W and dipping 50°NE. A single event at 30 km depth that locates on the implied dipping feature between the two swarms is further evidence for a single Moho-transition depth structure. We propose that basaltic or fluid emplacement at or near Moho depths weakens the upper mantle lid, facilitating lithospheric rupture of the Sierra Microplate. Similar to the LT sequence, the SV event is also associated with increased upper crustal seismicity. An 27 October 2011, Mw 4.7 earthquake occurred directly above the deep SV sequence at the base of the upper crustal seismogenic zone ( 15 km depth).

Active vibration control of structures undergoing bending vibrations

NASA Technical Reports Server (NTRS)

Pla, Frederic G. (Inventor); Rajiyah, Harindra (Inventor)

1995-01-01

An active vibration control subassembly for a structure (such as a jet engine duct or a washing machine panel) undergoing bending vibrations caused by a source (such as the clothes agitator of the washing machine) independent of the subassembly. A piezoceramic actuator plate is vibratable by an applied electric AC signal. The plate is connected to the structure such that vibrations in the plate induced by the AC signal cause canceling bending vibrations in the structure and such that the plate is compressively pre-stressed along the structure when the structure is free of any bending vibrations. The compressive prestressing increases the amplitude of the canceling bending vibrations before the critical tensile stress level of the plate is reached. Preferably, a positive electric DC bias is also applied to the plate in its poling direction.

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.

Active-source 3-D tomography near Nias and Batu Islands, offshore central Sumatra

NASA Astrophysics Data System (ADS)

Karplus, M.; Henstock, T.; McNeill, L. C.; Vermeesch, P. M.; Hall, T. R.; Harmon, N.; Barton, P. J.

2013-12-01

Wide-angle reflection and refraction tomography constrain 3-D lithospheric P-wave velocity structure beneath the central Sumatra subduction zone from Nias Island to Siberut, offshore Indonesia at the southern boundary of the 2005 megathrust earthquake rupture. This area includes the earthquake segment boundary near the Batu Islands where the Investigator Fracture Zone is subducted beneath the Eurasian plate. We report along- and across-strike variations in structure of the downgoing slab and overriding plate. Seismic wide-angle data were collected during cruise SO198-1 in May-June 2008. Air gun shots were recorded by 47 temporary ocean bottom seismometers (OBS) deployed in a roughly 200 km by 190 km area, 10 three-component long-term OBS (with differential pressure gauge), and 52 land stations. First arrival refraction modeling using ray tracing and least squares inversion has yielded a lithospheric P-wave velocity model, best-resolved in the top 25 km. We observe velocities of ~4.5-6 km/s within the accretionary prism, which varies by several km in its depth extent. The forearc basin is underlain by high velocities of ~7-8 km/s as shallow as 8 km depth. This high velocity region is likely older forearc oceanic crust, as seen in Cascadia and near Simeulue, offshore Sumatra. The top of the subducting slab ranges in depth from ~10 km near the trench to ~20 km beneath the prism. The top of the slab dips approximately 4-4.5° towards the NE between the trench and the prism. Earthquake hypocenters show the slab dip steepens significantly NE of the forearc basin. We compare our velocity models with models derived from other regions to the north and south along-strike in the Sumatra Subduction Zone, including the 2004-2005 segment boundary at Simeulue. Multi-channel seismic reflection data show that fault structures and reflectivity change considerably along- and across-strike in the central Sumatra subduction zone. Furthermore, regional earthquake locations indicate rupture segmentation along the plate boundary. The Nias segment in the north ruptured in the 2005 M8.7 earthquake. The weakly-coupled Batu segment experiences sporadic clusters of events near the break in the forearc slope. The offshore forearc west of Siberut is characterized by almost aseismic behavior, reflecting the locked state of the plate interface, which hasn't ruptured since the 1797 M8.6-8.8 earthquake. The subducting Investigator Fracture Zone is believed to act as a barrier for propagation of slip during large ruptures. We compare our velocity model with reflection data and rupture segments to characterize differences in the lower plate, upper plate, and plate boundary properties.

Upper Mantle Discontinuity Structure Beneath the Western Atlantic Ocean and Eastern North America from SS Precursors

NASA Astrophysics Data System (ADS)

Schmerr, N. C.; Beghein, C.; Kostic, D.; Baldridge, A. M.; West, J. D.; Nittler, L. R.; Bull, A. L.; Montesi, L.; Byrne, P. K.; Hummer, D. R.; Plescia, J. B.; Elkins-Tanton, L. T.; Lekic, V.; Schmidt, B. E.; Elkins, L. J.; Cooper, C. M.; ten Kate, I. L.; Van Hinsbergen, D. J. J.; Parai, R.; Glass, J. B.; Ni, J.; Fuji, N.; McCubbin, F. M.; Michalski, J. R.; Zhao, C.; Arevalo, R. D., Jr.; Koelemeijer, P.; Courtier, A. M.; Dalton, H.; Waszek, L.; Bahamonde, J.; Schmerr, B.; Gilpin, N.; Rosenshein, E.; Mach, K.; Ostrach, L. R.; Caracas, R.; Craddock, R. A.; Moore-Driskell, M. M.; Du Frane, W. L.; Kellogg, L. H.

2015-12-01

Seismic discontinuities within the mantle arise from a wide range of mechanisms, including changes in mineralogy, major element composition, melt content, volatile abundance, anisotropy, or a combination of the above. In particular, the depth and sharpness of upper mantle discontinuities at 410 and 660 km depth are attributed to solid-state phase changes sensitive to both mantle temperature and composition, where regions of thermal heterogeneity produce topography and chemical heterogeneity changes the impedance contrast across the discontinuity. Seismic mapping of this topography and sharpness thus provides constraint on the thermal and compositional state of the mantle. The EarthScope USArray is providing unprecedented access to a wide variety of new regions previously undersampled by the SS precursors. This includes the boundary between the oceanic plate in the western Atlantic Ocean and continental margin of eastern North America. Here we use a seismic array approach to image the depth, sharpness, and topography of the upper mantle discontinuities, as well as other possible upper mantle reflectors beneath this region. This array approach utilizes seismic waves that reflect off the underside of a mantle discontinuity and arrive several hundred seconds prior to the SS seismic phase as precursory energy. In this study, we collected high-quality broadband data SS precursors data from shallow focus (< 30 km deep), mid-Atlantic ridge earthquakes recorded by USArray seismometers in Alaska. We generated 4th root vespagrams to enhance the SS precursors and determine how they sample the mantle. Our data show detection of localized structure on the discontinuity boundaries as well as additional horizons, such as the X-discontinuity and a potential reflection from a discontinuity near the depth of the lithosphere-asthenosphere boundary. These structures are related to the transition from predominantly old ocean lithosphere to underlying continental lithosphere, as while deeper reflectors are associated with the subduction of the ancient Farallon slab. A comparison of the depth of upper mantle discontinuities to changes in seismic velocity and anisotropy will further quantify the relationship to mantle flow, compositional layering, and phases changes.

Clastic dikes of Heart Mountain fault breccia, northwestern Wyoming, and their significance

USGS Publications Warehouse

Pierce, W.G.

1979-01-01

Structural features in northwestern Wyoming indicate that the Heart Mountain fault movement was an extremely rapid, cataclysmic event that created a large volume of carbonate fault breccia derived entirely from the lower part of the upper plate. After fault movement had ceased, much of the carbonate fault breccia, here called calcibreccia, lay loose on the resulting surface of tectonic denudation. Before this unconsolidated calcibreccia could be removed by erosion, it was buried beneath a cover of Tertiary volcanic rocks: the Wapiti Formation, composed of volcanic breccia, poorly sorted volcanic breccia mudflows, and lava flows, and clearly shown in many places by inter lensing and intermixing of the calcibreccia with basal volcanic rocks. As the weight of volcanic overburden increased, the unstable water-saturated calcibreccia became mobile and semifluid and was injected upward as dikes into the overlying volcanic rocks and to a lesser extent into rocks of the upper plate. In some places the lowermost part of the volcanic overburden appears to have flowed with the calcibreccia to form dike like bodies of mixed volcanic rock and calcibreccia. One calcibreccia dike even contains carbonized wood, presumably incorporated into unconsolidated calcibreccia on the surface of tectonic denudation and covered by volcanic rocks before moving upward with the dike. Angular xenoliths of Precambrian rocks, enclosed in another calcibreccia dike and in an adjoining dikelike mass of volcanic rock as well, are believed to have been torn from the walls of a vent and incorporated into the basal part of the Wapiti Formation overlying the clastic carbonate rock on the fault surface. Subsequently, some of these xenoliths were incorporated into the calcibreccia during the process of dike intrusion. Throughout the Heart Mountain fault area, the basal part of the upper-plate blocks or masses are brecciated, irrespective of the size of the blocks, more intensely at the base and in places extending upward for several tens of meters. North of Republic Mountain a small 25-m-high upper-plate mass, brecciated to some degree throughout, apparently moved some distance along the Heart Mountain fault as brecciated rock. Calcibreccia dikes intrude upward from the underlying 2 m of fault breccia into the lower part of the mass and also from its top into the overlying volcanic rocks; an earthquake-related mechanism most likely accounts for the observed features of this deformed body. Calcibreccia dikes are more common within the bedding-plane phase of the Heart Mountain fault but also occur in its transgressive and former land-surface phases. Evidence that the Wapiti Formation almost immediately buried loose, unconsolidated fault breccia that was the source of the dike rock strongly suggests a rapid volcanic deposition over the area in which clastic dikes occur, which is at least 75 km long. Clastic dikes were injected into both the upper-plate and the volcanic rocks at about the same time, after movement on the Heart Mouuntain fault had ceased, and therefore do not indicate a fluid-flotation mechanism for the Heart Mountain fault. The difference between contacts of the clastic dikes with both indurated and unconsolidated country rock is useful in field mapping at localities where it is difficult to distinguish between volcanic rocks of the Cathedral Cliffs and Lamar River Formations, and the Wapiti Formation. Thus, calcibreccia dikes in the Cathedral Cliffs and Lamar River Formations show a sharp contact because the country rock solidified prior to fault movement, whereas calcibreccia dikes in the Wapiti Formation in many instances show a transitional or semifluid contact because the country rock was still unconsolidated or semifluid at the time of dike injection.

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.