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Sample records for accreting plate boundaries

  1. The memory of the accreting plate boundary and the continuity of fracture zones

    USGS Publications Warehouse

    Schouten, Hans; Klitgord, Kim D.

    1982-01-01

    A detailed aeromagnetic anomaly map of the Mesozoic seafloor-spreading lineations southwest of Bermuda reveals the dominant magnetic grain of the oceanic crust and the character of the accreting boundary at the time of crustal formation. The magnetic anomaly pattern is that of a series of elongate lobes perpendicular to the fracture zone (flowline) trends. The linear sets of magnetic anomaly peaks and troughs have narrow regions of reduced amplitude anomalies associated with the fracture zones. During the period of Mesozoic geomagnetic polarity reversals (when 1200 km of central North Atlantic seafloor formed), the Atlantic accreting boundary consisted of stationary, elongate, spreading center cells that maintained their independence even though sometimes only minor spatial offsets existed between cells. Normal oceanic crustal structure was formed in the spreading center cells, but structural anomalies and discontinuities characteristic of fracture zones were formed at their boundaries, which parallel flowlines of Mesozoic relative plate motion in the central North Atlantic. We suggest that the memory for a stationary pattern of independent spreading center cells resides in the young brittle lithosphere at the accreting boundary where the lithosphere is weakest; here, each spreading center cell independently goes through its cylce of stress buildup, stress release, and crustal accretion, after which its memory is refreshed. The temporal offset between the peaks of the accretionary activity that takes place within each cell may provide the mechanism for maintaining the independence of adjacent spreading center cells through times when no spatial offset between the cells exists.

  2. Oblique collision and accretion of the Netherlands Leeward Antilles island arc: A structural analysis of the Caribbean-South American plate boundary zone

    NASA Astrophysics Data System (ADS)

    Beardsley, Amanda Gail

    2007-12-01

    tectonics control the ongoing steady-state exhumation of the islands at a rate of 0.04 km/my. Most recently, the northeast escape of the Maracaibo block also drives deformation within the diffuse plate boundary zone. Overall, the Caribbean-South American plate boundary geometry has evolved with diachronous deformation, from west to east, accompanied by 135° of clockwise block rotation during collision and accretion of the Leeward Antilles since the Late Cretaceous.

  3. Models for rupture mechanics of plate boundaries and crustal deformation

    NASA Technical Reports Server (NTRS)

    Nur, A.

    1983-01-01

    The role of pull aparts and pushups in transcurrent systems, the rotation of faults and blocks within transcurrent fault systems, the role of accretion tectonics in plate boundary deformation, and power law creep behavior and the yielding at plate boundaries were investigated.

  4. The seismotectonics of plate boundaries

    NASA Technical Reports Server (NTRS)

    Berger, J.; Brune, J. N.; Goodkind, J.; Wyatt, F.; Agnew, D. C.; Beaumont, C.

    1981-01-01

    Research on the seismotectonics of plate boundaries is summarized. Instrumental development and an observational program designed to study various aspects of the seismotectonics of southern California and the northern Gulf of California are described. A unique superconducting gravimeter was further developed and supported under this program for deployment and operation at several sites. Work on Earth tides is also discussed.

  5. Plate Interface Rheology, Mechanical Coupling and Accretion during Subduction Infancy

    NASA Astrophysics Data System (ADS)

    Agard, P.; Yamato, P.; Mathieu, S.; Prigent, C.; Guillot, S.; Plunder, A.; Dubacq, B.; Monie, P.; Chauvet, A.

    2015-12-01

    Understanding subduction rheology in both space and time has been a challenge since the advent of plate tectonics. We herein focus on "subduction infancy", that is the first ~1-5 My immediately following subduction nucleation, when a newly born slab penetrates into the upper plate mantle and heats up. The only remnants of this critical yet elusive geodynamic step are thin metamorphic soles, commonly found beneath pristine, 100-1000 km long portions of oceanic lithosphere emplaced on continents (i.e., ophiolites). Through the (i) worldwide compilation of pressure-temperature conditions of metamorphic sole formation augmented by pseudosection thermodynamic modeling, (ii) calculations of the viscosity of materials along the plate interface and (iii) generic numerical thermal models, we provide a conceptual model of dynamic plate interface processes during subduction infancy (and initiation s.l.). We show in particular how major rheological switches across the subduction interface control slab penetration, and the formation of metamorphic soles. Due to the downward progression of hydration and weakening of the mantle wedge with cooling, the lower plate (basalt, sediment) and the upper plate (mantle wedge) rheologies equalize and switch over a restricted temperature-time-depth interval (e.g., at ~800°C and ~1 GPa, during 0.1-2 My, for high-temperature metamorphic sole formation). These switches result in episodes of maximum interplate mechanical coupling, thereby slicing the top of the slab and welding pieces (basalt, sediment) to the base of the mantle wedge. Similar mechanical processes likely apply for the later, deeper accretion and exhumation of high-temperature oceanic eclogites in serpentinite mélanges, or for the accretion of larger tectonic slices. This model provides constraints on the effective rheologies of the crust and mantle and general understanding, at both rock and plate scale, for accretion processes and early slab dynamics.

  6. ON HYDROMAGNETIC STRESSES IN ACCRETION DISK BOUNDARY LAYERS

    SciTech Connect

    Pessah, Martin E.; Chan, Chi-kwan E-mail: ckch@nordita.org

    2012-05-20

    Detailed calculations of the physical structure of accretion disk boundary layers, and thus their inferred observational properties, rely on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear viscosity satisfies this assumption by construction. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI) is inefficient in disk regions where, as expected in boundary layers, the angular frequency increases with radius. In order to shed light on physically viable mechanisms for angular momentum transport in this inner disk region, we examine the generation of hydromagnetic stresses and energy density in differentially rotating backgrounds with angular frequencies that increase outward in the shearing-sheet framework. We isolate the modes that are unrelated to the standard MRI and provide analytic solutions for the long-term evolution of the resulting shearing MHD waves. We show that, although the energy density of these waves can be amplified significantly, their associated stresses oscillate around zero, rendering them an inefficient mechanism to transport significant angular momentum (inward). These findings are consistent with the results obtained in numerical simulations of MHD accretion disk boundary layers and challenge the standard assumption of efficient angular momentum transport in the inner disk regions. This suggests that the detailed structure of turbulent MHD accretion disk boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity.

  7. The Rivera-Cocos Plate Boundary Revisited

    NASA Astrophysics Data System (ADS)

    Bandy, W. L.; Mortera-Gutierrez, C. A.; Michaud, F.; Ortega Ramírez, J.

    2013-05-01

    The nature of the boundary between the Rivera and Cocos plates has long been controversial. Early studies (predominantly earthquake studies) suggested that it was a NE oriented left lateral transform boundary. With the collection of multi-beam bathymetric data during the SEAMAT cruise of the N/O Jean Charcot in 1987 it became clear that this early proposal was not entirely correct as no clear transform morphology was observed. Shortly after the SEAMAT campaign, three main proposals emerged to explain this lack of transform morphology. The first two proposals favored the results of earthquake studies over the new multibeam data. The first proposed that the boundary is indeed a left-lateral transform boundary, you just cannot see it. In other words, it was a diffuse boundary and the resolution of the multi-beam data was not sufficient to reveal the associated deformation. The second proposal was that it was an east-west oriented, dextral transform, the proposal being based on the results of an earthquake directivity analysis. The third proposal favored the morphologic data over the earthquake data and proposed that the plate boundary was not a transform boundary, but was instead a divergent boundary, at least near the Middle America Trench in what is now called the EL Gordo Graben. Implicit in this proposal was that the earthquake activity did not reflect plate motions but rather were the result of local stresses. Since 2002, several marine geophysical campaigns have been conducted in the area of the Rivera-Cocos plate boundary with the aim of resolving this debate. During the 2002 BART and FAMEX campaigns of the N/O L'ATALANTE, multibeam bathymetric and seafloor backscatter data were collected along the boundary. During the MARTIC04 and MARTIC05 campaigns of the B/O EL PUMA dense total field magnetic surveys were conducted covering the entire plate boundary. Lastly, the multibeam coverage obtained during the BART/FAMEX campaigns was extended northward during the

  8. Viscoelastic deformation near active plate boundaries

    NASA Technical Reports Server (NTRS)

    Ward, S. N.

    1986-01-01

    Model deformations near the active plate boundaries of Western North America using space-based geodetic measurements as constraints are discussed. The first six months of this project were spent gaining familarity with space-based measurements, accessing the Crustal Dynamics Data Information Computer, and building time independent deformation models. The initial goal was to see how well the simplest elastic models can reproduce very long base interferometry (VLBI) baseline data. From the Crustal Dynamics Data Information Service, a total of 18 VLBI baselines are available which have been surveyed on four or more occasions. These data were fed into weighted and unweighted inversions to obtain baseline closure rates. Four of the better quality lines are illustrated. The deformation model assumes that the observed baseline rates result from a combination of rigid plate tectonic motions plus a component resulting from elastic strain build up due to a failure of the plate boundary to slip at the full plate tectonic rate. The elastic deformation resulting from the locked plate boundary is meant to portray interseismic strain accumulation. During and shortly after a large interplate earthquake, these strains are largely released, and points near the fault which were previously retarded suddenly catch up to the positions predicted by rigid plate models. Researchers judge the quality of fit by the sum squares of weighted residuals, termed total variance. The observed baseline closures have a total variance of 99 (cm/y)squared. When the RM2 velocities are assumed to model the data, the total variance increases to 154 (cm/y)squared.

  9. Delivery of volatiles to terrestrial planets during accretion: Setting the stage for plate tectonics

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, L.; Tikoo, S.

    2012-04-01

    A persistent problem in planetary science is how and when plate tectonics can begin in planetary evolution. On Earth, plate tectonics is thought to be facilitated by the low-viscosity asthenosphere, which obtains its low viscosity partly through low pressure, and partly through a water content on the order of hundreds of parts per million, likely trapped in the crystal structure of nominally anhydrous silicate minerals. Subduction zones introduce water contents of that magnitude to the mantle that circulates above the sinking oceanic plate, and subduction zones are sometimes cited as the process that hydrates an originally dry planetary interior. Thus there is a chicken-and-egg problem: If a damp asthenosphere is needed for plate tectonics, but plate tectonics itself creates the damp asthenosphere, how does the process initiate? Despite the existence of a metallic (reduced) core, both the compositions of meteorites and the certainty of radial mixing during accretion suggest that the Earth and other rocky planets accreted with some non-zero water content. Tracking water partitioning between magma ocean fluids and solidifying mantle minerals suggests that the planetary interior could begin with a non-zero water content. Here we present models for the interior water content of the Earth following accretion, and hypothesize about a dynamic processes that may have sped the development of plate tectonics. On an Earth-sized planet a magma ocean would solidify to produce very dense near-surface solids that also contain the bulk of the water held in the solid state, and the bulk of the incompatible elements. During gravitationally-driven overturn shallow, dense, damp solids carry their water as they sink into the perovskite stability zone and transform the bulk of their mineralogy into perovskite. The last solids that form near the surface exceed the likely water saturation levels of perovskite and will be forced to dewater as they cross the boundary into the lower mantle

  10. Circum-arctic plate accretion - Isolating part of a pacific plate to form the nucleus of the Arctic Basin

    USGS Publications Warehouse

    Churkin, M.; Trexler, J.H.

    1980-01-01

    A mosaic of large lithospheric plates rims the Arctic Ocean Basin, and foldbelts between these plates contain numerous allochthonous microplates. A new model for continental drift and microplate accretion proposes that prior to the late Mesozoic the Kula plate extended from the Pacific into the Arctic. By a process of circumpolar drift and microplate accretion, fragments of the Pacific basin, including parts of the Kula plate, were cut off and isolated in the Arctic Ocean, the Yukon-Koyukuk basin in Alaska, and the Bering Sea. ?? 1980.

  11. Diffuse oceanic plate boundaries: Strain rates, vertically averaged rheology, and comparisons with narrow plate boundaries and stable plate interiors

    NASA Astrophysics Data System (ADS)

    Gordon, Richard G.

    Diffuse plate boundaries occur in both oceanic and continental lithosphere and cover ≈ 15% of Earth's solid surface. The fastest plate speeds accommodated across diffuse oceanic plate boundaries are ≈ 15 mm/yr. The smallest strain rates averaged across narrow plate boundaries are at least 102 times larger than the largest strain rates across diffuse oceanic plate boundaries and at least 102 times larger than those across stable plate interiors. The effective viscosity (ηeff) of the lithosphere is estimated from the ratio of vertically averaged shear stresses to strain rates for three tectonic settings: (i) oceanic transform fault zones, for which ηeff = 3 ×1016 to 5×1019 Pa s, comparable to estimates for the asthenosphere, (ii) diffuse oceanic plate boundaries, for which ηeff = 1×1023 to 6×l023 Pa s, ≈ 10 times larger than for diffuse continental plate boundaries, and (iii) stable plate interiors, for which ηeff = 1x1024 to 2×1027 Pa s. The rheology of oceanic lithosphere over times longer than earthquake cycles is modeled as a plastic layer overlying a layer that deforms by creeping flow [Martinod and Davy, 1992]. Oceanic lithosphere deforms when the yield strength of the upper lithosphere is exceeded. The vertically averaged rheology of deforming oceanic lithosphere can be approximated by a power-law fluid for which ɛ. ∝ (τs)n where ɛ. is the rate of shear strain and τs is the shear stress. If the ratio of the yield strength of the upper lithosphere to the force required to deform the lower lithosphere at a strain rate of 10-16 s-1 is varied from 10-2 to 102 , the calculated value of n varies from ≈3 to ≈300. The map-view aspect ratio of a deforming zone in a thin sheet of power-law fluid is proportional to n-½ [England et al., 1985]. A profile of displacement versus distance inferred from a seismic profile across the Central Indian Basin (India-Capricorn diffuse oceanic plate boundary), where the lithosphere is about 60-Myr old

  12. Accretion/underplating, detachment and exhumation: short/long-term rheology of the subduction plate interface

    NASA Astrophysics Data System (ADS)

    Agard, Philippe; Angiboust, Samuel; Plunder, Alexis; Guillot, Stéphane; Yamato, Philippe; Oncken, Onno; Ruh, Jonas; Burov, Evgueni; Bonnet, Guillaume

    2016-04-01

    The presence of km-scale accreted terranes/units in both ancient and present-day subduction zones attests to changes in strain localization along the plate interface, whereby these terranes/units get detached from the downgoing slab (or, in places, are eroded away from the tip of the upper plate) and either directly exhumed or accreted/underplated below the upper plate before final exhumation. The rock record (P-T-t data) indicates that, for a given subduction zone, exhumation is episodic: no more than a few My compared to the ~100 My lifetime of typical subduction zones. Not much is known, however, regarding this process and important open questions remain: what exactly is episodic (i.e., detachment from the slab and/or exhumation?), for how long and where? How is mechanical coupling impacted by the initial structure of the incoming plates (structural/lithological heterogeneities, thermo-fluid regime, geodynamic boundary conditions, etc...)? We herein present both new and literature structural and P-T-t data ranging from shallow (i.e., 15-20 km) to intermediate depths (~100 km) along the subduction interface, that span a range from long-term to short-lived events of underplating and/or exhumation, and confront them with the recent wealth of geophysical data gathered on subduction zones. Structural and petrological data indicate that the slicing of km-scale units mostly occurs at specific depths where major mechanical changes occur along the plate interface: at 30-40 km (downdip of the seismogenic zone) and 70-80 km (where mechanical coupling between the two plates resumes and where eclogites get critically dense). This suggests that switches in mechanical coupling (i.e., in the rheology of the material) are key in controlling the ability to detach pieces from the slab (and that later exhumation is rather controlled by large-scale, lithospheric-scale boundary conditions). The study of rock remnants detached from the slab and underplated during subduction infancy (i

  13. Spherical accretion: the influence of inner boundary and quasi-periodic oscillations

    NASA Astrophysics Data System (ADS)

    Dhang, Prasun; Sharma, Prateek; Mukhopadhyay, Banibrata

    2016-09-01

    Bondi accretion assumes that there is a sink of mass at the centre - which in the case of a black hole (BH) corresponds to the advection of matter across the event horizon. Other stars, such as a neutron star (NS), have surfaces and hence the infalling matter has to slow down at the surface. We study the initial value problem in which the matter distribution is uniform and at rest at t = 0. We consider different inner boundary conditions for BHs and NSs: outflow boundary condition (mimicking mass sink at the centre) valid for BHs; and reflective and steady-shock (allowing gas to cross the inner boundary at subsonic speeds) boundary conditions for NSs. We also obtain a similarity solution for cold accretion on to BHs and NSs. 1D simulations show the formation of an outward-propagating and a standing shock in NSs for reflective and steady-shock boundary conditions, respectively. Entropy is the highest at the bottom of the subsonic region for reflective boundary conditions. In 2D this profile is convectively unstable. Using steady-shock inner boundary conditions, the flow is unstable to the standing accretion shock instability in 2D, which leads to global shock oscillations and may be responsible for quasi-periodic oscillations seen in the light curves of accreting systems. For steady accretion in the quiescent state, spherical accretion rate on to an NS can be suppressed by orders of magnitude compared to that on to a BH.

  14. The Plate Boundary Observatory Borehole Seismic Network

    NASA Astrophysics Data System (ADS)

    Hasting, M.; Eakins, J.; Anderson, G.; Hodgkinson, K.; Johnson, W.; Mencin, D.; Smith, S.; Jackson, M.; Prescott, W.

    2006-12-01

    As part of the NSF-funded EarthScope Plate Boundary Observatory, UNAVCO will install and operate 103 borehole seismic stations throughout the western United States. These stations continuously record three- component seismic data at 100 samples per second, using Geo-Space HS-1-LT 2-HZ geophones in a sonde developed by SONDI and Consultants (Duke University). Each seismic package is connected to an uphole Quanterra Q330 data logger and Marmot external buffer, from which UNAVCO retrieves data in real time. UNAVCO uses the Antelope software suite from Boulder Real-Time Technologies (BRTT) for all data collection and transfer, metadata generation and distribution, and monitoring of the network. The first stations were installed in summer 2005, with 19 stations installed by September 2006, and a total of 28 stations expected by December 2006. In a prime example of cooperation between the PBO and USArray components of EarthScope, the USArray Array Network Facility (ANF), operated by UC San Diego, handled data flow and network monitoring for the PBO seismic stations in the initial stages of network operations. We thank the ANF staff for their gracious assistance over the last several months. Data flow in real time from the remote stations to the UNAVCO Boulder Network Operations Center, from which UNAVCO provides station command and control; verification and distribution of metadata; and basic quality control for all data. From Boulder, data flow in real time to the IRIS DMC for final quality checks, archiving, and distribution. Historic data are available from June 2005 to the present, and are updated in real time with typical latencies of less than ten seconds. As of 1 September 2006, the PBO seismic network had returned 60 GB of raw data. Please visit http://pboweb.unavco.org for additional information on the PBO seismic network.

  15. Plate Boundary Observatory GPS Data Analysis

    NASA Astrophysics Data System (ADS)

    Herring, T. A.; King, R.; McClusky, S.; Murray, M.; Santillan, M.; Melbourne, T.; Anderson, G.

    2005-12-01

    The Plate Boundary Observatory GPS data analysis centers (ACs) at the Berkeley Seismological Laboratory (BSL) and Central Washington University (CWU), and the analysis center coordinator (ACC) at the Massachusetts Institute of Technology began establishing the GPS processing centers on April 1, 2005. The PBO GPS data analyses will be operational on October 1, 2005, with the regular delivery of daily SINEX solution files with full covariance and time series files designed for ease of analysis and plotting. The initial results for the PBO analyses will start with data from January 1, 2004 and contain position time series for 209 PBO Nucleus stations, 17 IGS reference frame stations, 9 CORS stations (to bridge Alaska to the continental United States), and all PBO stations as they come on line. The first PBO site was ready on January 11, 2004. The PBO ACs routinely generate rapid orbit analyses (1-day latency), primarily to check data quality, and initial final orbit analyses with 6-13 day latency. The timing of the generation of these products is based on the availability of the International GNSS Service rapid and final orbit products. Currently, between 280 and 300 stations are included in these rapid analyses and typically 310-315 stations are in the final analyses. The initial testing of the analysis procedures shows median north and east daily root-mean-square (rms) scatters of 1.0-1.3 mm for horizontal positions for a network encompassing North America and Central Pacific. The median height rms scatter is 5 mm. This talk will show results and products being generated by the PBO ACs and ACC, and compare the results between the GIPSY (CWU) and GAMIT (BSL) processing.

  16. Study on plate silencer with general boundary conditions

    NASA Astrophysics Data System (ADS)

    Liu, Gongmin; Zhao, Xiaochen; Zhang, Wenping; Li, Shuaijun

    2014-09-01

    A plate silencer consists of an expansion chamber with two side-branch rigid cavities covered by plates. Previous studies showed that, in a duct, the introduction of simply supported or clamped plates into an air conveying system could achieve broadband quieting from low to medium frequencies. In this study, analytical formulation is extended to the plate silencer with general boundary conditions. A set of static beam functions, which are a combination of sine series and third-order polynomial, is employed as the trial functions of the plate vibration velocity. Greens function and Kirchhoff-Helmholtz integral are used to solve the sound radiation in the duct and the cavity, and then the vibration velocity of the plate is obtained. Having obtained the vibration velocity, the pressure perturbations induced by the plate oscillation and the transmission loss are found. Optimization is carried out in order to obtain the widest stopband. The transmission loss calculated by the analytical method agrees closely with the result of the finite element method simulation. Further studies with regard to the plate under several different classical boundary conditions based on the validated model show that a clamped-free plate silencer has the worst stopband. Attempts to release the boundary restriction of the plate are also made to study its effect on sound reflection. Results show that a softer end for a clamped-clamped plate silencer helps increase the optimal bandwidth, while the same treatment for simply supported plate silencer will result in performance degradation.

  17. Macrobrecciation at a Plate Boundary: The Iskenderun Block

    NASA Astrophysics Data System (ADS)

    Sine, C. R.; Brumbaugh, D. S.

    2004-12-01

    The area of intersection of the East Anatolian and the Dead Sea fault zones in southeast Turkey and northwest Syria represents the intersection of three tectonic Plates: African,Anatolian, and Arabian. Widespread deformation occurs in the area of the plate triple junction including the presence of multiple faults bounding plate fragments along the plate tectonic boundaries. Earthquake fault plane solutions and epicenter clustering in the area of the intersectiong fault zones has been used to identify plate fragments. This study delineates a plate boundary near the mouth of the Gulf of Iskenderun based on linear trends in epicenters and the orientation of fault plane solution nodal planes. The boundary located near the mouth of the Gulf of Iskenderun is proposed to be the southern boundary of a plate fragment roughly the size of the state of Delaware, herein named the Iskenderun block. Plate motions and moho depths suggest that the Iskenderun block is a promontory that was originally joined to the African plate and has been caught up in the deformation at the Anatolian-Arabian-African triple junction and has been subsequently torn from the African plate.

  18. 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.

  19. Linking mantle dynamics, plate tectonics and surface processes in the active plate boundary zones of eastern New Guinea (Invited)

    NASA Astrophysics Data System (ADS)

    Baldwin, S.; Moucha, R.; Fitzgerald, P. G.; Hoke, G. D.; Bermudez, M. A.; Webb, L. E.; Braun, J.; Rowley, D. B.; Insel, N.; Abers, G. A.; Wallace, L. M.; Vervoort, J. D.

    2013-12-01

    Eastern New Guinea lies within the rapidly obliquely converging Australian (AUS)- Pacific (PAC) plate boundary zone and is characterized by transient plate boundaries, rapidly rotating microplates and a globally significant geoid high. As the AUS plate moved northward in the Cenozoic, its leading edge has been a zone of subduction and arc accretion. The variety of tectonic settings in this region permits assessment of the complex interplay among mantle dynamics, plate tectonics, and surface processes. Importantly, the timescale of tectonic events (e.g., subduction, (U)HP exhumation, seafloor spreading) are within the valid bounds of mantle convection models. A record of changes in bathymetry and topography are preserved in high standing mountain belts, exhumed extensional gneiss domes and core complexes, uplifted coral terraces, and marine sedimentary basins. Global seismic tomography models indicate accumulation of subducted slabs beneath eastern New Guinea at the bottom of the upper mantle (i.e., <660km depth). Some of the deeply subducted material may indeed be buoyant subducted AUS continental margin (to depths of ~250-300 km), as well as subducted continental material that has reached the point of no return (i.e., > 250-300 km). Preliminary global-scale backward advected mantle convection models, driven by density inferred from joint seismic-geodynamic tomography models, exhibit large-scale flow associated with these subducted slab remnants and predict the timing and magnitude (up to 1500 m) of dynamic topography change (both subsidence and uplift) since the Oligocene. In this talk we will explore the effects of large-scale background mantle flow and plate tectonics on the evolution of topography and bathymetry in eastern New Guinea, and discuss possible mechanisms to explain basin subsidence and surface uplift in the region.

  20. Tracking the India-Arabia Transform Plate Boundary during Paleogene Times.

    NASA Astrophysics Data System (ADS)

    Rodriguez, M.; Huchon, P.; Chamot-Rooke, N. R. A.; Fournier, M.; Delescluse, M.

    2014-12-01

    The Zagros and Himalaya mountain belts are the most prominent reliefs built by continental collision. They respectively result from Arabia and India collision with Eurasia. Convergence motions at mountain belts induced most of plate reorganization events in the Indian Ocean during the Cenozoic. Although critical for paleogeographic reconstructions, the way relative motion between Arabia and India was accommodated prior to the formation of the Sheba ridge in the Gulf of Aden remains poorly understood. The India-Arabia plate-boundary belongs to the category of long-lived (~90-Ma) oceanic transform faults, thus providing a good case study to investigate the role of major kinematic events over the structural evolution of a long-lived transform system. A seismic dataset crossing the Owen Fracture Zone, the Owen Basin, and the Oman Margin was acquired to track the past locations of the India-Arabia plate boundary. We highlight the composite age of the Owen Basin basement, made of Paleocene oceanic crust drilled on its eastern part, and composed of pre-Maastrichtian continental crust overlaid by Early Paleocene ophiolites on its western side. A major transform fault system crossing the Owen Basin juxtaposed these two slivers of lithosphere of different ages, and controlled the uplift of marginal ridges along the Oman Margin. This transform system deactivated ~40 Ma ago, coeval with the onset of ultra-slow spreading at the Carlsberg Ridge. The transform boundary then jumped to the edge of the present-day Owen Ridge during the Late Eocene-Oligocene period, before seafloor spreading began at the Sheba Ridge. This migration of the plate boundary involved the transfer of a part of the Indian oceanic lithosphere accreted at the Carlsberg Ridge to the Arabian plate. The episode of plate transfer at the India-Arabia plate boundary during the Late Eocene-Oligocene interval is synchronous with a global plate reorganization event corresponding to geological events at the Zagros and

  1. A diffuse plate boundary model for Indian Ocean tectonics

    NASA Technical Reports Server (NTRS)

    Wiens, D. A.; Demets, C.; Gordon, R. G.; Stein, S.; Argus, D.

    1985-01-01

    It is suggested that motion along the virtually aseismic Owen fracture zone is negligible, so that Arabia and India are contained within a single Indo-Arabian plate divided from the Australian plate by a diffuse boundary. The boundary is a zone of concentrated seismicity and deformation commonly characterized as 'intraplate'. The rotation vector of Australia relative to Indo-Arabia is consistent with the seismologically observed 2 cm/yr of left-lateral strike-slip along the Ninetyeast Ridge, north-south compression in the Central Indian Ocean, and the north-south extension near Chagos.

  2. Between the Disk and the Star: Boundary Layers in Astrophysical Accretion Disks

    NASA Astrophysics Data System (ADS)

    Rafikov, Roman

    Accretion disks are encountered in a wide variety of astrophysical settings: compact binaries, active galactic nuclei, star and planet formation. Whenever accretion proceeds onto a central object with a surface, a boundary layer forms at the inner edge of the disk. Energy release taking place in this layer is expected to dramatically modify spectra and give rise to variability of accreting objects. To properly interpret observations it is thus imperative to obtain a good working model of the boundary layer phenomenon. However, at the moment reconciliation of observations and theory of the boundary layers in grossly incomplete, and there are long-standing puzzles such as e.g. the missing boundary layer problem in accreting white dwarfs and young stars. The main reason for this unsatisfactory state of affairs is that the current theory is severely hampered by the lack of understanding of the mechanisms by which angular momentum and mass are transported across the boundary layer region. Our group has recently discovered a novel transport mechanism, which naturally emerges under the boundary layer conditions and has proven to be very robust. Using a suite of large-scale hydrodynamic and magnetohydrodynamic simulations we have shown that supersonic shear near the stellar surface is highly conducive to the excitation of a global instability, which relies on launching the acoustic modes in the system. Saturation of this instability results in a regular, non-axisymmetric, global pattern of acoustic waves that persists on very long time scales. These waves dissipate in weak shocks giving rise to global momentum transport, which in turn drives mass accretion. Transport of angular momentum and energy by these waves is intrinsically non-local and cannot be described in the framework of existing local models of effective viscosity. This new transport mechanism is efficient and robust. Its discovery calls for better and urgent understanding of how the boundary layer operate in a

  3. Composite transform-convergent plate boundaries: description and discussion

    USGS Publications Warehouse

    Ryan, H.F.; Coleman, P.J.

    1992-01-01

    The leading edge of the overriding plate at an obliquely convergent boundary is commonly sliced by a system of strike-slip faults. This fault system is often structurally complex, and may show correspondingly uneven strain effects, with great vertical and translational shifts of the component blocks of the fault system. The stress pattern and strain effects vary along the length of the system and change through time. These margins are considered to be composite transform-convergent (CTC) plate boundaries. Examples are given of structures formed along three CTC boundaries: the Aleutian Ridge, the Solomon Islands, and the Philippines. The dynamism of the fault system along a CTC boundary can enhance vertical tectonism and basin formation. This concept provides a framework for the evaluation of petroleum resources related to basin formation, and mineral exploration related to igneous activity associated with transtensional processes. ?? 1992.

  4. Dynamic behaviour of thin composite plates for different boundary conditions

    SciTech Connect

    Sprintu, Iuliana E-mail: rotaruconstantin@yahoo.com; Rotaru, Constantin E-mail: rotaruconstantin@yahoo.com

    2014-12-10

    In the context of composite materials technology, which is increasingly present in industry, this article covers a topic of great interest and theoretical and practical importance. Given the complex design of fiber-reinforced materials and their heterogeneous nature, mathematical modeling of the mechanical response under different external stresses is very difficult to address in the absence of simplifying assumptions. In most structural applications, composite structures can be idealized as beams, plates, or shells. The analysis is reduced from a three-dimensional elasticity problem to a oneor two-dimensional problem, based on certain simplifying assumptions that can be made because the structure is thin. This paper aims to validate a mathematical model illustrating how thin rectangular orthotropic plates respond to the actual load. Thus, from the theory of thin plates, new analytical solutions are proposed corresponding to orthotropic rectangular plates having different boundary conditions. The proposed analytical solutions are considered both for solving equation orthotropic rectangular plates and for modal analysis.

  5. BOLIVAR & GEODINOS: Investigations of the Southern Caribbean Plate Boundary

    NASA Astrophysics Data System (ADS)

    Levander, A.; Schmitz, M.; Working Groups, B.

    2006-12-01

    The southern Caribbean-South American plate boundary has many similarities to California's San Andreas system: 1) The CAR-SA system consists of a series of strands of active right lateral strike-slip faults extending >1000 km from the Antilles subduction zone. This system has several names and includes the El Pilar, Coche, San Sebastian, Moron, and Oca faults. 2) The CAR-SA relative velocity has been about 20 mm/yr of mostly right lateral motion since about 55 Ma, giving a total displacement on the CAR-SA plate boundary similar to that of the San Andreas system. 3) The plate boundary has about 10% convergence in western SA, with less as one moves eastward due to relative convergence between North and South America. 4) The CAR-SA system has fold and thrust belts best developed continentward of the strike-slip faults, similar to the San Andreas. 5) There is a big bend in the CAR plate boundary at approximately the same distance from the Antilles trench as the big bend in Southern California is from the Cascadia subduction zone. The tectonic origins of the CAR-SA plate boundary and the San Andreas are very different, however, despite the similarities between the systems. Rather than impingement of a ridge on a trench, the CAR-SA system is thought to have resulted from a continuous oblique collision of the southern end of a Cretaceous island arc system with the northern edge of South America. During this process the CAR island arc and the modern CAR plate overrode a proto-Caribbean plate and destroyed a Mesozoic passive margin on the northern edge of SA. BOLIVAR and GEODINOS are multi-disciplinary investigations of the lithosphere and deeper structures associated with the diffuse CAR-SA plate boundary zone. We review a number of observations regarding the plate boundary obtained or confirmed from these studies: 1) The Caribbean Large Igneous Province, being overridden by the Maracaibo block in western Venezuela, can be identified beneath Aruba and coastal Venezuela

  6. Iberian plate kinematics: A jumping plate boundary between Eurasia and Africa

    USGS Publications Warehouse

    Srivastava, S.P.; Schouten, Hans; Roest, W.R.; Klitgord, Kim D.; Kovacs, L.C.; Verhoef, J.; Macnab, R.

    1990-01-01

    THE rotation of Iberia and its relation to the formation of the Pyrenees has been difficult to decipher because of the lack of detailed sea-floor spreading data, although several models have been proposed1-7. Here we use detailed aeromagnetic measurements from the sea floor offshore of the Grand Banks of Newfoundland to show that Iberia moved as part of the African plate from late Cretaceous to mid-Eocene time, with a plate boundary extending westward from the Bay of Biscay. When motion along this boundary ceased, a boundary linking extension in the King's Trough to compression along the Pyrenees came into existence. Finally, since the late Oligocene, Iberia has been part of the Eurasian plate, with the boundary between Eurasia and Africa situated along the Azores-Gibraltar fracture zone.

  7. Boundary damping of flexural vibrations in beams and plates

    NASA Astrophysics Data System (ADS)

    Garrelick, Joel

    2003-04-01

    The damping of resonantly enhanced flexurally vibrating beams and plates is typically accomplished with surface treatments, viz. constrained or unconstrained damping layers. Alternatively, damping may be achieved at boundaries. In some sense this is a more fundamental approach in that for homogeneous plates, it is the boundaries that are solely responsible for resonant behavior. The theoretical performance of boundary treatments is unbounded, provided the treatment is full, that is continuous along the extent of the boundary. This is not the case however with partial coverage, where a portion of the boundary is left bare. The bounds for such treatments are explored in this paper. The treatment itself is defined in terms of a single bounce reflection coefficient (RC). It is found that for boundary damping in one dimension, viz., beams, the effective loss factor for individual modes is frequently invariant with either one or both ends treated, assuming RC constant. This is in contrast to the two-dimensional case, viz., thin plates, where analogous loss factor values are frequency dependent. Illustrative examples are presented and analyzed. [Work partially performed at CAA/Anteon Corp. and supported by NSWCCD and NSSC, Code 93R.

  8. Swath sonar mapping of Earth's submarine plate boundaries

    NASA Astrophysics Data System (ADS)

    Carbotte, S. M.; Ferrini, V. L.; Celnick, M.; Nitsche, F. O.; Ryan, W. B. F.

    2014-12-01

    The recent loss of Malaysia Airlines flight MH370 in an area of the Indian Ocean where less than 5% of the seafloor is mapped with depth sounding data (Smith and Marks, EOS 2014) highlights the striking lack of detailed knowledge of the topography of the seabed for much of the worlds' oceans. Advances in swath sonar mapping technology over the past 30 years have led to dramatic improvements in our capability to map the seabed. However, the oceans are vast and only an estimated 10% of the seafloor has been mapped with these systems. Furthermore, the available coverage is highly heterogeneous and focused within areas of national strategic priority and community scientific interest. The major plate boundaries that encircle the globe, most of which are located in the submarine environment, have been a significant focus of marine geoscience research since the advent of swath sonar mapping. While the location of these plate boundaries are well defined from satellite-derived bathymetry, significant regions remain unmapped at the high-resolutions provided by swath sonars and that are needed to study active volcanic and tectonic plate boundary processes. Within the plate interiors, some fossil plate boundary zones, major hotspot volcanoes, and other volcanic provinces have been the focus of dedicated research programs. Away from these major tectonic structures, swath mapping coverage is limited to sparse ocean transit lines which often reveal previously unknown deep-sea channels and other little studied sedimentary structures not resolvable in existing low-resolution global compilations, highlighting the value of these data even in the tectonically quiet plate interiors. Here, we give an overview of multibeam swath sonar mapping of the major plate boundaries of the globe as extracted from public archives. Significant quantities of swath sonar data acquired from deep-sea regions are in restricted-access international archives. Open access to more of these data sets would

  9. Repeating Earthquakes on the Queen Charlotte Plate Boundary

    NASA Astrophysics Data System (ADS)

    Hayward, T. W.; Bostock, M. G.

    2015-12-01

    The Queen Charlotte Fault (QCF) is a major plate boundary located off the northwest coast of North America that has produced large earthquakes in 1949 (M8.1) and more recently in October, 2012 (M7.8). The 2012 event was dominated by thrusting despite the fact that plate motions at the boundary are nearly transcurrent. It is now widely believed that the plate boundary comprises the QCF (i.e., a dextral strike-slip fault) as well as an element of subduction of the Pacific Plate beneath the North American Plate. Repeating earthquakes and seismic tremor have been observed in the vicinity of the QCF; providing insight into the spatial and temporal characteristics of repeating earthquakes is the goal of this research. Due to poor station coverage and data quality, traditional methods of locating earthquakes are not applicable to these events. Instead, we have implemented an algorithm to locate local (i.e., < 100 km distance to epicenter) earthquakes using a single, three-component seismogram. This algorithm relies on the P-wave polarization and, through comparison with larger local events in the Geological Survey of Canada catalogue, is shown to yield epicentral locations accurate to within 5-10 km. A total of 24 unique families of repeating earthquakes has been identified, and 4 of these families have been located with high confidence. Their epicenters locate directly on the trace of the QCF and their depths are shallow (i.e., 5-15 km), consistent with the proposed depth of the QCF. Analysis of temporal recurrence leading up to the 2012 M7.8 event reveals a non-random pattern, with an approximately 15 day periodicity. Further analysis is planned to study whether this behaviour persists after the 2012 event and to gain insight into the effects of the 2012 event on the stress field and frictional properties of the plate boundary.

  10. Boundary between stable and unstable regimes of accretion. Ordered and chaotic unstable regimes

    NASA Astrophysics Data System (ADS)

    Blinova, A. A.; Romanova, M. M.; Lovelace, R. V. E.

    2016-07-01

    We present a new study of the Rayleigh-Taylor unstable regime of accretion on to rotating magnetized stars in a set of high grid resolution three-dimensional magnetohydrodynamic simulations performed in low-viscosity discs. We find that the boundary between the stable and unstable regimes is determined almost entirely by the fastness parameter ωs = Ω⋆/ΩK(rm), where Ω⋆ is the angular velocity of the star and ΩK(rm) is the angular velocity of the Keplerian disc at the disc-magnetosphere boundary r = rm. We found that accretion is unstable if ωs ≲ 0.6. Accretion through instabilities is present in stars with different magnetospheric sizes. However, only in stars with relatively small magnetospheres, rm/R⋆ ≲ 7, do the unstable tongues produce chaotic hotspots on the stellar surface and irregular light curves. At even smaller values of the fastness parameter, ωs ≲ 0.45, multiple irregular tongues merge, forming one or two ordered unstable tongues that rotate with the angular frequency of the inner disc. This transition occurs in stars with even smaller magnetospheres, rm/R⋆ ≲ 4.2. Most of our simulations were performed at a small tilt of the dipole magnetosphere, Θ = 5°, and a small viscosity parameter α = 0.02. Test simulations at higher α values show that many more cases become unstable, and the light curves become even more irregular. Test simulations at larger tilts of the dipole Θ show that instability is present, however, accretion in two funnel streams dominates if Θ ≳ 15°. The results of these simulations can be applied to accreting magnetized stars with relatively small magnetospheres: Classical T Tauri stars, accreting millisecond X-ray pulsars, and cataclysmic variables.

  11. SIMULATIONS OF THE BOUNDARY LAYER BETWEEN A WHITE DWARF AND ITS ACCRETION DISK

    SciTech Connect

    Balsara, Dinshaw S.; Fisker, Jacob Lund; Godon, Patrick; Sion, Edward M. E-mail: jfisker@nd.edu E-mail: edward.sion@villanova.edu

    2009-09-10

    Using a 2.5D time-dependent numerical code we recently developed, we solve the full compressible Navier-Stokes equations to determine the structure of the boundary layer (BL) between the white dwarf (WD) and the accretion disk in nonmagnetic cataclysmic variable systems. In this preliminary work, our numerical approach does not include radiation. In the energy equation, we either take the dissipation function ({phi}) into account or we assume that the energy dissipated by viscous processes is instantly radiated away ({phi} = 0). For a slowly rotating nonmagnetized accreting WD, the accretion disk extends all the way to the stellar surface. There, the matter impacts and spreads toward the poles as new matter continuously piles up behind it. We carry out numerical simulations for different values of the alpha-viscosity parameter ({alpha}), corresponding to different mass accretion rates. In the high viscosity cases ({alpha} = 0.1), the spreading BL sets off a gravity wave in the surface matter. The accretion flow moves supersonically over the cusp making it susceptible to the rapid development of gravity wave and/or Kelvin-Helmholtz shearing instabilities. This BL is optically thick and extends more than 30 deg. to either side of the disk plane after only 3/4 of a Keplerian rotation period (t{sub K} = 19 s). In the low viscosity cases ({alpha} = 0.001), the spreading BL does not set off gravity waves and it is optically thin.

  12. The proximity of hotspots to convergent and divergent plate boundaries

    NASA Technical Reports Server (NTRS)

    Weinstein, Stuart A.; Olson, Peter L.

    1989-01-01

    An analysis of four different hotspot distributions, ranging from Morgan's (1972) original list of 19 to Vogt's (1981) list of 117 reveals that the hotspots are preferentially located near divergent plate boundaries. The probability of this proximity occurring by chance alone is quite remote, less than 0.01 for all four hotspot distributions. The same analysis also reveals that the hotspots are preferentially excluded from regions near convergent plate boundaries. The probability of this exclusion occurring by chance alone is 0.1 or less for three out of the four distributions examined. We interpret this behavior as being a consequence of the effects of large scale convective circulation on ascending mantle plumes. Mantle thermal plumes, the most probable source of hotspots, arise from instabilities in a basal thermal boundary layer. Plumes are suppressed from regions beneath convergent boundaries by descending flow and are entrained into the upwelling flow beneath spreading centers. Plate-scale convective circulation driven by subduction may also advect mantle thermal plumes toward spreading centers.

  13. Free, transverse vibrations of thin plates with discontinuous boundary conditions

    NASA Astrophysics Data System (ADS)

    Febbo, M.; Vera, S. A.; Laura, P. A. A.

    2005-03-01

    Vibrations of circular and rectangular plates clamped on part of the boundary and simply supported along the remainder are analyzed by means of a method of perturbation of boundary conditions. This approach appears to be simple and straightforward, giving excellent results for the first mode and its versatility permits to extend it to higher modes of vibration without difficulty. Furthermore, it is shown that the fundamental frequency coefficient can also be determined using a modified Galerkin approach and very simple polynomial coordinate functions which yield good engineering accuracy.

  14. Tectonics of the Nazca-Antarctic plate boundary

    NASA Technical Reports Server (NTRS)

    Anderson-Fontana, Sandra; Larson, Roger L.; Engeln, Joseph F.; Lundgren, Paul; Stein, Seth

    1987-01-01

    A new bathymetric chart of part of the Chile transform system is constructed, based mainly on an R/V Endeavor survey from 100 deg W to its intersection with the East Ridge of the Juan Fernandez microplate. A generally continuous lineated trend can be followed through the entire region, with the transform valley being relatively narrow and well-defined from 109 deg W to approximately 104 deg 30 min W. The fracture zone then widens to the east, with at least two probable en echelon offsets to the south at 104 deg and 102 deg W. Six new strike-slip mechanisms along the Chile Transform and one normal fault mechanism near the northern end of the Chile Rise, inverted together with other plate-motion data from the eastern portion of the boundary, produce a new best-fit Euler pole for the Nazca-Antarctic plate pair, providing tighter constraints on the relative plate motions.

  15. Active faults, stress field and plate motion along the Indo-Eurasian plate boundary

    NASA Astrophysics Data System (ADS)

    Nakata, Takashi; Otsuki, Kenshiro; Khan, S. H.

    1990-09-01

    The active faults of the Himalayas and neighboring areas are direct indicators of Recent and sub-Recent crustal movements due to continental collision between the Indian and Eurasian plates. The direction of the maximum horizontal shortening or horizontal compressive stress axes deduced from the strike and type of active faulting reveals a characteristic regional stress field along the colliding boundary. The trajectories of the stress axes along the transcurrent faults and the Eastern Himalayan Front, are approximately N-S, parallel to the relative motion of the two plates. However, along the southern margin of the Eurasian plate, they are NE-SW in the Western Himalayan Front and NW-SE to E-W in the Kirthar-Sulaiman Front, which is not consistent with the direction of relative plate motion. A simple model is proposed in order to explain the regional stress pattern. In this model, the tectonic sliver between the transcurrent faults and the plate margin, is dragged northward by the oblique convergence of the Indian plate. Thus, the direction of relative motion between the tectonic sliver and the Indian plate changes regionally, causing local compressive stress fields. Judging from the long-term slip rates along the active faults, the relative motion between the Indian and Eurasian plates absorbed in the colliding zone is about one fourth of its total amount; the rest may be consumed along the extensive strike-slip faults in Tibet and China.

  16. Owen Fracture Zone: The Arabia-India plate boundary unveiled

    NASA Astrophysics Data System (ADS)

    Fournier, M.; Chamot-Rooke, N.; Rodriguez, M.; Huchon, P.; Petit, C.; Beslier, M. O.; Zaragosi, S.

    2011-02-01

    We surveyed the Owen Fracture Zone at the boundary between the Arabia and India plates in the NW Indian Ocean using a high-resolution multibeam echo-sounder (Owen cruise, 2009) for search of active faults. Bathymetric data reveal a previously unrecognized submarine fault scarp system running for over 800 km between the Sheba Ridge in the Gulf of Aden and the Makran subduction zone. The primary plate boundary structure is not the bathymetrically high Owen Ridge, but is instead a series of clearly delineated strike-slip fault segments separated by several releasing and restraining bends. Despite an abundant sedimentary supply by the Indus River flowing from the Himalaya, fault scarps are not obscured by recent deposits and can be followed over hundreds of kilometres, pointing to very active tectonics. The total strike-slip displacement of the fault system is 10-12 km, indicating that it has been active for the past ~ 3 to 6 Ma if its current rate of motion of 3 ± 1 mm yr- 1 has remained stable. We describe the geometry of this recent fault system, including a major pull-apart basin at the latitude 20°N, and we show that it closely follows an arc of small circle centred on the Arabia-India pole of rotation, as expected for a transform plate boundary.

  17. ANGULAR MOMENTUM TRANSPORT AND VARIABILITY IN BOUNDARY LAYERS OF ACCRETION DISKS DRIVEN BY GLOBAL ACOUSTIC MODES

    SciTech Connect

    Belyaev, Mikhail A.; Stone, James M.; Rafikov, Roman R.

    2012-11-20

    Disk accretion onto a weakly magnetized central object, e.g., a star, is inevitably accompanied by the formation of a boundary layer near the surface, in which matter slows down from the highly supersonic orbital velocity of the disk to the rotational velocity of the star. We perform high-resolution two-dimensional hydrodynamical simulations in the equatorial plane of an astrophysical boundary layer with the goal of exploring the dynamics of non-axisymmetric structures that form there. We generically find that the supersonic shear in the boundary layer excites non-axisymmetric quasi-stationary acoustic modes that are trapped between the surface of the star and a Lindblad resonance in the disk. These modes rotate in a prograde fashion, are stable for hundreds of orbital periods, and have a pattern speed that is less than and of the order of the rotational velocity at the inner edge of the disk. The origin of these intrinsically global modes is intimately related to the operation of a corotation amplifier in the system. Dissipation of acoustic modes in weak shocks provides a universal mechanism for angular momentum and mass transport even in purely hydrodynamic (i.e., non-magnetized) boundary layers. We discuss the possible implications of these trapped modes for explaining the variability seen in accreting compact objects.

  18. Radiation-dominated boundary layer between an accretion disc and the surface of a neutron star: theory and observations

    NASA Astrophysics Data System (ADS)

    Gilfanov, M. R.; Sunyaev, R. A.

    2014-04-01

    Observations of low-mass X-ray binaries in our Galaxy and external galaxies have drawn attention to the accretion disc boundary layer where the accreting matter slows down from its Keplerian orbital velocity of about half of the speed of light to a neutron star's rotational velocity and in which it releases about half of its gravitational energy. Correspondingly, a hot spectral component appears in the emission of accreting neutron stars, which is absent in accreting black holes. We review different approaches to the problem of the radiation-dominated boundary layer. In particular, we consider the theory of a levitating spreading layer, which assumes that the accreting matter slows down while spreading over the neutron star surface.

  19. Crustal deformation and volcanism at active plate boundaries

    NASA Astrophysics Data System (ADS)

    Geirsson, Halldor

    Most of Earth's volcanoes are located near active tectonic plate boundaries, where the tectonic plates move relative to each other resulting in deformation. Likewise, subsurface magma movement and pressure changes in magmatic systems can cause measurable deformation of the Earth's surface. The study of the shape of Earth and therefore studies of surface deformation is called geodesy. Modern geodetic techniques allow precise measurements (˜1 mm accuracy) of deformation of tectonic and magmatic systems. Because of the spatial correlation between tectonic boundaries and volcanism, the tectonic and volcanic deformation signals can become intertwined. Thus it is often important to study both tectonic and volcanic deformation processes simultaneously, when one is trying to study one of the systems individually. In this thesis, I present research on crustal deformation and magmatic processes at active plate boundaries. The study areas cover divergent and transform plate boundaries in south Iceland and convergent and transform plate boundaries in Central America, specifically Nicaragua and El Salvador. The study is composed of four main chapters: two of the chapters focus on the magma plumbing system of Hekla volcano, Iceland and the plate boundary in south Iceland; one chapter focuses on shallow controls of explosive volcanism at Telica volcano, Nicaragua; and the fourth chapter focuses on co- and post-seismic deformation from a Mw = 7.3 earthquake which occurred offshore El Salvador in 2012. Hekla volcano is located at the intersection of a transform zone and a rift zone in Iceland and thus is affected by a combination of shear and extensional strains, in addition to co-seismic and co-rifting deformation. The inter-eruptive deformation signal from Hekla is subtle, as observed by a decade (2000-2010) of GPS data in south Iceland. A simultaneous inversion of this data for parameters describing the geometry and source characteristics of the magma chamber at Hekla, and

  20. The African Plate: A history of oceanic crust accretion and subduction since the Jurassic

    NASA Astrophysics Data System (ADS)

    Gaina, C.; Torsvik, T. H.; Labails, C.; van Hinsbergen, D.; Werner, S.; Medvedev, S.

    2012-04-01

    Initially part of Gondwana and Pangea, and now surrounded almost entirely by spreading centres, the African plate moved relatively slowly for the last 200 million years. Yet both Africa's cratons and passive margins were affected by tectonic stresses developed at distant plate boundaries. Moreover, the African plate was partly underlain by hot mantle (at least for the last 300 Ma) - either a series of hotspots or a superswell, or both - that contributed to episodic volcanism, basin-swell topography, and consequent sediment deposition, erosion, and structural deformation. A systematic study of the African plate boundaries since the opening of surrounding oceanic basins is presently lacking. This is mainly because geophysical data are sparse and there are still controversies regarding the ages of oceanic crust. The publication of individual geophysical datasets and more recently, global Digital Map of Magnetic Anomalies (WDMAM, EMAG2) prompted us to systematically reconstruct the ages and extent of oceanic crust around Africa for the last 200 Ma. Location of Continent Ocean Boundary/Continent Ocean Transition and older oceanic crust (Jurassic and Cretaceous) are updates in the light of gravity, magnetic and seismic data and models of passive margin formation. Reconstructed NeoTethys oceanic crust is based on a new model of microcontinent and intr-oceanic subduction zone evolution in this area.The new set of oceanic palaeo-age grid models constitutes the basis for estimating the dynamics of oceanic crust through time and will be used as input for quantifying the paleo-ridge push and slab pull that contributed to the African plate palaeo-stresses and had the potential to influence the formation of sedimentary basins.

  1. Exact time-dependent solutions for the thin accretion disc equation: boundary conditions at finite radius

    NASA Astrophysics Data System (ADS)

    Tanaka, Takamitsu

    2011-01-01

    We discuss Green's function solutions of the equation for a geometrically thin, axisymmetric Keplerian accretion disc with a viscosity prescription ν∝Rn. The mathematical problem was solved by Lynden-Bell & Pringle for the special cases with boundary conditions of zero-viscous torque and zero mass flow at the disc centre. While it has been widely established that the observational appearance of astrophysical discs depends on the physical size of the central object(s), exact time-dependent solutions with boundary conditions imposed at finite radius have not been published for a general value of the power-law index n. We derive exact Green's function solutions that satisfy either a zero-torque or a zero-flux condition at a non-zero inner boundary Rin > 0, for an arbitrary initial surface density profile. Whereas the viscously dissipated power diverges at the disc centre for the previously known solutions with Rin= 0, the new solutions with Rin > 0 have finite expressions for the disc luminosity that agree, in the limit t→∞, with standard expressions for steady-state disc luminosities. The new solutions are applicable to the evolution of the innermost regions of thin accretion discs.

  2. Turbulent thermal boundary layer on a permeable flat plate

    SciTech Connect

    Vigdorovich, I. I.

    2007-06-15

    Scaling laws are established for the profiles of temperature, turbulent heat flux, rms temperature fluctuation, and wall heat transfer in the turbulent boundary layer on a flat plate with transpiration. In the case of blowing, the temperature distribution represented in scaling variables outside the viscous sublayer has a universal form known from experimental data for flows over impermeable flat plates. In the case of suction, the temperature distribution is described by a one-parameter family of curves. A universal law of heat transfer having the form of a generalized Reynolds analogy provides a basis for representation of the heat flux distributions corresponding to different Reynolds numbers and transpiration velocities in terms of a function of one variable. The results are obtained without invoking any special closure hypotheses.

  3. Measuring Transient Signals in Plate Boundary Faults Zones with Strainmeters

    NASA Astrophysics Data System (ADS)

    Hodgkinson, Kathleen; Mencin, Dave; Phillips, David; Henderson, Brent; Gottlieb, Mike; Gallaher, Warren; Johnson, Wade; Pyatt, Chad; Van Boskirk, Elizabeth; Fox, Otina; Mattioli, Glen; Meertens, Chuck

    2014-05-01

    One of the fundamental goals the U.S. National Science Foundation (NSF) funded Earthscope program was to provide a high-quality, continuous geodetic data set that would allow the scientific community to study the evolution of plate boundary zones. Of particular importance was enabling investigation of the role aseismic transient deformation plays in the release of accumulated stress. For example, to allow the comparison of the amount of strain released through Episodic Tremor and Slip (ETS) events to that released in subduction zone earthquakes or, provide the ability to geodetically illuminate the kinematics of fault creep in strike-slip fault zones. The ability to easily integrate these measurements with compatible geophysical data sets was also an essential objective. With goals such as these in mind NSF funded the Plate Boundary Observatory (PBO) to record the continuous deformation field across the western US Plate Boundary. PBO, built and operated by UNAVCO, now consists of over 1100 GPS stations, 76 co-located borehole strain and seismic sites, 6 long baseline strainmeters, Depending on the scientific questions being addressed sites may also have tiltmeter, meteorological, pore pressure and meteorological instrumentation. This presentation will focus on the transient deformation signals recorded by the PBO strainmeter network. PBO strainmeters, which excel in recording signals on the order of nanostrain over hours, have provided unprecedented temporal resolution of aseismic transients such as ETS events in the Cascadia subduction zone, creep signals along the central section of the San Andreas fault system and tsunami generated strain waves. UNAVCO is responsible not only for the ongoing operation of PBO but also the generation of data products associated with each instrument type. In this presentation we will highlight some of the transient signals these instruments have captured, outline the processing steps required to extract these signals data and

  4. Prototypical Concepts and Misconceptions of Plate Tectonic Boundaries

    NASA Astrophysics Data System (ADS)

    Sibley, D. F.; Patino, L. C.

    2003-12-01

    Students of geology encounter many prototypical/exemplar concepts* that include representative, but not necessarily defining, features and characteristics. This study of students' prototypical representations of plate tectonic boundaries indicates that their representations are rich sources of information about their misconceptions about plate tectonics. After lectures in plate tectonics and mountain building, 353 students in a general education geology class were asked to draw a continent-continent convergent boundary. For this study, a correct answer is defined as having the major features in correct proportions as depicted in the plate boundary diagrams on the USGS web. Fifty-two percent of the drawings were either incorrect or incomplete such that they could not be interpreted. Only 48% were readily interpretable, and of these 22% drew the boundary correctly, showing a thickening of crust where two continents collide. Thirty-three percent drew the boundary showing concave slabs of continental crust as one might imagine two pieces of firm rubber pushed together on a rigid surface and 45% depicted mountains as one might imagine inverted ice cream cones on a rigid plank. Twenty-one senior class geology majors and graduate students were given the same assignment. Forty-eight percent rendered a correct drawing, whereas 38% drew the same ice cream cone on a plank type picture that 45% of the general education students drew. In a second class of 12 geology majors, only 1 student drew a cross section of a continent-ocean boundary similar to standard representation. Four of 12 drew mountains on the top of continental crust over a subduction zone but did not draw a compensating mass within the crust or lithosphere. Prototypical drawings provide more information about students' concepts than do most multiple-choice questions. For example, sixty-two percent of theses students who drew mountains similar to foam rubber pads pushed together on a desk or ice cream cones on a

  5. Direct simulation of the turbulent boundary layer on a plate

    NASA Astrophysics Data System (ADS)

    Krupa, V. G.

    2016-08-01

    A numerical method for the integration of three-dimensional Navier-Stokes equations for compressible fluid as applied to direct numerical simulation is proposed. By way of example, the boundary layer on a plate is simulated. The computations were carried out for Reθ = 1500. The computational grid consisted of a half billion nodes. The flow region includes the laminar, transitional, and turbulent zones. The numerically obtained distributions of average velocity, friction, and pulsations are compared with experimental data and available numerical solutions.

  6. Polarization Anisotropy Along the Anatolian African Plate Boundary

    NASA Astrophysics Data System (ADS)

    Sandvol, E.; Polat, G.; Lough, A.; Sahin, S.; Turkelli, N.

    2006-12-01

    This study focuses on mantle flow beneath and around the Anatolian plate using measurements of seismic anisotropy. Observations of shear wave splitting across the Anatolian plate have a NE-SW fast direction and lag time similar to that observed from temporary broadband stations within the plate, indicating that the anisotropic fabric may be relatively uniform throughout the upper mantle beneath the Anatolian plate. The extensive young basaltic volcanism, regional travel time tomography, and regional phase attenuation tomography all indicate that the lithospheric mantle beneath most of the Anatolian plate has largely been removed or is very thin. Unless exceptionally high anisotropy exists in the thinned lithosphere, the main contribution to the observed delay times (of order 1 s) must therefore be asthenospheric and thus reflect recent asthenospheric flow patterns. One exception appears to be a change in the fast direction across a region of concentrated extension in western Anatolia. We observe a change in the orientation of the splitting that is consistent with the direction of crustal extension. The African-Anatolian plate boundary is made up of two very different convergent margins: the Hellenic arc to the west and the Cyprian arc to the east. There is substantial evidence that the Hellenic arc is retreating and the Cyprian arc is relatively stationary. Furthermore, both earthquake hypocenters and tomographic models indicate that the Cyprian angle of subduction is much less steep than the subduction occurring along the Hellenic arc. This substantial geometric difference implies that there is a tear or gap in the subduction of African oceanic lithosphere beneath the Anatolian plate along what is called the Isparta Angle. We are investigating mantle dynamics and mantle flow around and through this possible tear in the lithosphere. We will use a combination of seismic tomographic methods (surface wave, body wave, and attenuation) as well as neotectonics studies to

  7. Features on Venus generated by plate boundary processes

    NASA Technical Reports Server (NTRS)

    Mckenzie, Dan; Ford, Peter G.; Johnson, Catherine; Parsons, Barry; Sandwell, David; Saunders, Stephen; Solomon, Sean C.

    1992-01-01

    Various observations suggest that there are processes on Venus that produce features similar to those associated with plate boundaries on earth. Synthetic aperture radar images of Venus, taken with a radar whose wavelength is 12.6 cm, are compared with GLORIA images of active plate boundaries, obtained with a sound source whose wavelength is 23 cm. Features similar to transform faults and to abyssal hills on slow and fast spreading ridges can be recognized within the Artemis region of Venus but are not clearly visible elsewhere. The composition of the basalts measured by the Venera 13 and 14 and the Vega 2 spacecraft corresponds to that expected from adiabatic decompression, like that which occurs beneath spreading ridges on earth. Structures that resemble trenches are widespread on Venus and show the same curvature and asymmetry as they do on earth. These observations suggest that the same simple geophysical models that have been so successfully used to understand the tectonics of earth can also be applied to Venus.

  8. How transpressive is the northern Caribbean plate boundary?

    NASA Astrophysics Data System (ADS)

    Corbeau, J.; Rolandone, F.; Leroy, S.; Meyer, B.; Mercier de Lépinay, B.; Ellouz-Zimmermann, N.; Momplaisir, R.

    2016-04-01

    Transpressive deformation at the northern Caribbean plate boundary is accommodated mostly by two major strike-slip faults, but the amount and location of accommodation of the compressional component of deformation are still debated. We collected marine geophysical data including multibeam bathymetry and multichannel seismic reflection profiles along this plate boundary around Hispaniola, in the Jamaica Passage, and in the Gulf of Gonâve. The data set allows us to image the offshore active strike-slip faults as well as the compressional structures. We confirm that the Enriquillo-Plantain-Garden Fault Zone (EPGFZ) in the Jamaica Passage has a primary strike-slip motion, as indicated by active left-lateral strike-slip-related structures, i.e., restraining bend, asymmetrical basin, en echelon pressures ridges, and horsetail splay. Based on topographic cross sections across the EPGFZ, we image a very limited compressional component, if any, for at least the western part of the Jamaica Passage. Toward the east of the Jamaica Passage, the fault trace becomes more complex, and we identify adjacent compressional structures. In the Gulf of Gonâve, distributed folding and thrust faulting of the most recent sediments indicate active pervasive compressional tectonics. Estimates of shortening in the Jamaica Passage and in the Gulf of Gonâve indicate an increase of the compressional component of deformation toward the east, which nonetheless remains very small compared to that inferred from block modeling based on GPS measurements.

  9. Stress accumulation and release at complex transform plate boundaries

    SciTech Connect

    Verdonck, D.; Furlong, K.P. )

    1992-10-01

    Finite element methods are used to model the dynamics of deformation along complex transform plate boundaries, specifically the San Andreas fault system, California. Effects of mantle rheology and fault geometry on the stress buildup and release are investigated. No prior knowledge of the earthquake cycle time or amount of fault slip is assumed that the results suggest that the San Andreas fault slips at low shear stress (about 15 MPa). Although the maximum stress on the fault is 15 MPa, models with an upper mantle shear zone deforming entirely by dislocation creep accumulate stresses that exceed 100 MPa, a stress level high enough to drive localized dynamic recrystallization and a shift in dominant deformation mechanism to diffusion creep. Models in which the mantle shear zone deform locally by diffusion creep reach a dynamic steady state where lithospheric shear stresses never exceed the specified fault stress anywhere in the model and indicate that the strength of the upper mantle is an important parameter in the dynamics of plate boundary deformation. 17 refs.

  10. The GEORED and Plate Boundary Observatory Engineer Exchange Program

    NASA Astrophysics Data System (ADS)

    Feaux, K.; Mora-Paez, H.

    2007-05-01

    In early 2007, the Colombian Institute of Geology and Mining - INGEOMINAS initiated GEORED (Geodesia: Red de Estudios de Deformación) in order to increase the knowledge of the geodynamics of northwestern South America. GEORED is an essential tool for determining crustal deformation and is primary in the analysis of inter- plate and intraplate deformation and the present seismic cycle. Some of the objectives of the project are to improve the technical, scientific, and operational capabilities of Colombian scientists regarding tectonic and volcanic deformation in Colombia, to implement a Colombian GPS permanent network for the study of geodynamics, with near real-time data retrieval and processing, and to establish a high precision geodetic reference frame for multipurpose activities within INGEOMINAS. Phase 1 of GEORED, which includes the installation of 30 permanent GPS stations in Colombia, will commence in early 2007. The Plate Boundary Observatory (PBO), part of the larger NSF-funded EarthScope project managed by UNAVCO, will study the three-dimensional strain field resulting from active plate boundary deformation across the Western United States. PBO is a large construction project involving the reconnaissance, permitting, installation, documentation, and maintenance of 875 permanent GPS stations scheduled for completion in September 2008. PBO is currently in the fourth year of the project, with over 550 GPS stations completed to date. INGEOMINAS recently became a member of the UNAVCO consortium. UNAVCO has been working with INGEOMINAS by providing technical support for the GEORED project relating to GPS receiver specifications. In the spirit of collaboration and outreach, INGEOMINAS and UNAVCO will begin an engineer exchange program starting in early summer 2007. The purpose of this outreach program is to provide a mechanism for the exchange of ideas relating to GPS station construction techniques, hardware designs, data communications, and data archiving

  11. Development of transtensional and transpressive plate boundaries due to noncircular (cycloid) relative plate motion

    SciTech Connect

    Cronin, V.S. )

    1990-05-01

    The trace of a transform fault commonly is assumed to be circular and concentric with the finite relative motion of the plates adjacent to the fault. These assumptions have led to controversy as the transform fault label has been applied to the San Andreas fault in California because the San Andreas fault is neither circular nor concentric with the motion of the Pacific plate relative to the North American plate. The assumption of circular relative plate motion over a finite time interval is not generally valid. When finite relative plate motion is not circular, the length and orientation of a transform fault must change through time. The length and orientation of ridge-ridge transform faults in oceanic crust evolve through the migration, propagation, and abandonment of ridge segments. Transform faults that bound continental crust evolve differently than do transform faults along mid-ocean ridges because continental transform faults typically do not have ridges at both ends and because of the rheological differences between oceanic and continental crust. Along continent-continent transform faults in which the initial displacement is entirely strike slip, later displacements will be progressively more divergent or convergent (i.e., transtensive or transpressive). Transtension can result in the development of deep basins with high heat flow. Transpression can result in folding, reverse faulting, and decoupling of the crust from its lower crustal or mantle lithosphere in the region adjacent to the transform fault. Regardless of whether the transform boundary becomes transtensional or transpressional, the boundary evolves from a discrete transform fault to a broader, structurally complex accommodation zone (sensu lato).

  12. Thermochronology and tectonics of the Leeward Antilles: Evolution of the southern Caribbean Plate boundary zone

    USGS Publications Warehouse

    van der Lelij, Roelant; Spikings, Richard A.; Kerr, Andrew C.; Kounov, Alexandre; Cosca, Michael; Chew, David; Villagomez, Diego

    2010-01-01

    Tectonic reconstructions of the Caribbean Plate are severely hampered by a paucity of geochronologic and exhumation constraints from anastomosed basement blocks along its southern margin. New U/Pb, 40Ar/39Ar, apatite fission track, and apatite (U-Th)/He data constrain quantitative thermal and exhumation histories, which have been used to propose a model for the tectonic evolution of the emergent parts of the Bonaire Block and the southern Caribbean Plate boundary zone. An east facing arc system intruded through an oceanic plateau during ~90 to ~87 Ma and crops out on Aruba. Subsequent structural displacements resulted in >80°C of cooling on Aruba during 70–60 Ma. In contrast, exhumation of the island arc sequence exposed on Bonaire occurred at 85–80 Ma and 55–45 Ma. Santonian exhumation on Bonaire occurred immediately subsequent to burial metamorphism and may have been driven by the collision of a west facing island arc with the Caribbean Plate. Island arc rocks intruded oceanic plateau rocks on Gran Roque at ~65 Ma and exhumed rapidly at 55–45 Ma. We attribute Maastrichtian-Danian exhumation on Aruba and early Eocene exhumation on Bonaire and Gran Roque to sequential diachronous accretion of their basement units to the South American Plate. Widespread unconformities indicate late Eocene subaerial exposure. Late Oligocene–early Miocene dextral transtension within the Bonaire Block drove subsidence and burial of crystalline basement rocks of the Leeward Antilles to ≤1 km. Late Miocene–recent transpression caused inversion and ≤1 km of exhumation, possibly as a result of the northward escape of the Maracaibo Block.

  13. Along-strike Variations of Subduction Parameters at the Chilean Plate Boundary

    NASA Astrophysics Data System (ADS)

    Hoffmann-Rothe, A.; Kukowski, N.; Oncken, O.

    2004-12-01

    Newly compiled data of the geometric, kinematic and mechanic properties and their variations along-strike the oblique Chilean subduction margin between 20° S and 46° S are used to weigh their competing influence on forearc deformation. Special emphasis lies on the formation of margin-parallel strike-slip systems. Among the parameters considered are the convergence rate and obliquity, the ocean floor age, the dip of the down-going and the slope of the overriding plate, the geodetic and seismic coupling depth, the interplate seismicity, the depth of the trench-fill and the mass transfer mode at the subduction front. Commonly discussed control factors for forearc deformation can be attributed to three major elements of a subduction system, namely (1) the plate kinematic boundary conditions, (2) the plate coupling properties that govern the effectiveness of force transmission from the subducting plate to the overriding plate, and (3) the upper plate heterogeneities affecting its rheology (e.g. elasticity, shear strength) or resistance to block motion (buttressing). An example is given for each of these elements: (1) Oblique convergence is a pre-requisite for the activation of margin-parallel strike-slip systems, but apparently not a sufficient condition. For example, strike-slip motion can presently be observed along the Liquiñe-Ofqui Fault Zone in southern Chile, while neither the Atacama Fault Zone nor the Precordilleran Fault System in northern Chile accommodate significant amounts of margin-parallel slip since the Pliocene. This difference can not be explained by variations of convergence rate or obliquity as the plate kinematic framework is almost constant along the Chilean trench. (2) The plate coupling force is a function of the frictionally coupled area on the plate interface and of the shear friction that needs to be overcome. Along the Chilean margin various factors affect coupling in opposing manner: The slab-dip is shallower in southern Chile compared to

  14. Vibration analysis of rectangular plates with general elastic boundary supports

    NASA Astrophysics Data System (ADS)

    Li, W. L.

    2004-06-01

    In this investigation, the Rayleigh-Ritz method is used to determine the modal characteristics of a rectangular plate with general elastic supports alone its edges. Each of the admissible functions here is composed of a trigonometric function and an arbitrary continuous function that is introduced to ensure the sufficient smoothness of the so-called residual displacement function at the edges. As a result, a drastic improvement of the convergence can be expected of the solution expressed as a series expansion in terms of the admissible functions. Perhaps more importantly, this study has developed a general approach for deriving a complete set of admissible functions that can be universally applied to various boundary conditions. Several numerical examples are given to demonstrate the accuracy and convergence of the current solution.

  15. Differential cooling across the accreted terrain-North American cratonic boundary in Idaho-Oregon

    NASA Astrophysics Data System (ADS)

    Fayon, A. K.; Tikoff, B.; Kahn, M.; Byerly, A.

    2014-12-01

    The Cretaceous-age margin of western North America, as exposed along the Idaho-Oregon border, juxtaposes accreted terrains to the west and cratonic North America to the east. The Idaho batholith intrudes exclusively east of this boundary. New (U-Th)/He zircon ages from samples collected across the boundary between 44 and 45 °N latitude illustrate the variability in cooling below 200 °C and further document the abrupt nature of this margin. Three samples collected from the accreted terrains near the Idaho border yield the oldest ages: 102.3 ± 1.6 Ma (± 1σ; Sparta Butte, OR); 88.6 ± 1.3 Ma (Snake River at Pittsburg Landing, ID); and 83.5 ± 1.4 Ma (above Pittsburg Landing, ID). These ages bracket the inferred timing of deformation within the western Idaho shear zone (WISZ), which currently demarcates this boundary. Immediately to the east, within the WISZ, samples yield ages of 76.2 ± 1.4 to 63.2 ± 1.0 Ma and record steady cooling following deformation. East of the WISZ, within the Atlanta lobe of the Idaho batholith, cooling ages vary from 65.0 ± 1.0 to 20.2 ± 0.3 Ma. The overall pattern of cooling ages is older on the margins of the Atlanta lobe and younger in the center closer to the Sawtooth Valley. Higher density sampling in the Sawtooth and White Cloud Mountains near Stanley, ID reveal internal young Miocene deformation associated with extension. Ages within the Sawtooth Mountains range from 34.2 ± 0.5 Ma (Atlanta lobe) to 20.2 ± 0.3 Ma (Sawtooth granite), whereas two samples of the Atlanta lobe from the White Cloud Mountains to the east yield ages of 68.5 ± 1.0 Ma and 64.2 ± 1.0 Ma. The cooling age pattern likely reflects exhumation of the Sawtooth Mountains along an E-dipping, low-angle normal fault during the Oligocene-Miocene. Overall, the pattern of cooling ages clearly demonstrates distinct domains of thermal stability - notably accreted terrains, WISZ, and the Atlanta lobe - with respect to cooling below 200 °C.

  16. The Plate Boundary Observatory: Community Focused Web Services

    NASA Astrophysics Data System (ADS)

    Matykiewicz, J.; Anderson, G.; Lee, E.; Hoyt, B.; Hodgkinson, K.; Persson, E.; Wright, J.; Torrez, D.; Jackson, M.

    2006-12-01

    The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations. UNAVCO provides access to data products from these stations, as well as general information about the PBO project, via the PBO web site (http://pboweb.unavco.org). GPS and strainmeter data products can be found using a variety of channels, including map searches, text searches, and station specific data retrieval. In addition, the PBO construction status is available via multiple mapping interfaces, including custom web based map widgets and Google Earth. Additional construction details can be accessed from PBO operational pages and station specific home pages. The current state of health for the PBO network is available with the statistical snap-shot, full map interfaces, tabular web based reports, and automatic data mining and alerts. UNAVCO is currently working to enhance the community access to this information by developing a web service framework for the discovery of data products, interfacing with operational engineers, and exposing data services to third party participants. In addition, UNAVCO, through the PBO project, provides advanced data management and monitoring systems for use by the community in operating geodetic networks in the United States and beyond. We will demonstrate these systems during the AGU meeting, and we welcome inquiries from the community at any time.

  17. The Accretion Flow and Boundary Layer Structure in the Dwarf Nova SS Aur

    NASA Astrophysics Data System (ADS)

    Nabizadeh, Armin; Balman, Solen; Godon, Patrick; Sion, Edward; Hertfelder, Marius

    2016-07-01

    We present X-ray analysis of dwarf novae SS Aur (51 ksec) using XMM-Newton Observatory archival data obtained in quiescence for a better understanding of the accretion flow structure. We find X-ray orbital modulations. We report power spectral analysis for EPIC (X-ray) and OM (UV) light curves suggesting high levels of red noise with no significant QPO or periodicities. We simultaneously fitted EPIC pn, MOS1 and MOS2 data using a model for interstellar medium absorption (tbabs) and a multi-temperature plasma emission model (cevmkl) as expected from low accretion rate quiescent dwarf novae. However, the composite model fit yields unacceptable reduced χ ^{2} values due to the existence of soft excess. The soft excess is well modeled using a blackbody model (kT˜˜24 eV) giving a better reduced χ ^{2} value over 3σ significance level. This may indicate the existence of optically thick boundary layer emission. We will discuss the origin of this excess. The best fitting model is a combination of a blackbody, a cevmkl and a power law with an interstellar absorption which yields a reduced χ ^{2} of 1.05. The fit also shows some oxygen and iron over abundances. SS Aur has a maximum thermal plasma temperature of ˜22 keV. The X-ray luminosity in the 0.1 to 50.0 keV energy band is ˜2.0×10 ^{33} ergs ^{-1}. Finally, we discuss these characteristics in the light of standard disk models and accretion flows and geometry in nonmagnetic cataclysmic variables.

  18. Distortion of a flat-plate boundary layer by free-stream vorticity normal to the plate

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Leib, S. J.; Cowley, S. J.

    1992-01-01

    A nominally uniform flow over a semiinfinite flat plate is considered. The analysis shows how a small streamwise disturbance in the otherwise uniform flow ahead of the plate is amplified by leading-edge bluntness effects and eventually leads to a small-amplitude but nonlinear spanwise motion far downstream from the leading edge of the plate. This spanwise motion is then imposed on the viscous boundary-layer flow at the surface of the plate - causing an order-one change in its profile shape. This ultimately reduces the wall shear stress to zero, causing the boundary layer to undergo a localized separation, which may be characterized as a kind of bursting phenomenon that could be related to the turbulent bursts observed in some flat-plate boundary-layer experiments.

  19. Plate boundary processes as alternatives to mantle plume effects on the Reykjanes Ridge

    NASA Astrophysics Data System (ADS)

    Martinez, F.; Hey, R. N.; Eason, D. E.

    2015-12-01

    The North Atlantic basin displays clear regional anomalies in depth and other features centered near Iceland. A current paradigm holds that these anomalies are due to a mantle plume and that the Reykjanes Ridge, located over this plume, is a sensitive recorder of its activity in the crust it accretes. Thus, many seafloor spreading features of the Reykjanes Ridge including axial reconfigurations from orthogonal to oblique spreading, elimination of segment offsets and transform faults, and formation of V-shaped ridges and troughs flanking the axis have been attributed to mantle plume thermal effects radiating outward from beneath Iceland. Based on new geophysical data from a R/V Marcus G Langseth cruise to the southern Reykjanes Ridge we propose an alternate hypothesis: that plate boundary processes superimposed on the larger regional anomalies can account for these seafloor spreading features. A key plate boundary process is sub-axial buoyant mantle upwelling because it can increase melt production and crustal thickness relative to passive mantle advection without changes in mantle temperature. We hypothesize that on a long and linear slow spreading ridge underlain by a regional gradient in mantle temperature and water content, buoyant mantle upwelling can propagate along axis and create many of the seafloor spreading effects currently attributed to radiating mantle plume thermal pulses. However, propagating buoyant mantle upwelling is fundamentally a wave-like phenomenon wherein only the form of upwelling propagates along axis, not actual mantle material. This has profoundly different implications for the formation of crustal structures than in mantle plume models, which require actual rapid radial mantle flow. This property of the sub-axial propagating buoyant mantle upwelling model, if correct, invalidates interpretation of prominent Reykjanes Ridge seafloor spreading features as indicators of regional mantle plume flow and requires reevaluation of geodynamic

  20. Measuring the Boundary Layer and Inner Accretion Disk Temperatures for WX Ceti during Superoutburst

    NASA Astrophysics Data System (ADS)

    Howell, Steve B.; Fried, Robert; Szkody, Paula; Sirk, Martin M.; Schmidt, Gary

    2002-07-01

    We obtained EUV photometry, optical spectroscopy, and multicolor optical photometry for WX Cet during its 1998 November superoutburst. WX Cet is only the second short-period, low mass transfer cataclysmic variable (TOAD) to ever be observed in the EUV. Our determined superhump period is consistent with that found by Kato et al. (0.059 day), and we confirm that superhumps are gray in the optical. The optical spectra provide direct evidence that the line emission region is optically thick, and our multiwavelength photometric measurements are used to determine the inner accretion disk and boundary layer temperatures during superoutburst. Using a determined distance to WX Cet of ~130 pc, we find TID=21,000 K and TBL~72,500 K. Both values are in good agreement with that expected by models of the superoutburst continuum being produced by the inner disk and boundary layer. Some observations were made with the Apache Point Observatory (APO) 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium (ARC).

  1. Average properties of compressible laminar boundary layer on flat plate with unsteady flight velocity

    NASA Technical Reports Server (NTRS)

    Moore, Franklin K; Ostrach, Simon

    1957-01-01

    The time-average characteristics of boundary layers over a flat plate in nearly quasi-steady flow are determined. The plate may be either insulated or isothermal. The time averages are found without specifying the plate velocity explicitly except that it is positive and has an average value.

  2. Free vibrations of thermally stressed orthotropic plates with various boundary conditions

    NASA Technical Reports Server (NTRS)

    Bailey, C. D.; Greetham, J. C.

    1973-01-01

    An analytical investigation of the vibrations of thermally stressed orthotropic plates in the prebuckled region is presented. The investigation covers the broad class of trapezoidal plates with two opposite sides parallel. Each edge of the plate may be subjected to different uniform boundary conditions. variable thickness and arbitrary temperature distributions (analytical or experimental) for any desired combination of boundary conditions may be prescribed. Results obtained using this analysis are compared to experimental results obtained for isotropic plates with thermal stress, and to results contained in the literature for orthotropic plates without thermal stress. Good agreement exists for both sets of comparisons.

  3. The Plate Boundary Observatory: Data Management Progress and Highlights

    NASA Astrophysics Data System (ADS)

    Anderson, G.; Eakins, J.; Hodgkinson, K.; Matykiewicz, J.; Boler, F.; Beldyk, M.; Hoyt, B.; Lee, E.; Persson, E.; Torrez, D.; Wright, J.; Jackson, M.; Prescott, W.

    2006-12-01

    The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations through the PBO Nucleus project. As of 1 September 2006, the PBO GPS network was halfway completed with 426 stations installed, of which 400 have returned data, and PBO handled data flow for 120 PBO Nucleus stations. Most of these stations return data to the UNAVCO Boulder Network Operations Center (NOC) on a daily basis, with 16 returning data on an hourly basis. Overall, the combined PBO and Nucleus networks had returned almost 150 GB of raw GPS data as of September 2006. These data are then processed by the PBO GPS Analysis Centers, at Central Washington University and the New Mexico Institute of Mining and Technology, and the PBO GPS Analysis Center Coordinator at MIT. These groups create a range of GPS products, including station position time series, GPS velocity vectors, and related information. As of September 2006, these centers processed data on a daily basis from about 590 stations; typical position uncertainties are under 1.5 mm horizontally and 4 mm vertically. All PBO GPS data products are archived at and available from the UNAVCO Facility, with a second archive at the IRIS Data Management Center (DMC). All these products may be accessed via the PBO web page at http://pboweb.unavco.org/?pageid=88. As part of PBO, UNAVCO will also install and operate the largest borehole seismic and strainmeter networks in North America, as well as tiltmeters and laser strainmeters. As of September 2006, 19 PBO borehole stations had been installed and two laser strainmeter stations

  4. The Plate Boundary Observatory: Data Management Progress and Highlights

    NASA Astrophysics Data System (ADS)

    Anderson, G.; Blackman, B.; Eakins, J.; Hodgkinson, K.; Matykiewicz, J.; Boler, F.; Beldyk, M.; Henderson, B.; Hoyt, B.; Lee, E.; Persson, E.; Smith, J.; Torrez, D.; Wright, J.; Jackson, M.; Meertens, C.

    2007-12-01

    The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three- dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters by October 2008, as well as manage data for 209 previously existing continuous GPS stations and one laser strainmeter through the PBO Nucleus project and 11 GPS stations installed by the USArray segment of EarthScope. As of 1 September 2007, UNAVCO had completed 680 PBO GPS stations and had upgraded 89% of the planned PBO Nucleus stations. Most of these stations return data to the UNAVCO Boulder Network Operations Center (NOC) on a daily basis, with about 40 stations returning data on an hourly basis. Overall, the combined PBO and Nucleus network has now provided almost 350 GB of raw standard rate data, which are routinely processed by the PBO GPS Analysis Centers, at Central Washington University and the New Mexico Institute of Mining and Technology, and the PBO GPS Analysis Center Coordinator at MIT. These groups create a range of GPS products, including station position time series, GPS velocity vectors, and related information. As of September 2007, these centers processed data on a daily basis from about 920 stations; typical position uncertainties are under 1.5 mm horizontally and 4 mm vertically. All PBO GPS data products are archived at and available from the UNAVCO Facility, with a second archive at the IRIS Data Management Center (DMC). All these products may be accessed via the PBO web page at http://pboweb.unavco.org/gps_data. As part of PBO, UNAVCO will also install and operate the largest borehole seismic and strainmeter networks in North America, as well as tiltmeters and laser strainmeters. As of September 2007, 41 PBO borehole stations

  5. The Earthscope Plate Boundary Observatory Akutan Alaskan Volcano Network Installation

    NASA Astrophysics Data System (ADS)

    Pauk, B.; Jackson, M.; Mencin, D.; Power, J.; Gallaher, W.; Basset, A.; Kore, K.; Hargraves, Z.; Peterson, T.

    2005-12-01

    During June and July of 2005, the Plate Boundary Observatory (PBO) installed eight permanent GPS stations on Akutan Volcano, in the central Aleutian Islands of Alaska. PBO worked closely with the Alaska Volcano Observatory and the Magmatic Systems Site Selection working group to install stations with a spatial distribution to monitor and detect both short and long term volcanic deformation in response to magmatic intrusions at depth and magma migration through the volcano's conduit system. All eight of the GPS stations were installed by PBO field crews with helicopter support provided by Evergreen Helicopters and logistical support from the Trident Seafood Corporation, the City of Akutan, and the Akutan Corporation. Lack of roads and drivable trails on the remote volcanic island required that all equipment be transported to each site from the village of Akutan by slinging gear beneath the helicopter and internal loads. Each station installed on the volcano consists of a standard short braced GPS monument, two solar panels mounted to an inclined structure, and a six foot high Plaschem enclosure with two solar panels mounted to one of the inclined sides. Each Plaschem houses 24 6 volt batteries that power a Trimble NetRS GPS receiver and one or two Intuicom radios. Data from each GPS receiver is telemetered directly or through a repeater radio to a base station located in the village of Akutan that transmits the data over the internet to the UNAVCO data archive at ftp://data-out.unavco.or/pub/PBO_rinex where it is made freely available to the public.

  6. Paleomagnetic constraints on Cenozoic deformation along the northwest margin of the Pacific-Australian plate boundary zone through New Zealand

    NASA Astrophysics Data System (ADS)

    Turner, Gillian M.; Michalk, Daniel M.; Little, Timothy A.

    2012-02-01

    New Zealand straddles the boundary between the Australian and Pacific plates, a zone of oblique continental convergence and transform motion. The actively deforming region offers a unique opportunity to study the dynamics of deformation, including vertical-axis rotation of rigid blocks within a transcurrent plate boundary zone. We present and interpret paleomagnetic data from three new and three previously published sites from the NW part of the South Island (NW Nelson region), where sedimentary strata dated between 36 and 10 Ma overlie the crystalline Paleozoic basement assemblages of the Gondwana margin. Compared with reference directions from the Australian apparent polar wander path, none of the results provide evidence of post-Eocene vertical-axis rotation. This suggests that for the past 36 Myr NW Nelson has remained a strong, coherent block that has moved as a contiguous part of the Australian plate. This is in marked contrast to the strongly rotated nature of more outboard accreted terranes to the east. For example, the Hikurangi Margin in the North Island (NW of the Alpine Fault) and the Marlborough region in the NE of the South Island (SE of the Alpine Fault), have both undergone diverse clockwise rotations of up to 140° since the early Paleogene. The NW tip of the South Island seems to have acted as a rigid backstop relative to these more complex oroclinal deformations. We infer that, because of its relatively stiff bulk rheology, it has not been drawn into the distributed plate boundary rotational deformation associated with the New Zealand Orocline.

  7. EVOLUTION OF WARPED ACCRETION DISKS IN ACTIVE GALACTIC NUCLEI. I. ROLES OF FEEDING AT THE OUTER BOUNDARIES

    SciTech Connect

    Li, Yan-Rong; Wang, Jian-Min; Cheng, Cheng; Qiu, Jie

    2013-02-10

    We investigate the alignment processes of spinning black holes and their surrounding warped accretion disks in a frame of two different types of feeding at the outer boundaries. We consider (1) fixed flows in which gas is continually fed with a preferred angular momentum, and (2) free flows in which there is no gas supply and the disks diffuse freely at their outer edges. As expected, we find that for the cases of fixed flows the black hole disk systems always align on timescales of several 10{sup 6} yr, irrespective of the initial inclinations. If the initial inclination angles are larger than {pi}/2, the black hole accretion transits from retrograde to prograde fashion, and the accreted mass onto the black holes during these two phases is comparable. On the other hand, for the cases of free flows, both alignments and anti-alignments can occur, depending on the initial inclinations and the ratios of the angular momentum of the disks to that of the black holes. In such cases, the disks will be consumed within timescales of 10{sup 6} yr by black holes accreting at the Eddington limit. We propose that there is a close connection between the black hole spin and the lifetime for which the feeding persists, which determines the observable episodic lifetimes of active galactic nuclei. We conclude that careful inclusion of the disk feeding at the outer boundaries is crucial for modeling the evolution of the black hole spin.

  8. TIME EVOLUTION OF THE THREE-DIMENSIONAL ACCRETION FLOWS: EFFECTS OF THE ADIABATIC INDEX AND OUTER BOUNDARY CONDITION

    SciTech Connect

    Janiuk, Agnieszka; Sznajder, Maciej; Moscibrodzka, Monika; Proga, Daniel

    2009-11-10

    We study a slightly rotating accretion flow onto a black hole, using the fully three-dimensional (3D) numerical simulations. We consider hydrodynamics of an inviscid flow, assuming a spherically symmetric density distribution at the outer boundary and a small, latitude-dependent angular momentum. We investigate the role of the adiabatic index and gas temperature, and the flow behavior due to non-axisymmetric effects. Our 3D simulations confirm axisymmetric results: the material that has too much angular momentum to be accreted forms a thick torus near the equator, and the mass accretion rate is lower than the Bondi rate. In our previous study of the 3D accretion flows, for gamma = 5/3, we found that the inner torus precessed, even for axisymmetric conditions at large radii. The present study shows that the inner torus precesses also for other values of the adiabatic index: gamma = 4/3, 1.2, and 1.01. However, the time for the precession to set increases with decreasing gamma. In particular, for gamma = 1.01, we find that depending on the outer boundary conditions, the torus may shrink substantially due to the strong inflow of the non-rotating matter, and the precession will have insufficient time to develop. On the other hand, if the torus is supplied by the continuous inflow of the rotating material from the outer radii, its inner parts will eventually tilt and precess, as was for the larger gamma's.

  9. Predicting earthquakes along the major plate tectonic boundaries in the Pacific

    USGS Publications Warehouse

    Spall, H.

    1978-01-01

    In an article in the last issue of the Earthquake Information Bulletin ("Earthquakes and Plate Tectonics," by Henry Spall), we saw how 90 percent of the world's earthquakes occur at the margins of the Earth's major crustal plates. however, when we look at the distribution of earthquakes in detail, we see that a number of nearly aseismic regions, or seismic gaps, can be found along the present-day plate boundaries. Why is this? And can we regard these areas as being more likely to be the sites for future larger earthquakes than those segments of the plate boundaries that have ruptured recently. 

  10. Overview on the Plate Boundaries Along the Western Mexican Pacific Margin

    NASA Astrophysics Data System (ADS)

    Mortera-Gutierrez, C. A.; Bandy, W. L.; Michaud, F.; Ortega Ramírez, J.

    2013-05-01

    The cinematic of the Pacific, Rivera and Cocos oceanic plates have a significant impact on the subduction process and seismic cycles occurring along the western Mexican Pacific margin of the North American and Caribbean plates. Sections of Pacific (PAC), Rivera (RIV), Cocos (COC), North American (NAM) and Caribbean (CAB) plate boundaries along the western margin of Mexico are not well constrained. From north to south: the transform-rift system at Gulf of California has been generally considered as part of PAC-NAM plate boundary. However results of the FAMEX cruise at 2002 evidenced that Tosco-Abreojos Fault System along the western margin of Baja California Peninsula is active. Should this tectonic structure be considered as a plate boundary? At the RIV plate northern corner (including Mazatlan Basin), the scatter seismicity recorded between Tamayo FZ and the Marias Islands restricts the characterization of the plate boundary between the RIV and NAM plates. Some authors have proposed that Tamayo FZ and Marias I. Escarpment are the RIV-NAM plate boundary. Recently other authors have called that RIV-NAM boundary is a geomorphology lineament that runs from a Rivera Rise transform at 23N to the northern end of Marias I. Escarpment. Even so this concept is not sustained with seismic activity. Further this thought would imply that the oceanic lithosphere of Mazatlan Basin would form part of NAM plate. Other thoughts are either that there is a diffuse RIV-NAM plate boundary to the north of the Maria Archipelago, or Middle America Subduction Zone is gradually extending northward of the Maria Is. While the plate boundary at SE corner of the RIV plate is neither well defined morphologically nor seismically constraint, offshore Colima Coast. Some authors have proposed that this zone is a diffuse plate boundary between RIV and COC plates, result of a NE-SW shear plate motion. Other authors have proposed that the RIV-COC boundary extends E-W from the El Gordo Graben (EGG) at

  11. Hydrological Effects in the EarthScope Plate Boundary Observatory

    NASA Astrophysics Data System (ADS)

    Meertens, C.; Wahr, J.; Borsa, A.; Jackson, M.; Wahr, A.

    2008-12-01

    The dense network of 1,100 continuously operating GPS stations in the Plate Boundary Observatory (PBO) is providing high quality position time series. Data are processed by PBO Analysis Centers at the New Mexico Institute of Mining and Technology and at Central Washington University. The results are combined by the Analysis Center Coordinator at the Massachusetts Institute of Technology and are made available from the UNAVCO Data Center in Boulder. Analysis software of Langbein, 2008, was used to estimate secular trends and annual variations in the time series. The results were interpreted in terms of hydrological loading and poroelastic effects, from both natural and anthropogenic changes in water storage. The effects of monument stability were also considered. The density of PBO observations allows for the identification of spatial patterns that appear coherent over relatively broad areas. Vertical annual signals of 8-10 mm peak-to-peak amplitude are evident at stations in the mountains of northern and central California and southern Oregon showing peak uplift in October and are correlated to hydrological loading. The vertical elastic loading signal, calculated from the 0.25 by 0.25 degree community Noah land-surface model, fits the annual signal well and appears also to model the secular trends, although the time duration of ~3 years is still limited. In contrast to mountainous regions, stations in the valleys of California show greater spatial variability ranging from stations with almost no detectable annual signal to stations with very large, 20-30 mm, amplitudes with peak uplift in March. The vertical signals are temporally correlated to ground-water variations caused by pumping for agricultural irrigation and likely are caused by poroelastic effects in the sediments rather than loading. Annual vertical signals in southern California, where not obviously influenced from localized ground-water fluctuations, are small with ~2 mm amplitude and may be due to

  12. Inter- and intra-plate deformation at North American plate boundaries

    NASA Technical Reports Server (NTRS)

    Beavan, John

    1986-01-01

    Alaska tectonics and earthquake hazard studies; Southern California tectonics (block rotation); spreading near the Salton Trough; California plate motion (fault zone kinematics); and Caribbean plate motion investigations are examined.

  13. Plate boundaries and evolution of the Solomon Sea region

    NASA Astrophysics Data System (ADS)

    Honza, E.; Davies, H. L.; Keene, J. B.; Tiffin, D. L.

    1987-09-01

    The Solomon Sea Plate was widely developed during late Oligocene, separating the proto-West Melanesian Arc from the proto-Trobriand Arc. Spreading in the Bismarck Sea and in the Woodlark Basin resulted from interaction between the Pacific and Australian Plates, specifically from the collision of the proto-West Melanesian Arc with north New Guinea, which occurred after arc reversal. This model explains the extensive Miocene, Pliocene, and Quaternary volcanism of the Papua New Guinea mainland as it related to southward subduction of the Trobriand Trough. Our interpreted plate motions are concordant with the geological evidence onshore and also with complex tectonic features in the Solomon Sea Basin Region.

  14. Investigation of the Interaction of External Disturbances with Roughened Flat Plate Boundary Layer

    NASA Technical Reports Server (NTRS)

    Davis, Sanford S.; Dietz, A. J.

    1996-01-01

    The interaction of an external disturbance with a laminar boundary layer over a flat plate with distributed roughness is investigated using combined experimental and numerical methods. The experiment is modeled with an unsteady boundary layer code using second order backward differencing. The simulation includes the second order scattering from roughness elements at and near the first streamwise station of predicted boundary layer instability. A comparison of experimental measurements of the boundary layer perturbation due to the wake from a vibrating ribbon with the computed first order forced boundary layer perturbation showed excellent agreement. Second order roughness induced eigenfunctions from boundary layer theory are examined and compared with other forms of excitation

  15. The Caribbean-South American plate boundary at 65°W: Results from wide-angle seismic data

    NASA Astrophysics Data System (ADS)

    Bezada, M. J.; Magnani, M. B.; Zelt, C. A.; Schmitz, M.; Levander, A.

    2010-08-01

    We present the results of the analysis of new wide-angle seismic data across the Caribbean-South American plate boundary in eastern Venezuela at about 65°W. The ˜500 km long profile crosses the boundary in one of the few regions dominated by extensional structures, as most of the southeastern Caribbean margin is characterized by the presence of fold and thrust belts. A combination of first-arrival traveltime inversion and simultaneous inversion of PmP and Pn arrivals was used to develop a P wave velocity model of the crust and the uppermost mantle. At the main strike-slip fault system, we image the Cariaco Trough, a major pull-apart basin along the plate boundary. The crust under the Southern Caribbean Deformed Belt exhibits a thickness of ˜15 km, suggesting that the Caribbean Large Igneous Province extends to this part of the Caribbean plate. The velocity structures of basement highs and offshore sedimentary basins imaged by the profile are comparable to those of features found in other parts of the margin, suggesting similarities in their tectonic history. We do not image an abrupt change in Moho depth or velocity structure across the main strike-slip system, as has been observed elsewhere along the margin. It is possible that a terrane of Caribbean island arc origin was accreted to South America at this site and was subsequently bisected by the strike-slip fault system. The crust under the continental portion of the profile is thinner than observed elsewhere along the margin, possibly as a result of thinning during Jurassic rifting.

  16. Structural acoustic control of plates with variable boundary conditions: design methodology.

    PubMed

    Sprofera, Joseph D; Cabell, Randolph H; Gibbs, Gary P; Clark, Robert L

    2007-07-01

    A method for optimizing a structural acoustic control system subject to variations in plate boundary conditions is provided. The assumed modes method is used to build a plate model with varying levels of rotational boundary stiffness to simulate the dynamics of a plate with uncertain edge conditions. A transducer placement scoring process, involving Hankel singular values, is combined with a genetic optimization routine to find spatial locations robust to boundary condition variation. Predicted frequency response characteristics are examined, and theoretically optimized results are discussed in relation to the range of boundary conditions investigated. Modeled results indicate that it is possible to minimize the impact of uncertain boundary conditions in active structural acoustic control by optimizing the placement of transducers with respect to those uncertainties. PMID:17614487

  17. Inter- and intra-plate deformation at North American plate boundaries

    NASA Technical Reports Server (NTRS)

    Beavan, John; Gilbert, Lewis E.; Scholz, Chris

    1992-01-01

    A geodetic network which spans the region between San Francisco and Lake Tahoe has been measured 5 times completely with triangulation in 1880, 1922, 1929, 1943, 1963. A resurvey with the Global Positioning System (GPS) in 1991 allows the formation of 1 coseismic and 4 interseismic epochs. The data from this network provide a unique opportunity to examine the temporal and spatial evolution of the strain field associated with the 1906 San Francisco earthquake in particular and with the Pacific-North American plate boundary in general. Calculations of strain rate from the network data lead to the following conclusions. (1) There is no resolvable (greater than 0.05 microradians/yr) strain in between Sutter Buttes and the Sierra Nevada. (2) Throughout the time since the 1906 earthquake, a region extending at least as far east as the westernmost Great Valley has been undergoing deformation related to Pac:Nam interaction and the associated earthquake cycle. (3) In the time and space of overlap, our results agree with those from the United States Geological Survey (USGS) trilateration data. Both data sets indicate that strain must be accumulating to the east of Vaca. (4) The San Andreas discrepancy cannot be accommodated in the Great Valley at the 1 sigma level of our results. It is possible to absorb it in that region at the 2 sigma level. (5) Strain rate is elevated in the years following the earthquake and decays slowly with time. It is possible that the rate in the Coast Ranges increases until around 1950 and then decays. With the exception of one epoch, strain rate in the Coast Ranges is consistently fault parallel, shows no sign changes, and is consistent with monotonic strain accumulation.

  18. The Tectonic Evolution of Kinematic Blocks Along Major Plate Boundaries: the Case History of the Hyblean Region (Central Mediterranean)

    NASA Astrophysics Data System (ADS)

    Catalano, S.; Romagnoli, G.; Tortorici, G.

    2008-12-01

    The Hyblean Region (SE Sicily) in the Central Mediterranean represents a crustal block, which is entrapped at the junction between two major plate boundaries. The former consists of the E-W oriented Nubia-Eurasia boundary and the latter is represented by an incipient, roughly N-S trending, divergent margin, which has propagated from the Italian Peninsula through the African continental domains of Sicily. Usually interpreted as part of the stable African platform, the Hyblean region, during the Quaternary, has actually played the role of an independent crustal block, if framed in the larger scale plate motion. Since about 1.5 Ma, the Hyblean Block, in fact, was isolated from the rest of the Africa margin, as consequence of the propagation of the divergent margin through the SE Sicily. Since the Middle Pleistocene (≤0.8Ma), the Hyblean Block was accreted to the Nubia-Eurasia boundary, as the result of a sudden east-ward jumping of the divergent margin, to its present location. The Quaternary evolution of the Hyblean Block has emphasized some peculiar tectonic, kinematic and dynamic features that, being potentially diagnostic also for the identification of microplates, can be summarised as follow: 1. Occurrence of main regional Quaternary (<1.5 Ma) tectonics that are incongruent with the stress-in-situ measurements, focal mechanisms and geodetic data; 2. Evidence of very recent positive tectonic inversion of the Early Quaternary structures, coupled with sudden change in the displacement rate, not accompanied by variation in the larger scale plate motion; 3. Distribution of high- magnitude seismicity (6≤M≤7) along the tectonic boundaries of the crustal block; 4. Distribution of low- magnitude seismicity within the block, mostly independent from the geometry of the major Quaternary tectonics. The recognition of the Hyblean Block represents a key constraint in modelling the large scale deformation of the Central Mediterranean region. The correction of the GPS

  19. Relationship between outer forearc subsidence and plate boundary kinematics along the Northeast Japan convergent margin

    NASA Astrophysics Data System (ADS)

    Regalla, Christine; Fisher, Donald M.; Kirby, Eric; Furlong, Kevin P.

    2013-12-01

    Tectonic erosion along convergent plate boundaries, whereby removal of upper plate material along the subduction zone interface drives kilometer-scale outer forearc subsidence, has been purported to explain the evolution of nearly half the world's subduction margins, including part of the history of northeast Japan. Here, we evaluate the role of plate boundary dynamics in driving forearc subsidence in northeastern Japan. A synthesis of newly updated analyses of outer forearc subsidence, the timing and kinematics of upper plate deformation, and the history of plate convergence along the Japan trench demonstrate that the onset of rapid fore-arc tectonic subsidence is contemporaneous with upper plate extension during the opening of the Sea of Japan and with an acceleration in convergence rate at the trench. In Plio-Quaternary time, relative uplift of the outer forearc is contemporaneous with contraction across the arc and a decrease in plate convergence rate. The coincidence of these changes across the forearc, arc, backarc system appears to require an explanation at the scale of the entire plate boundary. Similar observations along other western Pacific margins suggest that correlations between forearc subsidence and major changes in plate kinematics are the rule, rather than the exception. We suggest that a significant component of forearc subsidence at the northeast Japan margin is not the consequence of basal tectonic erosion, but instead reflects dynamic changes in plate boundary geometry driven by temporal variations in plate kinematics. If correct, this model requires a reconsideration of the mass balance and crustal recycling of continental crust at nonaccretionary margins.

  20. Laminar Convective Boundary Layer Slip Flow over a Flat Plate using Homotopy Analysis Method

    NASA Astrophysics Data System (ADS)

    Daniel, Yahaya Shagaiya

    2016-08-01

    In the present study, the influence of velocity slip and suction at the boundary on the steady laminar convective boundary layer flow over a flat plate with convective boundary condition is analyzed. Similarity transformation is used to transform the boundary layer equations which are coupled with partial differential equations into system of ordinary differential equations, which are then solved semi-analytically by homotopy analysis method. The results obtained are presented for several values of the physical governing parameter and comparison with the results published in literature are in perfect agreement. Increase in the slip parameter increases the velocity to a point that the momentum boundary layer becomes thinner. The convective parameter increases as the plate surface temperature increases. The suction on the viscous incompressible fluid suppresses the velocity field and Prandtl number increases by decreasing the temperature and the thermal boundary layer thickness as a result of increase in fluid viscosity.

  1. Simulating faults and plate boundaries with a transversely isotropic plasticity model

    NASA Astrophysics Data System (ADS)

    Sharples, W.; Moresi, L. N.; Velic, M.; Jadamec, M. A.; May, D. A.

    2016-03-01

    In mantle convection simulations, dynamically evolving plate boundaries have, for the most part, been represented using an visco-plastic flow law. These systems develop fine-scale, localized, weak shear band structures which are reminiscent of faults but it is a significant challenge to resolve the large- and the emergent, small-scale-behavior. We address this issue of resolution by taking into account the observation that a rock element with embedded, planar, failure surfaces responds as a non-linear, transversely isotropic material with a weak orientation defined by the plane of the failure surface. This approach partly accounts for the large-scale behavior of fine-scale systems of shear bands which we are not in a position to resolve explicitly. We evaluate the capacity of this continuum approach to model plate boundaries, specifically in the context of subduction models where the plate boundary interface has often been represented as a planar discontinuity. We show that the inclusion of the transversely isotropic plasticity model for the plate boundary promotes asymmetric subduction from initiation. A realistic evolution of the plate boundary interface and associated stresses is crucial to understanding inter-plate coupling, convergent margin driven topography, and earthquakes.

  2. Effect of Pressure Gradients on Plate Response and Radiation in a Supersonic Turbulent Boundary Layer

    NASA Technical Reports Server (NTRS)

    Frendi, Abdelkader

    1997-01-01

    Using the model developed by the author for zero-pressure gradient turbulent boundary layers, results are obtained for adverse and favorable pressure gradients. It is shown that when a flexible plate is located in an adverse pressure gradient area, it vibrates more than if it were in a favorable pressure gradient one. Therefore the noise generated by the plate in an adverse pressure gradient is much greater than that due to the plate in a favorable pressure gradient. The effects of Reynolds number and boundary layer thickness are also analyzed and found to have the same effect in both adverse and favorable pressure gradient cases. Increasing the Reynolds number is found to increase the loading on the plate and therefore acoustic radiation. An increase in boundary layer thickness is found to decrease the level of the high frequencies and therefore the response and radiation at these frequencies. The results are in good qualitative agreement with experimental measurements.

  3. Role of Transtension in Rifting at the Pacific-North America Plate Boundary

    NASA Astrophysics Data System (ADS)

    Stock, J. M.

    2011-12-01

    Transtensional plate motion can be accommodated either in a localized zone of transtensional rifting or over a broader region. Broader zones of deformation can be classified either as diffuse deformation or strain partitioning (one or more major strike-slip shear zones geographically offset from a region of a extensional faulting). The Pacific-North America plate boundary in southwestern North America was transtensional during much of its history and has exhibited the full range of these behaviors at different spatial scales and in different locations, as recorded by fault motions and paleomagnetic rotations. Here we focus on the northern Gulf of California part of the plate boundary (Upper and Lower Delfin basin segments), which has been in a zone of transtensional Pacific-North America plate boundary motion ever since the middle Miocene demise of adjacent Farallon-derived microplates. Prior to the middle Miocene, during the time of microplate activity, this sector of North America experienced basin-and-range normal faults (core complexes) in Sonora. However there is no evidence of continued extensional faulting nor of a Gulf-related topographic depression until after ca 12 Ma when a major ignimbrite (Tuff of San Felipe/ Ignimbrite of Hermosillo) was deposited across the entire region of the future Gulf of California rift in this sector. After 12 Ma, faults disrupted this marker bed in eastern Baja California and western Sonora, and some major NNW-striking right-lateral faults are inferred to have developed near the Sonoran coast causing offset of some of the volcanic facies. However, there are major tectonic rotations of the volcanic rocks in NE Baja California between 12 and 6 Ma, suggesting that the plate boundary motion was still occurring over a broad region. By contrast, after about 6 Ma, diminished rotations in latest Miocene and Pliocene volcanic rocks, as well as fault slip histories, show that plate boundary deformation became localized to a narrower

  4. Anisotropy from SKS splitting across the Pacific-North America plate boundary offshore southern California

    NASA Astrophysics Data System (ADS)

    Ramsay, Joseph; Kohler, Monica D.; Davis, Paul M.; Wang, Xinguo; Holt, William; Weeraratne, Dayanthie S.

    2016-07-01

    SKS arrivals from ocean bottom seismometer (OBS) data from an offshore southern California deployment are analyzed for shear-wave splitting. The project involved 34 OBSs deployed for 12 months in a region extending up to 500 kilometers west of the coastline into the oceanic Pacific plate. The measurement process consisted of removing the effects of anisotropy using a range of values for splitting fast directions and delay times to minimize energy along the transverse seismometer axis. Computed splitting parameters are unexpectedly similar to onland parameters, exhibiting WSW-ENE fast polarization directions and delays between 0.8 and 1.8 s, even for oceanic plate sites. This is the first SKS splitting study to extend across the entire boundary between the North America and Pacific plates, into the oceanic part of the Pacific plate. The splitting results show that the fast direction of anisotropy on the Pacific plate does not align with absolute plate motion (APM), and they extend the trend of anisotropy in southern California an additional 500 km west, well onto the oceanic Pacific plate. We model the finite strain and anisotropy within the asthenosphere associated with density-buoyancy driven mantle flow and the effects of APM. In the absence of plate motion effects, such buoyancy driven mantle flow would be NE-directed beneath the Pacific plate observations. The best-fit patterns of mantle flow are inferred from the tomography-based models that show primary influences from foundering higher-density zones associated with the history of subduction beneath North America. The new offshore SKS measurements, when combined with measurements onshore within the plate boundary zone, indicate that dramatic lateral variations in density-driven upper mantle flow are required from offshore California into the plate boundary zone in California and western Basin and Range.

  5. Anisotropy from SKS splitting across the Pacific-North America plate boundary offshore southern California

    NASA Astrophysics Data System (ADS)

    Ramsay, Joseph; Kohler, Monica D.; Davis, Paul M.; Wang, Xinguo; Holt, William; Weeraratne, Dayanthie S.

    2016-10-01

    SKS arrivals from ocean bottom seismometer (OBS) data from an offshore southern California deployment are analysed for shear wave splitting. The project involved 34 OBSs deployed for 12 months in a region extending up to 500 km west of the coastline into the oceanic Pacific plate. The measurement process consisted of removing the effects of anisotropy using a range of values for splitting fast directions and delay times to minimize energy along the transverse seismometer axis. Computed splitting parameters are unexpectedly similar to onland parameters, exhibiting WSW-ENE fast polarization directions and delays between 0.8 and 1.8 s, even for oceanic plate sites. This is the first SKS splitting study to extend across the entire boundary between the North America and Pacific plates, into the oceanic part of the Pacific plate. The splitting results show that the fast direction of anisotropy on the Pacific plate does not align with absolute plate motion (APM), and they extend the trend of anisotropy in southern California an additional 500 km west, well onto the oceanic Pacific plate. We model the finite strain and anisotropy within the asthenosphere associated with density-buoyancy driven mantle flow and the effects of APM. In the absence of plate motion effects, such buoyancy driven mantle flow would be NE-directed beneath the Pacific plate observations. The best-fit patterns of mantle flow are inferred from the tomography-based models that show primary influences from foundering higher-density zones associated with the history of subduction beneath North America. The new offshore SKS measurements, when combined with measurements onshore within the plate boundary zone, indicate that dramatic lateral variations in density-driven upper-mantle flow are required from offshore California into the plate boundary zone in California and western Basin and Range.

  6. Plate boundaries in the Woodlark Basin and Solomon Sea Region, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Goodliffe, A. M.; Cameron, M.

    2009-12-01

    The Solomon Sea and Woodlark Basin region of eastern Papua New Guinea is a tectonically complex region between the obliquely converging Pacific and Australian plates. Despite numerous marine geophysical surveys in the region, the exact nature of the tectonic boundaries between the Solomon Sea and the Woodlark Basin remains controversial. Marine geophysical data collected in the last decade provides additional insight into this region and clearly defines the boundaries of the Solomon Sea, Trobriand, Woodlark, and Australian plates. Multibeam bathymetry data collected in 2004 along the Trobriand Trough, together with seismic profiles across the trough, show a prominent deformation front in the trench that defines the southern boundary of the Solomon Sea plate. Petrologic data from volcanoes to the south of this boundary indicate that they have a subduction affinity. Heat flow profiles to the south of the plate boundary show a clear subduction signature. At the eastern termination of the Trobriand Trough the plate boundary forms a triple junction with the NE-SW trending Nubaru strike-slip fault. To the NE this major fault separates the Solomon Sea plate from the Woodlark plate. The morphology of this fault and a CMT solution indicate that it is right-lateral. To the SW the Nubaru strike-slip fault passes to the south of the Trobriand Trough, forming the southern boundary of the Trobriand plate (with the Trobriand Trough as the northern boundary). Further west the trend of the strike slip fault becomes more ENE-WSW. A significant extension component is evident as the fault passes to the north of Egum Graben and meets the Woodlark Basin spreading system at the current rifting to seafloor spreading transition directly to the east of Moresby Seamount. The revised tectonic model for this region has important implications for tectonic reconstructions that include an active rifting to spreading transition and prominent core complexes. In the past, models have assumed a

  7. Velocity Distribution in the Boundary Layer of a Submerged Plate

    NASA Technical Reports Server (NTRS)

    Hansen, M

    1930-01-01

    This report deals with the measurement of the velocity distribution of the air in the velocity of a plate placed parallel to the air flow. The measurements took place in a small wind tunnel where the diameter of the entrance cone is 30 cm and the length of the free jet between the entrance and exit cones is about 2.5 m. The measurements were made in the free jet where the static pressure was constant, which was essential for the method of measurement used.

  8. Relationship between the present-day stress field and plate boundary forces in the Pacific Northwest

    USGS Publications Warehouse

    Geist, E.L.

    1996-01-01

    The relationship between plate boundary forces and the observed stress field in the Pacific Northwest is established using numerical models of continental deformation. Because the orientation of the greatest horizontal principal stress throughout the Pacific Northwest differs considerably from the direction of convergence between the Juan de Fuca and North American plates, the relationship between the stress field and forces acting along the subduction zone has been unclear. To address this relationship, a two-dimensional finite element model developed by Bird [1989] is used that incorporates critical aspects of continental deformation such as a stratified rheology and interaction between thermal and mechanical components of deformation. Boundary conditions are specified in terms of either velocity or shear traction, depending on whether the computed shear stress at the plate boundary is less than or exceeds, respectively, a prescribed limit. Shear-stress limits on the subduction and transform plate boundaries are independently varied to determine the relative effect of forces along these boundaries on intraplate deformation. Results from this study indicate that the shear stress limit of both subduction and transform boundaries is low, and that the intraplate stress field is attributed, in part, to the normal component of relative plate motion along the transform boundaries. However, the models also indicate that although the subduction zone fault is weak, a minimum shear strength ( ??? 10 MPa) for the fault is necessary to explain the observed stress field. The balance among forces along the tectonic boundaries of North America results in a surprising degree of variation in the present-day stress field.

  9. Constraining Late Cretaceous to mid Eocene plate boundaries in the southwest Pacific

    NASA Astrophysics Data System (ADS)

    Matthews, K. J.; Williams, S.; Whittaker, J. M.; Müller, D.; Clarke, G. L.; Seton, M.; Flament, N. E.

    2013-12-01

    The southwest Pacific has undergone a complex tectonic history since the Late Cretaceous, involving multiple episodes of subduction, back-arc spreading and continental deformation. Starkly contrasting reconstructions have been proposed for this period, ranging from tectonic quiescence with no plate boundary between the Lord Howe Rise (LHR) and Pacific, to widespread subduction and back-arc spreading, and this disparity reflects sparse and ambiguous data. Placing further constraints on these reconstructions is crucial for a variety of applications, from global-scale geodynamic studies using plate circuits to basin-scale studies of paleogeographic evolution and vertical motions. Geologic and kinematic data from the southwest Pacific are reviewed to better constrain the tectonic history of the region from the Late Cretaceous to mid Eocene, including the timing and location of plate boundary activity. This facilitates better constraints on the time-dependent evolution of the southwest Pacific plate circuit so that motion between plate pairs is consistent with geologic data and known tectonic regimes. The southwest Pacific comprised three spreading ridges during this time: in the Southeast Indian Ocean, Tasman Sea and Amundsen Sea. However, at least one, and possibly two other plate boundaries also accommodated relative motions: in the West Antarctic Rift System (WARS) and between the LHR and Pacific. Uncertainties in the timing and nature of plate boundaries prevent the construction of a robust reconstruction model and the implementation of a southwest Pacific plate circuit. Some previous plate models include continuous subduction east of the LHR throughout the Late Cretaceous-Cenozoic, while an alternative scenario involves the absence of plate boundaries between the LHR and Pacific until 45 Ma. Geologic observations suggests that subduction initiated to the east of New Caledonia at c. 55 Ma, including dyke emplacement and metamorphism in New Caledonia, and arc

  10. Global isostatic geoid anomalies for plate and boundary layer models of the lithosphere

    NASA Technical Reports Server (NTRS)

    Hager, B. H.

    1981-01-01

    Commonly used one dimensional geoid models predict that the isostatic geoid anomaly over old ocean basins for the boundary layer thermal model of the lithosphere is a factor of two greater than that for the plate model. Calculations presented, using the spherical analogues of the plate and boundary layer thermal models, show that for the actual global distribution of plate ages, one dimensional models are not accurate and a spherical, fully three dimensional treatment is necessary. The maximum difference in geoid heights predicted for the two models is only about two meters. The thermal structure of old lithosphere is unlikely to be resolvable using global geoid anomalies. Stripping the effects of plate aging and a hypothetical uniform, 35 km, isostatically-compensated continental crust from the observed geoid emphasizes that the largest-amplitude geoid anomaly is the geoid low of almost 120 m over West Antarctica, a factor of two greater than the low of 60 m over Ceylon.

  11. Plate-tectonic boundary formation by grain-damage and pinning

    NASA Astrophysics Data System (ADS)

    Bercovici, David

    2015-04-01

    Shear weakening in the lithosphere is an essential ingredient for understanding how and why plate tectonics is generated from mantle convection on terrestrial planets. I present continued work on a theoretical model for lithospheric shear-localization and plate generation through damage, grain evolution and Zener pinning in two-phase (polycrystalline) lithospheric rocks. Grain size evolves through the competition between coarsening, which drives grain-growth, with damage, which drives grain reduction. The interface between phases controls Zener pinning, which impedes grain growth. Damage to the interface enhances the Zener pinning effect, which then reduces grain-size, forcing the rheology into the grain-size-dependent diffusion creep regime. This process thus allows damage and rheological weakening to co-exist, providing a necessary shear-localizing feedback. Moreover, because pinning inhibits grain-growth it promotes shear-zone longevity and plate-boundary inheritance. This theory has been applied recently to the emergence of plate tectonics in the Archean by transient subduction and accumulation of plate boundaries over 1Gyr, as well as to rapid slab detachment and abrupt tectonic changes. New work explores the saturation of interface damage at low interface curvature (e.g., because it is associated with larger grains that take up more of the damage, and/or because interface area is reduced). This effect allows three possible equilibrium grain-sizes for a given stress; a small-grain-size high-shear state in diffusion creep, a large grain-size low shear state in dislocation creep, and an intermediate state (often near the deformation map phase-boundary). The low and high grain-size states are stable, while the intermediate one is unstable. This implies that a material deformed at a given stress can acquire two stable deformation regimes, a low- and high- shear state; these are indicative of plate-like flows, i.e, the coexistence of both slowly deforming plates

  12. Receptivity of Flat-Plate Boundary Layer in a Non-Uniform Free Stream (Vorticity Normal to the Plate)

    NASA Technical Reports Server (NTRS)

    Kogan, M. N.; Ustinov, M. V.

    1997-01-01

    Work is devoted to study of free-stream vorticity normal to leading edge interaction with boundary layer over plate and resulting flow distortion influence on laminar-turbulent transition. In experiments made the wake behind the vertically stretched wire was used as a source of vortical disturbances and its effect on the boundary layer over the horizontally mounted plate with various leading edge shapes was investigated. The purpose of experiments was to check the predictions of theoretical works of M.E. Goldstein, et. al. This theory shows that small free-stream inhomogeneity interacting with leading edge produces considerable distortion of boundary layer flow. In general, results obtained confirms predictions of Goldstein's theory, i.e., the amplification of steady vortical disturbances in boundary layer caused by vortex lines stretching was observed. Experimental results fully coincide with predictions of theory for large Reynolds number, relatively sharp leading edge and small disturbances. For large enough disturbances the flow distortion caused by symmetric wake unexpectedly becomes antisymmetric in spanwise direction. If the leading edge is too blunt the maximal distortion takes place immediately at the nose and no further amplification was observed. All these conditions and results are beyond the scope of Goldstein's theory.

  13. Origin of oroclines in Paleozoic Australia: the role of inherited plate boundary irregularities and trench retreat

    NASA Astrophysics Data System (ADS)

    Rosenbaum, G.; Shaanan, U.; Hoy, D.; Abdullah, R.

    2015-12-01

    Paleozoic Australia is made of a series of orogenic belts that include the Delamerian, Lachlan and New England orogens, as well as the poorly defined Thomson Orogen. The origin of these belts has been attributed to subduction and accretionary processes along the ~N-S-striking (present coordinates) plate boundary of Gondwana. However, recent studies show that orogenic segments are strongly contorted, thus raising questions about the geodynamic origin of eastern Australia and Paleozoic plate tectonics in general. Results from the New England Orogen revealed that oroclinal bending has occurred simultaneously with basin formation and trench retreat. Geochronological provenance studies of detrital zircon show that these basins were situated in a back-arc position, indicating that back-arc extension may have played a crucial role in oroclinal bending. In addition, geochronological data of detrital zircon show that terranes that were once considered to be exotic were actually derived from local sources. The collective geological evidence suggests that deformation and oroclinal bending were driven by subduction-related processes possibly acting on inherited irregularities in the orientation of the plate boundary. The irregular geometries were further accentuated by trench migration (retreat and advance) that led to subduction segmentation, oroclinal bending, and alternating episodes of contraction and (back-arc) extension. In search of inherited plate boundary irregularities in Paleozoic Australia, we have studied the ~E-W boundary between the Lachlan and Thomson orogens. This lithospheric-scale boundary may reflect the original geometry of the plate boundary, which might have accommodated hundreds of km of dextral offset. This boundary may be part a much larger orogenic curvature, hitherto not recognised, and the development of which may have played a fundamental role in the formation of the smaller-scale oroclines in the Lachlan and New England orogens.

  14. Boundary-layer transition on a plate subjected to simultaneous spanwise and chordwise pressure gradients

    NASA Technical Reports Server (NTRS)

    Boldman, D. R.; Brinich, P. F.

    1974-01-01

    The boundary-layer transition on a short plate was studied by means of the china-clay visual technique. The plate model was mounted in a wind tunnel so that it was subjected to small simultaneous spanwise and chordwise pressure gradients. Results of the experimental study, which was performed at three subsonic velocities, indicated that the transition pattern was appreciably curved in the spanwise direction but quite smooth and well behaved. Reasonable comparisons between predictions of transition and experiment were obtained from two finite-difference two-dimensional boundary-layer calculation methods which incorporated transition models based on the concept of a transition intermittency factor.

  15. Evidence of left-lateral active motion at the North America-Caribbean plate boundary

    NASA Astrophysics Data System (ADS)

    Leroy, S. D.; Ellouz, N.; Corbeau, J.; Rolandone, F.; Mercier De Lepinay, B. F.; Meyer, B.; Momplaisir, R.; Granja, J. L.; Battani, A.; Burov, E. B.; Clouard, V.; Deschamps, R.; Gorini, C.; Hamon, Y.; LE Pourhiet, L.; Loget, N.; Lucazeau, F.; Pillot, D.; Poort, J.; Tankoo, K.; Cuevas, J. L.; Alcaide, J.; Poix, C. J.; Mitton, S.; Rodriguez, Y.; Schmitz, J.; Munoz Martin, A.

    2014-12-01

    The North America-Caribbean plate boundary is one of the least-known among large plate boundaries. Although it was identified early on as an example of a strike-slip fault in the north of Hispaniola, its structure and rate of motion remains poorly constrained. We present the first direct evidence for active sinistral strike-slip motion along this fault, based on swath seafloor mapping of the northern Haiti area. There is evidence for ~16.5 km of apparent strike-slip motion along the mapped segment of the Septentrional fault zone off Cap Haitien town which is terminated to the east onland Dominican republic and in the west to southern Cuban margin. By evaluating these new constraints within the context of geodetic models of global plate motions, we estimate an activity of the fault since 2 Ma with an angular velocity for the Caribbean plate relative to the North America predicted 6-12 mmyr-1 sinistral motion along the Septentrional fault zone. This transform fault was initiated around 20 million years ago in its western segment and since 2 Ma in its eastern segment in response to a regional reorganization of plate velocities and directions, which induced a change in configuration of plate boundaries.

  16. Tsunamis from Tectonic Sources along Caribbean Plate Boundaries

    NASA Astrophysics Data System (ADS)

    Lopez, A. M.; Chacon, S.; Zamora, N.; Audemard, F. A.; Dondin, F. J. Y.; Clouard, V.; Løvholt, F.; Harbitz, C. B.; Vanacore, E. A.; Huerfano Moreno, V. A.

    2015-12-01

    The Working Group 2 (WG2) of the Intergovernmental Coordination Group for the Tsunami and Other Coastal Hazards Warning System for the Caribbean and Adjacent Regions (ICG/CARIBE-EWS) in charge of Tsunami Hazards Assessment, has generated a list of tsunami sources for the Caribbean region. Simulating these worst-case, most credible scenarios would provide an estimate of the resulting effects on coastal areas within the Caribbean. In the past few years, several publications have addressed this issue resulting in a collection of potential tsunami sources and scenarios. These publications come from a wide variety of sources; from government agencies to academic institutions. Although these provide the scientific community with a list of sources and scenarios, it was the interest of the WG2 to evaluate what has been proposed and develop a comprehensive list of sources, therefore leaving aside proposed scenarios. The seismo-tectonics experts of the Caribbean within the WG2 members were tasked to evaluate comprehensively which published sources are credible, worst-cases, and consider other sources that have been omitted from available reports. Among these published sources are the GEM Faulted Earth Subduction Characterization Project, and the LANTEX/Caribe Wave annual exercise publications (2009-2015). Caribbean tectonic features capable of generating tsunamis from seismic dislocation are located along the Northeastern Caribbean, the Lesser Antilles Trench, and the Panamá and Southern Caribbean Deformed Belts. The proposed sources have been evaluated based on historical and instrumental seismicity as well as geological and geophysical studies. This paper presents the sources and their justification as most-probable tsunami sources based on the context of crustal deformation due to Caribbean plate interacting with neighboring North and South America plates. Simulations of these sources is part of a subsequent phase in which effects of these tectonically induced tsunamis

  17. Crustal Structure of the Caribbean-South American Diffuse Plate Boundary: Subduction Zone Migration and Polarity Reversal Along BOLIVAR Profile 64W

    NASA Astrophysics Data System (ADS)

    Clark, S. A.; Levander, A.; Magnani, M.; Zelt, C. A.; Sawyer, D. S.; Ave Lallemant, H. G.

    2005-12-01

    The BOLIVAR (Broadband Ocean-Land Investigation of Venezuela and the Antilles arc Region) project is an NSF funded, collaborative seismic experiment in the southeast Caribbean region. The purpose of the project is to understand the diffuse plate boundary created by the oblique collision between the Caribbean and South American plates. Profile 64W of the BOLIVAR experiment, a 450 km-long, N-S transect onshore and offshore Venezuela located at ~64°W longitude, images the deep crustal structures formed by this collision. The active source components of profile 64W include 300 km of MCS reflection data, 33 coincident OBSs, and 344 land seismic stations which recorded 7500 offshore airgun shots and 2 explosive land shots. Results from the reflection and refraction seismic data along 64W show complex crustal structure across the entire span of the diffuse plate boundary. The onshore portion of 64W crosses the fold and thrust belt of the Serrania del Interior, which formed at ~16 Ma by collision of the Caribbean forearc with the northern South American passive margin. Underlying the Serrania del Interior is a south-vergent, remnant Lesser Antillean subduction zone. As this Lesser Antilles subduction impinged on continental crust, it caused a polarity reversal and jump offshore to the north. Convergence was initially localized in the closure and inversion of the Grenada Basin. However, subduction could not develop because of the ~20-km-thick crust of the Aves Ridge; instead, north-vergent subduction initiated further to the north, where ~12-km-thick Caribbean oceanic crust of the Venezuela Basin began to subduct beneath the Aves Ridge in the Pliocene (~4 Ma) and appears to continue subducting today. Between the remnant subduction zone and the modern one, the El Pilar and Coche dextral strike-slip faults accommodate most of the transform motion of the plate boundary. From the Serrania del Interior to the Aves Ridge, ~260 km of accreted orogenic float comprises the diffuse

  18. Crustal Thickness Variations Along the Southeastern Caribbean Plate Boundary From Teleseismic and Active Source Seismic Data

    NASA Astrophysics Data System (ADS)

    Bezada, M. J.; Niu, F.; Baldwin, T. K.; Pavlis, G.; Vernon, F.; Rendón, H.; Zelt, C. A.; Schmitz, M.; Levander, A.

    2006-12-01

    coastal mountains, suggesting a significant portion of the high topography of the costal mountain ranges has a dynamic origin. Crustal thickness changes of more than 10km are observed crossing the coast in the plate boundary zone, but are not always directly associated with the surface expression of the strike-slip fault system.

  19. The Northwestern (Maghreb) boundary of the Nubia (Africa) Plate

    NASA Astrophysics Data System (ADS)

    Mauffret, Alain

    2007-01-01

    A study of the present compressional deformation of the Northwestern (Maghreb) Nubia (Africa) margin is derived from the analysis of more than 20,000 km of seismic profiles. In the western part the compression is distributed in a large zone with on-land compression in Algeria, mainly strike-slip deformation on the Algerian margin and folds and strike-slip faulting in Eastern Spain. In the middle of the Algerian margin, around Algiers, the evidences of compression become more obvious. In this area a ridge trending N-S that is interpreted as a middle to late Miocene spreading center interacted with the transpressional margin that trends E-W. North of the location of the Boumerdes-Zemmouri earthquake the oceanic crust is deformed by blind thrusts up to 60 km from the coast. These thrusts are south dipping and with the northward dipping thrusts located onshore form a wedge that maybe a positive flower structure at a crustal scale related to the right-lateral transpression of the margin. In the eastern part of the Northwestern (Maghreb) Nubia (Africa) Deformed Belt, off eastern Algeria and Tunisia, the deformation is more intense but limited to the north by the continental slope. Large late Miocene Tortonian folds are cut by the Messinian erosional surface but the present deformation is also evident. It is suggested that the deformation with a double vergence may be followed up to the north of Sicily. After the docking (18 Ma) of the Kabylies to the Africa Plate, the crust has been thinned and the Algerian Basin opened during the middle-late Miocene with an E-W direction. From the late Miocene to the Present the margin has been rethickened by transpression and uplifted.

  20. Dynamics of convergent plate boundaries: Insights from subduction-related serpentinite melanges from the northern edge of the Caribbean plate

    NASA Astrophysics Data System (ADS)

    García-Casco, A.

    2012-04-01

    Subduction-related rock complexes, many of them tectonic melanges, occur in the Central America-Caribbean-Andean belt. I review the lithology and P-T-t paths of HP rocks and offer interpretations and generalizations on the thermal estate of the subducting plate(s), the melange forming events, and the exhumation history of rock complexes formed in the northern branch of the Caribbean subduction zone (Cuba and nearby Guatemala and Dominican Republic; ca. 3000 km apart). These complexes contain high pressure rocks formed and exhumed at the convergent (Pacific-Atlantic) leading edge of the Caribbean plate during ca. 100 Ma (early Cretaceous-Oligocene), attesting for long lasting oceanic -followed by continental- subduction/accretion in the region. Lithologic data indicate a complex melange-forming process. In most cases, the HP rocks represent subducted MOR-related lithologies occurring as tectonic blocks within serpentinite-matrix melanges interpreted as exhumed fragments of the subduction channel(s). Most of these melanges, however, contain fragments of arc/forearc-related non metamorphic and metamorphic (low-P and high-P) sedimentary and igneous rocks. While the HP blocks of arc/forearc material indicate subduction erosion at depth, the interpretation of the LP and non-metamorphic blocks is not straight forward. Indeed, tectonic blocks of HP metamafic rocks are surrounded by antigorite-serpentinite which, in turn, is surrounded by a low-P, low-T (chrysotile-lizardite) serpentinite that makes much of the mélange. These relations indicate that the melanges represent, in fact, tectonic stacks of shallow low-T forearc serpentinite that incorporate tectonic blocks/slices of the subduction-channel (high-P, high-T serpentinite and HP metamafic blocks) and of the arc/forearc crust (low-P and non-metamorphic blocks). This picture is similar to that of HP continental margin-derived tectonic stacks containing exotic slices of antigoritite-serpentine melanges (with blocks of

  1. Post-rifting stress relaxation at the divergent plate boundary in Northeast Iceland

    USGS Publications Warehouse

    Foulger, G.R.; Jahn, C.-H.; Seeber, G.; Einarsson, P.; Julian, B.R.; Heki, K.

    1992-01-01

    Interaction of the elastic lithosphere with the underlying anelastic asthenosphere causes strain to propagate along the Earth's surface in a diffusion-like manner following tectonism at plate boundaries. This process transfers stress between adjacent tectonic segments and influences the temporal tectonic pattern along a plate boundary. Observations of such strain transients have been rare, and have hitherto been confined to strike-slip and underthrusting plate boundaries1. Here we report the observation of a strain transient at the divergent (spreading) plate boundary in Iceland. A Global Positioning System survey undertaken a decade after an episode of dyke intrusion accompanying several metres of crustal spreading reveals a spatially varying strain field with the expected diffusion-pulse shape and an amplitude three times greater than the 5.7 cm that would be expected from the average spreading rate2. A simple one-dimensional model with a thin elastic layer overlying a viscous layer fits the data well and yields a stress diffusivity of 1.1 ?? 0.3 m2 s-1. Combined with struc-tural information from magnetotelluric measurements, this implies a viscosity of 0.3-2 ?? 1019 Pa s - a value comparable to that derived for Iceland from post-glacial rebound23, but low compared with estimates for mantle viscosity obtained elsewhere3.

  2. Seismotectonics of plate boundaries. Final report, 1 November 1973-30 June 1981

    SciTech Connect

    Berger, J.; Brune, J.N.; Goodkind, J.; Wyatt, F.; Agnew, D.C.; Beaumont, C.

    1981-06-01

    Research on the seismotectonics of plate boundaries is summarized. Instrumental development and an observational program designed to study various aspects of the seismotectonics of southern California and the northern Gulf of California are described. A unique superconducting gravimeter was further developed and supported under this program for deployment and operation at several sites. Work on Earth tides is also discussed.

  3. Discovering plate boundaries: Laboratory and classroom exercises using geodetic data to develop students' understanding of plate motion

    NASA Astrophysics Data System (ADS)

    Olds, S. E.

    2010-12-01

    To introduce the concept of plate boundaries, typical introductory geology exercises include students observing and plotting the location of earthquakes and volcanoes on a map to visually demarcate plate boundaries. Accompanying these exercises, students are often exposed to animations depicting the movement of Earth’s tectonic plates over time. Both of these teaching techniques are very useful for describing where the tectonics plates have been in the past, their shapes, and where the plates are now. With the integration of data from current geodetic techniques such as GPS, InSAR, LiDAR, students can learn that not only have the tectonic plates moved in the past, but they are moving, deforming, and changing shape right now. Additionally, GPS data can be visualized using time scales of days to weeks and on the scale of millimeters to centimeters per year. The familiar temporal and spatial scales of GPS data also help students understand that plate tectonics is a process that is happening in the present and can ease the transition to thinking about processes that are typically described using deep time, a very difficult concept for students to grasp. To provide a more robust learning environment, UNAVCO has been incorporating high-precision GPS data into free, place-based, data-rich learning modules for educators and students in introductory Earth science courses at secondary and undergraduate levels. These modules integrate new scientific discoveries related to crustal deformation and explore applications of GPS, LiDAR, and InSAR techniques to research. They also provide students with case studies highlighting the process of scientific discovery, providing context and meaning. Concurrent to these efforts, tools to visualize the inter-relationships of geophysical and geologic processes, structures, and measurements including high-precision GPS velocity data are an essential part of the learning materials. Among the suite of visualization tools that UNAVCO has made

  4. Numerical modeling of the transitional boundary layer over a flat plate

    NASA Astrophysics Data System (ADS)

    Ivanov, Dimitry; Chorny, Andrei

    2015-11-01

    Our example is connected with fundamental research on understanding how an initially laminar boundary layer becomes turbulent. We have chosen the flow over a flat plate as a prototype for boundary-layer flows around bodies. Special attention was paid to the near-wall region in order to capture all levels of the boundary layer. In this study, the numerical software package OpenFOAM has been used in order to solve the flow field. The results were used in a comparative study with data obtained from Large Eddy Simulation (LES). The composite SGS-wall model is presently incorporated into a computer code suitable for the LES of developing flat-plate boundary layers. Presently this model is extended to the LES of the zero-pressure gradient, flat-plate turbulent boundary layer. In current study the time discretization is based on a second order Crank-Nicolson/Adams-Bashforth method. LES solver using Smagorinsky and the one-equation LES turbulence models. The transition models significantly improve the prediction of the onset location compared to the fully turbulent models.LES methods appear to be the most promising new tool for the design and analysis of flow devices including transition regions of the turbulent flow.

  5. Measurements of strain at plate boundaries using space based geodetic techniques

    NASA Technical Reports Server (NTRS)

    Robaudo, Stefano; Harrison, Christopher G. A.

    1993-01-01

    We have used the space based geodetic techniques of Satellite Laser Ranging (SLR) and VLBI to study strain along subduction and transform plate boundaries and have interpreted the results using a simple elastic dislocation model. Six stations located behind island arcs were analyzed as representative of subduction zones while 13 sites located on either side of the San Andreas fault were used for the transcurrent zones. The length deformation scale was then calculated for both tectonic margins by fitting the relative strain to an exponentially decreasing function of distance from the plate boundary. Results show that space-based data for the transcurrent boundary along the San Andreas fault help to define better the deformation length scale in the area while fitting nicely the elastic half-space earth model. For subduction type bonndaries the analysis indicates that there is no single scale length which uniquely describes the deformation. This is mainly due to the difference in subduction characteristics for the different areas.

  6. Seismic evidence for sharp lithosphere-asthenosphere boundaries of oceanic plates.

    PubMed

    Kawakatsu, Hitoshi; Kumar, Prakash; Takei, Yasuko; Shinohara, Masanao; Kanazawa, Toshihiko; Araki, Eiichiro; Suyehiro, Kiyoshi

    2009-04-24

    The mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics, and thus the understanding of the processes at the lithosphere-asthenosphere boundary (LAB) is fundamental to understand how our planet works. It is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the LAB. Data from borehole broadband ocean bottom seismometers show that the LAB beneath the Pacific and Philippine Sea plates is sharp and age-dependent. The observed large shear wave velocity reduction at the LAB requires a partially molten asthenosphere consisting of horizontal melt-rich layers embedded in meltless mantle, which accounts for the large viscosity contrast at the LAB that facilitates horizontal plate motions. PMID:19390042

  7. Seismic evidence for sharp lithosphere-asthenosphere boundaries of oceanic plates.

    PubMed

    Kawakatsu, Hitoshi; Kumar, Prakash; Takei, Yasuko; Shinohara, Masanao; Kanazawa, Toshihiko; Araki, Eiichiro; Suyehiro, Kiyoshi

    2009-04-24

    The mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics, and thus the understanding of the processes at the lithosphere-asthenosphere boundary (LAB) is fundamental to understand how our planet works. It is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the LAB. Data from borehole broadband ocean bottom seismometers show that the LAB beneath the Pacific and Philippine Sea plates is sharp and age-dependent. The observed large shear wave velocity reduction at the LAB requires a partially molten asthenosphere consisting of horizontal melt-rich layers embedded in meltless mantle, which accounts for the large viscosity contrast at the LAB that facilitates horizontal plate motions.

  8. Discovering Plate Boundaries Update: Builds Content Knowledge and Models Inquiry-based Learning

    NASA Astrophysics Data System (ADS)

    Sawyer, D. S.; Pringle, M. S.; Henning, A. T.

    2009-12-01

    Discovering Plate Boundaries (DPB) is a jigsaw-structured classroom exercise in which students explore the fundamental datasets from which plate boundary processes were discovered. The exercise has been widely used in the past ten years as a classroom activity for students in fifth grade through high school, and for Earth Science major and general education courses in college. Perhaps more importantly, the exercise has been used extensively for professional development of in-service and pre-service K-12 science teachers, where it simultaneously builds content knowledge in plate boundary processes (including natural hazards), models an effective data-rich, inquiry-based pedagogy, and provides a set of lesson plans and materials which teachers can port directly into their own classroom (see Pringle, et al, this session for a specific example). DPB is based on 4 “specialty” data maps, 1) earthquake locations, 2) modern volcanic activity, 3) seafloor age, and 4) topography and bathymetry, plus a fifth map of (undifferentiated) plate boundary locations. The jigsaw is structured so that students are first split into one of the four “specialties,” then re-arranged into groups with each of the four specialties to describe the boundaries of a particular plate. We have taken the original DPB materials, used the latest digital data sets to update all the basic maps, and expanded the opportunities for further student and teacher learning. The earthquake maps now cover the recent period including the deadly Banda Aceh event. The topography/bathymetry map now has global coverage and uses ice-free elevations, which can, for example, extend to further inquiry about mantle viscosity and loading processes (why are significant portions of the bedrock surface of Greenland and Antarctica below sea level?). The volcanic activity map now differentiates volcano type and primary volcanic lithology, allowing a more elaborate understanding of volcanism at different plate boundaries

  9. Receptivity of flat-plate boundary layer in a non-uniform free stream (vorticity normal to the plate)

    NASA Technical Reports Server (NTRS)

    Kogan, M. N.

    1994-01-01

    Recent progress in both the linear and nonlinear aspects of stability theory has highlighted the importance of the receptivity problem. One of the most unclear aspects of receptivity study is the receptivity of boundary-layer flow normal to vortical disturbances. Some experimental and theoretical results permit the proposition that quasi-steady outer-flow vortical disturbances may trigger by-pass transition. In present work such interaction is investigated for vorticity normal to a leading edge. The interest in these types of vortical disturbances arise from theoretical work, where it was shown that small sinusoidal variations of upstream velocity along the spanwise direction can produce significant variations in the boundary-layer profile. In the experimental part of this work, such non-uniform flow was created and the laminar-turbulent transition in this flow was investigated. The experiment was carried out in a low-turbulence direct-flow wind tunnel T-361 at the Central Aerohydrodynamic Institute (TsAGI). The non-uniform flow was produced by laminar or turbulent wakes behind a wire placed normal to the plate upstream of the leading edge. The theoretical part of the work is devoted to studying the unstable disturbance evolution in a boundary layer with strongly non-uniform velocity profiles similar to that produced by outer-flow vorticity. Specifically, the Tollmien-Schlichting wave development in the boundary layer flow with spanwise variations of velocity is investigated.

  10. Late Cretaceous to mid Eocene plate boundaries in the southwest Pacific

    NASA Astrophysics Data System (ADS)

    Matthews, Kara J.; Dietmar Müller, R.; Whittaker, Joanne; Flament, Nicolas; Seton, Maria

    2013-04-01

    The late Cretaceous to mid Eocene history of the southwest and southernmost Pacific has been subject to starkly contrasting interpretations, ranging from relative tectonic quiescence with the Lord Howe Rise (LHR) being part of the Pacific plate to a dynamic subduction setting. In the first scenario the Tasman Sea would have formed as a consequence of divergence between the Pacific and Australian plates, whereas in the second scenario it would have formed as a marginal basin associated with subduction. The first scenario is supported by a number of arguments, including a lack of evidence for deformation and tectonic activity in New Zealand during this period and a geodynamic modelling inference, namely that the bend in the Hawaiian-Emperor chain can be better reproduced if the LHR is part of the Pacific plate. The second scenario is supported by regional plate kinematic models reconciling a variety of observations including back-arc basin formation and destruction through time and the history of arc-continent collisions. The primary problem with the first scenario is the use of a plate circuit that leaves relative motion between East and West Antarctica unconstrained, leading to an improbable history of periodic compression and extension. The main problem with the alternative scenario is a lack of sampled late Cretaceous volcanic arc rocks east of the LHR. We analysed available geological and geophysical data to constrain the locations of and movements along the plate boundaries in the southwest and southern Pacific from the late Cretaceous to mid Eocene, and assessed how Pacific plate motion is best quantified during this period. Geological and geophysical evidence suggests that a plate boundary separated the Pacific plate from the LHR. The distribution of lower mantle slab material that is imaged by seismic tomography beneath New Zealand is best explained if subduction occurred to the east of the LHR during the entire late Cretaceous to mid Eocene period. Rocks

  11. Natural frequencies of thick, symmetrically-laminated, skew, trapezoidal plates with various boundary supports

    SciTech Connect

    Kapania, R.K.; Lovejoy, A.E.

    1994-12-31

    Increasing use of composite materials in structures requires an accurate method of predicting response. Transverse shear effects can play an important role in laminated structures, even those that are considered thin, and as a result, should not be neglected. The free vibration response of generally laminated, thick, skewed, trapezoidal plates is investigated due of the lack of information in this area. In the method developed, Chebychev polynomials are used as displacement functions in the Rayleigh-Ritz method. To account for various edge supports, free, simply supported, and clamped, appropriate linear and rotational springs are introduced to satisfy the essential boundary conditions. First-order shear theory is used to account for transverse shear effects, and rotary inertia is also included in the model. Convergence of the solution resulting from changes in spring values and number of terms in the series is investigated. To demonstrate the accuracy of the method, results for thin isotropic and laminated plates are compared to past results for various planforms and boundary conditions. Next, thick isotropic plate results are compared to available published results. Thick laminated plate results for various planforms and boundary conditions are then presented. Variations in natural frequencies due to geometric parameter changes, such as taper ratio and sweep angle, are also studied.

  12. Lower plate deformation structures along the Costa Rica erosive plate boundary - results from IODP Expedition 344 (CRISP 2)

    NASA Astrophysics Data System (ADS)

    Brandstätter, Jennifer; Kurz, Walter; Micheuz, Peter; Krenn, Kurt

    2015-04-01

    1414 is located ~1 km seaward of the deformation front offshore the Osa Peninsula and Caño Island. Primary science goals at Site U1414 included characterization of the alteration state of the magmatic basement. Brittle structures within the incoming plate (sites U1380, U1414) are mineralized extensional fractures and shear fractures. The shear fractures mainly show a normal component of shear. Within the sedimentary sequence both types of fractures dip steeply (vertical to subvertical) and strike NNE-SSW. Deformation bands trend roughly ENE-WSW, sub-parallel to the trend of the Cocos ridge. Structures in the Cocos Ridge basalt mainly comprise mineralized veins at various orientations. A preferred orientation of strike directions was not observed. Some veins show straight boundaries, others are characterized by an irregular geometry characterized by brecciated wall rock clasts embedded within vein precipitates. The vein mineralization was analysed in detail by RAMAN spectroscopy. Precipitation conditions and fluid chemistry were analysed by fluid inclusions entrapped within vein minerals. Vein mineralizations mainly consist of carbonate (fibrous aragonite, calcite), chalcedony, and quartz. Vein mineralization is mainly characterized by zoned antitaxial growth of carbonate fibres including a suture along the central vein domains. Quartz is often characterized by fibre growth of crystals perpendicular to the vein boundaries, too. These zoned veins additinally have wall rock alteration seams consisting of clay minerals. The precipitation sequence basically indicates that fluid chemistry evolved from an CO2-rich towards a SiO2- rich fluid.

  13. Geological record of fluid flow and seismogenesis along an erosive subducting plate boundary.

    PubMed

    Vannucchi, Paola; Remitti, Francesca; Bettelli, Giuseppe

    2008-02-01

    Tectonic erosion of the overriding plate by the downgoing slab is believed to occur at half the Earth's subduction zones. In situ investigation of the geological processes at active erosive margins is extremely difficult owing to the deep marine environment and the net loss of forearc crust to deeper levels in the subduction zone. Until now, a fossil erosive subduction channel-the shear zone marking the plate boundary-has not been recognized in the field, so that seismic observations have provided the only information on plate boundary processes at erosive margins. Here we show that a fossil erosive margin is preserved in the Northern Apennines of Italy. It formed during the Tertiary transition from oceanic subduction to continental collision, and was preserved by the late deactivation and fossilization of the plate boundary. The outcropping erosive subduction channel is approximately 500 m thick. It is representative of the first 5 km of depth, with its deeper portions reaching approximately 150 degrees C. The fossil zone records several surprises. Two décollements were simultaneously active at the top and base of the subduction channel. Both deeper basal erosion and near-surface frontal erosion occurred. At shallow depths extension was a key deformation component within this erosive convergent plate boundary, and slip occurred without an observable fluid pressure cycle. At depths greater than about 3 km a fluid cycle is clearly shown by the development of veins and the alternation of fast (co-seismic) and slow (inter-seismic) slip. In the deepest portions of the outcropping subduction channel, extension is finally overprinted by compressional structures. In modern subduction zones the onset of seismic activity is believed to occur at approximately 150 degrees C, but in the fossil channel the onset occurred at cooler palaeo-temperatures.

  14. Subcontinental-scale crustal velocity changes along the Pacific-North America plate boundary.

    PubMed

    Davis, J L; Wernicke, B P; Bisnath, S; Niemi, N A; Elósegui, P

    2006-06-29

    Transient tectonic deformation has long been noted within approximately 100 km of plate boundary fault zones and within active volcanic regions, but it is unknown whether transient motions also occur at larger scales within plates. Relatively localized transients are known to occur as both seismic and episodic aseismic events, and are generally ascribed to motions of magma bodies, aseismic creep on faults, or elastic or viscoelastic effects associated with earthquakes. However, triggering phenomena and systematic patterns of seismic strain release at subcontinental (approximately 1,000 km) scale along diffuse plate boundaries have long suggested that energy transfer occurs at larger scale. Such transfer appears to occur by the interaction of stresses induced by surface wave propagation and magma or groundwater in the crust, or from large-scale stress diffusion within the oceanic mantle in the decades following clusters of great earthquakes. Here we report geodetic evidence for a coherent, subcontinental-scale change in tectonic velocity along a diffuse approximately 1,000-km-wide deformation zone. Our observations are derived from continuous GPS (Global Positioning System) data collected over the past decade across the Basin and Range province, which absorbs approximately 25 per cent of Pacific-North America relative plate motion. The observed changes in site velocity define a sharp boundary near the centre of the province oriented roughly parallel to the north-northwest relative plate motion vector. We show that sites to the west of this boundary slowed relative to sites east of it by approximately 1 mm yr(-1) starting in late 1999.

  15. Subcontinental-scale crustal velocity changes along the Pacific-North America plate boundary.

    PubMed

    Davis, J L; Wernicke, B P; Bisnath, S; Niemi, N A; Elósegui, P

    2006-06-29

    Transient tectonic deformation has long been noted within approximately 100 km of plate boundary fault zones and within active volcanic regions, but it is unknown whether transient motions also occur at larger scales within plates. Relatively localized transients are known to occur as both seismic and episodic aseismic events, and are generally ascribed to motions of magma bodies, aseismic creep on faults, or elastic or viscoelastic effects associated with earthquakes. However, triggering phenomena and systematic patterns of seismic strain release at subcontinental (approximately 1,000 km) scale along diffuse plate boundaries have long suggested that energy transfer occurs at larger scale. Such transfer appears to occur by the interaction of stresses induced by surface wave propagation and magma or groundwater in the crust, or from large-scale stress diffusion within the oceanic mantle in the decades following clusters of great earthquakes. Here we report geodetic evidence for a coherent, subcontinental-scale change in tectonic velocity along a diffuse approximately 1,000-km-wide deformation zone. Our observations are derived from continuous GPS (Global Positioning System) data collected over the past decade across the Basin and Range province, which absorbs approximately 25 per cent of Pacific-North America relative plate motion. The observed changes in site velocity define a sharp boundary near the centre of the province oriented roughly parallel to the north-northwest relative plate motion vector. We show that sites to the west of this boundary slowed relative to sites east of it by approximately 1 mm yr(-1) starting in late 1999. PMID:16810252

  16. The Lower Engadine Window: sediment deposition and accretion in relation to the plate-tectonic evolution of the Eastern Alps

    NASA Astrophysics Data System (ADS)

    Waibel, A. F.; Frisch, W.

    1989-05-01

    been largely strike-slip and directed essentially E-W during the Cretaceous. An irregular leading edge of the Adriatic plate is proposed to account for Cretaceous high-pressure metamorphic events associated with higher rates of plate consumption in adjacent regions. N-S compressional movements in the Tertiary finally resulted in rapid underthrusting and continental accretion along most of the eastern Alpine arc.

  17. In-plane vibration analysis of annular plates with arbitrary boundary conditions.

    PubMed

    Shi, Xianjie; Shi, Dongyan; Qin, Zhengrong; Wang, Qingshan

    2014-01-01

    In comparison with the out-of-plane vibrations of annular plates, far less attention has been paid to the in-plane vibrations which may also play a vital important role in affecting the sound radiation from and power flows in a built-up structure. In this investigation, a generalized Fourier series method is proposed for the in-plane vibration analysis of annular plates with arbitrary boundary conditions along each of its edges. Regardless of the boundary conditions, the in-plane displacement fields are invariantly expressed as a new form of trigonometric series expansions with a drastically improved convergence as compared with the conventional Fourier series. All the unknown expansion coefficients are treated as the generalized coordinates and determined using the Rayleigh-Ritz technique. Unlike most of the existing studies, the presented method can be readily and universally applied to a wide spectrum of in-plane vibration problems involving different boundary conditions, varying material, and geometric properties with no need of modifying the basic functions or adapting solution procedures. Several numerical examples are presented to demonstrate the effectiveness and reliability of the current solution for predicting the in-plane vibration characteristics of annular plates subjected to different boundary conditions.

  18. In-Plane Vibration Analysis of Annular Plates with Arbitrary Boundary Conditions

    PubMed Central

    Qin, Zhengrong; Wang, Qingshan

    2014-01-01

    In comparison with the out-of-plane vibrations of annular plates, far less attention has been paid to the in-plane vibrations which may also play a vital important role in affecting the sound radiation from and power flows in a built-up structure. In this investigation, a generalized Fourier series method is proposed for the in-plane vibration analysis of annular plates with arbitrary boundary conditions along each of its edges. Regardless of the boundary conditions, the in-plane displacement fields are invariantly expressed as a new form of trigonometric series expansions with a drastically improved convergence as compared with the conventional Fourier series. All the unknown expansion coefficients are treated as the generalized coordinates and determined using the Rayleigh-Ritz technique. Unlike most of the existing studies, the presented method can be readily and universally applied to a wide spectrum of in-plane vibration problems involving different boundary conditions, varying material, and geometric properties with no need of modifying the basic functions or adapting solution procedures. Several numerical examples are presented to demonstrate the effectiveness and reliability of the current solution for predicting the in-plane vibration characteristics of annular plates subjected to different boundary conditions. PMID:24688416

  19. In-Flight Boundary-Layer Transition of a Large Flat Plate at Supersonic Speeds

    NASA Technical Reports Server (NTRS)

    Banks, D. W.; Frederick, M. A.; Tracy, R. R.; Matisheck, J. R.; Vanecek, N. D.

    2012-01-01

    A flight experiment was conducted to investigate the pressure distribution, local-flow conditions, and boundary-layer transition characteristics on a large flat plate in flight at supersonic speeds up to Mach 2.00. The tests used a NASA testbed aircraft with a bottom centerline mounted test fixture. The primary objective of the test was to characterize the local flow field in preparation for future tests of a high Reynolds number natural laminar flow test article. A second objective was to determine the boundary-layer transition characteristics on the flat plate and the effectiveness of using a simplified surface coating. Boundary-layer transition was captured in both analog and digital formats using an onboard infrared imaging system. Surface pressures were measured on the surface of the flat plate. Flow field measurements near the leading edge of the test fixture revealed the local flow characteristics including downwash, sidewash, and local Mach number. Results also indicated that the simplified surface coating did not provide sufficient insulation from the metallic structure, which likely had a substantial effect on boundary-layer transition compared with that of an adiabatic surface. Cold wall conditions were predominant during the acceleration to maximum Mach number, and warm wall conditions were evident during the subsequent deceleration.

  20. Plate boundary forces in the vicinity of Trinidad-the-transition from transpression to transtension in the Southern Caribbean plate boundary zones

    SciTech Connect

    Algar, S.T.; Pindell, J.L. )

    1993-02-01

    Deformation in the southern Caribbean plate boundary zones as recorded in the Northern Range of Trinidad initiated in the Oligocene with northward vergent gravity sliding of Northern Range sediments due to uplift and oversteepening of the previously passive margin by the eastward migration of the Caribbean flexural forebulge. Progressive east-southeast transvergence of the Caribbean Plate with respect to South America overthrust incorporated the Northern Range sediments into the Caribbean accretionary prism, thrusting them south-southeast to produce a Middle Miocene transpressive foreland fold and thrust belt in southern Trinidad. Late Miocene deformation within Trinidad was increasingly dominated by right-lateral strike-slop (RLSS) faulting, at the expense of transpressive compressional features. Right-stepping of RLSS motion initiated the Gulf of Paria and Caroni pull-apart basins, Since Early Pliocene these basins and other areas to the north of Trinidad have undergone north-south extension in addition to east-west trending RLSS. Such extension caused the northward withdrawal of Caribbean terranes from atop of the Northern Range, Resulting in rapid isostatically induced uplift (approximately 0.5 mmyr[sup -1]). This change in deformation style may relate to a hitherto unrecognized shift in the relative motion of the eastern Caribbean Plate with respect to South America: from east-southeast-directed transpression to east-northeast-directed transtension.

  1. MHD free convective boundary layer flow of a nanofluid past a flat vertical plate with Newtonian heating boundary condition.

    PubMed

    Uddin, Mohammed J; Khan, Waqar A; Ismail, Ahmed I

    2012-01-01

    Steady two dimensional MHD laminar free convective boundary layer flows of an electrically conducting Newtonian nanofluid over a solid stationary vertical plate in a quiescent fluid taking into account the Newtonian heating boundary condition is investigated numerically. A magnetic field can be used to control the motion of an electrically conducting fluid in micro/nano scale systems used for transportation of fluid. The transport equations along with the boundary conditions are first converted into dimensionless form and then using linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. The effects of different controlling parameters, namely, Lewis number, Prandtl number, buoyancy ratio, thermophoresis, Brownian motion, magnetic field and Newtonian heating on the flow and heat transfer are investigated. The numerical results for the dimensionless axial velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically and discussed. It is found that the rate of heat and mass transfer increase as Newtonian heating parameter increases. The dimensionless velocity and temperature distributions increase with the increase of Newtonian heating parameter. The results of the reduced heat transfer rate is compared for convective heating boundary condition and found an excellent agreement. PMID:23166688

  2. MHD Free Convective Boundary Layer Flow of a Nanofluid past a Flat Vertical Plate with Newtonian Heating Boundary Condition

    PubMed Central

    Uddin, Mohammed J.; Khan, Waqar A.; Ismail, Ahmed I.

    2012-01-01

    Steady two dimensional MHD laminar free convective boundary layer flows of an electrically conducting Newtonian nanofluid over a solid stationary vertical plate in a quiescent fluid taking into account the Newtonian heating boundary condition is investigated numerically. A magnetic field can be used to control the motion of an electrically conducting fluid in micro/nano scale systems used for transportation of fluid. The transport equations along with the boundary conditions are first converted into dimensionless form and then using linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. The effects of different controlling parameters, namely, Lewis number, Prandtl number, buoyancy ratio, thermophoresis, Brownian motion, magnetic field and Newtonian heating on the flow and heat transfer are investigated. The numerical results for the dimensionless axial velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically and discussed. It is found that the rate of heat and mass transfer increase as Newtonian heating parameter increases. The dimensionless velocity and temperature distributions increase with the increase of Newtonian heating parameter. The results of the reduced heat transfer rate is compared for convective heating boundary condition and found an excellent agreement. PMID:23166688

  3. MHD free convective boundary layer flow of a nanofluid past a flat vertical plate with Newtonian heating boundary condition.

    PubMed

    Uddin, Mohammed J; Khan, Waqar A; Ismail, Ahmed I

    2012-01-01

    Steady two dimensional MHD laminar free convective boundary layer flows of an electrically conducting Newtonian nanofluid over a solid stationary vertical plate in a quiescent fluid taking into account the Newtonian heating boundary condition is investigated numerically. A magnetic field can be used to control the motion of an electrically conducting fluid in micro/nano scale systems used for transportation of fluid. The transport equations along with the boundary conditions are first converted into dimensionless form and then using linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. The effects of different controlling parameters, namely, Lewis number, Prandtl number, buoyancy ratio, thermophoresis, Brownian motion, magnetic field and Newtonian heating on the flow and heat transfer are investigated. The numerical results for the dimensionless axial velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically and discussed. It is found that the rate of heat and mass transfer increase as Newtonian heating parameter increases. The dimensionless velocity and temperature distributions increase with the increase of Newtonian heating parameter. The results of the reduced heat transfer rate is compared for convective heating boundary condition and found an excellent agreement.

  4. An analytical method for vibration of laminated composite rectangular plates having arbitrary combinations of boundary conditions

    NASA Astrophysics Data System (ADS)

    Narita, Y.

    This work presents a method of analysis for solving the free vibration of symmetrically laminated composite rectangular plates having any combination of free, simply supported and clamped edges along four sides. This approach uses a Ritz method for the energy functional, and trial functions used for deflections are introduced so as to automatically include geometric boundary conditions for a prescribed boundary. A computer code was developed to calculate natural frequencies and mode shapes for the problem, and was used to demonstrate the effectiveness and accuracy of the present approach.

  5. Dynamic Stability Optimization of Laminated Composite Plates under Combined Boundary Loading

    NASA Astrophysics Data System (ADS)

    Shafei, Erfan; Kabir, Mohammad Zaman

    2011-12-01

    Dynamic stability and design optimization of laminated simply supported plates under planar conservative boundary loads are investigated in current study. Examples can be found in internal connecting elements of spacecraft and aerospace structures subjected to edge axial and shear loads. Designation of such elements is function of layup configuration, plate aspect ratio, loading combinations, and layup thickness. An optimum design aims maximum stability load satisfying a predefined stable vibration frequency. The interaction between compound loading and layup angle parameter affects the order of merging vibration modes and may stabilize the dynamic response. Laminated plates are assumed to be angle-plies symmetric to mid-plane surface. Dynamic equilibrium PDE has been solved using kernel integral transformation for modal frequency values and eigenvalue-based orthogonal functions for critical stability loads. The dictating dynamic stability mode is shown to be controlled by geometric stiffness distributions of composite plates. Solution of presented design optimization problem has been done using analytical approach combined with interior penalty multiplier algorithm. The results are verified by FEA approach and stability zones of original and optimized plates are stated as final data. Presented method can help designers to stabilize the dynamic response of composite plates by selecting an optimized layup orientation and thickness for prescribed design circumstances.

  6. Evidence for divergent plate-boundary characteristics and crustal spreading on venus.

    PubMed

    Head, J W; Crumpler, L S

    1987-12-01

    Detailed examination of the topography and morphology of western Aphrodite Terra reveals numerous features that are similar to terrestrial divergent plate-boundary characteristics. Individual domains between fracturezone-like discontinuities contain a variety of bilaterally symmetrical topographic elements that suggest that topographic features have been created at rise crests, rifted and separated, and moved laterally to their present symmetrical positions. The topographic and morphologic similarities, together with strikingly similar mirror-image map patterns on both sides of the rise axis, suggest that western Aphrodite Terra shares the characteristics of oceanic divergent plate boundaries, and is the site of crustal spreading on Venus. Topographic profiles are consistent with spreading rates of the order of several centimeters per year.

  7. The Setting of the Okhotsk-Sea Micro-Plate Northern Boundary and its Seismicity

    NASA Astrophysics Data System (ADS)

    Sedov, B. M.

    2004-12-01

    The Sea of Okhotsk is surrounded by seismic zones. That is why we believe that its water area corresponds spatially to hard platform. The Okhotsk-sea micro-plate in triangular form is located at the joint of the Pacific, North-Amerikan, and Eurasian plates. It is bounded from the west by sub-meridional zone of deep sesmogenic faults spreading through the Sakhalin island. From the east, micro-plate is bounded by subduction zones, extending along the Kuril Islans and the eastern coast of Kamchatka. The northern boundary of the Okhotsk-sea plate is considered differently by different authors. The analysis of data of the marine seismic exploration by the method of common deep point, deep seismic sounding, gravitation field and the anomalous magnetic field, and also the seismological observation by the equipment make possible to conclude that the northern boundary of the Okhotsk-sea micro-plate has the sublatitudinal extending and spatially coincides with wide zone of deep faults confided to the coast. On land and offshore, this zone is marked by the line of riftogenic basins filled with Cenozoic continental sediments. On the continent, their thickness is not more than 1500-2000m, although on the offshore it reaches 8-10 km. The basins are mostly spread in meridian direction. The epicenters of the crust earthquakes are spatially related with these basins. This fact testifies of the right-lateral faults. Cenozoic sediments in basins of land are broken by numerous fault-shifts with the summary amplitude of horizontal displacements up to 1.5 km and by the vertical ones up to the first hundreds of meters. The northern boundary of the Okhotsk-sea micro-plate is marked by the change of the Earth's crust type: the continental type on the north, and transitional type on the offshore. Geological and geophisical data make possible to suppose that the northern boundary of micro-plate in primagadanskaya part coincides with the Benioff paleozone that closed its active existence in

  8. Regional variations in tectonic geomorphology along a segmented convergent plate boundary pacific coast of Costa Rica

    NASA Astrophysics Data System (ADS)

    Wells, S. G.; Bullard, T. F.; Menges, C. M.; Drake, P. G.; Karas, P. A.; Kelson, K. I.; Ritter, J. B.; Wesling, J. R.

    1988-09-01

    Pacific coastal mountain/piedmont landforms of Costa Rica extend across the tectonic boundary between the forearc and magnetic arc region of an active convergent margin. This plate boundary became segmented circa 1 million years ago when the aseismic Cocos Ridge impinged upon the Middle America Trench offshore from the southernmost coastal area of Costa Rica. Morphometric analyses of 100 mountain fronts and numerous river long-profiles, radiometric dating, and field studies were conducted in two study areas located arcward from the plate boundary where oceanic lithosphere of the Cocos plate is being subducted beneath the Caribbean plate (region I) and the partially subducted aseismic ridge is uplifting the plate margin by isostatic and collisional processes (region II). Values of tectonic geomorphic parameters [mountain front sinuosity ( S), percent dissected facets ( Ffd), river concavity ( K)] are not only different statistically in regions I and II but are also different in the areas experiencing isostatic and collisional responses to the subducting aseismic ridge. In the area experiencing collisional responses, mountain fronts, developed along NE-dipping imbricate thrust and high-angle reverse faults, step upward and inland from the coast; morphometric data along with the divergence of river-terrace profiles from the coast piedmont inland toward the mountains indicates higher uplift rates along interior-range mountain fronts. Isostatic uplift in the outer forearc area in region II produces a distinctly different morphologic and neotectonic style characterized by regional uplift distributed across a number of blocks bounded by normal faults. Geomorphic analyses indicate a general southward trend of increasing tectonic uplift from region I into region II where the highest frequency of mountain fronts with low values of S and Ffd, as well as rivers with the highest values of K, occur over the crest of the subducted ridge. Field and historical seismic data for

  9. Slab dragging and the recent geodynamic evolution of the western Mediterranean plate boundary region

    NASA Astrophysics Data System (ADS)

    Spakman, Wim; Chertova, Maria V.; van den Berg, Arie P.; Thieulot, Cedric; van Hinsbergen, Douwe J. J.

    2016-04-01

    The Tortonian-Present geodynamic evolution of the plate boundary between North Africa and Iberia is characterized by first-order enigmas. This concerns, e.g., the diffuse tectonic activity of the plate boundary; the crustal thickening below the Rif; the closing of the northern Moroccan marine gateways prior to the Messinian Salinity Crisis; crustal extension of the central to eastern Betics; the origin and sense of motion of the large left-lateral Trans Alboran Shear Zone (TASZ) and Eastern Betic Shear Zone (EBSZ); and lithosphere delamination of the North African continental edge. Many explanations have been given for each of these seemingly disparate tectonic features, which invariably have been addressed in the plate tectonic context of the NW-SE relative plate convergence between the major plates since the Tortonian, mostly independently from each other. Usually there is no clear role for the subducted slab underlying the region, except for presumed rollback, either to SW or to the W, depending on the type of observations that require explanation. Here we integrate the dynamic role of the slab with the NW-SE relative plate convergence by 3-D numerical modelling of the slab evolution constrained by absolute plate motions (Chertova et al., JGR,2014 & Gcubed 2014). By combining observations and predictions from seismology, geology, and geodesy, with our numerical 3-D slab-mantle dynamics modelling, we developed a new and promising geodynamic framework that provides explanations of all noted tectonic enigmas in a coherent and connected way. From the Tortonian until today, we propose that mantle-resisted slab dragging combines with the NW-SE plate convergence across the (largely) unbroken plate boundary to drive the crustal deformation of the region. Slab dragging is the lateral transport, pushing or pulling, of slab through the mantle by the absolute motion of the subducting plate (Chertova et al., Gcubed, 2014). Because the slab is connected to both the Iberian

  10. Control of boundary layer transition location and plate vibration in the presence of an external acoustic field

    NASA Technical Reports Server (NTRS)

    Maestrello, L.; Grosveld, F. W.

    1991-01-01

    The experiment is aimed at controlling the boundary layer transition location and the plate vibration when excited by a flow and an upstream sound source. Sound has been found to affect the flow at the leading edge and the response of a flexible plate in a boundary layer. Because the sound induces early transition, the panel vibration is acoustically coupled to the turbulent boundary layer by the upstream radiation. Localized surface heating at the leading edge delays the transition location downstream of the flexible plate. The response of the plate excited by a turbulent boundary layer (without sound) shows that the plate is forced to vibrate at different frequencies and with different amplitudes as the flow velocity changes indicating that the plate is driven by the convective waves of the boundary layer. The acoustic disturbances induced by the upstream sound dominate the response of the plate when the boundary layer is either turbulent or laminar. Active vibration control was used to reduce the sound induced displacement amplitude of the plate.

  11. Plane Wave Diffraction by a Finite Plate with Impedance Boundary Conditions

    PubMed Central

    Nawaz, Rab; Ayub, Muhammad; Javaid, Akmal

    2014-01-01

    In this study we have examined a plane wave diffraction problem by a finite plate having different impedance boundaries. The Fourier transforms were used to reduce the governing problem into simultaneous Wiener-Hopf equations which are then solved using the standard Wiener-Hopf procedure. Afterwards the separated and interacted fields were developed asymptotically by using inverse Fourier transform and the modified stationary phase method. Detailed graphical analysis was also made for various physical parameters we were interested in. PMID:24755624

  12. Seismicity patterns in the Himalayan plate boundary and identification of the areas of high seismic potential

    NASA Astrophysics Data System (ADS)

    Khattri, K. M.; Tyagi, A. K.

    1983-07-01

    Space-time distribution of earthquakes along the Himalayan plate boundary has been investigated with a view to discerning fluctuations in seismicity rates associated with great earthquakes, the possibilities of epicentre migration and gaps in seismic activity. Data from 1800 to 1976 were considered. This study shows that all great earthquakes ( M ⩾ 8.0) were preceded by seismically quiescent periods of at least 19 years. Furthermore, earthquake quiescence has also been recognised to follow the great earthquakes. Three possible trends of migration of epicentres of great earthquakes have been recognised: (1) The first trend starts from the 1905 Kangra earthquake, the epicentres of subsequent earthquakes migrating eastwards along the plate boundary. (2) The second trend of migration starts from the great Nepal earthquake of 1833 associated with eastward migration. (3) The third trend commences from the great Assam earthquake of 1897 and shows a westward migration of earthquake epicentres. The middle section of the Himalayan convergent plate boundary (80°E to 90°E), in general, displays a relatively low level of seismicity as compared to the adjacent sections. A remarkable decrease in seismicity following the year 1970 has been observed along a section of the Himalaya which lies to the east of the rupture zone of the great 1905 Kangra earthquake. Since 1970 the seismicity rate has also dropped in the region lying in between the rupture zones of the great Assam earthquakes of 1897 and 1950, as has earlier been reported by Khattri and Wyss (1978). Such decreases in the level of seismicity along active plate boundaries have been demonstrated to be indicative of building up of stresses leading to future great earthquakes (Mogi, 1969; McCann et al., 1979).

  13. Unsteady boundary-layer flow over jerked plate moving in a free stream of viscoelastic fluid.

    PubMed

    Munawar, Sufian; Mehmood, Ahmer; Ali, Asif; Saleem, Najma

    2014-01-01

    This study aims to investigate the unsteady boundary-layer flow of a viscoelastic non-Newtonian fluid over a flat surface. The plate is suddenly jerked to move with uniform velocity in a uniform stream of non-Newtonian fluid. Purely analytic solution to governing nonlinear equation is obtained. The solution is highly accurate and valid for all values of the dimensionless time 0 ≤ τ < ∞. Flow properties of the viscoelastic fluid are discussed through graphs. PMID:24892060

  14. Unsteady Boundary-Layer Flow over Jerked Plate Moving in a Free Stream of Viscoelastic Fluid

    PubMed Central

    Mehmood, Ahmer; Ali, Asif; Saleem, Najma

    2014-01-01

    This study aims to investigate the unsteady boundary-layer flow of a viscoelastic non-Newtonian fluid over a flat surface. The plate is suddenly jerked to move with uniform velocity in a uniform stream of non-Newtonian fluid. Purely analytic solution to governing nonlinear equation is obtained. The solution is highly accurate and valid for all values of the dimensionless time 0 ≤ τ < ∞. Flow properties of the viscoelastic fluid are discussed through graphs. PMID:24892060

  15. Computation of plate wave dispersion diagrams and surface wave velocities without explicit boundary conditions.

    PubMed

    Laude, Vincent; Assouar, Badreddine; Hou, Zhilin

    2010-07-01

    We discuss the computation of the band structure of plate waves using the plane wave expansion (PWE) method. This method is generally used to formulate eigenvalue problems to compute dispersion diagrams for solid-solid phononic crystals. We show how the free surface boundary condition can be included implicitly in the form of the PWE solution, thus leading to an efficient eigenvalue problem. This generic method for wave dispersion is non-iterative and does not require an initial guess for the solution. Furthermore, surface acoustic wave velocities can be estimated from the slowest wave for large wave vectors. Examples for a single plate and a multilayer plate are given, and extension to piezoelectric materials is discussed.

  16. A great earthquake rupture across a rapidly evolving three-plate boundary.

    PubMed

    Furlong, Kevin P; Lay, Thorne; Ammon, Charles J

    2009-04-10

    On 1 April 2007 a great, tsunamigenic earthquake (moment magnitude 8.1) ruptured the Solomon Islands subduction zone at the triple junction where the Australia and Solomon Sea-Woodlark Basin plates simultaneously underthrust the Pacific plate with different slip directions. The associated abrupt change in slip direction during the great earthquake drove convergent anelastic deformation of the upper Pacific plate, which generated localized uplift in the forearc above the subducting Simbo fault, potentially amplifying local tsunami amplitude. Elastic deformation during the seismic cycle appears to be primarily accommodated by the overriding Pacific forearc. This earthquake demonstrates the seismogenic potential of extremely young subducting oceanic lithosphere, the ability of ruptures to traverse substantial geologic boundaries, and the consequences of complex coseismic slip for uplift and tsunamigenesis. PMID:19359581

  17. A great earthquake rupture across a rapidly evolving three-plate boundary.

    PubMed

    Furlong, Kevin P; Lay, Thorne; Ammon, Charles J

    2009-04-10

    On 1 April 2007 a great, tsunamigenic earthquake (moment magnitude 8.1) ruptured the Solomon Islands subduction zone at the triple junction where the Australia and Solomon Sea-Woodlark Basin plates simultaneously underthrust the Pacific plate with different slip directions. The associated abrupt change in slip direction during the great earthquake drove convergent anelastic deformation of the upper Pacific plate, which generated localized uplift in the forearc above the subducting Simbo fault, potentially amplifying local tsunami amplitude. Elastic deformation during the seismic cycle appears to be primarily accommodated by the overriding Pacific forearc. This earthquake demonstrates the seismogenic potential of extremely young subducting oceanic lithosphere, the ability of ruptures to traverse substantial geologic boundaries, and the consequences of complex coseismic slip for uplift and tsunamigenesis.

  18. 3D geometry of the strain-field at transform plate boundaries: Implications for seismic rupture

    SciTech Connect

    Bodin, P.; Bilham, R. |

    1994-11-01

    We examine the amplitude and distribution of slip on vertical frictionless faults in the zone of concentrated shear strain that is characteristic of transform plate boundaries. We study both a 2D and a 3D approximation to this strain field. Mean displacements on ruptures within the zone of concentrated shear strain are proportional to the shear strain at failure when they are short, and are limited by plate displacements since the last major earthquake when they are long. The transition between these two behaviors occurs when the length of the dislocation approaches twice the thickness of the seismogenic crust, approximately the breadth of the zone of concentrated shear strain observed geodetically at transform plate boundaries. This result explains the observed non-linear scaling relation between seismic moment and rupture length. A geometrical consequence of the 3D model, in which the strain-field tapers downward, is that moderate earthquakes with rupture lengths similar to the thickness of the crust tend to slip more at depth than near the surface. Seismic moments estimated from surface slip in moderate earthquakes (M less than or equal to 7) will thus be underestimated. Shallow creep, if its along-strike dimension is extensive, can reduce a surface slip deficit that would otherwise develop on faults on which M less than 7 events are typical. In the absence of surface creep or other forms of off-fault deformation great earthquakes may be necessary features of transform boundaries with downward-tapering strain-fields.

  19. The Dauki Thrust Fault and the Shillong Anticline: An incipient plate boundary in NE India?

    NASA Astrophysics Data System (ADS)

    Ferguson, E. K.; Seeber, L.; Steckler, M. S.; Akhter, S. H.; Mondal, D.; Lenhart, A.

    2012-12-01

    The Shillong Massif is a regional contractional structure developing across the Assam sliver of the Indian plate near the Eastern Syntaxis between the Himalaya and Burma arcs. Faulting associated with the Shillong Massif is a major source of earthquake hazard. The massif is a composite basement-cored asymmetric anticline and is 100km wide, >350km long and 1.8km high. The high relief southern limb preserves a Cretaceous-Paleocene passive margin sequence despite extreme rainfall while the gentler northern limb is devoid of sedimentary cover. This asymmetry suggests southward growth of the structure. The Dauki fault along the south limb builds this relief. From the south-verging structure, we infer a regional deeply-rooted north-dipping blind thrust fault. It strikes E-W and obliquely intersects the NE-SW margin of India, thus displaying three segments: Western, within continental India; Central, along the former passive margin; and Eastern, overridden by the west-verging Burma accretion system. We present findings from recent geologic fieldwork on the western and central segments. The broadly warped erosional surface of the massif defines a single anticline in the central segment, east of the intersection with the hinge zone of the continental margin buried by the Ganges-Brahmaputra Delta. The south limb of the anticline forms a steep topographic front, but is even steeper structurally as defined by the Cretaceous-Eocene cover. Below it, Sylhet Trap Basalts intrude and cover Precambrian basement. Dikes, presumably parallel to the rifted margin, are also parallel to the front, suggesting thrust reactivation of rift-related faults. Less competent Neogene clastics are preserved only near the base of the mountain front. Drag folds in these rocks suggest north-vergence and a roof thrust above a blind thrust wedge floored by the Dauki thrust fault. West of the hinge zone, the contractional structure penetrates the Indian continent and bifurcates. After branching into the

  20. Effect of plate permeability on nonlinear stability of the asymptotic suction boundary layer

    NASA Astrophysics Data System (ADS)

    Wedin, Hâkan; Cherubini, Stefania; Bottaro, Alessandro

    2015-07-01

    The nonlinear stability of the asymptotic suction boundary layer is studied numerically, searching for finite-amplitude solutions that bifurcate from the laminar flow state. By changing the boundary conditions for disturbances at the plate from the classical no-slip condition to more physically sound ones, the stability characteristics of the flow may change radically, both for the linearized as well as the nonlinear problem. The wall boundary condition takes into account the permeability K ̂ of the plate; for very low permeability, it is acceptable to impose the classical boundary condition (K ̂=0 ). This leads to a Reynolds number of approximately Rec=54 400 for the onset of linearly unstable waves, and close to Reg=3200 for the emergence of nonlinear solutions [F. A. Milinazzo and P. G. Saffman, J. Fluid Mech. 160, 281 (1985), 10.1017/S0022112085003482; J. H. M. Fransson, Ph.D. thesis, Royal Institute of Technology, KTH, Sweden, 2003]. However, for larger values of the plate's permeability, the lower limit for the existence of linear and nonlinear solutions shifts to significantly lower Reynolds numbers. For the largest permeability studied here, the limit values of the Reynolds numbers reduce down to Rec=796 and Reg=294 . For all cases studied, the solutions bifurcate subcritically toward lower Re, and this leads to the conjecture that they may be involved in the very first stages of a transition scenario similar to the classical route of the Blasius boundary layer initiated by Tollmien-Schlichting (TS) waves. The stability of these nonlinear solutions is also investigated, showing a low-frequency main unstable mode whose growth rate decreases with increasing permeability and with the Reynolds number, following a power law Re-ρ, where the value of ρ depends on the permeability coefficient K ̂. The nonlinear dynamics of the flow in the vicinity of the computed finite-amplitude solutions is finally investigated by direct numerical simulations, providing a

  1. In-Flight Boundary-Layer Transition on a Large Flat Plate at Supersonic Speeds

    NASA Technical Reports Server (NTRS)

    Banks, Daniel W.; Fredericks, Michael Alan; Tracy, Richard R.; Matisheck, Jason R.; Vanecek, Neal D.

    2012-01-01

    A flight experiment was conducted to investigate the pressure distribution, local flow conditions, and boundary-layer transition characteristics on a large flat plate in flight at supersonic speeds up to Mach 2.0. The primary objective of the test was to characterize the local flow field in preparation for future tests of a high Reynolds number natural laminar flow test article. The tests used a F-15B testbed aircraft with a bottom centerline mounted test fixture. A second objective was to determine the boundary-layer transition characteristics on the flat plate and the effectiveness of using a simplified surface coating for future laminar flow flight tests employing infrared thermography. Boundary-layer transition was captured using an onboard infrared imaging system. The infrared imagery was captured in both analog and digital formats. Surface pressures were measured with electronically scanned pressure modules connected to 60 surface-mounted pressure orifices. The local flow field was measured with five 5-hole conical probes mounted near the leading edge of the test fixture. Flow field measurements revealed the local flow characteristics including downwash, sidewash, and local Mach number. Results also indicated that the simplified surface coating did not provide sufficient insulation from the metallic structure, which likely had a substantial effect on boundary-layer transition compared with that of an adiabatic surface. Cold wall conditions were predominant during the acceleration to maximum Mach number, and warm wall conditions were evident during the subsequent deceleration. The infrared imaging system was able to capture shock wave impingement on the surface of the flat plate in addition to indicating laminar-to-turbulent boundary-layer transition.

  2. Boundary layer flow of air over water on a flat plate

    NASA Technical Reports Server (NTRS)

    Nelson, John; Alving, Amy E.; Joseph, Daniel D.

    1993-01-01

    A non-similar boundary layer theory for air blowing over a water layer on a flat plate is formulated and studied as a two-fluid problem in which the position of the interface is unknown. The problem is considered at large Reynolds number (based on x), away from the leading edge. A simple non-similar analytic solution of the problem is derived for which the interface height is proportional to x(sub 1/4) and the water and air flow satisfy the Blasius boundary layer equations, with a linear profile in the water and a Blasius profile in the air. Numerical studies of the initial value problem suggests that this asymptotic, non-similar air-water boundary layer solution is a global attractor for all initial conditions.

  3. Experiments on the stability of the flat-plate boundary layer with suction

    NASA Technical Reports Server (NTRS)

    Reynolds, G. A.; Saric, W. S.

    1982-01-01

    Experiments have been conducted in the VPI and SU Stability Wind Tunnel on a flat-plate wind-tunnel model equipped with porous suction panels. Detailed hot-wire measurements were conducted in the laminar boundary layer to investigate the stabilizing effects of suction on growing Tollmien-Schlichting waves, which were introduced into the boundary layer using a vibrating ribbon. Special care was taken to minimize external disturbances and to avoid extraneous experimental bias. The measurements, which included mean-flow and disturbance-amplitude profiles across the boundary layer, showed that suction applied through discrete porous strips can be as effective as suction applied continuously over a much longer streamwise length. The measurements also showed that suction is more effective when placed forward, nearer to the region of neutral stability, than when placed in the region of maximum growth rate. These results also provided meaningful comparison with recent theory.

  4. Extension and transtension in the plate boundary zone of the northeastern Caribbean

    SciTech Connect

    Speed, R.C. ); Larue, D.K. )

    1991-03-01

    The authors propose that the Caribbean (Ca)-North American (NA) plate boundary zone (pbz) from the Puerto Rico Trench to the Venezuelan Basin from Mona Canyon east has been in left-transtension over the last 15-20 ma. A boundary-normal component of extension occurs throughout the pbz and is a principal cause of the Puerto Rico Trench. Such extension is due to WNW velocity of NA-Ca and the northward pullaway of NA from its S-dipping slab, which is below Puerto Rico. Strike slip motion may be taken up among terranes in the pbz by rigid CCW rotation and by oblique slip at their boundaries. Rotation of the largest terrane, Puerto Rico-Virgin Islands (PRVI), has caused such major structures as the Muertos thrust and Anegada Passage. The model implies NA-Ca velocity estimated from Cayman transforms is more accurate than that from slip vectors from seisms in the NA slab.

  5. Plate boundaries in west Africa and their implications for Pangean continental fit

    NASA Astrophysics Data System (ADS)

    Venkatakrishnan, Ramesh; Culver, Stephen J.

    1988-04-01

    Geophysical and geologic data, together with geometric considerations, reveal the location and trend of the northern and southern boundaries of the Senegal microplate, west Africa. The Paleozoic southern margin follows the Koulountou branch of the Mauritanide fold belt from an exposed northeast trend around to a northwest trend beneath the cover of the Senegal-Mauritania basin. The northern boundary of the Senegal microplate is suggested to follow a northwest-southeast-trending zone 100 km south of the previously suggested margin. These plate boundaries explain the restricted rifting and collision of the Senegal microplate with the west African craton through the Paleozoic and elucidate the position of the Florida block in the Pangean assembly of North America, South America, and Africa.

  6. Plate boundary deformation at the latitude of the Salton Trough - northern Gulf of California (Invited)

    NASA Astrophysics Data System (ADS)

    Stock, J. M.

    2013-12-01

    Along the Pacific-North America plate boundary zone, the segment including the southern San Andreas fault to Salton Trough and northern Gulf of California basins has been transtensional throughout its evolution, based on Pacific-North America displacement vectors calculated from the global plate circuit (900 × 20 km at N54°W since 20 Ma; 460 × 20 km at N48°W since 11 Ma). Nevertheless, active seismicity and focal mechanisms show a broad zone of plate boundary deformation within which the inferred stress regime varies locally (Yang & Hauksson 2013 GJI), and fault patterns in some regions suggest ongoing tectonic rotation. Similar behavior is inferred to have occurred in this zone over most of its history. Crustal structure in this region is constrained by surface geology, geophysical experiments (e.g., the 2011 Salton Seismic Imaging Project (SSIP), USGS Imperial Valley 1979, PACE), and interdisciplinary marine and onland studies in Mexico (e.g., NARS-Baja, Cortes, and surveys by PEMEX). Magnetic data (e.g., EMAG-2) aids in the recognition of large-scale crustal provinces and fault boundaries in regions lacking detailed geophysical surveys. Consideration of existing constraints on crustal thickness and architecture, and fault and basin evolution suggests that to reconcile geological deformation with plate motion history, the following additional factors need to be taken into account. 1) Plate boundary displacement via interacting systems of rotating blocks, coeval with slip on steep strike slip faults, and possibly related to slip on low angle extensional faults (e.g, Axen & Fletcher 1998 IGR) may be typical prior to the onset of seafloor spreading. This fault style may have accommodated up to 150 km of plate motion in the Mexican Continental Borderland and north of the Vizcaino Peninsula, likely between 12 and 15 Ma, as well as explaining younger rotations adjacent to the Gulf of California and current deformation southwest of the Salton Sea. 2) Geophysical

  7. Tectonic mélange as fault rock of subduction plate boundary

    NASA Astrophysics Data System (ADS)

    Kimura, Gaku; Yamaguchi, Asuka; Hojo, Megumi; Kitamura, Yujin; Kameda, Jun; Ujiie, Kohtaro; Hamada, Yohei; Hamahashi, Mari; Hina, Shoko

    2012-09-01

    An assemblage of quantitative data sets is examined to evaluate tectonic mélange as a plate boundary fault rocks in subduction zone. The research object is the latest Cretaceous Mugi mélange in the Shimanto Belt, southwest Japan. Systematic age younging from pelagic to terrigenous through hemipelagic sediments is well-documented even though original stratigraphy is disrupted. Systematic shear fabric consistent with ancient plate convergence is reconstructed. The mélange was formed at temperatures of ~ 130-200 °C by cataclastic comminution of sandstone layers accompanied by tensile cracking, and plastic deformation and the dehydration of clayey shale matrix, with subsequent peeling off and underplating of the oceanic basement. The temperature setting for the Mugi mélange indicates around the up-dip limit of the seismogenic zone, therefore includes various fault rocks suggestive of earthquake fault; pseudotachylyte, fluidized ultracataclasite with heating evidence, amorphous silica and so on. These suggest that fluid induced lubrication was dominated. Localized cataclastic shear, which is a candidate of small earthquake or very low frequency earthquake, is also recognized especially in sandstone blocks dominated portion in mélange. These observations are consistent with the mélange being a fault rock along the plate boundary that records various types of earthquakes in a subduction zone. The quantitative examination of the Mugi mélange suggests several criteria to define the tectonic mélange of the plate boundary fault in subduction zone from other mélanges in orogenic belt.

  8. Seismotectonics of the Lwandle-Nubia plate boundary between South Africa and the Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Hartnady, Chris; Okal, Emile; Calais, Eric; Stamps, Sarah; Saria, Elifuraha

    2013-04-01

    The Lwandle (LW) plate shares a boundary with the Nubia (NU) plate, extending from a diffuse triple junction with the Rovuma plate in Southern Mozambique to a triple junction with the Antarctic plate along a segment of the Southwest Indian Ridge (SWIR). The LW-NU boundary terminates in the ~750 km-long, complex transform of the Andrew Bain Fracture Zone (ABFZ), but its exact locus is still unclear. Recent works locate it along the eastern boundary of the submarine Mozambique Ridge, parallel to the pre-existing, oceanic transform-fault fabric. However, an early concept of the LW block ('ambiguous region' of Hartnady, 1990, Fig. 2) indicates a more westerly trajectory in the north that includes parts of South Africa, with a southerly extension across old oceanic crust of the submarine Natal Valley and Transkei Basin. This proposed boundary is marked by several, aligned epicentres of moderate to strong earthquakes (1941, 1942, 1956, 1969, 1972, 1975, 1981 and 1989). Our re-examination of seismographic records from the 1975 'intraplate' earthquake (-37.62°N, 30.98°E, mb5.0), in the oceanic crust of the distal Transkei Basin, shows a thrust-faulting focal mechanism along a nodal plane striking N272°E. The largest (ML4.2) of a series of three small earthquakes in the Natal Valley in 2009, close to a zone of recent seafloor deformation mapped in 1992, has similar first-motion patterns at Southern African seismograph stations. When the 1975 slip-vector result (N173°E) is combined with a normal-faulting slip vector (N078°E) from a 1986 onland earthquake (-30.53°N, 28.84°E, mb5.0) near the Lesotho-KZN border, and both are incorporated into the wider data-set previously used to solve for East African Rift kinematics, they produce a LW-NU rotation pole that is located south of Africa, near the Agulhas Plateau, and approximately 950 km from the Natal Valley deformation zone. The modeled low rate of right-lateral, LW-NU slip (~0.50-0.75 mm/yr) across this LW-NU boundary

  9. GEM Plate Boundary Simulations for the Plate Boundary Observatory: A Program for Understanding the Physics of Earthquakes on Complex Fault Networks via Observations, Theory and Numerical Simulation

    NASA Astrophysics Data System (ADS)

    Rundle, J. B.; Rundle, P. B.; Klein, W.; de sa Martins, J.; Tiampo, K. F.; Donnellan, A.; Kellogg, L. H.

    The last five years have seen unprecedented growth in the amount and quality of geodetic data collected to characterize crustal deformation in earthquake-prone areas such as California and Japan. The installation of the Southern California Integrated Geodetic Network (SCIGN) and the Bay Area Regional Deformation (BARD) network are two examples. As part of the recently proposed Earthscope NSF/GEO/EAR/MRE initiative, the Plate Boundary Observatory (PBO) plans to place more than a thousand GPS, strainmeters, and deformation sensors along the active plate boundary of the western coast of the United States, Mexico and Canada (http://www.earthscope.org/pbo.com.html). The scientific goals of PBO include understanding how tectonic plates interact, together with an emphasis on understanding the physics of earthquakes. However, the problem of understanding the physics of earthquakes on complex fault networks through observations alone is complicated by our inability to study the problem in a manner familiar to laboratory scientists, by means of controlled, fully reproducible experiments. We have therefore been motivated to construct a numerical simulation technology that will allow us to study earthquake physics via numerical experiments. To be considered successful, the simulations must not only produce observables that are maximally similar to those seen by the PBO and other observing programs, but in addition the simulations must provide dynamical predictions that can be falsified by means of observations on the real fault networks. In general, the dynamical behavior of earthquakes on complex fault networks is a result of the interplay between the geometric structure of the fault network and the physics of the frictional sliding process. In constructing numerical simulations of a complex fault network, we will need to solve a variety of problems, including the development of analysis techniques (also called data mining), data assimilation, space-time pattern definition

  10. The Role of History-Dependent Rheology in Plate Boundary Lubrication for Generating One-Sided Subduction

    NASA Astrophysics Data System (ADS)

    Tagawa, Michio; Nakakuki, Tomoeki; Kameyama, Masanori; Tajima, Fumiko

    2007-05-01

    We have developed a two-dimensional dynamical model of asymmetric subduction integrated into the mantle convection without imposed plate velocities. In this model we consider that weak oceanic crust behaves as a lubricator on the thrust fault at the plate boundary. We introduce a rheological layer that depends on the history of the past fracture to simulate the effect of the oceanic crust. The thickness of this layer is set to be as thin as the Earth's oceanic crust. To treat 1-kilometer scale structure at the plate boundary in the 1000-kilometer scale mantle convection calculation, we introduce a new numerical method to solve the hydrodynamic equations using a couple of uniform and nonuniform grids of control volumes. Using our developed models, we have systematically investigated effects of basic rheological parameters that determine the deformation strength of the lithosphere and the oceanic crust on the development of the subducted slab, with a focus on the plate motion controlling mechanism. In our model the plate subduction is produced when the friction coefficient (0.004 0.008) of the modeled oceanic crust and the maximum strength (400 MPa) of the lithosphere are in plausible range inferred from the observations on the plate driving forces and the plate deformation, and the rheology experiments. In this range of the plate strength, yielding induces the plate bending. In this case the speed of plate motion is controlled more by viscosity layering of the underlying mantle than by the plate strength. To examine the setting of the overriding plate, we also consider the two end-member cases in which the overriding plate is fixed or freely-movable. In the case of the freely-movable overriding plate, the trench motion considerably changes the dip angle of the deep slab. Especially in the case with a shallow-angle plate boundary, retrograde slab motion occurs to generate a shallow-angle deep slab.

  11. Distributed Plate Boundary Deformation Across the San Andreas Fault System, Central California

    NASA Astrophysics Data System (ADS)

    Dyson, M.; Titus, S. J.; Demets, C.; Tikoff, B.

    2007-12-01

    Plate boundaries are now recognized as broad zones of complex deformation as opposed to narrow zones with discrete offsets. When assessing how plate boundary deformation is accommodated, both spatially and temporally, it is therefore crucial to understand the relative contribution of the discrete and distributed components of deformation. The creeping segment of the San Andreas fault is an ideal location to study the distribution of plate boundary deformation for several reasons. First, the geometry of the fault system in central California is relatively simple. Plate motion is dominated by slip along the relatively linear strike-slip San Andreas fault, but also includes lesser slip along the adjacent and parallel Hosgri-San Gregorio and Rinconada faults, as well as within the borderlands between the three fault strands. Second, the aseismic character of the San Andreas fault in this region allows for the application of modern geodetic techniques to assess creep rates along the fault and across the region. Third, geologic structures within the borderlands are relatively well-preserved allowing comparison between modern and ancient rates and styles of deformation. Continuous GPS stations, alignment arrays surveys, and other geodetic methods demonstrate that approximately 5 mm/yr of distributed slip is accumulated (on top of the fault slip rate) across a 70-100 km wide region centered on the San Andreas fault. New campaign GPS data also suggest 2-5 mm/yr of deformation in the borderlands. These rates depend on the magnitude of the coseismic and postseismic corrections that must be made to our GPS time series to compensate for the 2003 San Simeon and 2004 Parkfield earthquakes, which rupture faults outside, but near the edges of our GPS network. The off-fault deformation pattern can be compared to the style of permanent deformation recorded in the geologic record. Fold and thrust belts in the borderlands are better developed in the Tertiary sedimentary rocks west of

  12. How diking affects the longer-term structure and evolution of divergent plate boundaries

    NASA Astrophysics Data System (ADS)

    Trippanera, Daniele; Acocella, Valerio; Ruch, Joel; Rivalta, Eleonora

    2015-04-01

    Recurrent diking episodes along divergent plate boundaries, as at Dabbahu (2005, Afar) or at Bardarbunga (2014, Iceland) , highlight the possibility to have m-wide opening in a short time (days to weeks). This suggests a prominent role of magma enhancing transient plate separations. However, the role of diking on a longer term (> 102 years) and its influence on the structure and the evolution of a divergent plate boundary is still poorly investigated. Here we use field surveys along the oceanic Icelandic and continental Ethiopian plate boundaries, along five eruptive fissures and four rift segments. Field observations have also been integrated with analogue and numerical models of dike emplacement to better understand the effect of dike emplacement at depth and at the surface. Our results show that the dike-fed eruptive fissures are systematically associated with graben structures formed by inward dipping normal faults having throws up to 10 m and commonly propagating downward. Moreover, rift segments (i.e. mature rift zones), despite any asymmetry and repetition, are characterized by the same features as the eruptive fissures, the only difference lying in the larger size (higher fault throws, up to 40 m, and wider deformation zones). Analogue and numerical models of dike intrusion confirm that all the structural features observed along the rift segments may be dike-induced; these features include downward propagating normal faults bordering graben structures, contraction at the base of the hanging walls of the faults and upward propagating faults. Simple calculations based on the deeper structure of the eroded rift segments in eastern and western Iceland also suggest that all the fault slip in the active rift segments may result from diking. These results suggest that the overall deformation pattern of eruptive fissures and rift segments may be explained only by dike emplacement. In a magmatic rift, the regional tectonic stress may rarely be high enough to be

  13. The boundary between the Indian and Asian tectonic plates below Tibet.

    PubMed

    Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Kumar, Prakash; Pei, Shunping; Kind, Rainer; Zhang, Zhongjie; Teng, Jiwen; Ding, Lin; Gao, Xing; Xu, Qiang; Wang, Wei

    2010-06-22

    The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy. PMID:20534567

  14. Free vibration of two elastically coupled rectangular plates with uniform elastic boundary restraints

    NASA Astrophysics Data System (ADS)

    Du, Jingtao; Li, Wen L.; Liu, Zhigang; Yang, Tiejun; Jin, Guoyong

    2011-02-01

    An analytical method is derived for determining the vibrations of two plates which are generally supported along the boundary edges, and elastically coupled together at an arbitrary angle. The interactions of all four wave groups (bending waves, out-of-plane shearing waves, in-plane longitudinal waves, and in-plane shearing waves) have been taken into account at the junction via four types of coupling springs of arbitrary stiffnesses. Each of the transverse and in-plane displacement functions is expressed as the superposition of a two-dimensional (2-D) Fourier cosine series and several supplementary functions which are introduced to ensure and improve the convergence of the series representation by removing the discontinuities that the original displacement and its derivatives will potentially exhibit at the edges when they are periodically expanded onto the entire x- y plane as mathematically implied by a 2-D Fourier series. The unknown expansions coefficients are calculated using the Rayleigh-Ritz procedure which is actually equivalent to solving the governing equation and the boundary and coupling conditions directly when the assumed solutions are sufficiently smooth over the solution domains. Numerical examples are presented for several different coupling configurations. A good comparison is observed between the current results and the FEA models. Although this study is specifically focused on the coupling of two plates, the proposed method can be directly extended to structures consisting of any number of plates.

  15. The boundary between the Indian and Asian tectonic plates below Tibet.

    PubMed

    Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Kumar, Prakash; Pei, Shunping; Kind, Rainer; Zhang, Zhongjie; Teng, Jiwen; Ding, Lin; Gao, Xing; Xu, Qiang; Wang, Wei

    2010-06-22

    The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy.

  16. Quasi-simultaneous interaction method for solving 2D boundary layer flows over plates and airfoils

    NASA Astrophysics Data System (ADS)

    Bijleveld, H. A.; Veldman, A. E. P.

    2012-11-01

    This paper studies unsteady 2D boundary layer flows over dented plates and a NACA 0012 airfoil. An inviscid flow is assumed to exist outside the boundary layer and is solved iteratively with the boundary layer flow together with the interaction method until a matching solution is achieved. Hereto a quasi-simultaneous interaction method is applied, in which the integral boundary layer equations are solved together with an interaction-law equation. The interaction-law equation is an approximation of the external flow and based on thin-airfoil theory. It is an algebraic relation between the velocity and displacement thickness. The interaction-law equation ensures that the eigenvalues of the system of equations do not have a sign change and that no singularities occur. Three numerical schemes are used to solve the boundary layer flow with the interaction method. These are: a standard scheme, a splitting method and a characteristics solver. All schemes use a finite difference discretization. The three schemes yield comparable results for the simulations carried out. The standard scheme is deviating most from the splitting and characteristics solvers. The results show that the eigenvalues remain positive, even in separation. As expected, the addition of the interaction-law equation prevents a sign change of the eigenvalues. The quasi-simultaneous interaction scheme is applicable to the three numerical schemes tested.

  17. Separation in the mixed convection boundary-layer radial flow over a constant temperature horizontal plate

    NASA Astrophysics Data System (ADS)

    Fernandez-Feria, R.; del Pino, C.; Fernández-Gutiérrez, A.

    2014-10-01

    The boundary-layer flow of a horizontal current emerging radially from a cylindrical vertical surface of radius r0 with a constant velocity over a heated horizontal wall at constant temperature is analyzed. The boundary-layer equations are made dimensionless with a radial characteristic length in which natural and forced convection become of the same order of magnitude, so that the Prandtl (Pr) number and Gr2/Re5 are the only nondimensional parameters governing the problem, where Gr and Re are the Grashof and Reynolds numbers based on r0, respectively. A similarity solution valid at the leading edge of the boundary-layer flow is obtained. It contains, as the first order correction to Blasius' thermal boundary layer solution, the effect of buoyancy, and as the second order correction the effect of the radial divergence of the flow. This solution is used to start the numerical integration of the equations to provide a criterion for when separation occurs. It is found that separation, based on the boundary layer model, occurs for Gr < B(Pr)Re5/2, where the Prandtl's number function B is characterized numerically and found to be almost constant. This separation location law is compared with experimental results for air flowing over a heated horizontal plate at constant temperature, finding a qualitative good agreement.

  18. Active faulting south of the Himalayan Front: Establishing a new plate boundary

    NASA Astrophysics Data System (ADS)

    Yeats, Robert S.; Thakur, V. C.

    2008-06-01

    New tectonic uplifts south of the Salt Range Thrust and Himalayan Front Thrust (HFT) represent an outward step of the plate boundary from the principal tectonic displacement zone into the Indo-Gangetic Plain. In Pakistan, the Lilla Anticline deforms fine-grained overbank deposits of the Jhelum River floodplain 15 km south of the Salt Range. The anticline is overpressured in Eocambrian non-marine strata. In northwest India south of Dehra Dun, the Piedmont Fault (PF) lies 15 km south of the HFT. Coalescing fans derived from the Himalaya form a piedmont (Old Piedmont Zone) 15-20 km wide east of the Yamuna River. This zone is uplifted as much as 15-20 m near the PF, and bedding is tilted 5-7° northeast. Holocene thermoluminescence-optically-stimulated luminescence dates for sediments in the Old Piedmont Zone suggest that the uplift rate might be as high as several mm/a. The Old Piedmont Zone is traced northwest 200 km and southeast another 200 km to the Nepal border. These structures, analogous to protothrusts in subduction zones, indicate that the Himalayan plate boundary is not a single structure but a series of structures across strike, including reactivated parts of the Main Boundary Thrust north of the range front, the HFT sensu stricto, and stepout structures on the Indo-Gangetic Plain. Displacement rates on all these structures must be added to determine the local India-Himalaya convergence rate.

  19. Paleoseismicity of the North American-Caribbean plate boundary (Septentrional fault), Dominican Republic

    USGS Publications Warehouse

    Prentice, C.S.; Mann, P.; Taylor, F.W.; Burr, G.; Valastro, S.

    1993-01-01

    The Septentrional fault zone, the major North American-Caribbean plate-boundary fault in Hispaniola, is a likely source of large earthquakes in the Dominican Republic. An excavation into a Holocene alluvial fan deposited across the fault in the central Cibao Valley, Dominican Republic, provides evidence that it has been at least 430 yr and probably more than 740 yr since the last ground-rupturing earthquake along this segment of the fault. On the basis of these data and published estimates of the plate-tectonic slip rate, it is proposed that the Septentrional fault is a source of high seismic potential in the densely populated and rapidly developing Cibao Valley in the northern Dominican Republic. -Authors

  20. Flat plate heat transfer for laminar transition and turbulent boundary layers using a shock tube

    NASA Technical Reports Server (NTRS)

    Brostmeyer, J. D.; Nagamatsu, H. T.

    1984-01-01

    Heat transfer results are presented for laminar, transition, and turbulent boundary layers for a Mach number of 0.12 with gas temperatures of 425 K and 1000 K over a flat plate at room temperature. The measurements were made in air for a Reynolds number range of 600 to 6 million. The heat transfer measurements were conducted in a 70-ft long, 4 in. diameter shock tube. Reflecting wedges were used to reflect the incident shock wave to produce a flow Mach number of 0.12 behind the reflected shock wave. Thin film platinum heat gages were mounted on the plate surface to measure the local heat flux. The laminar results for gas temperatures of 425 K to 1000 K agree well with theory. The turbulent results are also close to incompressible theory, with the 1000 K flow case being slightly higher. The transition results lie between the laminar and turbulent predictions.

  1. Laminar-Boundary-Layer Oscillations and Transition on a Flat Plate

    NASA Technical Reports Server (NTRS)

    Schubauer, G B; Skramstad, H K

    1948-01-01

    This is an account of an investigation in which oscillations were discovered in the laminar boundary layer along a flat plate. These oscillations were found during the course of an experiment in which transition from laminar to turbulent flow was being studied on the plate as the turbulence in the wind stream was being reduced to unusually low values by means of damping screens. The first part of the paper deals with experimental methods and apparatus, measurements of turbulence and sound, and studies of transition. A description is then given of the manner in which oscillations were discovered and how they were found to be related to transition, and then how controlled oscillations were produced and studied in detail.

  2. Prehistoric earthquakes on the Caribbean-South American plate boundary, central Range Fault, Trinidad

    USGS Publications Warehouse

    Prentice, Carol S.; Crosby, Christopher J.; Weber, John C.; Ragona, Daniel

    2010-01-01

    Recent geodetic studies suggest that the Central Range fault is the principal plate-boundary structure accommodating strike-slip motion between the Caribbean and South American plates. Our study shows that the fault forms a topographically prominent lineament in central Trinidad. Results from a paleoseismic investigation at a site where Holocene sediments have been deposited across the Central Range fault indicate that it ruptured the ground surface most recently between 2710 and 550 yr B.P. If the geodetic slip rate of 9–15 mm/yr is representative of Holocene slip rates, our paleoseismic data suggest that at least 4.9 m of potential slip may have accumulated on the fault and could be released during a future large earthquake (M > 7).

  3. Prehistoric earthquakes on the Caribbean-South American plate boundary, central range fault, Trinidad

    USGS Publications Warehouse

    Prentice, C.S.; Weber, J.C.; Crosby, C.J.; Ragona, D.

    2010-01-01

    Recent geodetic studies suggest that the Central Range fault is the principal plate-boundary structure accommodating strike-slip motion between the Caribbean and South American plates. Our study shows that the fault forms a topographically prominent lineament in central Trinidad. Results from a paleoseismic investigation at a site where Holocene sediments have been deposited across the Central Range fault indicate that it ruptured the ground surface most recently between 2710 and 550 yr B.P. If the geodetic slip rate of 9-15 mm/yr is representative of Holocene slip rates, our paleoseismic data suggest that at least 4.9 m of potential slip may have accumulated on the fault and could be released during a future large earthquake (M > 7). ?? 2010 Geological Society of America.

  4. Relaxation of the accelerating-gas boundary layer to the test-gas boundary layer on a flat plate in an expansion tube

    NASA Technical Reports Server (NTRS)

    Gupta, R. N.; Trimpi, R. L.

    1973-01-01

    An analytic investigation of the relaxation of the accelerating-gas boundary layer to the test-gas boundary layer over a flat plate mounted in an expansion tube has been conducted. In this treatment, nitrogen has been considered as the test gas and helium as the accelerating gas. The problem is analyzed in two conically similar limits: (1) when the time lag between the arrival of the shock and the interface at the leading edge of the plate is very large, and (2) when this time lag is negligible. The transient laminar boundary-layer equations of a perfect binary-gas mixture are taken as the flow governing equations. These coupled equations have been solved numerically by Gauss-Seidel line-relaxation method. The results predict the transient behavior as well as the time required for an all-helium accelerating-gas boundary layer to relax to an all-nitrogen boundary layer.

  5. Inherited segmentation of the Iberian-African margins and tectonic reconstruction of a diffuse plate boundary.

    NASA Astrophysics Data System (ADS)

    Fernàndez, Manel; Torne, Montserrat; Vergés, Jaume; Casciello, Emilio

    2016-04-01

    Diffuse plate-boundary regions are characterized by non-well defined contacts between tectonic plates thus making difficult their reconstruction through time. The Western Mediterranean is one of these regions, where the convergence between the African and Iberian plates since Late Cretaceous resulted in the Betic-Rif arcuate orogen, the Gulf of Cadiz imbricate wedge, and the Alboran back-arc basin. Whereas the Iberia-Africa plate boundary is well defined west to the Gorringe Bank and along the Gloria Fault, it becomes much more diffuse eastwards with seismicity spreading over both the south-Iberian and north-African margins. Gravity data, when filtered for short wavelengths, show conspicuous positive Bouguer anomalies associated with the Gorringe Bank, the Gulf of Cadiz High and the Ronda/Beni-Bousera peridotitic massifs reflecting an inherited Jurassic margin segmentation. The subsequent Alpine convergence between Africa and Iberia reactivated these domains, producing crustal-scale thrusting in the Atlantic segments and eventually subduction in the proto-Mediterranean segments. The Jurassic segmentation of the Iberia-Africa margins substantiates the double-polarity subduction model proposed for the region characterized by a change from SE-dipping polarity in the Gorringe, Gulf of Cadiz and Betic-Rif domains, to NW-dipping polarity in the proto-Algerian domain. Therefore, the Algerian and Tyrrhenian basins in the east and the Alboran basin in the west are the result of SSE-E and NW-W retreating slabs of oceanic and/or hyper-extended Tethyan domains, respectively.

  6. The Northern Caribbean Plate Boundary Offshore Hispaniola: Strike-slip and Compressive Tectonic Processes

    NASA Astrophysics Data System (ADS)

    Corbeau, J.; Rolandone, F.; Leroy, S. D.; Mercier De Lepinay, B. F.; Meyer, B.; Ellouz, N.

    2014-12-01

    The boundary between the Caribbean plate and the North American plate is transpressive due to the oblique collision between these two plates. The transpressive movement is partitioned and accommodated in the Hispaniola region along two left-lateral strike-slip structures surrounding a fold-and-thrust belt. New multibeam bathymetry data and multichannel seismic reflection profiles have been recently collected during the Haiti-SIS and Haiti-SIS 2 cruises, along part of the northern Caribbean plate boundary between Cuba, Jamaica and Hispaniola. From the north to the south, three types of deformations are observed. In the Windward Passage, the analysis of the data set reveals that the movement on the Oriente fault between Cuba and Hispaniola is purely left-lateral strike-slip according to the GPS measurements. In the Gonave basin, west of Hispaniola, the deformation is compressive. A series of folds is identified and moves toward the southwest. The Enriquillo-Plantain-Garden Fault (EPGF) is localized in the Jamaica Passage, between Jamaica and Hispaniola. The analysis of the data set reveals that the left-lateral EPGF recently intersects inherited basins from the eastern Cayman Trough margin. The study of the actual EPGF active trace shows that this fault moves with a pure strike-slip component, at least in its western part: the presence of a little push-up structure and a set of three en echelon folds is highlighting in the western part of the Jamaica Passage. The shortening rate in the inherited basins crossed by the EPGF increases from west to east (5.8% to 8.5%), indicating that a thrusting component is also accommodated around the EPGF.

  7. Crustal Deformation at the Arabian Plate-Boundary observed by InSAR

    NASA Astrophysics Data System (ADS)

    Jonsson, S.; Cavalié, O.; Akoglu, A. M.; Wang, T.; Xu, W.; Feng, G.; Dutta, R.; Abdullin, A. K.

    2013-12-01

    The Arabian plate is bounded by a variety of active plate boundaries, with extension in the Red Sea and Gulf of Aden to the south, compression in Turkey and Iran to the north, and transform faults to the west and to the east. Internally, however, the Arabian plate has been shown to be tectonically rather stable, despite evidence of recent volcanism and earthquake faulting. We use InSAR observations to study recent tectonic and volcanic activity at several locations at the Arabian plate boundary as well within the plate itself. The region near the triple junction between the Arabian, Eurasian, and Anatolian plates has often been the focus of studies on continental deformation behavior and interseismic deformation. Here we use large-scale InSAR data processing to map the deformation near the triple junction and find the deformation to be focused on major faults with little intra-plate deformation. The eastern part of the East Anatolian Fault appears to have a very shallow locking depth with limited fault-normal deformation. Several major earthquakes that have occurred in recent years on the Arabian plate boundary, including the 2011 magnitude 7.1 Van earthquake in eastern Turkey. It occurred as a result of convergence of the Arabian plate towards Eurasia and caused significant surface deformation that we have analyzed with multiple coseismic InSAR, GPS, and coastal uplift observations. We use high-resolution Cosmo-Skymed and TerraSAR-X data to derive 3D coseismic displacements from offsets alone, as some of the interferograms are almost completely incoherent. By identifying point-like targets within the images, we were able to derive accurate pixel offsets between SAR sub-images containing such targets, which we used to estimate the 3D coseismic displacements. The derived 3D displacement field helped in constraining the causative northward dipping thrust-fault. The Qadimah fault is a recently discovered fault located on the Red Sea coast north of Jeddah and under the

  8. Architectural Blueprint for Plate Boundary Observatories based on interoperable Data Management Platforms

    NASA Astrophysics Data System (ADS)

    Kerschke, D. I.; Häner, R.; Schurr, B.; Oncken, O.; Wächter, J.

    2014-12-01

    Interoperable data management platforms play an increasing role in the advancement of knowledge and technology in many scientific disciplines. Through high quality services they support the establishment of efficient and innovative research environments. Well-designed research environments can facilitate the sustainable utilization, exchange, and re-use of scientific data and functionality by using standardized community models. Together with innovative 3D/4D visualization, these concepts provide added value in improving scientific knowledge-gain, even across the boundaries of disciplines. A project benefiting from the added value is the Integrated Plate boundary Observatory in Chile (IPOC). IPOC is a European-South American network to study earthquakes and deformation at the Chilean continental margin and to monitor the plate boundary system for capturing an anticipated great earthquake in a seismic gap. In contrast to conventional observatories that monitor individual signals only, IPOC captures a large range of different processes through various observation methods (e.g., seismographs, GPS, magneto-telluric sensors, creep-meter, accelerometer, InSAR). For IPOC a conceptual design has been devised that comprises an architectural blueprint for a data management platform based on common and standardized data models, protocols, and encodings as well as on an exclusive use of Free and Open Source Software (FOSS) including visualization components. Following the principles of event-driven service-oriented architectures, the design enables novel processes by sharing and re-using functionality and information on the basis of innovative data mining and data fusion technologies. This platform can help to improve the understanding of the physical processes underlying plate deformations as well as the natural hazards induced by them. Through the use of standards, this blueprint can not only be facilitated for other plate observing systems (e.g., the European Plate

  9. Evolution of southern Caribbean plate boundary, vicinity of Trinidad and Tobago

    NASA Technical Reports Server (NTRS)

    Robertson, Paul; Burke, Kevin

    1989-01-01

    The tectonic evolution of the southeastern corner of the Caribbean is examined, using field data from the El Pilar fault zone of Trinidad and offshore seismic data. It is found that the dominant process in the region's tectonic evolution is strike-slip motion on at least five major fault systems in a 250-km wide east-west-trending plate-boundary zone extending from Grenada in the north to the Orinoco River in the south. The geological effects of this evolution over the past 30 m y are described.

  10. Seismicity at the convergent plate boundary offshore Crete, Greece, observed by an amphibian network

    NASA Astrophysics Data System (ADS)

    Becker, D.; Meier, T.; Bohnhoff, M.; Harjes, H.-P.

    2010-04-01

    We investigate microseismic activity at the convergent plate boundary of the Hellenic subduction zone on- and offshore south-eastern Crete with unprecedented precision using recordings from an amphibian seismic network. The network configuration consisted of up to eight ocean bottom seismometers as well as five temporary short-period and six permanent broadband stations on Crete and surrounding islands. More than 2,500 local and regional events with magnitudes up to M L = 4.5 were recorded during the time period July 2003-June 2004. The magnitude of completeness varies between 1.5 on Crete and adjacent areas and increases to 2.5 in the vicinity of the Strabo trench 100 km south of Crete. Tests with different localization schemes and velocity models showed that the best results were obtained from a probabilistic earthquake localization using a 1-D velocity model and corresponding station corrections obtained by simultaneous inversion. Most of the seismic activity is located offshore of central and eastern Crete and interpreted to be associated with the intracrustal graben system (Ptolemy and Pliny trenches). Furthermore, a significant portion of events represents interplate seismicity along the NNE-ward dipping plate interface. The concentration of seismicity along the Ptolemy and Pliny trenches extends from shallow depths down to the plate interface and indicates active movement. We propose that both trenches form transtensional structures within the Aegean plate. The Aegean continental crust between these two trenches is interpreted as a forearc sliver as it exhibits only low microseismic activity during the observation period and little or no internal deformation. Interplate seismicity between the Aegean and African plates forms a 100-km wide zone along dip from the Strabo trench in the south to the southern shore-line of Crete in the north. The seismicity at the plate contact is randomly distributed and no indications for locked zones were observed. The plate

  11. A Reference Crustal and Plate-Boundary Velocity Model of Japan

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    The study of velocity structure using earthquake data has been remarkably progressed by development of seismic observation networks, improvement of the methodology, and increase in processing power. Recent studies on 3D velocity structures have produced tomographic images with resolution of a few kilometers (e.g., Matsubara et al., 2005; Nakamichi et al., 2007). In addition to these traveltime analyses, waveform studies such as receiver function analyses have been developed to image the configuration of continental Moho and oceanic plate boundaries (e.g., Yamauchi et al., 2003; Shiomi et al., 2004). Reflection and refraction surveys with controled sources have also been providing information on 2D and 3D velocity structures (e.g., Sato et al., 2005; Special Project for Earthquake Disaster Mitigation in Urban Areas). Thus, plenty of structural property models exist over the Japan islands, but the validity of an individual model is confined to its study area. Therefore, it is essential to build a reference crustal and plate-boundary velocity model for the whole Japan by combining them all together. If this sort of reference velocity model over the Japan islands is available under a unified criterion, it will be valuable for many fields of seismology and Earth sciences. We here construct a reference crustal and plate-boundary velocity model of Japan by integrating 2D models from seismic profiling and receiver functions, 3D models of seismic tomography, and other geophysical data such as gravity anomalies. The goal of this study is to construct a 3D laterally heterogeneous seismic velocity structure model, which clarifies the topography of the Conrad and Moho discontinuities and shapes of the oceanic plates, like the SCEC Unified Velocity Model (e.g., Magistrale et al., 1996). We first make a preliminary Japan model by compiling information on the topography of the Conrad and Moho discontinuities and subducting plates. To this end, we collect 2D seismic velocity models

  12. Flowfield measurements in a separated and reattached flat plate turbulent boundary layer

    NASA Technical Reports Server (NTRS)

    Patrick, William P.

    1987-01-01

    The separation and reattachment of a large-scale, two-dimensional turbulent boundary layer at low subsonic speed on a flat plate has been studied experimentally. The separation bubble was 55 cm long and had a maximum bubble thickness, measured to the height of the mean dividing streamline, of 17 cm, which was twice the thickness of the inlet boundary layer. A combination of laser velocimetry, hot-wire anemometry, pneumatic probing techniques, and flow visualization were used as diagnostics. Principal findings were that an outer inviscid rotational flow was defined which essentially convected over the blockage associated with the inner, viscously dominated bubble recirculation region. A strong backflow region in which the flow moved upstream 100 percent of the time was measured near the test surface over the central 35 percent of the bubble. A laminar backflow boundary layer having pseudo-turbulent characteristics including a log-linear velocity profile was generated under the highly turbulent backflow. Velocity profile shapes in the reversed flow region matched a previously developed universal backflow profile at the upstream edge of the separation region but not in the steady backflow region downstream. A smoke flow visualization movie and hot-film measurements revealed low frequency nonperiodic flapping at reattachment. However, forward flow fraction data at reattachment and mean velocity profiles in the redeveloping boundary layer downstream of reattachment correlated with backward-facing step data when the axial dimension was scaled by the distance from the maximum bubble thickness to reattachment.

  13. Direct simulation of flat-plate boundary layer with mild free-stream turbulence

    NASA Astrophysics Data System (ADS)

    Wu, Xiaohua; Moin, Parviz

    2014-11-01

    Spatially evolving direct numerical simulation of the flat-plate boundary layer has been performed. The momentum thickness Reynolds number develops from 80 to 3000 with a free-stream turbulence intensity decaying from 3 percent to 0.8 percent. Predicted skin-friction is in agreement with the Blasius solution prior to breakdown, follows the well-known T3A bypass transition data during transition, and agrees with the Erm and Joubert Melbourne wind-tunnel data after the completion of transition. We introduce the concept of bypass transition in the narrow sense. Streaks, although present, do not appear to be dynamically important during the present bypass transition as they occur downstream of infant turbulent spots. For the turbulent boundary layer, viscous scaling collapses the rate of dissipation profiles in the logarithmic region at different Reynolds numbers. The ratio of Taylor microscale and the Kolmogorov length scale is nearly constant over a large portion of the outer layer. The ratio of large-eddy characteristic length and the boundary layer thickness scales very well with Reynolds number. The turbulent boundary layer is also statistically analyzed using frequency spectra, conditional-sampling, and two-point correlations. Near momentum thickness Reynolds number of 2900, three layers of coherent vortices are observed: the upper and lower layers are distinct hairpin forests of large and small sizes respectively; the middle layer consists of mostly fragmented hairpin elements.

  14. Dynamics of continental accretion.

    PubMed

    Moresi, L; Betts, P G; Miller, M S; Cayley, R A

    2014-04-10

    Subduction zones become congested when they try to consume buoyant, exotic crust. The accretionary mountain belts (orogens) that form at these convergent plate margins have been the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North American Cordilleras and southwest Pacific subduction zones. The geologic record contains abundant accretionary orogens, such as the Tasmanides, along the eastern margin of the supercontinent Gondwana, and the Altaïdes, which formed on the southern margin of Laurasia. In modern and ancient examples of long-lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back-arc basin development, often related to subduction rollback and transient episodes of orogenesis and crustal shortening, coincident with accretion of exotic crust. Here we present three-dimensional dynamic models that show how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back-arc region. The complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, and infer that this is a recurrent and global phenomenon.

  15. Estimation of broadband acoustic power radiated from a turbulent boundary layer-driven reinforced finite plate section due to rib and boundary forces.

    PubMed

    Rumerman, M L

    2002-03-01

    Previous papers considered an infinite fluid-loaded plate with parallel line attachments, driven by a wave-number-white pressure excitation invariant in the direction of an attachment, and established the conditions and procedure for estimating the broadband radiated power by assuming the ribs to radiate independently. This paper applies those results to a finite rectangular ribbed plate, and extends the methodology to include the contribution of the plate's boundary support forces to the radiation and the consideration of excitation that varies in the direction parallel to the ribs. The approach is relevant to problems of sound radiation by underwater stiffened steel plates driven by turbulent boundary layer (TBL) pressures, and is also applicable to stiffened circular cylindrical shells when the response is dominated by bending. Comparisons of sample calculations with results of rigorous models validate the approximation.

  16. Influences of Electrical Boundary Conditions on Second-Harmonic Generation of Ultrasonic Guided Wave Propagation in a Piezoelectric Plate

    NASA Astrophysics Data System (ADS)

    Deng, Mingxi; Xiang, Yanxun

    The influences of electrical boundary conditions on second-harmonic generation (SHG) of ultrasonic guided wave propagation in a piezoelectric plate are analyzed. Based on the modal expansion analysis for waveguide excitation, an accurate description for the SHG effect of primary ultrasonic guided wave propagation in a piezoelectric plate has been presented within a second-order perturbation approximation. The formal solution of the double frequency guided waves, constituting the field of second harmonic, has been developed. The analytical results clearly reveal that the SHG effect of primary guided wave propagation is closely related to the electric boundary conditions of the piezoelectric plate. It is found that under different electrical boundary conditions there is an evident difference in the SHG effect of ultrasonic guided waves, and that the SHG effect is highly sensitive to the electrical boundary conditions.

  17. The behavior of a convergent plate boundary - Crustal deformation in the South Kanto district, Japan

    NASA Technical Reports Server (NTRS)

    Scholz, C. H.; Kato, T.

    1978-01-01

    The northwesternmost part of the Sagami trough, a part of the Philippine Sea-Eurasian plate boundary, was ruptured during the great South Kanto earthquake in 1923. Very extensive and frequent geodetic measurements of crustal deformation have been made in the South Kanto district since the 1890's, and these constitute the most complete data set on crustal movements in the world. These data were reanalyzed and interpreted and according to our interpretation indicate the following sequence of events. The coseismic movements were due to oblique thrust and right lateral slip of about 8 m on a fault outcropping at the base of the Sagami trough. This was followed by postseismic deformation resulting from reversed afterslip of 20-60 cm that occurred at an exponentially decaying rate in time. The interseismic deformation is produced by steady subduction at a rate of about 1.8 cm/yr. During subduction the top 10-15 km of the plate boundary is apparently locked, while deeper parts slip aseismically at an irregular rate. No significant precursory deformation was observed. The recurrence time for 1923 type earthquakes is 200-300 years. The Boso and Miura peninsulas are broken into a series of fault-bound blocks that move semi-independently of the surrounding region. The subduction zone itself, where it is exposed on land, is shown to be a wide zone encompassing several faults that are active at different times.

  18. Fluid flow and heat transfer of carbon nanotubes along a flat plate with Navier slip boundary

    NASA Astrophysics Data System (ADS)

    Khan, W. A.; Khan, Z. H.; Rahi, M.

    2014-06-01

    Homogeneous flow model is used to study the flow and heat transfer of carbon nanotubes (CNTs) along a flat plate subjected to Navier slip and uniform heat flux boundary conditions. This is the first paper on the flow and heat transfer of CNTs along a flat plate. Two types of CNTs, namely, single- and multi-wall CNTs are used with water, kerosene or engine oil as base fluids. The empirical correlations are used for the thermophysical properties of CNTs in terms of the solid volume fraction of CNTs. For the effective thermal conductivity of CNTs, Xue (Phys B Condens Matter 368:302-307, 2005) model has been used and the results are compared with the existing theoretical models. The governing partial differential equations and boundary conditions are converted into a set of nonlinear ordinary differential equations using suitable similarity transformations. These equations are solved numerically using a very efficient finite difference method with shooting scheme. The effects of the governing parameters on the dimensionless velocity, temperature, skin friction, and Nusselt numbers are investigated and presented in graphical and tabular forms. The numerical results of skin friction and Nusselt numbers are compared with the available data for special cases and are found in good agreement.

  19. Divergent plate boundaries and crustal spreading on Venus: Evidence from Aphrodite Terra

    NASA Technical Reports Server (NTRS)

    Crumpler, L. S.; Head, James W.

    1989-01-01

    The modes of lithospheric heat transfer and the tectonic styles may differ between Earth and Venus, depending on how the high surface temperature (700 K = 430 C), dense and opaque atmosphere (approx. 10 MPa = 100 bars), lack of water oceans, and the other known ways in which Venus differs from Earth, influence basic lithospheric processes, thermal gradient, upper mantle temperature, thermal and chemical evolution, and convection. A fundamental question is whether the lithosphere of Venus is horizontally stable, like the other terrestrial planets, or is mobile like that on Earth. The variety of characteristics, their integrated relationships, and their predictable behavior throughout Western Aphrodite Terra are similar to those features known to occur in association with the terrestrial seafloor at spreading centers and divergent plate boundaries. It is concluded that Western Aphrodite Terra represents the site of crustal spreading centers and divergent plate boundaries. The extent of similar characteristics and processes elsewhere on Venus outside of the 13,000 km long Western and Eastern Aphrodite Terra rise is unknown at the present, but their presence in other areas of the equatorial highlands, suggested from recent analysis, may be tested with forthcoming Magellan data.

  20. Regional deformation from the 2004 Macquarie Ridge great earthquake, Australia-Pacific plate boundary zone

    NASA Astrophysics Data System (ADS)

    Burgette, R. J.; Watson, C. S.; Tregoning, P.

    2009-12-01

    The transpressional Australia-Pacific plate boundary south of New Zealand has produced some of the largest strike-slip earthquakes in the instrumental record, including the 23 December 2004 Mw ~ 8.1 earthquake. The oceanic setting of this plate boundary limits terrestrial GPS measurements to sites on Macquarie Island (the only subaerial portion of Macquarie Ridge), southeastern Australia, and New Zealand. We investigate coseismic and postseismic deformation from the 2004 earthquake by analyzing GPS data at 16 sites and compare observed GPS vertical velocity with a relative sea level dataset that spans 96 years. Horizontal coseismic offsets decrease systematically with distance from the earthquake epicenter: 24 mm at Macquarie Island (530 km south of the epicenter) to < 2 mm at mainland Australia and the North Island of New Zealand (> 1800 km from epicenter). We invert the horizontal displacements for a best fitting set of fault parameters using an elastic half-space dislocation model. The modeling results are similar to those reported from seismological techniques: predominantly lateral slip occurred on a fault within the Australian plate, west of the main plate boundary, with a moment magnitude of ~8.0. Due to the symmetry of far-field elastic deformation, the geodetic data cannot discriminate between the two possible nodal planes. We prefer left-lateral slip on a NNW-striking fault based on the orientation of the aftershock pattern and fracture zones. We observe transient postseismic horizontal velocity changes at all of the GPS sites with significant coseismic displacements. Postseismic site velocities are significantly different from the pre-earthquake tectonic velocities. Preliminary modeling suggests that most of the postseismic deformation results from viscoelastic relaxation rather than afterslip. In the four years following the earthquake, the total postseismic deformation is approximately equal in magnitude to the coseismic offset observed at each site

  1. The Tertiary dynamics of the northern Eastern Alps (Austria): changing palaeostresses in a collisional plate boundary

    NASA Astrophysics Data System (ADS)

    Peresson, Herwig; Decker, Kurt

    1997-05-01

    Six Tertiary deviatoric palaeostress tensor groups from 165 stations in the Calcareous Alps describe the upper crustal dynamics of the leading edge of the Adriatic plate during protracted continental collision with the European lower plate. Palaeostress changes are correlated to the kinematic evolution of the plate boundary and to independently derived plate kinematic data of the Alpine-Carpathian-Pannonian area. Each palaeostress direction is defined by 32 to 89 individual tensors which constrain: (1) Late Eocene to ?Oligocene NW-directed compression during thrusting and dextral shearing on WNW-striking faults; NW-directed compression along the northern margin of the Adriatic plate is correlated to its N-directed translation combined with a counterclockwise rotation. (2a) ?Late Eocene to Early Miocene N-directed compression during N-directed thrusting of Penninic and Helvetic units and the Molasse; (2b) Early to Middle Miocene N-directed strike-slip compression during the onset of eastward lateral extrusion; the change from NW- to N-directed compression is interpreted to result from strain partitioning at the Periadriatic fault which has formed the new Adriatic plate boundary since the Oligocene. Dextral shearing on this fault accommodated continued anticlockwise rotation and decoupled the northern Eastern Alps from the rotational component. N-directed compression in the Calcareous Alps paralleled the N-directed translation of the Adriatic plate. (3) Middle Miocene NE-directed compression of thrust- and strike-slip type during lateral extrusion; NE-directed compression in the Calcareous Alps resulted from the drag of the eastward extruding central Eastern Alps. Sinistral shear stress was transmitted across the ENE-trending Salzach-Ennstal fault. NE-oriented σ1-axes include 45° with the E-W-striking zone of distributed sinistral shear in the Calcareous Alps. (4) Middle Miocene E-directed extension associated with orogen-parallel normal faulting of the central

  2. Coseismic slip resolution along a plate boundary megathrust: the Nankai Trough, southwest Japan

    USGS Publications Warehouse

    Sagiya, Takeshi; Thatcher, Wayne

    1999-01-01

    Geodetic survey measurements are used to estimate the coseismic slip distribution in the 1944 Tonankai (Mw=8.1) and 1946 Nankaido (Mw=8.3) earthquakes and to assess quantitatively the degree to which this slip is resolved on the plate boundary megathrust. Data used include 798 angle changes from triangulation surveys, 328 leveling section differences, and 5 coseismic tidal gage offsets. Many of the nominally coseismic triangulation data span ∼50 years, nearly half the earthquake cycle, and correction for interseismic deformation using post-1950 observations is applied. Microseismicity is used to define the configuration of the plate boundary interface and approximate it with a continuous, multisegment fault model. Because the onshore geodetic data have very limited resolving power for offshore fault segments, offshore coseismic slip was constrained by Satctke's [1993] estimation based on tsunami data. The majority of the coseismic slip occurs between 15 and 25 km depth. Although resolution declines toward the trench axis, it is sufficiently good to define two distinct high-slip regions, one off southeastern Shikoku Island (11 m maximum) and the other offshore of Kii Peninsula (3 m maximum). The slip magnitude off southeastern Shikoku, coupled with the plate convergence rate, would imply an recurrence interval of about 270 years, much-longer than the average repeat time of ∼120 years for historical great earthquakes on the Nankai Trough. However, the maximum coseismic slip is sensitive to the assumed fault geometry, and slippage on trough-parallel splay faults could significantly decrease the maximum slip to about 6 m.

  3. Large-Eddy Simulation of the Flat-plate Turbulent Boundary Layer at High Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Inoue, Michio

    The near-wall, subgrid-scale (SGS) model [Chung and Pullin, "Large-eddy simulation and wall-modeling of turbulent channel flow'', J. Fluid Mech. 631, 281--309 (2009)] is used to perform large-eddy simulations (LES) of the incompressible developing, smooth-wall, flat-plate turbulent boundary layer. In this model, the stretched-vortex, SGS closure is utilized in conjunction with a tailored, near-wall model designed to incorporate anisotropic vorticity scales in the presence of the wall. The composite SGS-wall model is presently incorporated into a computer code suitable for the LES of developing flat-plate boundary layers. This is then used to study several aspects of zero- and adverse-pressure gradient turbulent boundary layers. First, LES of the zero-pressure gradient turbulent boundary layer are performed at Reynolds numbers Retheta based on the free-stream velocity and the momentum thickness in the range Retheta = 103-1012. Results include the inverse skin friction coefficient, 2/Cf , velocity profiles, the shape factor H, the Karman "constant", and the Coles wake factor as functions of Re theta. Comparisons with some direct numerical simulation (DNS) and experiment are made, including turbulent intensity data from atmospheric-layer measurements at Retheta = O (106). At extremely large Retheta , the empirical Coles-Fernholz relation for skin-friction coefficient provides a reasonable representation of the LES predictions. While the present LES methodology cannot of itself probe the structure of the near-wall region, the present results show turbulence intensities that scale on the wall-friction velocity and on the Clauser length scale over almost all of the outer boundary layer. It is argued that the LES is suggestive of the asymptotic, infinite Reynolds-number limit for the smooth-wall turbulent boundary layer and different ways in which this limit can be approached are discussed. The maximum Retheta of the present simulations appears to be limited by machine

  4. Experimental study of boundary layer transition with elevated freestream turbulence on a heated flat plate

    NASA Technical Reports Server (NTRS)

    Sohn, Ki-Hyeon; Reshotko, Eli

    1991-01-01

    A detailed investigation to document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional, and low Reynolds number turbulent boundary layers are presented. Measurements were acquired in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities (TI) from 0.4 to 6 percent. The distributions of skin friction, heat transfer rate and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for R(sub theta) is less than 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length. The measured laminar value of Reynolds analogy factor was as much as 53 percent higher than the Pr(sup -2/3). A small dependence of turbulent results on TI was observed. Conditional sampling performed in the transitional boundary layer indicated the existence of a near-wall drop in intermittency, pronounced at certain low intermittencies, which is consistent with the cross-sectional shape of turbulent spots observed by others. Non-turbulent intervals were observed to possess large magnitudes of near-wall unsteadiness and turbulent intervals had peak values as much as 50 percent higher than were measured at fully turbulent stations. Non-turbulent and turbulent profiles in transitional boundary layers cannot be simply treated as Blasius and fully turbulent profiles, respectively. The boundary layer spectra indicate predicted selective amplification of T-S waves for TI is approximately 0.4 percent. However, for TI is approximately 0.8 and 1.1 percent, T-S waves are localized very near the wall and do not play a dominant role in transition process.

  5. Experimental study of boundary layer transition with elevated freestream turbulence on a heated flat plate

    NASA Astrophysics Data System (ADS)

    Sohn, Ki-Hyeon; Reshotko, Eli

    1991-02-01

    A detailed investigation to document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional, and low Reynolds number turbulent boundary layers are presented. Measurements were acquired in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities (TI) from 0.4 to 6 percent. The distributions of skin friction, heat transfer rate and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for R(sub theta) is less than 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length. The measured laminar value of Reynolds analogy factor was as much as 53 percent higher than the Pr(sup -2/3). A small dependence of turbulent results on TI was observed. Conditional sampling performed in the transitional boundary layer indicated the existence of a near-wall drop in intermittency, pronounced at certain low intermittencies, which is consistent with the cross-sectional shape of turbulent spots observed by others. Non-turbulent intervals were observed to possess large magnitudes of near-wall unsteadiness and turbulent intervals had peak values as much as 50 percent higher than were measured at fully turbulent stations. Non-turbulent and turbulent profiles in transitional boundary layers cannot be simply treated as Blasius and fully turbulent profiles, respectively. The boundary layer spectra indicate predicted selective amplification of T-S waves for TI is approximately 0.4 percent. However, for TI is approximately 0.8 and 1.1 percent, T-S waves are localized very near the wall and do not play a dominant role in transition process.

  6. Coefficient of Variation Estimates for the Plate Boundary Fault System of California

    NASA Astrophysics Data System (ADS)

    Biasi, G. P.; Scharer, K. M.

    2015-12-01

    The number of high-quality paleoseismic records on major strike-slip faults of California has increased in recent years to the point that patterns in earthquake recurrence are emerging. The degree of predictability in time intervals between ground-rupturing earthquakes can be measured by the CoV (coefficient of variation). The CoV approximately normalizes for mean recurrence, and is thus useful to isolate the temporal variability of earthquake records. CoV estimates are themselves uncertain because input dates are actually probability distributions and because paleoseismic records are short and not necessarily representative samples from the underlying recurrence distribution. Radiocarbon dating uncertainty can be incorporated by sampling from event PDFs and compiling sample CoV estimates. Uncertainty due to the brevity of the site event record is larger, and neglect of it can lead to improbable estimates. Long records are now available on the San Andreas and San Jacinto faults in Southern California, and the San Andreas and Hayward faults in northern California. These faults accommodate most of the Pacific-North American relative plate motion in their respective regions. CoV estimates from sites with 8 or more events cluster around 0.63, but are as low as 0.4 for the southern Hayward fault. Sites with fewer events give similar estimates, though with lower resolution. The one prominent outlier, Burro Flats, with a CoV near 1.0, is in a region of severe fault complexity and rapid fault-normal compression. Quasi-periodic recurrence is emerging as a general property for these plate boundary faults. Some individual site records allow that, at low probabilities, recurrence could be random in time. When the ensemble is considered together, however, it is improbable that we would see the observed degree of agreement among boundary fault paleoseismic records; the more likely explanation is that quasi-periodic recurrence is a real property of the boundary fault system.

  7. Numerical investigation of hypersonic flat-plate boundary layer transition mechanism induced by different roughness shapes

    NASA Astrophysics Data System (ADS)

    Zhou, Yunlong; Zhao, Yunfei; Xu, Dan; Chai, Zhenxia; Liu, Wei

    2016-10-01

    The roughness-induced laminar-turbulent boundary layer transition is significant for high-speed aerospace applications. The transition mechanism is closely related to the roughness shape. In this paper, high-order numerical method is used to investigate the effect of roughness shape on the flat-plate laminar-to-turbulent boundary layer transition. Computations are performed in both the supersonic and hypersonic regimes (free-stream Mach number from 3.37 up to 6.63) for the square, cylinder, diamond and hemisphere roughness elements. It is observed that the square and diamond roughness elements are more effective in inducing transition compared with the cylinder and hemisphere ones. The square roughness element has the longest separated region in which strong unsteadiness exists and the absolute instability is formed, thus resulting in the earliest transition. The diamond roughness element has a maximum width of the separated region leading to the widest turbulent wake region far downstream. Furthermore, transition location moves backward as the Mach number increases, which indicates that the compressibility significantly suppresses the roughness-induced boundary layer transition.

  8. The roof plate boundary is a bi-directional organiser of dorsal neural tube and choroid plexus development.

    PubMed

    Broom, Emma R; Gilthorpe, Jonathan D; Butts, Thomas; Campo-Paysaa, Florent; Wingate, Richard J T

    2012-11-01

    The roof plate is a signalling centre positioned at the dorsal midline of the central nervous system and generates dorsalising morphogenic signals along the length of the neuraxis. Within cranial ventricles, the roof plate gives rise to choroid plexus, which regulates the internal environment of the developing and adult brain and spinal cord via the secretion of cerebrospinal fluid. Using the fourth ventricle as our model, we show that the organiser properties of the roof plate are determined by its boundaries with the adjacent neuroepithelium. Through a combination of in ovo transplantation, co-culture and electroporation techniques in chick embryos between embryonic days 3 and 6, we demonstrate that organiser properties are maintained by interactions between the non-neural roof plate and the neural rhombic lip. At the molecular level, this interaction is mediated by Delta-Notch signalling and upregulation of the chick homologue of Hes1: chairy2. Gain- and loss-of-function approaches reveal that cdelta1 is both necessary and sufficient for organiser function. Our results also demonstrate that while chairy2 is specifically required for the maintenance of the organiser, its ectopic expression is not sufficient to recapitulate organiser properties. Expression of atonal1 in the rhombic lip adjacent at the roof plate boundary is acutely dependent on both boundary cell interactions and Delta-Notch signalling. Correspondingly, the roof plate boundary organiser also signals to the roof plate itself to specify the expression of early choroid plexus markers. Thus, the roof plate boundary organiser signals bi-directionally to acutely coordinate the development of adjacent neural and non-neural tissues.

  9. The roof plate boundary is a bi-directional organiser of dorsal neural tube and choroid plexus development

    PubMed Central

    Broom, Emma R.; Gilthorpe, Jonathan D.; Butts, Thomas; Campo-Paysaa, Florent; Wingate, Richard J. T.

    2012-01-01

    The roof plate is a signalling centre positioned at the dorsal midline of the central nervous system and generates dorsalising morphogenic signals along the length of the neuraxis. Within cranial ventricles, the roof plate gives rise to choroid plexus, which regulates the internal environment of the developing and adult brain and spinal cord via the secretion of cerebrospinal fluid. Using the fourth ventricle as our model, we show that the organiser properties of the roof plate are determined by its boundaries with the adjacent neuroepithelium. Through a combination of in ovo transplantation, co-culture and electroporation techniques in chick embryos between embryonic days 3 and 6, we demonstrate that organiser properties are maintained by interactions between the non-neural roof plate and the neural rhombic lip. At the molecular level, this interaction is mediated by Delta-Notch signalling and upregulation of the chick homologue of Hes1: chairy2. Gain- and loss-of-function approaches reveal that cdelta1 is both necessary and sufficient for organiser function. Our results also demonstrate that while chairy2 is specifically required for the maintenance of the organiser, its ectopic expression is not sufficient to recapitulate organiser properties. Expression of atonal1 in the rhombic lip adjacent at the roof plate boundary is acutely dependent on both boundary cell interactions and Delta-Notch signalling. Correspondingly, the roof plate boundary organiser also signals to the roof plate itself to specify the expression of early choroid plexus markers. Thus, the roof plate boundary organiser signals bi-directionally to acutely coordinate the development of adjacent neural and non-neural tissues. PMID:23052907

  10. Localised Plate Motion on Venus

    NASA Astrophysics Data System (ADS)

    Ghail, R. C.

    1996-03-01

    The volcanic and tectonic features observed in Dali Vinculum, Parga Vinculum and Imdr Regio are concentrated at long, narrow, curvilinear zones, with relatively minor volcanism and tectonism between these zones. These zones, whilst more diffuse than terrestrial plate boundaries, nevertheless define the margins of tectonic plates. In contrast to Earth, however, it appears that venusian plates are neither created nor destroyed by lateral motion. Rather, plates are thinned and intruded at vincula plate boundaries, vertically accreted by small-scale intra-plate (planitia) volcanism and perhaps destroyed by delamination of thickened crust in tesserae and montane regions such as Thetis Regio and Ishtar Terra. The diversity in age both between and within these three areas together with the evidence for infrequent, small scale resurfacing in the planitiae are difficult to reconcile with a non-uniformitarian geological process.

  11. Hurricane Mountain Formation melange: history of Cambro-Ordovician accretion of the Boundary Mountains terrane within the northern Appalachian orthotectonic zone

    SciTech Connect

    Boone, G.M.; Boudette, E.L.

    1985-01-01

    The Hurricane Mountain Formation (HMF) melange and associated ophiolitic and volcanogenic formations of Cambrian and lowermost Ordovician age bound the SE margin of the Precambrian Y (Helikian) Chain Lakes Massif in western Maine. HMF melange matrix, though weakly metamorphosed, contains a wide variety of exotic greenschist to amphibolite facies blocks as components of its polymictic assemblage, but blocks of high-grade cratonal rocks such as those of Chain Lakes or Grenville affinity are lacking. Formations of melange exposed in structural culminations of Cambrian and Ordovician rocks NE of the HMF in Maine and in the Fournier Group in New Brunswick are lithologically similar and probably tectonically correlative with the HMF; taken together, they may delineate a common pre-Middle Ordovician tectonic boundary. The authors infer that the Hurricane Mountain and St. Daniel melange belts define the SE and NW margins of the Boundary Mountains accreted terrane (BMT), which may consist of cratonal basement of Chain Lakes affinity extending from eastern Gaspe (deBroucker and St. Julien, 1985) to north-central New Hampshire. The Laurentian continental margin, underlain by Grenville basement, underplated the NW margin of this terrane, marked by the SDF suture zone, in late Cambrian to early Ordovician time, while terranes marked by Cambrian to Tremadocian (.) lithologies dissimilar to the Boundary Mountains terrane were accreted to its outboard margin penecontemporaneously. The docking of the Boundary Mountains terrane and the initiation of its peripheral melanges are equated to the Penobscottian disturbance.

  12. EarthScope Plate Boundary Observatory Data in the College Classroom (Invited)

    NASA Astrophysics Data System (ADS)

    Eriksson, S. C.; Olds, S. E.

    2009-12-01

    The Plate Boundary Observatory (PBO) is the geodetic component of the EarthScope project, designed to study the 3-D strain field across the active boundary zone between the Pacific and North American tectonics plates in the western United States. All PBO data are freely available to scientific and educational communities and have been incorporated into a variety of activities for college and university classrooms. UNAVCO Education and Outreach program staff have worked closely with faculty users, scientific researchers, and facility staff to create materials that are scientifically and technically accurate as well as useful to the classroom user. Availability of processed GPS data is not new to the geoscience community. However, PBO data staff have worked with education staff to deliver data that are readily accessible to educators. The UNAVCO Data for Educators webpage, incorporating an embedded Google Map with PBO GPS locations and providing current GPS time series plots and downloadable data, extends and updates the datasets available to our community. Google Earth allows the visualization GPS data with other types of datasets, e.g. LiDAR, while maintaining the self-contained and easy-to-use interface of UNAVCO’s Jules Verne Voyager map tools, which have multiple sets of geological and geophysical data. Curricular materials provide scaffolds for using EarthScope data in a variety of forms for different learning goals. Simple visualization of earthquake epicenters and locations of volcanoes can be used with velocity vectors to make simple deductions of plate boundary behaviors. Readily available time series plots provide opportunities for additional science skills, and there are web and paper-based support materials for downloading data, manipulating tables, and using plotting programs for processed GPS data. Scientists have provided contextual materials to explore the importance of these data in interpreting the structure and dynamics of the Earth. These data

  13. The fluid budget of a continental plate boundary fault: Quantification from the Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Menzies, Catriona D.; Teagle, Damon A. H.; Niedermann, Samuel; Cox, Simon C.; Craw, Dave; Zimmer, Martin; Cooper, Matthew J.; Erzinger, Jörg

    2016-07-01

    Fluids play a key role in modifying the chemical and physical properties of fault zones, which may prime them for repeated rupture by the generation of high pore fluid pressures and precipitation of commonly weak, secondary minerals. Fluid flow paths, sources and fluxes, and the permeability evolution of fault zones throughout their seismic cycles remain poorly constrained, despite their importance to understanding fault zone behaviour. Here we use geochemical tracers of fluid-rock exchange to determine budgets for meteoric, metamorphic and mantle fluids on a major compressional tectonic plate boundary. The Alpine Fault marks the transpressional Pacific-Australian plate boundary through South Island, New Zealand and appears to fail in regular (329 ± 68 yrs) large earthquakes (Mw ∼ 8) with the most recent event in 1717 AD. Significant convergent motion has formed the Southern Alps and elevated geothermal gradients in the hangingwall, which drive crustal fluid flow. Along the Alpine Fault the Alpine Schist of the Pacific Plate is thrust over radiogenic metasedimentary rocks on the Australian plate. The absence of highly radiogenic (87Sr/86Sr > 0.7200) strontium isotope ratios of hangingwall hot springs and hydrothermal minerals formed at a range of depths in the Alpine Fault damage zone indicates that the fluid flow is restricted to the hangingwall by a cross-fault fluid flow barrier throughout the seismogenic crust. Helium isotope ratios measured in hot springs near to the Alpine Fault (0.15-0.81 RA) indicate the fault is a crustal-scale feature that acts as a conduit for fluids from the mantle. Rock-exchanged oxygen, but meteoric water-like hydrogen isotope signatures of hydrothermal veins indicate that partially rock-exchanged meteoric fluids dominate down to the top of the brittle to ductile transition zone at ∼6 km. Geochemical tracer transport modelling suggests only ∼0.02 to 0.05% of total rainfall west of the Main Divide penetrates to depth, yet this

  14. Tectonic lineaments in the cenozoic volcanics of southern Guatemala: Evidence for a broad continental plate boundary zone

    NASA Technical Reports Server (NTRS)

    Baltuck, M.; Dixon, T. H.

    1984-01-01

    The northern Caribbean plate boundary has been undergoing left lateral strike slip motion since middle Tertiary time. The western part of the boundary occurs in a complex tectonic zone in the continental crust of Guatemala and southernmost Mexico, along the Chixoy-Polochic, Motogua and possibly Jocotan-Chamelecon faults. Prominent lineaments visible in radar imagery in the Neogene volcanic belt of southern Guatemala and western El Salvador were mapped and interpreted to suggest southwest extensions of this already broad plate boundary zone. Because these extensions can be traced beneath Quaternary volcanic cover, it is thought that this newly mapped fault zone is active and is accommodating some of the strain related to motion between the North American and Caribbean plates. Onshore exposures of the Motoqua-Polochic fault systems are characterized by abundant, tectonically emplaced ultramafic rocks. A similar mode of emplacement for these off shore ultramafics, is suggested.

  15. Comprehensive Analysis of Convective Heat Transfer in Parallel Plate Microchannel with Viscous Dissipation and Constant Heat Flux Boundary Conditions

    NASA Astrophysics Data System (ADS)

    Kushwaha, Hari Mohan; Sahu, Santosh Kumar

    2016-06-01

    This paper reports the hydrodynamically and thermally fully developed, laminar, incompressible, forced convective heat transfer characteristics of gaseous flows through a parallel plate microchannel with different constant heat flux boundary conditions. The first order velocity slip and viscous dissipation effects are considered in the analysis. Here, three different thermal boundary conditions such as: both plates kept at different constant heat fluxes, both plates kept at equal constant heat fluxes and one plate kept at constant heat flux and other one insulated are considered for the analysis. The deviation in Nusselt number between the model that considers both first order velocity slip and temperature jump and the one that considers only velocity slip is reported. Also, the effect of various heat flux ratios on the Nusselt number is reported in this analysis. In addition, the deviation in Nusselt number between first and second order slip model is discussed in this study.

  16. Seismicity and Seismic Hazard along the Western part of the Eurasia-Nubia plate boundary

    NASA Astrophysics Data System (ADS)

    Bezzeghoud, Mourad; Fontiela, João; Ferrão, Celia; Borges, José Fernando; Caldeira, Bento; Dib, Assia; Ousadou, Farida

    2016-04-01

    The seismic phenomenon is the most damaging natural hazard known in the Mediterranean area. The western part of the Eurasia-Nubia plate boundary extends from the Azores to the Mediterranean region. The oceanic part of the plate boundary is well delimited from the Azores Islands, along the Azores-Gibraltar fault to approximately 12°W (west of the Strait of Gibraltar). From 12°W to 3.5°E, including the Iberia-Nubia region and extending to the western part of Algeria, the boundary is more diffuse and forms a wider area of deformation. The boundary between the Iberia and Nubia plates is the most complex part of the margin. This region corresponds to the transition from an oceanic boundary to a continental boundary, where Iberia and Nubia collide. Although most earthquakes along this plate boundary are shallow and generally have magnitudes less than 5.5, there have been several high-magnitude events. Many devastating earthquakes, some of them tsunami-triggering, inflicted heavy loss and considerable economic damage to the region. From 1920 to present, three earthquakes with magnitudes of about 8.0 (Mw 8.2, 25 November 1941; Ms 8.0, 25 February 1969; and Mw 7.9, 26 May 1975) occurred in the oceanic region, and four earthquakes with magnitudes of about 7.0 (Mw 7.1, 8 May 1939, Santa Maria Island and Mw 7.1, January 1980, Terceira and Graciosa Islands, both in the Azores; Ms 7.1, 20 May 1931, Azores-Gibraltar fracture zone; and Mw 7.3, 10 October 1980, El Asnam, Algeria) occurred along the western part of the Eurasia-Nubia plate boundary. In general, large earthquakes (M ≥7) occur within the oceanic region, with the exception of the El Asnam (Algeria) earthquakes. Some of these events caused extensive damage. The 1755 Lisbon earthquake (˜Mw 9) on the Portugal Atlantic margin, about 200 km W-SW of Cape St. Vincent, was followed by a tsunami and fires that caused the near-total destruction of Lisbon and adjacent areas. Estimates of the death toll in Lisbon alone (~70

  17. Direct drag measurements in a turbulent flat-plate boundary layer with turbulence manipulators

    NASA Astrophysics Data System (ADS)

    Lynn, T. B.; Bechert, D. W.; Gerich, D. A.

    1995-10-01

    The effect of turbulence manipulators on the turbulent boundary layer above a flat plate has been investigated. These turbulence manipulators are often referred to as Large Eddy Break Up (LEBU) devices. The basic idea is that thin blades or airfoils are inserted into the turbulent flow in order to reduce the fluctuating vertical velocity component v' above the flat plate. In this way, the turbulent momentum transfer and with it the wall shear stress downstream of the manipulator should be decreased. In our experiments, for comparison, a merely drag-producing wire also was inserted into the boundary layer. In particular, the trade-off between the drag of the turbulence manipulator and the drag reduction due to the shear-stress reduction on the flat plate downstream of the manipulator has been considered. The measurements were carried out with very accurate force balances for both the manipulator drag and the shear stress on the flat plate. As it turns out, no net drag reduction is found for a fairly large set of configurations. A single thin blade as a manipulator performed best, i.e., it was closest to break-even. However, a further improvement is unlikely, because the device drag of the thin blade elements used here has already been reduced to only that due to laminar skin friction, and is thus the minimum possible drag. Airfoils performed slightly worse, because their device drag was higher. A purely drag-producing wire device performed disastrously. The wire device, which consisted of a wire with another thin wire wound around it to suppress coherent vortex shedding and vibration, was designed to have (and did have) the same drag as the airfoil manipulator with which it was compared. The comparison showed that airfoil and blade manipulators recovered 75 90% of their device drag through a shear-stress reduction downstream, whereas the wire device recovered only about 25 30% of its device drag. Conventional LEBU manipulators with airfoils or thin blades produce

  18. Patterns of seismogenesis for giant plate-boundary earthquakes in island-arc-type subduction systems

    NASA Astrophysics Data System (ADS)

    Kirby, S. H.

    2006-12-01

    The global record of giant earthquake occurrence in subduction zones during the instrumental and historical eras is woefully short; only about 16 events with magnitudes above 8.4 are reasonably well documented since 1700. We find no examples of giant (M > 8.4) interplate thrust events and/or wide-ranging tsunamis sourced in the classic island arcs with fast backarc spreading (Bonin, Marianas, Tonga-Kermadec, Vanuatu, and South Scotia). The Sumatra-Andaman Earthquake of 2004 (SAE) ruptured a sector of the INDIA-BURMA subduction boundary and evidently had no known historical antecedents, suggesting that the return time may be many centuries to millennia and consistent with low convergence rates. Moreover, the persistence of rupture to the north in the weakly volcanic Nicobar/Andaman sector gives one pause to reflect on the assumption that island arcs, especially those with active back-arc spreading such as the Marianas, do not produce great interplate- thrust earthquakes. The Andaman/Nicobar subduction segment is an unusual island arc. Only two arc volcanoes occur between the convergent plate boundary west of the Andamans and the backarc ridge/transform system to the east. Backarc spreading in the Andaman/ Nicobar segment is unusual because the NNW spreading directions are nearly parallel to the trench/deformation-front as do the INDIA-BURMA plate motions across it. This geometry suggests that arc-normal extension, trench migration and associated slab normal motions may not mechanically decouple this subduction system. The Nicobar sector of the rupture for the 2004 event is roughly 200 km wide judging from the aftershock distribution; a distribution that persists to the east under the Nicobar Islands, suggesting that the plate-boundary dip is very shallow in that latitude range. If this is correct, then the down-dip limitation on seismogenic slip set by serpentinized forearc mantle (Hyndman et al., 2003) may not control rupture width as it apparently does for many

  19. Multibeam investigation of the active North Atlantic plate boundary reorganization tip

    NASA Astrophysics Data System (ADS)

    Hey, Richard; Martinez, Fernando; Höskuldsson, Ármann; Eason, Deborah E.; Sleeper, Jonathan; Thordarson, Sigvaldi; Benediktsdóttir, Ásdís; Merkuryev, Sergey

    2016-02-01

    The previous orthogonal ridge/transform staircase geometry south of Iceland is being progressively changed to the present continuous oblique Reykjanes Ridge spreading geometry as North America-Eurasia transform faults are successively eliminated from north to south. This reorganization is commonly interpreted as a thermal phenomenon, caused by warmer Iceland plume mantle progressively interacting with the ridge, although other diachronous seafloor spreading reorganizations are thought to result from tectonic rift propagation. New marine geophysical data covering our reinterpretation of the reorganization tip near 57°N show successive transform eliminations at a propagation velocity of ∼110 km/Myr, ten times the spreading half rate, followed by abrupt reorganization slowing at the Modred transform as it was converted to a migrating non-transform offset. Neither the simple thermal model nor the simple propagating rift model appears adequate to explain the complicated plate boundary reorganization process.

  20. Recovering physical property information from subduction plate boundaries using 3D full-waveform seismic inversion

    NASA Astrophysics Data System (ADS)

    Bell, R. E.; Morgan, J. V.; Warner, M.

    2013-12-01

    Our understanding of subduction margin seismogenesis has been revolutionised in the last couple of decades with the discovery that the size of the seismogenic zone may not be controlled simply by temperature and a broad spectrum of seismic behaviour exists from stick-slip to stable sliding. Laboratory and numerical experiments suggest that physical properties, particularly fluid pressure may play an important role in controlling the seismic behaviour of subduction margins. Although drilling can provide information on physical properties along subduction thrust faults at point locations at relatively shallow depths, correlations between physical properties and seismic velocity using rock physics relationships are required to resolve physical properties along the margin and down-dip. Therefore, high resolution seismic velocity models are key to recovering physical property information at subduction plate boundaries away from drill sites. 3D Full waveform inversion (FWI) is a technique pioneered by the oil industry to obtain high-resolution high-fidelity models of physical properties in the sub-surface. 3D FWI involves the inversion of low-frequency (>2 to <7 Hz), early arriving (principally transmitted) seismic data, to recover the macro (intermediate to long-wavelength) velocity structure. Although 2D FWI has been used to improve velocity models of subduction plate boundaries before, 3D FWI has not yet been attempted. 3D inversions have superior convergence and accuracy, as they sample the subsurface with multi-azimuth multiply-crossing wavefields. In this contribution we perform a suite of synthetic tests to investigate if 3D FWI could be used to better resolve physical property information along subduction margin plate boundaries using conventionally collected 3D seismic data. We base our analysis on the Muroto Basin area of the Nankai margin and investigate if the acquisition parameters and geometry of the subduction margin render 3D seismic data collected across

  1. Multi-scale geometry of flow structures in a flat-plate turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Bermejo-Moreno, Ivan; Atkinson, Callum; Chumakov, Sergei; Soria, Julio; Wu, Xiaohua

    2010-11-01

    We study the geometry of structures educed from the enstrophy and dissipation fields obtained from a DNS of a flat-plate turbulent boundary layer (J. Fluid Mech. 630, 5-41, 2009) following the non-local multi-scale methodology introduced in J. Fluid Mech. 603, 101-135, 2008. We compare the results with those of homogeneous isotropic turbulence. In the present analysis, geometric parameters are combined with physical quantities associated with the flow structures. Their evolution in time is studied through a series of snapshots obtained from the simulation, following a moving subdomain. Individual structures are tracked in time, relating their physical and geometric properties at the local and structure levels. The validity of two local identification criteria for the eduction of vortex tubes and sheets in wall-bounded flows is also evaluated.

  2. Plate tectonics and offshore boundary delimitation: Tunisia-Libya case at the International Court of Justice

    NASA Astrophysics Data System (ADS)

    Stanley, Daniel Jean

    1982-03-01

    The first major offshore boundary dispute where plate tectonics constituted a significant argument was recently brought before the International Court of Justice by Libya and Tunisia concerning the delimitation of their continental shelves. Libya placed emphasis on this concept to determine natural prolongation of its land territory under the sea. Tunisia contested use of the entire African continental landmass as a reference unit and views geography, geomorphology and bathymetry as relevant as geology. The Court pronounced that “It is the outcome, not the evolution in the long-distant past, which is of importance.” Moreover, it is the present-day configuration of coasts and seabed that are the main factors, not geology.

  3. XFEM simulation of a quenched cracked glass plate with moving convective boundaries

    NASA Astrophysics Data System (ADS)

    Ghaffari, Diyako; Rash Ahmadi, Samrand; Shabani, Farzin

    2016-02-01

    A moving quenched soda-lime glass plate with an initial edge crack is modeled, applying the eXtended finite-element method (XFEM) in order to investigate the stress field components and Von Mises stress around the crack. The convective heat with moving boundaries is considered in thermal formulation. The Crank-Nicolson time integration scheme is reformed and adjusted with a view to accurately solving the system of transient heat conduction matrix equations. In order to simulate the whole stages of the problem formulation, MATLAB XFEM (MXFEM) codes are written and employed. The stress distribution contours are plotted in detail and the stress fields around the crack tip are compared quantitatively. The variations of stress intensity factors (SIFs) during crack propagation are obtained through the calculation of the domain form of the interaction integral. In order to verify the procedure and display the ability of the developed formulation, the results are compared with experimental outputs from the literature.

  4. Data Access and Web Services at the EarthScope Plate Boundary Observatory

    NASA Astrophysics Data System (ADS)

    Matykiewicz, J.; Anderson, G.; Henderson, D.; Hodgkinson, K.; Hoyt, B.; Lee, E.; Persson, E.; Torrez, D.; Smith, J.; Wright, J.; Jackson, M.

    2007-12-01

    The EarthScope Plate Boundary Observatory (PBO) at UNAVCO, Inc., part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 880 continuous GPS stations, 103 borehole strainmeter stations, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations and one previously existing laser strainmeter. UNAVCO provides access to data products from these stations, as well as general information about the PBO project, via the PBO web site (http://pboweb.unavco.org). GPS and strainmeter data products can be found using a variety of access methods, incuding map searches, text searches, and station specific data retrieval. In addition, the PBO construction status is available via multiple mapping interfaces, including custom web based map widgets and Google Earth. Additional construction details can be accessed from PBO operational pages and station specific home pages. The current state of health for the PBO network is available with the statistical snap-shot, full map interfaces, tabular web based reports, and automatic data mining and alerts. UNAVCO is currently working to enhance the community access to this information by developing a web service framework for the discovery of data products, interfacing with operational engineers, and exposing data services to third party participants. In addition, UNAVCO, through the PBO project, provides advanced data management and monitoring systems for use by the community in operating geodetic networks in the United States and beyond. We will demonstrate these systems during the AGU meeting, and we welcome inquiries from the community at any time.

  5. Recording Plate Boundary Deformation Processes Around The San Jacinto Fault, California

    NASA Astrophysics Data System (ADS)

    Hodgkinson, K.; Mencin, D.; Borsa, A.; Fox, O.; Walls, C.; Van Boskirk, E.

    2012-04-01

    The San Jacinto Fault is one of the major faults which form the San Andreas Fault System in southern California. The fault, which lies to the west of the San Andreas, is one of the most active in the region. While strain rates are higher along the San Andreas, 23-37 mm/yr compared to 12-22 mm/yr along the San Jacinto, there have been 11 earthquakes of M6 and greater along the San Jacinto in the past 150 years while there have been none of this magnitude on the San Andreas in this region. UNAVCO has installed an array of geodetic and seismic instruments along the San Jacinto as part of the Plate Boundary Observatory (PBO). The network includes 25 GPS stations within 20 km of the surface trace with a concentration of borehole instrumentation in the Anza region where there are nine boreholes sites. Most of the borehole sites contain a GTSM21 4-component strainmeter, a Sonde-2 seismometer, a MEMS accelerometer and a pore pressure sensor. Thus, the array has the capability to capture plate boundary deformation processes with periods of milliseconds (seismic) to decades (GPS). On July 7th 2010 a M5.4 earthquake occurred on the Coyote Creek segment of the fault. The event was preceded by a M4.9 earthquake in the same area four weeks earlier and four earthquakes of M5 and greater within a 20 km radius of the epicenter in the past 50 years. In this study we will present the signals recorded by the different instrument types for the July 7th 2010 event and will compare the coseismic displacements recorded by the GPS and strainmeters with the displacement field predicted by Okada [1992]. All data recorded as part of the PBO observatory are publically available from the UNAVCO, the IRIS Data Management Center and the Northern California Earthquake Data Center.

  6. Logistical Support for the Installation of the Plate Boundary Observatory GPS and Borehole Strainmeter Networks

    NASA Astrophysics Data System (ADS)

    Kurnik, C.; Austin, K.; Coyle, B.; Dittmann, T.; Feaux, K.; Friesen, B.; Johnson, W.; Mencin, D.; Pauk, B.; Walls, C.

    2007-12-01

    The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three- dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters by October 2008. Such a broad network presents significant logisitical challenges, including moving supplies, equipment, and personnel around 6 million square kilometers, and this requires accurate tracking and careful planning. The PBO logistics chain includes the PBO headquarters at UNAVCO in Boulder, Colorado and five regional offices in the continental United States and Alaska, served by dozens of suppliers spread across the globe. These offices are responsible for building and maintaining sites in their region. Most equipment and supplies first arrive in Boulder, where they are tagged and entered into a UNAVCO-wide equipment database, assembled and quality checked as necessary, and sent on to the appropriate regional office. Larger items which are costly to store and ship from Boulder, such as batteries or long sections of stainless steel pipe and bar required for monuments, are shipped directly from the supplier to each region as needed. These supplies and equipment are also tracked through the ordering, delivery, installation, and maintenance cycle via Earned Value Management techniques which allow us to meet NSF and other Federal procurement rules. Early prototypes and assembly configurations aid the development of material and supply budgets. A thorough understanding of Federal procurement rules at project start up is critical as the project moves forward.

  7. Tectonic activity evolution of the Scotia-Antarctic Plate boundary from mass transport deposit analysis

    NASA Astrophysics Data System (ADS)

    Pérez, Lara F.; Bohoyo, Fernando; Hernández-Molina, F. Javier; Casas, David; Galindo-Zaldívar, Jesús; Ruano, Patricia; Maldonado, Andrés.

    2016-04-01

    The spatial distribution and temporal occurrence of mass transport deposits (MTDs) in the sedimentary infill of basins and submerged banks near the Scotia-Antarctic plate boundary allowed us to decode the evolution of the tectonic activity of the relevant structures in the region from the Oligocene to present day. The 1020 MTDs identified in the available data set of multichannel seismic reflection profiles in the region are subdivided according to the geographic and chronological distributions of these features. Their spatial distribution reveals a preferential location along the eastern margins of the eastern basins. This reflects local deformation due to the evolution of the Scotia-Antarctic transcurrent plate boundary and the impact of oceanic spreading along the East Scotia Ridge (ESR). The vertical distribution of the MTDs in the sedimentary record evidences intensified regional tectonic deformation from the middle Miocene to Quaternary. Intensified deformation started at about 15 Ma, when the ESR progressively replaces the West Scotia Ridge (WSR) as the main oceanic spreading center in the Scotia Sea. Coevally with the WSR demise at about 6.5 Ma, increased spreading rates of the ESR and numerous MTDs were formed. The high frequency of MTDs during the Pliocene, mainly along the western basins, is also related to greater tectonic activity due to uplift of the Shackleton Fracture Zone by tectonic inversion and extinction of the Antarctic-Phoenix Ridge and involved changes at late Pliocene. The presence of MTDs in the southern Scotia Sea basins is a relevant indicator of the interplay between sedimentary instability and regional tectonics.

  8. Irregular earthquake recurrence patterns and slip variability on a plate-boundary Fault

    NASA Astrophysics Data System (ADS)

    Wechsler, N.; Rockwell, T. K.; Klinger, Y.

    2015-12-01

    The Dead Sea fault in the Levant represents a simple, segmented plate boundary from the Gulf of Aqaba northward to the Sea of Galilee, where it changes its character into a complex plate boundary with multiple sub-parallel faults in northern Israel, Lebanon and Syria. The studied Jordan Gorge (JG) segment is the northernmost part of the simple section, before the fault becomes more complex. Seven fault-crossing buried paleo-channels, offset by the Dead Sea fault, were investigated using paleoseismic and geophysical methods. The mapped offsets capture the long-term rupture history and slip-rate behavior on the JG fault segment for the past 4000 years. The ~20 km long JG segment appears to be more active (in term of number of earthquakes) than its neighboring segments to the south and north. The rate of movement on this segment varies considerably over the studied period: the long-term slip-rate for the entire 4000 years is similar to previously observed rates (~4 mm/yr), yet over shorter time periods the rate varies from 3-8 mm/yr. Paleoseismic data on both timing and displacement indicate a high COV >1 (clustered) with displacement per event varying by nearly an order of magnitude. The rate of earthquake production does not produce a time predictable pattern over a period of 2 kyr. We postulate that the seismic behavior of the JG fault is influenced by stress interactions with its neighboring faults to the north and south. Coulomb stress modelling demonstrates that an earthquake on any neighboring fault will increase the Coulomb stress on the JG fault and thus promote rupture. We conclude that deriving on-fault slip-rates and earthquake recurrence patterns from a single site and/or over a short time period can produce misleading results. The definition of an adequately long time period to resolve slip-rate is a question that needs to be addressed and requires further work.

  9. Development of the Plate Boundary Observatory GPS Low Latency Salton Trough Radio Network

    NASA Astrophysics Data System (ADS)

    Walls, C.; Miller, S.; Wilson, B.; Lawrence, S.; Arnitz, E.

    2008-05-01

    UNAVCO is developing a 20 GPS station low latency radio network that spans the San Andreas and San Jacinto faults in the region of highest strain in southern California and the narrowest part of the North America-Pacific plate boundary. The Salton Trough Radio Network (STRN) is instrumented with Ethernet bridge Intuicom EB6+ (900 MHz) radios to transmit a high rate low latency data stream from each permanent GPS site for the purpose of the following: 1) telemeter 15 second data (1 MB/day/station) to the Plate Boundary Observatory archive, 2) accommodate the timely download of 1 and 5 sample per second data following large earthquakes (4 MB/hour/station), and 3) test the UStream of 1Hz BINEX and RTCM data. Three of four phases have been completed. Office radio testing yielded transfer rates of 30-50 KB/s with subsecond latency while streaming 1 Hz data. Latency climbed to ~1.8 seconds while simultaneously streaming 1 Hz and downloading hourly 1 and 5 sample per second data files. Field testing demonstrated rates on the order of 30 KB/s. At present the radios are installed and have transfer rates of 10-40 KB/s between sites that span 10-32 km. The final phase will be the installation of the main telemetry relay where master radios will be connected to a high speed ISP near the town of Brawley. The high-rate low latency UStream data will be available to researchers who are developing prototype earthquake early warning systems in Southern California. A goal of the STRN is to make the data available rapidly enough for GPS-derived coseismic and dynamic displacements to be integrated into early warning system earthquake models. The improved earthquake models will better assist emergency response. UStream data will also aid surveyors who wish to use PBO GPS stations as permanent, high-quality base stations in real-time kinematic surveys.

  10. Experimental study of the stability of boundary-layer flow along a heated, inclined plate

    NASA Astrophysics Data System (ADS)

    Zuercher, E. J.; Jacobs, J. W.; Chen, C. F.

    1998-07-01

    Experiments are conducted to study the longitudinal vortices that develop in the boundary layer on the upper surface of an inclined, heated plate. An isothermal plate in water is inclined at angles ranging from 20 to 60 degrees (from the vertical) while the temperature difference is varied from 2 to 23°C. A double-pass Schlieren system is used to visualize the vortices and particle image velocimetry (PIV) is used to measure velocities. In addition, a unique method is developed such that both the Schlieren visualization and PIV can be performed simultaneously. The wavelengths of the vortices and the critical modified Reynolds numbers (R˜) for the onset, merging, and breakup of the vortices are determined from Schlieren images for Pr=5.8. The critical values for R˜ and the critical wavelengths are compared to results of previous experiments and stability analyses. The spatial growth rates of vortices are determined by using the PIV measurements to determine how the circulation in the vortices grows with distance from the leading edge. This is the first time that the growth rate of the vortices have been found using velocity measurements. These spatial growth rates are compared to the results of Iyer & Kelly (1974) and found to be in general agreement. By defining a suitable circulation threshold, the critical R˜ for the onset of the vortices can be found from the growth curves.

  11. Source and sink of fluid in pelagic siliceous sediments along a cold subduction plate boundary

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Asuka; Hina, Shoko; Hamada, Yohei; Kameda, Jun; Hamahashi, Mari; Kuwatani, Tatsu; Shimizu, Mayuko; Kimura, Gaku

    2016-08-01

    Subduction zones where old oceanic plate underthrusting occurs are characterized by thick pelagic sediments originating from planktonic ooze as well as cold thermal conditions. For a better understanding of dehydration from pelagic sediments and fluid behavior, which would play a key role in controlling the dynamics in the shallow portion of the subduction zone, as observed in the 2011 Tohoku earthquake and tsunami, we investigate cherts in a Jurassic accretionary complex in Japan. The microstructure and microchemistry of these cherts indicate dissolution of SiO2 from a pressure solution seam and precipitation of SiO2 to the "white chert layer," which would act as a fluid conduit. The amount of water necessary to precipitate SiO2 in the white chert is ~ 102 times larger than that produced by compaction and silica/clay diagenesis. Other fluid sources, such as hydrated oceanic crust or oceanic mantle, are necessary to account for this discrepancy in the fluid budget. A large amount of external fluid likely contributed to rising pore pressure along cold plate boundaries.

  12. Extinct mid-ocean ridges and insights on the influence of hotspots at divergent plate boundaries

    NASA Astrophysics Data System (ADS)

    MacLeod, Sarah; Dietmar Müller, R.; Williams, Simon; Matthews, Kara

    2016-04-01

    We review all global examples of confirmed or suspected extinct mid-ocean ridges that are preserved in present-day ocean basins. Data on their spreading rate prior to extinction, time of cessation, length of activity, bathymetric and gravity signature are analysed. This analysis identifies some differences between subgroups of extinct ridges, including microplate spreading ridges, back-arc basin ridges and large-scale mid-ocean ridges. Crustal structure of extinct ridges is evaluated using gravity inversion to seek to resolve a long-standing debate on whether the final stages of spreading leads to development of thinned or thickened crust. Most of the ridges we assess have thinner crust at their axes than their flanks, yet a small number are found to have a single segment that is overprinted by an anomalous feature such as a seamount or volcanic ridge. A more complex cessation mechanism is necessary in these cases. The location of spreading centres at their time of cessation relative to hotspots was also evaluated using a global plate reconstruction. This review provides strong evidence for the long-term interaction of spreading centres with hotspots and plate boundaries have been frequently modified within the radius of a hotspot zone of influence.

  13. Tsunami effects at Korean Nuclear Power Plant Sites by Plate Boundary Earthquakes

    NASA Astrophysics Data System (ADS)

    Jin, Sobeom; Hyun, Seung Gyu; Bae, Jae Seok; Kim, Gun Hyeong; Yoon, Sung Bum

    2015-04-01

    Great earthquakes have occurred at the Nankai Trough due to the subduction of the Philippine Sea plate beneath Honshu, Japan. The 1707 Hoei tsunami associated with the Mw 8.7 earthquake, in particular, was the largest event generated in this area. The Nankai Trough is one of the most earthquake-prone area near Japan. And the tsunami affected to Korea according to a Korean historic literature. In this study, new hypothetical plate boundary earthquakes (Mw 9.6) ruptured simultaneously from the Nankai Trough to the Ryukyu Trench (NTRT) are proposed and applied to evaluate the tsunami effects at the Nuclear Power Plant Sites in Korea. In order to make reasonable tsunami sources the asperity model is adapted. The numerical model using the modified leap-frog finite difference scheme is employed to simulate the propagation of tsunami generated at NTRT. This numerical model considering the dispersion effect and inundation of tsunami is then employed to estimate the maximum tsunami heights. Predicted results will be used to make the measures against unexpected tsunami attacks.

  14. Prediction and measurement of heat transfer rates for the shock-induced unsteady laminar boundary layer on a flat plate

    NASA Technical Reports Server (NTRS)

    Cook, W. J.

    1972-01-01

    The unsteady laminar boundary layer induced by the flow-initiating shock wave passing over a flat plate mounted in a shock tube was theoretically and experimentally studied in terms of heat transfer rates to the plate for shock speeds ranging from 1.695 to 7.34 km/sec. The theory presented by Cook and Chapman for the shock-induced unsteady boundary layer on a plate is reviewed with emphasis on unsteady heat transfer. A method of measuring time-dependent heat-transfer rates using thin-film heat-flux gages and an associated data reduction technique are outlined in detail. Particular consideration is given to heat-flux measurement in short-duration ionized shocktube flows. Experimental unsteady plate heat transfer rates obtained in both air and nitrogen using thin-film heat-flux gages generally agree well with theoretical predictions. The experimental results indicate that the theory continues to predict the unsteady boundary layer behavior after the shock wave leaves the trailing edge of the plate even though the theory is strictly applicable only for the time interval in which the shock remains on the plate.

  15. Active faulting in northern Chile: ramp stacking and lateral decoupling along a subduction plate boundary?

    NASA Astrophysics Data System (ADS)

    Armijo, Rolando; Thiele, Ricardo

    1990-04-01

    Two large features parallel to the coastline of northern Chile have long been suspected to be the sites of young or active deformation: (1) The 700-km long Coastal Scarp, with average height (above sea level) of about 1000 m; (2) The Atacama Fault zone, that stretches linearly for about 1100 km at an average distance of 30-50 km from the coastline. New field observations combined with extensive analysis of aerial photographs demonstrate that both the Coastal Scarp and the Atacama Fault are zones of Quaternary and current fault activity. Little-degraded surface breaks observed in the field indicate that these fault zones have recently generated large earthquakes ( M = 7-8). Normal fault offsets observed in marine terraces in the Coastal Scarp (at Mejillones Peninsula) require tectonic extension roughly orthogonal to the compressional plate boundary. Strike-slip offsets of drainage observed along the Salar del Carmen and Cerro Moreno faults (Atacama Fault system) imply left-lateral displacements nearly parallel to the plate boundary. The left-lateral movement observed along the Atacama Fault zone may be a local consequence of E-W extension along the Coastal Scarp. But if also found everywhere along strike, left-lateral decoupling along the Atacama Fault zone would be in contradiction with the right lateral component of Nazca-South America motion predicted by models of present plate kinematics. Clockwise rotation with left-lateral slicing of the Andean orogen south of the Arica bend is one way to resolve this contradiction. The Coastal Scarp and the Atacama Fault zone are the most prominent features with clear traces of activity within the leading edge of continental South America. The great length and parallelism of these features with the subduction zone suggest that they may interact with the subduction interface at depth. We interpret the Coastal Scarp to be a west-dipping normal fault or flexure and propose that it is located over an east-dipping ramp stack at

  16. Crustal and upper mantle investigations of the Caribbean-South American plate boundary

    NASA Astrophysics Data System (ADS)

    Bezada, Maximiliano J.

    The evolution of the Caribbean --- South America plate boundary has been a matter of vigorous debate for decades and many questions remain unresolved. In this work, and in the framework of the BOLIVAR project, we shed light on some aspects of the present state and the tectonic history of the margin by using different types of geophysical data sets and techniques. An analysis of controlled-source traveltime data collected along a boundary-normal profile at ˜65°W was used to build a 2D P-wave velocity model. The model shows that the Caribbean Large Igenous Province is present offshore eastern Venezuela and confirms the uniformity of the velocity structure along the Leeward Antilles volcanic belt. In contrast with neighboring profiles, at this longitude we see no change in velocity structure or crustal thickness across the San Sebastian - El Pilar fault system. A 2D gravity modeling methodology that uses seismically derived initial density models was developed as part of this research. The application of this new method to four of the BOLIVAR boundary-normal profiles suggests that the uppermost mantle is denser under the South American continental crust and the island arc terranes than under the Caribbean oceanic crust. Crustal rocks of the island arc and extended island arc terranes of the Leeward Antilles have a relatively low density, given their P-wave velocity. This may be caused by low iron content, relative to average magmatic arc rocks. Finally, an analysis of teleseismic traveltimes with frequency-dependent kernels produced a 3D P-wave velocity perturbation model. The model shows the structure of the mantle lithosphere under the study area and clearly images the subduction of the Atlantic slab and associated partial removal of the lower lithosphere under northern South America. We also image the subduction of a section of the Caribbean plate under South America with an east-southeast direction. Both the Atlantic and Caribbean subducting slabs penetrate the

  17. Imaging the ascent path of fluids and partial melts at convergent plate boundaries by geophysical characteristics

    NASA Astrophysics Data System (ADS)

    Luehr, B. G.; Koulakov, I.; Kopp, H.; Rabbel, W.; Zschau, J.

    2011-12-01

    During the last decades many investigations were carried out at active continental margins to understand the link between the subduction of the fluid saturated oceanic plate and the process of ascent of fluids and partial melts forming a magmatic system that leads to volcanism at the earth surface. For this purpose structural information are needed about the slap itself, the part above it, the ascent paths as well as the storage of fluids and partial melts in the mantle and the crust above the down going slap up to the volcanoes on the surface. If we consider statistically the distance between the trench and the volcanic chain as well as the inclination angle of the down going plate, then the mean value of the depth distance down to the Wadati Benioff zone results of approximately 100 kilometers. Surprisingly, this depth range shows pronounced seismicity at most of all subduction zones. Additionally, mineralogical investigations in the lab have shown that the diving plate is maximal dehydrated around 100 km depth because of temperature and pressure conditions at this depth range. However, assuming a vertical fluid ascent there are exceptions. For instance at the Sunda Arc beneath Central Java the vertical distance results in approximately 150 km. But, in this case seismic investigations have shown that the fluids do not ascend vertically, but inclined even from a source area at around the 100 km depth. The ascent of the fluids and the appearance of partial melts as well as the distribution of these materials in the crust can be proved by seismic and seismological methods. With the seismic tomography these areas are imaged by lowered seismic velocities, high Vp/Vs ratios, as well as increased attenuation of seismic shear waves. But, to explore plate boundaries large and complex amphibious experiments are required, in which active and passive seismic investigations should be combined. They have to recover a range from before the trench to far behind the volcanic

  18. Episodic vs. Continuous Accretion in the Franciscan Accretionary Prism and Direct Plate Motion Controls vs. More Local Tectonic Controls on Prism Evolution

    NASA Astrophysics Data System (ADS)

    Dumitru, T. A.; Ernst, W. G.; Wakabayashi, J.

    2011-12-01

    Subduction at the Franciscan trench began ≈170-165 Ma and continues today off Oregon-Washington. Plate motion reconstructions, high-P metamorphic rocks, and the arc magmatic record suggest that convergence and thus subduction were continuous throughout this period, although data for 170 to 120 Ma are less definitive. About 25% of modern subduction zones are actively building an accretionary prism, whereas 75% are nonaccretionary, in which subduction erosion is gradually removing the prism and/or forearc basement. These contrasting behaviors in modern subduction zones suggest that the Franciscan probably fluctuated between accretionary and nonaccretionary modes at various times and places during its 170 million year lifespan. Accumulating geochronologic data are beginning to clarify certain accretionary vs. nonaccretionary intervals. (1) The oldest Franciscan rocks are high-P mafic blocks probably metamorphosed in a subophiolitic sole during initiation of subduction. They yield garnet Lu-Hf and hornblende Ar/Ar ages from ≈169 to 147 Ma. Their combined volume is extremely small and much of the Franciscan was probably in an essentially nonaccretionary mode during this period. (2) The South Fork Mountain Schist forms the structural top of the preserved wedge in northern California and thus was apparently the first genuinely large sedimentary body to accrete. This occurred at ≈123 Ma (Ar/Ar ages), suggesting major accretion was delayed a full ≈45 million years after the initiation of subduction. The underlying Valentine Spring Fm. accreted soon thereafter. This shift into an accretionary mode was nearly synchronous with the end of the Early Cretaceous magmatic lull and the beginning of the prolonged Cretaceous intensification of magmatism in the Sierra Nevada arc. (3) The Yolla Bolly terrane has generally been assigned a latest Jurassic to earliest Cretaceous age. Detrital zircon data confirm that some latest Jurassic sandstones are present, but they may be

  19. Production of three-dimensional, spatially stimulated disturbance waves by periodic blowing and suction in a plate boundary layer flow

    NASA Astrophysics Data System (ADS)

    Konzelmann, U.; Rist, U.; Fasel, H.

    An attempt has been made to study disturbance waves by numerically simulating temporally periodic blowing and suction through a hole in a plate. Modified mixed spectral and difference methods were used, and the resulting vortex strength components are shown. With a few modifications, the procedure can be used for realistic simulation of active boundary layer influences.

  20. Water Release from Cold Serpentinized Forearc Mantle During Subduction Associated with Changes in Incoming Oceanic Plate Thermal Structure and Plate Boundary Kinematics: New Insights into Serpentinite Belts and Plate-Boundary Rheology

    NASA Astrophysics Data System (ADS)

    Kirby, Stephen

    2016-04-01

    Kirby, Wang, and Brocher (Earth Planets and Space, 2014) recently showed how the change in kinematics of the California margin from subduction motion to continental transform motion with the birth and growth of the San Andreas Fault System (SAFS) beginning at about 33 Ma BP likely led to a warming of the former forearc mantle and the release of water from serpentinized mantle by dehydration and a likely increase in fluid pressures along the SAFS. Such a mantle source of pressurized water gives insights into both the low sliding resistance for the SAFS and the mobilization and ascent of some serpentinized mantle peridotites through the crust. Thermal modeling by others has also shown that changes in the incoming plate age and subduction rate can also lead to warming of the forearc mantle during subduction. This development gives insights into the Mesozoic and Paleogene ages of emplacement of some, but not all, California serpentinites. Recent mineralogical and geochemical observations of serpentinite blocks in serpentinize mélange bodies in the San Francisco Bay Area (Uno and Kirby, 2014 AGU Meeting and Lewis and Kirby, 2015 AGU Meeting) suggest that these rocks sustained multiple stages of serpentinization that are broadly consistent with the model of Kirby et al. (2014). A new development comes from interpretation of investigations in the literature of localized late-stage silica-carbonate-water alteration of serpentinite bodies in California that this alteration occurred largely in Neogene time when the highest rates of water release from the former forearc mantle probably occurred. This presentation also suggests that the occurrence of serpentinite belts emplaced in Cenozoic time during changing plate-boundary kinematics, such as the Cenozoic closing of the Tethys Ocean bordering Eurasia by subduction and collision and arc reversal and decreasing convergence rates under the Greater Antilles and Colombia and New Guinea, may give insights into the serpentinite

  1. How do long-offset oceanic transforms adapt to plate motion changes? The example of the Western Pacific-Antarctic plate boundary

    NASA Astrophysics Data System (ADS)

    Lodolo, Emanuele; Coren, Franco; Ben-Avraham, Zvi

    2013-03-01

    Oceanic transform faults respond to changes in the direction of relative plate motion. Studies have shown that short-offset transforms generally adjust with slight bends near the ridge axis, while long-offset ones have a remarkably different behavior. The western Pacific-Antarctic plate boundary highlights these differences. A set of previously unpublished seismic profiles, in combination with magnetic anomaly identifications, shows how across a former, ~1250 km long transform (the Emerald Fracture Zone), plate motion changes have produced a complex geometric readjustment. Three distinct sections are recognized along this plate boundary: an eastern section, characterized by parallel, multiple fault strand lineaments; a central section, shallower than the rest of the ridge system, overprinted by a mantle plume track; and a western section, organized in a cascade of short spreading axes/transform lineaments. This configuration was produced by changes that occurred since 30 Ma in the Australia-Pacific relative plate motion, combined with a gradual clockwise change in Pacific-Antarctic plate motion. These events caused extension along the former Emerald Fracture Zone, originally linking the Pacific-Antarctic spreading ridge system with the Southeast Indian ridge. Then an intra-transform propagating ridge started to develop in response to a ~6 Ma change in the Pacific-Antarctic spreading direction. The close proximity of the Euler poles of rotation amplified the effects of the geometric readjustments that occurred along the transform system. This analysis shows that when a long-offset transform older than 20 Ma is pulled apart by changes in spreading velocity vectors, it responds with the development of multiple discrete, parallel fault strands, whereas in younger lithosphere, locally modified by thermal anisotropies, tensional stresses generate an array of spreading axes offset by closely spaced transforms.

  2. Lithospheric Evolution of the Pacific-North American Plate Boundary Considered in Three Dimensions

    NASA Astrophysics Data System (ADS)

    Biasi, G. P.

    2006-12-01

    Tomographic imaging indicates that the heterogeneity observed in the crust of westernmost North America is underlain by mantle structures of a similar scale and heterogeneity. When likely scaling relationships are used to interpret mantle velocity images, it becomes clear that much of the boundary is explained by mantle lithospheric processes and the crustal evolution is just the surficial expression of strength beneath the surface. The Sierra Nevada block provides something of a Rosetta stone for this interpretation. We note first that Sierra Nevada terrain is not distinguished at the surface from faulted and even shattered batholithic rocks in southern California. It does differ in the upper mantle, because the Sierra Nevada is underlain by a high- velocity root along almost its entire strike. Where that root is missing, roughly south of the White Wolf fault, and east of the Kern Canyon fault, the surface rocks are deforming. The origin of the strong upper mantle component is self-evident near 39.5N latitude, where the contact between the subducting Gorda Slab and the Sierran mantle root can be imaged directly. The upper plate structure dates to latest Mesozoic through Laramide times, with the pattern apparently reinforced on the west to some extent during post-Laramide subduction. Since the genesis of batholithic rocks and the subsequent Laramide history are similar south of the Sierran block, we extrapolate that a similar mantle root would have been present also. This assumption is confirmed with two lines of evidence. First, the mechanical evolution of southern and central California blocks seems to require it. Second, the volumes of the "drips" beneath the Transverse Ranges and southern Sierras exceed reasonable bounds for material scavenged from the mantle lithosphere unless it had distinct initial conditions. The local sources of mantle lithospheric material that could have delaminated around the southern Sierran drip are volumetrically insufficient by a

  3. Lithospheric structure beneath the Caribbean- South American plate boundary from S receiver functions

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    We have analyzed teleseismic S-wave data recorded by the permanent national seismic network of Venezuela and the BOLIVAR broadband array (Broadband Onshore-offshore Lithospheric Investigation of Venezuela and the Antilles arc Region) deployed from 2003 to 2005. A total of 28 events with Mw > 5.7 occurring at epicentral distances from 55° to 85° were used. We made Sp receiver functions to estimate the rapid variations of lithospheric structure in the southern Caribbean plate boundary region to try to better understand the complicated tectonic history of the region. Estimated Moho depth ranges from ~20 km beneath the Caribbean Large Igneous Provinces to ~50 km beneath the Mérida Andes in western Venezuela and the Sierra del Interior in northeastern Venezuela. These results are consistent with previous receiver functions studies (Niu et al., 2007) and active source profiles (Schmitz et al., 2001; Bezada et al., 2007; Clark et al., 2008; Guedez, 2008; Magnani et al., 2009). Beneath the Maracaibo Block we observe a signal at a depth of 100 km dipping ~24° towards the continent, which we interpret as the top of the oceanic Caribbean slab that is subducting beneath South America from the west. The deeper part of the slab was previously imaged using P-wave tomography (Bezada et al, 2010), and the upper part inferred from intermediate depth seismicity (Malavé and Suarez, 1995). These studies indicate flat slab subduction beneath northern Colombia and northwestern Venezuela with the slab dipping between 20° - 30° beneath Lake Maracaibo. Like others we attribute the flat slab subduction to the uplift of the Mérida Andes (for example Kellogg and Bonini, 1982). In eastern Venezuela beneath the Sierra del Interior we also observe a deep signal that we interpret as deep South American lithosphere that is detaching from the overriding plate as the Atlantic subducts and tears away from SA (Bezada et al., 2010; Clark et al, 2008). The lithosphere-asthenosphere boundary (LAB

  4. Coexisting shortening and extension along the "Africa-Eurasia" plate boundary in southern Italy

    NASA Astrophysics Data System (ADS)

    Cuffaro, M.; Riguzzi, F.; Scrocca, D.; Doglioni, C.

    2009-04-01

    We performed geodetic strain rate field analyses along the "Africa (Sicily microplate)"-"Eurasia (Tyrrhenian microplate)" plate boundary in Sicily (southern Italy), using new GPS velocities from a data set spanning maximum ten years (1998-2007). Data from GPS permanent stations maintained from different institutions and the recent RING network, settled in Italy in the last five years by the Istituto Nazionale di Geofisica e Vulcanologia, were included into the analysis. Two dimensional strain and rotation rate fields were estimated by the distance weighted approach on a regularly spaced grid (30*30km), estimating the strain using all stations, but data from each station are weighted by their distance from the grid node by a constant a=70km that specifies how the effect of a station decays with distance from the node grid interpolation. Results show that most of the shortening of the Africa-Eurasia relative motion is distributed in the northwestern side offshore Sicily, whereas the extension becomes comparable with shortening on the western border of the Capo d'Orlando basin, and grater in the northeastern side, offshore Sicily, as directly provided by GPS velocities which show a larger E-ward component of sites located in Calabria with respect to those located either in northern Sicily or in the Ustica-Aeolian islands. Moreover, where shortening and extension have mostly a similar order of magnitude, two rotation rate fields can be detected, CCW in the northwestern side of Sicily, and CW in the northeastern one respectively. Also, 2-D dilatation field records a similar pattern, with negative values (shortening) in the northwestern area of Sicily close to the Ustica island, and positive values (extension) in the northeastern and southeastern ones, respectively. Principal shortening and extension rate axes are consistent with long-term geological features: seismic reflection profiles acquired in the southern Tyrrhenian seismogenic belt show active extensional faults

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  6. UNAVCO Plate Boundary Observatory 2007 Student Field Assistant Program in the Alaska Region

    NASA Astrophysics Data System (ADS)

    Marzulla, A.; Gasparich, S.; Pauk, B.; Feaux, K.; Jackson, M.

    2007-12-01

    The UNAVCO, Inc. Plate Boundary Observatory (PBO) Student Field Assistant Program strives to engage students in further study and careers in the Earth Sciences. Student Field Assistants from a variety of educational backgrounds ranging from high school graduates to master's level students spend a three to five month field season working in tandem with UNAVCO regional Field Engineers. The students work closely with senior staff to reconnaissance, install, and maintain a network of 875 permanent Global Positioning System (GPS) stations in one of the five PBO regions covering the western United States, including Alaska. Practical skills, such as power tool use, drilling, welding, firearms training, and proper field safety procedures, are taught and expected of the students. Installation and maintenance of new and existing GPS stations composes the bulk of the student's responsibilities and duties. When not in the field, students prepare gear and arrange logistics for site installations and maintenance as well as enter metadata and complete installation reports from recently constructed sites. An understanding of the operations of the GPS receivers and the scientific benefit of the network allows for an appreciation and great attention to detail during installation of the sites. Student assistance in the Alaska region during 2007 PBO AK field season was critical to the successful installation of 36 new GPS stations throughout Alaska. Significant benchmarks of the field season included installing six logistically difficult stations in Prince William Sounds, completing the Denali Fault GPS network, four new tiltmeters on Akutan Volcano, completing all installs on the Seward Peninsula as well as several new GPS stations throughout the western interior of the state. Alaska is a prominent area for much movement and deformation as the Pacific Plate subducts beneath the North American Plate resulting in an area of high volcanic activity and heightened crustal deformation. The

  7. Watching structural and geodynamic features of a plate boundary: Peceneaga-Camena Fault

    NASA Astrophysics Data System (ADS)

    Besutiu, L.; Zlagnean, L.

    2009-04-01

    The Peceneaga - Camena Fault represents one of the major lithosphere contacts on the Romanian territory. Its nature and dynamics have been subject to many geological and geophysical researches since the beginning of the 20th century. Based on geophysical evidence some authors consider PCF as a plate boundary, the strike-slip contact between the Moesian Micro-Plate (MoP) and East European Plate (EEP). Deep seismic soundings along the international line II had revealed its trans-crustal nature, with a 10 km step at both Conrad and Moho discontinuities. It is likely that the geodynamic evolution of this major tectonic accident is tightly connected to the opening of the W Black Sea basin. Seismic tomography studies have outlined strong fingerprints of the W Black Sea opening within its NW inland. In depth extension of PCF may be clearly seen within the tomography images down to more than 150 km. It seems that lithosphere expelled by the rifting split MoP into several compartments by creating or reactivating a NW trending major fault system to which the PCF belongs. After the W Black Sea rifting ended its evolution, the geodynamic engine in the area seems to be the active rifting in the SW Arabian Plate (red Sea and Aden Bay) pushing northward the Arabian Plate by about 48 mm/yr, and further on, pushing a MoP segment towards the Carpathians. Under this pushing, the above-mentioned MoP compartments move towards the Carpathians, staying together by friction. However, when tectonic forces overcome the friction, the slivers may relatively slip each other, thus generating earthquakes along their wedges. The presence of some scarce seismicity along PCF seems to confirm the idea. To check up the above mentioned geodynamic scenario, a geodetic experiment has been imagined to monitor PCF flanks displacement. Two Leica TC 1201 total stations were installed on the southern flank of PCF (belonging to MoP) in order to measure the distance to a laser reflector installed on the

  8. Plate tectonics and offshore boundary delimitation: Tunisia-Libya case at the International Court of Justice

    SciTech Connect

    Stanley, D.J.

    1983-03-01

    Advances in the technology for exploiting resources of the oceans, particularly recovery of hydrocarbons and minerals in deep water, is benefiting a growing number of nations. At the same time, however, economic and political pressures have induced concern and there is now a much increased emphasis on jurisdiction to divide the offshore areas between the 132 coastal nations. Negotiations affect research operations at sea and, in consequence, marine scientists have been made aware of offshore problems as highlighted by the Law of the Sea Treaty (UNCLOS III) and complications arising from the legal versus scientific definitions of continental shelves and margins. The first major offshore boundary case of international scope where plate tectonics has constituted a significant argument is the one recently brought before the International Court of Justice by Libya and Tunisia concerning the delimitation of their continental shelves. Of the two parties, Libya placed the greatest emphasis on this concept as a means to determine natural prolongation of its land territory into and under the sea. Tunisia contested Libya's use of the whole of the African continental landmass as a reference unit; in Tunisia's view, considerations of geography, geomorphology, and bathymetry are at least as relevant as are those of geology. In its landmark judgment (February 1982) - which almost certainly will have far-reaching consequences in future such boundary delimitation cases - the court pronounced that It is the outcome, not the evolution in the long-distant past, which is of importance, and that it is the present-day configuration of the coasts and sea bed which are the main factors to be considered, not geology.

  9. Great earthquakes, seismicity gaps and potential for earthquake disaster along the Himalaya plate boundary

    NASA Astrophysics Data System (ADS)

    Khattri, K. N.

    1987-06-01

    Analysis of the space-time patterns of seismicity in the Himalaya plate boundary has established the existence of three seismic gaps: (1) The "Kashmir gap" lying west of the 1905 Kangra earthquake; (2) the "Central gap", situated between the 1905 Kangra and the 1934 Bihar earthquakes; (3) the "Assam gap" between the 1897 and 1950 Assam earthquakes. This study has shown that the above great earthquakes were preceded as well as followed by long periods (⩾ 19 years) of decreased levels of seismic activity in the epicentral regions. Remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the Central gap as well as in the Assam gap. Local seismic investigation in the Assam gap confirms this feature and the seismicity suggests the existence there of an asperity. The local seismic investigations in Garhwal Himalaya have shown that the small earthquakes are confined to the upper 6-8 km of the crust and may have strike-slip motions. These earthquakes occur in a region where teleseismically recorded events were few.

  10. Tidal calibration of Plate Boundary Observatory borehole strainmeters: Roles of vertical and shear coupling

    USGS Publications Warehouse

    Roeloffs, Evelyn

    2010-01-01

    A multicomponent borehole strainmeter directly measures changes in the diameter of its cylindrical housing at several azimuths. To transform these measurements to formation strains requires a calibration matrix, which must be estimated by analyzing the installed strainmeter's response to known strains. Typically, theoretical calculations of Earth tidal strains serve as the known strains. This paper carries out such an analysis for 12 Plate Boundary Observatory (PBO) borehole strainmeters, postulating that each of the strainmeters' four gauges responds ("couples") to all three horizontal components of the formation strain tensor, as well as to vertical strain. Orientation corrections are also estimated. The fourth extensometer in each PBO strainmeter provides redundant information used to reduce the chance that coupling coefficients could be misleadingly fit to inappropriate theoretical tides. Satisfactory fits between observed and theoretically calculated tides were obtained for three PBO strainmeters in California, where the calculated tides are corroborated by other instrumentation, as well as for six strainmeters in Oregon and Washington, where no other instruments have ever recorded Earth tidal strain. Several strainmeters have unexpectedly large coupling coefficients for vertical strain, which increases the strainmeter's response to atmospheric pressure. Vertical coupling diminishes, or even changes the sign of, the apparent response to areal strain caused by Earth tides or deep Earth processes because near the free surface, vertical strains are opposite in sign to areal strain. Vertical coupling does not impair the shear strain response, however. PBO borehole strainmeters can provide calibrated shear strain time series of transient strain associated with tectonic or magmatic processes.

  11. Detailed Seismic Velocity Structure of the Plate Boundary, Cascadia Subduction Zone, from Prestack Waveform Inversion

    NASA Astrophysics Data System (ADS)

    Fortin, W.; Holbrook, W.; Tobin, H. J.; Keranen, K. M.; Everson, E.; Mallick, S.; Padhi, A.

    2013-12-01

    Understanding the geologic makeup of the Cascadia Subduction Zone (CSZ) has great importance for understanding seismic hazards in the coastal margin of the U.S. Pacific Northwest. The Cascadia margin is a potential earthquake and tsunami threat to the many millions who live in the area, yet details of its structure and mechanics remain poorly understood. In particular, the character of the subduction interface is elusive due to the CSZ's relatively aseismic behavior and low seismic reflectivity, making imaging difficult for passive and active source methods, respectively. In July 2012 seismic data were acquired as a part of the COAST project, spanning the important transition from the Cascadia basin, across the deformation front, and into the accretionary wedge. This modern data, coupled with sophisticated pre-stack full waveform seismic inversion methods, allows us to create highly detailed velocity models. While still computationally expensive, current computing clusters can perform these inversions with enough lateral density to yield highly detailed velocity information in both the vertical and horizontal. Here we present pre-stack full waveform inversions of a seismic line from the center of the COAST survey offshore Washington state as a cross section of the velocity structure of the CSZ. This detailed velocity model is a necessary initial step toward a detailed porosity cross section to be used to determine the role of fluids in the CSZ. Using these new data we investigate the lateral variability in reflectivity of the subducting plate boundary reflection in terms of its seismic velocity.

  12. Is the Teisseyre-Tornquist Zone an ancient plate boundary of Baltica?

    NASA Astrophysics Data System (ADS)

    Mazur, Stanislaw; Mikolajczak, Mateusz; Krzywiec, Piotr; Malinowski, Michal; Buffenmyer, Vinton; Lewandowski, Marek

    2015-12-01

    The Teisseyre-Tornquist Zone (TTZ) is generally regarded as a fossil plate boundary in Europe that extends 2000 km from the Baltic Sea to the Black Sea. We used an integrated approach merging potential fields and seismic data to explore crustal architecture across the TTZ in central Poland. The aim of the study was to test whether the TTZ coincides with an early Paleozoic (Caledonian) suture formed through the closure of the Tornquist Ocean along the SW Baltica margin. The suture is presumed to separate the East European Craton (EEC) from the Paleozoic terranes of Western Europe. Two seismic reflection lines from the PolandSPAN™ experiment were used to image the deep structure at the SW margin of the EEC. Lines PL-5300 and PL-5400 run NE-SW in central and northern Poland, respectively. The seismic interpretation down to top of basement was integrated with 2-D gravity and magnetic modeling to highlight the structure of the deep crust. Both the gravity and magnetic models show a suture that welds together two blocks at the base of crust. However, top of basement above the suture dips uniformly to the SW and is overlain by undisturbed lower Paleozoic and younger sediments. By implication, the suture must have developed in the Precambrian and both crustal blocks amalgamated belong to the EEC. Consequently, the Caledonian suture, formed by the closure of the Tornquist Ocean between Avalonia and Baltica, must be located farther southwest beneath thick upper Paleozoic and Mesozoic sediments.

  13. Chlorine isotope geochemistry of Icelandic thermal fluids: Implications for geothermal system behavior at divergent plate boundaries

    NASA Astrophysics Data System (ADS)

    Stefánsson, Andri; Barnes, Jaime D.

    2016-09-01

    The chlorine isotope composition of thermal fluids from Iceland were measured in order to evaluate the source of chlorine and possible chlorine isotope fractionation in geothermal systems at divergent plate boundaries. The geothermal systems studied have a wide range of reservoir temperatures from 40 to 437 °C and in-situ pH of 6.15 to 7.15. Chlorine concentrations range from 5.2 to 171 ppm and δ37 Cl values are -0.3 to + 2.1 ‰ (n = 38). The δ37 Cl values of the thermal fluids are interpreted to reflect the source of the chlorine in the fluids. Geothermal processes such as secondary mineral formation, aqueous and vapor speciation and boiling were found to have minimal effects on the δ37 Cl values. However, further work is needed on incorporation of Cl into secondary minerals and its effect on Cl isotope fractionation. Results of isotope geochemical modeling demonstrate that the range of δ37 Cl values documented in the natural thermal fluids can be explained by leaching of the basaltic rocks by meteoric source water under geothermal conditions. Magmatic gas partitioning may also contribute to the source of Cl in some cases. The range of δ37 Cl values of the fluids result mainly from the large range of δ37 Cl values observed for Icelandic basalts, which range from -0.6 to + 1.2 ‰.

  14. GPS Installation Progress in the Northern California Region of the Plate Boundary Observatory

    NASA Astrophysics Data System (ADS)

    Basset, A.; Coyle, B.; Williams, T.; Mann, D.; Finn, D.; Feaux, K.

    2008-12-01

    The Plate Boundary Observatory (PBO) is the geodetic component of the National Science Foundation (NSF) funded Earthscope Project. The final PBO GPS network will comprise 1100 continuously operating GPS stations installed throughout the Western US and Alaska. There are 448 Stations planned for California with 231 of these in Northern California (NCA). This poster will present a progress report and highlights of GPS installations in NCA over the past year up until the end of the five year project. In the fifth year of the project (beginning 10/1/2007 and ending 10/1/2008), we installed 40 additional stations for a total of 231 stations. The stations installed include; 8 station installed at Lassen Volcanic National Park, 2 additional stations built around Mount Shasta (8 total), 3 stations built in Yosemite National Park, 2 in the Mendocino National Forest, and 2 stations in Tahoe National Forest. The higher elevations stations required modification for use in areas of high snow load and high wind. Data from these stations are available from the UNAVCO archive. In addition to the installations, there was a gradual shift of resources from installation to the operation and maintenance aspects of the growing GPS network. Telemetry priorities moved from individual stations telemetry solutions to grouped telemetry solutions to increase efficiency and reduce costs.

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

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1987-01-01

    The nature and dynamics of time-dependent deformation along major seismic zones including the influence of irregularities in fault geometry on the earthquake cycle, and the processes contributing to the state of stress and rates of strain in plate interior regions were studied. The principle findings of the research are discussed.

  16. The Baja California Borderland and the Neogene Evolution of the Pacific-North American Plate Boundary

    NASA Astrophysics Data System (ADS)

    Fletcher, J. M.; Eakins, B. W.

    2001-12-01

    New observational data on Neogene faulting in the borderland of Baja California places important constraints on tectonic models for the evolution of the Pacific-North American (P-NA) plate boundary and rifting in the Gulf of California. Neogene faults in the borderland range from strike slip to normal slip and accommodate integrated transtension. Most have east-facing escarpments and likely reactivate the former east-dipping accretionary complex. Numerous lines of evidence indicate that Neogene faults are still active and accomplish a significant component ( ~1-5 mm/yr) of Pacific-North American shearing. Quaternary volcanoes are found offshore and along the Pacific coastal margin, Quaternary marine terraces are warped and uplifted as high as 200 masl. Many of the offshore faults have fresh escarpments and cut Holocene sediments. Extensive arrays of Quaternary fault scarps are found throughout the coastal region and in Bahia Magdalena they are clearly associated with major faults that bound recently uplifted islands. A prominent band of seismicity follows the coast and eight earthquakes (Ms>5.0) were teleseismically recorded between 1973 and 1998. This evidence for active shearing indicates that the Baja microplate has not yet been completely transferred to the Pacific plate. The best lithologic correlation that can be used to define the total Neogene slip across the borderland faults is the offset between the Magdalena submarine fan and its Baja source terrane. The distal facies of the fan drilled during DSDP leg 63 is dominated by mudstone and siltstone that contain reworked Paleogene cocoliths derived from strata correlative with the Tepetate formation found throughout the borderland and fine-grained sandstone derived from a source terrane of granitoid basement. The Middle Miocene La Calera formation of the Cabo trough is one of many granitoid-clast syn-rift alluvial deposits that could form the continental counterpart of the submarine fan near the mouth of the

  17. Ordovician ocean plate stratigraphy and thrust duplexes of the Ballantrae Complex, SW Scotland: Implications for the pelagic deposition rate and forearc accretion in the closing Iapetus Ocean

    NASA Astrophysics Data System (ADS)

    Fujisaki, Wataru; Asanuma, Hisashi; Suzuki, Kazue; Sawaki, Yusuke; Sakata, Shuhei; Hirata, Takafumi; Maruyama, Shigenori; Windley, Brian F.

    2015-11-01

    The Ballantrae Complex (at Bennane Lea in SW Scotland) contains important ocean plate stratigraphy (basalt, chert, mudstone, sandstone) in an accretionary prism that is associated with a classic Ordovician ophiolite. We used the ocean plate stratigraphy to sub-divide the prism into 11 tectonic units. To determine the depositional age of bedded cherts, zircons were separated from 9 tuff beds from 6 different units. All the tuffs have early to middle Ordovician ages, even though their present positions are mutually distant. These ages are consistent with microfossil records of radiolaria and graptolites. The stratigraphic-structural relationships demonstrate that the ocean plate stratigraphy has been repeated by bedding-parallel thrusts; this is typical of a modern accretionary duplex. We calculated the sedimentation rate of Early to Middle Ordovician bedded cherts at Bennane Lea on the basis of U-Pb zircon ages obtained from several tuff beds; the data indicate that the depositional rate (0.6-3 m/myr) was as slow as that of Mesozoic-Cenozoic equivalents defined by radiolaria. The age spectra of detrital zircons from Ballantrae sandstones show prominent single peaks at ca. 467 and 478 Ma, and a lack of Precambrian zircons. Integration of our new zircon ages with published isotopic data and palaeo-geographic maps indicates that the sandstones were deposited near an intra-oceanic arc and far from any continent containing Precambrian rocks. The pelagic-to-clastic sediments at Bennane Lea were deposited in the closing Iapetus Ocean from ca. 477 Ma to ca. 464 Ma, when they were accreted with the intra-oceanic arc of Ballantrae.

  18. Propagation of rifting along the Arabia-Somalia Plate Boundary: The Gulfs of Aden and Tadjoura

    NASA Astrophysics Data System (ADS)

    Manighetti, Isabelle; Tapponnier, Paul; Courtillot, Vincent; Gruszow, Sylvie; Gillot, Pierre-Yves

    1997-02-01

    The localization and propagation of rifting between Arabia and Somalia are investigated by assessing the deformation geometry and kinematics at different scales between the eastern Gulf of Aden and the Gulf of Tadjoura, using bathymetric, magnetic, seismological, and structural evidence. Large-scale, southwestward propagation of the Aden ridge, markedly oblique to the Arabia-Somalia relative motion vector, began about 30 Myr ago between the Error and Sharbithat ridges. It was an episodic process, with stages of rapid propagation, mostly at rates >10 cm/yr, interrupted by million year pauses on transverse discontinuities coinciding with rheological boundaries between different crustal provinces of the Arabia-Somalia plate. The longest pause was at the Shukra-El Sheik discontinuity (≈45°E), where the ridge tip stalled for ≈13 Myr, between ≈17 and ≈4 Ma. West of that discontinuity, rifting and spreading took place at an azimuth (≈N25°±10°E) and rate (1.2±0.3 cm/yr) different from those of the global Arabia-Somalia motion vector (≈N39°, ≈1.73 cm/yr), implying an additional component of movement (N65°±10°E, 0.7±0.2 cm/yr) due to rotation of the Danakil microplate. At Shukra-El Sheik, the typical oceanic ridge gives way to a narrow, WSW trending axial trough, resembling a large fissure across a shallow shelf. This trough is composed of about eight rift segments, which result from normal faulting and fissuring along N110°-N130°E trends. All the segments step to the left southwestward, mostly through oblique transfer zones with en échelon normal faults. Only two segments show clear, significant overlap. There is one clear transform, the Maskali fault, between the Obock and Tadjoura segments. The latter segment, which encroaches onland, is composed of two parallel subrifts (Iboli, Ambabbo) that propagated northwestward and formed in succession. The most recent, southwestern subrift (Ambabbo) represents the current tip of the Aden ridge. We propose

  19. Mélange as a Plate Boundary Rock and its Seismogenic Roof Thrust - An Example From the Shimanto Belt, Japan

    NASA Astrophysics Data System (ADS)

    Kitamura, Y.; Sato, K.; Ikesawa, E.; Kimura, G.; Kondo, H.; Ujiie, K.; Onishi, C. T.; Kawabata, K.; Hashimoto, Y.; Mukoyoshi, H.; Masago, H.

    2003-12-01

    A tectonic mélange of the ancient accretionary prism of the Shimanto Belt, Japan is investigated to understand a plate boundary process, especially of seismogenic zone in subduction zone. We analyzed deformation fabric, magnetic fabrics, deformation mechanisms and their thermal condition by using vitrinite reflectance. The investigated Mugi mélange is located in western Shikoku. In the Mugi mélange, systematic fabrics such as Y-P-R fabric formed by micro shear and pressure solution mechanisms are penetrated throughout the mélange pile. Magnetic ellipsoids obtained from the anisotropy of magnetic susceptibility (AMS) are highly oblate. Maximum and minimum axes of the ellipsoids are in accordance with shear orientation of mélange and mean pole of foliation, respectively. These facts suggest that the Mugi mélange was formed as a result of underthrusting of trench filling sediments. Vitrinite reflectance ranges from 2.52% to 3.08%, which correlates to the maximum paleo-temperature of ca. 240 §C to 260 §C. Pseudotachylite of the most reliable seismogenic rock was found from the upper boundary roof fault of the Mugi mélange. The fault is composed of about 1 m thick cataclastic zone injected by many veins. The overlying Hiwasa formation is sandstone-dominated and folded coherent piles. The finding of the pseudotachylite in this study area is another example from the ancient accretionary complex after the first one from the Okitsu mélange in western Shikoku Island. The setting of the pseudotachylite from the boundary fault between tectonic mélange and overlying folded coherent pile is quite similar to that of the first one. There is no thermal gap between the mélange and coherent piles but temperature obtained from vitrinite reflectance gradually rises in descending from the coherent piles to the mélange beyond the boundary fault. Such setting suggests that paleo-isotherm was parallel to the orientation of the boundary fault. The isotherm in the seismogenic

  20. The influence of plate boundary deformation on regional intraplate exhumation: evidence from the Irish Sea basin system, western UK

    NASA Astrophysics Data System (ADS)

    Holford, S. P.; Turner, J. P.; Green, P. F.; Williams, G. A.

    2005-12-01

    Elucidating the causes of exhumation within intraplate regions and passive margin settings is an outstanding problem with global tectonic significance. The application of thermochronological tools such as apatite fission-track analysis (AFTA) across apparently stable intraplate regions (e.g. NW Europe, SW Australia, Southern Africa) has repeatedly revealed evidence for extensive phases of km-scale exhumation, often with no obvious causal mechanisms. Here we present results from a study of the exhumation history of the Irish Sea basin system (western UK) using palaeothermal (AFTA and VR), compactional and seismic reflection data which highlights the dominant control that plate boundary processes exert over the uplift and exhumation of continental interiors. This intraplate Mesozoic-Cenozoic basin system occupies the transition between the European Alpine deformation front and the NE Atlantic passive margin. Numerous studies have identified this area as one of the most severely exhumed in NW Europe. Much of this exhumation has been ascribed to Palaeocene epeirogeny caused by the Iceland Plume. However, our results reveal an exhumation history of far greater complexity with major exhumation episodes during the early Cretaceous (120-115 Ma) and Neogene (<20 Ma) removing up to 3 km and 1.5 km of Mesozoic-Cenozoic sediments from this region respectively. Mapping of early Cenozoic exhumation patterns reveals major heterogeneities in exhumation magnitudes at intra-basinal (<10 km) and regional (<100 km) scales which cannot be ascribed to a purely epeirogenic process such as plume-driven uplift. These regional phases of intraplate exhumation are coincident with important phases of deformation at preexisting or incipient plate boundaries. Early Cretaceous exhumation was coeval with the onset of seafloor spreading in Bay of Biscay. Neogene exhumation was coincident with the late Alpine orogenesis, with abundant evidence for Neogene compressional shortening in this study area

  1. Kinematics of the New Zealand plate boundary: Relative motion by GPS across networks of 1000 km and 50 km spacing

    NASA Technical Reports Server (NTRS)

    Meertens, Charles M.; Rocken, Christian; Perin, Barbara; Walcott, Richard

    1993-01-01

    The NASA/DOSE 'Kinematics of the New Zealand Plate Boundary' experiment is a four-year cooperative Global Positioning System (GPS) experiment involving 6 universities and institutions in New Zealand and the United States. The investigation covers two scales, the first on the scale of plates (approximately 1000 km) and the second is on the scale of the plate boundary zone (approximately 50 km). In the first portion of the experiment, phase A, the objective is to make direct measurements of tectonic plate motion between the Australian and Pacific plates using GPS in order to determine the Euler vector of this plate pair. The phase A portion of this experiment was initiated in December 1992 with the first-epoch baseline measurements on the large scale network. The network will be resurveyed two years later to obtain velocities. The stations which were observed for phase A are shown and listed. Additional regional stations which will be used for this study are listed and are part of either CIGNET or other global tracking networks. The phase A portion of the experiment is primarily the responsibility of the UNAVCO investigators. Therefore, this report concentrates on phase A. The first year of NASA funding for phase A included only support for the field work. Processing and analysis will take place with the second year of funding. The second part of the experiemnt measured relative motion between the Australian and Pacific plates across the pate boundary zone between Hokitika and Christchurch on the South Island of New Zealand. The extent and rate of deformation will be determined by comparisons with historical, conventional surveys and by repeated GPS measurements to be made in two years. This activity was the emphasis of the LDGO portion of the study. An ancillary experiment, phase C, concentrated on plate boundary deformation in the vicinity of Wellington and was done as part of training during the early portion of the field campaign. Details of the objectives of the

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

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1987-01-01

    The focus of the research was in two broad areas during the most recent 6 month period: the nature and dynamics of time-dependent deformation along major seismic zones, including the influence of irregularities in fault geometry on the earthquake cycles, and the processes contributing to the state of stress and rates of strain in plate interior regions. The principal findings of the research to date are described.

  3. Mass Accretion Rate of Rotating Viscous Accretion Flow

    NASA Astrophysics Data System (ADS)

    Park, Myeong-Gu

    2009-11-01

    The mass accretion rate of transonic spherical accretion flow onto compact objects such as black holes is known as the Bondi accretion rate, which is determined only by the density and the temperature of gas at the outer boundary. A rotating accretion flow has angular momentum, which modifies the flow profile from the spherical Bondi flow, and hence its mass accretion rate, but most work on disc accretion has taken the mass flux to be given with the relation between that parameter and external conditions left uncertain. Within the framework of a slim α disk, we have constructed global solutions of the rotating, viscous, hot accretion flow in the Paczyński-Wiita potential and determined its mass accretion rate as a function of density, temperature, and angular momentum of gas at the outer boundary. We find that the low angular momentum flow resembles the spherical Bondi flow and its mass accretion rate approaches the Bondi accretion rate for the same density and temperature at the outer boundary. The high angular momentum flow on the other hand is the conventional hot accretion disk with advection, but its mass accretion rate can be significantly smaller than the Bondi accretion rate with the same boundary conditions. We also find that solutions exist only within a limited range of dimensionless mass accretion rate \\dot{m} ≡ \\dot{M}/\\dot{M}_B, where \\dot{M} is the mass accretion rate and \\dot{M}_B is the Bondi accretion rate: when the temperature at the outer boundary is equal to the virial temperature, solutions exist only for 0.05 ≲ \\dot{m} ≤ 1 when α = 0.01. We also find that the dimensionless mass accretion rate is roughly independent of the radius of the outer boundary but inversely proportional to the angular momentum at the outer boundary and proportional to the viscosity parameter, \\dot{m} ≃ 9.0 α λ^{-1} when 0.1 ≲ \\dot{m} ≲ 1, where the dimensionless angular momentum measure λ ≡ l out/lB is the specific angular momentum of gas at

  4. MASS ACCRETION RATE OF ROTATING VISCOUS ACCRETION FLOW

    SciTech Connect

    Park, Myeong-Gu

    2009-11-20

    The mass accretion rate of transonic spherical accretion flow onto compact objects such as black holes is known as the Bondi accretion rate, which is determined only by the density and the temperature of gas at the outer boundary. A rotating accretion flow has angular momentum, which modifies the flow profile from the spherical Bondi flow, and hence its mass accretion rate, but most work on disc accretion has taken the mass flux to be given with the relation between that parameter and external conditions left uncertain. Within the framework of a slim alpha disk, we have constructed global solutions of the rotating, viscous, hot accretion flow in the Paczynski-Wiita potential and determined its mass accretion rate as a function of density, temperature, and angular momentum of gas at the outer boundary. We find that the low angular momentum flow resembles the spherical Bondi flow and its mass accretion rate approaches the Bondi accretion rate for the same density and temperature at the outer boundary. The high angular momentum flow on the other hand is the conventional hot accretion disk with advection, but its mass accretion rate can be significantly smaller than the Bondi accretion rate with the same boundary conditions. We also find that solutions exist only within a limited range of dimensionless mass accretion rate m-dotident toM-dot/M-dot{sub B}, where M-dot is the mass accretion rate and M-dot{sub B} is the Bondi accretion rate: when the temperature at the outer boundary is equal to the virial temperature, solutions exist only for 0.05approxaccretion rate is roughly independent of the radius of the outer boundary but inversely proportional to the angular momentum at the outer boundary and proportional to the viscosity parameter, m-dotapprox =9.0 alphalambda{sup -1} when 0.1 approx

  5. Plate boundary evolution in the western-central Mediterranean: From the past to the present.

    NASA Astrophysics Data System (ADS)

    Wortel, Rinus; Faccenna, Claudio; Govers, Rob; Polonia, Alina; Baes, Marzieh

    2013-04-01

    The evolution of the Calabrian and Gibraltar arcs and that of the margins of northern Africa and Sicily are part of the final phase of opening of the western Mediterranean basins. Jointly, they are the central topic of the TopoMed project concerning the plate boundary reorganization of the western-central Mediterranean, one of the projects of the TOPO-EUROPE programme (EUROCORES/ESF). The structure and evolution of the Gibraltar arc region are discussed in a separate presentation. This final stage of opening shows intriguing lateral variations from the Calabrian Arc, via the northern margin of Sicily to the North-African (Algerian) margin. In concert, they provide an excellent opportunity to study the evolution of an expanding oceanic realm that may be at the verge of entering a new phase of closure. Our studies encompass detailed analyses of deep penetration seismic data, multibeam bathymetry and field observations, and numerical model experiments addressing lithospheric scale process-oriented aspects. Special attention is given to the aspect that the region is embedded in a context of ongoing Africa-Eurasia plate convergence and to the role of structures, inherited from earlier stages of basin opening, in controlling the recent and ongoing evolution. For the Calabrian accretionary wedge the focus is on assessing the present state of deformation, including seismic activity, and other accompanying processes. We show that the Calabrian wedge is segmented (in direction along the arc) in two different lobes, the western and eastern lobe corresponding with detached and still continuous parts of the subducting slab, respectively. For the Northern Sicily margin we propose that its earlier history involving STEP faulting has preconditioned the lithosphere structure to the extent that it promotes initiation of a new southward-dipping subduction zone. The northern African margin is in a very special transitional situation in which the retreating northward subduction has

  6. Preliminary study for active monitoring of the plate boundary using ACROSS: Synthetic and observed seismic records

    NASA Astrophysics Data System (ADS)

    Tsuruga, K.; Kasahara, J.; Hasada, Y.; Kunitomo, T.; Ikuta, R.; Watanabe, T.; Yamaoka, K.; Fujii, N.; Kumazawa, M.; Nagao, H.; Nakajima, T.; Saiga, A.; Satomura, M.

    2005-12-01

    travel times of reflected waves from the bottom of lower crust Moho (PmP) and from the upper boundary of the Philippine Sea plate (PxP). We believe that these results suggest the potentiality for active monitoring of the subtle changes of geophysical properties in the earth's structure using ACROSS signals in future. Acknowledgements: We appreciate the permission to use the seismic waveform data provided by the Research Group for Seismic Expedition in Central Japan.

  7. BOLIVAR: the Caribbean-South America plate boundary between 60W and 71W as imaged by seismic reflection data

    NASA Astrophysics Data System (ADS)

    Magnani, M.; Mann, P.; Clark, S. A.; Escalona, A.; Zelt, C. A.; Christeson, G. L.; Levander, A.

    2007-12-01

    We present the results of ~6000km of marine multi-channel seismic (MCS) reflection data collected offshore Venezuela as part of the Broadband Ocean Land Investigation of Venezuela and the Antilles arc Region project (BOLIVAR). The imaged area spans almost 12 degrees of longitude and 5 degrees of latitude and encompasses the diffuse plate boundary between South America (SA) and the SE Caribbean plate (CAR). This plate boundary has been evolving for at least the past 55My when the volcanic island arc that borders the CAR plate started colliding obliquely with the SA continent: the collision front has migrated from west to east. BOLIVAR MCS data show that the crustal architecture of the present plate boundary is dominated by the eastward motion of the Caribbean plate with respect to SA and is characterized by a complex combination of convergent and strike-slip tectonics. To the north, the reflection data image the South Caribbean Deformed Belt (SCDB) and the structures related to the thrusting of the CAR plate under the Leeward Antilles volcanic arc region. The data show that the CAR underthrusting continues as far east as the southern edge of the Aves ridge and detailed stratigraphic dating of the Venezuela basin and trench deposits suggests that the collision began in the Paleogene. The amount of shortening along the SCDB decreases toward the east, in part due to the geometry of plate motion vectors and in part as a result of the NNE escape of the Maracaibo block in western Venezuela. South of the SCDB the MCS profiles cross the Leeward Antilles island arc and Cenozoic sedimentary basins, revealing a complex history of Paleogene-Neogene multiphase extension, compression, and tectonic inversion, as well as the influence of the tectonic activity along the right-lateral El Pilar - San Sebastian fault system. East of the Bonaire basin the MCS data image the southern end of the Aves Ridge abandoned volcanic island arc and the southwestern termination of the Grenada basin

  8. 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

  9. The EarthScope Plate Boundary Observatory (PBO) Facility: Innovations, Transformations, and Impact

    NASA Astrophysics Data System (ADS)

    Jackson, M. E.; Mencin, D.; Feaux, K.

    2013-12-01

    The word 'transformation' is not used lightly in science. However, the transformative nature of the EarthScope Plate Boundary Observatory facility on the science community is large and measurable. The impact of the creation, execution and delivery of the PBO resulted in radical changes in the way the geodesy community views permanent, continuously operating (and often) real-time GPS and strain networks, open data policies, and the ability for consortium based facilities, such as UNAVCO, to manage and deliver on large National Science Foundation investments. Our presentation will explore these innovations and transformations from the community, facility, and science perspectives. In the genesis of the EarthScope proposal there was a distinct shift away from the PBO being managed and constructed by prominent PI's within the community to a vesting of the responsibility and authority in UNAVCO to execute on behalf of the entire community. This tipping away from individual PI concerns towards a communal behavior allowed the construction of a facility based on broad input from, and equal access for, any member of the geodesy community. The open and transparent nature of EarthScope, including the open data policy for both facility and PI derived data was truly transformative. One of the key tenants of the PBO was strict adherence to not redesigning unless absolutely necessary. For example PBO monumentation and data processing practices were adopted wholesale from the SCIGN project, while the station selection, project management, permitting practices, data downloading, metadata, and, data communications were refactored for optimum use for the broader geodesy community and to scale with the large geography that confronted PBO. The PBO strainmeter network, one of the largest in the world, started by looking at the procedures of 30 years of heterogeneous installations around the word then crafted, created, and amalgamated new drilling, grouting, installation, and data

  10. High-Resolution LiDAR Topography of the Plate-Boundary Faults in Northern California

    NASA Astrophysics Data System (ADS)

    Prentice, C. S.; Phillips, D. A.; Furlong, K. P.; Brown, A.; Crosby, C. J.; Bevis, M.; Shrestha, R.; Sartori, M.; Brocher, T. M.; Brown, J.

    2007-12-01

    GeoEarthScope acquired more than 1500 square km of airborne LiDAR data in northern California, providing high-resolution topographic data of most of the major strike-slip faults in the region. The coverage includes the San Andreas Fault from its northern end near Shelter Cove to near Parkfield, as well as the Rodgers Creek, Maacama, Calaveras, Green Valley, Paicines, and San Gregorio Faults. The Hayward fault was added with funding provided by the US Geological Survey, the City of Berkeley, and the San Francisco Public Utilities Commission. Data coverage is typically one kilometer in width, centered on the fault. In areas of particular fault complexity the swath width was increased to two kilometers, and in selected areas swath width is as wide as five kilometers. A five-km-wide swath was flown perpendicular to the plate boundary immediately south of Cape Mendocino to capture previously unidentified faults and to understand off-fault deformation associated with the transition zone between the transform margin and the Cascadia subduction zone. The data were collected in conjunction with an intensive GPS campaign designed to improve absolute data accuracy and provide quality control. Data processing to classify the LiDAR point data by return type allows users to filter out vegetation and produce high-resolution DEMs of the ground surface beneath forested regions, revealing geomorphic features along and adjacent to the faults. These data will allow more accurate mapping of fault traces in regions where the vegetation canopy has hampered this effort in the past. In addition, the data provide the opportunity to locate potential sites for detailed paleoseismic studies aimed at providing slip rates and event chronologies. The GeoEarthScope LiDAR data will be made available via an interactive data distribution and processing workflow currently under development.

  11. EarthScope Plate Boundary Observatory, Southwest Region - Communications, Challenges, and Cooperation

    NASA Astrophysics Data System (ADS)

    Turner, R. C.; Mann, D.; Walls, C. P.; Basset, A.; Lawrence, S.; Berglund, H. T.

    2015-12-01

    The Southwest Region of the EarthScope Plate Boundary Observatory is engaged in efforts to expand capabilities and renovate the network. These efforts include GNSS hardware modernization (in cooperation with state and local agencies), communications upgrades that improve data throughput and decrease recurring costs, co-location of prototype instruments for use in earthquake early warning, and working to ensure consistent high-quality data in the face of radio spectrum encroachment.The Global Positioning System (GPS) is but one of a growing number of global navigation satellite systems (GNSS) with the potential to improve geodetic observations. In addition to strategic deployment of GNSS-capable hardware, the Southwest region is currently developing an agreement with Caltrans to augment the network with GNSS systems at about a dozen stations. The upgrades will consist of a number of Caltrans-provided GLONASS-ready receivers and project is scheduled for completion by early 2016.The Southwest Region has continued to upgrade and build new radio networks to improve dependability, monitoring, and data download rates (including transfers of high-rate data). Here, we highlight one such network near Hollister, CA, which eliminated several cellular modems and improved reliability.UNAVCO and Scripps have been working in collaboration to augment a subset of GPS stations with low-cost strong-motion sensors for use in Earthquake Early Warning systems. To date, 21 PBO stations have been upgraded with MEMS accelerometers along the San Andreas and San Jacinto Faults in Northern and Southern California, 15 of which stream data to UNAVCO in real time.As the use of the radio frequency spectrum increases, PBO faces more radio frequency interference (RFI) in our data communications networks; in addition, RFI issues are beginning to impact GNSS data collection. Here we report on a PBO site suspected of suffering from RFI and discuss briefly mitigation efforts to minimize these effects.

  12. The Future of the Plate Boundary Observatory in the GAGE Facility and beyond 2018

    NASA Astrophysics Data System (ADS)

    Mattioli, G. S.; Bendick, R. O.; Foster, J. H.; Freymueller, J. T.; La Femina, P. C.; Miller, M. M.; Rowan, L.

    2014-12-01

    The Geodesy Advancing Geosciences and Earthscope (GAGE) Facility, which operates the Plate Boundary Observatory (PBO), builds on UNAVCO's strong record of facilitating research and education in the geosciences and geodesy-related engineering fields. Precise positions and velocities for the PBO's ~1100 continuous GPS stations and other PBO data products are used to address a wide range of scientific and technical issues across North America. A large US and international community of scientists, surveyors, and civil engineers access PBO data streams, software, and other on-line resources daily. In a global society that is increasingly technology-dependent, consistently risk-averse, and often natural resource-limited, communities require geodetic research, education, and infrastructure to make informed decisions about living on a dynamic planet. The western U.S. and Alaska, where over 95% of the PBO sensor assets are located, have recorded significant geophysical events like earthquakes, volcanic eruptions, and tsunami. UNAVCO community science provides first-order constraints on geophysical processes to support hazards mapping and zoning, and form the basis for earthquake and tsunami early warning applications currently under development. The future of PBO was discussed at a NSF-sponsored three-day workshop held in September 2014 in Breckenridge, CO. Over 40 invited participants and community members, including representatives from interested stakeholder groups, UNAVCO staff, and members of the PBO Working Group and Geodetic Infrastructure Advisory Committee participated in workshop, which included retrospective and prospective plenary presentations and breakout sessions focusing on specific scientific themes. We will present some of the findings of that workshop in order to continue a dialogue about policies and resources for long-term earth observing networks. How PBO fits into the recently released U.S. National Plan for Civil Earth Observations will also be

  13. Update on Plate Boundary Observatory (PBO) Activities in the PNW Region

    NASA Astrophysics Data System (ADS)

    Austin, K. E.; Fengler, K.; Doelger, S.

    2007-12-01

    The Plate Boundary Observatory (PBO), which is part of the larger NSF-funded EarthScope project, is nearing the end of year 3 of the installation phase of 852 continuously operating GPS stations in the Western United States. The Pacific Northwest (PNW) region will install 134 continuous GPS stations by the end of September 2008. The sites are distributed along the fore and back-arc of the Cascadia Subduction Zone and at Mt. St. Helens. At the end of September 2007, the PNW region will be several stations short of its installation goal of 110 GPS stations, mostly due to an unusually early and high danger wildfire season. The scientific priority during this past year was to concentrate installations in the Oregon back arc region, the Southwest Oregon fore arc region and the Idaho panhandle. In the last year UNAVCO has added 10 stations to the Pacific Northwest region, raising the number of stations from 124 to 134. The majority of these stations are located within the fore and back arc regions of Southern Oregon. In addition the UNAVCO installed its first building mounted site within a difficult area along the Southwest Oregon coast. UNAVCO will install its remaining 24 new continuous GPS stations in the Pacific Northwest in year 5. The remaining stations are distributed throughout the region, and comprise a mix of standard monuments, and strainmeter collocations. Our goal is to have all stations installed by August 31 2008. Reconnaissance work for all of the GPS sites have been completed, and have had permits submitted.

  14. Friction experiments on Alpine Fault DFDP core samples: Implications for slip style on plate boundary faults

    NASA Astrophysics Data System (ADS)

    Ikari, M.; Trütner, S.; Toy, V. G.; Carpenter, B. M.; Kopf, A.

    2014-12-01

    The Alpine Fault is a major plate-boundary fault zone that poses a significant seismic hazard in southern New Zealand, with the next major earthquake expected to be imminent. Core samples from the Alpine Fault were recovered from two Deep Fault Drilling Project pilot boreholes that penetrated the principal slip zone (PSZ). We show here that at room temperature and low effective stress (30 MPa), materials from within and very near the PSZ are weaker than the surrounding cataclasites (μ = 0.45), exhibit velocity-strengthening friction, and also tend to restrengthen (heal) rapidly. Under conditions appropriate for several kilometers depth on the Alpine Fault (100 MPa, 160 °C, fluid-saturated), a cataclasite/gouge sample located very near to the PSZ exhibits μ = 0.67, which is high compared to measurements performed at lower pressures and temperatures for the Alpine Fault and other major fault zones sampled by scientific drilling. Every major lithological unit tested under elevated P-T conditions exhibits both positive and negative values of friction velocity-dependence suggesting that they are all capable of earthquake nucleation. Using representative values of the friction velocity-dependent parameter a-b, the critical slip distance Dc, and previously documented elastic properties of the wall rock, estimated critical nucleation patch lengths may be as low as ~3 m. This small value is consistent with a seismic moment Mo = ~4x1010 or a Mw = ~1, which suggests that events of this size or larger are expected to occur as normal earthquakes and that slow or transient slip events are unlikely in the approximate depth range of 3-7 km. In conjunction with previous geodetic and seismologic observations, our results indicate that the Alpine Fault has a high potential for frictional instability throughout the brittle crust, in contrast with other major fault zones on which the uppermost portion is relatively stable.

  15. GPS Installation Progress in the Northern California Region of the Plate Boundary Observatory

    NASA Astrophysics Data System (ADS)

    Coyle, B.; Basset, A.; Williams, T.; Mann, D.; Finn, D.; Feaux, K.

    2007-12-01

    The Plate Boundary Observatory (PBO) is the geodetic component of the NSF funded EarthScope Project. The final PBO GPS network will comprise 875 continuously operating GPS stations installed throughout the Western US and Alaska. There are 449 Stations planned for California with 232 of these in Northern California (NCA). This poster will present a progress report and highlights of GPS installations in NCA over the past year. At the end of the third year of the project (10/2007), PBO NCA installed 131 GPS stations. In the fourth year of the project we installed 64 stations for a total of 195 stations. This total comprises 80% of the along the active transform margin, 70% of the sites on volcanoes and calderas and 67% of the sites covering the extensional regime of the Basin and Range. Highlights from this year include completing reconnaissance and permitting of GPS networks around the volcanoes at Mount Shasta and Mount Lassen. Six of the eight GPS stations planned for Mount Shasta were built and at varying azimuths and distances from the crater. Mount Lassen has 9 GPS stations, 6 stations in the Lassen Volcanic National Park and 3 more on surrounding National Forest Service property. Data from these stations are available from the UNAVCO archive. We expect to complete the Northern California part of the PBO GPS network by the end of Sept 2008. In order to accomplish this goal, we are working to finalize reconnaissance and permitting activities for sites whose initial permits were rejected. There will likely be a handful of sites that we will have to relocate from their originally proposed locations in order to get a permitted location.

  16. Monitoring the northern Chile megathrust with the Integrated Plate boundary Observatory Chile (IPOC)

    NASA Astrophysics Data System (ADS)

    Schurr, Bernd; Asch, Günter; Cailleau, Beatrice; Diaz, Guillermo Chong; Barrientos, Sergio; Vilotte, Jean-Pierre; Oncken, Onno

    2010-05-01

    thousand aftershocks during the following week using waveform cross-correlation and the double-difference algorithm. Aftershocks reveal that rupture during this earthquake was confined to the deeper part (35 - 55 km depth) of the seismogenic coupling zone, except near the Mejillones peninsula that marks rupture termination in the south. Here earthquake activity reaches to depths of 20 km and even shallower, possibly indicating upper plate activation. The sequence also features an M 6.8 earthquake that broke the oceanic slab on an almost vertical plane at the down-dip end of the megathrust rupture. Confrontation with the aftershock distribution of the 1995 M 8.0 Antofagasta earthquake on the adjoining southern segment reveals an intriguing mirror symmetry with an axis crossing the Mejillones peninsula, emphasizing the penisula's significance as a segment boundary. Since then activity inside the remaining seismic gap to the north picked up with three earthquakes exceeding magnitude 6, maybe heralding the next great rupture.

  17. Receptivity of Flat-Plate Boundary Layer in a Non-Uniform Free Stream (Vorticity Normal to the Plate)

    NASA Technical Reports Server (NTRS)

    Kogan, M. N.; Shumilkin, V. G.; Ustinov, M. V.; Zhigulev, S. V.

    1999-01-01

    Experimental and theoretical studies of low speed leading edge boundary layer receptivity to free-stream vorticity produced by upstream wires normal to the leading edge are discussed. Data include parametric variations in leading edge configuration and details of the incident disturbance field including single and multiple wakes. The induced disturbance amplitude increases with increases in the leading edge diameter and wake interactions. Measurements agree with the theory of M. E. Goldstein.

  18. Unsteady heat-flux measurements of second-mode instability waves in a hypersonic flat-plate boundary layer

    NASA Astrophysics Data System (ADS)

    Kegerise, Michael A.; Rufer, Shann J.

    2016-08-01

    In this paper, we report on the application of the atomic layer thermopile (ALTP) heat-flux sensor to the measurement of laminar-to-turbulent transition in a hypersonic flat-plate boundary layer. The centerline of the flat-plate model was instrumented with a streamwise array of ALTP sensors, and the flat-plate model was exposed to a Mach 6 freestream over a range of unit Reynolds numbers. Here, we observed an unstable band of frequencies that are associated with second-mode instability waves in the laminar boundary layer that forms on the flat-plate surface. The measured frequencies, group velocities, phase speeds, and wavelengths of these instability waves are consistent with data previously reported in the literature. Heat flux time series, and the Morlet wavelet transforms of them, revealed the wave-packet nature of the second-mode instability waves. In addition, a laser-based radiative heating system was used to measure the frequency response functions (FRF) of the ALTP sensors used in the wind tunnel test. These measurements were used to assess the stability of the sensor FRFs over time and to correct spectral estimates for any attenuation caused by the finite sensor bandwidth.

  19. Fate of sediment during plate convergence at the Mediterranean Ridge accretionary complex: Volume balance of mud extrusion versus subduction and/or accretion

    NASA Astrophysics Data System (ADS)

    Kopf, Achim

    1999-01-01

    Drilling results from two mud volcanoes on the Mediterranean Ridge accretionary complex as well as extensive geophysical surveys have provided new insights about the geometry of these domes at depth. Mud extrusion is related to buoyancy and plate convergence between Africa and Eurasia that caused back-thrust faulting of accreted strata containing overpressured mud at depth. The domes mainly consist of mud breccia formed of as much as 65% polymictic clasts embedded in a clayey matrix of presumed late Miocene age. Volumetric estimates of extruded mud in a well-studied area around the Olimpi mud-volcano field were balanced against sediment input at the deformation front. The results demonstrate that only a small fraction of rock mass having entered the subduction zone since the Messinian is needed to compensate for the mud expelled in the study area. Most of the sediment (95% or more) is either subducted or incorporated into the accretionary prism. The volume of gas expelled with the liquefied, overpressured mud was estimated to range between 1.68 × 106 and 2.85 × 107 m3/yr.

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

    NASA Astrophysics Data System (ADS)

    Solomon, Sean C.

    During our participation in the NASA Crustal Dynamics Project under NASA contract NAS-27339 and grant NAG5-814 for the period 1982-1991, we published or submitted for publication 30 research papers and 52 abstracts of presentations at scientific meetings. In addition, five M.I.T. Ph.D. students (Eric Bergman, Steven Bratt, Dan Davis, Jeanne Sauber, Anne Sheehan) were supported wholly or in part by this project during their thesis research. Highlights of our research progress during this period include the following: application of geodetic data to determine rates of strain in the Mojave block and in central California and to clarify the relation of such strain to the San Andreas fault and Pacific-North American plate motions; application of geodetic data to infer post seismic deformation associated with large earthquakes in the Imperial Valley, Hebgen Lake, Argentina, and Chile; determination of the state of stress in oceanic lithosphere from a systematic study of the centroid depths and source mechanisms of oceanic intraplate earthquakes; development of models for the state of stress in young oceanic regions arising from the differential cooling of the lithosphere; determination of the depth extent and rupture characteristics of oceanic transform earthquakes; improved determination of earthquake slip vectors in the Gulf of California, an important data set for the estimation of Pacific-North American plate motions; development of models for the state of stress and mechanics of fold-and-thrust belts and accretionary wedges; development of procedures to invert geoid height, residual bathymetry, and differential body wave travel time residuals for lateral variations in the characteristic temperature and bulk composition of the oceanic upper mantle; and initial GPS measurements of crustal deformation associated with the Imperial-Cerro Prieto fault system in southern California and northern Mexico. Full descriptions of the research conducted on these topics may be

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

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1991-01-01

    During our participation in the NASA Crustal Dynamics Project under NASA contract NAS-27339 and grant NAG5-814 for the period 1982-1991, we published or submitted for publication 30 research papers and 52 abstracts of presentations at scientific meetings. In addition, five M.I.T. Ph.D. students (Eric Bergman, Steven Bratt, Dan Davis, Jeanne Sauber, Anne Sheehan) were supported wholly or in part by this project during their thesis research. Highlights of our research progress during this period include the following: application of geodetic data to determine rates of strain in the Mojave block and in central California and to clarify the relation of such strain to the San Andreas fault and Pacific-North American plate motions; application of geodetic data to infer post seismic deformation associated with large earthquakes in the Imperial Valley, Hebgen Lake, Argentina, and Chile; determination of the state of stress in oceanic lithosphere from a systematic study of the centroid depths and source mechanisms of oceanic intraplate earthquakes; development of models for the state of stress in young oceanic regions arising from the differential cooling of the lithosphere; determination of the depth extent and rupture characteristics of oceanic transform earthquakes; improved determination of earthquake slip vectors in the Gulf of California, an important data set for the estimation of Pacific-North American plate motions; development of models for the state of stress and mechanics of fold-and-thrust belts and accretionary wedges; development of procedures to invert geoid height, residual bathymetry, and differential body wave travel time residuals for lateral variations in the characteristic temperature and bulk composition of the oceanic upper mantle; and initial GPS measurements of crustal deformation associated with the Imperial-Cerro Prieto fault system in southern California and northern Mexico. Full descriptions of the research conducted on these topics may be

  2. Unsteady Boundary Layer Flow and Heat Transfer of a Casson Fluid past an Oscillating Vertical Plate with Newtonian Heating

    PubMed Central

    Hussanan, Abid; Zuki Salleh, Mohd; Tahar, Razman Mat; Khan, Ilyas

    2014-01-01

    In this paper, the heat transfer effect on the unsteady boundary layer flow of a Casson fluid past an infinite oscillating vertical plate with Newtonian heating is investigated. The governing equations are transformed to a systems of linear partial differential equations using appropriate non-dimensional variables. The resulting equations are solved analytically by using the Laplace transform method and the expressions for velocity and temperature are obtained. They satisfy all imposed initial and boundary conditions and reduce to some well-known solutions for Newtonian fluids. Numerical results for velocity, temperature, skin friction and Nusselt number are shown in various graphs and discussed for embedded flow parameters. It is found that velocity decreases as Casson parameters increases and thermal boundary layer thickness increases with increasing Newtonian heating parameter. PMID:25302782

  3. Unsteady boundary layer flow and heat transfer of a Casson fluid past an oscillating vertical plate with Newtonian heating.

    PubMed

    Hussanan, Abid; Zuki Salleh, Mohd; Tahar, Razman Mat; Khan, Ilyas

    2014-01-01

    In this paper, the heat transfer effect on the unsteady boundary layer flow of a Casson fluid past an infinite oscillating vertical plate with Newtonian heating is investigated. The governing equations are transformed to a systems of linear partial differential equations using appropriate non-dimensional variables. The resulting equations are solved analytically by using the Laplace transform method and the expressions for velocity and temperature are obtained. They satisfy all imposed initial and boundary conditions and reduce to some well-known solutions for Newtonian fluids. Numerical results for velocity, temperature, skin friction and Nusselt number are shown in various graphs and discussed for embedded flow parameters. It is found that velocity decreases as Casson parameters increases and thermal boundary layer thickness increases with increasing Newtonian heating parameter.

  4. The turbulent boundary layer on a porous plate: An experimental study of the heat transfer behavior with adverse pressure gradients

    NASA Technical Reports Server (NTRS)

    Blackwell, B. F.; Kays, W. M.; Moffat, R. J.

    1972-01-01

    An experimental investigation of the heat transfer behavior of the near equilibrium transpired turbulent boundary layer with adverse pressure gradient has been carried out. Stanton numbers were measured by an energy balance on electrically heated plates that form the bottom wall of the wind tunnel. Two adverse pressure gradients were studied. Two types of transpiration boundary conditions were investigated. The concept of an equilibrium thermal boundary layer was introduced. It was found that Stanton number as a function of enthalpy thickness Reynolds number is essentially unaffected by adverse pressure gradient with no transpiration. Shear stress, heat flux, and turbulent Prandtl number profiles were computed from mean temperature and velocity profiles. It was concluded that the turbulent Prandtl number is greater than unity in near the wall and decreases continuously to approximately 0.5 at the free stream.

  5. MHD forced convective laminar boundary layer flow from a convectively heated moving vertical plate with radiation and transpiration effect.

    PubMed

    Uddin, Md Jashim; Khan, Waqar A; Ismail, A I Md

    2013-01-01

    A two-dimensional steady forced convective flow of a Newtonian fluid past a convectively heated permeable vertically moving plate in the presence of a variable magnetic field and radiation effect has been investigated numerically. The plate moves either in assisting or opposing direction to the free stream. The plate and free stream velocities are considered to be proportional to x(m) whilst the magnetic field and mass transfer velocity are taken to be proportional to x((m-1)/2) where x is the distance along the plate from the leading edge of the plate. Instead of using existing similarity transformations, we use a linear group of transformations to transform the governing equations into similarity equations with relevant boundary conditions. Numerical solutions of the similarity equations are presented to show the effects of the controlling parameters on the dimensionless velocity, temperature and concentration profiles as well as on the friction factor, rate of heat and mass transfer. It is found that the rate of heat transfer elevates with the mass transfer velocity, convective heat transfer, Prandtl number, velocity ratio and the magnetic field parameters. It is also found that the rate of mass transfer enhances with the mass transfer velocity, velocity ratio, power law index and the Schmidt number, whilst it suppresses with the magnetic field parameter. Our results are compared with the results existing in the open literature. The comparisons are satisfactory. PMID:23741295

  6. MHD forced convective laminar boundary layer flow from a convectively heated moving vertical plate with radiation and transpiration effect.

    PubMed

    Uddin, Md Jashim; Khan, Waqar A; Ismail, A I Md

    2013-01-01

    A two-dimensional steady forced convective flow of a Newtonian fluid past a convectively heated permeable vertically moving plate in the presence of a variable magnetic field and radiation effect has been investigated numerically. The plate moves either in assisting or opposing direction to the free stream. The plate and free stream velocities are considered to be proportional to x(m) whilst the magnetic field and mass transfer velocity are taken to be proportional to x((m-1)/2) where x is the distance along the plate from the leading edge of the plate. Instead of using existing similarity transformations, we use a linear group of transformations to transform the governing equations into similarity equations with relevant boundary conditions. Numerical solutions of the similarity equations are presented to show the effects of the controlling parameters on the dimensionless velocity, temperature and concentration profiles as well as on the friction factor, rate of heat and mass transfer. It is found that the rate of heat transfer elevates with the mass transfer velocity, convective heat transfer, Prandtl number, velocity ratio and the magnetic field parameters. It is also found that the rate of mass transfer enhances with the mass transfer velocity, velocity ratio, power law index and the Schmidt number, whilst it suppresses with the magnetic field parameter. Our results are compared with the results existing in the open literature. The comparisons are satisfactory.

  7. Seismo-electromagnetic phenomena in the western part of the Eurasia-Nubia plate boundary

    NASA Astrophysics Data System (ADS)

    Gonçalves da Silva, Hugo; Bezzeghoud, Mourad; Biagi, Pier; Namorado Rosa, Rui; Salgueiro da Silva, Manuel; Caldeira, Bento; Heitor Reis, Artur; Borges, José Fernando; Tlemçani, Mouhaydine; Manso, Marco

    2010-05-01

    This paper presents a future research plan that aims to monitor Seismo-electromagnetic (SEM) phenomena in the western part of the Eurasia-Nubia plate boundary (WENP). This region has a significant tectonic activity [1] combined with relatively low electromagnetic noise levels and for that reason presents the possibility to perform high quality SEM measurements. Further, it is known that low-frequency [ultra (ULF), very (VLF), and low-frequencies (LF)] electromagnetic (EM) waves produce more convincing earthquake precursors (compared to higher frequencies) because of less contamination, large skin depth, and low attenuation [2]. Thus, two SEM effects will be considered: ULF electromagnetic field emissions [3], and VLF/LF radio broadcastings [4]. With respect to the ULF measurements, as a start, three ULF sensors are planned to be installed in the South of Iberian Peninsula supported by the existing networks of seismic research stations. Subsequent development of this initial plan could result in the implementation of a lager ULF monitoring network not only in the Iberian Peninsula, but also in the rest of Europe. Possible integration in the SEGMA array is now under consideration. Another perspective is to use a portable station to track seismic events. Regarding the VLF/LF radio broadcastings, a receiver is planned to be mounted in University of Évora. Radio signals from up to 10 transmitters (in these bands) of interest to study the seismic activity in the WENP region will be monitored. Actually, the radio path from the transmitter to the receiver should cross the epicentral area, therefore two possible transmitters are the ones installed in Monaco (France) and Sicily (Italy). Furthermore, the system will integrate the INFREP network and in this context it will not be restricted to WENP region. With the development of these research plans we aim to collect novel SEM data emerging from the seismic activity in the WENP region. We expect to address the time

  8. The EarthScope Plate Boundary Observatory Alaska Region: Highlights from the 2012 Summer Field Season

    NASA Astrophysics Data System (ADS)

    Enders, M.; Bierma, R. M.; Boyce, E. S.; Willoughby, H.; Fend, M.; Feaux, K.

    2012-12-01

    UNAVCO has now completed its fourth year of operation and maintenance of the 138 continuous GPS stations, 12 tiltmeters and 31 data communications relays that comprise the Alaska region of the EarthScope Plate Boundary Observatory (PBO). The successful operation of the autonomous GPS and tiltmeter network in Alaska continues to be a challenge, because of logistics, weather, and other difficulties related to working in Alaska. PBO engineers continue to work on network enhancements to make the stations more robust, while improving overall data quality and station uptime to better serve the EarthScope science community. In the summer of 2012, PBO engineers completed maintenance activities in Alaska, which resulted in a 95% operational status for the Alaska network within PBO. PBO engineers completed a total of 87 maintenance visits in the summer of FY2012, including 62 routine maintenance and 25 unscheduled maintenance visits to GPS and data communications stations. We present a number of highlights and accomplishments from the PBO 2012 summer field season in Alaska, for example the deployment of a newly designed methanol fuel cell at AV35, a critical station that serves as the main repeater for the real time network on Unimak Island. In addition, PBO engineers also completed the installation of three Inmarsat BGAN terminals for data telemetry following successful testing at AC60 Shemya. Lastly, PBO engineers completed scheduled battery replacements at most of the PBO stations on Unimak Island, in collaboration with the USGS/Alaska Volcano Observatory. In addition to routine maintenance and planned station improvements to sites in Alaska, numerous critical repairs were made at stations on Unimak Island and elsewhere to ensure that the PBO network continues to function well and continues to meet the requirements stipulated by the NSF. We also present some of the station failures unique to Alaska, which we encountered during the course of the 2012 field season, as well

  9. Plate Boundary Observatory Southwest Region Network Operations, Expansion and Communications Hardening

    NASA Astrophysics Data System (ADS)

    Mann, D.; Walls, C. P.; Basset, A.; Turner, R.; Lawrence, S.; Feaux, K.; Mattioli, G. S.

    2014-12-01

    The Southwest Region of the Plate Boundary Observatory manages 480 continuously operating GPS stations located principally along the transform system of the San Andreas fault, Eastern California Shear Zone and the northern Baja peninsula. In the past year, network uptime averaged 98% with greater than 99% data acquisition. In an effort to modernize the network, we have started to replace Trimble NETRS receivers with GNSS capable NETR9 receivers. Currently, we have 431 NetRS receivers deployed in the region, and 48 NetR9 receivers. In addition, 82 stations (17%) stream 1 Hz data over the VRS3Net typically with <0.5 second latency and an average completeness of >92%. Based on their typical data download rates, approximately 252 (53%) of all stations are capable of streaming 1 Hz, but have not yet been added to the real time network because of lack of resources. In the immediate aftermath of the M8.2 Chile earthquake in April 2014, high rate data downloads from the entire SW network had a success rate of 95% and 71% for 1 Hz and 5 Hz data downloads respectively. We have continued to upgrade critical radio networks, including the San Francisco Bay Area, Anza Borrego, and Santa Barbara networks. These efforts are ongoing, but they have already significantly improved data download rates and dependability. We are also converting cell modem to radio communications whenever possible for increased reliability and cost savings. In December 2013 the 13-station Edison network expansion was completed through cost recovery contracts. These stations span coastal southern California in Orange, San Diego and Los Angeles counties including a hybrid site on the Elly oil platform. The primary purpose of the stations is to aid in the seismic source characterization of the San Onofre Nuclear Generating Station and assess the strain field associated with the Oceanside Blind Thrust and Newport Inglewood fault. The new stations fill a gap between SCIGN and PBO. Three sites have WXT520

  10. The Plate Boundary Observatory (PBO) Network in the PNW region of the United States

    NASA Astrophysics Data System (ADS)

    Hafner, K.; Austin, K.; Feaux, K.; Jackson, M.; Fengler, K.; Doelger, S.

    2007-05-01

    The Pacific Northwest Region (PNW) of the United States contains a variety of geologic regions and tectonic problems. These include the Cascadia Subduction Zone, Mt. St. Helens and the transition to the Basin and Range province. Since September of 2003, the Plate Boundary Observatory (PBO), which is part of the larger NSF-funded EarthScope project, has been installing a network of continuously operating GPS, strainmeter and tiltmeter instruments. There are currently 78 GPS, 13 strainmeter/borehole seismometers, and 4 tiltmeters operating in the PNW region. The data from this network has already been used to study Episodic Tremor Events (ETS) during September 2005 and January 2007, and renewed activity on Mt. St. Helens that began on September 23, 2004. The goal is have 134 continuously operating GPS stations by the end of September 2008. The locations of the GPS stations were determined by scientific committees. Whenever possible, multiple instruments are deployed at the same location, and share power and communications resources. Examples of this are GPS antennas mounted on top of strainmeter boreholes in the forearc region of western Washington and tiltmeters collecting data through GPS receivers on Mt. St. Helens. In addition, a number of stations provide real time kinematic data to professional surveyors within the region. During the fall of 2006, a 16 GPS and 4 tiltmeter station network was completed on Mt. St. Helens. Results from analysis of both PBO and USGS GPS stations on the mountain, show a radially inward and downward motion, with the maximum vertical offsets high on the mountain and the maximum horizontal offsets located at distances of 5-10km from the crater. Displacements are small over the 2004-present eruption with a maximum of 3cm of inward movement. GPS stations installed high on the mountain experience severe weather and heavy rime accumulations for approximately 6 months of the year. Ice build-up causes distortion of the GPS antenna phase

  11. Evolving seismogenic plate boundary megathrust and mega-splay faults in subduction zone (Invited)

    NASA Astrophysics Data System (ADS)

    Kimura, G.; Hamahashi, M.; Fukuchi, R.; Yamaguchi, A.; Kameda, J.; Kitamura, Y.; Hashimoto, Y.; Hamada, Y.; Saito, S.; Kawasaki, R.

    2013-12-01

    Understanding the fault mechanism and its relationship to the sesimo-tsunamigenesis is a key of the scientific targets of subduction zone and therefore NantroSEIZE project of IODP and future new drilling project of International Ocean Discovery Program keeps focusing on that. Mega-splay fault branched from plate boundary megathrust in subduction zone is located around the border between outer and inner wedges and is considered to cause great earthquake and tsunami such as 1960 Alaska earthquake, 1944 and 1946 Nankai-Tonankai earthquakes, and 2004 Sumatra earthquakes. Seismic reflection studies for the mega-splay fault in 2D and 3D in the Nankai forearc present the reflector with negative or positive polarities with various amplitudes and suggest complicated petrophysical properties and condition of the fault and its surroundings. The Nankai mega-splay fault at a depth of ~5km is going to be drilled and cored by NantroSEIZE experiments and is expected for great progress of understanding of the fault mechanics. Before drilling the really targeted seismogenic fault, we are conducting many exercises of geophysical and geological observations. The core-log-seismic integrated exercise for the exhumed mega-splay fault by drilling was operated for the Nobeoka thrust in the Shimanto Belt, Kyushu, Japan. The Nobeoka thrust was once buried in the depth >~10km and suffered maximum temperature >~300 dgree C. As the core recovery is ~99%, perfect correlation between the core and logging data is possible. Thickness of the fault zone is >200 m with a ~50 cm thick central fault core dividing the phyllitic hanging wall and the footwall of broken-melange like cataclasite. A-few-meter-thick discrete damage zones with fault cores are recognized by difference in physical properties and visual deformation textures at several horizons in the fault zone. Host rocks for those damaged zones are completely lithified cataclasites with abundant mineral veins, which record the older and deeper

  12. Completion of the 16 station Plate Boundary Observatory (PBO) network on Mt. St. Helens, WA

    NASA Astrophysics Data System (ADS)

    Austin, K.; Hafner, K.; Fengler, K.; Doelger, S.

    2006-12-01

    The Plate Boundary Observatory (PBO), part of the larger NSF-funded EarthScope project, is completing year 3 of the installation phase of 852 continuously operating GPS stations in the Western United States. Some of these GPS stations are focused specifically on centers of volcanic activity. Mt. St. Helens is one of these volcanic areas of interest in the Pacific Northwest (PNW) region. The PNW region will complete the installation of a 16 station GPS network on Mt. St. Helens during September 2006. This work also includes the co-location and installation of tiltmeters at four of the existing GPS sites. Network upgrades will be completed to handle the increase in data flow from the new GPS stations as well as the data from the tiltmeters and strainmeters. New GPS site installations include six helicopter accessible sites, and three drive to sites on the south flank of the mountain. Higher elevation sites will be outfitted with an eight battery, three solar panel power array to keep the stations operational during winter months. The remaining sites use a four battery, three solar panel array that has proved sufficient at other GPS locations over the past 2 winters. All stations will communicate via one of 2 radio networks set up on the mountain. The northern radio network transmits data for ten stations through a microwave connection at the Johnston Ridge observatory that also provides communications for PBO strainmeter, tiltmeter and CVO equipment. The remaining 10 stations on the south side of the mountain, are relayed through a hub at Washington State University's Vancouver Campus that is also providing data services for CVO. Results from analysis of data from both PBO and USGS GPS stations on the mountain, show a radially inward and downward motion, with the maximum vertical offsets high on the mountain and the maximum horizontal offsets located at distances of 5-10km from the crater. Displacements are small over the 2004-present eruption with a maximum of 3cm

  13. The Plate Boundary Observatory: Current status and plans for the next five years

    NASA Astrophysics Data System (ADS)

    Mattioli, G. S.; Feaux, K.; Meertens, C. M.; Mencin, D.; Miller, M.

    2013-12-01

    UNAVCO currently operates and maintains the NSF-funded Plate Boundary Observatory (PBO), which is the geodetic facility of EarthScope. PBO was designed and built from 2003 to 2008 with $100M investment from the NSF Major Research Equipment and Facilities Construction (MREFC) Program. UNAVCO operated and maintained PBO under a Cooperative Agreement (CA) with NSF from 2008 to 2013 and will continue PBO O&M for the next five years as part of the new Geodesy Advancing Geosciences and EarthScope (GAGE) Facility. PBO is largest continuous GPS and borehole geophysical network in the Americas, with 1100 continuous Global Positioning System (cGPS) sites, including several with multiple monuments, 79 boreholes, with 75 tensor strainmeters, 78 short-period, 3-component seismometers, and pore pressure sensors at 23 sites. PBO also includes 26 tiltmeters deployed at volcanoes in Alaska, Mt St Helens, and Yellowstone caldera and 6 long-baseline laser strainmeters. Surface meteorological sensors are collocated at 154 GPS sites. UNAVCO provides high-rate (1 Hz), low-latency (<1 s) GPS data streams (RT-GPS) from 382 stations in PBO. UNAVCO has delivered over 62 Tb of geodetic data to the EarthScope community since its PBO's inception in 2004. Over the past year, data return for the cGPS component of PBO is 98%, well above the data return metric of 85% set by the NSF, a result of efforts to upgrade power systems and communications infrastructure. In addition, PBO has set the standard for the design, construction, and operation of other multi-hazard networks across the Americas, including COCONet in the Caribbean region and TLALOCNet in Mexico. Funding to support ongoing PBO O&M has declined from FY2012 CA levels under the new GAGE Facility. The implications for data return and data quality metrics as well as replacement of aging PBO GPS instruments with GNSS-compatible systems are as yet unknown. A process to assess the cost of specific PBO components, data rates, enhanced

  14. 2011 Operations and Maintenance Activities in the East Region of UNAVCO's Plate Boundary Observatory

    NASA Astrophysics Data System (ADS)

    Dittmann, T.; Feaux, K.; Kasmer, D.; Jenkins, F.; Mencin, D.

    2011-12-01

    2011 marked Year 3 of Operations and Maintenance of the Plate Boundary Observatory (PBO). In the East Region of PBO, it was a year characterized by several major projects as well as scheduled ongoing maintenance activities. The most significant major project was a USGS/ARRA funded communications upgrade in Yellowstone National Park. This upgrade consisted of bringing 8 existing PBO stations within the Yellowstone volcanic region to near real-time communications. This work will be completed on time and in collaboration with the National Park Service. The upgrade promises to provide much faster latency for invaluable data being recorded for one of the most geodetically critical regions of the current PBO network. Another significant ongoing project in the East Region has been supporting the community that continues to use PBO data. In particular, support of Kristine Larson (Univ of CO) both in installing webcams at PBO sites for monitoring snow depth as well as supporting vegetative surveys at current PBO sites. Similarly, the East Region responded promptly to the community with requests for data quality issues that are station hardware related, including replacing GPS antennae and receivers. With regards to ongoing operations and maintenance projects, reasons for site visits in 2011 were dominated by two significant situations: battery replacement and CDMA modem swaps. 83 site visits were required as part of the Operations and Maintenance strategic battery plan of 5 year battery replacements. This proved to be a considerable challenge due to the scale and geography of the scheduled replacements- the sites were spread throughout the entire network, east to west and north to south. 20 station visits were required due to a Verizon upgrade of the older Alltel network purchased by Verizon. These stations are predominantly in the Rocky Mountain region, but often times had limited access to due weather. Overall, despite record snowfalls throughout the west, state of health

  15. Building a Global Data Network for Studies of Earth Processes at the World's Plate Boundaries

    NASA Astrophysics Data System (ADS)

    Lehnert, K. A.; Carbotte, S.; Tsuboi, S.; Weinrebe, W.

    2007-12-01

    The international geoscience community is engaged in scientifically aligned goals to understand the fundamental processes of crustal formation, modification and destruction at the Earth's plate boundaries through broad multi- disciplinary initiatives such as the InterRidge and InterMARGINS programs. These programs involve the collection of unique data sets during oceanic and terrestrial expeditions and subsequent laboratory work conducted by research institutions around the globe. These international research efforts would benefit significantly if data collections maintained as national efforts could be better linked and broader access were initiated. At present there are no formal agreements within these programs for data sharing between foreign partners. A workshop was convened in May 2007, jointly sponsored and funded by MARGINS, InterMARGINS, InterRidge, Ridge2000, the US National Science Foundation, and the German project "The Future Ocean", to explore current opportunities and challenges for international data exchange to support marine geoscience research broadly. Participants from 14 countries discussed technological, organizational, and cultural issues for building a global data network and agreed on a set of recommendations regarding science user needs, data documentation, data publication, metadata interoperability, and opportunities and obstacles for international data sharing. They underscored that (1) open public access to data is fundamental to verifiable scientific progress; (2) uniform best practices and standards for data acquisition, data submission to data centers, and data publication need to be developed and used routinely within the international community, facilitated by tools that automate metadata acquisition in the field and in the lab; (3) the proliferation of metadata standards needs to be minimized to achieve a uniform approach for scientific metadata building upon the work of existing community-based projects; (4) data centers should

  16. The thermal-mechanical evolution of crustal orogenic belts at convergent plate boundaries: A reappraisal of the orogenic cycle

    NASA Astrophysics Data System (ADS)

    Vanderhaeghe, Olivier

    2012-05-01

    Convergent plate boundaries are characterized by the development of crustal orogenic wedges and orogenic plateaus but also by gravitational collapse of previously thickened crust leading to the opening of intermontane and eventually oceanic back-arc basins. Foreland and extensional sedimentary basins in the plate boundary region are filled by the erosional products of the orogenic crust. Metamorphic rocks forming orogenic crust attest to burial and exhumation under contrasted geothermal gradients. These features portray the crustal orogenic cycle and are first-order indicators of the thermal and mechanical evolution of the crust within the plate boundary region. This evolution is controlled by complex interactions among (i) the dynamic balance among forces that arise from plate-tectonic, gravitational potential energy, and buoyancy, (ii) the thermal balance between deformation-induced and radioactive heat production and heat advection related to subduction, orogenic deformation, and magma transfer, and (iii) the mass transfer balance between uplift and erosion. To account for these geological characteristics, a generic model, that integrates results from physical modeling, is proposed for the thermal-mechanical evolution of crustal orogenic belts and for its implication in controlling the transition between the different phases of the orogenic cycle. In this model, the transition from low to high geothermal gradient is associated with increased heat production in the thickened crust owing to radioactive decay and deformation. Partial melting and rheologic weakening of the thermally mature thickened crust triggers gravity-driven lateral flow of the lower crust and controls the transition from wedge to orogenic plateau. Destruction of the orogenic crust is achieved in part by erosion but mostly by gravitational collapse. The style of extension is controlled by the rheology of the crust at the onset of gravitational collapse and its evolution as the crust thins and

  17. Deformation kinematics along oblique convergent plate boundary zones in the western United States, Japanese Islands, and Pakistan

    NASA Astrophysics Data System (ADS)

    Shen-Tu, Bingming

    Horizontal velocity gradient tensor field in the western U.S is estimated using moment tensors of earthquakes between 1850 to 1995. The velocity vectors obtained from the integration of the seismic strain rates across the entire plate boundary lie within 5° of the NUVEL-1A Pacific-North American plate motion direction. The magnitude of the earthquake-related velocity is 62% of the NUVEL-1A total Pacific-North American plate motion. The total velocity obtained from the Quaternary fault slip rate data across the entire plate boundary is within 2 mm/yr of the NUVEL-1A predicted Pacific (PA)-North American (NA) plate motion velocity, but directions are 6° anticlockwise of directions given by NUVEL-1A. The total velocity obtained from inversion of recent geodetic data is 2°--3° anticlockwise from the NUVEL-1A NA-PA velocity, but the difference between the two is not significant at the 95% confidence level. Relative motions within the deforming Japanese Islands with respect to the Sea of Japan are determined using earthquake records over the last 414 years, slip rates on Quaternary faults, and angular change rates obtained from triangulation in the last century. The directions of the principal strain axes obtained from seismic, geological, and geodetic data are in general agreement with each other, with the maximum shortening axis oriented in a WNW direction. Intraplate deformation in southwestern Japan determined from the seismic data accommodates a velocity of 5.5 +/- 2 (1sigma) mm/yr in a direction parallel to the Nankai trough, which is about 25% of the plate motion velocity component parallel to the Nankai trough between the Philippine Sea and Eurasian plates. A comparison of shear strain rates, principal strain rates, and velocity fields determined from geodetic data with those calculated from the elastic dislocation models involving interplate motion at the Japan trench indicates that the geodetic strain field in northern Honshu is primarily elastic strain

  18. Active Pacific North America Plate boundary tectonics as evidenced by seismicity in the oceanic lithosphere offshore Baja California, Mexico

    NASA Astrophysics Data System (ADS)

    Hauksson, Egill; Kanamori, Hiroo; Stock, Joann; Cormier, Marie-Helene; Legg, Mark

    2014-03-01

    Pacific Ocean crust west of southwest North America was formed by Cenozoic seafloor spreading between the large Pacific Plate and smaller microplates. The eastern limit of this seafloor, the continent-ocean boundary, is the fossil trench along which the microplates subducted and were mostly destroyed in Miocene time. The Pacific-North America Plate boundary motion today is concentrated on continental fault systems well to the east, and this region of oceanic crust is generally thought to be within the rigid Pacific Plate. Yet, the 2012 December 14 Mw 6.3 earthquake that occurred about 275 km west of Ensenada, Baja California, Mexico, is evidence for continued tectonism in this oceanic part of the Pacific Plate. The preferred main shock centroid depth of 20 km was located close to the bottom of the seismogenic thickness of the young oceanic lithosphere. The focal mechanism, derived from both teleseismic P-wave inversion and W-phase analysis of the main shock waveforms, and the 12 aftershocks of M ˜3-4 are consistent with normal faulting on northeast striking nodal planes, which align with surface mapped extensional tectonic trends such as volcanic features in the region. Previous Global Positioning System (GPS) measurements on offshore islands in the California Continental Borderland had detected some distributed Pacific and North America relative plate motion strain that could extend into the epicentral region. The release of this lithospheric strain along existing zones of weakness is a more likely cause of this seismicity than current thermal contraction of the oceanic lithosphere or volcanism. The main shock caused weak to moderate ground shaking in the coastal zones of southern California, USA, and Baja California, Mexico, but the tsunami was negligible.

  19. Continent-continent collision at the Pacific/Australian plate boundary: Lithospheric deformation, mountain building, and subsequent scientific endeavors

    NASA Astrophysics Data System (ADS)

    Okaya, D. A.; Stern, T. A.; Davey, F. J.

    2012-12-01

    Continental collision occurs at strike-slip plate boundaries where transform motion and oblique convergence create processes of surficial mountain building and deformation within the deeper crust and lithospheric mantle. The Pacific/Australian transform plate boundary in South Island, New Zealand, is characterized by active oblique continent-continent collision with an associated Southern Alps orogen that exhibits both high exhumation rates and rapid strike-slip movement. Beginning in the 1990s, this system was the focus of a decade-long collaborative USA-New Zealand multi-disciplinary study to understand lithospheric structure and processes involved in this transpression. Funded primarily by the NSF Continental Dynamics program and the New Zealand Science Foundation, this project known as SIGHT (South Island Geophysical Transect) with its companion SAPSE (Southern Alps Passive Seismic Experiment) included the following disciplines that involved substantial field observation experiments: seismic reflection, explosion refraction, onshore-offshore wide-angle reflection/refraction, regional and teleseismic passive seismology, magnetotellurics, laboratory petrophysics, gravity, regional geological investigations, and rheological analyses. More than fifty scientists and students from both nations participated in the combined set of studies that have led to over forty-five journal publications, an AGU Monograph, and a dozen graduate theses. Primary results of the project indicate the Pacific-Australian strike-slip plate boundary (Alpine fault) is not vertical but is eastward dipping and rheologically weak based on diverse geophysical data. Most deformation is within the Pacific plate that hosts the Southern Alps orogen. High mantle seismic velocities vertically disposed beneath the orogen suggest Pacific and perhaps Australian mantle lithosphere contribute to a zone of plate-boundary-parallel distributed mantle shortening. The crustal root of the overlying Southern Alps

  20. North America-Pacific plate boundary, an elastic-plastic megashear - Evidence from very long baseline interferometry

    NASA Technical Reports Server (NTRS)

    Ward, Steven N.

    1988-01-01

    Data obtained by Mark III VLBI measurements of radio signals from permanent and mobile VLBI sites for 5.5 years of observations, starting in October 1982, were used to derive a picture of the earth crust deformation near the North America-Pacific plate boundary. The data, which included the vector positions of the VLBI sites and their rate of change, were used for comparison with a number of lithospheric deformation models based upon the concept that the motions of points near the North America-Pacific plate boundary are a linear combination of North America and Pacific velocities. The best of these models were found to fit 95 percent of the variance in 139 VLBI length and transverse velocity observations. Instantaneous shear deformation associated with plate tectonics is apparently developing in a zone 450 km wide paralleling the San Andreas Fault; some of this deformation will be recovered through elastic rebound, while the rest will be permanently set through plastic processes. Because the VLBI data have not been collected for a significant fraction of the earthquake cycle, they cannot discriminate between elastic and plastic behaviors.

  1. Radiocarbon evidence for extensive plate-boundary rupture about 300 years ago at the Cascadia subduction zone

    USGS Publications Warehouse

    Nelson, A.R.; Atwater, B.F.; Bobrowsky, P.T.; Bradley, L.-A.; Clague, J.J.; Carver, G.A.; Darienzo, M.E.; Grant, W.C.; Krueger, H.W.; Sparks, R.; Stafford, Thomas W.; Stuiver, M.

    1995-01-01

    THE Cascadia subduction zone, a region of converging tectonic plates along the Pacific coast of North America, has a geological history of very large plate-boundary earthquakes1,2, but no such earthquakes have struck this region since Euro-American settlement about 150 years ago. Geophysical estimates of the moment magnitudes (Mw) of the largest such earthquakes range from 8 (ref. 3).to 91/2 (ref. 4). Radiocarbon dating of earthquake-killed vegetation can set upper bounds on earthquake size by constraining the length of plate boundary that ruptured in individual earthquakes. Such dating has shown that the most recent rupture, or series of ruptures, extended at least 55 km along the Washington coast within a period of a few decades about 300 years ago5. Here we report 85 new 14C ages, which suggest that this most recent rupture (or series) extended at least 900 km between southern British Columbia and northern California. By comparing the 14C ages with written records of the past 150 years, we conclude that a single magnitude 9 earthquake, or a series of lesser earthquakes, ruptured most of the length of the Cascadia subduction zone between the late 1600s and early 1800s, and probably in the early 1700s.

  2. Boundary layer flow and heat transfer on a moving plate in a copper-water nanofluid using Buongiorno model

    NASA Astrophysics Data System (ADS)

    Bakar, Nor Ashikin Abu; Bachok, Norfifah; Arifin, Norihan Md.

    2016-06-01

    The study of the steady two dimensional boundary layer flow of a copper (Cu)-water nanofluid on a moving plate is investigated. The assumption is the plate moves in the same or opposite direction to the free stream. The nonlinear partial differential equations are transformed into nonlinear ordinary differential equations using a similarity variables,then a shooting technique is used to solved it numerically. The numerical results for skin friction coefficient, the local Nusselt number, the local Sherwood number as well as the velocity, temperature and concentration profiles are obtained. The effect of nanoparticle volume fraction, Brownian motion and thermophoresis parameters on heat transfer are examined. The results show that the local Nusselt number and the local Sherwood number increase with increasing in the Brownian motion parameter Nb and thermophoresis parameter Nt.

  3. Crustal structure of a transform plate boundary: San Francisco Bay and the central California continental margin

    USGS Publications Warehouse

    Holbrook, W.S.; Brocher, T.M.; ten Brink, U.S.; Hole, J.A.

    1996-01-01

    lower-crustal velocity of Pacific oceanic crust suggest that it was underplated by magmatism associated with the nearby Pioneer seamount. The Salinian Block consists of a 15-km-thick layer of velocity 6.0-6.2 km/s overlying a 5-km-thick, high-velocity (7.0 km/s) lower crust that may be oceanic crust, Cretaceous arc-derived lower crust, or a magmatically underplated layer. The strong structural variability across the margin attests to the activity of strike-slip faulting prior to and during development of the transcurrent Pacific/North American plate boundary around 29 Ma. Copyright 1996 by the American Geophysical Union.

  4. EarthScope: Cyberinfrastructure to access Plate Boundary Observatory data products and services

    NASA Astrophysics Data System (ADS)

    Meertens, C. M.; Mattioli, G. S.; Miller, M.; Boler, F. M.; Crosby, C. J.; Mencin, D.; Phillips, D. A.; Snett, L.

    2013-12-01

    The wealth of data from geodetic observing systems, especially the Plate Boundary Observatory (PBO), presents major data management challenges. The challenges are driven by ingenious new uses of Global Positioning System (GPS) data, demands for higher-rate, lower latency data, the need for continued access and long term preservation of archival data, the expansion of data users into other science, engineering and commercial arenas, and the growth of enhanced products that expand the utility of the data. To meet these challenges, UNAVCO has established a comprehensive suite of data services encompassing sensor network data operations, data product generation (through the activities of partners at Massachusetts Institute of Technology, Central Washington University, New Mexico Institute of Mining and Technology, and the University of California, San Diego - UCSD), data management, access and archiving, and advanced cyberinfrastructure. PBO sensor systems include 1,100 continuously operating GPS stations, 79 borehole geophysical sites (with a combination of strainmeters, tiltmeters, seismometers, pore pressure gauges, and meteorological sensors), and 6 long baseline strainmeters. Imaging data acquired for EarthScope include large volumes of satellite synthetic aperture radar (SAR) and airborne LiDAR data. Core data products such as daily GPS position time series and derived crustal motion velocities have been augmented with real-time data streams and positions calculated every second from 367 PBO stations. Higher rate (5 Hz) data files are available for applications such as GPS seismology. Efforts are underway with UCSD to integrate GPS and accelerometers at a subset of PBO sites to increase the reliability and capability of the observations. These observations have utility for research and hazards mitigation. Ingenious methods of GPS data analysis, developed by the University of Colorado and the University Corporation for Atmospheric Research, measure snow depth

  5. What can we Learn From Small Non-Recoverable Strains at Plate Boundaries?

    NASA Astrophysics Data System (ADS)

    Lewis, J. C.; Pluhar, C. J.

    2003-12-01

    Background seismicity carries often overlooked information about how the crust responds to plate motions. Integrating focal mechanisms for background seismicity with (1) geologic observations, and (2) geodetic constraints, is critical to establishing a better understanding of both the rock record and contemporary deformation. Treating the crust as a micropolar continuum it is possible to constrain not only the orientations and relative magnitudes of the principal strains but also the vorticity of crustal blocks with respect to the large-scale continuum. We show the utility of this approach with examples from the Cascadia margin and the Coso Range (within the Eastern California shear zone). In the upper crust of the Cascadia margin, seismogenic strain appears to be dominated by accommodation of motion of the Oregon forearc block. This suggests that the shallow crust is responding to long-term motion of the Oregon forearc rather than the interseismic locking of the subduction megathrust. In the area west of Mt. Rainier, this response is marked by non-zero relative vorticity in a regime of N-S shortening and crustal thickening. To date, geologic studies necessary to evaluate the significance of this vorticity have not been completed. In contrast within the Coso Range of California, seismogenic strain at Wild Horse Mesa indicates a component of relative vorticity that is broadly consistent with paleomagnetically constrained finite rotations of the ca. 3 Ma lava flows that compose the mesa. This area is centered at a right-releasing step in the Eastern California shear zone and thus is experiencing active transtension. Stratigraphic constraints have been used to suggest that significant dextral shearing in this region initiated ca. 3.5-2 Ma. The seismogenic response to transtension is depth-dependent plane strain with crustal thinning above 5 km and horizontal dextral shearing from 5-8 km. Both structural levels indicate subhorizontal E-W maximum stretching. Relative

  6. EarthScope's Plate Boundary Observatory as the Mother of Invention (Invited)

    NASA Astrophysics Data System (ADS)

    Blewitt, G.; Hammond, W. C.; Kreemer, C.

    2013-12-01

    The Plate Boundary Observatory (PBO) component of EarthScope includes a network of over 1,100 permanent, continuously operating GPS stations. After 5 years of site selection, permitting, and construction, the network was completed in 2008. Having such an unprecedented number of high quality stations in western North America has enabled us to image geology in action, as it happens, such as contemporary uplift of the Sierra Nevada, and block rotation in the Walker Lane. Yet, when PBO was in its planning stages, questions were raised as to whether GPS analysis could keep up with the flood of data, while producing results with the highest achievable accuracy. The general consensus was that the challenge would be met by a combination of innovative data processing methods together with the inevitable progress in computer speed and capacity. Various innovations made by the geodetic community over the last decade have enabled massive operational processing of GPS data with high accuracy. For example, now in 2013, the Nevada Geodetic Laboratory operationally produces position time series and quality assurance data from all ~7,000 GPS geodetic stations in the world that make data publicly available. Of these stations, 4,000 have daily time series updated the next day, and 2,000 have 5-minute time series updated within 1-2 hours of real time. The RMS precision of daily positions for well-sited stations are at the level of 1-2 mm horizontal, and 3-6 mm vertical in the International Terrestrial Reference Frame (ITRF). For 5-minute positions, the precision is at the level of 6-12 mm horizontal, and 15-30 mm vertical. Here we review some of the innovations that have made all of this possible, which were in part driven by challenges presented by EarthScope. First of all, at the data processing level, much creative effort went into making computer processing time scale linearly with the number of GPS stations. The Precise Point Positioning (PPP) technique invented in 1997 has been

  7. Secular and annual hydrologic effects from the Plate Boundary Observatory GPS network

    NASA Astrophysics Data System (ADS)

    Meertens, C. M.; Wahr, J. M.; Borsa, A. A.; Jackson, M. E.; Herring, T.

    2009-12-01

    The Plate Boundary Observatory (PBO) GPS network is providing accurate and spatially coherent vertical signals that can be interpreted in terms of hydrological loading and poroelastic effects from both natural and anthropogenic changes in water storage. Data used for this analysis are the precise coordinate time series produced on a daily basis by PBO Analysis Centers at New Mexico Institute of Mining and Technology and at Central Washington University and combined by the Analysis Center Coordinator at the Massachusetts Institute of Technology. These products, as well as derived velocity solutions, are made freely available from the UNAVCO Data Center in Boulder. Analysis of secular trends and annual variations in the time series was made using the analysis software of Langbein, 2008. Spatial variations in the amplitude and phase of the annual vertical component of motion allow for identification of anthropogenic effects due to water pumping, irrigation, and reservoir lake variations, and of outliers due to instrumental or other local site effects. Vertical annual signals of 8-10 mm peak-to-peak amplitude are evident at stations in the mountains of northern and central California and the Pacific Northwest. The peak annual uplift is in October and is correlated to hydrological loading effects. Mountainous areas appear to be responding elastically to the load of the water contained in surface soil, fractures, and snow. Vertical signals are highest when the water load is at a minimum. The vertical elastic hydrologic loading signal was modeled using the 0.25 degree community NOAH land-surface model (LSM) and generally fits the observed GPS signal. Addition comparisons will be made using the Mosaic LSM and the NOAA “Leaky Bucket” hydrologic model. In contrast to mountain stations that are installed principally in bedrock, stations in the valleys of California are installed in sediments. Observations from these stations show greater spatial variability ranging from

  8. Stability of GNSS Monumentation: Analysis of Co-Located Monuments in the Plate Boundary Observatory

    NASA Astrophysics Data System (ADS)

    Blume, F.; Berglund, H. T.; Feaux, K.; Dittmann, S. T.; Walls, C. P.; Austin, K. E.; Mattioli, G. S.

    2013-12-01

    Geodetic-quality permanent GNSS stations have used a number of different monumentation styles for the purpose of ensuring that the motions of the GNSS antenna reflect those of the Earth's crust while minimizing non-tectonic motions near the surface. Monuments range from simple masts drilled into building roofs or bedrock that cost a few hundred dollars to machine-drilled-braced monuments in soil that cost tens of thousands. Monument stability can depend on their design, the construction techniques used to install them, and the local surface geology where they are installed. Previous studies have separately investigated pairs of identical monuments at a single site, monument type variations using global statistical analysis, and multiple monument styles at a single site. Despite these efforts, the stability of different styles of monumentation in similarly varying geologic conditions has not been adequately determined. Errors in GPS measurements can be dominated by error sources unrelated to the movement of the monument with respect to the Earth's crust, thus making it difficult to isolate monument instability. Contributions from GPS measurement error unrelated to monument stability include, but are not limited to: satellite orbits, satellite clocks, tropospheric delay, and ionospheric delay, antenna phase center variations, near-field multipath, far-field multipath. Installing multiple monuments with small antenna separations at a given test location can help to reduce GPS measurement errors. To increase the understanding of monument stability of various monument styles in diverse geologic conditions UNAVCO has constructed two additional monuments at five existing Plate Boundary Observatory stations during the past year. Deep drilled-braced, short drilled-braced, and single mast type monuments were installed at sites with bedrock at the surface; deep drilled-braced, short driven-braced and pillar type monuments were installed at sites with alluvium or soil at the

  9. Recent faulting and active shortening of the Middle Atlas Mountains, Morocco, within the diffuse African-Eurasian plate boundary

    NASA Astrophysics Data System (ADS)

    Rigby, M.; Gomez, F.; Zakir, A.; Hahou, Y.; Jabour, N.

    2007-12-01

    The NE-SW trending Middle Atlas Mountains are an active intracontinental mountain belt within the diffuse African - Eurasian plate boundary. The mountain belt is obliquely oriented to the NNW-SSE direction of Late Cenozoic plate convergence. Both shear and compressional features are exhibited with apparent slip partitioning: Folding and thrusting is concentrated in the Folded Middle Atlas, whereas strike-slip dominates in the Tabular Middle Atlas. In the central part of the Folded Middle Atlas, fault scarps of Quaternary alluvium, including a 4.5 meter (probably composite) scarp and a 1 meter (possibly single event) scarp, attest to recent faulting along the mountain front. Detailed topographic mapping of the scarps provides a basis for geomorphic analysis and degradation modeling. Furthermore, the reconstruction of longitudinal stream terrace profiles helps constrain a long term deformation history. Radiocarbon and pending cosmogenic dates provide age constraints on the faulted surfaces and the multiple stream terraces in the area. To place these active tectonic observations in a larger context, the fault and fold geometry has been assessed by completing a 10 km structural transect across the frontal thrust, providing basis for the construction of a balanced cross-section. By combining the structural geometry with the uplift rate, a minimum estimate of the rate of horizontal shortening in the Middle Atlas can be evaluated. Preliminary results suggest the Middle Atlas may accommodate 5 - 10 percent of the total 4.5 mm/yr convergence between the African and Eurasian plates. These results demonstrate that the Middle Atlas Mountains are a integral part of the diffuse plate boundary, as well as suggesting a modest level of earthquake hazard in the region.

  10. Experimental study of skin friction drag reduction on superhydrophobic flat plates in high Reynolds number boundary layer flow

    NASA Astrophysics Data System (ADS)

    Aljallis, Elias; Sarshar, Mohammad Amin; Datla, Raju; Sikka, Vinod; Jones, Andrew; Choi, Chang-Hwan

    2013-02-01

    In this paper, we report the measurement of skin friction drag on superhydrophobic-coated flat plates in high Reynolds (Re) number boundary layer flows, using a high-speed towing tank system. Aluminum flat plates with a large area (4 feet × 2 feet, 3/8 in. thick) and sharpened leading/trailing edges (1 in. long) were prepared as a boundary layer flow model. Spray coating of hydrophobic nanoparticles was applied to make two different types of superhydrophobic coatings: one with low contact angle and high contact angle hysteresis, and the other with high contact angle and low contact angle hysteresis. Skin friction drag of the superhydrophobic plates was measured in the flow speed up to 30 ft/s to cover transition and turbulent flow regimes (105 < ReL < 107), and was compared to that of an uncoated bare aluminum plate. A significant drag reduction was observed on the superhydrophobic plate with high contact angle and low contact angle hysteresis up to ˜30% in transition regime (105 < ReL < 106), which is attributed to the shear-reducing air layer entrapped on the superhydrophobic surface. However, in fully turbulence regime (106 < ReL < 107), an increase of drag was observed, which is ascribed to the morphology of the surface air layer and its depletion by high shear flow. The texture of superhydrophobic coatings led to form a rugged morphology of the entrapped air layer, which would behave like microscale roughness to the liquid flow and offset the drag-reducing effects in the turbulent flow. Moreover, when the superhydrophobic coating became wet due to the removal of air by high shear at the boundary, it would amplify the surface roughness of solid wall and increase the drag in the turbulent flow. The results illustrate that drag reduction is not solely dependent on the superhydrophobicity of a surface (e.g., contact angle and air fraction), but the morphology and stability of the surface air layer are also critical for the effective drag reduction using

  11. Consolidation patterns during initiation and evolution of a plate-boundary decollement zone: northern Barbados accretionary prism

    USGS Publications Warehouse

    Moore, J.C.; Klaus, A.; Bangs, N.L.; Bekins, B.; Bucker, C.J.; Bruckmann, W.; Erickson, S.N.; Hansen, O.; Horton, T.; Ireland, P.; Major, C.O.; Moore, G.F.; Peacock, S.; Saito, S.; Screaton, E.J.; Shimeld, J.W.; Stauffer, P.H.; Taymaz, T.; Teas, P.A.; Tokunaga, T.

    1998-01-01

    Borehole logs from the northern Barbados accretionary prism show that the plate-boundary decollement initiates in a low-density radiolarian claystone. With continued thrusting, the decollement zone consolidates, but in a patchy manner. The logs calibrate a three-dimensional seismic reflection image of the decollement zone and indicate which portions are of low density and enriched in fluid, and which portions have consolidated. The seismic image demonstrates that an underconsolidated patch of the decollement zone connects to a fluid-rich conduit extending down the decollement surface. Fluid migration up this conduit probably supports the open pore structure in the underconsolidated patch.

  12. Coupled effects of director orientations and boundary conditions on light induced bending of monodomain nematic liquid crystalline polymer plates

    NASA Astrophysics Data System (ADS)

    You, Yue; Xu, Changwei; Ding, Shurong; Huo, Yongzhong

    2012-12-01

    A photo-chromic liquid crystal polymers (LCPs) is a smart material for large light-activated variation or bending to transfer luminous energy into mechanical energy. We study the light induced behavior by modeling planar and homeotropic nematic network polymer plates. We effectively illustrate some reported experimental outcomes and theoretically predict some possible bending patterns. This paper constructs an understanding between the bending behaviors and interactions among the alignments, aspect ratios and boundary conditions, etc. Our work provides information on optimizing light induced bending in the process of micro-opto-mechanical system (MOMS) design.

  13. Three-dimensional turbulent boundary layer separation at the junction of a streamlined cylinder with a flat plate

    NASA Astrophysics Data System (ADS)

    Pierce, F. J.; Harsh, M. D.

    The application of the TiO2 oil-film technique to the surface flow visualization of the pressure-driven, three-dimensional turbulent boundary layer around a streamlined circular cylinder mounted normal to a flat plate is reported. The physical parameters of the low-speed wind tunnel used in this study, the test geometry, and the conditions of similitude are described, as are the properties of the TiO2 paint and preparation of model surfaces. The visualized results are discussed in light of Maskell's (1955) concept of three-dimensional flow separation and some previous experiments made by Barber (1978).

  14. Rotating Bondi Accretion Flow

    NASA Astrophysics Data System (ADS)

    Park, Myeong-Gu; Han, Du-Hwan

    2016-06-01

    The characteristics of accretion flow onto a black hole are determined by the physical condition of gas at large radius. When the gas has no angular momentum and is polytropic, the accretion flow becomes the classic Bondi flow. The mass accretion rate in such case is an eigenvalue and uniquely determined by the density and the temperature of the surrounding gas for a given black hole mass. When the gas has angular momentum above some critical value, the angular momentum of the gas should be removed by viscosity to reach the black hole horizon. We study, within the slim disk approximation, rotating polytropic accretion flow with alpha viscosity as an an extension of the Bondi flow. The characteristics of the accretion flow are now determined by the temperature, density, and angular momentum of the gas at the outer boundary. We explore the effects of the viscosity parameter and the outer boundary radius on the physical characteristic of the flow, especially on the mass accretion rate, and compare the result with previous works of Park (2009) and Narayan & Fabian (2011).

  15. Turbulent combined-convection boundary layer with aiding flows along a heated vertical flat plate at higher freestream velocity

    NASA Astrophysics Data System (ADS)

    Abedina, Mohammad Zoynal; Islam, Mohammed Moinul; Hanif, Md. Abu; Alam, Md. Jahangir

    2016-07-01

    A numerical investigation is performed in the turbulent combined-convection boundary layer with aiding flows in air along a heated vertical flat plate at a higher freestream velocity (Reδ0 = 600) by time-developing direct numerical simulation (DNS). At higher freestream velocity, the transition from laminar to turbulent delays for aiding flows and relatively a lower and higher heat transfer rates are observed, respectively, in the laminar and turbulent region compared to that of lower freestream velocity. The wall shear stresses are higher in the laminar region compared to that in the turbulent region, and at higher freestream velocity, the wall shear stress in the transition region shows a higher peak value. The intensity of velocity and temperature fluctuations for aiding flows with higher freestream velocity become appreciably lower than that for lower freestream velocity due to the laminarization of the boundary layer.

  16. Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench

    PubMed Central

    Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yoshiyuki

    2016-01-01

    It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15–18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface. PMID:27447546

  17. Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench

    NASA Astrophysics Data System (ADS)

    Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yoshiyuki

    2016-07-01

    It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15-18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface.

  18. Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench.

    PubMed

    Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yoshiyuki

    2016-01-01

    It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15-18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface. PMID:27447546

  19. Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench.

    PubMed

    Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yoshiyuki

    2016-07-22

    It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15-18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface.

  20. Rayleigh phase velocities in the upper mantle of the Pacific-North American plate boundary in southern California

    NASA Astrophysics Data System (ADS)

    Escobar, L.; Weeraratne, D. S.; Kohler, M. D.

    2013-05-01

    The Pacific-North America plate boundary, located in Southern California, presents an opportunity to study a unique tectonic process that has been shaping the plate tectonic setting of the western North American and Mexican Pacific margin since the Miocene. This is one of the few locations where the interaction between a migrating oceanic spreading center and a subduction zone can be studied. The rapid subduction of the Farallon plate outpaced the spreading rate of the East Pacific Rise rift system causing it to be subducted beneath southern California and northern Mexico 30 Ma years ago. The details of microplate capture, reorganization, and lithospheric deformation on both the Pacific and North American side of this boundary is not well understood, but may have important implications for fault activity, stresses, and earthquake hazard analysis both onshore and offshore. We use Rayleigh waves recorded by an array of 34 ocean bottom seismometers deployed offshore southern California for a 12 month duration from August 2010 to 2011. Our array recorded teleseismic earthquakes at distances ranging from 30° to 120° with good signal-to-noise ratios for magnitudes Mw ≥ 5.9. The events exhibit good azimuthal distribution and enable us to solve simultaneously for Rayleigh wave phase velocities and azimuthal anisotropy. Fewer events occur at NE back-azimuths due to the lack of seismicity in central North America. We consider seismic periods between 18 - 90 seconds. The inversion technique considers non-great circle path propagation by representing the arriving wave field as two interfering plane waves. This takes advantage of statistical averaging of a large number of paths that travel offshore southern California and northern Mexico allowing for improved resolution and parameterization of lateral seismic velocity variations at lithospheric and sublithospheric depths. We present phase velocity results for periods sampling mantle structure down to 150 km depth along the

  1. Kinematics to dynamics in the New Zealand Plate boundary zone: implications for the strength of the lithosphere

    NASA Astrophysics Data System (ADS)

    Lamb, Simon

    2015-05-01

    New Zealand straddles the boundary between the Australian and Pacific Plate. Cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation in a zone of continental lithosphere up to 250 km wide. I investigate the implications of the short-term kinematics for the strength of the deforming lithosphere. I use a compilation of seismic reflection/refraction studies and high quality receiver function analyses to determine both the regional structure of the crust, which ranges from 20 to 50 km thick, and fields of buoyancy stress (or GPE per unit volume). Deformation over thousands of years is quantified in terms of velocity and strain rate fields, based on an inversion of neotectonic fault slip and palaeomagnetic data, in the context of the short-term relative plate motions. Forces on the subduction megathrust, as well as deviatoric stresses in the behind subduction region, are calculated from simple 2-D force balances across the Hikurangi Margin, given negligible deviatoric stresses at the along-strike transition between backarc extension and compression. Average megathrust shear stresses are in the range 6-15 MPa, and average lithospheric stresses <20 MPa in the overriding plate. The regional lithospheric strength of the plate boundary zone, assuming a viscous rheology (Newtonian or power law), is determined from an inversion of the field of gradients of buoyancy stress (averaged over either the top 25 km of the crust, or 100-km-thick lithosphere) and strain rate, using the thin sheet stress balance equations, calibrated with the subduction force balance analysis. Effective viscosities for the deforming lithosphere and/or crust are in the range 0.1-5 × 1021 Pa s, with marked weakening in zones of high strain rate, and an abrupt transition to viscosities >1022 Pa s at the margins of the rigid plates. If lateral variations in effective viscosity are only due to non-Newtonian behaviour, these data indicate a bulk power law rheology, with

  2. Anatomy of a Plate Boundary at Shallow Crustal Levels: a Composite Section from the Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Barth, N. C.; Toy, V. G.; Boulton, C. J.; Carpenter, B. M.

    2010-12-01

    New Zealand's Alpine Fault is mostly a moderately SE-dipping dextral reverse plate boundary structure, but at its southern end, strike-slip-normal motion is indicated by offset of recent surfaces, juxtaposition of sediments, and both brittle and ductile shear sense indicators. At the location of uplift polarity reversal fault rocks exhumed from both the hangingwall Pacific and footwall Australian Plates are juxtaposed, offering a remarkably complete cross section of the plate boundary at shallow crustal levels. We describe Alpine Fault damage zone and fault core structures overprinted on Pacific and Australian plate mylonites of a variety of compositions, in a fault-strike perpendicular composite section spanning the reversal in dip-slip polarity. The damage zone is asymmetric; on the Australian Plate 160m of quartzose paragneiss-derived mylonites are overprinted by brittle faults and fractures that increase in density towards the principal slip surface (PSS). This damage zone fabric consists of 1-10m-spaced, moderately to steeply-dipping, 1-20cm-thick gouge-filled faults, overprinted on and sub-parallel to a mylonitic foliation sub-parallel to the PSS. On the Pacific Plate, only 40m of the 330m section of volcaniclastic-derived mylonites have brittle damage in the form of unhealed fractures and faults, as well as a pervasive greenschist facies hydrothermal alteration absent in the footwall. These damage-related structures comprise a network of small-offset faults and fractures with increasing density and intensity towards the PSS. The active Pacific Plate fault core is composed of ~1m of cataclasite grading into folded protocataclasite that is less folded and fractured with increasing distance from the PSS. The active Australian Plate fault core is <1.5m wide and consists of 3 distinct foliated clay gouges, as well as a 4cm thick brittle ultracataclasite immediately adjacent to the active PSS. The Australian Plate foliated clay gouge contains stringers of quartz

  3. Stress Transfer Processes during Great Plate Boundary Thrusting Events: A Study from the Andaman and Nicobar Segments

    NASA Astrophysics Data System (ADS)

    Andrade, V.; Rajendran, K.

    2010-12-01

    The response of subduction zones to large earthquakes varies along their strike, both during the interseismic and post-seismic periods. The December 26, 2004 earthquake nucleated at 3° N latitude and its rupture propagated northward, along the Andaman-Sumatra subduction zone, terminating at 15°N. Rupture speed was estimated at about 2.0 km per second in the northern part under the Andaman region and 2.5 - 2.7 km per second under southern Nicobar and North Sumatra. We have examined the pre and post-2004 seismicity to understand the stress transfer processes within the subducting plate, in the Andaman (10° - 15° N ) and Nicobar (5° - 10° N) segments. The seismicity pattern in these segments shows distinctive characteristics associated with the outer rise, accretionary prism and the spreading ridge, all of which are relatively better developed in the Andaman segment. The Ninety East ridge and the Sumatra Fault System are significant tectonic features in the Nicobar segment. The pre-2004 seismicity in both these segments conform to the steady-state conditions wherein large earthquakes are fewer and compressive stresses dominate along the plate interface. Among the pre-2004 great earthquakes are the 1881 Nicobar and 1941 Andaman events. The former is considered to be a shallow thrust event that generated a small tsunami. Studies in other subduction zones suggest that large outer-rise tensional events follow great plate boundary breaking earthquakes due to the the up-dip transfer of stresses within the subducting plate. The seismicity of the Andaman segment (1977-2004) concurs with the steady-state stress conditions where earthquakes occur dominantly by thrust faulting. The post-2004 seismicity shows up-dip migration along the plate interface, with dominance of shallow normal faulting, including a few outer rise events and some deeper (> 100 km) strike-slip faulting events within the subducting plate. The September 13, 2002, Mw 6.5 thrust faulting earthquake at

  4. Late Mesozoic- Cenozoic plate boundaries in the North Atlantic – Arctic: Quantitative reconstructions using Hellinger criterion in GPlates

    NASA Astrophysics Data System (ADS)

    Gaina, Carmen; Watson, Robin; Cirbus, Juraj

    2015-04-01

    uncertainties are combined with a regional model and used to infer the plate boundaries during the formation of Labrador Sea and Baffin Bay. Challenges for establishing the continuation of these plate boundaries the Arctic domain are also discussed. References Chang, T. (1988), Estimating the relative rotation of two tectonic plates from boundary crossings, J. Am. Stat. Assoc., 83, 1178-1183. Hellinger, S. J. (1981), The uncertainties of finite rotations in plate tectonics, J Geophys Res, 86, 9312-9318. Hanna, M.S and T. Chang (1990), On graphically representing the confidence region for an unknown rotation in three dimensions. Computers & Geosciences 16 (2), 163-194. Royer, J. Y., and T. Chang (1991), Evidence for Relative Motions between the Indian and Australian Plates during the Last 20 My from Plate Tectonic Reconstructions - Implications for the Deformation of the Indo-Australian Plate, J Geophys Res, 96(B7), 11779-11802.

  5. Discovering Plate Boundaries in Data-Integrated Environments: Preservice Teachers' Conceptualization and Implementation of Scientific Practices

    ERIC Educational Resources Information Center

    Sezen-Barrie, Asli; Moore, Joel; Roig, Cara E.

    2015-01-01

    Drawn from the norms and rules of their fields, scientists use variety of practices, such as asking questions and arguing based on evidence, to engage in research that will contribute to our understanding of Earth and beyond. In this study, we explore how preservice teachers' learn to teach scientific practices while teaching plate tectonic…

  6. Negligible convergence and lithospheric tearing along the Caribbean-South American plate boundary at 64°W

    NASA Astrophysics Data System (ADS)

    Clark, S. A.; Levander, A.; Magnani, M. B.; Zelt, C. A.

    2008-12-01

    Prior studies of the Caribbean-South American plate boundary have suffered from poor constraint on the structure of the crust and uppermost mantle. We use a recent wide-angle velocity model from the Broadband Ocean-Land Investigation of Venezuela and the Antilles arc Region project to constrain new seismic reflection data and previously published line drawing interpretations of the Caribbean-South American plate boundary at 64°W. Though commonly characterized as obliquely convergent, we determine that convergence is negligible in our study area. Previous estimates of Miocene to present north-south shortening onshore eastern Venezuela have commonly been 115 km or higher, but we constrain shortening to ˜35 km onshore, with an additional ˜30 km offshore. With such minor convergence, we conclude that uplift and basin subsidence in eastern Venezuela does not derive from typical collisional orogeny. Instead, the largely vertical tectonics likely result from mantle dynamics associated with an eastward propagating, near-vertical tear in the lithosphere along the former passive margin.

  7. Crustal deformation evidences for viscous coupling and fragmented lithosphere at the Nubia-Iberia plate boundary (Western Mediterranean)

    NASA Astrophysics Data System (ADS)

    Palano, Mimmo; González, Pablo J.; Fernández, José

    2016-04-01

    A spatially dense crustal velocity field, based on up to 15 years of GNSS observations at more than 380 sites and extensively covering the Iberian Peninsula and Northern Africa, allow us to provide new insights into two main tectonic processes currently occurring in this area. We detected a slow large-scale clockwise rotation of the Iberian Peninsula with respect to a local pole located closely to the northwestern sector of the Pyrenean mountain range (Palano et al., 2015). Although this crustal deformation pattern could suggest a rigid rotating lithosphere block, this model would predict significant shortening along the Western (off-shore Lisbon) and North Iberian margin which cannot totally ruled out but currently is not clearly observed. Conversely, we favour the interpretation that this pattern reflects the quasi-continuous straining of the ductile lithosphere in some sectors of South and Western Iberia in response to viscous coupling of the NW Nubia and Iberian plate boundary in the Gulf of Cádiz. Furthermore, the western Mediterranean basin appears fragmented into independent crustal tectonic blocks, which delimited by inherited lithospheric shear structures and trapped within the Nubia-Eurasia collision, are currently accommodating most of the plate convergence rate. Among these blocks, an (oceanic-like western) Algerian one is currently transferring a significant fraction of the Nubia-Eurasia convergence rate into the Eastern Betics (SE Iberia) and likely causing the eastward motion of the Baleares Promontory. Most of the observed crustal ground deformation can be attributed to processes driven by spatially variable lithospheric plate forces imposed along the Nubia-Eurasia convergence boundary. Nevertheless, the observed deformation field infers a very low convergence rates as observed also at the eastern side of the western Mediterranean, along the Calabro Peloritan Arc, by space geodesy (e.g. Palano, 2015). References Palano M. (2015). On the present

  8. The Plate Boundary Observatory Cascadia Network: Development and Installation of a Large Scale Real-time GPS Network

    NASA Astrophysics Data System (ADS)

    Austin, K. E.; Blume, F.; Berglund, H. T.; Feaux, K.; Gallaher, W. W.; Hodgkinson, K. M.; Mattioli, G. S.; Mencin, D.

    2014-12-01

    The EarthScope Plate Boundary Observatory (PBO), through a NSF-ARRA supplement, has enhanced the geophysical infrastructure in in the Pacific Northwest by upgrading a total of 282 Plate Boundary Observatory GPS stations to allow the collection and distribution of high-rate (1 Hz), low-latency (<1 s) data streams (RT-GPS). These upgraded stations supplemented the original 100 RT-GPS stations in the PBO GPS network. The addition of the new RT-GPS sites in Cascadia should spur new volcano and earthquake research opportunities in an area of great scientific interest and high geophysical hazard. Streaming RT-GPS data will enable researchers to detect and investigate strong ground motion during large geophysical events, including a possible plate-interface earthquake, which has implications for earthquake hazard mitigation. A Mw 6.9 earthquake occurred on March 10, 2014, off the coast of northern California. As a response, UNAVCO downloaded high-rate GPS data from Plate Boundary Observatory stations within 500 km of the epicenter of the event, providing a good test of network performance.In addition to the 282 stations upgraded to real-time, 22 new meteorological instruments were added to existing PBO stations. Extensive testing of BGAN satellite communications systems has been conducted to support the Cascadia RT-GPS upgrades and the installation of three BGAN satellite fail over systems along the Cascadia margin will allow for the continuation of data flow in the event of a loss of primary communications during in a large geophysical event or other interruptions in commercial cellular networks. In summary, with these additional upgrades in the Cascadia region, the PBO RT-GPS network will increase to 420 stations. Upgrades to the UNAVCO data infrastructure included evaluation and purchase of the Trimble Pivot Platform, servers, and additional hardware for archiving the high rate data, as well as testing and implementation of GLONASS and Trimble RTX positioning on the

  9. Hydromagnetic natural convection flow between vertical parallel plates with time-periodic boundary conditions

    NASA Astrophysics Data System (ADS)

    Adesanya, S. O.; Oluwadare, E. O.; Falade, J. A.; Makinde, O. D.

    2015-12-01

    In this paper, the free convective flow of magnetohydrodynamic fluid through a channel with time periodic boundary condition is investigated by taking the effects of Joule dissipation into consideration. Based on simplifying assumptions, the coupled governing equations are reduced to a set of nonlinear boundary valued problem. Approximate solutions are obtained by using semi-analytical Adomian decomposition method. The effect of pertinent parameters on the fluid velocity, temperature distribution, Nusselt number and skin friction are presented graphically and discussed. The result of the computation shows that an increase in the magnetic field intensity has significant influence on the fluid flow.

  10. Experiments of dike-induced deformation: Insights on the long-term evolution of divergent plate boundaries

    NASA Astrophysics Data System (ADS)

    Trippanera, D.; Ruch, J.; Acocella, V.; Rivalta, E.

    2015-10-01

    The shallow transport of magma occurs through dikes causing surface deformation. Our understanding of the effects of diking at the surface is limited, especially on the long term, for repeated intrusive episodes. We use analogue models to study the upper crustal deformation induced by dikes. We insert metal plates within cohesive sand with three setups: in setup A, the intrusion rises upward with constant thickness and in setups B and C, the intrusion thickens at a fixed depth, with final rectangular (setup B) or triangular (setup C) shape in section. Setup A creates a doming delimited by reverse faults, with secondary apical graben, without close correspondence in nature. In setups B and C, a depression flanked by two uplifted areas is bordered by inward dipping normal faults propagating downward and, for deeper intrusions in setup B, also by inner faults, reverse at the surface; this deformation is similar to what is observed in nature, suggesting a consistent physical behavior. Dikes in nature initially propagate developing a mode I fracture at the tip, subsequently thickened by magma intrusion, without any host rock translation in the propagation direction (as in setup A). The deformation pattern in setups B and C depends on the intrusion depth and thickness, consistently to what is observed along divergent plate boundaries. The early deformation in setups B and C is similar to that from a single rifting episode (i.e., Lakagigar, Iceland, and Dabbahu, Afar), whereas the late stages resemble the structure of mature rifts (i.e., Krafla, Iceland), confirming diking as a major process in shaping divergent plate boundaries.

  11. The Role of Hox in Pisiform and Calcaneus Growth Plate Formation and the Nature of the Zeugopod/Autopod Boundary.

    PubMed

    Reno, Philip L; Kjosness, Kelsey M; Hines, Jasmine E

    2016-07-01

    The mesopodium forms at the boundary between the zeugopod and autopod and is composed of short nodular bones that typically lack growth plates. Hoxa11 and Hoxa13 are expressed in mutually exclusive proximal-distal domains that demarcate the zeugopod/autopod boundary. Similarly, Hoxd genes are deployed in two distinct phases during limb development. The early phase corresponds to proximal segments including the zeugopod, and a late phase occurs in the digits. This arrangement produces a gap of low Hoxd expression that is traditionally viewed to correspond to the mesopodium. In contrast to the other mesopodials, the mammalian pisiform and calcaneus form true growth plates. We show that these bones, along with other proximal mesopodials, develop within the Hoxa11 and Hoxd11 expression domains. We also observe that the pisiform growth plate becomes disorganized with Hoxa11 or Hoxd11 loss of function, indicating a direct role for Hox11 in its development. Hoxa13 loss of function has minimal effect on the pisiform and proximal calcaneus as these bones still form secondary centers and undergo longitudinal growth. Consideration of the phenotypes resulting from hypodactyly (Hd) and synpolydactyly homolog (spdh) mutations, which result from altered HOXA13 and HOXD13 proteins, respectively, confirms that Hox13 plays a limited role in the development of the pisiform and calcaneus and suggests that they lie within the early phase of Hox expression. Therefore, with respect to patterns of ossification and gene expression, these bones share much more in common with the zeugopod than the autopod. Such an interpretation fits with the timing of autopod origins during tetrapod evolution.

  12. The Turbulent Boundary Layer Near the Air-Water Interface on a Surface-Piercing Flat Plate

    NASA Astrophysics Data System (ADS)

    Washuta, Nathan; Masnadi, Naeem; Duncan, James H.

    2015-11-01

    Turbulent fluctuations in the vicinity of the water free surface along a flat, vertically oriented surface-piercing plate are studied experimentally using a laboratory-scale experiment. In this experiment, a meter-wide stainless steel belt travels horizontally in a loop around two rollers with vertically oriented axes, which are separated by 7.5 meters. This belt device is mounted inside a large water tank with the water level set just below the top edge of the belt. The belt, rollers, and supporting frame are contained within a sheet metal box to keep the device dry except for one 6-meter-long straight test section between rollers. The belt is launched from rest with a 3- g acceleration in order to quickly reach steady state velocity. This creates a temporally evolving boundary layer analogous to the spatially evolving boundary layer created along a flat-sided ship moving at the same velocity, with a length equivalent to the length of belt that has passed the measurement region since the belt motion began. Cinematic Stereo PIV measurements are performed in planes parallel to the free surface by imaging the flow from underneath the tank in order to study the modification of the boundary layer flow field due to the effects of the water free surface. The support of the Office of Naval Research under grant N000141110029 is gratefully acknowledged.

  13. Turbulent Friction in the Boundary Layer of a Flat Plate in a Two-Dimensional Compressible Flow at High Speeds

    NASA Technical Reports Server (NTRS)

    Frankl, F.; Voishel, V.

    1943-01-01

    In the present report an investigation is made on a flat plate in a two-dimensional compressible flow of the effect of compressibility and heating on the turbulent frictional drag coefficient in the boundary layer of an airfoil or wing radiator. The analysis is based on the Prandtl-Karman theory of the turbulent boundary later and the Stodola-Crocco, theorem on the linear relation between the total energy of the flow and its velocity. Formulas are obtained for the velocity distribution and the frictional drag law in a turbulent boundary later with the compressibility effect and heat transfer taken into account. It is found that with increase of compressibility and temperature at full retardation of the flow (the temperature when the velocity of the flow at a given point is reduced to zero in case of an adiabatic process in the gas) at a constant R (sub x), the frictional drag coefficient C (sub f) decreased, both of these factors acting in the same sense.

  14. Preponderance of hairpin vortices and their life cycles in the outer region of the canonical flat-plate boundary layer

    NASA Astrophysics Data System (ADS)

    Wallace, James; Wu, Xiaohua

    2015-11-01

    While the dominance of hairpin vortices in the transitional and early turbulent regions of the zero-pressure-gradient, flat-plate boundary layer has been widely accepted, recent literature is divided on this issue at higher Reynolds numbers. Here we investigate the representative vortex structures in the outer region of the canonical boundary layer over the momentum thickness Reynolds number range of 1000 to 3000, using the DNS database of Wu, Moin and Hickey (Phys. Fluids 26, 091104). In the outer region of the boundary layer we observe that hairpin vortices comprise nearly fifty percent of all the vortical structures visualized with the swirling strength λci. Furthermore, these hairpins remain identifiable while they are advected downstream over distances corresponding to increases of about 300 - 400 in momentum thickness Reynolds numbers. Therefore, over the Reynolds number range studied, approximately three generations of hairpins go through their life cycles. This demonstrates that many of these outer region hairpin vortices are generated in the fully-turbulent region, and thus are not the debris of the upstream transition to turbulence. Coherent structures in the near-wall region will also be discussed.

  15. "Discovering Plate Boundaries in Data-Rich Environments": Supporting Pre-service Teachers involvement in Unique Practices of Geosciences

    NASA Astrophysics Data System (ADS)

    Barrie, A. S.; Moore, J.

    2012-12-01

    plate tectonics using key scientific practices. As a result of the educational activities developed in this project, we will try help teachers to overcome their challenges and develop the pedagogical skills that novice teachers need to use to teach plate tectonics by focusing on key scientific practices with the help of previously-developed educational resources. Learning about the processes that occur at plate boundaries will help future teachers (and their students) understand natural disasters such as earthquakes and volcanoes. Furthermore, the study will have a significant, and broader, impact by 'teaching the teachers' and empowering novice teachers to overcome the challenges of reading maps and using argumentation in science classrooms.

  16. Water Release from Cold Serpentinized Forearc Mantle During Subduction Associated with Changes in Incoming Oceanic Plate Thermal Structure and Plate Boundary Kinematics: New Insights

    NASA Astrophysics Data System (ADS)

    Kirby, S. H.

    2015-12-01

    Kirby, Wang, and Brocher (Earth Planets and Space, 2014) recently showed how the change in kinematics of the California margin from subduction motion to continental transform motion with the birth and growth of the San Andreas Fault System (SAFS) beginning at about 33 Ma BP likely led to a warming of the former forearc mantle and the release of water by serpentinite dehydration. Such discharges from serpentinized mantle increase fluid pressures along the SAFS under the Coast Ranges and this gives insights into both the low sliding resistance for the SAFS and the mobilization and ascent of some serpentinized mantle peridotites through the crust. Thermal modeling by others has also shown that changes in the incoming plate age and subduction rate can also lead to warming of the forearc mantle during subduction. This development gives insights into the Mesozoic and Paleogene ages of emplacement of some, but not all, California serpentinites. Recent mineralogical and geochemical observations of serpentinized blocks in serpentinize mélange bodies in the San Francisco Bay Area (Uno and Kirby, 2015; Lewis and Kirby, 2015, this session) suggest that these rocks sustained multiple stages of serpentinization that are broadly consistent with the model of Kirby et al. (2014). Previous studies of localized late-stage silica-carbonate-water alteration of serpentinite bodies in California by carbonated water suggest that this alteration occurred largely in Neogene time when the highest rate of water release from the former forearc mantle probably happened. I also suggest that the occurrence of serpentinite belts emplaced in Cenozoic time during changing plate-boundary kinematics, such as the Cenozoic closing of the Tethys Ocean bordering Eurasia and arc reversal and decreasing convergence rates under the Greater Antilles, may give insights into the serpentinite belts in those regions.

  17. To accrete or not accrete, that is the question

    USGS Publications Warehouse

    von, Huene R.

    1986-01-01

    Along modern convergent margins tectonic processes span a spectrum from accretion to erosion. The process of accretion is generally recognized because it leaves a geologic record, whereas the process of erosion is generally hypothetical because it produces a geologic hiatus. Major conditions that determine the dominance of accretion or erosion at modern convergent margins are: 1) rate and direction of plate convergence, 2) sediment supply and type in the trench, and 3) topography of the subducting ocean floor. Most change in structure has been ascribed to plate motion, but both erosion and accretion are observed along the same convergence margin. Thus sediment supply and topography are probably of equivalent importance to plate motion because both erosion and accretion are observed under constant conditions of plate convergence. The dominance of accretion or erosion at a margin varies with the thickness of trench sediment. In a sediment flooded trench, the proportions of subducted and accreted sediment are commonly established by the position of a decollement along a weak horizon in the sediment section. Thus, the vertical variation of sediment strength and the distribution of horizontal stress are important factors. Once deformation begins, the original sediment strength is decreased by sediment remolding and where sediment thickens rapidly, increases in pore fluid pressure can be pronounced. In sediment-starved trenches, where the relief of the subducting ocean floor is not smoothed over, the front of the margin must respond to the topography subducted as well as that accreted. The hypothesized erosion by the drag of positive features against the underside of the upper plate (a high stress environment) may alternate with erosion due to the collapse of a margin front into voids such as graben (a low stress environment). ?? 1986 Ferdinand Enke Verlag Stuttgart.

  18. Hypersonic Laminar Boundary Layer Velocimetry with Discrete Roughness on a Flat Plate

    NASA Technical Reports Server (NTRS)

    Bathel, Brett; Danehy, Paul M.; Inman, Jennifer A.; Watkins, A. Neal; Jones, Stephen B.; Lipford, William E.; Goodman, Kyle Z.; Ivey, Christopher B.; Goyne, Christopher P.

    2010-01-01

    Laminar boundary layer velocity measurements are made on a 10-degree half-angle wedge in a Mach 10 flow. Two types of discrete boundary layer trips were used to perturb the boundary layer gas. The first was a 2-mm tall, 4-mm diameter cylindrical trip. The second was a scaled version of the Orbiter Boundary Layer Transition (BLT) Detailed Test Objective (DTO) trip. Both 1-mm and 2.5-mm tall BLT DTO trips were tested. Additionally, side-view and plan-view axial boundary layer velocity measurements were made in the absence of these tripping devices. The free-stream unit Reynolds numbers tested for the cylindrical trips were 1.7x10(exp 6)/m and 3.3x10(exp 6)/m. The free-stream unit Reynolds number tested for the BLT DTO trips was 1.7x10(exp 6)/m. The angle of attack was kept at approximately 5-degrees for most of the tests resulting in a Mach number of approximately 8.3. These combinations of unit Reynolds numbers and angle of attack resulted in laminar flowfields. To study the precision of the measurement technique, the angle of attack was varied during one run. Nitric-oxide (NO) molecular tagging velocimetry (MTV) was used to obtain averaged axial velocity values and associated uncertainties. These uncertainties are as low as 20 m/s. An interline, progressive scan CCD camera was used to obtain separate images of the initial reference and shifted NO molecules that had been tagged by the laser. The CCD configuration allowed for sub-microsecond sequential acquisition of both images. The maximum planar spatial resolution achieved for the side-view velocity measurements was 0.07-mm in the wall-normal direction by 1.45-mm in the streamwise direction with a spatial depth of 0.5-mm. For the plan-view measurements, the maximum planar spatial resolution in the spanwise and streamwise directions was 0.69-mm by 1.28-mm, respectively, with a spatial depth of 0.5-mm. Temperature sensitive paint (TSP) measurements are provided to compliment the velocity data and to provide further

  19. Dynamics of the Pacific-North American Plate Boundary in the Western United States

    NASA Astrophysics Data System (ADS)

    Flesch, Lucy M.; Holt, William E.; Haines, A. John; Shen-Tu, Bingming

    2000-02-01

    The vertically averaged deviatoric stress tensor field within the western United States was determined with topographic data, geoid data, recent global positioning system observations, and strain rate magnitudes and styles from Quaternary faults. Gravitational potential energy differences control the large fault-normal compression on the California coast. Deformation in the Basin and Range is driven, in part, by gravitational potential energy differences, but extension directions there are modified by plate interaction stresses. The California shear zone has relatively low vertically averaged viscosity of about 1021 pascal.seconds, whereas the Basin and Range has a higher vertically averaged viscosity of 1022 pascal.seconds.

  20. Dynamics of the pacific-north american plate boundary in the western united states

    PubMed

    Flesch; Holt; Haines; Shen-Tu

    2000-02-01

    The vertically averaged deviatoric stress tensor field within the western United States was determined with topographic data, geoid data, recent global positioning system observations, and strain rate magnitudes and styles from Quaternary faults. Gravitational potential energy differences control the large fault-normal compression on the California coast. Deformation in the Basin and Range is driven, in part, by gravitational potential energy differences, but extension directions there are modified by plate interaction stresses. The California shear zone has relatively low vertically averaged viscosity of about 10(21) pascal.seconds, whereas the Basin and Range has a higher vertically averaged viscosity of 10(22) pascal.seconds. PMID:10657292

  1. Paleoseismic and Geomorphic Evidence for Quaternary Fault Slip on the Central Range Fault, South American-Caribbean Plate Boundary, Trinidad

    NASA Astrophysics Data System (ADS)

    Prentice, C. S.; Weber, J.; Crosby, C. J.

    2001-12-01

    The island of Trinidad is located along the transform plate boundary between the South American and Caribbean plates. GPS measurements show that relative motion along this boundary is nearly E-W right-lateral shear (Weber et al., 2001). Analysis and comparison of historic triangulation and GPS data suggest that a significant fraction (14+/-3 mm/yr) of the total plate-boundary motion (about 20 mm/yr) is being accommodated across the Central Range Fault in central Trinidad. Our new paleoseismic studies demonstrate that Quaternary surface rupture has occurred on this previously unrecognized, historically aseismic, active fault. Geomorphic evidence of Quaternary faulting along the Central Range Fault includes linear drainages, aligned topographic saddles and troughs, offset ridges, right-laterally deflected streams, and linear scarps. We mapped these features using 1:20,000 scale aerial photographs and field reconnaissance along a 25-km-long section between Pointe-a-Pierre on the west coast and Navet Dam. Geomorphic features near Manzanilla Bay on the east coast suggest that the Central Range Fault continues across the island as a Quaternary feature for another 25 km to the northeast. Marine geophysical surveys suggest this fault continues offshore to the west (Warm Springs fault), and steps to the north across the Gulf of Paria pull-apart basin to the El Pilar Fault. The extent of the fault offshore to the east is unknown. We exposed a 6-m-wide shear zone within Pliocene(?) material in a trench cut into a fluvial terrace, south of Samlalsingh Road near Bonne Aventure. The overlying Quaternary fluvial gravel is faulted and folded across the shear zone, and Quaternary fluvial deposits are faulted against the shear zone on the north side. A second excavation across a prominent scarp near Tabaquite, 12 km northeast of Samlalsingh Road, exposed a colluvial wedge and overlying unfaulted sediments. We interpret the colluvial wedge to represent deposits shed off the scarp in

  2. Transients in Pacific/North American Plate Boundary Deformation: Synthesis and Modeling of GPS and Borehole Strain Observations

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.; Frey, H. V. (Technical Monitor)

    2002-01-01

    This is the Final Technical Report on research conducted between 1 June 1997 and 14 September 2001 entitled "Transients in Pacific/North American plate boundary deformation: Synthesis and modeling of GPS and borehole strain observations." As the project title implies, our effort involved a geodetic study of strain transients, i.e., temporal variations in deformation rates, that occur within plate boundary zones and their relationship to earthquakes and plate motions. Important transients occur during and following large earthquakes, and there are also strain transients not apparently associated with earthquakes. A particularly intriguing class of transients, for which there is a modest but growing list of examples, are preseismic anomalies. Such earthquake precursors, if further documented and understood, would have obvious importance for earthquake hazard mitigation. Because the timescales for these diverse transients range over at least 6 orders of magnitude (minutes to years), no single geodetic technique is optimum. We therefore undertook a systematic synthesis of Global Positioning Satellite (GPS) and borehole strainmeter data in three areas in California where there are adequate numbers of both types of instruments (or their equivalent): the San Francisco Bay region (within the Bay Area Regional Deformation network), southern California (within the Southern California Integrated GPS Network), and Parkfield (where a two-color laser system provides a proxy for continuous GPS measurements). An integral component of our study was the elucidation of the physical mechanisms by which such transients occur and propagate. We therefore initiated the development of multiple forward models, using two independent approaches. In the first, we explored the response to specified earthquake slip in viscoelastic models that incorporated failure criteria and the geometry of major faults in California. In the second approach, we examined the dynamical response of a complex

  3. A 2-D tomographic model of the Juan de Fuca plate from accretion at axial seamount to subduction at the Cascadia margin from an active source ocean bottom seismometer survey

    NASA Astrophysics Data System (ADS)

    Horning, G.; Canales, J. P.; Carbotte, S. M.; Han, S.; Carton, H.; Nedimović, M. R.; Keken, P. E.

    2016-08-01

    We report results from a wide-angle controlled source seismic experiment across the Juan de Fuca plate designed to investigate the evolution of the plate from accretion at the Juan de Fuca ridge to subduction at the Cascadia margin. A two-dimensional velocity model of the crust and upper mantle is derived from a joint reflection-refraction traveltime inversion. To interpret our tomography results, we first generate a plausible baseline velocity model, assuming a plate cooling model and realistic oceanic lithologies. We then use an effective medium theory to infer from our tomography results the extent of porosity, alteration, and water content that would be required to explain the departure from the baseline model. In crust of ages >1 Ma and away from propagator wakes and regions of faulting due to plate bending, we obtain estimates of upper crustal hydration of 0.5-2.1 wt % and find mostly dry lower crust and upper mantle. In sections of the crust affected by propagator wakes we find upper estimates of upper crustal, lower crustal, and upper mantle hydration of 3.1, 0.8, and 1.8 wt %, respectively. At the Cascadia deformation front, we find that the amount of water stored at uppermost mantle levels in the downgoing JdF plate is very limited (<0.3 wt %), with most of the water carried into the subduction zone being stored in the oceanic crust.

  4. Do fluids control locking and seismic slip on the subduction fault? - evidence from the Chilean plate boundary

    NASA Astrophysics Data System (ADS)

    Oncken, Onno; Moreno, Marcos; Haberland, Christian; Rietbrock, Andreas; Angiboust, Samuel; Bedford, Jon

    2014-05-01

    A number of recent studies have suggested that the interseismic locking degree inverted from geodetic data at convergent plate boundaries may be closely related to slip distribution of subsequent megathrust earthquakes as found recently for the Maule 2010 and Tohoku 2011 earthquakes. The physical nature of locking, however, remains a matter of debate. We explore seismic, seismological and geodetic data collected from the southern part of the Maule 2010 earthquake rupture zone - overlapping with the northern termination of the Valdivia 1960 earthquake - in the decade before the event to identify the spatial variability of pore fluid pressure and effective stress along the plate interface zone. The reflection seismic and the seismological data exhibit well defined changes of reflectivity and Vp/Vs ratio along the plate interface that can be correlated with different parts of the coupling zone as well as with changes during the seismic cycle. High Vp/Vs domains, interpreted as zones of elevated pore fluid pressure, spatially correlate with lower locking degree, and exhibit higher background seismicity as expected for partly creeping domains. In turn, unstable slip associated to a higher degree of locking is promoted in lower pore fluid pressure domains. This relationship is particularly well expressed in the upper two thirds of the seismic coupling zone down to a depth of some 25 km at an estimated 250°C. In the gradient zone towards deeper domains locking gradually decreases to very low values, and the elevated Vp/Vs-ratio returns to standard values. At the same time seismic reflectivity remains high to some 35 km and then disappears with only minor S-wave reflectivity persisting down to the zone of intermediate depth seismicity at some 60 km depth that is again highlighted by bright reflections. This transition zone, at temperatures > 250°C is also largely coincident with aftershock clusters and a concentration of geodetically recorded afterslip following the

  5. Wide-angle seismic constraints on the evolution of the deep San Andreas plate boundary by Mendocino triple junction migration

    USGS Publications Warehouse

    Hole, J.A.; Beaudoin, B.C.; Henstock, T.J.

    1998-01-01

    Recent wide-angle seismic observations that constrain the existence and structure of a mafic layer in the lower crust place strong constraints on the evolution of the San Andreas plate boundary system in northern and central California. Northward migration of the Mendocino Triple Junction and the subducted Juan de Fuca lithospheric slab creates a gap under the continent in the new strike-slip system. This gap must be filled by either asthenospheric upwelling or a northward migrating slab attached to the Pacific plate. Both processes emplace a mafic layer, either magmatic underplating or oceanic crust, beneath the California Coast Ranges. A slab of oceanic lithosphere attached to the Pacific plate is inconsistent with the seismic observation that the strike-slip faults cut through the mafic layer to the mantle, detaching the layer from the Pacific plate. The layer could only be attached to the Pacific plate if large vertical offsets and other complex structures observed beneath several strike-slip faults are original oceanic structures that are not caused by the faults. Otherwise, if oceanic slabs exist beneath California, they do not migrate north to fill the growing slab gap. The extreme heat pulse created by asthenospheric upwelling is inconsistent with several constraints from the seismic data, including a shallower depth to the slab gap than is predicted by heat flow models, seismic velocity and structure that are inconsistent with melting or metamorphism of the overlying silicic crust, and a high seismic velocity in the upper mantle. Yet either the Pacific slab model or the asthenospheric upwelling model must be correct. While the mafic material in the lower crust could have been emplaced prior to triple junction migration, the deeper slab gap must still be filled. A preexisting mafic layer does not reduce the inconsistencies of the Pacific slab model. Such material could, however, compensate for the decrease in mafic magma that would be produced if

  6. Double diffusive magnetohydrodynamic (MHD) mixed convective slip flow along a radiating moving vertical flat plate with convective boundary condition.

    PubMed

    Rashidi, Mohammad M; Kavyani, Neda; Abelman, Shirley; Uddin, Mohammed J; Freidoonimehr, Navid

    2014-01-01

    In this study combined heat and mass transfer by mixed convective flow along a moving vertical flat plate with hydrodynamic slip and thermal convective boundary condition is investigated. Using similarity variables, the governing nonlinear partial differential equations are converted into a system of coupled nonlinear ordinary differential equations. The transformed equations are then solved using a semi-numerical/analytical method called the differential transform method and results are compared with numerical results. Close agreement is found between the present method and the numerical method. Effects of the controlling parameters, including convective heat transfer, magnetic field, buoyancy ratio, hydrodynamic slip, mixed convective, Prandtl number and Schmidt number are investigated on the dimensionless velocity, temperature and concentration profiles. In addition effects of different parameters on the skin friction factor, [Formula: see text], local Nusselt number, [Formula: see text], and local Sherwood number [Formula: see text] are shown and explained through tables.

  7. Double Diffusive Magnetohydrodynamic (MHD) Mixed Convective Slip Flow along a Radiating Moving Vertical Flat Plate with Convective Boundary Condition

    PubMed Central

    Rashidi, Mohammad M.; Kavyani, Neda; Abelman, Shirley; Uddin, Mohammed J.; Freidoonimehr, Navid

    2014-01-01

    In this study combined heat and mass transfer by mixed convective flow along a moving vertical flat plate with hydrodynamic slip and thermal convective boundary condition is investigated. Using similarity variables, the governing nonlinear partial differential equations are converted into a system of coupled nonlinear ordinary differential equations. The transformed equations are then solved using a semi-numerical/analytical method called the differential transform method and results are compared with numerical results. Close agreement is found between the present method and the numerical method. Effects of the controlling parameters, including convective heat transfer, magnetic field, buoyancy ratio, hydrodynamic slip, mixed convective, Prandtl number and Schmidt number are investigated on the dimensionless velocity, temperature and concentration profiles. In addition effects of different parameters on the skin friction factor, , local Nusselt number, , and local Sherwood number are shown and explained through tables. PMID:25343360

  8. Fluctuating pressures measured beneath a high-temperature, turbulent boundary layer on a flat plate at Mach number of 5

    NASA Technical Reports Server (NTRS)

    Parrott, Tony L.; Jones, Michael G.; Albertson, Cindy W.

    1989-01-01

    Fluctuating pressures were measured beneath a Mach 5, turbulent boundary layer on a flat plate with an array of piezoresistive sensors. The data were obtained with a digital signal acquisition system during a test run of 4 seconds. Data sampling rate was such that frequency analysis up to 62.5 kHz could be performed. To assess in situ frequency response of the sensors, a specially designed waveguide calibration system was employed to measure transfer functions of all sensors and related instrumentation. Pressure time histories were approximated well by a Gaussian prohibiting distribution. Pressure spectra were very repeatable over the array span of 76 mm. Total rms pressures ranged from 0.0017 to 0.0046 of the freestream dynamic pressure. Streamwise, space-time correlations exhibited expected decaying behavior of a turbulence generated pressure field. Average convection speed was 0.87 of freestream velocity. The trendless behavior with sensor separation indicated possible systematic errors.

  9. Heat exchange in boundary layer on permeable plate at injection and combustion

    NASA Astrophysics Data System (ADS)

    Lukashov, V. V.; Terekhov, V. V.; Hanjalič, K.

    2014-12-01

    The peculiarities of the heat and mass exchange in a laminar boundary layer with combustion at the injection of the fuel mixture H2/N2 through the permeable surface are considered. It is shown that at a certain value of the injection parameter, the value of the heat flux into the wall averaged over the length has a maximum. An analytic estimate is proposed for determining the maximum heat flux at the combustion depending on the injection intensity. The obtained relations agree with the results of experimental studies and numerical modelling.

  10. Heat exchange in boundary layer on permeable plate at injection and combustion

    NASA Astrophysics Data System (ADS)

    Lukashov, V. V.; Terekhov, V. V.; Hanjalič, K.

    2013-12-01

    The peculiarities of the heat and mass exchange in a laminar boundary layer with combustion at the injection of the fuel mixture H2/N2 through the permeable surface are considered. It is shown that at a certain value of the injection parameter, the value of the heat flux into the wall averaged over the length has a maximum. An analytic estimate is proposed for determining the maximum heat flux at the combustion depending on the injection intensity. The obtained relations agree with the results of experimental studies and numerical modelling.

  11. Interior Baja B.C. : Continuing Rotation on a Diffuse Plate Boundary

    NASA Astrophysics Data System (ADS)

    Symons, D. T.; Harris, M. J.; McCausland, P. J.; Blackburn, W. H.; Hart, C. J.

    2004-12-01

    Interior Baja B.C. - the Intermontane Belt (IMB) and Yukon-Tanana (YT) terranes of northwestern North America - provide a geological record of the complex interactions between the northeastern Pacific basin plates and craton. Geophysical evidence from earthquake seismology, gravity, global positioning system and heat flow data indicate motion of the IMB terranes toward the craton today. Paleomagnetic data show the YT terrane to be parautochthonous and part of the craton's ramp onto which the IMB terranes were obducted. Conversely the IMB terranes behaved as an allochthonous reasonably-coherent microplate with its own apparent polar wander path. Relative to the craton, the path dictates that: 1) from 0-54 Ma the IMB rotated steadily on the craton's ramp at 0.29±±0.11° /Ma or 16±6° clockwise (CW), consistent with Lithoprobe SNORCLE deep crustal seismic evidence for thin skinned tectonics; 2) from 54 to 102±14 Ma the IMB was offshore and was further rotated by 35±14° CW and translated northward by 8.3±7.0° (915±75 km), consistent with geological estimates for total dextral fault displacement and seafloor plate vectors; and 3) more speculatively, from Early Cretaceous to Early Jurassic, the IMB moved in concert with the craton off the western USA seaboard. This history fits with major geologic events such as extensive Eocene extension in southern British Columbia, development of the 1000 km-long Selwyn-Mackenzie orogenic arc in Yukon, YT terrane exposure on either side of the IMB, etc. Further it requires continuing crust-mantle interactions that extend some hundreds of kilometers into the craton today.

  12. Discovering Plate Boundaries in Data-integrated Environments: Preservice Teachers' Conceptualization and Implementation of Scientific Practices

    NASA Astrophysics Data System (ADS)

    Sezen-Barrie, Asli; Moore, Joel; Roig, Cara E.

    2015-08-01

    Drawn from the norms and rules of their fields, scientists use variety of practices, such as asking questions and arguing based on evidence, to engage in research that will contribute to our understanding of Earth and beyond. In this study, we explore how preservice teachers' learn to teach scientific practices while teaching plate tectonic theory. In particular, our aim is to observe which scientific practices preservice teachers use while teaching an earth science unit, how do they integrate these practices into their lessons, and what challenges do they face during their first time teaching of an earth science content area integrated with scientific practices. The study is designed as a qualitative, exploratory case study of seven preservice teachers while they were learning to teach plate tectonic theory to a group of middle school students. The data were driven from the video records and artifacts of the preservice teachers' learning and teaching processes as well as written reflections on the teaching. Intertextual discourse analysis was used to understand what scientific practices preservice teachers choose to integrate into their teaching experience. Our results showed that preservice teachers chose to focus on four aspects of scientific practices: (1) employing historical understanding of how the theory emerged, (2) encouraging the use of evidence to build up a theory, (3) observation and interpretation of data maps, and (4) collaborative practices in making up the theory. For each of these practices, we also looked at the common challenges faced by preservice teachers by using constant comparative analysis. We observed the practices that preservice teachers decided to use and the challenges they faced, which were determined by what might have come as in their personal history as learners. Therefore, in order to strengthen preservice teachers' background, college courses should be arranged to teach important scientific ideas through scientific practices

  13. Symmetry-based theory for mean velocities in the flat plate turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Chen, Xi; Hussain, Fazle; She, Zhen-Su

    2014-11-01

    A major difference from channel and pipe flow in zero-pressure-gradient turbulent boundary layer -ZPG-TBL is the streamwise development of the mean velocity components. We report a symmetry-based theory for ZPG-TBL, which yields a complete prediction for both the streamwise and vertical mean velocities, i.e. U (x , y) and V (x , y) . A significant result is the identification of a bulk flow constantκb, which achieves a highly accurate description of U above y + ~ 150; for a set of DNS data (Schlatter et al. 2010); the relative error is bounded within 0.1%. It is found that κb has a non-trivial streamwise development, and asymptote to 0.45 for large Re's the latter is consistent with the true Karman constant recently discovered for channel and pipe flows. The theory assumes a fractional scaling for the total stress, which yields, for the first time, an analytical prediction for V, Reynolds stress profile, friction coefficient and shape factor in ZPG-TBL, in good agreement with both DNS and experimental data. In conclusion, a complete analytical theory is viable for both laminar (i.e. Blasius) and turbulent boundary layers.

  14. Intrinsic ledges at interphase boundaries and the crystallography of precipitate plates

    SciTech Connect

    Mou, Y. . Dept. of Materials Science and Engineering)

    1994-09-01

    The structure of intrinsic ledges at interphase boundaries has been interpreted with extended O-lattice/DSC-lattice approaches. The distribution of structural ledges can be predicted if the spacing difference between parallel matrix and product planes is treated as a measure of the relaxed coincidence condition. A small rotation away from the low-index planar parallelism introduces a series of interfacial dislocations that cancels the spacing difference, resulting in a lattice invariant line. Misfit-compensating ledges at bcc:hcp interfaces are produced as a ledged interface intersects additional O-points that are recognized with the incorporation of previously omitted bcc atom positions into the O-lattice construction. Energetic consideration suggests that structural interfacial energy may decrease when a flat interface becomes ledged with misfit-compensating ledges. Burgers vectors associated with structural ledges and misfit-compensating ledges are displacement shift complete (DSC) lattice vectors. Precipitate and martensite crystallography may both include a lattice invariant line, but they are involved in different interphase boundary characteristics. Assumptions and implications in precipitate and martensite crystallography are discussed in the framework of the O-lattice theory and phenomenological theory of martensite crystallography.

  15. Most-Critical Transient Disturbances in an Incompressible Flat-Plate Boundary Layer

    NASA Astrophysics Data System (ADS)

    Monschke, Jason; White, Edward

    2015-11-01

    Transient growth is a linear disturbance growth mechanism that plays a key role in roughness-induced boundary-layer transition. It occurs when superposed stable, non-orthogonal continuous spectrum modes experience algebraic disturbance growth followed by exponential decay. Algebraic disturbance growth can modify the basic state making it susceptible to secondary instabilities rapidly leading to transition. Optimal disturbance theory was developed to model the most-dangerous disturbances. However, evidence suggests roughness-induced transient growth is sub-optimal yet leads to transition earlier than optimal theory suggests. This research computes initial disturbances most unstable to secondary instabilities to further develop the applicability of transient growth theory to surface roughness. The main approach is using nonlinear adjoint optimization with solutions of the parabolized Navier-Stokes and BiGlobal stability equations. Two objective functions were considered: disturbance kinetic energy growth and sinuous instability growth rate. The first objective function was used as validation of the optimization method. Counter-rotating streamwise vortices located low in the boundary layer maximize the sinuous instability growth rate. The authors would like to acknowledge NASA and the AFOSR for funding this work through AFOSR Grant FA9550-09-1-0341.

  16. Multiple major faults at the Japan Trench: Chemostratigraphy of the plate boundary at IODP Exp. 343: JFAST

    NASA Astrophysics Data System (ADS)

    Rabinowitz, Hannah S.; Savage, Heather M.; Plank, Terry; Polissar, Pratigya J.; Kirkpatrick, James D.; Rowe, Christie D.

    2015-08-01

    We determine the trace element stratigraphy of Site C0019, drilled during the Japan Fast Trench Drilling Project (JFAST) International Ocean Discovery Program (IODP) Expedition 343, to illuminate the structure of the plate boundary following the Tohoku-Oki earthquake of 2011. The stratigraphic units at the JFAST site are compared to undeformed Western Pacific sediments from two reference sites (Ocean Drilling Program (ODP) Site 1149 and Deep Sea Drilling Project (DSDP) Site 436). The trace element fingerprints in these reference sedimentary units can be correlated to individual JFAST samples. At the JFAST site, we find that the accretionary wedge and downgoing plate sediments in the core are composed primarily of Holocene to Eocene sediments. There are several age reversals and gaps within the sequence, consistent with multiple faults in the bottom 15 m of the JFAST core. Our results point to several candidate faults that could have slipped during the 2011 Tohoku-Oki earthquake, in addition to the pelagic clay layer that has been proposed as the main décollement fault.

  17. Plate motion

    SciTech Connect

    Gordon, R.G. )

    1991-01-01

    The motion of tectonic plates on the earth is characterized in a critical review of U.S. research from the period 1987-1990. Topics addressed include the NUVEL-1 global model of current plate motions, diffuse plate boundaries and the oceanic lithosphere, the relation between plate motions and distributed deformations, accelerations and the steadiness of plate motions, the distribution of current Pacific-North America motion across western North America and its margin, plate reconstructions and their uncertainties, hotspots, and plate dynamics. A comprehensive bibliography is provided. 126 refs.

  18. A sharp cadherin-6 gene expression boundary in the developing mouse cortical plate demarcates the future functional areal border.

    PubMed

    Terakawa, Youhei W; Inoue, Yukiko U; Asami, Junko; Hoshino, Mikio; Inoue, Takayoshi

    2013-10-01

    The mammalian cerebral cortex can be tangentially subdivided into tens of functional areas with distinct cyto-architectures and neural circuitries; however, it remains elusive how these areal borders are genetically elaborated during development. Here we establish original bacterial artificial chromosome transgenic mouse lines that specifically recapitulate cadherin-6 (Cdh6) mRNA expression profiles in the layer IV of the somatosensory cortex and by detailing their cortical development, we show that a sharp Cdh6 gene expression boundary is formed at a mediolateral coordinate along the cortical layer IV as early as the postnatal day 5 (P5). By further applying mouse genetics that allows rigid cell fate tracing with CreERT2 expression, it is demonstrated that the Cdh6 gene expression boundary set at around P4 eventually demarcates the areal border between the somatosensory barrel and limb field at P20. In the P6 cortical cell pellet culture system, neurons with Cdh6 expression preferentially form aggregates in a manner dependent on Ca(2+) and electroporation-based Cdh6 overexpression limited to the postnatal stages perturbs area-specific cell organization in the barrel field. These results suggest that Cdh6 expression in the nascent cortical plate may serve solidification of the protomap for cortical functional areas. PMID:22875867

  19. Development of second-mode instability in a Mach 6 flat plate boundary layer with two-dimensional roughness

    NASA Astrophysics Data System (ADS)

    Tang, Qing; Zhu, Yiding; Chen, Xi; Lee, Cunbiao

    2015-06-01

    Particle image velocimetry, PCB pressure sensors, and planar Rayleigh scattering are combined to study the development of second-mode instability in a Mach 6 flow over a flat plate with two-dimensional roughness. To the best of the authors' knowledge, this is the first time that the instantaneous velocity fields and flow structures of the second-mode instability waves passing through the roughness are shown experimentally. A two-dimensional transverse wall blowing is used to generate second-mode instability in the boundary layer and seeding tracer particles. The two-dimensional roughness is located upstream of the synchronization point between mode S and mode F. The experimental results showed that the amplitude of the second-mode instability will be greatly increased upstream of the roughness. Then it damps and recovers quickly in the vicinity downstream of the roughness. Further downstream, it acts as no-roughness case, which confirms Fong's numerical results [K. D. Fong, X. W. Wang, and X. L. Zhong, "Numerical simulation of roughness effect on the stability of a hypersonic boundary layer," Comput. Fluids 96, 350 (2014)]. It also has been observed that the strength of the amplification and damping effect depends on the height of the roughness.

  20. Interaction between central volcanoes and fissure swarms along divergent plate boundaries: an example from Askja Volcano, Northern Iceland.

    NASA Astrophysics Data System (ADS)

    Trippanera, Daniele; Ruch, Joel; Acocella, Valerio; Urbani, Stefano; Thordarson, Thor

    2016-04-01

    Central volcanoes located along divergent plate boundaries are typically part of a larger volcanic system that consists of a central edifice and a fissure swarm through which magma propagates and spreads plates apart. Regional normal faults and graben structures develop within the volcanic system, also dissecting portions of the central volcano with ring-faults faults and eruptive fissures related to the caldera structure. Both the fissure swarm and the caldera structure influence the pathway of the ascending magma, however, the influences of the structures on magma propagation and vice versa are not well defined and understood. Here we aim to understand the relationship between the activity of the central volcano structures (e.g. caldera ring faults, radial dykes and cone sheets) and those of the fissure swarm (e.g. regional normal faults, regional dikes). We focus on Askja volcano, located in the Northern Volcanic Zone of Iceland. It is comprised of three nested calderas, largely filled in with subaerial basaltic lava flows and surrounded by a massive hyaloclastite mountain on the Eastern side. Formation of the youngest, the Öskjuvatn caldera, was initiated during the 1874-1876 rifting episode on the Askja system. This major event was followed by several localized radial and circumferential magmatic intrusions taking place along the new-formed caldera ring fault, as well as intruding in the fissure swarm related to the regional tectonics. In order to characterize the influence of the caldera structure on the regional tectonics, we analysed the structural framework of the caldera and direct surroundings using remote sensing (optical imagery and high resolution DEM from TanDEM-X data). Then we made detailed field measurements (500 data) by analysing azimuth, dip, and opening of eruptive fissures, dikes, faults and extension fractures. Both remote sensing and field measurements have been then integrated producing a detailed structural map of Askja. Our results show

  1. Plate Boundary Observatory Strainmeter Recordings of The M6.0 August 24, 2014 South Napa Earthquake

    NASA Astrophysics Data System (ADS)

    Hodgkinson, Kathleen; Mencin, David; Phillips, David; Mattioli, Glen; Meertens, Charles

    2015-04-01

    The 2014 Mw6.0 South Napa earthquake nucleated at 11 km depth near the West Napa fault, one of a complex system of sub-parallel major right lateral faults north of San Francisco that together accommodate much of the relative motion between the Pacific and North American tectonic plates. The South Napa event was the largest to have shaken the San Francisco Bay Area (SFBA) in almost 25 years. A major goal of the NSF-funded EarthScope Plate Boundary Observatory (PBO), installed and maintained by UNAVCO, was to enable researchers to study the interaction between the faults that form a plate boundary zone, and in particular, to investigate the role that aseismic transients contribute to strain accumulation and release. To realize this goal, PBO includes borehole tensor strainmeters (BSMs) installed in several targeted regions, including on to the north and east of San Francisco. Two PBO BSMs have been operating in the SFBA since 2008: B057, north of San Francisco and 30 km from the epicenter, and B054, 3 km from the Hayward Fault and 40 km from the epicenter. We find the coseismic strains recorded by B057 are close to those predicted using elastic half-space dislocation theory and the seismically determined focal mechanism, while a more complicated variable slip model may be required for observations from B054. Months after the event, B057 continued to record a significant postseismic signal. In this presentation we document the coseismic signals recorded by the PBO BSMs and characterize the temporal behavior of the postseismic signal at B057. The PBO network includes over 1100 GPS, 75 BSMs, 79 seismometers and arrays of tiltmeters, pore pressure sensors and meteorological instrumentation. UNAVCO generates an Earthscope Level 2 processed strain time-series combined into areal and shear strains for the PBO BSM network; the raw data are available from the IRIS DMC in mSEED format. For events of interest, such as the South Napa earthquake, UNAVCO generates a 1-sps

  2. Magmatism at the Eurasian–North American modern plate boundary: Constraints from alkaline volcanism in the Chersky Belt (Yakutia)

    PubMed Central

    Tschegg, Cornelius; Bizimis, Michael; Schneider, David; Akinin, Vyacheslav V.; Ntaflos, Theodoros

    2011-01-01

    The Chersky seismic belt (NE-Russia) forms the modern plate boundary of the Eurasian−North American continental plate. The geodynamic evolution of this continent−continent setting is highly complex and remains a matter of debate, as the extent and influence of the Mid-Arctic Ocean spreading center on the North Asian continent since the Eocene remains unclear. The progression from a tensional stress regime to a modern day transpressional one in the Chersky seismic belt, makes the understanding even more complicated. The alkaline volcanism that has erupted along the Chersky range from Eocene through to the Recent can provide constraints on the geodynamic evolution of this continental boundary, however, the source and petrogenetic evolution of these volcanic rocks and their initiating mechanisms are poorly understood. We studied basanites of the central Chersky belt, which are thought to represent the first alkaline volcanic activity in the area, after initial opening of the Arctic Ocean basin. We present mineral and bulk rock geochemical data as well as Sr–Nd–Pb–Hf isotopes of the alkaline suite of rocks combined with new precise K–Ar and 40Ar/39Ar dating, and discuss an integrated tectono-magmatic model for the Chersky belt. Our findings show that the basanites were generated from a homogeneous asthenospheric mantle reservoir with an EM-1 isotopic flavor, under relatively ‘dry’ conditions at segregation depths around 110 km and temperatures of ~ 1500 °C. Trace element and isotope systematics combined with mantle potential temperature estimates offer no confirmation of magmatism related to subduction or plume activity. Mineral geochemical and petrographical observations together with bulk geochemical evidence indicate a rapid ascent of melts and high cooling rates after emplacement in the continental crust. Our preferred model is that volcanism was triggered by extension and thinning of the lithosphere combined with adiabatic upwelling of the

  3. Predictive wall model and LES applied to the flat-plate turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Inoue, M.; Mathis, R.; Marusic, I.; Pullin, D. I.

    2011-11-01

    An empirical inner-outer wall model (Mathis et al, JFM 2011) is used, together with time series of stream-wise, resolved-scale velocities within the logarithmic region obtained from large-eddy simulations (LES), to calculate turbulence intensities u ̲ ' 2 /uτ2 in the inner region of the zero-pressure gradient turbulent boundary layer. Comparisons are made of the LES-wall-model results with both equivalent predictions using experimental time series, and also with direct experimental measurements at Reτ = 7 , 300 , 13 , 600 and 19 , 000 . LES combined with the wall model are then used to extend the inner-layer predictions to Reynolds numbers within a gap in log (Reτ) space between laboratory measurements and surface-layer, atmospheric experiments.

  4. Focal Mechanisms at the convergent plate boundary in Southern Aegean, Greece.

    NASA Astrophysics Data System (ADS)

    Moshou, Alexandra; Papadimitriou, Eleftheria; Drakatos, George; Evangelidis, Christos; Karakostas, Vasilios; Vallianatos, Filippos; Makropoulos, Konstantinos

    2014-05-01

    Greece is characterized by high seismicity, mainly due to the collision between the European and the African lithospheric plates and the dextral strike slip motion along the North Anatolia Fault zone and North Aegean Trough. The subduction of the Eastern Mediterranean oceanic plate along the Hellenic Arc under the Aegean microplate along with the accompanied roll back of the descending slab is considered the main tectonic feature of the region (Papazachos and Comninakis 1971; Makropoulos and Burton 1984; Papazachos et al. 2000a, b). The divergent motion between the Aegean block and mainland Europe is indicated by an extension zone in the northern Aegean, with Crete and Aegean diverging from mainland Europe at a rate of about 3.5 cm yr-1 with Africa moving northward relative to Europe at a rate of about 1 cm yr-1 (Dewey et al., 1989; Papazachos et al., 1998; Mc-Clusky et al., 2000; Reilinger et al., 2006). In this tectonically complicated area diverge types of deformation are manifested, in addition to the dominant subduction processes. Aiming to shed more light in the seismotectonic properties and faulting seismological data from the Hellenic Unified Seismological Network (HUSN) were selected and analyzed for determining focal mechanisms using the method of moment tensor inversion, additional to the ones being available from the routine moment tensor solutions and several publications. Thus, 31 new fault plane solutions for events with magnitude M>4.0, are presented in this study, by using the software of Ammon (Randall et al., 1995). For this scope the data from at least 4 stations were used with an adequate azimuthal coverage and with an epicentral distance not more than 350 km. The preparation of the data includes the deconvolution of instruments response, then the velocity was integrated to displacement and finally the horizontal components were rotated to radial and transverse. Following, the signal was inverted using the reflectivity method of Kennett (1983

  5. Oceanic terranes of S-Central America - 200 Million years of accretion history recorded on the W-edge of the Caribbean Plate.

    NASA Astrophysics Data System (ADS)

    Baumgartner, P. O.; Flores, K.; Bandini, A.; Buchs, D.; Andjic, G.; Baumgartner-Mora, C.

    2012-04-01

    The W-edge of the Caribbean Plate is characterized by two major basement domains, separated today by a SW-NE trending diffuse fault zone located SE of the Nicoya Peninsula (Costa Rica) and possibly connecting with the Hess Escarpment. To the NW, in the area originally called "Chortis Block", oceanic island/arc basements range in age from Late Triassic to Early Cretaceous and form a complicated puzzle of geodynamic units. To the SE of this fault line, no age older than Turonian-Santonian (90-85 Ma) is known. This area only represents the trailing edge of the Caribbean Large Igensous Procince (CLIP). The Mesquito Composite Oceanic Terrane (MCOT) comprises the southern half of the "Chortis Block", classically considered as a continental fragment of N-America. The MCOT is defined by isolated outcrops of ultramafic, mafic oceanic/arc rocks, and radiolarites of Late Triassic, Jurassic and Early Cretaceous age: Rhaetian (latest Triassic) radiolarites found in the El Castillo Mélange (S-MCOT: S-Nicaragua/N- Costa Rica). They are associated with blocks of OIB-metabasalts. These rocks document the presence of a Late Triassic oceanic basement that must have been the substrate of the 174 -177 Ma old (Early/Middle Jurassic) Petit-Spot-like alkaline volcanics that intruded Early Jurassic radiolarites. These rocks form tectonic slivers in the middle Cretaceous Santa Rosa Accretionary Complex (relative autochthonous of the Santa Elena ultramafic unit, N-Costa Rica). The oldest rocks of the Nicoya Complex s. str. (NW-Nicoya Peninsula, Costa Rica) are Bajocian (Middle Jurassic) radiolarites, that occur as blocks magmatically engulfed in plateau-type basalts and intrusives that range in age thoughout the pre-Campanian Cretaceous (130-83 Ma). Middle and Late Jurassic metaradiolarites occur as blocks in the Siuna Serpentinite Médange (NE-Nicaragua), along with High-p, arc-related mafics. We envision an oceanic arc that collided in the latest Jurassic with the Agua Fria arc system

  6. Accretion and Subduction of Oceanic Lithosphere: 2D and 3D Seismic Studies of Off-Axis Magma Lenses at East Pacific Rise 9°37-40'N Area and Downgoing Juan de Fuca Plate at Cascadia Subduction Zone

    NASA Astrophysics Data System (ADS)

    Han, Shuoshuo

    Two thirds of the Earth's lithosphere is covered by the ocean. The oceanic lithosphere is formed at mid-ocean ridges, evolves and interacts with the overlying ocean for millions of years, and is eventually consumed at subduction zones. In this thesis, I use 2D and 3D multichannel seismic (MCS) data to investigate the accretionary and hydrothermal process on the ridge flank of the fast-spreading East Pacific Rise (EPR) at 9°37-40'N and the structure of the downgoing Juan de Fuca plate at the Cascadia subduction zone offshore Oregon and Washington. Using 3D multichannel seismic (MCS) data, I image a series of off-axis magma lenses (OAML) in the middle or lower crust, 2-10 km from the ridge axis at EPR 9°37-40'N. The large OAMLs are associated with Moho travel time anomalies and local volcanic edifices above them, indicating off-axis magmatism contributes to crustal accretion though both intrusion and eruption (Chapter 1). To assess the effect of OAMLs on the upper crustal structure, I conduct 2-D travel time tomography on downward continued MCS data along two across-axis lines above a prominent OAML in our study area. I find higher upper crustal velocity in a region ~ 2 km wide above this OAML compared with the surrounding crust. I attribute these local anomalies to enhanced precipitation of alteration minerals in the pore space of upper crust associated with high-temperature off-axis hydrothermal circulation driven by the OAML (Chapter 2). At Cascadia, a young and hot end-member of the global subduction system, the state of hydration of the downgoing Juan de Fuca (JdF) plate is important to a number of subduction processes, yet is poorly known. As local zones of higher porosity and permeability, faults constitute primary conduits for seawater to enter the crust and potentially uppermost mantle. From pre-stack time migrated MCS images, I observe pervasive faulting in the sediment section up to 200 km from the deformation front. Yet faults with large throw and

  7. Plate boundary readjustment in oblique convergence: Example of the Neogene of Hispaniola, Greater Antilles

    NASA Astrophysics Data System (ADS)

    Pubellier, Manuel; Mauffret, Alain; Leroy, Sylvie; Vila, Jean Marie; Amilcar, Helliot

    2000-08-01

    The Haitian fold-and-thrust belt is the major mountain belt of Haiti (western part of Hispaniola, Greater Antilles) and resembles a compressive restraining bend between the two major faults which have driven the opening of the Cayman Basin since the Eocene. During the rifting stage, from the middle to the late Eocene, this area underwent an extensional evolution with fissural volcanic activity along NE-SW tilted blocks. The Haitian fold-and-thrust belt was constructed from the Early Miocene until the Present by stacking sedimentary units into a collisional wedge perpendicular to the tilted blocks, which was propagating to the southwest. During the construction of the wedge, piggyback basins were formed and progressively uplifted. During the late Neogene, convergence is localized in the Cul-de-Sac-Enriquillo trough where the active front proceeds southward onto the Beata ridge. In this area, Miocene to Quaternary wrench structures of the lower plate, like the Southern Peninsula and the Enriquillo-Plantain Garden faults, are reactivated as normal faults, owing to the loading of the fold-and-thrust belt.

  8. Effects of Periodic Unsteady Wake Flow and Pressure Gradient on Boundary Layer Transition Along the Concave Surface of a Curved Plate. Part 3

    NASA Technical Reports Server (NTRS)

    Schobeiri, M. T.; Radke, R. E.

    1996-01-01

    Boundary layer transition and development on a turbomachinery blade is subjected to highly periodic unsteady turbulent flow, pressure gradient in longitudinal as well as lateral direction, and surface curvature. To study the effects of periodic unsteady wakes on the concave surface of a turbine blade, a curved plate was utilized. On the concave surface of this plate, detailed experimental investigations were carried out under zero and negative pressure gradient. The measurements were performed in an unsteady flow research facility using a rotating cascade of rods positioned upstream of the curved plate. Boundary layer measurements using a hot-wire probe were analyzed by the ensemble-averaging technique. The results presented in the temporal-spatial domain display the transition and further development of the boundary layer, specifically the ensemble-averaged velocity and turbulence intensity. As the results show, the turbulent patches generated by the wakes have different leading and trailing edge velocities and merge with the boundary layer resulting in a strong deformation and generation of a high turbulence intensity core. After the turbulent patch has totally penetrated into the boundary layer, pronounced becalmed regions were formed behind the turbulent patch and were extended far beyond the point they would occur in the corresponding undisturbed steady boundary layer.

  9. RADIATIVELY EFFICIENT MAGNETIZED BONDI ACCRETION

    SciTech Connect

    Cunningham, Andrew J.; Klein, Richard I.; McKee, Christopher F.; Krumholz, Mark R.; Teyssier, Romain

    2012-01-10

    We have carried out a numerical study of the effect of large-scale magnetic fields on the rate of accretion from a uniform, isothermal gas onto a resistive, stationary point mass. Only mass, not magnetic flux, accretes onto the point mass. The simulations for this study avoid complications arising from boundary conditions by keeping the boundaries far from the accreting object. Our simulations leverage adaptive refinement methodology to attain high spatial fidelity close to the accreting object. Our results are particularly relevant to the problem of star formation from a magnetized molecular cloud in which thermal energy is radiated away on timescales much shorter than the dynamical timescale. Contrary to the adiabatic case, our simulations show convergence toward a finite accretion rate in the limit in which the radius of the accreting object vanishes, regardless of magnetic field strength. For very weak magnetic fields, the accretion rate first approaches the Bondi value and then drops by a factor of {approx}2 as magnetic flux builds up near the point mass. For strong magnetic fields, the steady-state accretion rate is reduced by a factor of {approx}0.2 {beta}{sup 1/2} compared to the Bondi value, where {beta} is the ratio of the gas pressure to the magnetic pressure. We give a simple expression for the accretion rate as a function of the magnetic field strength. Approximate analytic results are given in the Appendices for both time-dependent accretion in the limit of weak magnetic fields and steady-state accretion for the case of strong magnetic fields.

  10. Young tectonics of a complex plate boundary zone: Indentation, rotation, and escape in Alaska

    NASA Astrophysics Data System (ADS)

    Wallace, W. K.; Ruppert, N. A.

    2012-12-01

    Convergence of thick crust of the Yakutat block with the southern margin of Alaska is widely recognized as a dominant influence on the tectonics of Alaska since at least late Miocene time. It is less clear how this convergence relates to the distribution, type, and orientation of geologic structures, and to the boundaries between the tectonic provinces that they define. We propose that convergence of Yakutat block includes two distinct components that influence deformation and topography in different ways: 1) The crust of the exposed, southern Yakutat block is too thick to subduct, which has caused the collisional St. Elias orogen. Detachment of the upper part of the mafic basement allows delamination and sinking of the remaining mafic crust and lithospheric mantle. The collisional orogen drives rigid counterclockwise rotation of the southern Alaska block south of the arcuate, right-lateral Denali fault. The western boundary of this block is a zone of distributed contraction in the western Alaska Range and Cook Inlet. 2) The northern part of the Yakutat block is thin enough to subduct but thick and buoyant enough to cause localized flat-slab subduction orthogonal to rotation of the southern Alaska block. Consequences include the gently antiformal Talkeetna Mountains that span the forearc basin, a gap in the magmatic arc, and a basement-involved fold-and-thrust belt in the northern Alaska Range. An arcuate oroclinal hinge from southern Alaska to the northeastern Brooks Range reflects indentation since at least Paleocene time. Traction above the subducted Yakutat block along the southern part of this hinge drives current indentation. North of the subducted Yakutat block, indentation is reflected by left-lateral block rotation that accommodates shortening between the Denali and Tintina faults and by contraction farther north along the northern edge of the arcuate northeastern Brooks Range. Western Alaska accommodates both northward indentation and westward convergence

  11. Subduction erosion and accretion in the Solomon Sea region

    NASA Astrophysics Data System (ADS)

    Honza, Eiichi; Miyazaki, Teruki; Lock, Jo

    1989-03-01

    The Solomon Sea region is an area of intense tectonic activity characterized by structural complexity, a high level of seismicity and volcanism, and rapid evolution of plate boundaries. There is little accretion in the eastern New Britain Trench. Accretion gradually increases westward with thick accretion in the western New Britain Trench and in the Trobriand Subduction System. The thick accretion in the western part of the New Britain Trench may be a result of collision from the north of Finisterre-Huon block with New Guinea mainland. The present boundary of the collision is along the Ram-Markham fault. Deformation structures and present day seismicity suggest that the northern block is under compression. Accretion has occurred in the sediment filled trenches in the Solomon Sea. The scale of the accretionary wedge depends on the amount of trench-fill sediment available. It is unlikely that there is no sediment supply to the eastern part of the New Britain Trench where no accretion is observed and subduction erosion may be occurring. There are two possible mechanisms for subduction erosion of sediment; either a rapid rate of subduction relative to the supply of sediment inhibiting sediment accumulation in the trench; or horizontal tensional force superimposed on both the forearc and backarc regions of the arc. Seafloor spreading in both the Manus and Woodlark basins is fan-like with nearby poles in the western margins of the basins. This may be a reflection of a horizontally compressional field in the western part and a tensional field in the eastern part of the Solomon Sea. Therefore it is possible to conclude that the consumption of sediment in the eastern New Britain Trench is related to the horizontal tensional field superimposed on both the forearc and backarc regions of the subduction system. Imbricated thrust and overthrust faults in the western New Britain Trench and Trobriand Trough are not linear over long distance, but form wavy patterns in blocks with

  12. The Mw 8.8, 1906 Colombia-Ecuador Subduction Earthquake: Seismic Structure and Thermal Regime of the Plate Boundary.

    NASA Astrophysics Data System (ADS)

    Collot, J.; Marcaillou, B.; Agudelo, W.; Ribodetti, A.; D'Acremont, E.

    2007-05-01

    The North Ecuador-SW Colombia active margin underwent four great subduction earthquakes in 1906 (Mw8.8), 1942(Mw7.8), 1958 (Mw7.7) and 1979(Mw8.2). The resulting seismotectonic segmentation of the margin may be a consequence of variable mass transfer, remarkable down-going plate basement relief, and margin transverse and along strike crustal faults. The margin basement consists of accreted oceanic terranes, and is underthrust by the northern flank of the19-km thick Carnegie Ridge, and 7-km-thick and structurally complex, Miocene Malpelo- Yaquina-Buenaventura spreading-transform system of the northern Nazca plate. The oceanic crust is covered by turbidite that strongly vary in thickness along the trench. South of 1°30'N, the oceanic crust shows N35- 75° and N120° faults and lineaments, and a N-trending chain of small seamounts, which delineate en-échelon, small pounded trench basins containing up to 500 m of turbidites. The steep adjacent inner trench slope is devoid of an accretionary wedge, but shows evidences for slope instabilities and mass wasting deposits. A 1-km thick subduction channel that is continuous with the hemipelagic cover of the oceanic crust is imaged landward, over a 30-km distance from the trench. This region shows evidence for thinning of the margin basement by seamount subduction, and correlates with the hypocenter of the 1942 subduction earthquake. North of 1°30'N, an up-to 4-km-thick deep-sea turbidite system has developed in the Colombia trench. The turbidite system is fed by the major Esmeraldas and Patia-Mira canyons and rivers, and dammed to the South by the Galera seamounts. This thick trenchfill appears to be dominantly subducting beneath an erosional margin basement between 1°30'N and 2°30'N, thus forming a km-thick subduction channel that is modulated by the subduction of a buried, large horst and graben structure. This region of thick sediment and rough oceanic crust subduction coincides with the hypocenters of the1958 and1979

  13. The northern Caribbean plate boundary in the Jamaica Passage: Structure and seismic stratigraphy

    NASA Astrophysics Data System (ADS)

    Corbeau, J.; Rolandone, F.; Leroy, S.; Mercier de Lépinay, B.; Meyer, B.; Ellouz-Zimmermann, N.; Momplaisir, R.

    2016-04-01

    Multibeam bathymetry data and multichannel seismic reflection profiles have been collected at the end of 2012 along the Enriquillo-Plantain-Garden Fault Zone (EPGFZ) in the Jamaica Passage, between Jamaica and Hispaniola. Analysis of the data set reveals the tectonic evolution and the stratigraphic complexity of the northern Caribbean boundary. Stratigraphic correlations with previous marine and on land studies are proposed to place the identified seismic sequences in their regional tectonic history. Two distinct crustal domains are interpreted. Typical stratigraphic sequences for the rifted blocks of the Eastern Cayman Trough margin are identified in five basins of the Jamaica Passage, highlighting the eastward limit of the Cayman Trough margin. These inherited basins are deformed and folded during a first phase of compression that could correspond to the regional tectonic rearrangement recorded in the early Miocene (about 20 Ma). A distinct crustal domain that we propose to relate to the Carib Beds (Caribbean typical reflectors A″, B″ and V) is identified in the southern part of the Jamaica Passage, indicating that the Caribbean Large Igneous Province could extend up to the extreme northeast part of the Lower Nicaragua Rise. The left-lateral EPGFZ currently cuts across two pre-existing basins, the Morant and Matley basins. During the activity of the EPGFZ, these basins are deformed and folded indicating a second phase of compression. In contrast, the Navassa basin, located in the middle of the Jamaica Passage, results from the strike-slip motion of the EPGFZ and is interpreted as an asymmetrical basin bordered by the EPGFZ only on its northern side.

  14. Comments on 'Transverse vibrations of simply supported elliptical and circular plates using boundary characteristic orthogonal polynomials in two variables' and some additional considerations

    NASA Astrophysics Data System (ADS)

    Laura, P. A. A.; Ercoli, L.

    1993-06-01

    Some of the results obtained in the paper by Singh and Chakraverty (1992) named in the title are compared with values available in the open literature. From these, it is concluded that the optimized Rayleigh method is convenient in the case of circular plates of nonuniform thickness, while the orthogonal polynomial approach is more convenient for treating rectangular and elliptical boundary shapes.

  15. Structural Evolution of the India-Arabia Plate Boundary from Miocene to Present-Day (NW Indian Ocean) and Comparison with the Dead Sea Fault (Eastern Mediterranean Sea).

    NASA Astrophysics Data System (ADS)

    Rodriguez, M.; Huchon, P.; Chamot Rooke, N.; Fournier, M.; Delescluse, M.; Ben Avraham, Z.; Ten Brink, U. S.

    2014-12-01

    Arabia is bounded by the Dead Sea Transform (DST) to the west and by the Owen Fracture Zone (OFZ) to the east. These present-day major strike-slip fault systems activated during the Plio-Pleistocene, which contrasts with the age of inception of strike-slip motion, assumed to begin around 13-18 Ma for the DST and around 20 Ma at the edge of the Owen-Murray Ridge (OMR) for the India-Arabia plate boundary. This discrepancy between the age of the active strike-slip systems and the age of inception of strike-slip motion raises the question of the kinematic driver for the transition between successive generations of strike-slip faults. Using a recent mutibeam and seismic dataset crossing the OFZ and the OMR, we provide a new geodynamic framework for the Miocene to present-day structural evolution of the India-Arabia plate boundary, and highlight some similarities with the structural evolution of the DST. We first document a Late Miocene episode of uplift of the OMR uplift along the Miocene India-Arabia plate boundary. The onset of this uplift is coeval with a plate reorganization event marked by the onset of intra-plate deformation in the Central Indian Ocean. The OFZ emplaced around 3 Ma, with major pull-apart basins opening (20°N Basin, Dalrymple Trough) dated at 2.4 Ma by far-field correlation with ODP Sites. The opening of pull-apart basins is coeval with the last structural reorganization of the Makran accretionnary wedge, marked by the regional M-unconformity, and with a major intensification of the Indian monsoon. A Late Miocene episode of folding is also recognized at the Lebanon ranges prior to the onset of the present-day DST, which occurred in the Late Pliocene-Early Pleistocene. The similarities between the geological history of the India-Arabia plate boundary and the DST in the Late Miocene and the Late Pliocene-Early Pleistocene suggest that both plate boundaries recorded the same kinematic changes. Late Miocene (i.e. Tortonian) deformation is widely

  16. Integration of the Plate Boundary Observatory and Existing GPS Networks in Southern California: A Multi Use Geodetic Network

    NASA Astrophysics Data System (ADS)

    Walls, C.; Blume, F.; Meertens, C.; Arnitz, E.; Lawrence, S.; Miller, S.; Bradley, W.; Jackson, M.; Feaux, K.

    2007-12-01

    The ultra-stable GPS monument design developed by Southern California Geodetic Network (SCIGN) in the late 1990s demonstrates sub-millimeter errors on long time series where there are a high percentage of observations and low multipath. Following SCIGN, other networks such as PANGA and BARGEN have adopted the monument design for both deep drilled braced monuments (DDBM = 5 legs grouted 10.7 meters into bedrock/stratigraphy) and short drilled braced monuments (SDBM = 4 legs epoxied 2 meters into bedrock). A Plate Boundary Observatory (PBO) GPS station consists of a "SCIGN" style monument and state of the art NetRS receiver and IP based communications. Between the years 2003-2008 875 permanent PBO GPS stations are being built throughout the United States. Concomitant with construction of the PBO the majority of pre-existing GPS stations that meet stability specifications are being upgraded with Trimble NetRS and IP based communications to PBO standards under the EarthScope PBO Nucleus project. In 2008, with completed construction of the Plate Boundary Observatory, more than 1100 GPS stations will share common design specifications and have identical receivers with common communications making it the most homogenous geodetic network in the World. Of the 875 total Plate Boundary Observatory GPS stations, 211 proposed sites are distributed throughout the Southern California region. As of August 2007 the production status is: 174 stations built (81 short braced monuments, 93 deep drilled braced monuments), 181 permits signed, 211 permits submitted and 211 station reconnaissance reports. The balance of 37 stations (19 SDBM and 18 DDBM) will be built over the next year from Long Valley to the Mexico border in order of priority as recommended by the PBO Transform, Extension and Magmatic working groups. Fifteen second data is archived for each station and 1 Hz as well as 5 Hz data is buffered to be triggered for download in the event of an earthquake. Communications

  17. Effects of Mach Number, Leading-Edge Bluntness, and Sweep on Boundary-Layer Transition on a Flat Plate

    NASA Technical Reports Server (NTRS)

    Jillie, Don W.; Hopkins, Edward J.

    1961-01-01

    The effects of leading-edge bluntness and sweep on boundary-layer transition on flat plate models were investigated at Mach numbers of 2.00, 2.50, 3.00, and 4.00. The effect of sweep on transition was also determined on a flat plate model equipped with an elliptical nose at a Mach number of 0.27. Models used for the supersonic investigation had leading-edge radii varying from 0.0005 to 0.040 inch. The free-stream unit Reynolds number was held constant at 15 million per foot for the supersonic tests and the angle of attack was 0 deg. Surface flow conditions were determined by visual observation and recorded photographically. The sublimation technique was used to indicate transition, and the fluorescent-oil technique was used to indicate flow separation. Measured Mach number and sweep effects on transition are compared with those predicted from shock-loss considerations as described in NACA Rep. 1312. For the models with the blunter leading edges, the transition Reynolds number (based on free-stream flow conditions) was approximately doubled by an increase in Mach number from 2.50 to 4.00; and nearly the same result was predicted from shock-loss considerations. At all super- sonic Mach numbers, increases in sweep reduced the transition Reynolds number and the amount of reduction increased with increases in bluntness. The shock-loss method considerably underestimated- the sweep effects, possibly because of the existence of crossflow instability associated with swept wings. At a Mach number of 0.27, no reduction in the transition Reynolds number with sweep was measured (as would be expected with no shock loss) until the sweep angle was attained where crossflow instability appeared.

  18. Geometric changes of plate boundaries along part of the northern Dead Sea Transform: Geochronologic and paleomagnetic evidence

    NASA Astrophysics Data System (ADS)

    Heimann, Ariel; Ron, Hagai

    1993-01-01

    The Korazim block, an elevated pressure-ridge, along with the faults bounding the Sea of Galilee and Hula pull-apart basins are internal structures of the Dead Sea Transform plate boundary. K-Ar dates and paleomagnetic data from basalt flows and sedimentary strata are utilized to determine the stratigraphy and the deformation of the region. The integration of the two methods, together with structural data, yield high-resolution age determination of the stratigraphic sequence and provides insight into the timing and style of deformation. The Korazim block is covered in its southern and central areas by Pliocene basalt flows (the Cover Basalt, 5.1-3.6 Ma, and Ruman Basalt, 2.9-2.2 Ma, formations) and in its northern area by basalts (Yarda Basalt, 0.9-0.8 Ma) and sediments (3.0-2.3 and 1.6-0.9 Ma) of Plio-Pleistocene age. The magnetic polarity of a total of 29 lava flows and intercalated sedimentary strata is mixed; the mean magnetic declination of the 29 sites shows an anomalous direction which yields 11.4° ± 4.0° counterclockwise rotation with respect to the expected field. The mean inclination of 46.0° ± 4.1° does not significantly deviate from the expected field. The anomalous declination is interpreted as the consequence of faulting and block rotation accommodating internal deformation. This deformation did not begin before late Pliocene to early Pleistocene, probably not before 0.9 Ma, and may still be active. Simultaneous right-lateral slip (of 50-175 m) with a small reverse component (of 30-90 m) along NW trending faults and 11° counterclockwise rotation created internal deformation of the Korazim pressure ridge. This deformation is the consequence of left-lateral slip along the Almagor strand of the Dead Sea transform, subparallel to the plate slip vector. Thus a compression component was formed which presumably led to the internal deformation of the Korazim block. The recent deformation of the Korazim block in relation to the age of adjacent

  19. Linear stability of a gas boundary layer flowing past a thin liquid film over a flat plate

    NASA Astrophysics Data System (ADS)

    Pelekasis, Nikolaos A.; Tsamopoulos, John A.

    2001-06-01

    The flow of a gas stream past a flat plate under the influence of rainfall is investigated. As raindrops sediment on the flat plate, they coalesce to form a water film that flows under the action of shear from the surrounding gas stream. In the limit of (a) large Reynolds number, Re, in the gas phase, (b) small rainfall rate, r[dot above], compared to the free-stream velocity, U[infty infinity], and (c) small film thickness compared to the thickness of the boundary layer that surrounds it, a similarity solution is obtained that predicts growth of the liquid film like x3/4; x denotes dimensionless distance from the leading edge. The flow in the gas stream closely resembles the Blasius solution, whereas viscous dissipation dominates inside the film. Local linear stability analysis is performed, assuming nearly parallel base flow in the two streams, and operating in the triple-deck regime. Two distinct families of eigenvalues are identified, one corresponding to the well-known Tollmien Schlichting (TS) waves that originate in the gas stream, and the other corresponding to an interfacial instability. It is shown that, for the air water system, the TS waves are convectively unstable whereas the interfacial waves exhibit a pocket of absolute instability, at the streamwise location of the applied disturbance. Moreover, it is found that as the inverse Weber number (We[minus sign]1) increases, indicating the increasing effect of surface tension compared to inertia, the pocket of absolute instability is translated towards larger distances from the leading edge and the growth rate of unstable waves decreases, until a critical value is reached, We[minus sign]1 [approximate] We[minus sign]1c, beyond which the family of interfacial waves becomes convectively unstable. Increasing the inverse Froude number (Fr[minus sign]1), indicating the increasing effect of gravity compared to inertia, results in the pocket of absolute instability shrinking until a critical value is reached, Fr

  20. Chemical and isotopic evidence of gas-influenced flow at a transform plate boundary: Monterey Bay, California

    USGS Publications Warehouse

    Martin, J.B.; Orange, D.L.; Lorenson, T.D.; Kvenvolden, K.A.

    1997-01-01

    Chemical and isotopic compositions of pore fluids document upward flow through communities of vesicomyid clams in Monterey Bay, California. Within the clam communities, the sulfate reduction zone is only 10 cm thick, and Ca and Mg concentrations decrease to values as low as 2.2 mM and 34.5 mM, respectively, at depths less than 30 cm below the sediment-water interface. Less than 5 m outside the communities, the base of the sulfate reduction zone is deeper than the greatest penetration of the cores (-30 cm), and Ca and Mg exhibit only minor changes from seawater values. The sediment exhibits no significant variation in grain size, mineralogy, organic carbon, nitrogen, or carbonate content throughout the region. The composition of pore fluid within clam communities results from upward flow of altered fluid rather than different diagenetic reactions within and outside the communities. Isotopically light dissolved inorganic carbon (DIC), with ??13C values ranging from -3.2 to -54.1???, could reflect carbon sources from either oxidized thermogenic methane and/or a mixture of oxidized microbial methane and solid organic carbon. The C1/(C2+C3) ratios (ranging from 34 to 1142) and the hydrogen and carbon isotopic compositions of methane (??D values of -109 to -156???; ??13C values of -30.6 to -86.6???) suggest that methane is primarily microbial but that a minor component could be thermally generated. Any thermogenic methane would have migrated from great depths, possibly >2 km. The presence of methane is likely to contribute to fluid flow by reducing the density of the fluids. Past fluid migration and venting are reflected by widespread carbonate mineralization at the sediment-water interface. This mineralization and the geographic distribution and proportions of microbial and thermogenic methane suggest that vent sites migrate when permeability is reduced during carbonate cementation. These results demonstrate that along with convergent and divergent plate boundaries

  1. Completion of the Southern California Plate Boundary Observatory GPS Network and Implementation of the Low Latency Salton Trough Network

    NASA Astrophysics Data System (ADS)

    Walls, C.; Miller, S.; Lawrence, S.; Wilson, B.; Jackson, M.; Feaux, K.

    2008-12-01

    Between 2003-2008 875 permanent PBO GPS stations have been built throughout the United States. Concomitant with construction of the PBO the majority of pre-existing GPS stations that meet stability specifications have been upgraded with Trimble NetRS and IP based communications to PBO standards under the EarthScope PBO Nucleus project. In October 2008, with completed construction of the Plate Boundary Observatory, more than 1100 GPS stations now share common design specifications and have identical receivers with common communications making it the most homogeneous geodetic network in the World. Of the 875 total Plate Boundary Observatory GPS stations, 216 sites are distributed throughout the Southern California region. 102 of the sites are built as SDBM, 111 DDBM, and 3 as strainmeter GPS hybrids. Fifteen second data is archived for each station and 1 Hz and 5 Hz data is buffered to be triggered for download in the event of an earthquake. Additionally, 125 of the existing former-SCIGN GPS stations have been integrated into the SoCal region of PBO, of which 25 have real-time data streams. The Salton Trough Radio Network (STRN) comprises of 20 stations equipped with Ethernet bridge Intuicom EB6+ (900 MHz) radios to transmit a high rate low latency data stream from each permanent GPS site. The high-rate low latency UStream data will be available to researchers who are developing prototype earthquake early warning systems in Southern California. A goal of the STRN is to make the data available rapidly enough for GPS-derived coseismic and dynamic displacements to be integrated into early warning system earthquake models. The improved earthquake models will better assist emergency response. UStream data will also aid surveyors who wish to use PBO GPS stations as permanent, high-quality base stations in real- time kinematic surveys. Requests for streaming data access at available GPS sites and latency statistics are located at http://pboweb.unavco.org/?pageid=107

  2. Observing active deformation of volcanoes in North America: Geodetic data from the Plate Boundary Observatory and associated networks

    NASA Astrophysics Data System (ADS)

    Puskas, C. M.; Phillips, D. A.; Mattioli, G. S.; Meertens, C. M.; Hodgkinson, K. M.; Crosby, C. J.; Enders, M.; Feaux, K.; Mencin, D.; Baker, S.; Lisowski, M.; Smith, R. B.

    2013-12-01

    The EarthScope Plate Boundary Observatory (PBO), operated by UNAVCO, records deformation of the geologically diverse North America western plate boundary, with subnetworks of instruments concentrated at selected active and potentially active volcanoes. These sensors record deformation and earthquakes and allow monitoring agencies and researchers to analyze changes in ground motion and seismicity. The intraplate volcanoes at Yellowstone and Long Valley are characterized by uplift/subsidence cycles, high seismicity, and hydrothermal activity but there have been no historic eruptions at either volcano. PBO maintains dense GPS networks of 20-25 stations at each of these volcanoes, with an additional 5 boreholes at Yellowstone containing tensor strainmeters, short-period seismometers, and borehole tiltmeters. Subduction zone volcanoes in the Aleutian Arc have had multiple historic eruptions, and PBO maintains equipment at Augustine (8 GPS), Akutan (8 GPS, 4 tiltmeters), and Unimak Island (14 GPS, 8 tiltmeters). The Unimak stations are at the active Westdahl and Shishaldin edifices and the nearby, inactive Isanotski volcano. In the Cascade Arc, PBO maintains networks at Mount St. Helens (15 GPS, 4 borehole strainmeters and seismometers, 8 borehole tiltmeters), Shasta (7 GPS, 1 borehole strainmeter and seismometer), and Lassen Peak (8 GPS). Data from many of these stations in the Pacific Northwest and California are also provided as realtime streams of raw and processed data. Real-time GPS data, along with high-rate GPS data, will be an important new resource for detecting and studying future rapid volcanic deformation events and earthquakes. UNAVCO works closely with the USGS Volcano Hazards Program, archiving data from USGS GPS stations in Alaska, Cascadia, and Long Valley. The PBO and USGS networks combined provide more comprehensive coverage than PBO alone, particularly of the Cascade Arc, where the USGS maintains a multiple instruments near each volcano. Ground

  3. Accretionary margin of north-western Hispaniola: morphology, structure and development of part of the northern Caribbean plate boundary

    USGS Publications Warehouse

    Dillon, William P.; Austin, James A.; Scanlon, K.M.; Terence, Edgar N.; Parson, L.M.

    1992-01-01

    Broad-range side-scan sonar (GLORIA) images and single- and multi-channel seismic reflection profiles demonstrate that the margin of north-western Hispaniola has experienced compression as a consequence of oblique North American-Caribbean plate convergence. Two principal morphological or structural types of accretionary wedges are observed along this margin. The first type is characterized by a gently sloping (???4??) sea floor and generally margin-parallel linear sets of sea-floor ridges that gradually deepen towards the flat Hispaniola Basin floor to the north. The ridges are caused by an internal structure consisting of broad anticlines bounded by thrust faults that dip southwards beneath Hispaniola. Anticlines form at the base of the slope and are eventually sheared and underthrust beneath the slope. In contrast, the second type of accretionary wedge exhibits a steeper (???6-16??) sea-floor slope characterized by local slumping and a more abrupt morphological transition to the adjacent basin. The internal structure appears chaotic on seismic reflection profiles and probably consists of tight folds and closely spaced faults. We suggest that changes in sea-floor declivity and internal structure may result from variations in the dip or frictional resistance of the de??collement, or possibly from changes in the cohesive strength of the wedge sediments. The observed pattern of thickening of Hispaniola Basin turbidites towards the insular margin suggests differential southwards tilting of the Hispaniola Basin strata, probably in response to North America-Caribbean plate interactions since the Early Tertiary. Based upon indirect age control from adjacent parts of the northern caribbean plate boundary, we infer a Late Eocene to Early Miocene episode of transcurrent motion (i.e. little or no tilting), an Early Miocene to Late Pliocene period of oblique convergence (i.e. increased tilt) during which the accretionary wedge began to be constructed, and a Late Pliocene to

  4. 800,000-Year Record of Plate Boundary Earthquakes in the Atacama Desert, Northern Chile

    NASA Astrophysics Data System (ADS)

    Baker, A. M.; Owen, L. A.; Rech, J.; Allmendinger, R. W.

    2010-12-01

    Coseismic cracks preserved in the hyper-arid Atacama Desert of Northern Chile provide a unique record of the seismic history of the modern Andean forearc, which has generated the largest earthquakes on earth. Loveless et al. (2009) mapped more than 50,000 cracks on satellite imagery and, based on boundary element modeling, suggested that they indicate repeated rupture of approximately the same segment. But, what is the time frame of the repeated rupture and what is the long-term strain rate of the forearc due to this process? West of Salar Grande, five overlapping fan surfaces contain different densities of coseismic cracks, allowing for such an assessment. The fan surfaces are highly indurated with gypsum and salt, resulting in excellent preservation of these brittle features. All surfaces are underlain by a tuff ~4 m.y. old. Older surfaces consistently have more and larger cracks than younger surfaces. Locally, cracks cutting across multiple surfaces have distinctly different widths and morphologies. Density is the number of cracks present per given length and total opening is the sum of the widths along that same length. Both crack density and total opening on each surface show a positive relationship to relative age, supporting the previously anecdotal evidence for reactivation of cracks through time with multiple events. Fresh, centimeter-scale cracks are also present on all surfaces, further supporting that these features record a history rather than a singular event. Three of the five fan surfaces have sufficiently large quartz clasts for exposure dating using 10Be and 26Al, providing absolute ages to use in calculating strain rate due to cracking. The oldest surface is 800±100 ky old. Samples from active channels constrain inheritance of cosmogenic nuclides, and nuclide ratios suggest no significant burial. Strain rates calculated from total opening and surface age range from 1.3x10^-15s^-1 to 2.4x10^-15s^-1 across the three surfaces. For comparison, we

  5. Coda Q and its Frequency Dependence in the Eastern Himalayan and Indo-Burman Plate Boundary Systems

    NASA Astrophysics Data System (ADS)

    Mitra, S.; Kumar, A.

    2015-12-01

    We use broadband waveform data for 305 local earthquakes from the Eastern Himalayan and Indo-Burman plate boundary systems, to model the seismic attenuation in NE India. We measure the decay in amplitude of coda waves at discreet frequencies (between 1 and 12Hz) to evaluate the quality factor (Qc) as a function of frequency. We combine these measurements to evaluate the frequency dependence of Qc of the form Qc(f)=Qof η, where Qo is the quality factor at 1Hz and η is the frequency dependence. Computed Qo values range from 80-360 and η ranges from 0.85-1.45. To study the lateral variation in Qo and η, we regionalise the Qc by combining all source-receiver measurements using a back-projection algorithm. For a single back scatter model, the coda waves sample an elliptical area with the epicenter and receiver at the two foci. We parameterize the region using square grids. The algorithm calculates the overlap in area and distributes Qc in the sampled grids using the average Qc as the boundary value. This is done in an iterative manner, by minimising the misfit between the observed and computed Qc within each grid. This process is repeated for all frequencies and η is computed for each grid by combining Qc for all frequencies. Our results reveal strong variation in Qo and η across NE India. The highest Qo are in the Bengal Basin (210-280) and the Indo-Burman subduction zone (300-360). The Shillong Plateau and Mikir Hills have intermediate Qo (~160) and the lowest Qo (~80) is observed in the Naga fold thrust belt. This variation in Qo demarcates the boundary between the continental crust beneath the Shillong Plateau and Mikir Hills and the transitional to oceanic crust beneath the Bengal Basin and Indo-Burman subduction zone. Thick pile of sedimentary strata in the Naga fold thrust belt results in the low Qo. Frequency dependence (η) of Qc across NE India is observed to be very high, with regions of high Qo being associated with relatively higher η.

  6. Jet-boundary and Plan-form Corrections for Partial-Span Models with Reflection-Plane, End-Plate, or No End-Plate in a Closed Circular Wind Tunnel

    NASA Technical Reports Server (NTRS)

    Sivells, James C; Deters, Owen J

    1946-01-01

    A method is presented for determining the jet-boundary and plan-form corrections necessary for application to test data for a partial-span model with a reflection plane, an end plate, or no end plate in a closed circular wind tunnel. Examples are worked out for a partial-span model with each of the three end conditions in the Langley 19-foot pressure tunnel and the corrections are applied to measured values of lift, drag, pitching-moment, rolling-moment, and yawing-moment coefficients.

  7. The northeast Japan margin: an example of slow accretion rather than tectonic erosion?

    NASA Astrophysics Data System (ADS)

    Regalla, C.; Fisher, D. M.; Kirby, E.; Furlong, K. P.

    2015-12-01

    Tectonic erosion at convergent plate boundaries is invoked to explain the evolution of nearly half the world's subduction zones. In northeast Japan, basal tectonic erosion is argued to explain regional Miocene forearc subsidence and the lack of a large, young accretionary prism. However, new analysis of upper and lower plate kinematics in northeast Japan suggest that both of can be explained by alternate mechanisms. New analysis of the timing and kinematics of deformation demonstrate that the onset of Miocene forearc tectonic subsidence was coeval with the initiation of upper plate extension and subsidence associated with the opening of the Sea of Japan, and with a rapid acceleration in local plate convergence. The coincidence of tectonic events across the upper and lower plates suggest they are both a response to lithospheric-scale processes, and that forearc tectonic subsidence represents a response to changes in plate boundary geometry, rather than tectonic erosion. New high resolution seismic profiles and 10Be geochronology of the outer wedge at the Japan Trench indicate that much of the incoming Pacific plate sediments are actively accreted, and while subducting horst and graben topography severely deforms the frontal prism, it is not an efficient mechanism for frontal tectonic erosion. The presence of a small, Plio-Quaternary accretionary wedge and the eastward younging of basal slope basin sediments argue that the outer forearc crustal structure could be explained as the result of slow, but relatively continuous frontal accretion throughout the Cenozoic. These data suggest that the northeast Japan margin has not experienced large quantities of tectonic erosion, but instead experienced: 1) forearc subsidence caused by plate velocity driven changes in slab geometry, and 2) slow accretion and frontal wedge growth disrupted by subduction of seafloor topography.

  8. Seismic heating signatures in the Japan Trench subduction plate-boundary fault zone: evidence from a preliminary rock magnetic `geothermometer'

    NASA Astrophysics Data System (ADS)

    Yang, Tao; Dekkers, Mark J.; Zhang, Bo

    2016-04-01

    Frictional heating during earthquake rupture reveals important information on earthquake mechanisms and energy dissipation. The amount of annealing varies widely and is, as yet, poorly constrained. Here we use magnetic susceptibility versus temperature measurements during cycling to increasingly elevated temperatures to constrain the maximum temperature a slip zone has experienced. The case study comprises sheared clay cored from the Japan Trench subduction plate-boundary fault zone (décollement), which accommodated the large slip of the 2011 Mw 9.0 Tohoku-oki earthquake. The décollement was cored during the Integrated Ocean Drilling Program (IODP) Expedition 343, the Japan Trench Fast Drilling Project (JFAST). Heating signatures with estimated maximum temperatures ranging from ˜300 to over 500 °C are determined close to the multiple slip surfaces within the décollement. Since it is impossible to tie a specific slip surface to a certain earthquake, thermal evidence for the cumulative effect of several earthquakes is unveiled. This as yet preliminary rock magnetic `geothermometer' would be a useful tool to detect seismic heating along faults that experienced medium temperature rise, a range which is difficult to assess with other approaches.

  9. A boundary-integral model for drop deformation between two parallel plates with non-unit viscosity ratio drops

    NASA Astrophysics Data System (ADS)

    Janssen, P. J. A.; Anderson, P. D.

    2008-10-01

    A boundary-integral method is presented for drop deformation between two parallel walls for non-unit viscosity ratio systems. To account for the effect of the walls the Green's functions are modified and all terms for the double-layer potential are derived. The full three-dimensional implementation is validated, and the model is shown to be accurate and consistent. The method is applied to study drop deformation in shear flow. An excellent match with small-deformation theory is found at low capillary numbers, and our results match with other BIM simulations for pressure-driven flows. For shear flow with moderate capillary numbers, we see that the behavior of a low-viscosity drop is similar to that of drop with a viscosity ratio of unity. High-viscosity drops, on the other hand, are prevented from rotating in shear flow, which results in a larger deformation, but less overshoot in the drop axes is observed. In contrast with unconfined flow, high-viscosity drops can be broken in shear flow between parallel plates; for low-viscosity drops the critical capillary number is higher in confined situations.

  10. Serpentinization Rates at Slow-Spreading Mid-Ocean Ridges: From Sample Scale to Plate-Boundary

    NASA Astrophysics Data System (ADS)

    Cannat, M.; Rouméjon, S.

    2015-12-01

    About 25% of the crust formed at slow spreading mid-ocean ridges includes a component of tectonically exhumed and partially serpentinized mantle-derived peridotites. Exhumation occurs along large offset normal faults (detachment faults). In this presentation we outline a conceptual and testable model for serpentinization at slow-spreading ridges, based on petrological observations of samples of variably serpentinized peridotites from the Mid Atlantic and Southwest Indian ridges, on tectonic and geophysical data and on current interpretations of plate-boundary processes at slow spreading ridges. Serpentinization at mid-ocean ridges is a heterogeneous and multistage process occurring along fractures, in the footwall of axial detachments. The initial and most pervasive stage of serpentinization results in the typical serpentine mesh texture. We propose that it occurs when hydrothermal fluids reach extensively microfractured fresh peridotite. Subsequent stages of serpentinization appear to involve higher fluid-rock ratio along larger fractures and veins that are spaced by at least a few decimeters. Experimental data indicate that each stage of serpentinization identified in a given sample may have occurred at very high rates relative to the rates of tectonic exhumation. However, serpentinization (initial and later stages) may be a protracted process at the km-scale, associated with complex fracturation of the detachment's footwall due to combined tectonic and reaction-induced stresses. We outline possible consequences of this conceptual model in terms of crustal structure, hydrogen production and of the relations between serpentinization and black smoker-type hydrothermal circulation at slow-spreading ridges.

  11. Plume Capture by Divergent Plate Motions: Implications for the Distribution of Hotspots, Geochemistry of Mid-Ocean Ridge Basalts, and Heat Flux from the Core-Mantle Boundary

    NASA Astrophysics Data System (ADS)

    Jellinek, A. M.; Richards, M. A.

    2001-12-01

    The coexistence of mantle plumes with plate-scale flow is problematic in geodynamics. Significant problems include the fixity of hotspots with respect to plate motions, the spatial distribution and duration of hotspots, the geophysical and geochemical signatures of plume-ridge interactions, and the relation between mantle plumes and heat flux across the core-mantle boundary. We present results from laboratory experiments aimed at understanding the effects of an imposed large-scale circulation on thermal convection at high Rayleigh number (up to 109) in a fluid with a strongly temperature-dependent viscosity. In a large tank, a layer of corn syrup is heated from below while being stirred by large-scale flow due to the opposing motions of a pair of conveyor belts immersed in the syrup at the top of the tank. Three regimes are observed, depending on the velocity ratio V of the imposed horizontal flow velocity to the rise velocity of plumes ascending from the hot boundary. When V<<1, large scale circulation has a negligible effect and convective upwelling occurs as randomly-spaced axisymmetric plumes that interact with one another. When V>10, plume instabilities are suppressed entirely and the heat flux from the hot lower boundary is carried by a central sheet-like upwelling. At intermediate V, ascending plumes are advected along the bottom boundary layer, and the heat flux from the boundary is found to scale (according to a simple boundary layer theory) with V and the ratio of the viscosity of cold fluid above the thermal boundary layer to the viscosity of the hottest fluid in contact with the bottom boundary. For large viscosity ratios (10-100), only about 1/5th or less of the total heat flux from the hot boundary layer is carried by plume instabilities, even for modest imposed horizontal flow velocities (V of order 1). When applied to Earth, our results suggest that plate-scale flow focuses ascending mantle plumes toward mid-ocean ridges, and that plumes may be

  12. Accretion of southern Alaska

    USGS Publications Warehouse

    Hillhouse, J.W.

    1987-01-01

    Paleomagnetic data from southern Alaska indicate that the Wrangellia and Peninsular terranes collided with central Alaska probably by 65 Ma ago and certainly no later than 55 Ma ago. The accretion of these terranes to the mainland was followed by the arrival of the Ghost Rocks volcanic assemblage at the southern margin of Kodiak Island. Poleward movement of these terranes can be explained by rapid motion of the Kula oceanic plate, mainly from 85 to 43 Ma ago, according to recent reconstructions derived from the hot-spot reference frame. After accretion, much of southwestern Alaska underwent a counterclockwise rotation of about 50 ?? as indicated by paleomagnetic poles from volcanic rocks of Late Cretaceous and Early Tertiary age. Compression between North America and Asia during opening of the North Atlantic (68-44 Ma ago) may account for the rotation. ?? 1987.

  13. The October 28, 2012 Mw 7.8 Haida Gwaii underthrusting earthquake and tsunami: Slip partitioning along the Queen Charlotte Fault transpressional plate boundary

    NASA Astrophysics Data System (ADS)

    Lay, Thorne; Ye, Lingling; Kanamori, Hiroo; Yamazaki, Yoshiki; Cheung, Kwok Fai; Kwong, Kevin; Koper, Keith D.

    2013-08-01

    The Pacific/North American plate boundary is undergoing predominantly right-lateral strike-slip motion along the Queen Charlotte and Fairweather transform faults. The Queen Charlotte Fault (QCF) hosted the largest historical earthquake in Canada, the 1949 MS 8.1 strike-slip earthquake, which ruptured from offshore northern Haida Gwaii several hundred kilometers northwestward. On January 5, 2013 an Mw 7.5 strike-slip faulting event occurred near the northern end of the 1949 rupture zone. Along central and southern Haida Gwaii the relative plate motion has ∼20% oblique convergence across the left-stepping plate boundary. There had been uncertainty in how the compressional component of plate motion is accommodated. The October 28, 2012 Mw 7.8 Haida Gwaii earthquake involved slightly (∼20°) oblique thrust faulting on a shallow (∼18.5°) northeast-dipping fault plane with strike (∼320°) parallel to the QCF, consistent with prior inferences of Pacific Plate underthrusting beneath Haida Gwaii. The rupture extended to shallow depth offshore of Moresby Island beneath a 25-30 km wide terrace of sediments that has accumulated in a wedge seaward of the QCF. The shallow thrusting caused seafloor uplift that generated substantial localized tsunami run-up and a modest far-field tsunami that spread across the northern Pacific, prompting a tsunami warning, beach closure, and coastal evacuation in Hawaii, although ultimately tide gauges showed less than 0.8 m of water level increase. The mainshock rupture appears to have spread with a ∼2.3 km/s rupture velocity over a length of ∼150 km, with slip averaging 3.3 m concentrated beneath the sedimentary wedge. The event was followed by a substantial aftershock sequence, in which almost all of the larger events involve distributed intraplate normal faulting extending ∼50 km oceanward from the QCF. The highly oblique slip partitioning in southern Haida Gwaii is distinctive in that the local plate boundary-parallel motion on

  14. Using high-resolution aeromagnetic survey to map tectonic elements of plate boundaries: An example from the Dead Sea Fault

    NASA Astrophysics Data System (ADS)

    Al-Zoubi, A. S.; ten Brink, U. S.; Rybakov, M.; Rotstein, Y.

    2004-12-01

    The Dead Sea Fault (DSF) is a transform plate boundary between the African and the Arabian plates. The 200-km-long DSF segment between the Gulf of Aqaba/Elat and the Dead Sea, which has the morphology of a rift valley, shows little seismic activity, and its surface trace is only intermittently visible. High-resolution magnetic data were collected in October 2003 aboard a Jordanian military helicopter flying at an altitude of 100 m over the southern 120-km-long section of this fault segment. The survey was part of a US-AID Middle Eastern Regional Cooperation project between Jordanian, Israeli, Palestinian, and American scientists. Data were collected along rift-perpendicular lines spaced 300 m apart, requiring frequent crossings between Israeli and Jordanian air spaces. The data were gridded at 75 m interval following resolution tests, reduced to pole, and incorporated into a GIS together with elevation, geology, and gravity maps to facilitate interpretation. The main findings of the magnetic survey are the absence of magnetic anomalies crossing the rift valley, and the presence of a rift-parallel regional lineament corresponding to the active trace of the DSF. The lineament extends NNE as an almost continuous trace from Elat, Israel, to the eastern side of the valley 5 km north of Rahmeh. Jordan. Another fault trace located 2-3 km to the west may overlap and continue NNE through Gebel A-Risha, and into the central Arava/Araba valley, where it is visible on the surface. Alternatively, the two traces may be connected. If an offset between the two traces exists, it may be small enough to allow an earthquake rupture to propagate across the offset, and generate an earthquake with a moment magnitude of up to 7.5. Traces of buried faults in the central Arava/Araba valley that were previously active in the DSF system, are visible as abrupt terminations of an area of short wavelength magnetic anomalies. These anomalies probably represent shallow subsurface magmatic

  15. Modulation of mantle plumes and heat flow at the core mantle boundary by plate-scale flow: results from laboratory experiments

    NASA Astrophysics Data System (ADS)

    Gonnermann, Helge M.; Jellinek, A. Mark; Richards, Mark A.; Manga, Michael

    2004-09-01

    We report results from analog laboratory experiments, in which a large-scale flow is imposed upon natural convection from a hot boundary layer at the base of a large tank of corn syrup. The experiments show that the subdivision of the convective flow into four regions provides a reasonable conceptual framework for interpreting the effects of large-scale flow on plumes. Region I includes the area of the hot thermal boundary layer (TBL) that is thinned by the large-scale flow, thereby suppressing plumes. Region II encompasses the critically unstable boundary layer where plumes form. Region III is the area above the boundary layer that is devoid of plumes. Region IV comprises the area of hot upwelling and plume conduits. Quantitative analysis of our experiments results in a scaling law for heat flux from the hot boundary and for the spatial extent of plume suppression. When applied to the Earth's core-mantle boundary (CMB), our results suggest that large-scale mantle flow, due to sinking lithospheric plates, can locally thin the TBL and suppress plume formation over large fractions of the CMB. Approximately 30% of heat flow from the core may be due to increased heat flux from plate-scale flow. Furthermore, CMB heat flux is non-uniformly distributed along the CMB, with large areas where heat flux is increased on average by a factor of 2. As a consequence, the convective flow pattern in the outer core may be affected by CMB heat-flux heterogeneity and sensitive to changes in plate-scale mantle flow. Because of plume suppression and 'focusing' of hot mantle from the CMB into zones of upwelling flow, plume conduits (hotspots) are expected to be spatially associated with lower-mantle regions of low seismic velocities, inferred as hot upwelling mantle flow.

  16. Earthquakes and Plate Boundaries

    ERIC Educational Resources Information Center

    Lowman, Paul; And Others

    1978-01-01

    Contains the contents of the Student Investigation booklet of a Crustal Evolution Education Project (CEEP) instructional modules on earthquakes. Includes objectives, procedures, illustrations, worksheets, and summary questions. (MA)

  17. Investigating crustal deformation associated with the North America-Pacific plate boundary in southern California with GPS geodesy

    NASA Astrophysics Data System (ADS)

    Spinler, Joshua C.

    The three largest earthquakes in the last 25 years in southern California occurred on faults located adjacent to the southern San Andreas fault, with the M7.3 1992 Landers and M7.1 1999 Hector Mine earthquakes occurring in the eastern California shear zone (ECSZ) in the Mojave Desert, and the M7.2 2010 El Mayor-Cucapah earthquake occurring along the Laguna Salada fault in northern Baja California, Mexico. The locations of these events near to but not along the southern San Andreas fault (SSAF) is unusual in that the last major event on the SSAF occurred more than 300 years ago, with an estimated recurrence interval of 215 +/- 25 years. The focus of this dissertation is to address the present-day deformation field along the North America-Pacific plate boundary in southern California and northern Baja California, through the analysis of GPS data, and elastic block and viscoelastic earthquake models to determine fault slip rates and rheological properties of the lithosphere in the plate boundary zone. We accomplish this in three separate studies. The first study looks at how strain is partitioned northwards along-strike from the southern San Andreas fault near the Salton Sea. We find that estimates for slip-rates on the southern San Andreas decrease from ~23 mm/yr in the south to ~8 mm/yr as the fault passes through San Gorgonio Pass to the northwest, while ~13-18 mm/yr of slip is partitioned onto NW-SE trending faults of the ECSZ where the Landers and Hector Mine earthquakes occurred. This speaks directly to San Andreas earthquake hazards, as a reduction in the slip rate would require greater time between events to build up enough slip deficit in order to generate a large magnitude earthquake. The second study focuses on inferring the rheological structure beneath the Salton Trough region. This is accomplished through analysis of postseismic deformation observed using a set of the GPS data collected before and after the 2010 El Mayor-Cucapah earthquake. By

  18. Slip rate and earthquake recurrence along the central Septentrional fault, North American-Caribbean plate boundary, Dominican Republic

    USGS Publications Warehouse

    Prentice, C.S.; Mann, P.; Pena, L.R.; Burr, G.

    2003-01-01

    The Septentrional fault zone (SFZ) is the major North American-Caribbean, strike-slip, plate boundary fault at the longitude of eastern Hispaniola. The SFZ traverses the densely populated Cibao Valley of the Dominican Republic, forming a prominent scarp in alluvium. Our studies at four sites along the central SFZ are aimed at quantifying the late Quaternary behavior of this structure to better understand the seismic hazard it represents for the northeastern Caribbean. Our investigations of excavations at sites near Rio Cenovi show that the most recent ground-rupturing earthquake along this fault in the north central Dominican Republic occurred between A.D. 1040 and A.D. 1230, and involved a minimum of ???4 m of left-lateral slip and 2.3 m of normal dip slip at that site. Our studies of offset stream terraces at two locations, Rio Juan Lopez and Rio Licey, provide late Holocene slip rate estimates of 6-9 mm/yr and a maximum of 11-12 mm/yr, respectively, across the Septentrional fault. Combining these results gives a best estimate of 6-12 mm/yr for the slip rate across the SFZ. Three excavations, two near Tenares and one at the Rio Licey site, yielded evidence for the occurrence of earlier prehistoric earthquakes. Dates of strata associated with the penultimate event suggest that it occurred post-A.D. 30, giving a recurrence interval of 800-1200 years. These studies indicate that the SFZ has likely accumulated elastic strain sufficient to generate a major earthquake during the more than 800 years since it last slipped and should be considered likely to produce a destructive future earthquake.

  19. Low-latency high-rate GPS data streams from the EarthScope Plate Boundary Observatory

    NASA Astrophysics Data System (ADS)

    Anderson, G.; Borsa, A.; Jackson, M.; Stark, K.

    2008-05-01

    Real-time processing of high rate GPS data can give precise (e.g., 5-10 mm for data recorded once per second) recordings of rapid volcanic and seismic deformation. These time series now provide an emerging tool for seismic, volcanic, and tsunami geodesy and early warning applications. UNAVCO, as part of the EarthScope Plate Boundary Observatory project, has developed the UStream system to provide streaming GPS data from some PBO and other UNAVCO-operated GPS stations. UStream is based on the Ntrip standard, a widely used protocol for streaming GNSS data over the Internet. Remote GPS stations provide a stream of BINEX data at 1 sample/sec to an Ntrip server at UNAVCO's Boulder offices, while simultaneously recording data locally in the event of communications failure. Once in Boulder, the data fork into three output streams: BINEX files stored at UNAVCO and streams of data in BINEX and RTCM 2.3 format. These streams flow to an Ntrip broadcaster that distributes data to Ntrip clients, which can be anything from low-latency processing systems to external data archiving systems. Current development efforts are geared toward providing data in RTCM 3.x format. This system is now operating in a public beta test mode, with data available from over 55 PBO and Nucleus GPS stations across the western United States. Data latencies from stations operating on mobile telephone communications are under 1.1 seconds at 95% confidence, and data completeness is typically more than 95% barring transient communications disruptions. Data from the system are available under the terms of the draft UNAVCO streaming data usage policy. For further information, please visit http://rtgps.unavco.org or send e-mail to rtgps@unavco.org.

  20. The Ionian and Alfeo-Etna fault zones: New segments of an evolving plate boundary in the central Mediterranean Sea?

    NASA Astrophysics Data System (ADS)

    Polonia, A.; Torelli, L.; Artoni, A.; Carlini, M.; Faccenna, C.; Ferranti, L.; Gasperini, L.; Govers, R.; Klaeschen, D.; Monaco, C.; Neri, G.; Nijholt, N.; Orecchio, B.; Wortel, R.

    2016-04-01

    The Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. While crustal shortening is taken up in the accretionary wedge, transtensive deformation accounts for margin segmentation along transverse lithospheric faults. One of these structures is the NNW-SSE transtensive fault system connecting the Alfeo seamount and the Etna volcano (Alfeo-Etna Fault, AEF). A second, NW-SE crustal discontinuity, the Ionian Fault (IF), separates two lobes of the CA subduction complex (Western and Eastern Lobes) and impinges on the Sicilian coasts south of the Messina Straits. Analysis of multichannel seismic reflection profiles shows that: 1) the IF and the AEF are transfer crustal tectonic features bounding a complex deformation zone, which produces the downthrown of the Western lobe along a set of transtensive fault strands; 2) during Pleistocene times, transtensive faulting reactivated structural boundaries inherited from the Mesozoic Tethyan domain which acted as thrust faults during the Messinian and Pliocene; and 3) the IF and the AEF, and locally the Malta escarpment, accommodate a recent tectonic event coeval and possibly linked to the Mt. Etna formation. Regional geodynamic models show that, whereas AEF and IF are neighboring fault systems, their individual roles are different. Faulting primarily resulting from the ESE retreat of the Ionian slab is expressed in the northwestern part of the IF. The AEF, on the other hand, is part of the overall dextral shear deformation, resulting from differences in Africa-Eurasia motion between the western and eastern sectors of the Tyrrhenian margin of northern Sicily, and accommodating diverging motions in the adjacent compartments, which results in rifting processes within the Western Lobe of the Calabrian Arc accretionary wedge. As such, it is primarily associated with Africa-Eurasia relative motion.

  1. Exploring anisotropic seismic property of the seismogenic plate boundary in the Nankai Trough using a seafloor borehole observatory

    NASA Astrophysics Data System (ADS)

    Araki, E.; Kimura, T.; Kodaira, S.; Miura, S.; Takaesu, M.; Takahashi, N.; Nakano, M.; Kaneda, Y.

    2014-12-01

    Stress state in the vicinity of a seismogenic fault would be a key parameter governing its fault dynamics. Stress analysis in a borehole such as breakout may give stress information, but drilling seismogenic fault at depth is still challenging and it is even more difficult to perform repeated stress measurements for temporal evolution of stress state. Here we consider applying seismic anisotropy as an index of stress state and by observing its temporal change to identify change of stress around the seismogenic fault. In this study, we explored techniques to assess seismic anisotropy in the Nankai Trough accretionary prism, using a borehole seismometer deployed in IODP borehole C0002G, which is located just above the Tonankai earthquake fault. The borehole seismometer is situated at about 900 m below 1966 m deep seafloor, and is operational since January 2013 when the observatory was connected to DONET seafloor cable network. We developed a technique to analyze seismic anisotropy on converted S-wave from microseismic noise records and applied the technique on the borehole seismometer records, by which we expect to evaluate temporal change of anisotropy continuously. We obtained anisotropy of a few percent. We further evaluated depth dependency of anisotropy direction and obtained the difference between the uppermost sedimentary basin and accretionary prism near the plate boundary. We also performed airgun array shooting around the borehole in November 2013 to check validity of the anisotropy result. We applied two different analysis on the airgun records, the one was P-wave seismic anisotropy from the travel time, and the other was S-wave anisotropy using converted S-wave from airgun P-wave. Preliminary results from these analysis were consistent with the microseismic noise analysis. Repeated airgun shooting is planned at the interval of a year or so to evaluate our ability to detect its temporal change.

  2. PBO H2O: Monitoring the Terrestrial Water Cycle with reflected GPS signals recorded by the Plate Boundary Observatory Network

    NASA Astrophysics Data System (ADS)

    Small, E. E.; Fairfax, E. J.; Chew, C. C.; Larson, K. M.

    2015-12-01

    Data from NSF's EarthScope Plate Boundary Observatory (PBO), and similar GPS networks worldwide, can be used to monitor the terrestrial water cycle. GPS satellites transmit L-band microwave signals, which are strongly influenced by water at the surface of the Earth. GPS signals take two different paths: (1) the "direct" signal travels from the satellite to the antenna; (2) the "reflected" signal interacts with the Earth's surface before travelling to the antenna. The direct signal is used by geophysicists to measure the position of the antenna. By analyzing these GPS data over multiple years, the motion of the site can be estimated. The effects of reflected signals are generally ignored by geophysicists because they are small. This is not happenstance, as significant effort has been made to design and deploy a GPS antenna that suppresses ground reflections. Our group has developed a remote sensing technique to retrieve terrestrial water cycle variables from GPS data. We extract the water cycle products from signal strength data that measures the interference between the direct and reflected GPS signals. The sensing footprint is intermediate in scale between in situ observations and most remote sensing measurements. Snow depth, snow water equivalent (SWE), near surface soil moisture, and an index of vegetation water content are currently estimated from nearly 500 PBO sites. These PBO H2O products are updated daily and are available online (http://xenon.colorado.edu/portal/index.php). Validation studies show that retrieved products are of sufficient quality to be used in a variety of applications. The root mean square error (RMSE) of GPS-based SWE is 2 cm, based on a comparison to snow survey data at nearly 20 GPS sites. The RMSE of near surface volumetric soil moisture is < 0.04 cm3 cm-3, sufficient for validation of SMAP soil moisture and similar products.

  3. Nonlinear Radiation Heat Transfer Effects in the Natural Convective Boundary Layer Flow of Nanofluid Past a Vertical Plate: A Numerical Study

    PubMed Central

    Mustafa, Meraj; Mushtaq, Ammar; Hayat, Tasawar; Ahmad, Bashir

    2014-01-01

    The problem of natural convective boundary layer flow of nanofluid past a vertical plate is discussed in the presence of nonlinear radiative heat flux. The effects of magnetic field, Joule heating and viscous dissipation are also taken into consideration. The governing partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations via similarity transformations and then solved numerically using the Runge–Kutta fourth-fifth order method with shooting technique. The results reveal an existence of point of inflection for the temperature distribution for sufficiently large wall to ambient temperature ratio. Temperature and thermal boundary layer thickness increase as Brownian motion and thermophoretic effects intensify. Moreover temperature increases and heat transfer from the plate decreases with an increase in the radiation parameter. PMID:25251242

  4. Nonlinear radiation heat transfer effects in the natural convective boundary layer flow of nanofluid past a vertical plate: a numerical study.

    PubMed

    Mustafa, Meraj; Mushtaq, Ammar; Hayat, Tasawar; Ahmad, Bashir

    2014-01-01

    The problem of natural convective boundary layer flow of nanofluid past a vertical plate is discussed in the presence of nonlinear radiative heat flux. The effects of magnetic field, Joule heating and viscous dissipation are also taken into consideration. The governing partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations via similarity transformations and then solved numerically using the Runge-Kutta fourth-fifth order method with shooting technique. The results reveal an existence of point of inflection for the temperature distribution for sufficiently large wall to ambient temperature ratio. Temperature and thermal boundary layer thickness increase as Brownian motion and thermophoretic effects intensify. Moreover temperature increases and heat transfer from the plate decreases with an increase in the radiation parameter.

  5. Plane elasto-plastic analysis of v-notched plate under bending by boundary integral equation method. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Rzasnicki, W.

    1973-01-01

    A method of solution is presented, which, when applied to the elasto-plastic analysis of plates having a v-notch on one edge and subjected to pure bending, will produce stress and strain fields in much greater detail than presently available. Application of the boundary integral equation method results in two coupled Fredholm-type integral equations, subject to prescribed boundary conditions. These equations are replaced by a system of simultaneous algebraic equations and solved by a successive approximation method employing Prandtl-Reuss incremental plasticity relations. The method is first applied to number of elasto-static problems and the results compared with available solutions. Good agreement is obtained in all cases. The elasto-plastic analysis provides detailed stress and strain distributions for several cases of plates with various notch angles and notch depths. A strain hardening material is assumed and both plane strain and plane stress conditions are considered.

  6. Nonlinear radiation heat transfer effects in the natural convective boundary layer flow of nanofluid past a vertical plate: a numerical study.

    PubMed

    Mustafa, Meraj; Mushtaq, Ammar; Hayat, Tasawar; Ahmad, Bashir

    2014-01-01

    The problem of natural convective boundary layer flow of nanofluid past a vertical plate is discussed in the presence of nonlinear radiative heat flux. The effects of magnetic field, Joule heating and viscous dissipation are also taken into consideration. The governing partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations via similarity transformations and then solved numerically using the Runge-Kutta fourth-fifth order method with shooting technique. The results reveal an existence of point of inflection for the temperature distribution for sufficiently large wall to ambient temperature ratio. Temperature and thermal boundary layer thickness increase as Brownian motion and thermophoretic effects intensify. Moreover temperature increases and heat transfer from the plate decreases with an increase in the radiation parameter. PMID:25251242

  7. Late 18th to early 19th century sea-level history and inter-seismic behavior along the western Myanmar plate boundary belt recorded by coral microatolls

    NASA Astrophysics Data System (ADS)

    Liu, Sze-Chieh; Shyu, J. Bruce H.

    2016-04-01

    Along the western Myanmar plate boundary belt, the Indian-Australian plate is subducting obliquely beneath the Burma micro-plate at a rate of about 23 mm/yr. Although information about the 1762 Arakan earthquake, the only major historical event occurred along this plate boundary belt, has been delineated recently from uplifted coastal features, constraints on the inter-seismic behavior of this belt is still very limited, due to the lack of high resolution instrumental records in the area. Therefore, we utilized coral microatolls to analyze relative sea level history, in order to obtain potential information of land-level change along the western coast of Myanmar. Our sample was collected from northwestern Ramree Island, approximately 80 km away from the trench. Previous studies suggest that the coral was uplifted and killed during a local earthquake event in 1848, and recorded relative sea level history of ~80 years prior to that event. Since the highest level of survival (HLS) of coral microatolls is constrained within a few centimeters of the lowest tide level of the area, the patterns of annual growth bands of the coral microatoll in x-radiograph provide us yearly record of relative sea level, and we used U-Th dating technique to constrain the age of the coral. Our results show that this coral microatoll may have recorded the inter-seismic subsidence of northwestern Ramree Island, punctuated by several climatic events that produced die-down records of the coral growth bands. We hope the data obtained from this coral microatoll, combined with previously reported information of the area, will enable us to further understand the seismic behavior of this major plate boundary belt.

  8. Plate-Tectonic Analysis of Shallow Seismicity: Apparent Boundary Width, beta-Value, Corner Magnitude, Coupled Lithosphere Thickness, and Coupling in 7 Tectonic Settings

    NASA Astrophysics Data System (ADS)

    Bird, P.; Kagan, Y. Y.

    2003-12-01

    A new plate model [Bird, 2003, G3, 10.1029/2001GC000252] is used to analyze the mean seismicities of 7 types of plate boundary (CRB continental rift boundary, CTF continental transform fault, CCB continental convergent boundary, OSR oceanic spreading ridge, OTF oceanic transform fault, OCB oceanic convergent boundary, SUB subduction zone). We compare the plate-like (non-orogen) regions of model PB2002 with the CMT catalog to select apparent boundary half-widths, and then assign 95% of shallow earthquakes to one of these settings. A tapered Gutenberg-Richter model of the frequency/moment relation is fit to the subcatalog for each setting by maximum-likelihood. Best-fitting β values range from 0.53 to 0.92, but all 95%-confidence ranges are consistent with a common value of 0.61-0.66. To better determine some corner magnitudes we expand the subcatalogs by: (1) inclusion of orogens; and (2) inclusion of years 1900-1975 from the catalog of Pacheco and Sykes [1992]. Combining both earthquake statistics and the plate-tectonic constraint on moment rate, corner magnitudes include: CRB 7.64-.26+.76, CTF 8.01-.21+.45, CCB 8.46-.39+.21, OCB 8.04-.22+.52, and SUB 9.58-.46+.48. Coupled lithosphere thicknesses are found to be: CRB 3.0-1.4+7.0 km; CTF 8.6-4.1+11 km; CCB 18-11+? km; OSR 0.13-0.09+.13 km for normal-faulting and 0.40-.21+? km for strike-slip; OTF 12-7.1+?, 1.6-0.5+1.4, and 1.5-0.6+1.2 km at low, medium, and high velocities; OCB 3.8-2.3+13.7 km, and SUB 18.0-10.8+? km. Generally high coupling of subduction and continental plate boundaries suggests that here all seismic gaps are dangerous unless proven to be creeping. Generally low coupling within oceanic lithosphere suggests a different model of isolated seismic asperities surrounded by large seismic gaps which may be permanent.

  9. Geologic observations of the northern boundary of the Caribbean plate across central America as seen by Seasat and SIR-A

    NASA Technical Reports Server (NTRS)

    Rebillard, P.; Dixon, T.; Farr, T.

    1982-01-01

    The radar data analyzed here extend from the Amatique Bay (Golfo de Honduras) in the northeast to the Pacific Ocean (Puenta Remedios) in the southwest. Space Shuttle Imaging Radar (SIR-A) data-take 18 overlaps the principal part of the Seasat mosaic. SIR-A data make possible more observations over the Central American Cordillera, where strong layover limited the amount of information obtained by Seasat. The radar coverage delineates the principal strike-slip faults of the region (Cuilco-Chixoy-Polochic, Motagua and Jocotan), which have acted as the Caribbean-Americas plate boundary. It also demarcates volcanic terranes related to subduction of the Cocos Plate under the Caribbean Plate. Within pumice fields of the Tertiary volcanic belt, the use of two Seasat look directions (rev 759 and rev 1211), in conjunction with SIR-A data, makes possible some rock discrimination.

  10. LDA measurements in the premixed V flame stabilized in the wake of a flat plate boundary layer

    SciTech Connect

    Trevino, C. ); Donnerhack, S. ); Peters, N. )

    1991-06-01

    This paper presents laser-doppler measurements and particle track photographs of V-shaped flame. The flame is stabilized behind a splitter plate in a two-dimensional premixed gas flow. In order to stabilize the flame, the splitter plate must be heated, indicating the importance of the thermal interaction between the flame and the plate. Based on theoretical concepts of the viscous flow at the trailing edge of a plate, an order of magnitude of the thermal penetration length is performed. This is compared with the preheat zone thickness.

  11. Hydrodynamic and Thermal Slip Effect on Double-Diffusive Free Convective Boundary Layer Flow of a Nanofluid Past a Flat Vertical Plate in the Moving Free Stream

    PubMed Central

    Khan, Waqar A.; Uddin, Md Jashim; Ismail, A. I. Md.

    2013-01-01

    The effects of hydrodynamic and thermal slip boundary conditions on the double-diffusive free convective flow of a nanofluid along a semi-infinite flat solid vertical plate are investigated numerically. It is assumed that free stream is moving. The governing boundary layer equations are non-dimensionalized and transformed into a system of nonlinear, coupled similarity equations. The effects of the controlling parameters on the dimensionless velocity, temperature, solute and nanofluid concentration as well as on the reduced Nusselt number, reduced Sherwood number and the reduced nanoparticle Sherwood number are investigated and presented graphically. To the best of our knowledge, the effects of hydrodynamic and thermal slip boundary conditions have not been investigated yet. It is found that the reduced local Nusselt, local solute and the local nanofluid Sherwood numbers increase with hydrodynamic slip and decrease with thermal slip parameters. PMID:23533566

  12. Using EarthScope Construction of the Plate Boundary Observatory to Provide Locally Based Experiential Education and Outreach

    NASA Astrophysics Data System (ADS)

    Jackson, M.; Eriksson, S.; Barbour, K.; Venator, S.; Mencin, D.; Prescott, W.

    2006-12-01

    EarthScope is an NSF-funded, national science initiative to explore the structure and evolution of the North American continent and to understand the physical processes controlling earthquakes and volcanoes. This large-scale experiment provides locally based opportunities for education and outreach which engage students at various levels and the public. UNAVCO is responsible for the Plate Boundary Observatory (PBO) component of EarthScope. PBO includes the installation and operations and maintenance of large networks of Global Positioning Satellite (GPS), strainmeter, seismometer, and tiltmeter instruments and the acquisition of satellite radar imagery, all of which will be used to measure and map the smallest movements across faults, the magma movement inside active volcanoes and the very wide areas of deformation associated with plate tectonic motion. UNAVCO, through its own education and outreach activities and in collaboration with the EarthScope E&O Program, uses the PBO construction activities to increase the understanding and public appreciation of geodynamics, earth deformation processes, and their relevance to society. These include programs for public outreach via various media, events associated with local installations, a program to employ students in the construction of PBO, and development of curricular materials by use in local schools associated with the EarthScope geographic areas of focus. PBO provides information to the media to serve the needs of various groups and localities, including interpretive centers at national parks and forests, such as Mt. St. Helens. UNAVCO staff contributed to a television special with the Spanish language network Univision Aquí y Ahora program focused on the San Andreas Fault and volcanoes in Alaska. PBO participated in an Education Day at the Pathfinder Ranch Science and Outdoor Education School in Mountain Center, California. Pathfinder Ranch hosts two of the eight EarthScope borehole strainmeters in the Anza

  13. Constraints on fault slip rates of the southern California plate boundary from GPS velocity and stress inversions

    USGS Publications Warehouse

    Becker, T.W.; Hardebeck, J.L.; Anderson, G.

    2005-01-01

    We use Global Positioning System (GPS) velocities and stress orientations inferred from seismicity to invert for the distribution of slip on faults in the southern California plate-boundary region. Of particular interest is how long-term slip rates are partitioned between the Indio segment of the San Andreas fault (SAF), the San Jacinto fault (SJF) and the San Bernardino segment of the SAE We use two new sets of constraints to address this problem. The first is geodetic velocities from the Southern California Earthquake Center's (SCEC) Crustal Motion Map (version 3 by Shen et al.), which includes significantly more data than previous models. The second is a regional model of stress-field orientations at seismogenic depths, as determined from earthquake focal mechanisms. While GPS data have been used in similar studies before, this is the first application of stress-field observations to this problem. We construct a simplified model of the southern California fault system, and estimate the interseismic surface velocities using a backslip approach with purely elastic strain accumulation, following Meade et al. In addition, we model the stress orientations at seismogenic depths, assuming that crustal stress results from the loading of active faults. The geodetically derived stressing rates are found to be aligned with the stress orientations from seismicity. We therefore proceed to invert simultaneously GPS and stress observations for slip rates of the faults in our network. We find that the regional patterns of crustal deformation as imaged by both data sets can be explained by our model, and that joint inversions lead to better constrained slip rates. In our preferred model, the SJF accommodates ???15 mm yr-1 and the Indio segment of the SAF ???23 mm yr-1 of right-lateral motion, accompanied by a low slip rate on the San Bernardino segment of the SAF 'Anomalous' fault segments such as around the 1992 Mw = 7.3 Landers surface rupture can be detected. There, observed

  14. The Teisseyre-Tornquist Zone - early Palaeozoic strike-slip plate boundary or Ediacaran rifted margin of Baltica?

    NASA Astrophysics Data System (ADS)

    Mazur, Stanislaw; Krzywiec, Piotr; Malinowski, Michal; Lewandowski, Marek; Buffenmeyer, Vinton; Green, Christopher

    2016-04-01

    area is dominated by high density lower crustal bodies similar to those that are found along present-day passive continental margins. Moreover, an extensive succession of the uppermost Neoproterozoic sediments is emplaced outboard of the southeastern section of the TTZ. These results obtained do not support the occurrence of a Palaeozoic terrane boundary along the TTZ. Instead, it is suggested that the crystalline basement of the EEC extends westward beyond the TTZ and continues in the substratum of the Permo-Mesozoic basin of central and western Poland. If the crustal keel underneath the TTZ indeed represents a fossil plate boundary, it must have formed in the Precambrian during the amalgamation of the Rodinia supercontinent. However, the contrast of crustal thickness across the TTZ between the EEC and the adjacent Palaeozoic Platform may have formed later during the Ediacaran rifting and subsequent break-up of the Tornquist Ocean. The Caledonian collisional suture must be located farther southwest in western Poland or NE Germany and deeply concealed beneath a thick cover of Palaeozoic and younger sediments.

  15. Recently active reverse faulting in the Atacama Basin area, northern Chile: Implications for the distribution of convergence across the western South America plate boundary

    NASA Astrophysics Data System (ADS)

    Shyu, J. H.; Gonzalez, G.; Simons, M.; Aron, F.; Veloso, A.

    2007-12-01

    The western South American margin is one of the most active continental plate boundaries in the world. The ongoing convergence between the Nazca plate, or formerly the Farallon plate, and the South American plate produced the wide deformation belt of the Andes. In order to obtain more information about the active deformations in the central Andean belt to better understand the current distribution of convergence across the orogen, we attempted to map major structures that appear to be active recently by their topographic expressions using SRTM DEM and Landsat satellite images, followed by field observations. Results of our mapping show that there are many reverse faults that may be recently active in the area surrounding the Atacama Basin, in the Preandean Depression in northern Chile. These include a series of active reverse faults and related folds at the southeastern corner of the Atacama Basin, a major fold system that may be produced by an underlying fault just east of the basin, and a series of folds that forms the Cordillera de la Sal in the northern and western part of the basin. At the southeastern corner of the Atacama Basin, several geomorphic features indicate that at least some of the structures there have been active quite recently, including small drainages that cut through the folds and form active alluvial fans. Similar features of active river incision across folds are also present in the northern part of the basin. The fold system east of the basin may be one of the most important structures in the area. Deformed lava flows and deflected drainages indicate that this structure has been active recently, and growth strata near the fold suggest that it has been active for several myr. If so, the structure may be a major reverse fault system that defines the eastern boundary of the Atacama Basin, and may thus be an important onland structure that is responsible for absorbing part of the plate convergence.

  16. Three-Dimensional Thermal Boundary Layer Corrections for Circular Heat Flux Gauges Mounted in a Flat Plate with a Surface Temperature Discontinuity

    NASA Technical Reports Server (NTRS)

    Kandula, M.; Haddad, G. F.; Chen, R.-H.

    2006-01-01

    Three-dimensional Navier-Stokes computational fluid dynamics (CFD) analysis has been performed in an effort to determine thermal boundary layer correction factors for circular convective heat flux gauges (such as Schmidt-Boelter and plug type)mounted flush in a flat plate subjected to a stepwise surface temperature discontinuity. Turbulent flow solutions with temperature-dependent properties are obtained for a free stream Reynolds number of 1E6, and freestream Mach numbers of 2 and 4. The effect of gauge diameter and the plate surface temperature have been investigated. The 3-D CFD results for the heat flux correction factors are compared to quasi-21) results deduced from constant property integral solutions and also 2-D CFD analysis with both constant and variable properties. The role of three-dimensionality and of property variations on the heat flux correction factors has been demonstrated.

  17. Deformation during terrane accretion in the Saint Elias orogen, Alaska

    USGS Publications Warehouse

    Bruhn, R.L.; Pavlis, T.L.; Plafker, G.; Serpa, L.

    2004-01-01

    The Saint Elias orogen of southern Alaska and adjacent Canada is a complex belt of mountains formed by collision and accretion of the Yakutat terrane into the transition zone from transform faulting to subduction in the northeast Pacific. The orogen is an active analog for tectonic processes that formed much of the North American Cordillera, and is also an important site to study (1) the relationships between climate and tectonics, and (2) structures that generate large- to great-magnitude earthquakes. The Yakutat terrane is a fragment of the North American plate margin that is partly subducted beneath and partly accreted to the continental margin of southern Alaska. Interaction between the Yakutat terrane and the North American and Pacific plates causes significant differences in the style of deformation within the terrane. Deformation in the eastern part of the terrane is caused by strike-slip faulting along the Fairweather transform fault and by reverse faulting beneath the coastal mountains, but there is little deformation immediately offshore. The central part of the orogen is marked by thrusting of the Yakutat terrane beneath the North American plate along the Chugach-Saint Elias fault and development of a wide, thin-skinned fold-and-thrust belt. Strike-slip faulting in this segment may he localized in the hanging wall of the Chugach-Saint Elias fault, or dissipated by thrust faulting beneath a north-northeast-trending belt of active deformation that cuts obliquely across the eastern end of the fold-and-thrust belt. Superimposed folds with complex shapes and plunging hinge lines accommodate horizontal shortening and extension in the western part of the orogen, where the sedimentary cover of the Yakutat terrane is accreted into the upper plate of the Aleutian subduction zone. These three structural segments are separated by transverse tectonic boundaries that cut across the Yakutat terrane and also coincide with the courses of piedmont glaciers that flow from

  18. 16 Years, 16 Cruises, 1.6 Billion Soundings: a Compilation of High-Resolution Multibeam Bathymetry of the Active Plate Boundary Along the Chilean Continental Margin

    NASA Astrophysics Data System (ADS)

    Weinrebe, W.; Flueh, E. R.; Hasert, M.; Behrmann, J. H.; Voelker, D.; Geersen, J.; Ranero, C. R.; Diaz-Naveas, J. L.

    2011-12-01

    Chile, a country stranding the active plate boundary between the South-American and the Nazca Plate is afflicted by recurrent earthquakes and hazardous volcanic eruptions. The strongest earthquake ever recorded occurred here, and volcanic hazards are frequent. Consequently, this area has been studied by geoscientists for many years to improve the understanding of subduction zone processes. Swath bathymetry mapping of the ocean floor has proven to bear a large potential for the interpretation of subduction-related processes, such as tectonic deformation of the marine forearc, release and migration of fluids as well as earthquake-triggered mass wasting. Multibeam bathymetry data of 16 major cruises of German, British, and Chilean research vessels recorded between 1995 and December 2010, in total more than 10,000 data files comprising about 1.6 billion soundings, have now been carefully reprocessed, compiled and merged into a unifying set of high-resolution bathymetric maps of the Chilean continental margin from latitude 40°S to 20°S. The imprint of subsurface processes on the surface morphology is well displayed in the case of the Chilean continental margin. The 3,500 km long Chilean convergent margin is not uniform, as various segments with different tectonic characteristics can be distinguished. Major factors that control margin morphology and thus the style of subduction are (1) relief and structure of the incoming oceanic plate, (2) supply of trench sediment, (3) turbidite transport within the trench, and (4) the input of terrigeneous sediments down the continental slope. A major segment boundary occurs at latitude 32°-33° S where the hotspot-related volcanic chain of Juan Fernandez is presently subducting. South of the area of ridge subduction the trench is filled with turbidites, and accretionary ridges develop across the base of the slope along most of the segment, whereas north of this boundary the turbiditic infill is reduced and subduction erosion is

  19. Abbot Ice Shelf, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of West Antarctica

    PubMed Central

    Cochran, James R; Tinto, Kirsty J; Bell, Robin E

    2015-01-01

    Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia. A well-defined boundary zone separates the mildly extended Abbot extensional terrain from the deeper Amundsen Embayment shelf basin. The shelf basin has an extension factor, β, of 1.5–1.7 with 80–100 km of extension occurring across an area now 250 km wide. Following this extension, rifting centered north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic Ice Sheet. The Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to incorporation into the Antarctic Plate at about 62 Ma. During the latter part of its independent existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence across the north-south trending Bellingshausen Gravity Anomaly structure at 94°W and compressive deformation on the continental slope between 94°W and 102°W. Farther west, the relative motion was extensional along an east-west trending zone occupied by the Marie Byrd Seamounts. Key Points: Abbot Ice Shelf is underlain by E-W rift basins created at ∼90 Ma Amundsen shelf shaped by subsidence, sedimentation, and passage of the ice sheet Bellingshausen plate boundary is located near the base of continental slope and rise PMID:26709352

  20. Vertical tectonics at a continental crust-oceanic plateau plate boundary zone: Fission track thermochronology of the Sierra Nevada de Santa Marta, Colombia

    NASA Astrophysics Data System (ADS)

    Villagómez, Diego; Spikings, Richard; Mora, AndréS.; GuzmáN, Georgina; Ojeda, GermáN.; CortéS, Elizabeth; van der Lelij, Roelant

    2011-08-01

    The topographically prominent Sierra Nevada de Santa Marta forms part of a faulted block of continental crust located along the northern boundary of the South American Plate, hosts the highest elevation in the world (˜5.75 km) whose local base is at sea level, and juxtaposes oceanic plateau rocks of the Caribbean Plate. Quantification of the amount and timing of exhumation constrains interpretations of the history of the plate boundary, and the driving forces of rock uplift along the active margin. The Sierra Nevada Province of the southernmost Sierra Nevada de Santa Marta exhumed at elevated rates (≥0.2 Km/My) during 65-58 Ma in response to the collision of the Caribbean Plateau with northwestern South America. A second pulse of exhumation (≥0.32 Km/My) during 50-40 Ma was driven by underthrusting of the Caribbean Plate beneath northern South America. Subsequent exhumation at 40-25 Ma (≥0.15 Km/My) is recorded proximal to the Santa Marta-Bucaramanga Fault. More northerly regions of the Sierra Nevada Province exhumed rapidly during 26-29 Ma (˜0.7 Km/My). Further northward, the Santa Marta Province exhumed at elevated rates during 30-25 Ma and 25-16 Ma. The highest exhumation rates within the Sierra Nevada de Santa Marta progressed toward the northwest via the propagation of NW verging thrusts. Exhumation is not recorded after ˜16 Ma, which is unexpected given the high elevation and high erosive power of the climate, implying that rock and surface uplift that gave rise to the current topography was very recent (i.e., ≤1 Ma?), and there has been insufficient time to expose the fossil apatite partial annealing zone.

  1. Effects of Ice Accretion on Aircraft Aerodynamics

    NASA Technical Reports Server (NTRS)

    Bragg, Michael B.

    1998-01-01

    The primary objective of this research was to support the development of a new ice accretion model by improving our physical understanding of the ice accretion process through experimental measurements. The focus was on the effect of the initial ice roughness (smooth/rough boundary) on the accretion process. This includes understanding the boundary-layer development over the roughness and especially its effect on the heat transfer which is fundamental to the ice accretion process. The research focused on acquiring the experimental data needed to formulate a new ice accretion physical model. Research was conducted to analyze boundary-layer data taken on a NACA 0012 airfoil with roughness to simulate the smooth/rough boundary. The effect of isolated roughness on boundary-layer transition was studied experimentally to determine if the classical critical roughness Reynolds number criteria could be applied to transition in the airfoil leading-edge area. The effect of simulated smooth/rough boundary roughness on convective heat transfer was studied to complete the study. During the course of this research the effect of free-stream wind tunnel turbulence on the boundary layer was measured. Since this quantity was not well known, research to accurately measure the wind tunnel turbulence in an icing cloud was undertaken. Preliminary results were attained and the final data were acquired, reduced and presented under a subsequent grant.

  2. Large-scale right-slip displacement on the East San Francisco Bay Region fault system, California: Implications for location of late Miocene to Pliocene Pacific plate boundary

    USGS Publications Warehouse

    McLaughlin, R.J.; Sliter, W.V.; Sorg, D.H.; Russell, P.C.; Sarna-Wojcicki, A. M.

    1996-01-01

    . Major transpression across the boundary between the Pacific and North American plates at about 3 to 5 Ma would have resulted in the transfer of significant slip back to the San Francisco Peninsula segment of the San Andreas fault. Since that time, the ESFBR fault system has continued to slip at rates of 11-14 mm/yr. If this interpretation is valid, the ESFBR fault system was the Pacific-North American plate boundary between 8 and 6 Ma, and this boundary has migrated both eastward and westward with time, in response to changing plate margin geometry and plate motions.

  3. Ridge push, mantle plumes and the speed of the Indian plate

    NASA Astrophysics Data System (ADS)

    Eagles, Graeme; Wibisono, Affelia D.

    2013-08-01

    The buoyancy of lithospheric slabs in subduction zones is widely thought to dominate the torques driving plate tectonics. In late Cretaceous and early Paleogene times, the Indian plate moved more rapidly over the mantle than freely subducting slabs sink within it. This signal event has been attributed to arrival of the Deccan-Réunion mantle plume beneath the plate, but it is unknown in which proportions the plume acted to alter the balance of existing plate driving torques and to introduce torques of its own. Our plate kinematic analysis of the Mascarene Basin yields a detailed Indian plate motion history for the period 89-60 Ma. Plate speed initially increases steadily until a pronounced acceleration in the period 68-64 Ma, after which it abruptly returns to values much like those beforehand. This pattern is unlike that suggested to result from the direct introduction of driving forces by the arrival of a thermal plume at the base of the plate. A simple analysis of the gravitational force related to the Indian plate's thickening away from its boundary with the African plate suggests instead that the sudden acceleration and deceleration may be related to uplift of part of that boundary during a period when it was located over the plume head. In this instance, torques related to plate accretion and subduction may have contributed in similar proportions to drive plate motion.

  4. The radiolarian evidence for the accretion of the Fu-saki Formation with the inferred oceanic plate stratigraphy: A case of weakly-metamorphosed accretionary complex in Ishigaki Jima, southern Ryukyu Arc, Japan

    NASA Astrophysics Data System (ADS)

    Nakae, Satoshi

    2013-09-01

    The island of Ishigaki Jima, located in the western part of the southern Ryukyu Arc, Japan, is underlain by a basement comprising the Tumuru and Fu-saki formations. The former is a pelitic glaucophane schist with a metamorphic age of 220-190 Ma, and the latter is a weakly metamorphosed accretionary complex, composed mainly of chert, mudstone and sandstone with minor amounts of limestone and mafic rocks. The Fu-saki Formation was weakly metamorphosed at ∼140 Ma. Latest Carboniferous-Early Jurassic microfossils have been obtained from the limestones, cherts and siliceous mudstones of this formation, but no fossils have been collected from the phyllitic mudstones. The radiolarian fauna of the phyllitic mudstones described herein indicates a late Pliensbachian-early Toarcian (Early Jurassic) age. This result, when combined with existing data, enables the reconstruction of an oceanic plate stratigraphy, showing a succession of (in ascending order) Upper Carboniferous-Triassic cherts, Sinemurian-lower Pliensbachian siliceous mudstones and upper Pliensbachian-lower Toarcian phyllitic mudstones and sandstones. The radiolarians from the phyllitic mudstones are important in constraining the timing of the accretion of the Fu-saki Formation to the base of the Tumuru Formation.

  5. A study of unsteady laminar boundary layer flow on a flat plate using a smoke-wire/silhouette flow visualization technique

    NASA Astrophysics Data System (ADS)

    Soria, J.; Chiu, W. K.; Norton, M. P.

    1990-05-01

    A smoke-wire/silhouette flow visualization technique has been developed for the study of unsteady boundary layer flow. In this technique, a thin wire coated with liquid paraffin is heated ohmically to produce fine smoke streaks as tracer particles. The unobstructed light rays that impinge on the front projection material are reflected back along their originating path with 98 percent efficiency. The light rays that go through the smoke are scattered by the smoke particles and hence do not return along their originating path. The resulting photograph is a high-contrast print with the smoke streaks visible as well-defined black images on an otherwise white background. Unsteady boundary layer flow due to transverse plate vibration has been investigated qualitatively to show the applicability of this new cinematographic method to the visualization of small-scale structures.

  6. Effect of strain-weakening on Oligocene-Miocene self-organization of the Australian-Pacific plate boundary fault in southern New Zealand: Insights from numerical modelling

    NASA Astrophysics Data System (ADS)

    Feng, Xiaojun; Jessell, Mark Walter; Amponsah, Prince Ofori; Martin, Roland; Ganne, Jérôme; Liu, Daqing; Batt, Geoffrey E.

    2016-10-01

    Tectonic inheritance acquired from past geological events can control the formation of new plate boundaries. The aim of this paper is to explore the role of inherited NE and NW trending fabrics and their rheological influence on the propagation of Oligocene-Miocene strike-slip faulting that matured to become the Australian-Pacific plate boundary fault in southern New Zealand. Strain weakening plays a significant role in controlling the formation, growth and evolution of strain localization. In this study, three-dimensional thermo-mechanical models have been used to explore the effect of strain weakening on the Oligocene-Miocene self-organization of strain localization. Strain weakening is simulated through decreasing either the coefficient of friction of upper crust, its cohesion, or the rheological viscosity contrast between the inherited structures and their surrounding wall rocks. Viscosity contrast is obtained by varying the viscosity of inherited structures. Softening coefficient (α) is a measure of strain weakening. Our experiments robustly demonstrate that a primary boundary shear zone becomes mature quicker when softening coefficients are increased. Deformation is focused along narrow high-strain shear zones in the centre of the model when the softening coefficients are high, whereas the strain is more diffuse with many shear zones spread over the model and possibly some high-strain shear zones focused near one border at lower softening coefficients. Varying the viscosity contrast has less effect on the distribution of maximum finite strain. Under simple-shear boundary conditions, NW trending inherited structures make a major contribution to forming early zones of highly focused strain, up to a shear strain of about γ = 3.7. During this process, most NE-trending structures move and rotate passively, accommodate less strain, or even be abandoned through time.

  7. Introducing tectonically and thermo-mechanically realistic lithosphere in the models of plume head -lithosphere interactions (PLI) including intra-continental plate boundaries.

    NASA Astrophysics Data System (ADS)

    Guillou-Frottier, L.; Burov, E.; Cloetingh, S.

    2007-12-01

    Plume-Lithosphere Interactions (PLI) in continets have complex topographic and magmatic signatures and are often identified near boundaries between younger plates (e.g., orogenic) and older stable plates (e.g., cratons), which represent important geometrical, thermal and rheological barriers that interact with the emplacement of the plume head (e.g., Archean West Africa, East Africa, Pannonian - Carpathian system). The observable PLI signatures are conditioned by plume dynamics but also by complex rheology and structure of continental lithosphere. We address this problem by considering a new free-surface thermo-mechanical numerical model of PLI with two stratified elasto-viscous-plastic (EVP) continental plates of contrasting age, thickness and structure. The results show that: (1) surface deformation is poly-harmonic and contains smaller wavelengths (50-500 km) than that associated with the plume head (>1000 km). (2) below intra-plate boundaries, plume head flattening is asymmetric, it is blocked from one side by the cold vertical boundary of the older plate, which leads to mechanical decoupling of crust from mantle lithosphere, and to localized faulting at the cratonic margin; (2) the return flow from the plume head results in sub-vertical down-thrusting (delamination) of the lithosphere at the margin, producing sharp vertical cold boundary down to the 400 km depth; (3) plume head flattening and migration towards the younger plate results in concurrent surface extension above the centre of the plume and in compression (pushing), down-thrusting and magmatic events at the cratonic margin (down-thrusting is also produced at the opposite border of the younger plate); these processes may result in continental growth at the "craton side"; (4) topographic signatures of PLI show basin-scale uplifts and subsidences preferentially located at cratonic margins. Negative Rayleigh-Taylor instabilities in the lithosphere above the plume head provide a mechanism for crustal

  8. Film Condensation with and Without Body Force in Boundary-Layer Flow of Vapor Over a Flat Plate

    NASA Technical Reports Server (NTRS)

    Chung, Paul M.

    1961-01-01

    Laminar film condensation under the simultaneous influence of gas-liquid interface shear and body force (g force) is analyzed over a flat plate. Important parameters governing condensation and heat transfer of pure vapor are determined. Mixtures of condensable vapor and noncondensable gas are also analyzed. The conditions under which the body force has a significant influence on condensation are determined.

  9. Kinematic framework of the Cocos-Pacific Plate Boundary from 13°N to the Orozco TRANSFORM FAULT: RESULTS FROM AN EXTENSIVE MAGNETIC AND SEAMARC II SURVEY

    NASA Astrophysics Data System (ADS)

    Madsen, John A.; Fornari, Daniel J.; Edwards, Margo H.; Gallo, David G.; Perfit, Michael R.

    1992-05-01

    During the summer of 1987, magnetic anomaly data were collected by surface ship as part of an extensive SeaMARC II investigation of the East Pacific Rise (EPR) from 13°N to the Orozco transform. The survey extended to either side of the rise axis onto seafloor at least 1.8 million years (m.y.) in age, enabling the recent evolution of the structural and kinematic framework of the plate boundary to be studied in detail. North of 13°50'N there has been a major perturbation in the evolution of the plate boundary. Swaths of lineaments that trend oblique to EPR-parallel topography form a north pointing, V-shaped discordant zone on the Pacific and Cocos plates that is broadly symmetric about the EPR axis. On the Pacific plate a zone of discordant morphology 130 km long and between 6 and 14 km wide with a structural grain that is highly oblique to the present-day spreading direction is observed on seafloor 0.9-1.8 m.y. in age. A similar but more subtle feature of the same age is also present on the Cocos plate. These zones of discordant lineaments can be correlated with changes in the magnetic lineation pattern. On the Pacific plate the disturbed zone lies between anomalies J and 2, creating greater than normal distance between the anomalies. On the Cocos plate the disturbed zone is characterized by a distinct, high-amplitude, northwestward trending magnetic anomaly. The observed structural grain and the changes in the magnetic anomaly patterns associated with the disturbed zones are very similar to those observed at propagating ridges. Based on the magnetic anomalies, a propagation rate of 10.8 cm/yr in a N10°W direction is estimated for the past 1.8 m.y. A detailed examination of the structures developed within the disturbed zone on the Pacifc plate indicates that the rift propagation in this area can best be explained by the model of Wilson (1990) which involves cyclic rift failure with inward curvature of both rift tips. Plate adjustment to the propagation event is

  10. Solution breakdown due to natural convection of the boundary-layer radial flow on a constant temperature horizontal plate

    NASA Astrophysics Data System (ADS)

    Fernandez-Feria, Ramon; Del Pino, Carlos; Fernández-Gutiérrez, Alberto

    2013-11-01

    The boundary-layer flow of a cold horizontal current exiting radially from a cylindrical vertical surface with a constant velocity over a hotter horizontal wall with constant temperature is analyzed. The temperature and velocity fields are coupled by buoyancy through the pressure gradients, so that the boundary-layer equations are made dimensionless with a radial characteristic length in which natural and forced convection become of the same order of magnitude, being the Prandtl number the only nondimensional parameter governing the problem. A similarity solution valid for the leading edge boundary-layer flow is obtained, yielding as a first order correction the effect of natural convection on Blasius' thermal boundary layer. This solution is also used to start the numerical integration of the equations to find out the location where the boundary-layer flow blows up due to the termination of the solution in a singularity. The physical nature of this singularity is analyzed and its position is characterized numerically. The heat flux from the horizontal wall up to this singularity is also characterized and qualitatively compared with previous experimental results from a related experimental setup.

  11. Effect of inherited structures on strike-slip plate boundaries: insight from analogue modelling of the central Levant Fracture System, Lebanon

    NASA Astrophysics Data System (ADS)

    Ghalayini, Ramadan; Daniel, Jean-Marc; Homberg, Catherine; Nader, Fadi

    2015-04-01

    Analogue sandbox modeling is a tool to simulate deformation style and structural evolution of sedimentary basins. The initial goal is to test what is the effect of inherited and crustal structures on the propagation, evolution, and final geometry of major strike-slip faults at the boundary between two tectonic plates. For this purpose, we have undertaken a series of analogue models to validate and reproduce the structures of the Levant Fracture System, a major NNE-SSW sinistral strike-slip fault forming the boundary between the Arabian and African plates. Onshore observations and recent high quality 3D seismic data in the Levant Basin offshore Lebanon demonstrated that Mesozoic ENE striking normal faults were reactivated into dextral strike-slip faults during the Late Miocene till present day activity of the plate boundary which shows a major restraining bend in Lebanon with a ~ 30°clockwise rotation in its trend. Experimental parameters consisted of a silicone layer at the base simulating the ductile crust, overlain by intercalated quartz sand and glass sand layers. Pre-existing structures were simulated by creating a graben in the silicone below the sand at an oblique (>60°) angle to the main throughgoing strike-slip fault. The latter contains a small stepover at depth to create transpression during sinistral strike-slip movement and consequently result in mountain building similarly to modern day Lebanon. Strike-slip movement and compression were regulated by steady-speed computer-controlled engines and the model was scanned using a CT-scanner continuously while deforming to have a final 4D model of the system. Results showed that existing normal faults were reactivated into dextral strike-slip faults as the sinistral movement between the two plates accumulated. Notably, the resulting restraining bend is asymmetric and segmented into two different compartments with differing geometries. One compartment shows a box fold anticline, while the second shows an

  12. Real feature of seismicity around Palau trench region, western Pacific: Is Palau trench aseismic silent plate boundary?

    NASA Astrophysics Data System (ADS)

    Ishihara, Y.; Shito, A.; Tanaka, S.; Suetsugu, D.

    2012-12-01

    Palau islands locate around plate converging zone in the western Pacific region. In the east off the Palau islands, obvious trench topography is developed whose bathymetry reaches about 6000 meters. Palau trench locates at the west side of Yap trench. However tectonic activity is quite different in the both trenches. Yap trench has active seismic activity associate with subduction process. Plate motion model shows clear convergent relative motion between Pacific plate and Philippine Sea plate at Yap trench. On the other hand, Palau trench doesn't have active seismicity according to ISC catalogue. In ten years in 2000's, only three small earthquakes are reported in ISC catalogue. Historically any great earthquake also is not reported. Recent plate motion model shows very low convergent motion at Palau trench though developed trench structure. Our group operates broadband seismic station at Palau (station code: PALU) for about 15 years. In our instant monitoring, local earthquakes sometime are recognized. We operated additional stations in Palau islands for six months to detect local earthquake and to locate hypocenters. Our objective of the research is evaluation of real seismicity of Palau region and final major interest is to understand tectonic activity of Palau trench. We install minimum network for hypocenter locating in Koror and Babeldaob islands, Palau that its array dimension is about 20 km. We use broadband seismographs and high resolution data loggers with GPS clock and solar power generators. We succeeded continuous recording without any troubles and clips of mass position. By careful motoring, we pick up greater than 70 local earthquakes in only six months. And we also tried to read the P and S wave arrival times. We succeeded to locate 27 hypocenters. The number of seismic events is much higher than initial estimation. The hypocenters locate east coast side of Palau islands where is trench side. The overview of distribution is parallel to trench

  13. A revised estimate of Pacific-North America motion and implications for Western North America plate boundary zone tectonics

    NASA Technical Reports Server (NTRS)

    Demets, Charles; Gordon, Richard G.; Stein, Seth; Argus, Donald F.

    1987-01-01

    Marine magnetic profiles from the Gulf of Californa are studied in order to revise the estimate of Pacific-North America motion. It is found that since 3 Ma spreading has averaged 48 mm/yr, consistent with a new global plate motion model derived without any data. The present data suggest that strike-slip motion on faults west of the San Andreas is less than previously thought, reducing the San Andreas discrepancy with geodetic, seismological, and other geologic observations.

  14. Changes in Student Knowledge and Views of Geohazards, Societal Risks, and Monitoring at Active Plate Boundaries Using a Data-Rich Curriculum

    NASA Astrophysics Data System (ADS)

    Selkin, P. A.; Goodell, L. P.; Teasdale, R.

    2015-12-01

    The "Living on the Edge: Building Resilient Societies on Active Plate Margins" curriculum consists of six data-rich activities, each intended for a 50-minute class, in which students assess risk at active plate boundaries due to earthquakes and volcanoes. Developed as part of the InTeGrate NSF STEP Center the peer-reviewed, publically available materials (http://serc.carleton.edu/104296) have been used at several institutions in diverse classroom settings including small laboratory sections, large lecture courses, medium-sized upper division courses and professional development programs for middle and high school teachers. Pre- and post-instruction surveys measured content knowledge and geoscience literacy, self-efficacy in using geologic data to assess hazards and risk, and attitudes towards the value of monitoring plate margins. The activities have overall positive effects on knowledge of geohazard concepts. Views about the value of scientific practice also became more positive: 74% of students indicated they "agree" or "strongly agree" that monitoring geologic activity has value to them personally (even if they don't live on an active plate margin) and 94% indicated that such monitoring is valuable to society. Most became more confident in evaluating geologic hazard and risk (>60% of students self-described increased confidence by one or more Likert levels). Student knowledge of both the types and limits of data in forecasting geological hazards and their effects also improved. However, attitudes toward sustainability and geoscience careers did not change. Learning and attitudinal improvements are true for all classroom types, but the degree of change varies with class size and the amount of time spent on activities. Learning data and instructor feedback suggest that interactive classroom activities that use real-world data to address societally relevant issues increase student learning and enhance students' ability to synthesize scientific information.

  15. Empirical Tsunami Hazard Assessment of Near-Field Plate-Boundary and Crustal Fault Sources Demonstrated for the Pacific Coast of Canada

    NASA Astrophysics Data System (ADS)

    Leonard, L. J.; Rogers, G. C.

    2015-12-01

    We demonstrate an empirical method for preliminary tsunami hazard assessment of near-field fault sources that lack long historic records, paleoseismic/paleotsunami data and/or adequate tsunami modelling studies. Along the Pacific coast of Canada, the North America plate boundary is characterized by varying degrees of convergence with adjacent oceanic plates and microplates. The 1700 M~9 Cascadia earthquake ruptured at least the full extent of Juan de Fuca plate subduction as far north as central Vancouver Island; paleoseismic data show that similar events have occurred approximately every 500 years throughout the Holocene, accompanied by large tsunamis. Further north along the margin, the paleoseismic and paleotsunami histories of the Explorer, Winona, and Haida Gwaii segments of the margin are unknown. The Explorer plate is subducting beneath Vancouver Island at about half the rate of the Juan de Fuca plate; this locked segment may rupture independently or it may slip concurrently with the rest of the Cascadia subduction zone system to the south. The tsunamigenic potential of the Winona segment off northern Vancouver Island is poorly understood. The occurrence of the 2012 M7.8 thrust earthquake off southern Haida Gwaii confirmed the tsunamigenic nature of partitioned convergent slip on this dominantly transform margin segment. Parts of the coastline face additional tsunami hazard from submarine crustal faults. For potentially tsunamigenic faults with unknown history, we use (1) geophysical data to constrain fault rupture area, (2) empirical relations to estimate earthquake magnitude from the rupture area, (3) plate motion models and geodetic data to constrain convergence and thrust earthquake recurrence rates, and (4) empirical relations to estimate near-field tsunami runup at coastal sites, given distance from the rupture. The success of this approach is demonstrated by general agreement between expected and observed earthquake magnitude and near-field tsunami

  16. Tsujal Marine Survey: Crustal Characterization of the Rivera Plate-Jalisco Block Boundary and its Implications for Seismic and Tsunami Hazard Assessment

    NASA Astrophysics Data System (ADS)

    Bartolome, R.; Danobeitia, J.; Barba, D. C., Sr.; Nunez-Cornu, F. J.; Cameselle, A. L.; Estrada, F.; Prada, M.; Bandy, W. L.

    2014-12-01

    During the spring of 2014, a team of Spanish and Mexican scientists explored the western margin of Mexico in the frame of the TSUJAL project. The two main objectives were to characterize the nature and structure of the lithosphere and to identify potential sources triggering earthquakes and tsunamis at the contact between Rivera plate-Jalisco block with the North American Plate. With these purposes a set of marine geophysical data were acquired aboard the RRS James Cook. This work is focus in the southern part of the TSUJAL survey, where we obtain seismic images from the oceanic domain up to the continental shelf. Thus, more than 800 km of MCS data, divided in 7 profiles, have been acquired with a 6km long streamer and using an air-gun sources ranging from 5800 c.i. to 3540 c.i. Furthermore, a wide-angle seismic profile of 190 km length was recorded in 16 OBS deployed perpendicular to the coast of Manzanillo. Gravity and magnetic, multibeam bathymetry and sub-bottom profiler data were recorded simultaneously with seismic data in the offshore area. Preliminary stacked MCS seismic sections reveal the crustal structure in the different domains of the Mexican margin. The contact between the Rivera and NA Plates is observed as a strong reflection at 6 s two way travel time (TWTT), in a parallel offshore profile (TS01), south of Manzanillo. This contact is also identified in a perpendicular profile, TS02, along a section of more than 100 km in length crossing the Rivera transform zone, and the plate boundary between Cocos and Rivera Plates. Northwards, offshore Pto. Vallarta, the MCS data reveals high amplitude reflections at around 7-8.5 s TWTT, roughly 2.5-3.5 s TWTT below the seafloor, that conspicuously define the subduction plane (TS06b). These strong reflections which we interpret as the Moho discontinuity define the starting bending of subduction of Rivera Plate. Another clear pattern observed within the first second of the MCS data shows evidences of a bottom

  17. Heat transfer on accreting ice surfaces

    NASA Technical Reports Server (NTRS)

    Yamaguchi, Keiko; Hansman, R. John, Jr.

    1993-01-01

    Based on previous observations of glaze ice accretion on aircraft surfaces, a multizone model with distinct zones of different surface roughness is demonstrated. The use of surface roughness in the LEWICE ice accretion prediction code is examined. It was found that roughness is used in two ways: (1) to determine the laminar to turbulent boundary-layer transition location; and (2) to calculate the convective turbulent heat-transfer coefficient. A two-zone version of the multizone model is implemented in the LEWICE code, and compared with experimental convective heat-transfer coefficient and ice accretion results. The analysis of the boundary-layer transition, surface roughness, and viscous flowfield effects significantly increased the accuracy in predicting heat-transfer coefficients. The multizone model was found to significantly improve the ice accretion prediction for the cases compared.

  18. Physical analysis and second-order modelling of an unsteady turbulent flow - The oscillating boundary layer on a flat plate

    NASA Technical Reports Server (NTRS)

    Ha Minh, H.; Viegas, J. R.; Rubesin, M. W.; Spalart, P.; Vandromme, D. D.

    1989-01-01

    The turbulent boundary layer under a freestream whose velocity varies sinusoidally in time around a zero mean is computed using two second order turbulence closure models. The time or phase dependent behavior of the Reynolds stresses are analyzed and results are compared to those of a previous SPALART-BALDWIN direct simulation. Comparisons show that the second order modeling is quite satisfactory for almost all phase angles, except in the relaminarization period where the computations lead to a relatively high wall shear stress.

  19. Exhumation History of an Oblique Plate Boundary: Investigating Kaikoura Mountain-building within the Marlborough Fault System, NE South Island New Zealand

    NASA Astrophysics Data System (ADS)

    Collett, C.; Duvall, A. R.; Flowers, R. M.; Tucker, G. E.

    2015-12-01

    The Kaikoura Mountains stand high as topographic anomalies in the oblique Pacific-Australian plate boundary zone known as the Marlborough Fault System (MFS), NE South Island New Zealand. The base of both the Inland and Seaward Kaikoura Ranges are bound on the SE by major, steeply NW-dipping, right lateral, active strike-slips (Clarence and Hope faults of the MFS, respectively). Previous geologic mapping, observations of predominantly horizontal fault slip at the surface from GPS and offset Quaternary deposits, and uplift of marine terraces, provide evidence for shortening and mountain-building via distributed deformation off of the main MFS strike-slip faults. However, quantitative estimates of the magnitude and spatial patterns of exhumation and of the timing of mountain-building in the Kaikouras are needed to understand more fully the nature of oblique deformation in the MFS. We present new apatite and zircon (U-Th)/He ages from opposite sides of the Hope and Clarence faults, spanning over 2 km of relief within the Kaikoura Mountains to identify spatial and temporal changes in exhumation rates in relation to the adjacent faults. Young (~3 Ma) apatite He ages and rapid (potentially > 1 mm/yr) exhumation rates from opposite sides of the faults are consistent with previously mentioned evidence of recent, regional, distributed deformation off of the main MFS faults. Moreover, early Miocene zircon He ages imply that parts of this region experienced an earlier phase of fault-related exhumation. Large changes in zircon He ages across the faults from ~20 Ma to > 100 Ma support hypotheses that portions of the Marlborough Faults may be re-activated, early Miocene thrusts. The zircon data are also consistent with the hypothesis of an early Miocene initiation of the oblique Pacific-Australian plate boundary in this region. Evidence for this comes from a change in sedimentation during this time from fine marine sediments to coarse, terrigenous conglomerates. Observing more

  20. Heat Transfer Analysis for Stationary Boundary Layer Slip Flow of a Power-Law Fluid in a Darcy Porous Medium with Plate Suction/Injection

    PubMed Central

    Aziz, Asim; Ali, Yasir; Aziz, Taha; Siddique, J. I.

    2015-01-01

    In this paper, we investigate the slip effects on the boundary layer flow and heat transfer characteristics of a power-law fluid past a porous flat plate embedded in the Darcy type porous medium. The nonlinear coupled system of partial differential equations governing the flow and heat transfer of a power-law fluid is transformed into a system of nonlinear coupled ordinary differential equations by applying a suitable similarity transformation. The resulting system of ordinary differential equations is solved numerically using Matlab bvp4c solver. Numerical results are presented in the form of graphs and the effects of the power-law index, velocity and thermal slip parameters, permeability parameter, suction/injection parameter on the velocity and temperature profiles are examined. PMID:26407162

  1. Heat Transfer Analysis for Stationary Boundary Layer Slip Flow of a Power-Law Fluid in a Darcy Porous Medium with Plate Suction/Injection.

    PubMed

    Aziz, Asim; Ali, Yasir; Aziz, Taha; Siddique, J I

    2015-01-01

    In this paper, we investigate the slip effects on the boundary layer flow and heat transfer characteristics of a power-law fluid past a porous flat plate embedded in the Darcy type porous medium. The nonlinear coupled system of partial differential equations governing the flow and heat transfer of a power-law fluid is transformed into a system of nonlinear coupled ordinary differential equations by applying a suitable similarity transformation. The resulting system of ordinary differential equations is solved numerically using Matlab bvp4c solver. Numerical results are presented in the form of graphs and the effects of the power-law index, velocity and thermal slip parameters, permeability parameter, suction/injection parameter on the velocity and temperature profiles are examined.

  2. Neotectonics of the Owen Fracture Zone (NW Indian Ocean): Structural evolution of an oceanic strike-slip plate boundary

    NASA Astrophysics Data System (ADS)

    Rodriguez, M.; Fournier, M.; Chamot-Rooke, N.; Huchon, P.; Bourget, J.; Sorbier, M.; Zaragosi, S.; Rabaute, A.

    2011-12-01

    The Owen Fracture Zone is a 800 km-long fault system that accommodates the dextral strike-slip motion between India and Arabia plates. Because of slow pelagic sedimentation rates that preserve the seafloor expression of the fault since the Early Pliocene, the fault is clearly observed on bathymetric data. It is made up of a series of fault segments separated by releasing and restraining bends, including a major pull-apart basin at latitude 20°N. Some distal turbiditic channels from the Indus deep-sea fan overlap the fault system and are disturbed by its activity, thus providing landmarks to date successive stages of fault activity and structural evolution of the Owen Fracture Zone from Pliocene to Present. We determine the durability of relay structures and the timing of their evolution along the principal displacement zone, from their inception to their extinction. We observe subsidence migration in the 20°N basin, and alternate activation of fault splays in the vicinity of the Qalhat seamount. The present-day Owen Fracture Zone is the latest stage of structural evolution of the 20-Myr-old strike-slip fault system buried under Indus turbiditic deposits whose activity started at the eastern foot of the Owen Ridge when the Gulf of Aden opened. The evolution of the Owen Fracture Zone since 3-6 Myr reflects a steady state plate motion between Arabia and India, such as inferred by kinematics for the last 20 Myr period. The structural evolution of the Owen Fracture Zone since 20 Myr, including fault segments propagation and migration, pull-apart basin opening and extinction, seems to be characterized by a progressive reorganization of the fault system, and does not require any major kinematics change.

  3. Slim accretion disks

    SciTech Connect

    Abramowicz, M.A.; Czerny, B.; Lasota, J.P.; Szuszkiewicz, E.

    1988-09-01

    A new branch of equilibrium solutions for stationary accretion disks around black holes is found. These solutions correspond to moderately super-Eddington accretion rates. The existence of the new branch is a consequence of an additional cooling due to general relativistic Roche lobe overflow and horizontal advection of heat. On an accretion rate versus surface density plane the new branch forms, together with the two standard branches (corresponding to the Shakura-Sunyaev accretion disk models) a characteristically S-shaped curve. This could imply a limit cycle-type behavior for black hole accretion flows with accretion rates close ot the Eddington one. 29 references.

  4. Investigation of the separated region ahead of three-dimensional protuberances on plates and cones in hypersonic flows with laminar boundary layers

    NASA Astrophysics Data System (ADS)

    Kumar, C. S.; Singh, T.; Reddy, K. P. J.

    2014-12-01

    Heat transfer rate and pressure measurements were made upstream of surface protuberances on a flat plate and a sharp cone subjected to hypersonic flow in a conventional shock tunnel. Heat flux was measured using platinum thin-film sensors deposited on macor substrate and the pressure measurements were made using fast acting piezoelectric sensors. A distinctive hot spot with highest heat flux was obtained near the foot of the protuberance due to heavy vortex activity in the recirculating region. Schlieren flow visualization was used to capture the shock structures and the separation distance ahead of the protrusions was quantitatively measured for varying protuberance heights. A computational analysis was conducted on the flat plate model using commercial computational fluid dynamics software and the obtained trends of heat flux and pressure were compared with the experimental observation. Experiments were also conducted by physically disturbing the laminar boundary layer to check its effect on the magnitude of the hot spot heat flux. In addition to air, argon was also used as test gas so that the Reynolds number can be varied.

  5. Abbot Ice Shelf, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of West Antarctica

    NASA Astrophysics Data System (ADS)

    Cochran, James R.; Tinto, Kirsty J.; Bell, Robin E.

    2015-05-01

    Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia. A well-defined boundary zone separates the mildly extended Abbot extensional terrain from the deeper Amundsen Embayment shelf basin. The shelf basin has an extension factor, β, of 1.5-1.7 with 80-100 km of extension occurring across an area now 250 km wide. Following this extension, rifting centered north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic Ice Sheet. The Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to incorporation into the Antarctic Plate at about 62 Ma. During the latter part of its independent existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence across the north-south trending Bellingshausen Gravity Anomaly structure at 94°W and compressive deformation on the continental slope between 94°W and 102°W. Farther west, the relative motion was extensional along an east-west trending zone occupied by the Marie Byrd Seamounts. The copyright line for this article was changed on 5 JUN 2015 after original online publication.

  6. Continental accretion: From oceanic plateaus to allochthonous terranes

    USGS Publications Warehouse

    Ben-Avraham, Z.; Nur, A.; Jones, D.; Cox, A.

    1981-01-01

    Some of the regions of the anomalously high sea-floor topography in today's oceans may be modern allochthonous terranes moving with their oceanic plates. Fated to collide with and be accreted to adjacent continents, they may create complex volcanism, cut off and trap oceanic crust, and cause orogenic deformation. The accretion of plateaus during subduction of oceanic plates may be responsible for mountain building comparable to that produced by the collision of continents. Copyright ?? 1981 AAAS.

  7. Diffuse Pacific-North American plate boundary: 1000 km of dextral shear inferred from modeling geodetic data

    USGS Publications Warehouse

    Parsons, T.; Thatcher, W.

    2011-01-01

    Geodetic measurements tell us that the eastern part of the Basin and Range Province expands in an east-west direction relative to stable North America, whereas the western part of the province moves to the northwest. We develop three-dimensional finite element representations of the western United States lithosphere in an effort to understand the global positioning system (GPS) signal. The models are constrained by known bounding-block velocities and topography, and Basin and Range Province deformation is represented by simple plastic (thermal creep) rheology. We show that active Basin and Range spreading by gravity collapse is expected to have a strong southward component that does not match the GPS signal. We can reconcile the gravitational component of displacement with observed velocity vectors if the Pacific plate applies northwest-directed shear stress to the Basin and Range via the Sierra Nevada block. This effect reaches at least 1000 km east of the San Andreas fault in our models. ?? 2011 Geological Society of America.

  8. Prediction of effect of high free stream turbulence on momentum transport and heat transfer in a flat plate turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Iyer, Ganesh Ramamurthy

    1998-12-01

    A modified low Reynolds number k-varepsilon model for predicting effects of high free stream turbulence (FST) on momentum transport and heat transfer in a flat plate turbulent boundary layer is presented. The prediction capabilities of four well tested k-varepsilon models (Launder-Sharma, K-Y Chien, Lam-Bremhorst and Jones-Launder) under high FST conditions (initial turbulence intensity, Tusbi>5%) were investigated using a partial differential equation solver. Predictions became poorer (overprediction up to more than 50% for skin friction coefficient and Stanton number, and underprediction of TKE up to more than 50%) as FST increased to about 26%. The high FST data sets against which the predictions were compared had initial FST intensities of 6.53% and 25.7%. Predictions clearly indicated a deficit of TKE levels in the boundary layer, when compared to experimental data. An additional production term which incorporated the effects of FST intensity (velocity scale) and length scale was included in the TKE equation. The constant csb{mu} in the equation for the transport coefficient musbt was modified using experimental data. This new model, then provided excellent results for Stanton number and skin friction coefficient (within ±3.5% of data) for both the data sets (Tusbi = 6.53% and Tusbi = 25.7%). TKE and other hydrodynamic results were excellent for Tusbi = 6.53%, but not so good for Tusbi = 25.7%. Further, this new model was implemented for calculating another case of flat plate turbulent boundary layer under high FST (Tusbi = 5.3%) subjected to pressure gradient. Results for skin friction and heat transfer coefficients were reasonably good (within 11% of experimental data). The present model incorporates physics of transport of free stream turbulence in turbulence modeling and provides a new method for simulating flows with high FST. Future work should concentrate on implementing this model for more cases with Tusbi going up to more than 20% and various length

  9. A New Estimate for Total Offset on the Southern San Andreas Fault: Implications for Cumulative Plate Boundary Shear in the Northern Gulf of California

    NASA Astrophysics Data System (ADS)

    Darin, M. H.; Dorsey, R. J.

    2012-12-01

    Development of a consistent and balanced tectonic reconstruction for the late Cenozoic San Andreas fault (SAF) in southern California has been hindered for decades by incompatible estimates of total dextral offset based on different geologic cross-fault markers. The older estimate of 240-270 km is based on offset fluvial conglomerates of the middle Miocene Mint Canyon and Caliente Formations west of the SAF from their presumed source area in the northern Chocolate Mountains NE of the SAF (Ehlig et al., 1975; Ehlert, 2003). The second widely cited offset marker is a distinctive Triassic megaporphyritic monzogranite that has been offset 160 ± 10 km between Liebre Mountain west of the SAF and the San Bernadino Mountains (Matti and Morton, 1993). In this analysis we use existing paleocurrent data and late Miocene clockwise rotation in the eastern Transverse Ranges (ETR) to re-assess the orientation of the piercing line used in the 240 km-correlation, and present a palinspastic reconstruction that satisfies all existing geologic constraints. Our reconstruction of the Mint Canyon piercing line reduces the original estimate of 240-270 km to 195 ± 15 km of cumulative right-lateral slip on the southern SAF (sensu stricto), which is consistent with other published estimates of 185 ± 20 km based on correlative basement terranes in the Salton Trough region. Our estimate of ~195 km is consistent with the lower estimate of ~160 km on the Mojave segment because transform-parallel extension along the southwestern boundary of the ETR during transrotation produces ~25-40 km of displacement that does not affect offset markers of the Liebre/San Bernadino correlation located northwest of the ETR rotating domain. Reconciliation of these disparate estimates places an important new constraint on the total plate boundary shear that is likely accommodated in the adjacent northern Gulf of California. Global plate circuit models require ~650 km of cumulative Pacific-North America (PAC

  10. Eclogites and related metamorphism in the North America-Caribbean plate boundary: An example from the Motagua fault zone, Guatemala (Invited)

    NASA Astrophysics Data System (ADS)

    Tsujimori, T.; Hernandez Pineda, G. A.

    2009-12-01

    Active volcanic arcs and strike-slip fault systems characterize the present-day Caribbean Plate margins. The northern boundary of the Caribbean plate in Guatemala is the Motagua fault zone (MFZ). Along the MFZ in central and eastern Guatemala, eclogite- and jadeitite-bearing serpentinite-matrix mélange are exposed stretching ˜200 km on either side of the Motagua-Polochic fault system. The MFZ eclogites and related high-pressure metamorphic rocks represent key evidence for testing existing competing Caribbean plate tectonic models (e.g., Harlow et al., 2008, GSA Abs. Prog. 40:452). The presence of lawsonite-eclogite and jadeite-eclogite with lawsonite-blueschist-facies overprinting in the south of the MFZ (Tsujimori et al., 2006, GSA Spec. Paper 403:147-68) indicates that the geotherm in the paleo-subduction zone is very low. Protoliths for these high-pressure rocks consist of uppermost oceanic crust including MORB-origin greenstones and cherts with minor trench turbidites. Epidote-paragonite-eclogites of layered gabbroic origin occur in the north of the MFZ. Although some N-MFZ eclogites record amphibolite-facies hydration and new mineral growth, eclogitic garnets preserve lawsonite-pseudomorph and glaucophane, suggesting a cold subduction zone. The lack of ubiquitous lawsonite in northern eclogites may be attributed to due to water under-saturated conditions. Considering recent geochronology that implies a coeval eclogite-facies metamorphism at ˜130 Ma (Bruekener et al., 2009, EPSL284:228-35) and petrologic similarities of host serpentinized spinel-lherzolite on either side of the MFZ, we can tentatively reconstruct the succession of a fragmented eclogite-facies metamorphosed oceanic crust. However, the correct interpretation of the paleo-subduction record and further understanding of a cold subduction-zone process at paleo-Caribbean plate margin requires a more comprehensive approach to focus on in-situ geochemical and isotopic analyses of prograde metamorphic

  11. Testing for an Absence of Regional Shortening (or Extension) Across the Caribbean - South American Plate Boundary Zone (PBZ)

    NASA Astrophysics Data System (ADS)

    Altimira, A.; Bird, D.

    2005-12-01

    Rotations among North American (NOAM), African, South American (SOAM) and Caribbean (CARIB) Plates for the past 60 My indicate dominant right-lateral transform motion and perhaps either shortening or extension across the CARIB-SOAM PBZ. Our testable model indicates that: From 60-45 Ma SOAM moved southward ca.200 km with respect to NOAM as CARIB squeezed into the Atlantic forcing the Yucatan and Grenada basins to open. Since 45 Ma CARIB has moved only east carrying fragments of the Caribbean Great Arc that had struck the west coast of SOAM at ca.70 Ma and shearing the passive margin of SOAM in a ca.250 km wide right-lateral transform PBZ between the thick continental lithosphere of SOAM and the thick oceanic plateau lithosphere of CARIB. Pull-aparts in the PBZ include the Falcon, Cariaco and Gulf of Paria basins and flower structure thrust belts include, the Serrania del Interior, Villa de Cura, Araya-Paria peninsula and the Northern Range of Trinidad. These thrust belts generated the loads that formed the East Venezuelan 150 km wide foreland basin. This model requires that: (1) all igneous and high P/T metamorphic ages in the thrust belts of Venezuela were acquired at or before ca. 70 Ma when the Great Arc of the Caribbean struck the west coast of SOAM; (2) Younger igneous ages in the northern part of the PBZ represent fragments of the southern end of the Lesser Antillean arc dragged into the PBZ as the arc slid by; and (3) Deformation in the PBZ began no earlier than the local time of passage of the southern end of the Lesser Antillean arc except in the Gulf of Paria region where halokinesis began earlier. Collision of the Panama arc (ca.7Ma) caused shortening on the west coast of SOAM and 70 km of northward escape of the triangular Maracaibo prism bounded by the Bocono and Santa Marta strike-slip faults and by a deep lithospheric-scale thrust. Restoring the Maracaibo prism aligns the Cuisa and Oca faults with the CARIB-SOAM east-west trending PBZ.

  12. The San Andreas fault in the San Francisco Bay region, California: Structure and kinematics of a Young plate boundary

    USGS Publications Warehouse

    Jachens, R.C.; Zoback, M.L.

    1999-01-01

    Recently acquired high-resolution aeromagnetic data delineate offset and/or truncated magnetic rock bodies of the Franciscan Complex that define the location and structure of, and total offset across, the San Andreas fault in the San Francisco Bay region. Two distinctive magnetic anomalies caused by ultramafic rocks and metabasalts east of, and truncated at, the San Andreas fault have clear counterparts west of the fault that indicate a total right-lateral offset of only 22 km on the Peninsula segment, the active strand that ruptured in 1906. The location of the Peninsula segment is well defined magnetically on the northern peninsula where it goes offshore, and can be traced along strike an additional ~6 km to the northwest. Just offshore from Lake Merced, the inferred fault trace steps right (northeast) 3 km onto a nearly parallel strand that can be traced magnetically northwest more than 20 km as the linear northeast edge of a magnetic block bounded by the San Andreas fault, the Pilarcitos fault, and the San Gregorio-Hosgri fault zone. This right-stepping strand, the Golden Gate segment, joins the eastern mapped trace of the San Andreas fault at Bolinas Lagoon and projects back onshore to the southeast near Lake Merced. Inversion of detailed gravity data on the San Francisco Peninsula reveals a 3 km wide basin situated between the two strands of the San Andreas fault, floored by Franciscan basement and filled with Plio-Quaternary sedimentary deposits of the Merced and Colma formations. The basin, ~1 km deep at the coast, narrows and becomes thinner to the southeast along the fault over a distance of ~12 km. The length, width, and location of the basin between the two strands are consistent with a pull-apart basin formed behind the right step in the right-lateral strike-slip San Andreas fault system and currently moving southeast with the North American plate. Slight nonparallelism of the two strands bounding the basin (implying a small component of convergence

  13. The Role of Serpentinites at Convergent Plate Boundaries: Using New Discoveries to Facilitate the Learning of Major Earth Processes

    NASA Astrophysics Data System (ADS)

    Ryan, J. G.

    2010-12-01

    A benefit of integrating a vital educational enterprise into a cutting-edge funded research initiative is the ability to bring new scientific discoveries quickly into the classroom without being bound to the textbook publication cycle. A key objective the MARGINS Data in the Classroom project was to facilitate the discovery-to-the-classroom transition of knowledge through the development of Web-deliverable, modular MARGINS “Mini-Lessons”. Some 34 Mini-Lessons are available for classroom use at http://serc.carleton.edu/margins/collection.html, and the development of new Mini-Lessons is a listed Education/Outreach priority of the successor GeoPRISMS Program. An important discovery that arose from the MARGINS Subduction Factory Initiative was the recognition that serpentinites - metamorphically hydrated products of ultramafic rocks rich in serpentine group minerals - are significant constituents of both the mantle wedge and downgoing plate. Serpentines are interesting mineralogically because of their distinctive physical properties, habits and appearance; and for their close affinities with olivine and Mg-rich pyroxenes. Given that serpentines primarily form through the hydration of olivine or Mg-rich pyroxenes, serpentinites constitute a reservoir of subduction-related H2O and entrained trace species in modified mantle rocks of the wedge or slab. As well, serpentine group minerals are interesting rheologically because, as sheet silicates, they can behave in a plastic fashion in rocks that are undergoing deformation, and can thus flow along faults in response to deforming stresses, or be easily entrained in fault rock assemblages along a subduction thrust. Two different MARGINS Mini-Lessons address the issue of serpentinite in subduction zone settings, focusing primarily on the observed occurrences of serpentinite seamounts in the forearc regions of the Mariana subduction system, a MARGINS Subduction Factory Focus Site, and their geochemical and geodynamic

  14. 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

  15. Dynamics of Continental Accretion

    NASA Astrophysics Data System (ADS)

    Moresi, L. N.; Betts, P. G.; Miller, M. S.

    2013-12-01

    Subduction zones become congested when they try to swallow buoyant exotic crust. Accretionary mountain belts (orogens) that form at these convergent plate margins are the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North and South American Cordilleras and southwest Pacific. The geologic record is riddled with accretionary orogens, such as the Tasmanides along the eastern margin of the supercontinent Gondwana and the Altaides that formed on the southern margin of Laurasia. Both the modern and ancient examples are characterised by episodic switches between extension and shortening associated with transitions from collision of exotic crust and subduction related rollback. We present three-dimensional dynamic models that show for the first time how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back arc region. The complexity of the morphology and evolution of the system are driven by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonal to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, but infer that this is a global phenomena throughout Earth's evolution.

  16. Modeled temperatures and fluid source distributions for the Mexican subduction zone: Effects of hydrothermal circulation and implications for plate boundary seismic processes

    NASA Astrophysics Data System (ADS)

    Perry, Matthew; Spinelli, Glenn A.; Wada, Ikuko; He, Jiangheng

    2016-02-01

    In subduction zones, spatial variations in pore fluid pressure are hypothesized to control the sliding behavior of the plate boundary fault. The pressure-temperature paths for subducting material control the distributions of dehydration reactions, a primary control on the pore fluid pressure distribution. Thus, constraining subduction zone temperatures are required to understand the seismic processes along the plate interface. We present thermal models for three margin-perpendicular transects in the Mexican subduction zone. We examine the potential thermal effects of vigorous fluid circulation in a high-permeability aquifer within the basaltic basement of the oceanic crust and compare the results with models that invoke extremely high pore fluid pressures to reduce frictional heating along the megathrust. We combine thermal model results with petrological models to determine the spatial distribution of fluid release from the subducting slab and compare dewatering locations with the locations of seismicity, nonvolcanic tremor, slow-slip events, and low-frequency earthquakes. Simulations including hydrothermal circulation are most consistent with surface heat flux measurements. Hydrothermal circulation has a maximum cooling effect of 180°C. Hydrothermally cooled crust carries water deeper into the subduction zone; fluid release distributions in these models are most consistent with existing geophysical data. Our models predict focused fluid release, which could generate overpressures, coincident with an observed ultraslow layer (USL) and a region of nonvolcanic tremor. Landward of USLs, a downdip decrease in fluid source magnitude could result in the dissipation in overpressure in the oceanic crust without requiring a downdip increase in fault zone permeability, as posited in previous studies.

  17. The ancestral cascades arc: Cenozoic evolution of the central Sierra Nevada (California) and the birth of the new plate boundary

    USGS Publications Warehouse

    Busby, C.J.; Hagan, J.C.; Putirka, K.; Pluhar, C.J.; Gans, P.B.; Wagner, D.L.; Rood, D.; DeOreo, S.B.; Skilling, I.

    2008-01-01

    We integrate new stratigraphic, structural, geochemical, geochronological, and magnetostratigraphic data on Cenozoic volcanic rocks in the central Sierra Nevada to arrive at closely inter-related new models for: (1) the paleogeography of the ancestral Cascades arc, (2) the stratigraphic record of uplift events in the Sierra Nevada, (3) the tectonic controls on volcanic styles and compositions in the arc, and (4) the birth of a new plate margin. Previous workers have assumed that the ancestral Cascades arc consisted of stratovolcanoes, similar to the modern Cascades arc, but we suggest that the arc was composed largely of numerous, very small centers, where magmas frequently leaked up strands of the Sierran frontal fault zone. These small centers erupted to produce andesite lava domes that collapsed to produce block-and-ash flows, which were reworked into paleocanyons as volcanic debris flows and streamflow deposits. Where intrusions rose up through water-saturated paleocanyon fill, they formed peperite complexes that were commonly destabilized to form debris flows. Paleocanyons that were cut into Cretaceous bedrock and filled with Oligocene to late Miocene strata not only provide a stratigraphic record of the ancestral Cascades arc volcanism, but also deep unconformities within them record tectonic events. Preliminary correlation of newly mapped unconformities and new geochronological, magnetostratigraphic, and structural data allow us to propose three episodes of Cenozoic uplift that may correspond to (1) early Miocene onset of arc magmatism (ca. 15 Ma), (2) middle Miocene onset of Basin and Range faulting (ca. 10 Ma), and (3) late Miocene arrival of the triple junction (ca. 6 Ma), perhaps coinciding with a second episode of rapid extension on the range front. Oligocene ignimbrites, which erupted from calderas in central Nevada and filled Sierran paleocanyons, were deeply eroded during the early Miocene uplift event. The middle Miocene event is recorded by growth

  18. m-Accretive extensions of a sectorial operator

    SciTech Connect

    Arlinskii, Yu M; Popov, A B

    2013-08-31

    A description of all the maximal accretive extensions and their resolvents is given for a densely defined closed sectorial operator in terms of abstract boundary conditions. These results are applied to parametrize all the m-accretive extensions of a symmetric operator in a planar model of one-centre point interaction. Bibliography: 40 titles.

  19. Accretion on to Magnetic White Dwarfs

    NASA Astrophysics Data System (ADS)

    Wickramasinghe, Dayal

    2014-01-01

    The Magnetic Cataclysmic Variables (MCVs) are close interacting binaries where mass is transferred from a late type secondary star to a magnetic white dwarf. Two modes of accretion can be identified depending on the strength of the magnetic field, the mass transfer rate and orbital parameters. (a) Disced Accretion: In the Intermediate polars (IPs), the mass transfer stream circularises and forms an accretion disc. Material couples on to field lines in a narrow inner transition region where the velocity in the orbital plane changes from Keplerian to co-rotation (b) Discless Accretion: In the polars, the accretion stream is disrupted by the magnetic field before it can circularise. Material couples on to field lines via an inner transition region where the velocity changes from essentially free fall to co-rotation. The polars have no counterparts in neutron star systems and their study provides unique insights into the complex nature of the magnetospheric boundary. The observed properties of accretion shocks at the white dwarf surface such as the anomalous soft-X-ray excess and its time variability provide strong support for the hypothesis that under certain circumstances the field channelled funnel flow is "blobby". This has been attributed to interchange instabilities such as the Magnetic Rayleigh-Taylor instability in the shocked gas at the stream-magnetosphere boundary where the stream fragments into discrete clumps of gas. As the clumps penetrate into the magnetosphere, they are shredded into smaller mass blobs via the Kelvin-Helmholtz instability that then couple on to field lines over an extended inner transition region in the orbital plane. The more massive blobs penetrate deep into the photosphere of the white dwarf releasing their energy as a reprocessed soft-X-ray black body component. Although similar instabilities are expected in the inner transition region in disced accretion albeit on a different scale there has been no direct observational evidence

  20. Strongly magnetized accretion discs require poloidal flux

    NASA Astrophysics Data System (ADS)

    Salvesen, Greg; Armitage, Philip J.; Simon, Jacob B.; Begelman, Mitchell C.

    2016-08-01

    Motivated by indirect observational evidence for strongly magnetized accretion discs around black holes, and the novel theoretical properties of such solutions, we investigate how a strong magnetization state can develop and persist. To this end, we perform local simulations of accretion discs with an initially purely toroidal magnetic field of equipartition strength. We demonstrate that discs with zero net vertical magnetic flux and realistic boundary conditions cannot sustain a strong toroidal field. However, a magnetic pressure-dominated disc can form from an initial configuration with a sufficient amount of net vertical flux and realistic boundary conditions. Our results suggest that poloidal flux is a necessary prerequisite for the sustainability of strongly magnetized accretion discs.

  1. Multi-dimensional structure of accreting young stars

    NASA Astrophysics Data System (ADS)

    Geroux, C.; Baraffe, I.; Viallet, M.; Goffrey, T.; Pratt, J.; Constantino, T.; Folini, D.; Popov, M. V.; Walder, R.

    2016-04-01

    This work is the first attempt to describe the multi-dimensional structure of accreting young stars based on fully compressible time implicit multi-dimensional hydrodynamics simulations. One major motivation is to analyse the validity of accretion treatment used in previous 1D stellar evolution studies. We analyse the effect of accretion on the structure of a realistic stellar model of the young Sun. Our work is inspired by the numerical work of Kley & Lin (1996, ApJ, 461, 933) devoted to the structure of the boundary layer in accretion disks, which provides the outer boundary conditions for our simulations. We analyse the redistribution of accreted material with a range of values of specific entropy relative to the bulk specific entropy of the material in the accreting object's convective envelope. Low specific entropy accreted material characterises the so-called cold accretion process, whereas high specific entropy is relevant to hot accretion. A primary goal is to understand whether and how accreted energy deposited onto a stellar surface is redistributed in the interior. This study focusses on the high accretion rates characteristic of FU Ori systems. We find that the highest entropy cases produce a distinctive behaviour in the mass redistribution, rms velocities, and enthalpy flux in the convective envelope. This change in behaviour is characterised by the formation of a hot layer on the surface of the accreting object, which tends to suppress convection in the envelope. We analyse the long-term effect of such a hot buffer zone on the structure and evolution of the accreting object with 1D stellar evolution calculations. We study the relevance of the assumption of redistribution of accreted energy into the stellar interior used in the literature. We compare results obtained with the latter treatment and those obtained with a more physical accretion boundary condition based on the formation of a hot surface layer suggested by present multi

  2. Accelerated plate tectonics.

    PubMed

    Anderson, D L

    1975-03-21

    The concept of a stressed elastic lithospheric plate riding on a viscous asthenosphere is used to calculate the recurrence interval of great earthquakes at convergent plate boundaries, the separation of decoupling and lithospheric earthquakes, and the migration pattern of large earthquakes along an arc. It is proposed that plate motions accelerate after great decoupling earthquakes and that most of the observed plate motions occur during short periods of time, separated by periods of relative quiescence.

  3. Gravity inversion using seismically derived crustal density models and genetic algorithms: an application to the Caribbean-South American Plate boundary

    NASA Astrophysics Data System (ADS)

    Bezada, Maximiliano J.; Zelt, Colin A.

    2011-05-01

    define the known model despite greater standard deviations of the solutions and the occurrence of artefacts in the mean solutions. The algorithm was applied to four profiles across the Caribbean-South America Plate boundary. Some general patterns in the distribution of Δρ were observed consistently in the profiles and are correlated with the interpretations of the velocity models. Positive Δρ values in the sedimentary layer, negative Δρ values for island arc and extended island arc crust with an abrupt change to positive values in South American crust, and positive values in the mantle under the continent and island arc with a transition to negative values under the Caribbean oceanic crust.

  4. The Campaign GPS Component of